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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Monolithically interconnected GaAs solar cells: A new interconnection technology for high voltage solar cell output

Photovoltaic linear concentrator arrays can benefit from high performance solar cell technologies being developed at AstroPower. Specifically, these are the integration of thin GaAs solar cell and epitaxial lateral overgrowth technologies with the application of monolithically interconnected solar cell (MISC) techniques. This MISC array has several advantages which make it ideal for space concentrator systems. These are high system voltage, reliable low cost monolithically formed interconnections, design flexibility, costs that are independent of array voltage, and low power loss from shorts, opens, and impact damage. This concentrator solar cell will incorporate the benefits of light trapping by growing the device active layers over a low-cost, simple, PECVD deposited silicon/silicon dioxide Bragg reflector. The high voltage-low current output results in minimal 12R losses while properly designing the device allows for minimal shading and resistance losses. It is possible to obtain open circuit voltages as high as 67 volts/cm of solar cell length with existing technology. The projected power density for the high performance device is 5 kW/m for an AMO efficiency of 26% at 1 5X. Concentrator solar cell arrays are necessary to meet the power requirements of specific mission platforms and can supply high voltage power for electric propulsion systems. It is anticipated that the high efficiency, GaAs monolithically interconnected linear concentrator solar cell array will enjoy widespread application for space based solar power needs. Additional applications include remote man-portable or ultra-light unmanned air vehicle (UAV) power supplies where high power per area, high radiation hardness and a high bus voltage or low bus current are important. The monolithic approach has a number of inherent advantages, including reduced cost per interconnect and increased reliability of array connections. There is also a high potential for a large number of consumer products. Dual-use applications can include battery chargers and remote power supplies for consumer electronics products such as portable telephones/beepers, portable radios, CD players, dashboard radar detectors, remote walkway lighting, etc.

Dinetta, L. C.↗
NASA NTRS2000

Defining the Vortex Boundary Using N2O Measurements

Defining the stratospheric vortex boundary is typically done using; the Nash criterion,(a) which determines the maximum gradient of Ertel's potential vorticity (EPV) in the vicinity of maximum zonal winds. However, such a procedure is insensitive to small-scale variations near the boundary, because EPV maps rely on interpolation from sparse data, and are therefore only accurate over large areas. An examination was made of high-speed N2O measurements during SOLVE, from Argus ER-2 flights across the vortex boundary in the 1999-2000 Arctic winter, to see whether sharp changes in N2O concentrations co-occur sufficiently well with the Nash definition of the vortex edge to serve as a reliable alternate definition.

Greenblatt, Jeffery↗
NASA NTRS2006

March 2003 EOS Aqua AMSR-E Arctic Sea Ice Field Campaign

An overview of the March 2003 coordinated sea ice field campaign in the Alaskan Arctic is presented with reference to the papers in this special section. This campaign is part of the program to validate the Aqua Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) sea ice products. Standard AMSR-E sea ice products include sea ice concentration, sea ice temperature, and snow depth on sea ice. The validation program consists of three elements, namely: 1) satellite data comparisons; 2) coordinated satellite/aircraft surface measurements; and 3) modeling and sensitivity analyses. Landsat-7 and RADARSAT observations were used in comparative studies with the retrieved AMSR-E sea ice concentrations. The aircraft sensors provided high-resolution microwave imagery of the surface, atmospheric profiles of temperature and humidity, and digital records of sea ice conditions. When combined with in situ measurements, aircraft data were used to validate the AMSR-E sea ice temperature and snow-depth products. The modeling studies helped interpret the field-data comparisons, provided insight on the limitations of the AMSR-E sea ice algorithms, and suggested potential improvements to the AMSR-E retrieval algorithms.

Cavalieri, Donald J.↗
NASA NTRS2008

Acid Vapor Weathering of Apatite and Implications for Mars

Phosphorus is an essential nutrient for terrestrial life, and therefore may be important in characterizing habitability on Mars. In addition, phosphate mobility on Mars has been postulated as an indicator of early aqueous activity [1]. Rock surfaces analyzed by the Spirit Mars Exploration Rover indicate elemental concentrations consistent with the loss of a phosphate-containing mineral [2], and the highly altered Paso Robles deposit contains ~5% P2O5, modeled as 8-10 % phosphate [3]. Depending on the pH of the solution, phosphate can exist as one of four charge states, which can affect its solubility, reactivity and mobility. Phosphate may therefore prove a useful and interesting tracer of alteration conditions on Mars. Acid vapor weathering has been previously studied as a potentially important process on Mars [4-6], and Paso Robles may have been formed by reaction of volcanic vapors with phosphate-bearing rock [3, 7]. Here we present preliminary results of acid vapor reactions in a Parr vessel [6] using fluorapatite, olivine and glass as single phases and in a mixture.

