We show that the GPE with cubic nonlinearity, as a model to describe the one dimensional Bose-Einstein condensates loaded into a harmonically confined optical lattice, presents a set of ground states which is orbitally stable for any value of the self-interaction (attractive and repulsive) parameter and laser intensity. We also derive a new formalism which gives explicit expressions for the minimum energy E min and the associated chemical potential µ 0 . Based on these formulas, we generalize the variational method to obtain approximate solutions, at any order of approximation, for E min , µ 0 and the ground state.
O artigo trabalha as concepções de Winnicott e Lacan a respeito do tempo. Em Winnicott, o tempo é pensado no plano da diferença ontológica, enquanto que Lacan privilegia a diferença sexual. Pretende-se mostrar como essas duas idéias a respeito da temporalidade implicam distintas concepções sobre a constituição subjetiva, assim como diferentes estratégias clínicas. Com relação ao tempo, Winnicott será associado ao filósofo Henri Bergson e à sua noção de duração.
A quantum well (QW) in the presence of a homogeneous electric field forms a system with continuous energy spectrum. Its density of states (DOS) is calculated. A general DOS formula is applied which avoids the well-known difficulties for systems with continuous spectra. The Schrodinger equation is solved exactly, and the 1D DOS is expressed in closed analytical form by means of Airy functions of first and second kind. Quasistationary energy levels are defined as zeros of a certain 4 x 4 matrix. Their positions are calculated in dependence on the field strength over a wide range. The 1D DOS peaks arising from quasistationary levels are studied for different field strengths. The same is done for the 1D DOS in a larger energy interval ranging from far below the QW bottom up to far above the QW barriers. Franz-Keldysh oscillations as well as QW interferences are observed above the barriers.Ein Quantum-Well (QW) im homogenen elektrischen Feld ist ein System mit kontinuierlichem Energiespektrum. Seine Zustandsdichte (DOS) wird berechnet. Dabei wird eine allgemeine DOS Formel verwendet, die die bekannten Schwierigkeiten vermeidet, die bei Systemen mit kontinuierlichem Energiespektrum auftreten. Die Schrodinger-Gleichung wird exakt gelost, und die 1D DOS wird in geschlossener analytischer Form durch Airy-Funktionen erster und zweiter Art ausgedruckt. Quasistationiire Energieniveaus werden als Nullstellen einer gewissen 4 x 4-Matrix definiert. Ihre Positionen in Abhangigkeit von der Feldstiirke werden in einem weiten Bereich berechnet. Die den quasistationiiren Niveaus entsprechenden Maxima der 1D DOS werden fur verschiedene Feldstlrken untersucht. Das gleiche wird durchgefuhrt fur die 1D DOS in einem grol3eren Energieintervall, das von weit unterhalb des QW-Bodens bis weit oberhalb der QW-Barrieren reicht. Fur Energien oberhalb der Barrieren werden Franz-Keldysh-Oszillationen und QW-Interferenzen beobachtet.
It was pointed out recently /1, 2/ that in the study of the energy spectrum of charge c a r r i e r s in quantum wells (QWs) it is necessary to consider correctly the band nonparabolicity effects in host materials.Up to now there is no unique simple criterion to incorporate such effects into the theory /1 to 3/. One way is to consider that the nonparabolicity effects are properly characterized by the dispersion relation 2 2 4 E = -+ u k 2m* -+ 1) San L.gzaro y L , Habana, Cuba.
Including the nonparabolicity and anisotropy effects the two-dimensional cyclotron mass of electrons in GaAs is studied in the presence of a magnetic field parallel to the growth direction of the system. Numerical calculations for different quantum wells are reported and a comparison is made with recently reported experimental results.Unter EinschluB von Nichtparabolizitatseffekten und Anisotropie wird die zweidimensionale Zyklotronmasse der Elektronen in GaAs in einem magnetischen Feld parallel zur Wachstumsrichtung des Systems untersucht. Numerische Rechnungen fur verschiedene Quantenwells werden angegeben und mit aktuellen experimentellen Ergebnissen verglichen.
O artigo se insere numa pesquisa mais ampla acerca das novas formas de padecimento psíquico que se apresentam na atualidade. Essas formas, que têm na compulsão uma figura-tipo, colocam em xeque a modalidade de escuta, de entendimento teórico e de intervenção clínica do psicanalista. Discutimos aqui os principais impasses trazidos por esses pacientes ao dispositivo psicanalítico, procurando nele apontar algumas possibilidades de abertura ou transformação. On the compulsions and the psychoanalytical setting. The article is part of a wider research about the new forms of psychical suffering as they appear in our present time. Those forms - compulsion is their prototype - inquire the psychoanalytical way of listening, of theoretical understanding and of clinical intervening. It is discussed here the main problems brought to the psychoanalytical setting by those patients, looking for some possibilities of opening or transformation
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