Binding energy of excitons in parabolic quantum wells in uniform electric and magnetic fields

Parameterized equations have been derived using variational calculation for energy levels of Wannier excitons in 2D-parabolic quantum wells in uniform electric and magnetic fields. The formulation has been performed in the framework of the effective mass approximation and two-band model. Illustrations have been given for GaAlAsGaAs-GaAlAs and CdMnTe-CdTe-CdMnTe parabolic quantum wells. The comparison with existing data displays good agreement

A theoretical model for exciton binding energies in rectangular and parabolic spherical finite quantum dots

. Using the variational method in real space and the effective-mass theory, we present quite an advanced semi-analytic approach susceptible for calculating the binding energy Eb of Wannier excitons in semiconductor quantum dot structures with rectangular and parabolic shapes of the confining potential in the so-called strong-confinement regime. Illustration is given for CdS, ZnSe, CdSe, GaAs structures of crystallites for both rectangular and parabolic quantum dots, and it displays a very good agreement between the experimental and theoretical results reported in literature

Parametrized Equations for Excitons in Quantum Wires

A set of analytic equations for calculating the binding energies of excitons in T-shaped and squared quantum well wires are established within the effective mass approximation and the two-band model. The resolution is performed in the framework of the variational method. The projections of the relative movement in a lateral plane (2D exciton) and along the free movement direction (1D exciton) are examined as limiting cases. Binding energies and spatial extensions of the exciton as functions of the size of the wire for both the ground and the first excited states are calculated in the case of GaAs/GaAlAs heterostructures for T-shaped and squared geometries. The method is applied to calculate the effects on the excitons induced by the application of crossed electric and magnetic fields. Comparison between quantum wells, T-wires and squared wires is given

Ontological addiction theory: attachment to me, mine, and I

Background: Ontological addiction theory (OAT) is a novel metaphysical model of psychopathology and posits that human beings are prone to forming implausible beliefs concerning the way they think they exist, and that these beliefs can become addictive leading to functional impairments and mental illness. The theoretical underpinnings of OAT derive from the Buddhist philosophical perspective that all phenomena, including the self, do not manifest inherently or independently. Aims and methods: This paper outlines the theoretical foundations of OAT along with indicative supportive empirical evidence from studies evaluating meditation awareness training as well as studies investigating non-attachment, emptiness, compassion, and loving-kindness. Results: OAT provides a novel perspective on addiction, the factors that underlie mental illness, and how beliefs concerning selfhood are shaped and reified. Conclusion: In addition to continuing to test the underlying assumptions of OAT, future empirical research needs to determine how ontological addiction fits with extant theories of self, reality, and suffering, as well with more established models of addiction

Polarizability of D+X complex in bulk semiconductors

The electric polarizability α of ionized-donor-bound exciton D+X in bulk semiconductor is calculated for all values of the effective electron-to-hole mass ratio σ included in the range of stability (σ<σχ). The calculation is performed within the variational method by using 56-term wave function. An asymptotic behavior of α in the vicinity of the critical value σc is deduced. We have also calculated the limiting value σ for which the polarizability equals that of D− system

Formación de hidroxiapatita, Ca5(PO4)3∙OH, en presencia de silicatos

Hydroxyapatite Ca5(PO4)3OH (HAp) is a crystalline phase which has several applications within the domain of special cements. This phase takes an important role in the cement reactions for the reconstruction of skeletal functions (medical domain). It is used also to improve properties of dental material. On the other hand, it is investigated to develop chemically bonded ceramics. In this paper we study the formation of HAp with β-C2S and C5PS, using some compositions in the rich lime portion of the system CaO-SiO2-P2O5-H2O (at atmospheric pressure and open system). These compositions lie in the range of: CaO: 67-71 %; SiO2: 3-18%; P2O5: 9-29% (Wt%). The preparations are made using solid state reactions, with thermal treatment at open system. The identification of phases was carried out using X-ray diffraction, Infra-Red absorption and Differential Thermal Analysis. We delimit a spectroscopy little domain lies in the range of CaO-69,5-70%; P2O5-16,2-19,5%; SiO2-11,1-13,6%. Within this domain, the crystalline phases solid state compatibility at temperature near 1000ºC are HAp, β-C2S, C5PS.La hidroxiapatita, Ca5(PO4)3OH (HAp), es una fase cristalina que tiene diversas aplicaciones en el ámbito de determinados cementos especiales. Esa fase juega un importante papel en las reacciones de cementos utilizados en medicina para la reconstrucción defunciones del esqueleto. Se utiliza también para mejorar propiedades de materiales de aplicación odontológica. Por otra parte, se está estudiando para desarrollar conglomerantes cerámicos. En el presente trabajo se estudia la compatibilidad en estado sólido de la HAp con β-C2S y C5PS utilizando, a presión atmosférica y recinto abierto, composiciones en la zona rica en cal del sistema CaO-SiO2-P2O5-H2O dentro de los límites siguientes. CaO: 67-71 %; SiO2: 3-18%; P2O5: 9-29% (en peso). El tratamiento térmico se realizó en estado sólido y en atmósfera abierta. La identificación de las fases se realizó a través de Difracción de Rayos X, Espectroscopia de Absorción Infrarroja y Análisis Térmico Diferencial. Se define una pequeña zona del diagrama de composición: CaO=69,5-70%; P2O5=16,2-19,5%; SiO2=11,1-13,6%. En este campo las fases cristalinas compatibles en estado sólido, formadas a 1.000ºC, son HAp, β-C2S y C5PS

