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Full-Text Articles in Physics

Thermal Conductivity And Particle Agglomeration In Alumina Nanofluids: Experiment And Theory, Jonathan Selinger, Elena V. Timofeeva, Alexei N. Gavrilov, James M. Mccloskey, Yuriy V. Tolmachev Dec 2007

Thermal Conductivity And Particle Agglomeration In Alumina Nanofluids: Experiment And Theory, Jonathan Selinger, Elena V. Timofeeva, Alexei N. Gavrilov, James M. Mccloskey, Yuriy V. Tolmachev

Chemical Physics Publications

In recent years many experimentalists have reported an anomalously enhanced thermal conductivity in liquid suspensions of nanoparticles. Despite the importance of this effect for heat transfer applications, no agreement has emerged about the mechanism of this phenomenon, or even about the experimentally observed magnitude of the enhancement. To address these issues, this paper presents a combined experimental and theoretical study of heat conduction and particle agglomeration in nanofluids. On the experimental side, nanofluids of alumina particles in water and ethylene glycol are characterized using thermal conductivity measurements, viscosity measurements, dynamic light scattering, and other techniques. The results show that the ...


X-Ray Microscopy Study Of Chromonic Liquid Crystal Dry Film Texture, K. V. Kaznatcheev, P. Dudin, Oleg Lavrentovich, A. P. Hitchcock Dec 2007

X-Ray Microscopy Study Of Chromonic Liquid Crystal Dry Film Texture, K. V. Kaznatcheev, P. Dudin, Oleg Lavrentovich, A. P. Hitchcock

Chemical Physics Publications

Soft x-ray spectromicroscopy has been used to investigate the degree of the molecular alignment of sulfonated benzo[de]benzo[4.5]imidazo[2,1-a]isoquinoline[7,1], a lyotropic chromonic liquid crystal (LCLC). LCLC thin films cast from concentrated aqua solution (20 % wt.), aligned by shear flow and dried, show strong linear dichroism in their C-, N-, O-, S-K edge near edge x-ray spectra (NEXAFS). The carbon K edge has been used for quantitative evaluation of the orientational texture of the films at a submicron spatial scale. This has verified there is predominantly in-plane alignment of the LC director. To ...


Forward Lambda Production And Nuclear Stopping Power In D+Au Collisions At Root S(Nn)=200 Gev, B. I. Abelev, Quan Li, Star Collaboration Dec 2007

Forward Lambda Production And Nuclear Stopping Power In D+Au Collisions At Root S(Nn)=200 Gev, B. I. Abelev, Quan Li, Star Collaboration

Chemical Physics Publications

We report the measurement of Lambda and (Lambda) over bar yields and inverse slope parameters in d+Au collisions at root s(NN)=200 GeV at forward and backward rapidities (y=+/- 2.75), using data from the STAR forward time projection chambers. The contributions of different processes to baryon transport and particle production are probed exploiting the inherent asymmetry of the d+Au system. Comparisons to model calculations show that baryon transport on the deuteron side is consistent with multiple collisions of the deuteron nucleons with gold participants. On the gold side, HIJING-based models without a hadronic rescattering phase do ...


Effects Of Dielectric Relaxation On The Director Dynamics Of Uniaxial Nematic Liquid Crystals, Mingxia Gu, Ye Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich Dec 2007

Effects Of Dielectric Relaxation On The Director Dynamics Of Uniaxial Nematic Liquid Crystals, Mingxia Gu, Ye Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

The dielectric anisotropy of liquid crystals causes director reorientation in an applied electric field and is thus at the heart of electro-optic applications of these materials. The components of the dielectric tensor are frequency dependent. Until recently, this frequency dependence was not accounted for in a description of director dynamics in an electric field. We theoretically derive the reorienting dielectric torque acting on the director, taking into account the entire frequency spectrum of the dielectric tensor. The model allows one to include the effects of multiple relaxations in both parallel and perpendicular components of the dielectric tensor, thus generalizing a ...


