Papers by Luis A. Santos Laureano
Computer Communications, Apr 1, 2000
In the past few years there has been an enthusiastic interest in mobile agent technology and seve... more In the past few years there has been an enthusiastic interest in mobile agent technology and several platforms have been developed. Some of them have only been used for research purposes while others have been deployed as commercial products. The community is now looking for applications where these platforms can be effectively used. Some comparisons about the functionality of some mobile agent systems have been presented in the literature. However, to the best of our knowledge, there has been no reported study that compares the real performance of the platforms.
Fast and affordable computing systems currently support walkthroughs into virtual reconstructed s... more Fast and affordable computing systems currently support walkthroughs into virtual reconstructed sites, with fast frame rate generation of synthetic images. However, archaeologists still complain about the lack of realism in these interactive tours, mainly due to the false ambient illumination. Accurate visualizations require physically based global illumination models to render the scenes, which are computationally too demanding. Faster systems and novel rendering techniques are required: current clusters provide a feasible ...
Environ Technol, 1993
... a critical analysis. Auteur(s) / Author(s). BIDONE ED (1) ; FERNANDES HM ; SILVA FILHO EV (1)... more ... a critical analysis. Auteur(s) / Author(s). BIDONE ED (1) ; FERNANDES HM ; SILVA FILHO EV (1) ; TRINDADE DOS SANTOS LF (1) ; Affiliation(s) du ou des auteurs / Author(s) Affiliation(s). (1) Univ. federal fluminense, dep. geoquimica, 24210 Niteroi, BRESIL Résumé / Abstract. ...
The partially attractive character of the dipole-dipole interaction leads to phonon instability i... more The partially attractive character of the dipole-dipole interaction leads to phonon instability in dipolar Bose-Einstein condensates, which is followed by collapse in 3D geometries. We show that in 2D, the nature of the post-instability dynamics is fundamentally different, due to the stabilization of 2D solitons. As a result, a transient gas of attractive solitons is formed, and collapse may be avoided. In the presence of an harmonic trap, the post-instability dynamics is characterized by a transient pattern formation followed by the creation of stable 2D solitons. This dynamics should be observable in ongoing experiments, allowing for the creation of stable 2D solitons for the first time ever in quantum gases.
Amer J Cardiol, 1983
hypokinetic as visualized on 2-dimensional echocardiography before reperfusion was akinetic on bo... more hypokinetic as visualized on 2-dimensional echocardiography before reperfusion was akinetic on both echocardiography and angiography after reperfusion. In addition, the apex became hypokinetic despite reperfusion. There was no thallium uptake in the inferior wall after thrombolysis, and the serial electrocardiogram suggested extension of the initial inferior MI to the posterior wall. These observations suggesting no benefit from reperfusion and possible deterioration after thrombolysis did not result from either an inordinate delay in reperfusion or early reocclusion of the artery.
Eprint Arxiv 0905 3312, May 20, 2009
We analyze by means of Matrix-Product-State simulations the correlation dynamics of strongly-corr... more We analyze by means of Matrix-Product-State simulations the correlation dynamics of strongly-correlated superfluid Bose gases in one-dimensional time-dependent optical lattices. We show that, as for the case of abrupt quenches, a quasi-adiabatic modulation of the lattice is characterized by a relatively long transient regime for which quasi-local single-particle correlation functions have already converged to a new equilibrium, whereas long-range correlations and particularly the quasi-condensate fraction may still present a very significant dynamics well after the end of the lattice modification. We also address the issue of adiabaticity by considering the fidelity between the time-evolved state and the ground-state of the final lattice.
Mutagenesis, Jan 22, 2015
Formaldehyde (FA) is a commonly used chemical in anatomy and pathology laboratories as a tissue p... more Formaldehyde (FA) is a commonly used chemical in anatomy and pathology laboratories as a tissue preservative and fixative. Because of its sensitising properties, irritating effects and cancer implication, FA accounts probably for the most important chemical-exposure hazard concerning this professional group. Evidence for genotoxic effects and carcinogenic properties in humans is insufficient and conflicting, particularly in regard to the ability of inhaled FA to induce toxicity on other cells besides first contact tissues, such as buccal and nasal cells. To evaluate the effects of exposure to FA in human peripheral blood lymphocytes, a group of 84 anatomy pathology laboratory workers exposed occupationally to FA and 87 control subjects were tested for chromosomal aberrations (CAs) and DNA damage (comet assay). The level of exposure to FA in the workplace air was evaluated. The association between genotoxicity biomarkers and polymorphic genes of xenobiotic-metabolising and DNA repair...
