Comparison of AIS Versus TMS Data Collected over the Virginia Piedmont

The Airborne Imaging Spectrometer (AIS, NS001 Thematic Mapper Simlulator (TMS), and Zeiss camera collected remotely sensed data simultaneously on October 27, 1983, at an altitude of 6860 meters (22,500 feet). AIS data were collected in 32 channels covering 1200 to 1500 nm. A simple atmospheric correction was applied to the AIS data, after which spectra for four cover types were plotted. Spectra for these ground cover classes showed a telescoping effect for the wavelength endpoints. Principal components were extracted from the shortwave region of the AIS (1200 to 1280 nm), full spectrum AIS (1200 to 1500 nm) and TMS (450 to 12,500 nm) to create three separate three-component color image composites. A comparison of the TMS band 5 (1000 to 1300 nm) to the six principal components from the shortwave AIS region (1200 to 1280 nm) showed improved visual discrimination of ground cover types. Contrast of color image composites created from principal components showed the AIS composites to exhibit a clearer demarcation between certain ground cover types but subtle differences within other regions of the imagery were not as readily seen

Calibration of the CH and CN Variations Among Main Sequence Stars in M71 and in M13

An analysis of the CN and CH band strengths measured in a large sample of M71 and M13 main sequence stars by Cohen (1999a,b) is undertaken using synthetic spectra to quantify the underlying C and N abundances. In the case of M71 it is found that the observed CN and CH band strengths are best matched by the {\it{identical}} C/N/O abundances which fit the bright giants, implying: 1) little if any mixing is taking place during red giant branch ascent in M71, and 2) a substantial component of the C and N abundance inhomogeneities is in place before the main sequence turn-off. The unlikelihood of mixing while on the main sequence requires an explanation for the abundance variations which lies outside the present stars (primordial inhomogeneities or intra-cluster self enrichment). For M13 it is shown that the 3883\AA CN bands are too weak to be measured in the spectra for any reasonable set of expected compositions. A similar situation exists for CH as well. However, two of the more luminous program stars do appear to have C abundances considerably greater than those found among the bright giants thereby suggesting deep mixing has taken place on the M13 red giant branch.Comment: 14 pages, 4 figures, accepted for publication by A

Research on gravitational mass sensors Quarterly progress report no. 1, 15 Oct. 1964 - 14 Jan. 1965

Lunar orbiter and deep space probe gravitational sensor for determining mass distribution of moon and asteroid

A state space approach to chemical plant fault detection

Imperial Users onl

Research on gravitational mass sensors quarterly progress report no. 2, 15 jan. - 14 apr. 1965

Cruciform sensor head, phase shift tuned amplifier, and air bearing support for sensor for detecting presence of small moving mass through gravitational interaction

Atomic hydrogen cleaning of GaSb(001) surfaces

We show that the (001) surface of GaSb can be cleaned efficiently by exposure to atomic hydrogen at substrate temperatures in the range 400–470 °C. This treatment removes carbon and oxygen contamination, leaving a clean, ordered surface with a symmetric (1 × 3) reconstruction after a total H2 dose of approximately 150 kL. An ordered but partially oxidized surface is generated during cleaning, and the removal of this residual oxide is the most difficult part of the process. Auger electron spectroscopy and low energy electron diffraction were used to monitor the chemical cleanliness and the ordering of the surface during the cleaning process, whereas high resolution electron energy loss spectroscopy was used to probe the electronic structure in the near-surface region. The results obtained indicates that this cleaning procedure leaves no residual electronic damage in the near-surface region of the Te-doped (n ~ 5 × 1017 cm – 3) samples of GaSb(001) studied

The soft X-ray afterglow of gamma ray bursts, a stringent test for the fireball model

I consider the recent discovery of a soft X-ray source inside the error box of the gamma ray burst GB 960720 by the SAX, ASCA and ROSAT satellites, in terms of the fireball model. I show that the ejecta shell, which, after causing the burst is cold and dense, but still relativistic, keeps plowing through the interstellar medium, heating up the just-shocked matter which then emits X-rays. I compute the radiation emitted by this matter. I show that, up to about two months after the burst, in the cosmological scenario a soft X-ray (0.1-10 keV) flux of at least 10^(-13) erg / s cm^2, well within current observational capabilities, is generated, explaining the observations of the three satellites. Instead, in the Galactic Halo scenario a flux 3 orders of magnitude lower is expected. Detection of this non-thermal, declining flux in a statistically significant number of objects would simultaneously establish the fireball model and the cosmological nature of gamma ray bursts.Comment: Replaces previous version: now it does include figure. Accepted for publication in the Astrophysical Journal Letter

Cultivation and use of bryophytes as experimental material

Bryophytes can be grown successfully if keptmoist, supplied with nutrients, and out of direct sunlight. They remain greener on peat than on sand. However, difficulties were encountered when attempting to grow mosses and liverworts in an unshaded glasshouse, in spring and summer. Even spraying hourly with water did not prevent scorching and desiccation. Growth can be measured using a variety of techniques; height measurement and shoot elongation from thread markers proved the most reliabl

Pair plasma cushions in the hole-boring scenario

Pulses from a 10 PW laser are predicted to produce large numbers of gamma-rays and electron-positron pairs on hitting a solid target. However, a pair plasma, if it accumulates in front of the target, may partially shield it from the pulse. Using stationary, one-dimensional solutions of the two-fluid (electron-positron) and Maxwell equations, including a classical radiation reaction term, we examine this effect in the hole-boring scenario. We find the collective effects of a pair plasma "cushion" substantially reduce the reflectivity, converting the absorbed flux into high-energy gamma-rays. There is also a modest increase in the laser intensity needed to achieve threshold for a non-linear pair cascade.Comment: 17 pages, 5 figures. Accepted for publication in Plasma Physics and Controlled Fusion. Typos corrected, reference update