Non-Markovian Dynamics of Charge Carriers in Quantum Dots

We have investigated the dynamics of bound particles in multilevel current-carrying quantum dots. We look specifically in the regime of resonant tunnelling transport, where several channels are available for transport. Through a non-Markovian formalism under the Born approximation, we investigate the real-time evolution of the confined particles including transport-induced decoherence and relaxation. In the case of a coherent superposition between states with different particle number, we find that a Fock-space coherence may be preserved even in the presence of tunneling into and out of the dot. Real-time results are presented for various asymmetries of tunneling rates into different orbitals.Comment: 9 pages, 3 figures, International Workshop on Physics-Based Mathematical Models for Low-Dimensional Semiconductor Nanostructures. BIRS, November 18-23, 200

Near-Infrared Time-Series Photometry in the Field of Cygnus OB2 Association I - Rotational Scenario For Candidate Members

In the last decades, the early pre main sequence stellar rotational evolution picture has been constrained by studies targeting different young regions at a variety of ages. Observational studies suggest a mass-rotation dependence, and for some mass ranges a connection between rotation and the presence of a circumstellar disk. Not still fully explored, though, is the role of environmental conditions on the rotational regulation. We investigate the rotational properties of candidate members of the young massive association Cygnus OB2. The Stetson variability index, Lomb-Scargle periodogram, Saunders statistics, string/rope length method, and visual verification of folded light curves were applied to select 1224 periodic variable stars. Completeness and contamination of the periodic sample was derived from Monte Carlo simulations, out of which 894 periods were considered reliable. Our study was considered reasonably complete for periods from 2 to 30 days. The general rotational scenario seen in other young regions is confirmed by Cygnus OB2 period distributions, with disked stars rotating on average slower than non-disked stars. A mass-rotation dependence was also verified, but as in NGC 6530, lower mass stars are rotating on average slower than higher mass stars, with an excess of slow rotators among the lower mass population. The effect of the environment on the rotational properties of the association was investigated by re-analysing the results while taking into account the incident UV radiation arising from O stars in the association. Results compatible with the disk-locking scenario were verified for stars with low UV incidence, but no statistical significant relation between rotation and disk presence was verified for stars with high UV incidence suggesting that massive stars can have an important role on regulating the rotation of nearby low mass stars.Comment: Submitted on December 23, 201

General spherically symmetric elastic stars in Relativity

The relativistic theory of elasticity is reviewed within the spherically symmetric context with a view towards the modeling of star interiors possessing elastic properties such as theones expected in neutron stars. Emphasis is placed on generality in the main sections of the paper, and the results are then applied to specific examples. Along the way, a few general results for spacetimes admitting isometries are deduced, and their consequences are fully exploited in the case of spherical symmetry relating them next to the the case in which the material content of the spacetime is some elastic material. This paper extends and generalizes the pioneering work by Magli and Kijowski [1], Magli [2] and [3], and complements, in a sense, that by Karlovini and Samuelsson in their interesting series of papers [4], [5] and [6].Comment: 23 page

Entropy from the foam II

A simple model of spacetime foam, made by two different types of wormholes in a semiclassical approximation, is taken under examination: one type is a collection of $N_{w}$ Schwarzschild wormholes, while the other one is made by Schwarzschild-Anti-de Sitter wormholes. The area quantization related to the entropy via the Bekenstein-Hawking formula hints a possible selection between the two configurations. Application to the charged black hole are discussed.Comment: Revtex 3.0, 10 pages, Replaced version with minor changes and one ref. adde

Short-lived solar burst spectral component at f approximately 100 GHz

A new kind of burst emission component was discovered, exhibiting fast and distinct pulses (approx. 60 ms durations), with spectral peak emission at f approx. 100 GHz, and onset time coincident to hard X-rays to within approx. 128 ms. These features pose serious constraints for the interpretation using current models. One suggestion assumes the f approx. 100 GHz pulses emission by synchrotron mechanism of electrons accelerated to ultrarelativistic energies. The hard X-rays originate from inverse Compton scattering of the electrons on the synchrotron photons. Several crucial observational tests are needed for the understanding of the phenomenon, requiring high sensitivity and high time resolution (approx. 1 ms) simultaneous to high spatial resolution (0.1 arcsec) at f approx. 110 GHz and hard X-rays

Estudo e implementação de modelo mais preciso para determinação da granulometria do solo por atenuação de raios gama.

bitstream/CNPDIA-2009-09/11030/1/BPD19_2007.pd

Avaliação geral, resultados, perspectivas e uso de ferramentas de agricultura de precisão.

Resumo: A agricultura de Precisão aplica o conceito da espacialização ou da análise da variabilidade espacial dos fatores que influenciam a produção agropecuária. Dessa forma, a AP é bastante dependente de instrumentos que auxiliam na aquisição, tratamento e transmissão dos dados nos campos agrícolas, transformando-os em informações úteis para o manejo sítio específico. Neste projeto componente estão sendo desenvolvidos e adaptados equipamentos, sensores, métodos, programas computacionais e uma plataforma de rede de sensores sem fio, denominadas de ferramentas de AP São apresentados resultados de equipamentos para a medida da matéria orgânica e umidade dos solos e de doenças de plantas; bancada de ensaios para a aplicação de insumos; esfera instrumentada para a avaliação de impactos no transporte de hortifrútis; modelagem, processamento de imagens e visão computacional; rede de sensores sem fio; robótica e projetos de sistemas embarcados para máquinas e implementos agrícolas. Participam deste Projeto Componente as seguintes Unidades da Embrapa e parceiros: Embrapa Instrumentação, Embrapa Informática, CSEM Brasil, Embrapa Pecuária Sudeste, Embrapa Pecuária Sul, Embrapa Trigo, Embrapa Hortaliças, Embrapa Florestas, Centro Internacional de la Papa (Peru) e membros da Força Tarefa ISOBUS