YSM Issue 90.4

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COUNTERPOINT GOOD PROSPECTS FOR NEUTRINO PHYSICS ►BY ISABEL SANDS In the time it takes you to read this sentence, more than 100 billion neutrinos from the sun will pass through your fingertip. You’re not likely to notice—the neutrino is a tiny, subatomic particle with virtually no mass. It interacts with matter through two of the four fundamental forces of nature: gravity and the weak nuclear force, which causes radioactivity. However, even this gravitational interaction is feeble due to the neutrino’s infinitesimal mass. And yet, despite its imperceptible nature, this elusive particle may be the key to unlocking some of the deepest secrets of the physical universe. Neutrinos have no electric charge and belong to a class of subatomic particles called leptons. Leptons possess very little mass, do not undergo strong interactions, and are characterized as the building blocks of matter. According to our current understanding of particle physics, there are three “flavors” of neutrino: the electron, muon, and tau neutrino. Each of these uncharged leptons associates with a specific type of charged leptin—the electron neutrino matches with the electron, while the muon and tau neutrinos pair with the electron’s heavier, less stable siblings: the muon and tau particles. Some physicists, however, have hypothesized the existence of a fourth flavor: a “sterile” neutrino that only interacts with gravity, making it difficult to detect. Recently, measurements from the Daya Bay power plant in China generated excitement over the possibility of sterile neutrinos. Nuclear reactors produce a flow of electron antineutrinos, which are the antiparticles of electron neutrinos. Physicists can model this flow by understanding the reactions that occur within the nuclear reactors. But at the Daya Bay power plant, these models predicted a higher number of flowing antineutrinos than were experimentally within the IMAGE COURTESY OF YALE WRIGHT LABORATORY ►The result of a US-China-Russia collaboration, the Daya Bay reactor neutrino experiment promises to shed light on the mysterious nature of neutrinos. reactor. This phenomenon, called the “reactor antineutrino anomaly,” has also been measured at other sites. Neutrinos can spontaneously change flavors in a phenomenon called “oscillation,” so is it possible that some percentage of neutrinos are oscillating into undetectable, sterile neutrinos? Careful analysis of the data from Daya Bay initially seemed to rule out sterile neutrinos. As nuclear reactors consume fuel, the elemental composition of the fuel changes. Scientists found that the degree of antineutrino deficit varies with the fuel’s composition. Thus, they suspect that these elemental changes are responsible for the antineutrino anomaly. Specifically, they hypothesize that isotopes of uranium—forms of the atom with a different atomic mass—are the primary culprits. They believe they are overestimating the number of antineutrinos produced by uranium due to the variation between isotopes. However, further analysis has revealed that uranium isotopes cannot entirely explain the antineutrino anomaly. Karsten Heeger, a Yale physics professor and the director of Yale’s Wright Laboratory, is currently working on the Daya Bay experiment. “The immediate conclusion people jumped to was, ‘Oh, this might explain everything about the reactor antineutrino anomaly!’” Heeger said. “But it does not. People have now taken a closer look and realized that two effects could be taking place, wrong nuclear physics and sterile neutrinos.” The combined effect of the two theories fits the data better than that of either hypothesis alone, which leads Heeger to believe that multiple causes contribute to the anomaly. Heeger is now leading a new, Yale-led neutrino experiment called PROSPECT at the Oak Ridge National Laboratory’s research reactor. By using only one isotope in the fuel for the reactor at Oak Ridge, PROSPECT will be able to test nuclear reactor models more precisely. “We can see if over the distance of several meters, these neutrinos oscillate into sterile neutrinos,” he said. The implications of this research are certain to be profound. “Instead of neutrinos being a byproduct, we’re now starting to see them as a way to probe into nuclear reactions,” Heeger remarked. PROSPECT will hopefully provide data that allows scientists to refine their nuclear reaction models. PROSPECT also has the potential to transform modern physics: sterile neutrinos are not included in the Standard Model, the theory that describes all known elementary particles. If PROSPECT finds evidence for sterile neutrinos, “It would revolutionize particle physics,” Heeger said. “It would require us to come up with something completely new and different.” Researchers and students at the Wright Laboratory will complete construction on PROSPECT this fall, and installation at Oak Ridge National Laboratory will take place by the end of the year. Heeger says there may be a definitive answer to the antineutrino anomaly by 2018, but for now, he remains cautious. “I have no predictions,” he said. “We need to get the data.” 34 Yale Scientific Magazine October 2017 www.yalescientific.org
