Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Fragmentation”

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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Tholins - Organic chemistry of interstellar grains and gas

The paper discusses tholins, defined as complex organic solids formed by the interaction of energy - for example, UV light or spark discharge - with various mixtures of cosmically abundant gases - CH4, C2H6, NH3, H2O, HCHO, and H2S. It is suggested that tholins occur in the interstellar medium and are responsible for some of the properties of the interstellar grains and gas. Additional occurrences of tholins are considered. Tholins have been produced experimentally; 50 or so pyrolytic fragments of the brown, sometimes sticky substances have been identified by gas chromatography-mass spectrometry, and the incidence of these fragments in tholins produced by different procedures is reported.

Sagan, C.↗
NASA NTRS1979

A tidal theory for the origin of the solar nebula

A model for the origin of the solar nebula is developed with attention to the significance of angular momentum considerations. Evidence that stars are born in groups rather than singly is examined. It is shown that protostars which are members of typical galactic clusters have some probability of undergoing a gravitational encounter with another star while they are collapsing. According to the model, these encounters impart disproportionate amounts of angular momentum to the later material to fall in toward already centrally condensed fragments. The amount of central condensation of a fragment is the overriding factor in determining its stability against destruction by tidal forces. The encounter also imparts angular momentum to matter that is still accreting onto the protosun.

Kobrick, M.↗
NASA NTRS1978

The Yamato-74659 ureilite and some new findings on the Yamato achondritic pyroxenes

A cube-like fragment with an approximately 4 mm edge was taken from the Yamato-74659 meteorite for the mineralogical and crystallographic examination discussed in the present paper. An analysis of powdered fragments by a standard wet chemical method showed that it matched to weathered ureilite. The chemical composition was found to differ from other ureilites in that the FeO content (8.83 wt%) is the lowest among known ureilites and it is richer in SiO2 contents (42.91 wt%).

Takeda, H.↗
NASA NTRS1979

A statistical model for the initial stellar mass function

The nonlinear stages of the fragmentation of a collapsing molecular cloud are modeled by coagulation theory. Several distinct physical processes are discussed, including protostellar fragment coalescence, gas accretion, and binary formation. This work confirms and extends the earlier result of Nakano (1966) that an approximately self-similar limiting form of the mass spectrum develops after several mean initial collision times. An approximate solution to the velocity-averaged coagulation equation is given for an arbitrary power-law dependence of the coalescence rate on mass, with dimensional dependence proportional to m to the power lambda; i.e., the asymptotic mass spectrum varies as m to the -3 lambda/2 power at small masses and cuts off exponentially at large masses, the characteristic mass depending on the number of collision times elapsed. Simple physical arguments suggest that lambda may increase with increasing mass, but is restricted to the range from 2/3 to 4/3. A large fraction of collisions could result in binary formation.

Silk, J.↗
NASA NTRS1979

Gas drag in primordial circumplanetary envelopes - A mechanism for satellite capture

Known properties of the current solar system and Bodenheimer's (1977) model of early Jovian evolution are employed to develop a mechanism for satellite capture based on gas drag in primordial circumplanetary envelopes. In particular, the deceleration and fragmentation of two parent bodies passing through an extended primordial Jovian nebula may account for the clusters of prograde and retrograde satellites of Jupiter. Subsequently, the fragments probably underwent limited orbital evolution, and were dispersed by collision with a stray body. The heavy element cores of the outer planets may also be due to primordial gas drag capture. Nebular drag capture of the Martian satellites Phobos and Deimos, Neptune's Nereid and Triton, and Saturn's Phoebe and Iapetus is also conceivable.

Pollack, J. B.↗
NASA NTRS1978

The nature of rays and sources of highland material in Mare Crisium

Although highland fragments are rare in the Luna 24 core, they should provide an important source of information on the sequence of formation and lithology of lunar east-limb basins. The numerous rays that cross the Crisium basin suggest several sources of highland materials. Both deposition of primary ejecta and reworking of local material were most likely responsible for the formation of ray systems in Mare Crisium. In addition to the fact that Luna 24 landed near the uprange end of a Giordano Bruno ray, incomplete sampling of the uppermost layer and formation of the ray by reworking of in situ regolith suggest that its materials may be scarce or not present in the core. Highland fragments present are most likely to be representative of several highland sources.

Maxwell, T. A.↗
NASA NTRS1979

Empirical data on the origin of 'new' comets

The mass distribution of a group of 62 comets from the sample of Marsden et al (1978) was determined by assuming that the size of a comet is in proportion to the surface area of its vaporizing nucleus. A bimodal distribution was found, with a gap between magnitudes 8.1 and 9. The 50 brighter comets (magnitudes 1 to 8) have been tentatively identified as true 'new' comets; their size distribution cannot be fit to a constant slope on a log-log graph. These comets were apparently formed by a mechanism which differs from the fragmentation process. The 12 fainter may be fragments of comets which split or dimmed during their first passages. Results indicate that new comets could be identified with pristine planetesimals; they decay rapidly, probably by splitting when they enter the inner solar system.

