Plasma processing of interstellar PAHs into solar system kerogen     

Wdowiak TJ  Lee W  Cronin J  Beegle LW  Robinson MS 《Planetary and Space Science》1995,43(10-11):1175-1182

Processes resulting in the formation of hydrocarbons of carbonaceous chondrites and the identity of the interstellar molecular precursors involved are an objective of investigations into the origin of the solar system and perhaps even life on earth. We have combined the resources and experience of an astronomer and physicists doing laboratory simulations with those of a chemical expert in the analysis of meteoritic hydrocarbons, in a project that investigated the conversion of polycyclic aromatic hydrocarbons (PAHs) formed in stellar atmospheres into alkanes found in meteorites. Plasma hydrogenation has been found in the University of Alabama at Birmingham Astrophysics Laboratory to produce from the precursor PAH naphthalene, a new material having an IR absorption spectrum (Lee, W. and Wdowiak, T.J., Astrophys. J. 417, L49-L51, 1993) remarkably similar to that obtained at Arizona State University of the benzene-methanol extract of the Murchison meteorite (Cronin, J.R. and Pizzarello, S., Geochim. Cosmochim. Acta 54, 2859-2868, 1990). There are astrophysical and meteoritic arguments for PAH species from extra-solar sources being incorporated into the solar nebula, where plasma hydrogenation is highly plausible. Conversion of PAHs into alkanes could also have occurred in the interstellar medium. The synthesis of laboratory analogs of meteoritic hydrocarbons through plasma hydrogenation of PAH species is underway, as is chemical analysis of those analogs. The objective is to clarify this heretofore uninvestigated process and to understand its role during the origin of the solar system as a mechanism of production of hydrocarbon species now found in meteorites. Results have been obtained in the form of time-of-flight spectroscopy and chemical analysis of the lab analog prepared from naphthalene.  相似文献   

Charged dust in the outer planetary magnetospheres     

Jay Roderick Hill  D. A. Mendis 《Earth, Moon, and Planets》1979,21(1):3-16

We assume that typical interplanetary grains are fragile, aggregates of the Brownlee type, and discuss the physical and dynamical processes associated with their entry into the Jovian magnetosphere. Limiting ourselves to the equatorial plane of the planet, we show that grains traversing the outer edge of the co-rotating magnetodisc (r35R _J ) are rapidly charged up to large negative potentials on both the day and the night sides. A parent grain of radiusR _g 20 is electrostatically disrupted when it attains a potential of about –220 V. While the eventual potential achieved by the smallest fragments (R _g 0.1 ) are controlled by the rapid field emission of electrons, those of the larger fragments (R _g 1 ) are set by the plasma and photoemission currents.All the negatively charged fragments are strongly attracted towards the planet by the (radial) corotational electric field and some are stably trapped. We suggest that the sudden enhancement by about 2 orders of magnitude of the interplanetary dust flux measured by Pioneer 10, at about 30R _J from Jupiter result from the combination of these two effects.The different brightness asymmetries between the leading and the trailing sides of the outer and inner Galilean satellites appear to be a natural consequence of the way the trajectories of these charged dust grains intersect these satellite surfaces. Finally, the similarity in the brightness asymmetries between the Jovian and Saturnian satellites, and our belief that they have a similar cause, leads us to the expectation that Saturn's magnetic momentM and spin , are parallel as in the case of Jupiter, with the limit of plasma co-rotation lying between the satellites Rhea and Iapetus.  相似文献   

On the astrometric detection of neighboring planetary systems,II     

George Gatewood  Lee Breakiron  Ronald Goebel  Steven Kipp  Jane Russell  John Stein 《Icarus》1980,41(2):205-231

Extensive testing suggests that astrometric techniques can be employed to detect and study virtually any planetary system that may exist within 40 light years (12.5 parsec) of the Sun. Following the conclusion of Paper I [G. Gatewood, Icarus27 (1976), 1–12], the astrometric group at the Allegheny Observatory began an intensive survey of 20 nearby stars to detect the nonlinear variations in their motion that planetary systems would induce. Several tests conducted to further our understanding of the limitations of this survey indicated that the photographic detector itself is responsible for the majority of the random error. A new photoelectric detector has been designed and a simplified prototype of it successfully tested. The new detector is expected to be able to utilize virtually all of the astrometric information transmitted through the Earth's atmosphere. This is sufficient to determine relative positions to within an accuracy of approximately 1 milliarcsec/hr. Such precisions exceed the design capabilities of the best existing astrometric telescopes, thus a feasibility study has been conducted for the design of an improved instrument. The study concludes that a new ground-based telescope and the new detector combined should be able to study stars as faint as the 17th magnitude with an annual accuracy of a few tenths of a milliarcsecond. However, to obtain the ultimate accuracy possible from current technology, we must place an astrometric system above the Earth's atmosphere. A space-borne instrument utilizing the new detector would in theory have sufficient accuracy to detect any Earth-like planet orbiting any of the several hundred stars nearest the Sun.  相似文献   

