Low surface brightness galaxies mass profiles as a consequence of galactic evolution

This paper presents a principal components analysis of rotation curves from a sample of low surface brightness galaxies. The physical meaning of the principal components is investigated, and related to the intrinsic properties of the galaxies. The rotation curves are re-scaled using the optical disk scale, the resulting principal component decomposition demonstrates that the whole sample is properly approximated using two components. The ratio of the second to the first component is related to the halo steepness in the central region, is correlated to the gas fraction in the galaxy, and is un-correlated to other parameters. As a consequence the gas fraction appear as a fundamental variable with respect to the galaxies rotation curves, and its correlation with the halo steepness is especially important. Since the gas fraction is related to the degree of galaxy evolution, it is very likely that the steepness of the halo at the center is a consequence of galaxy evolution. More evolved galaxies have shallower central profile and statistically less gas, most likely as a consequence of more star formation and supernovae. The differences in evolution, gas fractions and halo central steepness of the galaxies could be due to the influence of different environments.Comment: 8 pages, 4 figure

Predicting the duration of leveraged buyouts.

We employ newly developed split hazard modeling to estimate the conditional probability that a firm eventually return to public status following a leveraged buyout (LBO), and the conditional probability of reversion to public status in a given year for a firm that eventually may reverse. Our results, based on 343 LBO transactions, imply that not all LBO firms expect eventual reversion to public status. In addition, we find that those LBO decisions that are expected to enhance value the most are less likely to reverse eventually. We also find that eventual reversal probabilities and the timing of reversals for divisional LBOs are not significantly different from full-firm LBOs.Leveraged buyouts;

Perceptions and determinants of partnership trust in the context of Community-Based Participatory Research

Trust is difficult to conceptualize and define because of its diverse applications in different disciplines. Historic mistrust between vulnerable communities and researchers based on past adverse experiences can negatively affect the ability to collaborate and conduct effective research with such populations. Community Based-Participatory Research (CBPR) is a collaborative approach to research that can reduce historic mistrust and health disparities among minority populations. Although how trust development occurs in CBPR partnerships has been explored, there is a need to determine how to move from one stage to the next in fostering and maintaining that trust. The present study contributes to this discussion by addressing the lack of a shared operational definition of partnership trust and of how to measure it in the CBPR literature. We modified Dietz and Den Hartog’s (2006) Multi-dimensional Measure of Trust Model to investigate contextual factors that influence perceptions and development of trust in collaborative partnerships pursuing the reduction of health disparities. We conducted focus groups and key informant interviews with English and Spanish speaking stakeholders of a culturally relevant health promotion organization in the southeastern United States. Stakeholders reported experiencing different types of partnership trust depending on their role, and the length and nature of involvement with the organization. We identified determinants of partnership trust among stakeholders, including organizational, socio-economic, and cultural determinants. Most study participants agreed that trust with Hispanic communities is built slowly, with personal face-to-face contact and follow-up, and that engaging stakeholders throughout the process of working together in an intentional way is vital to building and maintaining trust. Findings of this study will inform the development of a culturally and linguistically relevant quantitative instrument to measure partnership trust in the context of CBPR

Proliferation and fragmentation: Transactions costs and the value of aid

The problem of the proliferation of the number of aid donors and aid channels continues to worsen. It is widely and plausibly believed that this significantly; reduces the value of aid by increasing direct and indirect transactions costs. We contribute to the existing literature by: (a) categorising the apparent adverse effects of proliferation; (b) producing a reliable and fair indicator of the relative degree to which the main bilateral donors proliferate or concentrate their aid; (c) giving some explanation of why some donors proliferate more than others; (d) constructing a reliable measure of the extent to to which recipients suffer from the problem of fragmentation in the sources of their aid; and (e) demonstrating that the worst proliferators among the aid donors are especially likely); to be suppliers of aid to recipients suffering most from fragmentation. There are significant implications for aid policy