Delsemme, A. H.↗
NASA NTRS1979

Emplacement of Fahrenheit crater ejecta at the Luna-24 site

The likelihood that the gabbroic and monomineralic fragments in the Luna-24 soils were excavated during the Fahrenheit cratering event can be assessed by considering the quantity, characteristics, and mode of deposition of Fahrenheit ejecta in the vicinity of the Luna-24 site. The original morphology of Fahrenheit's ejecta deposits is inferred by examining a fresh crater, Lichtenberg B, of a comparable site that formed in a similar type of target material. On the basis of this analogy, a probability of over 80% was calculated that the Luna-24 site was morphologically disturbed by the deposition of Fahrenheit ejecta. The relative abundance, gabbroic composition, and unshocked character of the holocrystalline fragments discovered in the Luna-24 core sample are consistent with the widespread occurrence of Fahrenheit deposits and the characteristics of Fahrenheit ejecta anticipated at the Luna-24 range.

Settle, M.↗
NASA NTRS1978

Meteoritic material in lunar highland samples from the Apollo 11 and 12 sites

Radiochemical neutron activation analyses for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Te, Tl, U and Zn were carried out on 11 samples from the Apollo 11 and 12 sites (two samples of rock 12013, one granitic and one KREEPy; 4 KREEP fragments from 2-4 mm soil 12033,2; 4 anorthositic fragments from 1-3 mm soil 10085,104; 1 sample of 'Luny' rock-felsite-KREEP breccia 12013 10085,31 LR-1). Most Apollo 12 samples were found to have an Imbrium meteoritic component; others, typified by the Luny breccia, apparently contain a new meteoritic component of low Re content. Components of higher Ir/Au ratio (3L, 5L and 7) were found in Apollo 11 anorthositic samples; the fact that their enrichment in meteoritic siderophiles parallels that of Fe, Mg, REE and other KREEP elements is consistent with progressive contamination of an anorthositic crust. The Luny rock was tentatively classified Group 2, supporting the assignment of this group to Serenitatis.

Janssens, M.-J.↗
NASA NTRS1978

Core 74001/2 - Grain size and petrology as a key to the rate of in-situ reworking and lateral transport on the lunar surface

A suite of samples from the double drive tube 74001/2 has been studied. Material from this core mainly consists of orange and black droplets interpreted to be volcanic pyroclastic ejecta. Grain size analysis indicates that this material is very homogeneous in its grain size properties. It is also the finest and best sorted suite of soil samples in the lunar collection having a mean grain size of 40 microns and a mean standard deviation of 1.75 phi. The upper 5.5 cm of this core has apparently undergone in situ reworking by meteorites over a period of about 10 million years. This reworked zone contains 'exotic' grains including basalt, mineral fragments, vitric breccias, and agglutinates. One type of agglutinate is unique and has been made primarily from orange and black glass droplets melted and welded together by micrometeorite impacts. Other agglutinates are made mainly from basaltic fragments and minerals. The amount of 'exotic' material added to the core combined with an estimate of the location of the source areas for the 'exotic' material allows us to estimate that a maximum of about 0.36 gm per sq cm of regolith surface is added from a radius of about 1 meter in 10 million years. Furthermore, no more than about 0.01 gm per sq cm of regolith surface is added from a radius of about 100 meters in 10 million years.

Mckay, D. S.↗
NASA NTRS1979

Expansion cooled CO nuclear pumped laser

The paper describes a series of experiments designed to investigate the performance of a fission fragment excited CO laser with gasdynamic cooling. The experiments use a wall source of fission fragments to provide excitation of CO or CO gas mixtures. A separate investigation examines the effects on vibrational excitation distribution of CO or CO gas mixtures with the addition of UF6.

Davis, J. F.↗
NASA NTRS1980

Dissemination, resuspension, and filtration of carbon fibers

Carbon fiber transport was studied using mathematical models established for other pollution problems. It was demonstrated that resuspension is not a major factor contributing to the risk. Filtration and fragmentation tests revealed that fiber fragmentation shifts the fiber spectrum to shorter mean lengths in high velocity air handling systems.