Hausrath, E. M.↗
NASA NTRS2016

Characterization of Particulate Matter Profiling and Alveolar Deposition from Biomass Burning in Northern Thailand: The 7-SEAS Study

Biomass burning (BB) frequently occurs in SouthEast Asia (SEA), which significantly affects the air quality and could consequently lead to adverse health effects. The aim of this study was to characterize particulate matter (PM) and black carbon (BC) emitted from BB source regions in SEA and their potential of deposition in the alveolar region of human lungs. A 31-day characterization of PM profiling was conducted at the Doi Ang Khang (DAK) meteorology station in northern Thailand in March 2013. Substantial numbers of PM (10147 +/- 5800 # per cubic centimeter) with a geometric mean diameter (GMD) of 114.4 +/- 9.2 nm were found at the study site. The PM of less than 2.5 micron in aerodynamic diameter (PM sub 2.5) hourly-average mass concentration was 78.0 +/- 34.5 per cubic microgram whereas the black carbon (BC) mass concentration was 4.4 +/- 2.6 micrograms per cubic meter. Notably, high concentrations of nanoparticle surface area (100.5 +/- 54.6 square micrometers per cubic centimeter) emitted from biomass burning can be inhaled into the human alveolar region. Significant correlations with fire counts within different ranges around DAK were found for particle number, the surface area concentration of alveolar deposition, and BC. In conclusion, biomass burning is an important PM source in SEA, particularly nanoparticles, which has high potency to be inhaled into the lung environment and interact with alveolar cells, leading to adverse respiratory effects. The fire counts within 100 to 150 km shows the highest Pearson's r for particle number and surface area concentration. It suggests 12 to 24 hr could be a fair time scale for initial aging process of BB aerosols. Importantly, the people lives in this region could have higher risk for PM exposure.

biomass burning↗
NASA NTRS2019

Decadal-Scale Vegetation Change Driven by Salinity at Leading Edge of Rising Sea Level

As sea levels rise, low-lying coastal forests increasingly are subject to stressors such as inundation and saltwater exposure. At long timescales (for example, centuries), the extent of inundation and saltwater exposure will increase; however, on a decadal timescale, the role of these drivers may differ in both magnitude and direction. To investigate the drivers of decadal-scale vegetation change, we measured the changes in five metrics of vegetation composition and structure between 2003/2004 and 2016/ 2017 at 98 plots distributed across a vegetation gradient from coastal forest to brackish marshes (< 0.5–18 ppt). We used elevation as a proxy of inundation vulnerability and soil sodium concentration as a proxy of saltwater exposure, and we investigated relationships between these two variables and the change in vegetation conditions between the two sampling periods. Soil sodium concentration was a significant predictor of vegetation change for all five vegetation metrics, whereas the effect of elevation was not significant for any of the metrics. The one site that was affected by wildfire twice during the duration of the study shifted almost completely from forest to marsh with limited regeneration ofwoody vegetation observed in 2016/ 2017. Our results show that salinization in our system is a more important driver of vegetation change than inundation potential. Furthermore, the effects of drought-induced salinization could be amplified by the elevated risk of wildfire during droughts. Forecasting the response of coastal wetlands to rising sea levels will require a better understanding of the individual and combined effects of salinity, droughts, and wildfires on vegetation.

