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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Crystal structure and magnetic properties in semiconducting Eu 3-δ Zn x Sn y As 3 with Eu-Eu dimers

Magnetic structure and crystal symmetry, which primarily determine the time-reversal and inversion symmetry, may give rise to numerous exotic quantum phenomena in magnetic semiconductors and semimetals when arranged in different patterns. Here, a new layered magnetic semiconductor, Eu 3-δ Zn x Sn y As 3 , was discovered and high-quality single crystals were grown using the Sn flux. According to structural characterization by x-ray diffraction and atomic-resolution scanning transmission electron microscopy, Eu 3-δ Zn x Sn y As 3 is found to crystallize in a hexagonal symmetry with the space group P6 3 /mmc (No. 194). After examining different specimens, we conclude that their stoichiometry is fixed at ~Eu 2.6 Zn 0.65 Sn 0.85 As 3 , which meets the chemical charge balance. Eu 3-δ Zn x Sn y As 3 is composed of septuple (Eu 1-δ Sn y As 2 )-Eu-(Zn x As)-Eu sequences. The shortest Eu–Eu distance in the system is between two Eu layers separated by Zn x As along the c-axis. Magnetization measurement shows an antiferromagnetic ordering in Eu 3-δ Zn x Sn y As 3 at T N ~ 12 K, where the magnetic easy-axis is along the c-axis, and Mössbauer spectroscopy observes magnetic hyperfine splitting on Eu and Sn at 6 K. Magnetic anisotropy is significantly different from the ones along the ab-plane in other layered Eu-based magnetic semimetals. Heat capacity measurements confirm the magnetic transition around 12 K. Electrical resistivity measurement indicates semiconductor behavior with a band gap of ~0.86 eV. Finally, various Eu-based magnetic semiconductors could provide a tunable platform to study potential topological and magnetic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nanometer-Scale Measurement of Grid Finger Electrical Conduction Pathways to Detect Series Resistance Degradation of Utility-Scale Silicon Solar Cells

Here, we report on an electrical conduction mechanism for series resistance (Rs) degradation observed in a utility-scale photovoltaic power plant by imaging the local resistance at the Ag/Si interface of the c-Si front metallization. Scanning spreading resistance microscopy imaging with nanometer (nm) scale spatial resolution revealed that the number of point or small-area electrical contacts decreased substantially in a degraded cell compared to an unaffected cell, demonstrating the root cause of Rs degradation. The decrease in electrical contacts is likely caused by a structural change - the Ag particles in contact with the Si cell (or via a nm-thickness tunneling glass layer) aggregate into bulk Ag, and a highly resistive glass frit forms a belt shape at the Ag/Si interface. This resistive belt, with a thickness of ~1 um, blocks the current conduction from the cell emitter to the Ag grid. Our microscopy results help to unravel unambiguously the degradation mechanism and demonstrate an example of the multiscale characterization approach for understanding degradation in field-weathered PV module.

14 SOLAR ENERGY↗
DOE OSTI2020

Cross-section of electrical impact excitation in bulk n-type monocrystalline Al:Cr:ZnSe

Middle-infrared luminescence of bulk Al:Cr:ZnSe crystal under direct electrical excitation of Cr 2+ , 5 E− 5 T 2 transition, is reported. Effective cross-section of electrical excitation was estimated based on comparative luminescence measurements under electrical and optical (1560 nm) excitations. Calculation of the threshold current density for lasing under electrical excitation of this material was also performed.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Material variability as measured by low temperature electrical resistivity.

Low temperature electrical resistivity was used to determine the material variability (1) between different manufacturers, (2) between different heats from the same manufacturer, and (3) within a given heat for Al 2024, Al-5% Mg alloys, Inconel 718, A286 stainless, and AISI 316. Generally, the coefficient of variation for solution annealed alloys ranged from 1.2 to 14% between manufacturers, 0.8 to 5.1% between heats, and 0.1 to 1.6% within a heat with stainless steels at the low ends and Al 2024 at the high ends. The variability is increased if the material is in a precipitation-hardened condition. A statistical analysis suggests that the variability within a heat is non-normal.

Clark, A. F.↗
NASA NTRS1974

Investigation of electron dynamics in the magnetosphere with electron beams injected from sounding rockets

This paper describes an empirical study of the basic mechanisms by which electrons precipitate from the geomagnetic field to produce 'auroral X rays' during periods of geomagnetic activity. The study was based on data obtained by the Echo satellites. Echo I, launched in 1970, injected 40 keV, 0.1 amp electron pulses at low latitude (L ? 2.6) and successfully measured the returning pulses from the conjugate region. Electric fields and multiple Coulomb scattering were studied. Echo II, launched in 1972 from high latitude (L ? 8) studied the interaction of the beams with background radiation and the detailed motion of the beams near the rocket. Evidence for a beam plasma instability was obtained. Echo III launched in April 1974, (L ? 5.5) detected a series of conjugate echoes during the presence of a strong convective field in the magnetosphere. It was shown that the electric field measurement in the ionosphere using the incoherent backscatter radar and detectors on the rocket was transferred to the equatorial plane as though field lines were equipotentials.

Winckler, J. R.↗
NASA NTRS1980

Method and automated apparatus for detecting coliform organisms

Method and automated apparatus are disclosed for determining the time of detection of metabolically produced hydrogen by coliform bacteria cultured in an electroanalytical cell from the time the cell is inoculated with the bacteria. The detection time data provides bacteria concentration values. The apparatus is sequenced and controlled by a digital computer to discharge a spent sample, clean and sterilize the culture cell, provide a bacteria nutrient into the cell, control the temperature of the nutrient, inoculate the nutrient with a bacteria sample, measures the electrical potential difference produced by the cell, and measures the time of detection from inoculation.

