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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Baseband signal combiner for large aperture antenna array

The invention provides a means whereby the baseband output signals of all but one of the receivers associated with each of the antennas are summed and used as a correlation reference for the baseband signal not contained in the summed signal, thereby providing a plurality of correlation or alignment loops, each having an output signal related to the phase difference between its input baseband signal and the summed signal. The invention further provides a means for subtracting an output or error signal generated in one of the correlation loops whose baseband signal has a predetermined phase delay from all the other alignment loops, thereby avoiding interaction and reflection effects in the signal combiner. A variable phase delay means for each of the other baseband signals is controlled by its corresponding correlation loop.

Easterling, M. E.↗
NASA NTRS1987

Phase closure with a rotational shear interferometer

A simple and efficient way is proposed for achieving phase closure in an optical telescope (to enable recovering Fourier transform phases that would otherwise be corrupted by atmospheric and instrumental errors), by means of rotational shear interferometry. In a rotational shear interferometer, one images the telescope aperture onto the interferometer and then interferes the aperture with itself in a rotated orientation. To achieve the maximum frequency content permitted by the telescope, the shear has to be 180 deg, but better dynamic range and SNR are possible for lower frequencies. Drawbacks of the proposed method compared to radio astronomy are noted, and different approaches are indicated as to how to collect and use the phase closure data. Phase closure can be realized on existing telescopes and existing interferometers with special modifications. Although not all base lines are possible, the extra constraints provided by the closure phases greatly reduce the ambiguity now existing in phaseless image reconstruction.

Ribak, Erez↗
NASA NTRS2005

Inference of Ice Cloud Properties from High-spectral Resolution Infrared Observations

The theoretical basis is explored for inferring the microphysical properties of ice crystal from high-spectral resolution infrared observations. A radiative transfer model is employed to simulate spectral radiances to address relevant issues. The extinction and absorption efficiencies of individual ice crystals, assumed as hexagonal columns for large particles and droxtals for small particles, are computed from a combination of the finite- difference time-domain (FDTD) technique and a composite method. The corresponding phase functions are computed from a combination of FDTD and an improved geometric optics method (IGOM). Bulk scattering properties are derived by averaging the single- scattering properties of individual particles for 30 particle size distributions developed from in situ measurements and for additional four analytical Gamma size distributions for small particles. The non-sphericity of ice crystals is shown to have a significant impact on the radiative signatures in the infrared (IR) spectrum; the spherical particle approximation for inferring ice cloud properties may result in an overest&ation of the optical thickness and an inaccurate retrieval of effective particle size. Furthermore, we show that the error associated with the use of the Henyey-Greenstein phase function can be as larger as 1 K in terms of brightness temperature for larger particle effective size at some strong scattering wavenumbers. For small particles, the difference between the two phase functions is much less, with brightness temperatures generally differing by less than 0.4 K. The simulations undertaken in this study show that the slope of the IR brightness temperature spectrum between 790-960/cm is sensitive to the effective particle size. Furthermore, a strong sensitivity of IR brightness temperature to cloud optical thickness is noted within the l050-1250/cm region. Based on this spectral feature, a technique is presented for the simultaneous retrieval of the visible optical thickness and effective particle size from high spectral resolution infrared data under ice cloudy con&tion. The error analysis shows that the uncertainty of the retrieved optical thickness and effective particle size has a small range of variation. The error for retrieving particle size in conjunction with an uncertainty of 5 K in cloud'temperature, or a surface temperature uncertainty of 2.5 K, is less than 15%. The corresponding e m r in the uncertainty of optical thickness is within 5-2096, depending on the value of cloud optical thickness. The applicability of the technique is demonstrated using the aircraft-based High- resolution Interferometer Sounder (HIS) data from the Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) in 1996 and the First ISCCP Regional Experiment - Arctic Clouds Experiment (FIRE-ACE) in 1998.

