1,458 research outputs found
Strong field limit analysis of gravitational retro-lensing
We present a complete treatment in the strong field limit of gravitational
retro-lensing by a static spherically symmetric compact object having a photon
sphere. The results are compared with those corresponding to ordinary lensing
in similar strong field situations. As examples of application of the
formalism, a supermassive black hole at the galactic center and a stellar mass
black hole in the galactic halo are studied as retro-lenses, in both cases
using the Schwarzschild and Reissner-Nordstrom geometries.Comment: 11 pages, 1 figure; v2: minor changes. Accepted for publication in
Physical Review
Lung ultrasound can differentiate Pneumocystis jiroveci versus other etiologies among critically ill AIDS patients with pneumonia
Prediction in forensic science: a critical examination of common understandings
In this commentary, we argue that the term 'prediction' is overly used when in fact, referring to foundational writings of de Finetti, the correspondent term should be inference. In particular, we intend (i) to summarize and clarify relevant subject matter on prediction from established statistical theory, and (ii) point out the logic of this understanding with respect practical uses of the term prediction. Written from an interdisciplinary perspective, associating statistics and forensic science as an example, this discussion also connects to related fields such as medical diagnosis and other areas of application where reasoning based on scientific results is practiced in societal relevant contexts. This includes forensic psychology that uses prediction as part of its vocabulary when dealing with matters that arise in the course of legal proceedings
La naturaleza decisoria de las conclusiones de los expertos en ciencia forense (The decisionalization of individualization)
En la ciencia forense y ramas de la ciencia adyacentes, tanto investigadores del ámbito académico como quienes las practican continúan divergiendo en la percepción y comprensión del término “individualización”, es decir, la defensa de la tesis de que es posible reducir un conjunto de potenciales donantes de un vestigio forense a una única fuente. En concreto, se ha puesto de manifiesto que recientes cambios que entienden la práctica de la individualización como una decisión no son más que un mero cambio de etiqueta [1], dejando los cambios fundamentales en el orden del pensar y del entender aún pendientes. Es más, asociaciones profesionales y expertos huyen de adherirse a la noción de decisión tal y como la define la teoría formal de la decisión en la que la individualización puede contextualizarse, principalmente por las dificultades para tratar sobre las medidas de deseabilidad o no de las consecuencias de las decisiones (por ejemplo, utilizando las funciones de utilidad). Apoyándose en investigaciones existentes en esta área, este artículo presenta y discute sobre conceptos fundamentales de utilidades y costes, con particular referencia a su aplicación a la individualización forense. El artículo subraya que una adecuada comprensión de las herramientas de la decisión no solo reduce el número de asignaciones individuales que la aplicación de la teoría de la decisión requiere, sino que también muestra cómo esas asignaciones pueden relacionarse significativamente con las propiedades constituyentes del problema de la decisión en el mundo real al que se aplica la teoría. Se argumenta que la “decisionalización” de la individualización requiere esa percepción fundamental para iniciar cambios en las comprensiones subyacentes de esos campos, no meramente en el ámbito de sus etiquetas
Strong Gravitational Lensing by Sgr A*
In recent years, there has been increasing recognition of the potential of
the galactic center as a probe of general relativity in the strong field. There
is almost certainly a black hole at Sgr A* in the galactic center, and this
would allow us the opportunity to probe dynamics near the exterior of the black
hole. In the last decade, there has been research into extreme gravitational
lensing in the galactic center. Unlike in most applications of gravitational
lensing, where the bending angle is of the order of several arc seconds, very
large bending angles are possible for light that closely approaches a black
hole. Photons may even loop multiple times around a black hole before reaching
the observer. There have been many proposals to use light's close approach to
the black hole as a probe of the black hole metric. Of particular interest is
the property of light lensed by the S stars orbiting in the galactic center.
This paper will review some of the attempts made to study extreme lensing as
well as extend the analysis of lensing by S stars. In particular, we are
interested in the effect of a Reissner-Nordstrom like 1/r^2 term in the metric
and how this would affect the properties of relativistic images.Comment: 13 pages, 9 figures. Submitted as invited review article for the GR19
issue of CQ
Bayes Factors for Forensic Decision Analyses with R
Bayes Factors for Forensic Decision Analyses with R provides a self-contained introduction to computational Bayesian statistics using R. With its primary focus on Bayes factors supported by data sets, this book features an operational perspective, practical relevance, and applicability—keeping theoretical and philosophical justifications limited. It offers a balanced approach to three naturally interrelated topics:
– Probabilistic Inference: Relies on the core concept of Bayesian inferential statistics, to help practicing forensic scientists in the logical and balanced evaluation of the weight of evidence.
– Decision Making: Features how Bayes factors are interpreted in practical applications to help address questions of decision analysis involving the use of forensic science in the law.
