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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Population assignment of migratory Westslope Cutthroat Trout (WCT) in the Clark Fork–Pend Oreille River basin

Abstract Objective The Clark Fork–Pend Oreille River basin of northeastern Washington and the Idaho Panhandle historically supported a robust metapopulation of the Westslope Cutthroat Trout (WCT) Oncorhynchus lewisi, a western native salmonid of high cultural and economic value. The construction of impassible hydroelectric dams and smaller instream barriers has prevented the return of migratory WCT to spawning tributaries, leading to the fragmentation of this metapopulation over the past 100 years. One such impassible barrier is Albeni Falls Dam (AFD) near Newport, Washington, which was completed without fish passage capabilities in 1955. We sought to examine large-scale genetic patterns in the study area and determine the most likely spawning tributary of origin for migratory WCT captured below AFD. Methods We created a genetic baseline representative of populations within the Clark Fork–Pend Oreille River basin from upstream and downstream of the dam using 191 biallelic single-nucleotide polymorphism genetic markers. Our data set included 124 collections, which allowed for an examination of population structure and hatchery influence across the study area and provided a robust tool for population assignment. Population assignment tests were conducted using the program RUBIAS. Result Population assignment tests were successful for all pure WCT of unknown origin despite potential influence from hatchery lineages across the study area. Of 83 migratory WCT captured below AFD, approximately 80% were assigned to tributaries upstream of AFD with a posterior assignment probability of at least 90%. Only one fish was assigned to a tributary downstream of AFD. Conclusion Our results indicate that AFD disrupts the natural metapopulation dynamics of WCT populations in the basin. Passage for WCT at this barrier would reestablish metapopulation connectivity within the basin by allowing migratory individuals to make genetic contributions to populations upstream of the dam.

Wells, Craig D. (ORCID:0000000258513250)↗
NASA NTRS1959

Preliminary Study of Capsule Recovery for the First Series of Project Mercury Orbital Flights

This report contains the results of a preliminary study of the search and. recovery operations required. for the safe and. expeditious return of the Mercury Recovery Capsule in the first series of orbital flights. The study is concerned primarily with the high-probability impact areas in the Atlantic Ocean. Emphasis is placed on safe recovery within reasonable time at least cost. A preliminary study of this nature is not able to provide final answers to all of the problems; the report instead constitutes a "first look" at the overall operation. Much of the report is therefore devoted to basic data, the building blocks from which recovery systems can be assembled and evaluated. These include the performance characteristics, reliability, and cost of the vehicles and equipment which may be used, and their compatibility with one another, with the capsule, and with the expected environment. The availability of vehicles and equipment has also been considered., although it is appreciated. that this may change from week to week where the forces are drawn from the military services. consideration of alternative vehicles, equipments, and systems, and their evaluation from the standpoint of effectiveness and. cost. While the equipment considered. is generally expected to be operational throughout 1960, consideration is also given to more advanced schemes which might effect reductions in recovery time, cost, or dependence upon the military forces.

Source record↗
NASA NTRS1985

Microwave responses of the western North Atlantic

Features and objects in the Western North Atlantic Ocean - the Eastern Seaboard of the United States - are observed from Earth orbit by passive microwaves. The intensities of their radiated flux signatures are measured and displayed in color as a microwave flux image. The features of flux emitting objects such as the course of the Gulf Stream and the occurrence of cold eddies near the Gulf Stream are identified by contoured patterns of relative flux intensities. The flux signatures of ships and their wakes are displayed and discussed. Metal data buoys and aircraft are detected. Signal to clutter ratios and probabilities of detection are computed from their measured irradiances. Theoretical models and the range equations that explain passive microwave detection using the irradiances of natural sources are summarized.

Stacey, J. M.↗
NASA NTRS1988

Issues on the use of meta-knowledge in expert systems

Meta knowledge is knowledge about knowledge; knowledge that is not domain specific but is concerned instead with its own internal structure. Several past systems have used meta-knowledge to improve the nature of the user interface, to maintain the knowledge base, and to control the inference engine. More extensive use of meta-knowledge is probable for the future as larger scale problems are considered. A proposed system architecture is presented and discussed in terms of meta-knowledge applications. The principle components of this system: the user support subsystem, the control structure, the knowledge base, the inference engine, and a learning facility are all outlined and discussed in light of the use of meta-knowledge. Problems with meta-constructs are also mentioned but it is concluded that the use of meta-knowledge is crucial for increasingly autonomous operations.

