Structure and dynamics of the Bok globule B335     

Margaret A. Frerking  William D. Langer  Robert W. Wilson 《Icarus》1985,61(1):22-26

CO maps of the Bok globule B335 are presented and used to derive its density profile, mass distribution, and rotational velocity structure. It is found that the cloud is in nearly hydrostatic equilibrium with a density profile that varies roughly as r^?1 in the core and r^?3 in the envelope. The observed rotation is unimportant in the force balance at the present stage of evolution.  相似文献   

A moment method for radiative transfer in an anisotropically-scattering slab medium with space-dependent albedoω(x)     

S. J. Wilson  F. S. Wan 《Astrophysics and Space Science》1987,137(1):107-113

The moment method is used to solve the radiative transfer problem in an anisotropic scattering plane medium with arbitrary space-dependent albedo(x). The results are compared with those obtained recently by Cengel and Özisik.  相似文献   

On ‘bimodality of the solar cycle’ and the duration of cycle 21     

Robert M. Wilson 《Solar physics》1987,108(1):195-200

The period-growth dichotomy of the solar cycle predicts that cycle 21, the present solar cycle, will be of long duration (>133 mo), ending after July 1987. Bimodality of the solar cycle (i.e., cycles being distributed into two groups according to cycle length, based on a comparison to the mean cycle period) is clearly seen in a scatter diagram of descent versus ascent durations. Based on the well-observed cycles 8–20, a linear fit for long-period cycles (being a relatively strong inverse relationship that is significant at the 5% level and having a coefficient of determination r ² 0.66) suggests that cycle 21, having an ascent of 42 mo, will have a descent near 99 mo; thus, cycle duration of about 141 mo is expected. Like cycle 11, cycle 21 occurs on the downward envelope of the sunspot number curve, yet is associated with an upward first difference in amplitude. A comparison of individual cycle, smoothed sunspot number curves for cycles 21 and 11 reveals striking similarity, which suggests that if, indeed, cycle 21 is a long-period cycle, then it too may have an extended tail of sustained, low, smoothed sunspot number, with cycle 22 minimum occurring either in late 1987 or early 1988.  相似文献   

On the proposed associations of solar neutrino flux with solar particles,cosmic rays,and the solar activity cycle     

Robert M. Wilson 《Solar physics》1987,112(1):1-15

It has been proposed that the observed solar neutrino flux exhibits important correlations with solar particles, galactic cosmic rays, and the sunspot cycle, with the latter correlation being opposite in phase and lagging behind the sunspot cycle by about one year. Re-examination of the data-available interval 1971–1981, employing various tests of statistical significance, however, suggests that such a claim is, at present, unwarrantable. For example, on the associations of solar neutrino flux and cosmic-ray flux with the Ap geomagnetic index, neither were found to be statistically significant (at the 95% level of confidence), regardless of the choice of lag (-1, 0, or +1 yr). Presuming linear fits, all correlations with Ap had coefficients of determination (r ², where r is the linear correlation coefficient) less than 16%, meaning that 16% of the variation in the selected test parameters could be explained by the variation in Ap. Similarly, on the associations of solar neutrino flux and cosmic ray flux with sunspot number, only the latter association proved to be of statistical importance. Using the best linear fits, the correlation between yearly averages of solar neutrino flux and sunspot number had r ² 19%, the correlation between weighted moving averages (of order 5) of solar neutrino flux and sunspot number had r ² 45%, and the correlation between cosmic-ray flux and sunspot number had r ² 76%, all correlations being inverse associations. Solar neutrino flux was found not to correlate strongly with cosmic-ray flux, and the Ap geomagnetic index was found not to correlate strongly with sunspot number.  相似文献   

Accuracy of close binary mass determinations from parallaxes     

W. Van Hamme  R. E. Wilson 《Astrophysics and Space Science》1985,110(1):169-175

Absolute masses for W Ursae Majoris and Algol-type close binaries can be determined from their parallax, if observed, and the relative sizes of the stars and their mass ratio, obtained from a light curve solution. An error propagation study compares the typical order of magnitude of the various terms involved, and shows how accurate parallaxes have to be in order to make the procedure work, i.e., making the parallax term not larger than the combined non-parallax terms, and producing reasonably low mass errors. Some comments are made on the possibilities with respect to the HIPPARCOS program.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).  相似文献   

U–Pb SHRIMP zircon geochronology and T–t–d history of the Kampa Dome, southern Tibet     

M.C. Quigley  Y. Liangjun  C. Gregory  A. Corvino  M. Sandiford  C.J.L. Wilson  L. Xiaohan 《Tectonophysics》2008,446(1-4):97-113

Structural, petrographic and geochronologic studies of the Kampa Dome provide insights into the tectonothermal evolution of orogenic crust exposed in the North Himalayan gneiss domes of southern Tibet. U–Pb ion microprobe dating of zircons from granite gneiss exposed at the deepest levels within the dome yields concordia ²⁰⁶Pb/²³⁸U age populations of 506 ± 3 Ma and 527 ± 6 Ma, with no evidence of new zircon growth during Himalayan orogenesis. However, the granite contains penetrative deformation fabrics that are also preserved in the overlying Paleozoic strata, implying that the Kampa granite is a Cambrian pluton that was strongly deformed and metamorphosed during Himalayan orogenesis. Zircons from deformed leucogranite sills that cross-cut Paleozoic metasedimentary rocks yield concordant Cambrian ages from oscillatory zoned cores and discordant ages ranging from ca. 491–32 Ma in metamict grains. Since these leucogranites clearly post-date the metasedimentary rocks they intrude, the zircons are interpreted as xenocrysts that are probably derived from the Kampa granite. The Kampa Dome formed via a series of progressive orogenic events including regional ~ N–S contraction and related crustal thickening (D₁), predominately top-to-N ductile shearing and crustal extension (D₂), top-to-N brittle–ductile faulting and related folding on the north limb of the dome, localized top-to-S faulting on the southern limb of the dome, and crustal doming (D₃), and continued N–S contraction, E–W extension and doming (D₄). Structural and geochronologic variability amongst adjacent North Himalayan gneiss domes may reflect changes in the magnitude of crustal exhumation along the North Himalayan antiform, possibly relating to differences in the mid-crustal geometry of the exhuming fault systems.  相似文献   

