8,047 research outputs found
Chaotic behavior of the Compound Nucleus, open Quantum Dots and other nanostructures
It is well established that physical systems exhibit both ordered and chaotic
behavior. The chaotic behavior of nanostructure such as open quantum dots has
been confirmed experimentally and discussed exhaustively theoretically. This is
manifested through random fluctuations in the electronic conductance. What
useful information can be extracted from this noise in the conductance? In this
contribution we shall address this question. In particular, we will show that
the average maxima density in the conductance is directly related to the
correlation function whose characteristic width is a measure of energy- or
applied magnetic field- correlation length. The idea behind the above has been
originally discovered in the context of the atomic nucleus, a mesoscopic
system. Our findings are directly applicable to graphene.Comment: 10 pages, 5 figures. Contribution to: "4th International Workshop on
Compound-Nuclear Reactions and Related Topics (CNR*13)", October 7-11, 2013,
Maresias, Brazil. To appear in the proceeding
Improved WKB approximation for quantum tunneling: Application to heavy ion fusion
In this paper we revisit the one-dimensional tunneling problem. We consider
Kemble's approximation for the transmission coefficient. We show how this
approximation can be extended to above-barrier energies by performing the
analytical continuation of the radial coordinate to the complex plane. We
investigate the validity of this approximation by comparing their predictions
for the cross section and for the barrier distribution with the corresponding
quantum mechanical results. We find that the extended Kemble's approximation
reproduces the results of quantum mechanics with great accuracy.Comment: 8 pages, 6 figures, in press, in European. Phys. Journal A (2017
Welfare Impacts of the Mexico Potato Quarantine
Under the North American Free Trade Agreement (NAFTA) tariffs on U.S. potato imports to Mexico were phased out by 1993. Citing phytosanitary issues, in 1996, the Mexican government placed quantitative restrictions on U.S. potato imports and restricted their import only to designated border areas. This article estimates the welfare cost of restricting U.S. potato imports into Mexico. We find that removing trade restrictions may lead to over 1.8 million tons of new imports into Mexico, a gain of consumer surplus of 4.0 billion pesos per year, and a loss of 2.9 billion pesos of producer surplus.international trade, non-tariff barriers, potatoes, quarantine, sanitary and phytosanitary barriers, welfare loss, Agribusiness, Agricultural and Food Policy, Crop Production/Industries, Environmental Economics and Policy, Food Consumption/Nutrition/Food Safety, Health Economics and Policy, International Relations/Trade, Political Economy, F13, L13, Q13, Q17, C35,
Symmetry Breaking Study with Deformed Ensembles
A random matrix model to describe the coupling of m-fold symmetry in
constructed. The particular threefold case is used to analyze data on
eigenfrequencies of elastomechanical vibration of an anisotropic quartz block.
It is suggested that such experimental/theoretical study may supply powerful
means to discern intrinsic symmetries in physical systems.Comment: 12 pages, 5 figure
Approximate transmission coefficients in heavy ion fusion
In this paper we revisit the one-dimensional tunnelling problem. We consider
different approximations for the transmission through the Coulomb barrier in
heavy ion collisions at near-barrier energies. First, we discuss approximations
of the barrier shape by functional forms where the transmission coefficient is
known analytically. Then, we consider Kemble's approximation for the
transmission coefficient. We show how this approximation can be extended to
above-barrier energies by performing the analytical continuation of the radial
coordinate to the complex plane. We investigate the validity of the different
approximations considered in this paper by comparing their predictions for
transmission coefficients and cross sections of three heavy ion systems with
the corresponding quantum mechanical results.Comment: 12 pages, 6 figure
Optimal network topologies for information transmission in active networks
This work clarifies the relation between network circuit (topology) and
behavior (information transmission and synchronization) in active networks,
e.g. neural networks. As an application, we show how to determine a network
topology that is optimal for information transmission. By optimal, we mean that
the network is able to transmit a large amount of information, it possesses a
large number of communication channels, and it is robust under large variations
of the network coupling configuration. This theoretical approach is general and
does not depend on the particular dynamic of the elements forming the network,
since the network topology can be determined by finding a Laplacian matrix (the
matrix that describes the connections and the coupling strengths among the
elements) whose eigenvalues satisfy some special conditions. To illustrate our
ideas and theoretical approaches, we use neural networks of electrically
connected chaotic Hindmarsh-Rose neurons.Comment: 20 pages, 12 figure
A study of local approximation for polarization potentials
We discuss the derivation of an equivalent \textit{l}-independent
polarization potential for use in the optical Schr\"{o}dinger equation that
describes the elastic scattering of heavy ions. Three diffferent methods are
used for this purpose. Application of our theory to the low energy scattering
of the halo nucleus Li from a C target is made. It is found that
the notion of \textit{l}-independent polarization potential has some validity
but can not be a good substitute for the \textit{l}-dependent local equivalent
Feshbach polarization potential.Comment: 8 pages, 4 figure
How large is the spreading width of a superdeformed band?
Recent models of the decay out of superdeformed bands can broadly be divided
into two categories. One approach is based on the similarity between the
tunneling process involved in the decay and that involved in the fusion of
heavy ions, and builds on the formalism of nuclear reaction theory. The other
arises from an analogy between the superdeformed decay and transport between
coupled quantum dots. These models suggest conflicting values for the spreading
width of the decaying superdeformed states. In this paper, the decay of
superdeformed bands in the five even-even nuclei in which the SD excitation
energies have been determined experimentally is considered in the framework of
both approaches, and the significance of the difference in the resulting
spreading widths is considered. The results of the two models are also compared
to tunneling widths estimated from previous barrier height predictions and a
parabolic approximation to the barrier shape
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