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Ordered Droplet Structures at the Liquid Crystal Surface and Elastic-Capillary Colloidal Interactions

physical Review Letters 2004年第11期93卷 117801-117801页

作者： I. I. Smalyukh S. Chernyshuk B. I. Lev A. B. Nych U. Ognysta V. G. Nazarenko O. D. Lavrentovich Liquid Crystal Institute and Chemical Physics Interdisciplinary Program Kent State University Kent Ohio 44242 USA Institute of Physics Prospect Nauki 46 Kyiv-39 03039 Ukraine Japan Science and Technology Corporation Yokoyama Nano-structured Liquid Crystal Project 5-9-9 Tokodai Ibaraki 300-2635 Japan

We demonstrate a variety of ordered patterns, including hexagonal structures and chains, formed by colloidal particles (droplets) at the free surface of a nematic liquid crystal (LC). The surface placement introduces a new type of particle interaction as compared to particles entirely in the LC bulk. Namely, director deformations caused by the particles lead to distortions of the interface and thus to capillary attraction. The elastic-capillary coupling is strong enough to remain relevant even at the micron-scale when its buoyancy-capillary counterpart becomes irrelevant.

关键词： Liquid crystals

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Pretransitional fluctuations in the isotropic phase of a lyotropic chromonic liquid crystal

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physical Review E 2004年第5期70卷 051706-051706页

作者： Yu. A. Nastishin H. Liu S. V. Shiyanovskii O. D. Lavrentovich A. F. Kostko M. A. Anisimov Liquid Crystal Institute Kent University Kent Ohio 44242 USA Institute for Physical Optics 23 Dragomanov Str. Lviv 79005 Ukraine Institute for Physical Science and Technology and Department of Chemical Engineering University of Maryland College Park Maryland 20742 USA Department of Physics St. Petersburg State University of Refrigeration and Food Engineering St. Petersburg 191002 Russia

We have studied isotropic-to-nematic pretransitional fluctuations in an aqueous solution of disodium cromoglycate (cromolyn) by static and dynamic light scattering. Cromolyn is a representative of lyotropic chromonic liquid crystals with building units being elongated rods formed by aggregates of disk-like molecules. By combining light-scattering and viscosity measurements we have determined the correlation length and relaxation time of the orientational order-parameter fluctuations and estimated the size of the cromolyn aggregates. The pretransitional behavior of light scattering does not completely follow the classic Landau–de Gennes model. This feature is most probably associated with the variable length of cromolyn aggregates. We have observed a dramatic increase of the shear viscosity near the transition to the nematic phase, the fact which correlates with the idea of growing supramolecular aggregates. The steep temperature dependence of the viscosity is accompanied by a practically temperature-independent translational diffusion coefficient.

关键词： Liquid crystals

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Finite Size Effects on Thermal Denaturation of Globular Proteins

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physical Review Letters 2004年第26期93卷 268107-268107页

作者： Mai Suan Li Dmitri K. Klimov D. Thirumalai Institute of Physics Polish Academy of Sciences Al. Lotnikow 32/46 02-668 Warsaw Poland Institute for Physical Science and Technology University of Maryland College Park Maryland 20742 USA Bioinformatics and Computational Biology Program School of Computational Sciences George Mason University Manassas Virginia 20110 USA

Finite size effects on the cooperative thermal denaturation of proteins are considered. A dimensionless measure of cooperativity, Ωc, scales as Nζ, where N is the number of amino acids. Surprisingly, we find that ζ is universal with ζ=1+γ, where the exponent γ characterizes the divergence of the susceptibility for a self-avoiding walk. Our lattice model simulations and experimental data are consistent with the theory. Our finding rationalizes the marginal stability of proteins and substantiates the earlier predictions that the efficient folding of two-state proteins requires TF≈Tθ, where Tθ and TF are the collapse and folding transition temperatures, respectively.

关键词： .stability Transitions PRL ending susceptibility experimental data Thermal denaturation folding transition exponent unfolded native state Globular Proteins cooperativity two-state NBA

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High resolution fourier synthesis hard X-ray imaging based on CdTe strip detectors

High resolution fourier synthesis hard X-ray imaging based o...

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IEEE Symposium on Nuclear science (NSS/MIC)

作者： R. Miyawaki H. Niko Y. Okada M. Kokubun K. Makishima H. Negoro J. Kotoku Y. Terada T. Tanaka T. Mitani K. Nakazawa T. Takahashi R. Ohno M. Funaki Y. Kuroda K. Genba M. Onishi Department of Physics University of Tokyo Tokyo Japan Department of Physics Nihon University Tokyo Japan Department of Physics Tokyo Institute of Technology Tokyo Japan Institute for Physical and Chemical Research Saitama Japan Institute of Space and Astronautical Science/JAXA Kanagawa Japan Acrorad Company Limited Okinawa Japan Mitsubishi Heavy Industries Limited Aichi Japan

