Kinematic structure in the young Sigma Orionis association

We have used precise radial velocity measurements for a large number of candidate low-mass stars and brown dwarfs, to show that the young Sigma Ori ``cluster'' consists of two spatially superimposed components which are kinematically separated by 7 km/s in radial velocity, and which have different mean ages. We examine the relationship of these two kinematic groups to other populations in the Orion OB1 association and briefly discuss the consequence of mixed age samples for ongoing investigations of the formation and evolution of low-mass objects in this much-observed region.Comment: MNRAS Letter in pres

Membership, binarity and accretion among very low-mass stars and brown dwarfs of the Sigma Orionis cluster

Intermediate resolution (R=7000) spectroscopy is presented for 76 photometrically selected very low mass (0.04<M<0.3M_{sun}) candidate members of the Sigma Orionis cluster. More than two thirds appear to be genuine cluster members on the basis of Li I absorption, weak Na I features and radial velocities. Photometric selection alone therefore appears to be very effective in identifying cluster members in this mass range. Only 6 objects appear to be certain non-members, however a substantial subset of 13 have ambiguous or contradictory indications of membership and lack Li absorption. Four candidate binary cluster members are identified. Consideration of sampling and precision leads us to conclude that either the fraction of very low mass stars and brown dwarfs in small separation (a<1au) binary systems is larger than in field M-dwarfs, or the distribution of separations is much less skewed towards large separations. This conclusion hinges critically on the correct identification of the small number of binary candidates, but is significant even when only Li-rich candidate members are considered. Broadened H alpha emission, indicative of circum(sub)stellar accretion discs is found in 5 or 6 of the candidate cluster members, 3 of which probably have substellar masses. The fraction of accretors (10+/-5 per cent) is similar to that found in stars of higher mass in the cluster using H alpha emission as a diagnostic, but much lower than found for very low mass stars and brown dwarfs of younger clusters. The timescale for accretion rates to drop to less than 10^{-11} M_sun/yr is hence less than the age of the Sigma Ori cluster (3 to 7 Myr) for most low-mass objects (abridged).Comment: Accepted for publication in MNRA

Typhoid toxin exhausts the RPA response to DNA replication stress driving senescence and Salmonella infection.

Salmonella Typhi activates the host DNA damage response through the typhoid toxin, facilitating typhoid symptoms and chronic infections. Here we reveal a non-canonical DNA damage response, which we call RING (response induced by a genotoxin), characterized by accumulation of phosphorylated histone H2AX (γH2AX) at the nuclear periphery. RING is the result of persistent DNA damage mediated by toxin nuclease activity and is characterized by hyperphosphorylation of RPA, a sensor of single-stranded DNA (ssDNA) and DNA replication stress. The toxin overloads the RPA pathway with ssDNA substrate, causing RPA exhaustion and senescence. Senescence is also induced by canonical γΗ2ΑΧ foci revealing distinct mechanisms. Senescence is transmitted to non-intoxicated bystander cells by an unidentified senescence-associated secreted factor that enhances Salmonella infections. Thus, our work uncovers a mechanism by which genotoxic Salmonella exhausts the RPA response by inducing ssDNA formation, driving host cell senescence and facilitating infection

Are There Age Spreads in Star Forming Regions?

A luminosity spread at a given effective temperature is ubiquitously seen in the Hertzsprung-Russell (HR) diagrams of young star forming regions and often interpreted in terms of a prolonged period (>=10 Myr) of star formation. I review the evidence that the observed luminosity spreads are genuine and not caused by astrophysical sources of scatter. I then address whether the luminosity spreads necessarily imply large age spreads, by comparing HR diagram ages with ages from independent clocks such as stellar rotation rate, the presence of circumstellar material and lithium depletion. I argue that whilst there probably is a true luminosity dispersion, there is little evidence to support age spreads larger than a few Myr. This paradox could be resolved by brief periods of rapid accretion during the class I pre main-sequence phase.Comment: To appear in the proceedings of JENAM10: Star Clusters in the Era of Large Surveys, 8 page

A hazard model of the probability of medical school dropout in the United Kingdom

From individual level longitudinal data for two entire cohorts of medical students in UK universities, we use multilevel models to analyse the probability that an individual student will drop out of medical school. We find that academic preparedness—both in terms of previous subjects studied and levels of attainment therein—is the major influence on withdrawal by medical students. Additionally, males and more mature students are more likely to withdraw than females or younger students respectively. We find evidence that the factors influencing the decision to transfer course differ from those affecting the decision to drop out for other reasons

Diagrams for heat kernel expansions

A diagramatic heat kernel expansion technique is presented. The method is especially well suited to the small-derivative expansion of the heat kernel, but it can also be used to reproduce the results obtained by the approach known as covariant perturbation theory. The new technique gives an expansion for the heat kernel at coincident points. It can also be used to obtain the derivative of the heat kernel and this is useful for evaluating the expectation values of the stress-energy tensor.Comment: 17 pages, 4 figures, ReVTe

Exposure to diesel exhaust particles increases susceptibility to invasive pneumococcal disease.

