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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A unified exploration of the chronology of the Galaxy

The Milky Way has distinct structural stellar components linked to its formation and subsequent evolution, but disentangling them is non-trivial. With the recent availability of high-quality data for a large numbers of stars in the Milky Way, it is a natural next step for research in the evolution of the Galaxy to perform automated explorations with unsupervised methods of the structures hidden in the combination of large-scale spectroscopic, astrometric, and asteroseismic data sets. We determine precise stellar properties for 21 076 red giants, mainly spanning 2–15 kpc in Galactocentric radii, making it the largest sample of red giants with measured asteroseismic ages available to date. We explore the nature of different stellar structures in the Galactic disc by using Gaussian mixture models as an unsupervised clustering method to find substructure in the combined chemical, kinematic, and age subspace. The best-fitting mixture model yields four distinct physical Galactic components in the stellar disc: the thin disc, the kinematically heated thin disc, the thick disc, and the stellar halo. We find hints of an age asymmetry between the Northern and Southern hemisphere, and we measure the vertical and radial age gradient of the Galactic disc using the asteroseismic ages extended to further distances than previous studies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Internal energy balance and aerodynamic heating predictions for hypersonic turbulent boundary layers

The elemental equation governing heat transfer in aerodynamic flows is the internal energy equation. For a boundary layer flow, a double integration of the Reynolds-averaged form of this equation provides an expression of the wall heat flux in terms of the integrated effects, over the boundary layer, of various physical processes: turbulent dissipation, mean dissipation, turbulent heat flux, etc. Recently available direct numerical simulation data for a Mach 11 cold-wall turbulent boundary layer allows a comparison of the exact contributions of these terms in the energy equation to the wall heat flux with their counterparts modeled in the Reynolds-averaged Navier-Stokes (RANS) framework. Various approximations involved in RANS, both closure models as well as approximations involved in adapting incompressible RANS models to a compressible form, are assessed through examination of the internal energy balance. There are a number of potentially problematic assumptions and terms identified through this analysis. Here, the effect of compressibility corrections of the dilatational dissipation type is explored, as is the role of the modeled turbulent dissipation, in the context of wall heat flux predictions. The results indicate several potential avenues for RANS model improvement for hypersonic cold-wall boundary-layer flows.

42 ENGINEERING↗
DOE OSTI2023

Effect of image resolution on automated classification of chest X-rays

Deep learning (DL) models have received much attention lately for their ability to achieve expert-level performance on the accurate automated analysis of chest X-rays (CXRs). Recently available public CXR datasets include high resolution images, but state-of-the-art models are trained on reduced size images due to limitations on graphics processing unit memory and training time. As computing hardware continues to advance, it has become feasible to train deep convolutional neural networks on high-resolution images without sacrificing detail by downscaling. This study examines the effect of increased resolution on CXR classification performance. We used the publicly available MIMIC-CXR-JPG dataset, comprising 377,110 high resolution CXR images for this study. We applied image downscaling from native resolution to 2048 × 2048 pixels, 1024 × 1024 pixels, 512 × 512 pixels, and 256 × 256 pixels and then we used the DenseNet121 and EfficientNet-B4 DL models to evaluate clinical task performance using these four downscaled image resolutions. We find that while some clinical findings are more reliably labeled using high resolutions, many other findings are actually labeled better using downscaled inputs. We qualitatively verify that tasks requiring a large receptive field are better suited to downscaled low resolution input images, by inspecting effective receptive fields and class activation maps of trained models. Lastly, we show that stacking an ensemble across resolutions outperforms each individual learner at all input resolutions while providing interpretable scale weights, indicating that diverse information is extracted across resolutions.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Identifying Meteorological Drivers for Errors in Modeled Winds along the Northern California Coast

