Space processing of chalcogenide glasses

Chalcogenide glasses are discussed as good infrared transmitters, possessing the strength, corrosion resistance, and scale-up potential necessary for large 10.6-micron windows. The disadvantage of earth-produced chalcogenide glasses is shown to be an infrared absorption coefficient which is unacceptably high relative to alkali halides. This coefficient is traced to optical nonhomogeneities resulting from environmental and container contamination. Space processing is considered as a means of improving the infrared transmission quality of chalcogenides and of eliminating the following problems: optical inhomogeneities caused by thermal currents and density fluctuation in the l-g earth environment; contamination from the earth-melting crucible by oxygen and other elements deleterious to infrared transmission; and, heterogeneous nucleation at the earth-melting crucible-glass interface

Use of the VAD technique and measurements of momentum flux in the stratosphere at Aercibo, part 4.3A

The Arecibo 430-MHz radar was used in the velocity-azimuth display (VAD) mode to obtain radial velocity measurements at 16 azimuth directions from which the three-dimensional wind field and momentum flux can be calculated. The radar was operated on a nearly continuous basis for a seven-day period in May of 1982 and the elapsed time between start and finish of a VAD scan was approximately 35 minutes. Radial velocities were measured in the upper troposphere and lower stratosphere (6-24 km) with at height resolution of 150 meters at a zenith angle of 15 deg. Vertical and horizontal velocities are calculated from the sums and differences, respectively, of radial velocity pairs, i.e., at azimuth directions AZ and AZ + 180 degrees. Momentum flux at a particular azimuth is calculated by taking the difference between the square of radial velocities at AZ and AZ + 180 degrees. It should be noted that measurements of radial velocity pairs are not simultaneous but are time delayed by approximately 15-25 minutes. This period, the time required to rotate the antenna feed and take measurements at AZ and AZ + 180 deg, effectively limits sampling of velocities and momentum fluxes to longer period gravity waves and planetary waves

Space processing of chalcogenide glass

The manner in which the weightless, containerless nature of in-space processing can be successfully utilized to improve the quality of infrared transmitting chalcogenide glasses is determined. The technique of space processing chalcogenide glass was developed, and the process and equipment necessary to do so was defined. Earthbound processing experiments with As2S3 and G28Sb12Se60 glasses were experimented with. Incorporated into these experiments is the use of an acoustic levitation device

Antarctic measurements of ozone, water vapor, and aerosol extinction by Sage 2 in the spring of 1987

Recent measurements of ozone, water vapor, and aerosol extinction from the spring of 1987 are presented and compared to 1985 and 1986. The observed changes to variations in meteorological conditions in the vortex for these three years are noted. March ozone data at similar latitudes for these three years will be used to investigate coupling between severity of the springtime depletion and early fall values. Researchers also investigate correlations between the measured species of water vapor, ozone, and aerosols throughout the vortex region

Smaller, Closer, Dirtier: Diesel Backup Generators in California

Quantifies the threat to air quality and human health by backup generators, and examines air quality in Los Angeles, San Diego, Sacramento, and Fresno, with some analysis of San Francisco as well

Rainfall-triggered landslides, anthropogenic hazards, and mitigation strategies

Rainfall-triggered landslides are part of a natural process of hillslope erosion that can result in catastrophic loss of life and extensive property damage in mountainous, densely populated areas. As global population expansion on or near steep hillslopes continues, the human and economic costs associated with landslides will increase. Landslide hazard mitigation strategies generally involve hazard assessment mapping, warning systems, control structures, and regional landslide planning and policy development. To be sustainable, hazard mitigation requires that management of natural resources is closely connected to local economic and social interests. A successful strategy is dependent on a combination of multi-disciplinary scientific and engineering approaches, and the political will to take action at the local community to national scale

A dynamical and kinematical model of the Galactic stellar halo and possible implications for galaxy formation scenarios

