Federal University of Espirito Santo

Vitoria, Brazil

Time filter

Source Type

Bakke K.,Federal University of Paraiba | Belich H.,Federal University of Espirito Santo
Annals of Physics | Year: 2015

We study a possible scenario of the Lorentz symmetry violation background that allows us to build an analogue of the Landau system for a nonrelativistic Dirac neutral particle interacting with a field configuration of crossed electric and magnetic fields. We also discuss the arising of analogues of the Rashba coupling, the Zeeman term and the Darwin term from the Lorentz symmetry breaking effects, and the influence of these terms on the analogue of the Landau system confined to a two-dimensional quantum ring. Finally, we show that this analogy with the Landau system confined to a two-dimensional quantum ring allows us to establish an upper bound for the Lorentz symmetry breaking parameters. © 2014 Elsevier Inc.

Krohling R.A.,Federal University of Espirito Santo | Campanharo V.C.,Federal University of Espirito Santo
Expert Systems with Applications | Year: 2011

The selection of the best combat responses to oil spill in the sea when several alternatives have to be evaluated with different weights for each criterion consist of a multicriteria decision making (MCDM) problem. In this work, firstly the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) is described. Secondly, its expansion known as fuzzy TOPSIS to handle uncertain data is presented. Next, based on fuzzy TOPSIS we propose a fuzzy TOPSIS for group decision making, which is applied to evaluate the ratings of response alternatives to a simulated oil spill. The case study was carried out for one of the largest Brazilian oil reservoirs. The results show the feasibility of the fuzzy TOPSIS framework to find out the best combat responses in case of accidents with oil spill in the sea. © 2010 Elsevier Ltd. All rights reserved.

Amaral A.R.S.,Federal University of Espirito Santo
Computers and Operations Research | Year: 2013

In this paper, we study a problem that occurs in the row layout of facilities. Among n facilities, suppose that there are t facilities with some characteristic in common so that they should be arranged along one row, leaving the remainder (n-t) facilities to be arranged on a parallel row. The objective is to order the facilities in the two rows such that some cost function is minimized. This problem is called the parallel row ordering problem (PROP). The PROP is a generalization of the single row facility layout problem (SRFLP). Here, a mixed integer programming (MIP) formulation of the PROP is presented which extends a MIP formulation of the SRFLP. We show that a PROP with n facilities may be solved faster than a SRFLP with n facilities. Theoretical and experimental comparisons of the SRFLP and the PROP formulations are presented. © 2013 Elsevier Ltd.

Mattos Ribeiro G.,HEC Montréal | Mattos Ribeiro G.,Federal University of Espirito Santo | Laporte G.,HEC Montréal
Computers and Operations Research | Year: 2012

The cumulative capacitated vehicle routing problem (CCVRP) is a variation of the classical capacitated vehicle routing problem in which the objective is the minimization of the sum of arrival times at customers, instead of the total routing cost. This paper presents an adaptive large neighborhood search heuristic for the CCVRP. This algorithm is applied to a set of benchmark instances and compared with two recently published memetic algorithms. © 2011 Elsevier Ltd. All rights reserved.

Rodrigues M.E.,Federal University of Espirito Santo | Oporto Z.A.A.,Federal University of Espirito Santo
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

A thermodynamic analysis of the black hole solutions coming from the Einstein-Maxwell-dilaton theory in 4D is done. By considering the canonical and grand-canonical ensemble, we apply standard method as well as a recent method known as geometrothermodynamics. We are particularly interested in the characteristics of the so called phantom black hole solutions. We will analyze the thermodynamics of these solutions, the points of phase transition and their extremal limit. The thermodynamic stability is also analyzed. We obtain a mismatch between the results of the geometrothermodynamics method when compared with the ones obtained by the specific heat, revealing a weakness of the method, as well as possible limitations of its applicability to very pathological thermodynamic systems. We also found that normal and phantom solutions are locally and globally unstable, except for certain values of the coupled constant of the Einstein-Maxwell-dilaton action. We also show that the anti-Reissner-Nordstrom solution does not possess extremal limit nor phase transition points, contrary to the Reissner-Nordstrom case. © 2012 American Physical Society.

