12,399 research outputs found
No-horizon theorem for spacetimes with spacelike G1 isometry groups
We consider four-dimensional spacetimes which obey the
Einstein equations , and admit a global spacelike
isometry group. By means of dimensional reduction and local
analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on
which guarantees that 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 -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 -CDM model by means
of a particular combination of parameters so that the Chaplygin gas and the
-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 clÃnicos. 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 perÃodo de três anos de follow-up. A
recuperação neurológica não se correlacionou com a idade dos doentes, o nÃvel 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
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