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Dive into the research topics where Marcelo B. Ribeiro is active.

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Featured researches published by Marcelo B. Ribeiro.


Astronomy and Astrophysics | 2011

Cosmic distance duality relation and the shape of galaxy clusters

R. F. L. Holanda; J. A. S. Lima; Marcelo B. Ribeiro

Observations in the cosmological domain are heavily dependent on the validity of the cosmic distance-duality (DD) relation, D_L(z) (1 + z)^{2}/D_{A}(z) = 1, an exact result required by the Etherington reciprocity theorem where D_L(z) and D_A(z) are, respectively, the luminosity and angular diameter distances. In the limit of very small redshifts D_A(z) = D_L(z) and this ratio is trivially satisfied. Measurements of Sunyaev-Zeldovich effect (SZE) and X-rays combined with the DD relation have been used to determine D_A(z)from galaxy clusters. This combination offers the possibility of testing the validity of the DD relation, as well as determining which physical processes occur in galaxy clusters via their shapes. We use WMAP (7 years) results by fixing the conventional LCDM model to verify the consistence between the validity of DD relation and different assumptions about galaxy cluster geometries usually adopted in the literature. We assume that


Journal of Bone and Joint Surgery, American Volume | 2012

Adipose-Derived Stem-Cell Treatment of Skeletal Muscle Injury

Ramon Peçanha; Luiza de Lima e Silva Bagno; Marcelo B. Ribeiro; Anna Beatriz Robottom Ferreira; Milton Ozório Moraes; Gisele Zapata-Sudo; Tais Hanae Kasai-Brunswick; Antonio C. Campos-de-Carvalho; Regina Coeli dos Santos Goldenberg; João Pedro Saar Werneck-de-Castro

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Astronomy and Astrophysics | 2012

Probing the cosmic distance-duality relation with the Sunyaev-Zel’dovich effect, X-ray observations and supernovae Ia

R. F. L. Holanda; J. A. S. Lima; Marcelo B. Ribeiro

is a function of the redshift parametrized by two different relations: \eta(z) = 1 + \eta_{0}z, and \eta(z)=1 + \eta_{0}z/(1+z), where \eta_0 is a constant parameter quantifying the possible departure from the strict validity of the DD relation. In order to determine the probability density function (PDF) of \eta_{0}, we consider the angular diameter distances from galaxy clusters recently studied by two different groups by assuming elliptical (isothermal) and spherical (non-isothermal)


Physica A-statistical Mechanics and Its Applications | 2006

Zipf law for Brazilian cities

Newton J. Moura Jr.; Marcelo B. Ribeiro

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Physica A-statistical Mechanics and Its Applications | 2011

The Gompertz–Pareto income distribution

F. Chami Figueira; Newton J. Moura Jr.; Marcelo B. Ribeiro

models. The strict validity of the DD relation will occur only if the maximum value of \eta_{0} PDF is centered on \eta_{0}=0. It was found that the elliptical


European Physical Journal B | 2009

Evidence for the Gompertz curve in the income distribution of Brazil 1978–2005

Newton J. Moura Jr.; Marcelo B. Ribeiro

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The Astrophysical Journal | 1992

On modeling a relativistic hierarchical (fractal) cosmology by Tolman's spacetime. II - Analysis of the Einstein-de Sitter model

Marcelo B. Ribeiro

model is in good agreement with the data, showing no violation of the DD relation (PDF peaked close to \eta_0=0 at 1-sigma), while the spherical (non-isothermal) one is only marginally compatible at 3-sigma.


The Astrophysical Journal | 1993

On Modeling a Relativistic Hierarchical (Fractal) Cosmology by Tolman's Spacetime. III. Numerical Results

