972 resultados para Quasi-1D confinement


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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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In this study, we investigate the possibility of mode localization occurrence in a non-periodic Pfluger's column model of a rocket with an intermediate concentrated mass at its middle point. We discuss the effects of varying the intermediate mass magnitude and its position and the resulting energy confinement for two cases. Free vibration analysis and the severity of mode localization are appraised, without decoupling the system, by considering as a solution basis the fundamental free response or dynamical solution. This allows for the reduction of the dimension of the algebraic modal equation that arises from satisfying the boundary and continuity conditions. By using the same methodology, we also consider the case of a cantilevered Pluger's column with rotational stiffness at the middle support instead of an intermediate concentrated mass. (c) 2008 Elsevier Ltd. All rights reserved.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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We theoretically study many-body excitations in three different quasi-one-dimensional (Q1D) electron systems: (i) those formed on the surface of liquid Helium; (ii) in two coupled semiconductor quantum wires; and (iii) Q1D electrons embedded in polar semiconductor-based quantum wires. Our results show intersubband coupling between higher subbands and the two lowest subbands affecting even the lower energy intersubband plasmons on the liquid Helium surface. Concerning the second system, we show a pronounced extra peak appearing in the intersubband impurity spectral function for temperatures as high as 20 K. We finally show coupled intersubband plasmon-phonon modes surviving for temperatures up to 300 K.

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In the present work we numerically simulated the motion of particles coorbital to a small satellite under the Poynting-Robertson light drag effect in order to verify the symmetry suggested by Dermott et al. (1979, 1980) on their ring confinement model. The results reveal a more complex scenario, especially for very small particles (micrometer sizes), which present chaotic motion. Despite the complexity of the trajectories the particles remain confined inside the coorbital region. However, the dissipative force caused by the solar radiation also includes the radiation pressure component which can change this configuration. Our results show that the inclusion of the radiation pressure, which is not present in the original confinement model, can destroy the configuration in a time much shorter than the survival time predicted for a dust particle in a horseshoe orbit with a satellite.

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An analytical approximate method for the Dirac equation with confining power law scalar plus vector potentials, applicable to the problem of the relativistic quark confinement, is presented. The method consists in an improved version of a saddle-point variational approach and it is applied to the fundamental state of massless single quarks for some especial cases of physical interest. Our treatment emphasizes aspects such as the quantum-mechanical relativistic Virial theorem, the saddle-point character of the critical point of the expectation value of the total energy, as well as the Klein paradox and the behaviour of the saddle-point variational energies and wave functions.

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In this work we develop an approach to obtain analytical expressions for potentials in an impenetrable box. In this kind of system the expression has the advantage of being valid for arbitrary values of the box length, and respect the correct quantum limits. The similarity of this kind of problem with the quasi exactly solvable potentials is explored in order to accomplish our goals. Problems related to the break of symmetries and simultaneous eigenfunctions of commuting operators are discussed.

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We previously reported that truncation of the N-terminal 79 amino acids of alpha(1D)-adrenoceptors (Delta(1-79)alpha(1D)-ARs) greatly increases binding site density. In this study, we determined whether this effect was associated with changes in alpha(1D)-AR subcellular localization. Confocal imaging of green fluorescent protein (GFP)-tagged receptors and sucrose density gradient fractionation suggested that full-length alpha(1D)-ARs were found primarily in intracellular compartments, whereas Delta(1-79)alpha(1D)-ARs were translocated to the plasma membrane. This resulted in a 3- to 4-fold increase in intrinsic activity for stimulation of inositol phosphate formation by norepinephrine. We determined whether this effect was transplantable by creating N-terminal chimeras of alpha(1)-ARs containing the body of one subtype and the N terminus of another (alpha(1A) NT-D, alpha(1B) NT-D, alpha(1D) NT-A, and alpha(1D)NT-B). When expressed in human embryonic kidney 293 cells, radioligand binding revealed that binding densities of alpha(1A)- or alpha(1B)-ARs containing the alpha(1D)-N terminus decreased by 86 to 93%, whereas substitution of alpha(1A)- or alpha(1B)-N termini increased alpha(1D)-AR binding site density by 2- to 3-fold. Confocal microscopy showed that GFP-tagged alpha(1D)NT-B-ARs were found only on the cell surface, whereas GFP-tagged alpha(1B)NT-D-ARs were completely intracellular. Radioligand binding and confocal imaging of GFP-tagged alpha(1D)- and Delta(1-79)alpha(1D)-ARs expressed in rat aortic smooth muscle cells produced similar results, suggesting these effects are generalizable to cell types that endogenously express alpha(1D)-ARs. These findings demonstrate that the N-terminal region of alpha(1D)-ARs contain a transplantable signal that is critical for regulating formation of functional bindings, through regulating cellular localization.

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We carry out a numerical and analytic analysis of the Yang-Lee zeros of the ID Blume-Capel model with periodic boundary conditions and its generalization on Feynman diagrams for which we include sums over all connected and nonconnected rings for a given number of spins. In both cases, for a specific range of the parameters, the zeros originally on the unit circle are shown to depart from it as we increase the temperature beyond some limit. The curve of zeros can bifurcate- and become two disjoint arcs as in the 2D case. We also show that in the thermodynamic limit the zeros of both Blume-Capel models on the static (connected ring) and on the dynamical (Feynman diagrams) lattice tend to overlap. In the special case of the 1D Ising model on Feynman diagrams we can prove for arbitrary number of spins that the Yang-Lee zeros must be on the unit circle. The proof is based on a property of the zeros of Legendre polynomials.

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The photonic modes of Thue-Morse and Fibonacci lattices with generating layers A and B, of positive and negative indices of refraction, are calculated by the transfer-matrix technique. For Thue-Morse lattices, as well for periodic lattices with AB unit cell, the constructive interference of reflected waves, corresponding to the zero(th)-order gap, takes place when the optical paths in single layers A and B are commensurate. In contrast, for Fibonacci lattices of high order, the same phenomenon occurs when the ratio of those optical paths is close to the golden ratio. In the long wavelength limit, analytical expressions defining the edge frequencies of the zero(th) order gap are obtained for both quasi-periodic lattices. Furthermore, analytical expressions that define the gap edges around the zero(th) order gap are shown to correspond to the = 0 and = 0 conditions.

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The magnetic-field and confinement effects on the Land, factor in AlxGa1-xAs parabolic quantum wells under magnetic fields applied parallel or perpendicular to the growth direction are theoretically studied. Calculations are performed in the limit of low temperatures and low electron density in the heterostructure. The g factor is obtained by taking into account the effects of non-parabolicity and anisotropy of the conduction band through the 2 x 2 Ogg-McCombe Hamiltonian, and by including the cubic Dresselhaus spin-orbit term. A simple formula describing the magnetic-field dependence of the effective Land, factor is analytically derived by using the Rayleigh-Schrodinger perturbation theory, and it is found in good agreement with previous experimental studies devoted to understand the behavior of the g factor, as a function of an applied magnetic field, in semiconductor heterostructures. Present numerical results for the effective Land, factor are shown as functions of the quantum-well parameters and magnetic-field strength, and compared with available experimental measurements.