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Klein, J.

Publications and source records attributed to Klein, J..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Planar rotational magnetic micromotors with integrated shaft encoder and magnetic rotor levitation

Deep x-ray lithography and electroplating may be combined to form a fabrication tool for micromechanical devices with large structural heights, to 500 micron, and extreme edge acuities, less than 0.1 micron-run-out per 100 micron of height. This process concept which originated in Germany as LIGA may be further extended by adding surface micromachining. This extension permits the fabrication of precision metal and plastic parts which may be assembled into three-dimensional micromechanical components and systems. The processing tool may be used to fabricate devices from ferromagnetic material such as nickel and nickel-iron alloys. These materials when properly heat treated exhibit acceptable magnetic behavior for current to flux conversion and marginal behavior for permanent magnet applications. The tool and materials have been tested via planar, magnetic, rotational micromotor fabrication. Three phase reluctance machines of the 6:4 configuration with 280 micron diameter rotors have been tested and analyzed. Stable rotational speeds to 34,000 rpm with output torques above 10 x 10(exp -9) N-m have been obtained. The behavior is monitored with integrated shaft encoders which are photodiodes which measure the rotor response. Magnetic levitation of the rotor via reluctance forces has been achieved and has reduced frictional torque losses to less than 1 percent of the available torque. The results indicate that high speed limits of these actuators are related to torque ripple. Hysteresis motors with magnetic bearings are under consideration and will produce high speed rotational machines with excellent sensor application potential.

Guckel, Henry↗
NASA NTRS1994

Simulations of Terrestrial in-situ Cosmogenic-Nuclide Production

Targets of silicon and silicon dioxide were irradiated with spallation neutrons to simulate the production of long-lived radionuclides in the surface of the Earth. Gamma-ray spectroscopy was used to measure Be-7 and Na-22, and accelerator mass spectrometry was used to measure Be-10, C-14, and Al-26. The measured ratios of these nuclides are compared with calculated ratios and with ratios from other simulations and agree well with ratios inferred from terrestrial samples.

Reedy, R. C.↗
NASA NTRS1993

Exposure history of the lunar meteorite, Elephant Moraine 87521

We report the noble gas concentrations and the Al-26, Be-10, Cl-36, and Ca-41 activities of the Antarctic lunar meteorite Elephant Moraine 87521. Although the actual exposure history of the meteorite may have been more complex, the following model history accounts satisfactorily for the cosmogenic nuclide data: A first stage of lunar irradiation for about 1 Ma at a depth of 1-5 g/sq cm followed, not necessarily directly, by a second one for 26 Ma at about 565 g/sq cm; launch from the moon less than 0.1 Ma ago; and arrival on earth 15-50 ka ago. The small concentration of trapped gases shows that except for some material that may have been introduced at the moment of launch, EET 87521 spent less than 1 Ma at a lunar depth less than 1 g/sq cm. EET 87521 has a K/Ar age in the range 3.0-3.4 Ga, which is typical for lunar mare basalts.

Vogt, S.↗
NASA NTRS1993

Cosmogenic radionuclides on LDEF: An unexpected Be-10 result

Following the discovery of the atmospheric derived cosmogenic radionuclide Be-7 on the Long Duration Exposure Facility (LDEF), a search began for other known nuclides produced by similar mechanisms. None of the others have the narrow gamma-ray line emission of Be-7 decay which enabled its rapid detection and quantification. A search for Be-10 atoms on LDEF clamp plates using accelerator mass spectrometry is described. An unexpected result was obtained.

Gregory, J. C.↗
NASA NTRS1993

Al-26-Mg-26 ages of iron meteorites

An exposure age for an iron meteorite can be calculated from measurements of a radioactive nuclide and a stable nuclide that are produced by similar sets of nuclear reactions, provided that the stable nuclide is present with low initial abundance. The standard methods rely on either K-40 (t(sub 1/2) = 1.26 Gy), K-39, and K-41 or on a shorter-lived radionuclide and a stable, noble gas isotope. Widely used pairs of this type include Cl-36/Ar-36 and Al-26/Ne-21. Other pairs that may serve the purpose for iron meteorites contain many stable isotopes besides those of K and the noble gases that are produced partly by cosmic rays. We consider here the calculation of exposure ages, t(sub 26), from measurements of Al-26 (t(sub 1/2) = 0.7 My) and (stable) Mg-26. Ages based on Al-26/Mg-26 ratios, like those based on Cl-36/Ar-36 ratios, are 'buffered' against changes in relative production rates due to shielding because decay of the radioactive nuclide accounts for a good part of the inventory of the stable nuclide.

