Search NASA⌕ Search

Engineering topics

Brecher, A.

Publications and source records attributed to Brecher, A..

17 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Approaches to the utilization of space for CO2 research

A system study of the potential of space technology to monitor climate changes and improve the understanding of the coupling beteen CO2 and cloud cover is summarized. The basis for the study is scientific data requirements pertinent to the U.S. Department of Energy's CO2 Research Program. The capabilities of space-based sensor systems are matched to meet these requirements. New sensor system concepts are identified, including a Space Shuttle-launched recalibration package to provide for continuity of measurement and recalibration between satellites, a high-orbit radiation budget satellite, or parallax sensor to measure cloud altitude, a passive method for the direct measurements of CO2 and a high-altitude powered platform to monitor select regional parameters. Space-based sensor systems that could be the development focus for the time frames of 0-5, 5-10 and 10-20 years are recommended.

Glaser, P.↗
NASA NTRS1979

The magnetic effects of brecciation and shock in meteorites. II - The ureilites and evidence for strong nebular magnetic fields. III - The achondrites

Magnetic studies were conducted on samples of the ureilitic meteorites Goalpara, Havero, Novo Urei, and Kenna. Measurements included bulk magnetic susceptibility, natural remanent magnetization (NRM), saturation remanence, and the demagnetization behavior of NRM and saturation remanence. An approximate 'fossil' magnetic field intensity was determined by analysis of coercivity spectra of NRM and saturation remanence after reheating. It was found that the magnetic susceptibility of ureilites increased with severity of shock, and the NRM intensity decreases while its coercivity spectrum generally hardens with increasing shock. Goalpara and Kenna are distinguished by unexpectedly homogeneous, strong, stable, and directionally clustered NRM, indicative of a unique original magnetizing event. The results support the assertion that both ureilites and carbonaceous chondrites have formed from related nebular material and provide further evidence for a strong external magnetic field during the accretional stages and throughout an early bombardment stage.

Brecher, A.↗
NASA NTRS1977

The magnetic effects of brecciation and shock in meteorites. I - The LL-chondrites

The magnetic behavior of eight LL chondrites is analyzed in detail, and some implications for their modes of formation and evolutionary history are examined. Petrographic features of the specimens are described, and their initial magnetic characteristics are discussed. The demagnetization behavior of the initial magnetization is investigated along with the saturation remanence behavior and paleomagnetic-field intensities. The results indicate that a magnetic field of 0.01 to 0.1 Oe may have been present during postimpact cooling and that severe shock metamorphism may have given rise to the observed magnetic moments and behavior, even in the absence of ambient magnetic fields.

Brecher, A.↗
NASA NTRS1977

The thermoremanence hypothesis and the origin of magnetization in iron meteorites

The intensity, relative stability and directional behavior in alternating field demagnetization of natural, saturation, thermal and spontaneous magnetization were studied for a variety of iron meteorites. Results show that remanence and relative stability increase from the coarser to the finer-grained samples. In addition, natural remanent magnetization coercivity spectra are found to soften with coarsening of the grain size. The link between fine structure and magnetization direction in octahedrites is also discussed. The combined effect of magnetocrystalline- and shape-anisotropy of the crystallographically ordered ferromagnetic kamacite alpha-phase renders the iron meteorites of little use for the study of ancient solar system fields.

Brecher, A.↗
NASA NTRS1976

Textural remanence - A new model of lunar rock magnetism

In reexamining the accumulated magnetic data on lunar rocks, several common patterns of magnetic behavior are recognized. Their joint occurrence strongly suggests a new model of lunar rock magnetism, which is based on partial preferred textural alignment of the spontaneous moments of magnetic grains without requiring the existence of ancient lunar magnetic fields. This magnetic fabric, mimetic to locally oriented petrofabric, gives rise to an apparent 'textural remanent magnetization'. In order to account for the observed intensity of 'stable remanence' in lunar rocks, only a minute fraction (0.001 to 0.00001) of the single-domain iron grains present need be preferentially aligned. Several mechanisms operating on the lunar surface, including shock and diurnal thermal cycling, appear adequate for producing the required type and degree of magnetic alignment in all lunar rock classes. The model is supported by a wide variety of direct and indirect evidence, and its predictions (e.g., regarding anisotropic susceptibility and remanence acquisition) can be experimentally tested.

Brecher, A.↗
NASA NTRS1975

The low-temperature electrical properties of carbonaceous meteorites

Electrical conductivities and dielectric constants have been measured over the temperature range 90-300 K on several carbonaceous chondrites and some terrestrial analogues. The conductivities of meteorites of different petrologic subtypes range over many orders of magnitude and the low-temperature activation energies are typically much smaller than those observed in terrestrial materials at higher temperatures. The electrical properties of carbonaceous chondrites vary systematically with chemical-mineralogical characteristics in that: (1) activation energy at low temperature is greater in the more volatile-rich meteorites containing hydrated silicates, and (2) conductivity is greater in the more reduced meteorites of higher petrologic subtype. These new data on the electrical properties of chondrites hold important implications for both the thermal and magnetic histories of small bodies in the early solar system.

