HEAO-A nominal scanning observation schedule

The HEAO-A observatory, scheduled for launch in late June 1977, will spend most of its orbital lifetime in a scanning mode, spining from 0.03 to 0.1 rpm about an axis aligned with the sun. The dates of availability in the scan band are given for a list of 248 X-ray sources. Celestial maps of source locations and scan planes, and examples of the nighttime elevation of available sources are presented. This document is intended to aid ground-based observers in planning coordinated observations with HEAO-A

Double Exchange in a Magnetically Frustrated System

This work examines the magnetic order and spin dynamics of a double-exchange model with competing ferromagnetic and antiferromagnetic Heisenberg interactions between the local moments. The Heisenberg interactions are periodically arranged in a Villain configuration in two dimensions with nearest-neighbor, ferromagnetic coupling $J$ and antiferromagnetic coupling $-\eta J$. This model is solved at zero temperature by performing a $1/\sqrt{S}$ expansion in the rotated reference frame of each local moment. When $\eta$ exceeds a critical value, the ground state is a magnetically frustrated, canted antiferromagnet. With increasing hopping energy $t$ or magnetic field $B$, the local moments become aligned and the ferromagnetic phase is stabilized above critical values of $t$ or $B$. In the canted phase, a charge-density wave forms because the electrons prefer to sit on lines of sites that are coupled ferromagnetically. Due to a change in the topology of the Fermi surface from closed to open, phase separation occurs in a narrow range of parameters in the canted phase. In zero field, the long-wavelength spin waves are isotropic in the region of phase separation. Whereas the average spin-wave stiffness in the canted phase increases with $t$ or $\eta$, it exhibits a more complicated dependence on field. This work strongly suggests that the jump in the spin-wave stiffness observed in Pr$_{1-x}$Ca$_x$MnO$_3$ with $0.3 \le x \le 0.4$ at a field of 3 T is caused by the delocalization of the electrons rather than by the alignment of the antiferromagnetic regions.Comment: 28 pages, 12 figure

Capabilities of the GRO/BATSE for monitoring of discrete sources

Although the Burst and Transient Source Experiment (BATSE) to be flown on the Gamma Ray Observatory has as its primary objective the detection of gamma ray bursts, its uncollimated design will enable it to serve a unique function as an all-sky monitor for bright hard X-ray and low-energy gamma ray sources. Pulsating sources may be detected by conventional techniques such as summed-epoch and Fourier analyses. The BATSE will, in addition, be able to use Earth occultation in an unprecedented way to monitor sufficiently bright sources as often as several times per day over approx. 85% of the sky. Estimates of the expected BATSE sensitivity using both of these techniques are presented

Short-Range Ordered Phase of the Double-Exchange Model in Infinite Dimensions

Using dynamical mean-field theory, we have evaluated the magnetic instabilities and T=0 phase diagram of the double-exchange model on a Bethe lattice in infinite dimensions. In addition to ferromagnetic (FM) and antiferromagnetic (AF) phases, we also study a class of disordered phases with magnetic short-range order (SRO). In the weak-coupling limit, a SRO phase has a higher transition temperature than the AF phase for all fillings p below 1 and can even have a higher transition temperature than the FM phase. At T=0 and for small Hund's coupling J_H, a SRO state has lower energy than either the FM or AF phases for 0.26\le p 0 limit but appears for any non-zero value of J_H.Comment: 11 pages, 3 figures, published versio

Fractional ℏ\hbar-scaling for quantum kicked rotors without cantori

Previous studies of quantum delta-kicked rotors have found momentum probability distributions with a typical width (localization length $L$) characterized by fractional $\hbar$-scaling, ie $L \sim \hbar^{2/3}$ in regimes and phase-space regions close to `golden-ratio' cantori. In contrast, in typical chaotic regimes, the scaling is integer, $L \sim \hbar^{-1}$. Here we consider a generic variant of the kicked rotor, the random-pair-kicked particle (RP-KP), obtained by randomizing the phases every second kick; it has no KAM mixed phase-space structures, like golden-ratio cantori, at all. Our unexpected finding is that, over comparable phase-space regions, it also has fractional scaling, but $L \sim \hbar^{-2/3}$. A semiclassical analysis indicates that the $\hbar^{2/3}$ scaling here is of quantum origin and is not a signature of classical cantori.Comment: 5 pages, 4 figures, Revtex, typos removed, further analysis added, authors adjuste

Effects of predation on Zostera marina L. seed abundance

Predator effects on Zostera marina L. seed abundance were studied in the York River, VA, USA, using enclosure and exclosure caging experiments. Seeds were placed in cages in two concurrent experiments. The first experiment was a predator exclosure experiment to test the effects of excluding predators, using a full predator exclosure cage, a partial exclosure top-only cage, a partial exclosure side-only cage and uncaged plots. The second experiment was a predator enclosure experiment, using two highly abundant macro-benthic predators in the Chesapeake Bay: the decapod crustacean Callinectes sapidus Rathbun and the sciaenid fish Micropogonias undulatus L. Additionally, two-week long trials of sequentially protected and exposed seeds were also performed. Replicate treatment plots were sampled by removing the top 5–10 cm of the sediment surface with a suction sampler and still viable seeds in each plot were counted. Full exclosure cages contained significantly higher numbers of seeds than the uncaged or partial caged treatments. Seed abundances in the C. sapidus enclosure cages were significantly less than the full exclusion cage, but not significantly different than the uncaged treatments. Seed abundances in the M. undulatus cages were not significantly different than the full exclusion cage. The least number of seeds were found in the uncaged and partial cage treatments. Results of the sequentially protected and exposed trials were similar to results from the one-week uncaged treatments. These experiments suggest that seed predation can affect the abundance of Z. marina seeds, possibly causing up to 65% of the seed losses observed in these experiments. Results suggest that seed predation has the potential to be an important force governing the sexual reproductive success and propagation of eelgrass beds and that the degree of seed loss via predation may be related to predator and primary food abundances

Polymers for spacecraft hardware materials specifications and engineering information Monthly technical progress report no. 18, Nov. 10 - Dec. 9, 1965

Chemical test procedures for analyzing potting compound bases for spacecraft construction material

Polymers for spacecraft hardware materials specifications and engineering information Monthly technical progress report no. 19, Dec. 10, 1965 - Jan. 9, 1966

Thermal vacuum weight loss determinations of polymers for spacecraft construction material application

Dynamics of Impurity and Valence Bands in GaMnAs within the Dynamical Mean Field Approximation

We calculate the density-of-states and the spectral function of GaMnAs within the dynamical mean-field approximation. Our model includes the competing effects of the strong spin-orbit coupling on the J=3/2 GaAs hole bands and the exchange interaction between the magnetic ions and the itinerant holes. We study the quasi-particle and impurity bands in the paramagnetic and ferromagnetic phases for different values of impurity-hole coupling at the Mn doping of x=0.05. By analyzing the anisotropic angular distribution of the impurity band carriers at T=0, we conclude that the carrier polarization is optimal when the carriers move along the direction parallel to the average magnetization.Comment: 6 pages, 4 figure