Observational studies of star formation: A preliminary report     

Martin Cohen  Leonard V. Kuhi 《Earth, Moon, and Planets》1978,19(2):203-205

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An equation of state at subnuclear densities     

William D. Langer  Leonard C. Rosen  Jeffrey M. Cohen  A. G. W. Cameron 《Astrophysics and Space Science》1969,5(3):259-271

An equation of state for cold matter above white dwarf densities is evaluated. The gas is considered to be a mixture of degenerate neutrons, protons and electrons combined with nuclei of one type (that is only oneA andZ value). We derive the equilibrium equations for the mixture and calculate the number densities as well as theA andZ of the nucleus. Finally we calculate an equation of state, which smoothly goes over to that of a neutron, proton electron gas mixture at a density of 5×10¹³ g/cm³.  相似文献   

A New Datum for use in the Body Wave Travel Time Inverse Problem     

Leonard E. Johnson  Freeman Gilbert 《Geophysical Journal International》1972,30(4):373-380

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Neutron star models based on an improved equation of state     

Jeffrey M. Cohen  William D. Langer  Leonard C. Rosen  A. G. W. Cameron 《Astrophysics and Space Science》1970,6(2):228-239

Using an equation of state for cold degenerate matter which takes nuclear forces and nuclear clustering into account, neutron star models are constructed. Stable models were obtained in the mass range above 0.065M and density range 10^14.08 to 10^15.4 gm/cm³. All of these models were found to be bound. The outer crystalline layer of the star was found to have a thickness of 200 m or more depending on the mass of the model.  相似文献   

Large velocity discontinuities in the solar wind     

Leonard F. Burlaga 《Solar physics》1969,7(1):72-86

In the course of 3000 hours observation of the interplanetary plasma, the plasma and magnetic-field experiments on Explorer 34 have detected 11 discontinuous solar-wind speed changes, not associated with shocks, of more than 60 km/sec in less than 3 min. These events, called uD's, may show a velocity change of either sign, but the plasma density and temperature are not found to change appreciably across them. Each speed discontinuity occurs simultaneously with a directional discontinuity in the magnetic field. High-resolution magnetic-field data show that sometimes the directional changes occur as rotational fans, and at other times they are erratic or occur within the time resolution of the magnetic-field experiment, 2.6 sec. The flow direction of the solar wind changed at 2 of the 11 uD's. The quiet nature of the field and plasma on each side of these events gives the impression that they are stable. The existence of these uD's is shown to be consistent with the theory of the Helmholtz instability. In particular, the additional observation that the magnetic-field direction change, , at a uD tends to be near 90° is consistent with the theory, for uD's with small may become unstable as they move from the sun.  相似文献   

The soft-bottom macrobenthos of North Carolina estuaries     

Jeffrey?L.?HylandEmail author  W.?Leonard?Balthis  Martin?Posey  Courtney?T.?Hackney  Troy?Alphin 《Estuaries and Coasts》2004,27(3):501-514

The structure of macro infaunal (>0.5 mm sieve size) assemblages was examined in samples of unconsolidated substrates collected during the summers of 1994–1997 at 208 stations throughout North Carolina estuaries. Numerical classification (cluster analysis) of stations resulted in 14 distinct site groups that reflected discernible habitatrelated patterns in species distributions. Multiple discriminant analysis, performed on synoptic abiotic variables (depth, salinity, dissolved oxygen, pH, percent silt-clay), showed that the separation of site groups was related primarily to salinity. Percent silt-clay had a secondary influence on the separation of sites within similar salinity zones. Species diversity among site groups generally decreased with decreasing salinity and increasing mud content of sediment. Nodal analysis showed a wide range in constancy and fidelity of species assemblages within site groups. Some assemblages dominated by euryhaline species had no particular affinity with any one site group. The strongest affinities, as evidenced by high values of both constancy and fidelity, were displayed by an assemblage of oligochaetes, insect larvae, gammaridean amphipods, and the clamCorbicula fluminea in tidal freshwater muds; and an assemblage of haustoriid amphipods, the bivalveDonax variabilis, the polychaeteParaonis fulgens, and unidentified echinoids at high-salinity sites in outer Pamlico Sound near ocean inlets. A series of stations with impaired benthic assemblages in polluted habitats emerged from the cluster analysis and was distinguishable from other site groups that reflected a greater influence of natural controlling factors (such as salinity and sediment type) on species distributions. These results suggest that the interaction of both anthropogenic and natural environmental controlling factors is important in defining the structure of these infaunal assemblages.  相似文献   

