Non-Bragg-gap solitons in one-dimensional Kerr-metamaterial Fibonacci heterostructures

ABSTRACT: A detailed study of non-Bragg-gap solitons in one-dimensional Kerr-metamaterial quasiperiodic Fibonacci heterostructures is performed. The transmission coefficient is numerically obtained by combining the transfermatrix formalism in the metamaterial layers with a numerical solution of the nonlinear differential equation in the Kerr slabs, and by considering the loss effects in the metamaterial slabs. A switching from states of no transparency in the linear regime to high-transparency states in the nonlinear regime is observed for both zero-order and plasmon-polariton gaps. The spatial localization of the non-Bragg-gap solitons is also examined, and the symmetry properties of the soliton waves are briefly discussed

Effects Of Non-parabolicity And In-plane Magnetic Fields On The Cyclotron Effective Mass And G -factor In Gaas-(ga,al)as Quantum Wells

The envelope-function approach is used to theoretically study the effects of in-plane magnetic fields on the cyclotron effective mass and Landé g -factor associated to conduction electrons in single GaAs-(Ga,Al)As quantum wells. Non-parabolic and anisotropy effects are included in the calculations within the Ogg-McCombe effective Hamiltonian to describe the electron states in the semiconductor heterostructure. The electronic structure and both the cyclotron effective mass and Landé g -factor were obtained, by expanding the corresponding envelope wave functions in terms of harmonic-oscillator wave functions, as functions of the in-plane magnetic field, cyclotron orbit-center position, and quantum-well widths. This procedure allows us to consider the different terms in the Hamiltonian on equal footing, avoiding therefore the use of approximate methods to obtain the envelope wave functions and the corresponding energy spectrum. 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Self-similarity And Anti-self-similarity Of The Effective Landé G Factor In Gaas-(ga,al)as Fibonacci Superlattices Under In-plane Magnetic Fields

