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Search Results: 1 - 10 of 4712 matches for " Wolfgang Kratzer "
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Sonographically guided lymph node biopsy: Complication rates  [PDF]
Michael Mueller, Genia Wittich, Suemeyra Oeztuerk, Wolfgang Kratzer, Mark Martin Haenle, Richard Andrew Mason
Open Journal of Clinical Diagnostics (OJCD) , 2012, DOI: 10.4236/ojcd.2012.22006
Abstract: Purpose: The study investigated the rate of complications associated with sonographically guided lymph node biopsies and assessed potential risk factors. Methods: A total of 536 sonographically guided puncture procedures (283 males, 52.8%; 253 females, 47.2%; average age 57.0 ± 16.0 years; range 14 - 87 years) were performed in 469 patients for the work-up of unclear lymphadenopathy. Events, complications and potential risk factors, were prospectively documented. Results: The 469 patients underwent a total of 536 puncture procedures (PP) including 663 punctures and 1485 passes. Lymph node localizations were intraabdominal (55.2%, n = 296), cervical (22.4%, n = 120), inguinal (12.9%, n = 69), axillary (7.8%, n = 42) and other (1.7%, n = 9). No complications were documented during the entire study period. There was no increased risk of complications documented for the potential risk factors number of punctures, the number of passes, the localization, diameter of the lymph node (s), puncture technique, needle gauge, as well as patients’ sex, age and coagulation parameters, and the experience of the examiner. Conclusions: Our findings confirm the safety of percutaneous sonographically guided lymph node biopsies in different regions of the body in patients with adequate coagulation parameters undergoing pre-interventional color Doppler ultrasound examination.
Prevalence of celiac disease in Germany: A prospective follow-up study
Wolfgang Kratzer,Monika Kibele,Atilla Akinli,Marc Porzner
World Journal of Gastroenterology , 2013, DOI: 10.3748/wjg.v19.i17.2612
Abstract: AIM: To determine the prevalence of celiac disease in a randomly selected population sample. METHODS: A total of 2157 subjects (1036 males; 1121 females) participating in a population-based cross-sectional study underwent laboratory testing for tissue transglutaminase and antibodies to immunoglobulin A, endomysium and antigliadin. In a second step, all subjects who had been examined serologically were surveyed using a questionnaire that included questions specific to celiac disease. Subjects with positive antibody titers and those with histories positive for celiac disease then underwent biopsy. At the first follow up, antibody titers were again determined in these subjects and subjects were questioned regarding symptoms specific for celiac disease and disorders associated with celiac disease. The second follow up consisted of a telephone interview with subjects positive for celiac disease. RESULTS: Antibody tests consistent with celiac disease were reported in eight subjects, corresponding to an overall prevalence of 1:270 (8/2157). The prevalence among women was 1:224 and 1:518 in men. Classical symptoms were observed in 62.5% of subjects. Atypical celiac disease was present in 25.0%, and transient celiac disease in 12.5%. False-negative test results were returned in three subjects. This yields a sensitivity and specificity of 62.5% and 50.0%, respectively, for tissue transglutaminase immunoglobulin-A antibody; of 62.5% and 71.4% respectively, for endomysium antibody; and of 62.5% and 71.4%, respectively, for antigliadin antibody. CONCLUSION: The prevalence rate in our collective lies within the middle tertile of comparable studies in Europe. The use of a single antibody test for screening purposes must be called into question.
Percutaneous ultrasonographically guided liver punctures: an analysis of 1961 patients over a period of ten years
Mueller Michael,Kratzer Wolfgang,Oeztuerk Suemeyra,Wilhelm Manfred
BMC Gastroenterology , 2012, DOI: 10.1186/1471-230x-12-173
Abstract: Background Ultrasonographically guided punctures of the liver represent a decisive tool in the diagnosis of many diseases of the liver. Objective of the study was to determine the extent to which the complication rate for ultrasonographically guided punctures of the liver is affected by less comprehensively studied risk factors. Methods A total of 2,229 liver biopsies were performed in 1,961 patients (55.5% males; 44.5% females). We recorded actual complications and assessed the following risk factors: needle gauge, puncture technique, examiner experience, coagulation status, puncture target (focal lesion versus parenchyma), lesion size, patient sex and age. Results he rate of complications stood at 1.2% (n = 27), of which 0.5% (n = 12) were major and 0.7% (n = 15) minor complications. A significant increase in complications involving bleeding was observed with larger-gauge needles compared with smaller-gauge needles and for cutting biopsy punctures compared with aspiration biopsies (Menghini technique). In the bivariate analysis complications were 2.7 times more frequent in procedures performed by experienced examiners compared with those with comparatively less experience. Lower values for Quick’s test and higher partial thromboplastin times were associated with a higher rate of bleeding. Neither the puncture target, lesion size or patient sex exerted any measurable influence on the puncture risk. Advanced patient age was associated with a higher rate of complications involving bleeding. Conclusions Our study helps to establish the importance of potential and less comprehensively studied risk factors and may contribute to further reduction in complications rates in routine clinical practice.
