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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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NASA NTRS2022

Ultraviolet Spectropolarimetry Conservative and Nonconservative Mass Transfer in OB Interacting Binaries

The current consensus is that at least half of the OB stars are formed in binary or multiple star systems. The evolution of OB stars is greatly influenced by whether the stars begin as close binaries, and the evolution of the binary systems depend on whether the mass transfer is conservative or nonconservative. FUV/NUV spectropolarimetry is poised to answer the latter question. This paper discusses how the Polstar spectropolarimetry mission can characterize the degree of nonconservative mass transfer that occurs at various stages of binary evolution, from the initial mass reversal to the late Algol phase, and quantify its amount. The proposed instrument combines spectroscopic and polarimetric capabilities, where the spectroscopy can resolve Doppler shifts in UV resonance lines with 10 km/s precision, and polarimetry can resolve linear polarization with 10 −3 precision or better. The spectroscopy will identify absorption by mass streams and other plasmas seen in projection against the stellar disk as a function of orbital phase, as well as scattering from extended splash structures, including jets. The polarimetry tracks the light coming from material not seen against the stellar disk, allowing the geometry of the scattering to be tracked, resolving ambiguities left by the spectroscopy and light-curve information. For example, nonconservative mass streams ejected in the polar direction will produce polarization of the opposite sign from conservative transfer accreting in the orbital plane. Time domain coverage over a range of phases of the binary orbit are well supported by the Polstar observing strategy. Special attention will be given to the epochs of enhanced systemic mass loss that have been identified from IUE observations (pre-mass reversal and tangential gas stream impact). We show how the history of systemic mass and angular momentum loss/gain episodes can be inferred via ensemble evolution through the r–q diagram. Combining the above elements will significantly improve our understanding of the mass transfer process and the amount of mass that can escape from the system, an important channel for changing the final mass and ultimate supernova of a large number of massive stars found in binaries at close enough separation to undergo interaction.

Geraldine J. Peters↗

NASA NTRS1993

The development of a natural language interface to a geographical information system

This paper will discuss a two and a half year long project undertaken to develop an English-language interface for the geographical information system GRASS. The work was carried out for NASA by a small business, Netrologic, based in San Diego, California, under Phase 1 and 2 Small Business Innovative Research contracts. We consider here the potential value of this system whose current functionality addresses numerical, categorical and boolean raster layers and includes the display of point sets defined by constraints on one or more layers, answers yes/no and numerical questions, and creates statistical reports. It also handles complex queries and lexical ambiguities, and allows temporarily switching to UNIX or GRASS.

Toledo, Sue Walker↗

NASA NTRSDate not supplied

Reference Command Optimization for the Transition Flight Mode of a Lift plus Cruise Vehicle

Advanced air mobility mainly utilizes vehicles that are capable of vertical takeoff and landing (VTOL) for the simplicity of operation and large-scale deployment. However, VTOL vehicles need specialized trajectory and command design for the transition phase, where the vehicles transition between rotor-borne flight and wing-borne flight. Since VTOL vehicles are commonly designed as over-actuated systems for redundancy, one challenge that arises is actuator ambiguity, where it is unclear how to uniquely command actuators for the VTOL vehicle to track a given trajectory. We propose a method to design optimal reference commands for the transition mode. By formulating an 𝑙 1 -norm cost function on the rotor thrusts of the vehicle, we can achieve economical operation of the rotors such that they only operate when necessary and efficiently utilize the aerodynamics to save energy from reduced rotor actuation. We validate our approach in simulations and show its benefit compared to the commonly used differential flatness-based method.

John L Bullock↗

DOE OSTI2025

Influence of strain-rate on the response of elastomeric architected materials

Architected materials have shown substantial promise in impact mitigation and protective applications, and there has accordingly been great interest in better characterizing their response at elevated strain rates due to impact. There remains ambiguity regarding the contribution of inertial and material responses to strain rate sensitivity, and, in particular, when these effects begin to gain dominance in the impact response of an architected material. The response of soft polymer architected materials as a function of strain rate, in particular, has been little investigated. We characterize the experimental impact response of four soft polymer architected lattice geometries across varying strain rates in the intermediate strain rate regime (∼10 3 s −1 ) using split-Hopkinson pressure bar loading and high speed video characterization of the resulting deformation fields. In conclusion, our results highlight the interplay of influence between constituent material, lattice geometry, length scale, and strain rate in determining the onset of significant inertia effects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1992

ERS-1 scatterometer calibration and validation activities at ECMWF. B: From radar backscatter characteristics to wind vector solutions

