707 research outputs found
Counting Integer flows in Networks
This paper discusses new analytic algorithms and software for the enumeration
of all integer flows inside a network. Concrete applications abound in graph
theory \cite{Jaeger}, representation theory \cite{kirillov}, and statistics
\cite{persi}. Our methods clearly surpass traditional exhaustive enumeration
and other algorithms and can even yield formulas when the input data contains
some parameters. These methods are based on the study of rational functions
with poles on arrangements of hyperplanes
From geometric quantization to Moyal quantization
We show how the Moyal product of phase-space functions, and the Weyl
correspondence between symbols and operator kernels, may be obtained directly
using the procedures of geometric quantization, applied to the symplectic
groupoid constructed by ``doubling'' the phase space.Comment: 7 two-column pages, RevTeX, UCR--FM--03--9
Estimating the incidence of equine viral arteritis and the sensitivity of its surveillance in the French breeding stock
Equine viral arteritis (EVA) may have serious economic impact on the equine industry. For this reason, it is monitored in many countries, especially in breeding stock, to avoid its spread during breeding activities. In France, surveillance is mainly based on serological tests, since mares are not vaccinated, but difficulties in interpreting certain series of results may impair the estimation of the number of outbreaks. In this study, we propose specific rules for identifying seroconversion in order to estimate the number of outbreaks that were detected by the breeding stock surveillance component (BSSC) in France between 2006 and 2013. A consensus among multidisciplinary experts was reached to consider seroconversion as a change in antibody titer from negative to at least 32, or as an eight-fold or greater increase in antibody level. Using these rules, 239 cases and 177 outbreaks were identified. Subsequently, we calculated the BSSC's sensitivity as the ratio of the number of detected outbreaks to the total number of outbreaks that occurred in breeding stock (including unreported outbreaks) estimated using a capture-recapture model. The total number of outbreaks was estimated at 215 (95% credible interval 195-249) and the surveillance sensitivity at 82% (CrI95% 71-91). Our results confirm EVA circulation in French breeding stock, show that neutralizing antibodies can persist up to eight years in naturally infected mares and suggest that certain mares have been reinfected. This study shows that the sensitivity of the BSSC is relatively high and supports its relevance to prevent the disease spreading through mating
Joint inversion of teleseismic and GOCE gravity data: application to the Himalayas
Our knowledge and understanding of the 3-D lithospheric structure of the Himalayas and the Tibetan Plateau is still challenging although numerous geophysical studies have been performed in the region. The GOCE satellite mission has the ambitious goal of mapping Earth's gravity field with unprecedented precision (i.e. an accuracy of 1-2 mGal for a spatial resolution of 100âkm) to observe the lithosphere and upper-mantle structure. Consequently, it gives new insights in the lithospheric structure beneath the Himalayas and the Tibetan Plateau. Indeed, the GOCE gravity data now allow us to develop a new strategy for joint gravimetry-seismology inversion. Combined with teleseismic data over a large region in a joint inversion scheme, they will lead to lithospheric velocity-density models constrained in two complementary ways. We apply this joint inversion scheme to the Hi-CLIMB (Himalayan-Tibetan Continental Lithosphere during Mountain Building) seismological network which was deployed in South Tibet and the Himalayas for a 3-yr period. The large size of the network, the high quality of the seismological data and the new GOCE gravity data set allow us to image the entire lithosphere of this active area in an innovative way. We image 3-D low velocity and density structures in the middle crust that fit the location of discontinuous low S-velocity zones revealed by receiver functions in previous geophysical studies. In the deeper parts of our velocity model we image a positive anomaly interpreted to be the heterogenous Indian lithosphere vertically descending beneath the centre of the Tibetan Platea
INTERMEDIATE SUMS ON POLYHEDRA II:BIDEGREE AND POISSON FORMULA
Abstract. We continue our study of intermediate sums over polyhedra,interpolating between integrals and discrete sums, whichwere introduced by A. Barvinok [Computing the Ehrhart quasi-polynomial of a rational simplex, Math. Comp. 75 (2006), 1449â1466]. By well-known decompositions, it is sufficient to considerthe case of affine cones s+c, where s is an arbitrary real vertex andc is a rational polyhedral cone. For a given rational subspace L,we integrate a given polynomial function h over all lattice slicesof the affine cone s + c parallel to the subspace L and sum up theintegrals. We study these intermediate sums by means of the intermediategenerating functions SL(s+c)(Ο), and expose the bidegreestructure in parameters s and Ο, which was implicitly used in thealgorithms in our papers [Computation of the highest coefficients ofweighted Ehrhart quasi-polynomials of rational polyhedra, Found.Comput. Math. 12 (2012), 435â469] and [Intermediate sums onpolyhedra: Computation and real Ehrhart theory, Mathematika 59(2013), 1â22]. The bidegree structure is key to a new proof for theBaldoniâBerlineâVergne approximation theorem for discrete generatingfunctions [Local EulerâMaclaurin expansion of Barvinokvaluations and Ehrhart coefficients of rational polytopes, Contemp.Math. 452 (2008), 15â33], using the Fourier analysis with respectto the parameter s and a continuity argument. Our study alsoenables a forthcoming paper, in which we study intermediate sumsover multi-parameter families of polytopes
