The causes for geographical variations in OS187/OS186 at the Cretaceous-Tertiary boundary

Researchers at Yale has approached the problem of the osmium isotopic composition of marine deposits formed in contact with both oxidized and reduced bottom waters. The measured (187) Os/(186) Os ratios of modern bulk sediment can be explained using mixing equations involving continental detrital, volcaniclastic, cosmogenic and hydrogeneous components. These studies show that sediments deposited under reducing marine conditions contain a hydrogenous component which is enriched in Re and has a radiogenic (187) Os/(186) Os ratio. The presence of such a hydrogenous component in the marine fish clay at Stevns Klint can account for the elevation of its (187) Os/(186) Os ration above the expected meteoritic value. Mass balance considerations require the Re/Os ratio of the phase precipitated from the terminal Cretaceous sea at Stevns Klint to have been about one tenth the value observed in contemporary deposits in the Black Sea, assuming Re has not been lost (or Os gained) subsequent to precipitation. In continental sections, the elevation of the (187) Os/(186) Os ratio in boundary layers may be due to precipitation from continental waters of crustally-derived radiogenic osmium either contemporaneous with the meteoritic (or mantle) osmium deposition or later during diagenesis

An introduction to Podospora anserina

An introduction to Podospora anserin

Properties of optically selected BL Lac candidates from the SDSS

\textbf{Context.} Deep optical surveys open the avenue for find large numbers of BL Lac objects that are hard to identify because they lack the unique properties classifying them as such. While radio or X-ray surveys typically reveal dozens of sources, recent compilations based on optical criteria alone have increased the number of BL Lac candidates considerably. However, these compilations are subject to biases and may contain a substantial number of contaminating sources. \textbf{Aims.} In this paper we extend our analysis of 182 optically selected BL Lac object candidates from the SDSS with respect to an earlier study. The main goal is to determine the number of bona fide BL Lac objects in this sample. \textbf{Methods.} We examine their variability characteristics, determine their broad-band radio-UV SEDs, and search for the presence of a host galaxy. In addition we present new optical spectra for 27 targets with improved S/N with respect to the SDSS spectra. \textbf{Results.} At least 59% of our targets have shown variability between SDSS DR2 and our observations by more than 0.1-0.27 mag de- pending on the telescope used. A host galaxy was detected in 36% of our targets. The host galaxy type and luminosities are consistent with earlier studies of BL Lac host galaxies. Simple fits to broad-band SEDS for 104 targets of our sample derived synchrotron peak frequencies between $13.5 \leq \mathrm{log}_{10}(\nu_{\mathrm{peak}}) \leq 16$ with a peak at $\mathrm{log}_{10} \sim 14.5$. Our new optical spectra do not reveal any new redshift for any of our objects. Thus the sample contains a large number of bona fide BL Lac objects and seems to contain a substantial fraction of intermediate-frequency peaked BL Lacs.Comment: Accepted for publication in A\&

A model study of the application of roof bolts under unsymmetrical loading conditions

When coal is extracted by the long wall mining method, two gate-roads on either side of the working face are driven with the advancing operation. In the surroundings of these openings the state of stress which existed prior to mining is not only disturbed by the drifting process of the gate-roads but also by the coal extraction in the long wall, resulting in an unsymmetrical stress distribution. Varying incremental pressure components and the high complexity of strata movements make it extremely difficult to control the rock behavior under unsymmetrical conditions by conventional support. Application of roof bolts as an auxiliary support can improve the control of the strata surrounding long wall gate-roads. To indicate the qualitative effect of roof bolts on the stress distribution around underground openings in stratified rock under unsymmetrical loading conditions, composite models made of photo-elastic material were tested in a 6 ft. diameter centrifuge, providing proper loading conditions. Stress distributions were permanently frozen into the models while under load. Test results indicate that the high shearing stresses which occur near the rigid abutment of the long wall gate-road and the bending stresses in the roof beams can be reduced considerably by the application of roof bolts in proper pattern arrangements. Since this study was concerned with the development of an experimental technique and simple structural conditions were chosen, an extension of this investigation to more complicated conditions is possible --Abstract, page i

An HFACS Analysis of German F-104 Starfighter Accidents

From 1961 onwards, Germany acquired 916 Lockheed F-104 Starfighters, of which 292 aircraft crashed and 116 pilots lost their lives. The purpose of this research project was to find out why these aircraft crashed and whether the Starfighters crashed for reasons different from those for other military aircraft in Germany. Seventy-one German F-104 accidents between 1978 and 1986 were analyzed by reviewing the original accident files. A Human Factors Analysis and Classification System (HFACS) Level-1 analysis was used as methodology. It was found that more than 50% of the reviewed German F-104 accidents occurred due to technology and/or physical environment. More than half of the sample’s accidents were engine related. It was concluded that the F-104 was indeed more accident-prone than other co-era types. Moreover, the J-79 engine was found to be a weak link in the F-104’s safety record, and the Starfighter’s unforgiving handling characteristics induced an elevated level of skill-based errors

Ground state structure of diluted antiferromagnets and random field systems

A method is presented for the calculation of all exact ground states of diluted antiferromagnets and random field systems in an arbitrary range of fields. It works by calculating all jump-fields B,\Delta where the system changes it's ground state. For each field value all degenerated ground states are represented by a set of (anti-) ferromagnetic clusters and a relation between the clusters. So a complete description of the ground state structure of these systems is possible. Systems are investigated up to size 48^3 on the whole field-range and up to 160^3 for some particular fields. The behavior of order parameters is investigated, the number of jumps is analyzed and the degree of degeneracy as functions of size and fields is calculated.Comment: 11 pages, 13 figures, LaTex, submitted to Physica