On self–killing and self–creating dynamos     

H. Fuchs  K.-H. Rdler  M. Rheinhard 《Astronomische Nachrichten》1999,320(3):129-133

Numerical studies with a spherical dynamo model have shown two remarkable phenomena. The model consists of a spherical body of an electrically conducting incompressible uid surrounded by free space. In addition to a rotation of the body an inner motion due to a given forcing is considered which satisfies a no–slip condition at the boundary. The full interaction of magnetic field and motion is taken into account. Starting from a fluid motion capable of dynamo action and a very weak magnetic field it was observed that the growing magnetic field destroys the dynamo property of the motion and then decays, and that the system ends up in a state with another motion incapable of dynamo action and zero magnetic field. In another case with a motion unable to prevent small magnetic fields from decay it proved to be possible that stronger magnetic fields deform it so that a dynamo starts to work which enables the system to approach a steady state with a finite magnetic field.  相似文献   

The adoption of best management practices to reduce agricultural water contamination   总被引：2，自引：0，他引：2  

T.J. Centner  J.E. Houston  A.G. Keeler  C. Fuchs   《Limnologica》1999,29(3):366

Nonpoint source water pollution generated by agricultural production is considered a major environmental issue in the United States and Europe. One strategy in the United States has been to adopt various measures, called best management practices (BMPs), to reduce water pollution. Our research addresses legal institutions and the applied use of BMPs, and discusses compensatory payments to reduce nitrogen fertilization levels. Models employed in Georgia and Baden-Wuerttemberg evaluate institutional constraints of payments to reduce nitrogen usage, penalties for excessive leaching, and financial incentives for meeting minimum mineralized nitrogen levels. By modeling net returns, preferred economic strategies for producers are identified. Results show that while BMPs can reduce agricultural nonpoint contamination, pollution abatement may be costly to producers. Thus, reduced pollution probably will require some type of government intervention.  相似文献   

Basin modeling meets rift analysis – A numerical modeling study from the Jeanne d'Arc basin,offshore Newfoundland,Canada     

Friedemann Baur  Ralf Littke  Hans Wielens  Carolyn Lampe  Thomas Fuchs 《Marine and Petroleum Geology》2010

The Jeanne d'Arc basin, on the Grand Banks offshore Newfoundland, is a confined, failed-rift basin. Its initial development and burial history were controlled by crustal stretching and thinning. This study provides a detailed analysis of the heat flow-, tectonic subsidence-, stretching factor-, maturation- and temperature history, based on 44 1D models- and one full 4D (space and time) model.  相似文献   

K. Sundermeyer: Const rained Dynamics. With Application to Yang-Mills Theory,General Relativity,Classical Spin,Dual String Model. Lecture Notes in Physics. Vol. 169. Springer-Verlag Berlin-Heidelberg-New York, 1982. Preis (soft cover) DM 33.-; approx. US $ 13.20     

H. Fuchs 《Astronomische Nachrichten》1985,306(3):128-128

  相似文献   

Kinematics of nearby Subdwarfs     

B. Fuchs  H. Jahreiss  R. Wielen 《Astrophysics and Space Science》1999,265(1-4):175-178

A sample of subdwarfs with accurate space velocities and standarized metallicities is presented. This was constructed by combining Hipparcos parallaxes and proper motions with radial velocities and metallicities from Carney et al. (1994; CLLA). The accurate Hipparcos parallaxes lead to an – upward – correction factor of 11% of the photometric distance scale of CLLA. The kinematical behaviour of the subdwarfs is discussed in particular in relation to their metallicities. Most of the stars turn out to be thick disk stars, but the sample contains also many genuine halo stars. While the extreme metal poor halo does not rotate, a population of subdwarfs with metallicities in the range −1.6≤ [Fe/H] ≤ −1.0 dex appears to rotate around the galactic center with a mean rotation speed of about 100 km s^-1. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

J. EHLERS (ed.) : Proceedings of the international school of physics „ENRICO FERMI”︁ Course LXVII. Isolated Gravitating- Systems in General Relativity. North-Holland Publ. Comp., Amsterdam/New York, 1979. XVI + 500 Seiten,Preis: Dfl. 175.-, US $85.25. ISBN 0-44445329-4     

Helmut Fuchs 《Astronomische Nachrichten》1982,303(2):130-130

  相似文献   

Deviation of circular geodesics in static spherically symmetric space-times     

H. Fuchs 《Astronomische Nachrichten》1990,311(5):271-276

For static spherically symmetric space-times the equations of geodesic deviation are solved for circular geodesics. We discuss the connection between the obtained solutions and the stability behaviour of the geodesics. The perihelion shift for test bodies moving on nearly circular geodesics is also derived.  相似文献   

GOCE gravitational gradients along the orbit   总被引：6，自引：3，他引：3  

Johannes Bouman  Sophie Fiorot  Martin Fuchs  Thomas Gruber  Ernst Schrama  Christian Tscherning  Martin Veicherts  Pieter Visser 《Journal of Geodesy》2011,85(11):791-805

