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Chylothorax is a well-recognized complication after neonatal cardiothoracic surgery. Management strategies include cessation of enteral feedings, repeated aspiration, chest drainage, and total parenteral nutrition. Somatostatin and its analogue, octreotide, have been used with promising results. The authors present three cases of neonatal postoperative chylothorax in which octreotide was used. After literature review, we can say that octreotide is relatively safe, and may reduce clinical course and complications associated with neonatal postoperative chylothorax. One should be aware of possible association between octreotide and necrotizing enterocolitis. Prospective controlled trials supporting octreotide use are lacking.

Using a variational procedure in the effective-mass and parabolic-band approximations we investigate the effects of in-plane magnetic fields on the exciton states in single GaAs/Ga1-xAlxAs quantum wells. Exciton properties are analyzed by using a simple hydrogen-like variational envelope wave-function. Present theoretical results are compared with available experimental measurements on the diamagnetic shift of the photoluminescence peak position of GaAs/Ga0.7Al0.3As quantum wells under in-plane magnetic fields [Phys. Rev. B 71 (2005) 045303].

We present a theoretical investigation, in the effective-mass approximation, of exciton mixing and Is - 2p ± internal transitions of neutral magnetoexcitons in GaAs-Ga 1-x Al x As quantum wells. Theoretical results are obtained by diagonalizing the Kohn-Luttinger Hamiltonian in the presence of an external magnetic field along the growth direction of the quantum well, with mixing of appropriate light- and heavy-hole exciton states taken into account. We first perform the exciton calculations in the diagonal approximation, and take the exciton-envelope wave functions as linear combinations of products of hole and electron quantum-well states with Gaussian functions. Effects of exciton mixing are then calculated within perturbation theory. Theoretical results for the exciton internal transitions from 1s-like to 2p ± -like magnetoexciton states in GaAs-Ga 1-x Al x As quantum wells, with well widths of 80 A, 100 A, 125 A, 150 A and 200 A, are found in overall agreement with optically detected resonance measurements.

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.

The metric signature topological transitions associated with the propagation of electromagnetic waves in a dispersive metamaterial with frequency-dependent and anisotropic dielectric and magnetic responses are examined in the present work. The components of the reciprocal-space metric tensor depend upon both the electric permittivity and magnetic permeability of the metamaterial, which are taken as Drude-like dispersive models. A thorough study of the frequency dependence of the metric tensor is presented which leads to the possibility of topological transitions of the isofrequency surface determining the wave dynamics inside the medium, to a diverging photonic density of states at some range of frequencies, and to the existence of large wave vectors’ modes propagating through the metamaterial.

A theoretical study of the intraband absorption properties of GaAs-Ga1−xAlxAs variably spaced semiconductor superlattices under crossed magnetic and electric fields is presented. Calculations are performed for the applied electric field along the growth-axis direction, whereas the magnetic field is considered parallel to the heterostructure layers. By defining a critical electric field so that the heterostructure energy levels are aligned in the absence of the applied magnetic fields, one finds that, in the weak magnetic-field regime, an abrupt red shift of the absorption coefficient maxima is obtained at fields equal to or larger than the critical electric field, a fact which may be explained from the localization properties of the electron wave functions. Results in the strong magnetic-field regime reveal a rich structure on the intraband absorption coefficient which may be explained from the strong dispersion exhibited by both the energy levels and transition strengths as functions of the generalized orbit-center position. Moreover, the possibility of occurrence of absorption in a wide frequency range is also demonstrated. Present calculated results may be of interest for future design and improvement of multilayered-based photovoltaic and solar-cell devices.