Abstract An accurate wind resource dataset is required for assessing the potential energy yield of floating offshore wind farms that are expected along the California outer continental shelf. The National Renewable Energy Laboratory has developed and disseminated an updated wind resource dataset offshore of California, using the Weather Research and Forecasting Model, referred to as the CA20 dataset. As compared to buoy lidar measurements that have become available recently, the CA20 dataset showed significant positive biases for 100-m wind speeds along Northern California wind energy lease areas. To investigate the meteorological drivers for the model errors, we first consider two 1-yr simulations run with two different planetary boundary layer (PBL) parameterizations: the Mellor–Yamada–Nakanishi–Niino (MYNN) PBL scheme (the chosen configuration in the CA20 dataset) and the Yonsei University PBL scheme (which significantly reduces the bias in modeled winds). By comparing the 1-yr simulations to the concurrent lidar buoy observations, we find that errors are larger with the MYNN PBL scheme in warm seasons. We then dive deeper into the analysis by running simulations for short-term (3-day) case studies to evaluate the sensitivity of initial/boundary condition forcings on model results. By analyzing the short-term simulations, we find that during synoptic-scale northerly flows driven by the North Pacific high and inland thermal low, a coastal warm bias in the MYNN simulation is mainly responsible for the modeled wind speed bias by altering the boundary layer thermodynamics. The results of our analysis will help guide the creation of an updated version of the CA20 dataset.

17 WIND ENERGY↗
DOE OSTI2023

Field Demonstration of the Brick Ontology to Scale up the Deployment of ASHRAE Guideline 36 Control Sequences

Many commercial buildings have a vast network of sensors as part of their building automation systems (BAS) that allows opportunities for energy consumption and cost savings by deploying advanced control sequences. However, this resource is often underutilized since BAS are typically programmed with simple control sequences with limited potential to deliver on these opportunities. The recent availability of ASHRAE Guideline 36 (G36) with advanced HVAC control sequences supports control retrofits in existing buildings to unlock much of the savings potential. However, barriers such as the lack of standard naming convention of building assets and data points, proprietary equipment and BAS, and the inherent uniqueness of buildings and their systems prevent building stakeholders from adopting any “plug-and-play” implementation of G36. Instead, control vendors must often undertake the manual and labor-intensive point mapping process to identify a data stream’s functional and spatial relationship within the HVAC system along with other relevant contexts and map it to the new control sequences. The vendor must carry out the point mapping process in each individual building since the mapping is unlikely to port over to another building. Even for the same building, the point mapping process can occur multiple times if various control vendors implement different control retrofits and/or multiple control retrofits happen over the lifecycle of the building. Then, there is the likelihood that G36 control sequences are programmed uniquely to the building, preventing the same implementation from being reused in another. Therefore, this paper presents a field demonstration of how we leveraged the Brick ontology with BACnet, OpenBuildingControl’s Control Description Language (CDL), and open-source support tools to implement scalable and portable advanced building controls. These tools provide standardized semantic descriptions and relationships of the building’s assets and data points (Brick), standardized communication protocol to read from and write to the building’s BAS (BACnet), and standardized code implementations (CDL) of standardized advanced control strategies (G36). We implemented G36’s hot water supply temperature setpoint reset in a Berkeley, CA building for this field demonstration. This field demonstration aims to show how integrating these tools may streamline the deployment of advanced control sequences such as G36 in a consistent manner regardless of differences found across buildings.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS1974

Application and sensitivity investigation of Fourier transforms for microwave radiometric inversions

Existing microwave radiometer technology now provides a suitable method for remote determination of the ocean surface's absolute brightness temperature. To extract the brightness temperature of the water from the antenna temperature equation, an unstable Fredholm integral equation of the first kind was solved. Fast Fourier Transform techniques were used to invert the integral after it is placed into a cross-correlation form. Application and verification of the methods to a two-dimensional modeling of a laboratory wave tank system were included. The instability of the Fredholm equation was then demonstrated and a restoration procedure was included which smooths the resulting oscillations. With the recent availability and advances of Fast Fourier Transform techniques, the method presented becomes very attractive in the evaluation of large quantities of data. Actual radiometric measurements of sea water are inverted using the restoration method, incorporating the advantages of the Fast Fourier Transform algorithm for computations.

