20,773 research outputs found
Why does the recently proposed simple empirical formula for the lowest excitation energies work so well?
It has recently been shown that a simple empirical formula, in terms of the
mass number and the valence nucleon numbers, is able to describe the main
trends of the lowest excitation energies of the natural parity even multipole
states up to in even-even nuclei throughout the entire periodic table.
In an effort to understand why such a simple formula is so capable, we
investigate the possibility of associating each term of the empirical formula
with the specific part of the measured excitation energy graph.Comment: 9 pages, 3 figure
Spin-dependent empirical formula for the lowest excitation energies of the natural parity states in even-even nuclei
We present an empirical expression which holds for the lowest excitation
energy of the natural parity states in even-even nuclei throughout the entire
periodic table. This formula contains spin-dependent factors so that it is
applied to different multipole states with the same model parameters in
contrast to the recently proposed empirical expression where the model
parameters had to be fitted for each multipole separately.Comment: 9 pages, 5 figure
A loss function approach to model specification testing and its relative efficiency
The generalized likelihood ratio (GLR) test proposed by Fan, Zhang and Zhang
[Ann. Statist. 29 (2001) 153-193] and Fan and Yao [Nonlinear Time Series:
Nonparametric and Parametric Methods (2003) Springer] is a generally applicable
nonparametric inference procedure. In this paper, we show that although it
inherits many advantages of the parametric maximum likelihood ratio (LR) test,
the GLR test does not have the optimal power property. We propose a generally
applicable test based on loss functions, which measure discrepancies between
the null and nonparametric alternative models and are more relevant to
decision-making under uncertainty. The new test is asymptotically more powerful
than the GLR test in terms of Pitman's efficiency criterion. This efficiency
gain holds no matter what smoothing parameter and kernel function are used and
even when the true likelihood function is available for the GLR test.Comment: Published in at http://dx.doi.org/10.1214/13-AOS1099 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
UV Upturn in Elliptical Galaxies: Theory
The UV upturn is the rising flux with decreasing wavelength between the Lyman
limit and 2500\AA found virtually in all bright spheroidal galaxies. It has
been a mystery ever since it was first detected by the OAO-2 space telescope
(Code & Welch 1979) because such old metal-rich populations were not expected
to contain any substantial number of hot stars. It was confirmed by following
space missions, ANS (de Boer 1982), IUE (Bertola et al. 1982) and HUT (Brown et
al. 1997). The positive correlation between the UV-to-optical colour (i.e., the
strength of the UV upturn) and the Mg2 line strength found by Burstein et al.
(1987) through IUE observations has urged theorists to construct novel
scenarios in which metal-rich () old ( a few Gyr)
stars become UV bright (Greggio & Renzini 1990; Horch et al. 1992). Also
interesting was to find using HUT that, regardless of the UV strength, the UV
spectral slopes at 1000--2000\AA in the six UV bright galaxies were nearly
identical suggesting a very small range of temperatures of the UV sources in
these galaxies (Brown et al. 1997), which corresponds to K. This, together with other evidence, effectively ruled out
young stars as the main driver of the UV upturn. A good review on the
observational side of the story is given in the next article by Tom Brown, as
well as in the recent articles of Greggio & Renzini (1999) and O'Connell
(1999).Comment: 6 figures; belated paper from Keele Conferenc
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