Exponents of the localization lengths in the bipartite Anderson model with off-diagonal disorder

We investigate the scaling properties of the two-dimensional (2D) Anderson model of localization with purely off-diagonal disorder (random hopping). In particular, we show that for small energies the infinite-size localization lengths as computed from transfer-matrix methods together with finite-size scaling diverge with a power-law behavior. The corresponding exponents seem to depend on the strength and the type of disorder chosen.Comment: 6 pages, 8 EPS-figures, requires phbauth.cl

The importance of spring atmospheric conditions for predictions of the Arctic summer sea ice extent

Recent studies have shown that atmospheric processes in spring play an important role for the initiation of the summer ice melt and therefore may strongly influence the September sea ice concentration (SSIC). Here a simple statistical regression model based on only atmospheric spring parameters is applied in order to predict the SSIC over the major part of the Arctic Ocean. By using spring anomalies of downwelling longwave radiation or atmospheric water vapor as predictor variables, correlation coefficients between observed and predicted SSIC of up to 0.5 are found. These skills of seasonal SSIC predictions are similar to those obtained using more complex dynamical forecast systems, despite the fact that the simple model applied here takes neither information of the sea ice state, oceanic conditions nor feedback mechanisms during summer into account. The results indicate that a realistic representation of spring atmospheric conditions in the prediction system plays an important role for the predictive skills of a model system.Swedish Research Council FORMA

Optical Spin Initialization and Non-Destructive Measurement in a Quantum Dot Molecule

The spin of an electron in a self-assembled InAs/GaAs quantum dot molecule is optically prepared and measured through the trion triplet states. A longitudinal magnetic field is used to tune two of the trion states into resonance, forming a superposition state through asymmetric spin exchange. As a result, spin-flip Raman transitions can be used for optical spin initialization, while separate trion states enable cycling transitions for non-destructive measurement. With two-laser transmission spectroscopy we demonstrate both operations simultaneously, something not previously accomplished in a single quantum dot.Comment: Accepted for publication in Phys. Rev. Let

HF spectrum occupancy and antennas

This paper deals with the research made during the COST 296 action in the WG2, WP 2.3 in the antennas and HF spectrum management fields, focusing the Mitigation of Ionospheric Effects on Radio Systems as the subject of this COST action.info:eu-repo/semantics/publishedVersio

Nonrelativistic Particle in Free Random Gauge Background

The problem of a nonrelativistic particle with an internal color degree of freedom, with and without spin, moving in a free random gauge background is discussed. Freeness is a concept developed recently in the mathematical literature connected with noncommuting random variables. In the context of large-N hermitian matrices, it means that the the multi-matrix model considered contains no bias with respect to the relative orientations of the matrices. In such a gauge background, the spectrum of a colored particle can be solved for analytically. In three dimensions, near zero momentum, the energy distribution for the spinless particle displays a gap, while the energy distribution for the particle with spin does not.Comment: 20 pages, 6 figure

Morfología y filogenia del rDNA de una subespecie mediterránea de Coolia Monotis (Dinophyceae) de Grecia

Sequences of LSU and SSU ribosomal RNA genes and phylogeny have not been widely investigated for the dinoflagellate Coolia monotis Meunier, and no information is available on the small and large rDNA subunits of Mediterranean strains. A strain isolated from the Thermaikos Gulf in northern Greece was identified as C. monotis—a new record for the Greek algal flora—using thecal morphology by light, epifluorescence and scanning electron microscopy. The small subunit and partial (D1/D2) large subunit sequences were analyzed and compared to other strains of C. monotis and dinoflagellates from various regions. Thecal architecture showed that the Greek strain of C. monotis was phenotypically similar, but not identical, to other strains reported in literature. The partial LSU sequence (700 bp) was found to vary by 113 bp positions (16%) from the C. monotis strain from New Zealand, whereas the SSU (1757 bp) had 15 bp differences (0.85%) from the strain from Norway. Phylogenetic tree construction showed that the Greek strain fell within the Coolia clade and had a close relationship with the families Ostreopsidaceae and Goniodomaceae of the order Gonyaulacales. Preliminary findings suggest the existence of different genotype strains of C. monotis with large intraspecific genetic variability and minimal morphological differentiation (similar phenotypes). Certain ecological and evolutionary implications of these findings are discussed.Las secuencias de los genes del RNA de las subunidades ribosomales grandes y pequeñas (LSU y SSU, respectivamente) y la filogenia del dinoflagelado Coolia monotis Meunier han sido poco investigadas, y no hay información disponible sobre los genes LSU y SSU de subespecies mediterráneas. Una subespecie aislada del golfo de Thermaikos en el norte de Grecia fue identificada como C. monotis –una nueva aportación a la flora algal griega– por medio de la morfología de la teca observada a través de microscopía óptica, de epifluorescia y electrónica. Las secuencias correspondientes a la subunidad pequeña y a la parte (D1/D2) de la subunidad grande fueron analizadas y comparadas a las de otras subespecies de C. monotis y otras especies de dinoflagelados de diversas regiones. La arquitectura de la teca mostró que la subespecie griega de C. monotis era fenotípicamente similar, pero no idéntica, a otras subespecies registradas en la literatura. Se encontró que la secuencia parcial de la LSU (700 pares de bases o bp) difería de la de C. monotis de Nueva Zelanda en las posiciones de 113 bp (16%), mientras que la SSU (1757 bp) se diferenciaba en 15 bp (0.85%) de la subespecie de Noruega. La construcción del árbol filogenetico demostró que la subespecie griega se situaba dentro de la rama de Coolia y presentaba una relación cercana con las familias Ostreopsidaceae y Goniodomaceae del orden Gonyaulacales. Resultados preliminares sugieren la existencia de diversos genotipos de la subespecie de C. monotis con una importante variabilidad genética intraespecífica y una mínima diferenciación morfológica (fenotipos similares). Se comentan diversas implicaciones ecológicas y evolutivas de estos resultados