Made available in DSpace on 2022-04-29T08:48:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-05-07 The localization properties of electromagnetic modes in one-dimensional disordered photonic superlattices are theoretically studied. The multilayered system is considered to be composed of alternating stacks of two different random-thickness slabs, characterized by nondispersive and/or frequency-dependent electric permittivities and magnetic permeabilities. Results for the localization length are evaluated by using an analytical model for weakly disordered systems as well as its general definition through the transmissivity properties of the heterostructure. Good agreement between both results is observed only for small amplitudes of disorder. The critical frequencies at which the localization length diverges are correctly predicted in the whole frequency spectrum by the analytical model and confirmed via the corresponding numerical calculations. The λ2 dependence of the localization length, previously observed in disordered heterostructures made of material of positive refractive indexes, are confirmed in the present work. In addition, new λ4 and λ -4 dependencies of the localization length in positive-negative disordered photonic superlattices are obtained, under certain specific conditions, in the long and short wavelength limits, respectively. The asymptotic behavior of the localization length in these limits is essentially determined by the particular frequency dispersion that characterizes the metamaterial used in the left-handed layers. When the effects of absorption are considered, then a divergence of the localization length is still observed, under some conditions, in the short wavelength limit. © 2012 American Physical Society. Instituto de Física Universidad de Antioquia, AA 1226, Medellín Faculdade de Ciências UNESP-Universidade Estadual Paulista, 17033-360, Bauru-SP Instituto de Física Universidade Federal de Alagoas, Maceió-AL, 57072-970 Instituto de Física Universidade Estadual de Campinas-UNICAMP, Campinas-SP, 13083-859 Faculdade de Ciências UNESP-Universidade Estadual Paulista, 17033-360, Bauru-SP

Made available in DSpace on 2022-04-29T08:48:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-09-21 A comprehensive study of the properties of light propagation through one-dimensional photonic disordered quasiperiodic superlattices, composed of alternating layers with random thicknesses of air and a dispersive metamaterial, is theoretically performed. The superlattices consist of the successive stacking of N quasiperiodic Fibonacci or Thue-Morse heterostructures. The width of the slabs in the photonic superlattice may randomly fluctuate around its mean value, which introduces a structural disorder into the system. It is assumed that the left-handed layers have a Drude-type dispersive response for both the dielectric permittivity and magnetic permeability, and Maxwell's equations are solved for oblique incidence by using the transfer-matrix formalism. The influence of both quasiperiodicity and structural disorder on the localization length and Brewster anomalies are thoroughly discussed. © 2011 American Physical Society. Instituto de Física Universidad de Antioquia, AA 1226, Medellín Faculdade de Ciências UNESP-Universidade Estadual Paulista, 17033-360 Bauru-SP Instituto de Física Universidade Federal de Alagoas, 57072-970 Maceió-AL Instituto de Física Universidade Estadual de Campinas-UNICAMP, 13083-859 Campinas-SP Faculdade de Ciências UNESP-Universidade Estadual Paulista, 17033-360 Bauru-SP

The propagation of light incident upon a 1D photonic superlattice consisting of successive stacking of alternate layers of a right-handed nondispersive material and a metamaterial, arranged to form a Cantor-like fractal, is considered. Plasmon-polariton excitations are thoroughly investigated within the transfer-matrix approach and shown to strongly depend on the Cantor step number N. More specifically, the number of plasmon-polariton bands corresponds to the number 2N −1 of metamaterial layers within the unit cell.

We study the properties of plasmon polaritons in one-dimensional photonic metamaterial superlattices resulting from the periodic repetition of a Fibonacci structure. We assume the system made up of positive refraction and metamaterial layers. A Drude-type dispersive response for both the dielectric permittivity and magnetic permeability of the left-handed material is considered. Maxwell's equations are solved for oblique incidence by using the transfer-matrix formalism. Our results show that the plasmon-polariton modes are considerably affected by the increasing of the Fibonacci-sequence order of the elementary cell. The loss of the long-range spatial coherence of the electromagnetic field along the growth direction, which is due to the quasiperiodicity of the elementary cell, leads to the splitting of the plasmon-polariton frequencies, resulting in a Cantor-type frequency spectra. Moreover, the calculated photonic dispersion indicates that if the plasma frequency is chosen within the photonic $⟨n(\ensuremath{\omega})⟩=0$ gap then the plasmon-polariton modes behave essentially as pure plasmon modes.

