Search NASA⌕ Search

SEARCH · Search NASA

Results for “reverse current”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Reconditioning experience at Marshall Space Flight Center

Problems encountered on Skylab prompted the development of a reconditioning circuit which involves a DC to DC converter, a circuit sensing device, and the capability of switching several size reconditioners onto a circuit. Across each cell there is a full bridge rectifier. During battery discharge, if there is low cell voltage, the reconditioning systems holds that voltage up and permits discharge to continue on the system. When the cell is good, the voltage is up about one volt, the diodes are back, or reversed biased, and the current drawn out of the system is very low. The system has a standby power thrown at about one volt. As the voltage drops on a cell, the circuit strts picking up the load and helps hold the overall battery voltage up.

Paschal, L. E.↗
NASA NTRS1982

Inductive electric field at the magnetopause

The electric field data for two crossings of the magnetopause by ISEE-1 on November 20, 1977, have been analyzed with high time resolution. In both cases the electric field has a negative dawn-dusk component in the boundary layer, so it must reverse somewhere within the current layer to the positive value outside. If there is a component parallel to the moving magnetopause current it is small, and by no means obvious. In the case of the exit crossing from the boundary layer to the magnetosheath the data show that the electric field vector is turning for about two seconds at roughly the satellite spin rate; this changing direction suggests that the electric field has a curl. Such a curl could be caused by a travelling localized perturbation of the magnetopause surface current associated with impulsive plasma transport through the magnetopause.

Heikkila, W. J.↗
NASA NTRS1984

Wave-particle interactions in the Venus wake and tail

The first descriptions of combined tail measurements from the Pioneer Venus plasma analyzer, magnetometer, and plasma wave detector are presented. The analysis concentrates on those orbits which are representative of the first tail passage. Summary plasma analyzer parameters are used to show that waves occurring at the boundary of the magnetotail can be identified as Doppler-shifted ion acoustic oscillations. High-density plasma distributions in the magnetotail region usually appear to be non-Maxwellian at the highest time resolution. These distorted distribution functions are generally accompanied by enhanced plasma wave signals and magnetic field reversals indicative of electric currents. A different time for the spacecraft entrance into the magnetotail from that previously defined is identified. It is shown that the wave activity in the Venus tail appears similar to the broadband noise identified in the earth's tail, except that at Venus the levels are usually higher.

Intriligator, D. S.↗
NASA NTRS1984

Research relative to plasma transport across the magnetopause

The concept of how magnetosheath plasma can cross the magnetopause is one of the key elements for a global view of the magnetosphere. According to this view, viscous interaction is the main process to produce convection of plasma in the magnetotail, resulting in auroral phenomena, and other related processes. The mechanism is illustrated herein. The key element is that the electric field is not constant, as assumed in reconnection theories, but reverse within the magnetopause current sheet. Particles, representing magnetosheath ions were traced as they impinge upon the magnetopause.

Heikkila, W. J.↗
NASA NTRS1987

Alternating-Polarity Arc Welding

Brief reversing polarity of welding current greatly improves quality of welds. NASA technical memorandum recounts progress in art of variable-polarity plasma-arc (VPPA) welding, with emphasis on welding of aluminum-alloy tanks. VPPA welders offer important advantages over conventional single-polarity gas/tungsten arc welders.

Schwinghamer, R. J.↗
NASA NTRS1986

Hyper-resistivity produced by tearing mode turbulence

Tearing mode turbulence produces a hyperresistivity or effective anomalous electron viscosity. The hyperresistivity is calculated for the mean magnetic field quasi-linearly, and for long-wavelength modes using the direct interaction approximation. The hyperresistivity accounts for current relaxation in reversed-field pinch experiments, and gives a magnetic fluctuation scaling of S to the -1/3. It causes enhanced tearing mode growth rates in the turbulent phase of tokamak disruptions. In astrophysics, it limits magnetic energy growth because of the dynamo effect, and may explain rapid reconnection phenomena such as solar flares.

