5,756 research outputs found
Infinite chain of N different deltas: a simple model for a Quantum Wire
We present the exact diagonalization of the Schrodinger operator
corresponding to a periodic potential with N deltas of different couplings, for
arbitrary N. This basic structure can repeat itself an infinite number of
times. Calculations of band structure can be performed with a high degree of
accuracy for an infinite chain and of the correspondent eigenlevels in the case
of a random chain. The main physical motivation is to modelate quantum wire
band structure and the calculation of the associated density of states. These
quantities show the fundamental properties we expect for periodic structures
although for low energy the band gaps follow unpredictable patterns. In the
case of random chains we find Anderson localization; we analize also the role
of the eigenstates in the localization patterns and find clear signals of
fractality in the conductance. In spite of the simplicity of the model many of
the salient features expected in a quantum wire are well reproduced.Comment: 28 pages, LaTeX, 13 eps figures (3 color
Simple model for a Quantum Wire II. Correlations
In a previous paper (Eur. Phys. J. B 30, 239-251 (2002)) we have presented
the main features and properties of a simple model which -in spite of its
simplicity- describes quite accurately the qualitative behaviour of a quantum
wire. The model was composed of N distinct deltas each one carrying a different
coupling. We were able to diagonalize the Hamiltonian in the periodic case and
yield a complete and analytic description of the subsequent band structure.
Furthermore the random case was also analyzed and we were able to describe
Anderson localization and fractal structure of the conductance. In the present
paper we go one step further and show how to introduce correlations among the
sites of the wire. The presence of a correlated disorder manifests itself by
altering the distribution of states and the localization of the electrons
within the systemComment: RevTex, 7 pages, 9 figures (3 greyscale, 6 coloured
Structure Theorem for Riemannian surfaces with arbitrary curvature
In this paper we prove that any Riemannian surface, with no restriction of
curvature at all, can be decomposed into blocks belonging just to some of these
types: generalized Y-pieces, generalized funnels and halfplanes.Comment: 15 pages, 1 latex file, 7 eps figure
PEM-West trajectory climatology and photochemical model sensitivity study prepared using retrospective meteorological data
Trajectory and photochemical model calculations based on retrospective meteorological data for the operations areas of the NASA Pacific Exploratory Mission (PEM)-West mission are summarized. The trajectory climatology discussed here is intended to provide guidance for flight planning and initial data interpretation during the field phase of the expedition by indicating the most probable path air parcels are likely to take to reach various points in the area. The photochemical model calculations which are discussed indicate the sensitivity of the chemical environment to various initial chemical concentrations and to conditions along the trajectory. In the post-expedition analysis these calculations will be used to provide a climatological context for the meteorological conditions which are encountered in the field
Microsimulating the Effects of Household Energy Price Changes in Spain
In this paper we present a microsimulation model to calculate the effects of hypothetical ex-ante price changes in the Spanish energy domain. The model rests on our prior estimation of a demand system which is especially designed for simultaneous analysis of different energy goods and uses household data from 1973 to 1995. Our objective is to obtain in-depth information on the behavioural responses by different types of households, which will allow us to determine the welfare effects of such price changes, their distribution across society and the environmental consequences within the residential sector. Although the model used is able to reproduce any type of price change, we illustrate the paper with an actual simulation of the effects of energy taxes that resemble a 50 Euro tax on CO2 (carbon dioxide) emissions. The results show a significant response by households, sizeable emission reductions, tax revenues, welfare changes and distributional effects. The simulated policy can thus be considered a feasible option to tackle some of the current and severe inefficiencies in Spanish energy and environmental domains.Energy, taxation, demand, Spain; CO2
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