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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.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

SiC As An Energetic Particle Detector

Several new technologies have been introduced recently in the region of semiconductor material for solid state detectors (SSD). Of particular interest is silicon carbide (SIC) since its band gap is larger than that of pure silicon, reducing its dark current and making SIC capable of operating at high temperatures and more tolerant of radiation damage. But the trade off is that a higher band gap also means fewer electron hole pairs generated, and thus a smaller signal, for detecting incident radiation. To determine what the lower limit of SiC detectors to energetic particles is, we irradiated a SiC diode with particles ranging in energy from 50 keV to 1.6 MeV and masses from 1 to 16 amu. We found that the SiC detectors sensitivity was comparable to that of pure silicon, with the SiC detector being able to measure particles down to 50 keV/amu and possibly lower.

Yan, F.↗
DOE OSTI2020

Interacting radiation after Planck and its implications for the Hubble tension

Standard cosmology predicts that prior to matter-radiation equality about 41% of the energy density was in free-streaming neutrinos. In many beyond Standard Model scenarios, however, the amount and free-streaming nature of this component is modified. For example, this occurs in models with new neutrino self-interactions or an additional dark sector with interacting light particles. Here, we consider several extensions of the standard cosmology that include a non-free-streaming radiation component as motivated by such particle physics models and use the final Planck data release to constrain them. This release contains significant improvements in the polarization likelihood which plays an important role in distinguishing free-streaming from interacting radiation species. Fixing the total amount of energy in radiation to match the expectation from standard neutrino decoupling we find that the fraction of free-streaming radiation must be ffs > 0.8 at 95% CL (combining temperature, polarization and baryon acoustic oscillation data). Allowing for arbitrary contributions of free-streaming and interacting radiation, the effective number of new non-free-streaming degrees of freedom is constrained to be Nfld < 0.6 at 95% CL. Cosmologies with additional radiation are also known to ease the discrepancy between the local measurement and CMB inference of the current expansion rate H0. We show that including a non-free-streaming radiation component allows for a larger amount of total energy density in radiation, leading to a mild improvement of the fit to cosmological data compared to previously discussed models with only a free-streaming component.

particle physics - cosmology connection↗
DOE OSTI2024

The Effect of Physically Based Ice Radiative Processes on Greenland Ice Sheet Albedo and Surface Mass Balance in E3SM

Abstract A significant portion of surface melt on the Greenland Ice Sheet (GrIS) is due to dark ice regions in the ablation zone, where solar absorption is influenced by the physical properties of the ice, light absorbing constituents (LACs), and the overlying crustal surface or melt ponds. Earth system models (ESMs) typically prescribe the albedo of ice surfaces as a constant value in the visible and near‐infrared spectral regions. This work advances ESM ice radiative transfer modeling by (a) incorporating a physically based radiative transfer model (SNow, ICe and Aerosol Radiation model Adding‐Doubling Version 4; SNICAR‐ADv4) into the Energy Exascale Earth System Model (E3SM), (b) determining spatially and temporally varying bare ice physical properties over the GrIS ablation zone from satellite observations to inform SNICAR‐ADv4, and (c) assessing the impacts on simulated GrIS albedo and surface mass balance associated with modeling of more realistic bare ice albedo. GrIS‐wide bare ice albedo in E3SMv2 is overestimated by ∼4% in the visible and ∼7% in the near‐infrared wavelengths compared to the Moderate Resolution Imaging Spectroradiometer. Our bare ice physical property retrieval method found that LACs, ice crustal surfaces, and melt ponds reduce visible albedo by 30% in the bare ice region of the GrIS ablation zone. The realistic bare ice albedo reduces surface mass balance by ∼145 Gt, or 0.4 mm of sea‐level equivalent between 2000 and 2021 compared to the default E3SM. This work highlights the importance of simulating bare ice albedo accurately and realistically to improve our ability to quantify changes in the GrIS surface mass and radiative energy budgets.

