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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Application of a hybrid computer to sweep frequency data processing

A hybrid computer program is presented which can process as many as 10 channels of sweep frequency data simultaneously. The program needs only the sine sweep signal used to drive the system, and its correponding quadrature component, to process the data. It can handle a maximum frequency range of 0.5 to 500 hertz. Magnitude and phase are calculated at logarithmically spaced points covering the frequency range of interest. When the sweep is completed, these results are stored in digital form. Thus, a tabular listing and/or a plot of any processed data channel or the transfer function relating any two of them is immediately available.

Milner, E. J.↗
NASA NTRS1992

Analysis of airframe/engine interactions for a STOVL aircraft with integrated flight/propulsion control

A multivariable analysis technique is used to evaluate the effects of the dynamic cross coupling between the airframe and engine subsystems in an advanced STOVL configuration. A critical frequency range is identified along with potentially poor stability robustness due to the airframe/engine interactions. Within the critical frequency range, stability and performance are found to be sensitive to variations in the coupling between the airframe's flight path angle and the engine's fuel flow rate. A stability sensitivity study indicates that the interactions between the flight path angle and the fuel flow rate are potentially the most critical with respect to stability and performance robustness.

Schierman, John D.↗
NASA NTRS2008

Auditory alert systems with enhanced detectability

Methods and systems for distinguishing an auditory alert signal from a background of one or more non-alert signals. In a first embodiment, a prefix signal, associated with an existing alert signal, is provided that has a signal component in each of three or more selected frequency ranges, with each signal component in each of three or more selected level at least 3-10 dB above an estimated background (non-alert) level in that frequency range. The alert signal may be chirped within one or more frequency bands. In another embodiment, an alert signal moves, continuously or discontinuously, from one location to another over a short time interval, introducing a perceived spatial modulation or jitter. In another embodiment, a weighted sum of background signals adjacent to each ear is formed, and the weighted sum is delivered to each ear as a uniform background; a distinguishable alert signal is presented on top of this weighted sum signal at one ear, or distinguishable first and second alert signals are presented at two ears of a subject.

Begault, Durand R.↗
NASA NTRS2007

Switched Band-Pass Filters for Adaptive Transceivers

Switched band-pass filters are key components of proposed adaptive, software- defined radio transceivers that would be parts of envisioned digital-data-communication networks that would enable real-time acquisition and monitoring of data from geographically distributed sensors. Examples of sensors to be connected to such networks include security cameras, radio-frequency identification units, and geolocation units based on the Global Positioning System. Through suitable software configuration and without changing hardware, these transceivers could be made to operate according to any of a number of complex wireless-communication standards that could be characterized by diverse modulation schemes, bandwidths, and data-handling protocols. The adaptive transceivers would include field-programmable gate arrays (FPGAs) and digital signal-processing hardware. In the receiving path of a transceiver, the incoming signal would be amplified by a low-noise amplifier (LNA). The output spectrum of the LNA would be processed by a band-pass filter operating in the frequency range between 900 MHz and 2.4 GHz. Then a down-converter would translate the signal to a lower frequency range to facilitate analog-to-digital conversion, which would be followed by baseband processing by one or more FPGAs. In the transmitting path, a digital stream would first be converted to an analog signal, which would then be up-converted to a selected frequency band before being applied to a transmitting power amplifier. The aforementioned band-pass filter in the receiving path would be a combination of resonant inductor-and-capacitor filters and switched band-pass filters. The overall combination would implement a switch function designed mathematically to exhibit desired frequency responses and to switch the signal in each frequency band to an analog-to-digital converter appropriate for that band to produce a digital intermediate-frequency signal for digital signal processing.

