Design of an Edge -coupled dual -ring Split-ring resonator

Electric permittivity and magnetic permeability control electromagnetic wave propagation th rough materials. I n naturally occu rring materials, these are positive. Artificial materials exhi b iting negative material properties have been reported : they are referred to as metamaterials. This paper concentrates on a ring-type split-ring resonator (SRR) exhibiting negative magnetic permeability. The design and synthesis of the SRR using the genetic-algorithm approach is explained in detail. A user-friendly g raphical user i nterface (G U I ) for an SRR optim izer and estimator using MATLAB TM is also presented

Optimizing the nipple-areola sparing mastectomy with double concentric periareolar incision and biodimensional expander-implant reconstruction: Aesthetic and technical refinements

Although the biodimensional anatomical expander-implant system (BEIS) is a reliable technique, little information has been available regarding outcome following nipple-areola sparing mastectomy (NSM). To perform the resection of glandular tissue, while improving the surgical access and maintaining the nipple-areola vascularization we have developed a new approach for NSM based on the double concentric periareolar incision (DCPI). The purpose of this study is to analyze the feasibility, surgical planning and its outcome following NSM. 18 patients underwent NSM reconstructions. Mean time of follow-up was 29 months. The technique was indicated in patients with small/moderate volume breasts. Flap complications were evaluated and information on aesthetic results and patient satisfaction were collected. 83.3% had tumors measuring 2 cm or less (T1) and 72.1% were stage 0 and 1. All patients presented peripherally tumors located (at least 5 cm from the nipple). Skin complications occurred in 11.1%. One patient (5.5%) presented small skin necrosis and a wound dehiscence was observed in one patient (5.5%). The aesthetic result was good/very good in 94.4 percent and the majority of patients were very satisfied/satisfied. No local recurrences were observed. All complications except one were treated by a conservative approach. DCPI-BEIS is a simple and reliable technique for NSM reconstruction. The success depends on patient selection, coordinated planning with the oncologic surgeon and careful intra-operative and post-operative management. (C) 2009 Elsevier Ltd. All rights reserved.

Microwave induced magnetoresistance oscillations and inelastic scattering time in double quantum wells

The interference of microwave-induced resistance oscillations and magneto-intersubband oscillations in double quantum wells exposed to a continuous microwave irradiation is under study. By comparing experimental and theoretical magnetoresistance traces at different temperatures, we confirm that the inelastic mechanism of photoresistance explains our observations up to T similar or equal to 4 K. For higher temperatures, our results suggest a deviation of the inelastic scattering time tau(in) from the predicted T(-2) dependence. (C) 2009 Elsevier B.V. All rights reserved.

QUANTUM HALL FERROMAGNET IN A DOUBLE WELL WITH VANISHING g-FACTOR.

We have studied the quantum Hall effect in Al(x)Ga(1-x)As-double well structure with vanishing g-factor. We determined the density-magnetic field n(s) - B diagrams for the longitudinal resistance R(xx). In spite of the fact that the n(s) - B diagram for conventional GaAs double wells shows a striking similarity with the theory, we observed the strong difference between these diagrams for double wells with vanishing g-factor. We argue that the electron-electron interaction is responsible for unusual behavior of the Landau levels in such a system.

MAGNETORESISTANCE OSCILLATIONS IN DOUBLE QUANTUM WELLS UNDER MICROWAVE IRRADIATION

We report in detail oscillatory magnetoresistance in double quantum wells under microwave irradiation. The experimental investigation contains measurements of frequency, power and temperature dependence. In theory, the observed interference oscillations are explained in terms of the influence of subband coupling on the frequency-dependent photoinduced part of the electron distribution function. Thus, the magnetoresistance shows the interference of magneto-intersubband and conventional microwave induced resistance oscillations.

Luminescence studies on nitride quaternary alloys double quantum wells

We present theoretical photoluminescence (PL) spectra of undoped and p-doped Al(x)In(1-xy)Ga(y)N/Al(X)In(1) (X) (Y)Ga(Y)N double quantum wells (DQWs). The calculations were performed within the k.p method by means of solving a full eight-band Kane Hamiltonian together with the Poisson equation in a plane wave representation, including exchange-correlation effects within the local density approximation. Strain effects due to the lattice mismatch are also taken into account. We show the calculated PL spectra, analyzing the blue and red-shifts in energy as one varies the spike and the well widths, as well as the acceptor doping concentration. We found a transition between a regime of isolated quantum wells and that of interacting DQWs. Since there are few studies of optical properties of quantum wells based on nitride quaternary alloys, the results reported here will provide guidelines for the interpretation of forthcoming experiments. (C) 2008 Elsevier B.V. All rights reserved.

The double Caldeira-Leggett model: Derivation and solutions of the master equations, reservoir-induced interactions and decoherence

In this paper we analyze the double Caldeira-Leggett model: the path integral approach to two interacting dissipative harmonic oscillators. Assuming a general form of the interaction between the oscillators, we consider two different situations: (i) when each oscillator is coupled to its own reservoir, and (ii) when both oscillators are coupled to a common reservoir. After deriving and solving the master equation for each case, we analyze the decoherence process of particular entanglements in the positional space of both oscillators. To analyze the decoherence mechanism we have derived a general decay function, for the off-diagonal peaks of the density matrix, which applies both to common and separate reservoirs. We have also identified the expected interaction between the two dissipative oscillators induced by their common reservoir. Such a reservoir-induced interaction, which gives rise to interesting collective damping effects, such as the emergence of relaxation- and decoherence-free subspaces, is shown to be blurred by the high-temperature regime considered in this study. However, we find that different interactions between the dissipative oscillators, described by rotating or counter-rotating terms, result in different decay rates for the interference terms of the density matrix. (C) 2010 Elsevier B.V. All rights reserved.

