The United Nations Basic Space Science Initiative: The TRIPOD concept

Since 1990, the United Nations is annually holding a workshop on basic space science for the benefit of the worldwide development of astronomy. Additional to the scientific benefits of the workshops and the strengthening of international cooperation, the workshops lead to the establishment of astronomical telescope facilities through the Official Development Assistance (ODA) of Japan. Teaching material, hands-on astrophysics material, and variable star observing programmes had been developed for the operation of such astronomical telescope facilities in an university environment. This approach to astronomical telescope facility, observing programme, and teaching astronomy has become known as the basic space science TRIPOD concept. Currently, a similar TRIPOD concept is being developed for the International Heliophysical Year 2007, consisting of an instrument array, data taking and analysis, and teaching space science.Comment: 8 pages, LaTe

Swift J2058.4+0516: Discovery of a Possible Second Relativistic Tidal Disruption Flare?

We report the discovery by the Swift hard X-ray monitor of the transient source Swift J2058.4+0516 (Sw J2058+05). Our multi-wavelength follow-up campaign uncovered a long-lived (duration >~ months), luminous X-ray (L_X,iso ~ 3 x 10^47 erg s^-1) and radio (nu L_nu,iso ~ 10^42 erg s^-1) counterpart. The associated optical emission, however, from which we measure a redshift of 1.1853, is relatively faint, and this is not due to a large amount of dust extinction in the host galaxy. Based on numerous similarities with the recently discovered GRB 110328A / Swift J164449.3+573451 (Sw J1644+57), we suggest that Sw J2058+05 may be the second member of a new class of relativistic outbursts resulting from the tidal disruption of a star by a supermassive black hole. If so, the relative rarity of these sources (compared with the expected rate of tidal disruptions) implies that either these outflows are extremely narrowly collimated (theta < 1 degree), or only a small fraction of tidal disruptions generate relativistic ejecta. Analogous to the case of long-duration gamma-ray bursts and core-collapse supernovae, we speculate that rapid spin of the black hole may be a necessary condition to generate the relativistic component. Alternatively, if powered by gas accretion (i.e., an active galactic nucleus [AGN]), Sw J2058+05 would seem to represent a new mode of variability in these sources, as the observed properties appear largely inconsistent with known classes of AGNs capable of generating relativistic jets (blazars, narrow-line Seyfert 1 galaxies).Comment: Minor typos correcte

A genetic variation map for chicken with 2.8 million single-nucleotide polymorphisms

We describe a genetic variation map for the chicken genome containing 2.8 million single-nucleotide polymorphisms ( SNPs). This map is based on a comparison of the sequences of three domestic chicken breeds ( a broiler, a layer and a Chinese silkie) with that of their wild ancestor, red jungle fowl. Subsequent experiments indicate that at least 90% of the variant sites are true SNPs, and at least 70% are common SNPs that segregate in many domestic breeds. Mean nucleotide diversity is about five SNPs per kilobase for almost every possible comparison between red jungle fowl and domestic lines, between two different domestic lines, and within domestic lines - in contrast to the notion that domestic animals are highly inbred relative to their wild ancestors. In fact, most of the SNPs originated before domestication, and there is little evidence of selective sweeps for adaptive alleles on length scales greater than 100 kilobases

Rationality of rigid quiver Grassmannians

We show that any quiver Grassmannian associated with a rigid representation of a quiver is a rational variety using torus localization techniques

Optimierung des Wachstums und der Charakterisierung mittels Molekularstrahlepitaxie hergestellter lokal tropfengeätzter GaAs-Quantenpunkte

In der Dissertation werden neue Techniken für das Wachstum und die Charakterisierung von lokal tropfengeätzten (LDE) GaAs Quantenpunkten (QDs) entwickelt und untersucht. Zunächst wurden die Auswirkungen von dielektrischen Schichten auf das Photolumineszenzspektrum (PL) von LDE-QDs untersucht und gezeigt, wie diese mittels Cleaved-Edge Messungen verringert werden können. Danach wurde eine anomale Intensitätssteigerung bei temperaturabhängiger PL-Spektroskopie festgestellt und für die spektrale Zuordnung von bimodalen QD-Moden genutzt. Mittels Gradientendeposition des Ätzmaterials konnte eine scharfe Übergangsfront der QDs geschaffen werden, mit deren Position sich die kritische Ätzmaterialmenge exakt bestimmen lässt. Mittels Gradientendeposition des Füllmaterials wurde eine starke Modulation der Emissionswellenlänge auf einem Wafer erreicht (795 nm bis 731 nm). Abschließend konnten mittels Anpassung der Rotationsperiode an die Depositionszeit global sehr homogene QDs hergestellt werden

Hydrogen diffusion in clinopyroxene at low temperatures (195°C–400°C) and consequences for subsurface processes

Studying diffusion of hydrogen in nominally anhydrous minerals, like clinopyroxene, at low temperatures is a challenging task due to experimental and analytical difficulties. In this study, to overcome these problems we have produced H concentration gradients in single crystals of natural diopsidic clinopyroxene by ion implantation and measured the nanoscale profiles before and after diffusion anneals using Nuclear Resonance Reaction Analysis. These steps allowed us to conduct experiments at temperatures between 195°C and 400°C. Obtained diffusion rates show a consistent Arrhenius relation $D_{H}$= 5.47($\pm$13.98) · $10^{−8}$ · exp (−115.64($\pm$11.5) kJ $mol^{−1}$/RT) $m^{2}s^{−1}$. Notably, our results lie well within the range of extrapolations from high temperature experiments ($\geq$600°C) of previous studies. This implies that fast diffusion of hydrogen (compared to other elements) extends to low temperatures. We used these results in a non-isothermal diffusion model that simulates the ascent of crystals (0.5, 1.0, and 2.0 mm) along two representative $\textit {P-T}$-paths from 600°C to 100°C, to assess potential re-equilibration of H contents in clinopyroxene at low temperatures. Our model highlights the need to carefully consider boundary conditions, which are a function of $\textit {P-T-f}$$O_{2}$, that control the concentration gradient at the crystal's rim. The results from this model help to assess, as a function of crystal size and cooling rate, when re-equilibration must be considered

A yeast artificial chromosome (YAC) library containing 10 haploid chicken genome equivalents

We report the construction of a YAC library that provides 10-fold redundant coverage of the chicken genome. The library was made by transforming S. cerevisiae AB 1380 with YAC constructs consisting of partially digested and size fractionated (>465 kb) EcoRI genomic fragments ligated to pCGS966 YAC vector arms. The primary library provides 8.5-fold redundant coverage and consists of 16,000 clones arrayed in duplicate 96-well microtiter plates and gridded on nylon membranes at high density (18,000 clones/484cm2). The average insert size, 634 kb, was derived from size fractionation of a random sample of 218 YACs. Hybridization of five unlinked chicken genes to colony blots revealed six or more positive clones. This is consistent with the theoretical expectation from average insert sizes and number of clones. A second collection of clones consists of a further 20,000 colonies, of which 20% contain inserts larger than 450 kb and 80% contain only coligated vector arms. We estimate that these clones provide a further 1.5-fold redundant coverage of the chicken genome; thus, the total collection of 36,000 clones provides 10-fold redundant coverage of the chicken genome. The library is intended as a resource for fine-scale analysis of the organization of the chicken genome and is presently being used to construct a contig map of chicken Chromosome (Chr) 16, which contains the MHC and nucleolar organizer