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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Sensitivity and vulnerability to summer heat extremes in major cities of the United States

Many cities are experiencing increases in extreme heat because of global temperature rise combined with the urban heat island effect. The heterogeneity of urban morphology also leads to fine-scale variability in potential for heat exposure. Yet, how this rise in temperature and local variability together impacts urban residents differently at exposure-relevant scales is still not clear. Here we map the Universal Thermal Climate Index, a more complete indicator of human heat stress at an unprecedentedly fine spatial resolution (1 m), for 14 major cities in the United States using urban microclimate modeling. We examined the different heat exposure levels across different socioeconomic and racial/ethnic groups in these cities, finding that income level is most consistently associated with heat stress. We further conducted scenario simulations for a hypothetical 1 °C increase of air temperature in all cities. Results show that a 1 °C increase would have a substantial impact on human heat stress, with impacts that differ across cities. The results of this study can help us better evaluate the impact of extreme heat on urban residents at decision-relevant scales.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Fast and accurate learned multiresolution dynamical downscaling for precipitation

Abstract. This study develops a neural-network-based approach for emulating high-resolution modeled precipitation data with comparable statistical properties but at greatly reduced computational cost. The key idea is to use combination of low- and high-resolution simulations (that differ not only in spatial resolution but also in geospatial patterns) to train a neural network to map from the former to the latter. Specifically, we define two types of CNNs, one that stacks variables directly and one that encodes each variable before stacking, and we train each CNN type both with a conventional loss function, such as mean square error (MSE), and with a conditional generative adversarial network (CGAN), for a total of four CNN variants. We compare the four new CNN-derived high-resolution precipitation results with precipitation generated from original high-resolution simulations, a bilinear interpolater and the state-of-the-art CNN-based super-resolution (SR) technique. Results show that the SR technique produces results similar to those of the bilinear interpolator with smoother spatial and temporal distributions and smaller data variabilities and extremes than the original high-resolution simulations. While the new CNNs trained by MSE generate better results over some regions than the interpolator and SR technique do, their predictions are still biased from the original high-resolution simulations. The CNNs trained by CGAN generate more realistic and physically reasonable results, better capturing not only data variability in time and space but also extremes such as intense and long-lasting storms. The new proposed CNN-based downscaling approach can downscale precipitation from 50 to 12 km in 14 min for 30 years once the network is trained (training takes 4 h using 1 GPU), while the conventional dynamical downscaling would take 1 month using 600 CPU cores to generate simulations at the resolution of 12 km over the contiguous United States.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

DSGAN

This study develops a neural network-based approach for emulating high-resolution modeled precipitation data with comparable statistical properties but at greatly reduced computational cost. The key idea is to use combination of low-and high- resolution simulations to train a neural network to map from the former to the latter. Specifically, we define two types of CNNs, one that stacks variables directly and one that encodes each variable before stacking, and we train each CNN type both with a conventional loss function, such as mean square error (MSE), and with a conditional generative adversarial network (CGAN), for a total of four CNN variants. We compare the four new CNN-derived high-resolution precipitation results with precipitation generated from original high resolution simulations, a bilinear interpolater and the state-of-the-art CNN-based super-resolution (SR) technique. Results show that the SR technique produces results similar to those of the bilinear interpolator with smoother spatial and temporal distributions and smaller data variabilities and extremes than the original high resolution simulations. While the new CNNs trained by MSE generate better results over some regions than the interpolator and SR technique do, their predictions are still not as close as the original high resolution simulations. The CNNs trained by CGAN generate more realistic and physically reasonable results, better capturing not only data variability in time and space but also extremes such as intense and long-lasting storms. The new proposed CNN-based downscaling approach can downscale precipitation from 50~km to 12~km in 14~min for 30~years

LIU, ZHENGCHUN↗
NASA NTRS1976

Martian albedo feature variations with season - Data of 1971 and 1973

A qualitative and quantitative study of some recent seasonal and secular albedo variations on Mars is presented, based on improved red-filter photographs obtained during the 1971 and 1973 apparitions. The measurement of albedo features showing significant changes and uncommonly bright areas is described in detail. Photographic differential photometry of 21 albedo features in three longitude regions is also discussed. The major findings are: (1) seasonal differences of the mean brightness ratios for most features were consistent with contrast changes shown on photographic maps, (2) seasonal variations of brightness with latitude and region occurred, (3) most albedo features were more variable during southern spring than summer, (4) a general loss of relative contrast was experienced during southern summer, and (5) no systematic dependence on solar phase angle was detected within the range spanned by both sets of photographs. Possible causes of the variations are considered.