Strauss, H. R.↗
NASA NTRS1987

Observations of annual and El Nino thermal and flow variations at 0 deg, 110 deg W and 0 deg, 95 deg W during 1980-1985

The paper describes the low-frequency (i.e., time scales longer than a month) upper ocean (above 250 m) current and temperature moored measurements conducted from March 1980 to September 1985 at 0, 110 deg W and from July 1981 to November 1983 (i.e., including the period of the 1982-1983 El Nino) at 0, 95 deg W. Estimates of the annual cycle were removed from the observations to determine the current and temperature fluctuations due to the 1982-1983 El Nino. The circulation of the upper ocean was found to be dramatically altered during the El Nino: the normally westward flowing surface current in autumn months reversed direction, and the equatorial undercurrent, normally considered to be a permanent feature, disappeared. Associated with the El Nino was a massive redistribution of heat throughout the mixed layer and the thermocline.

Halpern, David↗
NASA NTRS1991

Non-volatile, high density, high speed, Micromagnet-Hall effect Random Access Memory (MHRAM)

The micromagnetic Hall effect random access memory (MHRAM) has the potential of replacing ROMs, EPROMs, EEPROMs, and SRAMs because of its ability to achieve non-volatility, radiation hardness, high density, and fast access times, simultaneously. Information is stored magnetically in small magnetic elements (micromagnets), allowing unlimited data retention time, unlimited numbers of rewrite cycles, and inherent radiation hardness and SEU immunity, making the MHRAM suitable for ground based as well as spaceflight applications. The MHRAM device design is not affected by areal property fluctuations in the micromagnet, so high operating margins and high yield can be achieved in large scale integrated circuit (IC) fabrication. The MHRAM has short access times (less than 100 nsec). Write access time is short because on-chip transistors are used to gate current quickly, and magnetization reversal in the micromagnet can occur in a matter of a few nanoseconds. Read access time is short because the high electron mobility sensor (InAs or InSb) produces a large signal voltage in response to the fringing magnetic field from the micromagnet. High storage density is achieved since a unit cell consists only of two transistors and one micromagnet Hall effect element. By comparison, a DRAM unit cell has one transistor and one capacitor, and a SRAM unit cell has six transistors.

Wu, Jiin C.↗
NASA NTRS1992

Neutron, gamma ray, and temperature effects on the electrical characteristics of thyristors

Experimental data showing the effects of neutrons, gamma rays, and temperature on the electrical and switching characteristics of phase-control and inverter-type SCR's are presented. The special test fixture built for mounting, heating, and instrumenting the test devices is described. Four SCR's were neutron irradiated at 300 K and four at 365 K for fluences up to 3.2 x 10 exp 13 n/sq. cm, and eight were gamma irradiated at 300 K only for gamma doses up to 5.1 Mrads. The electrical measurements were made during irradiation and the switching measurements were made only before and after irradiation. Radiation induced crystal defects, resulting primarily from fast neutrons, caused the reduction of minority carrier lifetime through the generation of R-G centers. The reduction in lifetime caused increases in the on-state voltage drop and in the reverse and forward leakage currents, and decreases in the turn-off time.

Frasca, A. J.↗
NASA NTRS1992

Neutron, gamma ray, and temperature effects on the electrical characteristics of thyristors

Experimental data showing the effects of neutrons, gamma rays, and temperature on the electrical and switching characteristics of phase-control and inverter-type SCR's are presented. The special test fixture built for mounting, heating, and instrumenting the test devices is described. Four SCR's were neutron irradiated at 300 K and four at 365 K for fluences up to 3.2 x 10 exp 13 pn/sq. cm, and eight were gamma irradiated at 300 K only for gamma doses up to 5.1 Mrads. The electrical measurements were made during irradiation and the switching measurements were made only before and after irradiation. Radiation induced crystal defects, resulting primarily from fast neutrons, caused the reduction of minority carrier lifetime through the generation of R-G centers. The reduction in lifetime caused increases in the on-state voltage drop and in the reverse and forward leakage currents, and decreases in the turn-off time.

