Effects Of Crossed Electric And Magnetic Fields On The Electronic And Excitonic States In Bulk Gaas And Gaas Ga1-x Alx As Quantum Wells

The variational procedure in the effective-mass and parabolic-band approximations is used in order to investigate the effects of crossed electric and in-plane magnetic fields on the electronic and exciton properties in semiconductor heterostructures. Calculations are performed for bulk GaAs and GaAs Ga1-x Alx As quantum wells, for applied magnetic fields parallel to the layers and electric fields in the growth direction, and it is shown that the combined effects on the heterostructure properties of the applied crossed electric and magnetic fields and the direct coupling between the center-of-mass and internal exciton motions may be dealt with via a simple parameter representing the spatial distance between the centers of the electron and hole magnetic parabolas. Exciton properties are analyzed by using a simple hydrogenlike envelope excitonic wave function and present theoretical results are found in fair agreement with available experimental measurements on the diamagnetic shift of the photoluminescence peak position of GaAs Ga1-x Alx As quantum wells under in-plane magnetic fields. © 2007 The American Physical Society.753Whittaker, D.M., Fisher, T.A., Simmonds, P.E., Skolnick, M.S., Smith, R.S., (1991) Phys. Rev. Lett., 67, p. 887. , PRLTAO 0031-9007 10.1103/PhysRevLett.67.887Fritze, M., Perakis, I.E., Getter, A., Knox, W., Goossen, K.W., Cunningham, J.E., Jackson, S.A., (1996) Phys. Rev. Lett., 76, p. 106. , PRLTAO 0031-9007 10.1103/PhysRevLett.76.106Butov, L.V., Mintsev, A.V., Lozovik, Y.E., Campman, K.L., Gossard, A.C., (2000) Phys. Rev. B, 62, p. 1548. , PRBMDO 0163-1829 10.1103/PhysRevB.62.1548Parlangeli, A., Christianen, P.C.M., Maan, J.C., Soerensen, C.B., Lindelof, P.E., (2000) Phys. 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Controlling quantum entanglement through photocounts

We present a protocol to generate and control quantum entanglement between the states of two subsystems (the system ${\cal S}$) by making measurements on a third subsystem (the monitor ${\cal M}$), interacting with ${\cal S}$. For the sake of comparison we consider first an ideal, or instantaneous projective measurement, as postulated by von Neumann. Then we compare it with the more realistic or generalized measurement procedure based on photocounting on ${\cal M}$. Further we consider that the interaction term (between ${\cal S}$ and ${\cal M}$) contains a quantum nondemolition variable of ${\cal S}$ and discuss the possibility and limitations for reconstructing the initial state of ${\cal S}$ from information acquired by photocounting on ${\cal M}$.Comment: 12 pages, 3 figures, accepted for publication in Phys. Rev

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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Which mechanism underlies the water-like anomalies in core-softened potentials?

Using molecular dynamics simulations we investigate the thermodynamic of particles interacting with a continuous and a discrete versions of a core-softened (CS) intermolecular potential composed by a repulsive shoulder. Dynamic and structural properties are also analyzed by the simulations. We show that in the continuous version of the CS potential the density at constant pressure has a maximum for a certain temperature. Similarly the diffusion constant, $D$, at a constant temperature has a maximum at a density $\rho_{\mathrm{max}}$ and a minimum at a density $\rho_{\mathrm{min}}<\rho_{\mathrm{max}}$, and structural properties are also anomalous. For the discrete CS potential none of these anomalies are observed. The absence of anomalies in the discrete case and its presence in the continuous CS potential are discussed in the framework of the excess entropy.Comment: 8 page

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

Cleavage Device For Alkali Halides

This Note describes a cleavage device for alkali halides. This device was used in our laboratories for crystals of NaCl, KCl, and LiF with very good results. For this last crystal special care should be taken due to its cleaving characteristics; this harder material is quite difficult to handle. Our success in cleaving LiF under vacuum makes perhaps of general interest a description of the cleaving device. The freshly vacuum cleaved surface offers the possibility of initial nucleation studies of evaporated single crystal thin films. In order to simultaneously meet the needs of heating and high vacuum, the device is made of stainless steel. © 1973 The American Institute of Physics.449140

New upper bounds for the density of translative packings of three-dimensional convex bodies with tetrahedral symmetry

