6,872 research outputs found
A rotating cylinder in an asymptotically locally anti-de Sitter background
A family of exact solutions is presented which represents a rigidly rotating
cylinder of dust in a background with a negative cosmological constant. The
interior of the infinite cylinder is described by the Godel solution. An exact
solution for the exterior solution is found which depends both on the rotation
of the interior and on its radius. For values of these parameters less than a
certain limit, the exterior solution is shown to be locally isomorphic to the
Linet-Tian solution. For values larger than another limit, it is shown that the
exterior solution extends into a region which contains closed timelike curves.
At large distances from the source, the space-time is shown to be asymptotic
locally to anti-de Sitter space.Comment: To appear in Classical and Quantum Gravit
Ocean stratification under oscillatory surface buoyancy forcing
Laboratory experiments with overturning circulation driven by oscillatory heat fluxes at one boundary are used to explore implications, for the ocean stratification, of a cyclic fluctuation in sea-surface buoyancy forcing. Fluctuations having a range of periods spanning the timescale for global recycling of the ocean volume through the thermocline are considered, with emphasis on inter-hemispheric \u27see-saw\u27 oscillations. Episodic sinking of dense water in the oceans is represented by convection in a channel with a base that is cooled over a central region and subjected to oscillatory heating near both ends, while providing a constant total heat input. For this simplified system the time-average interior temperature is found to be insensitive to the forcing period, but does vary with oscillation amplitude, whereas the interior fluctuations increase with forcing period. The circulation and density field are significantly different from those given by a steady forcing equal to the time-average of the actual oscillatory forcing, even for high-frequency oscillations. The results indicate that the overall stratification lies between that expected from the strongest phase of deep sinking and that given by symmetric sinking in both hemispheres. Glacial cycles are predicted to involve significant temperature fluctuations in the abyssal ocean. However, they are too short for the ocean to remain in quasi-equilibrium with the changing boundary conditions
Wake Flows in Coastal Oceans: An Experimental Study of Topographic Effects
We consider the effects of coastal topography on the wake of an idealised headland model in a laboratory flume. Under a range of Reynolds numbers relevant to coastal oceans, we find that coherent eddies interact strongly with the headland shear layer and wake, affecting the width of the shear layer and the length of the wake. A preliminary investigation of turbulence statistics indicates that topography upstream of a headland can lead to a wider shear layer, a headland wake that extends further downstream, and enhanced horizontal diffusion out of the wake relative to the case with unperturbed oncoming flow
Resonant Auger decay of the core-excited CO molecule in intense X-ray laser fields
The dynamics of the resonant Auger (RA) process of the core-excited
CO(1s) molecule in an intense X-ray laser field is
studied theoretically. The theoretical approach includes the analogue of the
conical intersections of the complex potential energy surfaces of the ground
and `dressed' resonant states due to intense X-ray pulses, taking into account
the decay of the resonance and the direct photoionization of the ground state,
both populating the same final ionic states coherently, as well as the direct
photoionization of the resonance state itself. The light-induced non-adiabatic
effect of the analogue of the conical intersections of the resulting complex
potential energy surfaces gives rise to strong coupling between the electronic,
vibrational and rotational degrees of freedom of the diatomic CO molecule. The
interplay of the direct photoionization of the ground state and of the decay of
the resonance increases dramatically with the field intensity. The coherent
population of a final ionic state via both the direct photoionization and the
resonant Auger decay channels induces strong interference effects with distinct
patterns in the RA electron spectra. The individual impact of these physical
processes on the total electron yield and on the CO electron
spectrum are demonstrated.Comment: 13 figs, 1 tabe
Counterfactual entanglement and nonlocal correlations in separable states
It is shown that the outcomes of measurements on systems in separable mixed
states can be partitioned, via subsequent measurements on a disentangled
extraneous system, into subensembles that display the statistics of entangled
states. This motivates the introduction of the concept of "counterfactual"
entanglement, which can be associated with all separable mixed states including
those that are factorable. This type of entanglement gives rise to a new kind
of postselection-induced Bell inequality violation. The significance of
counterfactual entanglement, and its physical implications, are assessed
Heavy-Quark Diffusion and Hadronization in Quark-Gluon Plasma
We calculate diffusion and hadronization of heavy quarks in high-energy
heavy-ion collisions implementing the notion of a strongly coupled quark-gluon
plasma in both micro- and macroscopic components. The diffusion process is
simulated using relativistic Fokker-Planck dynamics for elastic scattering in a
hydrodynamic background. The heavy-quark transport coefficients in the medium
are obtained from non-perturbative -matrix interactions which build up
resonant correlations close to the transition temperature. The latter also form
the basis for hadronization of heavy quarks into heavy-flavor mesons via
recombination with light quarks from the medium. The pertinent resonance
recombination satisfies energy conservation and provides an equilibrium mapping
between quark and meson distributions. The recombination probability is derived
from the resonant heavy-quark scattering rate. Consequently, recombination
dominates at low transverse momentum () and yields to fragmentation at
high . Our approach thus emphasizes the role of resonance correlations in
the diffusion and hadronization processes. We calculate the nuclear
modification factor and elliptic flow of - and -mesons for Au-Au
collisions at the Relativistic Heavy Ion Collider, and compare their
decay-electron spectra to available data. We also find that a realistic
description of the medium flow is essential for a quantitative interpretation
of the data.Comment: 16 pages, 14 figure
Gambling: Electronic friends or a threat to one's health and personal development?
