Two-particle localization and antiresonance in disordered spin and qubit chains

We show that, in a system with defects, two-particle states may experience destructive quantum interference, or antiresonance. It prevents an excitation localized on a defect from decaying even where the decay is allowed by energy conservation. The system studied is a qubit chain or an equivalent spin chain with an anisotropic ($XXZ$) exchange coupling in a magnetic field. The chain has a defect with an excess on-site energy. It corresponds to a qubit with the level spacing different from other qubits. We show that, because of the interaction between excitations, a single defect may lead to multiple localized states. The energy spectra and localization lengths are found for two-excitation states. The localization of excitations facilitates the operation of a quantum computer. Analytical results for strongly anisotropic coupling are confirmed by numerical studies.Comment: Updated version, 13 pages, 5 figures To appear in Phys. Rev. B (2003

Reionization: Characteristic Scales, Topology and Observability

Recently the numerical simulations of the process of reionization of the universe at z>6 have made a qualitative leap forward, reaching sufficient sizes and dynamic range to determine the characteristic scales of this process. This allowed making the first realistic predictions for a variety of observational signatures. We discuss recent results from large-scale radiative transfer and structure formation simulations on the observability of high-redshift Ly-alpha sources. We also briefly discuss the dependence of the characteristic scales and topology of the ionized and neutral patches on the reionization parameters.Comment: 4 pages, 5 figures (4 in color), to appear in Astronomy and Space Science special issue "Space Astronomy: The UV window to the Universe", proceedings of 1st NUVA Conference ``Space Astronomy: The UV window to the Universe'' in El Escorial (Spain

Review of lobomycosis and lobomycosis-like disease (LLD) in Cetacea from South America. Scientific Committee document SC/60/DW13, International Whaling Commission, June 2008, Santiago, Chile

Caused by a yeast-like organism known as Lacazia loboi, Lobomycosis (or lacaziosis) naturally affects humans, common bottlenose dolphins (Tursiops truncates) inhabiting coastal waters from southern Brazil to Gulf of Mexico and Atlantic coast of Florida, as well as botos-cinza (Sotalia guianensis). These species are usually found in coastal waters, subject to runoff provided by large rivers and a considerable burden of associated contaminants. Histological and morphological studies demonstrated that the etiological agent of L. loboi infecting humans is different from the one found to infected dolphins. Moreover, it likely that dolphin-human infections do not occur although infected bottlenose dolphins were from populations engaged in cooperative fishing that involve a relative small number of dolphins and humans. The records of Lobomycosis and Lobomycosis-like disease (LLD) in Tramandaí estuary (29o58´S), Rio Grande do Sul, Brazil, represent the southernmost distribution of L. loboi. On the other hand, the northernmost distribution of this disease is reported in the southern portion of Indian River Lagoon (27°25´N), Florida, USA. LLD seems to be more widespread, infecting both toothed small cetaceans and baleen whales, from the tropical Atlantic to the Pacific. Future studies should evaluate the association with impaired immune function in affected dolphins and the emergency of Lobomycosis. It may be associated with an immunosuppressive factor of environmental origin, such as exposure to pesticides or other agricultural or industrial contaminants, introduced through runoff or point sources of pollution, altering conditions to favour disease emergence. Lobomycosis should be assigned as neglected tropical disease, as should be the case of LLD, if future investigations indicate their connection as an emerging pathogen, its pathogenicity and environment requirements

Probing Primordial Non-Gaussianity with Large-Scale Structure

We consider primordial non-Gaussianity due to quadratic corrections in the gravitational potential parametrized by a non-linear coupling parameter fnl. We study constraints on fnl from measurements of the galaxy bispectrum in redshift surveys. Using estimates for idealized survey geometries of the 2dF and SDSS surveys and realistic ones from SDSS mock catalogs, we show that it is possible to probe |fnl|~100, after marginalization over bias parameters. We apply our methods to the galaxy bispectrum measured from the PSCz survey, and obtain a 2sigma-constraint |fnl|< 1800. We estimate that an all sky redshift survey up to z~1 can probe |fnl|~1. We also consider the use of cluster abundance to constrain fnl and find that in order to be sensitive to |fnl|~100, cluster masses need to be determined with an accuracy of a few percent, assuming perfect knowledge of the mass function and cosmological parameters.Comment: 15 pages, 7 figure

Exact steady state solution of the Boltzmann equation: A driven 1-D inelastic Maxwell gas

The exact nonequilibrium steady state solution of the nonlinear Boltzmann equation for a driven inelastic Maxwell model was obtained by Ben-Naim and Krapivsky [Phys. Rev. E 61, R5 (2000)] in the form of an infinite product for the Fourier transform of the distribution function $f(c)$. In this paper we have inverted the Fourier transform to express $f(c)$ in the form of an infinite series of exponentially decaying terms. The dominant high energy tail is exponential, $f(c)\simeq A_0\exp(-a|c|)$, where $a\equiv 2/\sqrt{1-\alpha^2}$ and the amplitude $A_0$ is given in terms of a converging sum. This is explicitly shown in the totally inelastic limit ($\alpha\to 0$) and in the quasi-elastic limit ($\alpha\to 1$). In the latter case, the distribution is dominated by a Maxwellian for a very wide range of velocities, but a crossover from a Maxwellian to an exponential high energy tail exists for velocities $|c-c_0|\sim 1/\sqrt{q}$ around a crossover velocity $c_0\simeq \ln q^{-1}/\sqrt{q}$, where $q\equiv (1-\alpha)/2\ll 1$. In this crossover region the distribution function is extremely small, $\ln f(c_0)\simeq q^{-1}\ln q$.Comment: 11 pages, 4 figures; a table and a few references added; to be published in PR