Quantum control of electromagnetically induced transparency dispersion via atomic tunneling in a double-well Bose-Einstein condensate

Electromagnetically induced transparency (EIT) is an important tool for controlling light propagation and nonlinear wave mixing in atomic gases with potential applications ranging from quantum computing to table top tests of general relativity. Here we consider EIT in an atomic Bose-Einstein condensate (BEC) trapped in a double-well potential. A weak probe laser propagates through one of the wells and interacts with atoms in a three-level Lambda configuration. The well through which the probe propagates is dressed by a strong control laser with Rabi frequency Omega(mu), as in standard EIT systems. Tunneling between the wells at the frequency g provides a coherent coupling between identical electronic states in the two wells, which leads to the formation of interwell dressed states. The macroscopic interwell coherence of the BEC wave function results in the formation of two ultranarrow absorption resonances for the probe field that are inside of the ordinary EIT transparency window. We show that these new resonances can be interpreted in terms of the interwell dressed states and the formation of a type of dark state involving the control laser and the interwell tunneling. To either side of these ultranarrow resonances there is normal dispersion with very large slope controlled by g. We discuss prospects for observing these ultranarrow resonances and the corresponding regions of high dispersion experimentally.

Aharonov-Bohm oscillations in a quantum ring: Eccentricity and electric-field effects

The effects of an in-plane electric field and eccentricity on the electronic spectrum of a GaAs quantum ring in a perpendicular magnetic field are studied. The effective-mass equation is solved by two different methods: an adiabatic approximation and a diagonalization procedure after a conformal mapping. It is shown that the electric field and the eccentricity may suppress the Aharonov-Bohm oscillations of the lower energy levels. Simple expressions for the threshold energy and the number of flat energy bands are found. In the case of a thin and eccentric ring, the intensity of a critical field which compensates the main effects of eccentricity is determined. The energy spectra are found in qualitative agreement with previous experimental and theoretical works on anisotropic rings.

Quantum coherent tunneling between two atomic-molecular Bose-Einstein condensates

We study the quantum coherent tunneling dynamics of two weakly coupled atomic-molecular Bose-Einstein condensates (AMBEC). A weak link is supposed to be provided by a double-well trap. The regions of parameters where the macroscopic quantum localization of the relative atomic population occurs are revealed. The different dynamical regimes are found depending on the value of nonlinearity, namely, coupled oscillations of population imbalance of atomic and molecular condensate, including irregular oscillations regions, and macroscopic quantum self trapping regimes. Quantum means and quadrature variances are calculated for population of atomic and molecular condensates and the possibility of quadrature squeezing is shown via stochastic simulations within P-positive phase space representation method. Linear tunnel coupling between two AMBEC leads to correlations in quantum statistics.

Solitons in tunnel-coupled repulsive and attractive condensates

We study solitons in the condensate trapped in a double-well potential with far-separated wells, when the s-wave scattering length has different signs in the two parts of the condensate. By employing the coupled-mode approximation it is shown that there are unusual stable bright solitons in the condensate, with the larger share of atoms being gathered in the repulsive part. Such unusual solitons derive their stability from the quantum tunneling and correspond to the strong coupling between the parts of the condensate. The ground state of the system, however, corresponds to weak coupling between the condensate parts, with the larger share of atoms being gathered in the attractive part of the condensate.

Macroscopic quantum tunneling and resonances in coupled Bose-Einstein condensates with oscillating atomic scattering length

We study the macroscopic quantum tunneling, self-trapping phenomena in two weakly coupled Bose-Einstein condensates with periodically time-varying atomic scattering length.The resonances in the oscillations of the atomic populations are investigated. We consider oscillations in the cases of macroscopic quantum tunneling and the self-trapping regimes. The existence of chaotic oscillations in the relative atomic population due to overlaps between nonlinear resonances is showed. We derive the whisker-type map for the problem and obtain the estimate for the critical amplitude of modulations leading to chaos. The diffusion coefficient for motion in the stochastic layer near separatrix is calculated. The analysis of the oscillations in the rapidly varying case shows the possibility of stabilization of the unstable pi-mode regime. (C) 2000 Published by Elsevier B.V. B.V. PACS: 03.75.Fi; 05.30.Jp.

Universal zero-bias conductance through a quantum wire side-coupled to a quantum dot

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Quantum equivalence between the self-dual and the Maxwell-Chern-Simons models nonlinearly coupled to U(1) scalar fields

The use of master actions to prove duality at quantum level becomes cumbersome if one of the dual fields interacts nonlinearly with other fields. This is the case of the theory considered here consisting of U(1) scalar fields coupled to a self-dual field through a linear and a quadratic term in the self-dual field. Integrating perturbatively over the scalar fields and deriving effective actions for the self-dual and the gauge field we are able to consistently neglect awkward extra terms generated via master action and establish quantum duality up to cubic terms in the coupling constant. The duality holds for the partition function and some correlation functions. The absence of ghosts imposes restrictions on the coupling with the scalar fields.