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Search Results: 1 - 10 of 496628 matches for " L. P. G. Assis "
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The Bullough-Dodd model coupled to matter fields
P. E. G. Assis,L. A. Ferreira
Physics , 2007, DOI: 10.1016/j.nuclphysb.2008.01.004
Abstract: The Bullough-Dodd model is an important two dimensional integrable field theory which finds applications in physics and geometry. We consider a conformally invariant extension of it, and study its integrability properties using a zero curvature condition based on the twisted Kac-Moody algebra A_2^{(2)}. The one and two-soliton solutions as well as the breathers are constructed explicitly . We also consider integrable extensions of the Bullough-Dodd model by the introduction of spinor (matter) fields. The resulting theories are conformally invariant and present local internal symmetries. All the one-soliton solutions, for two examples of those models, are constructed using an hybrid of the dressing and Hirota methods. One model is of particular interest because it presents a confinement mechanism for a given conserved charge inside the solitons.
Impurity and boundary effects in one and two-dimensional inhomogeneous Heisenberg antiferromagnets
P. E. G. Assis,Valter L. Libero,K. Capelle
Physics , 2004, DOI: 10.1103/PhysRevB.71.052402
Abstract: We calculate the ground-state energy of one and two-dimensional spatially inhomogeneous antiferromagnetic Heisenberg models for spins 1/2, 1, 3/2 and 2. Our calculations become possible as a consequence of the recent formulation of density-functional theory for Heisenberg models. The method is similar to spin-density-functional theory, but employs a local-density-type approximation designed specifically for the Heisenberg model, allowing us to explore parameter regimes that are hard to access by traditional methods, and to consider complications that are important specifically for nanomagnetic devices, such as the effects of impurities, finite-size, and boundary geometry, in chains, ladders, and higher-dimensional systems.
Temporal dynamics in the one-dimensional quantum Zakharov equations for plasmas
A. P. Misra,S. Banerjee,F. Haas,P. K. Shukla,L. P. G. Assis
Physics , 2010, DOI: 10.1063/1.3356059
Abstract: The temporal dynamics of the quantum Zakharov equations (QZEs) in one spatial dimension, which describes the nonlinear interaction of quantum Langmuir waves (QLWs) and quantum ion-acoustic waves (QIAWs) is revisited by considering their solution as a superposition of three interacting wave modes in Fourier space. Previous results in the literature are modified and rectified. Periodic, chaotic as well as hyperchaotic behaviors of the Fourier-mode amplitudes are identified by the analysis of Lyapunov exponent spectra and the power spectrum. The periodic route to chaos is explained through an one-parameter bifurcation analysis. The system is shown to be destabilized via a supercritical Hopf-bifurcation. The adiabatic limits of the fully spatio-temporal and reduced systems are compared from the viewpoint of integrability properties.
Analytical considerations about the cosmological constant and dark energy
E. M. C. Abreu,L. P. G. De Assis,C. M. L. dos Reis
Physics , 2009, DOI: 10.1142/S0217751X09046254
Abstract: The accelerated expansion of the universe has now been confirmed by several independent observations including those of high redshift type Ia supernovae, and the cosmic microwave background combined with the large scale structure of the Universe. In this work we introduce families of analytical solutions for the scale factor different from the current literature. The knowledge of the scale factor behavior might shed some light on these questions since the entire evolution of a homogeneous isotropic Universe is contained in the scale factor. We use different parameters for these solutions and with these parameters we stablish a connection with the equation of state for different dark energy scenarios.
Planar Supersymmetric Quantum Mechanics of a Charged Particle in an External Electromagnetic Field
Ricardo C. Paschoal,José A. Helay?l-Neto,Leonardo P. G. de Assis
Physics , 2004, DOI: 10.1016/j.physleta.2005.09.016
Abstract: The supersymmetric quantum mechanics of a two-dimensional non-relativistic particle subject to external magnetic and electric fields is studied in a superfield formulation and with the typical non-minimal coupling of (2+1) dimensions. Both the N=1 and N=2 cases are contemplated and the introduction of the electric interaction is suitably analysed.
