How to make GaMnAs with high ferromagnetic phase transition temperature

We analyse the role of structural defects in GaMnAs and demonstrate how their density can be drastically reduced by in situ post-growth annealing under As capping. Modifications of the magnetic, transport, and structural properties of annealed GaMnAs layers are presented. The main result is that Curie temperatures are strongly increased relative to those of as-grown layers, typically from 70-80 K to 150-160 K. The annealed layers exhibit well-ordered smooth surfaces, suitable for further epitaxial overgrowth

Fast simulation of the leaky bucket algorithm

We use fast simulation methods, based on importance sampling, to efficiently estimate cell loss probability in queueing models of the Leaky Bucket algorithm. One of these models was introduced by Berger (1991), in which the rare event of a cell loss is related to the rare event of an empty finite buffer in an "overloaded" queue. In particular, we propose a heuristic change of measure for importance sampling to efficiently estimate the probability of the rare empty-buffer event in an asymptotically unstable GI/GI/1/k queue. This change of measure is, in a way, "dual" to that proposed by Parekh and Walrand (1989) to estimate the probability of a rare buffer overflow event. We present empirical results to demonstrate the effectiveness of our fast simulation method. Since we have not yet obtained a mathematical proof, we can only conjecture that our heuristic is asymptotically optimal, as k/spl rarr//spl infin/

The response of oilseed rape (Brassica napus ssp oliefera ) accessions with different glucosinolate and erucic acid contents to four isolates of Peronospora parasitica (downy mildew) and the identification of new sources of resistance

A total of 101 Brassica napus ssp. oleifera accessions with seed differing in glucosinolate and erucic acid contents were screened for resistance to four isolates of Peronospora parasitica at the cotyledon stage. Two groups of accessions with different resistance factors were identified. Lines that were homogeneous for resistance were selected from seedling populations of accessions that exhibited a heterogeneous reaction to some isolates. The resistance of one group differs from that of cv. Cresor, the only oilseed rape cultivar reported to have an isolate-specific gene for resistance to P. parasitica. The isolate specificity of the second group was identical to that of cv. Cresor. A comparison of the response of host accessions which expressed moderate to full susceptibility at the cotyledon stage, with no clear differential response to any of the four P. parasitica isolates, indicated that those with high glucosinolate and high erucic acid contents (12 accessions) were slightly but significantly less susceptible than those with high glucosinolate and low erucic acid (19 accessions), or low glucosinolate and low erucic acid contents (28 accessions). The mean differences between accessions with low erucic acid but differing in glucosinolate content were inconsistent. The last result was further confirmed by investigating the expression of resistance to three isolates of P. parasitica at three different seedling growth stages among 11 accessions of oilseed rape with seeds low in erucic acid but differing in glucosinolate content