Constraints On Dark Energy Models From Galaxy Clusters and Gravitational Lensing Data

The Sunyaev--Zel'dovich (SZ) effect is a global distortion of the Cosmic Microwave Background (CMB) spectrum as a result of its interaction with a hot electron plasma in the intracluster medium of large structures gravitationally viralized such as galaxy clusters (GC). Furthermore, this~hot gas of electrons emits X-rays due to its fall in the gravitational potential well of the GC. The~analysis of SZ and X-ray data provides a method for calculating distances to GC at high redshifts. On the other hand, many galaxies and GC produce a Strong Gravitational Lens (SGL) effect, which has become a useful astrophysical tool for cosmology. We use these cosmological tests in addition to more traditional ones to constrain some alternative dark energy (DE) models, including the study of the history of cosmological expansion through the cosmographic parameters. Using Akaike and Bayesian Information Criterion, we find that the $wCDM$ and $\Lambda CDM$ models are the most favoured by the observational data. In addition, we found at low redshift a peculiar behavior of slowdown of the universe, which occurs in dynamical DE models when we use data from GC.Comment: 21 page, 5 figures, 8 tables. Published: 22 January 2018, Universe, MDPI, Special Issue "Progress in Cosmology in the Centenary of the 1917 Einstein Paper

Self-sustained current oscillations in the kinetic theory of semiconductor superlattices

We present the first numerical solutions of a kinetic theory description of self-sustained current oscillations in n-doped semiconductor superlattices. The governing equation is a single-miniband Boltzmann-Poisson transport equation with a BGK (Bhatnagar-Gross-Krook) collision term. Appropriate boundary conditions for the distribution function describe electron injection in the contact regions. These conditions seamlessly become Ohm's law at the injecting contact and the zero charge boundary condition at the receiving contact when integrated over the wave vector. The time-dependent model is numerically solved for the distribution function by using the deterministic Weighted Particle Method. Numerical simulations are used to ascertain the convergence of the method. The numerical results confirm the validity of the Chapman-Enskog perturbation method used previously to derive generalized drift-diffusion equations for high electric fields because they agree very well with numerical solutions thereof.Comment: 26 pages, 16 figures, to appear in J. Comput. Phy

The Political Economy of Exchange Rate Policies in Argentina

This paper identifies three periods in Argentine exchange rate policy, corresponding with different development strategies and political coalitions. The first, periodic adjustments to a pegged rate until the mid-1970s, accompanied an Import Substitution Industrialization approach and a redistribution of income from agrarian to industrial production during an era of strong labor union influence. A second period, from the mid-1970s, marked by accelerated devaluations, represented efforts by both military and civilian governments to meet the demands of their respective constituencies while maintaining capital flows from abroad; these efforts culminated in hyperinflation. A third period, beginning in the early 1990s, was notable for exchange rate stability, based on the Convertibility Plan, as a broad consensus emerged that the exchange rate should be used for containing inflation rather than engaging in redistribution among domestic interest groups. The authors conclude that additional innovations in Argentina`s monetary and exchange rate policies may eventually be necessary.

Chaos in resonant-tunneling superlattices

Spatio-temporal chaos is predicted to occur in n-doped semiconductor superlattices with sequential resonant tunneling as their main charge transport mechanism. Under dc voltage bias, undamped time-dependent oscillations of the current (due to the motion and recycling of electric field domain walls) have been observed in recent experiments. Chaos is the result of forcing this natural oscillation by means of an appropriate external microwave signal.Comment: 3 pages, LaTex, RevTex, 3 uuencoded figures (1.2M) are available upon request from [email protected], to appear in Phys.Rev.

Chaotic motion of space charge wavefronts in semiconductors under time-independent voltage bias

A standard drift-diffusion model of space charge wave propagation in semiconductors has been studied numerically and analytically under dc voltage bias. For sufficiently long samples, appropriate contact resistivity and applied voltage - such that the sample is biased in a regime of negative differential resistance - we find chaos in the propagation of nonlinear fronts (charge monopoles of alternating sign) of electric field. The chaos is always low-dimensional, but has a complex spatial structure; this behavior can be interpreted using a finite dimensional asymptotic model in which the front (charge monopole) positions and the electrical current are the only dynamical variables.Comment: 12 pages, 8 figure

Perfiles de los visitantes en el turismo de naturaleza: análisis exploratorio en el entorno de Doñana

El turismo de naturaleza tiene una demanda cada vez mayor en los últimos años. En el presente trabajo se han estudiado los perfiles de los visitantes en el turismo de naturaleza. Para ello, este estudio se ha planteado en el entorno de Doñana. Este espacio natural es uno de los más importantes de España y de Europa. La muestra de estudio se ha compuesto de 130 turistas que visitaron o que tenían intención de visitar el Parque Nacional de Doñana. Como resultado, entre otros aspectos, se observa que el perfil dominante del turista está más próximo a un tipo de visitante ocasional de la naturaleza.Nature tourism has an increasing demand in last years. In this work it was studied the profiles of visitors to nature tourism. To this end, this study has arisen in Doñana. This natural area is one of the most important in Spain and Europe. The sample was composed of 130 tourists who had visited or intended to visit the National Park of Doñana. As a result, inter alia, it observed that the dominant profile of the tourist is closer to a kind of casual visitor of nature

A hybrid model for chaotic front dynamics: From semiconductors to water tanks

We present a general method for studying front propagation in nonlinear systems with a global constraint in the language of hybrid tank models. The method is illustrated in the case of semiconductor superlattices, where the dynamics of the electron accumulation and depletion fronts shows complex spatio-temporal patterns, including chaos. We show that this behavior may be elegantly explained by a tank model, for which analytical results on the emergence of chaos are available. In particular, for the case of three tanks the bifurcation scenario is characterized by a modified version of the one-dimensional iterated tent-map.Comment: 4 pages, 4 figure

Dynamics of Electric Field Domains and Oscillations of the Photocurrent in a Simple Superlattice Model

A discrete model is introduced to account for the time-periodic oscillations of the photocurrent in a superlattice observed by Kwok et al, in an undoped 40 period AlAs/GaAs superlattice. Basic ingredients are an effective negative differential resistance due to the sequential resonant tunneling of the photoexcited carriers through the potential barriers, and a rate equation for the holes that incorporates photogeneration and recombination. The photoexciting laser acts as a damping factor ending the oscillations when its power is large enough. The model explains: (i) the known oscillatory static I-V characteristic curve through the formation of a domain wall connecting high and low electric field domains, and (ii) the photocurrent and photoluminescence time-dependent oscillations after the domain wall is formed. In our model, they arise from the combined motion of the wall and the shift of the values of the electric field at the domains. Up to a certain value of the photoexcitation, the non-uniform field profile with two domains turns out to be metastable: after the photocurrent oscillations have ceased, the field profile slowly relaxes toward the uniform stationary solution (which is reached on a much longer time scale). Multiple stability of stationary states and hysteresis are also found. An interpretation of the oscillations in the photoluminescence spectrum is also given.Comment: 34 pages, REVTeX 3.0, 10 figures upon request, MA/UC3M/07/9

Prácticas de física : laboratorio I

1 archivo PDF (62 páginas)Conjunto de prácticas que indican el camino a seguir en el trabajo que realizara el alumno