Facemire, Jon↗
NASA NTRS1989

Reliability-based failure analysis of brittle materials

The reliability of brittle materials under a generalized state of stress is analyzed using the Batdorf model. The model is modified to include the reduction in shear due to the effect of the compressive stress on the microscopic crack faces. The combined effect of both surface and volume flaws is included. Due to the nature of fracture of brittle materials under compressive loading, the component is modeled as a series system in order to establish bounds on the probability of failure. A computer program was written to determine the probability of failure employing data from a finite element analysis. The analysis showed that for tensile loading a single crack will be the cause of total failure but under compressive loading a series of microscopic cracks must join together to form a dominant crack.

Powers, Lynn M.↗
NASA NTRS1990

Real-time adaptive aircraft scheduling

One of the most important functions of any air traffic management system is the assignment of ground-holding times to flights, i.e., the determination of whether and by how much the take-off of a particular aircraft headed for a congested part of the air traffic control (ATC) system should be postponed in order to reduce the likelihood and extent of airborne delays. An analysis is presented for the fundamental case in which flights from many destinations must be scheduled for arrival at a single congested airport; the formulation is also useful in scheduling the landing of airborne flights within the extended terminal area. A set of approaches is described for addressing a deterministic and a probabilistic version of this problem. For the deterministic case, where airport capacities are known and fixed, several models were developed with associated low-order polynomial-time algorithms. For general delay cost functions, these algorithms find an optimal solution. Under a particular natural assumption regarding the delay cost function, an extremely fast (O(n ln n)) algorithm was developed. For the probabilistic case, using an estimated probability distribution of airport capacities, a model was developed with an associated low-order polynomial-time heuristic algorithm with useful properties.

Kolitz, Stephan E.↗
NASA NTRS1992

Network problem threshold

Network transmission errors such as collisions, CRC errors, misalignment, etc. are statistical in nature. Although errors can vary randomly, a high level of errors does indicate specific network problems, e.g. equipment failure. In this project, we have studied the random nature of collisions theoretically as well as by gathering statistics, and established a numerical threshold above which a network problem is indicated with high probability.

Gejji, Raghvendra, R.↗
NASA NTRS2004

Scatter in Carbon/Silicon Carbide (C/SiC) Composites Quantified

Carbon-fiber-reinforced silicon carbide matrix (C/SiC) composites processed by chemical vapor infiltration are candidate materials for aerospace thermal structures. Carbon fibers can retain properties at very high temperatures, but they are known to have poor oxidation resistance in adverse, high-temperature environments. Nevertheless, the combination of CVI-SiC matrix with higher stiffness and oxidation resistance, the interfacial coating, and additional surface-seal coating provides the necessary protection to the carbon fibers, and makes the material viable for high-temperature space applications operating under harsh environments. Furthermore, C/SiC composites, like other ceramic matrix composites (CMCs), exhibit graceful non-catastrophic failure because of various inherent energy dissipating mechanisms. The material exhibits nonlinearity in deformation even at very low stress levels. This is the result of the severe matrix microcracking present in the as processed composite because of large differences between the coefficients of thermal expansion of the fiber and the matrix. Utilization of these advanced composites in next generation space vehicles will require innovative structural configurations, updated materials, and refined analyses. Structural safety issues for these vehicles are in direct competition with performance and cost. One would have to quantify the uncertainties associated with the design using formal probabilistic methods. Specifically four fundamental aspects on which analyses are based-- (1) loading conditions, (2) material behavior, (3) geometrical configurations, and (4) structural connections between the composite components and baseline structure--are stochastic in nature. A direct way to formally account for uncertainties is to develop probabilistic structural analysis methods where all participating variables are described by appropriate probability density functions. The present work, however, focuses on analyzing the stochastic material behavior of these advanced composites using formal probabilistic analysis methods. Often, some of the desirable property characteristics that allow composites to offer advantages over conventional structural materials (like tailoring of composite properties) and the complexity are in fact responsible for their greater statistical variability and the requirements for more characterization tests. Composite properties are anisotropic as well, having different properties in different directions. This means that characterization of a property such as stiffness--which will vary greatly depending on the orientation of the fiber relative to the direction of the testing--must be repeated for several different directions and loading conditions. The fabrication process for composites also introduces statistical variations in properties and geometry. A composite part is produced in a number of steps, each of which introduces statistical variability. The matrix is usually produced from a combination of raw materials; and the fiber, which has its own set of properties, is often coated or surface treated, introducing yet another source of variability.

