19,248 research outputs found

    Men Experiencing Homelessness: A Qualitative Investigation of Multiple Stigmas

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    Homelessness is a pervasive and problematic phenomenon. Unfortunately, programs designed to reduce or eliminate homelessness face a number of challenges. One such challenge involves difficulty engaging and retaining clientele who are experiencing homelessness in services. The literature suggests that one explanation for this difficulty involves the stigmatization experiences that individuals who are homeless accumulate over time. However, the relationship between stigmatization and the psychosocial functioning of individuals facing homelessness has rarely been investigated empirically, and it is unclear how well various theories of stigma apply to this unique population. The purpose of the current paper is to propose a grounded theory study of how a specific subgroup of the homeless population experiences and responds to multiple sources of social stigmatization: African American men experiencing homelessness and facing co-occurring mental illness and substance use disorders

    Evaluating the stability of atmospheric lines with HARPS

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    Context: In the search for extrasolar systems by radial velocity technique, a precise wavelength calibration is necessary for high-precision measurements. The choice of the calibrator is a particularly important question in the infra-red domain, where the precision and exploits still fall behind the achievements of the optical. Aims: We investigate the long-term stability of atmospheric lines as a precise wavelength reference and analyze their sensitivity to different atmospheric and observing conditions. Methods: We use HARPS archive data on three bright stars, Tau Ceti, Mu Arae and Epsilon Eri, spanning 6 years and containing high-cadence measurements over several nights. We cross-correlate this data with an O2 mask and evaluate both radial velocity and bisector variations down to a photon noise of 1 m/s. Results: We find that the telluric lines in the three data-sets are stable down to 10 m/s (r.m.s.) over the 6 years. We also show that the radial velocity variations can be accounted for by simple atmospheric models, yielding a final precision of 1-2 m/s. Conclusions: The long-term stability of atmospheric lines was measured as being of 10 m/s over six years, in spite of atmospheric phenomena. Atmospheric lines can be used as a wavelength reference for short-time-scales programs, yielding a precision of 5 m/s "out-of-the box". A higher precision, down to 2 m/s can be reached if the atmospheric phenomena are corrected for by the simple atmospheric model described, making it a very competitive method even on long time-scales.Comment: 7 pages, accepted for publication in A&

    Nomenclatorial corrections for Dasytidae and Malachiidae (Coleoptera)

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    Nomenclatorial corrections are proposed for 9 cases of homonymy and 5 cases of synonymy in the Dasytidae and Malachiidae. For the homonyms, the following new names are proposed: Aplocnemus montbabor Mayor, new name, for A. baborensis Pic 1922; Dasytes loboensis Mayor, new name, for D. nevadensis Pic 1954; Dasyte sminor Mayor, new name, for D. minutus Casey 1895; Amalthocuspici Mayor, new name, for A. metallicus (Pic 1955); Attalus tribandipennis Mayor, new name, for A. tricoloripennis Pic 1927; Attalus ulkei Mayor, new name, for A. laevicollis (Horn 1872); Laiuscephalus Mayor, new name, for L. verticalis Fairmaire; Sphinginopalpus mpumalangaensis Mayor, new name, for S. nigriceps Wittmer 1994; Sphinginopalpus rufinotus Mayor, new name, for S. rufithorax Wittmer 1994. Scelopristis Mayor new genus, is proposed for the species of Pristocelis LeConte 1862, a junior synonym of Trichochrous Motschulsky 1860; the available name Hadrocnemus Kraatz 1895 is proposed for the species of Apalochrus Erichson 1840 a senior objective synonym of Paritinus Abeille de Perrin 1891. The following new subjective synonyms are proposed: Pristoscelis Le Conte 1862 is a junior synonym of Trichochrous Motschulsky 1860; Anthocomus (Paremballus) Abeille de Perrin 1891 is a junior synonym of Anthocomus (Anthocomus) Erichson 1840; Anthocomus (Neotrotus) Abeille de Perrin 1891 is a juniorsynonym of Anthocomus (Celidus) Mulsant and Rey 1867; Amanicollops Pic 1908 is a junior synonym of Hadrocnemus Kraatz 1895. Paratinus Abeille de Perrin 1891 is a junior objective synonym of Apalochrus Erichson 1840). New combinations for North American species from Attalus Erichson, Anthocomus Erichson, Microlipus LeConte and Tanaops LeConte formalized here were suggested by Mayor (2002). The Characters indicating the close relationship of Neadasytes Hatch 1962 to Dasytastes Casey 1895, and of Paradasytes Hatch 1962 to Dasytellus Casey 1895 are discussed. Afrocolotes Wittmer 1960 and Olistherarthrus Champion 1922, listed as synonyms of Temnopsophus Horn 1872 by Evers (1989: 6), are here considered distinct genera. These changes are proposed here so that they can be included in a world catalog in preparation

    Transient Information Flow in a Network of Excitatory and Inhibitory Model Neurons: Role of Noise and Signal Autocorrelation

