574 research outputs found
Rainfall structural modelling in urban hydrology
International audienceThe aim of this work was to study the possibility of modeling a rainfall using an urban rain gauge network. This kind of network is quite new. But their existing will lead to a kind of modeling in which both space and time variations are taken into account; a rainfall is a set of homogenous subsets
Gravitational radiation from inspiralling compact binaries completed at the third post-Newtonian order
The gravitational radiation from point particle binaries is computed at the
third post-Newtonian (3PN) approximation of general relativity. Three
previously introduced ambiguity parameters, coming from the Hadamard self-field
regularization of the 3PN source-type mass quadrupole moment, are consistently
determined by means of dimensional regularization, and proved to have the
values xi = -9871/9240, kappa = 0 and zeta = -7/33. These results complete the
derivation of the general relativistic prediction for compact binary inspiral
up to 3.5PN order, and should be of use for searching and deciphering the
signals in the current network of gravitational wave detectors.Comment: 4 pages in 2-column format, LaTeX 2e, REVTeX 4, no figur
Product-Closing Approximation for Ranking-based Choice Network Revenue Management
Most recent research in network revenue management incorporates choice
behavior that models the customers' buying logic. These models are consequently
more complex to solve, but they return a more robust policy that usually
generates better expected revenue than an independent-demand model. Choice
network revenue management has an exact dynamic programming formulation that
rapidly becomes intractable. Approximations have been developed, and many of
them are based on the multinomial logit demand model. However, this parametric
model has the property known as the independence of irrelevant alternatives and
is often replaced in practice by a nonparametric model. We propose a new
approximation called the product closing program that is specifically designed
for a ranking-based choice model representing a nonparametric demand. Numerical
experiments show that our approach quickly returns expected revenues that are
slightly better than those of other approximations, especially for large
instances. Our approximation can also supply a good initial solution for other
approaches
Dimensional regularization of the third post-Newtonian gravitational wave generation from two point masses
Dimensional regularization is applied to the computation of the gravitational
wave field generated by compact binaries at the third post-Newtonian (3PN)
approximation. We generalize the wave generation formalism from isolated
post-Newtonian matter systems to d spatial dimensions, and apply it to point
masses (without spins), modelled by delta-function singularities. We find that
the quadrupole moment of point-particle binaries in harmonic coordinates
contains a pole when epsilon = d-3 -> 0 at the 3PN order. It is proved that the
pole can be renormalized away by means of the same shifts of the particle
world-lines as in our recent derivation of the 3PN equations of motion. The
resulting renormalized (finite when epsilon -> 0) quadrupole moment leads to
unique values for the ambiguity parameters xi, kappa and zeta, which were
introduced in previous computations using Hadamard's regularization. Several
checks of these values are presented. These results complete the derivation of
the gravitational waves emitted by inspiralling compact binaries up to the
3.5PN level of accuracy which is needed for detection and analysis of the
signals in the gravitational-wave antennas LIGO/VIRGO and LISA.Comment: 60 pages, LaTeX 2e, REVTeX 4, 10 PostScript files (1 figure and 9
Young tableaux used in the text
Light deflection by gravitational waves from localized sources
We study the deflection of light (and the redshift, or integrated time delay)
caused by the time-dependent gravitational field generated by a localized
material source lying close to the line of sight. Our calculation explicitly
takes into account the full, near-zone, plus intermediate-zone, plus wave-zone,
retarded gravitational field. Contrary to several recent claims in the
literature, we find that the deflections due to both the wave-zone 1/r
gravitational wave and the intermediate-zone 1/r^2 retarded fields vanish
exactly. The leading total time-dependent deflection caused by a localized
material source, such as a binary system, is proven to be given by the
quasi-static, near-zone quadrupolar piece of the gravitational field, and
therefore to fall off as the inverse cube of the impact parameter.Comment: 12 pages, REVTeX 3.0, no figur
Early-onset ventilator-associated pneumonia in adults randomized clinical trial: comparison of 8 versus 15 days of antibiotic treatment
International audiencePurposeThe optimal treatment duration for ventilator-associated pneumonia is based on one study dealing with late-onset of the condition. Shortening the length of antibiotic treatment remains a major prevention factor for the emergence of multiresistant bacteria.ObjectiveTo demonstrate that 2 different antibiotic treatment durations (8 versus 15 days) are equivalent in terms of clinical cure for early-onset ventilator-associated pneumonia.MethodsRandomized, prospective, open, multicenter trial carried out from 1998 to 2002.MeasurementsThe primary endpoint was the clinical cure rate at day 21. The mortality rate was evaluated on days 21 and 90.Results225 patients were included in 13 centers. 191 (84.9%) patients were cured: 92 out of 109 (84.4%) in the 15 day cohort and 99 out of 116 (85.3%) in the 8 day cohort (difference = 0.9%, odds ratio = 0.929). 95% two-sided confidence intervals for difference and odds ratio were [−8.4% to 10.3%] and [0.448 to 1.928] respectively. Taking into account the limits of equivalence (10% for difference and 2.25 for odds ratio), the objective of demonstrative equivalence between the 2 treatment durations was fulfilled. Although the rate of secondary infection was greater in the 8 day than the 15 day cohort, the number of days of antibiotic treatment remained lower in the 8 day cohort. There was no difference in mortality rate between the 2 groups on days 21 and 90.ConclusionOur results suggest that an 8-day course of antibiotic therapy is safe for early-onset ventilator-associated pneumonia in intubated patients
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