Taillie, Paul J.↗
NASA NTRSDate not supplied

SPACEFLIGHT-INDUCED CHANGES IN MICROBIAL VIRULENCE AND THE IMPACT TO THE HOST IMMUNE RESPONSE

INTRODUCTION Over the past 50 years, microorganisms have displayed unexpected responses relevant to infectious disease when grown in microgravity and microgravity analogue environments, including changes in final cell concentration, biofilm production, stress resistance, antibiotic sensitivity, gene expression, and virulence. In parallel, astronaut studies have characterized a persistent spaceflight-induced dysregulation of the human immune system; consisting of altered leukocyte distribution, reductions in T and NK cell function, altered cytokine profiles, and reactivation of latent herpesviruses. Further, astronauts have some degree of clinical incidence, primarily infectious disease episodes and atopic dermatitis. The impact of the microgravity environment on host-pathogen interactions and potential for clinical disease remains understudied and poorly characterized. SPECIFIC AIMS In the Host-Microorganism, Microbial Response aspect of this study, the following Specific Aims are being investigated, using the microbial pathogens, Salmonella enterica Enteritidis, Pseudomonas aeruginosa, Burkholderia cepacia, Streptococcus pneumoniae, and enterohemorrhagic Escherichia coli. Aim 1: Characterize the effect of spaceflight analogue culture on microbial pathogenesis-related stress responses and in vitro host-pathogen interactions. Analysis will include microbial stress responses as well as colonization and viability following pathogen challenge of three-dimensional (3-D) tissue co-culture models containing immune cells. We specifically selected obligate and opportunistic pathogens that are medically important and have been or are likely to be found aboard spacecraft. Aim 2: Characterize the effect of spaceflight analogue culture on the virulence potential of pathogenic microorganisms. Changes in virulence will be assessed using a mouse model of infection. SIGNIFICANCE The goal of this study is to use spaceflight analogue conditions to gain insight into the breadth of medically-significant International Space Station microorganisms that have altered virulence and the impact of those changes on the immune response of the host, including astronaut immune cells. This information will provide critical understanding into the impact of microgravity on potential alterations in microbial virulence and associated infectious disease risk to crew health during spaceflight missions.

C. M. Ott↗
NASA NTRS1984

Concentrations and isotope ratios of carbon, nitrogen and sulfur in ocean-floor basalts

Ocean floor basalts studied from the Galapagos Ridge, FAMOUS area, Cayman Trough and Kilauea east rift contain 20-200 ppm carbon and 0.3-2.8 ppn nitrogen as sums of the vesicle-filling gases CO2 and N2 and dissolved species. The wide range of carbon contents found is due partly to the different extent of outgassing of vesicle-filling gases and partly to depth dependency of dissolved CO2 in the basalts. Sulfate commonly exists with sulfide in these basalts, and the sulfate/sulfide ratio increases with increasing water content, perhaps reflecting the higher oxidation potential in basalt melt of the higher water content.

Sakai, H.↗
NASA NTRS1983

Homogeneous nucleation kinetics

Homogeneous nucleation kinetics are rederived in a manner fundamentally similar to the approach of classical nucleation theory with the following modifications and improvements. First, the cluster is a parent phase cluster and does not require energization to the parent state. Second, the thermodynamic potential used to describe phase stability is a continuous function along the pathway of phase decomposition. Third, the kinetics of clustering corresponds directly to the diffusional flux of monomers through the cluster distribution and are formally similar to classical theory with the resulting kinetic equation modified by two terms in the preexponential factor. These terms correct for the influence of a supersaturation dependent clustering within the parent phase and for the influence of an asymmetrical cluster concentration as a function of cluster size at the critical cluster size. Fourth, the supersaturation dependence of the nucleation rate is of the same form as that given by classical nucleation theory. This supersaturation dependence must however be interpreted in terms of a size dependent surface tension. Finally, there are two scaling laws which describe supersaturation to either constant nucleation rate or to the thermodynamically determined physical spinodal.

Rasmussen, D. H.↗
NASA NTRS1985

Progress in stratospheric hydroxyl measurement by balloon-borne lidar

Knowledge of the concentration of hydroxyl radical is crucial to understanding the chemistry of the stratosphere. Hydroxyl participates in several catalytic cycles which destroy ozone and strongly influences the cycles of chlorine and nitrogen oxides by its reactions which form or destroy reservoirs for chlorine and odd-nitrogen compounds. Measurements have been conducted of the concentration of hydroxyl radical between the altitudes of 32.5 and 38.5 km using the technique of laser-induced fluorescence. The results ranging from 4 to 9 x 10 to the 6th per cu cm (with an accuracy of + or - 50 percent) are about 2-3 times lower than predicted by current one-dimensional models, although the uncertainties in the determination and in the models are sufficiently large to explain the differences. A number of potential improvements to the instrument are discussed.

Heaps, W. S.↗
NASA NTRS1986

Integrated Thermal-structural-electromagnetic Design Optimization of Large Space Antenna Reflectors

The requirements for low mass and high electromagnetic (EM) performance in large, flexible space antenna structures is motivating the development of a systematic procedure for antenna design. In contrast to previous work which concentrated on reducing rms distortions of the reflector surface, thereby indirectly increasing antenna performance, the current work involves a direct approach to increasing electromagnetic performance using mathematical optimization. The thermal, structural, and EM analyses are fully integrated in the context of an optimization procedure, and consequently, the interaction of the various responses is accounted for directly and automatically. Preliminary results are presented for sizing cross-sectional areas of a tetrahedral truss reflector. The results indicate potential for this integrated procedure from the standpoint of mass reduction, performance increase, and efficiency of the design process.

