Appel editie 42.3

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42.3

Het verenigingsblad van W.S.G. Isaac Newton

ADVENTURES IN THE

DISCONTINUOUS

GALERKIN METHOD

Thesis article

Changing

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at a time

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CHAIRMAN’S NOTE

63

Right in front of you is already the third Appel of

the year, however it’s my very first. In February the

boards changed, introducing me and six other incredibly

enthusiastic mechanical engineers as the 63rd

board of our beloved association. As the chairman,

I feel honoured to lead and add to our association the upcoming

year. Unfortunately, as a board we immediately faced our first big

challenge: the coronavirus and all its consequences. But fear not,

we are highly motivated to do everything we can to keep Newton

as wonderful as it is now and to prepare for an amazing half year,

including the 11th lustrum, when the UT hopefully opens again

after the summer holidays.

The theme of this edition is light and darkness. We all know that

light consists of photons with different wavelengths. These wavelengths

determine the colour which we can perceive. Sometimes,

the spectrum is considered beyond what is visible to us, including

for example ultraviolet or infrared waves. Darkness is the

absence of light and appears to us as black.

Although light is one of the lower forms of energy, it is incredibly

important. Flowers and plants need light to survive, the human

body becomes healthier when receiving sunlight and it can even

improve a person’s mental state. We need light to see, countless of

people are afraid of the dark because then they cannot perceive

what is around them. It is not strange that therefore light and

dark are also often associated with good and bad.

I would like to end with one last remark: Although these times

might be dark, try to find your bright spots and enjoy them. For

example, I wish you a good time reading this newest edition of

the Appel!

Jonne van Haastregt

Chairman of W.S.G. Isaac Newton

Adunare Utile Dulci

INHOUD

Colofon

De Appel is een uitgave van het werktuigbouwkundig

studiegenootschap Isaac

Newton in samenwerking met de opleiding

Werktuigbouwkunde aan de faculteit

der Construerende Technische Wetenschappen

van de Universiteit Twente.

Redactie-adres

W.S.G. Isaac Newton t.a.v. de Appel

Postbus 217

7500 AE Enschede

[T] 053 - 489 25 31

[F] 053 - 489 40 05

[E] appel@isaacnewton.utwente.nl

Uitgave

Jaargang 42, nummer 3, mei 2020

Oplage

1100 exemplaren

Abonnementen

Abonnementen op de Appel zijn te verkrijgen

bij het bestuur van W.S.G. Isaac Newton.

Abonnementsprijs 25 euro per jaar

© 2020 de Appel

De redactie is op geen enkele wijze

verantwoordelijk voor de inhoud van de

aangeleverde kopij en houdt zich het recht

kopij in te korten en te wijzigen.

Hoofdredacteur

Almer Lagerweij

Eindredacteur

Michiel Louwé

Grafische vormgeving

Fedde Engelen

Jeroen van den Hoogen

Redactie

Ekaterina Antimirova

Daan Flier

Roland Guijs

Koen Kleverwal

Alicia Knijnenburg

Fausto Visser

Joachim van de Weg

Hugo Wesselink

Drukker

Drukbedrijf.nl

Joan Muyskenweg 114

1114 AN Amsterdam

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06

Adunare Utile Dulcie

Board Interview

12

Cameratechniek

Laat je verlichten

24

Down to Earth

Intercontinental study tour

46

Adventures in the discontinuous

galerkin method

Thesis article Joachim van

de Weg

4

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18 Foldable Phones

Lightening our lives in

the future

22 Association News

32 Sodium vapour

lamps

Deceivingly dim

34 Geschiedenis van

licht

Maken, gebruiken,

onderzoeken

40 Chips in de verlichting

43 Dark Matter

The darkest material in

the universe

51 Een ode aan het

oosten

Column Hugo

52 Quality Assurance

Committee Reporting

54 Scientia Vincere

Tenebras

Retrospect 62 nd board

REDACTIONEEL

Het is voor ons allen een bijzondere tijd, dat

geldt ook voor ons als redactieleden. Na

twee geslaagde edities van de Appel werd

het nu tijd om een derde te maken, geheel

vanaf thuis. Om eerlijk te zeggen is ons dat

heel goed afgegaan en kan ik met trots kijken

naar deze derde editie van ons verenigingsblad. Wat is er

veel gebeurd de afgelopen maanden, een deel van ons ging op

studiereis naar de andere kant van de wereld, waar menigeen

nog vast kwam te zitten door gestrande vluchten. Gelukkig

kan ik u vertellen dat al onze mede werktuigbouwkundigen

Nederland in goede gezondheid hebben mogen bereiken. Bij

deze nieuwe editie van de Appel komt ook een nieuwe editie

van het bestuur kijken, het 63e bestuur heeft het stokje

overgenomen van het vorige bestuur. Zowel het oude, als het

nieuwe bestuur, wordt uitgebreid besproken en toegelicht in

deze editie.

oplichten. De toekomst van een groeiende sector in Nederland

wordt besproken, fotonica. Over fotonen is zoveel te zeggen,

dat u ook wordt meegenomen in een geschiedenis over

het licht. Geheel aan de andere kant van dit spectrum staat

duisternis, dark matter is ook niet te missen, besluit u deze

Appel verder te lezen.

Het was een uitdaging om u dezelfde leeservaring te

kunnen bieden als u van ons gewend bent, ik kan u in ieder

geval beloven dat wij ons uiterste best hebben gedaan om er

wat moois van te maken. Ik wens u veel lees- en kijkplezier

toe met deze editie van de Appel.

Almer Lagerweij

Hoofdredacteur

Dit keer gaat het over licht en duisternis, want duisternis

is waar wij nu in tasten, met al deze onzekerheid over onze

toekomst. Toch hoop ik dat wij u, de lezer, wat licht in deze

donkere tijden kunnen bieden met onze artikelen, columns,

verenigingsnieuws en nog veel meer. Om u een idee te geven

wat u kunt verwachten te lezen zal ik een tipje van de sluier

DE APPEL 5

ADUNARE

UTILE

DULCI

Just as the tradition implies, an interview with the board was done at 9 o’clock, the morning after the

constitution drink. Some seemed definitely fresher than others, Jonne’s voice was no more. Luuk was not there

at all, while he is known for being on time. He got hurt during the constitution drink, but still after he went to

Aspen, just as the rest of the group. Jonne went home early, at 12:00 o’clock, Bart stayed to the bitter end.

Jonne almost couldn’t make it to Aspen, because his housemates stole his bike. Noor and Nicole went home

inbetween and were almost caught by the police for riding without lights. Halfway through the interview

Michel mentioned that he still was a tat drunk.

All and all, they felt like a 6.3 after a heavy night and a constitution drink to never forget. They were

reminiscing about the day before. The people they met and the gifts they’ve gotten. The fanciest gifts were

definitely the cigar box given by Simon Stevin and the typewriter given by the 56th board. Some other, more

funny, gifts were a cutout of a bodybuilder version of Sir Isaac Newton and a car door. There wasn’t much time

to appreciate the gifts however, since the Newton room had to be cleaned and opened for its members.

TEKST: ALMER LAGERWEIJ

6

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JONNE VAN

HAASTREGT

POSITION CHAIRMAN

BART BORGER

POSITION

VICE-CHAIRMAN

AGE

18

AGE

20

BIRTHPLACE

‘S GRAVENHAGE

BIRTHPLACE

DEN HAM

COMMITTEES

CREDITS

EJA, EJW, EJC, LUS-

TRUM

90

COMMITTEES

CREDITS

BORRELCIE, EJC, COM-

PUCIE

60

PLANS

A board year does not only consist of a constitution drink, they have

to run the whole organisation for a year and as every year, the Appel

gets a small insight in the future plans. A policy was made to help them

through the process of running the association of which the three

main points are are: improving involvement of members, creating a

foundation for an association at the VU and finally, the renovation of

the Newton chamber.

The first point is about the integration of the international students. The

main language of the Mechanical Engineering Bachelor became English

a couple of years ago, in order to attract more international students.

The influx of international students has grown with the years, however,

the majority of active students of Newton are Dutch. The international

students do not always feel at home, and they are not always aware that

Newton is for more than just study related matters. The board will focus

on involving more international students for their activities.

The next major point is to create a foundation for a sister association

for the UT/VU mechanical engineering students. These students are

now members of both Newton and Mens. It would be better for the VU

students to eventually have their own independent association. Newton

8

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THOMAS KAPER

POSITION SECRETARY

MICHEL NIJHUIS

POSITION

TREASURER

AGE

21

AGE

21

BIRTHPLACE

ASSEN

BIRTHPLACE

DIEREN

COMMITTEES

CREDITS

KIME

105

COMMITTEES

CREDITS

COLEXIE, KIME,

SPORTCIE

195

will encourage and assist in creating the beginnings of a sister association

at the VU.

The last thing is the renovation of the Newton chamber. The Newton

chamber is one of the most valuable assets of Newton and is in need of

some maintenance. The board is planning to make the chamber more

welcome through cleaning the chamber and reorganizing the storage

space. Some pieces of furniture will be restored and some parts of the

electronics will be fixed or replaced.

UNWANTED CHANGE OF PLANS

However the whole Corona situation throws a spanner in the works.

What kind of influence does this virus have on the policy plans of this

new board?

A highlight of each year, the annual Batavierenrace is cancelled unfortunately.

There is no way this can be organised in a Corona-proof way,

so this event has to wait until 2021. The board also planned different

activities to get to know the members of Isaac Newton, a lunch quiz.

Now, the only way to see each other is in the virtual Newton room on

Discord. The board made it possible to still have somewhat of interac-

DE APPEL 9

NICOLE RABOU

POSITION EXTERNAL AFFAIRS

LUUK SCHOLTEN

POSITION

INTERNAL AFFAIRS

AGE

20

AGE

21

BIRTHPLACE

VUGHT

BIRTHPLACE

GOUDA

COMMITTEES

CREDITS

EJC, KIME, EJA, FOTO-

CIE

75

COMMITTEES

CREDITS

EJC

60

tion members would have in the physical Newton room. In the Discord

there is room for people to chat, drink, work on assignments and play

video games together. The virtual Newton room is a big hit and now it is

still possible for members to have some interaction together and drink

away their sorrow. A fun activity was already planned using Discord,

the Minecraft party.

The board had many plans to upgrade the physical Newton room, but

unfortunately it is hard to build all the things they need at home, but

that will not stop them from trying. There are many committees, committed

to build things. The use of the workshop is now prohibited, but

they are practising their Solidworks skills now, so once it is possible

again, they can start building immediately.

As some of you know, this year is a lustrum year for our association,

we will turn 55 this year. This would have meant a year full of great

activities, but how these activities will turn out now is still unknown.

And then there is the Kick-in, the introduction period for young and

10 DE APPEL

NOOR LAMMERTS

VAN BUEREN

POSITION EDUCATION

AGE

BIRTHPLACE

19

UTRECHT

ADUNARE

UTILE

COMMITTEES

CREDITS

EJW, OUDERDAG

75

old(er) students, a period filled with great parties, sadly this will all have

to be done virtually. The board however, can probably still visit the dogroups.

With the end of the academic year coming in sight, the end of

the year barbeque is almost here, there is hope this can still continue,

with a maximum of 100 people.

We wish the new board a lot of success and fun, and hope everything

can go back to normal soon. a

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CAMERATECHNIEK

LAAT JE VERLICHTEN

DOOR ROLAND GUIJS

12 DE APPEL

Iedereen die ooit het lef heeft gehad om zijn of haar camera van de automatische stand

te halen en naar ‘M’ te draaien stortte op dat moment van de zelfgecreëerde apenrots af:

fotografie is blijkbaar toch iets meer dan domweg mikken en dan dat knopje rechtsboven

in klikken. Jezelf een goede fotograaf mogen noemen vergt toch net iets meer dan op een

mooie herfstdag met je vriendin naar het bos gaan en haar een handvol bladeren de lucht in

laten gooien. De foto is misschien wel scherp, maar het bos oogt toch plotseling wel heel erg

donker. Bedenkende dat fatsoenlijke lenzen al in ons midden zijn sinds onze landgenoot Antoni

van Leeuwenhoek aan het rommelen was met zand en glas, blijkt het toch moelijker dan door

de meesten gedacht om de juiste hoeveelheid licht die er doorheen komt in te stellen.

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Simpel gesteld zijn er drie manieren om te bepalen hoe licht een foto

wordt; sluitertijd, diafragma en de ISO. De combinatie van deze drie

waarden wordt uitgedrukt in de ‘Exposure Value’, oftewel de EV-waarde.

Op een diafragma van f/1.0, een ISO van 100 en een sluitertijd van 1 seconde

is de EV-waarde 0. Een gemiddelde kamer heeft

een EV van 5-7 en buiten in de volle zon ga

je al snel over de 15.

Beeldender is om de EVwaarde

te beschouwen

als een glas

bier. Een te

vol glas

staat

voor

een

overbelichte

foto, en een

onderbelichte

voor een niet volledig

gevuld glas. Om

een glas snel te vullen kan je

de tap helemaal opengooien, wat

gelijk staat aan het helemaal openen van

het diafragma. Het moment wanneer je het glas

onder de tap vandaan trekt bepaalt hoe lang het goudgele genot erin

kan stromen, idem de sluitertijd bepaalt hoe lang het licht op de sensor

kan vallen. De ISO waarde is het beste te vergelijken met de grootte van

het glas. Hoe lager de ISO waarde, hoe groter het glas. Hierin zit veel bier

(informatie van de foto) en weinig schuim (ruis), mits goed getapt. Zit er

echter te weinig druk op de tap, de omgeving is relatief donker, dan is

het beter om een kleiner glas te pakken, omdat je anders ellendig lang

moet wachten. Bij een te klein glas loop je echter het risico dat je alleen

maar schuim tapt en amper bier, wat uiteraard niet wenselijk is.

SLUITERTIJD

De sluitertijd is het meest voor zichzelf sprekende onderdeel van de zogeheten

‘belichtingsdriehoek’. Het bepaalt simpelweg hoe lang de sensor

wordt blootgesteld aan het licht en dit wordt bepaald met het timen

van een paneeltje die de sensor afdekt. Bijna alle camera’s beschikken

over een zogenaamde spleetsluiter. Deze bestaat uit een aantal horizontale

lamellen die afzonderlijk van elkaar over de sensor heen bewegen.

De ruimte tussen de lamellen is afhankelijk van de sluitertijd. Tot een

sluitertijd van 1/250s is deze afstand tussen de lamellen gelijk aan de

hoogte van de sensor. Deze waarde is niet zomaar gekozen, maar correspondeert

met de flitssynchronisatie tijd. Veel fotografen gebruiken

flitsers om hun object extra uit te lichten, en een dergelijke flits duurt

maar enkele milliseconden. Op dat moment moet dan ook de complete

sensor vrij zijn, om te zorgen dat deze compleet belicht wordt. Bij continu

licht speelt dit probleem niet. Als de sluitertijd hoger dan 1/250s

wordt ingesteld, wordt de spleet smaller gemaakt, zoals de naam al

doet vermoeden, doordat de losse lamellen sneller achter elkaar aan

bewegen. Op die manier wordt de belichtingstijd op de sensor verkort.

