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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Digital Alloy Absorber for Photodetectors

In order to increase the spectral response range and improve the mobility of the photo-generated carriers (e.g. in an nBn photodetector), a digital alloy absorber may be employed by embedding one (or fraction thereof) to several monolayers of a semiconductor material (insert layers) periodically into a different host semiconductor material of the absorber layer. The semiconductor material of the insert layer and the host semiconductor materials may have lattice constants that are substantially mismatched. For example, this may performed by periodically embedding monolayers of InSb into an InAsSb host as the absorption region to extend the cutoff wavelength of InAsSb photodetectors, such as InAsSb based nBn devices. The described technique allows for simultaneous control of alloy composition and net strain, which are both key parameters for the photodetector operation.

Hill, Cory J.↗
NASA NTRS2017

Gradient Compression Garments as a Countermeasure to Post-Space Flight Orthostatic Intolerance: Potential Interactions with the Maximum Absorbency Garment

Astronauts and cosmonauts may experience symptoms of orthostatic intolerance during re-entry, landing, and for several days post-landing following short- and long-duration spaceflight. Presyncopal symptoms have been documented in approximately 20% of short-duration and greater than 60% of long-duration flyers on landing day specifically during 5-10 min of controlled (no countermeasures employed at the time of testing) stand tests or 80 deg head-up tilt tests. Current operational countermeasures to orthostatic intolerance include fluid loading prior to and whole body cooling during re-entry as well as compression garments that are worn during and for up to several days after landing. While both NASA and the Russian space program have utilized compression garments to protect astronauts and cosmonauts traveling on their respective vehicles, a "next-generation" gradient compression garment (GCG) has been developed and tested in collaboration with a commercial partner to support future space flight missions. Unlike previous compression garments used operationally by NASA that provide a single level of compression across only the calves, thighs, and lower abdomen, the GCG provides continuous coverage from the feet to below the pectoral muscles in a gradient fashion (from approximately 55 mm Hg at the feet to approximately 16 mmHg across the abdomen). The efficacy of the GCG has been demonstrated previously after a 14-d bed rest study without other countermeasures and after short-duration Space Shuttle missions. Currently the GCG is being tested during a stand test following long-duration missions (~6 months) to the International Space Station. While results to date have been promising, interactions of the GCG with other space suit components have not been examined. Specifically, it is unknown whether wearing the GCG over NASA's Maximum Absorbency Garment (MAG; absorbent briefs worn for the collection of urine and feces while suited during re-entry and landing) will interfere with the effectiveness of the GCG or conversely whether the GCG will reduce the fluid absorption capabilities of the MAG. Methods: This operational, directed study, will (1) determine whether the effectiveness of the GCG is affected by the MAG with regard to cardiovascular responses to head-up tilt, the standard orthostatic intolerance test employed for astronauts and bed rest subjects; (2) determine whether the effectiveness of the MAG is compromised by the GCG tested by injecting a standard fluid volume (950 ml in 3 separate simulated "urine voids") at a standardized rate (30 ml/sec); and (3) determine whether comfort is affected by wearing the MAG under the GCG using a standardized questionnaire. Results from this study will guide future development and operational use of the GCG and MAG to maximize crew health, safety, and comfort.

Lee, S. M. C.↗
NASA NTRS2017

Impacts of Solar-Absorbing Aerosol Layers on the Transition of Stratocumulus to Trade Cumulus Clouds

The effects of an initially overlying layer of solar-absorbing aerosol on the transition of stratocumulus to trade cumulus clouds are examined using large-eddy simulations. For lightly drizzling cloud the transition is generally hastened, resulting mainly from increased cloud droplet number concentration (Nc) induced by entrained aerosol. The increased Nc slows sedimentation of cloud droplets and shortens their relaxation time for diffusional growth, both of which accelerate entrainment of overlying air and thereby stratocumulus breakup. However, the decrease in albedo from cloud breakup is more than offset by redistributing cloud water over a greater number of droplets, such that the diurnal-average shortwave forcing at the top of the atmosphere is negative. The negative radiative forcing is enhanced by sizable longwave contributions, which result from the greater cloud breakup and a reduced boundary layer height associated with aerosol heating. A perturbation of moisture instead of aerosol aloft leads to a greater liquid water path and a more gradual transition. Adding absorbing aerosol to that atmosphere results in substantial reductions in liquid water path (LWP) and cloud cover that lead to positive short-wave and negative longwave forcings on average canceling each other. Only for heavily drizzling clouds is the breakup delayed, as inhibition of precipitation overcomes cloud water loss from enhanced entrainment. Considering these simulations as an imperfect proxy for biomass burning plumes influencing Namibian stratocumulus, we expect regional indirect plus semi-direct forcings to be substantially negative to negligible at the top of the atmosphere, with its magnitude sensitive to background and perturbation properties.

