Challenges of relaxed n -type GaP on Si and strategies to enable low threading dislocation density
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Ryan D. Hool↗
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Origin, Transport, and Vertical Distribution of Atmospheric Polluntants over the Northern Sourth China Sea During the 7-SEAS-Dongsha Experiment
During the spring of 2010, comprehensive in situ measurements were made for the first time on a small atoll (Dongsha Island) in the northern South China Sea (SCS), a key region of the 7-SEAS (the Seven South East Asian Studies) program. This paper focuses on characterizing the source origins, transport processes, and vertical distributions of the Asian continental outflows over the region, using measurements including mass concentration, optical properties, hygroscopicity, and vertical distribution of the aerosol particles, as well as the trace gas composition. Cluster analysis of backward trajectories classified 52% of the air masses arriving at ground level of Dongsha Island as having a continental origin, mainly from northern China to the northern SCS, passing the coastal area and being confined in the marine boundary layer (0-0.5 km). Compared to aerosols of oceanic origin, the fine mode continental aerosols have a higher concentration, extinction coefficient, and single-scattering albedo at 550 nm (i.e., 19 vs. 14 microg per cubic meter in PM(sub 2.5); 77 vs. 59 M per meter in beta(sub e); and 0.94 vs. 0.90 in omega, respectively). These aerosols have a higher hygroscopicity (f at 85% RH = 2.1) than those in the upwind inland regions, suggesting that the aerosols transported to the northern SCS were modified by the marine environment. In addition to the near-surface aerosol transport, a significant upper-layer (3-4 km) transport of biomass-burning aerosols was observed. Our results suggest that emissions from both China and Southeast Asia could have a significant impact on the aerosol loading and other aerosol properties over the SCS. Furthermore, the complex vertical distribution of aerosols-coinciding-with-clouds has implications for remote-sensing observations and aerosol-cloud-radiation interactions.
pollutants↗
Annealing characteristics of irradiated hydrogenated amorphous silicon solar cells
It was shown that 1 MeV proton irradiation with fluences of 1.25E14 and 1.25E15/sq cm reduces the normalized I(sub SC) of a-Si:H solar cell. Solar cells recently fabricated showed superior radiation tolerance compared with cells fabricated four years ago; the improvement is probably due to the fact that the new cells are thinner and fabricated from improved materials. Room temperature annealing was observed for the first time in both new and old cells. New cells anneal at a faster rate than old cells for the same fluence. From the annealing work it is apparent that there are at least two types of defects and/or annealing mechanisms. One cell had improved I-V characteristics following irradiation as compared to the virgin cell. The work shows that the photothermal deflection spectroscopy (PDS) and annealing measurements may be used to predict the qualitative behavior of a-Si:H solar cells. It was anticipated that the modeling work will quantitatively link thin film measurements with solar cell properties. Quantitative predictions of the operation of a-Si:H solar cells in a space environment will require a knowledge of the defect creation mechanisms, defect structures, role of defects on degradation, and defect passivation and annealing mechanisms. The engineering data and knowledge base for justifying space flight testing of a-Si:H alloy based solar cells is being developed.
Payson, J. S.↗
The Cloud Absorption Radiometer HDF Data User's Guide
The purpose of this document is to describe the Cloud Absorption Radiometer (CAR) Instrument, methods used in the CAR Hierarchical Data Format (HDF) data processing, the structure and format of the CAR HDF data files, and methods for accessing the data. Examples of CAR applications and their results are also presented. The CAR instrument is a multiwavelength scanning radiometer that measures the angular distributions of scattered radiation.
