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Search Results: 1 - 10 of 3432 matches for " Tobias Gresch "
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Sequential resonant tunneling in quantum cascade lasers
Romain Terazzi,Tobias Gresch,Andreas Wittmann,Jér?me Faist
Physics , 2008, DOI: 10.1103/PhysRevB.78.155328
Abstract: A model of sequential resonant tunneling transport between two-dimensional subbands that takes into account explicitly elastic scattering is investigated. It is compared to transport measurements performed on quantum cascade lasers where resonant tunneling processes are known to be dominating. Excellent agreement is found between experiment and theory over a large range of current, temperature and device structures.
E-Commerce Business Models and Search Engine Dependency  [PDF]
Tobias Klatt
iBusiness (IB) , 2013, DOI: 10.4236/ib.2013.53B041

E-Commerce business models attracted a great deal of attention in the last years. An increasing number of bargains are realized via online transactions. However, some business models suffer distinctly under changes of search engine algorithms while others experience continuous stable traffic. This paper sheds light on the drivers of the unpunished e-commerce businesses based on a case-by-case analysis of 43 business models in the German Internet market. The analysis reveals that more stable business models are characterized by diversified customer arrivals which are obtained by a focused product management, multiple marketing channeling, freemium registration strategies and a subtle way to attract customer trust.

The Generalized wH Value  [PDF]
Tobias Hiller
Theoretical Economics Letters (TEL) , 2014, DOI: 10.4236/tel.2014.43034

In this note, we generalize the wHSh value [1] [2] for CO values.

Optimizing spin-orbit splittings in InSb Majorana nanowires
Alexey A. Soluyanov,Dominik Gresch,Roman M. Lutchyn,Bela Bauer,Chetan Nayak,Matthias Troyer
Physics , 2015,
Abstract: Semiconductor-superconductor heterostructures represent a promising platform for the detection of Majorana zero modes and subsequently the processing of quantum information using their exotic non-Abelian statistics. Theoretical modeling of such low-dimensional semiconductors is generally based on phenomenological effective models. However, a more microscopic understanding of their band structure and, especially, of the spin-orbit coupling of electrons in these devices is important for optimizing their parameters for applications in quantum computing. In this paper, we approach this problem by first obtaining a highly accurate effective tight-binding model from ab initio calculations in the bulk. This model is symmetrized and correctly reproduces both the band structure and the wavefunction character. It is then used to determine Dresselhaus and Rashba spin-orbit splittings induced by finite size effects and external electric field in zincblende InSb one- and two-dimensional nanostructures as a function of growth parameters. The method presented here enables reliable simulations of realistic devices, including those used to realize exotic topological states.
Type-II Weyl Semimetals
Alexey A. Soluyanov,Dominik Gresch,Zhijun Wang,QuanSheng Wu,Matthias Troyer,Xi Dai,B. Andrei Bernevig
Physics , 2015, DOI: 10.1038/nature15768
Abstract: Fermions in nature come in several types: Dirac, Majorana and Weyl are theoretically thought to form a complete list. Even though Majorana and Weyl fermions have for decades remained experimentally elusive, condensed matter has recently emerged as fertile ground for their discovery as low energy excitations of realistic materials. Here we show the existence of yet another particle - a new type of Weyl fermion - that emerges at the boundary between electron and hole pockets in a new type of Weyl semimetal phase of matter. This fermion was missed by Weyl in 1929 due to its breaking of the stringent Lorentz symmetry of high-energy physics. Lorentz invariance however is not present in condensed matter physics, and we predict that an established material, WTe$_2$, is an example of this novel type of topological semimetal hosting the new particle as a low energy excitation around a type-2 Weyl node. This node, although still a protected crossing, has an open, finite-density of states Fermi surface, likely resulting in a plethora physical properties very different from those of standard point-like Fermi surface Weyl points.
How Safe Is Conversion from Tacrolimus to Its Generic Drug?—A Single Center Experience  [PDF]
Tobias A. Marsen
Open Journal of Nephrology (OJNeph) , 2012, DOI: 10.4236/ojneph.2012.24012
Abstract: Background: Generically produced cyclosporine has long been approved in the treatment of organ transplant recipients and several publications have dealt with its use. For tacrolimus, however, very few data exist for safety and efficacy after conversion to its generic in kidney transplant recipients. Methods: In this single-center observational study, 14 kidney transplant carriers were converted to generic tacrolimus as part of aftercare, and graft function, fasting tacrolimus levels and the daily tacrolimus dose was pursued for up to 95 weeks. Results: Average drug doses changed from 3.64 ± 1.88 mg/day with the original to 3.33 ± 1.72 mg/day after conversion to generic tacrolimus (p = 0.33). Tacrolimus fasting levels were 6.23 ± 1.68 ng/ml before and 5.89 ± 1.15 ng/ml after conversion (p = 0.66). Average serum creatinine values of 2.26 ± 1.08 mg/dl after conversion did not differ from previous values of 1.99 ± 0.74 mg/dl (p = 0.15). Conclusions: These data support the assumption, that it is safe to convert stable kidney transplant patients from the original galenic formulation under close scrutiny to the generically produced substance. Conversion is easy to be implemented in the routine follow-up and thus represents an option in the therapy with calcineurin inhibitors, which will contribute to cost reduction in the health system.
Herbicidal Effects of Fungicides on Arable Weeds  [PDF]
Henning Nordmeyer, Tobias Koch
American Journal of Plant Sciences (AJPS) , 2014, DOI: 10.4236/ajps.2014.51006