Wang, Ray↗
DOE OSTI2023

A novel Doppler backscattering (DBS) system to simultaneously measure radio frequency plasma fluctuations and low frequency turbulence

A novel quadrature Doppler Backscattering (DBS) system has been developed and optimized for the E-band (60–90 GHz) frequency range using either O-mode or X-mode polarization in DIII-D plasmas. In general, DBS measures the amplitude of density fluctuations and their velocity in the lab frame. The system can simultaneously monitor both low-frequency turbulence (f < 10 MHz) and radiofrequency plasma density fluctuations over a selectable frequency range (20–500 MHz). Detection of high-frequency fluctuations has been demonstrated for low harmonics of the ion cyclotron frequency (e.g., 2f ci ~ 23 MHz) and externally driven high-frequency helicon waves (f = 476 MHz) using an adjustable frequency down conversion system. Importantly, this extends the application of DBS to a high-frequency spectral domain while maintaining important turbulence and flow measurement capabilities. This unique system has low phase noise, good temporal resolution (sub-millisecond), and excellent wavenumber coverage (k θ ~ 1–20 cm –1 and kr ≲ 30 cm –1 ). As a demonstration, localized internal DIII-D plasma measurements are presented from turbulence (f ≤ 5 MHz), Alfvenic waves (f ~ 6.5 MHz), ion cyclotron waves (f ≥ 20 MHz), as well as fluctuations around 476 MHz driven by an external high-power 476 MHz helicon wave antenna. In the future, helicon measurements will be used to validate GENRAY and AORSA modeling tools for prediction of helicon wave propagation, absorption, and current drive location for the newly installed helicon current drive system on DIII-D.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1975

Effect of precipitation on choice of frequency for SEASAT scatterometer

Precipitation backscatter limits the effectiveness of a remote sensing radar in a satellite. Scatterometer operation on SEASAT is considered in one of the following frequency ranges: 12.5 GHz; 13.4-14.0 GHz; and 14.4-15.35 GHz. The effect of backscatter from precipitation in these frequency ranges is compared.

Dome, G.↗
NASA NTRS1990

Computation of convective flow with gravity modulation in rectangular cavities

In this work, a computational study is presented for the investigation of gravity modulation (g-jitter) effects in thermally driven cavity flows at terrestrial and microgravity environments. The two-dimensional, time-dependent Navier-Stokes equations are numerically integrated by a time-split method using direct matrix solvers. Computations at terrestrial gravity are utilized to assess the effects of adiabatic side-wall boundary conditions as well as the full nonlinearity of the governing equations on the sinusoidally forced Benard problem studied by Gresho and Sani. The low-g calculations focus on the establishment of critical frequency ranges and consider the effects of modulation direction and randomness. The applicability of linear analysis in the excitable frequency range at low g is also discussed.

Biringen, S.↗
DOE OSTI2017

DIELECTRICALLY-LOADED WAVEGUIDE AS A MICROWAVE UNDULATOR FOR HIGH BRILLANCE X-RAYS AT 45 – 90 KeV

The HEM12 mode in a cylindrical, dielectrically-loaded waveguide provides E and H fields on the central axis that are significantly higher than the fields on the conducting walls. This structure, operating near the cutoff frequency of the HEM12 mode, spans a frequency range where the wavelength and phase velocity vary significantly. This property can be exploited to generate undulator action with short periods for the generation of high brightness xrays. The frequency range of interest would be from 18 to 34.5-GHz. The goal would be to generate x-rays on the fundamental mode over a range of 45 to 90-keV.The tunability would be achieved by changing the source frequency while maintaining a constant on-axis equivalent undulator field strength of 0.5-T.

Kustom, R. L.↗
NASA NTRS1987

Review of measurements of the RF spectrum of radiation from lightning

A review is presented of the measurements reported in the literature of the spectrum of electromagnetic radiation from lightning in the frequency range from 1 kHz to 1 GHz. Measurements have been made either by monitoring the power received at individual frequencies using a narrow bandwidth recording device or by recording the transient (time dependent) radiation with a wide bandwidth device and then Fourier transforming the waveform to obtain a spectrum. Measurements of the first type were made extensively in the 1950's and 1960's and several composite spectra have been deduced by normalizing the data of different investigators to common units of bandwidth and distance. The composite spectra tend to peak near 5 kHz and then decrease roughly as 1/(frequency) up to nearly 100 MHz where scatter in the data make the behaviour uncertain. The spectrum obtained with measurements of the second type is similar. Recent experiments have extended the frequency range covered to several 10's of MHz and include spectra for return strokes, the stepped leader and for some intracloud processes. The spectrum of first return strokes obtained in this manner is very similar to the spectrum of the composite flash obtained from the narrowband measurements.

