367 research outputs found

    Some propositions to find optimal conditions to simulate a flexible transport using an Agent-Based Model

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    This paper presents a method to assess the sensitivity of a flexible transport model based on agents and simulated using NetLogo. We simulate and we analyse a set of 124 transportation scenarios on several virtual networks and we assess their performance. Our main objective is to detect thresholds in the system scalability and efficiency. The research leads to three main results: (i) using Agent-Based Model, it is possible to significantly improve the global transport efficiency without any general objective function, (ii) there exists an optimal balance between the demand frequency and the number of simulated agents to simulate and perform a good flexible transport, (ii) to some extent, the network topological structure plays a non-negligible role in transport efficiency

    Molecular Hydrogen Emission Lines in Far Ultraviolet Spectroscopic Explorer Observations of Mira B

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    We present new Far Ultraviolet Spectroscopic Explorer (FUSE) observations of Mira A's wind-accreting companion star, Mira B. We find that the strongest lines in the FUSE spectrum are H2 lines fluoresced by H I Lyman-alpha. A previously analyzed Hubble Space Telescope (HST) spectrum also shows numerous Lyman-alpha fluoresced H2 lines. The HST lines are all Lyman band lines, while the FUSE H2 lines are mostly Werner band lines, many of them never before identified in an astrophysical spectrum. We combine the FUSE and HST data to refine estimates of the physical properties of the emitting H2 gas. We find that the emission can be reproduced by an H2 layer with a temperature and column density of T=3900 K and log N(H2)=17.1, respectively. Another similarity between the HST and FUSE data, besides the prevalence of H2 emission, is the surprising weakness of the continuum and high temperature emission lines, suggesting that accretion onto Mira B has weakened dramatically. The UV fluxes observed by HST on 1999 August 2 were previously reported to be over an order of magnitude lower than those observed by HST and the International Ultraviolet Explorer (IUE) from 1979--1995. Analysis of the FUSE data reveals that Mira B was still in a similarly low state on 2001 November 22.Comment: 23 pages, 6 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty; accepted by Ap

    Late-Type Red Supergiants: Too Cool for the Magellanic Clouds?

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    We have identified seven red supergiants (RSGs) in the Large Magellanic Cloud (LMC) and four RSGs in the Small Magellanic Cloud (SMC), all of which have spectral types that are considerably later than the average type observed in their parent galaxy. Using moderate-resolution optical spectrophotometry and the MARCS stellar atmosphere models, we determine their physical properties and place them on the H-R diagram for comparison with the predictions of current stellar evolutionary tracks. The radial velocities of these stars suggest that they are likely all members of the Clouds rather than foreground dwarfs or halo giants. Their locations in the H-R diagram also show us that those stars are cooler than the current evolutionary tracks allow, appearing to the right of the Hayashi limit, a region in which stars are no longer in hydrodynamic equilibrium. These stars exhibit considerable variability in their V magnitudes, and three of these stars also show changes in their effective temperatures (and spectral types) on the time-scales of months. One of these stars, [M2002] SMC 055188, was caught in an M4.5 I state, as late as that seen in HV 11423 at its recent extreme: considerable later, and cooler, than any other supergiant in the SMC. In addition, we find evidence of variable extinction due to circumstellar dust and changes in the stars' luminosities, also consistent with our recent findings for HV 11423 - when these stars are hotter they are also dustier and more luminous. We suggest that these stars have unusual properties because they are in an unstable (and short-lived) evolutionary phase.Comment: 26 pages, 6 figures; submitted to the Astrophysical Journa

    Discovery of a detached HI gas shell surrounding alpha Orionis

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    We report the detection of the HI line at 21 cm in the direction of alpha Ori with the Nancay Radiotelescope and with the Very Large Array. The observations confirm the previous detection of HI emission centered on alpha Ori, but additionally reveal for the first time a quasi-stationary detached shell of neutral atomic hydrogen ~4 arcmin. in diameter (0.24 pc at a distance of 200 pc). The detached shell appears elongated in a direction opposite to the star's space motion. A simple model shows that this detached atomic gas shell can result from the collision of the stellar wind from alpha Ori with the local interstellar medium (ISM). It implies that alpha Ori has been losing matter at a rate of ~ 1.2x10^-6 solar masses per year for the past 8x10^4 years. In addition, we report the detection of atomic hydrogen associated with the far-infrared arc located 6 arcmin. north-east of alpha Ori, that has been suggested to trace the bow shock resulting from the motion of the star through the ISM. We report also the detection by the Galaxy Evolution Explorer (GALEX) of a far-UV counterpart to this arc.Comment: Accepted for publication in the Monthly Notices; version with full resolution figures available at http://aramis.obspm.fr/~lebertre/paper-alphaOri_MNRAS.pd

    Quantification of Dendritic Cells and Osteoclasts in the Bone Marrow of Patients with Monoclonal Gammopathy

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    The purpose of this study was to find histological clues for reliable differentiation between monoclonal gammopathy of undetermined significance (MGUS) and myeloma when clinical parameters are controversial. Differential appearance of dendritic cells and osteoclasts, two cell types developing from the monocytic lineage upon distinct cytokine activation profile, might be a useful approach. Bone and bone-marrow biopsies performed in 105 patients were studied using histomorphometry after identification of osteoclasts (by histochemical identification of tartrate resistant acid phosphatase) and dendritic cells (by immunohistochemical detection of the S-100 protein). Patients were classified by the World Health Organization criteria but histopathological criteria were more adapted to identify MGUS (53 cases), myeloma (46), B-cell lymphoma (six) since six myeloma were not correctly classified. Histomorphometry was compared to 15 control cases. The number of marrow dendritic cell was significantly increased with B-cell lymphoma >MGUS >myeloma > controls. Dendritic cell were often mixed with lymphoma cells. Myeloma had increased bone resorption with a high osteoclast number and moderate increase in dendritic cells. B-cell lymphomas had a considerable increase in dendritic cell but presented mononucleated osteoclasts. These findings can help in the classification of MGUS in the early stages of the disease and could help to propose preventive treatments
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