Gambling has become quite common in Sweden. The Swedish National Institute of Public Health (2010) has reported that about 70% of the Swedish population has gambled at least once during the last 12 months. Half of the population had gambled with money by 18 years of age and about 11% had gambled for the first time when they were 12-years-old or younger. In the report from the Swedish National Institute of Public Health, gambling problems are related to health problems and risky alcohol consumption. The highest problem rate is found among men aged 18 to 24; almost 1 in 10 had some gambling problems. The share of problem gamblers is found to be twice as high among the under-age gamblers as it is among the population as a whole. Young people gamble less but develop gambling problems to a larger extent than adult gamblers. In this article young people's gambling and their gambling careers are analysed as a natural part of their internalisation of other adult habits
XMM-Newton observations of the BL Lac MS 0737+7441
We report on the XMM-Newton observations of the BL Lac object MS 0737.9+7441
during the performance verification phase. A simple power-law fit provides an
adequate description of the integrated spectrum in the 0.2-10 keV energy band.
The photon index is slightly steeper in the EPIC pn data with 2.38+-0.01
compared to the EPIC MOS data (2.28+-0.01). The difference is most probably due
to the present uncertainties in the calibration of the EPIC MOS and EPIC pn
data sets. We report evidence for intrinsic absorption in the distant BL Lac
above the Galactic column N_H,Gal=3.2*10^20 cm^-2 which is N_H,fit(z=0.315)=
(2.70+-0.20)*10^20cm^-2 in the EPIC pn data and N_H,fit(z=0.315)=
(3.25+-0.25)*10^20cm^-2 in the EPIC MOS data assuming neutral gas and solar
abundances. The flux variations are found to be of the order of 10 %.Comment: 4 pages, 4 Figures, accepted for publication in the special A&A
Letters issue for XMM-Newto
Diversity in the structures and ligand binding sites of nematode fatty acid and retinol binding proteins revealed by Na-FAR-1 from Necator americanus
Fatty acid and retinol binding proteins (FARs) comprise a family of unusual α-helix rich lipid binding proteins found exclusively in nematodes. They are secreted into host tissues by parasites of plants, animals and humans. The structure of a FAR protein from the free-living nematode Caenorhabditis elegans is available, but this protein (Ce-FAR-7) is from a subfamily of FARs that does not appear to be important at the host-parasite interface. We have therefore examined Na-FAR-1 from the blood-feeding intestinal parasite of humans, Necator americanus . The three dimensional structure of Na-FAR-1 in its ligand-free and ligand-bound forms, determined by nuclear magnetic resonance spectroscopy (NMR) and X-ray crystallography, respectively, reveals an a-helical fold similar to Ce-FAR-7, but Na-FAR-1 possesses a larger and more complex internal ligand binding cavity and an additional C-terminal a-helix. Titration of apo -Na-FAR-1 with oleic acid, analysed by NMR chemical shift perturbation, reveals that at least four distinct protein:ligand complexes can be formed. Na-FAR-1, and possibly other FARs, may have a wider repertoire for hydrophobic ligand binding, as confirmed here by our finding that a range of neutral and polar lipids co-purify with the bacterial recombinant protein. Finally, we show by immunohistochemistry that Na-FAR-1 is present in adult worms with a tissue distribution indicative of possible roles in nutrient acquisition by the parasite and in reproduction in the male
Generic coverings of plane with A-D-E-singularities
We generalize results of the paper math.AG/9803144, in which Chisini's
conjecture on the unique reconstruction of f by the curve B is investigated.
For this fibre products of generic coverings are studied. The main inequality
bounding the degree of a covering in the case of existence of two nonequivalent
coverings with the branch curve B is obtained. This inequality is used for the
proof of the Chisini conjecture for m-canonical coverings of surfaces of
general type for .Comment: 43 pages, 20 figures; to appear in Izvestiya Mat
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