Development of N/P AlGaAs free-standing top solar cells for tandem applications

The combination of a free standing AlGaAs top solar cell and an existing bottom solar cell is the highest performance, lowest risk approach to implementing the tandem cell concept. The solar cell consists of an AlGaAs substrate layer, an AlGaAs base layer, an AlGaAs emitter, and an ultra-thin AlGaAs window layer. The window layer is compositionally graded which minimizes reflection at the window layer/emitter interface and creates a built-in electric field to improve quantum response in the blue region of the spectrum. Liquid phase epitaxy (LPE) is the only viable method to produce this free standing top solar cell. Small (0.125 sq cm), transparent p/n AlGaAs top solar cells were demonstrated with optimum bandgap for combination with a silicon bottom solar cell. The efficiency of an AlGaAs/Si stack using the free standing AlGaAs device upon an existing silicon bottom solar cell is 24 pct. (1X, Air Mass Zero (AM0). The n/p AlGaAs top solar cell is being developed in order to facilitate the wiring configuration. The two terminal tandem stack will retain fit, form, and function of existing silicon solar cells. Progress in the development of large area (8 and 16 sq cm), free standing AlGaAs top solar cells is discussed

Local variations in spatial synchrony of influenza epidemics

Background: Understanding the mechanism of influenza spread across multiple geographic scales is not complete. While the mechanism of dissemination across regions and states of the United States has been described, understanding the determinants of dissemination between counties has not been elucidated. The paucity of high resolution spatial-temporal influenza incidence data to evaluate disease structure is often not available. Methodology and Findings: We report on the underlying relationship between the spread of influenza and human movement between counties of one state. Significant synchrony in the timing of epidemics exists across the entire state and decay with distance (regional correlation = 62%). Synchrony as a function of population size display evidence of hierarchical spread with more synchronized epidemics occurring among the most populated counties. A gravity model describing movement between two populations is a stronger predictor of influenza spread than adult movement to and from workplaces suggesting that non-routine and leisure travel drive local epidemics. Conclusions: These findings highlight the complex nature of influenza spread across multiple geographic scales. © 2012 Stark et al

Radio Astronomy

Contains research objectives and reports on three research projects.U. S. Navy (Office of Naval Research) under Contract Nonr- 3963(02)-Task 2National Aeronautics and Space Administration (Grant NsG-264-62)National Aeronautics and Space Administration (Grant NsG-250-62)National Aeronautics and Space Administration (Contract NaSr-l01

Toward a descriptive model of galactic cosmic rays in the heliosphere

Researchers review the elements that enter into phenomenological models of the composition, energy spectra, and the spatial and temporal variations of galactic cosmic rays, including the so-called anomalous cosmic ray component. Starting from an existing model, designed to describe the behavior of cosmic rays in the near-Earth environment, researchers suggest possible updates and improvements to this model, and then propose a quantitative approach for extending such a model into other regions of the heliosphere

Co/Ni element ratio in the galactic cosmic rays between 0.8 and 4.3 GeV/nucleon

In a one-day balloon flight of the Trans-Iron Galactic Element Recorder (TIGER) in 1997, the instrument achieved excellent charge resolution for elements near the Fe peak, permitting a new measurement of the element ratio Co/Ni. The best fit to the data, extrapolated to the top of the atmosphere, gives an upper limit for this ratio of 0.093±0.037 over the energy interval 0.8 to 4.3 GeV/nucleon; because a Co peak is not seen in the data, this result is given as an upper limit. Comparing this upper limit with calculations by Webber & Gupta suggests that at the source of these cosmic rays a substantial amount of the electron-capture isotope 59Ni survived. This conclusion is in conflict with the clear evidence from ACE/CRIS below 0.5 GeV/nucleon that there is negligible 59Ni surviving at the source. Possible explanations for this apparent discrepancy are discussed

Cosmic-Ray Spectra in Interstellar Space

At energies below ~300 MeV/nuc our knowledge of cosmic-ray spectra outside the heliosphere is obscured by the energy loss that cosmic rays experience during transport through the heliosphere into the inner solar system. This paper compares measurements of secondary electron-capture isotope abundances and cosmic-ray spectra from ACE with a simple model of interstellar propagation and solar modulation in order to place limits on the range of interstellar spectra that are compatible with both sets of data

GCR Neon Isotopic Abundances: Comparison with Wolf-Rayet Star Models and Meteoritic Abundances

Measurements of the neon isotopic abundances from the ACE-CRIS experiment are presented. These abundances have been obtained in seven energy intervals over the energy range of ~80≤E≤280 MeV/nucleon. The ^(22)Ne/^(20)Ne source ratio is derived using the measured ^(21)Ne/^(20)Ne abundance as a "tracer" of secondary production of the neon isotopes. We find that the ^(22)Ne/^(20)Ne abundance ratio at the cosmic-ray source is a factor of 5.0±0.2 greater than in the solar wind. The GCR ^(22)Ne/^(20)Ne ratio is also shown to be considerably larger than that found in anomalous cosmic rays, solar energetic particles, most meteoritic samples of matter, and interplanetary dust particles. Recent two-component Wolf-Rayet models provide predictions for the ^(22)Ne/^(20)Ne ratio and other isotope ratios. Comparison of the CRIS neon, iron, and nickel isotopic source abundance ratios with predictions indicate possible enhanced abundances of some neutron-rich nuclides that are expected to accompany the ^(22)Ne excess