Huang, Hung-Lung↗
DOE OSTI2021

Ab initio simulations on the pure Cr lattice stability at 0K: Verification with the Fe-Cr and Ni-Cr binary systems

Significant discrepancies have been observed and discussed on the lattice stability of Cr between the predictions from the ab initio calculations and the CALPHAD approach. In the current work, we carefully examined the possible structures for pure Cr and reviewed the history back from how Kaufman originally determined the Gibbs energy of FCC-Cr in the 1970s. The reliability of Cr lattice stability derived by the CALPHAD and ab initio approaches was systematically discussed. It is concluded that the Cr lattice stability based on the CALPHAD approach has large uncertainty. Meanwhile, we cannot claim that the ab initio H FCC-Cr is error-free as FCC-Cr is an unstable phase under ambient conditions. The present work shows that the ab initio HFCC-Cr can be a viable scientific approach. As both approaches have their limitations, the present work propose to integrate the ab initio results into the CALPHAD platform for the development of the next generation CALPHAD database. As a result, the Fe-Cr and Ni-Cr binary systems were chosen as two case studies demonstrating the capability to adopt the ab initio Cr lattice stability directly into the current CALPHAD database framework.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Integration of the Biot–Gassmann Fluid Substitution Method and Machine Learning-Based Velocity–Stress Relationship for Estimating In Situ Stresses

Recent advancements have shown that in situ stresses can be reliably estimated through an integrated machine/deep learning (ML/DL)-based framework, which relies on models trained and validated using true triaxial ultrasonic velocity (TUV) experimental data that involve measurements of ultrasonic velocity in saturated rocks under varying stress configurations. However, when the goal is to interpret lower frequency measurements, it may be more appropriate to run experiments on dry rocks and then obtain Biot–Gassmann-derived equivalent saturated velocities (low-frequency approximation) and employ these quantities for training ML/DL models to predict in situ stress. Whether the dispersion effect of frequency on the velocity–stress relationship substantially impacts in situ stress prediction is an important and unresolved question. This work presents an enhancement of ML/DL-based workflow by training and implementing ML/DL models using equivalent saturated acoustic velocities (low-frequency) obtained by applying Biot–Gassmann fluid substitution on the ultrasonic velocities of dry cores. The models were trained on TUV data sets derived from three subsurface cores extracted from the geothermal well 16B(78)-32 at the Utah FORGE site. Each core was subjected to 75 unique stress configurations for velocity measurement in the dry state. The ML/DL trained on the TUV data set with equivalent saturated velocities demonstrated promising performance to predict in situ stress in subsurface geological rocks using velocity–stress relationships with R 2 of 0.86, 0.971, and 0.975 and root mean squared error (RMSE) of 2.59, 1.92, and 1.80 for validation/testing phases of vertical, minimum horizontal, and maximum horizontal stress models, respectively. Additionally, interpretation and explanation by Shapley additive explanations (SHAP) analysis further improved scientific validation and model reliability for estimating in situ stresses.

colloids↗
DOE OSTI2021

Comment on the paper “Physical characterization of Bis(2,2-dinitropropyl) acetal and Bis(2,2-dinitropropyl) formal” by Alexander Edgar, Justine Yang, Manuel Chavez, Michelle Yang & Dali Yang

Errors are noted in the construction of the binary phase diagram in the paper “Physical characterization of Bis(2,2-dinitropropyl) acetal and Bis(2,2-dinitropropyl) formal” by Alexander Edgar, Justine Yang, Manuel Chavez, Michelle Yang & Dali Yang. The authors of that paper misinterpret differential scanning calorimetry (DSC) thermal features. All of the DSC data show features consistent with samples that are supercooled during testing. Such samples do not show solidus points and may not show liquidus points, rendering the constructed phase diagram invalid.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Optimal function estimation with photonic quantum sensor networks

The problem of optimally measuring an analytic function of unknown local parameters each linearly coupled to a qubit sensor is well understood, with applications ranging from field interpolation to noise characterization. Here we resolve a number of open questions that arise when extending this framework to Mach-Zehnder interferometers and quadrature displacement sensing. In particular, we derive lower bounds on the achievable mean square error in estimating a linear function of either local phase shifts or quadrature displacements. In the case of local phase shifts, these results prove, and somewhat generalize, a conjecture by Proctor []. For quadrature displacements, we extend proofs of lower bounds to the case of arbitrary linear functions. We provide optimal protocols achieving these bounds up to small (multiplicative) constants and describe an algebraic approach to deriving new optimal protocols, possibly subject to additional constraints. Using this approach, we prove necessary conditions for the amount of entanglement needed for any optimal protocol for both local phase and displacement sensing. Published by the American Physical Society 2024

