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Results for “ELECTRIC FIELD STRENGTH”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Charge control experiments on a CH-53E helicopter in a dusty environment

Charge control tests were carried out on a ground based, Marine Corps helicopter to determine if control of the electric fields acting on the engine exhaust gases could be used to reduce the electrification of the helicopter when it operated in a dusty atmosphere. The test aircraft was flown to a dusty, unpaved area and was then isolated electrically from the earth. When the helicopter engines were operated at ground idle with the rotor locked, the isolated aircraft charged positively, as had been observed previously. However, when the rotor brake was released and the turning rotor created a downdraft that raised dust clouds, the aircraft always became charged more positively, to potentials ranging form +30 to +45 kV. The dust clouds raised by the rotor downwash invariably carried negative space charges with concentrations of up to -100 nC/cu m and caused surface electric fields with strengths of up to 10 kV/m immediately down wind of the aircraft. The natural charging of the helicopter operating in these dust clouds was successfully opposed by control of the electric fields acting on the hot, electrically conductive exhaust gases. The control was achieved by placing electrostatic shield around the exhausts.

Moore, C. B.↗
NASA NTRS2007

Observed Enhancement of Reflectivity and Electric Field in Long-Lived Florida Anvils

A study of two long-lived Florida anvils showed that reflectivity >20 dBZ increased in area, thickness and sometimes magnitude at mid-level well downstream of the convective cores. In these same regions electric fields maintained strengths >10 kV m1 for many tens of minutes and became quite uniform over tens of kilometers. Millimetric aggregates persisted at 9 to 10 km for extended times and distances. Aggregation of ice particles enhanced by strong electric fields might have contributed to reflectivity growth in the early anvil, but is unlikely to explain observations further out in the anvil. The enhanced reflectivity and existence of small, medium and large ice particles far out into the anvil suggest that an updraft was acting, perhaps in weak convective cells formed by instability generated from the evaporation and melting of falling ice particles. We conclude that charge separation must have occurred in these anvils, perhaps at the melting level but also at higher altitudes, in order to maintain fields >10 kV m 1 at 9 to 10 km for extended periods of time over large distances. We speculate that charge separation occurred as a result of ice-ice particle collisions (without supercooled water being present) via either a non-inductive or perhaps even an inductive mechanism, given the observed broad ice particle spectra, the strong pre-existing electric fields and the many tens of minutes available for particle interactions. The observations, particularly in the early anvil, show that the charge structure in these anvils was quite complex.

Dye, James E.↗
NASA NTRS2007

Observed Enhancement of Reflectivity and Electric Field in Long-Lived Florida Anvils

A study of two long-lived Florida anvils showed that reflectivity greater than 20 dBZ increased in area, thickness and sometimes magnitude at mid-level well downstream of the convective cores. In these same regions electric fields maintained strengths greater than 10 kV m(sup -1) for many tens of minutes and became quite uniform over tens of kilometers. Millimetric aggregates persisted at 9 to 10 km for extended times and distances. Aggregation of ice particles enhanced by strong electric fields might have contributed to reflectivity growth in the early anvil, but is unlikely to explain observations further out in the anvil. The enhanced reflectivity and existence of small, medium and large ice particles far out into the anvil suggest that an updraft was acting, perhaps in weak convective cells formed by instability generated from the evaporation and melting of falling ice particles. We conclude that charge separation must have occurred in these anvils, perhaps at the melting level but also at higher altitudes, in order to maintain fields greater than 10 kV m(sup -1) at 9 to 10 km for extended periods of time over large distances. We speculate that charge separation occurred as a result of ice-ice particle collisions (without supercooled water being present) via either a noninductive or perhaps even an inductive mechanism, given the observed broad ice particle spectra, the strong pre-existing electric fields and the many tens of minutes available for particle interactions. The observations, particularly in the early anvil, show that the charge structure in these anvils was quite complex.

Dye, James E.↗
NASA NTRS1985

Runaway tails in magnetized plasmas

The evolution of a runaway tail driven by a dc electric field in a magnetized plasma is analyzed. Depending on the strength of the electric field and the ratio of plasma to gyrofrequency, there are three different regimes in the evolution of the tail. The tail can be (1) stable with electrons accelerated to large parallel velocities, (2) unstable to Cerenkov resonance because of the depletion of the bulk and the formation of a positive slope, (3) unstable to the anomalous Doppler resonance instability driven by the large velocity anisotropy in the tail. Once an instability is triggered (Cerenkov or anomalous Doppler resonance) the tail relaxes into an isotropic distribution. The role of a convection type loss term is also discussed.

Moghaddam-Taaheri, E.↗
NASA NTRS1991

Determination of cytoplasmic calcium concentration in Dryopteris spores: a developmentally non-disruptive technique for loading of the calcium indicator fura-2