Capen, C. F., Jr.↗
NASA NTRS1977

Variable pitch fan system for NASA/Navy research and technology aircraft

Preliminary design of a shaft driven, variable-pitch lift fan and lift-cruise fan was conducted for a V/STOL Research and Technology Aircraft. The lift fan and lift-cruise fan employed a common rotor of 157.5 cm diameter, 1.18 pressure ratio variable-pitch fan designed to operate at a rotor-tip speed of 284 mps. Fan performance maps were prepared and detailed aerodynamic characteristics were established. Cost/weight/risk trade studies were conducted for the blade and fan case. Structural sizing was conducted for major components and weights determined for both the lift and lift-cruise fans.

Ryan, W. P.↗
NASA NTRS1981

Improving streamflow estimates through the use of LANDSAT

Estimates of low flow and flood frequency in several southwestern Wisconsin basins were improved by determining land cover from LANDSAT imagery. With the use of estimates of land cover in multiple-regression techniques, the standard error of estimate (SE) for the least annual 7-day low flow for 2- and 10-year recurrence intervals of ungaged sites were lowered by 9% each. The SE of flood frequency in the 'Driftless Area' of Wisconsin for 10-, 50-, and 100-year recurrence intervals were lowered by 14%. Four of nine basin characteristics determined from satellite imagery were significant variables in the multiple-regression techniques, whereas only 1 of the 12 characteristics determined from topographic maps was significant. The percentages of land cover categories in each basin were determined by merging basin boundaries, digitized from quadrangles, with a classified LANDSAT scene. Both the basin boundary X-Y polygon coordinates and the satellite coordinates were converted to latitude-longitude for merging compatibility.

Allord, G. J.↗
NASA NTRS1981

Oceanic eddy variability measured by GEOS 3 altimeter crossover differences

Eddy statistics of sea height variations associated with dynamic ocean currents, gathered by GEOS 3 altimetry (25 cm), are discussed. Time variable flow is noted to be measureable using altimeter height and orbit information by means of three techniques: collinear tracks, where rms variability can be determined for mesoscale phenomena measured along parallel tracks; mean surfaces, using a 3-dimensional mapping of the sea surface for an accurate representation of the surface undulations; and crossover differences, such as between data tracks from GEOS and Seasat which have reduced ephemeris error over scales of a few thousand km. Mesoscale energetics have been found suitable for tracing meandering ocean currents by the crossover method. Possible sources of error are considered, including altimeter noise, orbit error, short wavelength continental shelf tides, etc., and it is determined that observations of mesoscale sea height appear to be limited only by uncertainties in the altimetry, which for Seasat was 5 cm over 60% of the world's oceans.

Cheney, R. E.↗
NASA NTRS1984

Geology of Dione

Dione is one of the most geologically complex of the Saturnian satellites. Crater counts and surface morphology indicates the geologic units observed are of variable age and origin. In an attempt to understand the processes which have affected Dione, a geologic map was prepared. Several geologic units were identified; ancient heavily cratered terrain, two plains units: cratered plains and lightly cratered plains, lobate deposits, crater rim deposits and bright wispy materials.

Plescia, J. B.↗
NASA NTRS1986

Thermospheric nitric oxide and its role in thermospheric dynamics and composition

The global distribution of thermospheric nitric oxide has been measured under different geophysical conditions by the Atmosphere Explorer (AE) and Solar Mesosphere Explorer (SME) satellites. These observations show a great variability in the NO concentration but the existence of a latitudinal gradient is clearly evidenced by statistical maps of the NO meridional distribution. A two dimensional zonally averaged chemical-dynamical model was used to investigate the importance of nitric oxide 5.3 micrometer cooling and its role on thermospheric temperature, dynamics and major gas composition. For this purpose, a 2-D background atmosphere code and an odd nitrogen code were coupled and run to steady state. The NO distribution obtained is in good agreement with the AE-D global picture calculated at solstice for solar minimum activity. The importance of each term in the thermodynamic equation was studied spatially. It is found that the NO I.R. cooling term competes with conduction in the upper thermosphere and reaches its maximum value near 200 km at high summer latitudes. The primary effect of including the NO cooling term is to increase the temperature in the upper winter thermosphere and decrease it in the other hemisphere, if the global average temperature is fixed. In general, the strength of the circulation is decreased and the thermal gradient is smoother. As a consequence of these changes in the wind and temperature fields, the O2, N2 and O densities also react to the effect of the NO cooling. The importance of this process depends on the level of solar activity which controls the NO distribution.

