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At least 847 records · Page 47

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NASA NTRS1989

Development and simulation study of a new inverse-pinch high Coulomb transfer switch

The inverse-pinch plasma switch was studied using a computer simulation code. The code was based on a 2-D, 2-temperature magnetohydrodynamic (MHD) model. The application of this code was limited to the disk-type inverse-pinch plasma switch. The results of the computer analysis appear to be in agreement with the experimental results when the same parameters are used. An inverse-pinch plasma switch for closing has been designed and tested for high-power switching requirements. An azimuthally uniform initiation of breakdown is a key factor in achieving an inverse-pinch current path in the switch. Thus, various types of triggers, such as trigger pins, wire-brush, ring trigger, and hypocycloidal-pinch (HCP) devices have been tested for uniform breakdown. Recently, triggering was achieved by injection of a plasma-ring (plasma puff) that is produced separately with hypocycloidal-pinch electrodes placed under the cathode of the main gap. The current paths at switch closing, initiated by the injection of a plasma-ring from the HCP trigger are azimuthally uniform, and the local current density is significantly reduced, so that damage to the electrodes and the insulator surfaces is minimized. The test results indicate that electron bombardment on the electrodes and the insulator surfaces is minimized. The test results indicate that electron bombardment on the electrodes is four orders of magnitude less than that of a spark-gap switch for the same switching power. Indeed, a few thousand shots with peak current exceeding a mega-ampere and with hold-off voltage up to 20 kV have been conducted without showing measurable damage to the electrodes and insulators.

Choi, Sang H.↗

NASA NTRS1990

A gamma-ray imaging telescope based on liquid xenon

A liquid-xenon time projection chamber (TPC) is discussed in terms of its utility as an imaging telescope for high energy astrophysics. The concept exploits the efficiency of xenon as an ionization and scintillation medium for imaging astrophysical gamma-ray sources. The design fundamentally follows the approach of an ionization calorimeter functioning as a TPC dedicated to 3D tracking. A schematic diagram of the instrument is presented, and the device measures the ionization signals - resulting from gamma-ray interactions with xenon - on collection electrodes. The liquid xenon instrument permits the identification of the direction of the Compton electron and thereby determines the location of the source. The energy region of 1-30 MeV is covered by the instrument, and source localization is possible for the entire range.

Aprile, Elena↗

NASA NTRS1991

Ground-based high energy astronomy

The specific aim of the project at hand is to study the changes in amplitude and phase of VLF radio waves to see if we can detect the ionospheric disturbance (the change in electron density) caused by a Gamma-Ray burst. The possible advantages of observing gamma-ray bursts through ionospheric disturbances are better localization of burst directions through a large network of VLF receiving points; measurement of total ionizing fluence of gamma-ray bursts; and comparison with satellite data (GOES and GRO) to derive properties of the ionosphere. There is a major problem here: the ionospheric disturbance caused by a Gamma-Ray burst is at best extremely difficult and at worse impossible to detect. So far only one vent has been detected via this method. Therefore, it was decided to study the ionospheric disturbance caused by solar flares first with the hope that they will teach us how to detect the elusive Gamma-Ray bursts. Much is to be learned about the ionosphere and its reaction to impulsive ionization.

Mcgruder, Charles H., III↗

NASA NTRS1991

Simulation of intense microwave pulse propagation in air breakdown environment

An experiment is conducted to examine the tail erosion phenomenon which occurs to an intense microwave pulse propagating in air breakdown environment. In the experiment, a 1 MW microwave pulse (1.1 microsec) is transmitted through a large plexiglas chamber filled with dry air at about 1-2 torr pressure. Two different degrees of tail erosion caused by two different mechanisms are identified. This experimental effort leads to the understanding of the fundamental behavior of tail erosion and provides a data base for validating the theoretical model. A theoretical model based on two coupled partial differential equations is established to describe the propagation on an intense microwave pulse in air breakdown environment. One is derived from the Poynting theorem, and the other one is the rate equation of electron density. A semi-empirical formula of the ionization frequency is adopted for this model. A transformation of these two equations to local time frame of reference is introduced so that they can be solved numerically with considerably reduced computation time. This model is tested by using it to perform the computer simulation of the experiment. The numerical results are shown to agree well with the experimental results.