Global tectonics of a despun planet     

H. Jay Melosh 《Icarus》1977,31(2):221-243

Mercury, the Moon, and many large satellites of the major planets have been tidally despun from an initially faster rotation. These bodies probably possessed equatorial bulges which relaxed as they lost their spin. An analysis of the stresses induced in an elastic shell by the relaxation of an equatorial bulge indicates that differential stresses may reach a few kilobars and that the tectonic pattern developed depends mainly upon the shell thickness. In every model studied the azimuthal stress σ_?? is larger (more compressive) than the meridional stress σθθ. For a thin elastic shell (thickness less than one-twentieth of the planet's radius) the zone from the equator to 48° latitude is characterized by strike-slip faulting. Poleward of this, normal faults and graben trending east-west are expected. Thicker elastic shells acquire an equatorial belt of thrust faults with east-west throw and rough north-south trends. These tectonic styles may be modified by a small (0.05-0.1%) radial expansion or contraction. Expansion shifts the polar normal faulting province toward the equator, while contraction shifts the equatorial provinces poleward. These patterns are not substantially altered by plastic yielding of the shell, although the equatorial thrust fault province is suppressed by strike-slip faulting until strike-slip faults occur poleward of 64.8° latitude. We conclude that there are many tectonic patterns consistent with despinning and radial contraction or expansion, but they must all be consistent with σ_?? > σθθ. These results also indicate that the polar regions of a despun planet are of particular interest in deciding whether a given lineament system is due to stresses induced by the relaxation of the planet's equatorial bulge.  相似文献   

Coherent amplification and pulsar phenomena     

Lee W. Casperson 《Astrophysics and Space Science》1977,48(2):389-399

A modification of the rotating-star model has been developed to interpret the periodic energy bursts from pulsars. This new configuration involves -directed oscilltion modes in the stellar atmosphere or magnetosphere, and most aspects of the typical pulse characteristics are well accounted for. Gain is provided by resonant interactions with particles trapped in the stellar magnetic field. The most significant feature is the fact that highly directional beaming of the output energy results as a natural consequence of coherence between the radiation fields emerging from various locations about the pulsar; and a localized radiation origin is not required.  相似文献   

The influence of amphibole fractionation on the evolution of calc-alkaline andesite and dacite tephra from the central Aleutians,Alaska   总被引：3，自引：1，他引：2  

Jay D. Romick  Suzanne Mahlburg Kay  Robert W. Kay 《Contributions to Mineralogy and Petrology》1992,112(1):101-118

Petrologic studies of tephra from Kanaga, Adak, and Great Sitkin Islands indicate that amphibole fractionation and magma mixing are important processes controlling the composition of calc-alkaline andesite and dacite magmas in the central Aleutians. Amphibole is ubiquitous in tephra from Kanaga and Adak Islands, whereas it is present only in a basaltic-andesite pumice from Great Sitkin. Dacitic tephra from Great Sitkin do not contain amphibole. Hornblende dacite tephra contain HB+PLAG+OX±OPX±CPX phenocrysts with simple zoning patterns, suggesting that the dacites evolved in isolated magma chambers. Andesitic tephra from Adak contain two pyroxene and hornbelende populations, and reversely zoned plagioclase, indicating a more complex history involving mixing and fractional crystallization. Mass balance calculations suggest that the andesitic tephra may represent the complements of amphibole-bearing cumulate xenoliths, both formed during the evolution of high-Al basalts. The presence of amphibole in andesitic and dacitic tephra implies that Aleutian cale-alkaline magmas evolve in the mid to lower crust under hydrous (>4 wt.% H₂O) and oxidizing (Ni–NiO) conditions. Amphibole-bearing andesites and pyroxene-bearing dacites from Great Sitkin indicates fractionation at several levels within the arc crust. Despite its absence in many calc-alkaline andesite and dacite lavas, open system behavior involving amphibole fractionation can explain the trace element characteristies of lavas found on Adak Island. Neither open nor closed system fractionation involving a pyroxene-bearing assemblage is capable of explaining the trace element concentrations or ratios found in the Adak suite. We envision a scenario where amphibole was initially a liquidus phase in many calc-alkaline magmas, but was later replaced by pyroxenes as the magmas rose to shallow levels within the crust. The mineral assemblage in these evolved lavas reflects shallow level equilibration of the magma, whereas the trace element chemistry provides evidence for a earlier, amphibole-bearing, mineral assemblage.  相似文献   

M computed from strong motion accelerograms recorded in Yugoslavia     

V. Lee  M. Trifunac  M. Herak  M. iv i   D. Herak 《地震工程与结构动力学》1990,19(8):1167-1179

It is shown that the new definition¹ of strong motion local magnitude M leads to stable estimates of magnitudes for earthquakes in Yugoslavia, with epicentral distances R <100 km and for 2.5 < M < 6.5. Tables with magnitudes computed using this new procedure are presented for all earthquakes contributing to the strong motion accelerogram files in EQINFOS for Yugoslavia.² The similarity of our findings with the analogous analyses for California suggests new possibilities for relative calibration between various local magnitude scales, which are used in southeastern Europe, and M_L in California.  相似文献   

