Controlling the polarisation correlation of photon pairs from a charge-tuneable quantum dot

Correlation between the rectilinear polarisations of the photons emitted from the biexciton decay in a single quantum dot is investigated in a device which allows the charge-state of the dot to be controlled. Optimising emission from the neutral exciton states maximises the operating efficiency of the biexciton decay. This is important for single dot applications such as a triggered source of entangled photons. As the bias on the device is reduced correlation between the two photons is found to fall dramatically as emission from the negatively charged exciton becomes significant. Lifetime measurements demonstrate that electronic spin-scattering is the likely cause.Comment: 3 figure

Inversion of exciton level splitting in quantum dots

The demonstration of degeneracy of exciton spin states is an important step toward the production of entangled photon pairs from the biexciton cascade. We measure the fine structure of exciton and biexciton states for a large number of single InAs quantum dots in a GaAs matrix; the energetic splitting of the horizontally and vertically polarized components of the exciton doublet is shown to decrease as the exciton confinement decreases, crucially passing through zero and changing sign. Thermal annealing is shown to reduce the exciton confinement, thereby increasing the number of dots with splitting close to zero

Soliton Solutions for ABS Lattice Equations II: Casoratians and Bilinearization

In Part I [arXiv:0902.4873 [nlin.SI]] soliton solutions to the ABS list of multi-dimensionally consistent difference equations (except Q4) were derived using connection between the Q3 equation and the NQC equations, and then by reductions. In that work central role was played by a Cauchy matrix. In this work we use a different approach, we derive the $N$-soliton solutions following Hirota's direct and constructive method. This leads to Casoratians and bilinear difference equations. We give here details for the H-series of equations and for Q1; the results for Q3 have been given earlier.Comment: 36 page

Critical coupling for dynamical chiral-symmetry breaking with an infrared finite gluon propagator

We compute the critical coupling constant for the dynamical chiral-symmetry breaking in a model of quantum chromodynamics, solving numerically the quark self-energy using infrared finite gluon propagators found as solutions of the Schwinger-Dyson equation for the gluon, and one gluon propagator determined in numerical lattice simulations. The gluon mass scale screens the force responsible for the chiral breaking, and the transition occurs only for a larger critical coupling constant than the one obtained with the perturbative propagator. The critical coupling shows a great sensibility to the gluon mass scale variation, as well as to the functional form of the gluon propagator.Comment: 19 pages, latex, 3 postscript figures, uses epsf.sty and epsf.tex. To be published in Phys. Lett.

Iron oxidation at low temperature (260–500 C) in air and the effect of water vapor

The oxidation of iron has been studied at low temperatures (between 260 and 500 C) in dry air or air with 2 vol% H2O, in the framework of research on dry corrosion of nuclear waste containers during long-term interim storage. Pure iron is regarded as a model material for low-alloyed steel. Oxidation tests were performed in a thermobalance (up to 250 h) or in a laboratory furnace (up to 1000 h). The oxide scales formed were characterized using SEM-EDX, TEM, XRD, SIMS and EBSD techniques. The parabolic rate constants deduced from microbalance experiments were found to be in good agreement with the few existing values of the literature. The presence of water vapor in air was found to strongly influence the transitory stages of the kinetics. The entire structure of the oxide scale was composed of an internal duplex magnetite scale made of columnar grains and an external hematite scale made of equiaxed grains. 18O tracer experiments performed at 400 C allowed to propose a growth mechanism of the scale

Determinação, identidade atlética e personalidade em praticantes e não praticantes de ginástica rítmica

