Suspension Flows in a Pipeline with Partial Phase Separation

The formulation of a model for the evolution of the flow of a solid-liquid mixture (coal-water) in a horizontal pipeline with partial phase separation is the aim of this work. Problems of instabilities due to complex eigenvalues, observed in previous models, seem to be completely solved in the present model, in which we give the genesis of the different terms written in the equations, coming from the natural definition of mass and momentum balance, and the consequent proof of well-posedness of the obtained PDE system with boundary-Cauchy data. The model describes a three-layer flow. Most of the material is carried by the upper layer, while the bottom layer consists of an immobile sediment. The intermediate layer grows to a maximum thickness and has the role of regulating the mass exchange between the extreme layers. In the last section we present some simulations for a particular choice of flow regime, and boundary-Cauchy data, that were suggested by experimental results provided by Snamprogetti (Fano, Italy).Comment: 29 pages, 7 figure

The Birthplace of Low-Mass X-ray Binaries: Field Versus Globular Cluster Populations

Recent Chandra studies of low-mass X-ray binaries (LMXBs) within early-type galaxies have found that LMXBs are commonly located within globular clusters of the galaxies. However, whether all LMXBs are formed within globular clusters has remained an open question. If all LMXBs formed within globular clusters, the summed X-ray luminosity of the LMXBs in a galaxy should be directly proportional to the number of globular clusters in the galaxy regardless of where the LMXBs currently reside. We have compared these two quantities over the same angular area for a sample of 12 elliptical and S0 galaxies observed with Chandra and found that the correlation between the two quantities is weaker than expected if all LMXBs formed within globular clusters. This indicates that a significant number of the LMXBs were formed in the field, and naturally accounts for the spread in field-to-cluster fractions of LMXBs from galaxy to galaxy. We also find that the "pollution" of globular cluster LMXBs into the field has been minimal within elliptical galaxies, but there is evidence that roughly half of the LMXBs originally in the globular clusters of S0 galaxies in our sample have escaped into the field. This is due to higher globular cluster disruption rates in S0s resulting from stronger gravitational shocks caused by the passage of globular clusters through the disks of S0 galaxies that are absent in elliptical galaxies.Comment: To appear in ApJ, 1 October 2005, v631 2 issue, 9 pages, 3 figures, typos and a few minor issues correcte

Modelling the frying of a non-deformable specimen by immersion in edible oil

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Continuity and differentiability of regression M functionals

This paper deals with the Fisher-consistency, weak continuity and differentiability of estimating functionals corresponding to a class of both linear and nonlinear regression high breakdown M estimates, which includes S and MM estimates. A restricted type of differentiability, called weak differentiability, is defined, which suffices to prove the asymptotic normality of estimates based on the functionals. This approach allows to prove the consistency, asymptotic normality and qualitative robustness of M estimates under more general conditions than those required in standard approaches. In particular, we prove that regression MM-estimates are asymptotically normal when the observations are $\phi$-mixing.Comment: Published in at http://dx.doi.org/10.3150/11-BEJ368 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

Vortex matter freezing in Bi2_{2}Sr2_{2}CaCu2_{2}O8_{8} samples with a very dense distribution of columnar defects

We show that the dynamical freezing of vortex structures nucleated at diluted densities in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ samples with a dense distribution of columnar defects, $B \sim 10^{-2} B_{\Phi}$ with $B_{\Phi}=5$\,kG, results in configurations with liquid-like correlations. We propose a freezing model considering a relaxation dynamics dominated by double-kink excitations driven by the local stresses obtained directly from experimental images. With this model we estimate the relaxation barrier and the freezing temperature. We argue that the low-field frozen vortex structures nucleated in a dense distribution of columnar defects thus correspond to an out-of-equilibrium non-entangled liquid with strongly reduced mobility rather than to a snapshot of a metastable state with divergent activation barriers as for instance expected for the Bose-glass phase at equilibrium.Comment: 12 pages, 7 figure

Emission Line Galaxies and Active Galactic Nuclei in WINGS clusters

We present the analysis of the emission line galaxies members of 46 low redshift (0.04 < z < 0.07) clusters observed by WINGS (WIde-field Nearby Galaxy cluster Survey, Fasano et al. 2006). Emission line galaxies were identified following criteria that are meant to minimize biases against non-star forming galaxies and classified employing diagnostic diagrams. We have examined the emission line properties and frequencies of star forming galaxies, transition objects and active galactic nuclei (AGNs: LINERs and Seyferts), unclassified galaxies with emission lines, and quiescent galaxies with no detectable line emission. A deficit of emission line galaxies in the cluster environment is indicated by both a lower frequency with respect to control samples, and by a systematically lower Balmer emission line equivalent width and luminosity (up to one order of magnitude in equivalent width with respect to control samples for transition objects) that implies a lower amount of ionised gas per unit mass and a lower star formation rate if the source is classified as Hii region. A sizable population of transition objects and of low-luminosity LINERs (approx. 10 - 20% of all emission line galaxies) is detected among WINGS cluster galaxies. With respect to Hii sources they are a factor of approx. 1.5 more frequent than (or at least as frequent as) in control samples. Transition objects and LINERs in cluster are most affected in terms of line equivalent width by the environment and appear predominantly consistent with "retired" galaxies. Shock heating can be a possible gas excitation mechanism able to account for observed line ratios. Specific to the cluster environment, we suggest interaction between atomic and molecular gas and the intracluster medium as a possible physical cause of line-emitting shocks.Comment: Astronomy and Astrophysics, accepte

The concentration-mass relation of clusters of galaxies from the OmegaWINGS survey

The relation between a cosmological halo concentration and its mass (cMr) is a powerful tool to constrain cosmological models of halo formation and evolution. On the scale of galaxy clusters the cMr has so far been determined mostly with X-ray and gravitational lensing data. The use of independent techniques is helpful in assessing possible systematics. Here we provide one of the few determinations of the cMr by the dynamical analysis of the projected-phase-space distribution of cluster members. Based on the WINGS and OmegaWINGS data sets, we used the Jeans analysis with the MAMPOSSt technique to determine masses and concentrations for 49 nearby clusters, each of which has ~60 spectroscopic members or more within the virial region, after removal of substructures. Our cMr is in statistical agreement with theoretical predictions based on LambdaCDM cosmological simulations. Our cMr is different from most previous observational determinations because of its flatter slope and lower normalization. It is however in agreement with two recent cMr obtained using the lensing technique on the CLASH and LoCuSS cluster data sets. In the future we will extend our analysis to galaxy systems of lower mass and at higher redshifts.Comment: Astronomy & Astrophysics in press. 11 pages, 6 figure