2,618 research outputs found
Experiments on asteroids using hard landers
Hard lander missions to asteroids are examined using the Westphal penetrator study as a basis. Imagery and chemical information are considered to be the most significant science to be obtained. The latter, particularly a detailed chemical analysis performed on an uncontaminated sample, may answer questions about the relationships of asteroids to meteorites and the place of asteroids in theories of the formation of the solar system
Is There a Disc in the Superluminal Quasars?
We present a new evidence of the accretion disc in active galactic nuclei, by
examining the properties of the Ha emission line versus viewing angle, in a
sample of superluminal (SL) quasars. Both line velocity width (FWHM) and rest
equivalent width (EW) correlate with viewing angle. These correlations are
quantitatively consistent with a disc geometry for both the line and the
underlying continuum source.Comment: 18 pages with 6 figures, accepted for publication in MNRA
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
An Alpha-p-x Analytical Instrument for Lunar Resource Investigations
An instrument using alpha backscattering, alpha-proton nuclear reactions, and x-ray production by alpha particles and other auxiliary sources can be used on lunar landers to provide detailed analytical information concerning the lunar surface material. This information is important scientifically and can be the basis for utilizing efficiently lunar resources to build lunar colonies in the future. This alpha particle instrument uses radioactive isotopes, silicon detectors for the alpha and proton modes, and mercuric iodide detectors operating at room temperature for the x-ray mode. The alpha and proton modes of the instrument can provide an analysis for all elements (except hydrogen) present in amounts greater than about 1 percent by atom. These modes have excellent sensitivity and accuracy for the lighter elements, in particular, directly determining the amount of oxygen in the lunar soil. This is an element of paramount significance for the lunar resource mission. The x-ray mode makes possible a determination of Ti, Fe, and other important metals with even greater accuracy. In general, the x-ray mode provides increased sensitivity for heavier elements, in many cases achieving a sensitivity of several hundred ppm
A Survey of Safety and Health at Work in Greece
The subject of Occupational Safety and Health (OSH) is increasingly gaining the interest of policy makers and researchers in European countries given that the economic and social losses from work-related injuries and diseases are quite substantial. Under this light, this paper will present an overview of the Greek legislation framework regarding OSH issues, and the current status of empirical research on the subject in Greece. In addition, the paper identifies the knowledge gaps and methodological shortcomings of the existing literature in order to contribute towards future research in the OSH field in Greece.Accidents at work; Occupational diseases; Safety
Spatio-temporal modelling of extreme storms
A flexible spatio-temporal model is implemented to analyse extreme
extra-tropical cyclones objectively identified over the Atlantic and Europe in
6-hourly re-analyses from 1979-2009. Spatial variation in the extremal
properties of the cyclones is captured using a 150 cell spatial regularisation,
latitude as a covariate, and spatial random effects. The North Atlantic
Oscillation (NAO) is also used as a covariate and is found to have a
significant effect on intensifying extremal storm behaviour, especially over
Northern Europe and the Iberian peninsula. Estimates of lower bounds on minimum
sea-level pressure are typically 10-50 hPa below the minimum values observed
for historical storms with largest differences occurring when the NAO index is
positive.Comment: Published in at http://dx.doi.org/10.1214/14-AOAS766 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A Tonks Giradeau Gas in the Presence of a Local Potential
The physics of a Tonks-Giradeau Gas in the presence of a local potential is
studied. In order to evaluate the single particle density matrix (SPDM) of the
many-body ground state, the Wiger-Jordan transformation is used. The
eigenvector with the largest eigenvalue of the SPDM corresponds to the
"Bose-Einstein Condensate"(BEC) State. We find that the "BEC" state density at
the positon of the local potential decreases, as expected, in the case of a
repulsive potential. For an attractive potential, it decreases or increases
depending on the strength of the potential. The superfluidity of this system is
investigated both numerically and perturbatively. An experimental method for
detecting the effect of an impurity in a Tonks-Giradueau gas is discussed.Comment: 14 pages, 5 figure
Nonlinear surface impurity in a semi-infinite 2D square lattice
We examine the formation of localized states on a generalized nonlinear
impurity located at, or near the surface of a semi-infinite 2D square lattice.
Using the formalism of lattice Green functions, we obtain in closed form the
number of bound states as well as their energies and probability profiles, for
different nonlinearity parameter values and nonlinearity exponents, at
different distances from the surface. We specialize to two cases: impurity
close to an "edge" and impurity close to a "corner". We find that, unlike the
case of a 1D semi-infinite lattice, in 2D, the presence of the surface helps
the formation of a localized state.Comment: 6 pages, 7 figures, submitted to PR
Automated online preconcentration system for the determination of trace amounts of lead using Pb-selective resin and inductively coupled plasma-atomic emission spectrometry
An automated sequential-injection online preconcentration system was developed for the determination of lead by inductively coupled plasma - atomic emission spectrometry (ICP-AES). The preconcentration of lead was performed with a minicolumn containing a lead-selective resin, Analig Pb-01, which was installed between a selection and a switching valve. In an acidic condition ( pH 1), lead could be adsorbed on the resin. The concentrated lead was afterward eluted with 25 mu L of 0.06 M nitrilotriacetic acid (NTA) solution ( pH 9) and was subsequently transported into the nebulizer of ICP-AES for quantification. The selectivity of the resin toward lead was examined using a solution containing a mixture of 61 elements. When a sample volume of 5 mL was used, the quantitative collection of lead ( >= 97%) was achieved, along with an enrichment factor of 19, a sampling frequency of 12 samples hr(-1), a detection limit of 70 pg mL(-1), and a lowest quantification limit of 100 pg mL(-1). The linear dynamic range was 0.1 to 5 ng mL(-1), and the relative standard deviation (n = 9) was 0.5% at a 5 ng mL(-1) Pb level. The detection limit of 30 pg mL(-1) and lowest quantification limit of 50 pg mL(-1) could be achieved when 10 mL of sample volume was used. The accuracy of the proposed method was validated by determining lead in the standard reference material of river water (SLRS-4), and its applicability to the determination of lead in environmental river water samples was demonstrated.</p
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