58 GEOSCIENCES↗
NASA NTRSDate not supplied

Direct Aerosol Radiative Effect Derived From CERES Data Products

The CERES team uses MODIS and VIIRS derived aerosol optical thickness to compute surface and in atmosphere irradiances. In producing the data products, aerosol optical thicknesses derived by Dark Target and Deep Blue algorithms are assimilated in an aerosol transport model. In addition, the aerosol transport model provides aerosol optical thicknesses under cloudy conditions and aerosol optical thicknesses over polar regions. These aerosol optical thicknesses are used for hourly irradiance computations in 11 grids. Global mean top-of-atmosphere direct aerosol radiative effects are -5.2 Wm-2 and -2.2 Wm-2 for, respectively, clear-sky and all-sky conditions. Spatial pattern of the trend of the computed clear-sky direct aerosol radiative effect agrees with that derived from CERES observations. In this presentation, the importance of seamless transition of aerosol optical thicknesses derived from MODIS to those derived from VIIRS is emphasized. Currently, the CERES team is working with MODIS dark target and deep blue teams to achieve the seamless transition in producing CERES Edition 4 data products.

Seiji Kato↗
DOE OSTI2022

Freeze-in from preheating

We consider the production of dark matter during the process of reheating after inflation. The relic density of dark matter from freeze-in depends on both the energy density and energy distribution of the inflaton scattering or decay products composing the radiation bath. Here, we compare the perturbative and non-perturbative calculations of the energy density in radiation. We also consider the (likely) possibility that the final state scalar products are unstable. Assuming either thermal or non-thermal energy distribution functions, we compare the resulting relic density based on these different approaches. We show that the present-day cold dark matter density can be obtained through freeze-in from preheating for a large range of dark matter masses.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1997

Will Global Change Effect Primary Productivity in Coastal Ecosystems?

Algae are the base of coastal food webs because they provide the source of organic carbon for the remaining members of the community. Thus, the rate that they produce organic carbon to a large extent controls the productivity of the entire ecosystem. Factors that control algal productivity range from the physical (e.g., temperature, light), chemical (e.g., nutrient levels) to the biological (e.g., grazing). Currently, levels of atmospheric carbon dioxide surficial fluxes of ultraviolet radiation are rising. Both of these environmental variables can have a profound effect on algal productivity. Atmospheric carbon dioxide may increase surficial levels of dissolved inorganic carbon. Our laboratory and field studies of algal mats and phytoplankton cultures under ambient and elevated levels of pCO2 show that elevated levels of inorganic carbon can cause an increase in photosynthetic rates. In some cases, this increase will cause an increase in phytoplankton numbers. There may be an increase in the excretion of fixed carbon, which in turn may enhance bacterial productivity. Alternatively, in analogy with studies on the effect of elevated pCO2 on plants, the phytoplankton could change their carbon to nitrogen ratios, which will effect the feeding of the planktonic grazers. The seasonal depletion of stratospheric ozone has resulted in elevated fluxes of UVB radiation superimposed on the normal seasonal variation. Present surface UV fluxes have a significant impact on phytoplankton physiology, including the inhibition of the light and dark reactions of photosynthesis, inhibition of nitrogenase activity, inhibition of heterocyst formation, reduction in motility, increased synthesis of the UV-screening pigment scytonemin, and mutation. After reviewing these issues, recent work in our lab on measuring the effect of UV radiation on phytoplankton in the San Francisco Bay Estuary will be presented.

