2,871 research outputs found
Dielectric Hysteresis, Relaxation Dynamics, and Non-volatile Memory Effect in Carbon Nanotube Dispersed Liquid Crystal
The self-organizing properties of nematic liquid crystals (LC) can be used to
template carbon nanotubes (CNTs) on a macroscopic dimension. The nematic
director field, coupled to the dispersed CNT long-axis, enables controlled
director reorientation using well-established methods of LC alignment
techniques, such as patterned-electrode-surface, electric fields, and magnetic
fields. Electric field induced director rotation of a nematic LC+CNT system is
of potential interests due to its possible applications as a nano
electromechanical system. The relaxation mechanism for a LC+CNT composite, on
the removal of the applied field, reveals the intrinsic dynamics of this
anisotropic system. Dielectric hysteresis and temperature dependence of the
dielectric constant coherently shows the ferroelectric-type behavior of the
LC+CNT system in the nematic phase. The strong surface anchoring of LC
molecules on CNT walls results in forming local isolated pseudo-nematic domains
in the isotropic phase. These domains, being anisotropic, respond to external
fields, but, do not relax back to the original state on switching of the field
off, showing non-volatile memory effect.Comment: 7 pages, 8 figure
Calorimetric study of the nematic to smectic-A phase transition in octylcyanobiphenyl-hexane binary mixtures
The continuous nematic to smectic-A (N-SmA) phase transition has been studied
by high-resolution ac-calorimetry in binary mixtures of the liquid crystal
octylcyanobiphenyl(8CB) and a non-mesogenic, low-molecular weight, solvent
n-hexane(hex) as a function of temperature and solvent concentration. Heating
and cooling scans about the N-SmA transition temperature were repeatedly
performed on pure and six 8CB+hex samples having hexane molar concentration
ranging from x_{hex}= 0.02 to 0.12. All 8CB+hex samples in this range of
x_{hex} remain macroscopically miscible and exhibit an N-SmA heat capacity peak
that shifts non-monotonically to lower temperature and evolves in shape, with a
reproducible hysteresis, as x_{hex} increases. The imaginary part of heat
capacity remains zero up to x^{TCP}_{hex}\simeq 0.07$ above which the distinct
peak is observed, corresponding to a jump in both the real and imaginary
enthalpy. A simple power-law analysis reveals an effective exponent that
increases smoothly from 0.30 to 0.50 with an amplitude ratio
A^{-}/A^{+}\rightarrow 1 as x_{hex}\rightarrow x^{TCP}_{hex}. This observed
crossover towards the N-SmA tricritical point driven by solvent concentration
is consistent with previous results and can be understood as weakening of the
liquid crystal intermolecular potential promoting increased nematic
fluctuations
Human Capital Externalities and Private Returns to Education in Kenya
We use survey data of full-time workers in Kenya to analyse the effect of human capital externalities on earnings and private returns to education. The estimation results show that education human capital generally associates with positive externalities, indicating that an increase in education benefits all workers. However, the results reveal that men benefit more from women's education than women do from men's schooling. The effects of human capital externalities on private returns to schooling are shown to vary substantially between rural and urban areas and across primary and higher levels of education.
Peano Structures and the Semantics of Iteration
In this paper closure theory is applied in order to obtain a uniform semantical treatment of both primitive and general iteration. In particular, the theory of Peano algebras has been extended to algebraic structures to inductively define both primitive and general iterates as structure homomorphisms, i.e. as fixed points of iteration equations
Monte Carlo simulation of uncoupled continuous-time random walks yielding a stochastic solution of the space-time fractional diffusion equation
We present a numerical method for the Monte Carlo simulation of uncoupled
continuous-time random walks with a Levy alpha-stable distribution of jumps in
space and a Mittag-Leffler distribution of waiting times, and apply it to the
stochastic solution of the Cauchy problem for a partial differential equation
with fractional derivatives both in space and in time. The one-parameter
Mittag-Leffler function is the natural survival probability leading to
time-fractional diffusion equations. Transformation methods for Mittag-Leffler
random variables were found later than the well-known transformation method by
Chambers, Mallows, and Stuck for Levy alpha-stable random variables and so far
have not received as much attention; nor have they been used together with the
latter in spite of their mathematical relationship due to the geometric
stability of the Mittag-Leffler distribution. Combining the two methods, we
obtain an accurate approximation of space- and time-fractional diffusion
processes almost as easy and fast to compute as for standard diffusion
processes.Comment: 7 pages, 5 figures, 1 table. Presented at the Conference on Computing
in Economics and Finance in Montreal, 14-16 June 2007; at the conference
"Modelling anomalous diffusion and relaxation" in Jerusalem, 23-28 March
2008; et
Global magnetic cycles in rapidly rotating younger suns
Observations of sun-like stars rotating faster than our current sun tend to
exhibit increased magnetic activity as well as magnetic cycles spanning
multiple years. Using global simulations in spherical shells to study the
coupling of large-scale convection, rotation, and magnetism in a younger sun,
we have probed effects of rotation on stellar dynamos and the nature of
magnetic cycles. Major 3-D MHD simulations carried out at three times the
current solar rotation rate reveal hydromagnetic dynamo action that yields
wreaths of strong toroidal magnetic field at low latitudes, often with opposite
polarity in the two hemispheres. Our recent simulations have explored behavior
in systems with considerably lower diffusivities, achieved with sub-grid scale
models including a dynamic Smagorinsky treatment of unresolved turbulence. The
lower diffusion promotes the generation of magnetic wreaths that undergo
prominent temporal variations in field strength, exhibiting global magnetic
cycles that involve polarity reversals. In our least diffusive simulation, we
find that magnetic buoyancy coupled with advection by convective giant cells
can lead to the rise of coherent loops of magnetic field toward the top of the
simulated domain.Comment: 4 pages, 3 figures, from IAU 273: The Physics of Sun and Star Spot
Achieving macro- and micro-roughness on Ti alloy by etching without prior sandblasting: a surface characterization
INTRODUCTION: Etching is currently the most popular method used to texture the surface of dental implants. Sandblasting prior to etching (SLA) is the only method to achieve a macro- and micro-surface texture with a Sa in the 1-2 μm range, a ‘moderately rough’ surface considered to be an optimized surface. However, SLA surfaces harbor remnant particles from the sandblasting process [l]. Some manufacturers consider the residual alumina particles as a foreign material worth getting rid of. Subsequently, they forgo an optimized moderately rough surface and stick to a ‘minimally rough’ micro-roughened surface displaying a Sa < 1 μm [l].
It has been recently claimed [2] that acid etching is typically not an appropriate treatment for α-β alloys because its biphasic nature leads to an enrichment of the Vanadium-rich β-phase on the surface.
The aim of the present paper is to show that it is feasible to achieve an optimized ‘moderately rough’ macro- and micro-textured surface on titanium alloy (Ti6Al4V) through etching only, without any prior sandblasting and to characterize the resulting surface
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