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

A Price-Based Royalty Tax?

transfer pricing; extractive industries; natural resource taxation; royalties; resource rent tax.This paper considers the merits of a price-based royalty, a royalty for which the rate varies with the product price, as a fiscal instrument for taxing extractive industries. In light of the literature on natural resources taxation, the case for a price-based royalty is appealing. A price-based royalty captures some of the desirable attributes of an income or resource rent tax, but in comparison to such taxes, it is easier to administer since revenue is much less sensitive to transfer price manipulation and tax avoidance efforts. In order to explore how a price-based royalty might provide some of the advantages of income- or rent-based taxation, the paper analyses the relationship between product prices and firm profits, using a dataset of the world’s largest extractive firms from the Forbes Global 2000 list during the period 2003-2014. This analysis indicates that, for both oil/gas and mining firms, there is a nearly one-to-one relationship between product prices and firm profitability; prices 1 per cent higher tend to be associated with profits about 0.76 per cent higher for oil/gas firms and about 1.38 per cent higher for mining firms. The paper concludes by recommending that tax policymakers give serious consideration to increasing the use of price-based royalties.DfID, NORAD

Weak-Field Thermal Hall Conductivity in the Mixed State of d-Wave Superconductors

Thermal transport in the mixed state of a d-wave superconductor is considered within the weak-field regime. We express the thermal conductivity, $\kappa_{xx}$, and the thermal Hall conductivity, $\kappa_{xy}$, in terms of the cross section for quasiparticle scattering from a single vortex. Solving for the cross section (neglecting the Berry phase contribution and the anisotropy of the gap nodes), we obtain $\kappa_{xx}(H,T)$ and $\kappa_{xy}(H,T)$ in surprisingly good agreement with the qualitative features of the experimental results for YBa$_{2}$Cu$_{3}$O$_{6.99}$. In particular, we show that the simple, yet previously unexpected, weak-field behavior, $\kappa_{xy}(H,T) \sim T\sqrt{H}$, is that of thermally-excited nodal quasiparticles, scattering primarily from impurities, with a small skew component provided by vortex scattering.Comment: 5 pages, 2 figures; final version as published in Phys Rev Let

Effect of external magnetic field on electron spin dephasing induced by hyperfine interaction in quantum dots

We investigate the influence of an external magnetic field on spin phase relaxation of single electrons in semiconductor quantum dots induced by the hyperfine interaction. The basic decay mechanism is attributed to the dispersion of local effective nuclear fields over the ensemble of quantum dots. The characteristics of electron spin dephasing is analyzed by taking an average over the nuclear spin distribution. We find that the dephasing rate can be estimated as a spin precession frequency caused primarily by the mean value of the local nuclear magnetic field. Furthermore, it is shown that the hyperfine interaction does not fully depolarize electron spin. The loss of initial spin polarization during the dephasing process depends strongly on the external magnetic field, leading to the possibility of effective suppression of this mechanism.Comment: 10 pages, 2 figure

Microwave conductivity of a d-wave superconductor disordered by extended impurities: a real-space renormalization group approach

Using a real-space renormalization group (RSRG) technique, we compute the microwave conductivity of a d-wave superconductor disordered by extended impurities. To do this, we invoke a semiclassical approximation which naturally accesses the Andreev bound states localized near each impurity. Tunneling corrections (which are captured using the RSRG) lead to a delocalization of these quasiparticles and an associated contribution to the microwave conductivity.Comment: 8 pages, 4 figures. 2 figures added to previous versio

Observation of Apparently Zero-Conductance States in Corbino Samples

Using Corbino samples we have observed oscillatory conductance in a high-mobility two-dimensional electron system subjected to crossed microwave and magnetic fields. On the strongest of the oscillation minima the conductance is found to be vanishingly small, possibly indicating an insulating state associated with these minima.Comment: 4 pages, 3 figures, RevTex