Calibration and validation activities for the ERS-1 scatterometer were carried out at ECMWF (European Center for Medium range Weather Forecast) complementary to the 'Haltenbanken' field campaign off the coast of Norway. At a Numerical Weather Prediction (NWP) center a wealth of verifying data is available both in time and space. This data is used to redefine the wind retrieval procedure given the instrumental characteristics. It was found that a maximum likelihood estimation procedure to obtain the coefficients of a reformulated sigma deg to wind relationship should use radar measurements in logarithmic rather than physical space, and use winds as the wind components rather than wind speed and direction. Doing this, a much more accurate transfer function than the one currently operated by ESA was derived. Sigma deg measurement space shows no signature of a separation in an upwind solution cone and a downwind solution cone. As such signature was anticipated in ESA's wind direction ambiguity removal algorithm, reconsideration of the procedure is necessary. Despite the fact that revisions have to be made in the process of wind retrieval; a grid potential is shown for scatterometry in meteorology and climatology.

Stoffelen, AD↗

NASA NTRS1992

Long-time behavior of material-surface curvature in isotropic turbulence

The behavior at large times of the curvature of material elements in turbulence is investigated using Lagrangian velocity-gradient time series obtained from direct numerical simulations of isotropic turbulence. The main objectives are: to study the asymptotic behavior of the pdf curvature as a function of initial curvature and shape; and to establish whether the curvature of an initially plane material element goes to a stationary probability distribution. The evidence available in the literature about the asymptotic curvature-pdf of initially flat surfaces is ambiguous, and the conjecture is that it is quasi-stationary. In this work several material-element ensembles of different initial curvatures and shapes are studied. It is found that, at long times the moments of the logarithm of curvature are independent of the initial pdf of curvature. This, it is argued, supports the view that the curvature attains a stationary distribution at long times. It is also shown that, irrespective of initial shape or curvature, the shape of any material element at long times is cylindrical with a high probability.

Girimaji, S. S.↗

DOE OSTI2025

Clarifying Terminology in Microbial Ecology: A Call for Precision in Scientific Communication

The rapid evolution of microbiology as a field of research has led to the introduction of new terminology and the adaptation of existing terms. However, inconsistencies in the use of these terms, including variations across different scientific disciplines, can lead to confusion and miscommunication within the scientific community. This article discusses the importance of precise terminology in microbiome research, highlighting examples where terms have been misused or redefined without clear justification. We also present a list of frequently used terms in microbial ecology along with their specific definitions. We argue that the misuse of terminology can hinder scientific progress by creating ambiguity and misunderstanding. To address this, we propose a set of guidelines for the consistent use of key terms and provide clear definitions for some of the most commonly misused or newly introduced terms in the field. The definitions provided herein will also function as a guide for young researchers new to the field of microbial ecology. Accurate and consistent use of terminology is crucial for effective communication and collaboration in microbiology research. By adhering to standardised definitions, researchers can ensure that their work is clearly communicated and contributes meaningfully to the progress of science.

definitions↗

NASA NTRS1984

Objective scatterometer wind ambiguity removal using smoothness and dynamical constraints

In the present investigation, a variational analysis method (VAM) is used to remove the ambiguity of the Seasat-A Satellite Scatterometer (SASS) winds. At each SASS data point, two, three, or four wind vectors (termed ambiguities) are retrieved. It is pointed out that the VAM is basically a least squares method for fitting data. The problem may be nonlinear. The best fit to the data and constraints is obtained on the basis of a minimization of the objective function. The VAM was tested and tuned at 12 h GMT Sept. 10, 1978. Attention is given to a case study involving an intense cyclone centered south of Japan at 138 deg E.

Hoffman, R. N.↗

DOE OSTI2024

Formally Verified ZTA Requirements for OT/ICS Environments with Isabelle/HOL

The clean energy transformation includes the integration of distributed energy resources with the power grid, which has led to a substantial increase in the complexity of power grids infrastructure and the underlying operational technology environment. Power grids infrastructure represents an operational technology environment that has become a system of systems, integrating heterogeneous devices which are both software-and hardware-intensive; as a result, there are increasing demands to exploit advances in the commodity of software-hardware infrastructures to improve energy systems requirements such as cybersecurity and resilience. In such a setting, system requirements at different levels mix, which leads to vulnerabilities and undesirable outcomes. The use of formal methods to characterize and prove system requirements removes ambiguity, increases automation, and provides high levels of assurance and reliability. In this paper, we contribute a methodology and a framework for the system-level verification of zero trust architecture requirements in operational technology environments. We define a formal specification for the core functionalities of operational technology environments, the corresponding invariants, and security proofs. Of particular note is our modular approach for the formal verification of asynchronous interactions in operational technology environments. The formal specification and the proofs have been mechanized using the interactive theorem proving environment Isabelle/HOL.

