Anisotropic Electron Spin Lifetime in (In,Ga)As/GaAs (110) Quantum Wells

Anisotropic electron spin lifetimes in strained undoped (In,Ga)As/GaAs (110) quantum wells of different width and height are investigated by time-resolved Faraday rotation and time-resolved transmission and are compared to the (001)-orientation. From the suppression of spin precession, the ratio of in-plane to out-of-plane spin lifetimes is calculated. Whereas the ratio increases with In concentration in agreement with theory, a surprisingly high anisotropy of 480 is observed for the broadest quantum well, when expressed in terms of spin relaxation times.Comment: 4 pages, 4 figures, revise

Research and applications: Artificial intelligence

The program is reported for developing techniques in artificial intelligence and their application to the control of mobile automatons for carrying out tasks autonomously. Visual scene analysis, short-term problem solving, and long-term problem solving are discussed along with the PDP-15 simulator, LISP-FORTRAN-MACRO interface, resolution strategies, and cost effectiveness

One, four or 100 genera? A new classification of the cone snails

International audienc

Experimental analysis of sample-based maps for long-term SLAM

This paper presents a system for long-term SLAM (simultaneous localization and mapping) by mobile service robots and its experimental evaluation in a real dynamic environment. To deal with the stability-plasticity dilemma (the trade-off between adaptation to new patterns and preservation of old patterns), the environment is represented at multiple timescales simultaneously (5 in our experiments). A sample-based representation is proposed, where older memories fade at different rates depending on the timescale, and robust statistics are used to interpret the samples. The dynamics of this representation are analysed in a five week experiment, measuring the relative influence of short- and long-term memories over time, and further demonstrating the robustness of the approach

Phase transitions in optimal unsupervised learning

We determine the optimal performance of learning the orientation of the symmetry axis of a set of P = alpha N points that are uniformly distributed in all the directions but one on the N-dimensional sphere. The components along the symmetry breaking direction, of unitary vector B, are sampled from a mixture of two gaussians of variable separation and width. The typical optimal performance is measured through the overlap Ropt=B.J* where J* is the optimal guess of the symmetry breaking direction. Within this general scenario, the learning curves Ropt(alpha) may present first order transitions if the clusters are narrow enough. Close to these transitions, high performance states can be obtained through the minimization of the corresponding optimal potential, although these solutions are metastable, and therefore not learnable, within the usual bayesian scenario.Comment: 9 pages, 8 figures, submitted to PRE, This new version of the paper contains one new section, Bayesian versus optimal solutions, where we explain in detail the results supporting our claim that bayesian learning may not be optimal. Figures 4 of the first submission was difficult to understand. We replaced it by two new figures (Figs. 4 and 5 in this new version) containing more detail

Variabilidade espacial de características químicas de um Cambissolo cultivado com mamão no semi-árido do Rio Grande do Norte.

Este trabalho teve como objetivo avaliar a variabilidade espacial de atributos químicos de um Cambissolo Háplico léptico (CX), sob cultivo de mamão, por meio da geoestatística. A área amostrada apresentou 43 pontos amostrais, onde foram coletadas amostras de solo, na camada de 0 - 0,2 m, e amostras do tecido foliar. Nas amostras de solo determinou-se pH, CE, Ca, Mg, Na, K, P, C. A partir dessas análises calculou-se a CTC, S, V e PST. Os dados foram avaliados por estatística descritiva e por meio de técnicas geoestatísticas. O coeficiente de variação indicou variabilidade baixa para pH e V (%), e alta para P e CE, enquanto as demais variáveis apresentaram variação alta. A maioria das variáveis apresentaram dependência espacial, sendo o esférico o modelo ajustado a todos os semivariogramas. O efeito pepita teve pequena contribuição na variância total dos dados, indicando forte dependência espacial para todas as variáveis estudadas. Houve pequena variação na distância até onde as características químicas do solo apresentaram dependência espacial

Population inversion of a NAHS mixture adsorbed into a cylindrical pore

A cylindrical nanopore immersed in a non-additive hard sphere binary fluid is studied by means of integral equation theories and Monte Carlo simulations. It is found that at low and intermediate values of the bulk total number density the more concentrated bulk species is preferentially absorbed by the pore, as expected. However, further increments of the bulk number density lead to an abrupt population inversion in the confined fluid and an entropy driven prewetting transition at the outside wall of the pore. These phenomena are a function of the pore size, the non-additivity parameter, the bulk number density, and particles relative number fraction. We discuss our results in relation to the phase separation in the bulk.Comment: 7 pages, 8 Figure

Security Evaluation of Support Vector Machines in Adversarial Environments

Support Vector Machines (SVMs) are among the most popular classification techniques adopted in security applications like malware detection, intrusion detection, and spam filtering. However, if SVMs are to be incorporated in real-world security systems, they must be able to cope with attack patterns that can either mislead the learning algorithm (poisoning), evade detection (evasion), or gain information about their internal parameters (privacy breaches). The main contributions of this chapter are twofold. First, we introduce a formal general framework for the empirical evaluation of the security of machine-learning systems. Second, according to our framework, we demonstrate the feasibility of evasion, poisoning and privacy attacks against SVMs in real-world security problems. For each attack technique, we evaluate its impact and discuss whether (and how) it can be countered through an adversary-aware design of SVMs. Our experiments are easily reproducible thanks to open-source code that we have made available, together with all the employed datasets, on a public repository.Comment: 47 pages, 9 figures; chapter accepted into book 'Support Vector Machine Applications

Wall-Resolved Large Eddy Simulations of Transonic Shock-Induced Flow Separation

This paper reports the wall-resolved large eddy simulations of shock-induced boundary layer separation over an axisymmetric bump for a flow Mach number of 0.875 and a chord-based Reynolds number of 2.763 million. The incoming boundary layer has a momentum-thickness Reynolds number of 6600 at one and a half chord lengths upstream of the leading edge. The calculations simulate the experiment by Bachalo and Johnson (AIAA Journal, Vol. 24, No. 3, 1986), except that the tunnel walls are ignored and the simulations are performed assuming free air with as many as 24 billion grid points. The effects of domain span, grid resolution and time step on the predictions are examined. The results are found to show some sensitivity to the studied parameters. Owing to the outer boundary conditions, the predicted surface pressure distribution as well as the flow separation and reattachment locations tend to agree better with the experimental results from the larger (6 6 ft) tunnel than those from the smaller (2 2 ft) tunnel. The predicted Reynolds shear stress profiles in the separated region differ by as much as 31%from the experimental results that were only obtained in the smaller tunnel. The most accurate surface pressure distribution obtained in this study lies within the scatter of the measurements taken in the two facilities

Efeito da aplicação de doses de boro via foliar na cultura do melão.

Objetivando avaliar o efeito da aplicação via foliar de doses de Boro na cultura do melão foi desenvolvido o presente trabalho em condições de campo. Foram aplicadas 7 doses de Boro através de ácido bórico. O experimento foi desenvolvido em delineamento blocos ao acaso com 3 repetições. Após finalização do experimento, pode-se constatar que das variáveis analisadas apenas a produtividade para o mercado externo (ME), a produtividade comercial (PC), a produtividade total (PT) e o BRIX, responderam à aplicação de doses de B. Para todas as variáveis, o aumento da dose de B proporcionou uma diminuição da produtividade. Apenas o BRIX dos frutos aumentou com o aumento da dose de B.1 CD-ROM