A high resolution imaging detector for TeV gamma-ray astronomy

Details are presented of an atmospheric Cherenkov telescope for use in very high energy gamma-ray astronomy which consists of a cluster of 109 close-packed photomultiplier tubes at the focus of a 10 meter optical reflector. The images of the Cherenkov flashes generated both by gamma-ray and charged cosmic-ray events are digitized and recorded. Subsequent off-line analysis of the images improves the significance of the signal to noise ratio by a factor of 10 compared with non-imaging techniques.     

THE BORGO SAN DONINO METEORITE: MINERALOGY AND CHEMISTRY

The principal data are collected about the fall, April 19, 1808, and the distribution of the fragments of the Borgo San Donino, Italy, meteorite (long. 44° 52′ N.; lat. 11° 03′ E.). An Almost complete individual, weighing 447 g is described in some detail. Crust morphology, mineralogical composition, chemical composition and petrology were studied. Optical data were established by microscopic analysis of both thin and polished sections. The Borgo San Donino is an ordinary LL-group chondrite, with a fundamentally hypochondritic texture and evident features of recrystallization and metamorphism. The presence of some anomalous chondrules is discussed     

Finite element simulation of freezing processes in soils

The finite element method, formulated for non-linear heat conduction, allows the solution of practically any ground freezing problem. Stabilization of wet soils by artificial freezing and freezing under roads induced by cold winter conditions are considered in this paper. Special features of the program used include parabolic isoparametric elements, a new time stepping scheme and an improved procedure for the estimation of thermal properties.     

Voyager 1 imaging and IRIS observations of Jovian methane absorption and thermal emission: Implications for cloud structure

Images from three filters of the Voyager 1 wide-angle camera were used to measure the continuum reflectivity and spectral gradient near 6000 Å and the 6190-Å band methane/continuum ratio for a variety of cloud features in Jupiter's atmosphere. The dark “barge” features in the North Equatorial Belt have anomalously strong positive continuum spectral gradients suggesting unique composition, probably not elemental sulfur. Methane absorption was shown at unprecedented spatial scales for the Great Red Spot and its immediate environment, for a dark barge feature in the North Equatorial Belt, and for two hot spot and plume regions in the North Equatorial Belt. Some small-scale features, unresolvable at ground-based resolution, show significant enhancement in methane absorption. Any enhancement in methane absorption is conspicuously absent in both hot spot regions with 5-μm brightness temperature 255°K. Methane absorption and 5-μm emission are correlated in the vicinity of the Great Red Spot but are anticorrelated in one of the plume hot spot regions. Methane absorption and simultaneously maps of 5-μm brightness temperature were quantitatively compared to realistic cloud structure models which include multiple scattering at 5 μm as well as in the visible. A curve in parameter space defines the solution to any observed quantity, ranging from a shallow atmosphere and thin NH₃ cloud to a deep atmosphere with a thick ammonia cloud. Without additional constraints, such as center-to-limb information, it is impossible to specify the NH₃ cloud optical depth and pressure of a deeper cloud top independently. Variability in H₂ quadrupole lines was also investigated and it was found that the constancy of the 4-0 S(1)-line equivalent width is consistent with the constancy of the methane 6190-Å band equivalent width at ground-based resolution, but the much greater variability of the 3-0 S(1) line is inconsistent with either the methane band or 4-0 S(1) line. In hot spot regions the 255°K brightness temperature requires a cloud optical depth of about 2 or less at 5 μm in the NH₃ cloud layer. To be consistent with the observed 6190-Å methane absorption in hot spot regions, the NH₃ cloud optical depth in the visible is about 7.5, implying that aerosols in hot spot regions have effective radii near 1 μm or less.     

A solar spicule model based upon calcium II K line radiative transfer studies

Monte Carlo radiative transfer techniques are used to develop a height-dependent spicule model based upon a more realistic configuration than has hitherto been considered. The spicule is represented by a uniform cylinder, of finite length, standing vertically upon a plane chromosphere. The observed, limb-darkened, anisotropic chromospheric flux incident upon the cylinder is incorporated into the transfer calculations.The resulting model is characterized by a random, line broadening velocity of 20 km/sec, with electron temperature increasing from 6 × 10³ K at the base to about 1.5 × 10⁴ K at 11500 km above the solar surface. The corresponding values of electron density are 8 × 10¹¹ cm^-3 and 4 × 10¹⁰ cm^-3. Contrast curves of the spicule model against the chromospheric background are computed and indicate that spicules should appear both bright and dark on the disk, depending upon their position with respect to the limb, the spectral frequency of observation and the viewing height.This work is based on a Ph.D. thesis submitted to the Department of Astro-Geophysics, University of Colorado.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

THE NAZARETH(b) METEORITE

The Nazareth(b) meteorite is a medium octahedrite found in 1968 near Nazareth, Texas. It contains 8.75% nickel and large schreibersite inclusions