Diluted manganese on the bond-centered site in germanium

The functional properties of Mn-doped Ge depend to large extent on the lattice location of the Mn impurities. Here, we present a lattice location study of implanted diluted Mn by means of electron emission channeling. Surprisingly, in addition to the expected substitutional lattice position, a large fraction of the Mn impurities occupies the bond-centered site. Corroborated by ab initio calculations, the bond-centered Mn is related to Mn-vacancy complexes. These unexpected results call for a reassessment of the theoretical studies on the electrical and magnetic behavior of Mn-doped Ge, hereby including the possible role of Mn-vacancy complexes

Phase Separation Driven by External Fluctuations

The influence of external fluctuations in phase separation processes is analysed. These fluctuations arise from random variations of an external control parameter. A linear stability analysis of the homogeneous state shows that phase separation dynamics can be induced by external noise. The spatial structure of the noise is found to have a relevant role in this phenomenon. Numerical simulations confirm these results. A comparison with order-disorder noise induced phase transitions is also made.Comment: 4 pages, 4 Postscript figures included in text. LaTeX (with Revtex macros

Lifshitz-Slyozov Scaling For Late-Stage Coarsening With An Order-Parameter-Dependent Mobility

The coarsening dynamics of the Cahn-Hilliard equation with order-parameter dependent mobility, $\lambda(\phi) \propto (1-\phi^2)^\alpha$, is addressed at zero temperature in the Lifshitz-Slyozov limit where the minority phase occupies a vanishingly small volume fraction. Despite the absence of bulk diffusion for $\alpha>0$, the mean domain size is found to grow as $\propto t^{1/(3+\alpha)}$, due to subdiffusive transport of the order parameter through the majority phase. The domain-size distribution is determined explicitly for the physically relevant case $\alpha = 1$.Comment: 4 pages, Revtex, no figure

An efficient GPU implementation for a faster simulation of unsteady bed-load transport

Computational tools may help engineers in the assessment of sediment transport during the decision-making processes. The main requirements are that the numerical results have to be accurate and simulation models must be fast. The present work is based on the 2D shallow water equations in combination with the 2D Exner equation. The resulting numerical model accuracy was already discussed in previous work. Regarding the speed of the computation, the Exner equation slows down the already costly 2D shallow water model as the number of variables to solve is increased and the numerical stability is more restrictive. In order to reduce the computational effort required for simulating realistic scenarios, the authors have exploited the use of Graphics Processing Units in combination with non-trivial optimization procedures. The gain in computing cost obtained with the graphic hardware is compared against single-core (sequential) and multi-core (parallel) CPU implementations in two unsteady cases

Phase separation dynamics in a concetration gradient

Phase separation dynamics with an initially nonuniform concentration are studied. Critical and off-critical behavior is observed simultaneously. A mechanism for an expanding phase-separated region is demonstrated and the time dependence of the concentration is determined. The final equilibrium state consists of a planar interface separating one phase from the other. The evolution to this state is characterized by an experimentally observable flux, j, crossing this interface. We find that j ~ t−2/3 if patterns are formed in the bulk and j ~ t−1/2 if the bulk remains homogeneous. The results are explained in terms of scaling arguments which are confirmed numerically.Peer ReviewedPreprin

The ATLAS Tracker Upgrade: Short Strips Detectors for the sLHC

It is foreseen to increase the luminosity of the Large Hadron Collider (LHC) at CERN around 2018 by about an order of magnitude, with the upgraded machine dubbed Super-LHC or sLHC. The ATLAS experiment will require a new tracker for SLHC operation. In order to cope with the order of magnitude increase in pile-up backgrounds at the higher luminosity, an all silicon detector is being designed. The new strip detector will use significantly shorter strips than the current SCT in order to minimise the occupancy. As the increased luminosity will mean a corresponding increase in radiation dose, a new generation of extremely radiation hard silicon detectors is required. A massive R&D programme is underway to develop silicon sensors with sufficient radiation hardness. New front-end electronics and readout systems are being designed to cope with the higher data rates. The challenges of powering and cooling a very large strip detector will be discussed. Ideas on possible schemes for the layout and support mechanics will be shown. A key issue for the upgrade is the development of silicon sensors with sufficient radiation hardness for the pixel and strip layers. We have developed planar detectors to be made on p-type wafers in a number of different designs. These prototype detectors were then produced by a leading manufacturer and irradiated to a set of fluences matched to sLHC expections. The irradiated sensors were subsequently tested wit h LHC-readout-electronics in order to study the radiation-induced degradation, and determine their performance after serious hadron irradiation of up to 1015 Neutron-equivalent. The signal suffers degradation as a function of irradiation. It is however evident that sufficient charge can still be recorded even at the highest fluence. We will give an overview of the ATLAS tracker upgrade, in particular focusing on innermost silicon strip layers. Results from a wide range of irradiated silicon detectors will be presented. We will draw conclusions on what type and design of strip detectors to employ for the upgrades of the tracking layers in the sLHC upgrades of LHC experiments

From subdiffusion to superdiffusion of particles on solid surfaces

We present a numerical and partially analytical study of classical particles obeying a Langevin equation that describes diffusion on a surface modeled by a two dimensional potential. The potential may be either periodic or random. Depending on the potential and the damping, we observe superdiffusion, large-step diffusion, diffusion, and subdiffusion. Superdiffusive behavior is associated with low damping and is in most cases transient, albeit often long. Subdiffusive behavior is associated with highly damped particles in random potentials. In some cases subdiffusive behavior persists over our entire simulation and may be characterized as metastable. In any case, we stress that this rich variety of behaviors emerges naturally from an ordinary Langevin equation for a system described by ordinary canonical Maxwell-Boltzmann statistics

Significance of respiratory diseases in the health management of sheep

Objectives of the present article are to review the financial significance of respiratory diseases and to indicate their relevance within the health management of sheep. In lambs, the principal adverse effects of the diseases are related to mortality, reduced carcass quality, veterinary expenses, decrease of average daily bodyweight gain and poor quality of lambs produced. In adult animals, financial losses are related to reduced production of affected sheep, need for early culling and death. Given the multi-faceted nature of these diseases, management practices (e.g., housing improvements, implementation of biosecurity provisions) need to be considered for their prevention; as environmental conditions also play a role in development of these diseases, they should be taken into account. Appropriate health measures (e.g., vaccinations) that improve animal immune response also will help control of the diseases