Bakke K.,Federal University of Paraiba | Belich H.,Federal University of Espirito Santo
Annals of Physics | Year: 2013

In this work, we discuss the relativistic Landau-He-McKellar-Wilkens quantization and relativistic bound states solutions for a Dirac neutral particle under the influence of a Coulomb-like potential induced by the Lorentz symmetry breaking effects. We present new possible scenarios of studying Lorentz symmetry breaking effects by fixing the space-like vector field background in special configurations. It is worth mentioning that the criterion for studying the violation of Lorentz symmetry is preserving the gauge symmetry. © 2013 Elsevier Inc.

Amaral A.R.S.,Federal University of Espirito Santo
Computers and Operations Research | Year: 2012

The corridor allocation problem (CAP) seeks an arrangement of facilities along a central corridor defined by two horizontal lines parallel to the x-axis of a Cartesian coordinate system. The objective is to minimize the total communication cost among facilities, while respecting two main conditions: (i) no space is allowed between two adjacent facilities; (ii) the left-most point of the arrangement on either line should have zero abscissa. The conditions (i) and (ii) are required in many applications such as the arrangement of rooms at office buildings or hospitals. The CAP is a NP-Hard problem. In this paper, a mixed-integer programming formulation of the CAP is proposed, which allows us to compute optimal layouts in reasonable time for problem instances of moderate sizes. Moreover, heuristic procedures are presented that can handle larger instances. © 2012 Elsevier Ltd. All rights reserved.

Marra V.,Federal University of Espirito Santo
Physics of the Dark Universe | Year: 2016

We propose that dark energy in the form of a scalar field could effectively couple to dark matter inhomogeneities. Through this coupling energy could be transferred to/from the scalar field, which could possibly enter an accelerated regime. Though phenomenological, this scenario is interesting as it provides a natural trigger for the onset of the acceleration of the universe, since dark energy starts driving the expansion of the universe when matter inhomogeneities become sufficiently strong. Here we study a possible realization of this idea by coupling dark energy to dark matter via the linear growth function of matter perturbations. The numerical results show that it is indeed possible to obtain a viable cosmology with the expected series of radiation, matter and dark-energy dominated eras. In particular, the current density of dark energy is given by the value of the coupling parameters rather than by very special initial conditions for the scalar field. In other words, this model-unlike standard models of cosmic late acceleration-does not suffer from the so-called "coincidence problem" and its related fine tuning of initial conditions. © 2016 Elsevier B.V.

Pavon D.,Autonomous University of Barcelona | Zimdahl W.,Federal University of Espirito Santo
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

In this Letter we consider three future singularities in different Friedmann-Lemaître-Robertson-Walker scenarios and show that the universe departs more and more from thermodynamic equilibrium as the corresponding singularity is approached. Though not proven in general, this feature may characterize future singularities of homogeneous and isotropic cosmologies. © 2012 Elsevier B.V.

Although there are several reported correlations among structural parameters, Young's modulus (E), thermal conductivity, electrical resistivity and coefficient of thermal expansion of carbon fibers in the longitudinal direction, a single physical model has not yet been established to explain quantitatively these properties. Here a model of continuous defective graphene nanoribbons (dGNR), which are arranged in stacks, is presented to predict a number of properties of mesophase pitch (MPP)-based carbon fibers in a single physical framework. Reported in situ tensile tests and other works support the assumption that, for MPP-based carbon fibers with E > 350 GPa, slightly misaligned perfect graphene regions of the dGNR are longitudinally in series with defective regions of an approximately constant length δ = 3 nm. The longitudinal properties of the dGNR depend strongly on the average longitudinal concentration of defective regions (x) of length δ, which can be estimated from the X-ray diffraction in-plane longitudinal coherence length (La||). The model was applied with success to high-and ultra-high-modulus commercial MPP-based carbon fibers; other fibers were also discussed. The values for the properties of the defective regions were determined and are consistent with the proposed model structure; relative values and scaling factors between properties were discussed. © 2014 Elsevier Ltd. All rights reserved.

Loading Federal University of Espirito Santo collaborators
Loading Federal University of Espirito Santo collaborators