Radiation↗
NASA NTRS1997

Superconductor Semiconductor Research for NASA's Submillimeter Wavelength Missions

Wideband, coherent submillimeter wavelength detectors of the highest sensitivity are essential for the success of NASA's future radio astronomical and atmospheric space missions. The critical receiver components which need to be developed are ultra- wideband mixers and suitable local oscillator sources. This research is focused on two topics, (1) the development of reliable varactor diodes that will generate the required output power for NASA missions in the frequency range from 300 GHZ through 2.5 THz, and (2) the development of wideband superconductive mixer elements for the same frequency range.

Crowe, Thomas W.↗
NASA NTRS2010

l/f Noise in the Superconducting Transition of a MgB2 Thin Film

The noise voltage spectral density in the superconducting transition of a MgB2 thin film on a SiN-coated Si thick substrate was measured over the frequency range 1 Hz-to-1 KHz. Using established bolometer noise theory the theoretical noise components due to Johnson, 1/f(excess) and phonon noise are modeled to the measured data. It is shown that for the case of a MgB2 thin film in the vicinity of the mid-point of transition, coupled to a heat sink via a fairly high thermal conductance (approximately equal to 10(sup -1) W/K)) that the measured noise voltage spectrum is 1/f limited and exhibits lit dependence with a varying between 0.3 and 0.5 in the measured frequency range. At a video frame rate frequency of 30 Hz the measured noise voltage density in the film is approximately equal to 61 nV /the square root of HZ, using this value an upper limit of electrical NEP approximately equal to 0.67pW / the square root of Hz is implied for a practical MgB2 bolometer operating at 36.1 K.

Lakew, B.↗
DOE OSTI2024

Performance evaluation of the USGS velocity model for the San Francisco Bay Area

In this study, we evaluated the performance of the United States Geological Survey velocity model developed for the San Francisco Bay Area (SFBA), version 21.1. The evaluation was performed through high-resolution three-dimensional physics-based ground motion simulations of seven small-magnitude earthquakes (ranging from magnitude 3.8 to 4.4) that occurred on the eastern side of the San Francisco Bay. The simulations were performed in the frequency range from 0 to 5 Hz with a minimum shear-wave velocity of 250 m/s, which allowed the capture of wave propagation effects of the near-surface soft materials that characterize local basins. Based on the direct comparison of Fourier amplitude spectra between recorded and simulated ground motions for more than 250 stations, we found that the velocity model generally performs well in the frequency range of 0.2–5 Hz. The median value of the Fourier amplitude residuals was found to be near zero for all seven earthquakes. The slight over-prediction of 0.2 log-natural units at frequencies above 3 Hz in our simulations was attributed to the potentially inaccurate representation of the source radiation pattern by a double-couple point source model, and simple representation of shallow small-scale underground structural complexity in the velocity model. Maps of spectral amplitude differences between the simulated and recorded data were used to identify areas responsible for systematic ground motion over-predictions or under-predictions. For example, while some sub-domains over soft sediments show over-prediction patterns, the block east of the Hayward fault is prone to exhibit patterns of under-prediction. These maps can be used to guide future refinements of the SFBA velocity model. Since our simulation methodology allows for the decoupling of the source and wave propagation effects, the ground motion data generated by our simulations can also be used to quantify the epistemic uncertainty due to the velocity model, in empirically based ground motion estimates for the SFBA.

