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Search Results: 1 - 10 of 34244 matches for " Thomas Stephan "
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Controlled Release of Construction Chemicals by Encapsulation  [PDF]
Henning von Daake, Thomas Ballweg, Dietmar Stephan
Journal of Encapsulation and Adsorption Sciences (JEAS) , 2016, DOI: 10.4236/jeas.2016.61002
Abstract: Encapsulation and controlled release of active agents is a common practice to improve processing and properties of materials and final products in different industries. Today, a large variety of chemical admixtures are used in construction materials, the performance of which could be improved by a better dosage control. This work presents investigations on the controlled release of encapsulated construction chemicals for future applications in construction materials. The high shear mixing technology was used to produce matrix based encapsulations by agglomeration applied to commercially available construction materials. The agglomeration process was varied by the use of different agitator types, the variation of the agitator speed and the application of additional coating materials. The particle size distribution as well as the particle shape of the produced agglomerates was analyzed by automatic image evolution and scanning electron microscopy. The release behavior of the capsules in aqueous solutions was investigated by UV spectroscopy. The obtained results confirmed a theoretical model for the encapsulation and release of admixtures, which was derived from pharmaceutical drug release concepts and adapted to construction materials. The results indicate that the matrix based encapsulation is a promising technique for future applications in the field of construction materials.
Year in review 2009: Critical Care - infection
Stephan Harbarth, Thomas Haustein
Critical Care , 2010, DOI: 10.1186/cc9268
Abstract: The year 2009 was again an interesting one for readers interested in the field of infection in critically ill patients. Several promising new approaches for the prevention of infections in the intensive care unit (ICU) setting were presented. Furthermore, progress was noted in the difficult area of antimicrobial stewardship and risk stratification of infected patients. Finally, several challenges related to influenza infections and the management of difficult-to-treat infections were tackled or better delineated [1]. The present short review will summarise the results of a selection of original studies, with a special focus on articles published in Critical Care in 2009.New insights were reported regarding the epidemiology of infection in ICUs. A global, observational study (EPIC II) on the prevalence and outcomes of infection in 1,265 ICUs was conducted in 75 countries in May 2007. Among the 13,796 patients, 9,084 (66%) patients received an antimicrobial agent and 7,087 (51%) patients were considered infected at the time of data collection [2]. Unfortunately, owing to methodological limitations, no clear-cut distinction could be made between community-associated and healthcare-associated infections. Among those patients who had stayed longer than 7 days in the ICU prior to the study day, however, more than 70% were infected, mostly with multidrug-resistant organisms (MDROs). A clear association was noted between prevalence of infection and hospital mortality, with Greece and Turkey having the highest mortality and Switzerland the lowest [2].Since this type of prevalence study does not allow one to draw any strong causal inferences between infection rates and excess mortality due to ICU-acquired infections, longitudinal cohort studies with more sophisticated analyses have to be conducted. For instance, a recent French ICU-based case-control study matched 1,725 deceased patients with 1,725 surviving control patients to determine the excess mortality related to ICU-ac
Variational Cluster Approximation to the Thermodynamics of Quantum Spin Systems
Stephan Filor,Thomas Pruschke
Physics , 2014, DOI: 10.1088/1367-2630/16/6/063059
Abstract: We derive a variational cluster approximation for Heisenberg spin systems at finite temperature based on the ideas of the self-energy functional theory by Potthoff for fermionic and bosonic systems with local interactions. Partitioning the real system into a set of clusters, we find an analytical expression for the auxiliary free energy, depending on a set of variational parameters defined on the cluster, whose stationary points provide approximate solutions from which the thermodynamics of spin models can be obtained. We explicitly describe the technical details of how to evaluate the free energy for finite clusters and remark on specific problems and possible limitations of the method. To test the approximation we apply it to the antiferromagnetic spin 1/2 chain and compare the results for varying cluster sizes and choices of variational parameters with the exact Bethe ansatz solution.
Intrinsic Means on the Circle: Uniqueness, Locus and Asymptotics
Thomas Hotz,Stephan Huckemann
Statistics , 2011,
Abstract: This paper gives a comprehensive treatment of local uniqueness, asymptotics and numerics for intrinsic means on the circle. It turns out that local uniqueness as well as rates of convergence are governed by the distribution near the antipode. In a nutshell, if the distribution there is locally less than uniform, we have local uniqueness and asymptotic normality with a rate of 1 / \surdn. With increased proximity to the uniform distribution the rate can be arbitrarly slow, and in the limit, local uniqueness is lost. Further, we give general distributional conditions, e.g. unimodality, that ensure global uniqueness. Along the way, we discover that sample means can occur only at the vertices of a regular polygon which allows to compute intrinsic sample means in linear time from sorted data. This algorithm is finally applied in a simulation study demonstrating the dependence of the convergence rates on the behavior of the density at the antipode.
Production of Gravitational Waves in the nMSSM
Huber, Stephan J.;Konstandin, Thomas
High Energy Physics - Phenomenology , 2007, DOI: 10.1088/1475-7516/2008/05/017
Abstract: During a strongly first-order phase transition gravitational waves are produced by bubble collisions and turbulent plasma motion. We analyze the relevant characteristics of the electroweak phase transition in the nMSSM to determine the generated gravitational wave signal. Additionally, we comment on correlations between the production of gravitational waves and baryogenesis. We conclude that the gravitational wave relic density in this model is generically too small to be detected in the near future by the LISA experiment. We also consider the case of a "Standard Model" with dimension-six Higgs potential, which leads to a slightly stronger signal of gravitational waves.