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    We investigate the performance of sparsely-connected networks of integrate-and-fire neurons for ultra-short term information processing. We exploit the fact that the population activity of networks with balanced excitation and inhibition can switch from an oscillatory firing regime to a state of asynchronous irregular firing or quiescence depending on the rate of external background spikes. We find that in terms of information buffering the network performs best for a moderate, non-zero, amount of noise. Analogous to the phenomenon of stochastic resonance the performance decreases for higher and lower noise levels. The optimal amount of noise corresponds to the transition zone between a quiescent state and a regime of stochastic dynamics. This provides a potential explanation on the role of non-oscillatory population activity in a simplified model of cortical micro-circuits.Comment: 27 pages, 7 figures, to appear in J. Physiology (Paris) Vol. 9

    Noise-enhanced computation in a model of a cortical column

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    Varied sensory systems use noise in order to enhance detection of weak signals. It has been conjectured in the literature that this effect, known as stochastic resonance, may take place in central cognitive processes such as the memory retrieval of arithmetical multiplication. We show in a simplified model of cortical tissue, that complex arithmetical calculations can be carried out and are enhanced in the presence of a stochastic background. The performance is shown to be positively correlated to the susceptibility of the network, defined as its sensitivity to a variation of the mean of its inputs. For nontrivial arithmetic tasks such as multiplication, stochastic resonance is an emergent property of the microcircuitry of the model network

    Investigation of the Praesepe cluster. III. Radial velocity and binarity of the F5-K0 Klein-Wassink stars

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    Coravel observations of 103 F5-K0 stars in the Praesepe cluster yielded 24 spectroscopic binaries (3 are non-members), and 20 orbits were determined, with periods from 4 to 7400 days. Based on a complete sample in the colour range 0.40 < B-V < 0.80 (80 stars, including KW 244 = TX Cnc), the companion star fraction CSF = 0.45. The percentage of spectroscopic binaries with P < 1000d is 20% (16/80). The combined photometric and spectroscopic analysis showed that 12 among 18 single-lined spectroscopic binaries are located within the "single" star sequence in the (V,B-V) diagram and cannot be detected by the photometric analysis in the UBV system. In addition, seven photometrically analysed binaries were not detected with the radial velocity observations, but are confirmed members. The number of single:binary:triple stars is 47:30:3.Comment: 10 pages, 3 tables, 7 eps figures. Accepted for A&A. LaTe

    Bilayer registry in a multicomponent asymmetric membrane : dependence on lipid composition and chain length

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    A question of considerable interest to cell membrane biology is whether phase segregated domains across an asymmetric bilayer are strongly correlated with each other and whether phase segregation in one leaflet can induce segregation in the other. We answer both these questions in the affirmative, using an atomistic molecular dynamics simulation to study the equilibrium statistical properties of a 3-component {\em asymmetric} lipid bilayer comprising an unsaturated POPC (palmitoyl-oleoyl-phosphatidyl-choline), a saturated SM (sphingomyelin) and cholesterol with different composition ratios. Our simulations are done by fixing the composition of the upper leaflet to be at the coexistence of the liquid ordered (lol_o) - liquid disordered (ldl_d) phases, while the composition of the lower leaflet is varied from the phase coexistence regime to the mixed ldl_d phase, across a first-order phase boundary. In the regime of phase coexistence in each leaflet, we find strong transbilayer correlations of the lol_o domains across the two leaflets, resulting in {\it bilayer registry}. This transbilayer correlation depends sensitively upon the chain length of the participating lipids and possibly other features of lipid chemistry, such as degree of saturation. We find that the lol_o domains in the upper leaflet can {\em induce} phase segregation in the lower leaflet, when the latter is nominally in the mixed (ldl_d) phase.Comment: 6 figure

    The Stellar Dynamics of Omega Centauri

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    The stellar dynamics of Omega Centauri are inferred from the radial velocities of 469 stars measured with CORAVEL (Mayor et al. 1997). Rather than fit the data to a family of models, we generate estimates of all dynamical functions nonparametrically, by direct operation on the data. The cluster is assumed to be oblate and edge-on but mass is not assumed to follow light. The mean motions are consistent with axisymmetry but the rotation is not cylindrical. The peak rotational velocity is 7.9 km/s at 11 pc from the center. The apparent rotation of Omega Centauri is attributable in part to its proper motion. We reconstruct the stellar velocity ellipsoid as a function of position, assuming isotropy in the meridional plane. We find no significant evidence for a difference between the velocity dispersions parallel and perpendicular to the meridional plane. The mass distribution inferred from the kinematics is slightly more extended than, though not strongly inconsistent with, the luminosity distribution. We also derive the two-integral distribution function f(E,Lz) implied by the velocity data.Comment: 25 Latex pages, 12 Postscript figures, uses aastex, epsf.sty. Submitted to The Astronomical Journal, December 199

    Mean-value identities as an opportunity for Monte Carlo error reduction

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    In the Monte Carlo simulation of both Lattice field-theories and of models of Statistical Mechanics, identities verified by exact mean-values such as Schwinger-Dyson equations, Guerra relations, Callen identities, etc., provide well known and sensitive tests of thermalization bias as well as checks of pseudo random number generators. We point out that they can be further exploited as "control variates" to reduce statistical errors. The strategy is general, very simple, and almost costless in CPU time. The method is demonstrated in the two dimensional Ising model at criticality, where the CPU gain factor lies between 2 and 4.Comment: 10 pages, 2 tables. References updated and typos correcte
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