58 GEOSCIENCES↗
DOE OSTI2013

Behaviour and stability of Trivelpiece-Gould modes in non-neutral plasma containing small density fraction of background gas ions

It is shown that the frequencies of Trivelpiece-Gould (TG) modes in non-neutral plasma can get into the low-frequency range due to the Doppler shift caused by plasma rotation in crossed fields. TG modes interact with the ion modes that leads to plasma instability. In paper the frequency spectrum of 'cold' electron plasma completely filling a waveguide and containing small density fraction of ions of background gas is determined numerically. For ions the kinetic description is used. Oscillations having azimuthal number m= 2 are considered. In this case both low- and upper-hybrid TG modes get into the low-frequency range. The spectrum consists of families of 'modified' ion cyclotron (MIC) modes and electron TG modes with the frequencies equal to hybrid frequencies with the Doppler shift. The growth rates of upper-hybrid modes are much faster than the growth rates of low-hybrid and MIC modes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Bi-directional Alfvén cyclotron instabilities in the mega-amp spherical tokamak

Alfvén cyclotron instabilities excited by velocity gradients of energetic beam ions were investigated in MAST experiments with super-Alfvénic neutral beam injection over a wide range of toroidal magnetic fields from ∼0.34 T to ∼0.585 T. In MAST discharges with high magnetic field, a discrete spectrum of modes in the sub-cyclotron frequency range is excited toroidally propagating counter to the beam and plasma current (toroidal mode numbers n < 0). At lower magnetic field ≤0.45 T, a discrete spectrum of Compressional Alfvén Eigenmodes (CAEs) with n > 0 arises, in addition to the modes with n < 0. At lowest magnetic fields, the CAEs with n > 0 become dominant, they are observed in frequency range from ∼250 kHz for n=1 to ∼3.5 MHz for n=15, well above the on-axis ion cyclotron frequency (∼2.5 MHz). The data is interpreted in terms of normal and anomalous Doppler resonances modified by magnetic drift terms due to inhomogeneity and curvature of the magnetic field. A Hall MHD model is applied for computing the eigenfrequencies and the spatial mode structure of CAEs and a good agreement with the experimental frequencies is found.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2007

Long-term Average Spectral and Spatial Distributions of Plasmaspheric Hiss Observed by the Akebono and IMAGE Satellites

The radiation belt slot region is known to result from losses of energetic electrons by enhanced pitch-angle scattering by whistler mode waves associated with plasmaspheric hiss emission. The distributions of whistler mode waves in the slot L range are therefore important for understanding the electron radiation belt. The sources and distributions of the waves are, however, still controversial. In the present study, using the Akebono/MCA data [1989-20051 and the IMAGE/RPI data [2000-20051, we have constructed the average plasmaspheric hiss spectral distributions over a broad frequency range. In addition, we have investigated the spatial distributions of plasmaspheric hiss with the wave map technique [Green et a1.(2005)]. Our study shows that the broadband plasmaspheric hiss are distributed in the frequency range of 100Hz to several kHz, and exhibit a broad intensive peak. The frequency of the intensity peak tends to increase with magnetic latitude. The frequencies of the most intense waves in the nominal slot L range (2<3) during quiet times (Dst>-50nT) are found to be between 300Hz and 600Hz on average. During high storm activity (Dst <-150nT), however, the peak frequencies become slightly lower. The intensity of plasmaspheric hiss clearly depends on substorm activity as measured by the AE index, consistent with Meredith et a1.(2004). The hiss wave intensity maps also show a strong local time asymmetry. The large amplitude waves are observed at 6:OO-19:OO MLT. From our extensive analysis, we have also found an L dependence of hiss activity, with the larger amplitude waves being observed at lower L during substorm active conditions. The same tendency can be found for solar activity. The average intensities of the waves during 1989-1991 and 2000-2001 are a few dB larger than those during 1992-1997 and 2005. The most intense waves are observed at lower L during high solar activity. The statistical study on spectrum features of the plasmaspheric hiss together with the spatial distribution show clear dependences of storm, substorm and solar activities.