A theoretical study of the effects of in-plane magnetic fields on the Landé g factor associated to conduction electrons in GaAs-(Ga,Al)As Fibonacci superlattices is presented. We have used the Ogg-McCombe effective Hamiltonian, which includes nonparabolic and anisotropy effects, in order to describe the electron states in the Fibonacci heterostructure. We have expanded the corresponding electron envelope wave functions in terms of harmonic-oscillator wave functions, and obtained the Landé g factor for magnetic fields related by even powers of the golden mean τ=(1+5)2. Theoretical results for GaAs-(Ga,Al)As Fibonacci superlattices, under magnetic-field values scaled by τ2n, clearly exhibit a self-similar (for even n) or anti-self-similar (for odd n) behavior for the Landé g factors, as appropriate. © 2006 The American Physical Society.743Merlin, R., Bajema, K., Clarke, R., Juang, F.Y., Bhattacharya, P.K., (1985) Phys. Rev. Lett., 55, p. 1768. , PRLTAO 0031-9007 10.1103/PhysRevLett.55.1768Wang, Y.Y., Maan, J.C., (1989) Phys. Rev. B, 40, p. 1955. , PRBMDO 0163-1829 10.1103/PhysRevB.40.1955Toet, D., Potemski, M., Wang, Y.Y., Maan, J.C., Tapfer, L., Ploog, K., (1991) Phys. Rev. Lett., 66, p. 2128. , PRLTAO 0031-9007 10.1103/PhysRevLett.66.2128Maan, J.C., Chitta, V., Toet, D., Potemski, M., Ploog, K., (1992) Springer Series in Solid-State Sciences, 101, p. 549. , edited by G. Landwehr (Springer, BerlinBruno-Alfonso, A., Oliveira, L.E., De Dios-Leyva, M., (1995) Appl. Phys. Lett., 67, p. 536. , APPLAB 0003-6951 10.1063/1.115180Bruno-Alfonso, A., Reyes-Gómez, E., Oliveira, L.E., De Dios-Leyva, M., (1995) J. Appl. Phys., 78, p. 15. , JAPIAU. 0021-8979. 10.1063/1.360240De Dios-Leyva, M., Bruno-Alfonso, A., Reyes-Gómez, E., Oliveira, L.E., (1995) J. Phys.: Condens. Matter, 7, p. 9799. , JCOMEL. 0953-8984. 10.1088/0953-8984/7/50/014Nielsen, M.A., Chuang, I.L., (2000) Quantum Computation and Quantum Information, , Cambridge University Press, CambridgeSalis, G., Kato, Y.K., Ensslin, K., Driscol, D.C., Gossard, A.C., Awschalom, D.D., (2001) Nature (London), 414, p. 619. , NATUAS 0028-0836 10.1038/414619aZutic, I., Fabian, J., Das Sarma, S., (2004) Rev. Mod. Phys., 76, p. 323. , RMPHAT 0034-6861 10.1103/RevModPhys.76.323Engel, H.-A., Loss, D., (2005) Science, 309, p. 586. , SCIEAS 0036-8075 10.1126/science.1113203Hermann, C., Weisbuch, C., (1977) Phys. Rev. B, 15, p. 823. , PLRBAQ 0556-2805 10.1103/PhysRevB.15.823Le Jeune, P., Robart, D., Marie, X., Amand, T., Brosseau, M., Barrau, J., Kalevich, V., Rodichev, D., (1997) Semicond. Sci. Technol., 12, p. 380. , SSTEET 0268-1242 10.1088/0268-1242/12/4/006Malinowski, A., Harley, R.T., (2000) Phys. Rev. B, 62, p. 2051. , PRBMDO 0163-1829 10.1103/PhysRevB.62.2051Sapega, V.F., Ruf, T., Cardona, M., Ploog, K., Ivchenko, E.L., Mirlin, D.N., (1994) Phys. Rev. B, 50, p. 2510. , PRBMDO 0163-1829 10.1103/PhysRevB.50.2510Medeiros-Ribeiro, G., Pinheiro, M.V.B., Pimentel, V.L., Marega, E., (2002) Appl. Phys. Lett., 80, p. 4229. , APPLAB 0003-6951 10.1063/1.1483112Hanson, R., Witkamp, B., Vandersypen, L.M.K., Willems Van Beveren, L.H., Elzerman, J.M., Kouwenhoven, L.P., (2003) Phys. Rev. Lett., 91, p. 196802. , PRLTAO 0031-9007 10.1103/PhysRevLett.91.196802Rashba, E.I., Efros, A.L., (2003) Phys. Rev. Lett., 91, p. 126405. , PRLTAO 0031-9007 10.1103/PhysRevLett.91.126405De Sousa, R., Das Sarma, S., (2003) Phys. Rev. B, 68, p. 155330. , PRBMDO 0163-1829 10.1103/PhysRevB.68.155330Prado, S.J., Trallero-Giner, C., Alcalde, A.M., Lopez-Richard, V., Marques, G.E., (2004) Phys. Rev. B, 69, p. 201310. , PRBMDO 0163-1829 10.1103/PhysRevB.69.201310Destefani, C.F., Ulloa, S.E., (2005) Phys. Rev. B, 71, p. 161303. , PRBMDO 0163-1829 10.1103/PhysRevB.71.161303Ogg, N.R., (1966) Proc. Phys. Soc. London, 89, p. 431. , PPSOAU 0370-1328 10.1088/0370-1328/89/2/326McCombe, B.O., (1969) Phys. Rev., 181, p. 1206. , PHRVAO 0031-899X 10.1103/PhysRev.181.1206Braun, M., Rössler, U., (1985) J. Phys. C, 18, p. 3365. , JPSOAW. 0022-3719. 10.1088/0022-3719/18/17/013Golubev, V.G., Ivanov-Omskii, V.I., Minervin, I.G., Osutin, A.V., Polyakov, D.G., (1985) Sov. Phys. JETP, 61, p. 1214. , SPHJAR 0038-5646De Dios-Leyva, M., Reyes-Gómez, E., Perdomo-Leiva, C.A., Oliveira, L.E., (2006) Phys. Rev. B, 73, p. 085316. , PRBMDO. 0163-1829. 10.1103/PhysRevB.73.085316Li, E.H., (2000) Physica e (Amsterdam), 5, p. 215. , PELNFM 1386-9477 10.1016/S1386-9477(99)00262-3Dresselhaus, G., (1955) Phys. Rev., 100, p. 580. , PHRVAO 0031-899X 10.1103/PhysRev.100.58