Monte Carlo and kinetic Monte Carlo methods
Peter Kratzer
Physics , 2009,
Abstract: This article reviews the basic computational techniques for carrying out multi-scale simulations using statistical methods, with the focus on simulations of epitaxial growth. First, the statistical-physics background behind Monte Carlo simulations is briefly described. The kinetic Monte Carlo (kMC) method is introduced as an extension of the more wide-spread thermodynamic Monte Carlo methods, and algorithms for kMC simulations, including parallel ones, are discussed in some detail. The step from the atomistic picture to the more coarse-grained description of Monte Carlo simulations is exemplified for the case of surface diffusion. Here, the aim is the derivation of rate constants from knowledge about the underlying atomic processes. Both the simple approach of Transition State Theory, as well as more recent approaches using accelerated molecular dynamics are reviewed. Finally, I address the point that simplifications often need to be introduced in practical Monte Carlo simulations in order to reduce the complexity of 'real' atomic processes. Different 'flavors' of kMC simulations and the potential pitfalls related to the reduction of complexity are presented in the context of simulations of epitaxial growth.
Stepsize control for Newton's method in the presence of singularities
Michael Kratzer
Mathematics , 2013,
Abstract: Singularities in the Jacobian matrix are an obstacle to Newton's method. We show that stepsize controls suggested by Deuflhard and Steinhoff can be used to detect and rapidly converge to such singularities.
Ultrasonographically detected gallbladder polyps: A reason for concern? A seven-year follow-up study
Wolfgang Kratzer, Mark M Haenle, Andrea Voegtle, Richard A Mason, Atilla S Akinli, Klaus Hirschbuehl, Andreas Schuler, Volker Kaechele, the Roemerstein study group
BMC Gastroenterology , 2008, DOI: 10.1186/1471-230x-8-41
Abstract: A total of 2,415 subjects (1,261 women; 1,154 men) underwent ultrasound examination of the gallbladder, in November 1996 as part of a prospective study. Subjects in whom GP were detected at the initial survey underwent follow-up ultrasound examinations after 30 and 84 months.At the initial survey gallbladder polyps were detected in 34 subjects (1.4%; females: 1.1%, range 14 to 74 years; males: 1.7%, range 19 to 63 years). Median diameter was 5 ± 2.1 mm (range 2 to10 mm) at the initial survey, 5 mm ± 2.8 mm (range 2 to 12 mm) at 30 months and 4 ± 2.3 mm (range 2 to 9 mm) at 84 months. At the time of first follow-up no change in diameter was found in 81.0% (n = 17), reduction in diameter in 4.8% (n = 1) and increase in diameter in 14.3% (n = 3). At the time of second follow-up no increase in polyp diameter was found in 76.9% (n = 10) and reduction in diameter in 7.7% (n = 1). No evidence of malignant disease of the gallbladder was found.Over a period of seven years little change was measured in the diameter of gallbladder polyps. There was no evidence of malignant disease of the gallbladder in any subject.The development and refinement of diagnostic imaging modalities such as computed tomography (CT), magnetic resonance imaging (MRI) and ultrasonography (US) and their widespread application have led to an increase in the coincidental diagnosis of gallbladder stones and gallbladder polyps [1,2]. As a result, clinicians are ever more frequently confronted with the question of how to proceed in cases of coincidentally discovered gallbladder polyps. The appropriate management of these entities remains controversial [3-5].Gallbladder polyps represent a heterogeneous group of changes in the gallbladder wall and include entities such as cholesterol polyps, inflammatory polyps, adenomas, leiomyomas and lipomas [6]. The prevalence of gallbladder polyps is reported in the range of 0.3–9.5%, depending on the population studied and on the study design. Prevalence figures in Europ
Improvement of MERIS level 2 products in Baltic Sea coastal areas by applying the Improved Contrast between Ocean and Land processor (ICOL) - data analysis and validation
Susanne Kratzer,Christian Vinterhav
Oceanologia , 2010,
Abstract: In this paper we compare the followingMERIS processors against sea-truthing data:the standard MERIS processor (MEGS 7.4.1), the Case 2Regional processor (C2R) of the German Institutefor Coastal Research (GKSS), and the Case 2Water Properties processor developed at the FreieUniversit t Berlin (FUB). Furthermore, the ImprovedContrast between Ocean and Land processor (ICOL), a prototypeprocessor for the correction of adjacency effects from land,was tested on all three processors, and the retrieval of level 2data was evaluated against sea-truthing data before and afterICOL processing.