GOCE is ESA’s gravity field mission and the first satellite ever that measures gravitational gradients in space, that is, the second spatial derivatives of the Earth’s gravitational potential. The goal is to determine the Earth’s mean gravitational field with unprecedented accuracy at spatial resolutions down to 100 km. GOCE carries a gravity gradiometer that allows deriving the gravitational gradients with very high precision to achieve this goal. There are two types of GOCE Level 2 gravitational gradients (GGs) along the orbit: the gravitational gradients in the gradiometer reference frame (GRF) and the gravitational gradients in the local north oriented frame (LNOF) derived from the GGs in the GRF by point-wise rotation. Because the V _XX , V _YY , V _ZZ and V _XZ are much more accurate than V _XY and V _YZ , and because the error of the accurate GGs increases for low frequencies, the rotation requires that part of the measured GG signal is replaced by model signal. However, the actual quality of the gradients in GRF and LNOF needs to be assessed. We analysed the outliers in the GGs, validated the GGs in the GRF using independent gravity field information and compared their assessed error with the requirements. In addition, we compared the GGs in the LNOF with state-of-the-art global gravity field models and determined the model contribution to the rotated GGs. We found that the percentage of detected outliers is below 0.1% for all GGs, and external gravity data confirm that the GG scale factors do not differ from one down to the 10⁻³ level. Furthermore, we found that the error of V _XX and V _YY is approximately at the level of the requirement on the gravitational gradient trace, whereas the V _ZZ error is a factor of 2–3 above the requirement for higher frequencies. We show that the model contribution in the rotated GGs is 2–35% dependent on the gravitational gradient. Finally, we found that GOCE gravitational gradients and gradients derived from EIGEN-5C and EGM2008 are consistent over the oceans, but that over the continents the consistency may be less, especially in areas with poor terrestrial gravity data. All in all, our analyses show that the quality of the GOCE gravitational gradients is good and that with this type of data valuable new gravity field information is obtained.  相似文献   

A quantitative vulnerability function for fluvial sediment transport   总被引：11，自引：6，他引：5  

Reinhold Totschnig  Walter Sedlacek  Sven Fuchs 《Natural Hazards》2011,58(2):681-703

In quantitative risk assessment, risk is expressed as a function of hazard, elements at risk exposed, and vulnerability. Vulnerability is defined as the expected degree of loss for an element at risk as a consequence of a certain event, following a natural-scientific approach combined with economic methods of loss appraisal. The resulting value ranges from 0 (no damage) to 1 (complete destruction). With respect to torrent processes, i.e., fluvial sediment transport, this concept of vulnerability—though widely acknowledged—did not result in sound quantitative relationships between process intensities and associated degrees of loss so far, even if considerable loss occurred during recent years. To close this gap and establish this relationship, data from three well-documented torrent events in the Austrian Alps were used to derive a quantitative vulnerability function applicable to residential buildings located on torrent fans. The method applied followed a spatially explicit empirical approach within a GIS environment and was based on process intensities, the spatial characteristics of elements at risk, and average reconstruction values on a local scale. Additionally, loss data were collected from responsible administrative bodies and analysed on an object level. The results suggest a modified Weibull distribution to fit best to the observed damage pattern if intensity is quantified in absolute values, and a modified Frechet distribution if intensity is quantified relatively in relation to the individual building height. Additionally, uncertainties resulting from such an empirical approach were studied; in relation to the data quality a 90% confidence band was found to represent the data range appropriately. The vulnerability relationship obtained allows for an enhanced quantification of torrent risk, but also for an inclusion in comprehensive vulnerability models including physical, social, economic, and institutional vulnerability. As a result, vulnerability to mountain hazards might decrease in the future.  相似文献   

Floodplain deposits: A geochemical archive of flood history – A case study on the River Rhine,Germany     

Z.A. Berner  S. Bleeck-Schmidt  D. Stüben  T. Neumann  M. Fuchs  M. Lehmann 《Applied Geochemistry》2012

Based on the correlation between discharge and carbonate content of the suspended load of the River Rhine, Germany, a systematic geochemical, mineralogical and granulometric study was carried out to verify whether this geochemical signal is transferred to floodplain deposits and in what way these sediments and their chemostratigraphic characterization can be used as a tool for the reconstruction of the river flood history. The analysis of the time resolved changes in the composition of particulate matter during a flood event revealed that the increase of carbonate content (represented by CaO, Sr) with discharge was coupled to a simultaneous decrease in the relative amount of siliciclastics (K₂O, Rb). The association of these two groups of diametrical parameters with specific grain size fractions (carbonates with 40–200 μm; siliciclastics with >200 μm) were found to be slightly shifted relative to each other and showed different gradients during the surging and fading flood wave. This, together with the covariance of elements pertaining to minerals with different density (e.g., carbonate and heavy minerals) suggests a chemical response to the changes in discharge, which is controlled primarily by hydraulic equivalence rather than grain size. There is also a time lag between the amount of suspended load and discharge, with a maximum in suspended load shortly after the peak discharge, when the flood has already started to abate. The flood plain sediments have similar composition to the suspended load, suggesting the direct transfer of the geochemical flood signal to the floodplain sediments.  相似文献