Entanglement witnessing in superconducting beamsplitters

We analyse a large class of superconducting beamsplitters for which the Bell parameter (CHSH violation) is a simple function of the spin detector efficiency. For these superconducting beamsplitters all necessary information to compute the Bell parameter can be obtained in Y-junction setups for the beamsplitter. Using the Bell parameter as an entanglement witness, we propose an experiment which allows to verify the presence of entanglement in Cooper pair splitters.Comment: 5 pages, 2 figures, accepted for publication in EP

COMPUTATIONAL ANALYSIS OF KNOWLEDGE SHARING IN COLLABORATIVE DISTANCE LEARNING

The rapid advance of distance learning and networking technology has enabled universities and corporations to reach out and educate students across time and space barriers. This technology supports structured, on-line learning activities, and provides facilities for assessment and collaboration. Structured collaboration, in the classroom, has proven itself a successful and uniquely powerful learning method. Online collaborative learners, however, do not enjoy the same benefits as face-to-face learners because the technology provides no guidance or direction during online discussion sessions. Integrating intelligent facilitation agents into collaborative distance learning environments may help bring the benefits of the supportive classroom closer to distance learners.In this dissertation, I describe a new approach to analyzing and supporting online peer interaction. The approach applies Hidden Markov Models, and Multidimensional Scaling with a threshold-based clustering method, to analyze and assess sequences of coded on-line student interaction. These analysis techniques were used to train a system to dynamically recognize when and why students may be experiencing breakdowns while sharing knowledge and learning from each other. I focus on knowledge sharing interaction because students bring a great deal of specialized knowledge and experiences to the group, and how they share and assimilate this knowledge shapes the collaboration and learning processes. The results of this research could be used to dynamically inform and assist an intelligent instructional agent in facilitating knowledge sharing interaction, and helping to improve the quality of online learning interaction

Detecting an exciton crystal by statistical means

We investigate an ensemble of excitons in a coupled quantum well excited via an applied laser field. Using an effective disordered quantum Ising model, we perform a numerical simulation of the experimental procedure and calculate the probability distribution function $P(M)$ to create $M$ excitons as well as their correlation function. It shows clear evidence of the existence of two phases corresponding to a liquid and a crystal phase. We demonstrate that not only the correlation function but also the distribution $P(M)$ is very well suited to monitor this transition.Comment: 5 pages, 5 figure

Kondo effect and spin-active scattering in ferromagnet-superconductor junctions

We study the interplay of superconducting and ferromagnetic correlations on charge transport in different geometries with a focus on both a quantum point contact as well as a quantum dot in the even and the odd state with and without spin-active scattering at the interface. In order to obtain a complete picture of the charge transport we calculate the full counting statistics in all cases and compare the results with experimental data. We show that spin-active scattering is an essential ingredient in the description of quantum point contacts. This holds also for quantum dots in an even charge state whereas it is strongly suppressed in a typical Kondo situation. We explain this feature by the strong asymmetry of the hybridisations with the quantum dot and show how Kondo peak splitting in a magnetic field can be used for spin filtering. For the quantum dot in the even state spin-active scattering allows for an explanation of the experimentally observed mini-gap feature.Comment: 14 pages, 7 figures, accepted by PR

Nanotransformation and current fluctuations in exciton condensate junctions

We analyze the nonlinear transport properties of a bilayer exciton condensate that is contacted by four metallic leads by calculating the full counting statistics of electron transport for arbitrary system parameters. Despite its formal similarity to a superconductor the transport properties of the exciton condensate turn out to be completely different. We recover the generic features of exciton condensates such as counterpropagating currents driven by excitonic Andreev reflections and make predictions for nonlinear transconductance between the layers as well as for the current (cross)correlations and generalized Johnson-Nyquist relationships. Finally, we explore the possibility of connecting another mesoscopic system (in our case a quantum point contact) to the bottom layer of the exciton condensate and show how the excitonic Andreev reflections can be used for transforming voltage at the nanoscale.Comment: 5 pages, 4 figures, accepted by PR

Efeito do armazenamento a baixa temperatura na viabilidade do ovo de Thaumastocoris peregrinus (Hemiptera, Thaumastocoridae).

Resumo

Influência da densidade de fêmeas no parasitismo de Cleruchoides noackae (Hymenoptera, Mymaridae) sobre ovos de Thaumastocoris peregrinus (Hemiptera, Thaumastocoridae).

Resumo

Avaliação de Cleruchoides noackae em Laboratório e Campo em Minas Gerais, Brasil.

Resumo