4,048 research outputs found
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
TRANSIT TIME IN ITAJAÍ-AÇÚ RIVER ESTUARY
O Estuário do rio Itajaí-Açu é um estuário altamente estratificado, e apresenta durante a maior parte do ano uma proeminente cunha salina. Devido a esta característica foi possível aplicar o modelo de caixa, baseado no teorema hidrográfico de Knudsen, para se estimar o balanço salino e o tempo de trânsito das águas fluvial e marinha no estuário. Este modelo possibilita verificar o estado estático das condições de mistura no estuário e não deve ser confundido com as condições médias do estuário. Uma característica positiva deste modelo é o fato dele precisar de um numero pequeno de parâmetros, como perfil de salinidade, volume do estuário e dados de corrente, estes últimos estimados a partir de dados de descarga fluvial. Foram analisados sete dias de dados, compreendendo um ciclo completo de maré (sizígia-quadratura). Dados de velocidade vertical, estimados pelo modelo, mostraram que as condições de maré de sizígia causam um maior grau de mistura. Para confirmar isto foi definido um coeficiente de mistura dado pela razão do conteúdo de água fluvial pelo de água de mistura, o que comprovou tal padrão. Quanto ao tempo de transito, verificou-se que em situações de média descarga, cerca de 215 m3.s-1, o tempo de trânsito da água marinha foi três vezes maior do que o da água fluvial. Os valores estimados foram de 13.2 horas para a água fluvial e 50.7 horas para água marinha.The Itajaí-Açu estuary is classified as a highly stratified and presents most of the time a salt wedge. Considering this characteristic, it was used a box model, based on Knudsen hidrographic teorem, to estimate the salt balance and the transit time of fluvial and marine waters in this estuary. This model enables to verify the steady state of mixture conditions and should not be confused as the mean conditions of the estuary. A positive characteristic of this model is that it needs a small number of parameters such as salinity profiles, the estuary volume and currents data, being the latter estimated from river discharge. Seven days of data were assessed, comprising a half synodical cycle (spring-neap tide). Vertical velocities data, estimated by the model, showed that spring tide condition causes a more effective mixing. It was stated a ratio of content of fluvial water to the content of mixohaline water, which confirmed the early findings of intensification of mixing during spring tide period. The estimation of the transit time of fluvial and marine water in the estuary for medium discharge condition, ~ 215 m3.s-1, were 13.2 and 50.7 hours, respectively. It shows that the marine water spends 3 times more time in the estuary than the fluvial water
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.
Power-Law Behavior of Power Spectra in Low Prandtl Number Rayleigh-Benard Convection
The origin of the power-law decay measured in the power spectra of low
Prandtl number Rayleigh-Benard convection near the onset of chaos is addressed
using long time numerical simulations of the three-dimensional Boussinesq
equations in cylindrical domains. The power-law is found to arise from
quasi-discontinuous changes in the slope of the time series of the heat
transport associated with the nucleation of dislocation pairs and roll
pinch-off events. For larger frequencies, the power spectra decay exponentially
as expected for time continuous deterministic dynamics.Comment: (10 pages, 6 figures
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