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Search Results: 1 - 10 of 193124 matches for " Rolf D. Theis "
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Muslim Americans in American Society—and in the German Classroom
Rolf D. Theis
American Studies Journal , 2008,
Abstract: Muslim Americans are newcomers on the ESL teaching agenda in Germany—and it is not only because of 9/11 that this minority group has moved into the focus of interest. Developments in German society have contributed to this situation. This article provides an outline of some basic ideas concerning Landeskunde/ Intercultural Studies, followed by an outline of ideas concerning a project on ‘Muslims in the U.S.’—based on teaching experience gained in a grade 12 classroom
Neutron scattering in molecular liquids: Influence of orientational degrees of freedom and the prepeak in a fragile glass former
Christoph Theis,Rolf Schilling
Physics , 1998,
Abstract: The intermediate scattering function S(q,t) for neutron scattering is expanded with respect to a complete set of correlation functions which describe the dynamical correlations in a molecular liquid. For the static ns-structure factor S(q) of a system of diatomic molecules the results of the expansion are compared with the exact results from a MD-imulation and it is shown that the Sears-expansion, which is commonly used to interpret such data, fails in the supercooled regime. The representation for S(q) is used to draw conclusions about the q-dependence and especially the origin of the prepeak.
Nonergodicity parameters for a molecular liquid: A comparison between mode coupling theory and simulation
Christoph Theis,Rolf Schilling
Physics , 1998, DOI: 10.1016/S0022-3093(98)00633-4
Abstract: We apply the mode coupling theory (MCT) which was recently worked out for molecular liquids to a liquid of diatomic, rigid molecules. Using the static correlators from a molecular dynamics simulation, we have solved the MCT-equations for the nonergodicity parameters within two approcimation schemes. We find that the critical temperature from our calculation underestimates the simulation result. The q-dependence of the critical nonergodicity parameter is well reproduced.
Neutron scattering and molecular correlations in a supercooled liquid
Christoph Theis,Rolf Schilling
Physics , 1999, DOI: 10.1103/PhysRevE.60.740
Abstract: We show that the intermediate scattering function $S_n(q,t)$ for neutron scattering (ns) can be expanded naturely with respect to a set of molecular correlation functions that give a complete description of the translational and orientational two-point correlations in the liquid. The general properties of this expansion are discussed with special focus on the $q$-dependence and hints for a (partial) determination of the molecular correlation functions from neutron scattering results are given. The resulting representation of the static structure factor $S_n(q)$ is studied in detail for a model system using data from a molecular dynamics simulation of a supercooled liquid of rigid diatomic molecules. The comparison between the exact result for $S_n(q)$ and different approximations that result from a truncation of the series representation demonstrates its good convergence for the given model system. On the other hand it shows explicitly that the coupling between translational (TDOF) and orientational degrees of freedom (ODOF) of each molecule and rotational motion of different molecules can not be neglected in the supercooled regime.Further we report the existence of a prepeak in the ns-static structure factor of the examined fragile glassformer, demonstrating that prepeaks can occur even in the most simple molecular liquids. Besides examining the dependence of the prepeak on the scattering length and the temperature we use the expansion of $S_n(q)$ into molecular correlation functions to point out intermediate range orientational order as its principle origin.
Test of the semischematic model for a liquid of linear molecules
Linda Fabbian,Rolf Schilling,Francesco Sciortino,Piero Tartaglia,Christoph Theis
Physics , 1998, DOI: 10.1103/PhysRevE.58.7272
Abstract: We apply to a liquid of linear molecules the semischematic mode-coupling model, previously introduced to describe the center of mass (COM) slow dynamics of a network-forming molecular liquid. We compare the theoretical predictions and numerical results from a molecular dynamics simulation, both for the time and the wave-vector dependence of the COM density-density correlation function. We discuss the relationship between the presented analysis and the results from an approximate solution of the equations from molecular mode-coupling theory [R. Schilling and T. Scheidsteger, Phys. Rev. E 56 2932 (1997)].
A trust-region method for stochastic variational inference with applications to streaming data
Lucas Theis,Matthew D. Hoffman
Statistics , 2015,
Abstract: Stochastic variational inference allows for fast posterior inference in complex Bayesian models. However, the algorithm is prone to local optima which can make the quality of the posterior approximation sensitive to the choice of hyperparameters and initialization. We address this problem by replacing the natural gradient step of stochastic varitional inference with a trust-region update. We show that this leads to generally better results and reduced sensitivity to hyperparameters. We also describe a new strategy for variational inference on streaming data and show that here our trust-region method is crucial for getting good performance.