Zhou, Xiaoli↗
NASA NTRS2017

NASA's Bio-Inspired Acoustic Absorber Concept

Transportation noise pollutes our worlds cities, suburbs, parks, and wilderness areas. NASAs fundamental research in aviation acoustics is helping to find innovative solutions to this multifaceted problem. NASA is learning from nature to develop the next generation of quiet aircraft.The number of road vehicles and airplanes has roughly tripled since the 1960s. Transportation noise is audible in nearly all the counties across the US. Noise can damage your hearing, raise your heart rate and blood pressure, disrupt your sleep, and make communication difficult. Noise pollution threatens wildlife when it prevents animals from hearing prey, predators, and mates. Noise regulations help drive industry to develop quieter aircraft. Noise standards for aircraft have been developed by the International Civil Aviation Organization and adopted by the US Federal Aviation Administration. The US National Park Service is working with the Federal Aviation Administration to try to balance the demand for access to the parks and wilderness areas with preservation of the natural soundscape. NASA is helping by conceptualizing quieter, more efficient aircraft of the future and performing the fundamental research to make these concepts a reality someday. Recently, NASA has developed synthetic structures that can absorb sound well over a wide frequency range, and particularly below 1000 Hz, and which mimic the acoustic performance of bundles of natural reeds. We are adapting these structures to control noise on aircraft, and spacecraft. This technology might be used in many other industrial or architectural applications where acoustic absorbers have tight constraints on weight and thickness, and may be exposed to high temperatures or liquids. Information about this technology is being made available through reports and presentations available through the NASA Technical Report Server, http:ntrs.nasa.gov. Organizations who would like to collaborate with NASA or commercialize NASAs technology are encouraged to contact the NASA Glenn Technology Transfer Office, https:technology.grc.nasa.gov. The NASA Glenn Office of Education https:www.nasa.govcentersglenneducationindex.html and the NASA Glenn Virtual Interchange for Nature-Inspired Exploration https:www.grc.nasa.govvine are also helping to make research like this accessible to the public and students of all ages.

Acoustics↗
NASA NTRS2018

Advantages of Measuring the Q Stokes Parameter in Addition to the Total Radiance I in the Detection of Absorbing Aerosols: a Proof of Concept Using Vector Radiative Transfer, Neural Networks, and Optimal Estimation

A simple but novel study was conducted to investigate whether an imager-type spectroradiometer instrument like MODIS, currently flying on board the Aqua and Terra satellites, or MERIS, which flew on board Envisat, could detect absorbing aerosols if they could measure the Q Stokes parameter in addition to the total radiance I, that is if they could also measure the linear polarization of the light. Accurate radiative transfer calculations were used to train a fast neural network forward model, which together with a simple statistical optimal estimation scheme was used to retrieve three aerosol parameters: aerosol optical depth, fraction of absorbing aerosols, and aerosol location. The aerosols were assumed to be located either between 0 and 2 km or between 2 and 4 km in the Earth’s atmosphere. From simulated data it was found that by itself the total radiance I was generally insufficient to retrieve all three aerosol parameters, but that together with the Q Stokes component it was possible to reliably retrieve values of aerosol optical depth, fraction, and location.