Gerard, J. C.↗
NASA NTRS1989

Deep circulations under simple classes of stratification

Deep circulations where the motion field is vertically aligned over one or more scale heights are studied under barotropic and equivalent barotropic stratifications. The study uses two-dimensional equations reduced from the three-dimensional primitive equations in spherical geometry. A mapping is established between the full primitive equations and general shallow water behavior and the correspondence between variables describing deep atmospheric motion and those of shallow water behavior is established.

Salby, Murry L.↗
NASA NTRS1990

A three-dimensional dynamic solution-adaptive mesh algorithm

A solution-adaptive grid algorithm has been developed for use in two and three dimensions. The algorithm uses a transformation from the cartesian coordinate system to a general coordinate space, which will be defined as a parallelepiped. A weighting function for adaption of the grid is developed that will allow adaption to the gradients of any combination of dependent variables in the flow. The adaption is carried out in the parametric space and a simple inverse mapping to return the new parametric space to the physical space is derived. The concept used to relocate the grid-points in the parametric space is based on the center of mass of distributed weights. Solution-adaptive results are presented for various laminar flows in two dimensions and for mathematical weighting functions in three dimensions.

Benson, Rusty A.↗
NASA NTRS1990

Kinematic analysis of 7 DOF anthropomorphic arms

A kinematic analysis of anthropomorphic seven-degree-of-freedom serial link spatial manipulators with revolute joints is presented. To uniquely determine joint angles for a given end-effector position and orientation, the redundancy is parameterized by a scalar variable which corresponds to the angle between the arm plane and a reference plane. The forward kinematic mappings from joint-space to end-effector coordinates and arm angle and the augmented Jacobian matrix which gives end-effector and arm angle rates as functions of joint rates are given. Conditions under which the augmented Jacobian becomes singular are given and are shown to correspond to the arm being either at a kinematically singular configuration or at a nonsingular configuration for which the arm angle ceases to parameterize the redundancy.

Kreutz-Delgado, K.↗
NASA NTRS1991

Transformation of two and three-dimensional regions by elliptic systems

A reliable linear system is presented for grid generation in 2-D and 3-D. The method is robust in the sense that convergence is guaranteed but is not as reliable as other nonlinear elliptic methods in generating nonfolding grids. The construction of nonfolding grids depends on having reasonable approximations of cell aspect ratios and an appropriate distribution of grid points on the boundary of the region. Some guidelines are included on approximating the aspect ratios, but little help is offered on setting up the boundary grid other than to say that in 2-D the boundary correspondence should be close to that generated by a conformal mapping. It is assumed that the functions which control the grid distribution depend only on the computational variables and not on the physical variables. Whether this is actually the case depends on how the grid is constructed. In a dynamic adaptive procedure where the grid is constructed in the process of solving a fluid flow problem, the grid is usually updated at fixed iteration counts using the current value of the control function. Since the control function is not being updated during the iteration of the grid equations, the grid construction is a linear procedure. However, in the case of a static adaptive procedure where a trial solution is computed and used to construct an adaptive grid, the control functions may be recomputed at every step of the grid iteration.

Mastin, C. Wayne↗
NASA NTRS1993

Incongruity, incongruity resolution, and mental states: The measure and modification of situational awareness and control

The research reported here describes the process of induction of various mental states. Our goals were to measure and to manipulate both the behavioral and the neurological correlates of particular mental states that have previously been demonstrated to be either beneficial or deleterious to in-flight performance situations. The experimental paradigm involved developing a context of which the participants were aware, followed by the introduction of an incongruity into that context. The empirical questions involved how the incongruity was resolved and the consequent effects on mental state. The dependent variables were measures of both the short-term ERP changes and the longer-term brain mapping indications of predominant mental states. The mission of NASA Flight Management Division and Human/Automation Integration Branch centers on the understanding and improvement of interaction between a complex system and a human operator. Specifically, the goal is improved efficiency through better operative procedures and control strategies. More efficient performance in demanding flight environments depends on improved situational awareness and replanning for fault management.