Employing Fourier-synthesis optics and one-dimensional position-sensitive detectors, we are developing a novel hard X-ray imager which can work in the ~10 keV to ~200 keV range either as a telescope or a microscope. As the detection part of our imager, we have developed a strip detector made of Schottky CdTe diode, with its cathode divided into 64 channels of 150 mum pitch. Electrodes of all channels are gold-stud bonded to a fanout board, and connected to low noise analog ASIC. We read out signals from all channels simultaneously. As the grid optics elements, one-dimensional modulation collimator grids of 1 mm thick tungsten have been manufactured, with 10 grid pitches ranging from 0.2 mm to 2 mm with harmonic ratios. Combining the CdTe strip detector and the modulation collimators, we have verified hard X-ray imaging performance of this system. Specifically, by observing an 241 Am source, we have successfully obtained an image in the 10-70 keV range

关键词： Image resolution X-ray imaging Strips X-ray detection X-ray detectors Optical noise Optical modulation Optical collimators Position sensitive particle detectors Telescopes

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Dynamics of fluctuations in a fluid below the onset of Rayleigh-Bénard convection

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physical Review E 2004年第2期69卷 021106-021106页

作者： Jaechul Oh José M. Ortiz de Zárate Jan V. Sengers Guenter Ahlers Department of Physics and iQUEST University of California Santa Barbara California 93106 USA Departamento de Física Aplicada I Facultad de Física Universidad Complutense 28040 Madrid Spain Institute for Physical Science and Technology and Departments of Chemical Engineering and Mechanical Engineering University of Maryland College Park Maryland 20742 USA

We present experimental data and their theoretical interpretation for the decay rates of temperature fluctuations in a thin layer of a fluid heated from below and confined between parallel horizontal plates. The measurements were made with the mean temperature of the layer corresponding to the critical isochore of sulfur hexafluoride above but near the critical point where fluctuations are exceptionally strong. They cover a wide range of temperature gradients below the onset of Rayleigh-Bénard convection, and span wave numbers on both sides of the critical value for this onset. The decay rates were determined from experimental shadowgraph images of the fluctuations at several camera exposure times. We present a theoretical expression for an exposure-time-dependent structure factor which is needed for the data analysis. As the onset of convection is approached, the data reveal the critical slowing down associated with the bifurcation. Theoretical predictions for the decay rates as a function of the wave number and temperature gradient are presented and compared with the experimental data. Quantitative agreement is obtained if allowance is made for some uncertainty in the small spacing between the plates, and when an empirical estimate is employed for the influence of symmetric deviations from the Oberbeck-Boussinesq approximation which are to be expected in a fluid with its density at the mean temperature located on the critical isochore.

关键词： Hydrodynamics

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Evolution of local electronic states from a metal to a correlated insulator in a NiS2−xSex solid solution

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physical Review B 2004年第16期70卷 161103(R)-161103(R)页

作者： K. Iwaya Y. Kohsaka S. Satow T. Hanaguri S. Miyasaka H. Takagi RIKEN (The Institute of Physical and Chemical Research) Wako Saitama 351-0198 Japan CREST Japan Science and Technology Agency Kawaguchi Saitama 332-0012 Japan Department of Advanced Materials Science The University of Tokyo Kashiwa Chiba 277-8651 Japan Department of Applied Physics The University of Tokyo Tokyo 113-8656 Japan

The evolution of local electronic states in NiS2−xSex pyrite as a bandwidth-controlled metal-insulator transition (MIT) approached from the metallic side is explored by scanning tunneling microscopy/spectroscopy (STM/STS). Atomically resolved images of Se∕S zigzag chains are observed on top of the cubic (100) surface, and a narrowing of the quasiparticle band near the Fermi level is clearly identified in tunneling spectra. In marked contrast to MIT’s control by doping, the local electronic states are found to be spatially homogeneous even in the vicinity of the MIT.

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Onset of Tethered Chain Overcrowding

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physical Review Letters 2004年第2期93卷 028301-028301页

作者： William Y. Chen Joseph X. Zheng Stephen Z. D. Cheng Christopher Y. Li Ping Huang Lei Zhu Huiming Xiong Qing Ge Ya Guo Rodric P. Quirk Bernard Lotz Lingfeng Deng Chi Wu Edwin L. Thomas Maurice Morton Institute and Department of Polymer Science The University of Akron Akron Ohio 44325-3909 USA Department of Materials Science and Engineering Drexel University Philadelphia Pennsylvania 19104 USA Polymer Program Institute of Materials Science and Department of Chemical Engineering The University of Connecticut Storrs Connecticut 06269-3136 USA Institute of Charles Sadron 6 Rue Boussingault Strasbourg 67083 France Departments of Physics and Chemistry Hong Kong Chinese University Sha Tin Hong Kong Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA

We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature Tx increased, the PEO or PLLA lamellar crystal thickness dL increased as well as the reduced tethering density σ˜ of the PS chains. The onset of tethered PS chains overcrowding in solution occurs at σ˜*∼3.7–3.8 as evidenced by an abrupt change in the slope between (dL)−1 and Tx. This results from the extra surface free energy created by the tethered chain that starts to affect the growth barrier of the crystalline blocks.