Li, Jason Y.↗
New Multispectral Cloud Retrievals from MODIS
The Moderate Resolution Imaging Spectroradiometer (MODIS) was developed by NASA and launched onboard the Terra spacecraft on December 18, 1999. It achieved its final orbit and began Earth observations on February 24, 2000. MODIS scans a swath width sufficient to provide nearly complete global coverage every two days from a polar-orbiting, sun-synchronous, platform at an altitude of 705 km, and provides images in 36 spectral bands between 0.415 and 14.235 micrometers with spatial resolutions of 250 m (2 bands), 500 m (5 bands) and 1000 m (29 bands). These bands have been carefully selected to enable advanced studies of land, ocean, and atmospheric processes. In this paper I will describe the various methods being used for the remote sensing of cloud properties using MODIS data, focusing primarily on the MODIS cloud mask used to distinguish clouds, clear sky, heavy aerosol, and shadows on the ground, and on the remote sensing of cloud optical properties, especially cloud optical thickness and effective radius of cloud drops and ice crystals. Results will be presented of MODIS cloud properties both over the land and over the ocean, showing the consistency in cloud retrievals over various ecosystems used in the retrievals. The implications of this new observing system on global analysis of the Earth's environment will be discussed.
Platnick, Steven↗
Photoluminescence Studies of ZnSe Starting Materials and Vapor Grown Bulk Crystals
Low-temperature photoluminescence (PL) spectra were measured on ZnSe starting materials provided by various vendors and on bulk crystals grown from these starting materials by physical vapor transport (PVT) to study the effects of purification and contamination during PVT process. The impurity levels in one set of starting material/grown crystal were also measured by glow discharge mass spectroscopy (GDMS). The purification effect of pre-growth heat treatments and the PVT process is evidenced from the GDMS results which showed orders of magnitude reduction in the Li and Na concentration and a factor of 3 reduction in the O content after growth. The PL spectra showed that the strong emissions associated with Li (or Na) in one of the starting materials disappeared after growth. The GDMS results also showed increases in the At and Si contents by orders of magnitude after growth. To evaluate the contamination of the crystal during the high temperature growth process, three growth runs were processed using similar growth parameters but different furnace environments. The PL spectra suggest that the At contamination originated from the fused silica ampoule and that the Inconel cartridge might have been the cause of the broad Cu green and Cu red bands observed in one of the grown crystals.
Su, Ching-Hua↗
Gamma-neutrino angular correlations in muon capture.
Using a high-resolution Ge(Li) spectrometer, it proved possible to observe several Doppler-broadened gamma-ray transitions in Al-28 excited by muon capture in Si-28. Several of these transitions are shown to be suitable for analysis in terms of angular correlations between the neutrino and a deexcitation nuclear gamma-ray. The observed transitions are interpreted in terms of gamma-neutrino correlation coefficients which are functions of the weak-interaction coupling constants.
Miller, G. H.↗
Concentrations and Origins of Atmospheric Lead and Other Trace Species at a Rural Site in Northern China
In this study we analyze the ambient levels of lead and other trace species in the bulk aerosol samples from a rural site approx.70 km ESE of Beijing in spring 2005. Lead (0.28+/-0.24 micro-g/cu m, average +/- standard deviation), along with several pollution \related trace elements, was enriched by over 100 fold relative to the Earth's crust. The ambient lead levels showing large synoptic variations were well-correlated with other anthropogenic pollutants (e.g., CO and SO2). The Unmix receptor model resolved four factors in the aerosol composition data: a biomass burning source, an industrial and coal combustion source, a secondary aerosol source, and a dust source. The first three sources were strongest in weak southerly winds ahead of cold fronts, while the dust source peaked in strong northerly winds behind cold fronts. The second source, primarily representing emissions from industrial processes and relatively small \scale coal burning such as in home and institutional heating, was identified as the main source of ambient lead in this study. Mobile sources might also contribute to this factor, but there was no distinct evidence of emissions due to combustion of leaded gasoline, despite a correlation between lead and CO. Potential source contribution function, calculated from backward trajectories and aerosol composition, further reveals that lead observed in this study was predominantly from the populated and industrialized areas to the south and SW of Xianghe, rather than Beijing to the west. Our results and several recent studies show that the lead levels in suburban areas near big cities in China, although generally lower than those in industrial districts and urban areas, are substantial (near or above 0.15 micro-g/cu m). More extensive studies on airborne lead and its emission sources in China are called for.
