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Search Results: 1 - 10 of 14967 matches for " Christian Scharf "
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Measurement of the drift velocities of electrons and holes in high-ohmic <100> silicon
Christian Scharf,Robert Klanner
Physics , 2015, DOI: 10.1016/j.nima.2015.07.057
Abstract: Measurements of the drift velocities of electrons and holes as functions of electric field and temperature in high-purity n- and p-type silicon with <100> orientation are presented. The measurements cover electric field values between 2.5 and 50 kV/cm and temperatures between 233 and 333 K. For both electrons and holes differences of more than 15 % are found between our <100> results and the <111> drift velocities from literature, which are frequently also used for simulating <100> sensors. For electrons, the <100> results agree with previous <100> measurements, however, for holes differences between 5 to 15 % are observed for fields above 10 kV/cm. Combining our results with published data of low-field mobilities, we derive parametrizations of the drift velocities in high-ohmic <100> silicon for electrons and holes for fields between 0 and 50 kV/cm, and temperatures between 233 and 333 K. In addition, new parametrizations for the drift velocities for electrons and holes are introduced, which provide somewhat better descriptions of existing data for <111> silicon, than the standard parametrization.
Determination of the electronics transfer function for current transient measurements
Christian Scharf,Robert Klanner
Physics , 2014, DOI: 10.1016/j.nima.2014.12.016
Abstract: We describe a straight-forward method for determining the transfer function of the readout of a sensor for the situation in which the current transient of the sensor can be precisely simulated. The method relies on the convolution theorem of Fourier transforms. The specific example is a planar silicon pad diode connected with a 50 $\Omega $ cable to an amplifier followed by a 5 GS/s sampling oscilloscope. The charge carriers in the sensor were produced by picosecond lasers with light of wavelengths of 675 and 1060 nm. The transfer function is determined from the 1060 nm data with the pad diode biased at 1000 V. It is shown that the simulated sensor response convoluted with this transfer function provides an excellent description of the measured transients for the laser light of both wavelengths, at voltages 50 V above the depletion voltage of about 90 V up to the maximum applied voltage of 1000 V. The method has been developed for the precise measurement of the dependence of the drift velocity of electrons and holes in high-ohmic silicon on crystal orientation, electric field and temperature. It can also be applied for the analysis of transient-current measurements of radiation-damaged solid state sensors, as long as sensors properties, like high-frequency capacitance, are not too different.
Supersymmetry Transformation of Quantum Fields
Christian Rupp,Rainer Scharf,Klaus Sibold
Physics , 2001,
Abstract: In the Wess-Zumino gauge, supersymmetry transformations become non-linear and are usually incorporated together with BRS transformations in the form of Slavnov-Taylor identities, such that they appear at first sight to be even non-local. Furthermore, the gauge fixing term breaks supersymmetry. In the present paper, we clarify in which sense supersymmetry is still a symmetry of the system and how it is realized on the level of quantum fields.
Schwarzschild Geodesics in Terms of Elliptic Functions and the Related Red Shift  [PDF]
Gunter Scharf
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.24036
Abstract: Using Weierstrassian elliptic functions the exact geodesics in the Schwarzschild metric are expressed in a simple and most transparent form. The results are useful for analytical and numerical applications. For example we calculate the perihelion precession and the light deflection in the post-Einsteinian approximation. The bounded orbits are computed in the post-Newtonian order. As a topical application we calculate the gravitational red shift for a star moving in the Schwarzschild field.
Noise Reduction and Image Quality Improvement of Low Dose and Ultra Low Dose Brain Perfusion CT by HYPR-LR Processing
Radko Krissak,Charles A. Mistretta,Thomas Henzler,Anastasios Chatzikonstantinou,Johann Scharf,Stefan O. Schoenberg,Christian Fink
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0017098
Abstract: To evaluate image quality and signal characteristics of brain perfusion CT (BPCT) obtained by low-dose (LD) and ultra-low-dose (ULD) protocols with and without post-processing by highly constrained back-projection (HYPR)–local reconstruction (LR) technique.
Stage-Related Alterations in Renal Cell Carcinoma – Comprehensive Quantitative Analysis by 2D-DIGE and Protein Network Analysis
Heike Junker,Simone Venz,Uwe Zimmermann,Andrea Thiele,Christian Scharf,Reinhard Walther
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0021867
Abstract: Renal cell carcinoma accounts for about 3% of adult malignancies and 85% of neoplasms arising from the kidney. To identify potential progression markers for kidney cancer we examined non-neoplastic and neoplastic kidney tissue from three groups of patients, which represent different tumor stages (pT1, pT2, pT3) by a fluorescence two-dimensional difference gel electrophoresis (2D-DIGE) approach combined with MALDI-ToF-MS/MS. Delta2D software package was used for gel image based quantification and statistical analysis. Thereby, a comprehensive Principal Component Analysis (PCA) could be performed and allowed a robust quality control of the experiment as well as a classification of the analyzed samples, which correlated with the predicted stages from the pathological examination. Additionally for selected candidate proteins we detected a correlation to the tumor grading as revealed by immunohistochemistry. On the 2D protein map 176 spots out of 989 were detected as at least 2-fold differentially expressed. These spots were analyzed by MALDI-ToF-MS/MS and 187 different proteins were identified. The functional clustering of the identified proteins revealed ten groups. Within these groups we found 86 enzymes, 63 proteins of unknown function, 14 transporter, 8 peptidases and 7 kinases. From the systems biology approach we could map many of these proteins in major pathways involved in remodelling of cytoskeleton, mitochondrial dysfunctions and changes in lipid metabolism. Due to complexity of the highly interconnected pathway network, further expression and functional validation of these proteins might provide new insights in kidney cancer progression to design novel diagnostic and therapeutic strategies.
