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Search Results: 1 - 10 of 18208 matches for " Christian Hagelüken "
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Recycling of gold from electronics: Cost-effective use through ‘Design for Recycling’
Christian Hagelüken,Christopher W Corti
Gold Bulletin , 2010, DOI: 10.1007/BF03214988
Abstract: The importance of the gold content of scrap electronics to the economics of recovery of gold and many other valuable metals is not always appreciated and this impacts on the “design for recycling” approach in selecting materials for new products, particularly in the European Union where the WEEE Directive aims to provide a closed loop economy. With a lower carbon footprint than primary-mined gold, recycled gold represents an important “green” source. The challenges faced in recycling electronic scrap to achieve a closed loop economy are discussed.
Surgical Treatment for Neonatal Hydrocephalus: Catheter-Based Cerebrospinal Fluid Diversion or Endoscopic Intervention?  [PDF]
Matthias Krause, Christos P. Panteliadis, Christian Hagel, Franz W. Hirsch, Ulrich H. Thome, Jürgen Meixensberger, Ulf Nestler
Open Journal of Modern Neurosurgery (OJMN) , 2018, DOI: 10.4236/ojmn.2018.81002
Abstract: Neonatal hydrocephalus can arise from a multitude of disturbances, among them congenital aqueductal stenosis, myelomeningocele or posthemorrhagic complications in preterm infants. Diagnostic work-up comprises transfontanellar ultrasonography, T2 weighted MRI and clinical assessment for rare inherited syndromes. Classification of hydrocephalus and treatment guidelines is based on detailed consensus statements. The recent evidence favors catheter-based cerebrospinal fluid diversion in children below 6 months, but emerging techniques such as neuroendoscopic lavage carry the potential to lower shunt insertion rates. More long-term study results will be needed to allow for individualized, multidisciplinary decision making. This article gives an overview regarding contemporary pathophysiological concepts, the latest consensus statements and most recent technical developments.
The Massive Dirac Equation in Kerr Geometry: Separability in Eddington-Finkelstein-Type Coordinates and Asymptotics
Christian R?ken
Physics , 2015,
Abstract: The separability of the massive Dirac equation in a rotating Kerr black hole background in horizon-penetrating advanced Eddington-Finkelstein-type coordinates is shown. To this end, the Kerr spacetime is described in the framework of the Newman-Penrose formalism by a local Carter tetrad, and the Dirac wave functions are given on a spin bundle in a chiral Newman-Penrose dyad representation. Applying mode analysis techniques, the Dirac equation is separated into coupled systems of radial and angular ordinary differential equations. Asymptotic radial solutions at infinity and the event and Cauchy horizons are explicitly derived and, by means of error estimates, the decay properties are analyzed. Solutions of the angular ordinary differential equations matching the Chandrasekhar-Page equation are discussed. These solutions are used in order to study the scattering of Dirac waves by the gravitational field of a Kerr black hole. This work provides the basis for a Hamiltonian formulation of the massive Dirac equation in a Kerr background in horizon-penetrating coordinates, for the spectral theory of the corresponding Dirac Hamiltonian, and for the construction of an integral representation of the Dirac propagator.
SL(2, C) and SU(2) Connection Variable Formulations of Kerr Isolated Horizon Geometries for Loop Quantum Gravity
Christian R?ken
Physics , 2013,
Abstract: A construction of both self-dual SL(2, C) and SU(2) connection variable formulations for the description of the degrees of freedom of classical, rotating Kerr isolated horizon geometries is presented. These descriptions are based on sets of connection Hamiltonian variables instead of the spacetime metric. The analysis is motivated in a concrete, physical manner based on the stationary, axisymmetric Kerr solution of the vacuum Einstein equations, evaluated in a proper, well-defined frame of reference, on which isolated horizon boundary conditions are imposed. Having derived the kinematical part of such an isolated horizon phase space setting, one can set up a conserved presymplectic structure for the study of dynamical aspects of black hole theory. Since black holes play a crucial role in various fields like quantum gravity, mathematical physics, astrophysics and cosmology, or numerical relativity, one has to deal with different models describing these objects. The quasi-local framework studied in this paper is appropriate for covering most of the physical settings involving black hole dynamics. Moreover, the SU(2) connection variable formulation of classical Kerr isolated horizons allows directly for a semiclassical treatment of rotating quantum black holes in the context of loop quantum gravity.
First-order quantum-gravitational correction to Friedmannian cosmology from covariant, holomorphic spinfoam cosmology
Christian R?ken
Physics , 2010, DOI: 10.1142/S0218271813500053
Abstract: The first-order loop quantum gravity correction of the simplest, classical general-relativistic Friedmann Hamiltonian constraint, emerging from a holomorphic spinfoam cosmological model peaked on homogeneous, isotropic geometries, is studied. The quantum Hamiltonian constraint, satisfied by the EPRL transition amplitude between the boundary cosmological coherent states, includes a contribution of the order of the Planck constant $\hbar$ that also appears in the corresponding semiclassical symplectic model. The analysis of this term gives a quantum-gravitational correction to the classical Friedmann dynamics of the scale factor yielding a small decelerating expansion (small accelerating contraction) of the universe. The robustness of the physical interpretation is established for arbitrary refinements of the boundary graphs. Also, mathematical equivalences between the semiclassical cosmological model and certain classical fluid and scalar field theories are explored.