Herzog, G. F.↗
NASA NTRS1993

Stable Ni isotopes and Be-10 and Al-26 in metallic spheroids from Meteor Crater, Arizona

The Canyon Diablo spheroids, which are found around Meteor Crater, Arizona, are nickel-enriched objects with diameters from less than 0.1 to several mm. Previous studies have suggested that the enrichment of nickel resulted either from shock-melting of S-rich areas followed by solidification of the liquids under strongly non-equilibrium conditions at rapid cooling rates during flight outward from the crater or from the selective oxidation of iron. Isotopic studies are an effective tool for constraining the degree of open-system evaporation experienced by a system. The purpose of this study was to see whether Ni isotopes had been fractionated by volatilization during spheroid formation. In addition, the cosmogenic nuclides Be-10 and Al-26 were measured to try to estimate the depths in the parent meteorite from which the spheroids came.

Xue, S.↗
NASA NTRS1992

Cosmogenic nuclides in core samples of the Chico L6 chondrite - Evidence for irradiation under high shielding

Results are presented from an analysis of core samples obtained from different depths of the Chico (New Mexico) L6 chondrite for various cosmogenic nuclides (Be-10, Al-26, and stable isotopes of He, Ne, and Ar). The relationships between the measured abundances of cosmogenic nuclides and cosmogenic Ne-22/Ne-21 ratio were compared with predictions of recent semiempirical models of Graf et al. (1990) and Reedy (1991), and it was found that both models closely reproduce the observed trends and absolute values of the data obtained. Noble gas data indicate that Chico experienced shielding similar to that of Jilin and greater than those of the Knyahinya or the Keyes chondrites. The exposure history for Chico is discussed.

Garrison, D. H.↗
NASA NTRS1992

Cosmogenic radioisotopes on LDEF surfaces

The radioisotope Be-7 was discovered in early 1990 on the front surface, and the front surface only, of the LDEF. A working hypothesis is that the isotope, which is known to be mainly produced in the stratosphere by spallation of nitrogen and oxygen nuclei with cosmic ray protons or secondary neutrons, diffuses upward and is absorbed onto metal surfaces of spacecraft. The upward transport must be rapid, that is, its characteristic time scale is similar to, or shorter than, the 53 day half-life of the isotope. It is probably by analogy with meteoritic metal atmospheric chemistry, that the form of the Be at a few 100 km altitude is as the positive ion Be(+) which is efficiently incorporated into the ionic lattice of oxides, such as Al2O3, Cr2O3, Fe2O3, etc., naturally occurring on surfaces of Al and stainless steel. Other radioisotopes of Be, Cl, and C are also produced in the atmosphere, and a search was begun to discover these. Of interest are Be-10 and C-14 for which the production cross sections are well known. The method of analysis is accelerator mass spectrometry. Samples from LDEF clamp plates are being chemically extracted, purified, and prepared for an accelerator run.

Gregory, J. C.↗
NASA NTRS1992

A comparison of three SAR interference filters

Three interference filters are discussed and their ability to remove the interference while leaving target signal data is quantified. The filters are adaptive frequency-domain spike filtering; adaptive frequency-domain interference determination and masking; and interference-target correlation masking. Using Jet Propulsion Laboratory Airborne Synthetic Aperture Radar (JPL AIRSAR) data, the algorithms are applied to three data sets. The resultant compressed Stokes matrix data are compared with the normally processed interference-free image in a quantitative sense. The algorithms are evaluated by measuring the polarization signature, SNR, equivalent number of looks, and impulse response of the processed images.

Chapman, B.↗
NASA NTRS1992

Radar measurement of forested areas during OTTER

To test a forest ecosystem model in the OTTER (Oregon ecosystem research) project, it is desirable to find forest canopy parameters via radar remote sensing measurements. Conventionally, forest biomass, along with quantities such as the leaf area index, drive the model. It is shown that the radar backscatter is not uniquely related to biomass. A sensitivity study is carried out using a forward scattering model to determine the variation of radar cross section as a function of several forest parameters. The results are used to find suitable quantities to recover via radar experiments. A parameter estimation scheme is developed to calculate some preliminary statistical properties of the forest.

Moghaddam, M.↗
NASA NTRS1991

Exposure histories of lunar meteorites - ALHA81005, MAC88104, MAC88105, and Y791197

The cosmogenic radionuclides Ca-41, Cl-36, Al-26, and Be-10 in the Allan Hills 81005, MacAlpine Hills 88104, MacAlpine Hills 88105, and Yamato 791197 meteorites were measured by accelerator mass spectrometry. Mn-53 in Allan Hills 81005 and Yamato 791197 was measured by neutron activation. These four lunar meteorites experienced similar histories. They were ejected from near the surface of the moon ranging in depth down to 400 g/sq cm and had very short transition times (less than 0.1 Ma) from the moon to the earth. A comparison of the cosmogenic nuclide concentrations in MacAlpine Hills 88104 and MacAlpine Hills 88105 clearly indicates that they are a pair from the same fall.

