New Young Stars and Brown Dwarfs in the Upper Scorpius Association

To improve the census of the Upper Sco association (~11 Myr, ~145 pc), we have identified candidate members using parallaxes, proper motions, and color-magnitude diagrams from several wide-field imaging surveys and have obtained optical and infrared spectra of several hundred candidates to measure their spectral types and assess their membership. We also have performed spectroscopy on a smaller sample of previously known or suspected members to refine their spectral types and evidence of membership. We have classified 530 targets as members of Upper Sco, 377 of which lack previous spectroscopy. Our new compilation of all known members of the association contains 1631 objects. Although the census of Upper Sco has expanded significantly over the last decade, there remain hundreds of candidates that lack spectroscopy. The precise parallaxes and proper motions from the second data release of Gaia should extend down to substellar masses in Upper Sco, which will greatly facilitate the identification of the undiscovered members.Comment: Astronomical Journal, in press; machine readable tables and fits spectra available at http://personal.psu.edu/kll207/usco.ta

Eg versus x relation from photoluminescence and electron microprobe investigations in p-type Hg1−xCdxTe (0.35 =< x =< 0.7)

Combined photoluminescence (at 10 T 300 K) and electron microprobe investigations have been carried out with HgCdTe samples grown from the melt or from solution. By exciting the samples through metallic masks with 200 μm diameter holes fixed with respect to the sample care was taken to pick-up both characteristic X-ray radiation as well as the photoluminescence from the same sample area. The Eg versus x relation determined in this way at T = 30 K has been compared with data from the interband absorption edge by other authors

Stationary Regime of Random Resistor Networks Under Biased Percolation

The state of a 2-D random resistor network, resulting from the simultaneous evolutions of two competing biased percolations, is studied in a wide range of bias values. Monte Carlo simulations show that when the external current $I$ is below the threshold value for electrical breakdown, the network reaches a steady state with a nonlinear current-voltage characteristic. The properties of this nonlinear regime are investigated as a function of different model parameters. A scaling relation is found between $/_0$ and $I/I_0$, where $$ is the average resistance, $_0$ the linear regime resistance and $I_0$ the threshold value for the onset of nonlinearity. The scaling exponent is found to be independent of the model parameters. A similar scaling behavior is also found for the relative variance of resistance fluctuations. These results compare well with resistance measurements in composite materials performed in the Joule regime up to breakdown.Comment: 9 pages, revtex, proceedings of the Merida Satellite Conference STATPHYS2

Ultrafast spatio-temporal dynamics of terahertz generation by ionizing two-color femtosecond pulses in gases

We present a combined theoretical and experimental study of spatio-temporal propagation effects in terahertz (THz) generation in gases using two-color ionizing laser pulses. The observed strong broadening of the THz spectra with increasing gas pressure reveals the prominent role of spatio-temporal reshaping and of a plasma-induced blue-shift of the pump pulses in the generation process. Results obtained from (3+1)-dimensional simulations are in good agreement with experimental findings and clarify the mechanisms responsible for THz emission

The land evaluation tool within the Tanzania Food and Land Productivity Information System - A new and simple Web-GIS application for public use

Within the framework of the transdisciplinary Trans-SEC project, financed by BMBF, it appeared necessary to develop a web-based GIS environment. This serves on the one hand the collection of available spatial data on the whole of Tanzania, but project internal data, too. Apart from natural resource data collections and a map viewer, two tools have been implemented. The first one is the Tanzania Food Security Monitor. It automatically calculates in a ten-days cycle based o the Water Requirement Sastisfaction Index the potential maize production in order to pre-inform on potential food shortages. The second tool is dedicated to land evaluation. The basic idea was to provide an easy to handle but flexible tool that allows mainly project developers to ex-ante evaluate the potential of agricultural innovations within their region of interest. The tool is based on FAO principles and provides background data layers that have been provided with respect to soil by ISRIC http://www.isric.org/content/african-soilgrids-250m-geotiffs) and with respect to climate by the Potsdam Institute for Climate Impact Research. In a guided way the user is led through five steps to produce and download the evaluation results. After choosing the area of interest, own data layers can be uploaded as geo-tiffs. The crucial step is selection of input layers and the parameterization of these. With respect to the evaluation algorithm a mixture of Storie Index and Averages was chosen, the ratio of which can be adapted. Finally the evaluation results can be downloaded as classified or non classified geo-tiffs for further processing in a desktop GIS. Since the procedure is globally applicable, it is intended to transfer the tool to other regions of the world

A direct D-bar reconstruction algorithm for recovering a complex conductivity in 2-D

A direct reconstruction algorithm for complex conductivities in $W^{2,\infty}(\Omega)$, where $\Omega$ is a bounded, simply connected Lipschitz domain in $\mathbb{R}^2$, is presented. The framework is based on the uniqueness proof by Francini [Inverse Problems 20 2000], but equations relating the Dirichlet-to-Neumann to the scattering transform and the exponentially growing solutions are not present in that work, and are derived here. The algorithm constitutes the first D-bar method for the reconstruction of conductivities and permittivities in two dimensions. Reconstructions of numerically simulated chest phantoms with discontinuities at the organ boundaries are included.Comment: This is an author-created, un-copyedited version of an article accepted for publication in [insert name of journal]. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at 10.1088/0266-5611/28/9/09500

Percolation with long-range correlated disorder

Long-range power-law correlated percolation is investigated using Monte Carlo simulations. We obtain several static and dynamic critical exponents as function of the Hurst exponent $H$ which characterizes the degree of spatial correlation among the occupation of sites. In particular, we study the fractal dimension of the largest cluster and the scaling behavior of the second moment of the cluster size distribution, as well as the complete and accessible perimeters of the largest cluster. Concerning the inner structure and transport properties of the largest cluster, we analyze its shortest path, backbone, red sites, and conductivity. Finally, bridge site growth is also considered. We propose expressions for the functional dependence of the critical exponents on $H$

Analysis of Stress Distribution in Torsional Shear Testing

The research described herein is concerned with the establishment of a specimen geometry that will lead to a more uniform stress distribution in cyclic torsional shear testing. This goal is realized by means of a parametric study using the method of finite elements and a homogeneous, isotropic, linear-elastic soil characterization. The results of these analyses provide a good qualitative measure of the relative effects of the several parameters under consideration. On the basis of the parametric study, design charts are developed which enable an appropriate specimen geometry to be selected for any specified degree of stress uniformity

Roughness of fracture surfaces

We study the fracture surface of three dimensional samples through a model for quasi-static fractures known as Born Model. We find for the roughness exponent a value of 0.5 expected for ``small length scales'' in microfracturing experiments. Our simulations confirm that at small length scales the fracture can be considered as quasi-static. The isotropy of the roughness exponent on the crack surface is also shown. Finally, considering the crack front, we compute the roughness exponents for longitudinal and transverse fluctuations of the crack line (both 0.5). They result in agreement with experimental data, and supports the possible application of the model of line depinning in the case of long-range interactions.Comment: 10 pages, 5 figures, Late