Magmatism in the eastern Aleutian Arc: temporal characteristic of igneous activity on Akutan Island   总被引：1，自引：0，他引：1  

Jay D. Romick  Michael R. Perfit  Samuel E. Swanson  Robert D. Shuster 《Contributions to Mineralogy and Petrology》1990,104(6):700-721

Lavas from Akutan Island, located in the eastern Aleutian arc at the transition between continental and oceanic crust, show a gradual change in their petrologic and chemical characteristics over the last 4 million years. The oldest lavas exposed on the island, the Hot Springs Bay Volcanics (HSBV), range from magnesian basalt to dacite (45%–62% SiO₂). The most mafic basalts contain salitic clinopyroxene, Cr- and Al-rich spinel, and pargasitic amphibole suggesting that they were derived from relatively hydrous magmas at greater pressures than lavas from the younger Akutan Volcanics (AKV) and the modern volcano (MOD). AKV lavas also range between basalt and dacite (46%–63% SiO₂), but contain no hydrous phenocrysts and seem to have fractionated within a shallow level magma chamber. Lavas from the modern volcano are andesitic (52%–57% SiO₂) and have a mineral assemblage similar to that of AKV lavas of similar composition. With the exception of clinopyroxene and spinel in the most mafic lavas, the compositions of plagioclase (An_92?45), olivine (Fo_88?51), orthopyroxene (En_69?56), and titanomagnetite (15%–21% TiO₂) phenocrysts found in these lavas are within the range observed in lavas from other Aleutian volcanoes. Variations in the major element chemistry of the older lavas can be reproduced by fractional crystallization of the observed mineral assemblages, however closed system crystal fractionation models are inadequate to explain the trace element variations. During the last 4 million years, La/Yb ratios have decreased (6.5–3.3 for HSBV lavas and 2.9–1.9 for MOD lavas) whereas Ba/La ratios appear to have increased slightly (37–43 for HSBV and AKV, and 41–45 of MOD). The lower La/Yb ratios of MOD lavas correspond with lower total abundances of the REE and slightly higher Sr and Pb isotopic ratios. The increased⁸⁷Sr/⁸⁶Sr ratios and Pb isotopic ratios in the MOD lavas, the less enriched LREE, and the higher Ba/La ratios may result from partial melting of an arc source which has experienced previous melting events but has continued to be contaminated by a component from the subducting slab. It may also indicate a change in the degree of partial melting of the underlying mantle, which corresponds to a different percentage of a slab derived component being incorporated into the overlying mantle.  相似文献   

Book reviews     

R. Grant athay  Jay M. Pasachoff 《Solar physics》1975,43(2):513-513

  相似文献   

Drying effects on sorption capacity of coastal sediment: The importance of architecture and polarity of organic matter     

Zhanfei Liu  Cindy Lee 《Geochimica et cosmochimica acta》2006,70(13):3313-3324

Investigations on how desiccation changes sorption of organic compounds by salt marsh sediments provide insight into the physical and chemical properties of these wide-spread coastal sediments. We measured sorption of compounds with different polarities (lysine, tyrosine, naphthalene and aniline) onto natural sediments and sediments that were dried and rewetted. Sorption of lysine by marsh sediment decreased significantly when the sediment was dried using a freeze-drier, oven, or desiccator, and sorption capacity was not restored when sediments were rewetted. In contrast to lysine, the sorption capacity of more hydrophobic compounds (tyrosine, aniline and naphthalene) increased significantly after salt marsh sediment was dried. These results suggest that drying greatly increased sediment hydrophobicity. Consistently, water drop penetration time, an index of hydrophobicity, was significantly lower for combusted sediments than for those that were simply dried. Sediments treated with EDTA, or boiled in seawater, exhibited a similar or even greater reduction in lysine sorption capacity compared with sediments that were dried. Water retention capacity of salt marsh sediment decreased 50% after sediment was dried. The effects of pH and salinity on lysine sorption in wet and dry sediments suggest that carboxyl groups play a major role in lysine sorption through cation ion exchange, and drying may reduce access to carboxyl groups. We hypothesize that the three-dimensional (3D) structure of organic matter, originating mainly from Spartina alterniflora, is an important factor controlling sorption capacity in salt marsh sediment. The drying process makes sedimentary organic matter change conformation, shrink in volume, and expose hydrophobic groups, thus becoming more hydrophobic. In environments with wet and dry cycles, the distribution of hydrophobic or hydrophilic compounds between solution and particulate phases could thus be influenced by the 3D structure and polarity of organic matter.  相似文献