formal methods↗

NASA NTRS1977

Spectra of cosmic gamma-ray bursts in the hard X-ray range

Hard X-ray measurements of six gamma-ray bursts observed by detectors on the OGO-5 and OSO-6 satellites during the period Oct. 1969 to Apr. 1971 are presented. Spectra for five of the six bursts were determined using measurements from both satellites in order to reduce ambiguities due to uncertain source locations. A significant fraction, 20 to 60%, of the energy of the bursts fall in the hard X-ray range (20 to 130 keV). The time-integrated spectra were fitted by power-law, exponential, and thermal bremsstrahlung functions. They are consistent with power-laws which steepen at energies approx. above 150 keV, as reported earlier for two other bursts. Evidence for spectral variability from event to event in the hard X-ray region is presented. The hard X-ray spectra of the gamma-ray bursts differ from those of the recently discovered 1 to 15 keV bursts.

Share, G. H.↗

NASA NTRS1977

Hard X-ray spectra of cosmic gamma-ray bursts

Hard X-ray measurements of six gamma-ray bursts observed during the period from October 1969 to April 1971 are presented. The measurements were made with detectors on the OGO-5 and OSO-6 satellites. Spectra for five of the six bursts have been determined using measurements from both satellites in order to reduce ambiguities due to uncertain source locations. A significant fraction, about 20-60%, of the energy of the bursts falls in the hard X-ray range (20-130 keV). The time-integrated spectra have been fitted by power-law, exponential, and thermal-bremsstrahlung functions. They are consistent with power laws which steepen at energies of at least 150 keV, as reported earlier for two other bursts. Evidence for spectral variability from event to event in the hard X-ray region is presented. For a power-law representation, the power-law index has values ranging from approximately unity to 2.5. The hard X-ray spectra of the gamma-ray bursts differ significantly from those of the recently discovered 1-15-keV X-ray bursts.

Kane, S. R.↗

NASA NTRS1988

Phase connection for geodesy - Results from a 245-km baseline

In an effort to greatly improve the measurement precision of VLBI observables used to determine geodetic baselines, the potential of utilizing fringe phase has been investigated. The 245-km baseline between Mojave and Owens Valley in CA has been most thoroughly studied for this purpose. In trying several different experimental designs, it appears that source scheduling is not the critical factor in determining when phase connection can be established. Normally, instrumental instabilities are also not limiting (although nominal functioning of the instrumentation is essential). The most serious factor in limiting opportunities for phase connection seems to be atmospheric variability. However, when the observation SNR is made large (greater than 50) to give very precise group delays (and hence enhance the chance of resolving phase ambiguities), the improvement in baseline uncertainty obtained using phase delays is only marginal compared with the corresponding group delay solution. For this case, the baseline error budget is dominated by stochastic variations in clock and atmospheric delay contributions rather than by observation noise.

Ray, J. R.↗

NASA NTRS1993

Calibration Results for J-ERS-1 SAR Data Produced by the Alaska SAR Facility

The Alaska SAR Facility has been receiving and processing SAR data from the J-ERS-1 satellite since Spring 1992. Corner reflectors have been set up for J-ERS-1 SAR calibration at a site near Delta Junction, in central Alaska. Image quality and calibration analysis results from the Delta Junction site and others will be presented in this paper. The impact of the 3-bit Analog-to-Digital Converter and the automatic stepping of the gain as a function of range in the J-ERS-1 radar receiver on calibration performance has been assessed. Preliminary observations on J-ERS-1 SAR data are that the average Signal-to-Noise ratio is generally fairly low, in the range 5-6dB. Azimuth ambiguity levels are higher than preflight analysis indicated. Over land, the dynamic range in the backscatter at L-band for approximately 36 degree incidence angle is often fairly high.

Freeman, A.↗

NASA NTRS1993

Calibration Results for J-ERS-1 SAR Data Produced by the Alaska SAR Facility

The Alaska SAR Facility has been receiving and processing SAR data from the J-ERS-1 satellite since Spring 1992. Corner reflectors have been set up for J-ERS-1 SAR calibration at a site near Delta Junction, in central Alaska. Image quality and calibration analysis results from the Delta Junction site and others will be presented in this paper. The impact of the 3-bit Analog-to-Digital Converter and the automatic stepping of the gain as a function of range in the J-ERS-1 radar receiver on calibration performance has been assessed. Preliminary observations on J-ERS-1 SAR data are that the average Signal-to-Noise ratio is generally fairly low, in the range 5-6 dB. Azimuth ambiguity levels are higher than preflight analysis indicated. Over land, the dynamic range in the backscatter at L-band for approximately 36 degree incidence angle is often fairly high...