– Operational Relevance: Combines inference and decision, backed up with practical examples and complete sample code in R, including sensitivity analyses and discussion on how to interpret results in context.
Over the past decades, probabilistic methods have established a firm position as a reference approach for the management of uncertainty in virtually all areas of science, including forensic science, with Bayes' theorem providing the fundamental logical tenet for assessing how new information—scientific evidence—ought to be weighed. Central to this approach is the Bayes factor, which clarifies the evidential meaning of new information, by providing a measure of the change in the odds in favor of a proposition of interest, when going from the prior to the posterior distribution. Bayes factors should guide the scientist's thinking about the value of scientific evidence and form the basis of logical and balanced reporting practices, thus representing essential foundations for rational decision making under uncertainty.
This book would be relevant to students, practitioners, and applied statisticians interested in inference and decision analyses in the critical field of forensic science. It could be used to support practical courses on Bayesian statistics and decision theory at both undergraduate and graduate levels, and will be of equal interest to forensic scientists and practitioners of Bayesian statistics for driving their evaluations and the use of R for their purposes
Estimating the parameters of the Sgr A* black hole
The measurement of relativistic effects around the galactic center may allow
in the near future to strongly constrain the parameters of the supermassive
black hole likely present at the galactic center (Sgr A*). As a by-product of
these measurements it would be possible to severely constrain, in addition,
also the parameters of the mass-density distributions of both the innermost
star cluster and the dark matter clump around the galactic center.Comment: Accepted for publication on General Relativity and Gravitation, 2010.
11 Pages, 1 Figur
Multiplex cytokine profile from dengue patients: MIP-1beta and IFN-gamma as predictive factors for severity
<p>Abstract</p> <p>Background</p> <p>Dengue virus pathogenesis is not yet fully understood and the identification of patients at high risk for developing severe disease forms is still a great challenge in dengue patient care. During the present study, we evaluated prospectively the potential of cytokines present in plasma from patients with dengue in stratifying disease severity.</p> <p>Methods</p> <p>Seventeen-cytokine multiplex fluorescent microbead immunoassay was used for the simultaneous detection in 59 dengue patients. GLM models using bimodal or Gaussian family were determined in order to associate cytokines with clinical manifestations and laboratory diagnosis.</p> <p>Results</p> <p>IL-1β, IFN-γ, IL-4, IL-6, IL-13, IL-7 and GM-CSF were significantly increased in patients with severe clinical manifestations (severe dengue) when compared to mild disease forms (mild dengue). In contrast, increased MIP-1β levels were observed in patients with mild dengue. MIP-1β was also associated with CD56+NK cell circulating rates. IL-1β, IL-8, TNF-α and MCP-1 were associated with marked thrombocytopenia. Increased MCP-1 and GM-CSF levels correlated with hypotension. Moreover, MIP-1β and IFN-γ were independently associated with both dengue severity and disease outcome.</p> <p>Conclusion</p> <p>Our data demonstrated that the use of a multiple cytokine assay platform was suitable for identifying distinct cytokine profiles associated with the dengue clinical manifestations and severity. MIP-β is indicated for the first time as a good prognostic marker in contrast to IFN-γ that was associated with disease severity.</p
Reissner-Nordstrom black hole lensing
In this paper we study the strong gravitational lensing scenario where the
lens is a Reissner-Nordstrom black hole. We obtain the basic equations and show
that, as in the case of Schwarzschild black hole, besides the primary and
secondary images, two infinite sets of relativistic images are formed. We find
analytical expressions for the positions and amplifications of the relativistic
images. The formalism is applied to the case of a low-mass black hole placed at
the galactic halo.Comment: 16 pages, 5 figure
Gravitational lensing in the strong field limit
We provide an analytic method to discriminate among different types of black
holes on the ground of their strong field gravitational lensing properties. We
expand the deflection angle of the photon in the neighbourhood of complete
capture, defining a strong field limit, in opposition to the standard weak
field limit. This expansion is worked out for a completely generic spherically
symmetric spacetime, without any reference to the field equations and just
assuming that the light ray follows the geodesics equation. We prove that the
deflection angle always diverges logarithmically when the minimum impact
parameter is reached. We apply this general formalism to Schwarzschild,
Reissner-Nordstrom and Janis-Newman-Winicour black holes. We then compare the
coefficients characterizing these metrics and find that different collapsed
objects are characterized by different strong field limits. The strong field
limit coefficients are directly connected to the observables, such as the
position and the magnification of the relativistic images. As a concrete
example, we consider the black hole at the centre of our galaxy and estimate
the optical resolution needed to investigate its strong field behaviour through
its relativistic images.Comment: 10 pages, 5 figures, in press on Physical Review
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