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Search Results: 1 - 10 of 121903 matches for " Felix T. Schmitt "
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Ultracold Bose gases in time-dependent 1D superlattices: response and quasimomentum structure
Markus Hild,Felix Schmitt,Ilona Türschmann,Robert Roth
Physics , 2007, DOI: 10.1103/PhysRevA.76.053614
Abstract: The response of ultracold atomic Bose gases in time-dependent optical lattices is discussed based on direct simulations of the time-evolution of the many-body state in the framework of the Bose-Hubbard model. We focus on small-amplitude modulations of the lattice potential as implemented in several recent experiment and study different observables in the region of the first resonance in the Mott-insulator phase. In addition to the energy transfer we investigate the quasimomentum structure of the system which is accessible via the matter-wave interference pattern after a prompt release. We identify characteristic correlations between the excitation frequency and the quasimomentum distribution and study their structure in the presence of a superlattice potential.
Influence of forest and grassland management on the diversity and conservation of butterflies and burnet moths (Lepidoptera, Papilionoidea, Hesperiidae, Zygaenidae)
Schmitt, T.
Animal Biodiversity and Conservation , 2003,
Abstract: The distribution of butterflies and burnet moths was investigated at 38 patches in the Oettinger Forst (Bavaria, Germany) in 2001. Forty-two butterfly and four burnet moth species were recorded. They were unequally distributed over the study area. The diversity was significantly lower in the forests than in the non forest patches. Windblows and meadows showed largely similar results but clearings had higher Shannon indices and Eveness and presented a trend to higher species numbers. The hay meadows had higher mean incidences of the 25 common species and exhibited a trend to higher numbers of individuals and species as well as higher mean Shannon indices than in the mulched meadows. The old quarries and sandpits harboured remarkable species, some of these occurring in high densities, thus underlining the conservation value of such structures in a non-target area for nature-conservation measurements.
Thickness-Dependent Coherent Phonon Frequency in Ultrathin FeSe/SrTiO$_{3}$ Films
Shuolong Yang,Jonathan A. Sobota,Dominik Leuenberger,Alexander F. Kemper,James J. Lee,Felix T. Schmitt,Wei Li,Rob G. Moore,Patrick S. Kirchmann,Zhi-Xun Shen
Physics , 2015, DOI: 10.1021/acs.nanolett.5b01274
Abstract: Ultrathin FeSe films grown on SrTiO$_{3}$ substrates are a recent milestone in atomic material engineering due to their important role in understanding unconventional superconductivity in Fe-based materials. Using femtosecond time- and angle-resolved photoelectron spectroscopy, we study phonon frequencies in ultrathin FeSe/SrTiO$_{3}$ films grown by molecular beam epitaxy. After optical excitation, we observe periodic modulations of the photoelectron spectrum as a function of pump-probe delay for 1 unit cell, 3 unit cell, and 60 unit cell thick FeSe films. The frequencies of the coherent intensity oscillations increase from 5.00(2) to 5.25(2) THz with increasing film thickness. By comparing with previous works, we attribute this mode to the Se A$_\textrm{1g}$ phonon. The dominant mechanism for the phonon softening in 1 unit cell thick FeSe films is a substrate-induced lattice strain. Our results demonstrate an abrupt phonon renormalization due to a lattice mismatch between the ultrathin film and the substrate.
Phase Diagram of Bosons in Two-Color Superlattices from Experimental Parameters
Felix Schmitt,Markus Hild,Robert Roth
Physics , 2009, DOI: 10.1103/PhysRevA.80.023621
Abstract: We study the zero-temperature phase diagram of a gas of bosonic 87-Rb atoms in two-color superlattice potentials starting directly from the experimental parameters, such as wavelengths and intensities of the two lasers generating the superlattice. In a first step, we map the experimental setup to a Bose-Hubbard Hamiltonian with site-dependent parameters through explicit band-structure calculations. In the second step, we solve the many-body problem using the density-matrix renormalization group (DMRG) approach and compute observables such as energy gap, condensate fraction, maximum number fluctuations and visibility of interference fringes. We study the phase diagram as function of the laser intensities s_2 and s_1 as control parameters and show that all relevant quantum phases, i.e. superfluid, Mott-insulator, and quasi Bose-glass phase, and the transitions between them can be investigated through a variation of these intensities alone.