Ruwweg is bij een sluitertijd van 1/500s de sluiter maar voor de helft

geopend, bij 1/1000s een kwart, bij 1/2000s een achste, etc. Hoe hoger de

sluitertijd, hoe hoger de vereiste mechanische precisie van de sluiter.

Camera’s met een hele korte sluitertijd zijn dan ook erg prijzig. Moderne

camera’s worden vaak uitgerust met sluiters van carbonvezel

of titanium om ze dun en slijtvast te maken. Omdat de sluiter een

van de weinige onderdelen van een camera is die bewegen, zijn deze

het meest gevoelig voor slijtage en bepalen dan ook de levensduur

en mede de dagwaarde van camera’s. Een professionele camera gaat

vaak meer dan 400.000 foto’s, ook bekend als clicks, mee.

Een alternatief voor de klassieke mechanische sluiter is de elektronisch

sluiter. In plaats van dat de sensor actief wordt afgedekt,

bepaalt de sensor zelf hoe lang deze de beeldinformatie uitleest. In

theorie werkt dit veel beter in vergelijking met in een hoog tempo

langsvliegende lamellen. Een groot nadeel van dit systeem echter is

de zogenaamde ‘rolling shutter’. De sensor leest namelijk het beeld lijn

voor lijn uit. Als het te fotograferen object snel beweegt, kan het dan ook

voorkomen dat er onscherpe of rare vormen ontstaan. Vooral goedkopere

camera’s hebben nog last van dit probleem. Moderne en duurdere

camera’s maken gebruiken van een ‘triggered global shutter’, waarbij

de hele sensor in een keer wordt uitgelezen. Het grote voordeel hiervan

is dat ‘rolling shutter’ niet optreedt, alleen kan de sensor niet alvast

beginnen met het uitlezen van de nieuwe belichting. De tijd tussen het

maken van foto’s of frames is dan ook gelimiteerd. Een ander nadeel van

elektronische sluiters is dat er rondom de sensor extra elektronica geplaatst

moet worden om deze aan te kunnen sturen. Als gevolg hiervan

wordt de lichtweg verstoord en kan hierdoor extra ruis ontstaan. Voor

toepassingen waar een hoge lichtgevoeligheid of hoge sluitertijden nodig

zijn geniet de conventionele sluiter dan ook nog steeds de voorkeur.

DIAFRAGMA

Iedereen die wel eens in een lens heeft gekeken moet de diafragmabladen

gezien hebben, het tweede onderdeel van de belichtingsdriehoek.

Deze bladen kunnen in en uit elkaar draaien, waardoor de opening ertussen

groter of kleiner wordt. Hierdoor wordt de het gat waar het licht

doorheen kan gaan en op de sensor kan vallen aangepast. Op oudere

lenzen en op dure cinema lenzen kunnen deze bladen handmatig aangepast

worden door een draairing op de lens, maar de meeste fotolenzen

doen dit met een motor die vanuit de camera ingesteld wordt. Een lens

met een groot maximaal diafragma wordt ook wel een een snelle lens

14 DE APPEL

EV-WAARDEN

OP DE CAMERA

Voor diegenen die een camera

iets beter bestudeerd hebben dan

simpelweg ermee richten en schieten, de

genoemde EV-waarden zijn niet gelijk aan

de EV-waarden die op de camera worden

getoond. Dit zijn de EV-waarden die bepaald

worden door de interne lichtmeter van de

camera. Als deze op nul staat, betekent dit

dat de camera dit als de juiste lichtopbrengst

beschouwd voor een mooi resultaat. Dit is

als de gemiddelde lichtopbrengst van de

opname 50% grijs is. Als je juist een overof

onderbelichte foto wil maken kan dat

op basis van deze balk bepaald worden.

genoemd. De benaming komt van het feit dat bij deze lenzen korte sluitertijden

gebruikt kunnen worden, oftewel het snel maken van een foto.

Hoe ver het diafragma open staat wordt uitgedrukt met het f-getal. Elke

f-stop betekent een verdubbeling of halvering van het licht vergeleken

met de opeenvolgende waarde. Deze f-stops zijn als volgt gedefineerd:

f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45 en f/64. Deze lijken

random gedefineerd, maar niets is minder waar. Ze staan namelijk voor

het de verhouding tussen je brandpuntsafstand en de diameter van de

diafragma. Stel dat je met een 120mm lens fotografeert en je diafragma

een diameter heeft van 15 mm, dan is de correspondeerde f-stop f/8.

Immers, 120/15=8. Elk opeen volgende f-stop betekent een een verdubbeling

van het licht. Om dat te krijgen, moet het oppervlakte gebied van

het diafragma ook verdubbeld worden, oftwel de diameter maal de wortel

van twee. De wortel van twee is ongeveer 1.41, wat de op het eerste

oog gekke volgorde verklaart.

Een groot diafragma verkrijg je dus bij het laagste getal. Door het openen

van het diafragma krijg je ook minder scherptediepte in de foto.

Scherptediepte is de afstand tussen het dichtsbijstaande en verste gedeelte

in de foto dat nog acceptabel scherp is. Bij weinig scherptediepte

is de achtergrond dus wazig. De vorm en kwaliteit van deze onscherpte

van de achtergrond wordt ook wel de bokeh genoemd. De reden dat er

meer scherptediepte onstaat bij het sluiten van het diafragma is omdat

de invallende lichtbundel smaller is geworden en hierdoor nog maar een

beetje convergeert. En hoe smaller de lichtbundel, hoe meer je lichtbron,

je object, in focus is. Als de diafragmaopening kleiner wordt, word de

lichtbundel automatisch ook kleiner en komt er dus meer in focus.

In tegenstelling tot fotolenzen gebruiken duurdere videolenzen vaak de

aanduiding t-stop in plaats van f-stop. Vaak zitten deze waarden dicht

bij elkaar, maar is de t-stop iets hoger. Het verschil tussen t-stops en

f-stops is dat de f-waarde de theoretische waarde is, en de t-waarde

daadwerkelijk ook gemeten is. De T staat dan ook voor ‘transmission’.

De reden dat het enkel videolenzen zijn die t-stops gebruiken ligt in de

nabewerking. Video’s worden vaak geschoten over verschilllende dagen

met verschillende lenzen. Al deze verschillende beelden horen dan bij

een scene, en de losse beelden moeten onderling kloppen. Het kloppend

maken hiervan is een tijdrovende klus en dus duur. Foto’s zijn allemaal

op zichzelf staande beelden en het corrigeren hiervan is dan ook veel

makkelijker. Daarnaast is het maximale verschil tussen een f- en t-stop

maximaal een derde van een stop, wat makkelijk te corrigeren is bij een

foto zonder dat dit terug te zien is in het resultaat. Ook zijn professionele

videolenzen aanzienlijk duurder dan fotolenzen, wat het voor fabrikanten

ook rendabel maakt om de lenzen te testen op de exacte t-waarden.

DE APPEL 15

ISO

Het derde onderdeel van de belichtingsdriehoek is de ISO waarde. De

naam ISO komt van de welbekende wereldwijde organisatie voor standaardisatie.

Door het verhogen van de ISO wordt de lichtgevoeligheid

van de sensor verhoogd. Dit lijkt een makkelijke manier om foto’s lichter

te maken, maar helaas, niets is minder waar. De cellen van de sensoren

functioneren het beste bij veel licht. Als er minder licht op valt, zijn ze

gevoeliger voor fouten. Dit leidt ertoe dat de kleur of helderheid niet

helemaal goed geregisteerd wordt. Bij voldoende belichte beelden is dit

geen probleem. Echter, als het donkerder wordt, sluipen er meer foutjes

in de opname. Daarnaast wordt het signaal digitaal versterkt door het

verhogen van de ISO. De aanwezige foutjes worden extra versterkt en

leiden tot ruis in de foto.

Een manier om toch meer licht op te vangen is door een grotere sensor

te gebruiken. Op een grotere sensor kunnen grotere cellen geplaatst

worden, die per stuk meer dus meer licht kunnen opvangen. Bovendien

hebben de sensoren minder onderlinge storing, want de kans op fouten

verkleint. Vooral bij hogere ISO waarden is goed te zien dat camera’s

met grote sensoren, zogeheten full frame camera’s, beter presteren. Met

name de Alpha lijn van Sony staat er bekend om om ruisvrije beelden op

te leveren bij hoge ISO waarden.

Het nadeel van grotere sensoren is de hogere productieprijs. Daarnaast

zijn de eisen die aan de lenzen voor fullframe gesteld worden groter,

waardoor deze ook duurder uitvallen. Ook is er niet altijd de mogelijkheid

om te kiezen voor een grotere sensor. Bij telefoons wordt de sensorgrootte

grotendeels bepaald door de behuizing van de telefoon. Hierdoor

wordt de kwaliteit van telefoonfoto’s al snel slecht bij matige belichting.

Een moderne oplossing voor dit probleem is het gebruik van dual iso.

Fotografen moeten altijd een afweging maken tussen het dynamisch

bereik en de ISO. Het dynamisch bereik is hoeveel informatie over de

belichting in een beeld zit, oftewel, hoe groot is het verschil tussen puur

zwart en wit. Dit is met name van belang voor de hoeveelheid detail

die er nog in schaduw en fel belichte stukken van een foto zitten. Door

de ISO omhoog te draaien versterkt de sensor de data die het afleest,

waardoor het meer informatie in de gel belichte delen van de foto, ook

bekend als de hooglichten, komt te zitten en je informatie verliest in de

schaduwen. Bij dual ISO wordt op een gegeven moment overgeschakeld

naar een ander type versterker, waardoor dit effect weer wordt teruggezet.

Op die manier wordt er aanzienlijk veel informatie gewonnen in

schaduwen, ten koste van de hooglichten. Het grote voordeel hiervan is

dat de ruisdrempel wordt teruggebracht. Bij dual ISO camera’s kan de

ruis dus afnemen door een hogere ISO waarden te kiezen.

Er zijn dus drie manieren om met je camera je foto lichter te maken,

maar allemaal hebben ze hun voor en nadelen. Al met al blijft dan toch

de makkelijkste oplossing om die fotoshoot met je vriendin op een ander

moment in de dag in te plannen of een iets lichter bos te kiezen. a

16 DE APPEL

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FOLDABLE PHONES

LIGHTENING OUR LIVES IN THE FUTURE

BY EKATERINA ANTIMIROVA

You have probably heard of the latest foldable phones such as the Samsung Galaxy

Fold and Motorola Razr bringing enthusiasm to tech hobbyists. Some of you could

learn about these from the sensational stories of those phones breaking within a few

days. These phones combining the latest technology and nostalgia from the early

2000s have been actively reviewed since a year. Especially now when we experience

the world virtually, day and night, this is a fitting time to look at how we got here and

learn more about these innovations.

18 DE APPEL

PHONES OVER TIME

When the technology finally allowed long cableless communications,

only the richest individuals could get the hold of these, such as Motorola’s

first commercial phone costing 3.670 euro released in 1983. These

bulky and awkward looking phones were the luxury product for many, a

symbol of status and establishment. Over time the engineers improved

the technology, for example when Nokia decreased the weight of their

phones by 12 times. They did that from 1982 to 1989 when introducing

Mobira Cityman 900. Over these years, consumers became accustomed

to the convenience of cableless communication. The demand for greater

options and more practical handling was on the rise. Outdated capabilities

could no longer satisfy growing demands of the consumers.

The legendary Nokia 3310.

Their expanded options, such as internal antenna and connection to

2G networks reflected on the developments of the phones in the near

future. Very soon, the miniature phones like Nokia 3310 (2000) were so

popular that many students up until 2009 still used them across the

world.

Motorola’s first commercial phone.

The introduction of lightweight Nokia’s Mobira Cityman 900 took place

along with the introduction of foldable MOTOROLA MICROTAC 9800X.

Smaller phones did not get immediate response. Their development took

place alongside the popularization of improved bulkier options. Eventually

these phones caught market attention in the late 1990’s such as

Nokia 8810 release in 1996. Smaller and miniature design allowed for

practical use. However, the first successful ones were luxury products.

With expanding options of these phones, more people relied on the

technology that allowed them to be connected and independent in their

lives. Phones became a necessary tool for a productive day. As the small

foldable and thick phones outsource their capabilities, they simply

could not provide their consumers more to satisfy growing tech savvy

and multitasking demands. The first touchscreen phones and tablets

were introduced commercially with IBM Simon in 1992 and iGesture

Pad in 1998. Eventually Apple bought the producer of the latter, Finger-

Works, in 2005. Using their innovative gesture recognition technology

for multi-tasking, Apple improved upon the concept. This altogether led,

of course, to the first iPhone. It, following the patterns in the tech industry,

was a highly successful and luxurious item that caught worldwide

attention and brought the new era in the mobile phone industry.

Ever since then these phones are getting thinner, larger, brighter, and

more complex. Having a phone is a necessity for school and work, for

quick access to good cameras, a variety of apps, and documents. Today’s

phones are miniature computers inside of our pockets, many of which

are more powerful than personal computers. They are growing bigger

and more powerful, however seeing the latest iPhone 11, some may fear

DE APPEL 19

euros. Despite being luxury products, they still come with unperfected

technology. This however is the beginning of the next stage in the

phone industry, currently Apple is patenting their design. So, within

upcoming years we expect prices to drop with improved technology and

greater competition.

SREENS THAT BEND

First technology that allowed for the existence of the foldable phones

is of course the screen. Modern screens have gone through quick and

impressive transformation. To begin with, IMB Simon had black-andwhite

160 × 293 pixel monochrome backlit LCD (Liquid-crystal display)

touchscreen measuring 4.5 inches by 1.4 inches. Liquid crystal is a state

of the special metals that when heated turns into gaseous crystalline

structure before completely vaporizing. These liquid crystals can rotate

the polarization of light as the light passes through the region. This

Apple iPhone 1.

that the current design of a rectangular thin touch screen with three or

four cameras is hitting the plateau.

Regular consumers are satisfied with older versions. Few need 100 GB of

storage, six cameras, and even larger pixel count. Those who buy these

phones either have specific needs or want to display their establishment.

Therefore, it should not come to a surprise that foldable phones

are marking a new step in communication technology.

This technology has been developing behind the scenes of the general

consumer market, but as of 2019 with Samsung Galaxy Fold, they filled

the imagination of consumers. Foldable phones already have all the sophisticated

technology including latest specifications processing power

that we already enjoy.

For those who love the size of their current phones for daily use but

find it inconvenient to be able to unfit them in their pockets and bags,

foldables like Motorola Razr (2020) will be helpful. These phones have

a regular shape when unfolded and can become half-size when folded.

The smaller outer screen allows you to look at notifications and time.

