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Search Results: 1 - 10 of 201069 matches for " P. Seidel "
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Braid group actions on derived categories of coherent sheaves
Paul Seidel,R. P. Thomas
Mathematics , 2000,
Abstract: This paper gives a construction of braid group actions on the derived category of coherent sheaves on a variety $X$. The motivation for this is Kontsevich's homological mirror conjecture, together with the occurrence of certain braid group actions in symplectic geometry. One of the main results is that when $\dim X \geq 2$, our braid group actions are always faithful. We describe conjectural mirror symmetries between smoothings and resolutions of singularities that lead us to find examples of braid group actions arising from crepant resolutions of various singularities. Relations with the McKay correspondence and with exceptional sheaves on Fano manifolds are given. Moreover, the case of an elliptic curve is worked out in some detail.
Symplectic cohomology and q-intersection numbers
Paul Seidel,Jake P. Solomon
Mathematics , 2010, DOI: 10.1007/s00039-012-0159-6
Abstract: Given a symplectic cohomology class of degree 1, we define the notion of an equivariant Lagrangian submanifold. The Floer cohomology of equivariant Lagrangian submanifolds has a natural endomorphism, which induces a grading by generalized eigenspaces. Taking Euler characteristics with respect to the induced grading yields a deformation of the intersection number. Dehn twists act naturally on equivariant Lagrangians. Cotangent bundles and Lefschetz fibrations give fully computable examples. A key step in computations is to impose the "dilation" condition stipulating that the BV operator applied to the symplectic cohomology class gives the identity. Equivariant Lagrangians mirror equivariant objects of the derived category of coherent sheaves.
Simulation of energy barrier distributions using real particle parameters and comparison with experimental obtained results
M. Büttner,M. Schiffler,P. Weber,P. Seidel
Physics , 2011,
Abstract: In this work we compare previously measured energy barriers over the course of temperature with the results of simulations of the behaviour of the energy barriers. For the measurements the temperature dependent magnetorelaxation method (TMRX) was used. For the simulations of the energy barrier distribution we have used the real particles properties such as anisotropy and core size volume of the fractions of two magnetically fractionated ferrofluids. There is a good agreement between the simulated behaviour and the experimental obtained results. The influence of the particle volume concentration and agglomeration on the energy barrier distribution has been investigated. Finally the simulations confirm a previously published explanation for an experimentally obtained relaxation effect.
Discharges of past flood events based on historical river profiles
D. Sudhaus,J. Seidel,K. Bürger,P. Dostal
Hydrology and Earth System Sciences Discussions , 2008,
Abstract: This paper presents a case study to estimate peak discharges of extreme flood events of Neckar River in south-western Germany during the 19th century. It was carried out within the BMBF research project RIMAX (Risk Management of Extreme Flood Events). The discharge estimations were made for the flood events of 1824 and 1882 based on historical cross profiles. The 1-D model Hydrologic Engineering Centers River Analysis System (HEC-RAS) was applied with different roughness coefficients. The results are compared (i) with contemporary historical calculations and (ii) in the case of a flood event in 1824 with the discharge simulation by the water balance model LARSIM (Large Area Runoff Simulation Model). These calculations are matched by the HEC-RAS simulation based on the standard roughness coefficients.
On the exposure of hemispherical photographs in forests
Becksch?fer P,Seidel D,Kleinn C,Xu J
iForest : Biogeosciences and Forestry , 2013, DOI: 10.3832/ifor0957-006
Abstract: At least 10 different methods to determine exposure for hemispherical photographs were used by scientists in the last two decades, severely hampering comparability among studies. Here, an overview of the applied methods is reported. For the standardization of photographic exposure, a time-consuming reference measurement in the open land towards the unobstructed sky was required so far. The two Histogram Methods proposed here make use of the technical advances of digital cameras which enable users to assess a photograph’s histogram directly at the location of measurement. This avoids errors occurring due to variations in sky lighting happening in the time span between taking the reference measurement and reaching the sample location within the forest. The Histogram Methods speed up and simplify taking hemispherical photographs, and introduce an objectively applicable, standardized approach. We highlight the importance of correct exposure by quantifying the overestimation of gap fraction resulting from auto-exposed photographs under a wide range of canopy openness situations. In our study, gap fraction derived from auto-exposed photographs reached values up to 900% higher than those derived from non-overexposed photographs. By investigating the size of the largest gap per photograph and the number of small gaps (gaps contributing less than 0.1% to gap fraction), we concluded that the overestimation of gap fraction resulted mainly from the overexposure of vegetation surrounding large gaps.
Potential of historical meteorological and hydrological data for the reconstruction of historical flood events – the example of the 1882 flood in southwest Germany
J. Seidel,F. Imbery,P. Dostal,D. Sudhaus
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2009,
Abstract: This paper presents a hydrometeorological reconstruction of the flood triggering meteorological situation and the simulation of discharges of the flood event of December 1882 in the Neckar catchment in Baden-Württemberg (southwest Germany). The course of the 1882 flood event in the Neckar catchment in southwest Germany and the weather conditions which led to this flood were reconstructed by evaluating the information from various historical sources. From these historical data, daily input data sets were derived for run-off modeling. For the determination of the precipitation pattern at the end of December 1882, the sparse historical data were modified by using a similar modern day precipitation pattern with a higher station density. The results of this run-off simulation are compared with contemporary historical data and also with 1-D hydraulic simulations using the HEC-RAS model.
Individual Counseling To Private Physicians Concerning Their Prescription Habits. A German Experience
Seidel J
Revue Médicale de l'Assurance Maladie , 2002,
Abstract: In order counteract ever-increasing prescription costs over the last few years combined with the precarious financial state of the health insurance fund of the German Land , Mecklembourg-Pomerany, the minister of social affairs, the health insurance fund and the Union of physicians contracting with the Land came to an agreement. The aim was to contain costs while guaranteeing that prescriptions remained of the highest quality. In order to accomplish this goal, the concerned players developed a common program of counseling and information directed at improving the prescription habits of private physicians. Beforehand, a pharmacy data bank (PLATO) had to be developed, permitting an analysis of the many aspects of the pharmacy prescriptions reimbursed by the health insurance fund. The article presents the preliminary results of this counseling and information-sharing initiative.
Derek Nurse 2008. Tense and Aspect in Bantu.
Seidel, Frank
Afrikanistik Online , 2009,
Abstract:
Swahili Lesebuch. Aus Pressetexten ausgew hlt
Seidel, Frank
Afrikanistik Online , 2007,
Abstract:
Design for an ageing population: promoting independence and quality of life
David Seidel
Australasian Medical Journal , 2009,
Abstract: Solutions to promote independent living in old age may occur at a systems level, where the health sciences,engineering and human factors work together. A better engineering response is needed directed at the problems encountered in the area of instrumental activities of daily living. Field studies can provide valuable insights, but surveydata are needed to complement and pinpoint areas for design improvement.
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