ANNUAL REPORT - MTA SzFKI

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Conference proceedings E.17. Oszlányi G, Sütő A; The charge flipping method: a new approach to solve periodic and aperiodic structures; Acta Cryst A; 63, s5, 2007, ( invited lecture at the 24-th European Crystallographic Meeting, Marrakesh, Morocco, August 22-27 2007) E.18. Tegze G, Gránásy L, Kvamme * B; Phase field modeling of the conversion of methane hydrate into carbon dioxide hydrate; In: Proceedings of 4 th WSEAS Int. Conf. on Heat and Mass Transfer, Gold Coast, Queensland, Australia, January 17- 19; pp. 27-29. E.19. Faigel G, Bortel G,Tegze M; Hard x-ray holographic methods; In: Proceedings of the NATO advanced research workshop on brilliant light in life and material sciences, Yerevan, Armenia, 17-21 July 2006; Springer, ed. by V. Tsakanov and H. Wiedemann; pp. 383-393, 2007 28
F. LIQUID CRYSTALS Á. Buka, T. Börzsönyi, N. Éber, K. Fodor-Csorba, I. Jánossy, T. Tóth-Katona, A. Vajda Synthesis. — Banana shaped compounds with a brand new architecture have been planned and synthesized. These compounds have a polymerizable double bond connected to position 5 of the central aromatic ring; we call this new family bell-shaped bananas. Though such compounds with symmetrical structure do not show liquid crystalline properties, they exhibit a melting point very close to room temperature. Therefore they are good candidates for being additives in liquid crystalline mixtures to obtain mesophases at, around and below room temperature. The compounds with asymmetrical structure have required developing a more complicated synthetic procedure. These compounds with either a chiral or a fluorinated terminal group exhibited mesophases, which are now under investigation. It has been shown that bent core (banana) compounds are miscible with some calamitic (rod like) nematics. A sequence of new mixtures has been prepared for flexoelectric investigations. Electric field driven pattern formation. — Electric-field induced pattern forming instabilities (electroconvection, EC) of nematic liquid crystals have systematically been overviewed. The standard hydrodynamic description of nematics predicts the occurrence of striped patterns (rolls) in three basic configurations depending on the initial director orientation (planar or homeotropic) as well as on the anisotropy of the dielectric permittivity ε a and that of the electrical conductivity σ a . For planar aligned compounds with ε a < 0, σ a > 0 the EC pattern develops from an anisotropic basic state. At homeotropic boundary conditions the alignment has a rotational symmetry (isotropy in the cell plane) which is either broken spontaneously during a Freedericksz transition preceding the pattern forming instability (quasi-anisotropic case), or - at opposite sign of the anisotropies (ε a > 0, σ a < 0) - the isotropy is broken as part of the pattern forming mechanism. Experiments carried out for various initial geometries, like decay of patterns in planar, or magnetic field effects, abnormal rolls and defect dynamics in homeotropic cells, have shown excellent agreement with the theoretical predictions. Though the standard model of electroconvection predicts no hydrodynamic instability for nematics with ε a < 0, σ a < 0, experiments have revealed convection patterns. This instability has been named as non-standard electroconvection (ns-EC). It has occurred in a bent core compound as well as in some nematics with an underlying smectic phase. We have characterized the ns-EC patterns in the latter compounds by measuring the frequency, thickness, and temperature dependence of the threshold voltage, the wave-number, and the roll orientation using polarizing microscopy or light diffraction, and compared them with the characteristics of the standard EC (s-EC). As in these compounds the conductivity anisotropy alters its sign on heating, a transition from ns-EC to s-EC could be induced by changing the temperature (Figure 1.a). We have also shown that at constant temperature a similar transition can be induced by the frequency or the applied voltage (Figure 1.b). For the first time, we have reported traveling rolls in ns-EC, and determined the dependence of the Hopf frequency on the temperature, the sample thickness and the driving frequency. We have identified flexoelectricity as a possible source for the existence of the ns-EC patterns. 29
Page 1 and 2: ANNUAL REPORT 2007 RESEARCH INSTITU
Page 3 and 4: Dear Reader, It is my pleasure to h
Page 5 and 6: Key figures Permanent staff of the
Page 8 and 9: A. STRONGLY CORRELATED SYSTEMS J. S
Page 10 and 11: presented detailed study should hel
Page 12 and 13: B. COMPLEX SYSTEMS F. Iglói, R. Ju
Page 14 and 15: B.3. B.4. B.5. B.6. B.7. B.8. B.9.
Page 16 and 17: the α2 reconstruction increases on
Page 18 and 19: C.2. C.3. Kádas K, Vitos L, Johans
Page 20 and 21: C.27. Ropo * M, Kokko * K, Punkkine
Page 22 and 23: I 25 4 3 Fig. 2. Average intensity
Page 24 and 25: See also H.6. and nanostructured Pd
Page 26 and 27: Ab initio structure solution. — I
Page 28 and 29: ESA PECS 98021 Phase field modeling
Page 32 and 33: Fig. 1. ns-EC to s-EC transition in
Page 34 and 35: Publications Articles F.1. F.2. Bö
Page 36 and 37: G. ELECTRON CRYSTALS G. Kriza, P. M
Page 38 and 39: H. METAL PHYSICS K. Tompa, I. Bakon
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Page 42 and 43: I. METALLURGY AND MAGNETISM L.K. Va
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Page 52 and 53: Macromolecular Compounds (Visokomol
Page 54 and 55: defined coordination sphere was fou
Page 56 and 57: László Temleitner temla@szfki.hu
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Page 62 and 63: M. LASER PHYSICS K. Rózsa, G. Bán
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Page 76 and 77: E-Mail: Kárpát Ferencz optilab@t-
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Publications: Articles R.1. Földv
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S. CHARACTERIZATION AND POINT DEFEC
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groups of the Li 2 B 4 O 7 lattice.
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S.10. Lengyel K, Kovács L, Péter
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entanglement one has to find method
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T.7. T.8. T.9. Asbóth JK, Domokos
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EDUCATION Graduate and postgraduate
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Laboratory practice and seminars
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G. Dravecz (ELTE and Université de
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⎯ K. Kamarás: Editorial Board Me
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CONFERENCES ⎯ Electrochemistry se
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TABLE of CONTENTS PREFACE 1 KEY FIG
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