Search NASA⌕ Search

SEARCH · Search NASA

Results for “solar absorption cooling”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

The calculation of theoretical chromospheric models and the interpretation of solar spectra from rockets and spacecraft

Calculated results based on two chromospheric flare models F1 and F2 of Machado, et al., (1980) are presented. Two additional models are included: F1*, which has enhanced temperatures relative to the weak-flare model F1 in the upper photosphere and low chromosphere, and F3 which has enhanced temperatures relative to the strong flare model F2 in the upper chromosphere. Each model is specified by means of a given variation of the temperature as a function of column mass. The corresponding variation of particle density and the geometrical height scale are determined by assuming hydrostatic equilibrium. The coupled equations of statistical equilibrium is solved as is radiative transfer for H, H-, He I-II, C I-IV, Si I-II, Mg I-II, Fe, Al, O I-II, Na, and Ca II. The overall absorption and emission of radiation by lines throughout the spectrum is determined by means of a reduced set of opacities sampled from a compilation of over 10 to the 7th power individual lines. That the white flight flare continuum may arise by extreme chromospheric overheating as well as by an enhancement of the minimum temperature region is also shown. The radiative cooling rate calculations for our brightest flare model suggest that chromospheric overheating provides enhanced radiation that could cause significant heating deep in the flare atmosphere.

Avrett, E. H.↗
NASA NTRS2015

Investigating Sensitivity to Saharan Dust in Tropical Cyclone Formation Using Nasa's Adjoint Model

As tropical cyclones develop from easterly waves coming of the coast of Africa they interact with dust from the Sahara desert. There is a long standing debate over whether this dust inhibits or advances the developing storm and how much influence it has. Dust can surround the storm and absorb incoming solar radiation, cooling the air below. As a result an energy source for the system is potentially diminished, inhibiting growth of the storm. Alternatively dust may interact with clouds through micro-physical processes, for example by causing more moisture to condense, potentially increasing the strength. As a result of climate change, concentrations and amount of dust in the atmosphere will likely change. It it is important to properly understand its effect on tropical storm formation. The adjoint of an atmospheric general circulation model provides a very powerful tool for investigating sensitivity to initial conditions. The National Aeronautics and Space Administration (NASA) has recently developed an adjoint version of the Goddard Earth Observing System version 5 (GEOS-5) dynamical core, convection scheme, cloud model and radiation schemes. This is extended so that the interaction between dust and radiation is also accounted for in the adjoint model. This provides a framework for examining the sensitivity to dust in the initial conditions. Specifically the set up allows for an investigation into the extent to which dust affects cyclone strength through absorption of radiation. In this work we investigate the validity of using an adjoint model for examining sensitivity to dust in hurricane formation. We present sensitivity results for a number of systems that developed during the Atlantic hurricane season of 2006. During this period there was a significant outbreak of Saharan dust and it is has been argued that this outbreak was responsible for the relatively calm season. This period was also covered by an extensive observation campaign. It is shown that the adjoint can provide insight into the sensitivity and reveals a relatively low sensitivity to dust compared to, for example, the thermodynamic variables. However a secondary sensitivity though moisture is seen. If dust dries the air it can significantly reduce the cyclone intensity through the moisture.

Tropical Cyclones↗
NASA NTRS2003

A New Fitting Procedure for the Blended He I 1083 nm Multiplet

The He I 1083 nm multiplet is a powerful tool for observing the outer solar atmosphere but is difficult to analyze because the lines are weak, highly variable, and spectrally blended, both internally and with other neighboring solar and telluric lines. After separation from nearby spectral features, two components of the He I multiplet are resolved. Fitting these lines with two unconstrained Gaussian profiles always gives a ratio of major to minor component of less than half the value which would be expected for optically thin lines. One possibility for explaining the discrepancy between the weakness of the lines and the ratio of the spectral components is to assume that the line formation regions are concentrated in laterally unresolved, optically thick structures with small filling factor. However, we present here a least-squares fitting technique using cubic splines with fixed breakpoints with the constraint that the blend is the sum of three identically shaped profiles shifted in wavelength according to the atomic structure of the blend and weighted by the corresponding statistics weights, in agreement with optically thin line formation. The basis functions for the fitting procedure have no built-in spectral symmetry or shape. The resulting underlying profiles tend to be asymmetric with excess absorption to the blue, consistent with formation by "hot" and "cool" spatial elements within the observed volume, with the hotter regions having differential motion toward the observer. The results agree well with NASA/XSO Spectromagnetograph observations in quiet sun and coronal holes. Partial funding of this research was provided through the NASA Sun-Earth Connection SR&T program.

