Hydrodynamical simulations of the decay of high-speed molecular turbulence – II. Divergence from isothermality     

Georgi Pavlovski  Michael D. Smith  Mordecai-Mark Mac Low 《Monthly notices of the Royal Astronomical Society》2006,368(2):943-958

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Potential protostars in cloud cores     

Robert L. Hurt  Mary Barsony  Alwyn Wootten 《Astrophysics and Space Science》1995,224(1-2):489-490

We present H₂CO observations of young protostar candidates in the Serpens Cloud Core. We find evidence for dense molecular gas in the cores of these objects that is warmer than the surrounding dust. The strong emission and gas properties support the premise that many of these sources may be very young protostars.  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   

Natural recolonization of a productive tropical pond: Day to day variations in the photosynthetic parameters     

Robert Arfi  Daniel Guiral  Jean-Pascal Torreton 《Aquatic Sciences - Research Across Boundaries》1991,53(1):39-54

Chlorophyll pigments (CHL), primary productivity (PP) and particulate nitrogen (N_p) in relation to several environmental factors were monitored during planktonic colonization of an aquaculture pond (Layo, Côte d'Ivoire). How interactions between the organisms are established in an initially azoic environment were investigated. From March, 15 (D1) to March, 31 (D16), the system transformation went through three stages. First, a precolonization by heterotrophic microbial community from D1 to D2 (N_p < 1 m maximum at D2: 243 mg m^–2; CHL around 0). Then, a pioneer microalgal community developped from D3 to D7 (maximum CHL on D6: 19 mg m^–2; PP: 1.0 g C m^–2 d^–1) with a significant contribution of picoplankton (CHL and PP < 3 m: 33 and 23% of the total, respectively). Finally, a second microalgal colonization was noticed from D9 to D12 (maximum CHL: 55 mg m^–2, PP: 2.8 g C m^–2 d^–1), largely dominated by nanoplankton (CHL and PP > 3 m: 95 and 99% of the total, respectively). Overall, photosynthetic activity appeared to be closely linked to algal biomass. The study of autotrophic biomass and activity in different size classes in relation to the other parameters allowed us to precise the origin of the biomass fluctuations. The first bloom appeared to be controlled by selective grazing on small algae. The second algal development ended when N requirement represented at least 69% of N supply (in the N — NH₄ form). This control was enhanced by the appearance of rotifers, leading to a more complex equilibrium.  相似文献   

V792 Her=HD 155638: A totally eclipsing RS CVn binary     

Charles H. Nelson  Douglas S. Hall  Francis C. Fekel  Robert E. Fried  Richard E. Lines  Helen C. Lines 《Astrophysics and Space Science》1991,182(1):1-17

Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27^d.07±0^d.07, which is slightly different from the 27^d.5384±0^d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R _h=2.58R ,R _c=12.28R ,M _h=1.40M ,M _c=1.46M ,i=80^o.61 and velocity semi-amplitudesK _c=48.36 km s^–1±0.79 km s^–1, andK _h=50.50 km s^–1±0.33 km s^–1. The apparent magnitudes areV _h=9 ^m .73 andV _c=8 ^m .48. The distance to HD 155638 was estimated to be 310 parsecs.  相似文献   

The role of magnetohydrodynamics in heliospheric space plasma physics research     

Murray Dryer  Zdenka Kopal Smith  Shi Tsan Wu 《Astrophysics and Space Science》1988,144(1-2):407-425

Magnetohydrodynamics (MHD) is a fairly recent extension of the field of fluid mechanics. While much remains to be done, it has successfully been applied to the contemporary field of heliospheric space plasma research to evaluate the macroscopic picture of some vital topics via the use of conducting fluid equations and numerical modeling and simulations. Some representative examples from solar and interplanetary physics are described to demonstrate that the continuum approach to global problems (while keeping in mind the assumptions and limitations therein) can be very successful in providing insight and large scale interpretations of otherwise intractable problems in space physics.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.  相似文献   

Development of a real-time algorithm for detection of solar wind discontinuities     

D. Vandev  K. Danov  P. Mateev  P. Petrov  M. Kartalev  N. Trendafilov  Z. K. Smith  M. Dryer 《Astrophysics and Space Science》1986,120(2):211-221

A study is presented of an algorithm, based on the statistical analysis of interplanetary magnetic field data, for the real-time detection of discontinuities in the solar wind. The analysis is based on the application of a sliding or searching algorithm together with a minimum variance treatment. A demonstration is given for a Pioneer data set from 29 August, 1966. This particular data set was chosen because it has been extensively studied (in terms of the fast forward MHD shock wave) by previous groups who utilized the three-dimensional Rankine-Hugoniot shock equations after identifying the shock on a subjective basis. Our procedure differs in that it is perfectly objective because of its searching technique. For this particular data set we identify the original shock with excellent agreement with the earlier studies of its normal vector, as well as an additional shock and tangential discontinuity, neither of which had been identified previously.  相似文献   

Archean high-Mg monzodiorite–syenite,epidote skarn,and biotite–sericite gold lodes in the Granny Smith–Wallaby district,Australia: U–Pb and Re–Os chronometry of two intrusion-related hydrothermal systems     

Andreas G. Mueller  Gregory C. Hall  Alexander A. Nemchin  Holly J. Stein  Robert A. Creaser  Douglas R. Mason 《Mineralium Deposita》2008,43(3):337-362

