Modeling Meteoroid Densities for Spacecraft Risk Assessment

This report describes the methodologies and algorithms that NASAs Meteoroid Environment Office (MEO) currently utilizes to measure meteoroid densities. We discuss the needs for an accurate model for the meteoroid density distribution in its Meteoroid Engineering Model (MEM), and its potential implications for spacecraft design. The recently developed process is heavily derived from that of previous work, although subtle differences exist. A thorough comparison of the best-fit densities derived for sixty meteoroids in and with the process described here shows that discrepancies in final densities larger than a factor of two are measured for 20% of our test events. Such a level of discrepancy suggests that any density calculated using similar methods cannot be assumed to represent a unique fit to the data. Additional observational data for meteoroids beyond those utilized in this work will be essential for producing more reliable and repeatable density measurements

Health Effects of Temporary Jobs in Europe

Over the last two decades, temporary employment has gained importance in the European Union. The implications of this development for the health of the workforce are not yet established. Using a unique individual-level data set for 27 European countries, this paper evaluates whether temporary employment is interrelated with self-assessed health. We find pronounced differences in self-assessed health by employment status across European countries. Furthermore, in the EU full-time permanent employed workers report the best health, followed by temporary and part-time employed workers. These differences largely vanish, when taking into account the potential endogeneity between employment status and self-assessed health. However, repeated temporary contracts have a significant negative impact on health.Temporary employment; fixed-term contracts; self-assessed health

Phase transition for loop representations of Quantum spin systems on trees

We consider a model of random loops on Galton-Watson trees with an offspring distribution with high expectation. We give the configurations a weighting of $\theta^{\#\text{loops}}$. For many $\theta>1$ these models are equivalent to certain quantum spin systems for various choices of the system parameters. We find conditions on the offspring distribution that guarantee the occurrence of a phase transition from finite to infinite loops for the Galton-Watson tree.Comment: 16 pages, 1 figur

Silicon isotopes as a tracer for silicate utilization in the Peruvian upwelling

EGU2011-6081 Natural stable isotopes are a powerful tool in marine sciences to investigate biological processes, such as present and past nutrient utilization. In this study we present the first dissolved silicon isotope data in the upwelling area off Peru, where one of the world’s largest Oxygen Minimum Zones (OMZ) is located. Silicon is the most important component required for phytoplankton (diatom) growth, which dominates primary productivity in this region. Stable Si isotopes are fractionated during diatom growth in that the lighter Si isotopes are preferentially incorporated into diatoms with a fractionation factor of -1.1 promille. The Si isotope composition of dissolved silicic acid of the corresponding surface waters is therefore left isotopically heavier. The Si isotope composition, 30Si/28Si, is expressed as δ30Si values, which stand forh deviations from a given standard (NBS28). Investigation of the dissolved seawater Si isotope composition thus provides a measure for the utilization and, combined with information on the Si isotope composition of the water masses upwelling off Peru, it is a measure for the supply pathways of Si to the coastal upwelling centres. Surface waters on the shelf off Peru are mainly fed by the Equatorial Undercurrent, which mainly consists of waters originating from the western and Central Pacific and which has a characteristic δ30Si of +1.5 promille. In areas and during phases of intense upwelling the fractionation of Si isotopes was observed to be weaker due to upwelling-driven supply of less fractionated Si (δ30Si = 1.7 promille, from water depths of around 100-150 m, whereas under weak upwelling conditions fractionation is higher (δ30Si ~3 promille due to a more complete utilization of the available dissolved silicate. The distribution of dissolved δ30Si correlates strongly with particulate biogenic silicate (opal) concentrations in that highest opal concentrations in the surface waters show the lowest δ30Si values thus strongest upwelling intensity. The most extreme δ30Si values in surface waters (δ30Si = 4.5 promille are observed offshore where silicic acid concentrations are nearly zero. Furthermore we compare the δ30Si data with the dissolved nitrogen isotope distribution, which in addition to nitrate utilization is mainly influenced by denitrification and annamox processes in the OMZ. Combined silicon and nitrogen isotope compositions can thus help to disentangle different fractionation processes within the nitrogen cycle

HST-COS Spectroscopy of the Cooling Flow in Abell 1795 - Evidence for Inefficient Star Formation in Condensing Intracluster Gas