Density-functional study of hydrogen chemisorption on vicinal Si(001) surfaces
E. Pehlke,P. Kratzer
Physics , 1998, DOI: 10.1103/PhysRevB.59.2790
Abstract: Relaxed atomic geometries and chemisorption energies have been calculated for the dissociative adsorption of molecular hydrogen on vicinal Si(001) surfaces. We employ density-functional theory, together with a pseudopotential for Si, and apply the generalized gradient approximation by Perdew and Wang to the exchange-correlation functional. We find the double-atomic-height rebonded D_B step, which is known to be stable on the clean surface, to remain stable on partially hydrogen-covered surfaces. The H atoms preferentially bind to the Si atoms at the rebonded step edge, with a chemisorption energy difference with respect to the terrace sites of >sim 0.1 eV. A surface with rebonded single atomic height S_A and S_B steps gives very similar results. The interaction between H-Si-Si-H mono-hydride units is shown to be unimportant for the calculation of the step-edge hydrogen-occupation. Our results confirm the interpretation and results of the recent H_2 adsorption experiments on vicinal Si surfaces by Raschke and Hoefer described in the preceding paper.
Electron-hole spectra created by adsorption on metals from density-functional theory
M. Timmer,P. Kratzer
Physics , 2008, DOI: 10.1103/PhysRevB.79.165407
Abstract: Non-adiabaticity in adsorption on metal surfaces gives rise to a number of measurable effects, such as chemicurrents and exo-electron emission. Here we present a quantitative theory of chemicurrents on the basis of ground-state density-functional theory (DFT) calculations of the effective electronic potential and the Kohn-Sham band structure. Excitation probabilities are calculated both for electron-hole pairs and for electrons and holes separately from first-order time-dependent perturbation theory. This is accomplished by evaluating the matrix elements (between Kohn-Sham states) of the rate of change of the effective electronic potential between subsequent (static) DFT calculations. Our approach is related to the theory of electronic friction, but allows for direct access to the excitation spectra. The method is applied to adsorption of atomic hydrogen isotopes on the Al(111) surface. The results are compatible with the available experimental data (for noble metal surfaces); in particular, the observed isotope effect in H versus D adsorption is described by the present theory. Moreover, the results are in qualitative agreement with computationally elaborate calculations of the full dynamics within time-dependent density-functional theory, with the notable exception of effects due to the spin dynamics. Being a perturbational approach, the method proposed here is simple enough to be applied to a wide class of adsorbates and surfaces, while at the same time allowing us to extract system-specific information.
Two-stage crystallization of charged colloids at low supersaturations
Kai Kratzer,Axel Arnold
Physics , 2014,
Abstract: We report simulations on the homogeneous liquid-fcc nucleation of charged colloids for both low and high contact energy values. As a precursor for crystal formation, we observe increased local order at the position where the crystal will form, but no correlations with the local density. Thus, the nucleation is driven by order fluctuations rather than density fluctuations. Our results also show that the transition involves two stages in both cases, first a transition liquid-bcc, followed by a bcc-hcp/fcc transition. Both transitions have to overcome free energy barriers, so that a spherical bcc-like cluster is formed first, in which the final fcc-like structure is nucleated mainly at the surface of the crystallite. This means that the bcc-fcc phase transition is a heterogeneous nucleation, even though we start from a homogeneous bulk liquid. The height of the bcc-hcp/fcc free energy barrier strongly depends on the contact energies of the colloids. For low contact energy this barrier is low, so that the bcc-hcp/fcc transition happens spontaneously. For the higher contact energy, the second barrier is too high to be crossed spontaneously by the colloidal system. However, it was possible to ratchet the system over the second barrier and to transform the bcc nuclei into the stable hcp/fcc phase. The transitions are dominated by the first liquid-bcc transition and can be described by Classical Nucleation Theory using an effective surface tension.
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