Implications of the Measured Image Size for the Radio Afterglow of GRB 030329

We use data on the image size of the radio afterglow of GRB 030329 (Taylor et al. 2004) to constrain the physical parameters of this explosion. Together with the observed broad band spectrum, this data over-constrains the physical parameters, thus enabling to test different GRB jet models for consistency. We consider two extreme models for the lateral spreading of the jet: model 1 with relativistic expansion in the local rest frame, and model 2 with little lateral expansion as long as the jet is highly relativistic. We find that both models are consistent with the data for a uniform external medium, while for a stellar wind environment model 1 is consistent with the data but model 2 is disfavored by the data. Our derivations can be used to place tighter constraints on the dynamics and structure of GRB jets in future afterglows, following a denser monitoring campaign for the temporal evolution of their image size.Comment: 12 pages, 6 figues; submitted to Ap

Afterglow Observations Shed New Light on the Nature of X-ray Flashes

X-ray flashes (XRFs) and X-ray rich gamma-ray bursts (XRGRBs) share many observational characteristics with long duration GRBs, but the reason for which their prompt emission peaks at lower photon energies, $E_p$, is still under debate. Although many different models have been invoked in order to explain the lower $E_p$ values, their implications for the afterglow emission were not considered in most cases, mainly because observations of XRF afterglows have become available only recently. Here we examine the predictions of the various XRF models for the afterglow emission, and test them against the observations of XRF 030723 and XRGRB 041006, the events with the best monitored afterglow light curves in their respective class. We show that most existing XRF models are hard to reconcile with the observed afterglow light curves, which are very flat at early times. Such light curves are, however, naturally produced by a roughly uniform jet with relatively sharp edges that is viewed off-axis (i.e. from outside of the jet aperture). This type of model self consistently accommodates both the observed prompt emission and the afterglow light curves of XRGRB 041006 and XRF 030723, implying viewing angles $\theta_{obs}$ from the jet axis of $(\theta_{obs}-\theta_0)\sim 0.15\theta_0$ and $\sim \theta_0$, respectively, where $\theta_0\sim 3$ deg is the jet half-opening angle. This suggests that GRBs, XRGRBs and XRFs are intrinsically similar relativistic jets viewed from different angles, corresponding to $\gamma(\theta_{obs}-\theta_0)$ of less than 1, between 1 and a few, and more than a few, respectively, where $\gamma$ is the Lorentz factor. Future observations with Swift could help test this unification scheme in which GRBs, XRGRBs and XRFs share the same basic physics and differ only by their orientation relative to our line of sight.Comment: some references added, small typos corrected, and the important role of HETE II emphasize

Simulations of GRB Jets in a Stratified External Medium: Dynamics, Afterglow Lightcurves, Jet Breaks and Radio Calorimetry

The dynamics of GRB jets during the afterglow phase is most reliably and accurately modelled using hydrodynamic simulations. All published simulations, however, have considered only a uniform external medium, while a stratified external medium is expected around long duration GRB progenitors. Here we present simulations of the dynamics of GRB jets and the resulting afterglow emission for both uniform and stratified external media with $\rho \propto r^{-k}$ for k = 0, 1, 2. The simulations are performed in 2D using the special relativistic version of the Mezcal code. The dynamics for stratified external media are broadly similar to those derived for expansion into a uniform external medium. The jet half-opening angle start increasing logarithmically with time once the Lorentz factor drops below 1/theta_0. For larger k values the lateral expansion is faster at early times and slower at late times with the jet expansion becoming Newtonian and slowly approaching spherical symmetry over progressively longer timescales. We find that contrary to analytic expectations, there is a reasonably sharp jet break in the lightcurve for k = 2 although the shape of the break is affected more by the viewing angle than by the slope of the external density profile. Steeper density profiles are found to produce more gradual jet breaks while larger viewing angles cause smoother and later appearing jet breaks. The counter-jet becomes visible as it becomes sub-relativistic, and for k=0 this results in a clear bump-like feature in the light curve. However, for larger k values the jet decelerates more gradually, causing only a mild flattening in the radio light curve that might be hard to discern when k=2. Late time radio calorimetry is likely to consistently over-estimate the true energy by up to a factor of a few for k=2, and either over-predict or under-predict it by a smaller factor for k = 0,1.Comment: 10 pages, 13 figures, submitted to Ap

Health, Healthcare Access, and Use of Traditional Versus Modern Medicine in Remote Peruvian Amazon Communities: A Descriptive Study of Knowledge, Attitudes, and Practices

There is an urgent need for healthcare research, funding, and infrastructure in the Peruvian Amazon. We performed a descriptive study of health, health knowledge and practice, and healthcare access of 13 remote communities of the Manatí and Amazon Rivers in northeastern Peru. Eighty-five adults attending a medical boat service were interviewed to collect data on socioeconomic position, health, diagnosed illnesses, pain, healthcare access, and traditional versus modern medicine use. In this setting, poverty and gender inequality were prevalent, and healthcare access was limited by long distances to the health post and long waiting times. There was a high burden of reported pain (mainly head and musculoskeletal) and chronic non-communicable diseases, such as hypertension (19%). Nearly all participants felt that they did not completely understand their diagnosed illnesses and wanted to know more. Participants preferred modern over traditional medicine, predominantly because of mistrust or lack of belief in traditional medicine. Our findings provide novel evidence concerning transitional health beliefs, hidden pain, and chronic non-communicable disease prevalence in marginalized communities of the Peruvian Amazon. Healthcare provision was limited by a breach between health education, knowledge, and access. Additional participatory research with similar rural populations is required to inform regional healthcare policy and decision-making