Germination of Dryopteris spores is mediated by the physiologically active, far-red-absorbing form of phytochrome, Pfr, and external Ca2+ is necessary for the transduction of the light signal. Because knowledge about the cytoplasmic calcium ion concentration, [Ca2+]i, is of great importance for understanding the role of calcium during signal transduction, this value was measured using fura-2 in fern spores undergoing the normal developmental progression into germination. Fura-2 was loaded into the spores by electroporation, which does not disrupt the normal process of germination. The intensity of the fluorescence emission of the loaded fura-2 was analysed by a microspectrophotometric assay of single spores, and successful loading could be obtained by the application of ten electrical pulses (field strength 7.5 kV cm-1, half-life (time constant) 230 microseconds). Fura-2 was alternately excited by light of wavelengths 355 and 385 nm through an inverted fluorescence microscope, and the emitted fura-2 fluorescence was collected by a silicon-intensified video camera. The cytoplasmic calcium ion concentration was calculated from the ratio of the camera output obtained for both wavelengths and displayed by a pseudo-color technique. Spores responded to changes of the extracellular Ca2+ concentration, and this observation is considered as evidence that fura-2 is loaded into the cytoplasm. The substitution of a low external [Ca2+] (1 mM ethyleneglycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA)) by 1 mM CaCl2 caused a fast increase of [Ca2+]i from approx. 50 nM to above 500 nM. In contrast, the subsequent substitution of CaCl2 by EGTA decreased [Ca2+]i again below 100 nM within 0.5 h. Furthermore, the application of ionomycin could initiate a change in [Ca2+]i according to the Ca2+ gradient established between the extracellular medium and cytoplasm. In spores sown on a Ca(2+) -free medium, [Ca2+]i, analysed in a buffer containing EGTA, was found to be around 50 nM during the first days of cultivation, independent of the irradiation protocol. However, if spores were grown in darkness on a Ca(2+) -containing medium and analysed in EGTA, [Ca2+]i was significantly higher (> or = 500 nM). In red-light-irradiated spores, [Ca2+]i was found to decrease with increasing time after irradiation, and was determined to be less than 100 nM when analysis was done 44 h after germination was initiated by the light treatment.

NASA Discipline Plant Biology↗
NASA NTRS2005

Electrical Characterization of Defects in SiC Schottky Barriers

We have been investigating the effect of screw dislocation and other structural defects on the electrical properties of SiC. SiC is a wide-bandgap semiconductor that is currently received much attention due to its favorable high temperature behavior and high electric field breakdown strength. Unfortunately, the current state-of-the-art crystal growth and device processing methods produce material with high defect densities, resulting in a limited commercial viability

Schnabel, C. M.↗
NASA NTRS2013

Development of a Real Time Internal Charging Tool for Geosynchronous Orbit

The high-energy electron fluxes encountered by satellites in geosynchronous orbit pose a serious threat to onboard instrumentation and other circuitry. A substantial build-up of charge within a satellite's insulators can lead to electric fields in excess of the breakdown strength, which can result in destructive electrostatic discharges. The software tool we've developed uses data on the plasma environment taken from NOAA's GOES-13 satellite to track the resulting electric field strength within a material of arbitrary depth and conductivity and allows us to monitor the risk of material failure in real time. The tool also utilizes a transport algorithm to simulate the effects of shielding on the dielectric. Data on the plasma environment and the resulting electric fields are logged to allow for playback at a variable frame rate.

Posey, Nathaniel A.↗
NASA NTRS1986

The effect of vertical drift on the equatorial F-region stability

Time-dependent ionospheric model calculations for day-time and night-time solutions are presented. The behavior of the growth rate and ion-electron recombination rate for the Rayleigh-Taylor instability on the F-region bottomside is examined as a function of the vertical eastward electric field-magnetic field strength drift velocity. It is observed that on the bottomside F-layer the growth rate exceeds the ion-electron recombination rate even without vertical drift; however, an eastward electric field-magnetic field strength drift can produce an increase in the growth rate by an order of magnitude. The calculated data are compared with previous research and good correlation is detected. The formation of bubbles from a seeding mechanism is investigated.

Hanson, W. B.↗
NASA NTRS2018

Modal Q Factor and Modal Overlap of Electrically Small Avionics Box

Estimating the electromagnetic field strength in avionics boxes and other small enclosures at the design stage requires an estimate of the Q factor of the cavity modes. When the enclosure is small, it is typically under-moded so that Q measurement techniques which are standard practice in over-moded reverberation chambers may not be a robust measure. Furthermore, practical antenna used to measure Q in a small cavity may have a strong influence on the result obtained, as reported by Tait et al, IEEE Trans. EMC 55 2 2012. This paper reports the results of testing to determine the Q factor of a small aperture enclosure, used in a statistical power balance model to predict the electric field strength. The contributors to the total Q are identified. A novel S(sub 11) curve fitting method to measure modal Q is introduced and compared with the time domain method for measuring Q.

Statistical Electromagnetics↗
NASA NTRS2001

Embedded Coplanar Strips Traveling-Wave Photomixers

The electric field distribution in photomixers with electrodes deposited on the surface has already been calculated. It was shown that the strength of the electric field diminishes rapidly with depth. It was argued that the resulting reduction of the effective interaction volume of the device lowers the optical-to-heterodyne conversion. In this paper, we will present the results of our investigation on the influence of the electrode placement on the performance of photomixers. We have fabricated and measured traveling-wave photomixer devices which have both embedded and surface electrodes - the nominal spacing between the electrodes was 2 micrometers. Devices were made using either low-temperature-grown (LTG)-GaAs or ErAs:GaAs as the photoconductive material. The dark current, photocurrent, and radio frequency (RF) emission were measured at nominally 1 THz. The experimental data show a surprising difference in the behavior of ErAs:GaAs devices when the electrodes are embedded. A factor of two increase in RF radiation is observed for electric fields < 20 kV/cm. No such improvement was observed for the LTG-GaAs devices. We argue that the distinctive behavior of the two photoconductive materials is due to differences in the crystal structure - LTG-GaAs is isotropic, while ErAs:GaAs is uniaxial. We find that the carrier mobility in-plane (parallel) to the ErAs layers in the ErAs:GaAs superlattice is larger than orthogonal to these layers. The data indicate that carrier velocity overshoot is responsible for the excess radiation produced for the embedded electrode ErAs:GaAs devices.

Wyss, R. A.↗