Fock space localization, return probability, and conductance of disordered interacting electrons

We numerically simulate the low-energy properties of interacting electrons in a random potential using the Hartree-Fock based exact diagonalization method. In particular, we investigate how the transport properties are influenced by the combined effects of disorder and correlations in the presence of the electron spin. To this end we calculate the participation number of many-particle states in Fock space, the return probability of single-particle excitations, and the Kubo-Greenwood conductance. It turns out that in the strongly localized regime interactions increase the conductance whereas for weak disorder interactions decrease the conductance. In contrast, single-particle excitations in general experience a localizing influence of the interactions.Comment: 4 pages, 4 eps figures, Proc. of the Symposium on Wave Propagation and Electronic Structure in Disordered Systems, FORTH, Heraklion, Crete, Greece (June 2000

Characterization of Mott-insulating and superfluid phases in the one-dimensional Bose--Hubbard model

We use strong-coupling perturbation theory, the variational cluster approach (VCA), and the dynamical density-matrix renormalization group (DDMRG) method to investigate static and dynamical properties of the one-dimensional Bose--Hubbard model in both the Mott-insulating and superfluid phases. From the von Neumann entanglement entropy we determine the central charge and the transition points for the first two Mott lobes. Our DMRG results for the ground-state energy, momentum distribution function, boson correlation function decay, Mott gap, and single particle-spectral function are reproduced very well by the strong-coupling expansion to fifth order, and by VCA with clusters up to 12 sites as long as the ratio between the hopping amplitude and on-site repulsion, t/U, is smaller than 0.15 and 0.25, respectively. In addition, in the superfluid phase VCA captures well the ground-state energy and the sound velocity of the linear phonon modes. This comparison provides an authoritative estimate for the range of applicability of these methods. In strong-coupling theory for the Mott phase, the dynamical structure factor is obtained from the solution of an effective single-particle problem with an attractive potential. The resulting resonances show up as double-peak structure close to the Brillouin zone boundary. These high-energy features also appear in the superfluid phase which is characterized by a pronounced phonon mode at small momenta and energies, as predicted by Bogoliubov and field theory. In one dimension, there are no traces of an amplitude mode in the dynamical single-particle and two-particle correlation functions.Comment: 15 pages, 12 figure

Ion energy distributions in inductively coupled plasmas having a biased boundary electrode

In many plasma materials processing applications requiring energetic ion bombardment such as plasma etching, control of the time-averaged ion energy distributions (IEDs) to surfaces is becoming increasingly important to discriminate between surface processes having different threshold energies. Inductively coupled plasmas (ICPs) are attractive in this regard since the plasma potential is low and so the energy of ion fluxes can be more finely tuned with externally applied biases. In these situations, pulsed plasmas provide another level of control as the IEDs from different times during the pulse power period can be combined to create the desired time-averaged IED. A recent development in controlling of IEDs in ICPs is the use of a boundary electrode (BE) in which a continuous or pulsed dc bias is applied to shift the plasma potential and modify the IEDs to surfaces without significant changes in the bulk plasma properties. Combinations of pulsing the ICP power and the BE bias provide additional flexibility to craft IEDs. In this paper we discuss results from a computational investigation of IEDs to a grounded substrate in low-pressure (a few to 50 mTorr) ICPs sustained in argon. Results are compared with experimental measurements of plasma properties and IEDs. We demonstrate the ability to customize IEDs consisting of three energy peaks corresponding to the plasma potential during the plasma active glow, plasma afterglow and the plasma potential with the applied boundary voltage.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98615/1/0963-0252_21_6_065009.pd

Decision Analysis for Management of Natural Hazards

Losses from natural hazards, including geophysical and hydrometeorological hazards, have been increasing worldwide. This review focuses on the process by which scientific evidence about natural hazards is applied to support decision making. Decision analysis typically involves estimating the probability of extreme events; assessing the potential impacts of those events from a variety of perspectives; and evaluating options to plan for, mitigate, or react to events. We consider issues that affect decisions made across a range of natural hazards, summarize decision methodologies, and provide examples of applications of decision analysis to the management of natural hazards. We conclude that there is potential for further exchange of ideas and experience between natural hazard research communities on decision analysis approaches. Broader application of decision methodologies to natural hazard management and evaluation of existing decision approaches can potentially lead to more efficient allocation of scarce resources and more efficient risk management