Thermal evolution and physics of melt extraction on the ureilite parent body     

Lionel Wilson  Cyrena Anne Goodrich 《Geochimica et cosmochimica acta》2008,72(24):6154-6176

We develop a physical model of the thermal history of the ureilite parent body (UPB) that numerically tracks the history of its heating, hydration, dehydration, partial melting and smelting as a function of its formation time and the initial values of its composition, formation temperature and water ice content. Petrologic and chemical data from the main group (non-polymict) ureilite meteorites, which sample the interior of the UPB between depths corresponding to pressures in the range 3-10 MPa, are used to constrain the model. We find that to achieve the ∼30% melting inferred for ureilites from all sampled depths, the UPB must have had a radius between ∼80 and ∼130 km and must have accreted about 0.55 Ma after CAI formation. Melting began in the body at ∼1 Ma after CAI, and the time at which 30% melting was reached varied with depth in the asteroid but was always between ∼4.5 and ∼5.8 Ma after CAI. The total rate at which melt was produced in the UPB varied from more than 100 m³ s⁻¹ in the very early stages of melting at ∼1 Ma after CAI to ∼5 m³ s⁻¹ between 2 and 3 Ma after CAI, decreasing to extremely small values as the end of melting was approached beyond ∼5 Ma. Although the initial period of high melt production occupied only a short time around 1 Ma after CAI, it corresponded to ∼half (16%) of total silicate melting, and all strictly basaltic (i.e. plagioclase-saturated) melts must have been produced during this period.A very efficient melt transport network, consisting of a hierarchy of veins and larger pathways (dikes), developed quickly at the start of melting, ensuring rapid (timescales of months) transport of any single parcel of melt to shallow levels, thus ensuring that chemical interaction between melts and the rocks through which they subsequently passed was negligible. Volatile (mainly carbon monoxide) production due to smelting began at the start of silicate melting in the shallowest parts of the UPB and at later times at greater depths. Except at the very start and very end of melting, the volatile content of the melts produced was always high - generally between 15 and 35 mass % - and most of the melt produced was erupted at the surface of the UPB with speeds well in excess of the escape velocity and was lost into space. However, we show that 30% melting at the 3 MPa pressure level was only possible if ∼15% of the total melt produced in the asteroid was retained as a small number (∼5) of very extensive, sill-like intrusions centered at a depth of ∼7 km below the surface, near the base of the ∼8 km thick outer crust of the asteroid that was maintained at temperatures below the basalt solidus by conductive heat loss to the surface. The horizontal extents of these sills occupied about 75% of the surface area of the UPB, and the sills acted as buffers between the steady supply of melt from depth and the intermittent explosive eruption of the melt into space. We infer that samples from these intrusions are preserved as the rare feldspathic (loosely basaltic) clasts in polymict ureilites, and show that the cooling histories of the sills are consistent with these clasts reaching isotopic closure at ∼5 Ma after CAI, as given by ²⁶Al-²⁶Mg, ⁵³Mn-⁵³Cr and Pb-Pb age dates.  相似文献   

Defect properties of albite     

Stephan Lowitzer  Dan J. Wilson  Björn Winkler  Victor Milman  Julian D. Gale 《Physics and Chemistry of Minerals》2008,35(3):129-135

Knowledge of the defect properties of Lunar and Mercurian minerals has recently become important, with the advent of models which attempt to explain the formation of the thin exosphere of these celestial bodies. Here, we have calculated the formation energies of sodium and oxygen vacancies in the mineral albite (NaAlSi₃O₈), as well as the Schottky defect energy for the removal of a Na₂O unit. We have employed both the supercell and Mott–Littleton approaches, using Kohn–Sham density functional theory and classical interatomic potential methods. As well as reporting the defect energies and structures, we comment upon the relative merits of the methods used.  相似文献   

Walleye pollock respond to trawling vessels     

De Robertis  Alex; Wilson  Christopher D. 《ICES Journal of Marine Science》2006,63(3):514-522

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An experimental analysis of spatial competition in a dense infaunal community: The importance of relative effects     

W. Herbert Wilson  Jr 《Estuarine, Coastal and Shelf Science》1984,18(6)

A densely populated soft-sediment community was experimentally analysed for interspecific competition for space in laboratory experiments. No interspecific competitive interactions leading to a decrease in survivorship could be documented over a five-week period. The four most abundant species all coexisted in laboratory microcosms. The two tube-buiding species, the tanaid Leptochelia dubia and the polychaete Rhynchospio arenincola, could not exclude the mobile bivalve Transennella tantilla or the burrowing amphipod Paraphoxus spinosus. None of the species increases its emigration frequency when other species are present. Paraphoxus is found to be a browsing predator on Phynchospio but inflicts no detectable mortality. The coexistence of these species is permitted by virtue of the fact that none of the species can alter the soft-sediment habitat sufficiently to make the habitat unsuitable for the other species.  相似文献