Adelman, H. M.↗
NASA NTRS1989

Mineralogical sinks for biogenic elements on Mars

The efficacy of biochemical reactions on Mars should depend not only on concentrations of the biogenic elements H, C, N, O, and S but also on the forms (compounds and water-souble ions) that are available to those elements. It is possible that mineralogical reactions could act to lock biogenic elements into relatively inaccessible inorganic forms or, alternatively, to shelter sensitive organic compounds from chemically hostile environments. Recognition of these competing pathways is essential in planning sampling mission and in situ experiments directed toward assessing the biological potential of Mars.

Gooding, J. L.↗
NASA NTRS1994

On the relevance of the methane oxidation cycle to ozone hole chemistry

High concentrations of active chlorine are clearly responsible for the observed ozone depletion during the Antarctic polar spring. However, the mechanism behind the activation of chlorine from the reservoirs species HCl and ClONO2 and the maintenance of extremely high levels of active chlorine after polar sunrise is less well understood. Here, we focus on the influence of the methane oxidation cycle on 'ozone hole' chemistry through its effect on HOx and ClOx radicals. We demonstrate the great potential importance of the heterogeneous reaction HCl + HOCl yields Cl2 + H2O and the gasphase reaction ClO + CH3O2 yields ClOO + CH3O under sunlight conditions in polar spring. Under these conditions, the heterogeneous reaction is the main sink for HOx radicals. Through this channel, the HCl reservoir may be almost completely depleted. The gas phase reaction may control the levels of the CH3O2 radical, provided that high levels of ClO exist. Otherwise this radical initiates a sequence of reactions leading to a considerable loss of active chlorine. Moreover, the production of HOx radicals is reduced, and thereby the efficiency of the heterogeneous reaction limited. The two reactions together may accomplish the complete conversion of HCl into active chlorine, thereby leading to a rapid destruction of ozone.

Mueller, Rolf↗
NASA NTRS1993

Solubility and cation exchange in phosphate rock and saturated clinoptilolite mixtures

Mixtures of zeolite and phosphate rock (PR) have the potential to provide slow-release fertilization of plants in synthetic soils by dissolution and ion-exchange reactions. This study was conducted to examine solubility and cation-exchange relationships in mixtures of PR and NH4- and K-saturated clinoptilolite (Cp). Batch-equilibration experiments were designed to investigate the effect of PR source, the proportion of exchangeable K and NH4, and the Cp to PR ratio on solution N, P, K, and Ca concentrations. The dissolution and cation-exchange reactions that occurred after mixing NH4- and K-saturated Cp with PR increased the solubility of the PR and simultaneously released NH4 and K into solution. The more reactive North Carolina (NC) PR rendered higher solution concentrations of NH4 and K when mixed with Cp than did Tennessee (TN) PR. Solution P concentrations for the Cp-NC PR mixture and the Cp-TN PR mixture were similar. Solution concentrations of N, P, K, and Ca and the ratios of these nutrients in solution varied predictably with the type of PR, the Cp/PR ratio, and the proportions of exchangeable K and NH4 on the Cp. Our research indicated that slow-release fertilization using Cp/PR media may provide adequate levels of N, P, and K to support plant growth. Solution Ca concentrations were lower than optimum for plant growth.

NASA Discipline Number 61-10↗
NASA NTRS2015

Investigation of Gas Seeding for Planar Laser-Induced Fluorescence in Hypersonic Boundary Layers

Numerical simulations of the gas-seeding strategies required for planar laser-induced fluorescence in a Mach 10 (approximately Mach 8.2 postshock) airflow were performed. The work was performed to understand and quantify the adverse effects associated with gas seeding and to assess various types of seed gas that could potentially be used in future experiments. In prior experiments, NO and NO2 were injected through a slot near the leading edge of a flatplate wedge model used in NASA Langley Research Center's 31 in. Mach 10 air tunnel facility. In this paper, nitric oxide, krypton, and iodine gases were simulated at various injection rates. Simulations showing the deflection of the velocity boundary layer for each of the cases are presented. Streamwise distributions of velocity and concentration boundary-layer thicknesses, as well as vertical distributions of velocity, temperature, and mass distributions, are presented for each of the cases. A comparison between simulated streamwise velocity profiles and experimentally obtained molecular tagging velocimetry profiles using a nitric oxide seeding strategy is performed to verify the influence of such a strategy on the boundary layer. The relative merits of the different seeding strategies are discussed. The results from a custom solver based on OpenFOAM version 2.2.1 are compared against results obtained from ANSYS® Fluent version 6.3.

