18,807 research outputs found
Weak disorder expansion for localization lengths of quasi-1D systems
A perturbative formula for the lowest Lyapunov exponent of an Anderson model on a strip is presented. It is expressed in terms of an energy-dependent doubly stochastic matrix, the size of which is proportional to the strip width. This matrix and the resulting perturbative expression for the Lyapunov exponent are evaluated numerically. Dependence on energy, strip width and disorder strength are thoroughly compared with the results obtained by the standard transfer matrix method. Good agreement is found for all energies in the band of the free operator and this even for quite large values of the disorder strength
Current reversal and exclusion processes with history-dependent random walks
A class of exclusion processes in which particles perform history-dependent
random walks is introduced, stimulated by dynamic phenomena in some biological
and artificial systems. The particles locally interact with the underlying
substrate by breaking and reforming lattice bonds. We determine the
steady-state current on a ring, and find current-reversal as a function of
particle density. This phenomenon is attributed to the non-local interaction
between the walkers through their trails, which originates from strong
correlations between the dynamics of the particles and the lattice. We
rationalize our findings within an effective description in terms of
quasi-particles which we call front barriers. Our analytical results are
complemented by stochastic simulations.Comment: 5 pages, 6 figure
Infrared luminescence of ZnO:Cu<sup>2+</sup>(d<sup>9</sup>)
The 2E(D)â 2T2(D) emission of substitutional Cu2+ in ZnO has been observed in the 3700â5800-cmâ1 spectral range under 50-keV electron-beam excitation at cryogenic temperatures. The excitation mechanisms of this cathodoluminescence are discussed and compared with concurrent photoluminescence experiments
Collective Diffusion and a Random Energy Landscape
Starting from a master equation in a quantum Hamiltonian form and a coupling
to a heat bath we derive an evolution equation for a collective hopping process
under the influence of a stochastic energy landscape. There results different
equations in case of an arbitrary occupation number per lattice site or in a
system under exclusion. Based on scaling arguments it will be demonstrated that
both systems belong below the critical dimension to the same universality
class leading to anomalous diffusion in the long time limit. The dynamical
exponent can be calculated by an expansion. Above the
critical dimension we discuss the differences in the diffusion constant for
sufficient high temperatures. For a random potential we find a higher mobility
for systems with exclusion.Comment: 15 pages, no figure
SPIRE imaging of Mâ82: Cool dust in the wind and tidal streams
Mâ82 is a unique representative of a whole class of galaxies, starbursts with superwinds, in the Very Nearby Galaxy Survey with Herschel. In addition, its interaction with the Mâ81 group has stripped a significant portion of its interstellar medium from its disk. SPIRE maps now afford better characterization of the far-infrared emission from cool dust outside the disk, and sketch a far more complete picture of its mass distribution and energetics than previously possible. They show emission coincident in projection with the starburst wind and in a large halo, much more extended than the PAH band emission seen with Spitzer. Some complex substructures coincide with the brightest PAH filaments, and others with tidal streams seen in atomic hydrogen. We subtract the far-infrared emission of the starburst and underlying disk from the maps, and derive spatially-resolved far-infrared colors for the wind and halo. We interpret the results in terms of dust mass, dust temperature, and global physical conditions. In particular, we examine variations in the dust physical properties as a function of distance from the center and the wind polar axis, and conclude that more than two thirds of the extraplanar dust has been removed by tidal interaction, and not entrained by the starburst wind
Characterization and evolution of organized shallow convection in the downstream North Atlantic trades
Four previously identified patterns of meso-scale cloud organization in the trades -- called Sugar, Gravel, Flowers and Fish -- are studied using long-term records of ground-based measurements, satellite observations and reanalyses. A neural network trained to detect these patterns is applied to satellite imagery to identify periods during which a particular pattern is over the Barbados Cloud Observatory. Surface based remote sensing at the observatory is composited and shows that the patterns can be distinguished by differences in cloud macro-physical structures. Variations in total cloudiness among the patterns are dominated by variations in cloud-top cloudiness. Cloud amount near cloud base varies little. Each pattern is associated with a distinct atmospheric environment whose characteristics are traced back to origins that are not solely within the trades. Sugar air-masses are characterized by weak winds and of tropical origin. Fish are driven by convergence lines originating from synoptical disturbances. Gravel and Flowers are most native to the trades, but distinguish themselves with slightly stronger winds and stronger subsidence in the first case and greater stability in the latter. These results suggest that due to the tight bound of the patterns to wind and air-mass origin, the patterns with the higher cloud fraction, Flowers and Fish, will be disfavoured in a warming climate with more equable sea-surface temperatures and fewer mid-latitudinal disturbances
The dust morphology of the elliptical Galaxy M86 with SPIRE
We present Herschel-SPIRE observations at 250â500âÎŒm of the giant elliptical galaxy Mâ86 and examine the distribution of the resolved cold dust emission and its relation with other galactic tracers. The SPIRE images reveal three dust components: emission from the central region; a dust lane extending north-south; and a bright emission feature 10âkpc to the south-east. We estimate that ~10^6âM_â of dust is spatially coincident with atomic and ionized hydrogen, originating from stripped material from the nearby spiral NGC 4438 due to recent tidal interactions with Mâ86. The gas-to-dust ratio of the cold gas component ranges from ~20â80. We discuss the different heating mechanisms for the dust features
Wigner Crystal in One Dimension
A one--dimensional gas of electrons interacting with long--range Coulomb
forces () is investigated. The excitation spectrum consists
of separate collective charge and spin modes, with the charge excitation
energies in agreement with RPA calculations. For arbitrarily weak Coulomb
repulsion density correlations at wavevector decay extremely slowly and
are best described as those of a one--dimensional Wigner crystal. Pinning of
the Wigner crystal then leads to the nonlinear transport properties
characteristic of CDW. The results allow a consistent interpretation of the
plasmon and spin excitations observed in one--dimensional semiconductor
structures, and suggest an interpretation of some of the observed features in
terms of ``spinons''. A possible explanation for nonlinear transport phenomena
is given.Comment: 10 pages, RevTe
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