Alberta. Border disease virus isolated from twin lambs          下载免费PDF全文

Lees VW  Loewen KG  Deregt D  Knudsen R 《The Canadian veterinary journal. La revue veterinaire canadienne》1991,32(8):501

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Relationship between equivalent salt solution series of different soils     

N. S. JAYAWARDANE  P. S. BLACKWELL 《European Journal of Soil Science》1991,42(1):95-102

Equivalent salt solution series have been previously defined as solutions with combinations of sodium absorption ratio (SAR) and electrolyte concentration (E_c) producing the same extent of clay swelling in a given soil. The present study shows that there is a high (r²>0.96) positive correlation between log E_c and log SAR of equivalent salt solutions series, in the equation: where a₁ and b₁ are constants for each equivalent salt solution series for a given soil. Log a₁ could also be represented as a linear function of b₁ resulting in the equation: where a₂ and b₂ are constants for a given soil. Solving this equation using any given value of b₁ yields the combinations of SAR and E_c which make up each equivalent salt solution series for a given soil. The relationship between log a₁ and b₂ for three soils from western United States, namely Waukena, Pachappa and Grangeville, was similar, with their combined data having a r² value of 0.96. This indicated that a single set of equivalent salt solution series values could be used for these three soils which have different clay contents and clay mineralogy. Prediction of hydraulic conductivity decreases with E_c reduction at given values of SAR in red-brown and alluvial soils from southern Tasmania, using the equivalent salt solution series values for Waukena soil, showed similar patterns to measured values and also to those predicted using the equivalent salt solution values applicable to the respective Tasmanian soils. Thus, available data indicate that the same set of equivalent salt series could be applied to the five soils studied. If further testing shows that a single set of equivalent salt solutions values could be applied to all or large groups of soils, this would facilitate the application of the equivalent salt solution concept to predict salt solution flow in the field.  相似文献   

Tales retold     

Hull DL 《Science (New York, N.Y.)》1991,252(5008):993-994

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Ventures in popularization     

Nye MJ 《Science (New York, N.Y.)》1991,252(5008):980-981

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How the retinoblastoma gene may onhibit cell growth     

M J 《Science (New York, N.Y.)》1991,252(5012):1492

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The Idea of the NOrmal     

Schabas M 《Science (New York, N.Y.)》1991,251(4999):1373

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Explaining the avocado illusion     

Hershenson M 《Science (New York, N.Y.)》1991,251(4997):1005

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Auger electron angular distributions from surfaces: direct comparison with isoenergetic photoelectrons     

Terminello LJ  Barton JJ 《Science (New York, N.Y.)》1991,251(4998):1218-1220

Angular distribution patterns of Auger electrons and of photoelectrons from a Cu (001) surface were measured at the same electron kinetic energy. These measurements reveal that the low kinetic energy angular distributions for Cu Auger electrons and Cu 3p(3/2) photoelectrons differ substantially. This direct comparison between the photoelectron and Auger electron angular distributions demonstrates that, in some circumstances, the Auger process produces a complicated source wave whose nature must be explored before Auger angular distributions can be used for surface structure analysis.  相似文献   

Atomic-resolution electrochemistry with the atomic force microscope: copper deposition on gold     

Manne S  Hansma PK  Massie J  Elings VB  Gewirth AA 《Science (New York, N.Y.)》1991,251(4990):183-186

The atomic force microscope (AFM) was used to image an electrode surface at atomic resolution while the electrode was under potential control in a fluid electrolyte. A new level of subtlety was observed for each step of a complete electrochemical cycle that started with an Au(111) surface onto which bulk Cu was electrodeposited. The Cu was stripped down to an underpotential-deposited monolayer and finally returned to a bare Au(111) surface. The images revealed that the underpotential-deposited monolayer has different structures in different electrolytes. Specifically, for a perchloric acid electrolyte the Cu atoms are in a close-packed lattice with a spacing of 0.29 +/- 0.02 nanometer (nm). For a sulfate electrolyte they are in a more open lattice with a spacing of 0.49 +/- 0.02 nm. As the deposited Cu layer grew thicker, the Cu atoms converged to a (111)-oriented layer with a lattice spacing of 0.26 +/- 0.02 nm for both electrolytes. A terrace pattern was observed during dissolution of bulk Cu. Images were obtained of an atomically resolved Cu monolayer in one region and an atomically resolved Au substrate in another in which a 30 degrees rotation of the Cu monolayer lattice from the Au lattice is clearly visible.  相似文献   

This Week in SCIENCE     

Guyer RL 《Science (New York, N.Y.)》1991,252(5010):1227

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