An alternative formulation of classical electromagnetic duality

By introducing a doublet of electromagnetic four dimensional vector potentials, we set up a manifestly Lorentz covariant and SO(2) duality invariant classical field theory of electric and magnetic charges. In our formulation one does not need to introduce the concept of Dirac string.Comment: 14 pages, no figures, Latex, minor corrections, references and acknowledgements adde

A simple prescription for simulating and characterizing gravitational arcs

Simple models of gravitational arcs are crucial to simulate large samples of these objects with full control of the input parameters. These models also provide crude and automated estimates of the shape and structure of the arcs, which are necessary when trying to detect and characterize these objects on massive wide area imaging surveys. We here present and explore the ArcEllipse, a simple prescription to create objects with shape similar to gravitational arcs. We also present PaintArcs, which is a code that couples this geometrical form with a brightness distribution and adds the resulting object to images. Finally, we introduce ArcFitting, which is a tool that fits ArcEllipses to images of real gravitational arcs. We validate this fitting technique using simulated arcs and apply it to CFHTLS and HST images of tangential arcs around clusters of galaxies. Our simple ArcEllipse model for the arc, associated to a S\'ersic profile for the source, recovers the total signal in real images typically within 10%-30%. The ArcEllipse+S\'ersic models also automatically recover visual estimates of length-to-width ratios of real arcs. Residual maps between data and model images reveal the incidence of arc substructure. They may thus be used as a diagnostic for arcs formed by the merging of multiple images. The incidence of these substructures is the main factor preventing ArcEllipse models from accurately describing real lensed systems.Comment: 12 pages, 11 figures, accepted for publication in A&

Evolving the Bowen-York initial data for spinning black holes

The Bowen-York initial value data typically used in numerical relativity to represent spinning black hole are not those of a constant-time slice of the Kerr spacetime. If Bowen-York initial data are used for each black hole in a collision, the emitted radiation will be partially due to the ``relaxation'' of the individual holes to Kerr form. We compute this radiation by treating the geometry for a single hole as a perturbation of a Schwarzschild black hole, and by using second order perturbation theory. We discuss the extent to which Bowen-York data can be expected accurately to represent Kerr holes.Comment: 10 pages, RevTeX, 4 figures included with psfi

Stochastic bias of colour-selected BAO tracers by joint clustering-weak lensing analysis

The baryon acoustic oscillation (BAO) feature in the two-point correlation function of galaxies supplies a standard ruler to probe the expansion history of the Universe. We study here several galaxy selection schemes, aiming at building an emission-line galaxy (ELG) sample in the redshift range $0.6<z<1.7$, that would be suitable for future BAO studies, providing a highly biased galaxy sample. We analyse the angular galaxy clustering of galaxy selections at the redshifts 0.5, 0.7, 0.8, 1 and 1.2 and we combine this analysis with a halo occupation distribution (HOD) model to derive the properties of the haloes these galaxies inhabit, in particular the galaxy bias on large scales. We also perform a weak lensing analysis (aperture statistics) to extract the galaxy bias and the cross-correlation coefficient and compare to the HOD prediction. We apply this analysis on a data set composed of the photometry of the deep co-addition on Sloan Digital Sky Survey (SDSS) Stripe 82 (225 deg$^2$), of Canda-France-Hawai Telescope/Stripe 82 deep \emph{i}-band weak lensing survey and of the {\it Wide-Field Infrared Survey Explorer}infrared photometric band W1. The analysis on the SDSS-III/constant mass galaxies selection at $z=0.5$ is in agreement with previous studies on the tracer, moreover we measure its cross-correlation coefficient $r=1.16\pm0.35$. For the higher redshift bins, we confirm the trends that the brightest galaxy populations selected are strongly biased ($b>1.5$), but we are limited by current data sets depth to derive precise values of the galaxy bias. A survey using such tracers of the mass field will guarantee a high significance detection of the BAO.Comment: 17 pages, 15 figures, submitted to MNRA

The collision of boosted black holes: second order close limit calculations

We study the head-on collision of black holes starting from unsymmetrized, Brill--Lindquist type data for black holes with non-vanishing initial linear momentum. Evolution of the initial data is carried out with the ``close limit approximation,'' in which small initial separation and momentum are assumed, and second-order perturbation theory is used. We find agreement that is remarkably good, and that in some ways improves with increasing momentum. This work extends a previous study in which second order perturbation calculations were used for momentarily stationary initial data, and another study in which linearized perturbation theory was used for initially moving holes. In addition to supplying answers about the collisions, the present work has revealed several subtle points about the use of higher order perturbation theory, points that did not arise in the previous studies. These points include issues of normalization, and of comparison with numerical simulations, and will be important to subsequent applications of approximation methods for collisions.Comment: 20 pages, RevTeX, 6 figures included with psfi

Classical electromagnetic field theory in the presence of magnetic sources

Using two new well defined 4-dimensional potential vectors, we formulate the classical Maxwell's field theory in a form which has manifest Lorentz covariance and SO(2) duality symmetry in the presence of magnetic sources. We set up a consistent Lagrangian for the theory. Then from the action principle we get both Maxwell's equation and the equation of motion of a dyon moving in the electro-magnetic field.Comment: 10 pages, no figure

Exposição à teratógenos e anormalidades oculares congênitas em pacientes brasileiros portadores da sequência de Möbius