Jones, H. P.↗
NASA NTRS2012

The Fast Evolution of SN 2010bh Associated with XRF 100316D

The first observational evidence of a connection between supernovae (SNe) and gamma-ray bursts (GRBs) was found about a decade ago. Since then, only half a dozen spectroscopically confirmed associations have been discovered and XRF 1003160 associated with the type-Ic SN 20lObh is among the latest. Aims. We constrain the progenitor radius, the host-galaxy extinction, and the physical parameters of the explosion of XRF l00316D/SN 20lObh at z 0.059. We study the SN brightness and colours in the context of GRB-SNe. Methods. We began observations with the Gamma-Ray burst Optical and Near-infrared Detector (GROND) 12 hours after the GRB trigger and continued until 80 days after the burst. GROND provided excellent photometric data in six filter bands covering a wavelength range from approximately 350 to 1800 nm, significantly expanding the pre-existing data set for this event. Combining GROND and Swift data, the early broad-band spectral energy distribution (SED) is modelled with a blackbody and afterglow component attenuated by dust and gas absorption. The temperature and radius evolution of the thermal component are analysed and combined with earlier measurements available from the literature. Templates of SN 1998bw are fitted to the SN itself to directly compare the lightcurve properties. Finally, a two-component parametrized model is fitted to the quasi-bolometric light curve. which delivers physical parameters of the explosion. Results. The best-fit models to the broad-band SEDs imply moderate reddening along the line of sight through the host galaxy (A(sub v.host = 1.2 +/- 0.1 mag). Furthermore, the parameters of the blackbody component reveal a cooling envelope at an apparent initial radius of 7 x 10(exp 11) cm, which is compatible with a dense wind surrounding a Wolf-Rayet star. A multicolor comparison shows that SN 2010bh is 60 - 70% as bright as SN 1998bw. Reaching maximum brightness at 8 - 9 days after the burst in the blue bands, SN 20lObh proves to be the most rapidly evolving GRB-SNe to date. Modelling of the quasi-bolometric light curve yields M(sub Ni) = 0.21 +/- 0.03 solar M and M(sub ej) = 2.6 +/- 0.2 solar M, typical of values within the GRB-SN population. The kinetic energy is E(sub k) = (2.4 +/- 0.7) x 10(exp 52) erg, which is making this SN the second most energetic GRB-SN after SN 1998bw. Conclusions. This supernova has one of the earliest peaks ever recorded and thereafter fades more rapidly than other GRB-SNe, hypernovae, or typical type-Ic SNe. This could be explained by a thin envelope expanding at very high velocities, which is therefore unable to retain the gamma-rays that would prolong the duration of the SN event.

Olivares E., F.↗
NASA NTRS2014

Optical Properties of Nanosatellite Hardware

Over the last decade, a number of very small satellites have been launched into space. These have been called nanosatellites (generally of a weight between 1 and 10 kg) or picosatellites (weight <1 kg). This also includes CubeSats, which are based on 10-cm cube units. With the addition of the Japanese Experiment Module (JEM) Small Satellite Orbital Deployer (J-SSOD) to the International Space Station (ISS), CubeSats are easily cycled through the JEM airlock and deployed into space (fig. 1). The number of CubeSats launched since 2003 was approaching 100 at the time of publication, and the authors expect this trend in research to continue, particularly for high school and college flight experiments. Because these spacecraft are so small, there is usually no allowance for shielding or active heating or cooling of the avionics and other hardware. Parts that are usually ignored in the thermal analysis of larger spacecraft may contribute significantly to the heat load of a tiny satellite. In addition, many small satellites have commercial-off-the-shelf (COTS) components. To reduce costs, many providers of COTS components do not include the optical and physical parameters necessary for accurate thermal analysis. Marshall Space Flight Center participated in the development and analysis of the Space Missile Defense Command-Operational Nanosatellite Effect (SMDC-ONE) and the Edison Demonstration of Smallsat Networks (EDSN) nanosatellites. These optical property measurements are documented here in hopes that they may benefit future nanosatellite and picosatellite programs and aid thermal analysis to ensure project goals are met, with the understanding that material properties may vary by vendor, batch, manufacturing process, and preflight handling. Where possible, complementary data are provided from ground simulations of the space environment and flight experiments, such as the Materials on International Space Station Experiment (MISSE) series. NASA gives no recommendation, endorsement, or preference, either expressed or implied, concerning materials and vendors used. Solar absorptance was calculated from spectral reflectance measurements made from 250 to 2,800 nm with an AZ Technology Laboratory Portable Spectroreflectometer (LPSR) model 300. ASTM E-903 was the test method used under normal laboratory conditions, and ASTM E-490 was the solar spectral irradiance data used to calculate solar absorptance. Most of the samples were flat, but stray light was minimized as much as possible with either a blackbody or black cloth as sample background. The LPSR has repeatability of approximately +/-1%, where solar absorptance is given as range, that is, from actual measurements taken across the sample. Infrared emittance measurements were made with an AZ Technology TEMP 2000A infrared reflectometer. This instrument measures the total hemispheric reflectance averaged over 3-35 micrometer wavelengths. ASTM E-408 was the test method used under normal laboratory conditions. 3 Stray light was minimized as much as possible. The TEMP 2000A has repeatability of approximately +/-0.5%, where infrared emittance is given as a range, that is, from actual measurements taken across the sample.