关键词： .PS chains tethered chains PEO PS PEO or PLLA tethered PS

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Observation of millimeter-wave radiation generated by the interaction between an electron beam and a photonic crystal

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physical Review E 2004年第4期69卷 045601(R)-045601(R)页

作者： K. Yamamoto R. Sakakibara S. Yano Y. Segawa Y. Shibata K. Ishi T. Ohsaka T. Hara Y. Kondo H. Miyazaki F. Hinode T. Matsuyama S. Yamaguti K. Ohtaka Photodynamics Research Center The Institute of Physical and Chemical Research (RIKEN) Sendai 980-0845 Japan Department of Physics Tohoku University Sendai 980-8578 Japan Institute of Multidisciplinary Research for Advanced Materials Tohoku University Sendai 980-8577 Japan Department of Applied Physics Tohoku University Sendai 980-8579 Japan Laboratory of Nuclear Science Tohoku University Sendai 982-0826 Japan Graduate School of Science and Technology Chiba University Chiba 263-8522 Japan Center for Frontier Science Chiba University Chiba 263-8522 Japan

We observed directional light emission in the millimeter-wave region when a high-energy (150 MeV) electron beam passes just above a photonic crystal made of polytetrafluoroethylene beads (≃3.2mm in diameter). The relation between the momentum and the energy of the emitted photons strongly suggests that the observed light is generated by the umklapp scattering process that changes the evanescent waves emitted by the electron beam into observable ones. By comparing the observed spectra with calculated ones based on the photonic band structure, we found that generated photons excite the photonic band modes making them observable as enhanced fine structures in the emission spectra.

关键词： Millimeter waves

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Two-Dimensional Charge Order in Layered 2-1-4 Perovskite Oxides

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physical Review Letters 2004年第23期92卷 236403-236403页

作者： Shigeki Onoda Yukitoshi Motome Naoto Nagaosa Tokura Spin SuperStructure Project ERATO Japan Science and Technology Corporation Department of Applied Physics University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8656 Japan RIKEN (The Institute of Physical and Chemical Research) 2-1 Hirosawa Wako Saitama 351-0198 Japan CREST Department of Applied Physics University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8656 Japan Correlated Electron Research Center National Institute of Advanced Industrial Science and Technology Tsukuba Central 4 1-1-1 Higashi Tsukuba Ibaraki 305-8562 Japan

Monte Carlo simulations are performed on the three-dimensional (3D) Ising model with the 2-1-4 layered perovskite structure as a minimal model for checkerboard charge ordering phenomena in layered perovskite oxides. Because of the interlayer frustration, only 2D long-range order emerges with a finite correlation length along the c axis. Critical exponents of the transition change continuously as a function of the interlayer coupling constant. The interlayer long-range Coulomb interaction decays exponentially and is negligible even between the second-neighbor layers. Instead, monoclinic distortion of a tetragonal unit cell lifts the macroscopic degeneracy to induce a 3D charge ordering. The dimensionality of the charge order in La0.5Sr1.5MnO4 is discussed from this viewpoint.

关键词： Perovskite

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Raman study of the metal-insulator transition in pyrochlore Mo oxides

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physical Review B 2004年第10期70卷 100401(R)-100401(R)页

作者： K. Taniguchi T. Katsufuji S. Iguchi Y. Taguchi H. Takagi Y. Tokura Department of Advanced Materials Science University of Tokyo Kasiwa 277-8581 Japan Department of Physics Waseda University Tokyo 169-8555 Japan PRESTO JST Kawaguchi 332-0012 Japan Department of Applied Physics University of Tokyo Tokyo 113-8656 Japan Institute for Materials Research Tohoku University Sendai 980-8577 Japan Correlated Electron Research Center (CERC) National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba 305-8562 Japan Institute of Physical and Chemical Research (RIKEN) Saitama 351-0198 Japan Spin Superstructure (SSS) Project ERATO Japan Science and Technology Corporation (JST) Tsukuba 305-8562 Japan

Raman scattering spectra have been investigated for the correlated 4d-electron system, R2Mo2O7 (R=Nd, Sm, Gd, Tb,Dy,Nd1−xDyx), which undergoes a metal-insulator transition with changing the rare-earth ion R, or equivalently the one-electron bandwidth. It is found that several phonon peaks modulating the Mo−O−Mo bond angle appear in the metallic phase (R=Nd, Sm, Gd, Nd1−xDyx), whereas they are remarkably suppressed in intensity in the insulating phase (R=Tb,Dy). This result indicates that the phonon modes of R2Mo2O7 are coupled with the electron-hole excitation across the Fermi level, thus probing sensitively the low-energy charge dynamics in the vicinity of the bandwidth-control Mott transition.

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