Marcelo B. Ribeiro

BACKGROUND The aim of the present study was to investigate whether adipose-derived stem cells could contribute to skeletal muscle-healing. METHODS Adipose-derived stem cells of male rats were cultured and injected into the soleus muscles of female rats. Two and four weeks after injections, muscles were tested for tetanic force (50 Hz). Histological analysis was performed to evaluate muscle collagen deposition and the number of centronucleated muscle fibers. In order to track donor cells, chimerism was detected with use of real-time polymerase chain reaction targeting the male sex-determining region Y (SRY) gene. RESULTS Two weeks after cell injection, tetanus strength and the number of centronucleated regenerating myofibers, as well as the number of centronucleated regenerating myofibers, were higher in the treated group than they were in the control group (mean and standard error of the mean, 79.2 ± 5.0% versus 58.3 ± 8.1%, respectively [p < 0.05]; and 145 ± 36 versus 273 ± 18 per 10³ myofibers, respectively [p < 0.05]). However, there were no significant differences at four weeks. Treatment did not decrease collagen deposition. Male gene was not detected in female host tissue at two and four weeks after engraftment by polymerase chain reaction analysis. CONCLUSIONS Adipose-derived stem-cell therapy increased muscle repair and force at two weeks, but not four weeks, after injection, suggesting that adipose-derived stem-cell administration may accelerate muscle repair; however, the rapid disappearance of injected cells suggests a paracrine mechanism of action.


Astronomy and Astrophysics | 2005

Cosmological distances and fractal statistics of galaxy distribution

Marcelo B. Ribeiro

Context. The angular diameter distances toward galaxy clusters can be determined with measurements of Sunyaev-Zel’dovich effect and X-ray surface brightness combined with the validity of the distance-duality relation, DL(z)(1 + z) 2 /DA(z) = 1, where DL(z )a nd DA(z) are, respectively, the luminosity and angular diameter distances. This combination enables us to probe galaxy cluster physics or even to test the validity of the distance-duality relation itself. Aims. We explore these possibilities based on two different, but complementary approaches. Firstly, in order to constrain the possible galaxy cluster morphologies, the validity of the distance-duality relation (DD relation) is assumed in the ΛCDM framework (WMAP7). Secondly, by adopting a cosmological-model-independent test, we directly confront the angular diameters from galaxy clusters with two supernovae Ia (SNe Ia) subsamples (carefully chosen to coincide with the cluster positions). The influence of the different SNe Ia light-curve fitters in the previous analysis are also discussed. Methods. We assumed that η is a function of the redshift parametrized by two different relations: η(z) = 1 + η0z ,a ndη(z) = 1 + η0z/(1 + z), where η0 is a constant parameter quantifying the possible departure from the strict validity of the DD relation. In order to determine the probability density function (PDF) of η0, we considered the angular diameter distances from galaxy clusters recently studied by two different groups by assuming elliptical and spherical isothermal β models and spherical non-isothermal β model. The strict validity of the DD relation will occur only if the maximum value of η0 PDF is centered on η0 = 0. Results. For both approaches we find that the elliptical β model agrees with the distance-duality relation, whereas the non-isothermal spherical description is, in the best scenario, only marginally compatible. We find that the two-light curve fitters (SALT2 and MLCS2K2) present a statistically significant conflict, and a joint analysis involving the different approaches suggests that clusters are endowed with an elliptical geometry as previously assumed. Conclusions. The statistical analysis presented here provides new evidence that the true geometry of clusters is elliptical. In principle, it is remarkable that a local property such as the geometry of galaxy clusters might be constrained by a global argument like the one provided by the cosmological distance-duality relation.


The Astrophysical Journal | 2007

Differential Density Statistics of the Galaxy Distribution and the Luminosity Function

Vinicius Albani; Alvaro Iribarrem; Marcelo B. Ribeiro; William R. Stoeger

This work studies the Zipf law for cities in Brazil. Data from censuses of 1970, 1980, 1991 and 2000 were used to select a sample containing only cities with 30,000 inhabitants or more. The results show that the population distribution in Brazilian cities does follow a power-law similar to the ones found in other countries. Estimates of the power-law exponent were found to be 2.22±0.34 for the 1970 and 1980 censuses, and 2.26±0.11 for censuses of 1991 and 2000. More accurate results were obtained with the maximum likelihood estimator, showing an exponent equal to 2.41 for 1970 and 2.36 for the other 3 years.

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Alvaro Iribarrem

Federal University of Rio de Janeiro

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Newton J. Moura Jr.

Brazilian Institute of Geography and Statistics

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Amanda R. Lopes

Federal University of Rio de Janeiro

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J. A. S. Lima

University of São Paulo

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Elcio Abdalla

University of São Paulo

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F. Chami Figueira

Federal University of Rio de Janeiro

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