1,120,920 research outputs found
On The Age Estimation of LBDS 53W091
The recent spectral analysis of LBDS 53W091 by Spinrad and his collaborators
has suggested that this red galaxy at z=1.55 is at least 3.5 Gyr old. This
imposes an important constraint on cosmology, suggesting that this galaxy
formed at z > 6.5, assuming recent estimates of cosmological parameters. We
have performed chi^2 tests to the continuum of this galaxy using its UV
spectrum and photometric data (RJHK). We have used the updated Yi models that
are based on the Yale tracks. We find it extremely difficult to reproduce such
large age estimates, under the assumption of the most probable input
parameters. Using the same configuration as in Spinrad et al. (solar abundance
models), our analysis suggests an age of approximately 1.4 -- 1.8 Gyr. The
discrepancy between Spinrad et al.'s age estimate (based on the 1997 Jimenez
models) and ours originates from the large difference in the model integrated
spectrum: the Jimenez models are much bluer than the Yi models and the Bruzual
\& Charlot (BC) models. Preliminary tests favor the Yi and BC models. The
updated age estimate of LBDS 53W091 would suggest that this galaxy formed
approximately at z=2-3.Comment: LaTeX, 18 eps files Accepted for publication in ApJ (Feb 10, 2000,
vol 530), uses emulateapj.st
Analysis of factors influencing the ultrasonic fetal weight estimation
Objective: The aim of our study was the evaluation of sonographic fetal weight estimation taking into consideration 9 of the most important factors of influence on the precision of the estimation. Methods: We analyzed 820 singleton pregnancies from 22 to 42 weeks of gestational age. We evaluated 9 different factors that potentially influence the precision of sonographic weight estimation ( time interval between estimation and delivery, experts vs. less experienced investigator, fetal gender, gestational age, fetal weight, maternal BMI, amniotic fluid index, presentation of the fetus, location of the placenta). Finally, we compared the results of the fetal weight estimation of the fetuses with poor scanning conditions to those presenting good scanning conditions. Results: Of the 9 evaluated factors that may influence accuracy of fetal weight estimation, only a short interval between sonographic weight estimation and delivery (0-7 vs. 8-14 days) had a statistically significant impact. Conclusion: Of all known factors of influence, only a time interval of more than 7 days between estimation and delivery had a negative impact on the estimation
The application of amino acid racemization in the acid soluble fraction of enamel to the estimation of the age of human teeth
Estimation of age-at-death for skeletonised forensic remains is one of the most significant problems in forensic anthropology. The majority of existing morphological and histological techniques are highly inaccurate, and show a bias towards underestimating the age of older individuals. One technique which has been successful in forensic age estimation is amino acid racemization in dentine. However, this method cannot be used on remains where the post-mortem interval is greater than 20 years. An alternative approach is to measure amino acid racemization in dental enamel, which is believed to be more resistant to change post-mortem. The extent of amino acid racemization in the acid soluble fraction of the enamel proteins was determined for modem known age teeth. A strong correlation was observed between the age of the tooth and the extent of racemization. No systematic bias in the direction of age estimation errors was detected. For the majority of teeth analyzed, the presence of dental caries did not affect the results obtained. In a minority of cases, carious teeth showed a higher level of racemization than would be expected given the age of the individual. These results indicate that amino acid racemization in enamel has the potential to be used in age estimation of skeletal remains. (C) 2007 Elsevier Ireland Ltd. All rights reserved
A Bayesian estimation of the helioseismic solar age
The helioseismic determination of the solar age has been a subject of several
studies because it provides us with an independent estimation of the age of the
solar system. We present the Bayesian estimates of the helioseismic age of the
Sun, which are determined by means of calibrated solar models that employ
different equations of state and nuclear reaction rates. We use 17 frequency
separation ratios
from 8640
days of low- BiSON frequencies and consider three likelihood functions
that depend on the handling of the errors of these ratios.
Moreover, we employ the 2010 CODATA recommended values for Newton's constant,
solar mass, and radius to calibrate a large grid of solar models spanning a
conceivable range of solar ages. It is shown that the most constrained
posterior distribution of the solar age for models employing Irwin EOS with
NACRE reaction rates leads to Gyr, while models
employing the Irwin EOS and Adelberger, et al., Reviews of Modern Physics, 83,
195 (2011) reaction rate have Gyr. Implementing
OPAL EOS in the solar models results in reduced evidence ratios (Bayes factors)
and leads to an age that is not consistent with the meteoritic dating of the
solar system. An estimate of the solar age that relies on an helioseismic age
indicator such as turns out to be essentially independent of the
type of likelihood function. However, with respect to model selection,
abandoning any information concerning the errors of the ratios
leads to inconclusive results, and this stresses the importance of evaluating
the trustworthiness of error estimates.Comment: 4 pages, three Tables, A&A to appea
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