EXEMPLO DE CARTOGRAFIA DAS FORMAĂĂES SUPERFICIAIS EM ZONA TROPICAL: O MAPA A SE DE CAMAĂARI - BAHIA
Un essai de cartographie des formations superficielles, sans l'utilisation des couleurs, a Ă©tĂ© rĂ©alisĂ© dans un secteur de Ia rĂ©gion de Camaçari (Etat de Bahia), caractĂ©risĂ© par un relief dĂ©veloppĂ© Ă partir d'un substrat gĂ©ologique contrastĂ© (socle cristallin et bassin sĂ©dimentaire). L'association des formes et des formations qu'elles portent dans un systĂȘme adaptĂ© aux limitations de Ia cartographie en noir et blanc et I'utilisation de symboles gĂ©omorphologiques ont permi d'ateindre les objectifs projetĂ©s en reprĂ©sentant les Ă©lĂ©ments indispensables Ă Ia comprĂ©hension de Ia rĂ©gion
Sharp error terms for return time statistics under mixing conditions
We describe the statistics of repetition times of a string of symbols in a
stochastic process. Denote by T(A) the time elapsed until the process spells
the finite string A and by S(A) the number of consecutive repetitions of A. We
prove that, if the length of the string grows unbondedly, (1) the distribution
of T(A), when the process starts with A, is well aproximated by a certain
mixture of the point measure at the origin and an exponential law, and (2) S(A)
is approximately geometrically distributed. We provide sharp error terms for
each of these approximations. The errors we obtain are point-wise and allow to
get also approximations for all the moments of T(A) and S(A). To obtain (1) we
assume that the process is phi-mixing while to obtain (2) we assume the
convergence of certain contidional probabilities
Polarimetry of an Intermediate-age Open Cluster: NGC 5617
We present polarimetric observations in the UBVRI bands of 72 stars located
in the direction of the medium age open cluster NGC 5617. Our intention is to
use polarimetry as a tool membership identification, by building on previous
investigations intended mainly to determine the cluster's general
characteristics rather than provide membership suitable for studies such as
stellar content and metallicity, as well as study the characteristics of the
dust lying between the Sun and the cluster. The obsevations were carried out
using the five-channel photopolarimeter of the Torino Astronomical Observatory
attached to the 2.15m telescope at the Complejo Astron\'omico El Leoncito
(CASLEO; Argentina. We are able to add 32 stars to the list of members of NGC
5617, and review the situation for others listed in the literature. In
particular, we find that five blue straggler stars in the region of the cluster
are located behind the same dust as the member stars are and we confirm the
membership of two red giants. The proposed polarimetric memberships are
compared with those derived by photometric and kinematical methods, with
excellent results. Among the observed stars, we identify 10 with intrinsic
polarization in their light. NGC 5617 can be polarimetrically characterized
with and . The spread in polarization
values for the stars observed in the direction of the cluster seems to be
caused by the uneven distribution of dust in front of the cluster's face.
Finally, we find that in the direction of the cluster, the interstellar medium
is apparently free of dust, from the Sun's position up to the
Carina-Sagittarius arm, where NGC 5617 seems to be located at its farthest
border
Revisiting the area of the open cluster Stock 16
Deep CCD UBV(RI)C photometry has been carried out in the area of the open cluster Stock 16. The different photometric diagrams indicate the presence of three superimposed stellar groups, all composed of early type stars. The first of them, the cluster Stock 16, suffers from slightly variable reddening with a mean color excess ăEB-Vă = 0.51. The second group, reddened by ăEB-Vă = 0.84, includes the Wolf-Rayet star WR50 (a WC7+OB), and the third one, with a mean ăE B-Vă = 1.18, also includes another Wolf-Rayet star, WR 51 (a WN4+OB?). Our results confirm the distance and reddening already stated for Stock 16 but include new members. Concerning the other two highly reddened groups, we show that the first one - located at a distance of 3600 pc - is probably related to an anonymous OB association behind Cen OB1 also at 3600 pc already mentioned in the literature; the other seems to be a distant OB association - at more than 9000 pc - which may belong to the Scutum-Crux spiral arm. In these two groups we find evidence that the absorption law, A V/EB-V = R amounts to 4.0 approximately. The ages of the different star populations in the zone range from 5 Ă 106 yr to 6.4 Ă 106 yr for Stock 16, 8 Ă 106 for the second most reddened group and 5 Ă 106 for the probable association in Scutum-Crux. A determination of the IMF slope of Stock 16 was also carried out for stars in the mass range 1.8 < M < 14 M â, giving a normal value x = 1.3.Este documento tiene una correcciĂłn (ver documento relacionado).Facultad de Ciencias AstronĂłmicas y GeofĂsicasInstituto de AstrofĂsica de La Plat
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