Holmes, J. J.↗
NASA NTRS1974

On the development of an interactive resource information management system for analysis and display of spatiotemporal data

The recent availability of timely synoptic earth imagery from the Earth Resources Technology Satellites (ERTS) provides a wealth of information for the monitoring and management of vital natural resources. Formal language definitions and syntax interpretation algorithms were adapted to provide a flexible, computer information system for the maintenance of resource interpretation of imagery. These techniques are incorporated, together with image analysis functions, into an Interactive Resource Information Management and Analysis System, IRIMAS, which is implemented on a Texas Instruments 980A minicomputer system augmented with a dynamic color display for image presentation. A demonstration of system usage and recommendations for further system development are also included.

Schell, J. A.↗
NASA NTRS1975

Application of Fourier transforms for microwave radiometric inversions

Existing microwave radiometer technology now provides a suitable method for remote determination of the ocean surface's absolute brightness temperature. To extract the brightness temperature of the water from the antenna temperature, an unstable Fredholm integral equation of the first kind is solved. Fourier transform techniques are used to invert the integral after it is placed into a cross correlation form. Application and verification of the methods to a two-dimensional modeling of a laboratory wave tank system are included. The instability of the ill-posed Fredholm equation is examined and a restoration procedure is included which smooths the resulting oscillations. With the recent availability and advances of fast Fourier transform (FFT) techniques, the method presented becomes very attractive in the evaluation of large quantities of data.

Holmes, J. J.↗
NASA NTRS1978

Response of terrestrial microorganisms to a simulated Martian environment

Soil samples from Cape Canaveral were subjected to a simulated Martian environment and assayed periodically over 45 days to determine the effect of various environmental parameters on bacterial populations. The simulated environment was based on the most recent available data, prior to the Viking spacecraft, describing Martian conditions and consisted of a pressure of 7 millibars, an atmosphere of 99.9% CO2 and 0.1% O2, a freeze-thaw cycle of -65 C for 16 h and 24 C for 8 h, and variable moisture and nutrients. Reduced pressure had a significant effect, reducing growth under these conditions. Slight variations in gaseous composition of the simulated atmosphere had negligible effect on growth. The freeze-thaw cycle did not inhibit growth, but did result in a slower rate of decline after growth had occurred. Dry samples exhibited no change during the 45-day experiment, indicating that the simulated Martian environment was not toxic to bacterial populations. Psychrotrophic organisms responded more favorably to this environment than mesophiles, although both types exhibited increases of approximately 3 logs in 7 to 14 days when moisture and nutrients were available.

Foster, T. L.↗
NASA NTRS1981

Research on design feasibility of high-power light-weight dc-to-dc converters for space power applications

Utilizing knowledge gained from past experience with experimental current-or-voltage step-up dc-to-dc converter power stages operating at output powers up to and in excess of 2 kW, a new experimental current-or-voltage step-up power stage using paralleled bipolar junction transistors (BJTs) as the controlled power switch, was constructed during the current reporting period. The major motivation behind the construction of this new experimental power stage was to improve the circuit layout so as to reduce the effects of stray circuit parasitic inductances resulting from excess circuit lead lengths and circuit loops, and to take advantage of the layout improvements which could be made when some recently-available power components, particularly power diodes and polypropylene filter capacitors, were incorporated into the design.

Wilson, T. G.↗
NASA NTRS1981

Echelle spectroscopy with a charge-coupled device /CCD/

The recent availability of large format CCD's with high quantum efficiency makes it possible to achieve significant advances in high dispersion astronomical spectroscopy. An echelle CCD combination excels or equals other techniques presently available, and offers the advantage of complete spectral coverage of several thousand Angstroms in a single exposure. Attention is given to experiments which were conducted with a CCD camera head and an echelle spectrograph on a 4-meter telescope. It was found possible to achieve a signal-to-noise ratio of 150/1 on a 13th magnitude star at 6000 A in a two-hour exposure at 0.16 A/pixel, limited primarily by photon statistics. For fainter objects, readout noise is the limiting factor in precision. For 20 electron rms readout noise, an S/N = 15/1 at 18th magnitude is expected, all other things being equal.

