A new two-sphere singularity in general relativity

The Florides solution, proposed as an alternative to the interior Schwarzschild solution, represents a static and spherically symmetric geometry with vanishing radial stresses. It is regular at the center, and is matched to an exterior Schwarzschild solution. The specific case of a constant energy density has been interpreted as the field inside an Einstein cluster. In this work, we are interested in analyzing the geometry throughout the permitted range of the radial coordinate without matching it to the Schwarzschild exterior spacetime at some constant radius hypersurface. We find an interesting picture, namely, the solution represents a three-sphere, whose equatorial two-sphere is singular, in the sense that the curvature invariants and the tangential pressure diverge. As far as we know, such singularities have not been discussed before. In the presence of a large negative cosmological constant (anti-de Sitter) the singularity is removed.Comment: 17 pages, 3 figure

Boundary sources in the Doran - Lobo - Crawford spacetime

We take a null hypersurface (the causal horizon) generated by a congruence of null geodesics as the boundary of the Doran-Lobo-Crawford spacetime, to be the place where the Brown-York quasilocal energy is located. The components of the outer and inner stress tensors are computed and shown to depend on time and on the impact parameter $b$ of the test particle trajectory. The surface energy density $\sigma$ on the boundary is given by the same expression as that obtained previously for the energy stored on a Rindler horizon.Comment: 4 pages, title changed, no figures, minor text change

Radial stability analysis of the continuous pressure gravastar

Radial stability of the continuous pressure gravastar is studied using the conventional Chandrasekhar method. The equation of state for the static gravastar solutions is derived and Einstein equations for small perturbations around the equilibrium are solved as an eigenvalue problem for radial pulsations. Within the model there exist a set of parameters leading to a stable fundamental mode, thus proving radial stability of the continuous pressure gravastar. It is also shown that the central energy density possesses an extremum in rho_c(R) curve which represents a splitting point between stable and unstable gravastar configurations. As such the rho_c(R) curve for the gravastar mimics the famous M(R) curve for a polytrope. Together with the former axial stability calculations this work completes the stability problem of the continuous pressure gravastar.Comment: 17 pages, 5 figures, References corrected, minor changes wrt v1, matches published versio

The LISA PathFinder DMU and Radiation Monitor

The LISA PathFinder DMU (Data Management Unit) flight model was formally accepted by ESA and ASD on 11 February 2010, after all hardware and software tests had been successfully completed. The diagnostics items are scheduled to be delivered by the end of 2010. In this paper we review the requirements and performance of this instrumentation, specially focusing on the Radiation Monitor and the DMU, as well as the status of their programmed use during mission operations, on which work is ongoing at the time of writing.Comment: 11 pages, 7 figures, prepared for the Proceedings of the 8th International LISA Symposium, Classical and Quantum Gravit

Environmental effects on galaxy evolution. II: quantifying the tidal features in NIR-images of the cluster Abell 85

This work is part of a series of papers devoted to investigate the evolution of cluster galaxies during their infall. In the present article we imaged in NIR a selected sample of galaxies through- out the massive cluster Abell 85 (z = 0.055). We obtained (JHK) photometry for 68 objects, reaching 1 mag/arcsec^2 deeper than 2MASS. We use these images to unveil asymmetries in the outskirts of a sample of bright galaxies and develop a new asymmetry index, alpha_An, which allows to quantify the degree of disruption by the relative area occupied by the tidal features on the plane of the sky. We measure the asymmetries for a subsample of 41 large area objects finding clear asymmetries in ten galaxies, most of them being in groups and pairs projected at different clustercentric distances, some of them located beyond R500 . Combining information on the Hi-gas content of blue galaxies and the distribution of sub-structures across Abell 85, with the present NIR asymmetry analysis, we obtain a very powerful tool to confirm that tidal mechanisms are indeed present and are currently affecting a fraction of galaxies in Abell 85. However, when comparing our deep NIR images with UV-blue images of two very disrupted (jellyfish) galaxies in this cluster, we discard the presence of tidal 1 interactions down to our detection limit. Our results suggest that ram-pressure stripping is at the origin of such spectacular disruptions. We conclude that across a complex cluster like Abell 85, environment mechanisms, both gravitational and hydrodynamical, are playing an active role in driving galaxy evolution.Comment: 30 pages, 13 figures, Accepted for Publication in A

Bloodstream infections as a marker of community-acquired sepsis severity. Results from the Portuguese community-acquired sepsis study (SACiUCI study)

