Rutile-bearing refractory eclogites: missing link between continents and depleted mantle   总被引：9，自引：0，他引：9  

Rudnick RL  Barth M  Horn I  McDonough WF 《Science (New York, N.Y.)》2000,287(5451):278-281

A mass imbalance exists in Earth for Nb, Ta, and possibly Ti: continental crust and depleted mantle both have subchondritic Nb/Ta, Nb/La, and Ti/Zr, which requires the existence of an additional reservoir with superchondritic ratios, such as refractory eclogite produced by slab melting. Trace element compositions of minerals in xenolithic eclogites derived from cratonic lithospheric mantle show that rutile dominates the budget of Nb and Ta in the eclogites and imparts a superchondritic Nb/Ta, Nb/La, and Ti/Zr to the whole rocks. About 1 to 6 percent by weight of eclogite is required to solve the mass imbalance in the silicate Earth, and this reservoir must have an Nb concentration >/= 2 parts per million, Nb/La >/= 1.2, and Nb/Ta between 19 and 37-values that overlap those of the xenolithic eclogites. As the mass of eclogite in the continental lithosphere is significantly lower than this, much of this material may reside in the lower mantle, perhaps as deep as the core-mantle boundary.  相似文献   

Binary Pulsar PSR 1913 + 16: Model for Its Origin     

Van Horn HM  Sofia S  Savedoff MP  Duthie JG  Berg RA 《Science (New York, N.Y.)》1975,188(4191):930-933

The existing observational data for the binary pulsar PSR 1913 + 16 are sufficient to give a rather well-defined model for the system. On the basis of evolutionary considerations, the pulsar must be a neutron star near the upper mass limit of 1.2 solar masses (M.). The orbital inclination is probably high, i>/= 700, and the mass of the unseen companion probably lies close to the upper limit of the range 0.25 M. to 1.0 M.. The secondary cannot be a main sequence star and is probably a degenerate helium dwarf. At the 5.6-kiloparsec distance indicated by the dispersion measure, the magnetic dipole model gives an age of approximately 4 x 104 years, a rate of change of the pulsar period of P approximately 2 nanoseconds per day, and a surface magnetic field strength approximately (1/3) that of the Crab pulsar. The pulsar is fainter than an apparent magnitude V approximately + 26.5 and is at least approximately 80 times fainter than the Crab pulsar in the x-ray band. The companion star should be fainter than V approximately + 30, and a radio supernova remnant may be detectable near the position of the pulsar at a flux level of 相似文献   

Response     

Morris CE  Horn R 《Science (New York, N.Y.)》1991,253(5021):801

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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   

Auswirkung unterschiedlicher Bodenbearbeitung auf die mechanische Belastbarkeit von Ackerböden     

R. Horn 《植物养料与土壤学杂志》1986,149(1):9-18

Effect of different tillage systems on the mechanical compressibility of arable soils The influence of different tillage systems (Zero-tillage, minimum tillage with rotary tiller and conventional tillage with moldboard plow) on the mechanical compressibility of two soils, a Regosol from loess-colluvium, and a Vertisol from mesocoic clay has been investigated as well as the causes and consequences for penetration resistance and air permeability. In addition the bulk density and the pore size distribution of aggregates have been investigated with regard to a possible explanation for the often described difference in stability in untilled or minimum tilled soils when compared to tilled ones. The results clearly demonstrate the higher mechanical stability of the untilled or minimum tilled soils as compared to tilled soils, which may result in better growing condition for plants. The higher stability is the result of a more vertical oriented pore geometry and stress distribution and can be explained by measured differences in the bulk density and pore size distribution within the aggregates too.  相似文献   

Fiedler,H.J.: Bodennutzung und Bodenschutz. VEB Gustav Fischer Verlag,Jena, 1990; 268 S., 34 Abb., 48 Tab., 10 Übersichten,DM 70,-. ISBN 3-334-00302-7.     