Li, Can↗
Influence of several metal ions on the gelation activation energy of silicon tetraethoxide
The effects of nine metal cations (Li(+), Na(+), Mg(2+), Ca(2+), Sr(2+), Cu(2+), Al(3+), La(3+), and Y(3+) on silica gel formation has been investigated by studying the hydrolysis and polycondensation of silicon tetraethoxide (TEOS) in the presence of metal nitrates. The influence of water: TEOS mole ratio, metal ion concentration, and the reaction temperature has been investigated. The overall activation energy for gel formation has been determined from the temperature dependence of the time of gelation for each system. The activation energy for -Si-O-Si- network formation is found to be 54.5 kJ/mol. The gel formation time as well as the activation energy sharply increase in the presence of Cu(2+), Al(3+), La(3+) and Y(3+). In contrast, the presence of Li(+), Na(+), Mg(2+), Ca(2+), or, Sr(2+) lowers the gelation time, but has no appreciable effect on the activation energy. This difference may be attributed to the participation or nonparticipation of the metal ions in the formation of the three-dimensional polymeric network during the polycondensation step. The concentration of metal ion (Mg(2+), Ca(2+), Y(3+) or the water: TEOS mole ratio had no appreciable effect on the gelation activation energy. A simple test has been proposed to determine whether a metal ion would act as a network intermediate or modifier in silica and other glassy networks.
Bansal, Narottam P.↗
Influence of several metal ions on the gelation activation energy of silicon tetraethoxide
The effects of nine metal cations Li(+), Na(+), Mg(2+), Ca(2+), Sr(2+), Cu(2+), Al(3+), La(3+), and Y(3+) on silica gel formation has been investigated by studying the hydrolysis and polycondensation of silicon tetraethoxide (TEOS) in the presence of metal nitrates. The influence of water:TEOS mole ratio, metal ion concentration, and the reaction temperature has been investigated. The overall activation energy for gel formation has been determined from the temperature dependence of the time of gelation for each system. The activation energy for -Si-O-Si- network formation is found to be 54.5 kJ/mol. The gel formation time as well as the activation energy sharply increase in the presence of Cu(2+), Al(3+), La(3+) and Y(3+). In contrast, the presence of Li(+), Na(+), Mg(2+), Ca(2+), or Sr(2+) lowers the gelation time, but has no appreciable effect on the activation energy. This difference may be attributed to the participation or nonparticipation of the metal ions in the formation of the three-dimensional polymeric network during the polycondensation step. The concentration of metal ion Mg(2+), Ca(2+), Y(3+) or the water:TEOS mole ratio had no appreaciable effect on the gelation activation energy. A simple test has been proposed to determine whether a metal ion would act as a network intermediate or modifier in silica and other glassy networks.
Bansal, Narottam P.↗
Cross sections relevant to gamma ray astronomy
Gamma-ray production cross sections were measured for protons and alpha particles incident on targets consisting of nuclei of high cosmic abundance: C-12, N-14, O-16, Ne-20, Mg-24, Si-28 and Fe-56. Solid or gaseous targets were bombarded by monoenergetic beams of protons and alpha particles, and gamma rays were detected by two Ge(Li) detectors. The proton energy for each target was varied from threshold to about 24 MeV (lab); for alphas the range was from threshold to about 27 MeV. For most transitions, it was possible to measure the total cross section by placing the detectors at 30.5 deg and 109.9 deg where the fourth-order Legendre polynomial is zero. For the case of the 16O (E sub gamma = 6.13 MeV, multipolarity E3) cross sections, yields were measured at four angles. Absolute cross sections were obtained by integrating the beam current and by measuring target thicknesses and detector efficiencies. The Ge(Li) detector resolution was a few keV (although the peak widths were greater, due to Doppler broadening).
Dyer, P.↗
An Overview of Power, Energy Storage, and Conversion Efforts for 2014 SBIR Phases I and II
Technological innovation is the overall focus of NASA's Small Business Innovation Research (SBIR) program. The program invests in the development of innovative concepts and technologies to help NASA's mission directorates address critical research and development needs for agency projects. NASA's Small Business Innovation Research (SBIR) program focuses on technological innovation by investing in development of innovative concepts and technologies to help NASA mission directorates address critical research needs for Agency programs. This report highlights 15 of the innovative SBIR 2014 Phase I and II projects that focus on one of NASA Glenn Research Center's six core competencies-Power, Energy Storage and Conversion. The technologies cover a wide spectrum of applications such as high-radiation-tolerant ceramic voltage isolators, development of hermetic sealing glasses for solid oxide fuel cells, rechargeable lithium metal cells, high-efficiency direct methane solid oxide fuel cell systems, Li metal protection for high-energy space batteries, isolated bidirectional direct current converters for distributed battery energy applications, and high-efficiency rad-hard ultrathin Si photovoltaic cell technology for space. Each article describes an innovation and technical objective and highlights NASA commercial and industrial applications. This report provides an opportunity for NASA engineers, researchers, and program managers to learn how NASA SBIR technologies could help their programs and projects, and lead to collaborations and partnerships between the small SBIR companies and NASA that would benefit both.
