Autonomous navigation accuracy using simulated horizon sensor and sun sensor observations

A relatively simple autonomous system which would use horizon crossing indicators, a sun sensor, a quartz oscillator, and a microprogrammed computer is discussed. The sensor combination is required only to effectively measure the angle between the centers of the Earth and the Sun. Simulations for a particular orbit indicate that 2 km r.m.s. orbit determination uncertainties may be expected from a system with 0.06 deg measurement uncertainty. A key finding is that knowledge of the satellite orbit plane orientation can be maintained to this level because of the annual motion of the Sun and the predictable effects of Earth oblateness. The basic system described can be updated periodically by transits of the Moon through the IR horizon crossing indicator fields of view

The Production of Ring-necked Pheasants in Winnebago County, lowa

In the fall of 1935, the Iowa Cooperative Wildlife Research Unit inaugurated field investigations on the ring-necked pheasant, Phasianus colchicus, on the Winnebago Research Area, sections 9-12, 13-16, and 21-24, Eden Township, Winnebago County. Early investigations (Green, 1938) were centered around winter mortality of pheasants and the improvement of habitat to alleviate winter losses. In 1939-41 intensive investigations were shifted to the nesting and production of the ring-necked pheasant on a 1520-acre plot lying within sections 13, 14, 15, 23 and 24 (Baskett, 1947). Although the pheasants were increasing in numbers during 1939 and 1940, in 1941 and accelerated rate of summer production was noted. Instead of the usual 150-175 percent rate of summer increase over the spring population, production jumped to 220 percent in spite of the largest observed spring density - 125 birds per section. A parallel rise in the 1941 rate of production was also recorded in North Dakota (Bach, 1944)

Magnetization and EPR studies of the single molecule magnet Ni4_4 with integrated sensors

Integrated magnetic sensors that allow simultaneous EPR and magnetization measurements have been developed to study single molecule magnets. A high frequency microstrip resonator has been integrated with a micro-Hall effect magnetometer. EPR spectroscopy is used to determine the energy splitting between the low lying spin-states of a Ni$_4$ single crystal, with an S=4 ground state, as a function of applied fields, both longitudinal and transverse to the easy axis at 0.4 K. Concurrent magnetization measurements show changes in spin-population associated with microwave absorption. Such studies enable determination of the energy relaxation time of the spin system.Comment: 4 pages, 4 figures, accepted for publication (Proceedings of the 10th Joint MMM/Intermag Conference, which will be published as special issues of the Journal of Applied Physics

Tunneling Splittings in Mn12-Acetate Single Crystals

A Landau-Zener multi-crossing method has been used to investigate the tunnel splittings in high quality Mn$_{12}$-acetate single crystals in the pure quantum relaxation regime and for fields applied parallel to the magnetic easy axis. With this method several individual tunneling resonances have been studied over a broad range of time scales. The relaxation is found to be non-exponential and a distribution of tunnel splittings is inferred from the data. The distributions suggest that the inhomogeneity in the tunneling rates is due to disorder that produces a non-zero mean value of the average transverse anisotropy, such as in a solvent disorder model. Further, the effect of intermolecular dipolar interaction on the magnetic relaxation has been studied.Comment: Europhysics Letters (in press). 7 pages, including 3 figure

More Evidence for a Distribution of Tunnel Splittings in Mn12_{12}-acetate

In magnetic fields applied parallel to the anisotropy axis, the magnetization of Mn$_{12}$ has been measured in response to a field that is swept back and forth across the resonances corresponding to steps $N=4,5,...9$. The fraction of molecules remaining in the metastable well after each sweep through the resonance is inconsistent with expectations for an ensemble of identical molecules. The data are consistent instead with the presence of a broad distribution of tunnel splittings. A very good fit is obtained for a Gaussian distribution of the second-order anisotropy tunneling parameter $X_E=-\ln(\mid E\mid/2D)$. We show that dipolar shuffling is a negligible effect which cannot explain our data.Comment: minor corrections (PACS nos, signs in Fig. 2

Abrupt Transition between Thermally-Activated Relaxation and Quantum Tunneling in a Molecular Magnet

We report Hall sensor measurements of the magnetic relaxation of Mn$_{12}$ acetate as a function of magnetic field applied along the easy axis of magnetization. Data taken at a series of closely-spaced temperatures between 0.24 K and 1.4 K provide strong new evidence for an abrupt ``first-order'' transition between thermally-assisted relaxation and magnetic decay via quantum tunneling.Comment: 4 pages, including 7 figure

A Proposed Comparison of Fall Roadside Pheasant Counts and Flushing Rates

Although the fall roadside pheasant census (Bennett and Hendrickson, 1938) has reflected the fall pheasant population from an administrative standpoint for the past 17 years within the primary range in Iowa (Kozicky, et al., 1952), there still exist the problems of correlating these roadside counts to actual populations or flushing rates. Inasmuch as we do not have any known method of obtaining exact numbers of birds for a given ·section of land at the present time, we cannot develop a method of interpreting the roadside count as reflecting a mean number of birds per acre in the primary pheasant range within a, specified confidence limits. However, it may be possible to relate the index obtained from the roadside count to birds flushed per hour on a section of land. The evaluation would be of assistance to administrators and sportsmen alike. The sportsmen are interested in knowing just how many birds they can expect to flush in an hour of hunting, based on roadside counts, and the administrator would like confirmation on the correlation, if any, between the roadside count and flushing rates