Freeman, A.↗

NASA NTRS1992

Problem footprints in Magellan altimetry data

The intensity, time-delay, and frequency content of radar echoes from the Magellan altimetry system are reduced to several parameters that are of great use in addressing many geological issues of the surface of Venus. These parameters include planetary radius, power reflection coefficient (reflectivity, both uncorrected and corrected for diffuse scattering), rms slope, and scattering functions (the behavior of backscatter as a function of incidence angle). Because the surface of Venus often reflects radio energy in unpredictable ways, models of radar scattering and their associated algorithms occasionally fail to accurately solve for the above surface parameters. Methods for identifying possible 'problem' altimetry data footprints, and techniques for resolving some key ambiguities are presented.

Plaut, Jeffrey J.↗

NASA NTRS2006

On Ambiguities in SAR Design

Ambiguities are an aliasing effect caused by the periodic sampling of the scene backscatter inherent to pulsed radar systems such as Synthetic Aperture radar (SAR). In this paper we take a fresh look at the relationship between SAR range and azimuth ambiguity constraints on the allowable pulse repetition frequency (PRF) and the antenna length. We show that for high squint angles smaller antennas may be feasible in some cases. For some applications, the ability to form a synthetic aperture at high squint angles is desirable, but the size of the antenna causes problems in the design of systems capable of such operation. This is because the SAR system design is optimized for a side-looking geometry. In two examples design examples we take a suboptimum antenna size and examine the performance in terms of azimuth resolution and swath width as a function of squint angle. We show that for stripmap SARs, the swath width is usually worse for off-boresight squint angles, because it is severely limited by range walk, except in cases where we relax the spatial resolution. We consider the implications for the design of modest-resolution, narrow swath, scanning SAR scatterometers .

Synthetic Aperture radar (SAR)↗

NASA NTRS2022

A Generalized Dual-Frequency Ratio (DFR) Approach for Rain Retrievals

The dual-frequency ratio of radar reflectivity factors (DFR) has been shown to be a useful quantity as it is independent of the number concentration of the particle size distribution and primarily a function of the mass-weighted particle diameter, Dm. A drawback of DFR-related methods for rain estimation, however, is the non-unique relationship between Dm and DFR. At Ku- and Ka-band frequencies, two solutions for Dm exist when DFR is less than zero. This ambiguity generates multiple solutions for the range profiles of the particle size parameters. We investigate characteristics of these solutions for both the initial-value (forward) and final-value (backward) forms of the equations. To choose one of among many possible range profiles of Dm, number concentration and rain rate, R, independently measured path attenuations are used. For the backward approach the possibility exists of dispensing with externally measured path attenuations by achieving consistency between the input and output path attenuations. The methods are tested by means of a simulation based on disdrometer-measured raindrop size distributions and the results are compared with a simplified version of the operational R-Dm method.

Robert Meneghini↗

NASA NTRS2002

Retrievals of Profiles of Fine And Coarse Aerosols Using Lidar And Radiometric Space Measurements

In couple of years we expect the launch of the CALIPSO lidar spaceborne mission designed to observe aerosols and clouds. CALIPSO will collect profiles of the lidar attenuated backscattering coefficients in two spectral wavelengths (0.53 and 1.06 microns). Observations are provided along the track of the satellite around the globe from pole to pole. The attenuated backscattering coefficients are sensitive to the vertical distribution of aerosol particles, their shape and size. However the information is insufficient to be mapped into unique aerosol physical properties and vertical distribution. Infinite number of physical solutions can reconstruct the same two wavelength backscattered profile measured from space. CALIPSO will fly in formation with the Aqua satellite and the MODIS spectro-radiometer on board. Spectral radiances measured by MODIS in six channels between 0.55 and 2.13 microns simultaneously with the CALIPSO observations can constrain the solutions and resolve this ambiguity, albeit under some assumptions. In this paper we describe the inversion method and apply it to aircraft lidar and MODIS data collected over a dust storm off the coast of West Africa during the SHADE experiment. It is shown that the product of the single scattering albedo, omega, and the phase function, P, for backscattering can be retrieved from the synergism between measurements avoiding a priori hypotheses required for inverting lidar measurements alone. The resultant value of (omega)P(180 deg.) = 0.016/sr are significantly different from what is expected using Mie theory, but are in good agreement with recent results obtained from lidar observations of dust episodes. The inversion is robust in the presence of noise of 10% and 20% in the lidar signal in the 0.53 and 1.06 pm channels respectively. Calibration errors of the lidar of 5 to 10% can cause an error in optical thickness of 20 to 40% respectively in the tested cases. The lidar calibration errors cause degradation in the ability to fit the MODIS data. Therefore the MODIS measurements can be used to identify the calibration problem and correct for it. The CALIPSO-MODIS measurements of the profiles of fine and coarse aerosols, together with CALIPSO measurements of clouds vertical distribution, is expected to be critically important in understanding aerosol transport across continents and political boundaries, and to study aerosol-cloud interaction and its effect on precipitation and global forcing of climate.

Kaufman, Yoram↗