3,949 research outputs found
Magnetic studies of GaN nanoceramics
The synthesis, morphology and magnetization measurements of GaN nanoceramics
obtained under high pressure are reported. In particular the effect of grain
size on magnetic properties of GaN nanopowders and nanoceramics was
investigated. It was found that for the GaN nanoceramic characterized by the
stronger deformation of nanocrystalline grains the diamagnetic signal changes
with external magnetic field similarly to the Meissner effect in
superconductors.Comment: 3 pages, 4 figures, accepted Appl.Phys.Let
SO(5) superconductor in a Zeeman magnetic field: Phase diagram and thermodynamic properties
In this paper we present calculations of the SO(5) quantum rotor theory of
high-T superconductivity in Zeeman magnetic field. We use the spherical
approach for five-component quantum rotors in three-dimensional lattice to
obtain formulas for critical lines, free energy, entropy and specific heat and
present temperature dependences of these quantities for different values of
magnetic field. Our results are in qualitative agreement with relevant
experiments on high-T cuprates.Comment: 4 pages, 2 figures, to appear in Phys. Rev. B, see http://prb.aps.or
Transition in a numerical model of contact line dynamics and forced dewetting
We investigate the transition to a Landau-Levich-Derjaguin film in forced
dewetting using a quadtree adaptive solution to the Navier-Stokes equations
with surface tension. We use a discretization of the capillary forces near the
receding contact line that yields an equilibrium for a specified contact angle
called the numerical contact angle. Despite the well-known
contact line singularity, dynamic simulations can proceed without any explicit
additional numerical procedure. We investigate angles from to
and capillary numbers from to where the mesh size
is varied in the range of to of the capillary length
. To interpret the results, we use Cox's theory which involves a
microscopic distance and a microscopic angle . In the numerical
case, the equivalent of is the angle and we find
that Cox's theory also applies. We introduce the scaling factor or gauge
function so that and estimate this gauge function by
comparing our numerics to Cox's theory. The comparison provides a direct
assessment of the agreement of the numerics with Cox's theory and reveals a
critical feature of the numerical treatment of contact line dynamics: agreement
is poor at small angles while it is better at large angles. This scaling factor
is shown to depend only on and the viscosity ratio . In the
case of small , we use the prediction by Eggers [Phys. Rev. Lett.,
vol. 93, pp 094502, 2004] of the critical capillary number for the
Landau-Levich-Derjaguin forced dewetting transition. We generalize this
prediction to large and arbitrary and express the critical
capillary number as a function of and . An analogy can be drawn
between and the numerical slip length.Comment: This version of the paper includes the corrections indicated in Ref.
[1
Relativity and the lead-acid battery
The energies of the solid reactants in the lead-acid battery are calculated
ab initio using two different basis sets at non-relativistic, scalar
relativistic, and fully relativistic levels, and using several
exchange-correlation potentials. The average calculated standard voltage is
2.13 V, compared with the experimental value of 2.11 V. All calculations agree
in that 1.7-1.8 V of this standard voltage arise from relativistic effects,
mainly from PbO2 but also from PbSO4
Numerical Simulation of Superparamagnetic Nanoparticle Motion in Blood Vessels for Magnetic Drug Delivery
A numerical model is developed for the motion of superparamagnetic
nanoparticles in a non-Newtonian blood flow under the influence of a magnetic
field. The rheological properties of blood are modeled by the Carreau flow and
viscosity, and the stochastic effects of Brownian motion and red blood cell
collisions are considered. The model is validated with existing data and good
agreement with experimental results is shown. The effectiveness of magnetic
drug delivery in various blood vessels is assessed and found to be most
successful in arterioles and capillaries. A range of magnetic field strengths
are modeled using equations for both a bar magnet and a point dipole: it is
shown that the bar magnet is effective at capturing nanoparticles in limited
cases while the point dipole is highly effective across a range of conditions.
A parameter study is conducted to show the effects of changing the dipole
moment, the distance from the magnet to the blood vessel, and the initial
release point of the nanoparticles. The distance from the magnet to the blood
vessel is shown to play a significant role in determining nanoparticle capture
rate. The optimal initial release position is found to be located within the
tumor radius in capillaries and arterioles to prevent rapid diffusion to the
edges of the blood vessel prior to arriving at the tumor, and near the edge of
the magnet when a bar magnet is used.Comment: Fixed the title spacin
Surface Quality of a Work Material Influence on Vibrations in a Cutting Process
The problem of stability in the machining processes is an important task. It
is strictly connected with the final quality of a product. In this paper we
consider vibrations of a tool-workpiece system in a straight turning process
induced by random disturbances and their effect on a product surface. Basing on
experimentally obtained system parameters we have done the simulations using
one degree of freedom model. The noise has been introduced to the model by the
Langevin equation. We have also analyzed the product surface shape and its
dependence on the level of noise.Comment: 12 pages, PDF of figures can be obtained from
http://archimedes.pol.lublin.pl/~raf/graf/fpic.pd
Neel Order and Electron Spectral Functions in the Two-Dimensional Hubbard Model: a Spin-Charge Rotating Frame Approach
Using recently developed quantum SU(2)xU(1) rotor approach, that provides a
self-consistent treatment of the antiferromagnetic state we have performed
electronic spectral function calculations for the Hubbard model on the square
lattice. The collective variables for charge and spin are isolated in the form
of the space-time fluctuating U(1) phase field and rotating spin quantization
axis governed by the SU(2) symmetry, respectively. As a result interacting
electrons appear as composite objects consisting of bare fermions with attached
U(1) and SU(2) gauge fields. This allows us to write the fermion Green's
function in the space-time domain as the product CP^1 propagator resulting from
the SU(2) gauge fields, U(1) phase propagator and the pseudo-fermion
correlation function. As a result the problem of calculating the spectral line
shapes now becomes one of performing the convolution of spin, charge and
pseudo-fermion Green's functions. The collective spin and charge fluctuations
are governed by the effective actions that are derived from the Hubbard model
for any value of the Coulomb interaction. The emergence of a sharp peak in the
electron spectral function in the antiferromagnetic state indicates the decay
of the electron into separate spin and charge carrying particle excitations.Comment: 16 pages, 5 figures, submitted to Phys. Rev.
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