No-horizon theorem for spacetimes with spacelike G1 isometry groups

We consider four-dimensional spacetimes $(M,{\mathbf g})$ which obey the Einstein equations ${\mathbf G}={\mathbf T}$, and admit a global spacelike $G_{1}={\mathbb R}$ isometry group. By means of dimensional reduction and local analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on ${\mathbf T}$ which guarantees that $(M,{\mathbf g})$ cannot contain apparent horizons. Given any (3+1) spacetime with spacelike translational isometry, the no-horizon condition can be readily tested without the need for dimensional reduction. This provides thus a useful and encompassing apparent horizon test for $G_{1}$-symmetric spacetimes. We argue that this adds further evidence towards the validity of the hoop conjecture, and signals possible violations of strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra

A note on the cylindrical collapse of counter-rotating dust

We find analytical solutions describing the collapse of an infinitely long cylindrical shell of counter-rotating dust. We show that--for the classes of solutions discussed herein--from regular initial data a curvature singularity inevitably develops, and no apparent horizons form, thus in accord with the spirit of the hoop conjecture.Comment: 8 pages, LaTeX, ijmpd macros (included), 1 eps figure; accepted for publication in Int. J. Mod. Phys.

Strong curvature singularities in quasispherical asymptotically de Sitter dust collapse

We study the occurrence, visibility, and curvature strength of singularities in dust-containing Szekeres spacetimes (which possess no Killing vectors) with a positive cosmological constant. We find that such singularities can be locally naked, Tipler strong, and develop from a non-zero-measure set of regular initial data. When examined along timelike geodesics, the singularity's curvature strength is found to be independent of the initial data.Comment: 16 pages, LaTeX, uses IOP package, 2 eps figures; accepted for publication in Class. Quantum Gra

Modeling the spectrum of gravitational waves in the primordial Universe

Recent observations from type Ia Supernovae and from cosmic microwave background (CMB) anisotropies have revealed that most of the matter of the Universe interacts in a repulsive manner, composing the so-called dark energy constituent of the Universe. The analysis of cosmic gravitational waves (GW) represents, besides the CMB temperature and polarization anisotropies, an additional approach in the determination of parameters that may constrain the dark energy models and their consistence. In recent work, a generalized Chaplygin gas model was considered in a flat universe and the corresponding spectrum of gravitational waves was obtained. The present work adds a massless gas component to that model and the new spectrum is compared to the previous one. The Chaplygin gas is also used to simulate a $\Lambda$-CDM model by means of a particular combination of parameters so that the Chaplygin gas and the $\Lambda$-CDM models can be easily distinguished in the theoretical scenarios here established. The lack of direct observational data is partialy solved when the signature of the GW on the CMB spectra is determined.Comment: Proc. of the Conference on Magnetic Fields in the Universe: from laboratories and stars to primordial structures, AIP(NY), eds. E. M. de Gouveia Dal Pino, G. Lugones & A. Lazarian (2005), in press. (8 pages, 11 figures

TRAUMATIC SPINAL CORD INJURY: Neurologic and Functional Recovery

Objectivo: Avaliar a recuperação neurológica e funcional dos doentes com Traumatismo Vertebro-Medular (TVM). Métodos: Foi realizado um estudo retrospectivo, que incluiu os 93 doentes com o diagnóstico de TVM admitidos no Serviço de Fisiatria do Hospital Geral de Santo António, entre Janeiro de 1993 e Dezembro de 2002. Os dados demográficos e médicos foram recolhidos dos processos clínicos. O registo da avaliação de cada doente foi efectuado na admissão, à data da alta hospitalar e 1 e 3 anos após a lesão. O estado neurológico foi classificado de acordo com os critérios da American Spinal Injury Association (ASIA), e o estado funcional através da Medida de Independência Funcional (MIF). Resultados: 87% doentes eram do sexo masculino, sendo a média de idades de 40 anos. Os acidentes de viação e as quedas foram a causa mais frequente da lesão. A maioria dos traumatismos foi dorsal e cervical (45% e 42% respectivamente). O tratamento inicial incluiu: administração intravenosa de metilprednisolona, que ocorreu nas primeiras oito horas após lesão em 54% dos casos; intervenção cirúrgica precoce, realizada em 77%. Registou-se maior recuperação nos doentes com lesão medular incompleta, particularmente naqueles classificados como C na escala da ASIA. Foi encontrada uma associação estatisticamente significativa entre os resultados obtidos no internamento e os registados no período de três anos de follow-up. A recuperação neurológica não se correlacionou com a idade dos doentes, o nível de lesão, administração de corticoides em altas doses ou cirurgia realizada nas primeiras 24 horas após a lesão (p >0,05). Os resultados funcionais registados através da MIF revelaram-se bastante favoráveis, particularmente os que foram alcançados em regime de internamento. Conclusões: Os resultados revelados neste estudo demonstram o considerável potencial para uma recuperação neurológica após um TVM, enfatizando a importância do investimento na continuidade dos programas de reabilitação nos anos que se seguem à lesão, particularmente nas lesões incompletas. Study Design: A retrospective study was conducted Objective: Evaluate the neurologic and functional recovery in patients with Traumatic Spinal Cord Injury (TSCI). Methods: A retrospective study was conducted, including the 93 patients with a diagnosis of TSCI admitted for rehabilitation in the Physical and Rehabilitation Medicine Department, Santo António General Hospital, between January 1993 and December 2002. Demographic and clinical data were collected from the hospital charts. The patients were evaluated at admission for rehabilitation, before discharging, 1 year and 3 years after injury. Neurologic status was registered according to the standards of the American Spinal Injury Association (ASIA) and functional status by the Functional Independence Measure (FIM). Results: The sample population was 87% men, with a mean age of 40 years. Motor vehicle accidents and falls were the commonest mechanism of injury. The majority sustained dorsal and cervical lesions (45% and 42% respectively). The initial management included: intravenous high dose methylprednisolone, administered within eight hours after injury in 54% of the sample; early surgical stabilization, performed on 77%. Incomplete cord injury carried a better prognosis of motor improvement, especially the patients classified as C on the ASIA Impairment Scale (AIS). A significant statistical association was found between the outcomes obtained during the initial rehabilitation, and the ones achieved on the 3 year followup period. The neurologic recovery was not related with the patient’s age, injury level, high dose steroid administration or surgery performed in the first 24 hours after injury (p >0,05). The FIM scores demonstrated the favourable functional outcomes achieved, especially during the inpatient rehabilitation. Conclusions: The results of this study further demonstrate the considerable potential for neurologic recovery after TSCI, emphasizing the importance of the rehabilitation investment continuity, especially for the ones with incomplete cord injury

Multilayer Complex Network Descriptors for Color-Texture Characterization

A new method based on complex networks is proposed for color-texture analysis. The proposal consists on modeling the image as a multilayer complex network where each color channel is a layer, and each pixel (in each color channel) is represented as a network vertex. The network dynamic evolution is accessed using a set of modeling parameters (radii and thresholds), and new characterization techniques are introduced to capt information regarding within and between color channel spatial interaction. An automatic and adaptive approach for threshold selection is also proposed. We conduct classification experiments on 5 well-known datasets: Vistex, Usptex, Outex13, CURet and MBT. Results among various literature methods are compared, including deep convolutional neural networks with pre-trained architectures. The proposed method presented the highest overall performance over the 5 datasets, with 97.7 of mean accuracy against 97.0 achieved by the ResNet convolutional neural network with 50 layers.Comment: 20 pages, 7 figures and 4 table