On the Nature of Black Holes in Loop Quantum Gravity
Christian R?ken
Physics , 2012, DOI: 10.1088/0264-9381/30/1/015005
Abstract: A genuine notion of black holes can only be obtained in the fundamental framework of quantum gravity resolving the curvature singularities and giving an account of the statistical mechanical, microscopic degrees of freedom able to explain the black hole thermodynamical properties. As for all quantum systems, a quantum realization of black holes requires an operator algebra of the fundamental observables of the theory which is introduced in this study based on aspects of loop quantum gravity. From the eigenvalue spectra of the quantum operators for the black hole area, charge and angular momentum, it is demonstrated that a strict bound on the extensive parameters, different from the relation arising in classical general relativity, holds, implying that the extremal black hole state can neither be measured nor can its existence be proven. This is, as turns out, a result of the specific form of the chosen angular momentum operator and the corresponding eigenvalue spectrum, or rather the quantum measurement process of angular momentum. Quantum mechanical considerations and the lowest, non-zero eigenvalue of the loop quantum gravity black hole mass spectrum indicate, on the one hand, a physical Planck scale cutoff of the Hawking temperature law and, on the other hand, give upper and lower bounds on the numerical value of the Immirzi parameter. This analysis provides an approximative description of the behavior and the nature of quantum black holes.
Self-Adjointness of the Dirac Hamiltonian for a Class of Non-Uniformly Elliptic Boundary Value Problems
Felix Finster,Christian R?ken
Mathematics , 2015,
Abstract: We consider a boundary value problem for the Dirac equation in a four-dimensional, smooth, asymptotically flat Lorentzian manifold admitting a Killing field which is timelike near and tangential to the boundary. A self-adjoint extension of the Dirac Hamiltonian is constructed. Our results also apply to the situation that the space-time includes horizons, where the Hamiltonian fails to be elliptic.
Nestin Modulates Glucocorticoid Receptor Function by Cytoplasmic Anchoring
Rudolph Reimer, Heike Helmbold, Beata Szalay, Christian Hagel, Heinrich Hohenberg, Wolfgang Deppert, Wolfgang Bohn
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0006084
Abstract: Nestin is the characteristic intermediate filament (IF) protein of rapidly proliferating progenitor cells and regenerating tissue. Nestin copolymerizes with class III IF-proteins, mostly vimentin, into heteromeric filaments. Its expression is downregulated with differentiation. Here we show that a strong nestin expression in mouse embryo tissue coincides with a strong accumulation of the glucocorticoid receptor (GR), a key regulator of growth and differentiation in embryonic development. Microscopic studies on cultured cells show an association of GR with IFs composed of vimentin and nestin. Cells lacking nestin, but expressing vimentin, or cells expressing vimentin, but lacking nestin accumulate GR in the nucleus. Completing these networks with an exogenous nestin, respectively an exogenous vimentin restores cytoplasmic anchoring of GR to the IF system. Thus, heteromeric filaments provide the basis for anchoring of GR. The reaction pattern with phospho-GR specific antibodies and the presence of the chaperone HSC70 suggest that specifically the unliganded receptor is anchored to the IF system. Ligand addition releases GR from IFs and shifts the receptor into the nucleus. Suppression of nestin by specific shRNA abolishes anchoring of GR, induces its accumulation in the nucleus and provokes an irreversible G1/S cell cycle arrest. Suppression of GR prior to that of nestin prevents entry into the arrest. The data give evidence that nestin/vimentin specific anchoring modulates growth suppression by GR. We hypothesize that expression of nestin is a major determinant in suppression of anti-proliferative activity of GR in undifferentiated tissue and facilitates activation of this growth control in a precise tissue and differentiation dependent manner.
Quantum plasma modification of the Lane-Emden equation for stellar structure
Reinhard Schlickeiser,Ian Lerche,Christian R?ken
Physics , 2012,
Abstract: The proper quantum plasma treatment of the electron gas in degenerate stars such as white dwarfs provides an additional quantum contribution to the electron pressure. The additional pressure term modifies the equation for hydrostatic equilibrium, resulting in the quantum modified Lane-Emden equation for polytropic equation of states. The additional pressure term also modifies the expression for the limiting Chandrasekhar mass of white dwarfs. An approximate solution is derived of the quantum modified Lane-Emden equation for general polytropic indices, and it is demonstrated that the quantum corrections reduce the standard Chandrasekhar mass and enhance the white dwarf radius by negligibly small values only.
An exact analytical solution for the interstellar magnetic field in the vicinity of the heliosphere
Christian R?ken,Jens Kleimann,Horst Fichtner
Physics , 2014, DOI: 10.1088/0004-637X/805/2/173
Abstract: An analytical representation of the interstellar magnetic field in the vicinity of the heliosphere is derived. The three-dimensional field structure close to the heliopause is calculated as a solution of the induction equation under the assumption that it is frozen into a prescribed plasma flow resembling the characteristic interaction of the solar wind with the local interstellar medium. The usefulness of this analytical solution as an approximation to self-consistent magnetic field configurations obtained numerically from the full MHD equations is illustrated by quantitative comparisons.
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