In the present study, the herbicidal effects of two fungicides with the active ingredients expoxiconazole, fluxapyroxad, pyraclostrobin and fenpropimorph on the two arable weeds Lamium purpureum L. and Chenopodium album L. were investigated. The experiments were conducted in a climate chamber under defined conditions. Sowing pods were prepared and plants at the cotyledon leaf stage were pricked out in test pods. Fungicides were applied at six application rates: 0%, 12.5%, 25%, 50%, 100% and 200% of the maximum registered dose rate in Germany. Seven days after application, the first assessment was conducted, regarding growth stage, quantity of plants and visible plant damage. Fourteen days after application, the second and final assessment was conducted, regarding growth stage, quantity of plants, visible plant damage and the fresh weight of the plants. There were herbicidal effects of the fungicides, which were presumably due to the active ingredient epoxiconazole. Epoxiconazole has effects on enzymes that are dependent on cytochrome P-450 and inhibits sterol biosynthesis and probably gibberellin synthesis. By doing so, these fungicides have similar effects to plant growth regulators. Weed species showed differential sensitivities, contractions and growth inhibition and ED50-values were calculated. Notwithstanding the probably minor relevance of the present results in agricultural practice, some effects on arable weeds might result if fungicides are applied at an early growth stage in the field. In some cases, the crop-weed competition could be shifted to the benefit of the crop. Nevertheless, the results are interesting for the field of weed research and for the assessment of the ecotoxicology of fungicides.

Multi-Criteria Decision Analysis for Usage Based Optimization of Powertrains  [PDF]
Tobias Hellberg, Martin Meywerk
Engineering (ENG) , 2016, DOI: 10.4236/eng.2016.86029
Abstract: The electrification of powertrains leads to an increasing diversification of powertrain configurations. Each single configuration has its specific advantages which appear depending on the usage profile. To find the usage based optimal powertrain in consideration of a variety of evaluation criteria, the powertrains have to be optimized for the usage profile and characteristics have to be extracted from the usage profile. The carbon dioxide emissions of the optimized powertrains and usage based criteria are used in a multi-criteria decision analysis to determine the optimal powertrain for a specific usage profile. The description of characteristic maps forms the objective function of a minimization problem. The determined carbon dioxide emissions are one criterion in a multi-criteria decision process. All considered criteria are at least partly objective so that subjective ratings are eliminated as far as possible. The result is an optimized powertrain for a desired usage under the consideration of objective criteria that are extracted from the usage profile.
Gaussian approximations for stochastic systems with delay: chemical Langevin equation and application to a Brusselator system
Tobias Brett,Tobias Galla
Physics , 2013, DOI: 10.1063/1.4867786
Abstract: We present a heuristic derivation of Gaussian approximations for stochastic chemical reaction systems with distributed delay. In particular we derive the corresponding chemical Langevin equation. Due to the non-Markovian character of the underlying dynamics these equations are integro-differential equations, and the noise in the Gaussian approximation is coloured. Following on from the chemical Langevin equation a further reduction leads to the linear-noise approximation. We apply the formalism to a delay variant of the celebrated Brusselator model, and show how it can be used to characterise noise-driven quasi-cycles, as well as noise-triggered spiking. We find surprisingly intricate dependence of the typical frequency of quasi-cycles on the delay period.
Generating functionals and Gaussian approximations for interruptible delay reactions
Tobias Brett,Tobias Galla
Physics , 2015, DOI: 10.1103/PhysRevE.92.042105
Abstract: We develop a generating functional description of the dynamics of non-Markovian individual-based systems, in which delay reactions can be terminated before completion. This generalises previous work in which a path-integral approach was applied to dynamics in which delay reactions complete with certainty. We construct a more widely applicable theory, and from it we derive Gaussian approximations of the dynamics, valid in the limit of large, but finite population sizes. As an application of our theory we study predator-prey models with delay dynamics due to gestation or lag periods to reach the reproductive age. In particular we focus on the effects of delay on noise-induced cycles.
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