BACKGROUND: The World Health Organization estimates that air pollution is responsible for 7 million deaths per annum, with 7% of these attributable to pneumonia. Many of these fatalities have been linked to exposure to high levels of airborne particulates, such as diesel exhaust particles (DEPs). OBJECTIVES: We sought to determine whether exposure to DEPs could promote the progression of asymptomatic nasopharyngeal carriage of Streptococcus pneumoniae to invasive pneumococcal disease. METHODS: We used mouse models and in vitro assays to provide a mechanistic understanding of the link between DEP exposure and pneumococcal disease risk, and we confirmed our findings by using induced sputum macrophages isolated from healthy human volunteers. RESULTS: We demonstrate that inhaled exposure to DEPs disrupts asymptomatic nasopharyngeal carriage of S pneumoniae in mice, leading to dissemination to lungs and blood. Pneumococci are transported from the nasopharynx to the lungs following exposure to DEPs, leading to increased proinflammatory cytokine production, reduced phagocytic function of alveolar macrophages, and consequently, increased pneumococcal loads within the lungs and translocation into blood. These findings were confirmed by using DEP-exposed induced sputum macrophages isolated from healthy volunteers, demonstrating that impaired innate immune mechanisms following DEP exposure are also at play in humans. CONCLUSION: Lung inhaled DEPs increase susceptibility to pneumococcal disease by leading to loss of immunological control of pneumococcal colonisation, increased inflammation, tissue damage, and systemic bacterial dissemination

The Malcolm Boat (38CH803): Discovery, Stabilization, Excavation, and Preservation of an Historic Sea Going Small Craft in the Ashley River, Charleston County, South Carolina

The following report details the results of an investigation of the remains of a small historic sailing craft, The Malcolm Boat (38CH803), discovered in a mud bank of the Ashley River in 1985. The investigation, conducted in June of 1992, with partial funding support from the South Carolina Department of Archives and History, revealed that the vessel was a small ocean-going hull dating to the last quarter of the eighteenth century and the first quarter of the nineteenth. The analysis presented discusses the vessel\u27s age, method of construction and function as a coastal or possibly inter-islander trader, and places the vessel within a regional maritime historical context. Historical context is provided in the form of the background history of shipbuilding in South Carolina and a preliminary typology of local small craft. Methods of site stabilization for intertidal zone sites are discussed with recommendations for future work in this new area of investigation in the state.https://scholarcommons.sc.edu/archanth_books/1194/thumbnail.jp

The Herschel Comprehensive (U)LIRG Emission Survey (HerCULES): CO Ladders, fine structure lines, and neutral gas cooling

(Ultra) Luminous Infrared Galaxies ((U)LIRGs) are objects characterized by their extreme infrared (8-1000 $\mu$m) luminosities ($L_{LIRG}>10^{11}$L$_\odot$ and $L_{ULIRG}>10^{12}$ L$_\odot$). The Herschel Comprehensive ULIRG Emission Survey (HerCULES; PI van der Werf) presents a representative flux-limited sample of 29 (U)LIRGs that spans the full luminosity range of these objects (10$^{11}\leq L_\odot \geq10^{13}$). With the \emph{Herschel Space Observatory}, we observe [CII] 157 $\mu$m, [OI] 63 $\mu$m, and [OI] 145 $\mu$m line emission with PACS, CO J=4-3 through J=13-12, [CI] 370 $\mu$m, and [CI] 609 $\mu$m with SPIRE, and low-J CO transitions with ground-based telescopes. The CO ladders of the sample are separated into three classes based on their excitation level. In 13 of the galaxies, the [OI] 63 $\mu$m emission line is self absorbed. Comparing the CO excitation to the IRAS 60/100 $\mu$m ratio and to far infrared luminosity, we find that the CO excitation is more correlated to the far infrared colors. We present cooling budgets for the galaxies and find fine-structure line flux deficits in the [CII], [SiII], [OI], and [CI] lines in the objects with the highest far IR fluxes, but do not observe this for CO $4\leq J_{upp}\leq13$. In order to study the heating of the molecular gas, we present a combination of three diagnostic quantities to help determine the dominant heating source. Using the CO excitation, the CO J=1-0 linewidth, and the AGN contribution, we conclude that galaxies with large CO linewidths always have high-excitation CO ladders, and often low AGN contributions, suggesting that mechanical heating is important