Rothschild, Lynn J.↗
DOE OSTI2024

Search for Dark Matter Ionization on the Night Side of Jupiter with Cassini

We present a new search for dark matter (DM) using planetary atmospheres. We point out that annihilating DM in planets can produce ionizing radiation, which can lead to excess production of ionospheric H 3 + . We apply this search strategy to the night side of Jupiter near the equator. The night side has zero solar irradiation, and low latitudes are sufficiently far from ionizing auroras, leading to a low-background search. We use data on ionospheric H 3 + emission collected three hours either side of Jovian midnight, during its flyby in 2000, and set novel constraints on the DM-nucleon scattering cross section down to about 10 − 38 cm 2 . We also highlight that DM atmospheric ionization may be detected in Jovian exoplanets using future high-precision measurements of planetary spectra. Published by the American Physical Society 2024

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Precombination Cloud Collapse and Baryonic Dark Matter

A simple spherical model of dense baryon clouds in the hot big bang 'strongly nonlinear primordial isocurvature baryon fluctuations' is reviewed and used to describe the dependence of cloud behavior on the model parameters, baryon mass, and initial over-density. Gravitational collapse of clouds before and during recombination is considered including radiation diffusion and trapping, remnant type and mass, and effects on linear large-scale fluctuation modes. Sufficiently dense clouds collapse early into black holes with a minimum mass of approx. 1 solar mass, which behave dynamically like collisionless cold dark matter. Clouds below a critical over-density, however, delay collapse until recombination, remaining until then dynamically coupled to the radiation like ordinary diffuse baryons, and possibly producing remnants of other kinds and lower mass. The mean density in either type of baryonic remnant is unconstrained by observed element abundances. However, mixed or unmixed spatial variations in abundance may survive in the diffuse baryon and produce observable departures from standard predictions.

Hogan, Craig J.↗
DOE OSTI2025

Dark QCD: the Next Frontier in Dark Matter

There has been a surge of interest in hidden valley models with new, strong forces, sometimes called "dark QCD". These models propose asymmetric, composite dark matter in the form of "dark hadrons" that would evade direct and indirect bounds as well as typical collider DM searches for large missing transverse momentum accompanied by radiation. However, evidence of these models can still be found in collider datasets by targeting their unique phenomenological signatures, which include semivisible jets, emerging jets, and soft unclustered energy patterns. We will present the latest experimental results for these signatures and discuss the significant strides in exploring the vast space of dark QCD models. We will further discuss the prospects for dramatic expansions in sensitivity via machine learning.

Pedro, Kevin [Fermilab]↗
DOE OSTI2020

Measurement of the gamma ray background in the Davis cavern at the Sanford Underground Research Facility

Deep underground environments are ideal for low background searches due to the attenuation of cosmic rays by passage through the earth. However, they are affected by backgrounds from γ -rays emitted by 40 K and the 238 U and 232 Th decay chains in the surrounding rock. The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a liquid xenon TPC located within the Davis campus at the Sanford Underground Research Facility, Lead, South Dakota, at the 4850-foot level. In order to characterise the cavern background, in-situ γ -ray measurements were taken with a sodium iodide detector in various locations and with lead shielding. The integral count rates (0–3300 keV) varied from 596 Hz to 1355 Hz for unshielded measurements, corresponding to a total flux from the cavern walls of 1.9 ± 0.4 γ cm −2 s −1 . The resulting activity in the walls of the cavern can be characterised as 220 ± 60 Bq/kg of 40 K, 29 ± 15 Bq/kg of 238 U, and 13 ± 3 Bq/kg of 232 Th.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Decoding the B → K ν ν excess at Belle II: Kinematics, operators, and masses

An excess in the branching fraction for B + → K + ν ν recently measured at Belle II may be a hint of new physics. We perform thorough likelihood analyses for different new physics scenarios such as B → K X with a new invisible particle X , or B → K χ χ through a scalar, vector, or tensor current with χ being a new invisible particle or a neutrino. We find that vector-current three-body decay with m X ≃ 0.6 GeV—which may be dark matter—is most favored, while two-body decay with m X ≃ 2 GeV is also competitive. The best-fit branching fractions for the scalar and tensor cases are a few times larger than for the two-body and vector cases. Past measurements provide further discrimination, although the best-fit parameters stay similar. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1984

Studies of radiative transfer in planetary atmospheres

Progress is reported in modeling cometary emission in the 18-cm OH transition with specific application and predictions for Comet Halley. Radiative transfer is also being studied in rough and porous media. The kinematics of the cold, dark interstellar cloud Li34N were examined, and CO monitoring of Venus and Mars continues. Analysis of 3.4 mm maps of the lunar surface shows thermal anomalies associated with such surface features as the Crater Copernicus, Mare Imbrium, Mare Nubium, Mare Serenitatis, and Mare Tranquillatis.

