68 research outputs found
Orientational instabilities in nematics with weak anchoring under combined action of steady flow and external fields
We study the homogeneous and the spatially periodic instabilities in a
nematic liquid crystal layer subjected to steady plane {\em Couette} or {\em
Poiseuille} flow. The initial director orientation is perpendicular to the flow
plane. Weak anchoring at the confining plates and the influence of the external
{\em electric} and/or {\em magnetic} field are taken into account. Approximate
expressions for the critical shear rate are presented and compared with
semi-analytical solutions in case of Couette flow and numerical solutions of
the full set of nematodynamic equations for Poiseuille flow. In particular the
dependence of the type of instability and the threshold on the azimuthal and
the polar anchoring strength and external fields is analysed.Comment: 12 pages, 6 figure
Switching dynamics of surface stabilized ferroelectric liquid crystal cells: effects of anchoring energy asymmetry
We study both theoretically and experimentally switching dynamics in surface
stabilized ferroelectric liquid crystal cells with asymmetric boundary
conditions. In these cells the bounding surfaces are treated differently to
produce asymmetry in their anchoring properties. Our electro-optic measurements
of the switching voltage thresholds that are determined by the peaks of the
reversal polarization current reveal the frequency dependent shift of the
hysteresis loop. We examine the predictions of the uniform dynamical model with
the anchoring energy taken into account. It is found that the asymmetry effects
are dominated by the polar contribution to the anchoring energy. Frequency
dependence of the voltage thresholds is studied by analyzing the properties of
time-periodic solutions to the dynamical equation (cycles). For this purpose,
we apply the method that uses the parameterized half-period mappings for the
approximate model and relate the cycles to the fixed points of the composition
of two half-period mappings. The cycles are found to be unstable and can only
be formed when the driving frequency is lower than its critical value. The
polar anchoring parameter is estimated by making a comparison between the
results of modelling and the experimental data for the shift vs frequency
curve. For a double-well potential considered as a deformation of the
Rapini-Papoular potential, the branch of stable cycles emerges in the low
frequency region separated by the gap from the high frequency interval for
unstable cycles.Comment: 35 pages, 15 figure
CEM03 and LAQGSM03 - new modeling tools for nuclear applications
An improved version of the Cascade-Exciton Model (CEM) of nuclear reactions
realized in the code CEM2k and the Los Alamos version of the Quark-Gluon String
Model (LAQGSM) have been developed recently at LANL to describe reactions
induced by particles and nuclei for a number of applications. Our CEM2k and
LAQGSM merged with the GEM2 evaporation/fission code by Furihata have
predictive powers comparable to other modern codes and describe many reactions
better than other codes; therefore both our codes can be used as reliable event
generators in transport codes for applications. During the last year, we have
made a significant improvements to the intranuclear cascade parts of CEM2k and
LAQGSM, and have extended LAQGSM to describe photonuclear reactions at energies
to 10 GeV and higher. We have produced in this way improved versions of our
codes, CEM03.01 and LAQGSM03.01. We present a brief description of our codes
and show illustrative results obtained with CEM03.01 and LAQGSM03.01 for
different reactions compared with predictions by other models, as well as
examples of using our codes as modeling tools for nuclear applications.Comment: 12 pages, 10 figures, to be published in Journal of Physics:
Conference Series: Proc. Europhysics Conf. on New Trends in Nuclear Physics
Applications and Technologies (NPDC19), Pavia, Italy, September 5-9, 200
РОЛЬ УЛЬТРАЗВУКА В МЕХАНИЗМАХ АНОДНО-КАТОДНЫХ ВЗАИМОДЕЙСТВИЙ ПРИ ЭЛЕКТРОИСКРОВОМ ЛЕГИРОВАНИИ
The paper reveals results of investigations on mass transfer kinetics and dynamics of coating formation while using integral electrospark alloying method with additional ultrasonic exposure at different stages of formation. Nowadays, a classical method for electrospark alloying with hard-alloy anodes and impulse AC voltage frequency on the vibration exciter coil from 20 to 1600 Hz has been mainly used for application of protective and strengthening coatings within permissible thickness and characteristics. The key aspect of ultrasonic exposure application (frequency 22–44 kHz) during electrospark alloying is the possibility to increase further thickness of coatings to be formed even after reaching a brittle fracture threshold of the coating material. Methodology of the executed research activity has been based on integrated studies (gravimetric, metallographic, X-ray diffraction and electron microscopic) of coatings which are to be formed through compositions produced while using method of high-energy hot compaction and a “refractory carbide (WC) and a binding material“ system in the form of alloy based on nickel from the series of “colmonoy” Ni – Ni3B system which is alloyed with additions of copper and silicon. The initial surface treatment within ultrasonic frequency range (22–44 kHz) contributes to a noticeable increase in the mass transfer rate, which is primarily determined by chemical composition and thermodynamic stability of anodes. It is due to surface activation in the process of its preliminary deformation at ultrasonic frequency which creates additional conditions for striking of a spark.The final ultrasonic treatment improves coating quality due to its additional forging that leads to an increase of its structure homogeneity and density.