Role Of Molecular Shape On Bent-Core Liquid-Crystal Structures, C. Bailey, Antal Jakli Nov 2007

Role Of Molecular Shape On Bent-Core Liquid-Crystal Structures, C. Bailey, Antal Jakli

Chemical Physics Publications

We show how frustrations in molecular packing generated by molecular substitutions and electrostatic potentials necessitate a local C(1) symmetry and lead to spontaneous polarization splay and layer bending in bent-core liquid crystals. By estimation of the entropic changes due to curvature, we calculated the elastic constants that drive the spontaneous layer bend and polarization splay and obtained length scales of these deformations. Finally, we propose a structural phase diagram which describes how the experimentally observed helical superstructures, layer undulation, polarization splay, and spontaneous fiber formation depend on the direction and magnitude of the spontaneous polarization.


Wide-Angle Achromatic Prism Beam Steering For Infrared Countermeasure Applications, Philip J. Bos, Henry Garcia, Vassili Sergan Nov 2007

Wide-Angle Achromatic Prism Beam Steering For Infrared Countermeasure Applications, Philip J. Bos, Henry Garcia, Vassili Sergan

Chemical Physics Publications

A two-rotating-prism system is an inexpensive lightweight two-dimensional beam steering device. It can be designed to be achromatic over a wide spectral range. However, the current two-prism achromatic design has a singularity problem at the center of the "field of view": if a beam is to be steered through the center, one of the prisms must make an instantaneous 90 flip. In our work we proposed a solution to this problem by adding a third prism to the system. The main thrust of this study was optimization of the apparatus by minimizing dispersion effects as well as predicting the theoretical ...


A Polymer-Stabilized Single-Layer Color Cholesteric Liquid Crystal Display With Anisotropic Reflection, Shin-Ying Lu, Liang-Chy Chien Sep 2007

A Polymer-Stabilized Single-Layer Color Cholesteric Liquid Crystal Display With Anisotropic Reflection, Shin-Ying Lu, Liang-Chy Chien

Chemical Physics Publications

The authors report a method of fabricating single-layer color cholesteric liquid crystal displays from a polymer-stabilized cholesteric liquid crystal. The reflective wavelength can be electrically switched to reflect blue or green from a cell initially reflecting a red color. The color change is a result of the compression to the helical pitches in planar layers in response to the applied voltage. The unique feature of the polymer stabilization is in the fact that the electrically switched colors preserve good reflectivity and the colors are reversible with voltage ramping. Conspicuously, the polymer-stabilized cholesteric display exhibits anisotropic reflection and has a temperature ...


Levitation, Lift, And Bidirectional Motion Of Colloidal Particles In An Electrically Driven Nematic Liquid Crystal, Oleg P. Pishnyak, S. Tang, J. R. Kelly, Sergij V. Shiyanovskii, Oleg Lavrentovich Sep 2007

Levitation, Lift, And Bidirectional Motion Of Colloidal Particles In An Electrically Driven Nematic Liquid Crystal, Oleg P. Pishnyak, S. Tang, J. R. Kelly, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We study electric-field-induced dynamics of colloids in a nematic cell, experimentally and by computer simulations. Solid particles in the nematic bulk create director distortions of dipolar type. Elastic repulsion from the walls keeps the particles in the middle of cell. The ac electric field reorients the dipoles and lifts them to top or bottom, depending on dipole orientation. Once near the walls, the colloids are carried along two antiparallel horizontal directions by nematic backflow. Computer simulations of the backflow agree with the experiment.


Partonic Flow And Phi-Meson Production In Au+Au Collisions At Root S(Nn)=200 Gev, B. I. Abelev, Quan Li, Star Collaboration Sep 2007

Partonic Flow And Phi-Meson Production In Au+Au Collisions At Root S(Nn)=200 Gev, B. I. Abelev, Quan Li, Star Collaboration

Chemical Physics Publications

We present first measurements of the phi-meson elliptic flow (v(2)(p(T))) and high-statistics p(T) distributions for different centralities from root s(NN) = 200 GeV Au+Au collisions at RHIC. In minimum bias collisions the v(2) of the phi meson is consistent with the trend observed for mesons. The ratio of the yields of the Omega to those of the phi as a function of transverse momentum is consistent with a model based on the recombination of thermal s quarks up to p(T)similar to 4 GeV/c, but disagrees at higher momenta. The nuclear modification ...