Finckenor, M. M.↗
DOE OSTI2024

Tuning the spontaneous exchange bias effect in La 1.5 Sr 0.5 CoMnO 6 with sintering temperature

Here, in this study, we present a study of the influence of microstructure on the magnetic properties of polycrystalline samples of the La 1.5 Sr 0.5 CoMnO 6 double perovskite, with primary attention to the spontaneous exchange bias effect, a fascinating recently discovered phenomena for which some materials exhibit unidirectional magnetic anisotropy after being cooled in zero magnetic fields. By sintering La 1.5 Sr 0.5 CoMnO 6 at different temperatures, we obtained samples with distinct average grain sizes, ranging from 1.54-6.65 μm. A detailed investigation of the material's structural, morphologic, electronic, and magnetic properties using x-ray powder diffraction, powder neutron diffraction, x-ray absorption near edge structure spectroscopy, scanning electron microscopy, and ac and dc magnetometry has revealed a systematic enhancement of the exchange bias effect with increasing the average grain size. This evolution is discussed in terms of changes in the material's porosity and grain morphology and its influence on the exchange couplings at the magnetic interfaces.

14 SOLAR ENERGY↗
DOE OSTI2025

Passive radiative thermal management using phase-change metasurfaces

Abstract Realizing innovative composite materials with passive thermal management capabilities and minimal ecological footprints is a challenging but much sought-after goal that would have a transformative effect on renewable energy sciences. We demonstrate an environmentally friendly metasurface utilizing vanadium dioxide (VO 2 ) that offers responsiveness to ambient temperature and potentially long-term stability. The metasurface enables passive thermal management by self-adjusting its absorptivity and emissivity response over a broad bandwidth ranging from visible to mid-infrared (IR) wavelengths. Above the VO 2 phase transition the metasurface exhibits increased mid-IR emissivity and reduced visible/near-IR absorptivity, creating an efficient radiative emission channel in the first atmospheric transparency window with reduced absorption of solar radiation. In contrast, below VO 2 ’s transition temperature, the metasurface increasingly absorbs sun light while minimizing mid-IR radiative heat losses. Moreover, a functional silicon layer eliminates the need for an additional capping layer commonly employed to protect VO 2 from environmental degradation. The additional protective layer often impedes the use and performance of VO 2 based devices in terrestrial as well as spacecraft applications. Therefore, the proposed durable and eco-friendly metasurface will be an excellent candidate for essential passive thermal regulation systems across residential and terrestrial applications.

42 ENGINEERING↗
NASA NTRS2006

Properties of CIRRUS Overlapping Clouds as Deduced from the GOES-12 Imagery Data

Understanding the impact of cirrus clouds on modifying both the solar reflected and terrestrial emitted radiations is crucial for climate studies. Unlike most boundary layer stratus and stratocumulus clouds that have a net cooling effect on the climate, high-level thin cirrus clouds can have a warming effect on our climate. Many research efforts have been devoted to retrieving cirrus cloud properties due to their ubiquitous presence. However, using satellite observations to detect and/or retrieve cirrus cloud properties faces two major challenges. First, they are often semitransparent at visible to infrared wavelengths; and secondly, they often occur over a lower cloud system. The overlapping of high-level cirrus and low-level stratus cloud poses a difficulty in determining the individual cloud top altitudes and optical properties, especially when the signals from cirrus clouds are overwhelmed by the signals of stratus clouds. Moreover, the operational satellite retrieval algorithms, which often assume only single layer cloud in the development of cloud retrieval techniques, cannot resolve the cloud overlapping situation properly. The new geostationary satellites, starting with the Twelfth Geostationary Operational Environmental Satellite (GOES-12), are providing a new suite of imager bands that have replaced the conventional 12-micron channel with a 13.3-micron CO2 absorption channel. The replacement of the 13.3-micron channel allows for the application of a CO2-slicing retrieval technique (Chahine et al. 1974; Smith and Platt 1978), which is one of the important passive satellite methods for remote sensing the altitudes of mid to high-level clouds. Using the CO2- slicing technique is more effective in detecting semitransparent cirrus clouds than using the conventional infrared-window method.

