3,561 research outputs found

    Investigations of a Two-Phase Fluid Model

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    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

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    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

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    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

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    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

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    In this paper we present calculations of the SO(5) quantum rotor theory of high-Tc_{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-Tc_{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

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    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 θΔ\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 1515^\circ to 110110^\circ and capillary numbers from 0.000850.00085 to 0.20.2 where the mesh size Δ\Delta is varied in the range of 0.00350.0035 to 0.060.06 of the capillary length lcl_c. To interpret the results, we use Cox's theory which involves a microscopic distance rmr_m and a microscopic angle θe\theta_e. In the numerical case, the equivalent of θe\theta_e is the angle θΔ\theta_\Delta and we find that Cox's theory also applies. We introduce the scaling factor or gauge function ϕ\phi so that rm=Δ/ϕr_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 θΔ\theta_\Delta and the viscosity ratio qq. In the case of small θe\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 θe\theta_e and arbitrary qq and express the critical capillary number as a function of θe\theta_e and rmr_m. An analogy can be drawn between rmr_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

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    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

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    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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