3,452 research outputs found
Nonequilibrium dynamical mean-field theory for bosonic lattice models
We develop the nonequilibrium extension of bosonic dynamical mean field
theory (BDMFT) and a Nambu real-time strong-coupling perturbative impurity
solver. In contrast to Gutzwiller mean-field theory and strong coupling
perturbative approaches, nonequilibrium BDMFT captures not only dynamical
transitions, but also damping and thermalization effects at finite temperature.
We apply the formalism to quenches in the Bose-Hubbard model, starting both
from the normal and Bose-condensed phases. Depending on the parameter regime,
one observes qualitatively different dynamical properties, such as rapid
thermalization, trapping in metastable superfluid or normal states, as well as
long-lived or strongly damped amplitude oscillations. We summarize our results
in non-equilibrium "phase diagrams" which map out the different dynamical
regimes.Comment: 18 pages, 8 figure
Hund’s coupling driven photocarrier relaxation in the two-band Mott insulator
We study the relaxation dynamics of photocarriers in the paramagnetic Mott insulating phase of the half-filled two-band Hubbard model. Using nonequilibrium dynamical mean-field theory, we excite charge carriers across the Mott gap by a short hopping modulation, and simulate the evolution of the photodoped population within the Hubbard bands. We observe an ultrafast charge-carrier relaxation driven by the emission of local spin excitations with an inverse relaxation time proportional to the Hund's coupling. The photodoping generates additional side-bands in the spectral function, and for strong Hund's coupling, the photodoped population also splits into several resonances. The dynamics of the local many-body states reveals two effects, thermal blocking and kinetic freezing, which manifest themselves when the Hund's coupling becomes of the order of the temperature or the bandwidth, respectively. These effects, which are absent in the single-band Hubbard model, should be relevant for the interpretation of experiments on correlated materials with multiple active orbitals. In particular, the features revealed in the nonequilibrium energy distribution of the photocarriers are experimentally accessible, and provide information on the role of the Hund's coupling in these materials
Theory of photoinduced ultrafast switching to a spin-orbital ordered `hidden' phase
Photoinduced hidden phases are often observed in materials with intertwined
orders. Understanding the formation of these non-thermal phases is challenging
and requires a resolution of the cooperative interplay between different orders
on the ultrashort timescale. In this work, we demonstrate that non-equilibrium
photo-excitations can induce a state with spin-orbital orders entirely
different from the equilibrium state in the three-quarter-filled two-band
Hubbard model. We identify a general mechanism governing the transition to the
hidden state, which relies on a non-thermal partial melting of the intertwined
orders mediated by photoinduced charge excitations in the presence of strong
spin-orbital exchange interactions. Our study theoretically confirms the
crucial role played by orbital degrees of freedom in the light-induced dynamics
of strongly correlated materials and it shows that the switching to hidden
states can be controlled already on the fs timescale of the electron dynamics
Die Eisenbahnbrücken des Lehrter Bahnhofs in Berlin - Ein ganzheitliches FE-Berechnungskonzept
Der Komplexität moderner Brückenbauwerke scheinen die verwendeten Berechungsmodelle oft nicht angemessen. Tragwerksberechnungen basieren in vielen Fällen noch auf der Vorgehensweise, das Brückenbauwerk in Einzelbauteile zu zerlegen und mit unterschiedlichen Teilmodellen zu behandeln. Das erscheint, auch vor dem Hintergrund ständig wachsender Rechnerleistung, nicht mehr zeitgemäß. Dies gilt zum Beispiel auch für die gängige Praxis, flächenhafte Brückenüberbauten mit Balkenmodellen zu berechnen. Der vorliegende Beitrag stellt ein ganzheitliches Berech-nungskonzept vor, welches auf der Basis eines einzigen FE-Modells die Berechnung des Gesamtbauwerks erlaubt. Damit wird für alle Bauteile neben der Zustandsgrößenberechnung auch die Bemessung von Stahl- und Spannbetonbauteilen bis hin zu Nachweisen wie zur Beschränkung der Rissbreite geführt. Die Anwendung dieses Berechnungskonzeptes wird am Beispiel der Eisenbahnüberführung des neuen Lehrter Bahn-hofs in Berlin gezeigt. Das verwendete FE-Modell umfasst Baugrund, Fundamente, Stahl- bzw. Gußstahlunterkonstruktion sowie den Stahl- bzw. Spannbetonüberbau. Besonderheiten sind unter anderem die Modellierung des plattenbalkenartigen Überbaus durch exzentrische, vorspannbare Schalenelemente und das getrennte Vorhalten von tragwerks- und lastbezogenen Eingabefiles. Damit gelingt die sequentielle Erfassung unterschiedlicher Bettungsmoduli zur Simulation statischer und dynamischer Beanspruchungen, die Berücksichtigung des Anspannens und der Interaktion zwischen vorgespannten Stahlverbänden zur Aufnahme von Horizontallasten sowie die Berücksichtigung unterschiedlicher statischer Systeme bei der Herstellung des Spannbetonüberbaus
Enhanced pairing susceptibility in a photodoped two-orbital Hubbard model
Local spin fluctuations provide the glue for orbital-singlet spin-triplet pairing in the doped Mott insulating regime of multiorbital Hubbard models. At large Hubbard repulsion U, the pairing susceptibility is nevertheless tiny because the pairing interaction cannot overcome the suppression of charge fluctuations. Using nonequilibrium dynamical mean field simulations of the two-orbital Hubbard model, we show that out of equilibrium the pairing susceptibility in this large-U regime can be strongly enhanced by creating a photoinduced population of the relevant charge states. This enhancement is supported by the long lifetime of photodoped charge carriers and a built-in cooling mechanism in multiorbital Hubbard systems
A digitally printed optoelectronic nose for the selective trace detection of nitroaromatic explosive vapours using fluorescence quenching
We report on a fluorescent optoelectronic nose for the trace detection of nitroaromatic explosive vapours. The sensor arrays, fabricated by aerosol-jet printing, consist of six different commercially available polymers as transducers. We assess the within-batch reproducibility of the printing process and we report that the sensor polymers show efficient fluorescence quenching capabilities with detection limits of a few parts-per-billion in air. We further demonstrate the nose\u27s ability to discriminate between several nitroaromatics including nitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene at three different concentrations using linear discriminant analysis. Our approach enables the realization of highly integrated optical sensor arrays in optoelectronic noses for the sensitive and selective detection of nitroaromatic explosive trace vapours using a potentially low-cost digital printing technique suitable for high-volume fabrication
Resistenzmechanismen von Tumoren gegen Platinkomplexe: Neue Drug Targets und diagnostische Marker
The ARGUS Vertex Trigger
A fast second level trigger has been developed for the ARGUS experiment which
recognizes tracks originating from the interaction region. The processor
compares the hits in the ARGUS Micro Vertex Drift Chamber to 245760 masks
stored in random access memories. The masks which are fully defined in three
dimensions are able to reject tracks originating in the wall of the narrow
beampipe of 10.5\,mm radius.Comment: gzipped Postscript, 27 page
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