Human Mobility in a Continuum Approach

Human mobility is investigated using a continuum approach that allows to calculate the probability to observe a trip to anyarbitrary region, and the fluxes between any two regions. The considered description offers a general and unified framework, in which previously proposed mobility models like the gravity model, the intervening opportunities model, and the recently introduced radiation model are naturally resulting as special cases. A new form of radiation model is derived and its validity is investigated using observational data offered by commuting trips obtained from the United States census data set, and the mobility fluxesextracted from mobile phone data collected in a western European country. The new modeling paradigm offered by this description suggests that the complex topological features observed in large mobility and transportation networks may be the result of a simple stochastic process taking place on an inhomogeneous landscape.Comment: 13 pages, 3 figure

Two Coregulated Efflux Transporters Modulate Intracellular Heme and Protoporphyrin IX Availability in Streptococcus agalactiae

Streptococcus agalactiae is a major neonatal pathogen whose infectious route involves septicemia. This pathogen does not synthesize heme, but scavenges it from blood to activate a respiration metabolism, which increases bacterial cell density and is required for full virulence. Factors that regulate heme pools in S. agalactiae are unknown. Here we report that one main strategy of heme and protoporphyrin IX (PPIX) homeostasis in S. agalactiae is based on a regulated system of efflux using two newly characterized operons, gbs1753 gbs1752 (called pefA pefB), and gbs1402 gbs1401 gbs1400 (called pefR pefC pefD), where pef stands for ‘porphyrin-regulated efflux’. In vitro and in vivo data show that PefR, a MarR-superfamily protein, is a repressor of both operons. Heme or PPIX both alleviate PefR-mediated repression. We show that bacteria inactivated for both Pef efflux systems display accrued sensitivity to these porphyrins, and give evidence that they accumulate intracellularly. The ΔpefR mutant, in which both pef operons are up-regulated, is defective for heme-dependent respiration, and attenuated for virulence. We conclude that this new efflux regulon controls intracellular heme and PPIX availability in S. agalactiae, and is needed for its capacity to undergo respiration metabolism, and to infect the host

Projeto Meninos do Rio: mundo da vida, adolescência e riscos de saúde The Meninos do Rio Program: lifeworld, adolescence, and health risks

Este trabalho tem o objetivo de investigar os riscos de saúde em adolescentes de dois municípios do Vale do Rio São Francisco - Ibiaí e Morada Nova - e do Aglomerado Urbano Morro das Pedras, em Belo Horizonte. Articula-se ao trabalho de ensino e extensão voltado para a promoção de saúde do adolescente realizado pela Universidade Federal de Minas Gerais nessas localidades e utiliza como referencial teórico-metodológico primeiro a Teoria da Ação Comunicativa de Habermas. É um estudo qualitativo e quantitativo que utiliza a associação de vários procedimentos: aplicação de questionários nas escolas de ensino médio e fundamental, observação participante, grupos focais e entrevistas. Sexualidade, trabalho e violência aparecem como os principais temas, associam-se a vários riscos, e sua importância se acentua com os altos percentuais encontrados, em adolescentes de ambas as faixas etárias abordadas, 10-14 e 15-19 anos. Entre os primeiros, o trabalho associa-se a quase todos os riscos. A relação entre o contexto e as práticas dos adolescentes, assim como as contradições detectadas entre elas, foram analisadas e interpretadas valendo-se da tese da colonização do mundo da vida, proposta por Habermas.<br>This study focuses on health risks among teenagers from two towns in the São Francisco River Valley (Ibiaí and Morada Nova) and slums in Morro das Pedras, Belo Horizonte, Minas Gerais State, Brazil. The study discusses teaching and extracurricular activities by the Federal University in Minas Gerais in these localities, aimed at promoting health in adolescence. The authors use the Habermas communicative action theory as the main theoretical and methodological approach. The research adopted a qualitative and quantitative methodology, including dynamic observation, focus groups, interviews, and questionnaires answered by high school students. Sexuality, work, and violence were the main themes and were associated with numerous health risks. Work in the 10-to-14-year-old group was associated with nearly all types of health risks. The authors analyze the relations between context and adolescent behavior using the Habermasian concept of lifeworld colonization

Labor market institutions and the efficiency of interregional migration:A Cross-Nation Comparison

An important question for economists concerns the effectiveness, or efficiency, of interregional migration as a labor market adjustment mechanism. We have considered the many dimensions of this issue in Chapter 1. Hoover and Giarratani (1984) suggest that this question of efficiency can be addressed at three different levels of inquiry by: (1) examining ratios of net to total gross flows of migrants between pairs of regions; (2) determining whether migrants benefit from their actions in terms of enhanced employment and/or income opportunity; and (3) assessing the contribution of interregional migration to aggregate output or, more broadly, to social welfare. Although a perfectly homogeneous labor force is required for (1) to assume economic meaning, and (3) is often considered unopera-tional due to the difficulty of measuring migration externalities, a number of recent studies have addressed the question of migration efficiency (directly and indirectly) along the lines of (2) above

Large turbulent reservoirs of cold molecular gas around high-redshift starburst galaxies

International audienceStarburst galaxies at the peak of cosmic star formation are among the most extreme starforming engines in the universe, producing stars over ~100 Myr. The star formation rates of these galaxies, which exceed 100 $M_\odot$ per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Starburst galaxies are therefore ideal targets to unravel the critical interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH$^+$, is a most useful molecule for such studies because it cannot form in cold gas without supra-thermal energy input, so its presence highlights dissipation of mechanical energy or strong UV irradiation. Here, we report the detection of CH$^+$(J=1-0) emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts z~2.5. This line has such a high critical density for excitation that it is emitted only in very dense ($>10^5$ cm$^{-3}$) gas, and is absorbed in low-density gas. We find that the CH$^+$ emission lines, which are broader than 1000 km s$^{-1}$, originate in dense shock waves powered by hot galactic winds. The CH$^+$ absorption lines reveal highly turbulent reservoirs of cool ($T\sim 100$K), low-density gas, extending far outside (>10 kpc) the starburst cores (radii <1 kpc). We show that the galactic winds sustain turbulence in the 10 kpc-scale environments of the starburst cores, processing these environments into multi-phase, gravitationally bound reservoirs. However, the mass outflow rates are found to be insufficient to balance the star formation rates. Another mass input is therefore required for these reservoirs, which could be provided by on-going mergers or cold stream accretion. Our results suggest that galactic feedback, coupled jointly to turbulence and gravity, extends the starburst phase instead of quenching it