614 research outputs found
Research of the optical communications groups at University of Aveiro and Institute of Telecommunications - Aveiro Pole
This paper summarizes the research activities of the optical communications group at University of Aveiro and Institute of
Telecommunications – Aveiro pole. Several activities like clock recovery systems, both electrical and all optical, electrical
equalizers for very high bit rate DST systems, post-detection filters for multigigabit optical receivers, soliton systems,
simulation work on WDM, DST, EDFA and short pulse generation for high bit rate systems are presented
Gravitational Collapse: Expanding and Collapsing Regions
We investigate the expanding and collapsing regions by taking two well-known
spherically symmetric spacetimes. For this purpose, the general formalism is
developed by using Israel junction conditions for arbitrary spacetimes. This
has been used to obtain the surface energy density and the tangential pressure.
The minimal pressure provides the gateway to explore the expanding and
collapsing regions. We take Minkowski and Kantowski-Sachs spacetimes and use
the general formulation to investigate the expanding and collapsing regions of
the shell.Comment: 12 pages, 4 figures, accepted for publication in Gen. Relativ. Gra
Aerobic exercise prevents cardiomyocyte damage caused by oxidative stress in early cardiovascular disease by increasing vascularity while L-arginine supplementation prevents it by increasing activation of the enzyme nitric oxide synthase
L-Arginine and chronic exercise reduce oxidative stress. However, it is unclear how they affect cardiomyocytes during cardiovascular disease (CVD) development. The aim of this research was to investigate the possible effects of L-arginine supplementation and aerobic training on systemic oxidative stress and their consequences on cardiomyocytes during cardiometabolic disease onset caused by excess fructose. Wistar rats were allocated into four groups: control (C), fructose (F, 10% fructose in water), fructose training (FT; moderate running, 50-70% of the maximal velocity), and fructose arginine (FA; 880 mg/kg/day). Fructose was given for two weeks and fructose plus treatments for the subsequent eight weeks. Body composition, blood glucose, insulin, lipid profile, lipid peroxidation, nitrite, metalloproteinase-2 (MMP-2) activity, left ventricle histological changes, microRNA-126, -195, and -146, eNOS, p-eNOS, and TNF-α expressions were analyzed. Higher abdominal fat mass, triacylglycerol level, and insulin level were observed in the F group, and both treatments reversed these alterations. Myocardial vascularization was impaired in fructose-fed groups, except in FT. Cardiomyocyte hypertrophy was observed in all fructose-fed groups. TNF-α levels were higher in fructose-fed groups than in the C group, and p-eNOS levels were higher in the FA than in the C and F groups. Lipid peroxidation was higher in the F group than in the FT and C groups. During CVD onset, moderate aerobic exercise reduced lipid peroxidation, and both training and L-arginine prevented metabolic changes caused by excessive fructose. Myocardial vascularization was impaired by fructose, and cardiomyocyte hypertrophy appeared to be influenced by pro-inflammatory and oxidative environments
Dimensional Dependence of Black Hole Formation in Self-Similar Collapse of Scalar Field
We study classical and quantum self-similar collapses of a massless scalar
field in higher dimensions, and examine how the increase in the number of
dimensions affects gravitational collapse and black hole formation. Higher
dimensions seem to favor formation of black hole rather than other final
states, in that the initial data space for black hole formation enlarges as
dimension increases. On the other hand, the quantum gravity effect on the
collapse lessens as dimension increases. We also discuss the gravitational
collapse in a brane world with large but compact extra dimensions.Comment: Improved a few arguments and added a figur
Gravitational Collapse of Phantom Fluid in (2+1)-Dimensions
This investigation is devoted to the solutions of Einstein's field equations
for a circularly symmetric anisotropic fluid, with kinematic self-similarity of
the first kind, in -dimensional spacetimes. In the case where the radial
pressure vanishes, we show that there exists a solution of the equations that
represents the gravitational collapse of an anisotropic fluid, and this
collapse will eventually form a black hole, even when it is constituted by the
phantom energy.Comment: 10 page
Gravitational collapse of a Hagedorn fluid in Vaidya geometry
The gravitational collapse of a high-density null charged matter fluid,
satisfying the Hagedorn equation of state, is considered in the framework of
the Vaidya geometry. The general solution of the gravitational field equations
can be obtained in an exact parametric form. The conditions for the formation
of a naked singularity, as a result of the collapse of the compact object, are
also investigated. For an appropriate choice of the arbitrary integration
functions the null radial outgoing geodesic, originating from the shell
focussing central singularity, admits one or more positive roots. Hence a
collapsing Hagedorn fluid could end either as a black hole, or as a naked
singularity. A possible astrophysical application of the model, to describe the
energy source of gamma-ray bursts, is also considered.Comment: 14 pages, 2 figures, to appear in Phys. Rev.