Brecher, A.↗
NASA NTRS1975

Paleomagnetic systematics of ordinary chondrites

The investigation shows that the decrease in intensity and the increase in stability of natural remanent magnetization (NRM) to alternating field (AF) demagnetization roughly parallel the decrease in Ni-Fe metal content and the corresponding enrichment of the metal phases in Ni. The stability of NRM within a chemical type appears to decrease with increasing degree of metamorphism, a feature interpretable in terms of composition, size, and shape of metal grains. Paleofield intensities required to imprint the NRM as thermo-chemical remanence are in the range from 0.01 to 0.3 Oe.

Brecher, A.↗
NASA NTRS1975

Consortium studies of matrix of light gray breccia 73215

A description is presented of the preliminary results of interdisciplinary studies of matrix samples. The significance of the 73215 studies is considered and the relationship of 73215 to other Apollo 17 highland breccias is discussed. According to a tentative hypothesis 73215 is an aggregate of fragments plus melt generated in a very large impact, possibly the Serenitatis basin-forming event. If this is correct, studies of this sample will make it possible to date the Serenitatis event and will provide an insight into the breccia-forming processes associated with such events. Studies of the clasts in the breccia will provide an opportunity to formulate a partial characterization of the preimpact source terrain. An investigation of the deep lunar crust might perhaps also be possible.

James, O. B.↗
NASA NTRS1974

The paleomagnetic record in carbonaceous chondrites - Natural remanence and magnetic properties

Recent results of an intensive study of the natural remanence (NRM) and the magnetic properties of carbonaceous chondrites (CC) are summarized. It is convincingly demonstrated that the record of ancient magnetic fields has been preserved in these least-altered old samples of solar system material known. Intensities of specific NRM in the 13 meteorites surveyed span a broad range of values from 0.00005 to 0.5 emu/g. A low-temperature cleaning technique, based on the memory effect in magnetite grains, was followed by alternating field (af) demagnetization of the residual memory to exhibit the relative stability of NRM in the CC studied. No systematic correlation was found of either intensity or stability of NRM to af demagnetization with petrologic subtype, beyond a trend of increasing stability of memory from petrologic subtype C2 to subtype C4. The intensity and stability behavior of the saturation remanence are better suited for use in a magnetic classification of CC.

Brecher, A.↗
NASA NTRS1974

Comparative magnetic studies of some Apollo 17 rocks and soils and their implications

The lunar rock and soil specimens studied include samples of the orange and gray soil strata from adjancent sites on the South rim of Shorty Crater, two vesicular mare basalts, and a mare basalt of the dense aphanitic type. The magnetic characteristics of the soils are discussed along with a hysteresis behavior analysis of Apollo 17 rocks. The remanent properties are examined, giving attention to viscous remanence, NRM stability, saturation isothermal remanence, and heating experiments.

Brecher, A.↗
NASA NTRS1973

On the primordial condensation and accretion environment and the remanent magnetization of meteorites

In the context of various models for the early evolution of a solar nebula, the possible roles assigned to ambient magnetic fields and the paleointensities required to establish the stable natural remanent magnetization observed in meteorites, are discussed. It is suggested that the record of paleofields present during condensation, growth, and accumulation of grains is likely to have been preserved as chemical or thermochemical remanence in unaltered meteoritic material. Fine particle theories appear adequate for treating meteoritic remanence, if models based on corresponding types of permanent magnet materials, e.g., powder ferrites for chondrites and diffusion hardened alloys for iron meteorites, are adopted.

Brecher, A.↗
NASA NTRS1973

Magnetic and Moessbauer studies of Apollo 16 rock chips 60315,51 and 62295,27

Analysis of the Moessbauer spectra of two Apollo 16 rocks showed that 60315,51 is much richer in iron metal and troilite, but poorer in olivine, than 62295,27. The values of magnetic parameters, derived from hysteresis loops at 175 and 300 K, indicate the high metal contents and the predominance of coarse multidomain grains in both rocks. These coexist with a superparamagnetic grain fraction in 60315 and with a small single-domain grain fraction in 62295. The high Fe(0)/Fe(2+) ratios, the nonlinear acquisition of laboratory thermoremanence, and the drastic changes in magnetic parameters upon heating support the proposed formation of both rocks from the lunar regolith, with incorporation of shocked meteoritic metal grains during high-temperature impact events and simultaneous acquisition of magnetic remanence. Values estimated for ancient lunar magnetic fields by comparing the natural remanence with laboratory thermoremanence acquired in fields of 0.05 and 0.5 Oe, range from 0.01 to more than 1 Oe.

Brecher, A.↗