Nishiizumi, K.↗
NASA NTRS1991

Exposure histories of the lunar meteorites - MAC88104, MAC88105, Y791197, and Y86032

Four lunar meteorites were analyzed for the cosmogenic radionuclides Be-10, Al-26, Cl-36, and Ca-41. Histories of exposure to cosmic rays were modelled in terms of two-stage irradiations, each with a long first stage on the moon, lasting a time T sub 2pi greater than 5 Ma at a burial depth d sub 2pi(g/sq cm), followed by a second stage in space, i.e., the transit time between the moon and the earth, lasting a time T sub 4pi (Ma) in a body of typical metereological size. It is inferred that the production rate is of the order of 5/Ma and the arrival rate worldwide is about 3,000,000 meteorites/Ma. It is concluded that each impact event large enough to produce lunar meteorites sends a large number of them to the earth.

Vogt, S.↗
NASA NTRS1991

Ca-41 in iron falls, Grant and Estherville - Production rates and related exposure age calculations

Results are presented of the first phase of a Ca-41 cosmogenic studies program aimed at establishing baseline concentrations and trends in selected meteorites and the use of Ca-41 in estimating exposure ages and preatmospheric meteorite radii. The average Ca-41 saturation activity recorded in four small iron falls is 24 +/-1 dpm/kg. This finding, together with measurements at the center and surface of the large iron Grant, indicates that production of Ca-41 from spallation on iron is weakly dependent on shielding to depths as large as 250 g/sq cm. The (K-41)-Ca-41 exposure age of Grant is estimated at 330 +/-50 My, and an upper limit to its terrestrial age of 43 +/-15 ky. A comparison of the Ca-41 contents of stony and metallic material separated from the mesosiderite Estherville identifies low-energy neutron capture on native Ca as a second important channel of production. It is found that the Ca-41 signal in the stone phase from three meteorites correlates with their size, and that the inferred low-energy neutron fluxes vary by a factor of at least 20.

Fink, D.↗
NASA NTRS1991

In situ Be-10-Al-26 exposure ages at Meteor Crater, Arizona

A new method of dating the surface exposure of rocks from in situ production of Be-10 and Al-26 has been applied to determine the age of Meteor Crater, Arizona. A lower bound on the crater age of 49,200 + or - 1,700 years has been obtained by this method.

Nishiizumi, K.↗
NASA NTRS1991

Polarimetric radar measurements of a tropical rainforest

In Mar. 1990, the NASA/JPL DC-8 Airborne Synthetic Aperture Radar (AIRSAR) was flown over an area in northern Belize and the surrounding areas of Guatamala and Mexico. We have extracted the three-frequency polarimetric signatures of a variety of natural areas and have found that many appear to have a unique radar signature, if all polarizations and frequencies are examined.

Durden, S.↗
NASA NTRS1991

The interactions of atmospheric cosmogenic radionuclides with spacecraft surfaces

The discovery of the cosmogenic radionuclide Be-7 on the front surface of the Long Duration Exposure Facility (LDEF) has opened new opportunities to study several unexplored regions of space science. The experiments have shown that the Be-7 found was concentrated in a thin surface layer of spacecraft material. The only reasonable source of the isotope is the atmosphere through which the spacecraft passed. It is expected that the uptake of Be in such circumstances will depend on the chemical form of the Be and the chemical nature of the substrate. It was found that the observed concentration of Be-7 does differ between metal surfaces and organic surfaces such as PTFE (Teflon). It is noted however, that (1) organic surfaces are etched by the atomic oxygen found under these orbital conditions, and (2) the relative velocity of the species is 8 km/s relative to the surface and the interaction chemistry and physics may differ from the norm. Be-7 is formed by disintegration of O and N nuclei under cosmic ray proton bombardment. Many other isotopes are produced by cosmic ray reactions, and some of these are suited to measurement by the extremely sensitive methods of accelerator mass spectrometry.

Gregory, John C.↗
NASA NTRS1991

Exposure history of individual cosmic particles

Cosmogenic Be-10 and Al-26 were measured in a suite of stony cosmic spherules derived from deep-sea sediments and the Greenland ice cap. These spherules show clear evidence of exposure to galactic cosmic ray and solar cosmic ray bombardment on time scales from a few times 100,000 years up to as much as 10 to the 7th years. The exposure took place in the inner solar system, not in highly eccentric orbits. When they reached the earth, the particles were not much larger than their present size, but it is not excluded that most of their cosmic ray exposure took place very close to the surface of an asteroidal body.

Nishiizumi, K.↗