Derks, Peter L.↗
NASA NTRS2001

Multi-Epoch XMM Observations of NGC4258

The goal of this project is to better understand whether the well known, warped accretion disk around the supermassive black hole in NGC4258 is responsible for the observed X-ray absorbing column of gas. The active galactic nuclei (AGN) paradigm suggests that doughnut-like tori obscure black holes, not warped disks. Using radio interferometry, we have mapped the disk and its orientation. Through time monitoring radio observations we are following the rotation and variability in the disk structure. The disk crosses the line of sight to the black hole, if it is clumpy, then we will observe variations in the X-ray spectrum of NGC4258 on month to year time scales. We have reduced 14 epochs of very long base interferometry (VLBI) observations that we use to characterize the structure of the maser-laden accretion disk and its evolution. Five epochs of data remain to be reduced in the next year. We have received distributions of data for two of our four intended epochs of X-ray Multimirror Mission (XMM) observation. Because the first two epochs are relatively close in time, and because community understanding of how to calibrate XMM data has until recently been relatively immature, we are waiting until we receive the third epoch of data before we reduce the several datasets. Delivery of the third epoch should take place late this year. The last epoch of XMM observation will take place in mid-2002. In the next year, we will begin to combine constraints on disk clumpiness with estimates of X-ray variability observed by XMM.

Greenhill, Lincoln J.↗
NASA NTRS2006

The Glacier and Land Ice Surface Topography Interferometer (GLISTIN): A Novel Ka-band Digitally Beamformed Interferometer

The estimation of the mass balance of ice sheets and glaciers on Earth is a problem of considerable scientific and societal importance. A key measurement to understanding, monitoring and forecasting these changes is ice-surface topography, both for ice-sheet and glacial regions. As such NASA identified 'ice topographic mapping instruments capable of providing precise elevation and detailed imagery data for measurements on glacial scales for detailed monitoring of ice sheet, and glacier changes' as a science priority for the most recent Instrument Incubator Program (IIP) opportunities. Funded under this opportunity is the technological development for a Ka-Band (35GHz) single-pass digitally beamformed interferometric synthetic aperture radar (InSAR). Unique to this concept is the ability to map a significant swath impervious of cloud cover with measurement accuracies comparable to laser altimeters but with variable resolution as appropriate to the differing scales-of-interest over ice-sheets and glaciers.

ice surface topography↗
NASA NTRS2015

Advances in Remote Sensing for Vegetation Dynamics and Agricultural Management

Spaceborne remote sensing has led to great advances in the global monitoring of vegetation. For example, the NASA Global Inventory Modeling and Mapping Studies (GIMMS) group has developed widely used datasets from the Advanced Very High Resolution Radiometer (AVHRR) sensors as well as the Moderate Resolution Imaging Spectroradiometer (MODIS) map imagery and normalized difference vegetation index datasets. These data are valuable for analyzing vegetation trends and variability at the regional and global levels. Numerous studies have investigated such trends and variability for both natural vegetation (e.g., re-greening of the Sahel, shifts in the Eurasian boreal forest, Amazonian drought sensitivity) and crops (e.g., impacts of extremes on agricultural production). Here, a critical overview is presented on recent developments and opportunities in the use of remote sensing for monitoring vegetation and crop dynamics.

variability↗
NASA NTRS2019

Low-Thrust Trajectory Design for a Cislunar CubeSat Leveraging Structures from the Bicircular Restricted Four-Body Problem

The upcoming Lunar IceCube (LIC) mission will deliver a 6U CubeSat to a low lunar orbit via a ride-share opportunity during NASAs Artemis 1 mission. This presents a challenging trajectory design scenario, as the vast change in energy required to transfer from the initial deployment state to the destination orbit is compounded by the limitations of the LICs low-thrust engine. This investigation addresses these challenges by developing a trajectory design framework that utilizes dynamical structures available in the Bicircular Restricted Four-Body Problem (BCR4BP) along with a robust direct collocation algorithm. Maps are created that expedite the selection of invariant manifold paths from a periodic staging orbit in the BCR4BP that offer favorable connections between the LIC transfer phases. Initial guesses assembled from these maps are passed to a direct collocation algorithm that corrects them in the BCR4BP while including the variable low-thrust acceleration of the spacecraft engine. Results indicate that the ordered motion provided by the BCR4BP and the robustness of direct collocation combine to offer an efficient and adaptable framework for designing a baseline trajectory for the LIC mission.

Pritchett, Robert↗