Irvine, W. M.↗
NASA NTRS1989

Dark surfaces of asteroids and comets - Evidence for macromolecular carbon compounds

The presence of very low-albedo material on the surfaces of some classes of asteroids (C,P,D) and most comets appears to be related to macromolecular carbon compounds on these bodies. Preliminary detections of an organic spectral signature have been reported for some asteroids. The complex refractory organics that occur in some meteorites are probably the material that makes low-albedo asteroids dark. Comet surfaces and ejected dust particles are also very low albedo, apparently resulting from the radiation processing of organic ices.

Cruikshank, D. P.↗
NASA NTRS1991

Development of a low pass far infrared filter for Lunar Observer horizon sensor application

A study was conducted to (1) determine the feasibility of design and fabrication of a low pass filter with a relatively sharp cut-on at higher wavelengths (i.e. 30-40 microns), using metallic mesh technique; and (2) investigate whether the combination of this filter and a suitable IR detector, as a part of a Lunar Observer (LO) horizon sensor, is capable of detecting radiation emanating from two blackbody sources kept at temperatures simulating space and the surface temperature of dark or lit sides of the moon. Various designs of multilayer metallic mesh filters with different mesh parameters and substrate thicknesses were simulated. Using mesh parameters corresponding to the optimum four-layer filter design, a filter was fabricated on a 6.35 micron thick mylar substrate. The transmission curve of the fabricated filter is very close to what the simulation predicted. Room temperature signal level tests were performed on the combination of filter-detector assemblies. The data obtained from these tests indicate that the assembly can detect temperature differences as low as few degrees K between two black bodies.

Mobasser, Sohrab↗
NASA NTRS1993

Cosmic background radiation anisotropy at degree angular scales - Further results from the South Pole

We report further results from the University of California at Santa Barbara program to measure anisotropy in the cosmic background radiation at angular scales near 1 deg, an angular range corresponding to the largest scales where structure is observed. A 30 GHz high electron mobility transistor amplifier-based detector was coupled to the Advanced Cosmic Microwave Explorer, a 1 m off-axis Gregorian telescope. We present data that represent 64 of the total of 500 hr acquired with this system during the 1990-1991 season. The data have a statistical error of 13.5/micro-K/pixel. These are the smallest error bars of any data set of this type published to date. The data contain a significant signal with a maximum likelihood Delta T/T roughly 1 x 10 exp -5. The spectrum of the signal seen in slightly less than 2 sigma away from the thermal spectrum expected of primordial fluctuations in the cosmic background radiation. If the source of the fluctuations is primordial, then the data are consistent with cold dark matter scenarios when normalized to the large-scale anisotropy observed by COBE, while if the origin of the signal is foreground emission or another form of contaminant then the data are marginally inconsistent with standard cold dark matter models. In either case, the data are sufficiently sensitive to provide a crucial test of many models.

Schuster, Jeffrey↗
NASA NTRS1994

Biospheric effects of a large extraterrestrial impact: Case study of the Cretaceous/Tertiary boundary crater

The Chicxulub Crater in Yucatan, Mexico, is the primary candidate for the impact that caused mass extinctions at the Cretaceous/Tertiary boundary. The target rocks at Chicxulub contain 750 to 1500 m of anhydrite (CaSO4), which was vaporized upon impact, creating a large sulfuric acid aerosol cloud. In this study we apply a hydrocode model of asteroid impact to calculate the amount of sulfuric acid produced. We then apply a radiative transfer model to determine the atmospheric effects. Results include 6 to 9 month period of darkness followed by 12 to 26 years of cooling.