Dill, W. P.↗
NASA NTRS1980

Use of an electrical resistance hygrometer to measure human sweat rates

The application of the resistance hygrometer as a tool to measure the localized sweat rate from the human body in both the active and passive sweat regions was studied. It was found that the physiological function of the skin membrane and fluid carrier transport phenomena from the outer skin have an indistinguishable effect on the observed findings from the instrument. The problems associated with the resistance hygrometer technique are identified and the usage of the instrument in the physiological experimentation from the engineering standpoint is evaluated.

Suga, T.↗
NASA NTRS1983

Measuring Power Flow in Electric Vehicles

Instrument accommodates fast rise and fall times of waveforms characteristic of modern, efficient power controllers. Power meter multiplies analog signals proportional to voltage and current, and converts resulting signal to frequency. Two mechanical counters provided: one for charging, one for discharging.

Griffin, Daniel C., Jr↗
NASA NTRS1999

Specification, Measurement, and Control of Electrical Switching Transients

There have been several instances of susceptibility to switching transients. The Space Shuttle Spacelab Remote Acquisition Unit (RAU-A standard interface between Spacelab payloads and the Shuttle communications system) will shut down if the input 28 Vdc bus drops below 22 volts for more than 80 gs. Although a MIL-STD-461 derivative CS06 requirement was levied on the RAU, it failed to find this susceptibility. A heavy payload on one aircraft sags the 28 volt bus below 20 volts for milliseconds. Dc-dc converters have an operating voltage. A typical 28 Vdc-to-5 Vdc converter operates within tolerance when input potential is between 17-40 Vdc, A hold-up capacitor can be used to extend the time this range is presented to the convener when the line potential sags or surges outside this range. The designer must know the range of normal transients in order to choose the correct value of hold-up. This report describes the phenomena of electrical power bus transients induced by the switching of loads both on and off the bus, and control thereof.

Javor, K.↗
NASA NTRS1999

Langmuir Probe Distortions and Probe Compensation in an Inductively Coupled Plasma

In many RF discharges, Langmuir probe measurements are usually made against a background of sinusoidal (and not so sinusoidal) fluctuations in the plasma parameters such as the plasma potential (Vp), the electron number density (ne), and the electron temperature (Te). The compensation of sinusoidal fluctuations in Vp has been extensively studied and is relatively well understood. Less attention has been paid to the possible distortions introduced by small fluctuations in plasma density and/or plasma temperature, which may arise in the sheath and pre-sheath regions of RF discharges. Here, we present the results of a model simulation of probe characteristics subject to fluctuations in both Vp and ne. The modeling of probe distortion due to possible fluctuations in Te is less straightforward. A comparison is presented of calculations with experimental measurements using a compensated and uncompensated Langmuir probe in an inductively coupled GEC reference cell plasma, operating on Ar and Ar/CF4 mixtures. The plasma parameters determined from the compensated probe characteristics are compared to previous measurements of others made in similar discharges, and to our own measurements of the average electron density derived from electrical impedance measurements.

Ji, J. S.↗
NASA NTRS2013

Study of the Effects of the Electric Field on Charging Measurements on Individual Micron-size Dust Grains by Secondary Electron Emissions

The dust charging by electron impact is an important dust charging process in Astrophysical, Planetary, and the Lunar environments. Low energy electrons are reflected or stick to the grains charging the dust grains negatively. At sufficiently high energies electrons penetrate the grain leading to excitation and emission of electrons referred to as secondary electron emission (SEE). Available theoretical models for the calculation of SEE yield applicable for neutral, planar or bulk surfaces are generally based on Sternglass Equation. However, viable models for charging of individual dust grains do not exist at the present time. Therefore, the SEE yields have to be obtained by some experimental methods at the present time. We have conducted experimental studies on charging of individual micron size dust grains in simulated space environments using an electrodynamic balance (EDB) facility at NASA-MSFC. The results of our extensive laboratory study of charging of individual micron-size dust grains by low energy electron impact indicate that the SEE by electron impact is a very complex process expected to be substantially different from the bulk materials. It was found that the incident electrons may lead to positive or negative charging of dust grains depending upon the grain size, surface potential, electron energy, electron flux, grain composition, and configuration. In this paper we give a more elaborate discussion about the possible effects of the AC field in the EDB on dust charging measurements by comparing the secondary electron emission time-period (tau (sub em) (s/e)) with the time-period (tau (sub ac) (ms)) of the AC field cycle in the EDB that we have briefly addressed in our previous publication.

Tankosic, D.↗
DOE OSTI2023

Electrostatic charge buildup and electrostatic discharge monitoring system and method

A system for monitoring electrostatic charge buildup and electrostatic discharge (ESD) remotely comprises a plurality of electrostatic charge measurement units and a data acquisition device. Each electrostatic charge measurement unit includes a primary charge plate, a static sensor device, a secondary charge plate, and a shielded cable. The primary charge plate is positioned proximal to an object. The static sensor device includes an input sensor at which an electric voltage is measured and outputs an electronic signal whose level varies according to the measured electric voltage. The secondary charge plate is positioned in proximity to the input sensor of the static sensor device. The shielded cable includes an inner conductor electrically connected to the primary charge plate and the secondary charge plate and an outer conductor electrically connected to electrical ground. The data acquisition device receives the electronic signal from the static sensor device of each electrostatic charge measurement unit.

Schantz, Eric T.↗
NASA NTRS1964

Ultra-sensitive transducer advances micro-measurement range

An ultrasensitive piezoelectric transducer, that converts minute mechanical forces into electrical impulses, measures the impact of micrometeoroids against space vehicles. It has uniform sensitivity over the entire target area and a high degree of stability.

Rogallo, V. L.↗