Kuo, S. P.↗

NASA NTRS1995

Cheap, Easy-To-Read Frequency Monitor For Pulsed Laser

Electronic circuit provides bar-graph display of difference between carrier frequency of pulsed laser transmitter and frequency of another laser serving as local oscillator in receiver. Display device linear array of light-emitting diodes (LED's), each representing 1-MHz portion of beat-frequency range from 20 to 40 MHz. Middle LED and neighbors green; LED's representing edges of passband yellow; LED's of frequencies outside passband red. Operator determines approximate relative frequency of transmitter at a glance by observing color and position of illuminated LED.

Esporoles, Carlos↗

NASA NTRS1996

Materials For Improved Josephson-Junction Devices

Number of superconductive, normally conductive, and insulating materials proposed for use in fabricating improved superconductor/insulator/superconductor (SIS) and superconductor/normal conductor/superconductor (SNS) electronic devices capable of operation at frequencies up into terahertz range. Such devices particularly useful as electrically nonlinear circuit elements of mixers and local oscillators in heterodyne receivers.

Vasquez, Richard P.↗

NASA NTRS1995

Noise Temperature and IF Bandwidth of a 530 GHz Heterodyne Receiver Employing a Diffusion-Cooled Superconducting Hot-Electron Mixer

We report on the first heterodyne measurements with a diffusion-cooled hot-electron bolometer mixer in the submillimeter wave band, using a waveguide mixer cooled to 2.2 K. The best receiver noise temperature at a local oscillator frequency of 533 GHz and an intermediate frequency of 1.4 GHz was 650 K (double sideband). The 3 dB IF roll-off frequency was around 1.7 to 1.9 GHz, with a weak dependence on the device bias conditions.

Skalare, A.↗

NASA NTRS1998

Substrate Effects for Atomic Chain Electronics

A substrate for future atomic chain electronics, where adatoms are placed at designated positions and form atomically precise device components, is studied theoretically. The substrate has to serve as a two-dimensional template for adatom mounting with a reasonable confinement barrier and also provide electronic isolation, preventing unwanted coupling between independent adatom structures. For excellent structural stability, we demand chemical bonding between the adatoms and substrate atoms, but then good electronic isolation may not be guaranteed. Conditions are clarified for good isolation. Because of the chemical bonding, fundamental adatom properties are strongly influenced: a chain with group IV adatoms having two chemical bonds, or a chain with group III adatoms having one chemical bond is semiconducting. Charge transfer from or to the substrate atoms brings about unintentional doping, and the electronic properties have to be considered for the entire combination of the adatom and substrate systems even if the adatom modes are well localized at the surface.

Yamada, Toshishige↗

NASA NTRS1995

Comparisions of modeled N(+), O(+), H(+) and He(+) in the midlatitude ionospherewith mean densities and temperatures from Atmosphere Explorer

In this study, Atmosphere Explorer data and model results for the ion and electron temperature and the density of N(+), O(+), H(+), and He(+) between 120 and 1400 km altitude are compared for two midlatitude ranges (L=2 and L=4), noon and midnight local time, winter and summer, at solar minimum. The data for the heavy atomic ions (O(+) and N(+)) show that their densities are greater at noon than at midnight for a given season and greater in summer than winter for a given local time. There is only a weak latitudinal variation in the density of these ions. The data show that the light ion (H(+) and He(+)) densities are greater at midnight than at noon and are generally greater in winter than summer. There is a strong latitudinal variation of the light ion densities, with the densities decreasing with increasing latitude. The model densities are in good agreement with the AE densities for N(+), O(+), and H(+). Model He(+) densities are lower, by a factor of 2 or more, than the measured densities. Model ion and electron temperatures agree well with the measured temperatures with only a modest increase in plasmapheric heating.

Craven, P. D.↗

NASA NTRS2004

Compensating for Effects of Humidity on Electronic Noses

A method of compensating for the effects of humidity on the readouts of electronic noses has been devised and tested. The method is especially appropriate for use in environments in which humidity is not or cannot be controlled for example, in the vicinity of a chemical spill, which can be accompanied by large local changes in humidity. Heretofore, it has been common practice to treat water vapor as merely another analyte, the concentration of which is determined, along with that of the other analytes, in a computational process based on deconvolution. This practice works well, but leaves room for improvement: changes in humidity can give rise to large changes in electronic-nose responses. If corrections for humidity are not made, the large humidity-induced responses may swamp smaller responses associated with low concentrations of analytes. The present method offers an improvement. The underlying concept is simple: One augments an electronic nose with a separate humidity and a separate temperature sensor. The outputs of the humidity and temperature sensors are used to generate values that are subtracted from the readings of the other sensors in an electronic nose to correct for the temperature-dependent contributions of humidity to those readings. Hence, in principle, what remains after corrections are the contributions of the analytes only. Laboratory experiments on a first-generation electronic nose have shown that this method is effective and improves the success rate of identification of analyte/ water mixtures. Work on a second-generation device was in progress at the time of reporting the information for this article.