Funding Information: This work was mostly supported by an unrestricted grant from ASSUCIP (Associação dos Amigos da Unidade de Cuidados Intensivos Polivalente, Hospital Geral de Santo António, Porto, Portugal) as well as by grants from GIS (Grupo de Infecção e Sepsis, Hospital de São João, Porto, Portugal) Merck Sharp & Dohme and Eli Lilly. CL received a grant from Fundação para a Ciência e Tecnologia (PIC/IC/83312/2007). All other authors report that they have no other competing interests to declare related to the topic of this manuscript.Clin Microbiol Infect 2013; 19: 242-248 The impact of bloodstream infection (BSI) on admission to hospital on the outcome of patients with community-acquired sepsis (CAS) admitted to intensive-care units (ICU) is largely unknown. We selected 803 adult patients consecutively admitted with CAS to one of 17 Portuguese ICU, in whom blood cultures were collected before initiation of antibiotic therapy during a 12-month period. A BSI was identified on hospital admission in 160 (19.9%) patients. Those with and without BSI had similar mean Simplified Acute Physiology Score (SAPS) II and age. The presence of BSI was independently associated with mortality in ICU (adjusted odds ratio 1.86; 95% confidence interval 1.20-2.89; p 0.005). On the 4th day in ICU, patients with BSI were found to be significantly more dependent on vasopressor support (p 0.002) but not on ventilatory support. Cumulative ICU mortality was significantly higher in BSI patients from the 9th day onwards. A seasonal variation of BSI isolates was noted: gram-negative BSI were more common in the summer, whereas in the winter, gram-positive infections were more frequent (p 0.024), without mortality differences.publishersversionpublishe

Bloodstream infections as a marker of community-acquired sepsis severity. Results from the Portuguese community-acquired sepsis study (SACiUCI study)

Funding Information: This work was mostly supported by an unrestricted grant from ASSUCIP (Associação dos Amigos da Unidade de Cuidados Intensivos Polivalente, Hospital Geral de Santo António, Porto, Portugal) as well as by grants from GIS (Grupo de Infecção e Sepsis, Hospital de São João, Porto, Portugal) Merck Sharp & Dohme and Eli Lilly. CL received a grant from Fundação para a Ciência e Tecnologia (PIC/IC/83312/2007). All other authors report that they have no other competing interests to declare related to the topic of this manuscript.Clin Microbiol Infect 2013; 19: 242-248 The impact of bloodstream infection (BSI) on admission to hospital on the outcome of patients with community-acquired sepsis (CAS) admitted to intensive-care units (ICU) is largely unknown. We selected 803 adult patients consecutively admitted with CAS to one of 17 Portuguese ICU, in whom blood cultures were collected before initiation of antibiotic therapy during a 12-month period. A BSI was identified on hospital admission in 160 (19.9%) patients. Those with and without BSI had similar mean Simplified Acute Physiology Score (SAPS) II and age. The presence of BSI was independently associated with mortality in ICU (adjusted odds ratio 1.86; 95% confidence interval 1.20-2.89; p 0.005). On the 4th day in ICU, patients with BSI were found to be significantly more dependent on vasopressor support (p 0.002) but not on ventilatory support. Cumulative ICU mortality was significantly higher in BSI patients from the 9th day onwards. A seasonal variation of BSI isolates was noted: gram-negative BSI were more common in the summer, whereas in the winter, gram-positive infections were more frequent (p 0.024), without mortality differences.publishersversionpublishe

LISA and LISA PathFinder, the endeavour to detect low frequency GWs

This is a review about LISA and its technology demonstrator, LISA PathFinder. We first describe the conceptual problems which need to be overcome in order to set up a working interferometric detector of low frequency Gravitational Waves (GW), then summarise the solutions to them as currently conceived by the LISA mission team. This will show that some of these solutions require new technological abilities which are still under development, and which need proper test before being fully implemented. LISA PathFinder (LPF) is the the testbed for such technologies. The final part of the paper will address the ideas and concepts behind the PathFinder as well as their impact on LISA.Comment: 25 pages, 21 figures, presented at the Spanish Relativity Meeting, Mallorca September 2006. Will be published in Journal of Physics: Conference Series, IOP. To be published in Journal of Physics: Conference Series, IO

Semidefinite Representation of the kk-Ellipse

The $k$-ellipse is the plane algebraic curve consisting of all points whose sum of distances from $k$ given points is a fixed number. The polynomial equation defining the $k$-ellipse has degree $2^k$ if $k$ is odd and degree $2^k{-}\binom{k}{k/2}$ if $k$ is even. We express this polynomial equation as the determinant of a symmetric matrix of linear polynomials. Our representation extends to weighted $k$-ellipses and $k$-ellipsoids in arbitrary dimensions, and it leads to new geometric applications of semidefinite programming.Comment: 16 pages, 5 figure