Physical Review Letters, 2009
The partially attractive character of the dipole-dipole interaction leads to phonon instability i... more The partially attractive character of the dipole-dipole interaction leads to phonon instability in dipolar Bose-Einstein condensates, which is followed by collapse in 3D geometries. We show that in 2D, the nature of the post-instability dynamics is fundamentally different, due to the stabilization of 2D solitons. As a result, a transient gas of attractive solitons is formed, and collapse may be avoided. In the presence of an harmonic trap, the post-instability dynamics is characterized by a transient pattern formation followed by the creation of stable 2D solitons. This dynamics should be observable in ongoing experiments, allowing for the creation of stable 2D solitons for the first time ever in quantum gases.
Journal of Non Crystalline Solids, 2003
Bulk oxyhalide glasses have been prepared in the TeO 2 -ZnO-ZnX 2 and TeO 2 -PbO-PbX 2 systems (X... more Bulk oxyhalide glasses have been prepared in the TeO 2 -ZnO-ZnX 2 and TeO 2 -PbO-PbX 2 systems (X ¼ Cl, Br, I) and the corresponding glass-forming regions have been determined. Their density and characteristic temperatures were also determined. The glass-forming regions increased in the direction I fi Br fi Cl and were largest for the zinc-tellurite compositions. For the TeO 2 -ZnO-ZnCl 2 system, compositions with 20 mol% ZnO presented the highest glass-forming ability and had high thermal stability and good infrared transmittance. The progressive replacement of TeO 2 by ZnCl 2 improved the optical quality of the glasses, as well as their thermal stability, but they became more hygroscopic. Erbium chloride was added to two base glass compositions, 40TeO 2 -20ZnO-40ZnCl 2 and 60TeO 2 -20ZnO-20ZnCl 2 (in mol%) and bulk glass samples could be obtained with additions of up to 10 mol% ErCl 3 . Photoluminescence measurements of the erbium-doped glasses, at 1.5 lm, showed highest fluorescence intensity for the 60TeO 2 -20ZnO-20ZnCl 2 compositions, especially with 3 mol% ErCl 3 with a corresponding metastable level lifetime of $6 ms. Higher concentrations of erbium caused a decrease of both properties.
Journal of Materials Science Materials in Medicine, Jun 1, 2008
Calcium phosphate cements are biomaterials made from a mixture of calcium phosphate powder in aqu... more Calcium phosphate cements are biomaterials made from a mixture of calcium phosphate powder in aqueous solutions that forms a paste that reacts at the body temperature and hardens as a result of precipitation reactions. These cements are commonly used in dentistry and orthopedic bone filling surgeries, which require extremely invasive procedures. The challenge consists in formulating an injectable paste by additives incorporation. In this work, three different additives (carboxymethylcellulose, agar polymer and sodium alginate) were incorporated to tricalcium phosphate, in concentrations of 0.4, 0.8, 1.6, 3.2 and 6.4 wt.%. Injectability was evaluated through a new method developed for this purpose. Results showed that it was possible to obtain injectable compositions of alpha-tricalcium phosphate cement. It was verified that the injectability depends on the rheological behavior of the pastes and injection time. In this study, pastes with viscosity suitable for good homogenization and injection were obtained.
Structural Engineering International, Oct 31, 2007
Field load testing is an effective method to evaluate bridge performance and to calibrate structu... more Field load testing is an effective method to evaluate bridge performance and to calibrate structural models. This paper presents the load tests of the cable-stayed Rainha Santa Isabel Bridge which crosses the Mondego River near Coimbra, in Portugal. During these tests, several parameters were measured, like vertical displacements of the deck, horizontal displacements of the mast, rotations, strains and stay forces. Different types of equipment were used in order to get more accurate measurements. The experimental results are compared with the analytical values computed with a finite element model of the bridge.
We study the influence of three laser beams on the center of mass motion of cold atoms with inter... more We study the influence of three laser beams on the center of mass motion of cold atoms with internal energy levels in a tripod configuration. We show that similar to electrons in graphene the atomic motion can be equivalent to the dynamics of ultra-relativistic two-component Dirac fermions. We propose and analyze an experimental setup for observing such a quasi-relativistic motion of ultracold atoms. We demonstrate that the atoms can experience negative refraction and focussing by Veselago-type lenses. We also show how the chiral nature of the atomic motion manifests itself as an oscillation of the atomic internal state population which depends strongly on the direction of the center of mass motion. For certain directions an atom remains in its initial state, whereas for other directions the populations undergo oscillations between a pair of internal states.