In this paper we determine new upper bounds for the maximal density of translative packings of superballs in three dimensions (unit balls for the $l_3^p$-norm) and of Platonic and Archimedean solids having tetrahedral symmetry. These bounds give strong indications that some of the lattice packings of superballs found in 2009 by Jiao, Stillinger, and Torquato are indeed optimal among all translative packings. We improve Zong's recent upper bound for the maximal density of translative packings of regular tetrahedra from $0.3840\ldots$ to $0.3745\ldots$, getting closer to the best known lower bound of $0.3673\ldots$. We apply the linear programming bound of Cohn and Elkies which originally was designed for the classical problem of packings of round spheres. The proofs of our new upper bounds are computational and rigorous. Our main technical contribution is the use of invariant theory of pseudo-reflection groups in polynomial optimization

Correlation of mixed lymphocyte culture with chronic graft-versus-host disease following allogeneic stem cell transplantation

The purpose of the present study was to evaluate the mixed lymphocyte culture as a predictive assay of acute and chronic graft-versus-host disease (GVHD). We studied 153 patients who received a first bone marrow transplantation from human leukocyte antigen-identical siblings. Acute GVHD was observed in 26 of 128 (20.3%) patients evaluated and chronic GVHD occurred in 60 of 114 (52.6%). One-way mixed lymphocyte culture (MLC) assays were performed by the standard method. MLC results are reported as the relative response (RR) from donor against patient cells. The responses ranged from -47.0 to 40.7%, with a median of 0.5%. The Kaplan-Meier probability of developing GVHD was determined for patients with positive and negative MLC. There was no significant difference in incidence of acute GVHD between the groups studied. However, the incidence of chronic GVHD was higher in recipients with RR >4.5% than in those with RR 4.5%), 2.9 for those who received peripheral blood progenitor cells as a graft, and 2.2 for patients who developed previous acute GVHD. MLC was not useful for predicting acute GVHD, but MLC with RR >4.5% associated with other risk factors could predict the development of chronic GVHD, being of help for the prevention and/or treatment of this late complication.56757

A utilização do ELISA empregando antígenos homólogos e heterólogos para a detecção de IgG e subclasses (IgG1 e IgG2) no diagnóstico de Leishmaniose visceral canina

Indirect immunofluorescence is the method recommended for the diagnosis of visceral leishmanisis in dogs, however, the accuracy of this technique is low and its use on a large scale is limited. Since ELISA does not present these limitations, this technique might be an option for the detection of IgG or specific IgG1 and IgG2 subclasses. Canine ehrlichiosis is an important differential diagnosis of American Visceral Leishmaniasis (AVL). The present study compared ELISA using Leishmania chagasi and Leishmania braziliensis antigen for the detection of anti-Leishmania IgG and subclasses in serum samples from 37 dogs naturally infected with L. chagasi (AVL) and in samples from four dogs co-infected with L. braziliensis and L. chagasi (CI). The occurrence of cross-reactivity was investigated in control serum samples of 17 healthy dogs (HC) and 35 infected with Ehrlichia canis (EC). The mean optical density obtained for the detection of IgG was significantly higher when L. chagasi antigen was used, and was also higher in subgroup VLs (symptomatic) compared to subgroup Vla (asymptomatic). The correlation between IgG and IgG1 was low. The present results suggest that IgG ELISA using homologous antigen yields the best results, permitting the diagnosis of asymptomatic L. chagasi infection and the discrimination between cases of AVL and ehrlichiosis in dogs.A imunofluorescência indireta é o método recomendado para o diagnóstico de leishmaniose visceral em cães, entretanto, a acurácia dessa técnica é baixa e seu uso em grande escala é limitado. Uma vez que o ELISA não apresenta essas limitações, essa técnica poderia ser uma opção para a detecção de IgG ou subclasses IgG1 e IgG2 específicas. A ehrlichiose canina é um importante diagnóstico diferencial de Leishmaniose Visceral Americana (LVA). O presente estudo comparou o ELISA usando antígenos de Leishmania chagasi e Leishmania braziliensis para a detecção de IgG e subclasses anti-Leishmania em amostras de soro de 37 cães naturalmente infectados com L. chagasi (LVA) e em amostras de quatro cães co-infectados (CI). A ocorrência de reatividade cruzada foi investigada em amostras de soro controle de 17 animais saudáveis (HC) e 35 de infectados por Ehrlichia canis (EC). A média de densidade óptica obtida para a detecção de IgG foi significantemente maior quando o antígeno de L. chagasi foi usado e também mais elevada no subgrupo LVs (sintomático) quando comparado ao subgrupo LVa (assintomático). A correlação entre IgG e IgG1 foi baixa. O presente resultado sugere que ELISA IgG empregando antígeno homólogo, produz os melhores resultados, permitindo o diagnóstico de infecção assintomática por L. chagasi e a discriminação entre casos de LVA e ehrlichiose em cães