Purpose: To assess the sociodemographic profiles, teratogen exposures, and ocular congenital abnormalities in Brazilian patients with Möbius sequence. Method: Forty-four patients were recruited from the Brazilian Möbius Sequence Society. This cross-section comprised 41 patients (age, mean ± standard deviation, 9.0 ± 5.5 years) who fulfilled the inclusion criteria. The parent or caregiver answered a questionnaire regarding sociodemographic data and pregnancy history. Patients underwent ophthalmological assessments. They were subdivided into groups according to misoprostol exposure during pregnancy, and the two groups were compared. Results: Mothers/caregivers reported unplanned pregnancies in 36 (88%) cases. Of these, 19 (53%) used misoprostol during their first trimesters. A stable marital status tended to be more frequent in the unexposed group (P=0.051). Incomplete elementary school education was reported by two (11%) mothers in the exposed group and by three (14%) mothers in the unexposed group (P=0.538). The mothers' gestational exposures to cocaine, marijuana, alcohol, and cigarettes were similar in both groups (P=0.297, P=0.297, P=0.428, and P=0.444, respectively). One (5%) case of Rubella infection during pregnancy was found in the unexposed group. The main malformations in the exposed and unexposed groups were the following: strabismus (72% and 77%, respectively), lack of emotional tearing (47% and 36%, respectively), and lagophthalmos (32% and 41%, respectively). Conclusion: Stable marital statuses tended to be more frequent among mothers that did not take misoprostol during pregnancy. Exposures to other teratogens and the main ocular abnormalities were similar in both groups.Objetivo: Descrever o perfil sóciodemográfico, exposição à teratógenos e anormalidades oculares congênitas em pacientes brasileiros portadores da sequência de Möbiu Método: Quarenta e quatro pacientes recrutados da Sociedade Brasileira de Sequência de Möbius foram examinados. Este estudo transversal incluiu 41 pacientes que preencheram os critérios de inclusão do estudo (média das idades: 9,0 ± 5,5 anos). Mãe/responsável dos pacientes responderam a um questionário sobre perfil sóciodemográfico e história gestacional. Foi realizado exame oftalmológico de todos os pacientes. Eles foram agrupados em dois grupos de acordo com a exposição ao misoprostol durante a gestação e seus dados foram comparados. Resultados: Mães/responsáveis referiram gravidez indesejada em 36 (88%) dos casos. Destas, 19 (53%) fizeram uso de misoprostol no primeiro trimestre de gestação. Houve uma tendência do grupo de mães não expostas ao misoprostol de terem um estado civil estável (P=0,051). Duas (11%) mães do grupo de expostas ao misoprostol relataram primeiro grau incompleto e três (14%) do grupo de não expostas (P=0,538). A exposição das mães à cocaína, maconha, álcool e cigarro foi similar em ambos os grupos (P=0,297, P=0,297, P=0,428, P=0,444, respectivamente). Houve um caso (5%) de Rubéola no grupo de mães não expostas. As principais malformações associadas nos pacientes expostos e não expostos foram, respectivamente: estrabismo (72% e 77%), e diminuição da lágrima emocional (47% e 36%) e lagoftalmia (32% and 41%). Conclusão: Estado civil estável foi mais frequente em mães que não fizeram uso de misoprostol durante a gestação. Exposição à outros teratógenos e malformações oculares tiveram distribuição semelhante em ambos os grupos.Fundação Altino Ventura Department of OphthalmologyHospital de Olhos de Pernambuco Department of OphthalmologyUniversity of Illinois Department of Ophthalmology &amp; Visual ScienceUniversidade Federal de São Paulo (UNIFESP) Department of OphthalmologyAssociação de Assistência à Criança DeficienteSanta Casa de Misericórdia de São Paulo Department of OphthalmologyUniversidade de São Paulo Faculdade de Medicina Departments of Neurology and PediatricsUniversidade de São Paulo Instituto de Biociências Department of BiologyUniversidade de São Paulo Department of OphthalmologyUniversidade Federal de Pernambuco Department of Pediatric SurgeryUniversidade de São Paulo Department of PsychiatryServices Group in Epileptic Child PsychiatryInstituto Cema Department of OphthalmologyUNIFESP, Department of OphthalmologySciEL

Caribbean Corals in Crisis: Record Thermal Stress, Bleaching, and Mortality in 2005

BACKGROUND The rising temperature of the world's oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropical Atlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin. METHODOLOGY/PRINCIPAL FINDINGS Satellite-based tools provided warnings for coral reef managers and scientists, guiding both the timing and location of researchers' field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles. CONCLUSIONS/SIGNIFICANCE Thermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA Coral Reef Watch's Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate.This work was partially supported by salaries from the NOAA Coral Reef Conservation Program to the NOAA Coral Reef Conservation Program authors. NOAA provided funding to Caribbean ReefCheck investigators to undertake surveys of bleaching and mortality. Otherwise, no funding from outside authors' institutions was necessary for the undertaking of this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Marker-free image registration of electron tomography tilt-series

<p>Abstract</p> <p>Background</p> <p>Tilt series are commonly used in electron tomography as a means of collecting three-dimensional information from two-dimensional projections. A common problem encountered is the projection alignment prior to 3D reconstruction. Current alignment techniques usually employ gold particles or image derived markers to correctly align the images. When these markers are not present, correlation between adjacent views is used to align them. However, sequential pairwise correlation is prone to bias and the resulting alignment is not always optimal.</p> <p>Results</p> <p>In this paper we introduce an algorithm to find regions of the tilt series which can be tracked within a subseries of the tilt series. These regions act as landmarks allowing the determination of the alignment parameters. We show our results with synthetic data as well as experimental cryo electron tomography.</p> <p>Conclusion</p> <p>Our algorithm is able to correctly align a single-tilt tomographic series without the help of fiducial markers thanks to the detection of thousands of small image patches that can be tracked over a short number of images in the series.</p