Bringewatt, Jacob↗
DOE OSTI2024

Deep Learning-enhanced Block-Diagram Modeling of Solar Power Systems

Data-driven models of power system inverter-based resources are desired to run simulations faster than with detailed electromagnetic transient models, to hide proprietary design details, to support control system design applications, and to aggregate the effects of distributed energy resources. This paper applies a customized Hammerstein Wiener framework to train block diagram models from thousands of electromagnetic transient simulations or experimental test records. The block diagram models integrate with larger grid simulations as voltagecontrolled current sources or current-controlled voltage sources for several simulators. Guidelines for block architecture and training are presented. Three-phase balanced, three-phase unbalanced, and single-phase examples all achieve an acceptable root mean square error of no more than 0.05 per-unit.

Mcdermott, Thomas E. [Private consulting company]↗
DOE OSTI2024

In situ characterization of two unknown ultrashort laser pulses using four-wave mixing in gas

Accurate characterization of two ultrashort laser pulses is of great interest in many ultrafast pump-probe experiments. We demonstrate a method based on four-wave mixing (FWM) in a gas which could be easily implemented into many existing pump-probe setups with minimal modifications for accurate, in situ characterization of both unknown pulses. This technique is tested on pairs of unknown pulses at wavelengths of 400/800 nm, and 266/400 nm. We measured the spectrogram of the pulse generated through FWM of the two unknown pulses by scanning the delay between two unknown pulses. The retrieval algorithm converges to accurately predict the intensity and the phase profiles of both unknown pulses with a trace error of < 1% and the accuracy is verified using an independent pulse characterization device.

Nambu, Noa (ORCID:0000000197303400)↗
NASA NTRS1972

Non-planar tests using the wind tunnel free-flight technique.

Results from the first bi-planar wind tunnel free-flight test program designed to investigate the difference between planar and nonplanar dynamic stability are presented. The test provides perhaps the best free-flight angular documentation of arbitrary nonplanar motion yet obtained. Two widely different configurations, a blunt 60-deg cone and a sharp 10-deg half-angle cone, were tested. Comparisons between the angular motion from raw data and the analytical fits indicate a phasing difference. An examination of possible causes discounts experimental errors as an explanation and points strongly toward an inadequacy of the theoretical force model.

Jaffe, P.↗
NASA NTRS1978

Frequency selection and calibration of a water vapor radiometer

The calibration coefficients of existing water vapor radiometers are dependent upon meteorology profiles. This is shown to be due mainly to incorrect frequency pairs. By properly selecting an optimum frequency pair, the dependency can be reduced to a relatively small amount which can be handily adjusted by surface measurement alone. Hence, a universal calibration equation is applicable to all environmental conditions - site, seasonal and diurnal variations. Optimum frequency pairs are systematically searched. Error analysis indicates that calibration for the water vapor phase delay accurate to less than 2 cm is possible at all elevation angles greater than 15 degrees.

Wu, S. C.↗
NASA NTRS1979

Some aspects of stratospheric chemical response to solar particle precipitations. I - Potential roles of N2/A3Sigma/ and ion-chemistry

Large amounts of long lived N2(A3Sigma) are created by the energy degradation of precipitating solar particles. Laboratory data suggest that in the stratosphere N2(A3Sigma) are efficiently converted into N2O. Through reactions with O(1D), N2O may gradually release NO and thereby influence the long term aspects of stratospheric chemical response. During the daytime, negative ions may transform an active NO(x) into an inactive HNO3. At night both negative and positive ion chemistry generate HO(x). Omission of ionic chemistry results in considerable underestimation of O3 depletion during the initial phases of solar particle events, and thereby introduces significant error in the estimation of the nature of the prompt response.

Prasad, S. S.↗
NASA NTRS1981

A comparison of head and manual control for a position-control pursuit tracking task

Head control was compared with manual control in a pursuit tracking task involving proportional controlled-element dynamics. An integrated control/display system was used to explore tracking effectiveness in horizontal and vertical axes tracked singly and concurrently. Compared with manual tracking, head tracking resulted in a 50 percent greater rms error score, lower pilot gain, greater high-frequency phase lag and greater low-frequency remnant. These differences were statistically significant, but differences between horizontal- and vertical-axis tracking and between 1- and 2-axis tracking were generally small and not highly significant. Manual tracking results were matched with the optimal control model using pilot-related parameters typical of those found in previous manual control studies. Head tracking performance was predicted with good accuracy using the manual tracking model plus a model for head/neck response dynamics obtained from the literature.