Frasca, A. J.↗
NASA NTRS1994

Ionospheric convection during the magnetic storm of 20-21 March 1991

We report on the response of high-latitude ionospheric convection during the magnetic storm of March 20-21 1990. IMP-8 measurements of solar wind plasma and interplanetary magnetic field (IMF), ionospheric convection flow measurements from the Wick and Goose Bay coherent radars, EISCAT, Millstone Hill and Sondrestorm incoherent radars and three digisondes at Millstone Hill, Goose Bay and Qaanaaq are presented. Two intervals of particular interest have been indentified. The first starts with a storm sudden commencement at 2243 UT on March 20 and includes the ionospheric activity in the following 7 h. The response time of the ionospheric convection to the southward tuning of the IMF in the dusk to midnight local times is found to be approximately half that measured in a similar study at comparable local times during more normal solar wind conditions. A subsequent reconfiguration of the nightside convection pattern was also observed, although it was not possible to distinguish between effects due to possible changes in B(sub y) and effects due to substorm activity. The second interval, 1200-2100 UT 21 March 1990, included a southward turning of the IMF which resulted in the B(sub z) component becoming -10 nT. The response time on the dayside to this change in the IMF at the magnetopause was approximately 15 min to 30 min which is a factor of approximately 2 greater than those previously measured at higher latitudes. A movement of the nightside flow reversal, possibly driven by current systems associated with the substorm expansion phases, was observed, implying that the nightside convection pattern can be dominated by substorm activity.

Taylor, J. R.↗
NASA NTRS1994

Characterization of Thermophotovoltaic Cells

Thermophotovoltaic (TPV) research has entered a period of rapid expansion after 30 years of effort, yet there is still no comprehensive method of TPV cell characterization. Simple procedures allow the derivation of temperature coefficients for Voc and Isc as well as the intensity coeffcient for Voc.

temperature thermophotovoltaic cells (TPV)↗
NASA NTRS2016

Interdecadal Trichodesmium Variability in Cold North Atlantic Waters

Studies of the nitrogen cycle in the ocean generally assume that the distribution of the marine diazotroph, Trichodesmium, is restricted to warm, tropical, and subtropical oligotrophic waters. Here we show evidence that Trichodesmium are widely distributed in the North Atlantic. We report an approximately vefold increase during the 1980s and 1990s in Trichodesmium presence near the British Isles with respect to the average over the last 50 years. A potential explanation is an increase in the Saharan dust source starting in the 1980s, coupled with changes in North Atlantic winds that opened a pathway for dust transport. Results from a coarse-resolution model in which winds vary but iron deposition is climatologically fixed suggest frequent nitrogen limitation in the region and reversals of the Portugal current, but it does not simulate the observed changes in Trichodesmium. Our results suggest that Trichodesmium may be capable of growth at temperatures below 20C and challenge assumptions about their latitudinal distribution. Therefore, we need to reevaluate assumptions about the temperature limitations of Trichodesmium and the dinitrogen (N2) xation capabilities of extratropical strains, which may have important implications for the global nitrogen budget.

Rivero-Calle, Sara↗
NASA NTRS2015

Schottky Diode Derating for Survivability in a Heavy Ion Environment

In this paper, we irradiate a number of silicon power Schottky diodes from a variety of manufacturers. The tested diodes represent a wide assortment of reverse voltages and forward currents. Additionally, we review correlations between single-event failures in Schottky diodes and device electrical parameters. The spatial locations of failures in the diode are discussed, as well as a possible explanation for why the failures occur. Based on these correlations to date, we propose a derating scheme for Schottky diodes flown in a heavy ion environment and suggest screening procedures for decreasing the risks of such failures.

Radiation effects↗
NASA NTRS1983

Magnetic structure of the boundary layer

While magnetospheric convection appears to be driven by both magnetic reconnection and the 'viscous' dragging of closed flux tubes acting in varying proportions but with reconnection predominating as a cause, the action of the closed flux tubes of the low latitude boundary layer seems to predominate in driving system 1 field aligned currents and discrete auroras. ISEE boundary layer data for the magnetic shear effects associated with field aligned currents has occasionally shown a reverse draping of boundary layer field lines whose cause may be plasma entry around the cusps, a north-south asymmetry in current flow to the polar regions, or magnetic reconnection at high latitudes. Boundary layer encounter character and distribution asymmetries suggest that the boundary layer and/or plasma mantle may differ substantially at the dawn and dusk sides of the magnetosphere, and that their properties may have seasonal dependencies.

