Determination of spin polarization in InAs/GaAs self-assembled quantum dots

The spin polarization of electrons trapped in InAs self-assembled quantum dot ensembles is investigated. A statistical approach for the population of the spin levels allows one to infer the spin polarization from the measure values of the addition energies. From the magneto-capacitance spectroscopy data, the authors found a fully polarized ensemble of electronic spins above 10 T when $\mathbf{B}\parallel[001]$ and at 2.8 K. Finally, by including the g-tensor anisotropy the angular dependence of spin polarization with the magnetic field $\mathbf{B}$ orientation and strength could be determined.Comment: 3 pages, 2 figures, Accepted Appl. Phys. Let

Chiral corrections to baryon properties with composite pions

A calculational scheme is developed to evaluate chiral corrections to properties of composite baryons with composite pions. The composite baryons and pions are bound states derived from a microscopic chiral quark model. The model is amenable to standard many-body techniques such as the BCS and RPA formalisms. An effective chiral model involving only hadronic degrees of freedom is derived from the macroscopic quark model by projection onto hadron states. Chiral loops are calculated using the effective hadronic Hamiltonian. A simple microscopic confining interaction is used to illustrate the derivation of the pion-nucleon form factor and the calculation of pionic self-energy corrections to the nucleon and Delta(1232) masses.Comment: 29 pages, Revtex, 4 ps figure

Lande g-tensor in semiconductor nanostructures

Understanding the electronic structure of semiconductor nanostructures is not complete without a detailed description of their corresponding spin-related properties. Here we explore the response of the shell structure of InAs self-assembled quantum dots to magnetic fields oriented in several directions, allowing the mapping of the g-tensor modulus for the s and p shells. We found that the g-tensors for the s and p shells show a very different behavior. The s-state in being more localized allows the probing of the confining potential details by sweeping the magnetic field orientation from the growth direction towards the in-plane direction. As for the p-state, we found that the g-tensor modulus is closer to that of the surrounding GaAs, consistent with a larger delocalization. These results reveal further details of the confining potentials of self-assembled quantum dots that have not yet been probed, in addition to the assessment of the g-tensor, which is of fundamental importance for the implementation of spin related applications.Comment: 4 pages, 4 figure

Vacuum fluctuations of a scalar field near a reflecting boundary and their effects on the motion of a test particle

The contribution from quantum vacuum fluctuations of a real massless scalar field to the motion of a test particle that interacts with the field in the presence of a perfectly reflecting flat boundary is here investigated. There is no quantum induced dispersions on the motion of the particle when it is alone in the empty space. However, when a reflecting wall is introduced, dispersions occur with magnitude dependent on how fast the system evolves between the two scenarios. A possible way of implementing this process would be by means of an idealized sudden switching, for which the transition occurs instantaneously. Although the sudden process is a simple and mathematically convenient idealization it brings some divergences to the results, particularly at a time corresponding to a round trip of a light signal between the particle and the wall. It is shown that the use of smooth switching functions, besides regularizing such divergences, enables us to better understand the behavior of the quantum dispersions induced on the motion of the particle. Furthermore, the action of modifying the vacuum state of the system leads to a change in the particle energy that depends on how fast the transition between these states is implemented. Possible implications of these results to the similar case of an electric charge near a perfectly conducting wall are discussed.Comment: 17 pages, 8 figure

Planeamento de uma mobilidade urbana sustentável e eficiente: metodologia para avaliar a descarbonização do setor

No âmbito da aplicação dos fundos europeus estruturais e de investimento no período de programação 2014-2020 torna-se necessário, na temática da mobilidade, dar cumprimento ao seguinte Objetivo Temático ?Apoiar a transição para uma economia de baixo teor de carbono em todos os sectores?, que estabelece, entre outras, a Prioridade de Investimento 4.5, que visa a promoção de estratégias de baixo teor de carbono para todos os tipos de territórios, nomeadamente as zonas urbanas, incluindo a promoção da mobilidade urbana multimodal sustentável e eficiente. Da análise da metodologia existente para quantificar o volume de emissões do setor dos transportes utilizado pela Direção Geral de Energia e Geologia é possível concluir que a determinação desses valores não permite definir estratégias que visem a redução das emissões neste setor. Deste modo, a metodologia desenvolvida permitirá estimar o valor correspondente a um número de viagens de transporte motorizados para um determinado volume de emissões de GEE (tonCO2) e assim definir o quadro da repartição modal mais eficiente para os padrões de mobilidade urbana a atingir por um, ou vários, municípios de uma região. Assim, neste artigo será apresentada uma metodologia que vise estimar a diminuição do número de viagens em transporte individual, que possam ser transferidas para modos de transporte mais eficientes e menos poluentes, como o autocarro e os modos ativos, de modo a que se possa atingir o valor meta de CO2 para 2023.info:eu-repo/semantics/publishedVersio

Sustainable mobility in a mid-sized city : a multimodal approach

Transportation systems of mid-sized cities play an important role in guaranteeing a sustainable development of the surrounding areas. Sustainable principles applied to the study of urban mobility involve the consideration of all different travel modes, as well as the territory where all modes interact and establish points of connection. Consequently, a multimodal approach is necessary, especially to encourage a more effective and sustainable use of the system and to promote greener modes of transport, like pedestrians and cyclists, or other less pollutant modes. The paper presents a case study on the city of Viana do Castelo, which is located in the North of Portugal with approximately 37000 inhabitants in 33.6 square kilometres. It is considered a mid-sized city with a large number of different transport modes, namely trains, buses, ferryboats, cyclists and pedestrians, which provide an opportunity to develop and apply a multimodal approach towards a more sustainable city environment

The role of public transport in the achievement of urban sustainable mobility in mid-sized cities

Mid-sized cities or villages often have important issues associated with the relation between demand and supply of transport, due to its own spatial dimension and also due to the territory sprawl derived from years of deficient land use planning. Traditionally, public transport was mainly designed to cover and serve the entire municipality, giving a rural character to this service. Presently, some of these cities are sufficiently large to support the adoption of an urban public transport. The main question is how to create a public transport service in mid-sized cities integrated with the existing transport and parking system, so that more sustainable patterns of mobility can be achieved. For this purpose, a case study will be presented regarding the creation and planning of an urban public transport service for the city of Barcelos, located in Northern Portugal