Stamnes, Snorre↗
NASA NTRS2020

The Variable and Non-Variable X-Ray Absorbers in Compton-Thin Type II Active Galactic Nuclei

We have conducted an extensive X-ray spectral variability study of a sample of 20 Compton-thin type II galaxies using broadband spectra from XMM-Newton, Chandra, and Suzaku. The aim is to study the variability of the neutral intrinsic X-ray obscuration along the line of sight and investigate the properties and location of the dominant component of the X-ray-obscuring gas. The observations are sensitive to absorption columns of N(sub H) ∼ 10(exp 20.5–24) cm(exp -2) of fully and partially covering neutral and/or lowly ionized gas on timescales spanning days to well over a decade. We detected variability in the column density of the full-covering absorber in 7/20 sources, on timescales of months to years, indicating a component of compact-scale X-ray-obscuring gas lying along the line of sight of each of these objects. Our results imply that torus models incorporating clouds or over-dense regions should account for line-of-sight column densities as low as ∼a few ×10(exp 21) cm(exp -2). However, 13/20 sources yielded no detection of significant variability in the full-covering obscurer, with upper limits of ΔN(sub H) spanning 10(exp 21–23) cm(exp -2). The dominant absorbing media in these systems could be distant, such as kiloparsec-scale dusty structures associated with the host galaxy, or a homogeneous medium along the line of sight. Thus, we find that overall, strong variability in full-covering obscurers is not highly prevalent in Compton-thin type IIs, at least for our sample, in contrast to previous results in the literature. Finally, 11/20 sources required a partial-covering, obscuring component in all or some of their observations, consistent with clumpy near-Compton-thick compact-scale gas.

Active galaxies↗
NASA NTRSDate not supplied

Development and Analysis of Energy Absorbing Subfloor Concepts to Improve eVTOL Crashworthiness

To help ensure safe transportation within electric Vertical Take-off and Landing (eVTOL) vehicles the National Aeronautics and Space Administration (NASA) has been developing novel energy absorbing (EA) design technologies to improve crashworthiness within the unique design constraints of these vehicles. As part of this effort, a series of lightweight energy absorbing subfloor concepts were developed for potential use within eVTOL vehicle design. The capability of the subfloor designs was first evaluated through finite element (FE) model simulation in both component and vehicle level impact conditions. Knowledge gained from these analyses were used to iterate upon the design prior to fabrication. Fabrication and testing of the subfloor designs has begun and will be used to verify predicted capability. Results from FE model analysis was used to down select to a final subfloor geometry for additional component level optimization and full-scale test validation.

eVTOL↗
NASA NTRSDate not supplied

Development of Energy Absorbing Subfloor Concepts to Improve Crashworthiness of eVTOL Aircraft

To help ensure safe transportation within electric Vertical Take-off and Landing (eVTOL) vehicles the National Aeronautics and Space Administration (NASA) has been developing novel energy absorbing (EA) design technologies to improve crashworthiness within the unique design constraints of these vehicles. As part of this effort, a series of lightweight energy absorbing subfloor concepts were developed for potential use within eVTOL vehicle design. The capability of the subfloor designs was first evaluated through finite element (FE) model simulation in both component and vehicle level impact conditions. Knowledge gained from these analyses were used to iterate upon the design prior to fabrication. Fabrication and testing of the subfloor designs has begun and will be used to verify predicted capability. Results from FE model analysis was used to down select to a final subfloor geometry for additional component level optimization and full-scale test validation.

Crashworthiness↗
NASA NTRS2023

Observations Suggest That North African Dust Absorbs Less Solar Radiation Than Models Estimate

Desert dust accounts for a large fraction of shortwave radiation absorbed by aerosols, which adds to the climate warming produced by greenhouse gases. However, it remains uncertain exactly how much shortwave radiation dust absorbs. Here, we leverage in-situ measurements of dust single-scattering albedo to constrain absorption at mid-visible wavelength by North African dust, which accounts for approximately half of the global dust. We find that climate and chemical transport models overestimate North African dust absorption aerosol optical depth (AAOD) by up to a factor of two. This occurs primarily because models overestimate the dust imaginary refractive index, the effect of which is partially masked by an underestimation of large dust particles. Similar factors might contribute to an overestimation of AAOD retrieved by the Aerosol Robotic Network, which is commonly used to evaluate climate and chemical transport models. The overestimation of dust absorption by models could lead to substantial biases in simulated dust impacts on the Earth system, including warm biases in dust radiative effects.

