The origin of the red luminescence in Mg-doped GaN

Optically-detected magnetic resonance (ODMR) and positron annihilation spectroscopy (PAS) experiments have been employed to study magnesium-doped GaN layers grown by metal-organic vapor phase epitaxy. As the Mg doping level is changed, the combined experiments reveal a strong correlation between the vacancy concentrations and the intensity of the red photoluminescence band at 1.8 eV. The analysis provides strong evidence that the emission is due to recombination in which electrons both from effective mass donors and from deeper donors recombine with deep centers, the deep centers being vacancy-related defects.Comment: 4 pages, 3 figure

Research Notes: University of Wisconsin

Tissue culture methods may benefit soybean breeders if whole plants can be differentiated from aneuploid, mutated, fused, or haploid cells. However, in order to realize this potential, it must be possible to derive plantlets from previously undifferentiated tissues - and ultimately from masses of callus cells. This report summarizes the information we obtained concerning adventitious budding from soybean tissues (Kimball and Bingham, 1973), early stages of embryo formation within masses of callus cells, and actual differentiation of plantlets from callus tissue

Convergence of the all-time supremum of a L\'evy process in the heavy-traffic regime

In this paper we derive a technique of obtaining limit theorems for suprema of L\'evy processes from their random walk counterparts. For each $a>0$, let $\{Y^{(a)}_n:n\ge 1\}$ be a sequence of independent and identically distributed random variables and $\{X^{(a)}_t:t\ge 0\}$ be a L\'evy processes such that $X_1^{(a)}\stackrel{d}{=} Y_1^{(a)}$, $\mathbb E X_1^{(a)}<0$ and $\mathbb E X_1^{(a)}\uparrow0$ as $a\downarrow0$. Let $S^{(a)}_n=\sum_{k=1}^n Y^{(a)}_k$. Then, under some mild assumptions, $\Delta(a)\max_{n\ge 0} S_n^{(a)}\stackrel{d}{\to} R\iff\Delta(a)\sup_{t\ge 0} X^{(a)}_t\stackrel{d}{\to} R$, for some random variable $R$ and some function $\Delta(\cdot)$. We utilize this result to present a number of limit theorems for suprema of L\'evy processes in the heavy-traffic regime

Packing and Hausdorff measures of stable trees

In this paper we discuss Hausdorff and packing measures of random continuous trees called stable trees. Stable trees form a specific class of L\'evy trees (introduced by Le Gall and Le Jan in 1998) that contains Aldous's continuum random tree (1991) which corresponds to the Brownian case. We provide results for the whole stable trees and for their level sets that are the sets of points situated at a given distance from the root. We first show that there is no exact packing measure for levels sets. We also prove that non-Brownian stable trees and their level sets have no exact Hausdorff measure with regularly varying gauge function, which continues previous results from a joint work with J-F Le Gall (2006).Comment: 40 page

From Navas to Kaltoft: The European Court of Justice’s evolving definition of disability and the implications for HIV-positive individuals

This article will examine the definition of disability developed by the European Court of Justice for the purposes of the Employment Equality Directive and examine whether it is sufficient for the purpose of bringing People Living with HIV/AIDS within its scope. The article will argue that in order to adequately protect People Living with HIV/AIDS within the EU from discrimination, the European Court of Justice needs to ensure that a coherent EU wide definition of disability, based fully upon the social model of disability, is adopted. This is necessary in order to ensure adequate protection not only for People Living with HIV/AIDS but for all individuals with disabilities from discrimination throughout the EU. In addition to this central argument, this paper will argue that the lack of a coherent definition of disability grounded in the social model fragments protection for People Living with HIV/AIDS across the EU leading to a number of possible unintended consequences

Global clustering coefficient in scale-free networks

In this paper, we analyze the behavior of the global clustering coefficient in scale free graphs. We are especially interested in the case of degree distribution with an infinite variance, since such degree distribution is usually observed in real-world networks of diverse nature. There are two common definitions of the clustering coefficient of a graph: global clustering and average local clustering. It is widely believed that in real networks both clustering coefficients tend to some positive constant as the networks grow. There are several models for which the average local clustering coefficient tends to a positive constant. On the other hand, there are no models of scale-free networks with an infinite variance of degree distribution and with a constant global clustering. In this paper we prove that if the degree distribution obeys the power law with an infinite variance, then the global clustering coefficient tends to zero with high probability as the size of a graph grows

How well do we forecast the aurora?

Michaela K Mooney and co-authors evaluate a space weather forecast model in the same way that weather forecasts are assessed, work that won the 2019 Rishbeth Prize for best poster