Hones, E. W., Jr.↗
NASA NTRS1998

Seasonal Cycles of Meridional Overturning and Heat Transport of the Indian Ocean

A general circulation model of the Indian Ocean is fitted to monthly averaged climatological temperatures, salinities, and surface fluxes using the adjoint method. Interannual variability is minimized by penalizing the temporal drift from one seasonal cycle to another during a two-year integration. The resultant meridional overturning and heat transport display large seasonal variations, with maximum amplitudes of 18 and 22 (x 10(exp 6) cubic m/s) for the overturning and 1.8 and 1.4 (x 10(exp 15) W) for heat transport near 10 S and 10 N, respectively. A dynamical decomposition of the overturning and heat transport shows that the time-varying Ekman How plus its barotropic compensation can explain a large part of the seasonal variations in overturning and heat transport. The maximum variations at 10 deg N and 10 deg S are associated with monsoon reversal over the northern Indian Ocean and changes of the easterlies over the southern Indian Ocean. An external mode with variable topography has a moderate contribution where the Somali Current and the corresponding gyre reverse direction seasonally. Contribution front vertical shear (thermal wind and ageostrophic shear) is dominant near the southern boundary and large near the Somali Current latitudes. The dominant balance in the zonally integrated heat budget is between heat storage change and heat transport convergence except south of 15 S. Optimization with seasonal forcings improves estimates of sea surface temperatures, but the annual average overturning and heat transport are very similar to previous results with annual mean forcings. The annual average heat transport consists of roughly equal contributions from time-mean and time-varying fields of meridional velocities and temperatures in the northern Indian Ocean. indicating a significant rectification to the heat transport due to the time-varying fields. The time-mean and time-varying contributions are primarily due to the overturning and horizontal gyre, respectively. Inclusion of TOPEX data enhances the seasonal cycles of the estimated overturning and heat transport in the central Indian Ocean significantly and improves the estimated equatorial zonal flows but leads 10 unrealistic estimates of the velocity structure near the Indonesian Throughflow region, most likely owing to the deficiencies in the lateral boundary conditions.

Lee, Tong↗
NASA NTRS1993

Characterization of the IMF By-dependent field-aligned currents in the cleft region based on DE 2 observations

The magnetic field and plasma data from 47 passes of DE-2 are used to study the IMF By-dependent distribution of field-aligned currents in the cleft region. It is proposed that the low-latitude cleft current (LCC) region is not an extension of the region 1 or region 2 current system and that a pair of LCCs and high-latitude cleft currents (HCCs) constitutes the cleft field-aligned current regime. The proposed pair of cleft field-aligned currents is explained with a qualitative model in which this pair of currents is generated on open field lines that have just been reconnected on the dayside magnetopause. The electric fields are transmitted along the field lines to the ionosphere, creating a poleward electric field and a pair of field-aligned currents when By is positive; the pair of field-aligned currents consists of a downward current at lower latitudes and an upward current at higher latitudes. In the By negative case, the model explains the reversal of the field-aligned current direction in the LCC and HCC regions.

Taguchi, S.↗
NASA NTRS2000

Inception of Snapover and Gas Induced Glow Discharges

Ground based experiments of the snapover phenomenon were conducted in the large vertical simulation chamber at the Glenn Research Center (GRC) Plasma Interaction Facility (PIF). Two Penning sources provided both argon and xenon plasmas for the experiments. The sources were used to simulate a variety of ionospheric densities pertaining to a spacecraft in a Low Earth Orbital (LEO) environment. Secondary electron emission is believed responsible for dielectric surface charging, and all subsequent snapover phenomena observed. Voltage sweeps of conductor potentials versus collected current were recorded in order to examine the specific charging history of each sample. The average time constant for sample charging was estimated between 25 and 50 seconds for all samples. It appears that current drops off by approximately a factor of 3 over the charging time of the sample. All samples charged in the forward and reverse bias directions, demonstrated hysteresis. Current jumps were only observed in the forward or positive swept voltage direction. There is large dispersion in tile critical snapover potential when repeating sweeps on any one sample. The current ratio for the first snapover region jumps between 2 and 4.6 times, with a standard deviation less than 1.6. Two of the samples showed even larger current ratios. It is believed the second large snapover region is due to sample outgassing. Under certain preset conditions, namely at the higher neutral gas background pressures, a perceptible blue-green glow was observed around the conductor. The glow is believed to be a result of secondary electrons undergoing collisions with an expelled tenuous cloud of gas, that is outgassed from the sample. Spectroscopic measurements of the glow discharge were made in an attempt to identify specific lines contributing to the observed glow.

Galofaro, J. T.↗