Murthy, Pappu L. N.↗
DOE OSTI2025

Re-examining urban rainfall enhancement over North America

Abstract Quantifying intensification/suppression of precipitation over urban areas relative to their rural surroundings can inform efforts to reduce urban flooding. Few studies have systematically addressed whether urban areas exhibit a higher/lower probability of precipitation and/or higher/lower annual total precipitation and/or intensification/weakening of intense precipitation events relative to nearby rural areas across a range of hydroclimatic conditions and urban contexts. Here we address this literature gap using the IMERG V07 data set and analyses of rural and urban samples drawn from 47 conurbations across North America. Specifically, we quantify whether/how precipitation regimes over the urban grid cells differ from those in rural grid cells located 100–250 km from the city center and at a similar elevation. As in previous research, there is evidence that both the probability of precipitation and annual total precipitation are typically higher in the urban grid cells. However, most conurbations have lower upper percentile precipitation rates in the urban sample and lower median precipitation rates above the 95th percentile than are present in samples drawn from rural grid cells. Thus, these conurbations are not, on average, intensifying high-magnitude precipitation events over urban grid cells. Further, the total volume of water accumulated at the surface during events of equivalent duration is not systematically higher over the urban areas, and 20 year return period values of 30 min and wettest pentad precipitation are also not systematically higher over the urban areas. The nature of urban modification of precipitation is a strong function of the prevailing hydroclimate. For example, the heaviest rainfall periods are enhanced over urban grid cells within regional hydroclimates where the overall probability of precipitation and annual total precipitation are low. Conversely, there is evidence for urban suppression of the highest percentile precipitation rates in wetter hydroclimates.

Pryor, Sara C. (ORCID:0000000348473440)↗
DOE OSTI2022

Probabilistic constrained Bayesian inversion for transpiration cooling

Abstract To enable safe operations in applications such as rocket combustion chambers, the materials require cooling to avoid material damage. Here, transpiration cooling is a promising cooling technique. Numerous studies investigate possibilities to simulate and evaluate the complex cooling mechanism. One naturally arising question is the amount of coolant required to ensure a safe operation. To study this, we introduce an approach that determines the posterior probability distribution of the Reynolds number using an inverse problem and constraining the maximum temperature of the system under parameter uncertainties. Mathematically, this chance inequality constraint is dealt with by a generalized polynomial chaos expansion of the system. The posterior distribution will be evaluated by different Markov chain Monte Carlo based methods. A novel method for the constrained case is proposed and tested among others on two‐dimensional transpiration cooling models.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Human-induced changes to the global ocean water masses and their time of emergence

The World Ocean is rapidly changing, with global and regional modification of temperature and salinity, resulting in widespread and irreversible impacts. While the most pronounced observed temperature and salinity changes are located in the upper ocean, changes in water masses at depth have been identified and will probably strengthen in the future. In this study, using 11 climate models, we define when anthropogenic temperature and salinity changes are expected to emerge from natural variability in the ocean interior along density surfaces. The models predict that in 2020, 20–55% of the Atlantic, Pacific and Indian basins have an emergent anthropogenic signal; reaching 40–65% in 2050 and 55–80% in 2080. The well-ventilated Southern Ocean water masses emerge very rapidly, as early as the 1980–1990s, while the Northern Hemisphere water masses emerge in the 2010–2030s. Our results highlight the importance of maintaining and augmenting an ocean observing system capable of detecting and monitoring persistent anthropogenic changes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Improved information criteria for Bayesian model averaging in lattice field theory

Bayesian model averaging is a practical method for dealing with uncertainty due to model specification. Use of this technique requires the estimation of model probability weights. Here, we revisit the derivation of estimators for these model weights. Use of the Kullback-Leibler divergence as a starting point leads naturally to a number of alternative information criteria suitable for Bayesian model weight estimation. We explore three such criteria, known to the statistics literature before, in detail: a Bayesian analog of the Akaike information criterion which we call the BAIC, the Bayesian predictive information criterion, and the posterior predictive information criterion (PPIC). We compare the use of these information criteria in numerical analysis problems common in lattice field theory calculations. We find that the PPIC has the most appealing theoretical properties and can give the best performance in terms of model-averaging uncertainty, particularly in the presence of noisy data, while the BAIC is a simple and reliable alternative.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1983

Sixth foray for pristine nonmare rocks and an assessment of the diversity of lunar anorthosites

A compositional and petrographic characterization of 11 nonmare samples shows five to be pristine, and four probably pristine. Five of the 11 are unique anorthosites that considerably extend the diversity of lunar anorthosites. Alkali anorthosites are rich in incompatible elements. The nature of the correlations between longitude and such parameters as Eu and Sm concentrations, and Sc/Sm, Ti/Sm, and Ca/Na ratios, has been elucidated for the case of the pristine samples because five are fro a western site (Apollo 14). The ratios determined for the ferroan anorthosite 14312c are close to normal, but significantly displaced in the direction of the nonferroan, western pristine rocks. This suggests that the composition-longitude relationships are as old as the late stages of the crystallization of the putative magma ocean.