Showing their true colors: a practical approach to volume rendering from serial sections
Stephan Handschuh, Thomas Schwaha, Brian D Metscher
BMC Developmental Biology , 2010, DOI: 10.1186/1471-213x-10-41
Abstract: Here we provide a set of protocols for acquiring high-resolution 3D images of diverse microscopic samples through volume rendering based on serial light microscopical sections using the 3D reconstruction software Amira (Visage Imaging Inc.). We overcome several technical obstacles and show that these renderings are comparable in quality and resolution to 3D visualizations using other methods. This practical approach for visualizing 3D micro-morphology in full color takes advantage of both the sub-micron resolution of light microscopy and the specificity of histological stains, by combining conventional histological sectioning techniques, digital image acquisition, three-dimensional image filtering, and 3D image manipulation and visualization technologies.We show that this method can yield "true"-colored high-resolution 3D views of tissues as well as cellular and sub-cellular structures and thus represents a powerful tool for morphological, developmental, and comparative investigations. We conclude that the presented approach fills an important gap in the field of micro-anatomical 3D imaging and visualization methods by combining histological resolution and differentiation of details with 3D rendering of whole tissue samples. We demonstrate the method on selected invertebrate and vertebrate specimens, and propose that reinvestigation of historical serial section material may be regarded as a special benefit.Understanding developmental processes in this age of sophisticated genetic and functional analyses depends just as much on accurate knowledge of microscopic anatomy as it did in the time of classical embryology. Today, a broad assemblage of analysis and visualization techniques is used to generate, revise, and re-evaluate morphological data. Modern 3D imaging and visualization methods are yielding new insights by displaying morphological structures as well as gene expression patterns to micron or sub-micron resolutions (reviewed in [1]). Recently, different tomogr
Dissociation of ultracold molecules with Feshbach resonances
Stephan Dürr,Thomas Volz,Gerhard Rempe
Physics , 2004, DOI: 10.1103/PhysRevA.70.031601
Abstract: Ultracold molecules are associated from an atomic Bose-Einstein condensate by ramping a magnetic field across a Feshbach resonance. The reverse ramp dissociates the molecules. The kinetic energy released in the dissociation process is used to measure the widths of 4 Feshbach resonances in 87Rb. This method to determine the width works remarkably well for narrow resonances even in the presence of significant magnetic-field noise. In addition, a quasi-mono-energetic atomic wave is created by jumping the magnetic field across the Feshbach resonance.
Anelastic Versus Fully Compressible Turbulent Rayleigh-Bénard Convection
Jan Verhoeven,Thomas Wieseh?fer,Stephan Stellmach
Physics , 2015, DOI: 10.1088/0004-637X/805/1/62
Abstract: Numerical simulations of turbulent Rayleigh-B\'enard convection in an ideal gas, using either the anelastic approximation or the fully compressible equations, are compared. Theoretically, the anelastic approximation is expected to hold in weakly superadiabatic systems with $\epsilon = \Delta T / T_r \ll 1$, where $\Delta T$ denotes the superadiabatic temperature drop over the convective layer and $T_r$ the bottom temperature. Using direct numerical simulations, a systematic comparison of anelastic and fully compressible convection is carried out. With decreasing superadiabaticity $\epsilon$, the fully compressible results are found to converge linearly to the anelastic solution with larger density contrasts generally improving the match. We conclude that in many solar and planetary applications, where the superadiabaticity is expected to be vanishingly small, results obtained with the anelastic approximation are in fact more accurate than fully compressible computations, which typically fail to reach small $\epsilon$ for numerical reasons. On the other hand, if the astrophysical system studied contains $\epsilon\sim O(1)$ regions, such as the solar photosphere, fully compressible simulations have the advantage of capturing the full physics. Interestingly, even in weakly superadiabatic regions, like the bulk of the solar convection zone, the errors introduced by using artificially large values for $\epsilon$ for efficiency reasons remain moderate. If quantitative errors of the order of $10\%$ are acceptable in such low $\epsilon$ regions, our work suggests that fully compressible simulations can indeed be computationally more efficient than their anelastic counterparts.
Spin texture of generic helical edge states
Alexia Rod,Thomas L. Schmidt,Stephan Rachel
Physics , 2015,
Abstract: We study the spin texture of a generic helical liquid, the edge modes of a two-dimensional topological insulator with broken axial spin-symmetry. By considering honeycomb and square lattice realizations of topological insulators, we show that in all cases the generic behavior of a momentum-dependent rotation of the spin quantization axis is realized. Here we establish this mechanism also for disk geometries with continuous rotational symmetry. Finally, we demonstrate that the rotation of spin-quantization axis remains intact for arbitrary geometries, i.e. in the absence of any continuous symmetry. We also calculate the dependence of this rotation on the model and material parameters. Finally we propose a spectroscopy measurement which should directly reveal the rotation of the spin-quantization axis of the helical edge states.
Meson and Baryon dispersion relations with Brillouin fermions
Stephan Durr,Giannis Koutsou,Thomas Lippert
Physics , 2012, DOI: 10.1103/PhysRevD.86.114514
Abstract: We study the dispersion relations of mesons and baryons built from Brillouin quarks on one N_f=2 gauge ensemble provided by QCDSF. For quark masses up to the physical strange quark mass, there is hardly any improvement over the Wilson discretization, if either action is link-smeared and tree-level clover improved. For quark masses in the range of the physical charm quark mass, the Brillouin action still shows a perfect relativistic behavior, while the Wilson action induces severe cut-off effects. As an application we determine the masses of the \Omega_c^0, \Omega_{cc}^+ and \Omega_{ccc}^{++} baryons on that ensemble.
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