185 research outputs found
Phase behavior of a nematic liquid crystal in contact with a chemically and geometrically structured substrate
A nematic liquid crystal in contact with a grating surface possessing an
alternating stripe pattern of locally homeotropic and planar anchoring is
studied within the Frank--Oseen model. The combination of both chemical and
geometrical surface pattern leads to rich phase diagrams, involving a
homeotropic, a planar, and a tilted nematic texture. The effect of the groove
depth and the anchoring strengths on the location and the order of phase
transitions between different nematic textures is studied. A zenithally
bistable nematic device is investigated by confining a nematic liquid crystal
between the patterned grating surface and a flat substrate with strong
homeotropic anchoring.Comment: 7 pages, 7 figure
Effective free energy method for nematic liquid crystals in contact with structured substrates
We study the phase behavior of a nematic liquid crystal confined between a
flat substrate with strong anchoring and a patterned substrate whose structure
and local anchoring strength we vary. By first evaluating an effective surface
free energy function characterizing the patterned substrate we derive an
expression for the effective free energy of the confined nematic liquid
crystal. Then we determine phase diagrams involving a homogeneous state in
which the nematic director is almost uniform and a hybrid aligned nematic state
in which the orientation of the director varies through the cell. Direct
minimization of the free energy functional were performed in order to test the
predictions of the effective free energy method. We find remarkably good
agreement between the phase boundaries calculated from the two approaches. In
addition the effective energy method allows one to determine the energy
barriers between two states in a bistable nematic device.Comment: 10 pages, 7 figures, submitte
Layer dynamics of a freely standing smectic-A film
We study the hydrodynamics of a freely-standing smectic-A film in the
isothermal, incompressible limit theoretically by analyzing the linearized
hydrodynamic equations of motion with proper boundary conditions. The dynamic
properties for the system can be obtained from the response functions for the
free surfaces. Permeation is included and its importance near the free surfaces
is discussed. The hydrodynamic mode structure for the dynamics of the system is
compared with that of bulk systems. We show that to describe the dynamic
correlation functions for the system, in general, it is necessary to consider
the smectic layer displacement and the velocity normal to the layers,
, together. Finally, our analysis also provides a basis for the
theoretical study of the off-equilibrium dynamics of freely-standing smectic-A
films.Comment: 22 pages, 4 figure
INFLUENCE OF MODIFCATION ON THE REFINEMENT OF PRIMARY SILICON CRYSTALS IN HYPEREUTECTIC SILUMIN AlSi21CuNi
On the paper the influence of modifying micro additives on the refinement of primary silicon crystals in the hypereutectic AlSi21CuNi piston silumin have been examined. As the modifiers there were used micro additives of Phosphorus in the form of AlCu19P1.4 and CuP12 pre-alloys, sulfur in the form of CuS and iron in the powdered form. The modifying micro additives were used separately and together. Micro additions of iron were used together with phosphorus. Sulfur micro addition provided the frag-mentation of the primary silicon crystals, but not as effective as the phosphorus micro additive. The best effect of fragmentation of the primary silicon crystals was ensured by the combined addition of phosphorus in the form of AlCu19P1,4 pre alloy with a micro additive of powdered iron which re-duced the average size of the primary silicon crystals from 114 μm to 20 μm
Fluids of platelike particles near a hard wall
Fluids consisting of hard platelike particles near a hard wall are
investigated using density functional theory. The density and orientational
profiles as well as the surface tension and the excess coverage are determined
and compared with those of a fluid of rodlike particles. Even for low densities
slight orientational packing effects are found for the platelet fluid due to
larger intermolecular interactions between platelets as compared with those
between rods. A net depletion of platelets near the wall is exhibited by the
excess coverage, whereas a change of sign of the excess coverage of hard-rod
fluids is found upon increasing the bulk density.Comment: 6 pages, 9 figure
Wetting of Curved Surfaces
As a first step towards a microscopic understanding of the effective
interaction between colloidal particles suspended in a solvent we study the
wetting behavior of one-component fluids at spheres and fibers. We describe
these phenomena within density functional theory which keeps track of the
microscopic interaction potentials governing these systems. In particular we
properly take into account the power-law decay of both the fluid-fluid
interaction potentials and the substrate potentials. The thicknesses of the
wetting films as a function of temperature and chemical potential as well as
the wetting phase diagrams are determined by minimizing an effective interface
potential which we obtain by applying a sharp-kink approximation to the density
functional. We compare our results with previous approaches to this problem.Comment: 54 pages, 17 figures, accepted for publication in Physica
Rods Near Curved Surfaces and in Curved Boxes
We consider an ideal gas of infinitely rigid rods near a perfectly repulsive
wall, and show that the interfacial tension of a surface with rods on one side
is lower when the surface bends towards the rods. Surprisingly we find that
rods on both sides of surfaces also lower the energy when the surface bends. We
compute the partition functions of rods confined to spherical and cylindrical
open shells, and conclude that spherical shells repel rods, whereas cylindrical
shells (for thickness of the shell on the order of the rod-length) attract
them. The role of flexibility is investigated by considering chains composed of
two rigid segments.Comment: 39 pages including figures and tables. 12 eps figures. LaTeX with
REVTe
THE METHODOLOGY FOR DETECTING AND MANAGING THE ABUSE OF IT SYSTEMS
This paper focuses on the processes of dealing with security breaches which are becomingone of the most pressing problems in every organization whose systems are connected to theglobal web. The study presents the most widely used methodologies which were designed inorder to detect and react to security violations in a systematic and efficient way. Based onpresented methodologies, announced and supported by such credible organizations as SANS,NIST, CERT R or ISO, authors present their own methodology. It takes into account selectedaspects of these methodologies, with the purpose of creation a systematic and coherentapproach to the process of detecting and reacting to abuses in IT systems
Influence of Homeotropic Anchoring Walls upon Nematic and Smectic Phases
McMillan liquid crystal model sandwiched between strong homeotropic anchoring
walls is studied. Phase transitions between isotropic, nematic, and smectic A
phases are investigated for wide ranges of an interaction parameter and of the
system thickness. It is confirmed that the anchoring walls induce an increase
in transition temperatures, dissappearance of phase transitions, and an
appearance of non-spontaneous nematic phase. The similarity between influence
of anchoring walls and that of external fields is discussed.Comment: 5 pages, 6 figure
Liquid crystal films on curved surfaces: An entropic sampling study
The confining effect of a spherical substrate inducing anchoring (normal to
the surface) of rod-like liquid crystal molecules contained in a thin film
spread over it has been investigated with regard to possible changes in the
nature of the isotropic-to-nematic phase transition as the sample is cooled.
The focus of these Monte Carlo simulations is to study the competing effects of
the homeotropic anchoring due to the surface inducing orientational ordering in
the radial direction and the inherent uniaxial order promoted by the
intermolecular interactions. By adopting entropic sampling procedure, we could
investigate this transition with a high temperature precision, and we studied
the effect of the surface anchoring strength on the phase diagram for a
specifically chosen geometry. We find that there is a threshold anchoring
strength of the surface below which uniaxial nematic phase results, and above
which the isotropic fluid cools to a radially ordered nematic phase, besides of
course expected changes in the phase transition temperature with the anchoring
strength. In the vicinity of the threshold anchoring strength we observe a
bistable region between these two structures, clearly brought out by the
characteristics of the corresponding microstates constituting the entropic
ensemble.Comment: 14 pages, 5 figure
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