Warren, P. H.↗
NASA NTRS1987

Helicity fluctuations in incompressible turbulent flows

Results from direct numerical simulations of several homogeneous flows and fully developed turbulent channel flow indicate that the probability distribution function (pdf) of relative helicity density exhibits at most a 20 percent deviation from a flat distribution. Isotropic flows exhibit a slight helical nature but the presence of mean strain in homogeneous turbulence suppresses helical behavior. All the homogeneous turbulent flows studied show no correlation between relative helicity density and the dissipation of turbulent kinetic energy. The channel flow simulations indicate that, except for low-dissipation regions near the outer edge of the buffer layer, there is no tendency for the flow to be helical. The strong peaks in the relative helicity density pdf and the association of these peaks with regions of low dissipation found in previous simulations by Pelz et al.(1985) are not observed.

Rogers, Michael M.↗
NASA NTRS1991

Extreme ultraviolet transmission of a synthetic diamond thin film

Measurements are presented of a thin film of synthetic diamond at various wavelengths in the extreme ultraviolet. The synthetic diamond combines the transmission properties of carbon with the strength, density, and ruggedness of a natural diamond. The Extreme Ultraviolet Transmission (EUV) of a film of the synthetic diamond has shown the existence of a thin surface layer of silicon, probably in the form of silicon carbide, which is not a contaminant layer.

Vallerga, John V.↗
NASA NTRS1999

Polar Layered Terrains: Links Between the Martian Volatile and Dust Cycles

The nature, origin and evolution of the polar layered terrains are a major mystery of Martian climate. Almost every aspect of these enigmatic terrains surrounding, and probably underlying, the polar residual ice caps is in contention. Are the polar laminae forming today? Are they inactive or even eroding, being mere relics of the past? Are the north and south polar layered terrains fundamentally different in composition, age or process? Are they a physical record of past, possibly cyclic, climate change and, if so, can we learn to read that record? We know from past Mariner 9 and Viking orbital observations that there are layered terrains at high latitudes, defined by alternating bands of visually lighter and darker material appearing in stacks hundreds of meters thick with individual bands as thin as could then be resolved (tens of meters). In this talk, aspects of the polar layered terrains will be reviewed with emphasis on issues likely to be addressed with data from ongoing and near-term flight missions to Mars. Particular attention will be given to what might be learned from observing the present seasonal cycles of dust, water and carbon dioxide on Mars, in conjunction with in situ data from one site on the south polar layered terrain.

Zurek, R. W.↗
NASA NTRS2004

An Off-Axis Model for GRB 031203

The low luminosity radio emission of the unusually faint GRB 031203 has been argued to support the idea of a class of intrinsically sub-energetic gamma-ray bursts (GRBs), currently comprising two members. While low energy GRBs probably exist, we show that the collective prompt and multiwavelength observations of the afterglow of GRB 031203, do not necessarily require a sub-energetic nature for that event. In fact, the data are more consistent with a typical, powerful GRB seen at an angle of about twice the opening angle of the central jet. The (redshift corrected) peak energy, E(sub p), of GRB 031203 then becomes approximately 2 MeV, similar to many other GRBs.

Ramirez-Ruiz, Enrico↗
NASA NTRS2008

Design of Launch Abort System Thrust Profile and Concept of Operations

This paper describes how the Abort Motor thrust profile has been tailored and how optimizing the Concept of Operations on the Launch Abort System (LAS) of the Orion Crew Exploration Vehicle (CEV) aides in getting the crew safely away from a failed Crew Launch Vehicle (CLV). Unlike the passive nature of the Apollo system, the Orion Launch Abort Vehicle will be actively controlled, giving the program a more robust abort system with a higher probability of crew survival for an abort at all points throughout the CLV trajectory. By optimizing the concept of operations and thrust profile the Orion program will be able to take full advantage of the active Orion LAS. Discussion will involve an overview of the development of the abort motor thrust profile and the current abort concept of operations as well as their effects on the performance of LAS aborts. Pad Abort (for performance) and Maximum Drag (for separation from the Launch Vehicle) are the two points that dictate the required thrust and shape of the thrust profile. The results in this paper show that 95% success of all performance requirements is not currently met for Pad Abort. Future improvements to the current parachute sequence and other potential changes will mitigate the current problems, and meet abort performance requirements.

Litton, Daniel↗