Preference incorporation in MOEA/D using an outranking approach with imprecise model parameters

Multi-objective Optimization Evolutionary Algorithms (MOEAs) face numerous challenges when they are used to solve Many-objective Optimization Problems (MaOPs). Decomposition-based strategies, such as MOEA/D, divide an MaOP into multiple single-optimization sub-problems, achieving better diversity and a better approximation of the Pareto front, and dealing with some of the challenges of MaOPs. However, these approaches still require one to solve a multi-criteria selection problem that will allow a Decision-Maker (DM) to choose the final solution. Incorporating preferences may provide results that are closer to the region of interest of a DM. Most of the proposals to integrate preferences in decomposition-based MOEAs prefer progressive articulation over the “a priori” incorporation of preferences. Progressive articulation methods can hardly work without comparable and transitive preferences, and they can significantly increase the cognitive effort required of a DM. On the other hand, the “a priori” strategies do not demand transitive judgements from the DM but require a direct parameter elicitation that usually is subject to imprecision. Outranking approaches have properties that allow them to suitably handle non-transitive preferences, veto conditions, and incomparability, which are typical characteristics of many real DMs. This paper explores how to incorporate DM preferences into MOEA/D using the “a priori” incorporation of preferences, based on interval outranking relations, to handle imprecision when preference parameters are elicited. Several experiments make it possible to analyze the proposal's performance on benchmark problems and to compare the results with the classic MOEA/D without preference incorporation and with a recent, state-of-the-art preference-based decomposition algorithm. In many instances, our results are closer to the Region of Interest, particularly when the number of objectives increases

A Taste Of Photonics: Band Structure, Null Gaps, Non-bragg Gaps, And Symmetry Properties Of One-dimensional Superlattices

We have investigated the propagation of plane waves through one-dimensional superlattices composed of alternate layers characterized by two different refractive indexes, which may take on positive as well as negative values. For both indices of refraction positive we have found null-gap points for commensurate values of the optical path lengths of each layer at which the superlattice becomes transparent. We have determined the symmetry properties of the electromagnetic field demonstrating the degeneracy of the solutions at these points. Furthermore, we have been able to characterize non-Bragg gaps that show up in frequency regions in which the average refractive index is null, by obtaining analytically the non-Bragg gap width which depends only on the ratio b/a of the layer widths.6726Rayleigh, L., (1887) Phil. Mag, 24 (256), p. 5. , SVeselago, V.G., (1968) Sov. Phys. Usp, 10, p. 509Parimi, P.V., Lu, W.T., Vodo, P., Sridhar, S., (2003) Nature, 426, p. 404Cubuku, E., Aydin, K., Ozbay, E., Foteinopolou, S., Soukoulis, C.M., (2003) Phys. Rev. Lett, 91, p. 207401Yeh, P., Yariv, A., Hong, C.-S., (1977) J. Opt. Soc. Am, 67, p. 423Cavalcanti, S.B., de Dios-Leyva, M., Reyes-Gómez, E., Oliveira, L.E., (2006) Phys. Rev. B, 74, p. 153102(2007) Phys. Rev. E, 75, p. 026607Eleftheriades, G.V., Yyer, A.K., Kremer, P.C., (2002) IEEE Trans. Microwave Theory Tech, 50, p. 2702Li, J., Zhou, L., Chan, C.T., Sheng, P., (2003) Phys. Rev. Lett, 90, p. 08390

Divergent modulation of nociception by glutamatergic and GABAergic neuronal subpopulations in the periaqueductal gray