York, D. G.↗
NASA NTRS1982

On the interaction of auroral protons with the earth's atmosphere

The interaction of energetic auroral protons with the atmosphere is investigated. The results of a random number algorithm that describes the proton-hydrogen interconversion reactions as the beam loses energy are adopted to construct an energy deposition curve applicable over a wide range of initial proton energies. Ionization rates and production rates of ejected electrons are computed and emission rates of hydrogen Balmer alpha and beta lines are evaluated using recently available low energy cross-sections.

Rees, M. H.↗
NASA NTRS1983

Steady flow approximations to the helium r-process

A steady flow approximation to the r-process is presented and used for numerical experiments with physical quantities to determine the sensitivity of the process to variations in those quantities. The effect of neutron capture cross sections along the capture path and of recently available improved beta decay rates on the r-process are discussed. The peaks in the observed r-process yield curve near mass numbers 80 and 130 are roughly characterized by a neutron number density of 10 to the 20th per cu/cm; the mean beta decay rates are about 10/s, and the freezing time is comparable to or less than 0.1 s. The peak near mass number 195 is roughly characterized by a neutron number density of 10 to the 21st/cm, the mean beta decay rates are about 100/s, and the freezing time is comparable to or less than 0.01 s. The flow path of the steady state r-process is sensitively dependent upon the neutron capture cross sections in the flow network and on the values of the beta decay rates.

Cameron, A. G. W.↗
NASA NTRS1984

Redesign and cascade tests of a supercritical controlled diffusion stator blade-section

A supercritical stator blade section, previously tested in cascade, and characterized by a flat-roof-top suction surface Mach number distribution, has been redesigned and retested. At near design conditions, the losses and air turning were improved over the original blade by 50 percent and 7 percent respectively. The key element in the improved performance was a small blade reshaping. This produced a continuous flow acceleration over the first one-third chord of the suction surface which successfully prevented a premature laminar separation bubble. Several recently available inviscid analysis and one fully viscous (Navier-Stokes) analysis code were used in the redesign process. The validity of these codes was enhanced by the test results.

Schmidt, J. F.↗
NASA NTRS1984

Redesign and cascade tests of a supercritical controlled diffusion stator blade-section

A supercritical stator blade section, previously tested in cascade, and characterized by a flat-roof-top suction surface Mach number distribution, has been redesigned and retested. At near design conditions, the losses and air turning were improved over the original blade by 50 percent and 7 percent, respectively. The key element in the improved performance was a small blade reshaping. This produced a continuous flow acceleration over the first one-third chord of the suction surface which successfully prevented a premature laminar separation bubble. Several recently available inviscid analysis codes and one fully viscous (Navier-Stokes) analysis code were used in the redesign process. The validity of these codes was enhanced by the test results. Previously announced in STAR as N84-22533

Schmidt, J. F.↗
NASA NTRS1984

The geochemical behavior of refractory noble metals and lithophile trace elements in refractory inclusions in carbonaceous chondrites

Recent models of Ca, Al-rich (CAI) inclusion petrogenesis, and the recent availability of thermodynamic data have led to the reexamination of the geochemical behavior of the refractory noble metals (RNM) and several lithophile refractory trace elements in CAI's in the context of distillation models. Here, pertinent chemical and mineralogical properties of the various classes of refractory inclusions are reviewed, and calculations of the stability of LRTE-RNM alloys and several LRTE oxides under nebular conditions are presented. The calculations, observations and experimental results are applied to a new model of the origin of refractory metal nuggets, and a specific mechanism is identified for producing Group II chemical patterns in a cold star nebula by fractionating interstellar dust at low temperature on the basis of physical differences between different populations of pre-solar grains.

Fegley, B., Jr.↗
NASA NTRS1985

A modeling analysis program for the JPL Table Mountain Io sodium cloud data

The necessary personnel software base was established to accomplish the data processing requirements for this project. Conversion of software required in reformatting the raw Io sodium cloud data was completed and data processing activities were initiated. Slit spectra data acquired by the JPL Table Mountain Io sodium cloud observing program were reviewed and their scientific value assessed. The lifetime description for sodium atoms in the Io sodium cloud model was improved by incorporating the most recently available temperatures and densities for ions and electrons in the plasma torus.

Smyth, W. H.↗