Formación de hidroxiapatita, Ca5(P04)3 OH, en presencia de silicatos Formation d´hydroxyapatite, Ca5(PO4)3 OH, en milieu silicate

[EN] Hydroxyapatite Ca^(POJpH (líAp) is a crystalline phase which has several applications within the domain of special cements. This phase takes an important role in the cement reactions for the reconstruction of skeletal functions (medical domain). It is used also to improve properties of dental material. On the other hand, it is investigated to develop chemically bonded ceramics. in this paper we study the formation of HAp with ¡3 - C^ and CJ^S, using some compositions in the rich lime portion of the system CaO-SiO^-Pfi^-Hfi (at atmospheric pressure and open system). These compositions lie in the range of: CaO-67- 71%; SiO^-3-18%; Pp-9-29% (Wt%). The preparations are made using solid state rections, with thermal treatment at open system. The identification of phases was carried out using X-ray diffraction, Infra-Red absorption and Dijferentiel Thermal Analysis.We delimit a spectroscopy little domain lies in the range of CaO-69,5-70%; Pfl-16,2-19,5%; SiO^-11,1-13,6%. Within this domain, the crystalline phases solid state compatibility at temperature near lOOO^C are HAp,J3 - CJS, C,.PS.[ES] La hidroxiapatita, Ca^(POJpH -(HAp), es una fase cristalina que tiene diversas aplicaciones en el ámbito de determinados cementos especiales. Esa fase juega un importante papel en las reacciones de cementos utilizados en medicina para la reconstrucción defunciones del esqueleto. Se utiliza también para mejorar propiedades de materiales de aplicación odontológica. Por otra parte, se está estudiando para desarrollar conglomerantes cerámicos. En el presente trabajo se estudia la compatibilidad en estado sólido de la HAp conJS-CJSy C^S utilizando, a presión atmosférica y recinto abierto, composiciones enlazona rica en cal del sistema CaO - SiO^ - Pp^ Lip dentro de los limites siguientes. CaO: 67-71 % ; SiO^: 318% ; PPy 9-29% (en peso). El tratamiento térmico se realizó en estado sólido y en atmósfera abierta. La identificación de las fases se realizó a través de Difracción de Rayos X, Espectroscopia de Absorción Infrarroja y Análisis Térmico Diferencial.Se dejlne una pequeña zona del diagrama de composición: CaO 69,5-70%: PPr 16,2-19,5%; SiO- 11,1-13,6%. En este campo las fases cristalinas compatibles en estado sólido, formadas a l.OOO^C, son HAp,J^-CJSy CJPSPeer reviewe

PIEZOTRANSMISSION BEHAVIOR OF FERROMAGNETIC EuO UNDER MAGNETIC FIELD

Dans un précédent article, nous avons décrit le comportement du signal de piézotransmission de l'Oxyde d'Europium lorsque la température varie. Ce signal, [MATH] Tr/Tr, qui est directement relié au coefficient de pression de la transition optique observée change son signe à la temperature de Curie. Dans la région ferromagnétique la comparaison des mesures d'absorption et de piézotransmission met en évidence deux contributions du spectre "d'absorption apparente". Un faible champ magnétique supprime l'une d'elles. Les spectres de piézotransmission ont alors la même allure dans la région ferromagnétique H [MATH] Hs et dans la région paramagnétique. Cette forme est caractéristique d'une transition bande à bande. Les spectres d'absorption et de piézotransmission sont fortement influencés dans la région ferromagnétique, par la diffusion de la lumière due aux domaines magnétiques et doivent donc être analysés avec attention.It was reported in a previous paper that piezotransmission signal (ATr/Tr) changes its sign at the Curie temperature Tc. It can be shown that the piezotransmission signal is directly related to the pressure coefficient of the optical transition observed (4f 5d). Transmission and piezotransmission measurements have been carried out and in the ferromagnetic state on other contribution to the "apparent optical absorption" appears. Under a small magnetic field this other contribution disappears. Indeed the piezotransmission spectra have the same shape in the ferromagnetic state under a magnetic field than in the paramagnetic state. The shape is characteristic of a band to band transition. The piezotransmission and optical absorption in the ferromagnetic range are thus strongly influenced by light diffusion by domains and must be carefully analysed