Statistics of Substructures in Dark Matter Haloes

We study the amount and distribution of dark matter substructures within dark matter haloes, using a large set of high-resolution simulations ranging from group size to cluster size haloes, and carried our within a cosmological model consistent with WMAP 7-year data. In particular, we study how the measured properties of subhaloes vary as a function of the parent halo mass, the physical properties of the parent halo, and redshift. The fraction of halo mass in substructures increases with increasing mass. There is, however, a very large halo-to-halo scatter that can be explained only in part by a range of halo physical properties, e.g. concentration. At given halo mass, less concentrated haloes contain significantly larger fractions of mass in substructures because of the reduced strength of tidal disruption. Most of the substructure mass is located at the outskirts of the parent haloes, in relatively few massive subhaloes. This mass segregation appears to become stronger at increasing redshift, and should reflect into a more significant mass segregation of the galaxy population at different cosmic epochs. When haloes are accreted onto larger structures, their mass is significantly reduced by tidal stripping. Haloes that are more massive at the time of accretion (these should host more luminous galaxies) are brought closer to the centre on shorter time-scales by dynamical friction, and therefore suffer of a more significant stripping. The halo merger rate depends strongly on the environment with substructure in more massive haloes suffering more important mergers than their counterparts residing in less massive systems. This should translate into a different morphological mix for haloes of different mass.Comment: 13 pages, 11 figures and 1 table. MNRAS 2011 in pres

Unimodal generalized pseudo-Anosov maps

An infinite family of generalized pseudo-Anosov homeomorphisms of the sphere S is constructed, and their invariant foliations and singular orbits are described explicitly by means of generalized train tracks. The complex strucure induced by the invariant foliations is described, and is shown to make S into a complex sphere. The generalized pseudo-Anosovs thus become quasiconformal automorphisms of the Riemann sphere, providing a complexification of the unimodal family which differs from that of the Fatou/Julia theory.Comment: Published by Geometry and Topology at http://www.maths.warwick.ac.uk/gt/GTVol8/paper31.abs.htm

Paper folding, Riemann surfaces, and convergence of pseudo-Anosov sequences

A method is presented for constructing closed surfaces out of Euclidean polygons with infinitely many segment identifications along the boundary. The metric on the quotient is identified. A sufficient condition is presented which guarantees that the Euclidean structure on the polygons induces a unique conformal structure on the quotient surface, making it into a closed Riemann surface. In this case, a modulus of continuity for uniformizing coordinates is found which depends only on the geometry of the polygons and on the identifications. An application is presented in which a uniform modulus of continuity is obtained for a family of pseudo-Anosov homeomorphisms, making it possible to prove that they converge to a Teichm\"uller mapping on the Riemann sphere.Comment: 75 pages, 18 figure

Circular velocity profiles of dark matter haloes

We use a high-resolution simulation of a galaxy-sized dark matter halo, published simulated data as well as four cluster-sized haloes from Fukushige, Kawai & Makino to study the inner halo structure in a Lambda cold dark matter cosmology. We find that the circular velocity curves are substantially better described by Stoehr et al. (SWTS) profiles than by Navarro, Frenk & White (NFW) or Moore et al. profiles. Our findings confirm that no asymptotic slope is reached and that the profiles are nearly universal, but not perfectly. The velocity profiles curve at a_constant_ rate in log(r) over the full converged range in radii and the corresponding extrapolated density profiles reach a finite maximum density. We find, that the claim of a strong discrepancy between the observed inner slopes of the density profiles of low surface brightness galaxies (LSB) and their simulated counterparts on the grounds of currently available observations and simulations is unfounded. In addition, if the SWTS profile turns out to be a good description of the halo profile for the regions that cannot be probed with simulations of today, then even in these regions the agreeement between simulations and observations is very reasonable.Comment: 7 pages, 3 figures, replaced with version accepted to MNRA

Generalised Bose-Einstein phase transition in large-mm component spin glasses

It is proposed to understand finite dimensional spin glasses using a $1/m$ expansion, where $m$ is the number of spin components. It is shown that this approach predicts a replica symmetric state in finite dimensions. The point about which the expansion is made, the infinite-$m$ limit, has been studied in the mean-field limit in detail and has a very unusual phase transition, rather similar to a Bose-Einstein phase transition but with $N^{2/5}$ macroscopically occupied low-lying states.Comment: 4 pages (plus a few lines), 3 figures. v2: minor error corrected. v3: numerics supplemented by analytical arguments, references added, figure of density of states adde