Light propagation through 1D disordered structures composed of alternating layers, with random thicknesses, of air and a dispersive metamaterial is theoretically investigated. Both normal and oblique incidences are considered. By means of numerical simulations and an analytical theory, we have established that Anderson localization of light may be suppressed: (i) in the long wavelength limit, for a finite angle of incidence which depends on the parameters of the dispersive metamaterial; (ii) for isolated frequencies and for specific angles of incidence, corresponding to Brewster anomalies in both positive- and negative-refraction regimes of the dispersive metamaterial. These results suggest that Anderson localization of light could be explored to control and tune light propagation in disordered metamaterials., Comment: 4 two-column pages, 3 figures

We discuss the propagation of electromagnetic waves in layered structures made up of alternate layers of air and metamaterials. The role played by absorption on the existence of electric and magnetic plasmon polaritons is investigated. Results show that plasmon-polariton modes are robust even in the presence of rather large absorption.

We analyze one-dimensional photonic superlattices which alternate layers of air and a left-handed material. We assume Drude-type dispersive responses for the dielectric permittivity and magnetic permeability of the left-handed material. Maxwell's equations and the transfer-matrix technique are used to derive the dispersion relation for the propagation of obliquely incident optical fields. The photonic dispersion indicates that the growth-direction component of the electric (or magnetic) field leads to the propagation of electric (or magnetic) plasmon polaritons, for either TE or TM configurations. Furthermore, we show that if the plasma frequency is chosen within the photonic $=0$ zeroth-order bandgap, the coupling of light with plasmons weakens considerably. As light propagation is forbidden in that particular frequency region, the plasmon-polariton mode reduces to a pure plasmon mode., Comment: 4 pages, 4 figures

A standard plane-wave expansion technique is used to investigate the evolution of the photonic band structure of a two-dimensional honeycomb lattice composed by cylindrical shell rods with dielectric permittivities 1 and 2, and embedded in a background with permittivity 3. We have considered the effect of dispersive dielectric responses as well as the influence of an externally applied magnetic field aiming to obtain efficient tunable bandgaps. Present results suggest that a combination of a doped semiconductor constituent with an anisotropic geometry, which breaks symmetry and unfolds degeneracies, provides an efficient realization of photonic systems with tunable bandgaps.

A. Bruno-Alfonso, E. Reyes-Gomez, S. B. Cavalcanti, and L. E. Oliveira Faculdade de Ciencias, UNESP-Universidade Estadual Paulista, 17033-360, Bauru, Sao Paulo, Brazil Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin, Colombia Instituto de Fisica, Universidade Federal de Alagoas, Maceio, Alagoas, 57072-970, Brazil Inmetro, Campus de Xerem, Duque de Caxias, Rio de Janeiro, 25250-020, Brazil Instituto de Fisica, Universidade Estadual de Campinas-UNICAMP, CP 6165, Campinas, Sao Paulo, 13083-970, Brazil Received 14 May 2008; published 4 September 2008

The variational procedure, in the effective-mass and parabolic-band approximations, is used in order to investigate the effects of crossed electric and magnetic fields on the exciton states in $\mathrm{Ga}\mathrm{As}∕{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ coupled double quantum wells. Calculations are performed for double quantum wells under applied magnetic fields parallel to the layers and electric fields in the growth direction. The exciton envelope wave function is obtained through a variational procedure using a hydrogenic $1s$-like wave function and an expansion in a complete set of trigonometric functions for the electron and hole wave functions. We take into account intersubband mixing brought about by the Coulomb interaction of electron-hole pairs in double quantum wells and present a detailed analysis of the properties of direct and indirect exciton states in these systems. The present study clearly reveals anticrossing effects on the dispersion with applied voltage (or growth-direction electric field) of the photoluminescence peaks associated with direct and indirect excitons. Calculated results are found in good agreement with available experimental measurements on the photoluminescence peak position associated with direct and indirect excitons in $\mathrm{Ga}\mathrm{As}\text{\ensuremath{-}}{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ double quantum wells under growth-direction applied electric fields or under applied in-plane magnetic fields.

