37,334 research outputs found
Accurate calculation of resonances in multiple-well oscillators
Quantum--mechanical multiple--well oscillators exhibit curious complex
eigenvalues that resemble resonances in models with continuum spectra. We
discuss a method for the accurate calculation of their real and imaginary
parts
Bares 2.0 wave buoy and sustainable buoy network
The aim of this article is to show the operation of the Bares 2.0 wave buoy
and the Bares network developed by HCTech. In the marine sector it is highly important
to know the state of the sea for applications such as the construction of ports,
the study of the impact of waves in coastal areas, the development and calibration
of forecasting wave models, the knowledge of the state of the maritime navigation
channels, etc. Some of the great difficulties that exist in order to obtain the information
of ocean waves is the high cost of the buoys, installation and maintenance. The
Bares network aims to cover areas of high oceanographic interest, the target is a
sustainable network of buoys that facilitate the access to wave data. The features
of this network are the optimized cost, high reliability and reduced maintenance.Peer Reviewe
From thermal to excited-state quantum phase transitions ---the Dicke model
We study the thermodynamics of the full version of the Dicke model, including
all the possible values of the total angular momentum , with both
microcanonical and canonical ensembles. We focus on how the excited-state
quantum phase transition, which only appears in the microcanonical description
of the maximum angular momentum sector, , change to a standard thermal
phase transition when all the sectors are taken into account. We show that both
the thermal and the excited-state quantum phase transitions have the same
origin; in other words, that both are two faces of the same phenomenon. Despite
all the logarithmic singularities which characterize the excited-state quantum
phase transition are ruled out when all the -sectors are considered, the
critical energy (or temperature) still divides the spectrum in two regions: one
in which the parity symmetry can be broken, and another in which this symmetry
is always well defined.Comment: Submitted to PRE. Comments are welcome. V2: Updated to match
published versio
The confined hydrogen atom with a moving nucleus
We study the hydrogen atom confined to a spherical box with impenetrable
walls but, unlike earlier pedagogical articles on the subject, we assume that
the nucleus also moves. We obtain the ground-state energy approximately by
means of first--order perturbation theory and by a more accurate variational
approach. We show that it is greater than the one for the case in which the
nucleus is clamped at the center of the box. Present approach resembles the
well-known treatment of the helium atom with clamped nucleus
Energy efficiency and integration of urban electrical transport systems: EVS and metro-trains of two real European lines
Transport is a main source of pollutants in cities, where air quality is a major concern. New transport technologies, such as electric vehicles, and public transport modalities, such as urban railways, have arisen as solutions to this important problem. One of the main difficulties for the adoption of electric vehicles by consumers is the scarcity of a suitable charging infrastructure. The use of the railway power supplies to charge electric vehicle batteries could facilitate the deployment of charging infrastructure in cities. It would reduce the cost because of the use of an existing installation. Furthermore, electric vehicles can use braking energy from trains that was previously wasted in rheostats. This paper presents the results of a collaboration between research teams from University of Rome Sapienza and Comillas Pontifical University. In this work, two real European cases are studied: an Italian metro line and a Spanish metro line. The energy performance of these metro lines and their capacity to charge electric vehicles have been studied by means of detailed simulation tools. Their results have shown that the use of regenerated energy is 98% for short interval of trains in both cases. However, the use of regenerated energy decreases as the train intervals grow. In a daily operation, an important amount of regenerated energy is wasted in the Italian and Spanish case. Using this energy, a significant number of electric vehicles could be charged every day
Simple one-dimensional quantum-mechanical model for a particle attached to a surface
We present a simple one-dimensional quantum-mechanical model for a particle
attached to a surface. We solve the Schr\"odinger equation in terms of Weber
functions and discuss the behavior of the eigenvalues and eigenfunctions. We
derive the virial theorem and other exact relationships as well as the
asymptotic behaviour of the eigenvalues. We calculate the zero-point energy for
model parameters corresponding to H adsorbed on Pd(100) and also outline the
application of the Rayleigh-Ritz variational method
Phase diagram of a polydisperse soft-spheres model for liquids and colloids
The phase diagram of soft spheres with size dispersion has been studied by
means of an optimized Monte Carlo algorithm which allows to equilibrate below
the kinetic glass transition for all sizes distribution. The system
ubiquitously undergoes a first order freezing transition. While for small size
dispersion the frozen phase has a crystalline structure, large density
inhomogeneities appear in the highly disperse systems. Studying the interplay
between the equilibrium phase diagram and the kinetic glass transition, we
argue that the experimentally found terminal polydispersity of colloids is a
purely kinetic phenomenon.Comment: Version to be published in Physical Review Letter
Separation and fractionation of order and disorder in highly polydisperse systems
Microcanonical Monte Carlo simulations of a polydisperse soft-spheres model
for liquids and colloids have been performed for very large polydispersity, in
the region where a phase-separation is known to occur when the system (or part
of it) solidifies. By studying samples of different sizes, from N=256 to N=864,
we focus on the nature of the two distinct coexisting phases. Measurements of
crystalline order in particles of different size reveal that the solid phase
segregates between a crystalline solid with cubic symmetry and a disordered
phase. This phenomenon is termed fractionation.Comment: 8 pages, 5 figure
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