A 2d Honeycomb Photonic Crystal Under Applied Magnetic Fields

The band-structure properties of a photonic two-dimensional honeycomb lattice formed by cylindrical semiconductor shell rods with dielectric permitivities ε 1 and ε 2, and embedded in a background with permitivity ε 3, is studied by using an standard plane-wave expansion. The properties of bandgaps and density of states, considering dispersive dielectric responses, are investigated together with the possibility of fabricating systems with tunable photonic bandgaps, due to the Voigt magneto-optical effect, under the influence of an external magnetic field. © 2008 SPIE.7138J. D. Joannopoulos, R. D. Meade, J. N. Winn, Photonic Crystals: Molding the Flow of Light, Princeton University Press, Princeton, 1995E. Istrate and E. H. Sargent, Rev. Mod. Phys. 78, 455 (2006)Xu, C., Hu, X., Li, Y., Liu, X., Fu, R., Zi, J., (2003) Phys. Rev. B, 68, p. 193201Kee, C.-S., Kim, J.-E., Park, H.Y., Park, I., Lim, H., (2000) Phys. Rev. B, 61, p. 15523Anderson, C.M., Giapis, K.P., (1996) Phys. Rev. Lett, 77, p. 2949Rezaei, B., Kalafi, M., (2006) Optics Commun, 266, p. 159Busch, K., John, S., (1999) Phys. Rev. Lett, 83, p. 967S. B. Cavalcanti, M. de Dios-Leyva, E. Reyes-Gómez, and L. E. Oliveira, Phys. Rev. B 74, 153102 (2006)ibid., Phys. Rev. E 75, 026607 (2007)Ho, K.M., Chan, C.T., Soukoulis, C.M., (1990) Phys. Rev. Lett, 65, p. 315

Acceptor-related Photoluminescence Spectra Of Gaas Quantum-wire Microcrystals: A Model Calculation

The acceptor-related photoluminescence spectrum of a GaAs quantum-wire microcrystal is investigated theoretically using a model calculation within the effective-mass approximation, with the acceptor envelope wave functions and binding energies calculated by a variational procedure. Typical theoretical photoluminescence spectra show two peaks associated with transitions from the n=1 conduction-subband electron gas to acceptors at the on-center and on-edge positions in the wire, in good agreement with the recent experimental results by Hiruma et al. [Appl. Phys. Lett. 59, 431 (1991)]. © 1993 The American Physical Society.47201386413867Akamai Technologies, Inc.,IEEE Computer Society Technical Committee on Distributed Processing (TCDP),IEEE Computers Society,International Research Institute on Autonomic Network Computing,Technical Committee on Distributed Processin

Binding Energies And Density Of Impurity States Of Shallow Hydrogenic Impurities In Cylindrical Quantum-well Wires

The binding energies of hydrogenic impurities in both infinite and finite GaAs-(Ga,Al)As cylindrical quantum-well wires are calculated as functions of the wire radius and of the impurity location in the well for different radii of the wires using a variational procedure within the effective-mass approximation. Assuming there is no intentional doping, we treat the impurity position as a random variable and define a density of impurity states that we have calculated as a function of the impurity binding energy. As a general feature, the density of impurity states presents two structures associated with impurities at the center and at the edge of the quantum-well wire that may be important in the understanding of absorption and photoluminescence experiments of doped GaAs-(Ga,Al)As quantum-well wires. © 1991 The American Physical Society.4321824182

The charge-dyon bound system in the spherical quantum well

The spherical wave functions of charge-dyon bounded system in a rectangular spherical quantum dot of infinitely and finite height are calculated. The transcendent equations, defining the energy spectra of the systems are obtained. The dependence of the energy levels from the wall sizes is found.Comment: 8 pages, 5 figure

Photo-Induced Spin Dynamics in Semiconductor Quantum Wells

We experimentally investigate the dynamics of spins in GaAs quantum wells under applied electric bias by photoluminescence (PL) measurements excited with circularly polarized light. The bias-dependent circular polarization of PL (PPL) with and without magnetic field is studied. ThePPLwithout magnetic field is found to be decayed with an enhancement of increasing the strength of the negative bias. However,PPLin a transverse magnetic field shows oscillations under an electric bias, indicating that the precession of electron spin occurs in quantum wells. The results are discussed based on the electron–hole exchange interaction in the electric field

Erratum to: Binding Energy and Spin-Orbit Splitting of a Hydrogenic Donor Impurity in AlGaN/GaN Triangle-Shaped Potential Quantum Well

In the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling, the binding energyEband spin-orbit split energy Г of the ground state of a hydrogenic donor impurity in AlGaN/GaN triangle-shaped potential heterointerface are calculated. We find that with the electric field of the heterojunction increasing, (1) the effective width of quantum well decreases and (2) the binding energy increases monotonously, and in the mean time, (3) the spin-orbit split energy Г decreases drastically. (4) The maximum of Г is 1.22 meV when the electric field of heterointerface is 1 MV/cm

Diminishing benefits of urban living for children and adolescents’ growth and development