Variaciones termodinámicas de la descarbonatación de un crudo conteniendo cenizas volantes bajas en cal

In this paper, the authors analyse the decomposition of a low lime saturation factor (LSF) raw mix -obtained by adding low calcium fly ash to standard portland cement- when heated to around 1000 °C. The decarbonation temperatures and variation in enthalpy taking place during calcite decomposition were determined by DTA and isothermal calorimetric measurement. The resulting belitic clinker had a LSF factor ranging from 75 to 85%. The presence of fly ash was observed to retard the onset of decarbonation and lower the peak and final decarbonation temperatures. Decarbonation enthalpy was also found to decrease with fly ash contentEl objetivo del presente trabajo es estudiar durante su tratamiento térmico, alrededor de 1.000 °C, la evolución de la descomposición de un crudo que posee un factor de saturación de cal (LSF) bajo. Este crudo se ha elaborado adicionando cenizas volantes bajas en calcio a un crudo de cemento portland ordinario. La temperatura de descarbonatación y la variación de la entalpia durante la descomposición de la calcita se determinan por ATD y calorimetría isotérmica. Los resultados muestran la formación de un clinker belítico con un LSF entre 85 y 75%. Asimismo, se demuestra que la presencia de cenizas volantes retarda el comienzo de la descarbonatación y disminuye la temperatura máxima y final del proceso de descarbonatación. El valor de la entalpia de la descarbonatación disminuye con la presencia de cenizas volantes

Investigaciones en las zonas ricas en CaO del sistema CaO-SiO2-P2O5

A detailed study has been carried out to explain the influence of Pp^ in silicate phases and in industrial raw meals upon their mineralogical compositions. Some compositions in the lime rich portion of the CaO-SiO2-P2O5 system are studied using laboratory reactants. The results showed that the compositions lying in the range of CaO = 69,5-70,1; P2O5= 16,2-19,5; SiO2 = 11,1-13,6 (wt%) give, at 1000 °C, the mineralogical composition (HAp, β-C2S, C5PS) which can develop a high strength in chemically bonded ceramics. At high temperature (1400 ºC) these compositions give a large amount of silicocarnotite (C5PS) and 2C2.C3P phase. A selected composition of the industrial raw meal with added phosphate: CaO = 62,66; SiO2 -= 17,33; Al2O3 = 4,88; Fe2O3 = 4,29; P2O5 = 8,73; MgO = 2,09 (wt%) forms at 1350 ºC a clinker containing high amount of α-C2S to replace C3S. Such a clinker may have good applications in the synthesis of active belite cement.Se estudia con detalle la influencia del P2O5 sobre las composiciones mineralógicas en fases silicato y en un crudo industrial. Asimismo se estudian algunas composiciones de la zona rica en cal del sistema CaO-SiO2-P2O5 utilizando reactivos químicos. Los resultados demuestran que, a presión atmosférica y recinto abierto, las composiciones dentro de los límites CaO = 69,5-70,1; P2O5= 16,2-19,5; SiO2 = 11,1-13,6 (% en peso) dan a 1000ºC la composición mineralógica siguiente: HAp, β-C2S, C5PS; pueden desarrollar una alta resistencia química en "chemically bonded ceramics". A altas temperaturas (1400°C) producen una elevada proporción de silicocarnotita (C5PS S) y la fase 2C2.C3P. Con la adición de fosfato a una determinada dosificación de crudo industrial (CaO = 62,66; SiO2 = 17,33; Al2O3 = 4,88; Fe2O3 = 4,29; P2O5 = 8,73; MgO = 2,09 -% en peso-) se forma, a 1350°C, un clinker que contiene una alta proporción de α-C2S que reemplaza al C3S. Este clinker puede tener buenas aplicaciones en la obtención de cementos belíticos