Replacing coal with wood: sustainable, eco-neutral, conservation harvest of natural tree-fall in old-growth forests     

Leonard Ornstein 《Climatic change》2009,95(3-4):439-447

Kleidon (2009) concludes that warm climates impose important constraints on the evolution of large brains relative to body size, confirming our previous hypothesis (Schwartzman and Middendorf 2000). Here we update the case for our hypothesis and present a first approximation estimate of the cooling required for hominin brain size increase using a simple model of heat loss. We conclude that Pleistocene glacial episodes were likely sufficient to serve as prime releasers for emergence of Homo habilis and Homo erectus. In addition, we propose that atmospheric oxygen levels may been an analogous constraint on insect encephalization.  相似文献   

A feather hydrogen isoscape for Mexico     

Keith A. Hobson  Steven L. Van Wilgenburg  Keith Larson  Leonard I. Wassenaar 《Journal of Geochemical Exploration》2009

Developing useful biological isoscapes for areas of the world is a priority. This is the case for Mexico that hosts a large percentage of North America's Neotropical migrant birds. Here we investigated the use of House Sparrow (Passer domesticus) feathers to create a spatially explicit feather deuterium isoscape for that country using samples (n = 461) that were collected across Mexico. Considerable and useful spatial hydrogen isotopic structure was observed, suggesting that isotopes may be a potential forensic tool for evaluating origins of Mexican derived fauna and flora. The most positive feather δD values occurred in the northeast and most negative in the south-central part of the country, roughly matching δD patterns observed in groundwater. A weak negative isotopic relationship was found with altitude in both the Pacific and Atlantic drainage systems. The most parsimonious model describing isotopic spatial variation in feathers between 300 and 3000 m a.s.l. included groundwater δD (δD_gw; precipitation proxy), sex, amount of precipitation, and the coefficient of variation in amount of precipitation. Overall, δD_gw was a poor predictor of sparrow δD_f values for all of Mexico. However, this relationship was considerably strengthened when we considered sex separately, removed the Baja peninsula from our sample, and considered the Atlantic and Pacific drainage basins separately. The strongest relationship between δD_gw and δD_f was found for female sparrows in the Atlantic drainage basin (r² = 0.464). We recommend that researchers interested in inferring origins of migratory birds and other animals in Mexico create species specific isotopic basemaps that may be guided by the isotopic patterns we have observed for House Sparrows and groundwater.  相似文献   

Intensity and Magnetic Field Distribution of Sunspots     

Trevor Leonard  Debi Prasad Choudhary 《Solar physics》2008,252(1):33-41

We study the relationship between the brightness (I) and magnetic field (B) distributions of sunspots using 272 samples observed at the San Fernando Observatory and the National Solar Observatory, Kitt Peak, whose characteristics varied widely. We find that the I – B relationship has a quadratic form for the spots with magnetic field less than about 2000 G. The slope of the linear part of the I – B curve varies by about a factor of three for different types of spots. In general the slope increases as the spot approaches disk center. The I – B slope does not have a clear dependency on the spot size but the lower limit appears to increase as a function of the ratio of umbra and penumbra area. The I – B slope changes as a function of age of the sunspots. We discuss various sunspot models using these results.  相似文献   

Orbital Evolution of Příbram and Neuschwanstein     

Leonard Kornoš  Juraj Tóth  Peter Vereš 《Earth, Moon, and Planets》2008,102(1-4):59-65

The orbital evolution of the two meteorites Příbram and Neuschwanstein on almost identical orbits and also several thousand clones were studied in the framework of the N-body problem for 5,000 years into the past. The meteorites moved on very similar orbits during the whole investigated interval. We have also searched for photographic meteors and asteroids moving on similar orbits. There were five meteors found in the IAU MDC database and six NEAs with currently similar orbits to Příbram and Neuschwanstein. However, only one meteor 161E1 and one asteroid 2002 QG46 had a similar orbital evolution over the last 2,000 years.  相似文献