A theoretical study, within the effective-mass approximation, of the effects of applied magnetic fields on excitons in disk-shaped GaAs-Ga1-xAlxAs quantum dots is presented. Magnetic fields are applied in the growth direction of the semiconductor heterostructure. The parity of the excitonic envelope function related to the simultaneous exchange of ze→-ze and zh→-zh is a good quantum number and the wave function, both the odd and even parity, can be expanded as combination of products of the quantum well electron and hole function that preserves the parity with appropriate Gaussian functions. We have simultaneously obtained the energies of the excitonic ground and excited states and discuss the behavior of these energies as a function of the magnetic field.

The dependence of the electron Landé g-factor on carrier confinement in quantum wells recently gained both experimental and theoretical interest. The g factor of electrons in GaAs-(Ga,Al)As quantum wells is of special interest, as it changes its sign at a certain value of the well width. In the present work, the effects of an in-plane magnetic field on the cyclotron effective mass and on the Landé g^-factor in single GaAs-(Ga,Al)As quantum wells are studied. Theoretical calculations are performed in the framework of the effective-mass and non-parabolic-band approximations. The Ogg-McCombe Hamiltonian is used for the conduction-band electrons in the semiconductor heterostructure, and the Landé g^-factor theoretically evaluated is found in good agrement with available experimental measurements.

The effects of crossed electric and magnetic fields on the electronic and exciton properties in semiconductor heterostructures have been investigated within the effective-mass and parabolic band approximations for both bulk GaAs and GaAs-Ga1-xAl xAs quantum wells. The combined effects on the heterostructure properties of the applied crossed electric/magnetic fields together with the direct coupling between the exciton center of mass and internal exciton motions may be dealt with via a simple parameter representing the distance between the electron and hole magnetic parabolas. Calculations lead to the expected behavior for the exciton dispersion in a wide range of the crossed electric/magnetic fields, and present theoretical results are found in good agreement with available experimental measurements.

The Ogg-McCombe effective Hamiltonian for the electron in the conduction band together with the non-parabolic and effective-mass approximations were used in a theoretical study of the cyclotron effective mass and electron effective Landé g||-factor in semiconductor GaAs-Ga1-xAl xAs quantum wells under an applied magnetic field parallel to the growth direction of the quantum well. Calculations are performed as a function of the applied magnetic field, and for different widths of the GaAs-Ga1-xAl xAs quantum wells. Results for the electron cyclotron effective mass and g||-factor are found in quite good agreement with experimental data.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2014-02-26T17:25:21Z No. of bitstreams: 1 WOS000238575800050.pdf: 160330 bytes, checksum: 10f14bebba39a540b2177930d32d5295 (MD5) Made available in DSpace on 2014-02-26T17:25:21Z (GMT). No. of bitstreams: 1 WOS000238575800050.pdf: 160330 bytes, checksum: 10f14bebba39a540b2177930d32d5295 (MD5) Previous issue date: 2006-06-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:26:30Z No. of bitstreams: 1 WOS000238575800050.pdf: 160330 bytes, checksum: 10f14bebba39a540b2177930d32d5295 (MD5) Made available in DSpace on 2014-05-20T13:26:30Z (GMT). No. of bitstreams: 1 WOS000238575800050.pdf: 160330 bytes, checksum: 10f14bebba39a540b2177930d32d5295 (MD5) Previous issue date: 2006-06-01 Coherent properties and Rabi oscillations in two-level donor systems, under terahertz excitation, are theoretically investigated. Here we are concerned with donor states in bulk GaAs and GaAs-(Ga,Al)As quantum dots. We study confinement effects, in the presence of an applied magnetic field, on the electronic and on-center donor states in GaAs- (Ga,Al)As dots, as compared to the situation in bulk GaAs, and estimate some of the associated decay rate parameters. Using the optical Bloch equations with damping, we study the time evolution of the Is and 2p(+) states in the presence of an applied magnetic field and of a terahertz laser. We also discuss the role played by the distinct dephasing rates on the photocurrent and calculate the electric dipole transition moment. Results indicate that the Rabi oscillations are more robust as the total dephasing rate diminishes, corresponding to a favorable coherence time. Univ Fed Fluminense, Dept Fis, BR-24210340 Niteroi, RJ, Brazil Univ Estadual Feira Santana, Dept Fis, BR-44031460 Feira de Santana, BA, Brazil Univ Estadual Paulista, Fac Ciências, Dept Matemat, BR-17033360 Bauru, SP, Brazil Univ Estadual Campinas, Inst Fis, BR-13083970 Campinas, SP, Brazil Univ Fed Rio de Janeiro, Inst Fis, BR-21945970 Rio de Janeiro, Brazil Univ Estadual Paulista, Fac Ciências, Dept Matemat, BR-17033360 Bauru, SP, Brazil