Ab-initio phase diagram of ultracold 87-Rb in an one-dimensional two-color superlattice
Felix Schmitt,Markus Hild,Robert Roth
Physics , 2010,
Abstract: We investigate the ab-initio phase diagram of ultracold 87-Rb atoms in an one-dimensional two-color superlattice. Using single-particle band structure calculations we map the experimental setup onto the parameters of the Bose-Hubbard model. This ab-initio ansatz allows us to express the phase diagrams in terms of the experimental control parameters, i.e., the intensities of the lasers that form the optical superlattice. In order to solve the many-body problem for experimental system sizes we adopt the density-matrix renormalization-group algorithm. A detailed study of convergence and finite-size effects for all observables is presented. Our results show that all relevant quantum phases, i.e., superfluid, Mott-insulator, and quasi Bose-glass, can be accessed through intensity variation of the lasers alone. However, it turns out that the phase diagram is strongly affected by the longitudinal trapping potential.
Sharp Bounds in Stochastic Network Calculus
Florin Ciucu,Felix Poloczek,Jens Schmitt
Computer Science , 2013,
Abstract: The practicality of the stochastic network calculus (SNC) is often questioned on grounds of potential looseness of its performance bounds. In this paper it is uncovered that for bursty arrival processes (specifically Markov-Modulated On-Off (MMOO)), whose amenability to \textit{per-flow} analysis is typically proclaimed as a highlight of SNC, the bounds can unfortunately indeed be very loose (e.g., by several orders of magnitude off). In response to this uncovered weakness of SNC, the (Standard) per-flow bounds are herein improved by deriving a general sample-path bound, using martingale based techniques, which accommodates FIFO, SP, EDF, and GPS scheduling. The obtained (Martingale) bounds gain an exponential decay factor of ${\mathcal{O}}(e^{-\alpha n})$ in the number of flows $n$. Moreover, numerical comparisons against simulations show that the Martingale bounds are remarkably accurate for FIFO, SP, and EDF scheduling; for GPS scheduling, although the Martingale bounds substantially improve the Standard bounds, they are numerically loose, demanding for improvements in the core SNC analysis of GPS.
Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator Bi$_2$Se$_3$
Jonathan A. Sobota,Shuolong Yang,Alexander F. Kemper,J. J. Lee,Felix T. Schmitt,Wei Li,Robert G. Moore,James G. Analytis,Ian R. Fisher,Patrick S. Kirchmann,Thomas P. Devereaux,Zhi-Xun Shen
Physics , 2013, DOI: 10.1103/PhysRevLett.111.136802
Abstract: We characterize the occupied and unoccupied electronic structure of the topological insulator Bi$_2$Se$_3$ by one-photon and two-photon angle-resolved photoemission spectroscopy and slab band structure calculations. We reveal a second, unoccupied Dirac surface state with similar electronic structure and physical origin to the well-known topological surface state. This state is energetically located 1.5 eV above the conduction band, which permits it to be directly excited by the output of a Ti:Sapphire laser. This discovery demonstrates the feasibility of direct ultrafast optical coupling to a topologically protected, spin-textured surface state.
Editorial Theorie der Entwicklung – Entwicklung der Theorie Post-Development und Postkoloniale Theorien als Herausforderung für eine Geographische Entwicklungsforschung
M. Neuburger ,T. Schmitt
Geographica Helvetica (GH) , 2012,
Abstract: No abstract available.
Visualizing the Radiation of the Kelvin-Helmholtz Instability
Axel Huebl,David Pugmire,Felix Schmitt,Richard Pausch,Michael Bussmann
Physics , 2014, DOI: 10.1109/TPS.2014.2327392
Abstract: Emerging new technologies in plasma simulations allow tracking billions of particles while computing their radiative spectra. We present a visualization of the relativistic Kelvin-Helmholtz Instability from a simulation performed with the fully relativistic particle-in-cell code PIConGPU powered by 18,000 GPUs on the USA's fastest supercomputer Titan [1].
Software Design Principles of a DFS Tower A-CWP Prototype
Felix Schmitt,Ralf Heidger,Stephen Straub,Benjamin Wei?
Computer Science , 2013,
Abstract: SESAR is supposed to boost the development of new operational procedures together with the supporting systems in order to modernize the pan-European air traffic management (ATM). One consequence of this development is that more and more information is presented to - and has to be processed by - air traffic control officers (ATCOs). Thus, there is a strong need for a software design concept that fosters the development of an advanced (tower) controller working position (A-CWP) that comprehensively integrates the still counting amount of information while reducing the data management workload of ATCOs. We report on our first hands-on experiences obtained during the development of an A-CWP prototype that was used in two SESAR validation sessions.
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