INN VATI N STATION Decluttering our Landfills ►BY LESLIE SIM Half of the plastics we use today are used once and then left to accumulate in landfills. This statistic is symbolic of a greater issue: given our ever-increasing rate of plastic consumption, overstuffed landfills will create dire problems for future generations. And while humans eventually will have to face the consequences of plastic pollution on land— if we aren’t doing so already—plastic pieces are currently floating in our oceans, being ingested by marine animals and contaminating natural habitats. Reducing our plastic consumption is certainly one way to address this issue, but researcher Yiqi Yang and his team at the University of Nebraska-Lincoln have an even better solution: biodegradable plastics. Yang believes that his lab may have found a way to create a cost-effective biodegradable plastic that targets the textile industry, where polyester plastics are a big source of plastic consumption. Production of these plastics requires a lot of petroleum, a limited resource. Other researchers have designed biodegradable plastics in the past. For example, polylactic acid (PLA) was the first and largest-scale biopolymer produced from annually renewable resources such as corn starch and sugarcane. Biopolymers like PLA are very long molecules consisting of a biologicallyrelevant repeating subunit. However, PLA’s limitations make it ineffective for use in the textile industry: “Others have been able to find biodegradable products such as PLA, but those products cannot be used widely in the textile industry because they are easily hydrolyzed at high temperature,” Yang said. Hydrolysis refers to the degradation of a plastic by breakdown into its subunits. PLA-based plastics risk being too soft and too easily broken-down, and are thus not suitable for textile materials. While engineers have made some progress, the main problem today isn’t finding a biodegradable product, but rather one that is both costeffective for manufacturers and has the properties necessary for a quality plastic. The plastics we use daily have the opposite problem. Most plastics are too stable and stick around in landfills or natural habitats for a long time, unable to biodegrade. After some experiments, however, Yang and his team have developed a biodegradable plastic without those shortcomings. In their experiments, the team obtained two biopolymers, poly-L-lysine (PLL) and poly-D-lysine (PDL). With these biopolymers, they formed plastic fibers and employed a thermal treatment to form tighter structures with strong interactions between the polymers. This key process ultimately decreased the plastic’s sensitivity to hydrolysis, especially at high temperatures. Several experiments testing the new plastic’s properties show that Yang’s team may indeed have the key to tackling the two main problems in plastic development (hydrolysis and softness at high temperatures). However, until their materials are examined in large-scale production, they can’t say for sure whether their plastic will work on the industrial scale. The next step for Yang and his team is to test the plastic on a small scale in the textile industry. From there, they can target other industries. Nonetheless, Yang and his team have gotten a step closer to making a product that will hopefully prove useful in decreasing, if not eliminating, plastic waste. The impact of a biodegradable plastic in reducing plastic pollution is far-reaching. Currently, animals on land and in oceans are easily harmed by ingesting plastic microparticles or by getting caught in large pieces of plastic. For humans, plastic remains in our landfills for far too long, and we’re running out of space. Yang also cautions that tap water from all around the world contains microscopic pieces of plastic, and without our knowing, we could be accumulating plastic in our bodies. Since demand for plastic is growing exponentially as the human population grows, it is especially critical for us to find a sustainable resource that meets our needs without damaging our environment. As we move in the direction of finding cost-effective and useful forms of biodegradable plastic, we can rest assured that researchers like Yang and his team are on the case. www.yalescientific.org October 2017 Yale Scientific Magazine 35
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Page 5 and 6: F R O M T H E E D I T O R Reaching
Page 7 and 8: in brief NEWS The Twists and Turns
Page 9 and 10: neuroscience NEWS NOW YOU HEAR ME,
Page 11 and 12: public health NEWS NOT SO SWEET Met
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Page 15 and 16: THE SEARCH Mathematical model expla
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Page 21 and 22: molecular biology FOCUS However, if
Page 23 and 24: organic chemistry FOCUS key player
Page 25 and 26: genetics FEATURE NATURE AND NURTURE
Page 27 and 28: geology and geophysics FEATURE ΜIC
Page 29 and 30: low-density gas circling the galaxy
Page 31 and 32: molecular biology FEATURE a profess
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Page 37 and 38: ALUMNI PROFILE SANDY CHANG (YC ‘8
Page 39: cartoon FEATURE BEFORE/AFTER ►BY

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