Chang, Fu-Lung↗
NASA NTRS2014

Simultaneous Retrieval of Aerosol Properties and Clear-Sky Direct Radiative Effect Over the Global Ocean from MODIS

A unified satellite algorithm is presented to simultaneously retrieve aerosol properties (aerosol optical depth; AOD and aerosol type) and clear-sky shortwave direct radiative effect (hereafter, DREA) over ocean. The algorithm is applied to Moderate Resolution Imaging spectroradiometer (MODIS) observations for a period from 2003 to 2010 to assess the DREA over the global ocean. The simultaneous retrieval utilizes lookup table (LUT) containing both spectral reflectances and solar irradiances calculated using a single radiative transfer model with the same aerosol input data. This study finds that aerosols cool the top-of-atmosphere (TOA) and bottom-of-atmosphere (BOA) by 5.2 +/- 0.5 W/sq m and 8.3 W/sq m, respectively, and correspondingly warm the atmosphere (hereafter, ATM) by 3.1 W/sq m. These quantities, solely based on the MODIS observations, are consistent with those of previous studies incorporating chemical transport model simulations and satellite observations. However, the DREAs at BOA and ATM are expected to be less accurate compared to that of TOA due to low sensitivity in retrieving aerosol type information, which is related with the atmospheric heating by aerosols, particularly in low AOD conditions; consequently, the uncertainties could not be quantified. Despite the issue in the aerosol type information, the present method allows us to confine the DREA attributed only to fine-mode dominant aerosols, which are expected to be mostly anthropogenic origin, in the range from 1.1 W/sq m to 1.3 W/sq m at TOA. Improvements in size-resolved AOD and SSA retrievals from current and upcoming satellite instruments are suggested to better assess the DREA, particularly at BOA and ATM, where aerosol absorptivity induces substantial uncertainty.

MODIS↗
NASA NTRS2021

Less Atmospheric Radiative Heating By Dust Due to the Synergy of Coarser Size and Aspherical Shape

Mineral dust aerosols cool and warm the atmosphere by scattering and absorbing solar (shortwave: SW) and thermal (longwave: LW) radiation. However, significant uncertainties remain in dust radiative effects, largely due to differences in the dust size distribution and spectral optical properties simulated in Earth system models. Dust models typically underestimate the coarse dust load (more than 2.5 µm in diameter) and assume a spherical shape, which leads to an overestimate of the fine dust load (less than 2.5 µm) after the dust emissions in the models are scaled to match observed dust aerosol optical depth at 550 nm (DAOD550). Here, we improve the simulated dust properties with data sets that leverage measurements of size-resolved dust concentration, asphericity factor, and refractive index in a coupled global chemical transport model with a radiative transfer module. After the adjustment of size-resolved dust concentration and spectral optical properties, the global and annual average of DAOD550 from the simulation increases from 0.023 to 0.029 and falls within the range of a semi-observationally based estimate (0.030 ± 0.005). The reduction of fine dust load after the adjustment leads to a reduction of the SW cooling at the top of the atmosphere (TOA). To improve agreement against a semi-observationally based estimate of the radiative effect efficiency at TOA, we find that a less absorptive SW dust refractive index is required for coarser aspherical dust. Thus, only a minor difference is estimated for the net global dust radiative effect at TOA (−0.08 vs. −0.00 W m−2 on a global scale). Conversely, our sensitivity simulations reveal that the surface warming is substantially enhanced near the strong dust source regions (less cooling to −0.23 from −0.60 W m−2 on a global scale). Thus, less atmospheric radiative heating is estimated near the major source regions (less heating to 0.15 from 0.59 W m−2 on a global scale), because of enhanced LW warming at the surface by the synergy of coarser size and aspherical shape.

simulated dust properties↗
DOE OSTI2022

In-situ Characterizations of Microstructural Degradation of Perovskite Solar Cells