An Off-Axis Model for GRB 031203

The low luminosity radio emission of the unusually faint GRB 031203 has been argued to support the idea of a class of intrinsically sub-energetic gamma-ray bursts (GRBs), currently comprising two members. While low energy GRBs probably exist, we show that the collective prompt and multiwavelength observations of the afterglow of GRB 031203 do not necessarily require a sub-energetic nature for that event. In fact, the data are more consistent with a typical, powerful GRB seen at an angle of about twice the opening angle of the central jet. The (redshift corrected) peak energy, E_p, of GRB 031203 then becomes ~ 2 MeV, similar to many other GRBs.Comment: 4 pages, 3 figures; ApJL in pres

Masses of a Fourth Generation with Two Higgs Doublets

We use sampling techniques to find robust constraints on the masses of a possible fourth sequential fermion generation from electroweak oblique variables. We find that in the case of a light (115 GeV) Higgs from a single electroweak symmetry breaking doublet, inverted mass hierarchies are possible for both quarks and leptons, but a mass splitting more than M(W) in the quark sector is unlikely. We also find constraints in the case of a heavy (600 GeV) Higgs in a single doublet model. As recent data from the Large Hadron Collider hints at the existence of a resonance at 124.5 GeV and a single Higgs doublet at that mass is inconsistent with a fourth fermion generation, we examine a type II two Higgs doublet model. In this model, there are ranges of parameter space where the Higgs sector can potentially counteract the effects of the fourth generation. Even so, we find that such scenarios produce qualitatively similar fermion mass distributions.Comment: v2: 9 pages, 7 figures, improved analysis of Higgs decay constraints, typos corrected and reference adde

Manejo de heridas crónicas con terapia de presión negativa ambulatoria por profesionales de enfermería en el servicio de clínica de heridas del H.G.R N° 251

El empleo de la terapia de presión negativa es una opción ampliamente extendida para el manejo de heridas crónicas, promueve la curación mediante la aplicación de presión negativa, de manera que el uso de niveles controlados de presión subatmosférica y succión controlada, acelera la resolución de las mismas favoreciendo la vascularización y el desbridamiento. Actualmente, este sistema se considera una intervención fundamental en el tratamiento de las heridas complejas, las cuales suponen un reto terapéutico importante y muchas veces generan un largo y costoso egreso hospitalario. Gracias a la terapia de vacío se puede disminuir el tamaño de dichas heridas a la par que se protegen de la infección, haciendo innecesario el uso prioritario de colgajos libres y grandes intervenciones. La terapia de presión negativa se remonta a miles de años atrás, se utilizó por primera vez como tratamiento complementario; a nivel básico, la presión negativa constituye un apósito sofisticado, estéril y cerrado con propiedades que hacen que el entorno para la cicatrización de la herida sea húmedo

Identificación de bacterias halófilas tolerantes a metales pesados

Los metales pesados son materiales empleados en procesos tecnológicos y actividades antropogénicas, algunas veces son liberados al medio ambiente provocando deterioro de flora, fauna y salud humana por lo que se han implementado diferentes estrategias para eliminarlos o reducirlos del medio ambiente como los tratamientos químicos, los cuales utilizan las propiedades físicas y químicas de los contaminantes o del medio contaminado para transformar, separar o inmovilizarlos pero muchas veces estos tratamientos presentan como desventaja el requerir un tratamiento secundario o disposición final del contaminante, lo que genera un costo económico y ambiental. También existen los métodos biológicos (biorremediación) que utilizan principalmente plantas, hongos y bacterias principalmente. Existen ambientes que presentan parámetros fisicoquímicos extremos ya sea de temperatura, pH, presión, salinidad etc., en estos ambientes se desarrollan microorganismos extremófilos los cuales requieren de condiciones extremas para desarrollarse, tal es el caso de las bacterias halófilas, las cuales requieren cierta concentración de salinidad para desarrollarse

Covariance Estimation from Compressive Data Partitions using a Projected Gradient-based Algorithm

Covariance matrix estimation techniques require high acquisition costs that challenge the sampling systems' storing and transmission capabilities. For this reason, various acquisition approaches have been developed to simultaneously sense and compress the relevant information of the signal using random projections. However, estimating the covariance matrix from the random projections is an ill-posed problem that requires further information about the data, such as sparsity, low rank, or stationary behavior. Furthermore, this approach fails using high compression ratios. Therefore, this paper proposes an algorithm based on the projected gradient method to recover a low-rank or Toeplitz approximation of the covariance matrix. The proposed algorithm divides the data into subsets projected onto different subspaces, assuming that each subset contains an approximation of the signal statistics, improving the inverse problem's condition. The error induced by this assumption is analytically derived along with the convergence guarantees of the proposed method. Extensive simulations show that the proposed algorithm can effectively recover the covariance matrix of hyperspectral images with high compression ratios (8-15% approx) in noisy scenarios. Additionally, simulations and theoretical results show that filtering the gradient reduces the estimator's error recovering up to twice the number of eigenvectors.Comment: submitted to IEEE Transactions on Image Processin