Elber, W.↗
NASA NTRS1979

Gaseous NH4Cl revisited - A computational investigation of the potential surface and properties

An investigation of the potential surface and properties of the ground state of gaseous NH4Cl is presented. The calculations, which utilize a good basis set and include investigation of the valence correlation effects, result in a description of gaseous NH4Cl as a weakly bound complex with NH3 and HCl structures essentially equivalent to those of the isolated fragments. The charge distributions within the fragments are modifed in the complex, however, and there is a small amount of charge transfer. The results are in reasonable agreement with estimate of D sub 0, super 0 from high temperature mass spectroscopic investigations and vibrational frequencies from matrix experiments. The equilibrium constant for the reversible reaction NH4Cl yields NH3 + HCl indicates that the homogeneous formation of NH4Cl does not represent a significant chemical sink for HCl in the upper atmosphere

Raffenetti, R. C.↗
NASA NTRS1979

Star and planetary system formation in collapsing, viscous, rotating clouds

The results of a preliminary investigation of several processes that are of interest both for the formation of stars and for the evolution of planetary systems are presented. It is shown that turbulent viscosity is capable of playing an important role in conveying angular momentum over time scales that are short enough to be significant. Meridional circulation can also act in this fashion during some phases of the evolution. This transport may reduce the probability of formation of the rings that have been found by most earlier investigators. Transport and mixing on a faster than cooling time scale should also inhibit usual modes of fragmentation and the present work casts some doubt on the multiple successive fragmentation scenarios that lead from a massive molecular cloud to a collection of roughly solar mass protostars. The conditions that are probable in the disks that would exist at varying phases of collapse are examined and it is concluded that turbulent viscosity would be very important in a pre-solar nebula.

Wiita, P. J.↗
NASA NTRS1979

A special class of planetary collisions - Theory and evidence

Collisions between comparable-sized planetary bodies are a special class of collisions, rarer than other collisions, but producing interesting products, such as unfractured dumbbell-shaped contact binaries, partly brecciated elongated bodies, totally brecciated spheroidal bodies, and perhaps co-orbiting binary pairs or swarms. Qualitative and rough quantitative theories are presented to indicate collision outcomes. Contact binaries or fractured elongated bodies as large as tens or hundreds of kilometers across can be produced - larger than hitherto considered. Lengths about 20 to 200 km are most probable for igneous or ordinary chondritic elongated objects formed by collision, but other lengths could result from tidal evolution of pairs. Though most elongated asteroids are probably collision fragments, as usually assumed, some may instead be accretionary products. Trojan asteroid 624 Hektor is a candidate. Some polymict, genomict, and monomict brecciated meteorites may be better explained by large-scale fragmentation and immediate gravitational re-assembly of parent bodies than by local-scale processes of cratering on parent-body surfaces.

Hartmann, W. K.↗
NASA NTRS1979

The erosion of planetary and satellite atmospheres by energetic atomic particles

Analytic expressions are presented which may be used to compute the sputter-erosion yield from any unimolecular gravitationally bound gas by any atomic charged particle of any energy. A calculation of solar wind proton and alpha particle induced erosion of the CO2 atmosphere of Mars predicts molecular sputtering yields. An expression for the emission yield of energetic molecular fragments produced in primary knock-on events is given in closed form; such fragment emission is of secondary importance for mass loss compared to the molecular yield itself. Erosion by radiation belt protons of a hypothetical thin O2 atmosphere associated with the Jovian satellite Ganymede is considered, and molecular sputtering yields for proton energies are determined.

Haff, P. K.↗
NASA NTRS1980

Sources of orbital debris and the projected environment for future spacecraft

The major source of the nearly 5000 objects currently observed orbiting the earth is from rocket explosions. These explosions have almost certainly produced an even larger unobserved population. If the current trend continues, collisions between orbiting fragments and other space objects could be frequent. By the year 2000 satellite fragmentation by hypervelocity collisions could become the major source of earth orbiting objects, resulting in a self propagating debris belt. The flux within this belt could exceed the meteoroid flux, affecting future spacecraft design.

Kessler, D. J.↗
NASA NTRS1980

Collision avoidance in space

Collisions in earth orbital space between operational payloads and various forms of space debris (nonoperational payloads, nonfunctional mission-related objects and fragments resulting from collisions and explosions) are discussed and possible means of avoiding them are considered. From 10,000 to 15,000 objects are estimated to be in earth orbital space, most of which represent spacecraft fragments and debris too small to be detected and tracked by earth-based sensors, and it is considered likely that some of them will be or have already been involved in direct collisions with the ever increasing number of operational satellites and space stations. Means of protecting proposed large space structures and smaller spacecraft from significant damage by larger space objects, particularly in the 400-4000 km altitude range where most debris occurs, include structural redundancy and the double shielding of sensitive components. Other means of collision avoidance are the collection or relocation of satellites, rocket bodies and other objects by the Space Shuttle, the prevention of explosions and the disposal of spent rocket parts by reentry. Finally, a management structure would be required to administer guidelines for the prevention and elimination of space debris.

Kessler, D. J.↗