Other users who are working on the road and generally carry their tablets

with them everywhere , will find phones like the Samsung Galaxy

Fold especially appealing.

These foldable phones when executed accurately are exciting; they inspire

future innovators. However, these phones are currently expensive:

Samsung’s phone costs around 2000 euros and Motorola’s goes for 1500

Twisted nematic (TN) display technology.

means that the light wave will twist as it passes through the crystal.

Modern displays place this crystal between two polarizing layers with

a difference of 90 degrees. This created the twisted nematic structure.

Without voltage the light can pass through both via the created twist.

However, when the voltage is supplied, the liquid crystal falls apart,

hence light can no longer pass through.

Later the color display was developed where each individually controlled

pixel had three individually controlled LCD segments with red,

green, and blue color filters. Controlling the amount of light that passes

through each pixel allows to mix base colors thus creating any desired

picture. In most modern displays light comes from the LED (light emitting

diode) or fluorescent lamp on the background. But the earlier versions

relied on the ambient background and mirrors. At the moment LCD

screens are the most common display types. These screens work well

for outdoor view, natural colors, and sharp images.

Another up-and-coming technology that is simpler and does not require

backlight and filtering is OLED (Organic Light Emitting Diode)

displays. These displays are known for faster response, better contrast

20 DE APPEL

than LCD, and longer battery life. OLED is made from thin films of lightemitting

organic materials, organic being carbon and hydrogen. These

films are placed between two conductors. When the electrical current is

applied, bright light is emitted. This light travels through the respective

color filters of a given pixel. The technology is not perfected yet, and

future advances in ink-jet printing will make the production process

faster and cheaper. But in the story of foldable phones, the OLED wins

de facto as it can be flexed and folded, when the outer screen is plastic.

While some issues were caused by people themselves destroying fragile

protective displays, others fail mechanically. Consumers expect these

hinges to be smooth, quick, controllable and strong. The best hinge will

be the one that we do not realize is even there. Most importantly, the interaction

with the fragile display is intricate. Any mechanical failure or

debris could lead to the screen bulging and breaking, before one fixes it.

Some of the first foldable phones, including Galaxy Fold, folded the display

in a crease that created high concentration failure points. These

issues lead to unwanted seams and bulges, while some even break the

phones all too soon. Improving upon these mistakes, engineers developed

the hinge that loops display in to avoid the crease like one in

Motorola Razr. But as extreme reviewers showed, these mechanisms are

still vulnerable to dust which creates irritating cracking sound with

every fold and eventually leads to screen failure.

And what about unfortunate circumstances when one sits on a phone?

The hinge will simply break with little force. All in all, these phones are

fragile.

Flexible OLED display.

Lastly, there are always improvements on the OLED displays that

further help the folding. The so-called AMOLED (Active Matrix OLED)

display family is an advanced version of OLED with an additional layer

of thin film transmitter (TFT). These transmitters are arranged in a matrix

and they effectively facilitate more rapid frequency of the pixels.

This TFT matrix also contains a storage capacitor that allows for larger

displays. The AMOLED family provides thinner and more flexible displays,

faster refresh rate, higher contrast ratio. They pay however with

higher power use.

However, just finding an effective folding screen is still not enough for a

successful and effective folding phone. When folded inwards the front of

the screen is awkward to use and does not feel like a regular phone such

as in Samsung Galaxy Flip. This is unattractive to consumers who are so

used to instant feedback with few visual pollutions. The folding screen

outwards is the solution for that problem, so that there is no edge at the

hinge. Current phones like Huawei Mate X/Xs show the beauty of such

design but also reveal the inherent flaw. These screens are quite fragile,

since plastic is quite soft in these, and will have scratches even with

most careful users. The screen alone however is not enough to make

phones appeal to picky consumers.

EFFECTIVE HINGE TECHNOLOGY

Some of the first things we learn when reading reviews about the recent

foldable phones are their failures. The screens are fragile. The hinges

are not dustproof or waterproof at the moment. Stories with titles

“Samsung delays its $2.000 folding phone after test units break” and

“Samsung’s $2.000 folding phone is breaking for some users after two

days” catch consumer’s attention and discourage potential buyers. And

for a reason.

Razr’s hinge technology.

However, one must not take these problems as a display of failure, rather

as an opportunity to improve. The mechanical challenge here provides

a unique design to create a strong and effective mechanism while

preserving the fragile screen. At the same time, sooner rather than later

these phones will have to be waterproof and dustproof. That along with

economies of scale, the cost will become acceptable for regular users

and we will step into the next era of the phone industry. a

DE APPEL 21

ASSOCIATION NEWS

IN THE PICTURE

CONSTITUTION DRINK

As the boards have changed once again, a party was called for. This

year, the constitution drink was held during the Thursday afternoon

on the 6th of February. The board was led into the basement by an

honour hedge, made up of old board members. When the newly formed

board was settled on the stage in the back of Diepzat, the old

members formed a defensive line to keep the new board safe while

various groups came to “recipieren ”. The first groups to come and

congratulate the new board, were of course the old boards of the association,

all bringing their own bottle of Apfelkorn for the new and the

old boards to enjoy. After which, the families of the new board members

were invited to come up the stage and congratulate them. Bart’s

family was well represented and the parents of several other board

members are present as well. Bart’s parents were not very surprised

at the whole event as they had experienced it before, however the

other parents definitely did not know what to expect. Some enjoyed

it more than others, despite the warnings they had gotten from the

new and old board members. Jan Bossink, an honorary member of the

association, was present this year once again at both the GMA and

the constitution drink and was also congratulating the board with

their constitution and sharing some advice for the upcoming year.

Lisa Gommer also came by to congratulate the board on behalf of the

teachers. By this time, the other study associations, disputen and

houses were invited up to the stage one by one. However, as the drinks

J

had been poured generously all afternoon already, things started to

become a bit rowdy and the first real “bras” attempts were being performed.

Luckily, the old board members were well prepared and held

off most of the attempts fairly easily, however Luuk almost got seized.

Sadly, during this attempt Luuk got hurt and had to be taken out of

the basement, resulting in the constitution drink being ended with

only six out of seven members on the stage. With the great efforts

of the BorrelCie, taking care of everyone being hydrated and cooled

down with cold beer all afternoon, it is safe to say that the drink was

a big success.

22

DE APPEL

GENERAL MEMBERS ASSEMBLY

The day before the constitution drink, the 5th of February, the General

Assembly was held where the 62nd board was presenting

their annual report and the change of boards was being approved.

Once the report and the final balance of the 62nd board were approved

by the GMA, the change of boards was suggested and approved

as well. A break was held, before the GMA was continued, now led

by the 63rd board for the first time, discussing the new policy and

budget. Some choices and changes were made to improve the new

policy and budget, but the new board was truly in function from

this point on.

ACTIVE MEMBERS ACTIVITY

As the 62nd board was coming to the end of their board year, the

active members activity was held on the 3rd of February to thank

all members that have supported them during their year. The activity

was started with a presentation in which they revealed the

active members gift to all people that had “kept them covered”. The

gift, thought of appropriately with keeping someone covered, was

an umbrella. After the presentation, everyone was invited to come

to “de Tapperij” in Hengelo for unlimited drinks and a few games of

lasertag and some games of pool. When the time was up in de Tapperij,

the party continued on to the Vesting Bar to end the evening

there.

ORIGAMI COURSE

With the Corona situation as of late, making it so that no physical

activities could be organised, activities such as the origami course

were being held instead. The origami course was held over a video

chat program and instructions were given by Jonne who had practiced

a few origamis to fold. Bunnies, frogs and apples were folded

under his instruction. As the measures for the Corona crisis have

been extended, more activities are being organised in the same online

manner to make sure everyone can still enjoy themselves in

these challenging times.

BATTLE OF THE BOARDS

As always, with the change of boards, a competition had to be held

to see who is the superiour board. The AXI set up a competition for

the old board and the newly appointed board to be able to determine

who would win this year. This, of course, was paired with some

flour, condiments and other food fight inducing products. The first

challenges were completed as they should have been, however when

the previously named products were given to the old and new board

members, this quickly escalated. In the end, it was obvious to the

AXI, who also acted as judges, that the winners were the members

of the newly formed 63rd board!

DE APPEL 23

IC TOUR

DOWN TO EARTH

Wedsnesday February 12th 2020. Twenty-eight students are

gathered at the main entrance of the UT. Most of them show

some sign tiredness, but most look amazingly eager: an exciting

journey of three weeks is about to start. Together with four

accompanists, split over the three weeks, the students are

headed to Indonesia and Australia. Fires, heavy floods and even

earthquakes could not stop the committee from organizing an

amazing trip Down Under.

24 DE APPEL

After a heavy goodbye from friends and family, it was time to leave

for Schiphol. These two hours already proved challenging, with no bathroom

breaks and a lot of students drinking beer. Luckily, the route

was provided with no traffic jams and everyone arrived safely at

Schiphol. Here, already the first ‘buddy checks’ were carried out and

everyone turned out to be there, how nice! After everyone was deemed

fit to fly, we could go aboard and fly to our first stop: Doha. Onboard

there were multiplayer games, one hour of free Wi-Fi and a very wide

selection of cocktails, which meant everyone survived the flight pretty

well. Doha airport turned out to have an almost see-through train, riding

from one gate to another. This made the two and a half hour overlay

easy to survive and within no time everyone was on board of the

next flight. Destination: Jakarta. What a city! Cruising in our bus with

green-leathered chairs that could bend more than those in the airplanes,

we felt very save. Not because of the traffic, but rather because of

the terrific skills of our bus driver, as well as the comforting words of

our guide, Hadi. Even though Google Maps made us believe that our

route would only take ten minutes, we were lucky to be there in forty.

The traffic is chaos. If an ambulance would want to pass you would not

hear it, because of all the honking everywhere. The arrangement of

the buildings is exactly the same: markets consisting of four pieces of

wood are situated next to a local car dealer. Why not?

In the hotel, everyone got some time to freshen up before we had to

leave for our dinner. Even though everyone was quite tired, the buddy

checks were soon completed, because a great first evening awaited.

The committee arranged for a dinner in the Skyebar, the second highest

building in Jakarta. Once we finally found the right building,

we had to go almost sixty floors up. Normally that takes several minutes

in the elevator. Luckily, this one took less than a minute. The

view from up the restaurant was beautiful and the city looked even

more enormous. After a delicious dinner we discovered the rooftop bar

where the view on the other side of the city could be admired. Soon,

however, fatigue kicked in and since our alarm was set for 05:30 in the

morning, everyone headed to bed soon.

The first breakfast in Indonesia did not disappoint us, since we were

served with nasi. Some, however, were still clinging to home so chose

for bread instead. We soon left for the first company visit: KHI pipes, a

manufacturer of pipes. We were kindly welcomed and a lot of people

were introduced. They even provided us with some treats from Holland

Bakery, which were unfortunately not real Dutch treats. After a

general introduction and a safety movie, we were approved to visit the

factory. This was enormous and we could see everything. Afterwards

there was time for some last questions, followed by many thank you

from both sides. Before we went to the next company, it was time for

some lunch. Somehow, we ended up at a resort with a walking buffet.

It all tasted very good. Some were courageous enough to try some

spices, who were rewarded with a soaking shirt. Luckily, that would

dry soon enough at the following company, Krakatau-Posco, which is

the biggest steel manufacturer of Indonesia. Their terrain was even

more enormous than the previous company and the temperature inside

rose far beyond the one outside, which was already above thirty

degrees Celsius. The production process was in one word amazing,

with the highlight the rolling of the plates of steel. Back in Jakarta,

everyone could go their separate ways. Some stayed closer to the ho-

DE APPEL 25

tel, others visited the city centre or harbour. All with one commonality:

exploring Jakarta’s night life.

Saturday it was time to leave Jakarta for Bandung. Already the first people

had fallen ill, which caused some delay in leaving. This also caused

our bus trip to be shorter since we skipped a detour. In Bandung we

experienced the first rain. The hotel did not allow us to walk the three

meters from the exit of the bus to the entrance of the hotel in the rain,

so we were accompanied by one of the staff members who held an umbrella

over our heads. After settling in and exploring the indoor pool, it

was time for dinner in one of the many restaurants in the close-by mall.

None was big enough to fit all thirty of us, so we decided to split up.

Most of us got together eventually at the karaoke bar next to the hotel

where everyone’s singing talent was revealed. This caused throat ache

for some the next morning. Luckily, speaking was not necessary for we

went rafting. We had plenty of time to go there, were it not for the bus

driver heading the wrong way. Therefore, we did not arrive on time.

Again. This could not stop the perfect mood of the instructor, so we

were soon dragged in by his enthusiasm. The team building activities

turned out to be more for the giggles of the bystanders. It did not matter

however, because we were pumped to start rafting. In two tiny pickups

we left for the starting location and soon we arrived at the boats. Even

though our instructor told us the necessary Indonesian words to survive,

the pronunciation of the raft instructors sounded different and we

could not make anything of it. This only caused more fun on both sides

and it did not harm the entire tour. Eventually everyone arrived wet,

but uninjured.

The next morning, the alarm already went off at 05:30, but luckily two

students had planned entertainment for the morning. They arranged

a morning workout with music pumping through the lobby. Tiredness

changed into enthusiasm and everyone was ready to eat breakfast and

leave for the company visit. The road there was quite amazing, with a

lot of tea fields. We arrived at the geothermal plant and received a warm

welcome. With a presentation, a tour through the control room and a

close-up at the turbines, the visit was concluded. On our way back we

stopped at the tea fields to make pictures for our family and friends at

home. How beautiful they have become. We then drove back to Bandung

and everyone could decide how they wanted to spend their evening:

some ill in bed, others having dinner and beers at the mall.

26 DE APPEL

Our last day in Bandung was spent visiting ITB, the technical university

of Bandung, which was founded back in 1920 by multiple Dutch engineers.

Two department heads of mechanical engineering told us how a

study mechanical engineering is organized there. Two students gave us

a tour to several labs and around the campus. After a goodbye and many

thanks, we went for lunch, where most chose the Burger King over Indonesian

food. What a pity. Some then went for a spa treatment, where

others visited the cinema for an Indonesian movie. Everyone gathered

at the train station where the night train to Yogjakarta, Yogja for short,

awaited. Where some night trains have beds, this one had not, and we

were presented with airplane seats. Since everyone was very tired, this

proved no problem for most. The one thing that did keep people from

sleeping through the entire night, was the horn of the train driver that

he seemed to be using every two minutes. Luckily upon arrival it turned

out that we could immediately go in our hotel rooms and since we had

the morning off, most used it to get some sleep. Also eating breakfast,

doing laundry and watching Harry Potter proved to be very popular

activities. A couple of hours later we gathered for a jeep tour close to

the Merapi volcano. The museum that we visited with our jeeps was

quite impressive, as were the driving skills of everyone’s driver. When it

started raining, some groups used their roof cover, where others just accepted

their fate. With a last couple of rounds with the jeep in the river,

the jeep tour had finished, with some of the group drenched. Since the

rain did not stop for the rest of the day, all afternoon plans were cancelled

and we had a relatively quiet evening.