R. Horn 《植物养料与土壤学杂志》1991,154(3):237-237

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Comment on “Effects of agricultural machinery with high-axle load on soil properties of normally managed fields” (Authors L. Schäfer-Landefeld, R. Brandhuber, S. Fenner, H.-J. Koch, N. Stockfisch. Soil Till. Res. 75 (2004) 75–86)     

Wilfried Ehlers  Michael J. Goss  Rainer Horn 《Soil & Tillage Research》2005,80(1-2):251-254

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Bestimmung von Mikronährstoffen und Schwermetallen in Böden mit dem Verfahren der Elektro‐Ultrafiltration (EUF) durch Zugabe von DTPA     

Dietmar Horn 《植物养料与土壤学杂志》2006,169(1):83-86

With the electro–ultrafiltration (EUF) technique, the plant availability of several plant nutrients in soils can be characterized. The basic principle of EUF is that an electric field is induced using platinum electrodes. Ions in the soil suspension move either to the cathode or to the anode and are filtrated through ultra‐membrane filters. In the standard EUF procedure, two extractions steps are used: 30 min at 20°C and 5 min at 80°C. However, the determination of micronutrients and heavy metals with the standard EUF procedure is not possible, because the solubility of these elements in water is low and most of the watersoluble elements are precipitated when passing the platinum electrodes. The addition of DTPA, a well known complexing agent, during a third EUF fraction (5 min at 80°C) enables extraction of micronutrients and heavy metals. Highest concentrations in the 33 soils of the study were found for iron, followed by zinc, manganese, lead, copper, and nickel. Lower concentrations were obtained for cobalt, chromium, cadmium, and molybdenum. For two soils, the EUF/DTPA procedure was compared to CaCl₂/DTPA and EDTA soil extraction methods, showing that higher or comparable amounts were found with CaCl₂/DTPA and much higher amounts with the EDTA method. These results reveal that the EUF/DTPA technique in principle can be used for the determination of plant‐available micronutrients and heavy metals. However, in a next step the relationship between EUF/DTPA‐extractable elements and their availability for plants needs to be quantified.  相似文献   

Statistical Modeling of the Partitioning of Nonylphenol in Soil     

Sebastian Krahe  Rolf-Alexander Düring  Johan A. Huisman  Andreas L. Horn  Stefan Gäth 《Water, air, and soil pollution》2006,172(1-4):221-237

Partition coefficients K _P of nonylphenol (NP) in soil were determined for 193 soil samples which differed widely in content of soil organic carbon (SOC), hydrogen activity, clay content, and in the content of dissolved organic carbon (DOC). By means of multiple linear regression analysis (MLR), pedotransfer functions were derived to predict partition coefficients from soil data. SOC and pH affected the sorption, though the latter was in a range significantly below the pK_a of NP. Quality of soil organic matter presumably plays an important but yet not quantified role in sorption of NP. For soil samples with SOC values less than 3 g kg^?1, model prediction became uncertain with this linear approach. We suggest that using only SOC and pH data results in good prediction of NP sorption in soils with SOC higher than 3 g kg^?1. Considering the varying validity of the linear model for different ranges of the most sensitive parameter SOC, a more flexible, nonlinear approach was tested. The application of an artificial neuronal network (ANN) to predict sorption of NP in soils showed a sigmoidal relation between K _P and SOC. The nonlinear ANN approach provided good results compared to the MLR approach and represents an alternative tool for prediction of NP partitioning coefficients.  相似文献   

Eine Methode zur permanenten pH-Wert-Registrierung mittels keramischer Saugkerzen im Mineralbodeninput eines sauren Waldbodens     

Thomas Türk  Rainer Horn 《植物养料与土壤学杂志》1991,154(2):131-136

A new method for permanent registration of pH value in mineral soil input of an acid forest soil The organic top layers of acid forest soils in low mountain ranges of Germany which receive acid precipitation are of special ecological interest to the observation for their saisonal chemical behaviour. Root systems of young spruce forests tend to accumulate in these layers because of Al-toxicity in mineral soil. Conventional procedures for a weekly sampling of soil solution do not account for short term events. Thus, a measuring device for permanent pH-logging of soil solution in mineral soil input was developed. A microprocessor controls the vacuum in the ceramic cups containing pH-glass electrodes in order to maintain steady water flux into the cups. The accuracy of the measured pH was tested with a theoretical equilibrium modell concerning CO₂-degassing and with a laboratory experiment. Below pH 4.7 no influence of CO₂-losses on the pH inside the cups occurs. Permanent measurements in mineral soil of a spodosol in The Fichtelgebirge showed fluctuations of higher pH values immediately after precipitation and decreasing values later on. In late spring this behaviour is not yet pronounced.  相似文献