Rabi oscillations in coherent optical excitations in bulk GaAs and quantum dot two-level systems may be converted into deterministic photocurrents, with the impurities or dots providing the tag for each qubit. Here we perform a theoretical analysis of the damping of Rabi oscillations in two-level semiconductor systems. Present calculations, through optical Bloch equations on excitonic two-level In x Ga 1− x As quantum-dot systems, are found in good agreement with the corresponding experimental data. Calculated results indicate that the nature underlying the dephasing mechanism associated to the damping of the measured Rabi oscillations, which has previously remained as an open question, may be associated with a field-dependent recombination rate related to the inhomogeneous broadening of the excitonic lines in the In x Ga 1− x As two-level QD system.

A theoretical study, within the effective-mass approximation, of the effects of applied magnetic fields on excitons trapped in quantum dots/interface defects is presented. Actual traps are formed by fluctuations either incomposition or structure size in narrow GaAs/Ga 1 - x Al x As quantum wells. Exciton trapping is taken into account through a model quantum dot formed by monolayer fluctuations in the z direction, and lateral confinement, via a parabolic potential, in the exciton-in plane coordinate. Magnetic fields are applied in the growth direction of the semiconductor heterostructure, and the various magnetoexciton states are obtained in the effective-mass approximation by an expansion of the exciton-envelope wave functions in terms of products of hole and electron quantum-well states with appropriate Gaussian functions for the various excitonic states. Theoretical results are found in overall agreement with available experimental measurements.

Quantum confinement, magnetic-field effects, and laser coupling with the two low-lying states of electrons bound to donor impurities in semiconductors may be used to coherently manipulate the two-level donor system in order to establish the appropriate operational conditions of basic quantum bits (qubits) for solid-state based quantum computers. Here we present a detailed theoretical calculation of the damped Rabi oscillations and time evolution of the 1s and 2p+ donor states in bulk GaAs under an external magnetic field and in the presence of terahertz laser radiation, and their influence on the measured photocurrent. We also detail the possible experimental conditions under which decoherence is weak and qubit operations are efficiently controlled., 5 pages, 3 figures

We present a theoretical study, within the effective-mass approximation, of the magnetoabsorption spectra of intraexcitonic terahertz transitions of light-hole and heavy-hole confined magnetoexcitons in GaAs-~Ga,Al!As quantum wells. The semiconductor quantum wells are studied under magnetic fields applied in the growth direction of the semiconductor heterostructure. The various magnetoexciton states are obtained in the effective-mass approximation by an expansion of the exciton-envelope wave functions in terms of products of hole and electron quantum-well states with appropriate Gaussian functions for the various excitonic states. Intramagnetoexciton transitions are theoretically studied by exciting the allowed excitonic transitions with s1 ~or s2! far-infrared radiation circularly polarized in the plane of the GaAs-~Ga,Al!As quantum well. Theoretical results are obtained for the intramagnetoexciton transition energies and magneto-absorption spectra associated with excitations from 1s-like to 2p6 , and 3p6-like magnetoexciton states, and found in overall agreement with optically detected resonance measurements.

