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Search Results: 1 - 10 of 31405 matches for " Thomas Walther "
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On the $b$-functions of hypergeometric systems
Thomas Reichelt,Christian Sevenheck,Uli Walther
Mathematics , 2015,
Abstract: For any integer $d\times (n+1)$ matrix $A$ and parameter $\beta\in\CC^d$ let $M_A(\beta)$ be the associated $A$-hypergeometric (or GKZ) system in the variables $x_0,\ldots,x_n$. We describe bounds for the (roots of the) $b$-function for restriction of both $M_A(\beta)$ and its Fourier transform to the hyperplanes $(x_j=0)$.
Visions beyond Control: The Role of Art in Exploring Dual-Use Bioethics Education for Scientists  [PDF]
Gerald Walther
Creative Education (CE) , 2013, DOI: 10.4236/ce.2013.412A2006
Abstract: In the wake of the anthrax attacks in the US in 2001, the Biological Weapons Convention has increasingly focused its efforts on reducing the risk of bioterrorism. One of the questions that received particular attention was how to prevent the misuse of benign biological research for malign purposes. The argument is that modern biological research is rife with research that is dual-use in nature, i.e. that it can be used either for benign or malign purposes. Over the last decade, the debate has increasingly focussed on the role and responsibility of the scientific community in addressing this issue. Education in dual-use ethics has been considered as one of the major factors that can help with the dual-use problem. However, even general science ethics education is limited at the moment and presents a challenge to any lecturer. In discussing the views of Martin Heidegger and Richard Rorty’s interpretation of Heidegger, this article argues for the use of art and bioart as educational vehicles to help scientists explore their roles and responsibilities with regard to their own research and its dual-use nature.
Remote Water Temperature Measurements Based on Brillouin Scattering with a Frequency Doubled Pulsed Yb:doped Fiber Amplifier
Kai Schorstein,Alexandru Popescu,Marco G?bel,Thomas Walther
Sensors , 2008, DOI: 10.3390/s8095820
Abstract: Temperature profiles of the ocean are of interest for weather forecasts, climate studies and oceanography in general. Currently, mostly in situ techniques such as fixed buoys or bathythermographs deliver oceanic temperature profiles. A LIDAR method based on Brillouin scattering is an attractive alternative for remote sensing of such water temperature profiles. It makes it possible to deliver cost-effective on-line data covering an extended region of the ocean. The temperature measurement is based on spontaneous Brillouin scattering in water. In this contribution, we present the first water temperature measurements using a Yb:doped pulsed fiber amplifier. The fiber amplifier is a custom designed device which can be operated in a vibrational environment while emitting narrow bandwidth laser pulses. The device shows promising performance and demonstrates the feasibility of this approach. Furthermore, the current status of the receiver is briefly discussed; it is based on an excited state Faraday anomalous dispersion optical filter.
Implantación transapical de la válvula aórtica
Roberto Battellini,Thomas Walther,J?rg Kempfert,Michael Borger
Revista Argentina de Cardiología , 2009,
Abstract: El reemplazo valvular aórtico por estenosis es notoriamente alto, hasta un 30% en poblaciones estudiadas, lo cual implica en determinados grupos un riesgo quirúrgico elevado. En este artículo se describe la implantación transapical de la válvula, un procedimiento miniinvasivo y en principio sin circulación extracorpórea. Se indica preferentemente en pacientes ancianos con alto riesgo operatorio, en aquellos con aortas gravemente calcificadas y en otros con revascularizaciones coronarias previas. El estudio de la geometría aórtica es esencial: la ecocardiografía transesofágica da la mejor medida del diámetro de la raíz aórtica y la tomografía computarizada determina exactamente el diámetro del anillo y tiene la posibilidad agregada de medir la distancia desde el anillo a los ostia coronarios. Se debe contar con la posibilidad de circulación extracorpórea en carácter de stand-by. Por una peque a toracotomía anterolateral se accede a la punta del corazón donde se cateteriza el ventrículo hacia la posición aórtica con control radioscópico. La valvuloplastia, la inserción de la vaina transapical y el posicionamiento de la prótesis son las maniobras siguientes. El posicionamiento de la válvula constituye el paso más crítico, pero con esta técnica es más eficaz. En los últimos casos, mediante el software denominado DYNA CT, se han logrado mejores perspectivas en un punto crucial para el desarrollo definitivo. Desde febrero de 2006 hasta diciembre 2008 se implantaron 192 válvulas por vía transapical en pacientes con una edad media de 82,5 ± 5,7 a os. La mortalidad a los 30 días fue del 8,9% y en el seguimiento alejado a 256 ± 213 días fue del 12,8%. Esta técnica debe ser realizada en un quirófano híbrido por un equipo especializado y debidamente entrenado de cirujanos, cardiólogos y anestesistas para obtener resultados óptimos.REV ARGENT CARDIOL 2009;77:96-100.
Is reduced-density-matrix functional theory a suitable vehicle to import explicit correlations into density-functional calculations?