Rapid progress has been achieved in perovskite solar cells (PSCs), and their efficiencies have improved from 3.8 % to 24.2 % in less than a decade. With low-cost processing, PSCs have shown exciting photovoltaic (PV) properties, such as effective optical absorption, a long carrier lifetime, and unique defect tolerance. While recent studies demonstrated improved stability up to 100 days, PSC technology is still challenged to meet the stringent industry requirements for commercialization. Despite considerable efforts, the underlying physical mechanisms for the inferior stability of PSCs are not well understood. One reason for this divergence is that many established measurement techniques (e.g., quantum efficiency, photoluminescence) probe the properties on length scales far greater than that of electronic and/or structural inhomogeneity (i.e., < 1 μm near grain boundaries) and therefore characterize convoluted and/or averaged properties. Ion/electron beam-based techniques have been extensively used to access the microstructures of PSCs, enabling atomic/nanoscale structural, chemical, optical, and electrical characterizations. For example, focused ion beam (FIB) milling produces an atomically smooth surface that minimizes the artifacts attributed to the surface roughness. FIB techniques can also create a well-defined cross-section of PSCs without mechanical damage in a physical cleaving sample preparation. While powerful, there are some concerns about possible beam damage of inorganic-organic perovskites via chemical-bond breakage and local heating. This project aims to comprehensively understand how the microstructural/interfacial properties of PSCs (e.g., Methylammonium Lead Iodide [MAPbI 3 ]) are modified under the irradiating ion beams. Specifically, we investigate the sub-surface properties of PSCs before and after Ar-ion beam injections. Kelvin probe force microscopy (KPFM) measures the contact potential differences (CPDs). Photoluminescence (PL) microscopy in conjunction with Finite-Difference Time-Domain (FDTD) simulations infers the formation of a “dead layer” (< 15 nm) on the subsurface of MAPbI 3 during Ar+ milling processes while preserving the initial bulk properties. The x-ray photoemission spectroscopy (XPS) confirms this modified surface is a lead-rich and iodine-deficient surface. We initiate customizing in-situ measurement setup while measuring the local optical and electrical properties of PSC under thermal (cooling, heating) and light stressors. Our results provide in-depth knowledge of the ion-beam impact on metal-halide perovskites and how this modified sub-surface impacts their properties under accelerated stressors of light and heat. Intensive Monte Carlo simulations of an electron beam interacting with PSCs provide the beam energy distribution in PSCs, proposing possible measurement conditions of using e-beam with minimizing beam damage. Our in-situ measurement platform can accommodate the diverse architecture of PSC devices for studying deterioration mechanisms under mixed environmental stressors.

14 SOLAR ENERGY↗
NASA NTRS2011

Landsat Data Continuity Mission

The Landsat Data Continuity Mission (LDCM) is currently under development and is on schedule to launch the 8th satellite in the Landsat series in December of 2012. LDCM is a joint project between the National Aeronautics and Space Administration (NASA) and the United States Geological Survey (USGS). NASA is responsible for developing and launching the flight hardware and on-orbit commissioning and USGS is responsible for developing the ground system and operating the system onorbit after commissioning. Key components of the flight hardware are the Operational Land Imager (OLI), nearing completion by Ball Aerospace & Technologies Corp in Boulder, CO, the Thermal Infrared Sensor (TIRS), being built by NASA's Goddard Space Flight Center and the spacecraft, undergoing integration at Orbital Sciences Corp in Gilbert, Arizona. The launch vehicle will be an Atlas-5 with launch services provided by NASA's Kennedy Space Center. Key ground systems elements are the Mission Operations Element, being developed by the Hammers Corporation, and the Collection Activity Planning Element, Ground Network Element, and Data Processing and Archive System, being developed internally by the USGS Earth Resources Observations and Science (EROS) Center. The primary measurement goal of LDCM is to continue the global coverage of moderate spatial resolution imagery providing continuity with the existing Landsat record. The science goal for this imagery is to monitor land use and land cover, particularly as it relates to global climate change. Together the OLI and TIRS instruments on LDCM replace the ETM+ instrument on Landsat-7 with significant enhancements. The OLI is a pushbroom design instrument where the scanning mechanism of the ETM+ is effectively replaced by a long line of detectors. The OLI has 9 spectral bands with similar spatial resolution to ETM+: 7 of them similar to the reflective spectral bands on ETM+ and two new bands. The two new bands cover (1) the shorter wavelength blue part of the spectrum to help with coastal studies and aerosol analyses/atmospheric correction and (2) an atmospheric water absorption band, where the Earth surface is generally not visible, but Cirrus clouds are, to aid in cloud detection and screening. The radiometry of OLI benefits from improved SNR, dynamic range and quantization. OLI is undergoing system testing with a delivery scheduled for Spring 2011. The TIRS is also a pushbroom design and used QWIPS detectors that require cooling to 43K using a cryocooler. It.has two spectral bands, effectively splitting the ETM+ band 6 in half, that can be used as a split window to aid in atmospheric correction. It has nominally 100 m spatial resolution as opposed to the 60 m of Landsat-7 ETM+: TIRS has commenced integration and test, with a delivery to the spacecraft vendor scheduled for Winter 2011-2012. The Orbital spacecraft currently being integrated for LDCM will have improved capabilities for pointing over previous missions. These capabilities will allow the OLI and TIRS instruments to point off-nadir the equivalent of one WRS-2 path to increase the chances of coverage for high priority targets, particularly in the event of natural disasters. Also, the pointing capability will allow the calibration of the OLI using the sun (roughly weekly), the moon (monthly), stars (during commissioning) and the Earth (at 90 deg from normal orientation, a.k.a., side slither) quarterly. The solar calibration will be used for OLI absolute and relative calibration, the moon for trending the stability of the OLI response, the stars will be used for Line of Sight determination and the side slither will be an alternate OLI and relative gain determination methodology. The spacecraft is scheduled to begin integration with the OLI instrument in Summer 2011. The LDCM data processing and archive system (DPAS), located at USGS EROS, generates the products for distribution to users. Like Landsat-7 this includes an image assessment system for characrizing instrument performance and updating calibration parameters. Products will be generated that include the spectral bands from both instruments, terrain corrected and registered to the geoid. Also, like Landsat-7, data products will be distributed at no charge to the user. The current status and plans of the space and ground segments of the LDCM project will be presented along with performance predictions as available. More detailed information on the two instruments is intended to be presented in separate papers.