flywheels↗
Investigating the Effects of Gamma Radiation on Selected Chemicals for Use in Biosignature Detection Instruments on the Surface of Jupiter's Moon Europa
Jupiter's moon Europa is a prime target for the search for potential signs of life in the solar system. The Europa Lander Science Definition Team Report outlined investigations and measurement requirements on a future Europa Lander and has led us to consider application of powerful techniques such as pyrolysis and derivatization gas chromatography mass spectrometry (GC-MS) and laser desorption mass spectrometry (LD-MS) to elucidate the organic composition of near-surface ice and minerals. Definitive identification of chemical biosignatures using such techniques is strongly enabled by the use of various chemicals, such as perfluorotributylamine (PFTBA) for the MS calibration, α-cyano-hydroxycinnamic acid (CHCA) for matrix-assisted laser desorption and ionization (MALDI) and N,N-dimethylformamide dimethyl acetal (DMF-DMA), N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA) and tetramethylammonium hydroxide (TMAH) for wet chemistry GC-MS protocols. The jovian radiation environment is known to represent a uniquely challenging risk to mission performance and lifetime, principally due to high radiation levels. To assess the potential ionizing radiation damage to these important chemicals, we tested their effectiveness following gamma radiation exposure doses up to the anticipated Europa Lander rating requirement of 300 krad(Si). The chemicals were sealed in glass ampules under vacuum (<10 mTorr), to reduce trapped oxygen gas, as the oxidation by O2 may be enhanced in the presence of radiation. We report that all five chemicals exposed to total ionizing doses of 0, 150 and 300 krad(Si) maintained their full effectiveness, and no significant degradation was observed.
Radiation↗
The contamination of lunar highland rocks by KREEP - Interpretation by mixing models
A mixing model method was used to determine the component abundance in the Apollo 16 and 17 soils. This method uses the chemical composition of the soils for up to 30 elements and a weighted least-squares mixing model technique. Elements included in the calculations are: Si, Ti, Al, Ca, Fe, Mg, P, Cr, Mn, Na, K, Rb, Ba, U, Th, La, Ce, Sm, Eu, Sr, Yb, Y, Sc, V, Zr, Nb, Co, Ni, Li, Au, and Ir. The method was used to examine the possibility that some of the highland rocks such as VHA and low-K Fra Mauro basalt are mixtures. The results of the mixing model calculations show that it is possible that these rocks are mixtures of KREEP, troctolite, 'anorthosites', and a meteoritic component. The Rb-Sr systematics are consistent with such a model for the genesis of the highland rocks. KREEP has high relative concentrations of Rb, U, and radiogenic Sr and Pb and its model age of about 4.4 AE dominates the model age of all the 'contaminated' highland rocks.
Schonfeld, E.↗
New Multispectral Cloud Retrievals from MODIS
The Moderate Resolution Imaging Spectroradiometer (MODIS) was developed by NASA and launched onboard the Terra spacecraft on December 18, 1999. It achieved its final orbit and began Earth observations on February 24, 2000. MODIS scans a swath width sufficient to provide nearly complete global coverage every two days from a polar-orbiting, sun- synchronous, platform at an altitude of 705 km, and provides images in 36 spectral bands between 0.415 and 14.235 microns with spatial resolutions of 250 m (two bands), 500 m (five bands) and 1000 m (29 bands). In this paper we will describe the various methods being used for the remote sensing of cloud properties using MODIS data, focusing primarily on the MODIS cloud mask used to distinguish clouds, clear sky, heavy aerosol, and shadows on the ground, and on the remote sensing of cloud optical properties, especially cloud optical thickness and effective radius of water drops and ice crystals. Additional properties of clouds derived from multispectral thermal infrared measurements, especially cloud top pressure and emissivity, will also be described. Results will be presented of MODIS cloud properties both over the land and over the ocean, showing the consistency in cloud retrievals over various ecosystems used in the retrievals. The implications of this new observing system on global analysis of the Earth's environment will be discussed.