Pope, Kevin O.↗
NASA NTRS2000

Ion Transmission to the Focal Plane of the Chandra X-Ray Observatory

The severe degradation in spectrometric performance observed by the AXAF CCD Imaging Spectrometer (ACIS) instrument on-board the Chandra X-ray Observatory (CXO) was associated with a sharp increase in charge transfer inefficiency combined with relatively constant dark current. It was also observed that damage occurred only during passage through the earth's radiation belts, and only when ACIS remained in the focal plane during the passage. Subsequent measurements and analyses support the conjecture that the damaging radiation entered through the Observatory's High-Resolution Mirror Assembly (HRMA) aperture. A mechanism whereby low energy magnetospheric protons and/or heavier ions are scattered through the HRMA and reach the focal plane with just enough energy to stop in the CCD's charge transfer region currently provides a reasonably consistent explanation of all observed phenomena. In this paper, we will describe analyses which support this conclusion. Simulations using standard ion transmission codes were used to generate a bi-directional response function (BDRF) for the mirror surfaces and transmission through the various path elements. The BDRF was convolved with the geometry via ray-trace. Damage estimates using measured proton fluence and ground measurements of ACIS- type CCD damage vs. proton energy will be presented and compared with observed on- orbit damage.

Kolodziejczak, J. J.↗
NASA NTRS2007

Metallic Concepts for Repair of Reinforced Carbon-Carbon Space Shuttle Leading Edges

The Columbia accident has focused attention on the critical need for on-orbit repair concepts for wing leading edges in the event that potentially catastrophic damage is incurred during Space Shuttle Orbiter flight. The leading edge of the space shuttle wings consists of a series of eleven panels on each side of the orbiter. These panels are fabricated from reinforced carbon-carbon (RCC) which is a light weight composite with attractive strength at very high temperatures. The damage that was responsible for the loss of the Colombia space shuttle was deemed due to formation of a large hole in one these RCC leading edge panels produced by the impact of a large piece of foam. However, even small cracks in the RCC are considered as potentially catastrophic because of the high temperature re-entry environment. After the Columbia accident, NASA has explored various means to perform on-orbit repairs in the event that damage is sustained in future shuttle flights. Although large areas of damage, such as that which doomed Columbia, are not anticipated to re-occur due to various improvements to the shuttle, especially the foam attachment, NASA has also explored various options for both small and large area repair. This paper reports one large area repair concept referred to as the "metallic over-wrap." Environmental conditions during re-entry of the orbiter impose extreme requirements on the RCC leading edges as well as on any repair concepts. These requirements include temperatures up to 3000 F (1650 C) for up to 15 minutes in the presence of an extremely oxidizing plasma environment. Figure 1 shows the temperature profile across one panel (#9) which is subject to the highest temperatures during re-entry. Although the RCC possesses adequate mechanical strength at these temperatures, it lacks oxidation resistance. Oxidation protection is afforded by converting the outer layers of the RCC to SiC by chemical vapor deposition (CVD). At high temperatures in an oxidizing environment, the SiC layer forms a protective SiO2 scale. However, CVD processing to form the SiC layer can result in the formation of small cracks in the outer surface. Hence, as a final fabrication step, a sodium silicate glass, known as "Type A," is applied as a sealant to fill any surface porosity and/or cracks in the coating and the outer portions of the RCC[1]. At relatively low temperatures, the Type A glass melts and flows into the cracks providing oxidation protection at the higher temperatures. In addition, the Type A coating, provides a "dark" coating with a high emissivity. This high emissivity allows the RCC to transfer heat by radiating outward to space as well as dispersing heat within the leading edge cavity. Lastly, the Type A possesses low catalycity which reduces surface temperatures by limiting oxygen recombination on the surface during re-entry.

Ritzert, Frank↗