8,370 research outputs found
Density-functional study of defects in two-dimensional circular nematic nanocavities
We use density--functional theory to study the structure of two-dimensional
defects inside a circular nematic nanocavity. The density, nematic order
parameter, and director fields, as well as the defect core energy and core
radius, are obtained in a thermodynamically consistent way for defects with
topological charge (with radial and tangential symmetries) and .
An independent calculation of the fluid elastic constants, within the same
theory, allows us to connect with the local free--energy density predicted by
elastic theory, which in turn provides a criterion to define a defect core
boundary and a defect core free energy for the two types of defects. The radial
and tangential defects turn out to have very different properties, a feature
that a previous Maier--Saupe theory could not account for due to the simplified
nature of the interactions --which caused all elastic constants to be equal. In
the case with two defects in the cavity, the elastic r\'egime cannot
be reached due to the small radii of the cavities considered, but some trends
can already be obtained.Comment: 9 figures. Accepted for publication in liquid crystal
Biaxial nematic and smectic phases of parallel particles with different cross sections
We have calculated the phase diagrams of one--component fluids made of five
types of biaxial particles differing in their cross sections. The orientation
of the principal particle axis is fixed in space, while the second axis is
allowed to freely rotate. We have constructed a free-energy density functional
based on fundamental--measure theory to study the relative stability of nematic
and smectic phases with uniaxial, biaxial and tetratic symmetries. Minimization
of the density functional allows us to study the phase behavior of the biaxial
particles as a function of the cross-section geometry. For low values of the
aspect ratio of the particle cross section, we obtain smectic phases with
tetratic symmetry, although metastable with respect to the crystal, as our MC
simulation study indicates. For large particle aspect ratios and in analogy
with previous work [Phys. Chem. Chem. Phys. 5, 3700 (2003)], we have found a
four--phase point where four spinodals, corresponding to phase transitions
between phases with different symmetries, meet together. The location of this
point is quite sensitive to particle cross section, which suggests that
optimizing the particle geometry could be a useful criterion in the design of
colloidal particles that can exhibit an increased stability of the biaxial
nematic phase with respect to other competing phases with spatial order.Comment: 13 pages, 12 figures, submitted to PR
ESMO Clinical Practice Guideline update on the use of immunotherapy in early stage and advanced renal cell carcinoma
Not availabl
Capillary and anchoring effects in thin hybrid nematic films and connection with bulk behavior
By means of a molecular model, we examine hybrid nematic films with
antagonistic anchoring angles where one of the surfaces is in the strong
anchoring regime. If anchoring at the other surface is weak, and in the absence
of wetting by the isotropic phase, the anchoring transition may interact with
the capillary isotropic-nematic transition in interesting ways. For general
anchoring conditions on this surface we confirm the existence of the step-tilt,
biaxial phase and the associated transition to the linear,
constant-tilt-rotation, configuration. The step-like phase is connected with
the bulk isotropic phase for increasing film thickness so that the latter
transition is to be interpreted as the capillary isotropic-nematic transition.
Finally, we suggest possible global surface phase diagrams.Comment: 7 pages, 5 figure
Some thoughts about nonequilibrium temperature
The main objective of this paper is to show that, within the present
framework of the kinetic theoretical approach to irreversible thermodynamics,
there is no evidence that provides a basis to modify the ordinary Fourier
equation relating the heat flux in a non-equilibrium steady state to the
gradient of the local equilibrium temperature. This fact is supported, among
other arguments, through the kinetic foundations of generalized hydrodynamics.
Some attempts have been recently proposed asserting that, in the presence of
non-linearities of the state variables, such a temperature should be replaced
by the non-equilibrium temperature as defined in Extended Irreversible
Thermodynamics. In the approximations used for such a temperature there is so
far no evidence that sustains this proposal.Comment: 13 pages, TeX, no figures, to appear in Mol. Phy
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