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Search Results: 1 - 10 of 2305 matches for " Axel Bruchhausen "
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Critical coupling to Tamm plasmons
Baptiste Auguie,Axel Bruchhausen,Alejandro Fainstein
Physics , 2014, DOI: 10.1088/2040-8978/17/3/035003
Abstract: The conditions of critical coupling of light to Tamm plasmons are investigated with comprehensive numerical simulations, highlighting the parameters that maximise absorption of incident light in the metal layer. The asymmetric response in reflection and absorption with respect to the direction of incidence is discussed, the two cases yielding different optimal coupling conditions. These findings are relevant for the design of optimised Tamm structures, particularly in applications such as narrow-band thermal emitters, field-enhanced spectroscopy and refractive-index sensing.
Health Care between Medicine and Religion : The Case of Catholic Western Germany around 1800
Bruchhausen, Walter
Hygiea Internationalis : an Interdisciplinary Journal for the History of Public Health , 2007,
Abstract: The current revision of the relationship between religion and medicine in the ‘post-secular’ or ‘desecularised’ society invites a new look on their function for each other at the beginning of the modern era, i.e. the political and economic secularisation during the dissolution of the Ancient Empires in Europe. Exemplified by the Prince-Archbishoprics of Western Germany, the consequences of the church’s change from state power to mere pastoral care are demonstrated for the three groups of Catholic physicians in academic medicine, priests in rural health care and nuns in nursing. During the turn from the enlightenment idea of religion serving medicine to the romantic concept of medicine contributing to religion their activities shifted dramatically: Whereas more members of religious congregations entered nursing than before, priests had to give up any medical work and Christian doctors were forced to cope with the separation between academic medicine and the religious world view.
Observation of Zone-Folded Acoustic Phonons in Terahertz Quantum Cascade Lasers using Picosecond Ultrasonics
Axel Bruchhausen,Mike Hettich,James Lloyd-Hughes,Milan Fischer,Mattias Beck,Giacomo Scalari,Jér?me Faist,Thomas Dekorsy
Physics , 2010,
Abstract: We have investigated the time-resolved vibrational properties of terahertz quantum cascade lasers by means of ultra-fast laser spectroscopy. By the observation of the acoustic folded branches, and by analyzing the involved phonon modes it is possible to extract accurate structural information of these devices, which are essential for their design and performance.
Green’s Function Approach to the Bose-Hubbard Model  [PDF]
Matthias Ohliger, Axel Pelster
World Journal of Condensed Matter Physics (WJCMP) , 2013, DOI: 10.4236/wjcmp.2013.32020

We use a diagrammatic hopping expansion to calculate finite-temperature Green functions of the Bose-Hubbard model which describes bosons in an optical lattice. This technique allows for a summation of subsets of diagrams, so the divergence of the Green function leads to non-perturbative results for the boundary between the superfluid and the Mott phase for finite temperatures. Whereas the first-order calculation reproduces the seminal mean-field result, the second order goes beyond and shifts the phase boundary in the immediate vicinity of the critical parameters determined by high-precision Monte-Carlo simulations of the Bose-Hubbard model. In addition, our Greens function approach allows for calculating the excitation spectrum both for zero and finite temperature and for determining the effective masses of particles and holes.