Levison, W. H.↗
NASA NTRS1982

On the adequacy of the fixed locations of the surface-based international network for inferring interannual ozone variability

The influence of the geographical distribution and the number of the surface stations in the ozone detecting network on changes in global ozone inferred from the surface measurements is investigated by comparison with information obtained from satellite backscattered UV observations on the Nimbus 4 with nearly complete global coverage for the period 1970-1972. Results show that the geographical distribution of the stations does not properly represent different latitudes. While the number of stations in the north temperate zone appears adequate to represent monthly ozone averages to within 0.5% except during the early phase of the Northern Hemisphere spring maximum, the resultant error in the derived change in north temperature zone ozone between 1970-1972 is 0.5%. In the tropical and south temperate zones the smaller number of stations reduces precision, and the ozone averages for use in deriving seasonal variability and trends are uncertain by about 1%. However, in the south temperature zone, the average from the sample may differ as much as 5% in some months from the averages derived from the full set. It is concluded that the resulting uncertainty in the global averages is comparable in size to typical yearly changes.

Heath, D. F.↗
NASA NTRS1986

Near-field Testing of the 15-meter Model of the Hoop Column Antenna

The technical results from near-field testing of the 15-meter model of the hoop column antenna at the Martin Marietta Denver Aerospace facility are documented. The antenna consists of a deployable central column and a 15 meter hoop, stiffened by cables into a structure with a high tolerance repeatable surface and offset feed location. The surface has been configured to have four offset parabolic apertures, each about 6 meters in diameter, and is made of gold plated molybdenum wire mesh. Pattern measurements were made with feed systems radiating at frequencies of 7.73, 11.60, 2.27, 2.225, and 4.26 (all in GHz). This report (Volume 1) covers the testing from an overall viewpoint and contains information of generalized interest for testing large antennas. This volume discusses the deployment of the antenna in the Martin Facility and the measurements to determine mechanical stability and trueness of the reflector surface, gives the test program outline, and gives a synopsis of antenna electromagnetic performance. Three techniques for measuring surface mechanical tolerances were used (theodolites, metric cameras, and near-field phase), but only the near-field phase approach is included. The report also includes an error analysis. A detailed listing of the antenna patterns are provided for the 2.225 Ghz feed in Volume 3 of this report, and for all other feeds in Volume 2.

Hoover, J.↗
NASA NTRS1993

Simulation motion effect on single axis compensatory tracking

An experiment that examined how changes in a motion platform drive filter affect pilot-vehicle performance and opinion was conducted on the NASA Ames Vertical Motion Simulator. Pilots controlled a simplified helicopter model in the vertical or the directional axis and tracked a randomly moving target aircraft in the presence of a random disturbance. With both tasks, variations from full motion to fixed-base conditions were made in the high-pass drive filter gain and natural frequency. The results indicate that vertical motion did not affect the open-loop pilot-vehicle target-tracking crossover frequency, but target-tracking phase margins improved with increased filter gain or decreased natural frequency. Vertical disturbance-rejection crossover frequency increased with decreasing filter natural frequency, while disturbance rejection phase margins improved with increasing filter gain. Vertical tracking errors increased significantly when all vertical motion was removed. No significant differences were measured among the directional configurations, which indicates that pure yaw motion cues may not be as important as previously thought in flight simulation.

Schroeder, Jeffery A.↗
NASA NTRS1994

Software For Calibration Of Polarimetric SAR Data

POLCAL (Polarimetric Radar Calibration) software tool intended to assist in calibration of synthetic-aperture radar (SAR) systems. In particular, calibrates Stokes-matrix-format data produced as standard product by NASA/Jet Propulsion Laboratory (JPL) airborne imaging synthetic aperture radar (AIRSAR). Version 4.0 of POLCAL is upgrade of version 2.0. New options include automatic absolute calibration of 89/90 data, distributed-target analysis, calibration of nearby scenes with corner reflectors, altitude or roll-angle corrections, and calibration of errors introduced by known topography. Reduces crosstalk and corrects phase calibration without use of ground calibration equipment. Written in FORTRAN 77.

Van Zyl, Jakob↗