Quantum Size Effects
Mostrando 13-24 de 28 artigos, teses e dissertações.
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13. AplicaÃÃo de mÃtodos correlacionados de estrutura eletrÃnica ao estudo de estados excitados de molÃculas em fase gasosa e em soluÃÃo
Ab-initio electronic structure calculations, at correlated level, are applied to the study of excited states of molecules in gas-phase and solution. The electron correlated methods comprise the multiconfigurational SCF (MCSCF), and the multi-reference CI method with single and double excitations (MR-CISD), which is used in combination with MCSCF, then provid
Publicado em: 2005
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14. Caracterização optica de pontos quanticos de CdTe em matriz vitrea
Quanturn confinement effects in semiconductor nanoerystais have attracted a significant amount of interest in the last few years, because of their new optical properties and aiso because of their potential for optical device applications. ln this thesis the size-dependent optical properties of nanometer-scale semiconductor crystallites (or quantum dots) in d
Publicado em: 2002
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15. Tunelamento assistido por caos em estados localizados
We have studied the effects of chaos on the tunneling of particles. As a model we used a one dimensional double well-type quartic potencial, perturbed by a periodic driving. The driving force introduces chaos and the sistem becomes mixed, exhibiting islands of regular motion immersed in a sea of chaos in its classical phase space. By altering the amplitude a
Publicado em: 2002
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16. Estudo de confinamento quantico em semicondutores II-VI : poços quanticos e pontos quanticos
In this work we present a study of quantum confinement in semiconductor structures of the group II-VI, both quantum wells and quantum dots. For the quantum wells we present photoinduced intersubband absorption measurements in HgCdTe undoped quantum wells. We photoexcited the electrons necessary to observe this transition. The transition energies are well des
Publicado em: 1995
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17. Efeitos de tamanho em cadeias de Heisenberg-ising com interações antiferromagneticas
Finite Heisenberg-Ising quantum chains, for spin s = 1/2 and periodic boundary conditions, are exactly solved by numerical methods diagonalizing the Hamiltonian using the Lanczos method up to size N = 28 spins. Interesting physical quantities are computed, including the ground state energy, the mass gap, the spin-wave velocity, and correlation functions. Sca
Publicado em: 1991
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18. Polaronic effects in one and two dimensional semiconductor heterostructures. / Efeitos polarônicos em estruturas semicondutoras em uma e duas dimensões.
In this work we study the polaronic effects on the two dimensional electron gas present in semiconductor heteroestructures (GaAs-AlGaAs heterojunctions and quantum wells) when a uniform magnetic field is applied perpendicular to the interface, using second order perturbation theory. By taking into account the effect of nonparabolicity and screening of the el
Publicado em: 1988
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19. Quantum dot artificial solids: Understanding the static and dynamic role of size and packing disorder
This perspective examines quantum dot (QD) superlattices as model systems for achieving a general understanding of the electronic structure of solids and devices built from nanoscale components. QD arrays are artificial two-dimensional solids, with novel optical and electric properties, which can be experimentally tuned. The control of the properties is prim
The National Academy of Sciences.
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20. Architecture with designer atoms: Simple theoretical considerations
The distinct electronic states of assemblies of metallic quantum dots are discussed in a simple approximation where each dot is mimicked as an “atom” that carries one valence electron. Because of their large size, the charging energy of the dots, I = energy required to add another electron, is much smaller than for ordinary atoms. The Coulomb blocki
The National Academy of Sciences.
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21. Quantal transmitter release at somatic motor-nerve terminals: stochastic analysis of the subunit hypothesis.
Here we analyze the problem of determining whether experimentally measured spontaneous miniature end-plate currents (MEPCs) indicate that quanta are composed of subunits. The properties of MEPCs at end plates with or without secondary clefts at the neuromuscular junction are investigated, using both stochastic and deterministic models of the action of a quan
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22. Increasing quantal size at the mouse neuromuscular junction and the role of choline.
1. In frog a variety of treatments have been shown to increase quantal size at the neuromuscular junction (NMJ), apparently by releasing more acetylcholine (ACh) per quantum. The present experiments were undertaken to see whether similar changes occur at the mouse NMJ. 2. None of the hormones tested, adrenaline, insulin or corticosteroids, significantly incr
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23. Effects of variance in mini amplitude on stimulus-evoked release: a comparison of two models.
The strength of synaptic connections between two neurons is characterized by the number of release sites (N) on the presynaptic cell, the probability (p) of transmitter release at those sites in response to a stimulus, and the average size (A) of the postsynaptic response from each site. Quantal analysis can determine N, p, and A, but the large variance in t
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24. Self-organization in leaky threshold systems: The influence of near-mean field dynamics and its implications for earthquakes, neurobiology, and forecasting
Threshold systems are known to be some of the most important nonlinear self-organizing systems in nature, including networks of earthquake faults, neural networks, superconductors and semiconductors, and the World Wide Web, as well as political, social, and ecological systems. All of these systems have dynamics that are strongly correlated in space and time,
National Academy of Sciences.