Thursday, we headed for Quicktractors. Even though the company was

different than expected, it still made tractors and we all felt at home.

A key factor here was the collaboration with Kubota, a large Japanese

manufacturer of small engines. The factory turned out to be largely automated,

which was completely different from the company we visited

thereafter. ED Aluminium produce aluminium cookware in the traditional

way and car parts using a CNC machine. Especially the traditional

manufacturing of the cookware stunned a lot of students. The rest of

the afternoon was therefore filled with exploring the pool and in the

evening, everyone looked for a place to eat at the very popular Malioboro

street.

The university of Yogjakarta was the last company visit in Yogja, but

also in Indonesia. The university asked a couple of their student teams

DE APPEL 27

to be present so we could ask about their progress and organization

and vice versa. Two students also joined our bus for a tour around the

campus, where we stopped at several important buildings or hotspots

of the university. Back at the hotel and after a shower, some sleep or a

visit to a temple, we headed for the last evening dinner with our two accompanists.

A visit to Cubic Club and another club concluded their last

evening. In the morning we finally visited the Borobudur temple. Since

everyone was healthy again, all students could join this time. The committee

had decided to leave early, which caused some sad faces at first.

Later, everyone was very happy with this decision because the temple

had no trees to give shadows and the sun did a very good job that day.

Our guide at the temple told us some interesting stories about its history

and afterwards we were free to roam the grounds. The temple itself

was very impressive, though we were happy to leave after a couple of

hours in the heat. A heavy goodbye from our two accompanists awaited

and afterwards we were left on our own. The Scavenger Hunt was next

on the programme with seven teams aiming to win. Taking a ride in a

scooter taxi, singing the Newton anthem, switching clothes with a local,

asking to go to the toilet because you have diarrhea, were just some of

the challenges to gain points. Reunited at dinner, everyone shared their

stories whilst enjoying food from the food court.

The next day we had a flight to Bali. After a delicious western lunch,

with burgers, we went to the harbour where quite a nice boat was waiting

for us. ‘What happens in Bali, stays in Bali’, so unfortunately, not

a lot can be told about this legendary evening. However, it can be said

that some have lost more than others. For more details, please visit the

(online) Thursday afternoon drinks. The results from the evening before

were still visible during breakfast. Half of the group had rented cars to

cruise the inland and the other half decided to go to the beach and tan

over there. Some were too enthusiastic and their tanning resulted in

more red than brown skin to be shown later on. In the evening it was

time to leave Indonesia and head towards Australia.

Having arrived in Adelaide, after a 5 hour flight, we felt immediately

more at home. The air was not as humid and the temperature not above

30 degrees, what a relief! Since everyone was quite stiff from our flight,

we headed straight towards the Wildlife Zoo where we saw kangaroos,

wallabies and koalas. We could even touch all of them! This cheered

everyone up which made the meeting with the local ME students that

evening actually very fun. The next morning was a bit of a chaos, since

breakfast had to be shared between pairs of houses. Which resulted in

bargaining with the neighbours over who got to keep the ham. Luckily,

we still arrived at the university of Adelaide on time. After a structured

tour to the labs and a tour around campus, we visited a start-up from

students at the university. Presentations as well as questions from both

28 DE APPEL

sides followed and everyone could head home to prepare for barbecuing

at our holiday park.

On Thursday we visited two companies. The first company used to be

quite big in numbers but decayed over the years. The man that gave

us a tour worked there for decennia and could describe perfectly how

it used to run there. And also about how many colleagues he had lost

due to illnesses. We soon jumped in the bus for the next visit to a company

which manufactures components for automotive and aerospace

industry. A real difference with the other visit. Back at the camping, we

once again used the barbecues and enjoyed the local specialty known

as Goon. As if two company visits on one day is not enough, the next

day we had three. This could not fit in the programme however, so we

had to split up in the afternoon. In the morning we were still together

visiting the South Australia Space Industry Centre. The tour covered

their brand-new innovation hub, which used to be an old hospital. In

the afternoon we visited a company which did maintenance on airplane

motors. The employer who gave the tour was very capable, knowing

everything about every process! The other company who renovated

and maintained airplanes. We even got to see their hangar where they

disassembled and assembled all their airplanes, very cool! The last evening

in Adelaide was once again spent at the camping cooking food. No

barbecue today, instead there was shoarma and pasta. Since everyone

gained a lot of energy from all the beer and Goon, we went to the city

centre and enjoyed the last day in Adelaide.

With tired eyes from either the lack of sleep or the labour of cleaning

the houses, we left our camping and continued our journey to the last

city: Sydney. Our hostel is right next to Sydney central station, situated

in the centre of the city. Having found the right rooms, we headed to

Spice Alley, since some were a bit homesick for Indonesia. The spices

turned out to be not so bad and everyone soon headed to the gay parade.

Following the noise, we easily found the parade, it even showed

on Google Maps. Finding a place where we could see the carriages was

far trickier. Luckily, we did see them and the entire parade was quite

impressive. The party, as well as several students, continued to the local

bars till late in the night. Most of us returned home, however, since we

visited the Blue Mountains the next day there was a bit of sleep to catch

up on. With six hours of free time and a ticket to use two cable trains

and a steep train, everyone could do what they wanted. Some decided to

take the train down and walk 900 steps up in the burning sun. Others

found this idea less attractive and chose to take the cable train and

walk down from there. But in the end, everyone arrived back six hours

later having had a great experience. The Australian experience continued

since we ate kangaroo the same evening. Furthermore, the Sydney

Opera House was just around the corner so should not be missed.

DE APPEL 29

Some already felt the muscle ache the next morning, but most were

eager enough to visit companies again. First up was Sydney University,

where we visited the robotics lab. We were told about several research

topics, from picking fruit to designing submarines and drones. During

the campus tour we discovered that the buildings were quite old and

beautiful. The next company used a nuclear reactor to produce isotopes

used in medicine and research. The women giving the tour seemed

to know everything and no one left with questions unanswered. The

next day we visited once again a steel manufacturer, but this time in

Australia. Once we were equipped with the right gear and had seen the

instruction movie, we could visit the plant. We were allowed to see more

than usually at a steel factory, which made the students more eager to

watch. After getting dinner, we gathered for a pub quiz. The location was

quite close to home, namely in the cellar of the hostel, which changed

into a dance club in the evenings. Unfortunately, no team made the top

three, so instead we chose to make the best of the night by drinking

beer. Some stayed at the club, others went for special beers in another

part of town. A couple hours later we returned to the club, which had

now transformed into a breakfast place. Unfortunately, the smell of the

previous evening still lingered, so most decided to leave immediately.

If some students still needed to catch some sleep from the night before,

today was perfect for this. After nearly three hours on the road,

we arrived at the power plant. There we were surprised to see that a

group of twelve-year-olds had the same tour as we did. The presentation

was also adjusted to make sure these kiddos could understand it. Once

we asked our questions, we saw the concentration of the kiddos slowly

fade away. The presenter would also answer almost no questions due

to fear for the media. The tour did not give us any more information

since we had one person to give it and sixty kiddos and students to follow

it. Luckily, kangaroos found the plant very habitable, so there was

still enough to see for us. Back in Sydney, the committee had a surprise

activity planned for the evening. It turned out to be a fancy six-course

dinner on a boat. The food, view and drinks made for a perfect evening

and everyone left the boat in a very happy state. Since most still had a

lot of energy left, we went either in the city centre or in the bar below

our hostel to dance the just gained calories off.

30 DE APPEL

The last day has arrived. After our disappointing visit yesterday, no one

was really eager to visit the last company. Our feelings changed soon,

however. Hycast Metals uses investment casting to cast metals. Therefore,

very complex shapes can be produced. Two men gave a tour around

the factory, with a lot of passion and enthusiasm. Since we could also

see everything in the factory, everyone remained very interested. One

question followed after the other and before we knew we had concluded

our final company visit. The last bag with stroopwafels and notebook

was handed out and we made our last group picture. Upon arrival the

rain had not stopped, so the Bondi Beach visit was cancelled. No one

really minded, because now we had some free time to roam the streets

or catch some more sleep before the final evening. The last dinner took

place at a Mexican restaurant. Since everyone was quite hungry, most

ordered a starter and a main meal. The starter, however, turned out to be

almost enough to fill a belly, so we had some trouble finishing our meals.

To buy some time, the non-committee students had prepared a thankyou

for the committee members. A great speech and six handmade didgeridoos

were given as presents for the committee members. After this,

everyone was finally done and we headed to the Ivy Pool Bar, where

we had two lounges for ourselves. The only catch from the committee

was that we had to drink a certain amount of beer and wine, since we

already paid for it in advance. Everyone tried their very best and we had

nearly succeeded when suddenly we had to go. Apparently one student

was kicked out of the bar. Luckily, he managed to sneak back in past the

bouncers and the challenge could continue! Not so much later, we had

finally finished and left the pool bar to either continue in the city centre

or return home, with a stop for some extra food. The next morning

mainly consisted of saying goodbyes and wishing everyone either a safe

flight home or a safe journey elsewhere. After reminiscing some of the

events of the past weeks, it is clear that no one will ever forget this time.

A huge thank you to all who joined and especially to committee who realized

the tour, it was truly an amazing and unforgettable experience! k

DE APPEL 31

SODIUM

VAPOUR

LAMPS

DECEIVINGLY DIM

BY FAUSTO VISSER

At night when the streetlights turn on, the neighbourhoods are doused in light. The

street lighting in public places can be very different depending on when the lights

were installed. One must recognise the characteristic amber glow which floods into

the streets at night. Nowadays these are being phased out and are slowly replaced

by white lamps. The highways in The Netherlands and especially in Belgium are well lit

with this colour light. Have you ever wondered why these lights are yellow instead of

the normal white lamps? I certainly hope so because the next paragraphs will cover

this in depth.

32 DE APPEL

In the 1930’s the first trials with these lamps were run between the

small towns of Beek and Geleen. This was to replace the existing mercury

lamps that were in place as the defacto lighting in that time. Sodium

lamps showed real promise as a much more efficient form of lighting.

These bulbs can produce around 100 lumen per watt which is a lot considering

modern LED lighting can provide around the same efficiency.

Especially when considering that the previous mercury vapour lamps

could only produce around 50 lumens of light per watt. This seems like

a major improvement as this lamp would seem twice as efficient as the

old ones.

A UNIT FOR OUR EYES

To further explain we will dive into the unit of lumens. The lumen is

a derived unit and not one of the base SI unit. The lumen is defined as

candela · steradians. Candela (cd) is the SI base unit for light intensity

and the steradian describes the solid angle. Just like with radians where

with 2 pi the entire circumference of a circle will be traversed, 4 pi

steradians is the entire area of radiated sphere. Say for example all light

would only radiate out the top half of a lamp, that would be 2 pi steradians.

Be that for what it may, the candela part is more interesting for now.

Candela, as said before, quantifies the intensity of light or in other words

electromagnetic radiation. But the measure is meant only for visible

light, so you might ask what the limit for what counts as visible light is.

What we define as visible light is only dependant on the workings of the

human eye, there is nothing intrinsically different about the electromagnetic

radiation in this range compared to most other wave lengths.

Normally we adhere to about 380 to 740 nm for this range. But when

defining a unit any haziness defeats the whole purpose, a standard way

of windowing was necessary. In 1924 the Commission internationale de

l’éclairage (CIE) decided upon the following standard weighting of each

wavelength. The CIE is still relevant now in the design world as it works

together with ISO and is the governing body for the CIE colour space. It

was not enough to simply decide upon an upper and a lower bound as

the perceived brightness gets lower when moving towards the edge of

the visible range. As such a weighting curve is applied.

MEASURING ‘BRIGHTNESS’

Effectively the incoming brightness is multiplied by a wavelength specific

factor and then summed to get the total incoming intensity. This

luminosity function was constructed based on subjective testing with

subjects. Subjects were shown two different wavelengths and were to

choose which was brighter. The function is generally considered to be

representative of the human visual brightness perception it is still empirical

in origin. And thus also open for debate, remarkably no major

changes have ever occurred to the official standard recognised by ISO.

Even though there have been proposed new curves that would increase

the influence of the short wavelength, around blue and violet light.

This curve tries to capture the perceived intensity per wavelength by

the average human eye. The visual experience of humans is dependent

on the individual contributions of many parts of the optical system.

Currently the sensor cells are important as these are the actual parts

that convert the incoming light to an electrical stimulus. These cells

are present in the human eye in a few variations, the cone cells and the

rod cells. The rod cells provide the contrast by being very sensitive but

not skewed to one side of the colour spectrum. The cone cells provide

our colour vision on a trichromatic basis, three different variants that

either are triggered by short, medium or long wavelengths help us differentiate

which ‘colour’ is entering our eye.

EFFECTIVENESS OF LIGHTING

Using this background knowledge we can expand upon the sodium

vapour lamps. The lamps provide a very narrow range of wavelengths

around the yellow colour. Virtually monochromatic as it would only

output 589 nm light concentrated in a 1 nm wide band. To state the

obvious street lighting is used almost exclusively at night, cone cells

that provide colour vision are not sensitive enough in the night and

thus provide little information. Night time vision or scotopic vision relies

wholly on the performance of the rod cells to provide contrast. If we

look at the graph we can see that the amber light lines up well with our

colour vision with a weighting of about 0.85. But in contrast the excitation

in the rod cells is marginal at only 0.1. This means that at night

this light only excites the working vision system very little. As standard

only the photopic curve (the green line) is used to calculate the light

output in candela, thus effectively these sodium vapour lamps only stimulate

our eye eight times less than the candela number would suggest.

In current times LED’s have become powerful enough to entirely replace

the current sodium vapour lighting. Just in terms of lumens per watt

these lamps are very comparable. But due to how the human eye works

combined with our way of measuring light the difference is going to be

much greater than the numbers at first suggest. F

1

0.5

Luminousity function [-]

Photopic Vision

Scotopic Vision

Sodium Vapour Peak

0

350 400 450 500 550 600 650 700 750 800

wavelength [nm]

Human scotopic and photopic vision.

DE APPEL 33

GESCHIEDENIS VAN HET LICHT

MAKEN, GEBRUIKEN, ONDERZOEKEN

DOOR KOEN KLEVERWAL

We staan er waarschijnlijk niet

vaak bij stil, maar het is een enorme

luxe dat na het indrukken van een knop

een hele kamer, zelfs een heel huis verlicht

is. Dit is een luxe die pas tientallen jaren bestaat.

Daarvoor zijn er veel verschillende methodes van

verlichting geweest, sommige beter dan andere. Naast het

gebruik van licht, werd er ook veelvoudig onderzoek naar gedaan.

Hier onder volgt een overzicht van de geschiedenis van het licht.

