51 research outputs found
Primordial Nucleosynthesis for the New Cosmology: Determining Uncertainties and Examining Concordance
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) have
a long history together in the standard cosmology. The general concordance
between the predicted and observed light element abundances provides a direct
probe of the universal baryon density. Recent CMB anisotropy measurements,
particularly the observations performed by the WMAP satellite, examine this
concordance by independently measuring the cosmic baryon density. Key to this
test of concordance is a quantitative understanding of the uncertainties in the
BBN light element abundance predictions. These uncertainties are dominated by
systematic errors in nuclear cross sections. We critically analyze the cross
section data, producing representations that describe this data and its
uncertainties, taking into account the correlations among data, and explicitly
treating the systematic errors between data sets. Using these updated nuclear
inputs, we compute the new BBN abundance predictions, and quantitatively
examine their concordance with observations. Depending on what deuterium
observations are adopted, one gets the following constraints on the baryon
density: OmegaBh^2=0.0229\pm0.0013 or OmegaBh^2 = 0.0216^{+0.0020}_{-0.0021} at
68% confidence, fixing N_{\nu,eff}=3.0. Concerns over systematics in helium and
lithium observations limit the confidence constraints based on this data
provide. With new nuclear cross section data, light element abundance
observations and the ever increasing resolution of the CMB anisotropy, tighter
constraints can be placed on nuclear and particle astrophysics. ABRIDGEDComment: 54 pages, 20 figures, 5 tables v2: reflects PRD version minor changes
to text and reference
Composition and natural history of a Cerrado snake assemblage at Itirapina, SĂŁo Paulo state, southeastern Brazil
Larval development of Plagioscion squamosissimus (Heckel) (Perciformes, Sciaenidae) of Itaipu reservoir (ParanĂĄ river, Brazil)
The aim of the present study was to characterize the larval development of Plagioscion squamosissimus (Heckel, 1840) morphometrically, collected at Itaipu reservoir from March 1988 to April 1990. It was obtained the samples monthly, with a conic-cylindrical plankton net with 0.5mm mesh. The morphological description of the larvae of P. squamosissimus was based on different stages of development. The specimens less than 6mm long present a moderate sized head and those that are larger than this length, present a large head. The pectoral fins are in an elevated position, near the operculum bones, and the ventral fins are in thoracic positions, the body has a moderate height, the eyes are small to moderate and the mouth is large with caniniform teeth. This species presents a proportional growth among the different parts of the body, as can be seen by the high correlation coefficient values (r>0.98; p<0.001)
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