The Granny Smith (37 t Au production) and Wallaby deposits (38 t out of a 180 t Au resource) are located northeast of Kalgoorlie, in 2.7 Ga greenstones of the Eastern Goldfields Province, the youngest orogenic belt of the Yilgarn craton, Western Australia. At Granny Smith, a zoned monzodiorite–granodiorite stock, dated by a concordant titanite–zircon U–Pb age of 2,665 ± 3 Ma, cuts across east-dipping thrust faults. The stock is fractured but not displaced and sets a minimum age for large-scale (1 km) thrust faulting (D2), regional folding (D1), and dynamothermal metamorphism in the mining district. The local gold–pyrite mineralization, controlled by fractured fault zones, is younger than 2,665 ± 3 Ma. In augite–hornblende monzodiorite, alteration progressed from a hematite-stained alkali feldspar–quartz–calcite assemblage and quartz–molybdenite–pyrite veins to a late reduced sericite–dolomite–albite assemblage. Gold-related monazite and xenotime define a U–Pb age of 2,660 ± 5 Ma, and molybdenite from veins a Re–Os isochron age of 2,661 ± 6 Ma, indicating that mineralization took place shortly after the emplacement of the main stock, perhaps coincident with the intrusion of late alkali granite dikes. At Wallaby, a NE-trending swarm of porphyry dikes comprising augite monzonite, monzodiorite, and minor kersantite intrudes folded and thrust-faulted molasse. The conglomerate and the dikes are overprinted by barren (<0.01 g/t Au) anhydrite-bearing epidote–actinolite–calcite skarn, forming a 600-m-wide and >1,600-m-long replacement pipe, which is intruded by a younger ring dike of syenite porphyry pervasively altered to muscovite + calcite + pyrite. Skarn and syenite are cut by pink biotite–calcite veins, containing magnetite + pyrite and subeconomic gold–silver mineralization (Au/Ag = 0.2). The veins are associated with red biotite–sericite–calcite–albite alteration in adjacent monzonite dikes. Structural relations and the concordant titanite U–Pb age of the skarn constrain intrusion-related mineralization to 2,662 ± 3 Ma. The main-stage gold–pyrite ore (Au/Ag >10) forms hematite-stained sericite–dolomite–albite lodes in stacked D2 reverse faults, which offset skarn, syenite, and the biotite–calcite veins by up to 25 m. The molybdenite Re–Os age (2,661 ± 10 Ma) of the ore suggests a genetic link to intrusive activity but is in apparent conflict with a monazite–xenotime U–Pb age (2,651 ± 6 Ma), which differs from that of the skarn at the 95% confidence level. The time relationships at both gold deposits are inconsistent with orogenic models invoking a principal role for metamorphic fluids released during the main phase of compression in the fold belt. Instead, mineralization is related in space and time to late-orogenic, magnetite-series, high-Mg monzodiorite–syenite intrusions of mantle origin, characterized by Mg/(Mg + Fe_TOTAL) = 0.31–0.57, high Cr (34–96 ppm), Ni (22–63 ppm), Ba (1,056–2,321 ppm), Sr (1,268–2,457 ppm), Th (15–36 ppm), and rare earth elements (total REE: 343–523 ppm). At Wallaby, shared Ca–K–CO₂ metasomatism and Th-REE enrichment (in allanite) link Au–Ag mineralization in biotite–calcite veins to the formation of the giant epidote skarn, implicating a Th + REE-rich syenite pluton at depth as the source of the oxidized hydrothermal fluid. At Granny Smith, lead isotope data and the Rb–Th–U signature of early hematite-bearing wall-rock alteration point to fluid released by the source pluton of the differentiated alkali granite dikes.  相似文献   

The Mordor Alkaline Igneous Complex,Central Australia: PGE-enriched disseminated sulfide layers in cumulates from a lamprophyric magma     

Stephen J. Barnes  J. A. C. Anderson  T. R. Smith  L. Bagas 《Mineralium Deposita》2008,43(6):641-662

The Mordor Alkaline Igneous Complex (MAIC) is a composite intrusion comprising a body of syenite and a funnel-shaped layered mafic–ultramafic intrusion of lamprophyric parentage, the Mordor Mafic–Ultramafic Intrusion or MMUI. The MMUI is highly unusual among intrusions of lamprophyric or potassic parentage in containing primary magmatic platinum-group element (PGE)-enriched sulfides. The MMUI sequence consists largely of phlogopite-rich pyroxenitic cumulates, with an inward dipping conformable layer of olivine-bearing cumulates divisible into a number of cyclic units. Stratiform-disseminated sulfide accumulations are of two types: disseminated layers at the base of cyclic units, with relatively high PGE tenors; and patchy PGE-poor disseminations within magnetite-bearing upper parts of cyclic units. Sulfide-enriched layers at cycle bases contain anomalous platinum group element contents with grades up to 1.5 g/t Pt+Pd+Au over 1-m intervals, returning to background values of low parts per billion (ppb) on a meter scale. They correspond to reversals in normal fractionation trends and are interpreted as the result of new magma influxes into a continuously replenished magma chamber. Basal layers have decoupled Cu and PGE peaks reflecting increasing PGE tenors up-section, due to increasing R factors during the replenishment episode, or progressive mixing of between resident PGE-poor magma and more PGE-enriched replenishing magma. The presence of PGE enriched sulfides in cumulates from a lamprophyric magma implies that low-degree partial melts do not necessarily leave sulfides and PGEs in the mantle restite during partial melting. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献