34

DE APPEL

De eerste mensen leefden enkel met het natuurlijke licht, overdag van

de zon en ‘s nachts van de sterren. Hier en daar zou wel een brandje zijn

geweest, maar het duurde tot 400000 voor Christus voordat mensen

met opzet vuur maakten. Naast licht bracht het meer voordelen met

zich mee. Het zorgde voor warmte en de mogelijkheid tot koken. Hiermee

leefden de mensen een lange tijd, tot in 13000 voor Christus mensen

primitief lampjes gingen maken. Deze bestonden uit holle stenen of

schelpen met hierin wat mos en dierlijk vet.

Rond 3000 voor Christus hadden de Egyptenaren het ontwerp van de

primitieve lampjes verbeterd, in de vorm van een olie lampje. Bestaand

uit een reservoir met hierin een lont die werd aangestoken, wat zorgde

voor een stabiel vuurtje.

Daarnaast is er ook de mythe dat de Egyptenaren al elektrisch licht hadden.

In de tempel voor de godin Hathor zijn drie stenen reliëfs gevonden

die veel weg hebben van een gloeilamp. Bestaand uit een glazen omhulsel,

met een gloeidraad erin en een draad die eruit loopt. Als dit geen

bewijs is dat de Egyptenaren bezoek hebben gekregen van aliens, weet

ik het ook niet meer.

De volgende grote stap in de geschiedenis van het licht is de ontwikkeling

van kaarsen. Rond het jaar honderd begonnen de Romeinen met

het maken van kaarsen. Deze kaarsen verschillen niet zo heel veel met

onze huidige kaarsen. De kaars bestond uit een lont omwikkelt met bijenwas.

Ook worden er nog steeds primitieve olielampen gebruikt. Na

deze ontwikkeling gebeurde er een lange tijd niks nieuws qua methoden

verlichting.

Wel werd er onderzoek gedaan naar het fenomeen licht. Onderzoek naar

licht begon al bij de oude Grieken. De grote namen zoals Socrates, Plato

en Aristoteles filosofeerden over van alles, en ook over het licht. De volgende

quote van Aristoteles laat zien dat ze in die tijd toch al enig idee

hadden van licht nou precies is: “De essentie van licht is wit licht. Kleuren

zijn opgemaakt uit een mengsel van licht en donker.”

Euclides, een wiskundige die leefde rond 300 voor Christus, heeft alle

kennis die vergaard was over licht, reflectie, diffusie en het zicht samengevat

in het boek Optics. De concepten vastgelegd in dit boek hadden

grote invloed op het onderzoek van Newton naar licht. Maar tussen Euclides

en Newton was er nog een grote en waarschijnlijk wat onbekende

onderzoeker bezig met onderzoek naar licht.

De onderzoeker, in Europa bekend als Alhazen, was rond de 11de eeuw

druk bezig met onderzoek naar optica. Gedurende 10 jaar schreef hij het

zevendelige Book of Optics. Het boek focuste vooral op weerleggen van

de emissie theorie. Hoewel dit gek klinkt, een theorie tot die tijd over het

algemeen als de waarheid genomen werd. Die theorie hield in dat dat je

zicht had doordat er een zogenaamde oogstraling uit je ogen kwam, die

reflecteerde op de omgeving en weer opgevangen werd door je ogen, wat

er voor zorgde die je kon zien. Aan de hand van de kennis van toen over

lichtreflectie en de anatomie van het oog heeft Alhazen een bewijs tegen

de emissie theorie kunnen vinden. Uit een onderzoek uit 2002 bleek

dat 50 procent van de volwassen nog geloofden in deze emissie theorie.

NEWTON VS HUYGENS

De volgende in de rij belangrijke onderzoekers van het licht zijn Newton

en Huygens, die beide andere standpunten hadden over wat licht nou

precies was.

Newton heeft in zijn boek Opticks de fundamentele aard van het licht

geanalyseerd, aan de hand van de breking van het licht door prisma’s

Egyptische olielamp.

DE APPEL 35

en lenzen, diffractie en reflectie. Het belangrijkste uit het boek is dat, in

tegenstelling tot Aristoteles, Newton dacht dat wit licht alle mogelijke

tinten licht bestond. Ook dacht Newton dat licht uit deeltjes bestond.

Dit is waar hij anders dacht over de aard van het licht dan Huygens.

De Nederlandse Huygens is bekend van zijn werk met lenzen en zijn

ontdekkingen op het astronomie gebied. Zo ontdekte hij de maan van

Saturnus, de ringen van Saturnus en de orionnevel, dat allen met zijn

zelf gefabriceerde telescoop. Daarnaast hield hij zich ook bezig met onderzoek

naar licht. Door licht als golven te zien kon hij de fenomenen

reflectie en refractie uitleggen. Na meerdere rumoerige debatten tegen

van Newton werd de theorie van Huygens als algemeen correct gezien.

DOUBLE SLIT EXPERIMENT

Een kleine honderd jaar later, in het begin van de negentiende eeuw,

is door de fysicus Thomas Young, de Young bij ons bekend van van de

Young’s modulus, bewezen dat licht daadwerkelijk uit golven bestaat,

door de bekende “Double slits experiments”. Een korte uitleg van deze

experimenten is als volgt: Licht schijnt vanuit een lichtbron door twee

parallelle spleten in een donkere ruimte. Als licht daadwerkelijk uit golven

bestond zou het licht uit de spleten op sommige plekken uitdoven

en op sommige plekken juist versterken. Dat patroon van versterking en

uitdoving zou zichtbaar moeten zijn als licht uit golven bestond, als licht

uit deeltjes bestaat was dat niet het geval. Uit Young’s experimenten

was dat patroon van interferentie duidelijk zichtbaar en had hij hiermee

bewezen dat licht uit golven bestond.

GLOEILAMP

Toen Thomas Young nog een jong jochie was, was er voor het eerst in

tijden weer een duidelijke verbetering op het gebied van verlichting. In

1780 verbeterde Ami Argand de al bestaande olie lamp aanzienlijk. Zijn

lamp brandde langer en feller dan alle voorgaande olielampen. Rond dezelfde

tijd dat deze uitvinding plaatsvond was een andere wetenschapper

ook aan het stoeien met lampen. William Murdoch maakte een lamp

gebaseerd op steenkool gas. Naast de uitvindingen van Argand en Murdoch

gebaseerd op respectievelijk olie en gas, werd er in die tijd ook al

geëxperimenteerd met elektriciteit.

Hierna was de grootste uitvinding op het gebied van verlichting, een

die we tot deze dag nog steeds gebruiken, de gloeilamp. Thomas Edison

heeft die uitvinding op zijn eigen naam geschreven, maar in werkelijkheid

is het een hele rits aan uitvinders die telkens verder bouwden op

elkaars werk, zoals met veel uitvindingen. De basis was al gelegd door

Humphry Davy. Ruim 40 jaar later had de Britse wetenschapper Warren

de la Rue een efficiënte gloeilamp gemaakt. Alleen, had deze lamp wel

meerdere problemen. Het grootste probleem met die lamp was dat er

platina in gebruikt werd en platina is niet per se goedkoop.

In 1848 had een andere Britse uitvinder een uurwerk mechanisme toegevoegd

aan zijn lamp om de benodigde koolstofstaven van de lamp te

besparen, anders zouden deze namelijk vrij snel eroderen. Maar, dit ontwerp

had ook weer een groot probleem. De batterijen die nodig waren

om de lamp en het uurwerk te laten draaien waren ontzettend duur, dus

dit ontwerp was ook geen commercieel succes.

Een andere Britse uitvinder, de chemicus Joseph Swan, heeft in de jaren

60 van de 19de eeuw het probleem qua kosten opgelost, dat deed hij door

het platina te vervangen door verkoold papier. In 1878 kreeg Swan een

patent op zijn ontwerp, maar desondanks werkte zijn ontwerp zeker niet

vlekkeloos. Swan plaatste zijn gloeidraad in een vacuüm, maar de vacuümpompen

waren bij lange niet zo efficiënt als ze nu zijn, zijn prototype

werkte lang genoeg voor een demonstratie, maar niet lang genoeg om

praktisch te zijn voor dagelijks leven.

Edison had de lamp van Swan verbeterd door te experimenten met verschillende

gloeidraden, die het langer volhielden in het vacuüm dat toen

mogelijk was. Uiteindelijk vond hij er een die het 1200 uur kon volhouden.

Hiermee was de basis voor de moderne gloeilamp gelegd.

NEON

Begin twintigste eeuw was een ander soort lamp populair, namelijk

neon verlichting. De basis van de benodigde technologie is in 1675 al gelegd,

voor de tijd van elektriciteit. De Franse astronoom Jean Picard zag

een vage gloed van een buis gevuld met kwik afkomen. Wanneer de buis

geschud werd, begon die gloed feller te worden. Alhoewel ze in die tijd

nog niet wisten hoe het werkte, werd er wel onderzoek na gedaan. Later

bleek dat die gloed veroorzaakt werd door statische elektriciteit. Begin

1900 waren er inmiddels al meerdere lampen gebaseerd op dit principe.

Deze bestonden uit glazen buizen met verschillende gassen, en door dan

een spanning aan te brengen begint de buis te gloeien. De fransman

Georges Claude deed dit met het net ontdekte neon gas. In december

Neon.

36 DE APPEL

Edison’s gloeilamp.

DE APPEL 37

Double slit experiment.

1910 kreeg hij het patent op de eerste neon lamp en 10 jaar later was neon

verlichting overal een populaire verschijning.

EINSTEIN

Toen Huygens met zijn theorie kwam dat licht een golf was, werd dit

uiteindelijk als de waarheid aanvaard. Het enige wat het deze theorie

niet kon verklaren is het foto-elektrisch effect van licht. Dit houdt in

dat wanneer een atoom voldoende energie opneemt van licht, er een

elektron kan loskomen. Maar, licht als een deeltje zien verklaart andere

eigenschappen het licht ook weer niet. Hier komt Einstein in het plaatje.

Einstein was een van de eerste die uitging van dat licht zowel een golf

als een deeltje kan zijn. Hij koos ervoor om licht als een deeltje te beschouwen

wanneer dat goed uitkwam en licht als een golf te beschouwen

wanneer dat goed uitkwam. Ook beschrijf Einstein licht te bestaan

uit fotonen. Deze revolutionaire ideeën hebben geholpen bij het begrijpen

van licht, maar werden nog wel als

LASER

Einstein kwam met de suggestie dat onder de juiste omstandigheden

atomen hun extra energie konden afgeven in de vorm van licht, ofwel

spontaan of door stimulatie met licht. Deze uitspraak ligt aan het begin

van de LASER. De Duitse fysicus Rudolf Walther Ladenburg is de

eerste gestimuleerde emissie zag plaatsvinden. Echter bleek er in die

tijd geen praktisch gebruik aan te zitten. Pas later, rond 1950 gingen

mensen weer met dit concept aan de slag. MASERs werden gebouwd.

MASER staat voor “Microwave Amplification by the Stimulated Emission

of Radiation”. Het bleek dat MASERs helaas maar voor enkele applicaties

bruikbaar waren. Op de techniek werd wel verder gebouwd. Apparaten

ontstonden met golflengte rond infrarood- of zichtbaar licht, in plaats

van microgolven. Deze apparaten zijn de apparaten die we nu kennen

als LASERs.

TERUGKOMEND OP DE DOUBLE SLIT EXPERI-

MENTS

Licht blijft een ingewikkeld iets. Als we terug gaan naar de “Double slit

experiments” en het feit dat licht zowel een deeltje als golf kan zijn zou

je denken dat, wanneer er meerdere fotonen door de spleten gestuurd

worden, een interferentie patroon ontstaat, maar als je er maar één foton

tegelijk doorstuurt je geen interferentie patroon krijgt, maar uiteindelijk

achter elke spleet een lijn. Dat bleek niet zo te zijn, er ontstaat juist

wel een interferentie patroon bij een enkele foton. De foton interfereert

met zichzelf. Heel simpel gezegd: de foton ‘zet zichzelf om’ naar golven,

hiervan gaat 33 procent door de linkerspleet, 33 procent door de rechterspleet

en 33 procent raakt de barrière.

Deze versie van het Double split experiment nog een keer uitgevoerd,

alleen wilden wetenschappers het gedrag van een foton observeren.

Het resultaat was alleen anders dan verwacht, het interferentie patroon

was niet zichtbaar, daarentegen was er een streep zichtbaar achter elke

spleet. Doordat de foton geobserveerd werd, vond de ‘omzetting’ van

deeltje naar golf niet meer plaats of voor de spleet.

Nog een andere versie van de Double slit experiment maakt het geheel

nog wat verwarrender. John Wheeler, een Amerikaanse natuurkundige,

wou onderzoeken of licht door had hoe het systeem dat gebruikt werd

om het te onderzoeken in elkaar zat. Wheeler voegde een extra plaat

met spleten toe aan het experiment, die bestuurd konden worden, zodat

er een of twee spleten open waren. Hoeveel spleten open stonden werd

veranderd tijdens de vlucht van de foton. Het idee hiervan is dat de foton

van te voren moet beslissen welke route het neemt, en een deeltje

of een golf is, en daarna iets te veranderen zodat het de andere vorm

gekozen zou hebben. Dus laten beginnen als golf en dan iets aanpassen

zodat deeltje beter was geweest. Het blijkt dat wanneer dit gebeurt licht

kiest voor wat het beste is na de verandering, zonder dat die verandering

al plaatsgevonden heeft. Zo beïnvloedt de verandering in de toekomst

het heden, zonder dat de keuze voor de verandering gemaakt is. Dit onderzoek

heeft bewezen dat licht zowel een deeltje en een golf kan zijn,

tegelijkertijd.

CONCLUSIE

Licht blijkt toch een verdraaid lastig iets, of iets simpels. Om het compleet

te snappen is haast niet te doen. Gelukkig is het licht aanzetten

met ‘a push of a button’ gedaan. k

38 DE APPEL

where

great

minds

work

Wij zijn een groep High Tech bedrijven in Noord-Nederland die de krachten hebben gebundeld om samen

te werken aan oplossingen voor de grote uitdagingen van de toekomst ‘on the edge of technology’; ‘the

internet of things’, big data, robotics, 3D printing en alternative energy. Dat doen we door de modernste

High Tech te gebruiken of waar nodig zélf te ontwikkelen. Dat kan door de unieke samenwerking van onze

R&D-afdelingen, waarin onderlinge concurrentie heeft plaatsgemaakt voor het versterken van elkaar. Het

resultaat is meer dan 50 nieuwe productintroducties per jaar wereldwijd. Productintroducties die onder

andere mensenlevens redden, de bediening van complexe systemen kinderlijk eenvoudig maken, producten

afstemmen op de individuele wensen en behoeften van consumenten en data toegankelijk maakt om de

kwaliteit van voedsel te verbeteren. Onze samenwerking heet Innovatiecluster Drachten en vormt ‘The heart

of the smart factory region’ van Noord-West Europa.

icdrachten.nl

CHIPS

IN DE VERLICHTING

DOOR ALMER LAGERWEIJ

In de computingwereld speelt Nederland al geruime tijd goed mee. Iedereen kent ASML

wel, dat vanuit Veldhoven de technische grenzen verlegt om de befaamde wet van Moore

enigszins in stand te houden door chipstructuren op steeds kleinere schaal te kunnen maken.