Mortality inequalities measured by socioeconomic indicators in Brazil: a scoping review
OBJECTIVE Summarize the literature on the relationship between composite socioeconomic indicators and mortality in different geographical areas of Brazil. METHODS This scoping review included articles published between January 1, 2000, and August 31, 2020, retrieved by means of a bibliographic search carried out in the Medline, Scopus, Web of Science, and Lilacs databases. Studies reporting on the association between composite socioeconomic indicators and all-cause, or specific cause of death in any age group in different geographical areas were selected. The review summarized the measures constructed, their associations with the outcomes, and potential study limitations. RESULTS Of the 77 full texts that met the inclusion criteria, the study reviewed 24. The area level of composite socioeconomic indicators analyzed comprised municipalities (n = 6), districts (n = 5), census tracts (n = 4), state (n = 2), country (n = 2), and other areas (n = 5). Six studies used composite socioeconomic indicators such as the Human Development Index, Gross Domestic Product, and the Gini Index; the remaining 18 papers created their own socioeconomic measures based on sociodemographic and health indicators. Socioeconomic status was inversely associated with higher rates of all-cause mortality, external cause mortality, suicide, homicide, fetal and infant mortality, respiratory and circulatory diseases, stroke, infectious and parasitic diseases, malnutrition, gastroenteritis, and oropharyngeal cancer. Higher mortality rates due to colorectal cancer, leukemia, a general group of neoplasms, traffic accident, and suicide, in turn, were observed in less deprived areas and/or those with more significant socioeconomic development. Underreporting of death and differences in mortality coverage in Brazilian areas were cited as the main limitation. CONCLUSIONS Studies analyzed mortality inequalities in different geographical areas by means of composite socioeconomic indicators, showing that the association directions vary according to the mortality outcome. But studies on all-cause mortality and at the census tract level remain scarce. The results may guide the development of new composite socioeconomic indicators for use in mortality inequality analysis
Energy Contents of Some Well-Known Solutions in Teleparallel Gravity
In the context of teleparallel equivalent to General Relativity, we study
energy and its relevant quantities for some well-known black hole solutions.
For this purpose, we use the Hamiltonian approach which gives reasonable and
interesting results. We find that our results of energy exactly coincide with
several prescriptions in General Relativity. This supports the claim that
different energy-momentum prescriptions can give identical results for a given
spacetime. We also evaluate energy-momentum flux of these solutions.Comment: 16 pages, accepted for publication in Astrophys. Space Sc
Theory and Applications of Non-Relativistic and Relativistic Turbulent Reconnection
Realistic astrophysical environments are turbulent due to the extremely high
Reynolds numbers. Therefore, the theories of reconnection intended for
describing astrophysical reconnection should not ignore the effects of
turbulence on magnetic reconnection. Turbulence is known to change the nature
of many physical processes dramatically and in this review we claim that
magnetic reconnection is not an exception. We stress that not only
astrophysical turbulence is ubiquitous, but also magnetic reconnection itself
induces turbulence. Thus turbulence must be accounted for in any realistic
astrophysical reconnection setup. We argue that due to the similarities of MHD
turbulence in relativistic and non-relativistic cases the theory of magnetic
reconnection developed for the non-relativistic case can be extended to the
relativistic case and we provide numerical simulations that support this
conjecture. We also provide quantitative comparisons of the theoretical
predictions and results of numerical experiments, including the situations when
turbulent reconnection is self-driven, i.e. the turbulence in the system is
generated by the reconnection process itself. We show how turbulent
reconnection entails the violation of magnetic flux freezing, the conclusion
that has really far reaching consequences for many realistically turbulent
astrophysical environments. In addition, we consider observational testing of
turbulent reconnection as well as numerous implications of the theory. The
former includes the Sun and solar wind reconnection, while the latter include
the process of reconnection diffusion induced by turbulent reconnection, the
acceleration of energetic particles, bursts of turbulent reconnection related
to black hole sources as well as gamma ray bursts. Finally, we explain why
turbulent reconnection cannot be explained by turbulent resistivity or derived
through the mean field approach.Comment: 66 pages, 24 figures, a chapter of the book "Magnetic Reconnection -
Concepts and Applications", editors W. Gonzalez, E. N. Parke
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