Universal Off-Axis Light Transmission Properties Of The Bright State In Perfectly Compensated Liquid Crystal Devices, Yong-Kyu Jang, Philip J. Bos Jul 2007

Universal Off-Axis Light Transmission Properties Of The Bright State In Perfectly Compensated Liquid Crystal Devices, Yong-Kyu Jang, Philip J. Bos

Chemical Physics Publications

We studied the off-axis light transmission characteristics of the bright state of common liquid crystal device modes. The dark state of these device modes is optically compensated to have minimum light transmittance at all angles. Our research shows there is an unexpected universal shape of the off-axis light transmission value in its bright state, regardless of what liquid crystal mode is used. To understand this surprising fact, we consider simple dark and bright state models in terms of phase retardation and transmittance.


Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray Jun 2007

Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray

Chemical Physics Publications

The distance of closest approach of hard particles is a key parameter of their interaction and plays an important role in the resulting phase behavior. For nonspherical particles, the distance of closest approach depends on orientation, and its calculation is surprisingly difficult. Although overlap criteria have been developed for use in computer simulations [ Vieillard-Baron J. Chem. Phys. 56 4729 (1972); Perram and Wertheim J. Comput. Phys. 58 409 (1985)], no analytic solutions have been obtained for the distance of closest approach of ellipsoids in three dimensions, or, until now, for ellipses in two dimensions. We have derived an analytic expression ...


Distance Of Closest Approach Of Two Arbitrary Hard Ellipsoids, Xiaoyu Zheng, Wilder Iglesias, Peter Palffy-Muhoray Jun 2007

Distance Of Closest Approach Of Two Arbitrary Hard Ellipsoids, Xiaoyu Zheng, Wilder Iglesias, Peter Palffy-Muhoray

Chemical Physics Publications

The distance of closest approach of hard particles is a key parameter of their interaction and plays an important role in the resulting phase behavior. For nonspherical particles, the distance of closest approach depends on orientation, and its calculation is surprisingly difficult. Although overlap criteria have been developed for use in computer simulations [ Vieillard-Baron J. Chem. Phys. 56 4729 (1972); Perram and Wertheim J. Comput. Phys. 58 409 (1985)], no analytic solutions have been obtained for the distance of closest approach of ellipsoids in three dimensions, or, until now, for ellipses in two dimensions. We have derived an analytic expression ...


Determination Of Interphase Line Tension In Langmuir Films, Jacob R. Wintersmith, Lu Zhou, Andrew J. Bernoff, J. Adin Mann Jr, Edgar E. Kooijman, Elizabeth K. Mann Jun 2007

Determination Of Interphase Line Tension In Langmuir Films, Jacob R. Wintersmith, Lu Zhou, Andrew J. Bernoff, J. Adin Mann Jr, Edgar E. Kooijman, Elizabeth K. Mann

Biological Sciences Publications

A Langmuir film is a molecularly thin film on the surface of a fluid; we study the evolution of a Langmuir film with two coexisting fluid phases driven by an interphase line tension and damped by the viscous drag of the underlying subfluid. Experimentally, we study a 4′-8-alkyl[1,1′-biphenyl]-4-carbonitrile (8CB) Langmuir film via digitally imaged Brewster angle microscopy in a four-roll mill setup which applies a transient strain and images the response. When a compact domain is stretched by the imposed strain, it first assumes a bola shape with two tear-drop shaped reservoirs connected by a ...


Field-Induced And Polymer-Stabilized Two-Dimensional Cholesteric Liquid Crystal Gratings, Shin-Woong Kang, Liang-Chy Chien May 2007

Field-Induced And Polymer-Stabilized Two-Dimensional Cholesteric Liquid Crystal Gratings, Shin-Woong Kang, Liang-Chy Chien

Chemical Physics Publications

The authors experimentally demonstrate an electrically switchable gratings based on polymer-stabilized, field-induced two-dimensional square-lattice pattern of a cholesteric liquid crystal. A dependence of the two-dimensional diffraction patterns with the magnitude of applied voltage is observed for before and after the polymer stabilization. The diffraction efficiency reaches 84% calculated for the zero order light intensity at the applied voltage of 0.23 V/mu m for a 10 mu m thick sample.