In-Situ Hydroelectrothermal Deposition of Silicate Layers on Stainless Steel Surfaces  [PDF]
Jaybalan Tamahrajah, Axel Brehm
Advances in Materials Physics and Chemistry (AMPC) , 2015, DOI: 10.4236/ampc.2015.59038
Abstract: The deposition of zeolites on solid support materials is possible by means of electrochemical methods, impregnation processes, as well as in-situ syntheses. Electrochemical deposition of zeolites has been reported as well, however with readily synthesized zeolite structures. Adhesive deposition of zeolites on stainless steel (S316) has been reported. This report investigates the feasibility of the deposition of silicates by in-situ hydroelectrothermal means. The investigation was done in aqueous solutions of pH = 7 to 13 at different temperatures (25°C to 70°C) by linear sweep method. Deposition was done at a saturated H2 atmosphere to ensure prior deposition of thin iron oxide film on the surface and formation of Fe-O-Si-linkages. This was proven by Raman measurement of the samples. Further linear sweep experiments in the presence of silica show monodentate and bidentate Fe-O-Si linkages on the surface, proven by IR-measurements. Presence of dissolved silica was done by UV-Vis with the molybdate yellow method. The best results are achieved at 70°C at pH 13 and ﹣4 mV (vs Ag/AgCl) or 200 mV (vs SHE). Discontinuous homogeneous layers are found on the stainless steel surface observed by SEM, EDX measurements and electrochemical measurements. Layer discontinuties are caused due to low silica concentration at equilibrium hydrothermal conditions, especially in the absence of silicic acid. All results shown are for the best results achieved except for linear sweep measurements and solubility constants of dissolved silica.
Confinement of acoustical vibrations in a semiconductor planar phonon cavity
M. Trigo,A. Bruchhausen,A. Fainstein,B. Jusserand,V. Thierry-Mieg
Physics , 2002, DOI: 10.1103/PhysRevLett.89.227402
Abstract: Extending the idea of optical microcavities to sound waves, we propose a {\it phonon cavity} consisting of two semiconductor superlattices enclosing a spacer with thickness determined by the acoustic wavelength at the center of the first zone-center folded minigap. We show that acoustical phonons can be confined in these layered structures, and propose Raman experiments which are able to probe these novel excitations. The Raman experiments take profit of an optical microcavity scattering geometry that, through the forward-scattering contribution, gives access to the zone-center excitations. We report experimental results of Raman scattering in a structure based in GaAs/AlAs materials that demonstrate unambiguously the observation of phonon cavity confined acoustical vibrations. The experimental results compare precisely with photoelastic model calculations of the Raman spectra of the proposed phonon-cavity embedded optical microcavity.
Cavity polariton optomechanics: Polariton path to fully resonant dispersive coupling in optomechanical resonators
G. Rozas,A. E. Bruchhausen,A. Fainstein,B. Jusserand,A. Lema?tre
Physics , 2014, DOI: 10.1103/PhysRevB.90.201302
Abstract: Resonant photoelastic coupling in semiconductor nanostructures opens new perspectives for strongly enhanced light-sound interaction in optomechanical resonators. One potential problem, however, is the reduction of the cavity Q-factor induced by dissipation when the resonance is approached. We show in this letter that cavity-polariton mediation in the light-matter process overcomes this limitation allowing for a strongly enhanced photon-phonon coupling without significant lifetime reduction in the strongly-coupled regime. Huge optomechanical coupling factors in the PetaHz/nm range are envisaged, three orders of magnitude larger than the backaction produced by the mechanical displacement of the cavity mirrors.
Polariton-mediated Raman scattering in microcavities: A Green's function approach
L. M. Leon Hilario,A. A. Aligia,A. M. Lobos,A. Bruchhausen
Physics , 2009, DOI: 10.1016/j.spmi.2007.07.013
Abstract: We present calculations of the intensity of polariton-mediated inelastic light scattering in semiconductor microcavities within a Green's function framework. In addition to reproducing the strong coupling of light and matter, this method also enables the inclusion of damping mechanisms in a consistent way. Our results show excellent agreement with recent Raman scattering experiments.
Theory of polariton mediated Raman scattering in microcavities
L. M. Leon Hilario,A. Bruchhausen,A. M. Lobos,A. A. Aligia
Physics , 2007, DOI: 10.1088/0953-8984/19/176210
Abstract: We calculate the intensity of the polariton mediated inelastic light scattering in semiconductor microcavities. We treat the exciton-photon coupling nonperturbatively and incorporate lifetime effects in both excitons and photons, and a coupling of the photons to the electron-hole continuum. Taking the matrix elements as fitting parameters, the results are in excellent agreement with measured Raman intensities due to optical phonons resonant with the upper polariton branches in II-VI microcavities with embedded CdTe quantum wells.
Nuclear Power and Radioactive Contamination  [PDF]
Nils-Axel M?rner
Journal of Environmental Protection (JEP) , 2014, DOI: 10.4236/jep.2014.53021

Nuclear power was designed to produce electric power. Each part of the chain from uranium mining to handling of the waste is linked to serious contamination risks, however. Uranium mining is generally linked to local to regional contamination. The fuel production also produces depleted uranium at a ratio of 1:7. The reactors are operating under danger of accidents. Numerous minor accidents and endless temporary shut-downs are occasionally mixed with disastrous accidents. The Chernobyl (1986) and Fukushima (2011) accidents are notorious. The radioactive contamination from those accidents is still incomprehensible and will keep serious destructions of the environment for centuries to come. The handling of the high-level nuclear waste remains unsolved. Methods proposed in Sweden, Finland and France seem likely to lead to disastrous radioactive contaminations in the future. The only way out of this dilemma seems to be a disposal where the waste, though effectively sealed-off in the bedrock, remains accessible and controllable. At present, the “cost & benefit” balance seems strongly tilted over to the “far too costly side”, however.

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