18,828 research outputs found
The delayed contribution of low and intermediate mass stars to chemical galactic enrichment: An analytical approach
We find a new analytical solution for the chemical evolution equations,
taking into account the delayed contribution of all low and intermediate mass
stars (LIMS) as one representative star that enriches the interstellar
medium.This solution is built only for star formation rate proportional to the
gas mass in a closed box model. We obtain increasing C/O and N/O ratios with
increasing O/H, behavior impossible to match with the Instantaneous Recycling
Approximation (IRA). Our results, obtained by two analytical equations, are
very similar to those found by numerical models that consider the lifetimes of
each star. This delayed model reproduces successfully the evolution of C/O-O/H
and Y-O relations in the solar vicinity. This analytical approximation is a
useful tool to study the chemical evolution of elements produced by LIMS when a
galactic chemical evolutionary code is not available.Comment: 19 pages, 5 figures, to be published in the RevMexAA in October 200
Classical and quantum free motions in the tomographic probability representation
Based on a geometric picture, the example of free particle motion for both
classical and quantum domains is considered in the tomographic probability
representation. Wave functions and density operators as well as optical and
symplectic tomograms are obtained as solutions of kinetic classical and quantum
equations for the state tomograms. The difference of tomograms of free particle
for classical and quantum states is discussed.Comment: Contibution to the conference "Folding and Unfolding: Interactions
from Geometry". Workshop in honour of Giuseppe Marmo 65--th birtday. Ischia,
Naples 8--12 June 2011. To appear in International Journal of Geometric
Methods in Modern Physic
Detecting spatial homogeneity in the world trade web with Detrended Fluctuation Analysis
In a spatially embedded network, that is a network where nodes can be
uniquely determined in a system of coordinates, links' weights might be
affected by metric distances coupling every pair of nodes (dyads). In order to
assess to what extent metric distances affect relationships (link's weights) in
a spatially embedded network, we propose a methodology based on DFA (Detrended
Fluctuation Analysis). DFA is a well developed methodology to evaluate
autocorrelations and estimate long-range behaviour in time series. We argue it
can be further extended to spatially ordered series in order to assess
autocorrelations in values. A scaling exponent of 0.5 (uncorrelated data) would
thereby signal a perfect homogeneous space embedding the network. We apply the
proposed methodology to the World Trade Web (WTW) during the years 1949-2000
and we find, in some contrast with predictions of gravity models, a declining
influence of distances on trading relationships.Comment: 15 pages, 7 figure
Metric on the space of quantum states from relative entropy. Tomographic reconstruction
In the framework of quantum information geometry, we derive, from quantum
relative Tsallis entropy, a family of quantum metrics on the space of full
rank, N level quantum states, by means of a suitably defined coordinate free
differential calculus. The cases N = 2, N = 3 are discussed in detail and
notable limits are analyzed. The radial limit procedure has been used to
recover quantum metrics for lower rank states, such as pure states. By using
the tomographic picture of quantum mechanics we have obtained the Fisher- Rao
metric for the space of quantum tomograms and derived a reconstruction formula
of the quantum metric of density states out of the tomographic one. A new
inequality obtained for probabilities of three spin-1/2 projections in three
perpendicular directions is proposed to be checked in experiments with
superconducting circuits.Comment: 31 pages. No figures. Abstract and Introduction rewritten. Minor
corrections. References adde
D-brane Instantons as Gauge Instantons in Orientifolds of Chiral Quiver Theories
Systems of D3-branes at orientifold singularities can receive
non-perturbative D-brane instanton corrections, inducing field theory operators
in the 4d effective theory. In certain non-chiral examples, these systems have
been realized as the infrared endpoint of a Seiberg duality cascade, in which
the D-brane instanton effects arise from strong gauge theory dynamics. We
present the first UV duality cascade completion of chiral D3-brane theories, in
which the D-brane instantons arise from gauge theory dynamics. Chiral examples
are interesting because the instanton fermion zero mode sector is topologically
protected, and therefore lead to more robust setups. As an application of our
results, we provide a UV completion of certain D-brane orientifold systems
recently claimed to produce conformal field theories with conformal invariance
broken only by D-brane instantons.Comment: 50 pages, 32 figures. v2: version published in JHEP with references
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