A theoretical study of the internal transitions of confined magnetoexcitons in GaAs-Ga1-xAlxAs quantum wells is presented, with the magnetic field applied along the growth direction of the semiconductor heterostructure. The various exciton-envelope wavefunctions are described as products of electron and hole solutions of the associated quantum-well potentials and symmetry-adapted Gaussian functions. The magnetoexciton states are simultaneously obtained by diagonalizing the appropriate Hamiltonian in the effective-mass approximation. Exciton internal transitions are theoretically investigated by studying the allowed magnetoexcitonic transitions using far-infrared (terahertz) radiation circularly polarized in the plane of the quantum well. Theoretical results are obtained for both the intramagnetoexciton transition energies and oscillator strengths associated with excitations from 1s-like to 2s-, 2p±-, and 3p±-like magnetoexciton states, and from 2p-- to 2s-like exciton states. The present results are compared with previous theoretical work and available optically detected resonance measurements.

A thorough study of the absorption effects on the plasmon polariton-gap solitoninduced transparency in 1D Kerr/metamaterial superlattices is presented. Results indicate that for frequencies close to the bottom or top edge of the bulk-like longitudinal plasmon-polariton gap, the transmission of a finite Kerr/metamaterial superlattice presents a multistable behavior, switching from very low values to the maximum transparency at particular values of the incident power even in the presence of loss effects. Moreover, calculations suggest the existence of resonant plasmon polariton-gap solitons of various orders depending on the particular value of the incident power. The present results reveal that plasmon polariton-gap soliton-induced resonant solutions lead to the transparency of a stack with nonlinear inclusions, a nonlinear optical analog of the electronic barrier-transmission resonances.

We have performed a theoretical study of various arrangements of one-dimensional heterostructures composed by bilayers made of nondispersive (A)/dispersive linear (B) materials and illuminated by an obliquely incident electromagnetic wave, which are shown to exhibit a robust bulk-like plasmon-polariton gap for frequencies below the plasma frequency. The origin of this gap stems from the coupling between photonic and plasmonic modes that may be of a magnetic (electric) origin in a transversal electric (traversal magnetic) configuration yielding a plasmon-polariton mode. By substituting the nondispersive linear layer by a nonlinear Kerr layer, we have found that, for frequencies close to the edge of the plasmon-polariton gap, the transmission of a finite superlattice presents a multistable behavior and it switches from very low values to the maximum transparency at particular values of the incident power. At these frequencies, for those singular points where transmission becomes maximum, we find localized plasmon-polariton-gap solitons of various orders depending on the particular value of the incident power. Present results reveal, therefore, new gap plasmon-soliton solutions that are hybrid modes stemming from the resonant coupling between the incoming electromagnetic wave and the plasmonic modes of the dispersive material, leading to the transparency of a stack with nonlinear inclusions.

A theoretical study of the growth-direction magnetic-field effects on the exciton photoluminescence peak energies in GaAs–Ga1−xAlxAs quantum-dot/ultrathin quantum-well systems is presented. Calculations are performed within the effective-mass approximation and taking into account nonparabolicity effects for both the conduction-band and valence-band effective masses. We use a simple 'QD+ultrathin QW' model heterostructure to mimic the actual physical system, and calculated results for the exciton diamagnetic shifts are found in overall agreement with recent experimental measurements.