Donor states in modulation-doped Si/SiGe heterostructures

We present a unified approach for calculating the properties of shallow donors inside or outside heterostructure quantum wells. The method allows us to obtain not only the binding energies of all localized states of any symmetry, but also the energy width of the resonant states which may appear when a localized state becomes degenerate with the continuous quantum well subbands. The approach is non-variational, and we are therefore also able to evaluate the wave functions. This is used to calculate the optical absorption spectrum, which is strongly non-isotropic due to the selection rules. The results obtained from calculations for Si/Si$_{1-x}$Ge$_x$ quantum wells allow us to present the general behavior of the impurity states, as the donor position is varied from the center of the well to deep inside the barrier. The influence on the donor ground state from both the central-cell effect and the strain arising from the lattice mismatch is carefully considered.Comment: 17 pages, 10 figure

Absorci?n de nutrimentos y Producci?n en la asociaci?n frijol (Phaseolus vulgaris L.), ma?z (Zea mays L.) y arroz (Oryza sativa L.)

Tesis (M. Sc) -- IICA, Turrialba (Costa Rica), 1975El presente trabajo constituy? una parte del Experimento Central iniciado por el Departamento de Cultivos y Suelos Tropicales del Centro Tropical de Investigaci?n y Ense?anza (CATIE) en Turrialba, Costa Rica, en suelos de la serie Instituto fase normal (Inceptisol, Typic dystropepts). El per?odo de investigaci?n comprendi? de Noviembre de 1973 a Noviembre de 1974. Los objetivos fueron: caracterizar el ?rea comprendida por el experimento central, desde el punto de vista qu?mico y determinar la absorci?n de nutrimentos y Producci?n en la asociaci?n: Frijol (Phaseolus vulgaris var. Jamapa), Ma?z (Zea mays var. Local) y Arroz (Oryza sativa var. C.R. 1113). El sistema estudiado comprendi? ocho tratamientos con 32 subtratamientos los cuales fueron seleccionados de los 54 tratamientos principales que constituy? el Experimento Central. Seg?n las caracter?sticas qu?mica y el respectivo mapa de fertilidad que se prepar?, el 81,5 por ciento del ?rea experimnetal posee una fertilidad de media a baja. De acuerdo al mapa elaborado sobre las condiciones de drenaje s?lo el 43,43 por ciento del ?rea total presenta buenas condiciones de drenaje. Los tratamientos seleccionados representaron los diferentes sistemas de Producci?n en estudio, desde el control (cultivo no alimenticio) a trav?s de sistemas monoculturales hasta la asociaci?n de dos o tres cultivos, sembrados en sucesi?n o en asociaci?n o con superposici?n variable. Los subtratamientos representaron niveles crecientes de tecnolog?a aplicada. Los cultivos de ma?z, arroz y frijol fueron probados en sistemas de monocultivo, bicultivo y tricultivo en un dise?o factorial 8 x 4 con dos repeticiones. La mayor exigencia de los cultivos desde el punto de vista de nutrici?n fue entre 30 y 60 d?as, siendo el orden de exigencia nutricional: ma?z>arroz>frijol. El ma?z se destac? por su poder de Producci?n de biomasa y de absorci?n de nutrimentos tanto en monocultivos como en asociaci?n. Los fertilizantes fueron un factor importante en los rendimientos y la eficiencia de los elementos integrantes de los fertilizantes fue K>N>S>P. La asociaci?n de cultivos afect? el rendimiento y Producci?n de carbohidratos, prote?nas y grasas, disminuyendo con relaci?n a los monocultivos respectivos. En cuanto a mejor utilizaci?n de la tierra indudablemente la asociaci?n ma?z-frijol-arroz fue sobresaliente, sin embargo, desde el punto de vista de extracci?n balanceada de nutrimentos la mejor asociaci?n fue ma?z-frijol. Como era de esperarse, el frijol se destac? como buen productor de prote?nas y el ma?z de carbohidratos. No se present? diferencia significativa entre las tecnolog?as aplicadas

Density of impurity states in doped narrow nanoring

Energy spectra of a neutral donor in a narrow nanoscopic toroidal-shaped ring are analyzed. It is shown that in the framework of the adiabatic approximation the problem is reduced to one dimen-sional wave equation for an anisotropic rotator. Calculation results show that the curves of the density states have pronounced Van Hove-type singularities corresponding to the donor position at the center of the ring. The contribution of different low-lying excited states in the density of the impurity states is discussed.Se analiza el espectro energético de una donadora neutra en un anillo nanoscópico delgado de forma toroidal. Se muestra que en el marco de la aproximación adiabática el problema se reduce a una ecuación de onda unidimensional para un rotor anisotrópico. Los resultados de los cálculos, muestran que las curvas de densidad de los estados tienen singularidades de tipo Van Hove correspondientes a la posición de la donadora en el centro del anillo. Se discute la contribución de los diferentes estados excitados más bajos a la densidad de estados de la impureza

Shallow Donor States In Gaas-(ga, Al)as Quantum Dots With Different Potential Shapes

