1,354 research outputs found
Wiedemann-Franz violation in the vortex state of a d-wave superconductor
We show that the Wiedemann-Franz law is violated in the vortex state of a
d-wave superconductor at zero temperature. We use a semiclassical approach,
which includes the Doppler shift on the quasiparticles as well as the Andreev
scattering from a random distribution of vortices. We also show that the vertex
corrections to the electrical conductivity due to the anisotropy of impurity
scattering become unimportant in the presence of a sufficiently large magnetic
field.Comment: To be published in Physica C as a proceeding of M2S-HTSC Rio 200
Force calculation on walls and embedded particles in multiparticle collision dynamics simulations
Colloidal solutions posses a wide range of time and length scales, so that it
is unfeasible to keep track of all of them within a single simulation. As a
consequence some form of coarse-graining must be applied. In this work we use
the Multi-Particle Collision Dynamics scheme. We describe a particular
implementation of no-slip boundary conditions upon a solid surface, capable of
providing correct force s on the solid bypassing the calculation of the
velocity profile or the stre ss tensor in the fluid near the surface. As an
application we measure the friction on a spherical particle, when it is placed
in a bulk fluid and when it is confined in a slit. We show that the
implementation of the no-slip boundary conditions leads to an enhanced Ensko g
friction, which can be understood analytically. Because of the long-range
nature of hydrodynamic interactions, the Stokes friction obtained from the
simulations is sensitive of the simulation box size. We address this topic for
the slit geometry, showing that that the dependence on the system size differs
very much from what is expected in a 3D system, where periodic boundary
conditions are used in all directions.Comment: To appear in Physical Review
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Analytical treatments of micro-channel and micro-capillary flows
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Extensive work in the field of micro-channel and micro-capillary flows using the extended Navier-Stokes equations are carried out in this paper by taking the diffusive mass transport into account and provided the basis for analytical treatments of these flows. The results are compared with experimental results for micro-channels and showed good agreement. It is found that a characteristic pressure is useful to explain the comparisons. In addition, the work on micro-channel flows is extended to micro-capillary flows, to provide analytical treatments of this class of flows. The analytical results show similar behavior to that of micro-channel flows. Comparisons between the analytical results and experimental findings are also presented and discussed by introducing the characteristic pressure
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Treatments of flows through micro-channels based on the Extended Navier-Stokes-Equations
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.The paper briefly refers to the present treatments of micro-channel flows that are based on the existing Navier-Stokes-Equations and the employment of wall-slip boundary conditions. The Maxwell slip velocity is employed for this purpose. This theoretical treatment is questioned. It is shown by the authors that the existing Navier-Stokes-Equations are incomplete. They do not contain terms for the self diffusion of mass. Introducing these terms yields the extended Navier-Stokes-Equations that allow micro-channel flows to be treated without the assumption of Maxwellian slip velocities at the wall. A pressure driven slip velocity occurs at the wall and it results as part of the solution for flows in micro-channels by the “Extended Navier-Stokes Equations”. Using these equations, analytical treatments of micro-channel flows are presented. Good agreement with existing experimental results is obtained
Transient magnetoconductivity of photoexcited electrons
Transient magnetotransport of two-dimensional electrons with
partially-inverted distribution excited by an ultrashort optical pulse is
studied theoretically. The time-dependent photoconductivity is calculated for
GaAs-based quantum wells by taking into account the relaxation of electron
distribution caused by non-elastic electron-phonon interaction and the
retardation of the response due to momentum relaxation and due to a finite
capacitance of the sample. We predict large-amplitude transient oscillations of
the current density and Hall field (Hall oscillations) with frequencies
corresponding to magnetoplasmon range, which are initiated by the instability
owing to the absolute negative conductivity effect.Comment: 21 pages, 6 fig
Field-induced thermal metal-to-insulator transition in underdoped LSCO
The transport of heat and charge in cuprates was measured in undoped and
heavily-underdoped single crystal La_{2-x}Sr_xCuO_{4+delta} (LSCO). In
underdoped LSCO, the thermal conductivity is found to decrease with increasing
magnetic field in the T --> 0 limit, in striking contrast to the increase
observed in all superconductors, including cuprates at higher doping. The
suppression of superconductivity with magnetic field shows that a novel thermal
metal-to-insulator transition occurs upon going from the superconducting state
to the field-induced normal state.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding
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