26,284 research outputs found
SR-FTiR microscopy and FTIR imaging in the earth sciences
During the last decades, several books have been devoted to the application
of spectroscopic methods in mineralogy. Several short courses and meetings have
addressed particular aspects of spectroscopy, such as the analysis of hydrous
components in minerals and Earth materials. In these books, complete treatment
of the infrared theory and practical aspects of instrumentation and methods,
along with an exhaustive list of references, can be found. The present chapter
is intended to cover those aspects of infrared spectroscopy that have been
developed in the past decade and are not included in earlier reviews such as
Volume 18 of Reviews in Mineralogy. These new topics involve primarily: (1) the
use of synchrotron radiation (SR), which, although not a routine method, is now
rather extensively applied in infrared studies, in particular those requiring
ultimate spatial and time resolution and the analysis of extremely small
samples (a few tens of micrometers); (2) the development of imaging techniques
also for foreseen time resolved studies of geo-mineralogical processes and
environmental studies.Comment: 36 pages, 24 figures - Reviews in Mineralogy & Geochemistry - Vol. 78
(2013) in pres
Two populations of progenitors for type Ia SNe?
We use recent observations of type Ia Supernova (SN Ia) rates to derive, on
robust empirical grounds, the distribution of the delay time (DTD) between the
formation of the progenitor star and its explosion as a SN. Our analysis finds:
i) delay times as long as 3-4 Gyr, derived from observations of SNe Ia at high
redshift, cannot reproduce the dependence of the SN Ia rate on the colors and
on the radio-luminosity of the parent galaxies, as observed in the local
Universe; ii) the comparison between observed SN rates and a grid of
theoretical "single-population" DTDs shows that only a few of them are possibly
consistent with observations. The most successful models are all predicting a
peak of SN explosions soon after star formation and an extended tail in the
DTD, and can reproduce the data but only at a modest statistical confidence
level; iii) present data are best matched by a bimodal DTD, in which about 50%
of type Ia SNe (dubbed "prompt" SN Ia) explode soon after their stellar birth,
in a time of the order of 10^8 years, while the remaining 50% ("tardy" SN Ia)
have a much wider distribution, well described by an exponential function with
a decay time of about 3 Gyr. This fact, coupled with the well established
bimodal distribution of the decay rate, suggests the existence of two classes
of progenitors. We discuss the cosmological implications of this result and
make simple predictions. [Abridged]Comment: 11 pages, MNRAS, in press, modified after referee's comment
Cutoff-effects in the spectrum of dynamical Wilson fermions
We investigate the low-lying eigenvalues of the improved Wilson-Dirac
operator in the Schroedinger functional with two dynamical quark flavors. At a
lattice spacing of approximately 0.1 fm we find more very small eigenvalues
than in the quenched case. These cause problems with HMC-type algorithms and in
the evaluation of fermionic correlation functions. Through a simulation at a
finer lattice spacing we are able to establish their nature as cutoff-effectsComment: Lattice2004(machines), 3 pages, 3 figures, talk by R.
Kinetic and Exchange Energy Densities near the Nucleus
We investigate the behavior of the kinetic and the exchange energy densities
near the nuclear cusp of atomic systems. Considering hydrogenic orbitals, we
derive analytical expressions near the nucleus, for single shells, as well as
in the semiclassical limit of large non-relativistic neutral atoms. We show
that a model based on the helium iso-electronic series is very accurate, as
also confirmed by numerical calculations on real atoms up to two thousands
electrons. Based on this model, we propose non-local density-dependent
ingredients that are suitable for the description of the kinetic and exchange
energy densities in the region close to the nucleus. These non-local
ingredients are invariant under the uniform scaling of the density, and they
can be used in the construction of non-local exchange-correlation and kinetic
functionals.Comment: 11 pages, 7 figure
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