Приведены результаты исследований кинетики массопереноса и динамика формирования покрытий интегральным способом электроискрового легирования с дополнительным ультразвуковым воздействием на разных стадиях их формирования. В настоящее время для нанесения защитно-упрочняющих покрытий в пределах допустимых толщин и характеристик в основном применяется классический метод электроискрового легирования с использованием твердосплавных анодов и частотой импульсного переменного напряжения на катушке вибровозбудителя от 20 до 1600 Гц. Главной особенностью применения ультразвукового воздействия (частота 22–44 кГц) в процессе электроискрового легирования является возможность дальнейшего наращивания толщины формируемых покрытий даже после достижения порога хрупкого разрушения материала покрытия. Методика проводимой работы базировалась на комплексных гравиметрических, металлографических, рентгеноструктурных и электронно-микроскопических исследованиях формируемых покрытий на основе композиций, изготовленных методом высокоэнергетического горячего прессования, и системы «тугоплавкий карбид (WC) – связка» в виде сплава на основе никеля из серии «колмоной» системы Ni – Ni3B, легированной добавками меди и кремния. Первоначальная обработка поверхности в диапазоне ультразвуковых частот 22–44 кГц способствует заметному возрастанию скорости массопереноса, которая определяется прежде всего химическим составом и термодинамической устойчивостью анодов. Это объясняется активацией поверхности в процессе ее предварительного деформирования с ультразвуковой частотой с созданием дополнительных условий для возникновения искрового разряда. Завершающая ультразвуковая обработка улучшает качество покрытия вследствие его дополнительной проковки, приводя к увеличению однородности его структуры и повышению ее плотности
Three-dimensional pattern formation, multiple homogeneous soft modes, and nonlinear dielectric electroconvection
Patterns forming spontaneously in extended, three-dimensional, dissipative
systems are likely to excite several homogeneous soft modes (
hydrodynamic modes) of the underlying physical system, much more than quasi
one- and two-dimensional patterns are. The reason is the lack of damping
boundaries. This paper compares two analytic techniques to derive the patten
dynamics from hydrodynamics, which are usually equivalent but lead to different
results when applied to multiple homogeneous soft modes. Dielectric
electroconvection in nematic liquid crystals is introduced as a model for
three-dimensional pattern formation. The 3D pattern dynamics including soft
modes are derived. For slabs of large but finite thickness the description is
reduced further to a two-dimensional one. It is argued that the range of
validity of 2D descriptions is limited to a very small region above threshold.
The transition from 2D to 3D pattern dynamics is discussed. Experimentally
testable predictions for the stable range of ideal patterns and the electric
Nusselt numbers are made. For most results analytic approximations in terms of
material parameters are given.Comment: 29 pages, 2 figure
ROLE OF ULTRASOUND IN MECHANISMS OF ANODE-CATHODE INTERACTIONS DURING ELECTROSPARK ALLOYING
The paper reveals results of investigations on mass transfer kinetics and dynamics of coating formation while using integral electrospark alloying method with additional ultrasonic exposure at different stages of formation. Nowadays, a classical method for electrospark alloying with hard-alloy anodes and impulse AC voltage frequency on the vibration exciter coil from 20 to 1600 Hz has been mainly used for application of protective and strengthening coatings within permissible thickness and characteristics. The key aspect of ultrasonic exposure application (frequency 22–44 kHz) during electrospark alloying is the possibility to increase further thickness of coatings to be formed even after reaching a brittle fracture threshold of the coating material. Methodology of the executed research activity has been based on integrated studies (gravimetric, metallographic, X-ray diffraction and electron microscopic) of coatings which are to be formed through compositions produced while using method of high-energy hot compaction and a “refractory carbide (WC) and a binding material“ system in the form of alloy based on nickel from the series of “colmonoy” Ni – Ni3B system which is alloyed with additions of copper and silicon. The initial surface treatment within ultrasonic frequency range (22–44 kHz) contributes to a noticeable increase in the mass transfer rate, which is primarily determined by chemical composition and thermodynamic stability of anodes. It is due to surface activation in the process of its preliminary deformation at ultrasonic frequency which creates additional conditions for striking of a spark.The final ultrasonic treatment improves coating quality due to its additional forging that leads to an increase of its structure homogeneity and density
20.3 / E. Pozhidaev 20.3: Photo-aligned Ferroelectric Liquid Crystal Display with Memorized Gray
The new concept of the passive matrix ferroelectric liquid crystal display (FLCD) with a memorized grey scale is proposed. The physical origin of the gray scale in ferroelectric liquid crystal display is considered. The criterion of reliable bistability is derived dependent on FLC hysteretic behavior in electric field. A new approach for multiplex electronic addressing of the FLCD grey scale is given. A passively addressed 64×64 FLCD based on the photo-alignment technique is developed. New applications of passively addressed FLCD with a memorized grey scale are discussed. 1
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