Peter E. Bloechl,Christian F. J. Walther,Thomas Pruschke
Physics , 2011, DOI: 10.1103/PhysRevB.84.205101
Abstract: A variational formulation for the calculation of interacting fermion systems based on the density-matrix functional theory is presented. Our formalism provides for a natural integration of explicit many-particle effects into standard density-functional-theory based calculations and it avoids ambiguities of double-counting terms inherent to other approaches. Like the dynamical mean-field theory, we employ a local approximation for explicit correlations. Aiming at the ground state only, trade some of the complexity of Green's function based many-particle methods against efficiency. Using short Hubbard chains as test systems we demonstrate that the method captures ground state properties, such as left-right-correlation, beyond those accessible by mean-field theories.
Grand-Canonical Quantized Liquid Density-Functional Theory in a Car-Parrinello Implementation
Christian F. J. Walther,Serguei Patchkovskii,Thomas Heine
Physics , 2013, DOI: 10.1063/1.4813122
Abstract: Quantized Liquid Density-Functional Theory [Phys. Rev. E 2009, 80, 031603], a method developed to assess the adsorption of gas molecules in porous nanomaterials, is reformulated within the grand canonical ensemble. With the grand potential it is possible to compare directly external and internal thermodynamic quantities. In our new implementation, the grand potential is minimized utilizing the Car-Parrinello approach and gives, in particular for low temperature simulations, a significant computational advantage over the original canonical approaches. The method is validated against original QLDFT, and applied to model potentials and graphite slit pores.
Efficient Estimation of Band Gaps in Transition-Metal Oxides and Chalcogenides using Density Functional Theory
Wenqing Li,Christian F. J. Walther,Agnieszka Kuc,Thomas Heine
Physics , 2013,
Abstract: The performance of two modern density-functionals, HSE06 and TB-mBJ, on predicting electronic structures of metal oxides, chalcogenides and nitrides, is studied in terms of band gaps, band structure and projected density-of-states. Contrary to GGA, hybrid functionals and GGA+U, both new functionals are able to predict band gaps with an appreciable accuracy of 25% and thus allow the screening of various classes of (mixed) metal oxides at modest computational cost. The calculated electronic structures are largely unaffected by the choice of basis functions and software implementation.
Hydrogen adsorption in metal-organic frameworks: the role of nuclear quantum effects
Mohammad Wahiduzzaman,Christian F. J. Walther,Thomas Heine
Physics , 2014, DOI: 10.1063/1.4892670
Abstract: The role of nuclear quantum effects on the adsorption of molecular hydrogen in metal-organic frameworks (MOFs) has been investigated on grounds of Grand-Canonical Quantized Liquid Density-Functional Theory (GC-QLDFT) calculations. For this purpose, we have carefully validated classical H2 -host interaction potentials that are obtained by fitting Born-Oppenheimer ab initio reference data. The hydrogen adsorption has first been assessed classically using Liquid Density-Functional Theory (LDFT) and the Grand-Canonical Monte Carlo (GCMC) methods. The results have been compared against the semi-classical treatment of quantum effects by applying the Feynman-Hibbs correction to the Born-Oppenheimer-derived potentials, and by explicit treatment within the Grand-Canonical Quantized Liquid Density-Functional Theory (GC-QLDFT). The results are compared with experimental data and indicate pronounced quantum and possibly many-particle effects. After validation calculations have been carried out for IRMOF-1 (MOF-5), GC-QLDFT is applied to study the adsorption of H2 in a series of MOFs, including IRMOF-4, -6, -8, -9, -10, -12, -14, -16, -18 and MOF-177. Finally, we discuss the evolution of the H2 quantum fluid with increasing pressure and lowering temperature.
Feasibility of UV lasing without inversion in mercury vapor
Martin R. Sturm,Benjamin Rein,Thomas Walther,Reinhold Walser
Physics , 2014, DOI: 10.1364/JOSAB.31.001964
Abstract: We investigate the feasibility of UV lasing without inversion at a wavelength of $253.7$ nm utilizing interacting dark resonances in mercury vapor. Our theoretical analysis starts with radiation damped optical Bloch equations for all relevant 13 atomic levels. These master equations are generalized by considering technical phase noise of the driving lasers. From the Doppler broadened complex susceptibility we obtain the stationary output power from semiclassical laser theory. The finite overlap of the driving Gaussian laser beams defines an ellipsoidal inhomogeneous gain distribution. Therefore, we evaluate the intra-cavity field inside a ring laser self-consistently with Fourier optics. This analysis confirms the feasibility of UV lasing and reveals its dependence on experimental parameters.
Engineering and Characterization of an Enhanced Fluorescent Protein Voltage Sensor
Dimitar Dimitrov, You He, Hiroki Mutoh, Bradley J. Baker, Lawrence Cohen, Walther Akemann, Thomas Kn?pfel
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0000440
Abstract: Background Fluorescent proteins have been used to generate a variety of biosensors to optically monitor biological phenomena in living cells. Among this class of genetically encoded biosensors, reporters for membrane potential have been a particular challenge. The use of presently known voltage sensor proteins is limited by incorrect subcellular localization and small or absent voltage responses in mammalian cells. Results Here we report on a fluorescent protein voltage sensor with superior targeting to the mammalian plasma membrane and high responsiveness to membrane potential signaling in excitable cells. Conclusions and Significance This biosensor, which we termed VSFP2.1, is likely to lead to new methods of monitoring electrically active cells with cell type specificity, non-invasively and in large numbers, simultaneously.
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