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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Random Variables with Moment-Matching Staircase Density Functions

This paper proposes a family of random variables for uncertainty modeling. The variables of interest have a bounded support set, and prescribed values for the first four moments. We present the feasibility conditions for the existence of any of such variables, and propose a class of variables that conforms to such constraints. This class is called staircase because the density of its members is a piecewise constant function. Convex optimization is used to calculate their distributions according to several optimality criteria, including maximal entropy and maximal log-likelihood. The flexibility and efficiency of staircases enable modeling phenomena having a possibly skewed and/or multimodal response at a low computational cost. Furthermore, we provide a means to account for the uncertainty in the distribution caused by estimating staircases from data. These ideas are illustrated by generating empirical staircase predictor models. We consider the case in which the predictor matches the sample moments exactly (a setting applicable to large datasets), as well as the case in which the predictor accounts for the sampling error in such moments (a setting applicable to sparse datasets). A predictor model for the dynamics of an aeroelastic airfoil subject to flutter instability is used as an example. The resulting predictor not only describes the system's response accurately, but also enables carrying out a risk analysis for safe flight.

Luis G. Crespo↗
NASA NTRS2001

Narrow band emission from lithographically defined photonic bandgap structures in silicon: matching theory and experiment

The authors previously reported discovery of narrow, thermal emission bands from symmetrically patterned features etched into silicon wafers. In this paper, we report further results that show the measured absorption peaks for such patterned surfaces match theoretical calculations of the complete electrodynamic problem solved using the Transfer Matrix Method (TMM).

photonic↗
NASA NTRS2021

Constrained Inversion of a Microwave Snowpack Emission Model Using Dictionary Matching: Applications for GPM Satellite

This article presents a new algorithmic framework for multilayer inversion of the dense media radiative transfer (DMRT) equations of snowpack emission, with particular emphasis on the role of high-frequency microwave channels above 60 GHz. The approach relies on dictionary matching and locally constrained least squares. The results demonstrate that the algorithm can invert the DMRT model and retrieve depth, density, and grain size of a single-layer snowpack when dependencies of density and grain size on depth are properly accounted for. However, as the number of layers increases, the sensitivity of the inversion to observation noise grows markedly. Using observations, over the Great Plains in the United States, from the microwave imager onboard the global precipitation measurement (GPM, 10-166 GHz) core satellite, the initial results demonstrate that under a clear-sky condition and no vegetation canopy, the algorithm is capable to retrieve the snow depth and water equivalent of seasonal snow with a mean absolute error (MAE) of less than 0.15 m--when compared to the high-resolution analysis data from the SNOw Data Assimilation System (SNODAS).

Snow↗
NASA NTRSDate not supplied

Generative Framework Approach to Match Landsat and Sentinel-2 Data

Linear regression and histogram matching based techniques have been widely used to minimize the surface reflectance difference between two similar satellite observations such as Landsat-8/9 and Sentinel-2A/B products [1]. However, regionally or globally derived conversion factors may not be suitable for all land cover types and locations, resulting in noticeable residual differences between the sensors. Generative Adversarial Network (GAN) has shown promise in the field of image processing for domain or style transfer[2]. In this work we aim to minimize the surface reflectance difference between Landsat and Sentinel-2 products based on GAN.

Sujit Roy↗
NASA NTRS2024

Long-term effects of acute irradiation and isolation on crew age-matched mice

The future of space missions beyond low-Earth orbit presents exciting opportunities but may come with formidable health challenges. Astronauts face a unique combination of space stressors capable of exerting effects on the central nervous system (CNS) with possible sex-dependent differences. The interaction of these combined spaceflight stressors may induce oxidative stress, thereby altering brain integrity and behavioral performance. Understanding these changes is critical for safeguarding astronaut health and enabling successful exploration. By understanding the physiological responses to the combined effects of ionizing radiation (IR) and social isolation in the brain through immunohistochemistry (IHC), proteomics and cytokine expression analyses, we aim to identify CNS pathways ripe for countermeasure development to mitigate adverse brain changes with future deep space exploration. Here, we study the combined effects of simulated 5-ion galactic cosmic radiation (GCRsim) at acute dosage (5, 15, and 50 cGy) and social isolation on crew age-matched male and female mice at 124 days post-irradiation. We conducted analyses of hippocampal cytokine biomarkers and proteomic profiling on hippocampal lysates. Our findings reveal sex-specific regulation of hippocampal cytokines and proteomic profiles. Ongoing immunohistochemistry findings on the hippocampus will provide qualitative information regarding key protein expression and cellular changes such as microglial activation, blood brain barrier integrity, and neuroinflammation. With future plans for long-duration space missions, such as Mars exploration, understanding CNS changes over extended periods in mice can provide insights into potential long-term health impacts on astronauts. This project will provide us with valuable insights into sex-differences in neurobiological processes and disease mechanisms impacting men and women in space.

space radiation↗
NASA NTRS1969

Ratio matching of half-bridge weldable strain gages, computer program

Computer program reduces the unbalance of weldable half-bridge strain gage installations. The program calculates the two resistance ratios of each half-bridge gage, outputting a table of gages ranked according to resistance ratio. The tabulation forms a convenient record of gage characteristics.

Anderson, K. F.↗
NASA NTRS1969

The simulator to match the transports to come.

Flight simulator with large lateral motion for large and supersonic transport aircraft, emphasizing reproduction of cockpit accelerations due to supersonic engine thrust loss

Dusterberry, J. C.↗