Arisman, C. J.↗
NASA NTRS2017

Successful Validation of RNA Purification and Quantitative Real-Time PCR Analysis of Gene Expression on the International Space Station

The NASA Ames WetLab-2 system was developed to offer new on-orbit gene expression analysis capabilities to ISS researchers and can be used to conduct on-orbit RNA isolation and quantitative real time PCR (RT-qPCR) analysis of gene expression from a wide range of biological samples ranging from microbes to mammalian tissues. On orbit validation included three quantitative PCR (qPCR) runs using an E. coli genomic DNA template pre-loaded at three different concentrations. The flight Ct values for the DNA standards showed no statistically significant differences relative to ground controls although there was increased noise in Ct curves, likely due to microgravity-related bubble retention in the optical windows. RNA was successfully purified from both E. coli and mouse liver samples and successfully generated singleplex, duplex and triplex data although with higher standard deviations than ground controls, also likely due to bubbles. Using volunteer science activities, a potential bubble reduction strategy was tested and resulted in smooth amplification curves and tighter Cts between replicates. The WetLab-2 validation experiment demonstrates a novel molecular biology workbench on ISS which allows scientists to purify and stabilize RNA, and to conduct RT-qPCR analyses on-orbit with rapid results. This novel ability is an important step towards utilizing ISS as a National Laboratory facility with the capability to conduct and adjust science experiments in real time without sample return, and opens new possibilities for rapid medical diagnostics and biological environmental monitoring on ISS.

microgravity↗
NASA NTRS2023

Salt Distribution from Freezing Intrusions in Ice Shells on Ocean Worlds: Application to Europa

Several icy moons and dwarf planets appear to have hosted subsurface liquid water. Liquid water intruding upwards into the icy outer shells of these worlds freezes, forming ice and (from ocean solutes) non-ice solids. Here, we model concentrated aqueous solutions below 273 K to simulate the compositional evolution of freezing spherical intrusions. Starting solutions are based on five previously reported compositional end members for Europa's ocean. For moderate-pH end members dominated by chloride, sulfate, and/or carbonate, the solids formed include Ca-, Mg-, and Na-sulfates and -carbonates, as well as Na- and K-chlorides. For silica-rich, high-pH end members, abundant amorphous silica forms with, potentially, similarly abundant NaOH and KOH. We further develop a new numerical model to compute the spatial distribution of the formed solids and residual brine as freezing progresses. If non-ice solids settle to the bottom, their deposits tend to have stacked hourglass shapes, widening each time the crystallization temperature of a new solid is reached. We discuss the applicability of this model to vertical fractures and global freezing of a subsurface ocean. These results inform (i) how compositional heterogeneities may affect the thermophysical properties of ice shells, which in turn influence convective and cryovolcanic transport, (ii) the compatibility of brine pockets with physicochemical conditions suitable for microbial life, and (iii) possible measurements of compositional heterogeneities within ice shells by spacecraft such as NASA's Europa Clipper and ESA's JUICE missions. The methodology developed here is applicable to other ice-covered ocean worlds.

Planetary structure↗
NASA NTRSDate not supplied

Utilizing Radiocarbon and Thermo-optical Measurements to Quantify Source Contributions for Aircraft Engine Particulate Emissions

Recent technological advancements in aircraft engine technology and fuel sources have promising potential for reducing particulate emissions from aircraft engines. During the 2022 Boeing ecoDemonstrator ground-based field campaign, particle and trace gas emissions were sampled for four different fuels, including 100% sustainable aviation fuel (SAF), petroleum-based Jet A fuel, petroleum-based Jet A low sulfur fuel, and a SAF blend. Particulate emissions were collected on quartz microfiber filters and analysed for their radiocarbon content and their elemental carbon (EC) and organic carbon (OC) concentrations. In addition, the radiocarbon content of Jet A fuel, SAF, and aircraft engine oil was also measured. We used the radiocarbon content of the particulate emissions samples and source end members to quantify the relative contribution from engine oil and fuel to carbonaceous aerosol emissions. The results from this study can be used to understand how the implementation of technological advancements in aircraft engine technology and fuel sources will likely impact future aircraft particulate emissions.

Liz Wiggins↗