Dynamical properties of a nonequilibrium quantum dot close to localized-delocalized quantum phase transitions

We calculate the dynamical decoherence rate and susceptibility of a nonequilibrium quantum dot close to the delocalized-to-localized quantum phase transitions. The setup concerns a resonance-level coupled to two spinless fermionic baths with a finite bias voltage and an Ohmic bosonic bath representing the dissipative environment. The system is equivalent to an anisotropic Kondo model. As the dissipation strength increases, the system at zero temperature and zero bias show quantum phase transition between a conducting delocalized phase to an insulating localized phase. Within the nonequilibrium functional Renormalization Group (FRG) approach, we address the finite bias crossover in dynamical decoherence rate and charge susceptibility close to the phase transition. We find the dynamical decoherence rate increases with increasing frequency. In the delocalized phase, it shows a singularity at frequencies equal to positive or negative bias voltage. As the system crossovers to the localized phase, the decoherence rate at low frequencies get progressively smaller and this sharp feature is gradually smeared out, leading to a single linear frequency dependence. The dynamical charge susceptibility shows a dip-to-peak crossover across the delocalized-to-localized transition. Relevance of our results to the experiments is discussed.Comment: 7 pages, 7 figure

Bistability and instability of dark-antidark solitons in the cubic-quintic nonlinear Schroedinger equation

We characterize the full family of soliton solutions sitting over a background plane wave and ruled by the cubic-quintic nonlinear Schroedinger equation in the regime where a quintic focusing term represents a saturation of the cubic defocusing nonlinearity. We discuss existence and properties of solitons in terms of catastrophe theory and fully characterize bistability and instabilities of the dark-antidark pairs, revealing new mechanisms of decay of antidark solitons.Comment: 8 pages, 10 figures, accepted in PR

Technology transfer - A selected bibliography

Selected bibliography on technology transfe

Sequential deformation of plains along Tessera boundaries on Venus: Evidence from Alpha Regio

Tesserae are regions of elevated terrain characterized by two or more sets of ridges and grooves that intersect orthogonally. Tesserae comprise 15-20 percent of the surface of Venus, but the nature of their formation and evolution is not well understood; processes proposed to account for their characteristics are many and varied. Two types of tessera boundaries have been described: type 1 are generally embayed by plains; and type 2 boundaries are characterized by being linear at the 100-km scale and often associated with steep scarps or tectonic features. Margins such as the western edge of Alpha have been described as type 2. Some of the tessera have boundaries that display deformation of both the edge of the tessera and the adjoining plains. This study focuses on the western edge of Alpha Regio in an effort to characterize on occurrence of this type of boundary and assess the implications of the style in general. Using Magellan SAR imagery, lineament lengths, orientations, and spacing were measured for ten 50 x 60 km areas spanning 500 km of the western boundary. Structural characteristics and orientations were compared to stratigraphic units in order to assess the sequence and style of deformation

Connections of the Mesencephalic Locomotor Region (MLR) in the Cat

The cat entopeduncular nucleus (EN), which is the main output of the basal ganglia, is known to project to the mesencephalic tegmentum. We have been able to elicit antidromic responses in single EN neurons from the region of the mesencephalic locomotor region (MLR), then transect (precollicular-postmamillary) the brainstem and elicit rhythmic movements of the limbs by stimulation of the same site in the same animal. Injections of the fluorescent dye 2,4 diamidino phenylindole 2 HCL (DAPI) into this area induces retrograde labeling of cell bodies in EN and motor cortex. Injections of a tritiated amino acid (leucine) into the motor cortex induce terminal labeling in the area of the MLR. These studies describe convergent projections from EN and motor cortex to the MLR. These connections may be involved in the sequencing and ordering of voluntary movements in which locomotion is necessary

Faint dwarf galaxies in nearby clusters

Besides giant elliptical galaxies, a number of low-mass stellar systems inhabit the cores of galaxy clusters, such as dwarf elliptical galaxies (dEs/dSphs), ultra-compact dwarf galaxies (UCDs), and globular clusters. The detailed morphological examination of faint dwarf galaxies has, until recently, been limited to the Local Group (LG) and the two very nearby galaxy clusters Virgo and Fornax. Here, we compare the structural parameters of a large number of dEs/dSphs in the more distant clusters Hydra I and Centaurus to other dynamically hot stellar systems.Comment: 2 pages, 1 figure; to appear in "A Universe of Dwarf Galaxies: Observations, Theories, Simulations", held in Lyon, France (June 14-18, 2010), eds. M. Koleva, P. Prugniel & I. Vauglin, EAS Series (Paris: EDP

Entanglement and the Phase Transition in Single Mode Superradiance

We consider the entanglement properties of the quantum phase transition in the single-mode superradiance model, involving the interaction of a boson mode and an ensemble of atoms. For infinite system size, the atom-field entanglement of formation diverges logarithmically with the correlation length exponent. Using a continuous variable representation, we compare this to the divergence of the entropy in conformal field theories, and derive an exact expression for the scaled concurrence and the cusp-like non-analyticity of the momentum squeezing.Comment: 4 pages, 2 figue

Alternative determinism principle for topological analysis of chaos

The topological analysis of chaos based on a knot-theoretic characterization of unstable periodic orbits has proved a powerful method, however knot theory can only be applied to three-dimensional systems. Still, the core principles upon which this approach is built, determinism and continuity, apply in any dimension. We propose an alternative framework in which these principles are enforced on triangulated surfaces rather than curves and show that in dimension three our approach numerically predicts the correct topological entropies for periodic orbits of the horseshoe map.Comment: Accepted for publication as Rapid Communication in Physical Review

Extragalactic Background Light and Gamma-Ray Attenuation

Data from (non-) attenuation of gamma rays from active galactic nuclei (AGN) and gamma ray bursts (GRBs) give upper limits on the extragalactic background light (EBL) from the UV to the mid-IR that are only a little above the lower limits from observed galaxies. These upper limits now rule out some EBL models and purported observations, with improved data likely to provide even stronger constraints. We present EBL calculations both based on multiwavelength observations of thousands of galaxies and also based on semi-analytic models, and show that they are consistent with these lower limits from observed galaxies and with the gamma-ray upper limit constraints. Such comparisons "close the loop" on cosmological galaxy formation models, since they account for all the light, including that from galaxies too faint to see. We compare our results with those of other recent works, and discuss the implications of these new EBL calculations for gamma ray attenuation. Catching a few GRBs with groundbased atmospheric Cherenkov Telescope (ACT) arrays or water Cherenkov detectors could provide important new constraints on the high-redshift star formation history of the universe.Comment: 12 pages, 8 multi-panel figures, Invited talk at the 25th Texas Symposium on Relativistic Astrophysics, Heidelberg December 6-10, 201