Homer, Margie↗

NASA NTRS2000

Calcium localization and tipburn development in lettuce leaves during early enlargement

Tissue concentrations of Ca, Mg, and K were determined across immature leaves of lettuce (Lactuca sativa L. 'Buttercrunch') at different stages of enlargement using electron microprobe x-ray analysis. The analysis was with a wavelength dispersive spectrometer to permit detection of low concentrations of Ca. Patterns of mineral accumulation in immature leaves that were exposed were compared to patterns of accumulation in leaves that were enclosed within a developing head. The leaves developing without enclosure were free to transpire and developed normally whereas leaves developing with enclosure were restricted in transpiration and developed an injury that was characteristic of Ca deficiency. In the exposed leaves, Ca concentrations increased from an average of 1.0 to 2.1 mg g-1 dry weight (DW) as the leaves enlarged from 5 to 30 mm in length. In the enclosed leaves, Ca concentrations decreased from 1.0 to 0.7 mg g-1 DW as the leaves enlarged from 5 to 30 mm in length. At the tips of these enclosed leaves a larger decrease was found, from 0.9 to 0.3 mg g-1 DW during enlargement. Necrotic injury first became apparent in this tip area when the concentration was approximate to 0.4 mg g-1 DW. Magnesium concentrations across the exposed leaves were similar to concentrations across the enclosed leaves, and did not change with enlargement. Magnesium concentrations averaged 3.5. mg g-1 DW in both enclosed and exposed leaves during enlargement from 5 to 30 mm. In both exposed and enclosed leaves, K concentrations increased during enlargement from 40 to approximate to 60 mg g-1 DW. Potassium concentrations were highest toward the leaf apex and upper margin where injury symptoms occurred, and this may have enhanced injury development. This research documents the critical low levels of Ca (0.2 to 0.4 mg g-1 DW) that can occur in enclosed leaves of plants and which apparently leads to the marginal apex necrosis of developing leaves seen frequently on lettuce and other crops.

NASA Discipline Life Support Systems↗

NASA NTRS2019

Flight Readiness of Mochii S: Portable Spectroscopic Scanning Electron Microscope Facility on the International Space Station (ISS)

The ISS (International Space Station) currently lacks the capability to image and chemically analyze nano-to-micron scale particles from numerous engineering systems. To identify these particles, we must wait for a re-entry vehicle to return them from low earth orbit for ground-based SEM (Scanning Electron Microscope) / EDS (Energy Dispersive X-Ray Spectroscopy) analysis. This may take months, potentially delaying the affected system. Having an EDS-equipped SEM (Mochii S) aboard the ISS will accelerate response time thereby enhancing crew and vehicle safety by rapid and accurate identification of microscopic threats, especially in time-critical situations.The Mochii S payload will be stationed in the Japanese Experiment Module (JEM) powered by 120 VAC (Volts Alternating Current) inverter and connected to station Ethernet and WiFi (Fig. 1). To date the Mochii S payload has undergone testing for command and data handling, power quality, flight vibration, and radiation testing at Johnson Space Center (JSC). Mochii's high-RPM (Revolutions Per Minute) rotating vacuum pumps and high voltage systems have been reviewed to meet safety standards by JSC (Johnson Space Center) Engineering. Topology of the system in the JEM module has been baselined by ISS Safety and JAXA (Japan Space Exploration Agency). Digital controls to and from ISS over Joint Station LAN (Local Area Network) uplink have been simulated and the latencies and data rates have been found to be sufficient for successful operation of the payload from ground.Transporting sensitive electron optical instruments aboard a rocket that sustains 7G acceleration for 8 minutes and then operating it the unique microgravity (micro-g) environment is no trivial matter. To meet strict safety requirements and increase robustness for mission success, over 500 unique verifications must be completed before the payload is certified for spaceflight. Two of which will be discussed in detail are: vibroacoustic testing and magnetic susceptibility shielding and validation.

Mochii↗

NASA NTRS1973

Geophysical disturbance environment during the NASA/MPE barium release at 5 earth radii on September 21, 1971.