The ventrolateral periaqueductal gray (vlPAG) constitutes a major descending pain modulatory system and is a crucial site for opioid-induced analgesia. A number of previous studies have demonstrated that glutamate and GABA play critical opposing roles in nociceptive processing in the vlPAG. It has been suggested that glutamatergic neurotransmission exerts antinociceptive effects, whereas GABAergic neurotransmission exert pronociceptive effects on pain transmission, through descending pathways. The inability to exclusively manipulate subpopulations of neurons in the PAG has prevented direct testing of this hypothesis. Here, we demonstrate the different contributions of genetically defined glutamatergic and GABAergic vlPAG neurons in nociceptive processing by employing cell type-specific chemogenetic approaches in mice. Global chemogenetic manipulation of vlPAG neuronal activity suggests that vlPAG neural circuits exert tonic suppression of nociception, consistent with previous pharmacological and electrophysiological studies. However, selective modulation of GABAergic or glutamatergic neurons demonstrates an inverse regulation of nociceptive behaviors by these cell populations. Selective chemogenetic activation of glutamatergic neurons, or inhibition of GABAergic neurons, in vlPAG suppresses nociception. In contrast, inhibition of glutamatergic neurons, or activation of GABAergic neurons, in vlPAG facilitates nociception. Our findings provide direct experimental support for a model in which excitatory and inhibitory neurons in the PAG bidirectionally modulate nociception

An ACO-based Hyper-heuristic for Sequencing Many-objective Evolutionary Algorithms that Consider Different Ways to Incorporate the DM's Preferences

Many-objective optimization is an area of interest common to researchers, professionals, and practitioners because of its real-world implications. Preference incorporation into Multi-Objective Evolutionary Algorithms (MOEAs) is one of the current approaches to treat Many-Objective Optimization Problems (MaOPs). Some recent studies have focused on the advantages of embedding preference models based on interval outranking into MOEAs; several models have been proposed to achieve it. Since there are many factors influencing the choice of the best outranking model, there is no clear notion of which is the best model to incorporate the preferences of the decision maker into a particular problem. This paper proposes a hyper-heuristic algorithm—named HyperACO—that searches for the best combination of several interval outranking models embedded into MOEAs to solve MaOPs. HyperACO is able not only to select the most appropriate model but also to combine the already existing models to solve a specific MaOP correctly. The results obtained on the DTLZ and WFG test suites corroborate that HyperACO can hybridize MOEAs with a combined preference model that is suitable to the problem being solved. Performance comparisons with other state-of-the-art MOEAs and tests for statistical significance validate this conclusion

Imaging features of retroperitoneal extra-adrenal paragangliomas in 10 dogs

Retroperitoneal paragangliomas are rare tumors of the neuroendocrine system. Only a few canine case reports are available with rare descriptions of their imaging features. The objectives of this multi-center, retrospective case series study were to describe the diagnostic imaging features of confirmed retroperitoneal paragangliomas and specify their location. Medical records and imaging studies of 10 affected dogs with cytological or histopathologic results concordant with retroperitoneal paragangliomas were evaluated. Dogs had a median age of 9 years. Four of them had clinical signs and laboratory reports compatible with excessive production of catecholamines. Six ultrasound, four CT, four radiographic, and one MRI studies were included. The paragangliomas did not have a specific location along the aorta. They were of various sizes (median 33 mm, range: 9–85 mm of length). Masses had heterogeneous parenchyma in six of 10 dogs, regardless of the imaging modality. Strong contrast enhancement was found in all CT studies. Encircling of at least one vessel was detected in six of 10 masses, clear invasion of a vessel was identified in one of 10 masses. In five of 10 cases, the masses were initially misconstrued as lymph nodes by the on-site radiologist. Retroperitoneal paragangliomas appear along the abdominal aorta, often presenting heterogeneous parenchyma, possibly affecting the local vasculature, and displaying strong contrast enhancement on CT. Clinical signs can be secondary to mass effects or excessive catecholamine production. Underdiagnosis and misdiagnosis of this tumor are suspected as they can be silent, of small size, or confused with other structures

Shallow impurities in semiconductor superlattices: A fractional-dimensional space approach

A thorough detailed study of donor and acceptor properties in doped GaAs-(Ga,Al)As semiconductor superlattices is performed within the fractional-dimensional approach, in which the real anisotropic 'impurity+semiconductor superlattice' system is modeled through an effective isotropic environment with a fractional dimension. In this scheme, the fractional-dimensional parameter is chosen via an analytical procedure and involves no ansatz, and no fittings either with experiment or with previous variational calculations. The present fractional-dimensional calculated results for the donor and acceptor energies in GaAs-(Ga,Al)As semiconductor superlattices are found in quite good agreement with previous variational calculations and available experimental measurements. (C) 1999 American Institute of Physics. [S0021-8979(99)04408-4].85814045404