Confinement of two-dimensional excitons in a non-homogeneous magnetic field

The effective Hamiltonian describing the motion of an exciton in an external non-homogeneous magnetic field is derived. The magnetic field plays the role of an effective potential for the exciton motion, results into an increment of the exciton mass and modifies the exciton kinetic energy operator. In contrast to the homogeneous field case, the exciton in a non-homogeneous magnetic field can also be trapped in the low field region and the field gradient increases the exciton confinement. The trapping energy and wave function of the exciton in a GaAs two-dimensional electron gas for specific circular magnetic field configurations are calculated. The results show than excitons can be trapped by non-homogeneous magnetic fields, and that the trapping energy is strongly correlated with the shape and strength of the non-homogeneous magnetic field profile.Comment: 9 pages, 12 figure

Hysteresis and re-entrant melting of a self-organized system of classical particles confined in a parabolic trap

A self-organized system composed of classical particles confined in a two-dimensional parabolic trap and interacting through a potential with a short-range attractive part and long-range repulsive part is studied as function of temperature. The influence of the competition between the short-range attractive part of the inter-particle potential and its long-range repulsive part on the melting temperature is studied. Different behaviors of the melting temperature are found depending on the screening length ($\kappa$) and the strength ($B$) of the attractive part of the inter-particle potential. A re-entrant behavior and a thermal induced phase transition is observed in a small region of ($\kappa,B$)-space. A structural hysteresis effect is observed as a function of temperature and physically understood as due to the presence of a potential barrier between different configurations of the system.Comment: 8 pages, 6 figure

Exciton trapping in magnetic wire structures

The lateral magnetic confinement of quasi two-dimensional excitons into wire like structures is studied. Spin effects are take into account and two different magnetic field profiles are considered, which experimentally can be created by the deposition of a ferromagnetic stripe on a semiconductor quantum well with magnetization parallel or perpendicular to the grown direction of the well. We find that it is possible to confine excitons into one-dimensional (1D) traps. We show that the dependence of the confinement energy on the exciton wave vector, which is related to its free direction of motion along the wire direction, is very small. Through the application of a background magnetic field it is possible to move the position of the trapping region towards the edge of the ferromagnetic stripe or even underneath the stripe. The exact position of this 1D exciton channel depends on the strength of the background magnetic field and on the magnetic polarisation direction of the ferromagnetic film.Comment: 10 pages, 7 figures, to be published in J. Phys: Condens. Matte

Transition from single-file to two-dimensional diffusion of interacting particles in a quasi-one-dimensional channel

Diffusive properties of a monodisperse system of interacting particles confined to a \textit{quasi}-one-dimensional (Q1D) channel are studied using molecular dynamics (MD) simulations. We calculate numerically the mean-squared displacement (MSD) and investigate the influence of the width of the channel (or the strength of the confinement potential) on diffusion in finite-size channels of different shapes (i.e., straight and circular). The transition from single-file diffusion (SFD) to the two-dimensional diffusion regime is investigated. This transition (regarding the calculation of the scaling exponent ($\alpha$) of the MSD $$ $\propto t^{\alpha}$) as a function of the width of the channel, is shown to change depending on the channel's confinement profile. In particular the transition can be either smooth (i.e., for a parabolic confinement potential) or rather sharp/stepwise (i.e., for a hard-wall potential), as distinct from infinite channels where this transition is abrupt. This result can be explained by qualitatively different distributions of the particle density for the different confinement potentials.Comment: 13 pages, 11 figure

Querying knowledge graphs in natural language.

Knowledge graphs are a powerful concept for querying large amounts of data. These knowledge graphs are typically enormous and are often not easily accessible to end-users because they require specialized knowledge in query languages such as SPARQL. Moreover, end-users need a deep understanding of the structure of the underlying data models often based on the Resource Description Framework (RDF). This drawback has led to the development of Question-Answering (QA) systems that enable end-users to express their information needs in natural language. While existing systems simplify user access, there is still room for improvement in the accuracy of these systems. In this paper we propose a new QA system for translating natural language questions into SPARQL queries. The key idea is to break up the translation process into 5 smaller, more manageable sub-tasks and use ensemble machine learning methods as well as Tree-LSTM-based neural network models to automatically learn and translate a natural language question into a SPARQL query. The performance of our proposed QA system is empirically evaluated using the two renowned benchmarks-the 7th Question Answering over Linked Data Challenge (QALD-7) and the Large-Scale Complex Question Answering Dataset (LC-QuAD). Experimental results show that our QA system outperforms the state-of-art systems by 15% on the QALD-7 dataset and by 48% on the LC-QuAD dataset, respectively. In addition, we make our source code available

Developing Public-Private Key Pairs Using Highly-Available Technology

The investigation of IPv4 has investigated simulated annealing, and current trends suggest that the emulation of congestion control will soon emerge. In this paper, authors show the development of randomized algorithms. Our focus in this paper is not on whether the well-known decentralized algorithm for the development of agents by Z. Wang [3] runs in Θ(n) time, but rather on constructing an analysis of von Neumann machines (Swamp). Although it at first glance seems perverse, it is supported by previous work in the field

Repetibilidade para a determinação da viabilidade de pólen em dois estádios florais de açaizeiro tipo branco (Euterpe oleracea Mart.).

O objetivo deste trabalho foi avaliar a repetibilidade para dois estádios florais usados na avaliação da viabilidade polínica de genótipos de açaizeiro branco, assim como determinar o número ideal de medições. Foram coletadas três ráquilas de uma inflorescência em plena fase de floração de plantas conservados no Banco de Germoplasma de Açaí, BAG - Açaí, em Belém, PA, e retirados dois estádios florais botão em pré-antese (BPA) e flor recém aberta (FRA) para a determinação da viabilidade polínica. As estimativas de repetibilidade no espaço foram obtidas por três métodos estatísticos. Verificou-se que apenas a FRA apresentaram diferenças significativas entre genótipos, evidenciando diferenças ao nível de η% de probabilidade. Os coeficientes de repetibilidade para o estádio BPA apresentaram baixas magnitudes, não oferecendo confiabilidade na expressão do caráter, enquanto para o estádio FRA os coeficientes de repetibilidade exibiram maiores magnitudes. Esse último estádio floral teve, também, o maior coeficiente de determinação. O número mínimo de ráquilas necessárias para a avaliação do real valor dos genótipos deve ser de 11 ráquilas com confiabilidade de λ0%. Enquanto para flor aberta esse número seria bem maior, ráquilas, para obter o mesmo nível de confiabilidade