Markham, Brian↗
NASA NTRS2003

Estimates of the Spectral Aerosol Single Sea Scattering Albedo and Aerosol Radiative Effects during SAFARI 2000

Using measurements of the spectral solar radiative flux and optical depth for 2 days (24 August and 6 September 2000) during the SAFARI 2000 intensive field experiment and a detailed radiative transfer model, we estimate the spectral single scattering albedo of the aerosol layer. The single scattering albedo is similar on the 2 days even though the optical depth for the aerosol layer was quite different. The aerosol single scattering albedo was between 0.85 and 0.90 at 350 nm, decreasing to 0.6 in the near infrared. The magnitude and decrease with wavelength of the single scattering albedo are consistent with the absorption properties of small black carbon particles. We estimate the uncertainty in the single scattering albedo due to the uncertainty in the measured fractional absorption and optical depths. The uncertainty in the single scattering albedo is significantly less on the high-optical-depth day (6 September) than on the low-optical-depth day (24 August). On the high-optical-depth day, the uncertainty in the single scattering albedo is 0.02 in the midvisible whereas on the low-optical-depth day the uncertainty is 0.08 in the midvisible. On both days, the uncertainty becomes larger in the near infrared. We compute the radiative effect of the aerosol by comparing calculations with and without the aerosol. The effect at the top of the atmosphere (TOA) is to cool the atmosphere by 13 W/sq m on 24 August and 17 W/sq m on 6 September. The effect on the downward flux at the surface is a reduction of 57 W/sq m on 24 August and 200 W/sq m on 6 September. The aerosol effect on the downward flux at the surface is in good agreement with the results reported from the Indian Ocean Experiment (INDOEX).

Bergstrom, Robert W.↗
DOE OSTI2020

Direct Evidence of Photoinduced Charge Transport Mechanism in 2D Conductive Metal Organic Frameworks

Conductive metal organic frameworks (MOFs) represent a promising class of porous crystalline materials that have demon-strated potential in photo-electronics and photocatalytic applications. However, the lack of fundamental understanding on charge transport (CT) mechanism as well as the correlation of CT mechanism with their structure hampered their further development. Herein, we report the direct evidence of CT mechanism in 2D Cu-THQ MOFs and the correlation of temporal and spatial behaviors of charge carriers with their photoconductivity by combining three advanced spectroscopic methods including time resolved optical and X-ray absorption spectroscopy and terahertz spectroscopy. In addition to Cu-THQ, the CT in Cu/Zn-THQ after incorporating Zn2+ guest metal was also examined to uncover the contribution of through space pathway as the presence of the redox inactive 3d10 Zn2+ is expected to perturb the long range in-plane CT. We show that the hot carriers in Cu-THQ generated after photoexcitation are highly mobile and undergo fast localization to a lower energy state (cool carriers) with electrons occupying Cu center and holes in ligands. The cool carriers, which have super long lifetime (> 17 ns) are responsible for the long-term photoconductivity in Cu-THQ and transport through O-Cu-O motif with negligible contribution from interlayer ligand π-π stacking as incorporation of Zn2+ in Cu-THQ significantly reduced photoconductivi-ty. These unprecedent results not only demonstrate the capability to experimentally probe CT mechanism but also provide important insight in the rational design of 2D MOFs for photoelectronic and photocatalytic applications.