Fung, Shing↗
DOE OSTI2014

UNIVERSAL AUTO-CALIBRATION FOR A RAPID BATTERY IMPEDANCE SPECTRUM MEASUREMENT DEVICE

Electrochemical impedance spectroscopy has been shown to be a valuable tool for diagnostics and prognostics of energy storage devices such as batteries and ultra-capacitors. Although measurements have been typically confined to laboratory environments, rapid impedance spectrum measurement techniques have been developed for on-line, embedded applications as well. The prototype hardware for the rapid technique has been validated using lithium-ion batteries, but issues with calibration had also been identified. A new, universal automatic calibration technique was developed to address the identified issues while also enabling a more simplified approach. A single, broad-frequency range is used to calibrate the system and then scaled to the actual range and conditions used when measuring a device under test. The range used for calibration must be broad relative to the expected measurement conditions for the scaling to be successful. Validation studies were performed by comparing the universal calibration approach with data acquired from targeted calibration ranges based on the expected range of performance for the device under test. First, a mid-level shunt range was used for calibration and used to measure devices with lower and higher impedance. Next, a high excitation current level was used for calibration, followed by measurements using lower currents. Finally, calibration was performed over a wide frequency range and used to measure test articles with a lower set of frequencies. In all cases, the universal calibration approach compared very well with results acquired following a targeted calibration. Additionally, the shunts used for the automated calibration technique were successfully characterized such that the rapid impedance measurements compare very well with laboratory-scale measurements. These data indicate that the universal approach can be successfully used for onboard rapid impedance spectra measurements for a broad set of test devices and range of measurement conditions.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2025

Detection of high-frequency gravitational waves using SRF cavities

Today, apart from some isolated R\&D efforts, there are no GW experiments, yet which explore a large part of the vast frequency range above the LIGO/Virgo band. It is planned to establish an experiment at DESY and Fermilab to search for high-frequency GWs in the frequency range of 10\,kHz to 100\,MHz. The basic idea is to use superconducting radiofrequency (SRF) cavities to detect tiny harmonic deformations induced by GWs which change the boundary conditions of the oscillating electromagnetic field. This paper summarizes the challenging environmental boundary requirements, and the R\&D to operate a cavity using a LLRF system which pushes beyond state-of-the-art accuracy and resolutions and a seismic noise mitigated cryostat at 1.8\,K. The focus of this paper is the warm and cold commissioning of a prototype cavity, built 20 years ago during the MAGO collaboration, and its first measurement in our collaborative research project.

Giaccone, Bianca [Fermilab]↗
DOE OSTI2019

Structure of Magnetic Plasma Fluctuations in the Uragan-3M Torsatron at Rare Collision Frequencies

Fluctuations of the poloidal component of the plasma magnetic field in the frequency range of 0.5–50 kHz are studied in the Uragan-3M (U-3M) torsatron. Hydrogen plasma is produced and heated by RF fields at frequencies close to that of the ion cyclotron. The studies are carried out using a set of 15 magnetic sensors installed in one of the torus cross sections. RF heating provided the plasma with rare collision frequencies and the presence of the bootstrap current. The study is carried out when the maximum amplitude of magnetic fluctuations is observed and their connection with the plasma energy content is noticeable. Two types of vibrations are observed. In the first type, the current structure rotates with a certain frequency mainly in the direction of the rotation of electrons in the magnetic field, and the amplitude varies slowly with time (the rotating structure). For the second type, the spatial structure does not rotate, but its amplitude changes with a certain frequency (the standing structure). The frequencies of fluctuations and rotations are close for structures with a given poloidal wave number. The standing vibration structures with different poloidal wave numbers in this frequency range are correlated. The maximum amplitude of the rotating structures is observed with m = 2, and for the standing structures with m = 3 and reaches the values of B-tilde ≤ 0.3 G in the confinement region. The vibration frequency does not depend on poloidal wave number m for the studied cases; m = 0, 1, 2, 3.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