Atmospheric science↗
DOE OSTI2020

3D microstructures for rapid absorption/desorption in mechanically constrained liquid absorbents

An absorber or desorber contains one or more micro-channels that have a 3-D structured heat-exchanging surface and a membrane on the microchannel situated distal to the 3-D structured heat-exchanging surface, where the membrane is permeable to a solvent of a solution employed in the absorber or desorber. The 3-D structured surface promotes mixing of hot and cold solution between the 3-D structured heat-exchanging surface and a vapor-exchanging surface proximal to the membrane. The mixing reduces the differences in concentration and temperature of the bulk solution and the solution at the vapor-exchanging surface to enhance the efficiency and rate of absorption or desorption of the solvent.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Alloyed halide double perovskites as solar-cell absorbers

An alloyed halide double perovskite material, an alloyed halide double perovskite solar-cell absorber and solar cells constructed with such absorbers, the alloyed halide double perovskite material having the formula A2B1-aB′1-bDxX6, where A is an inorganic cation, an organic cation, a mixture of inorganic cations, a mixture of organic cations, or a mixture of one or more inorganic cations and one or more organic cations, where B is a metal, a mixture of metals, a metalloid, a mixture of metalloids, any mixture thereof, or is a vacancy, where B′ is a metal, a mixture of metals, a metalloid, a mixture of metalloids, any mixture thereof, or is a vacancy, where D is a dopant, and where X is a halide, a pseudohalide, a mixture of halides, a mixture of pseudohalides, or a mixture of halides and pseudohalides, and where x=a+b.

Karunadasa, Hemamala Indivari↗
DOE OSTI2023

System and method for integrated absorber intercooling via rich solvent stream using 3D-printed active packings

The present disclosure relates to an absorber column apparatus for removing a selected component of a gas. The apparatus may have a first zone, a second zone and a third zone, wherein the first and third zones form a first domain through which a first fluid laden with a select gaseous component to be removed therefrom flows along concurrently with a second fluid. The second fluid at least substantially removes the select gaseous component from the first fluid to create a third fluid. The first fluid leaves the absorber column as a fourth fluid with the select gaseous component at least substantially removed therefrom. The second zone forms an active packing zone including a structure which forms an independent second domain in thermal communication with the first domain. The second receives a quantity of the third fluid and channels it through the second zone to help cool at least one of the first and second fluids.

Moore, Thomas Charles Reading↗
DOE OSTI2024

Laboratory Upgrade Point Absorber (LUPA) CAD Files

The Laboratory Upgrade Point Absorber (LUPA) is an open-source wave energy converter designed and tested by Oregon State University. The computer-aided design (CAD) files are provided here in two forms: the original SOLIDWORKS (2021) model as "LUPA SOLIDWORKS.zip" and as a STEP file "LUPA-A1000.step". The bill of materials is provided as an Excel file with assemblies (LUPA-Axxx), part numbers (LUPA-Axxx-Pyyy), part descriptions, manufacturers, and manufacturer part numbers. This comprehensive CAD model represents LUPA as it was deployed in Fall 2022 testing at the O.H. Hinsdale Wave Research Laboratory. The mass properties including mass, center of gravity, and moments of inertia have been overridden for some parts and assemblies to match the physical device properties as determined from experiments. This appears as "overridden by user" when viewing mass properties in SOLIDWORKS. The LUPA-A1000.SLDASM file from the LUPA SOLIDWORKS.zip folder is the topmost assembly, open this file to see the entire model as one assembly. See "PMEC Page", "OpenEI Wiki Page", and the "Signature Project Page" resources below for more information on LUPA.