Energies of the ground and some excited states of on-centre donors (D O) in GaAs/Ga 1-xAl xAs spherical quantum dots are calculated, within the effective mass approximation, as functions of the R dot radius and for different potential shapes. We propose an exact numerical solution for the radial Schrödinger equation in a quantum dot with any arbitrary spherical potential by using a trigonometric sweep method. An evident increase in the binding energy is found as the soft-edqe-barrier potential model is considered. It is found that the D O binding energy increases as the dot size decreases up to a dot radius critical value R = R c and then, for R slightly smaller than R c, the impurity wave function spreads to the barrier region and the 3D character is rapidly restored. The properties of the D O shallow donors in a quantum dot with a double-step potential barrier and multiple barriers are analysed, and two peaks in the binding energy are found. Our results for the spherical-rectangular potential are in good agreement with previous calculations obtained using other methods.312333913396Johonson, N.F., (1995) J. Phys.: Condens. Matter, 7, p. 965Kastner, M.A., (1993) Phys. Today, 46 (1), p. 24Heitmann, D., Kotthaus, J.P., (1993) Phys. Today, 46 (6), p. 56Chakraborty, T., (1992) Comm. Condens. Matter Phys., 16, p. 35Ashoori, R.C., Stormer, H.L., Weiner, J.S., Pfeiffer, L.N., Baldwin, K.W., West, K.W., (1993) Phys. Rev. Lett., 71, p. 613Wang, Y., Chou, S.Y., (1993) IEEE Trans. Electron. Devices, 40, p. 2136Motohisa, J., Kumakura, K., Kishida, M., Yamazaki, T., Fukui, T., Hasegawa, H., Wada, K., (1995) Japan. J. Appl. Phys., 34, p. 1098Zhu, J.L., Xiong, J.J., Gu, B.L., (1990) Phys. Rev. B, 41, p. 6001. , and references therein for neutral donors in QDsZhu, J.L., (1989) Phys. Rev. B, 39, p. 8780Buczko, R., Bassani, F., (1996) Phys. Rev. B, 54, p. 2667Ribeiro, F.J., Latgé, A., (1994) Phys. Rev. B, 50, p. 4913Said, M.E., (1994) Physica B, 202, p. 202Xia, Z., Zhu, J., He, F., (1996) Superlatt. Microstruct., 19, p. 137Porras-Montenegro, N., Pérez-Merchancano, S.T., (1992) Phys. Rev. B, 46, p. 9780Paredes-Gutiérrez, H., Cuero-Yépez, J.C., Porras-Montenegro, N., (1994) J. Appl. Phys., 75 (10), p. 15Fedorenko, R.P., (1994) Introduction to Computational Physics, , Moscow: Physics-Technique University PressNelson, D.F., Miller, R.C., Tu, C.W., Sputz, S.K., (1987) Phys. Rev. B, 36, p. 8063Woods, R.D., Saxon, D.S., (1954) Phys. Rev., 95, p. 577Flügge, S., (1974) Practical Quantum Mechanics, , New York: SpringerYuh, P.F., Wang, K.L., (1989) J. Appl. Phys., 65 (11), p. 437

Model Structure For D- States In Gaas-(ga,al)as Quantum Wells

A simple model in which both electrons of the shallow-negative donor D- are instantaneously localized approximately at the same distance with respect to the ion nucleus is considered. Within this model, the D- Hamiltonian becomes separable, and the effect of the electron-electron interaction is essentially taken into account by the interaction of each of the electrons with a renormalized-nucleus effective charge which depends on the angle between the two electron vector positions. The trial function is taken as a product of two three-parameter one-particle wave functions to calculate the ground state energy as a function of the angle. Theoretical results for the D- energy, including zero-point energy corrections within the harmonic approximation, are obtained for D- states centered in GaAs-(Ga,Al)As quantum wells as a function of the well width, and for different values of the magnetic field, applied perpendicular to the interfaces of the heterostructure. Our results are in good agreement with experimental data and with theoretical calculations using variational or Monte Carlo techniques.2102605608Huant, S., Nayda, S.P., Etienne, B., (1990) Phys. Rev. Lett., 65, p. 1486Muller, E.R., Larsen, D.M., Waldman, J., Goodhue, W.B., (1992) Phys. Rev. Lett., 68, p. 2204Zhu, J.-L., Zhao, J.-H., Xiong, J.-J., (1994) Phys. Rev. B, 50, p. 1832Zhu, J.-L., Xu, S., (1994) Phys. Rev. B, 50, p. 12175Szwacka, T., Blinowski, J., Betancur, F.J., (1995) J. Phys: Condensed Matter, 7, p. 4489Dzyubenko, A.B., Sivachenko, A.Yu., (1993) Soviet Phys. - JETP Lett., 57, p. 487Pang, T., Louie, S.G., (1990) Phys. Rev. Lett., 65, p. 1635Bethe, A.A., Salpeter, E.E., (1957) Quantum Mechanics of One- and Two-electron Atoms, , Springer-Verlag, BerlinSingh, J., Birkedal, D., Lissenko, V.G., Hvam, J.M., (1996) Phys. Rev. B, 53, p. 15909Strzalkowski, I., Joshi, S., Crowell, C.R., (1976) Appl. Phys. Lett., 28, p. 35

Glicophyllum stylopterum

Angiosperm

Direct oral anticoagulants in antiphospholipid syndrome: A real life case series

Aim The aim of this study was to describe a case series of patients with primary or secondary antiphospholipid syndrome (APS) treated with direct oral anticoagulants (DOACs). Patients and methods Clinical charts of eight patients with thrombotic primary or secondary APS treated with direct oral anticoagulants (DOACs) between January 2012 and May 2015 were reviewed. Results The mean age was 45 ± 14.36 (range 27-69 years). Four patients had secondary APS (50%). All patients were initially treated with warfarin by a mean time of 70.87 ± 57.32 months (range 17-153 months). Changes in anticoagulation were defined by recurring thrombosis in five patients (62.5%) and life-threatening bleeding in the other three cases. Seven patients (87.5%) received rivaroxaban treatment and one patient (12.5%) apixaban. The mean follow-up period with DOACs was 19 ± 10.06 months (range 2-36 months). There was no recurrence of thrombosis by the time of data collection. Conclusions Despite not being the standard treatment in APS, we propose DOACs as a rational alternative for the management of patients with this diagnosis. Further interventional clinical studies are necessary for possible standardization of this therapy in APS patients