We re-analyse the kinematics of the system of blue horizontal branch field (BHBF) stars in the Galactic halo (in particular the outer halo), fitting the kinematics with the model of radial and tangential velocity dispersions in the halo as a function of galactocentric distance r proposed by Sommer-Larsen, Flynn & Christensen (1994), using a much larger sample (almost 700) of BHBF stars. The basic result is that the character of the stellar halo velocity ellipsoid changes markedly from radial anisotropy at the sun to tangential anisotropy in the outer parts of the Galactic halo (r greater than approx 20 kpc). Specifically, the radial component of the stellar halo's velocity ellipsoid decreases fairly rapidly beyond the solar circle, from approx 140 +/- 10 km/s at the sun, to an asymptotic value of 89 +/- 19 km/s at large r. The rapid decrease in the radial velocity dispersion is matched by an increase in the tangential velocity dispersion, with increasing r. Our results may indicate that the Galaxy formed hierarchically (partly or fully) through merging of smaller subsystems - the 'bottom-up' galaxy formation scenario, which for quite a while has been favoured by most theorists and recently also has been given some observational credibility by HST observations of a potential group of small galaxies, at high redshift, possibly in the process of merging to a larger galaxy (Pascarelle et al 1996).Comment: Latex, 16 pages. 2 postscript figures. Submitted to the Astrophysical Journal. also available at http://astro.utu.fi/~cflynn/outerhalo.htm

Novel Techniques for Constraining Neutron-Capture Rates Relevant for r-Process Heavy-Element Nucleosynthesis

The rapid-neutron capture process ($r$ process) is identified as the producer of about 50\% of elements heavier than iron. This process requires an astrophysical environment with an extremely high neutron flux over a short amount of time ($\sim$ seconds), creating very neutron-rich nuclei that are subsequently transformed to stable nuclei via $\beta^-$ decay. One key ingredient to large-scale $r$-process reaction networks is radiative neutron-capture ($n,\gamma$) rates, for which there exist virtually no data for extremely neutron-rich nuclei involved in the $r$ process. Due to the current status of nuclear-reaction theory and our poor understanding of basic nuclear properties such as level densities and average $\gamma$-decay strengths, theoretically estimated ($n,\gamma$) rates may vary by orders of magnitude and represent a major source of uncertainty in any nuclear-reaction network calculation of $r$-process abundances. In this review, we discuss new approaches to provide information on neutron-capture cross sections and reaction rates relevant to the $r$ process. In particular, we focus on indirect, experimental techniques to measure radiative neutron-capture rates. While direct measurements are not available at present, but could possibly be realized in the future, the indirect approaches present a first step towards constraining neutron-capture rates of importance to the $r$ process.Comment: 62 pages, 24 figures, accepted for publication in Progress in Particle and Nuclear Physic

Investigation on the influence of nematophagous fungi as feed additive on nematode infection risk of sheep and goats on pasture

Gastrointestinal nematodes in small ruminants cause high economic losses. Thus on most farms anthelmintic treatment is required. In response to increasing problems with anthelmintic resistance, biological control, for example the use of nematophagous fungi, has received significant attention. The aim of this study was to investigate the effect of Duddingtonia flagrans orally applied to small ruminants on natural infection with gastrointestinal nematodes in a field study in Northern Germany. 20 goats and 20 sheep were fed daily for 3 months with 5x105 spores of D. flagrans per kg bodyweight. Differences in body weight, faecal egg count and larval development in faeces and on pasture in comparison with same-sized control groups were analysed. After 3 months the control goats showed significantly higher mean faecal egg count than the fungus-fed group. No significant difference was found between the two sheep groups. The maximum in larval reduction in faeces was 81.3 % in the sheep groups and 67.9 % in the goat groups (not significant). At the end of the study the body weight gain in the fungus-treated groups was 1.7 kg higher in goats and 0.7 kg higher in sheep than in the control groups (not significant). Regarding the first-year-grazing goats only, the bodyweights revealed significant differences (p<0.05). No statistically significant differences were observed in pasture larval counts. In the study presented here, no clear effect of fungus could be observed. A modified feeding regimen, perhaps with permanent release boluses or feed blocks, may improve the efficacy. Furthermore, it seems that climatic conditions during the study period could have influenced the results and displayed how sensitive the fungus application may be on such parameters

Hole Spin Coherence in a Ge/Si Heterostructure Nanowire

Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si nanowire double quantum dot using a fast pulsed-gate method and dispersive readout. An inhomogeneous dephasing time $T_2^* \sim 0.18~\mathrm{\mu s}$ exceeds corresponding measurements in III-V semiconductors by more than an order of magnitude, as expected for predominately nuclear-spin-free materials. Dephasing is observed to be exponential in time, indicating the presence of a broadband noise source, rather than Gaussian, previously seen in systems with nuclear-spin-dominated dephasing.Comment: 15 pages, 4 figure