Verschillende universiteiten en bedrijven werken aan een kwantumcomputer die ongekende

eigenschappen zou moeten krijgen, mits de theorieën in de praktijk te brengen zijn. NXP

moeten we ook niet vergeten, leider op de snelgroeiende markt van chips voor auto’s.

Als het aan deze industrie in Nederland ligt, komt daar een nieuwe, belangrijke tak bij: fotonica.

Overheden, bedrijven en universiteiten kwamen vorig jaar overeen om de komende acht jaar

meer dan 240 miljoen euro te investeren in de Nederlandse fotonicasector, waarvan 100

miljoen in Twente. Verenigd in een publieke-private samenwerking genoemd PhotonDelta.

De regio Eindhoven speelt een belangrijke rol bij dit initiatief, maar ook de Novio Tech Campus

in Nijmegen, de Radboud Universiteit Nijmegen, evenals de universiteiten en techbedrijven in

Twente en Delft. Sinds 2018 huisvest het Photonics Integration Technology Center Twente zich

op het Kennispark. Dit nieuwe centrum, ook wel PITC Twente helpt met het overwinnen van

obstakels om de massaproductie van fotonicachips waar te maken.

40 DE APPEL

FOTONEN IN PLAATS VAN ELEKTRONEN

‘Fotonica’ is heel breed; het gaat om technologie die zich richt op het

opwekken, transporteren, bewerken en detecteren van licht, oftewel

fotonen. Zo vallen bijvoorbeeld beeldschermen, verlichting, lasers, zonnecellen,

sensoren en glasvezelnetwerken er allemaal onder. Waarin Nederland

nu wereldwijd het voortouw neemt, zijn de essentiële stappen in

de ontwikkeling en productie van chips die werken op basis van fotonen

in plaats van elektronen.

Deze chiptechnieken moeten een belangrijke rol gaan spelen bij onder

andere datacommunicatie, gezondheidszorg, duurzaamheid, mobiliteit,

veiligheid en landbouw. Naar schatting zijn al bijna driehonderd bedrijven

in Nederland actief op het gebied van fotonica. Daar moeten er nog

vele bijkomen als het aan Ton Backx ligt. Hij is directeur van het Institute

for Photonic Integration en voormalig topman van PhotonDelta. “In

1947 is de transistor uitgevonden, in 1958 volgde het eerste geïntegreerde

circuit, en in 1968 ontstond Intel, en formuleerde Gordon Moore zijn befaamde

wet. Micro-elektronica heeft sindsdien een enorme bijdrage aan

maatschappelijke ontwikkelingen geleverd en bijna alle apparaten zijn

ermee uitgerust. We staan nu aan het begin van een soortgelijke ontwikkeling,

maar dan met geïntegreerde fotonica.”

Ze botsen met het materiaalrooster en dat vertaalt zich als weerstand,

waardoor een signaal dat door dat materiaal wordt geleid, steeds zwakker

wordt. De beweeglijkheid van elektronen in het halfgeleidermateriaal

is dus beperkt en dat begrenst uiteindelijk de maximale frequentie waarvoor

de signalen nog versterkt kunnen worden. Naarmate we dichter bij

deze grensfrequentie komen, is steeds meer energie nodig om signalen te

versterken. Een belangrijk deel van deze energie komt vrij in de vorm van

warmte die moet worden afgevoerd. Bij fotonen speelt dit probleem niet,

de massa van een foton is altijd nul. Altijd. Fotonen hebben geen massa,

ook niet relativistisch. Ze hebben alleen energie.

MASSALOOS

Fotonen hebben op papier veel betere eigenschappen om signalen over te

brengen dan elektronen. Elektronen hebben lading en massa. Ze hebben

hoe dan ook een sterke interactie met het materiaal waarin ze bewegen.

DE APPEL 41

loopt, is Astron. De radiotelescopen van het instituut genereren

verscheidene terabits per seconde. Astron doet dan ook

al jaren onderzoek naar het gebruik van fotonische chips. De

Nederlandse fotonicasector verwacht dat op allerlei terreinen

waar erg grote hoeveelheden data moeten worden verwerkt,

fotonische chips nodig zullen zijn.

Bij het transport treden nauwelijks verliezen op en de warmteproductie

is minimaal. Ook hebben fotonen geen last van verstoring

door elektrische of magnetische velden. Het frequentiespectrum

van licht is daarbij ook nog veel groter, waardoor de potentiële

bandbreedte ook veel groter is.

De optimale kloksnelheid om data te verwerken met een op silicium

gebaseerde, ‘normale’ processor die te vinden is in je laptop met zo

weinig mogelijk verlies, lijkt ongeveer 3,5GHz te zijn. Daar zitten

we al meer dan tien jaar op. De kloksnelheid lijkt niet veel meer

omhoog te kunnen. Die begrenzing hangt samen met het energiegebruik.

De energie komt vrij in de vorm van warmte en we kunnen

de warmte niet meer kwijt. “Als we naar hogere snelheden willen,

moeten we naar een lagere hoeveelheid energie per bit”, stelt Backx.

Door geïntegreerde fotonica zou de kloksnelheid in theorie met een

factor duizend kunnen toenemen.

RED DE WERELD, GEBRUIK FOTONEN

Een op fotonica gebaseerde complexe processor als vervanger voor

de huidige processors die in computers te vinden zijn is nog toekomstmuziek.

De markt probeert momenteel toe te werken naar

de massaproductie van relatief eenvoudige photonic integrated circuits,

of pic’s. De eerste sector die hiervan op grote schaal gebruik

zal maken, is die van datacentra, waar Nederland vol mee zit. Het

energiegebruik van datacentra in combinatie met de exploderende

hoeveelheid te verwerken data is een groeiend probleem voor bedrijven

zoals Facebook, Microsoft en Google.

Datacentra gebruiken naar schatting 200 tot 400 TWh per jaar. Dat

is ongeveer één tot twee procent van de wereldwijde energieconsumptie.

In Nederland gebruiken datacentra ongeveer elf procent

van de totaal gebruikte elektrische energie. De verwachting is dat

dit wereldwijd gaat toenemen met 20 tot 40 procent. International

Data Corporation (IDC), voorspelt dat de totale hoeveelheid gegenereerde

data toeneemt van 33 zettabyte (dat is 10^21 bytes) in 2018

naar 175 zettabytes in 2025. In deze sector valt met zuinigere chips

dus enorme winst te halen.

Fotonische chips kunnen ook worden ingezet om optische dataverbindingen

op steeds kortere afstanden te realiseren. Dat is nodig,

want ook op moederbordniveau groeit de hoeveelheid data die

moet worden verwerkt en gaan ook hier de nadelen van elektronica

een rol spelen. Een Nederlandse organisatie die hier al tegenaan

WELK BASISMATERIAAL?

In Eindhoven zit een bedrijf dat ernaar streeft de fotonische

foundry van de Lage Landen te worden: Smart Photonics.

Toch is dit geen concurrent van LioniX, de pic-fabrikant uit

Enschede. In Eindhoven gooien ze het namelijk over een andere

boeg. Fotonische chips zijn in drie hoofdcategorieën onder

te verdelen en dat onderscheid is gebaseerd op het gebruikte

basismateriaal. Er zijn fotonische chips op basis van siliciumnitride

(Si3N4), indiumfosfide (InP) en silicium-on-isolator. Elk

van deze drie heeft zo zijn voor- en nadelen.

In Twente is de Tech sector gespecialiseerd in pic’s op basis van

siliciumnitride. Het voordeel is dat ze een hoge bandbreedte kunnen

bieden en weinig energie verliezen. Het nadeel is dat ze geen

actieve componenten kunnen bevatten. Dat betekent dat een laser

of photodiode altijd extern moet worden aangekoppeld. In de VS is

men sterk gericht op silicium-op-isolator. Dit materiaal heeft als

voordeel dat het kan worden gemaakt in de grote micro-elektronicafabrieken,

waar zeer goede apparatuur is voor grootschalige

productie, maar een nadeel is dat er geen lasers en optische versterkers

mee kunnen worden gemaakt.

In Eindhoven werken ze op de universiteit en bij de bedrijven met

indiumfosfide. In dit materiaal kunnen ze zowel passieve als actieve

onderdelen maken en zo de chip zelf licht laten genereren, moduleren

of versterken. In tegenstelling tot voor silicium is hiervoor nog

geen grootschalige infrastructuur aanwezig.

VAN GLOEILAMP TOT HALFGELEIDER

De regio Eindhoven heeft die toppositie in de Nederlandse fotonica

sector niet zomaar gekregen, vertelt Ton Backx. “De basis ligt bij

het Natlab van Philips. Daar hielden ze in de jaren zestig van de

vorige eeuw vrijdagmiddagsessies waarbij wetenschappers van

verschillende disciplines onderling discussies voerden. Een van die

discussies leidde tot een weddenschap welke technologie zo dicht

mogelijk data kon opslaan, magnetisch of optisch. Onderzoek bij het

Natlab leidde tot de ontwikkeling van eerst de videodisc en later de

compact disc. De toepassing in de praktijk in de jaren tachtig leidde

tot een enorme boost in de ontwikkeling van fotonica.” Eind jaren

negentig werd Eindhoven door de overheid tien miljoen gulden per

jaar toegezegd voor de ontwikkeling van geïntegreerde fotonica.

Mede hierdoor maakte een grote naam wat optisch onderzoek betreft

de overstap van Delft naar Eindhoven: Meint Smit.

Naast een enorme wereldwijde impact die de massaproductie van

fotonische chips mogelijk maakt is er lokaal ook een impact, de investeringen

in de fotonica industrie moeten ook de economie in

Twente een flinke impuls geven. Naast Mesa+/Nanolab van de UT

zijn er ook Twentse bedrijven zoals LioniX international en Phix die

hiervan profiteren. ‘’Phix heeft de ambitie uitgesproken binnen enkele

jaren een omzet van 1 tot 1,5 miljard euro te willen draaien met

daarbij duizenden arbeidsplaatsen. Aldus voorzitter van de Twente

Board, Geert Braaksma. a

42 DE APPEL

DARK MATTER

THE DARKEST MATERIAL IN THE UNIVERSE

BY DAAN FLIER

If someone were to ask you what the universe is made up of, you may say stars, black holes,

protons, electrons and a million other things. But no matter what you would say you would only

get up to 15% of everything in the universe, after all, that is all we can see. 85% of all the mass in

the universe is invisible to us, so called dark matter. After 50 years we only know through indirect

measurements that it exists and where it is located. Dark matter does not emit anything that we

have been able to measure nor does it interact with anything that we determine. If we looked

through a telescope at a place where dark matter is located we would only see the stars behind it.

This is truly the darkest material in the universe.

So, if dark matter is impossible to see, why should it exist? Well, there

are several reasons for assuming dark matter does in fact exist. The first

reason has to do with the expected galaxy rotation curve compared

to the what is actually measured using telescopes. The galaxy rotation

curve is a graph with on the horizontal axis the distance to the galactic

centre and on the vertical axis the velocity of stars or gases in that galaxy.

Since all stars are orbiting the galactic centre of a galaxy, it is the

centre of mass in that galaxy. The further away from the centre of mass

the weaker the gravitational pull would be, thus having a lower centripetal

force. For the stars to stay in orbit they would need to have a lower

velocity, similarly as to the planets in our solar system. This is captured

in Kepler’s third law, which states that the orbital velocities of planets

in planetary systems and moons orbiting planets decline with distance.

In 1957 Henk van de Hulst studied the Andromeda Galaxy using the

newly commissioned telescope in Dwingeloo. He found that the orbital

speeds of the outer stars were almost the same as the orbital speeds of

the stars closer to the centre of the galaxy. Other researchers found the

same results, which only could be possible if either Newtonian gravity

does not apply at a universal scale or that there was much more mass

in the galaxy.

Another reason to expect the existence of dark matter, occurs with gravitational

lensing. Einstein’s general theory of relativity describes how

mass concentrations distort the space around them. If the mass concentrations

are high enough this even allows for the bending of light, black

holes are an extreme example of this.

DE APPEL 43

Milky way rotation curve.

So, by examining the distortion of light from distant galaxies that are

in the same line of sight but behind a cluster of galaxies with a huge

amount of mass, it is possible to map where all the mass in the cluster

of galaxies is positioned. This can be seen in the bullet cluster, which is

a cluster created by the collision of two galaxies. The red area is where

the gas clouds of both galaxies collided and the blue area is where most

of the mass is calculated to be.

The final reason for why dark matter should exist is that shortly after

the Big Bang everything in the universe was almost uniformly distributed.

After some time, the small clumps that had a little bit extra mass

accumulated more mass. This is due to their higher gravitational pull,

and after a long time they would form stars, galaxies and even superclusters.

If there was only hydrogen (since no other elements had yet

been formed), there would never have been enough mass to create stars

or galaxies.

Even though no possible way to see or interact with dark matter has yet

been found, there are some things we know about it. First, since it interacts

with gravity, it has mass. There are some other theories that try to

explain certain observations without dark matter having mass, but they

are not widely accepted. The fact that it has not yet been detected tells a

lot as well, it cannot interact with the magnetic force or the strong force,

otherwise it would have been detected a long time ago. Furthermore, it

hardly interacts with normal matter. Luckily for us, considering that

Earth is inside a cloud of dark matter.

Another important characteristic, is that it is relatively slow. The small

clumps with extra mass created just after the Big Bang had to absorb

the mass of dark matter to increase their gravitational pull. So they

could absorb even more mass, increasing exponentially. If dark matter

would have been fast the gravitational pull of the small clumps would

have been too weak to slow the dark matter down. Instead the dark matter

would just float through the cosmos, preventing the small clumps

to grow into stars and galaxies. Finally, dark matter must be stable, as it

has been around since the Big Bang. The problem is that all these characteristics

combined rule out all the known elements.

If dark matter is not made of any of the particles that we know, than

what is it? One leading theory is that dark matter is made of axions.

Although these particles have not yet been proven to exist, they are

theorized to exist, based on complex theory. Specifically a violation of

the charge and parity symmetry by the weak force. Another theory is

that it is made of the weakly interacting massive particles (WIMPs). These

particles would only be subject to gravity and the sub-atomic weak

force. These have also not yet been proven to exist, despite years of research,

which causes some doubts for the validity of this theory. There

are a lot more theories involving everything from sterile neutrinos to

extra dimensions in space.

Currently there are three different ways that researchers are trying to

test all the different theories. One way is to create dark matter particles

inside a particle collider. Another uses direct detection to find the particles

itself and the last way is to look for the products of dark matter

particle annihilations.

In the Large Hadron Collider in Geneva, researchers try to create all

kinds of new particles among which possible dark matter candidates.

