An H-Theorem for the Lattice Boltzmann Approach to Hydrodynamics

The lattice Boltzmann equation can be viewed as a discretization of the continuous Boltzmann equation. Because of this connection it has long been speculated that lattice Boltzmann algorithms might obey an H-theorem. In this letter we prove that usual nine-velocity models do not obey an H-theorem but models that do obey an H-theorem can be constructed. We consider the general conditions a lattice Boltzmann scheme must satisfy in order to obey an H-theorem and show why on a lattice, unlike the continuous case, dynamics that decrease an H-functional do not necessarily lead to a unique ground state.Comment: 6 pages, latex, no figures, accepted for publication in Europhys. Let

Weak localization in ferromagnetic (Ga,Mn)As nanostructures

We report on the observation of weak localization in arrays of (Ga,Mn)As nanowires at millikelvin temperatures. The corresponding phase coherence length is typically between 100 nm and 200 nm at 20 mK. Strong spin-orbit interaction in the material is manifested by a weak anti-localization correction around zero magnetic field.Comment: 5 pages, 3 figure

Apprentice pay in Britain, Germany and Switzerland: Institutions, market forces and market power

This is the accepted version of the original publication in the European Journal of Industrial Relations, which is available online at http://ejd.sagepub.com/content/19/3/201.The pay of metalworking apprentices is high in Britain, middling in Germany and low in Switzerland. We analyse these differences using fieldwork evidence and survey data, drawing on both economic and institutionalist theories. Several institutional attributes influence apprentice pay, partly by affecting supply and demand in markets for training places. Institutional support for apprenticeship training appears to involve important complementarities in both Germany and Switzerland, in contrast to Britain’s less coherent and more market-driven approach.We thank the Hans-Böckler-Stiftung, Anglo-German Foundation, SKOPE (Oxford), the Swiss federal government (OPET/SERI) and WZB (Berlin) for financial support

Charge transfer and coherence dynamics of tunnelling system coupled to a harmonic oscillator

We study the transition probability and coherence of a two-site system, interacting with an oscillator. Both properties depend on the initial preparation. The oscillator is prepared in a thermal state and, even though it cannot be considered as an extended bath, it produces decoherence because of the large number of states involved in the dynamics. In the case in which the oscillator is intially displaced a coherent dynamics of change entangled with oscillator modes takes place. Coherency is however degraded as far as the oscillator mass increases producing a increasingly large recoherence time. Calculations are carried on by exact diagonalization and compared with two semiclassical approximations. The role of the quantum effects are highlighted in the long-time dynamics, where semiclassical approaches give rise to a dissipative behaviour. Moreover, we find that the oscillator dynamics has to be taken into account, even in a semiclassical approximation, in order to reproduce a thermally activated enhancement of the transition probability

Phase coherent transport in (Ga,Mn)As

Quantum interference effects and resulting quantum corrections of the conductivity have been intensively studied in disordered conductors over the last decades. The knowledge of phase coherence lengths and underlying dephasing mechanisms are crucial to understand quantum corrections to the resistivity in the different material systems. Due to the internal magnetic field and the associated breaking of time-reversal symmetry quantum interference effects in ferromagnetic materials have been scarcely explored. Below we describe the investigation of phase coherent transport phenomena in the newly discovered ferromagnetic semiconductor (Ga,Mn)As. We explore universal conductance fluctuations in mesoscopic (Ga,Mn)As wires and rings, the Aharonov-Bohm effect in nanoscale rings and weak localization in arrays of wires, made of the ferromagnetic semiconductor material. The experiments allow to probe the phase coherence length L_phi and the spin flip length L_SO as well as the temperature dependence of dephasing.Comment: 22 pages, 10 figure

Design of 12.5 kA current leads for the Large Hadron Collider using high temperature superconductor material

The Large Hadron Collider will be equipped with about 8000 superconducting magnets. Some 2600 current leads will feed the currents ranging from 25 to 12500 A. CERN aims to reduce the consumption of liquid helium, using high temperature superconductors in these leads. A development of leads for 12.5 kA is being conducted in collaboration with Oxford Instruments. The design options for these leads are described. A test rig and prototype lead have been made according to one of the options. Electrical contact tests are in progress on BSCCO-2212 and YBCO-123 samples. In the first run, the prototype carried 13000 A