High mobility two-dimensional electron system on hydrogen-passivated silicon(111) surfaces

We have fabricated and characterized a field-effect transistor in which an electric field is applied through an encapsulated vacuum cavity and induces a two-dimensional electron system on a hydrogen-passivated Si(111) surface. This vacuum cavity preserves the ambient sensitive surface and is created via room temperature contact bonding of two Si substrates. Hall measurements are made on the H-Si(111) surface prepared in aqueous ammonium fluoride solution. We obtain electron densities up to $6.5 \times 10^{11}$ cm$^{-2}$ and peak mobilities of $\sim 8000$ cm$^{2}$/V s at 4.2 K.Comment: to appear in Applied Physics Letter

Advanced automation in space shuttle mission control

The Real Time Data System (RTDS) Project was undertaken in 1987 to introduce new concepts and technologies for advanced automation into the Mission Control Center environment at NASA's Johnson Space Center. The project's emphasis is on producing advanced near-operational prototype systems that are developed using a rapid, interactive method and are used by flight controllers during actual Shuttle missions. In most cases the prototype applications have been of such quality and utility that they have been converted to production status. A key ingredient has been an integrated team of software engineers and flight controllers working together to quickly evolve the demonstration systems

Absolute intensity of radiation emitted by uranium plasmas

The absolute intensity of radiation emitted by fissioning and nonfissioning uranium plasmas in the spectral range from 350 nm to 1000 nm was measured. The plasma was produced in a plasma-focus apparatus and the plasma properties are simular to those anticipated for plasma-core nuclear reactors. The results are expected to contribute to the establishment of design criteria for the development of plasma-core reactors

Neutrino Scattering in a Magnetic Field

Motivated by the evidence for a finite neutrino mass we examine anew the interaction of neutrinos in a magnetic field. We present the rate for radiative scattering for both massless and massive neutrinos in the standard model and give the corresponding numerical estimates. We also consider the effects arising from a possible neutrino magnetic moment.Comment: 10 pages, 3 figures; Acknowledgements added 05.07.200

Integer quantum Hall effect on a six valley hydrogen-passivated silicon (111) surface

We report magneto-transport studies of a two-dimensional electron system formed in an inversion layer at the interface between a hydrogen-passivated Si(111) surface and vacuum. Measurements in the integer quantum Hall regime demonstrate the expected sixfold valley degeneracy for these surfaces is broken, resulting in an unequal occupation of the six valleys and anisotropy in the resistance. We hypothesize the misorientation of Si surface breaks the valley states into three unequally spaced pairs, but the observation of odd filling factors, is difficult to reconcile with non-interacting electron theory.Comment: 4 pages, 4 figures, to appear in Physical Review Letter

Design and performance of a fixed, nonaccelerating, guide vane cascade that operates over an inlet flow angle range of 60 deg

A unique set of wind tunnel guide vanes are designed with an inverse design code and analyzed with a panel method and an integral boundary layer code developed at the NASA Lewis Research Center. The fixed guide vanes, 80 feet long with 6-foot chord length, were designed for the NASA Ames 40 x 80/80 x 120 ft Wind Tunnel. Low subsonic flow is accepted over a 60 deg range of inlet angle from either the 40 x 80 leg or the 80 x 120 leg of the wind tunnel, and directed axially into the main leg of the tunnel where drive fans are located. Experimental tests of 1/10-scale models were conducted to verify design calculations

The Educational Adjustment Program Profile: A Queensland Initiative in the identification and Monitoring of Students with a Disability

The effective identification and monitoring of students with a disability is a complex and important aspect of educational service delivery for students with a disability in Queensland. Building on previous initiatives in this domain Education Queensland has piloted the development of the Educational Adjustment Program (EAP) profile. Based on the data from the initial survey sample of more than 1500 school age students with a disability across Queensland, this paper highlights: the design of the Education Adjustment Program Adjustment Profile (EAP); some of its psychometric properties; gender and Indigenous student dimensions within the data; and how the EAP instrument compares with the 1 to 6 ascertainment rating scale

A Two-Chain Path Integral Model Of Positronium

We have used a path integral Monte Carlo technique to simulate positronium (Ps) in a cavity. The primitive propagator is used, with a pair of interacting chains representing the positron and electron. We calculate the energy and radial distribution function for Ps enclosed in a hard, spherical cavity, and the polarizability of the model Ps in the presence of an electrostatic field. We find that the positron distribution near the hard wall differs significantly from that for a single particle in a hard cavity. This leads to systematic deviations from predictions of free-volume models which treat Ps as an effective, single particle. A virial-type estimator is used to calculate the kinetic energy of the particle in the presence of hard walls. This estimator is found to be superior to a kinetic-type estimator given the interaction potentials, cavity sizes, and chain lengths considered in the current study. (C) 2000 American Institute of Physics. [S0021-9606(00)50447-4]

Ames 40 X 80/80 X 120 Foot Wind Tunnel: Turning Vanes Design

A number of different turning vanes are designed for the NASA Ames wind tunnel. Computer codes are used to design and analyze the turning vanes to insure that they comply with their individual constraints. The presentation is given in viewgraph format and displays pressure coefficients for the different turning vanes as well as loss coefficients versus inlet flow angles

Influence of Perinatal Exposure to a Polychlorinated Biphenyl Mixture on Learning and Memory, Hippocampal Size, and Estrogen Receptor-Beta Expression

Author Institution: Department of Biological Sciences, Bowling Green State UniversityAuthor Institution: Department of Psychology, Bowling Green State UniversityPerinatal exposure to PCB has been reported to cause a variety of health effects including endocrine disruption, and immunologic, reproductive, neurologic, and behavioral deficits. In the present study, a mixture of two PCB congeners, one noncoplanar (PCB 47) and one coplanar (PCB 77), were administered to young female Sprague-Dawley rats by route of maternal dietary consumption (either 12.5 ppm or 25.0 ppm, w/w). Impact on learning and memory were examined by radial arm maze on postnatal day 24-27. After behavioral tests were completed, the rats were transcardially perfused, and brains were excised. Immunohistochemistry for ER- β was carried out on free-floating sections. Sections were stained with cresyl violet stain, and hippocampal area was measured. A subjective comparison of staining density suggested a greater intensity of ER- β staining in female rat hippocampus exposed to PCB 47/77 at 25 ppm concentration. A decrease in the hippocampal area measurement was observed in the case of 25 ppm PCB exposed rats. Significant behavioral effects involving spatial learning and memory were not observed. However, animals exposed to PCB 47/77 at 25 ppm displayed a trend toward improved performance. Taken together, the combination in PCB exposed rats of reduced hippocampal size, increased ER-β concentration, and unaltered behavior suggests the existence of compensatory mechanisms in the animals