A Reconstruction Approach for Imaging in 3D Cone Beam Vector Field Tomography
T. Schuster,D. Theis,A. K. Louis
International Journal of Biomedical Imaging , 2008, DOI: 10.1155/2008/174283
Abstract: 3D cone beam vector field tomography (VFT) aims for reconstructing and visualizing the velocity field of a moving fluid by measuring line integrals of projections of the vector field. The data are obtained by ultrasound measurements along a scanning curve which surrounds the object. From a mathematical point of view, we have to deal with the inversion of the vectorial cone beam transform. Since the vectorial cone beam transform of any gradient vector field with compact support is identically equal to zero, we can only hope to reconstruct the solenoidal part of an arbitrary vector field. In this paper we will at first summarize important properties of the cone beam transform for three-dimensional solenoidal vector fields and then propose a solution approach based on the method of approximate inverse. In this context, we intensively make use of results from scalar 3D computerized tomography. The findings presented in the paper will continuously be illustrated by pictures from first numerical experiments done with exact, simulated data.
Compact Formulations of the Steiner Traveling Salesman Problem and Related Problems
Adam N. Letchford,Saeideh D. Nasiri,Dirk Oliver Theis
Mathematics , 2012,
Abstract: The Steiner Traveling Salesman Problem (STSP) is a variant of the Traveling Salesman Problem (TSP) that is particularly suitable when dealing with sparse networks, such as road networks. The standard integer programming formulation of the STSP has an exponential number of constraints, just like the standard formulation of the TSP. On the other hand, there exist several known {\em compact} formulations of the TSP, i.e., formulations with a polynomial number of both variables and constraints. In this paper, we show that some of these compact formulations can be adapted to the STSP. We also briefly discuss the adaptation of our formulations to some closely-related problems.
Insect sting allergy. A study from 1980 to 2003 of patients who started treatment with venom immunotherapy between 1980 and 1998
Rolf Haye, Liv D?sen
Clinical and Molecular Allergy , 2005, DOI: 10.1186/1476-7961-3-12
Abstract: This is an open, single centre study on patients treated with venom IT 14 years or older with a history of a systemic allergic reaction to an insect sting, a positive skin prick test (SPT) or a positive RAST and willingness to comply with five years of IT. Clinical and laboratory data were registered prospectively at the start of IT and after five years of treatment until 2003 on patients who started IT between 1980 and 1998. Questionnaires were answered in 1989, 1993 and 2003. Statistical analysis was done with Pearson's chi square, Fisher's exact or the t-test.Of 315 patients treated, 44 were given bee, 248 common wasp and 23 both venoms. Of the common wasp sting incidents 5.5 % resulted in a severe allergic reaction (SAR) during adequate IT and 22% after cessation. Seventy-one per cent of the patients carried epinephrine. Precautionary steps were taken by 77% of the patients during or after inadequate IT. On or after adequate IT 83% felt completely or substantially safe. Surprisingly 29 % of those inadequately treated felt safer and 50% were satisfied with having had the opportunity to be treated. The SPT became negative in 68% of the wasp allergic patients after five years of adequate IT. Increased risk of experiencing SAR to a future sting in wasp allergic patients after cessation of adequate IT was significantly associated with a SAR due to IT during the rush regimen. SAR due to IT occurred very rarely during maintenance dosing.Adequate venom IT is very effective while ongoing but somewhat less effective after cessation, while inadequate treatment gives poor results. More of our patients should complete five years of IT and some should continue IT. The type of reaction to IT during incremental dosing may be of help in deciding who should continue beyond five years. Maintenance IT may be taken over by the general physician.After the study of Hunt et al [1] was published in 1978 showing the ineffectiveness of whole body insect extracts, we stopped using whole bo
Nasal septal perforation 1981–2005: Changes in etiology, gender and size
Liv D?sen, Rolf Haye
BMC Ear, Nose and Throat Disorders , 2007, DOI: 10.1186/1472-6815-7-1
Abstract: This is an open, prospective clinical study of patients seen at our hospital from 1981 to 2005. The clinical data of size, gender and etiology have been recorded consecutively.One hundred and ninety seven patients (100 male, 97 female) were evaluated. Between 1981 and 1995 nasal septal perforation was caused by surgery in 40 of 102 (39.2 %). In the period 1995 to and inclusive of 2005 this percentage decreased as septal resection has been replaced by septo/septorhinoplasty. The latter was the cause for septal perforation in 14.7% in the last period. Nasal steroid and decongestive sprays have emerged as an important cause (28.4 %) during the last ten years particularly in females. In the first period 44 (43.1 %) and in the last 53 (55.7 %) patients were females. There was a noticeable reduction in the number of septal perforations 15 mm or larger in the last period.Nasal steroid and decongestive sprays are now important causes for septal perforation. Information about this complication should be given with an advice to immediately report increasing and bothersome crusting and bleeding. Warning of the simultaneous use of nasal steroid and decongestive sprays should be addressed particularly to females. All patients with symptoms of septal perforation should promptly be referred to otolaryngologists for treatment.The treatment of nasal septal perforation (SP) is symptomatic (local application of ointments), prosthetic, or surgical. Surgery may be curative but the results are not always satisfactory as evidenced by the many different operative procedures that have been proposed [1-7]. Prevention of SP should be an important goal. The purpose of this study was to examine our clinical data to look for possible changes in the pattern of etiology in order to identify causes that may be suitable for preventive measures. We have also registered the size of the SP in order to establish whether the size would indicate that the patients should have been referred sooner.We have r
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