421 research outputs found
Metallicity determination in gas-rich galaxies with semiempirical methods
A study of the precision of the semiempirical methods used in the
determination of the chemical abundances in gas-rich galaxies is carried out.
In order to do this the oxygen abundances of a total of 438 galaxies were
determined using the electronic temperature, the and the P methods.
The new calibration of the P method gives the smaller dispersion for the low
and high metallicity regions, while the best numbers in the turnaround region
are given by the method. We also found that the dispersion correlates
with the metallicity. Finally, it can be said that all the semiempirical
methods studied here are quite insensitive to metallicity with a value of
dex for more than 50% of the total sample.
\keywords{ISM: abundances; (ISM): H {\sc ii} regions}Comment: 26 pages, 9 figures and 2 tables. To appear at AJ, January 200
Transference Principles for Log-Sobolev and Spectral-Gap with Applications to Conservative Spin Systems
We obtain new principles for transferring log-Sobolev and Spectral-Gap
inequalities from a source metric-measure space to a target one, when the
curvature of the target space is bounded from below. As our main application,
we obtain explicit estimates for the log-Sobolev and Spectral-Gap constants of
various conservative spin system models, consisting of non-interacting and
weakly-interacting particles, constrained to conserve the mean-spin. When the
self-interaction is a perturbation of a strongly convex potential, this
partially recovers and partially extends previous results of Caputo,
Chafa\"{\i}, Grunewald, Landim, Lu, Menz, Otto, Panizo, Villani, Westdickenberg
and Yau. When the self-interaction is only assumed to be (non-strongly) convex,
as in the case of the two-sided exponential measure, we obtain sharp estimates
on the system's spectral-gap as a function of the mean-spin, independently of
the size of the system.Comment: 57 page
Geometric inequalities from phase space translations
We establish a quantum version of the classical isoperimetric inequality
relating the Fisher information and the entropy power of a quantum state. The
key tool is a Fisher information inequality for a state which results from a
certain convolution operation: the latter maps a classical probability
distribution on phase space and a quantum state to a quantum state. We show
that this inequality also gives rise to several related inequalities whose
counterparts are well-known in the classical setting: in particular, it implies
an entropy power inequality for the mentioned convolution operation as well as
the isoperimetric inequality, and establishes concavity of the entropy power
along trajectories of the quantum heat diffusion semigroup. As an application,
we derive a Log-Sobolev inequality for the quantum Ornstein-Uhlenbeck
semigroup, and argue that it implies fast convergence towards the fixed point
for a large class of initial states.Comment: 37 pages; updated to match published versio
Tactics for Reasoning modulo AC in Coq
We present a set of tools for rewriting modulo associativity and
commutativity (AC) in Coq, solving a long-standing practical problem. We use
two building blocks: first, an extensible reflexive decision procedure for
equality modulo AC; second, an OCaml plug-in for pattern matching modulo AC. We
handle associative only operations, neutral elements, uninterpreted function
symbols, and user-defined equivalence relations. By relying on type-classes for
the reification phase, we can infer these properties automatically, so that
end-users do not need to specify which operation is A or AC, or which constant
is a neutral element.Comment: 16
Hypercontractive measures, Talagrand's inequality, and influences
We survey several Talagrand type inequalities and their application to
influences with the tool of hypercontractivity for both discrete and
continuous, and product and non-product models. The approach covers similarly
by a simple interpolation the framework of geometric influences recently
developed by N. Keller, E. Mossel and A. Sen. Geometric Brascamp-Lieb
decompositions are also considered in this context
Structural and nuclear characterizations of defects created by noble gas implantation in silicon oxide
Thermally grown silicon oxide layer was implanted at room temperature with 300keV Xe at fluences ranging from 0.5 to 5x10Xe/cm. Bubbles created after Xe-implantation provided a low-k silicon oxide that has potential use as a dielectric material for interconnects in Si integrated circuits. Transmission Electron Microscopy (TEM), Rutherford Backscattering Spectrometry (RBS) and Positron Annihilation Spectroscopy (PAS) were used to provide a comprehensive characterization of defects (bubbles, vacancy, gas atoms and other types of defects) created by Xe implantation in layer. These measurements suggest that the bubbles observed with TEM for all fluences were a consequence of the interaction between Xe and vacancies (V), with complexes created in the zone where V and Xe profiles overlap. Negatively charged defects such as (, and ) are also created after implantation
Study of the optimal conditions for NV- center formation in type 1b diamond, using photoluminescence and positron annihilation spectroscopies
We studied the parameters to optimize the production of negatively-charged
nitrogen-vacancy color centers (NV-) in type~1b single crystal diamond using
proton irradiation followed by thermal annealing under vacuum. Several samples
were treated under different irradiation and annealing conditions and
characterized by slow positron beam Doppler-broadening and photoluminescence
(PL) spectroscopies. At high proton fluences another complex vacancy defect
appears limiting the formation of NV-. Concentrations as high as 2.3 x 10^18
cm^-3 of NV- have been estimated from PL measurements. Furthermore, we inferred
the trapping coefficient of positrons by NV-. This study brings insight into
the production of a high concentration of NV- in diamond, which is of utmost
importance in ultra-sensitive magnetometry and quantum hybrid systems
applications
Type-based termination of recursive definitions
This paper introduces "lambda-hat", a simply typed lambda calculus
supporting inductive types and recursive function definitions with
termination ensured by types. The system is shown to enjoy subject
reduction, strong normalisation of typable terms and to be stronger than
a related system "lambda-G" in which termination is ensured by a syntactic guard condition. The system can, at will, be extended to also support coinductive types and corecursive function definitions.Information Society Technologies (IST) - Fifth Framework Programm (FP5) - TYPES.Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS XXI/C/EEI/14172/98.INRIA-ICCTI.Estonian Science Foundation (ETF) - grant no. 4155
Moments of unconditional logarithmically concave vectors
We derive two-sided bounds for moments of linear combinations of coordinates
od unconditional log-concave vectors. We also investigate how well moments of
such combinations may be approximated by moments of Gaussian random variables.Comment: 14 page
Towards a unified theory of Sobolev inequalities
We discuss our work on pointwise inequalities for the gradient which are
connected with the isoperimetric profile associated to a given geometry. We
show how they can be used to unify certain aspects of the theory of Sobolev
inequalities. In particular, we discuss our recent papers on fractional order
inequalities, Coulhon type inequalities, transference and dimensionless
inequalities and our forthcoming work on sharp higher order Sobolev
inequalities that can be obtained by iteration.Comment: 39 pages, made some changes to section 1
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