King, Michael D.↗
Recent Large Reduction in Sulfur Dioxide Emissions from Chinese Power Plants Observed by the Ozone Monitoring Instrument
The Ozone Monitoring Instrument (OMI) aboard NASA's Aura satellite observed substantial increases in total column SO2 and tropospheric column NO2 from 2005 to 2007, over several areas in northern China where large coal-fired power plants were built during this period. The OMI-observed SO2/NO2 ratio is consistent with the SO2/ NO2, emissions estimated from a bottom-up approach. In 2008 over the same areas, OMI detected little change in NO2, suggesting steady electricity output from the power plants. However, dramatic reductions of S0 2 emissions were observed by OMI at the same time. These reductions confirm the effectiveness of the flue-gas desulfurization (FGD) devices in reducing S02 emissions, which likely became operational between 2007 and 2008. This study further demonstrates that the satellite sensors can monitor and characterize anthropogenic emissions from large point sources.
Li, Can↗
Rapid Transpacific Transport in Autumn Observed by the A-Train Satellites
Transpacific transport of dust and pollutants is well documented for spring, but less so for other seasons. Here we investigate rapid transpacific transport in autumn utilizing the A-train satellites. In three episodes studied as examples, SO2 plumes over East Asia were detected by the Ozone Monitoring Instrument aboard the Aura satellite, and found to reach North America in 5-6 days. They were likely derived from anthropogenic sources, given that identical transport patterns of CO, a tracer for incomplete combustion, were simultaneously observed by the Aqua satellite. Trajectory analysis and meteorological data were employed to explore the meteorological circumstances surrounding these events: like many of their counterparts in spring, all three plumes were lifted to the free troposphere in warm conveyor belt associated with mid-latitude wave cyclones, and their migration to downwind region was regulated by the meteorology over the East Pacific. These cases provide further evidence that a fraction of S02 could escape wet scavenging, and be transported at much greater efficiency than NOx (NO + N02). An analysis of the S02 and CO data from September to November during 2005-2008 found 16 S02 long-range transport episodes, out of 62 Asian outflow events. While the counts are sensitive to the choice of criteria, they suggest that the long-range transport of Asian sulfur species occurs quite frequently, and could exert strong impacts on large downstream areas. This study also highlights the importance of transpacific transport in autumn, which has thus far been rarely studied and deserves more attention from the community.
Li. Can↗
An Assessment of Multimodel Simulations for the Variability of Western North Pacific Tropical Cyclones and Its Association with ENSO
An assessment of simulations of the interannual variability of tropical cyclones (TCs) over the western North Pacific (WNP) and its association with El Niño-Southern Oscillation (ENSO), as well as a subsequent diagnosis for possible causes of model biases generated from simulated large-scale climate conditions, are documented in the paper. The model experiments are carried out by the Hurricane Work Group under the U.S. Climate Variability and Predictability Research Program (CLIVAR) using five global climate models (GCMs) with a total of 16 ensemble members forced by the observed sea surface temperature and spanning the 28-yr period from 1982 to 2009. The results show GISS and GFDL model ensemble means best simulate the interannual variability of TCs, and the multimodel ensemble mean (MME) follows. Also, the MME has the closest climate mean annual number of WNP TCs and the smallest root-mean-square error to the observation. Most GCMs can simulate the interannual variability of WNP TCs well, with stronger TC activities during two types of El Niño-namely, eastern Pacific (EP) and central Pacific (CP) El Niño-and weaker activity during La Niña. However, none of the models capture the differences in TC activity between EP and CP El Niño as are shown in observations. The inability of models to distinguish the differences in TC activities between the two types of El Niño events may be due to the bias of the models in response to the shift of tropical heating associated with CP El Niño.
climate models↗