Modeling And Performance Limits Of A Large Aperture High-Resolution Wavefront Control System Based On A Liquid Crystal Spatial Light Modulator, Xinghua Wang, Bin Wang, Philip J. Bos Apr 2007

Modeling And Performance Limits Of A Large Aperture High-Resolution Wavefront Control System Based On A Liquid Crystal Spatial Light Modulator, Xinghua Wang, Bin Wang, Philip J. Bos

Chemical Physics Publications

The aberration introduced by the primary optical element of a lightweight large aperture telescope can be corrected with a diffractive optical element called the liquid crystal spatial light modulator. Such aberration is usually very large, which makes the design and modeling of such a system difficult. A method to analyze the system is introduced, and the performance limitation of the system is studied through extensive modeling. An experimental system is demonstrated to validate the analysis. The connection between the modeling data and the experimental data is given.


Thermodielectric Bistability In Dual Frequency Nematic Liquid Crystal, Y. Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich Mar 2007

Thermodielectric Bistability In Dual Frequency Nematic Liquid Crystal, Y. Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We report on a thermodielectric bistability in dual frequency nematic liquid crystals (LCs) caused by the anisotropic nature of dielectric heating and director reorientation in an electric field. The bistability is a result of the positive feedback loop: director reorientation -> anisotropic dielectric heating -> dielectric anisotrophy -> director reorientation. We demonstrate both experimentally and theoretically that two states with different temperature and director orientation, namely, a cold planar state and a hot homeotropic state coexist in a LC cell for a certain frequency and amplitude range of the applied voltage.


Analysis Of The Multireflection Effects In Compensated Liquid Crystal Devices, Yong-Kyu Jang, Philip J. Bos Feb 2007

Analysis Of The Multireflection Effects In Compensated Liquid Crystal Devices, Yong-Kyu Jang, Philip J. Bos

Chemical Physics Publications

The effect of multiple internal reflections on the extinction ratio of perfectly compensated liquid crystal devices is studied. We find the previously unexplained wavelength dependence of light leakage in an ideally compensated device is caused by the interference of the internally reflected ordinary and extraordinary waves. While these effects have not been previously made clear, they can place a limit on the performance of liquid crystal devices used as displays, optical switches, and optical attenuators.


Coexistence Of Two Colloidal Crystals At The Nematic-Liquid-Crystal-Air Interface, A. B. Nych, Institute Of Physics, Ukraine, V. M. Pergamenshchik, B. I. Lev, V. G. Nazarenko, I. Muševič, M. Škarabot, Oleg Lavrentovich Feb 2007

Coexistence Of Two Colloidal Crystals At The Nematic-Liquid-Crystal-Air Interface, A. B. Nych, Institute Of Physics, Ukraine, V. M. Pergamenshchik, B. I. Lev, V. G. Nazarenko, I. Muševič, M. Škarabot, Oleg Lavrentovich

Chemical Physics Publications

Glycerol droplets at a nematic-liquid-crystal–air interface form two different lattices—hexagonal and dense quasihexagonal—which are separated by the energy barrier and can coexist. Director distortions around each droplet form an elastic dipole. The first order transition between the two lattices is driven by a reduction of the dipole-dipole repulsion through reorientation of these dipoles. The elastic-capillary attraction is essential for the both lattices. The effect has a many-body origin.


Comment On "Intense Nonlinear Magnetic Dipole Radiation At Optical Frequencies: Molecular Scattering In A Dielectric Liquid", Peter Palffy-Muhoray Jan 2007

Comment On "Intense Nonlinear Magnetic Dipole Radiation At Optical Frequencies: Molecular Scattering In A Dielectric Liquid", Peter Palffy-Muhoray

Chemical Physics Publications

No abstract provided.