Skin diseases in cetaceans. Scientific Committee document SC/60/DW8, International Whaling Commission, June 2008, Santiago, Chile

Micro-organisms that are known or suspected to cause skin diseases in cetaceans are briefly reviewed. Viruses belonging to four families i.e. Caliciviridae, Herpesviridae, Papillomaviridae and Poxviridae were detected by electron microscopy, histology and molecular techniques in vesicular skin lesions, black dots perceptible by the touch, warts and tattoos in several species of odontocetes and mysticetes. Herpesviruses, poxviruses and likely a cutaneous papillomavirus are cetacean specific. Among bacteria, Dermatophilus spp., Erysipelothrix rhusiopathiae, Mycobacterium marinum, Pseudomonas spp., Streptococcus iniae and Vibrio spp. were isolated from ulcerative dermatitis, pyogranulomatous dermatitis and panniculitis, diamond skin disease and slow-healing ulcers and abscesses. Aeremonas spp., Mycobacterium marinum, Pseudomonas spp. and Vibrio spp. are normally present in the marine environment while Erysipelothrix rhusiopathiae and Streptococcus iniae are fish pathogens that may also infect captive dolphins. Most seem to be opportunistic pathogens, exploiting some break-down in the host’s defenses to initiate an infection. Selection of antibiotic-resistant bacteria through the prophylactic use of antibiotics in aquaculture is suggested to be a growing problem in South America and may account for the emergence of unusual cutaneous conditions. At least four groups of fungi i.e. Candida albicans, Fusarium spp., Trichophyton spp. and Lacazia loboi cause skin diseases. Candidiasis occurs predominantly in captive odontocetes. The lesions are often localized around the body orifices and may become extensive, granulating and ulcerated. Fusariosis is characterized by firm, erythematous, cutaneous nodules. Trichophyton spp. was isolated from widespread superficial nodules in an Atlantic T. truncates kept in captivity in Japan. Lobomycosis or lacaziosis is distinguished by grayish, whitish to slightly pink, verrucuous lesions, often in pronounced relief that may ulcerate. While initially described only in Tursiops truncates and Sotalia guianensis from the Americas, lobomycosis seems to be expanding to other continents. The role of ballast water in transporting fungi worldwide should be investigated. Finally, ciliated protozoans, likely Kyaroikeus cetarius, caused invasive dermatitis in small cetaceans from the USA and Korea. The aquatic environment of cetaceans is naturally home to bacteria and fungi but cetacean skin has several mechanisms to impede invasion. Chemical contaminants may affect natural skin barriers and depress the immune system. Wounds and specific viral infection (poxvirus, herpesvirus) may provide routes of entry

Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{$6\times 10^{19}$eV}. The anisotropy was measured by the fraction of arrival directions that are less than $3.1^\circ$ from the position of an active galactic nucleus within 75 Mpc (using the V\'eron-Cetty and V\'eron $12^{\rm th}$ catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating fraction is $(38^{+7}_{-6})$, compared with $21$ expected for isotropic cosmic rays. This is down from the early estimate of $(69^{+11}_{-13})$. The enlarged set of arrival directions is examined also in relation to other populations of nearby extragalactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-rays by the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has the largest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation function is shown for the enlarged set of arrival directions and compared to the isotropic expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201

Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory

Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle Physic

Measurement of D*+/- meson production in jets from pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

This paper reports a measurement of D*+/- meson production in jets from proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample recorded with the ATLAS detector with an integrated luminosity of 0.30 pb^-1 for jets with transverse momentum between 25 and 70 GeV in the pseudorapidity range |eta| < 2.5. D*+/- mesons found in jets are fully reconstructed in the decay chain: D*+ -> D0pi+, D0 -> K-pi+, and its charge conjugate. The production rate is found to be N(D*+/-)/N(jet) = 0.025 +/- 0.001(stat.) +/- 0.004(syst.) for D*+/- mesons that carry a fraction z of the jet momentum in the range 0.3 < z < 1. Monte Carlo predictions fail to describe the data at small values of z, and this is most marked at low jet transverse momentum.Comment: 10 pages plus author list (22 pages total), 5 figures, 1 table, matches published version in Physical Review

Nonlinear Integer Programming

Research efforts of the past fifty years have led to a development of linear integer programming as a mature discipline of mathematical optimization. Such a level of maturity has not been reached when one considers nonlinear systems subject to integrality requirements for the variables. This chapter is dedicated to this topic. The primary goal is a study of a simple version of general nonlinear integer problems, where all constraints are still linear. Our focus is on the computational complexity of the problem, which varies significantly with the type of nonlinear objective function in combination with the underlying combinatorial structure. Numerous boundary cases of complexity emerge, which sometimes surprisingly lead even to polynomial time algorithms. We also cover recent successful approaches for more general classes of problems. Though no positive theoretical efficiency results are available, nor are they likely to ever be available, these seem to be the currently most successful and interesting approaches for solving practical problems. It is our belief that the study of algorithms motivated by theoretical considerations and those motivated by our desire to solve practical instances should and do inform one another. So it is with this viewpoint that we present the subject, and it is in this direction that we hope to spark further research.Comment: 57 pages. To appear in: M. J\"unger, T. Liebling, D. Naddef, G. Nemhauser, W. Pulleyblank, G. Reinelt, G. Rinaldi, and L. Wolsey (eds.), 50 Years of Integer Programming 1958--2008: The Early Years and State-of-the-Art Surveys, Springer-Verlag, 2009, ISBN 354068274