16 TIDAL AND WAVE POWER↗
DOE OSTI2024

Laboratory Upgrade Point Absorber WEC-Sim Model with MoorDyn Moorings

This dataset includes a WEC-Sim and MoorDyn model of the Laboratory Upgrade Point Absorber (LUPA). LUPA is an open-source wave energy converter designed and tested by Oregon State University. The files provided here constitute a stable LUPA configuration with three mooring lines. This model is 1/20 scale, optimized for the O.H. Hinsdale Wave Lab at Oregon State University. This model of LUPA adds MoorDyn functionality for more accurate mooring predictions and uses a more stable, updated version of LUPA's current physical configuration. This model is for WEC-Sim Version 6.0. A recent update of WEC-Sim has changed some functionality of MoorDyn such that this model will not work with WEC-Sim Version 6.1.

16 TIDAL AND WAVE POWER↗
DOE OSTI2023

Dirichlet-type absorbing boundary conditions for peridynamic scalar waves in two-dimensional viscous media

Construction of absorbing boundary conditions (ABCs) for nonlocal models is generally challenging, primarily due to the fact that nonlocal operators are commonly associated with volume constrained boundary conditions. Moreover, application of Fourier and Laplace transforms, which are essential for the majority of available methods for ABCs, to nonlocal models is complicated. In this paper, we propose a simple method to construct accurate ABCs for peridynamic scalar wave-type problems in viscous media. The proposed ABCs are constructed in the time and space domains and are of Dirichlet type. Consequently, their implementation is relatively simple, since no derivatives of the wave field are required. The proposed ABCs are derived at the continuum level, from a semi-analytical solution of the exterior domain using harmonic exponential basis functions in space and time (plane-wave modes). The numerical implementation is done using a meshfree collocation approach employed within a boundary layer adjacent to the interior domain boundary. The modes satisfy the peridynamic numerical dispersion relation, resulting in a compatible solution of the interior region (near-field) with that of the exterior region (far-field). The accuracy and stability of the proposed ABCs are demonstrated with several numerical examples in two-dimensional unbounded domains.

42 ENGINEERING↗
DOE OSTI2020

Dirichlet absorbing boundary conditions for classical and peridynamic diffusion-type models

Diffusion-type problems in (nearly) unbounded domains play important roles in various fields of fluid dynamics, biology, and materials science. The aim of this paper is to construct accurate absorbing boundary conditions (ABCs) suitable for classical (local) as well as nonlocal peridynamic (PD) diffusion models. The main focus of the present study is on the PD diffusion formulation. The majority of the PD diffusion models proposed so far are applied to bounded domains only. In this study, we propose an effective way to handle unbounded domains both with PD and classical diffusion models. For the former, we employ a meshfree discretization, whereas for the latter the finite element method (FEM) is employed. The proposed ABCs are time-dependent and Dirichlet-type, making the approach easy to implement in the available models. The performance of the approach, in terms of accuracy and stability, is illustrated by numerical examples in 1D, 2D, and 3D.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Hydrothermal reactivity of neutron absorber composites

The stability of neutron absorber composite materials at hydrothermal conditions was tested in a series of two-week experiments to mimic spent nuclear fuel disposal. Coupons, composed of boron carbide (B 4 C) sintered with and encased in aluminum, were increasingly altered in experiments at 150, 230, and 300 °C and pressures of 150 bar. Alteration of aluminum to boehmite (γ-AlO(OH)) and hydrogen gas generation occurred over the range of investigated temperatures, but is most significant at 300 °C. We found that the formation of boron-bearing mineral phases was not detected; however, aqueous boron was present in the reaction fluids.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Advanced neutron absorber Ni-Cr-Mo-Gd alloys seawater corrosion mechanism and susceptibility study

Previous studies demonstrated the corrosion susceptibility of advanced neutron absorber (ANA) Ni-Cr-Mo-Gd in a seawater environment but remained inconclusive. In this paper, scanning electron microscopy was employed to identify the corrosion phase in Ni-Cr-Mo-Gd, and computational thermodynamic simulation was used to study phase corrosion potentials. Results showed that the Ni 5 Gd second phase, distributed along FCC grain boundaries in Ni-Cr-Mo-Gd, has lower corrosion potential than the substrate. Furthermore, heat treatment and alloy chemistry adjustment would not ameliorate the ANA corrosion susceptibility. Finally, isolating the Ni 5 Gd from the corrosion medium through advanced manufacturing is a viable way to improve the ANA corrosion resistance.

36 MATERIALS SCIENCE↗