Optimal growth and development in childhood and adolescence is crucial for lifelong health and well-being1–6. Here we used data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, to report the height and body-mass index (BMI) of children and adolescents aged 5–19 years on the basis of rural and urban place of residence in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The exception was for boys in most countries in sub-Saharan Africa and in some countries in Oceania, south Asia and the region of central Asia, Middle East and north Africa. In these countries, successive cohorts of boys from rural places either did not gain height or possibly became shorter, and hence fell further behind their urban peers. The difference between the age-standardized mean BMI of children in urban and rural areas was <1.1 kg m–2 in the vast majority of countries. Within this small range, BMI increased slightly more in cities than in rural areas, except in south Asia, sub-Saharan Africa and some countries in central and eastern Europe. Our results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified

Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults

Background Underweight and obesity are associated with adverse health outcomes throughout the life course. We estimated the individual and combined prevalence of underweight or thinness and obesity, and their changes, from 1990 to 2022 for adults and school-aged children and adolescents in 200 countries and territories. Methods We used data from 3663 population-based studies with 222 million participants that measured height and weight in representative samples of the general population. We used a Bayesian hierarchical model to estimate trends in the prevalence of different BMI categories, separately for adults (age ≥20 years) and school-aged children and adolescents (age 5–19 years), from 1990 to 2022 for 200 countries and territories. For adults, we report the individual and combined prevalence of underweight (BMI 2 SD above the median). Findings From 1990 to 2022, the combined prevalence of underweight and obesity in adults decreased in 11 countries (6%) for women and 17 (9%) for men with a posterior probability of at least 0·80 that the observed changes were true decreases. The combined prevalence increased in 162 countries (81%) for women and 140 countries (70%) for men with a posterior probability of at least 0·80. In 2022, the combined prevalence of underweight and obesity was highest in island nations in the Caribbean and Polynesia and Micronesia, and countries in the Middle East and north Africa. Obesity prevalence was higher than underweight with posterior probability of at least 0·80 in 177 countries (89%) for women and 145 (73%) for men in 2022, whereas the converse was true in 16 countries (8%) for women, and 39 (20%) for men. From 1990 to 2022, the combined prevalence of thinness and obesity decreased among girls in five countries (3%) and among boys in 15 countries (8%) with a posterior probability of at least 0·80, and increased among girls in 140 countries (70%) and boys in 137 countries (69%) with a posterior probability of at least 0·80. The countries with highest combined prevalence of thinness and obesity in school-aged children and adolescents in 2022 were in Polynesia and Micronesia and the Caribbean for both sexes, and Chile and Qatar for boys. Combined prevalence was also high in some countries in south Asia, such as India and Pakistan, where thinness remained prevalent despite having declined. In 2022, obesity in school-aged children and adolescents was more prevalent than thinness with a posterior probability of at least 0·80 among girls in 133 countries (67%) and boys in 125 countries (63%), whereas the converse was true in 35 countries (18%) and 42 countries (21%), respectively. In almost all countries for both adults and school-aged children and adolescents, the increases in double burden were driven by increases in obesity, and decreases in double burden by declining https://researchonline.ljmu.ac.uk/images/research_banner_face_lab_290.jpgunderweight or thinness. Interpretation The combined burden of underweight and obesity has increased in most countries, driven by an increase in obesity, while underweight and thinness remain prevalent in south Asia and parts of Africa. A healthy nutrition transition that enhances access to nutritious foods is needed to address the remaining burden of underweight while curbing and reversing the increase in obesity

Diminishing benefits of urban living for children and adolescents’ growth and development

AbstractOptimal growth and development in childhood and adolescence is crucial for lifelong health and well-being1–6. Here we used data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, to report the height and body-mass index (BMI) of children and adolescents aged 5–19 years on the basis of rural and urban place of residence in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The exception was for boys in most countries in sub-Saharan Africa and in some countries in Oceania, south Asia and the region of central Asia, Middle East and north Africa. In these countries, successive cohorts of boys from rural places either did not gain height or possibly became shorter, and hence fell further behind their urban peers. The difference between the age-standardized mean BMI of children in urban and rural areas was &lt;1.1 kg m–2 in the vast majority of countries. Within this small range, BMI increased slightly more in cities than in rural areas, except in south Asia, sub-Saharan Africa and some countries in central and eastern Europe. Our results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified.</jats:p

Absorción óptica relativa a impurezas donadoras en pozos cuánticos de GaAs-(Ga,Al)As bajo efectos de presión hidrostática

En este trabajo se presentan resultados teóricos sobre los efectos de presión hidrostática en el espectro de absorción óptica relativo a impurezas donadoras en pozos cuánticos de GaAs-(Ga,Al)As. Hemos calculado el espectro de absorción óptica relativo a impurezas donadoras considerando diferentes anchos del pozo cuántico y valores de la presión hidrostática. Nuestros resultados muestran dos estructuras bien definidas en el espectro de absorción: una de ellas asociadas con impure-zas localizadas cerca al centro del pozo y la otra para impurezas cerca de las paredes de la estructura. Adicionalmente, asociado con la variación con la presión del gap (brecha) en el GaAs, se muestra un importante corrimiento al azul del espectro de absorción