Journal of Non Crystalline Solids, Jun 1, 2007
A series of glasses in the (Ge,Si)O 2 -Nb 2 O 5 -(Na,K) 2 O system were prepared by melting and c... more A series of glasses in the (Ge,Si)O 2 -Nb 2 O 5 -(Na,K) 2 O system were prepared by melting and casting. Their density and characteristic temperatures were determined by Differential Thermal Analysis (DTA) and their structure was analyzed by infrared and polarized Raman spectroscopies. DTA data have indicated an increased glass thermal stability with the replacement of GeO 2 by SiO 2 . Kramers-Kronig analysis of the infrared specular reflectance data indicated a strong ionic character for the germanosilicate glasses. The Raman spectra of germanosilicate compositions were generally dominated by an intense Boson peak at $72 cm À1 and a high frequency, polarised peak at $880 cm À1 , related to NbO 6 octahedra with at least one non-bridging oxygen. The germanosilicate structure appears to be formed by alternating GeO 4 tetrahedra and NbO 6 octahedra, in addition to SiO 4 tetrahedra.
In this work, we present a methodology for the quantitative evaluation and comparison of Web site... more In this work, we present a methodology for the quantitative evaluation and comparison of Web site quality called Web-site Quality Evaluation Method (QEM). The core models and procedures for artifact evaluation are supported by the Logic Scoring of Preference (LSP) model and continuous preference logic as mathematical background. We discuss the process steps that the evaluators should follow by applying the Web-site QEM, namely: (a) Selecting a site or a set of competitive sites specific to a domain, (b) Specifying goals and the user view, (c) Specifying in a standard-compliant way, Web-site quality characteristics and attributes, (d) Defining the evaluation criterion for each attribute, and applying attribute measurement, (f) Aggregating elementary attributes to yield the global quality preference, and (g) Analyzing, assessing, and comparing partial and global outcomes. In order to illustrate the methodology we focus on a case study on typical museum sites where more than ninety components were involved regarding the general visitor view. The process results may be useful to understand, control, and improve the Web artifacts quality in small, medium and large-scale projects.
Phys Rev Lett, 2005
We demonstrate how to create artificial external non-Abelian gauge potentials acting on cold atom... more We demonstrate how to create artificial external non-Abelian gauge potentials acting on cold atoms in optical lattices. The method employs atoms with k internal states, and laser assisted state sensitive tunneling, described by unitary k×k matrices. The single-particle dynamics in the case of intense U(2) vector potentials lead to a generalized Hofstadter butterfly spectrum which shows a complex mothlike structure. We discuss the possibility to realize non-Abelian interferometry (Aharonov-Bohm effect) and to study many-body dynamics of ultracold matter in external lattice gauge fields.
Applied Physics B Lasers and Optics, Jun 18, 1999
We analyse the effects of atom-atom collisions on a collective laser cooling scheme. We derive a ... more We analyse the effects of atom-atom collisions on a collective laser cooling scheme. We derive a quantum master equation which describes the laser cooling in presence of atom-atom collisions in the weak-condensation regime. Using such equation, we perform Monte Carlo simulations of the population dynamics in one and three dimensions. We observe that the ground-state laser-induced condensation is maintained in the presence of collisions. Laser cooling causes a transition from a Bose-Einstein distribution describing collisionally induced equilibrium, to a distribution with an effective zero temperature. We analyse also the effects of atom-atom collisions on the cooling into an excited state of the trap.
Physical Review Letters, Dec 1, 2008
We study the role played by the magnetic dipole interaction in the decoherence of a lattice-based... more We study the role played by the magnetic dipole interaction in the decoherence of a lattice-based interferometer that employs an alkali Bose-Einstein condensate with a tunable scattering length. The different behavior we observe for two different orientations of the dipoles gives us evidence of the anisotropic character of the interaction. The experiment is correctly reproduced by a model we develop only if the long-range interaction between different lattice sites is taken into account. Our model indicates that dipolar interaction can be compensated by a proper choice of the scattering length and that the magnetic dipole interaction should not represent an obstacle for atom interferometry with Bose-Einstein condensates with a tunable interaction.
Phys Rev Lett, 2008
The dynamical stability of dark solitons in dipolar Bose-Einstein condensates is studied. For sta... more The dynamical stability of dark solitons in dipolar Bose-Einstein condensates is studied. For standard short-range interacting condensates dark solitons are unstable against transverse excitations in two and three dimensions. On the contrary, due to its non local character, the dipolar interaction allows for stable 3D stationary dark solitons, opening a qualitatively novel scenario in nonlinear atom optics. We discuss in detail the conditions to achieve this stability, which demand the use of an additional optical lattice, and the stability regimes.
Uploads
Papers by Luis A. Santos Laureano