204 research outputs found
Elastic constants of nematic liquid crystals of uniaxial symmetry
We study in detail the influence of molecular interactions on the Frank
elastic constants of uniaxial nematic liquid crystals composed of molecules of
cylindrical symmetry. A brief summary of the status of theoretical development
for the elastic constants of nematics is presented. Considering a pair
potential having both repulsive and attractive parts numerical calculations are
reported for three systems MBBA, PAA and 8OCB. For these systems the
length-to-width ratio is estimated from the experimentally proposed
structure of the molecules. The repulsive interaction is represented by a
repulsion between hard ellipsoids of revolution (HER) and the attractive
potential is represented by the quadrupole and dispersion interactions. From
the numerical results we observe that in the density range of nematics the
contribution of the quadrupole and dispersion interactions are small as
compared to the repulsive HER interaction. The inclusion of attractive
interaction reduces the values of elastic constants ratios. The temperature
variation of elastic constants ratios are reported and compared with the
experimental values. A reasonably good agreement between theory and experiment
is observed
Geometry, thermodynamics, and finite-size corrections in the critical Potts model
We establish an intriguing connection between geometry and thermodynamics in
the critical q-state Potts model on two-dimensional lattices, using the q-state
bond-correlated percolation model (QBCPM) representation. We find that the
number of clusters of the QBCPM has an energy-like singularity for q different
from 1, which is reached and supported by exact results, numerical simulation,
and scaling arguments. We also establish that the finite-size correction to the
number of bonds, has no constant term and explains the divergence of related
quantities as q --> 4, the multicritical point. Similar analyses are applicable
to a variety of other systems.Comment: 12 pages, 6 figure
Probing Landau quantisation with the presence of insulator-quantum Hall transition in a GaAs two-dimensional electron system
Magneto-transport measurements are performed on the two-dimensional electron
system (2DES) in an AlGaAs/GaAs heterostructure. By increasing the magnetic
field perpendicular to the 2DES, magnetoresistivity oscillations due to Landau
quantisation can be identified just near the direct insulator-quantum Hall
(I-QH) transition. However, different mobilities are obtained from the
oscillations and transition point. Our study shows that the direct I-QH
transition does not always correspond to the onset of strong localisation.Comment: 11 pages, 7 figure
Observation of Coalescence Process of Silver Nanospheres During Shape Transformation to Nanoprisms
In this report, we observed the growth mechanism and the shape transformation from spherical nanoparticles (diameter ~6 nm) to triangular nanoprisms (bisector length ~100 nm). We used a simple direct chemical reduction method and provided evidences for the growth of silver nanoprisms via a coalescence process. Unlike previous reports, our method does not rely upon light, heat, or strong oxidant for the shape transformation. This transformation could be launched by fine-tuning the pH value of the silver colloidal solution. Based on our extensive examination using transmission electron microscopy, we propose a non-point initiated growth mechanism, which is a combination of coalescence and dissolution–recrystallization process during the growth of silver nanoprisms
Investigation of the electrical conductivity of propylene glycol-based ZnO nanofluids
Electrical conductivity is an important property for technological applications of nanofluids that has not been widely studied. Conventional descriptions such as the Maxwell model do not account for surface charge effects that play an important role in electrical conductivity, particularly at higher nanoparticle volume fractions. Here, we perform electrical characterizations of propylene glycol-based ZnO nanofluids with volume fractions as high as 7%, measuring up to a 100-fold increase in electrical conductivity over the base fluid. We observe a large increase in electrical conductivity with increasing volume fraction and decreasing particle size as well as a leveling off of the increase at high volume fractions. These experimental trends are shown to be consistent with an electrical conductivity model previously developed for colloidal suspensions in salt-free media. In particular, the leveling off of electrical conductivity at high volume fractions, which we attribute to counter-ion condensation, represents a significant departure from the "linear fit" models previously used to describe the electrical conductivity of nanofluids
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