We present far-UV spectroscopy from the Cosmic Origins Spectrograph on the Hubble Space Telescope of a cool, star-forming filament in the core of Abell 1795. These data, which span 1025A - 1700A, allow for the simultaneous modeling of the young stellar populations and the intermediate-temperature (10^5.5 K) gas in this filament, which is far removed (~30 kpc) from the direct influence of the central AGN. Using a combination of UV absorption line indices and stellar population synthesis modeling, we find evidence for ongoing star formation, with the youngest stars having ages of 7.5 +/- 2.0 Myr and metallicities of 0.4 +/- 0.2 Zsun. The latter is consistent with the local metallicity of the intracluster medium. We detect the O VI (1038) line, measuring a flux of 4.0 +/- 0.9 x 10^-17 erg s^-1 cm^-2. The O VI (1032) line is redshifted such that it is coincident with a strong Galactic H2 absorption feature, and is not detected. The measured O VI (1038) flux corresponds to a cooling rate of 0.85 +/- 0.2 (stat) +/- 0.15 (sys) Msun/yr at ~10^5.5 K, assuming that the cooling proceeds isochorically, which is consistent with the classical X-ray luminosity-derived cooling rate in the same region. We measure a star formation rate of 0.11 +/- 0.02 Msun/yr from the UV continuum, suggesting that star formation is proceeding at 13 +/- 3% efficiency in this filament. We propose that this inefficient star formation represents a significant contribution to the larger-scale cooling flow problem.Comment: 6 pages, 4 figures. Accepted for publication in ApJ Letter

A Solid State \u3csup\u3e13\u3c/sup\u3eC-NMR Study of Diamonds and Graphites

The 13C-NMR spectra of gem quality and industrial diamonds show two resonances with the more intense resonance at high field. Two resonances are also shown in 13C-NMR spectra of various graphites; however, the low field resonance is of greater intensity than the high field resonance in the graphites. The resonances are very broad and they are assigned to graphite type (sp2) carbon and diamond type (sp3) carbon

Erfassung, Identifizierung, Vermehrung und Wiederansiedlung der Schwarzpappel Populus nigra in Sachsen-Anhalt

Durch den Flußlauf der Elbe und ihre Nebenflüsse sind in Sachsen-Anhalt aktuelle und potentielle Vorkommensgebiete der Schwarzpappel (Populus nigra) vorhanden. Die natürlichen Standorte der Schwarzpappel sind die Übergangszonen von Weichholzund Hartholzaue (ELLENBERG 1996), wie sie an naturnahen Flußufern zu finden sind. Im Gegensatz zu anderen Baumarten erträgt die Schwarzpappel wie auch Baumweidenarten Hochwasserstände von bis zu 90 Tagen und damit mittlere Hochwässer. Auf Grund der Konkurrenz der Baumarten der Hartholzaue und - wenn überhaupt vorhanden - des schmalen Streifens der Weichholzaue, verbleibt der Schwarzpappel nur ein sehr eingeschränkter Lebensraum entlang der Flüsse. Als Pionierbaumart kann die Schwarzpappel jedoch bei entsprechenden Bedingungen auch auf anderen Standorten wachsen, was für Populus-Arten in den nacheiszeitlichen Perioden nachgewiesen wurde (CWYNAR 1988). Die erfolgreiche Anpflanzung der Schwarzpappel als Straßenbaum in den Niederlanden (HEINZE 1998) und an Wasserläufen in England (WIENFIELD 1997) unterstreicht das. Diese Feststellung ist heute für Anstrengungen zur Erhaltung und Wiederansiedlung der Schwarzpappel wegen der nur noch selten vorhandenen Weichholzaue bedeutsam

Der Baumbestand des Bürgerparks in Osnabrück – 2006 und vor 50 Jahren

Der Baumbestand des Bürgerparks wurde in einer aktuellen Kartierung erfasst und mit dem Bestand der Veröffentlichung von Adler (1957) verglichen. Der aktuelle Bestand wurde in einer Karte und einer kommentierten Artenliste dokumentiert.The current tree species of the Bürgerpark in Osnabrück, Lower Saxony, Germany, were listed and compared with the listing by Adler (1957). The present tree distribution was mapped, together with comments