The collider uses magnets to accelerate particle beams to 99.9% the

speed of light, after which the beams are collided. According to Einstein’s

most famous equation, E = mc^2, the more energy the more massive

particles can be created. The hope is that a massive dark particle

can be created by colliding protons, but since a dark matter particle

should have negligible interactions with normal matter, it probably will

not be detected. The idea is that it may be detected indirectly as missing

energy and momentum that escaped the detectors, provided other collision

products are accounted for.

The second method is called direct detection and aims to observe the

effects of a dark matter particle hitting a detector. An example of this is

the SuperCryogenic Dark Matter Search, or SuperCDMS for short, which

tries to prove that dark matter consists of WHIMPs. To achieve this,

germanium and silicon detectors are placed inside a huge cryostat to be

cooled to temperatures below 100 mK. This is surrounded with shielding

and placed on the bottom of an abandoned mine in northern Minne-

44DE APPEL

Gravitational lensing.

Bullet cluster.

sota to reduce background particles. The detectors are just barely below

their critical temperature and any outside particle that collides with the

germanium and silicon crystal structure would create heat. This would

ensure that the detector would no longer be below its critical temperature,

which can be measured. Using this theory, it is possible to measure

the ionization and phonons produced by every particle interaction with

the detectors. These two measurements determine the energy deposited

in the crystal in each interaction, but also gives information about

what kind of particle caused the event. The ratio of Ionization signal to

phonon signal differs for particle interactions with atomic electrons and

atomic nuclei. The vast majority of background particle interactions are

electron recoils, while WIMPs are expected to produce nuclear recoils.

This would theoretically allow for the identification of WIMP interactions

even though they have not yet been found in the last 20 years.

A possible problem is that WIMPs are so weakly interacting that they

hardly ever interact inside the detectors.

The final detection method is indirect detection. Here the goal is not

to find the dark matter but the results of an interaction between dark

matter particles themselves. The different experiments try to find a

signal that cannot be attributed to anything else in the universe and

that match expected signals from dark matter. A major difficulty in such

searches is that various astrophysical sources can mimic signals expected

from dark matter, and so multiple signals are likely required for a

conclusive discovery.

Hopefully, by using one of these three methods we can find out what

dark matter actually is. Maybe it is something we already know, or it is

something that nobody has yet thought of. We know for sure that the

darkest material in the universe is one of the most exciting new frontiers

in astronomy and hopefully it will be solved in the next 50 years. d

Galaxy rotation curve of Messier 33.

DE APPEL 45

THESIS ARTICLE

ADVENTURES IN THE

DISCONTINUOUS

GALERKIN METHOD

BY JOACHIM VAN DE WEG

For those of you who have followed any course in the field of finite element methods,

computational fluid dynamics, discretization techniques and the like will probably know

that problems arise when considering turbulent flows. It was not for no reason that

during Fluid Mechanics I in the bachelor, Rob Hagmeijer used to say that laminar flow

was assuemd (while in most of the cases this is not justified). This problem is even more

apparent when considering more complicated techniques then the traditional Finite

Element Method, Finite Volume Method or Finite Difference Method. One of these

methods, is the arbitrarily high order Discontinuous Galerkin Finite Element Method,

DG-FEM for short. For my master assignment I investigated the possibilities of solving

discontinuous problems using the DG-FEM, under the supervision of mister CFD:

E. Van der Weide

To illustrate the problem with turbulence, consider

the images on at the bottom of this page. As you may

know, there are three main techniques in to solve turbulent

flows: Reynolds Averaged Navier Stokes (RANS),

Large Eddy Simulations (LES) and Direct Numerical

Simulation (DNS). As one can immediately see, the

results obtained using the different techniques are

radically different. It would go to far to get into the

details of each of the techniques, but we can say the

following: For accuracy, RANS is completely useless,

DNS is spot on and LES splits the middle between the

two. As far as computational cost goes: RANS is cheap,

LES is expensive and DNS is very expensive. That is

why in modern day design processes only RANS and

a bit of LES is used, simply because DNS is not viable

in a commercial setting. This cost difference between

RANS, LES and DNS stems from the fact that RANS the

grid size can be relatively coarse, whereas LES and

especially DNS require a very fine grid. This is the

case for all of the traditional methods: FDM, FVM and

FEM. Taking these demands to three dimensions, this

becomes a very large problem very quickly. However,

in the not so far future, the need for more accurate

solutions to the turbulent flows will increase. If one

could make a factor ten less prototypes by just using

more accurate solutions to the flow problems associated

with the problem, overall costs would go down.

Hence the need for more broader usability of DNS and

especially LES is required.

RESOLVED AND MODELED SCALES FOR

RANS, LES AND DNS

SOLUTIONS FOR A TURBULENT JET FLOW

LEFT: DNS, MIDDLE: LES, RIGHT: RANS

46 DE APPEL

Higher order methods

Now that we have established that using FEM/FVM/FDM in the coming

years will less and less of a solution the problems that will arise, the

quest for another technique starts. To start searching, the problems

with these techniques have to be established first. All of the traditional

techniques are, at best, second order accurate. This means that when

the grid is refined by a factor two, the result is at most four times as accurate

(however most of the time it will only be twice as accurate). This

is simply not good enough.

There are many other possibilities that have been developed and investigated

over the past decades, ever since commercial flight became

more accessible. Most of these methods however have other requirements

makeing them unsuitable for the problem we are facing. Some

require the use of a structured grid, others require very small time

steps and other methods are simply a patch to stop the bleeding from

the FVM. However, there a few good options. One of those options is

the Discontinuous Galerkin Finite Element Method, DG-FEM for short.

Discontinuous Galerkin Finite Element Method

The DG-FEM is an extension of the FDM and FVM. Both of these methods

divide the domain in cells, and then use Taylor approximations to

determine the values of the derivatives over the domain. The difference

between the FDM and FVM lies in the Taylor approximations: FDM uses

central discretizations and FVM uses so-called upwind discretization

schemes. For more details on this difference, follow the masters course

computational fluid dynamics. The DG-FEM also uses upwind discretization,

however it does so while obtaining a much higher accuracy.

The FVM makes use of a single value in the centre of each cell, and

applied the discretization on these values. This ensures that the schemes

are Total Variation Diminishing (TVD) and hence are always stable,

This can be done up until a second order scheme. The DG-FEM takes

a different approach. Instead of a single value in each cell on the domain,

it uses a polynomial in each cell of the domain. In other words,

the domain is filled with polynomails that meet at the cell boundaries.

Hence the name: Discontinuous. The usage of the polynomial allows

for an arbitrarily high order scheme: Taking a higher order polynomial

in each cell on the domain automatically yields a higher order scheme.

One could even use different order polynomials throughout the domain,

so that high order results are obtained in the parts of the domain which

are most critical and leave the rest of the domain lower order.

The problem with this approach is that it is no longer TVD and hence no

longer a stable scheme. This is not a problem for smooth problems with

relatively small variations in gradients over the domain. But since we

want to apply the scheme to turbulent flows, this in no way guaranteed.

In turbulent flows there will always be large variations in gradients,

and often even shock waves in the solutions.

To illustrate this property of turbulent flows (with shocks) two main test

cases are used throughout the field of fluid dynamics: Burgers Equation

and the Sod Shock problem. Burgers Equation is a scalar equation that

was defined to test the shock handling capabilities of discretization

schemes, and the Sod Shock Problem is a case of the inviscid 1D Euler

equations for gases. These problems are used because a simple exact

solution can be obtained for both problems, allowing for easy accuracy

studies. The definitions of these problems are shown at the bottom of

this page. Both problems are defined for the unitary domain, with Burgers

Equation running from t=0 to t=0.8 and Sod Shock Problem running

from t=0 to t=0.15.

To illustrate the problem with the DG-FEM, consider the solution obtained

for the Sod Shock problem (for Burgers Equation a similar problem

is present):

As is immediately clear from the figure, the solutions obtained using

DG-FEM are not great. There are significat deviations around the disconinuities

in the solution, throughout the time integration. Furthermore,

this is only the real part of the solution. Due to the wiggles in

the solution, the density locally dips below zero, which in itself is not

physical, resulting in a complex speed of sound and hence a complex so-

DEFINITION OF THE BURGERS EQUATION

DEFINITION OF THE SOD SHOCK PROBLEM

DE APPEL 47

lution. This is obviously total nonsense. This behaviour

is again caused by the DG-FEM not being TVD and

hence unstable. We can think of it as the polynomials

in the domain trying to wrap themselves around a

sharp corner, which obivously is never going to work.

Solving the problem

The above explained problem can be solved using

many different methods and techniques. However, a

lot of these methods diminish the initial advantages

that came with using the DG-FEM. This can range

from requiring a uniform or structured grid to demandig

a uniform polynomial order over the entire

domain, which makes using the DG-FEM not worth it.

One of the downsides often associated with the solutions

is a (much) more demanding time step requirement,

resulting in way smaller time steps. However, if

we are able to compute results at all, the time it takes

to compute can be taken as a small loss.

During my research I investigated and tested a few

methods that could be able to solve the problems. I

will only show one of the solutions here, since it will

take a bit more time and paper to explain all of the

methods.

Artificial Viscosity

A large part of the solution can actually be solved by

adding viscous effects to the equation. Adding this

will results in more smooth gradients over the domain,

naturally making it easier for the polynomial

to follow the solution. For Burgers equation this is as

easy as adding a second derivative:

Where the viscosity parameter is a function of the solution.

For the one dimensional Euler equations the

addition of artificial is not as straightforward, as it

requires the addition of the fluid stress tensor. This is

shown below, and this can also be implemented, albeit

with a lot more work required, both during the coding

stage but also when computing solutions. Again, the

viscosity parameters are functions of the flow solution.

The addition of numerical viscosiy has two major

downsides. First and foremost: The minimum time

step becomes much smaller due to the addition of a

second derivative in the solution. Since the changes in

the second derivative over the domain are much less

smooth, the time step should be much smaller. This

problem is even larger when the grid becomes finer

and finer, since a finer grid also requires a finer time

step. Computational times increase dramatically (with

my code in our beloved Matlab, the longest computations

took over 90 hours).

The second downside is that stabilizing terms are

required in order to force the solutions at the cell

boundaries towards each other. This is done using the

Symmetric Interior Penalty Method (SIP), and again

adds more complexity to the computations. You might

wonder why adding viscosity in this way is still a good

idea: It is the only solution that allows for non uniform

grids and non uniform polynomial orders over

the domain.

A last remark is that the viscosity is only added in

cells where the shock is present, i.e. where the solution

cannot be obtained without any addition to the

DG-FEM. This is done using a shock detection algorithm,

which flags cells that have a shock present and

subsequently the additional terms are added to those

cells only.

Entropy Boundness

For complex problems, e.g. Euler equation problems

with much more complex initial conditions or full Navier

Stokes problems, the addition of artificial viscocity

alone does not suffice. It is still possible for the

density to undershoot to below zero. Therefore, another

limiting method is required.

As you all know from Thermodynamics, entropy

should never decrease. This is used to address the undershoots

in pressure: For each cell in the domain, the

density is in each cell is limited to be larger or equal to

zero. Subsequently, the entropy is computed for each

cell and the pressure is adjusted to make sure that the

entropy is larger or equal to the entropy in that same

cell during the previous time step. Again, this adds

more complexity and computational cost, but it is the

only way to obtain solutions for complex problems.

For Burgers equation (or any scalar equation) this

plays no role, the addition of viscosity is enough. For

systems of equations a combination of artificial viscosity

and entropy boundness is required to obtain

good results. I will leave out the solutions to Burgers

equation and show three problems based on the Euler

equations.

ONE DIMENSIONAL EULER EQUATIONS WITH ADDED STRESS TENSOR

48 DE APPEL

Sod Shock problem

The solutions obtained for the sod Shock Problem suing the aforementioned

techniques are shown below.

SOLUTION TO THE SHU OSHER PROBLEM

640 CELLS, T=0.18

As is clear form the figure, the solutions are much better, there are almost

no overshoots left in the solution; the numerical solution matches

the exact solutions nearly exactly.

The shock wave present in the solution has forward moving velocity

of nearly mach 20, i.e. a very strong shock. The solutions to both problems

are shown on the following

page. The solutions obtained for

the Shu-Osher proplem are quite

accurate. The solutiosn to the Blast

wave problem are lesas accurate,

but with an even fine grid, better

results should be possible. There

was no time left to compute solutions

for finer grids, as the computational

times grow exponentially

for each step in grid size, resulting

in week long computations.

Conclusions

I hope that my effort to explain the

general line of my master thesis in

this short format was succesfull,

and that you maybe even consider

doing your own master thesis in

the same direction. If the latter is

not the case, do not worry: there

are a lot of possibilities regarding

master assignments. If you have

any questions regarding my thesis

or this article, please do not hesitate

to contact the editors of the Appel

with your questions, they can

give you my contact information. I will happily answer any questions

you might have. J

Shu-Osher and the Blast Wave problem

The last two problems are also based on the one dimensional Euler

equations, but have different initial conditions. For the Shu-Osher problem

the initial conditions are defined as:

The problem runs from t=0 to t=0.18. De sine wave present in the initial

defintion for the density is specifically added to test if the shock detection

algorithm only detects real shocks, and not quickly variating

smooth behaviour in the solution. This is clearly not the case, as the

plot on the right shows.

The blast wave problem has three sections and has the following initial

conditions:

CELLS DETECTED BY THE SHOCK DETECTION ALGORITHM DURING

THE COMPUTATION OF THE SHU-OSHER PROBLEM

DE APPEL 49

SOLUTION TO THE SHU OSHER PROBLEM

640 CELLS, T=0.18

SOLUTIONS TO THE BLAST WAVE PROBLEM

640 CELLS, T=0.0044

50 DE APPEL

COLUMN

HUGO WESSELINK

EEN ODE AAN HET

OOSTEN

Toen het moment voor mij daar was om te gaan studeren

twijfelde ik tussen de universiteiten in Delft en Twente, ik

had namelijk besloten dat het Werktuigbouwkunde moest

gaan worden en Eindhoven was geen optie. Een gegronde

reden had ik hier eigenlijk niet voor, maar in mijn hersenpan

was deze keuze duidelijk en dus zou de strijd moeten

worden gevoerd tussen het oosten en het westen. De doorslag

om voor Twente te gaan, was op dat moment een

puur praktisch besluit. Mensen die mij kennen

of vaker mijn columns lezen, zullen weten

dat ik uit een klein Achterhoeks dorpje

zo’n veertig kilometer verderop kom.

Zodoende kon ik in de begintijden van

mijn studie eerst de kat uit de boom

kijken en hoefde ik niet direct op kamers.

Daarnaast was er in Enschede

de mogelijkheid om redelijk makkelijk

naar het HBO te gaan, mocht de

universiteit toch te hoog gegrepen zijn.

Keuze gemaakt, Hugo ging in Enschede

studeren.

