3,561 research outputs found

### Investigations of a Two-Phase Fluid Model

We study an interface-capturing two-phase fluid model in which the
interfacial tension is modelled as a volumetric stress. Since these stresses
are obtainable from a Van der Waals-Cahn-Hilliard free energy, the model is, to
a certain degree, thermodynamically realistic. Thermal fluctuations are not
considered presently for reasons of simplicity. The utility of the model lies
in its momentum-conservative representation of surface tension and the
simplicity of its numerical implementation resulting from the volumetric
modelling of the interfacial dynamics. After validation of the model in two
spatial dimensions, two prototypical applications---instability of an initially
high-Reynolds-number liquid jet in the gaseous phase and spinodal decomposition
in a liquid-gas system--- are presented.Comment: Self unpacking uuencoded and compressed postscript file (423928
bytes). Includes 6 figure

### Shock structures in time averaged patterns for the Kuramoto-Sivashinsky equation

The Kuramoto-Sivashinsky equation with fixed boundary conditions is
numerically studied. Shocklike structures appear in the time-averaged patterns
for some parameter range of the boundary values. Effective diffusion constant
is estimated from the relation of the width and the height of the shock
structures.Comment: 6 pages, 7 figure

### Letter from S. Zaleski

1946. Letter from S. Zaleski, Delegate, T.K.T. (?) for New Zealand in Pahiatua, to the Polish YMCA attached to the Polish Armed Forces informing that books sent had been received. Dated September 27, 1946.https://digitalcommons.buffalostate.edu/ymcadocs/1078/thumbnail.jp

### Differential rotation of Kepler-71 via transit photometry mapping of faculae and starspots

Knowledge of dynamo evolution in solar-type stars is limited by the difficulty of using active region monitoring to measure stellar differential rotation, a key probe of stellar dynamo physics. This paper addresses the problem by presenting the first ever measurement of stellar differential rotation for a main-sequence solar-type star using starspots and faculae to provide complementary information. Our analysis uses modelling of light curves of multiple exoplanet transits for the young solar-type star Kepler-71, utilizing archival data from the Kepler mission. We estimate the physical characteristics of starspots and faculae on Kepler-71 from the characteristic amplitude variations they produce in the transit light curves and measure differential rotation from derived longitudes. Despite the higher contrast of faculae than those in the Sun, the bright features on Kepler-71 have similar properties such as increasing contrast towards the limb and larger sizes than sunspots. Adopting a solar-type differential rotation profile (faster rotation at the equator than the poles), the results from both starspot and facula analysis indicate a rotational shear less than about 0.005 rad d-1, or a relative differential rotation less than 2 per cent, and hence almost rigid rotation. This rotational shear contrasts with the strong rotational shear of zero-age main-sequence stars and the modest but significant shear of the modern-day Sun. Various explanations for the likely rigid rotation are considered

### 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$_{c}$ 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$_{c}$ 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
$\theta_\Delta$ 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 $15^\circ$ to
$110^\circ$ and capillary numbers from $0.00085$ to $0.2$ where the mesh size
$\Delta$ is varied in the range of $0.0035$ to $0.06$ of the capillary length
$l_c$. To interpret the results, we use Cox's theory which involves a
microscopic distance $r_m$ and a microscopic angle $\theta_e$. In the numerical
case, the equivalent of $\theta_e$ is the angle $\theta_\Delta$ and we find
that Cox's theory also applies. We introduce the scaling factor or gauge
function $\phi$ so that $r_m = \Delta/\phi$ 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 $\theta_\Delta$ and the viscosity ratio $q$. In the
case of small $\theta_e$, 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 $\theta_e$ and arbitrary $q$ and express the critical
capillary number as a function of $\theta_e$ and $r_m$. An analogy can be drawn
between $r_m$ and the numerical slip length.Comment: This version of the paper includes the corrections indicated in Ref.
[1

### Magnetic and transport parameters of LSMO and YBCO/LSMO films deposited on sapphire substrates

The La0.7Sr0.3MnO3 (LSMO) layers and YBa2Cu3O7-{\delta}/La0.7Sr0.3MnO3
(YBCO/LSMO) bilayers were grown by magnetron sputtering on sapphire (Al2O3 or
ALO) substrates. Temperature dependences of resistance of single LSMO films,
grown on ALO substrates were typical for polycrystalline manganite materials
and the resistance decreased with decrease of the temperature at medium
temperatures and increased at lower and higher temperatures. Deposition of a
top YBCO layer led to a drastic increase of the sample resistance. These
bilayers did not demonstrate a decreasing of the resistance with decrease of
temperature. Temperature dependence of the resistance of these samples was
interpreted in the framework of a phenomenological model of two intergrain
conduction channels. In framework of this model, parameters of the samples were
determined and discussed

### Possible origin of 60-K plateau in the YBa2Cu3O(6+y) phase diagram

We study a model of YBa2Cu3O(6+y) to investigate the influence of oxygen
ordering and doping imbalance on the critical temperature Tc(y) and to
elucidate a possible origin of well-known feature of YBCO phase diagram: the
60-K plateau. Focusing on "phase only" description of the high-temperature
superconducting system in terms of collective variables we utilize a
three-dimensional semi microscopic XY model with two-component vectors that
involve phase variables and adjustable parameters representing microscopic
phase stiffnesses. The model captures characteristic energy scales present in
YBCO and allows for strong anisotropy within basal planes to simulate oxygen
ordering. Applying spherical closure relation we have solved the phase XY model
with the help of transfer matrix method and calculated Tc for chosen system
parameters. Furthermore, we investigate the influence of oxygen ordering and
doping imbalance on the shape of YBCO phase diagram. We find it unlikely that
oxygen ordering alone can be responsible for the existence of 60-K plateau.
Relying on experimental data unveiling that oxygen doping of YBCO may introduce
significant charge imbalance between CuO2 planes and other sites, we show that
simultaneously the former are underdoped, while the latter -- strongly
overdoped almost in the whole region of oxygen doping in which YBCO is
superconducting. As a result, while oxygen content is increased, this provides
two counter acting factors, which possibly lead to rise of 60K plateau.
Additionally, our result can provide an important contribution to understanding
of experimental data supporting existence of multicomponent superconductivity
in YBCO.Comment: 9 pages, 8 figures, submitted to PRB, see http://prb.aps.or

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