Medicinal plants and other botanical products from the Brazilian Official Pharmacopoeia
Brand?o, Maria G. Lins;Cosenza, Gustavo P.;Moreira, Raquel Assis;Monte-Mor, Roberto L.M.;
Revista Brasileira de Farmacognosia , 2006, DOI: 10.1590/S0102-695X2006000300020
Abstract: in this paper, we describe the results of a thorough survey in the four editions of the brazilian official pharmacopoeia (fbras), in a search for data about the plants and other botanical products included in them. the growth of the pharmaceutical industry since the second half of last century markedly affected the brazilian official medicine. the paper analyses the transformation within the pharmacopoeia, focusing on the presence of monographs for native medicinal plants. the result showed a strong substitution of native american medicinal plants by industrialized medicine and foreign medicinal plants in fbras and confirms the necessity of investiments in research for the validation of brazilian native plants.
PT-symmetry in quasi-integrable models
P. E. G. Assis
Physics , 2015,
Abstract: We reinforce the observations of almost stable scattering in nonintegrable models and show that $\mathcal{PT}$-symmetry can be used as a guiding principle to select relevant systems also when it comes to integrability properties. We show that the presence of unbroken $\mathcal{PT}$-symmetry in classical field theories produces quasi-integrable excitations with asymptotically conserved charges.
A(2|1) spectral equivalences and nonlocal integrals of motion
P. E. G. Assis
Physics , 2012, DOI: 10.1088/1751-8113/46/19/195204
Abstract: We study the spectral correspondence between a particular class of Schrodinger equations and supersymmetric quantum integrable model (QIM). The latter, a quantized version of the Ablowitz-Kaupp-Newell-Segur (AKNS) hierarchy of nonlinear equations, corresponds to the thermodynamic limit of the Perk-Schultz lattice model. By analyzing the symmetries of the ordinary differential equation (ODE) in the complex plane, it is possible to obtain important objects in the quantum integrable model in exact form, under an exact spectral correspondence. In this manuscript our main interest lies on the set of nonlocal conserved inte- grals of motion associated to the integrable system and we provide a systematic method to compute their values evaluated on the vacuum state of the quantum field theory.
Potencial de pseudomonas spp. fluorescentes para biocontrole de alternaria ricini em mamoneira
Silva, Francisco de A.G. da;Peixoto, Cecília do N.;Assis, Sayonara M.P. de;Mariano, Rosa de L.R.;Padovan, Isaíras P.;
Brazilian Archives of Biology and Technology , 1998, DOI: 10.1590/S1516-89131998000100010
Abstract: the potential of fluorescent pseudomonas spp. to control alternaria leaf spot on castorbean, caused by alternaria ricini, was studied under greenhouse conditions. two periods for antagonist applications were tested: 48h before and simultaneously to the pathogen inoculation. among the antagonists tested ja4 and bj22 were the most effectives showing disease severity reduction of 20.9% and 17.8% respectively, when applied simultaneously. the effect of pseudomonas spp. on the micelial growth and sporulation was also studied throughout three different methods (funel, streak and celophane). inhibition of micelial growth and sporulation was observed. there was no correlation between in vitro and in vivo data. antibiosis was showed as a mode of action for pseudomonas spp. in relation to alternaria ricini. ultrastructural studies confirmed the inhibition of spore germination by the bacteria.
Sistema radicular de plantas de cobertura sob compacta??o do solo
Gon?alves, Wainer G.;Jimenez, Rodrigo L.;Araújo Filho, Jer?nimo V. de;Assis, Renato L. de;Silva, Gilson P.;Pires, Fábio R.;
Engenharia Agrícola , 2006, DOI: 10.1590/S0100-69162006000100008
Abstract: with the objective of evaluate the root growth capacity in the compacted soil layer, four vegetal species of the cover crops (amaranth, pearl millet adr500, finger millet and kenaf) were cultivated in columns of pvc with increasing levels of subsurface compaction (soil bulk densities: 1.18; 1.34; 1.51 and 1.60 mg m-3). the experiment was carried out in a greenhouse conditions, using a dusky red latosol. the subsurface compacted layer was restrictive to the roots growth of the studied species, causing the root concentrating to the surface. pearl millet adr500 and the amaranth were the species that had detached in the production of dry matter weight and developed itself in the compacted layers and below of them. pearl of millet adr500 presented the biggest root length density in all layers. finger millet and the amaranth had similar behavior in relation to the shoot length root. finger millet and kenaf had presented minor dry matter weight of root in relation to the other species. the kenaf presented minors values of dry matter, but it was not affected by the presence of compacted layers.
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