ATTENUATION OF CELL STIMULATING BACTERIA BY SPECIFIC AMINO ACIDS     

VAN Lanen JM  Baldwin IL  Riker AJ 《Science (New York, N.Y.)》1940,92(2396):512-513

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Myths and realities of space flight     

VAN Allen JA 《Science (New York, N.Y.)》1986,232(4754):1075-1076

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The Aerobee Sounding Rocket--A New Vehicle for Research in the Upper Atmosphere     

VAN Allen JA  Fraser LW  Floyd JF 《Science (New York, N.Y.)》1948,108(2818):746-747

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Observations of energetic ions from comet giacobini-zinner     

Hynds RJ  Cowley SW  Sanderson TR  Wenzel KP  VAN Rooijen JJ 《Science (New York, N.Y.)》1986,232(4748):361-365

During the encounter with comet Giacobini-Zinner, the energetic particle anisotropy spectrometer on the International Cometary Explorer spacecraft observed large fluxes of energetic ions, believed to result principally from ionization of the cometary atmosphere followed by pickup and acceleration by the ambient flow of the solar wind. These heavy cometary ions were observed from approximately 1 day before closest approach to about 2(1/2) days afterward. Three regimes of differing ion characteristics have been identified. An outer region with a scale of approximately 10(6) kilometers contains variable fluxes of antisolar-streaming pick-up ions in the undisturbed solar wind. In the middle region, of approximately 10(5) kilometers, fluxes have less large-scale variability and broader angular and energy distributions. This region is separated from the outer zone by a sharp transition. The inner region has a scale of approximately 10(4) kilometers and is characterized by reduced fluxes and complex angular distributions.  相似文献   

JAMES MCGIFFERT 1868-1943     

VAN Klooster HS 《Science (New York, N.Y.)》1943,98(2544):294-295

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Thin surfaces     

VAN Olphen H 《Science (New York, N.Y.)》1976,191(4224):281-282

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Dense astrophysical plasmas     

VAN Horn HM 《Science (New York, N.Y.)》1991,252(5004):384-389

Degenerate bodies composed primarily of dense hydrogen and helium plasmas range from giant planets to the so far hypothetical brown dwarfs. More massive objects begin their lives as nondegenerate stars and may end as white dwarfs, composed primarily of carbon and oxygen, or as neutron stars, with solid crusts of iron or heavier elements and cores of neutron matter. The physical properties of dense plasmas that are necessary to construct theoretical models of such degenerate stars include the equation of state, transport properties, and nuclear reaction rates.  相似文献   

Holocene vegetation in chaco canyon, new Mexico     

Betancourt JL  VAN Devender TR 《Science (New York, N.Y.)》1981,214(4521):656-658

Well-preserved plant remains in packrat middens chronicle vegetation change in Chaco Canyon over the past 11,000 years. Early Holocene evidence of communities dominated by Douglas fir, Rocky Mountain juniper, and limber pine in the San Juan Basin calls for revision of traditional constructs based on fossil pollen. Middle and late Holocene vegetation in the canyon was pinyon-juniper woodland up until Anasazi occupation between 1000 and 800 years ago. Instead of climate, Anasazi fuel needs may explain the drastic reduction of pinyon and juniper after 1230 years ago. The lack of pinyon-juniper recovery over the past millennium has implications for contemporary forest and range ecology.  相似文献   

VARIATION IN COMPOSITION OF STREAM BED SEDIMENTS IN A SMALL WATERCOURSE     

VAN DER PERK  MARCEL  VAN GAANS  PAULINE F. M. 《Water, air, and soil pollution》1997,96(1-4):107-131

We investigated the regional and temporal variation of the composition stream of bed sediments of the Langbroekerwetering, The Netherlands, in particular the effect of effluent discharges of sewage treatment plants on the sediment composition. Before we could map the chemistry of the bed sediments we had to examine two aspects which might obscure regional variation, namely variation due to differences in clay and organic matter content and short range variation. To remove the effect of clay and organic matter, the concentrations in the bed sediment were normalized to a standard sediment with 7% clay and 5% organic matter. By means of a nested sampling we ascertained that the sediments were highly variable within short distances. By increasing the effective support size by collecting composite samples, the regional differences can be mapped. The number of subsamples needed for a composite sample was established at 25. From the mapping of the study area it appears that the two existing effluent discharges affect the sediment composition locally. In particular, concentrations of N, P, K, Na, Zn, and Cu are raised due to the discharge of effluent. Inlet of water from the River Rhine and the occurence of flood waves are the main sources of temporal variation in the bed sediment composition in the Langbroekerwetering.  相似文献   

Field-based partition coefficients for trace elements in soil solutions   总被引：4，自引：0，他引：4  

D.C. GOODDY  P. SHAND  D.G. KINNIBURGH  W.H. VAN  RIEMSDIJK 《European Journal of Soil Science》1995,46(2):265-285

A total of 48 elements was detected in the soil solutions centrifuged from two acid sandy (humus-iron podzol) profiles from southern England. Concentrations ranged from mm for the major ions to mm for trace metals such as U and the rare earth elements. Field-based solid/solution partition coefficients, K_d, were determined by calculating the ratio of the amount of an element extracted by 0.43 m HNO₃ or a neutral salt (0.01 m CaCl₂ or 0.1 m Ba(NO₃)₂) to the concentration in the soil solution. These partition coefficients did not show the expected trend in selectivity. For example, Cd consistently had one of the highest K_d values, higher even than Cu. This was thought to be due in part to the nature of the K_d which reflects a balance between binding to the soil solids and to the dissolved organic carbon (DOC), which is present at relatively high concentrations (1–20 mm ) in the soil solutions. Because of the underlying functional similarity between metal binding by the solid and dissolved organic matter, the partition coefficient (and hence element mobility) will be relatively insensitive to changes in pH and metal-ion activity in the soil solution.  相似文献