The Movement Ecology of the Straw-Colored Fruit Bat, Eidolon helvum, in Sub-Saharan Africa Assessed by Stable Isotope Ratios
Gonzalo Ossa, Stephanie Kramer-Schadt, Alison J. Peel, Anne K. Scharf, Christian C. Voigt
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0045729
Abstract: Flying foxes (Pteropodidae) are key seed dispersers on the African continent, yet their migratory behavior is largely unknown. Here, we studied the movement ecology of the straw-colored fruit bat, Eidolon helvum, and other fruit bats by analyzing stable isotope ratios in fur collected from museum specimens. In a triple-isotope approach based on samples of two ecologically similar non-migratory pteropodids, we first confirmed that a stable isotope approach is capable of delineating between geographically distinct locations in Sub-Saharan Africa. A discriminant function analysis assigned 84% of individuals correctly to their capture site. Further, we assessed how well hydrogen stable isotope ratios (δ2H) of fur keratin collected from non-migratory species (n = 191 individuals) records variation in δ2H of precipitation water in sub-Saharan Africa. Overall, we found positive, negative and no correlations within the six studied species. We then developed a reduced major axis regression equation based on individual data of non-migratory species to predict where potentially migratory E. helvum (n = 88) would come from based on their keratin δ2H. Across non-migratory species, δ2H of keratin and local water correlated positively. Based on the isoscape origin model, 22% of E. helvum were migratory, i.e. individuals had migrated over at least 250 km prior to their capture. Migratory individuals came from locations at a median distance of about 860 km from the collection site, four even from distances of at least 2,000 km. Ground-truthing of our isoscape origin model based on keratin δ2H of extant E. helvum (n = 76) supported a high predictive power of assigning the provenance of African flying foxes. Our study highlights that stable isotope ratios can be used to explain the migratory behavior of flying foxes, even on the isotopically relatively homogenous African continent, and with material collected by museums many decades or more than a century ago.
Isotope shift in the Sulfur electron affinity: observation and theory
Thomas Carette,Cyril Drag,Oliver Scharf,Christophe Blondel,Christian Delsart,Charlotte Froese Fischer,Michel Godefroid
Physics , 2010, DOI: 10.1103/PhysRevA.81.042522
Abstract: The electron affinities eA(S) are measured for the two isotopes 32S and 34S (16752.9753(41) and 16752.9776(85) cm-1, respectively). The isotope shift in the electron affinity is found to be positive, eA(34S)-eA(32S) = +0.0023(70) cm-1, but the uncertainty allows for the possibility that it may be either "normal" (eA(34S) > eA(32S)) or "anomalous" (eA(34S) < eA(32S)). The isotope shift is estimated theoretically using elaborate correlation models, monitoring the electron affinity and the mass polarization term expectation value. The theoretical analysis predicts a very large specific mass shift that counterbalances the normal mass shift and produces an anomalous isotope shift, eA(34S)-eA(32S) = - 0.0053(24) cm-1. The observed and theoretical residual isotope shifts agree with each other within the estimated uncertainties.
Against Geometry: Nonstandard General Relativity  [PDF]
Gunter Scharf
Open Access Library Journal (OALib Journal) , 2015, DOI: 10.4236/oalib.1101389
Abstract: We show that the Schwarzschild solution can be embedded in a class of nonstandard solutions of the vacuum Einstein’s equations with arbitrary rotation curves. These nonstandard solutions have to be taken as physical, if dark matter as needed in the standard theory cannot be found. As a consequence general relativity is considered as a classical field theory in Minkowski space and not as a geometric theory in the sense of Einstein. Assuming an asymptotically flat rotation curve and introducing a material disk into this model we find a matter density in accordance with the Tully- Fisher relation.
From massive gravity to dark matter density II
G. Scharf
Physics , 2009,
Abstract: As previously observed the massless limit of massive gravity leads to a modification of general relativity. Here we study spherically symmetric solutions of the modified field equations which contain normal matter together with a dark energy density. If the dark density profile is assumed to be known, the whole problem is reduced to a linear first order differential equation which can be solved by quadratures.
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