14 SOLAR ENERGY↗
NASA NTRS2010

Multiphysics Modeling for Dimensional Analysis of a Self-Heated Molten Regolith Electrolysis Reactor for Oxygen and Metals Production on the Moon and Mars

The technology of direct electrolysis of molten lunar regolith to produce oxygen and molten metal alloys has progressed greatly in the last few years. The development of long-lasting inert anodes and cathode designs as well as techniques for the removal of molten products from the reactor has been demonstrated. The containment of chemically aggressive oxide and metal melts is very difficult at the operating temperatures ca 1600 C. Containing the molten oxides in a regolith shell can solve this technical issue and can be achieved by designing a self-heating reactor in which the electrolytic currents generate enough Joule heat to create a molten bath. In a first phase, a thermal analysis model was built to study the formation of a melt of lunar basaltic regolith irradiated by a focused solar beam This mode of heating was selected because it relies on radiative heat transfer, which is the dominant mode of transfer of energy in melts at 1600 C. Knowing and setting the Gaussian-type heat flux from the concentrated solar beam and the phase and temperature dependent thermal properties, the model predicts the dimensions and temperature profile of the melt. A validation of the model is presented in this paper through the experimental formation of a spherical cap melt realized by others. The Orbitec/PSI experimental setup uses an 3.6-cm diameter concentrated solar beam to create a hemispheric melt in a bed of lunar regolith simulant contained in a large pot. Upon cooling, the dimensions of the vitrified melt are measured to validate the thermal model. In a second phase, the model is augmented by multiphysics components to compute the passage of electrical currents between electrodes inserted in the molten regolith. The current through the melt generates Joule heating due to the high resistivity of the medium and this energy is transferred into the melt by conduction, convection and primarily by radiation. The model faces challenges in two major areas, the change of phase as temperature increases, and the dominance of radiative heat flux as heat transfer mechanism within the melt the change of phase concerns the regolith itself which is present in states ranging from a fine grain regolith with low thermal conductivity and low density to a vitrified melt with much higher thermal conductivity, and higher density. As the regolith is heated, it starts to soften around 1300 C the melt iS very viscous and evolving gas bubbles out in thick, lava-like fashion. By 1600 C the regolith is completely melted and the viscosity is low The second challenge resides in the proper modeling of the radiative heat flux requiring the addition of the computing-demanding radiative-heat-transfer function to the general heat transfer equation. The model Includes temperature-dependent properties (density, thermal conductivity, heat capacity, and viscosity, and absorption coefficients) and solves the radiative heat flux equation assuming gray (fine grains) and semi-transparent (melt) media and using an absorption coefficient spectral found in the literature for terrestrial minerals similar in composition to those of lunar regolith simulant

Dominguez, Jesus A.↗
NASA NTRS1994

HST eclipse mapping of dwarf nova OY Carinae in quiescence: An 'Fe II curtain' with Mach approx. = 6 velocity dispersion veils the white dwarf

Hubble Space Telescope (HST) observations of the eclipsing dwarf nova OY Car in its quiescent state are used to isolate the ultraviolet spectrum (1150-2500 A at 9.2 A Full Width at Half Maximum (FWHM) resolution) of the white dwarf, the accretion disk, and the bright spot. The white dwarf spectrum has a Stark-broadened photospheric L(alpha) absorption, but is veiled by a forest of blended Fe II features that we attribute to absorption by intervening disk material. A fit gives T(sub w) approx. = 16.5 x 10(exp 3) K for the white dwarf with a solar-abundance, log g = 8 model atmosphere, and T approx. = 10(exp 4) K, n(sub e) approx. = 10(exp 13)/cu cm, N(sub H) approx. = 10(exp 22) sq cm, and velocity dispersion delta V approx. = 60 km/s for the veil of homogeneous solar-abundance local thermodynamic equilibrium (LTE) gas. The veil parameters probably measure characteristic physical conditions in the quiescent accretion disk or its chromosphere. The large velocity dispersion is essential for a good fit; it lowers (chi square)/778 from 22 to 4. Keplerian shear can produce the velocity dispersion if the veiling gas is located at R approx. = 5 R(sub W) with (delta R)/R approx. = 0.3, but this model leaves an unobscured view to the upper hemisphere of the white dwarf, incompatible with absorptions that are up to 80% deep. The veiling gas may be in the upper atmosphere of the disk near its outer rim, but we then require supersonic (Mach approx. = 6) but sub-Keplerian (delta V/V(sub Kep) approx. = 0.07) velocity disturbances in this region to produce both the observed radial velocity dispersion and vertical motions sufficient to elevate the gas to z/R = cos i = 0.12. Such motions might be driven by the gas stream, since it may take several Kepler periods to reestablish the disk's vertical hydrostatic equilibrium. The temperature and column density of the gas we see as Fe II absorption in the ultraviolet are similar to what is required to produce the strong Balmer jump and line emissions seen in optical spectra of OY Car and similar quiescent dwarf novae. The outer accretion disk is detected at mid-eclipse with a spectrum that rises from 0.05 to 0.3 mJy between 2000 and 2500 A, consistent with combinations of cool blackbodies, blended Fe II emission lines, and Balmer continuum emission. The total disk flux density is 0.5 mJy at 2500 A, and this shallow disk eclipse implies a roughly flat surface brightness distribution. The bright spot, somewhat bluer than the disk, has a flux density rising from 0.05 to 0.15 mJy between 1600 and 2500 A. The C IV emission line has a broad shallow eclipse, but the radial velocity variations observed during the eclipse do not clearly distinguish between a disk or wind origin. The only possible indications of boundary layer emission are fast UV flares that appear to arise from near the central object -- not from the bright spot.