Hoewel ik het vast ook erg naar mijn zin had gehad

in Delft, ben ik tot op heden altijd erg tevreden geweest met

mijn keuze voor Twente. Nooit ben ik iets tegen gekomen

wat mij echt tegenstond of zo irriteerde dat het ondraaglijk

werd, afgezien van de steeds in prijs stijgende kroketten in

de kantine. Voor mijn stageopdracht wilde ik graag even

weg uit Enschede, om te kunnen zien hoe het buiten deze

kringen is en of de dingen hier anders gaan. Ik heb tenslotte

mijn hele leven in het oosten gewoond, dus een objectieve

samenvatting over de gang van zaken op de drie technische

universiteiten kon ik nog niet met enige vorm van zekerheid

schrijven.

De drie maanden weg van Enschede hebben er niet voor

gezorgd dat ik deze gave nu wel bezit, echter heeft het mij

wel het oosten nog meer doen waarderen. En dan in het

bijzonder onze universiteit en de opleiding werktuigbouw.

Het is briljant om te zien hoe er hier wordt gezorgd dat de

serieuze kant van de opleiding feilloos aansluit bij de ontspanning

en het plezier er omheen. Men ziet het nut in van

een borrelkelder, waar na een week hard studeren wat gedronken

kan worden en ruimte is voor slap geouwehoer. Je

wordt aangemoedigd om je bezig te houden met projecten,

verenigingen of evenementen buiten het curriculum om.

Niet strikt om zoveel mogelijk studenten te produceren met

een excellent CV en dit vervolgens in de promovideo

te knallen. Maar gewoon, omdat er over de hele

breedte het nut van persoonlijke ontwikkeling

en ontspanning gezien wordt.

Deze nuchtere sfeer welke zo typisch

is van het oosten en welke ik

van kinds af aan al heb ervaren hangt

ook rond werktuigbouwers, of dit nou

studenten, docenten of andere medewerkers

van de opleiding zijn. Het is

een sfeer die niet oordeelt wanneer je

allerlei wilde plannen hebt om naast je

studie uit te voeren, maar het ook prima

vindt als je dit allemaal niet wil. Dit zorgt er

voor dat bijna iedere werktuigbouwer dingen over

zichzelf te weten komt, dingen leert, of plekken van de wereld

ziet tijdens zijn studie wat niet door het opleidingsprogramma

zelf komt. Hoe vanzelfsprekend ik dit achtte voor

een universiteit, blijkt niet altijd even waar te zijn als het

vergeleken wordt met andere steden, het blijkt toch echt

typerend te zijn voor onze windstreek.

Daarom is een ode aan het oosten, en in het specifiek

aan werktuigbouwkunde op de UT, wel op zijn plaats. Eigenlijk

zouden we met zijn allen volgende week op het balkon

moeten gaan staan klappen voor de Twentse WB’er om

hem of haar te tonen hoe dankbaar we zijn. Helaas geeft dit

een hoop commotie en komt het misschien zelfs wel in de

krant. Het past niet bij onze nuchterheid om hier zo mee

te koop te gaan lopen. Nee, laten we maar gewoon rustig

verder gaan met waar we altijd al mee bezig waren. Het is

tenslotte best prima hoe het nu gaat. HW

DE APPEL 51

QUALITY ASSURANCE COMMITTEE

REPORTING

Every quartile, the Quality Assurance Committee (QAC) evaluates a selection of the Bachelor and Master

courses of Mechanical Engineering and the Master courses of Sustainable Energy Technology. We do this by

sending a questionnaire to all the students that follow a specific course. Thanks to everyone that fills in these

questionnaires, we are able to evaluate the different courses and write our reports. Thank you for your input!

In four editions of De Appel, we name the most important highlights of these evaluations. This way, you can

get a short view of the results of the committee and, in some cases, the comments of the lecturers. In this

edition, the courses of quartile 2 of the year 2019-2020 are mentioned. New this time are courses given on

the VU, given in green. The yellow courses are UT Bachelor courses, the blue ones Master courses. If you are

curious about the full report of a course, you can go to our website: http://www.utwente.nl/wb/evaluatie.

On behalf of the Quality Assurance Committee ME/SET,

ARJEN KRUIZE CHAIRMAN

11% 3,7

ELASTICITY THEORY

35% 4,2

LINEAR ALGEBRA

• The students were positive about having the exam before the

Christmas break.

• The whiteboard was not used clearly.

• The most useful reader was still in Dutch.

21%

PROJECT CONSUMER

PRODUCTS

• The expectations of the interactive document were unclear.

• This project is experienced as relevant, the students think it is interesting

to collaborate with other study programs.

• The students are satisfied with the role of their tutor.

28%

TRIBOLOGY

• Students indicated that they lacked practice exercises

• Students would like an increase in the amount of tutorials given.

18%

3,5

2,9

4,0

PROCESSES AND PROPERTIES

OF POLYMERS

• The teachers’ English and their availability for questions were very

well rated.

• Some students would prefer more tutorials to practice exercises.

• The use of English of the study material and on the canvas page

was very good.

24%

MATERIALS SCIENCE: ME-

TALS AND ALLOYS

• There was only one tutorial in Block 1, but the increased number of

tutorials in Block 3 were very helpful.

• Unfortunately, this report is considered not representative because

of the low number of responses, but the course did score very well

over all.

20%

4,1

3,6

PROJECT 1: MANUFACTU-

RING

• Tutors were not always available questions and it was unclear for

students what their exact role was.

• Students thought that the oral exams did not give everyone equal

opportunity to explain their contribution to the project.

35% 4,2

MECHANICS OF MATERIALS

• There were too many errors in the solution manual and that they

would like to have more practice exercises.

52 DE APPEL

This percentage represents the

amount of respondents out of the

total students taking the course.

%

The average score, ranging

from one to five, given by the

respondents.

X

40% 3,7

ADVANCED TOPICS IN FINI-

TE ELEMENT METHODS

• The course scores very well for a course that is given for the first

time.

• There are more tools required to understand working with Abaqus.

For example: tutorials, a manual, screenshots or examples during

the lectures.

• The students found the discussion board on Canvas and the lecture

about beams very helpful.

34%

3,4

ENERGY FROM BIOMASS

• The lectures were not always consistent with the schedule. It seemed

that a lot of lectures were cancelled.

• The study material was not always useful.

• The lectures have to be improved with clearer slides, more structure

and more possibilities to ask questions.

42% 3,2

MANUFACTURING FACILITY

DESIGN

• The English of the lecturer was not good and therefore needs to be

improved.

• The amount of different study material needs to be reduced.

• The lectures need to be improved. Students would like to learn more

from the lectures. Less reading from the slides and more examples

and applications can help the lectures a lot.

30% 4,4

POWER ENGINEERING &

SYSTEM INTEGRATION

• The course scores very well.

• The additional information during the lectures can be valuable but

also time consuming and may cause confusion.

• The students would like to have tutorials.

DE APPEL 53

6

FOTOGRAFIE JEROEN VAN DEN HOOGEN

“SCIENTIA VINC

54 DE APPEL

2

ERE TENEBRAS”

DE APPEL 55

JOEP VAN MANEN

The past year, my board and I have had the honour of managing our

great association. On 6-2 2019, we were constituted as the 62nd board of

W.S.G. Isaac Newton. After an intensive period of candidacy, where we

really got to know each other, the association and developed our plans

for the association, the time had come to take control. A year followed

in which 7 individuals paused their own lives to fully step into their role

as board member.

It has been a great experience to work with people so thoroughly committed

to keeping the association thriving. I really enjoyed my function

as chairman as it allowed me to work with every single one of my board

members on a broad variety of projects that were going on. With all the

activities that we as a board, but also our committees organized, there

were always activities to look forward to. I am grateful for the support

of our active members and former board members.

I have experienced a year to look back on with a broad smile on my face.

For me personally, the highlight of the year was the Beach Party. The

period leading up to the event, we spent more hours on board work than

asleep, but when the day came, it was amazing to see so many people

enjoying the party. The year went by in a flash, and I will definitely miss

the board life, but the countless great memories will remain.

62 “SCIENTIA VINCERE TENEBRAS” 62 “DOOR WETENSCHAP DE D

MITCHELL ROSSOU

For years, the thought was there: “Let’s do a board year, that’s going to

be so useful for the future!”. So when the opportunity arose to do the

62nd board of Newton, I took that chance. This turned out to be one of

the best decisions I ever made, as I’ve had such a fun and eventful year.

Even at my age, there was still a lot left to be learned.

The best example of this, is the organisation of our Beach Party. Together

with Ciska, I was tasked with finding sponsors for the event. This

was an all-new area for me, and was actually one of the things I really

wanted to learn while being the board. So Ciska and I listed possibilities

for companies to sponsor us and contacted companies that might be

interested. Obviously, we got a couple of no’s, but in the end, we set up

some great partnerships, ensuring this grand event could properly take

place.

Aside from the big event, I also learned how to narrowly work together

with people you’re basically seeing for 50 hours a week. It gets hard, and

you hit bumps along the way, but you get to know your fellow board

members and even yourself better in the end. It’s been an eye-opening

experience for me and would definitely recommend it to anyone who’s

interested!

56 DE APPEL

CISKA VAN DER VEEN

Last year I was happy to contribute to our wonderful association

by being part of the board. I always appreciated everything

Newton organises for their members and it was special to see

the other side of this. I enjoyed managing the association and

definitely learned a lot doing so, especially by organising a wide

range of activities all year long. A board year brings improvising

to another level and I learned you will always find a solution for

the obstacles you find along the way. Of course I got to know my

fellow board members really well past year and I have to say the

boys gave me a hard time every now and then. However, this

year and all the things we did together leave memories I do not

want to forget. My personal highlight was the Beachparty on

June 18th. It was a challenge to fix it all in time, but everything

fell into the right place on the day itself and the weather turned

out to be perfect. Working towards this event together with

my board and the support of the rest of the association was an

awesome experience. Other memorable moments were guiding

the ambitious committee that organised the symposium with

André Kuipers and supporting the committee that organised

the IC-tour to Indonesia and Australia. During this intense year

filled with coffee and fun activities, I got to know many great

persons and I am truly grateful for that. I would like to thank

all the old board members and active members for their support

and wish all the best for the 63rd board!

UISTERNIS OVERWINNNEN” 62 “SCIENTIA VINCERE TENEBRAS” 62

PIM VAN DER MEER

In the previous year, I had the privilege to be the board of our beautiful

association. On the 6th of February 2019, we started on this adventure,

and roughly 2 months ago this wonderful year came to an end. A year

full of excitement, surprises and determination. Together with my six

other board members, we made it a memorable year for ourselves and

the association.

During the year I was surprised over everything that is possible in our

association. From organizing incredible events which start out as merely

a small idea, to making sure our traditions stay in place. From hosting

a UT wide party, to having a symposium with André Kuipers. From

a standpoint of commissioner of external affairs, I was also amazed at

how important it is to provide our members with knowledge about the

work field we will end up in, and the enthusiasm of our members towards

orientating themselves in these fields.

The possibilities are endless, as long as you have a team with which you

can achieve your goals. Luckily, we as the 62nd board could rely on each

other and work together to make as much of our board year as possible.

There were good times and challenging times, but in the end we stuck

together, happy that we did this as a team, the same team that we started

out with. I would like to truly thank my fellow board members for this

amazing year. And to all the members who helped me and this association

grow the last year, I would like to say: “Nee, jullie bedankt!”

DE APPEL 57

JOCHEM DEN OS

In the previous year, I had the privilege to be the board of our beautiful

association. On the 6th of February 2019, we started on this adventure,

and roughly 2 months ago this wonderful year came to an

end. A year full of excitement, surprises and determination. Together

with my six other board members, we made it a memorable year for

ourselves and the association.

During the year I was surprised over everything that is possible in

our association. From organizing incredible events which start out as

merely a small idea, to making sure our traditions stay in place. From

hosting a UT wide party, to having a symposium with André Kuipers.

From a standpoint of commissioner of external affairs, I was also amazed

at how important it is to provide our members with knowledge

about the work field we will end up in, and the enthusiasm of our

members towards orientating themselves in these fields.

The possibilities are endless, as long as you have a team with which

you can achieve your goals. Luckily, we as the 62nd board could rely

on each other and work together to make as much of our board year as

possible. There were good times and challenging times, but in the end

we stuck together, happy that we did this as a team, the same team

that we started out with. I would like to truly thank my fellow board

members for this amazing year. And to all the members who helped

me and this association grow the last year, I would like to say: “Nee,

jullie bedankt!”

62 “SCIENTIA VINCERE TENEBRAS” 62 “DOOR WETENSCHAP DE D

RUBEN BOS

During the sixty second board of our beautiful association I had the pleasure

to be the Commissioner of Internal Affairs. Looking back, I can only

say that the year was even better than anticipated. Of course I had seen the

awesome years that previous board have had. But as a member you don’t

really see what a board does behind the scenes. Take the beach party for

instance, I hope that everybody shares my view that the event was a great

success. But for us, that was only the last step. We had just as much fun in

organizing it: having meetings with the UT for permission, promoting it to

as much students as possible and asking companies for sponsoring. These

activities took place weeks before the event itself, but it was so much fun to

do it together. Seeing that all work out in the end gives an amazing feeling.

For me, it was all the stuff behind the scenes that made it such an incredible

year for me. Having meetings with people that I would otherwise never

see. Going to places that I would otherwise never would have went to and

doing stuff that I otherwise never would have done. This gave me amazing

experiences and memories that I will never forget. But most of all, it gave

me a close group of friends that I’m sure to be keep seeing even after we’re

all done studying.

I want to thank all the members who have helped making last year as amazing

as it was. And I want to which the sixty third board the best of luck.

58 DE APPEL

SIEM BUSE

Over the past year, I have had the enormous pleasure to be a part of the 62nd

Board of our beautiful association. It was a year with a lot of ups and downs,

where we have constantly had to work hard to achieve all of the milestones

we set for ourselves. Thankfully, with great teamwork and a lot of enthusiastic

committees to support the association we were able to organize some

amazing events and activities. One that stands out to me in particular, is the

Beach Party that we organized behind the Horst. With the support of the

staff of the Horst amongst others, we were able to host this event for over

400 people. We placed a large stage where we had several DJ’s throughout

the day and the guests could get different drinks and food at the bars and

food trucks. Overall, there was a lot of positive feedback and I’m glad that we

were able to make the students forget about their exams for a bit and enjoy

the beautiful weather.

The board year went by very quickly, but I can gladly say that enjoyed every

moment of it. This year gave me an experience that I could not have gotten

in any other way and is something I will never forget in my lifetime. I want

to thank my other board members for all of their effort and I will always

remember the bond we have built during this year with all we went through

together.

Lastly, I hope that even in these difficult times, the 63rd board will enjoy

their year as much as I have and are able to improve our great association

even more.

UISTERNIS OVERWINNNEN” 62 “SCIENTIA VINCERE TENEBRAS” 62

DE APPEL 59

Appel editie 42.3

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