12,983 research outputs found
Inelastic Coulomb scattering rate of a multisubband Q1D electron gas
In this work, the Coulomb scattering lifetimes of electrons in two coupled
quantum wires have been studied by calculating the quasiparticle self-energy
within a multisubband model of quasi-one-dimensional (Q1D) electron system. We
consider two strongly coupled quantum wires with two occupied subbands. The
intrasubband and intersubband inelastic scattering rates are caculated for
electrons in different subbands. Contributions of the intrasubband,
intersubband plasmon excitations, as well as the quasiparticle excitations are
investigated. Our results shows that the plasmon exictations of the first
subband are the most important scattering mechanism for electrons in both
subbands.Comment: 9 pages, REVTEX, 2 figure
The Variable-Order Fractional Calculus of Variations
This book intends to deepen the study of the fractional calculus, giving
special emphasis to variable-order operators. It is organized in two parts, as
follows. In the first part, we review the basic concepts of fractional calculus
(Chapter 1) and of the fractional calculus of variations (Chapter 2). In
Chapter 1, we start with a brief overview about fractional calculus and an
introduction to the theory of some special functions in fractional calculus.
Then, we recall several fractional operators (integrals and derivatives)
definitions and some properties of the considered fractional derivatives and
integrals are introduced. In the end of this chapter, we review integration by
parts formulas for different operators. Chapter 2 presents a short introduction
to the classical calculus of variations and review different variational
problems, like the isoperimetric problems or problems with variable endpoints.
In the end of this chapter, we introduce the theory of the fractional calculus
of variations and some fractional variational problems with variable-order. In
the second part, we systematize some new recent results on variable-order
fractional calculus of (Tavares, Almeida and Torres, 2015, 2016, 2017, 2018).
In Chapter 3, considering three types of fractional Caputo derivatives of
variable-order, we present new approximation formulas for those fractional
derivatives and prove upper bound formulas for the errors. In Chapter 4, we
introduce the combined Caputo fractional derivative of variable-order and
corresponding higher-order operators. Some properties are also given. Then, we
prove fractional Euler-Lagrange equations for several types of fractional
problems of the calculus of variations, with or without constraints.Comment: The final authenticated version of this preprint is available online
as a SpringerBrief in Applied Sciences and Technology at
[https://doi.org/10.1007/978-3-319-94006-9]. In this version some typos,
detected by the authors while reading the galley proofs, were corrected,
SpringerBriefs in Applied Sciences and Technology, Springer, Cham, 201
Three-dimensional patchy lattice model: ring formation and phase separation
We investigate the structural and thermodynamic properties of a model of
particles with patches of type and patches of type . Particles
are placed on the sites of a face centered cubic lattice with the patches
oriented along the nearest neighbor directions. The competition between the
self-assembly of chains, rings and networks on the phase diagram is
investigated by carrying out a systematic investigation of this class of
models, using an extension of Wertheim's theory for associating fluids and
Monte Carlo numerical simulations. We varied the ratio
of the interaction between patches and
, , and between patches, (
is set to ) as well as the relative position of the patches, i.e., the
angle between the (lattice) directions of the patches. We found
that both and ( or ) have a
profound effect on the phase diagram. In the empty fluid regime () the
phase diagram is re-entrant with a closed miscibility loop. The region around
the lower critical point exhibits unusual structural and thermodynamic behavior
determined by the presence of relatively short rings. The agreement between the
results of theory and simulation is excellent for but
deteriorates as decreases, revealing the need for new theoretical
approaches to describe the structure and thermodynamics of systems dominated by
small rings.Comment: 26 pages, 10 figure
Effects of nucleus initialization on event-by-event observables
In this work we present a study of the influence of nucleus initializations
on the event-by-event elliptic flow coefficient, . In most Monte-Carlo
models, the initial positions of the nucleons in a nucleus are completely
uncorrelated, which can lead to very high density regions. In a simple, yet
more realistic model where overlapping of the nucleons is avoided, fluctuations
in the initial conditions are reduced. However, distributions are not
very sensitive to the initialization choice.Comment: 4 pages, 5 figures, to appear in the Bras. Jour. Phy
Diffusion-limited deposition with dipolar interactions: fractal dimension and multifractal structure
Computer simulations are used to generate two-dimensional diffusion-limited
deposits of dipoles. The structure of these deposits is analyzed by measuring
some global quantities: the density of the deposit and the lateral correlation
function at a given height, the mean height of the upper surface for a given
number of deposited particles and the interfacial width at a given height.
Evidences are given that the fractal dimension of the deposits remains constant
as the deposition proceeds, independently of the dipolar strength. These same
deposits are used to obtain the growth probability measure through Monte Carlo
techniques. It is found that the distribution of growth probabilities obeys
multifractal scaling, i.e. it can be analyzed in terms of its
multifractal spectrum. For low dipolar strengths, the spectrum is
similar to that of diffusion-limited aggregation. Our results suggest that for
increasing dipolar strength both the minimal local growth exponent
and the information dimension decrease, while the fractal
dimension remains the same.Comment: 10 pages, 7 figure
Diffusion-limited deposition of dipolar particles
Deposits of dipolar particles are investigated by means of extensive Monte
Carlo simulations. We found that the effect of the interactions is described by
an initial, non-universal, scaling regime characterized by orientationally
ordered deposits. In the dipolar regime, the order and geometry of the clusters
depend on the strength of the interactions and the magnetic properties are
tunable by controlling the growth conditions. At later stages, the growth is
dominated by thermal effects and the diffusion-limited universal regime
obtains, at finite temperatures. At low temperatures the crossover size
increases exponentially as T decreases and at T=0 only the dipolar regime is
observed.Comment: 5 pages, 4 figure
Anomalous magnetic and weak magnetic dipole moments of the lepton in the simplest little Higgs model
We obtain analytical expressions, both in terms of parametric integrals and
Passarino-Veltman scalar functions, for the one-loop contributions to the
anomalous weak magnetic dipole moment (AWMDM) of a charged lepton in the
framework of the simplest little Higgs model (SLHM). Our results are general
and can be useful to compute the weak properties of a charged lepton in other
extensions of the standard model (SM). As a by-product we obtain generic
contributions to the anomalous magnetic dipole moment (AMDM), which agree with
previous results. We then study numerically the potential contributions from
this model to the lepton AMDM and AWMDM for values of the parameter
space consistent with current experimental data. It is found that they depend
mainly on the energy scale at which the global symmetry is broken and the
parameter, whereas there is little sensitivity to a mild change in
the values of other parameters of the model. While the AMDM is of the
order of , the real (imaginary) part of its AWMDM is of the order of
(). These values seem to be out of the reach of the
expected experimental sensitivity of future experiments.Comment: 23 pages, 11 figures, new analysis and References adde
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