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

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

Structural and Financial Characteristics of U.S. Farms: 2001 Family Farm Report

Family farms vary widely in size and other characteristics, ranging from very small retirement and residential farms to establishments with sales in the millions of dollars. The farm typology developed by the Economic Research Service (ERS) categorizes farms into groups based primarily on occupation of the operator and sales class of the farm. The typology groups reflect operators' expectations from farming, position in the life cycle, and dependence on agriculture. The groups differ in their importance to the farm sector, product specialization, program participation, and dependence on farm income. These (and other) differences are discussed in this report.Agricultural Resource Management Study (ARMS), family farms, farm businesses, farm financial situation, farm operator household income, farm operators, farm structure, farm typology, female farm operators, government payments, spouses of farm operators, taxes, Agricultural Finance, Farm Management,

The complement system in renal homograft recipients

The whole serum complement and its components were studied in 24 recipients of 27 renal homografts. In 12 of 13 instances in which homograft rejection was diagnosed, it was accompanied by significant declines in CH50, IA50, C4, and C3 levels, and to a lesser degree in C1 and C2 levels. Fourteen patients had normal graft function during the postoperative course of study, and in 13 of the 14 the complement levels were within the normal range throughout. In two recipients with systemic lupus erythematosus, very low initial complement levels increased to normal levels following removal of the native kidneys, splenectomy, and the provision of a well-functioning homograft. Anticomplement activity and elevated titers of C1 and C3 inactivators were observed in some patients, but these did not correlate with the changes in CH50. The findings confirm that the complement system participates in renal homograft rejection. © 1972

Radiation-Induced Magnetoresistance Oscillations in a 2D Electron Gas

Recent measurements of a 2D electron gas subjected to microwave radiation reveal a magnetoresistance with an oscillatory dependence on the ratio of radiation frequency to cyclotron frequency. We perform a diagrammatic calculation and find radiation-induced resistivity oscillations with the correct period and phase. Results are explained via a simple picture of current induced by photo-excited disorder-scattered electrons. The oscillations increase with radiation intensity, easily exceeding the dark resistivity and resulting in negative-resistivity minima. At high intensity, we identify additional features, likely due to multi-photon processes, which have yet to be observed experimentally.Comment: 5 pages, 3 figures; final version as published in Phys Rev Let

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

Bound Magnetic Polaron Interactions in Insulating Doped Diluted Magnetic Semiconductors

The magnetic behavior of insulating doped diluted magnetic semiconductors (DMS) is characterized by the interaction of large collective spins known as bound magnetic polarons. Experimental measurements of the susceptibility of these materials have suggested that the polaron-polaron interaction is ferromagnetic, in contrast to the antiferromagnetic carrier-carrier interactions that are characteristic of nonmagnetic semiconductors. To explain this behavior, a model has been developed in which polarons interact via both the standard direct carrier-carrier exchange interaction (due to virtual carrier hopping) and an indirect carrier-ion-carrier exchange interaction (due to the interactions of polarons with magnetic ions in an interstitial region). Using a variational procedure, the optimal values of the model parameters were determined as a function of temperature. At temperatures of interest, the parameters describing polaron-polaron interactions were found to be nearly temperature-independent. For reasonable values of these constant parameters, we find that indirect ferromagnetic interactions can dominate the direct antiferromagnetic interactions and cause the polarons to align. This result supports the experimental evidence for ferromagnetism in insulating doped DMS.Comment: 11 pages, 7 figure

Effects of an in-plane magnetic field on c-axis sum rule and superfluid density in high-TcT_{c} cuprates

In layered cuprates, the application of an in-plane magnetic field $({\bf H})$ changes the c-axis optical sum rule and superfluid density $\rho_{s}$. For pure incoherent c-axis coupling, ${\bf H}$ has no effect on either quantities but it does if an additional coherent component is present. For the coherent contribution, different characteristic variations on ${\bf H}$ and on temperature result from the constant part $(t_{\perp})$ of the hopping matrix element and from the part $(t_{\phi})$ which has zero on the diagonal of the Brillouin zone. Only the constant part $(t_{\perp})$ leads to a dependence on the direction of ${\bf H}$ as well as on its magnitude.Comment: 3 figure

Interacting random Dirac fermions in superconducting cuprates

We study the effects of quasiparticle interactions on disorder-induced localization of Dirac-like nodal excitations in superconducting high-$T_c$ cuprates. As suggested by the experimental ARPES and terahertz conductivity data in $Bi_2Sr_2CaCu_2O_{8+\delta}$, we focus on the interactions mediated by the order parameter fluctuations near an incipient second pairing transition $d\to d+is$. We find interaction corrections to the density of states, specific heat, and conductivity as well as phase and energy relaxation rates and assess the applicability of the recent localization scenarios for non-interacting random Dirac fermions to the cuprates

Fractional electric charge of a magnetic vortex at nonzero temperature

An ideal gas of twodimensional Dirac fermions in the background of a pointlike magnetic vortex with arbitrary flux is considered. We find that this system acquires fractional electric charge at finite temperatures and determine the functional dependence of the thermal average and quadratic fluctuation of the charge on the temperature, the vortex flux, and the continuous parameter of the boundary condition at the location of the vortex.Comment: 25 pages, 5 figures, journal version, minor changes, Eqs.(3.2)-(3.5) correcte