Horne, Keith↗
NASA NTRS2014

Data Processing and Experimental Design for Micrometeorite Impacts in Small Bodies

Comets and asteroids have been altered from their original "pristine" state by impacts occurring throughout their 4.5 billion year lives: [1]. Proof of shock deformation has been detected in the crystal structure of several Stardust samples from Comet Wild 2 [2, 3]. Analyses indicated that the planar dislocations in the crystal structure of the minerals had been imparted by impacts sustained during their lives, and not due to the aerogel capture process. Distortions to crystal structure also affect the ideal absorption spectra in the infrared, and [4], thus providing indirect evidence of its impact history and a means of remotely investigating the impact history of small bodies through comparing laboratory spectra with spectra observed by telescopes or spacecraft. -The effects of impacts propagating shock waves through minerals were investigated through laboratory impact experiments. Utilizing NASA Johnson Space Center's Experimental Impact Laboratory, projectiles were fired from the vertical gun at velocities ranging from 2.0 to 2.8 km/sec, projected impact velocities between Kuiper Belt Objects. Two types of projectiles were used, including spherical alumina ceramic, whose density mimics that of rock, and cylinders made from the same material that they impacted. The target materials chosen for testing included: OLIVINES forsterite (Mg2SiO4) and fayalite, Fe2SiO4); PYROXENES enstatite (Mg2Si2O6) and diopside (MgCaSi2O6); and CARBONATES magnesite (MgCO3) and siderite (FeCO3). Targets were impacted at either 25 C or cooled to -20 C to examine the effects of temperature, if any, on lattice distortions during the shock propagation. As comets and asteroids can undergo a wide range of temperatures in their orbital lifetimes, the effect of temperature on the equation of state of minerals being shocked needs to be examined for interpreting the results of these experiments. The porosity of the target mineral is varied by either grinding it into a powder/granular texture or as whole mineral rocks to investigate the differences in shock propagation when voids are present. By varying velocity, ambient temperature, and porosity, we can investigate different variables affecting impacts in the solar system. -Data indicates that there is a non-linear relationship between peak shock pressure and the variation in infrared spectral absorbances by the distorted crystal structure. The maximum variability occurs around 37 GPa in enstatite and forsterite. The particle size distribution of the impacted material similarly changes with velocity/peak shock pressure. -The experiments described above are designed to measure the near- to mid-IR effects from these changes to the mineral structure. See Lederer et al., this meeting for additional experimental results.

Jensen, E.↗
NASA NTRS1994

The chromospheric structure of the cool giant star g Herculis

Non-Local Thermodynamic Equilibrium (LTE) calculations of semiempirical chromospheric models are presented for 30 g Her (M6 III). This star is one of the coolest (T(sub eff) = 3250 K) SRb (semiregular) variable stars and has a mass perhaps as great as 4 solar mass. Chromospheric features we have observed in its spectrum include Mg II h and k; C II) UV0.01, which is sensitive to electron density; Mg I lambda 2852; Ca II H, K, and IRT; Ca I lambda 4227 and lambda 6573; Al II) UV 1; and H alpha. We pay special attention to fitting the C II intersystem lines and the Mg II resonance lines but use all the other features as constraints to some extent. The equations of radiative transfer and statistical equilibrium are solved self-consistently for H I, H(-), H2, He I, C I, C II, Na I, Mg I, Mg II, Al I, Al II, Ca I, and Ca II with the equivalent two-level technique. To simplify these calculations, a one-dimensional hydrostatic, plane-parallel atmosphere is assumed. We investigate 10 separate 'classical' chromospheric models, differing most importantly in total mass column density above the temperature minimum. Synthetic spectra from these models fit some but not all of the observations. These comparisons are discussed in detail. However, we find that no single-component classical model in hydrostatic equilibrium is able to reproduce both the Mg II line profiles and the relative strengths of the CII) lines. In all these models, chromospheric emission features are formed relatively close to the star (approximately less than 0.05 R(sub *). The circumstellar environment has a thick, cool component overlying the Mg II emission region, which is relatively static and very turbulent. Finally, we find that thermalization in the Mg II h and k lines in the coolest giant stars is controlled by continuum absorption from Ca I 4p 4p3 P0 bound-free opacity and not collisional de-excitation as is the case for warmer K giants.

Luttermoser, Donald G.↗