The geophysical disturbance environment was quiet during the NASA/MPE barium release at 5 earth radii on September 21, 1971. At the time of the release, the magnetosphere was in the late recovery phase of a principal magnetic storm, the provisional Dst value was -13 gammas, and the local horizontal disturbance at Great Whale River was near zero. Riometer and other observations indicated low-level widespread precipitation of high-energy electrons at Great Whale River before, during, and after the release. Cloudy sky at this station prevented optical observation of aurora. No magnetic or ionospheric effects attributable to the barium release were detected at Great Whale River.

Davis, T. N.↗

NASA NTRS1977

Chatanika observations of the latitudinal structure of electric fields and particle precipitation on November 21, 1975

By using a new multiposition experimental procedure the incoherent scatter radar facility of Chatanika, Alaska, has been used to obtain detailed latitudinal structure of ion velocities and electric fields in the afternoon and midnight sectors during a period of moderate magnetic disturbance. In particular, the latitudinal and local time structure of the Harang discontinuity has been investigated. In agreement with other observations it is found that the convection flow direction changes from westward through south to eastward over a fairly wide local time range (1-2 hours), the highest latitudes displaying the widest region. The Harang discontinuity encounter is accompanied by an abrupt increase in electron precipitation, the most intense part being located slightly east of the center of the discontinuity. It is suggested that this injection is due to processes closely connected with the discontinuity region itself, rather than to a substorm-related energization.

Wedde, T.↗

NASA NTRS1978

Adhesion of a bimetallic interface

The Hohenberg-Kohn and Kohn-Sham formalisms are used to examine binding (binding energy as a function of separation) for combinations of the simple metals Al(111), Zn(0001), Mg(0001), and Na(110) in contact. Similar metal contacts between Al, Zn, Mg, and Na are examined self-consistently in an ab initio calculation using the Kohn-Sham formalism. Crystallinity is included using the Aschroft pseudopotential via first order perturbation theory for the electron-ion interaction; and the ion-ion interaction is included exactly via a lattice sum. Binding energy was determined both in the local-density approximation and including gradient corrections to the exchange and correlation energy. Binding was found in all cases. In dissimilar metal contacts, interfacial bonding was greater than that in the weaker material predicting the possibility of metallic transfer. The nonzero position of the energy minimum in like metal contacts is explained in terms of consistency between the Ashcroft pseudopotential and the bulk charge density. Good agreement with experimental surface energies is obtained in the self-consistent calculation when nonlocal terms are included.

Ferrante, J.↗

NASA NTRS1981

Improved LEEM ranges over four decades

Low-energy electron magnetometer is suitable for terrestrial and aerial applications. Electron beam strikes tantalum collector plates in device, amplifying current and converting it to frequency. Current difference increases with beam deflection, providing measure of local field strength. LEEM operation requires no liquid helium unlike superconducting quantum interference device. LEEM sensitivity compares favorably with that of optical absorption magnetometers, and microsecond response range makes analyzing fast magnetic transients and signatures possible.

Singh, J. J.↗

NASA NTRS1979

Low-altitude signatures of the boundary layers

Low altitude measurements reveal two distinct types of dayside boundary-layer plasmas. The first type is characterized by a proton distribution whose average energy decreases with increasing latitude and generally shows cool, unaccelerated electron fluxes. This type is observed only near noon and is correlated with southward interplanetary magnetic field (IMF). The second type is characterized by a 'V' signature in which the proton average energy first decreases then briefly increases as a function of latitude. The electron distribution in the latter case is hotter and often shows evidence of small scale acceleration regions. This type can be seen at all local times in the dayside and at noon is correlated with a northward IMF. It is suggested that the type 1 plasma is the low altitude signature of the plasma mantle and the type 2 plasma is the low altitude signature of the low latitude boundary layer.

Reiff, P. H.↗

NASA NTRS1999

Multi-Spacecraft Observations of Interplanetary Shocks

Using multi-spacecraft observations primarily from ACE and WIND, and from IMP 8 and Geotail when available, the 3-dimensional structure of interplanetary shocks on the hundred Earth radii scale will be discussed. The complete magnetic field, and solar wind ion and electron data sets were used to fit the shocks with a full non-linear least squares fit "Rankine-Hugoniot" technique yielding the local shock surface normals and speeds with associated uncertainties. Multi-spacecraft results reveal that on the distance scale of ACE's L1 halo orbit the shocks deviate significantly from a simple planar geometry. This result has important consequences for the prediction of the exact arrival times of interplanetary shocks at the Earth's magnetosphere, and hence, on the reliability of space weather predictions. It also has implications on the coherence scale of solar wind structures and their evolution from the Sun to Earth.

Szabo, A.↗