2,216 research outputs found
Characterization of a dense aperture array for radio astronomy
EMBRACE@Nancay is a prototype instrument consisting of an array of 4608
densely packed antenna elements creating a fully sampled, unblocked aperture.
This technology is proposed for the Square Kilometre Array and has the
potential of providing an extremely large field of view making it the ideal
survey instrument. We describe the system,calibration procedures, and results
from the prototype.Comment: 17 pages, accepted for publication in A&
Deciphering African tropical forest dynamics in the Anthropocene: How social and historical sciences can elucidate forest cover change and inform forest management
Forests bear the historical legacies of human activities over thousands of years, including agriculture, trade, disease and resource extraction. Many of these activities may represent indices of the proposed geological epoch of the Anthropocene. Modifications to soil, topography and vegetation evidence anthropogenic influences. Yet studies of vegetation change throughout the humid tropics tend to occlude these by focussing on forest dynamics, timber, and biodiversity through permanent sample plots or forestry inventory plots. We highlight how history and social science can be combined with ecology to help better understand human signatures in forest dynamics. We (1) critically review ecological methods in the light of the environmental and social history of the Afrotropics; (2) map current plot networks for West and Central Africa in relation to the Human Footprint Index; (3) using two case-studies, demonstrate how history and social science bring new insights and inferences to plot-based studies; all leading to (4) novel forms of interdisciplinary collaboration for sustainable forest conservation, management and restoration
Hydrogen Energy Storage: New Techno-Economic Emergence Solution Analysis
International audienceThe integration of various renewable energy sources as well as the liberalization of electricity markets are established facts in modern electrical power systems. The increased share of renewable sources within power systems intensifies the supply variability and intermittency. Therefore, energy storage is deemed as one of the solutions for stabilizing the supply of electricity to maintain generation-demand balance and to guarantee uninterrupted supply of energy to users. In the context of sustainable development and energy resources depletion, the question of the growth of renewable energy electricity production is highly linked to the ability to propose new and adapted energy storage solutions. The purpose of this multidisciplinary paper is to highlight the new hydrogen production and storage technology, its efficiency and the impact of the policy context on its development. A comprehensive techno/socio/economic study of long term hydrogen based storage systems in electrical networks is addressed. The European policy concerning the different energy storage systems and hydrogen production is explicitly discussed. The state of the art of the techno-economic features of the hydrogen production and storage is introduced. Using Matlab-Simulink for a power system of rated 70 kW generator, the excess produced hydrogen during high generation periods or low demand can be sold either directly to the grid owners or as filled hydrogen bottles. The affordable use of Hydrogen-based technologies for long term electricity storage is verified
Parameter estimators of random intersection graphs with thinned communities
This paper studies a statistical network model generated by a large number of
randomly sized overlapping communities, where any pair of nodes sharing a
community is linked with probability via the community. In the special case
with the model reduces to a random intersection graph which is known to
generate high levels of transitivity also in the sparse context. The parameter
adds a degree of freedom and leads to a parsimonious and analytically
tractable network model with tunable density, transitivity, and degree
fluctuations. We prove that the parameters of this model can be consistently
estimated in the large and sparse limiting regime using moment estimators based
on partially observed densities of links, 2-stars, and triangles.Comment: 15 page
Identification of a Likely Radio Counterpart of the Rapid Burster
We have identified a likely radio counterpart to the low-mass X-ray binary
MXB 1730-335 (the Rapid Burster). The counterpart has shown 8.4 GHz radio
on/off behavior correlated with the X-ray on/off behavior as observed by the
RXTE/ASM during six VLA observations. The probability of an unrelated, randomly
varying background source duplicating this behavior is 1-3% depending on the
correlation time scale. The location of the radio source is RA 17h 33m 24.61s;
Dec -33d 23' 19.8" (J2000), +/- 0.1". We do not detect 8.4 GHz radio emission
coincident with type II (accretion-driven) X-ray bursts. The ratio of radio to
X-ray emission during such bursts is constrained to be below the ratio observed
during X-ray persistent emission at the 2.9-sigma level. Synchrotron bubble
models of the radio emission can provide a reasonable fit to the full data set,
collected over several outbursts, assuming that the radio evolution is the same
from outburst to outburst, but given the physical constraints the emission is
more likely to be due to ~hour-long radio flares such as have been observed
from the X-ray binary GRS 1915+105.Comment: 28 pages, 4 figures; accepted for publication in ApJ (no changes
RJaCGH: Bayesian analysis of aCGH arrays for detecting copy number changes and recurrent regions
Summary: Several methods have been proposed to detect copy number changes and recurrent regions of copy number variation from aCGH, but few methods return probabilities of alteration explicitly, which are the direct answer to the question ‘is this probe/region altered?’ RJaCGH fits a Non-Homogeneous Hidden Markov model to the aCGH data using Markov Chain Monte Carlo with Reversible Jump, and returns the probability that each probe is gained or lost. Using these probabilites, recurrent regions (over sets of individuals) of copy number alteration can be found
Application of an Equilibrium Vaporization Model to the Ablation of Chondritic and Achondritic Meteoroids
We modeled equilibrium vaporization of chondritic and achondritic materials
using the MAGMA code. We calculated both instantaneous and integrated element
abundances of Na, Mg, Ca, Al, Fe, Si, Ti, and K in chondritic and achondritic
meteors. Our results are qualitatively consistent with observations of meteor
spectra.Comment: 8 pages, 4 figures; in press, Earth, Moon, and Planets, Meteoroids
2004 conference proceeding
Deconvolving Instrumental and Intrinsic Broadening in Excited State X-ray Spectroscopies
Intrinsic and experimental mechanisms frequently lead to broadening of
spectral features in excited-state spectroscopies. For example, intrinsic
broadening occurs in x-ray absorption spectroscopy (XAS) measurements of heavy
elements where the core-hole lifetime is very short. On the other hand,
nonresonant x-ray Raman scattering (XRS) and other energy loss measurements are
more limited by instrumental resolution. Here, we demonstrate that the
Richardson-Lucy (RL) iterative algorithm provides a robust method for
deconvolving instrumental and intrinsic resolutions from typical XAS and XRS
data. For the K-edge XAS of Ag, we find nearly complete removal of ~9.3 eV FWHM
broadening from the combined effects of the short core-hole lifetime and
instrumental resolution. We are also able to remove nearly all instrumental
broadening in an XRS measurement of diamond, with the resulting improved
spectrum comparing favorably with prior soft x-ray XAS measurements. We present
a practical methodology for implementing the RL algorithm to these problems,
emphasizing the importance of testing for stability of the deconvolution
process against noise amplification, perturbations in the initial spectra, and
uncertainties in the core-hole lifetime.Comment: 35 pages, 13 figure
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