A personalidade pode representar papel importante no desempenho desportivo e exerce uma forte contribuição para a formação da identidade dos sujeitos (Costa & McCrae, 1992). A determinação (Grit), é definida como perseverança e paixão para metas a longo prazo, é um traço de personalidade diferencial que faz com que os indivíduos com coeficiente de inteligência equiparados possam alcançar o sucesso (Duckworth, Peterson, Matthews & Kelly, 2007). A presente pesquisa teve como objetivo analisar as relações entre os constructos psicológicos Determinação, Identidade Atlética (IA) e Personalidade entre praticantes e não praticantes de Ginástica Rítmica (GR). Para alcançar este objetivo, foram realizados três estudos: uma revisão sistemática de literatura com o objetivo de expor um balanço geral do constructo determinação; um estudo que analisou as relações entre os constructos psicológicos e um estudo para analisar as relações entre variáveis de perfil sócio demográfico e determinação. A revisão sistemática de literatura foi composta por 23 artigos que seguiram as diretrizes de Petticrew e Roberts (2006). Participaram no estudo 109 meninas com idade superior a 12 anos (M = 14,42; anos SD = 2,26) das quais 49 eram praticantes de GR e 60 não eram praticantes. Para mensurar os constructos psicológicos foram utilizados os questionários “Grit Scale” (Duckworth, Peterson, Matthews & Kelly, 2007) adaptado para a versão da língua portuguesa em processo de validação fatorial exploratória (Cunha, Rosado & Pesca, 2017) intitulado como Grit Scale – 6 itens; a versão adaptada do “AIMS” de 10 itens na língua portuguesa (Cabrita, Rosado, Leite & Sousa, 2014) e o Inventario de Avaliação da Personalidade NEO-FFI-20 na versão portuguesa (Bertoquini & Ribeiro, 2005). A maior parte dos estudos ainda são de origem norte americana e as pesquisas sugerem relações positivas de determinação com os constructos centrais da Psicologia Positiva, como uma forma de buscar a felicidade através do sucesso e da Psicologia Cognitiva, uma vez que os estudos apontam que a determinação está relacionada a conscienciosidade, uma das dimensões da Personalidade. Após análises de correlação de Pearson e ANOVA “one-way” foi constatado que Determinação, IA e Personalidade obtiveram relações positivas e significativas. Adicionalmente, as dimensões conscienciosidade e extroversão, dos traços de personalidade, também foram relacionadas com a determinação. Apenas a prática desportiva foi fator determinante para níveis de determinação mais elevados. A escassez de referências aponta a necessidade de futuras pesquisas sobre a determinação uma vez que há resultados divergentes na literatura e lacunas a serem preenchidas principalmente no âmbito desportivo. O desporto alavanca níveis de determinação e este traço está relacionado a personalidade e a identidade do atleta.The personality may an important role in sports performance and can make a strong contribution to the formation of the subjects' identity (Costa & Mc Crae, 1992). Grit is perseverance and passion for long-term goals, and is a trait of differential personality that makes people with equal IQs achieve success (Duckworth, Peterson, Matthews & Kelly, 2007). The aim of present research was to analyze the relations between the psychological constructs Grit, Athletic Identity and Personality between gymnasts and non-gymnasts of Rhythmic Gymnastics (GR). To achieve this goal, three studies were carried out: a systematic review of literature with the objective of exposing a general balance of the grit construct; A study that analyzed the relationships between psychological constructs and a study to analyze the relationships between profile variables and grit. 109 girls aged 12 years and over (M = 14.42; years SD = 2.26) were studied. Of these, 49 were RG gminasts and 60 were non-gymnasts, and 23 studies comprised a systematic literature review in which they followed guidelines the Petticrew & Roberts (2006). The measure the psychological constructs, the "Grit Scale" (Duckworth, Peterson, Matthews & Kelly (2007) were used questionnaires adapted to the Portuguese language version in the validation process (Cunha, Rosado & Pesca, 2017); The adapted version of the "AIMS" of 10 ítems in the Portuguese language (Cabrita, Rosado, Leite & Sousa, 2014) and the NEO-FFI-20 personality assessment inventory in the Portuguese version (Bertoquini and Ribeiro, 2005). Most studies are still of American origin, and research suggests positive gritting relationships with the central constructs of positivist psychology, as a way of pursuing happiness through success, and cognitive psychology since studies point out that grit is related to Conscientiousness. After analysis of Pearson correlation and ANOVA one-way, Grit, AI and Personality obtained positive and significant relationships. Additionally, the dimensions of conscientiousness and extraversion of personality traits were also related to the grit. Only sporting practice was a determining factor for higher grit levels. The scarcity of references indicates the need for future research on the grit since there are divergent results in the literature and gaps to be filled mainly in the sports field. The sport leverages levels of grit and this trait is related to personality and the identity of the athlete

Influence of Rotations on the Critical State of Soil Mechanics

The ability of grains to rotate can play a crucial role on the collective behavior of granular media. It has been observed in computer simulations that imposing a torque at the contacts modifies the force chains, making support chains less important. In this work we investigate the effect of a gradual hindering of the grains rotations on the so-called critical state of soil mechanics. The critical state is an asymptotic state independent of the initial solid fraction where deformations occur at a constant shear strength and compactness. We quantify the difficulty to rotate by a friction coefficient at the level of particles, acting like a threshold. We explore the effect of this particle-level friction coefficient on the critical state by means of molecular dynamics simulations of a simple shear test on a poly-disperse sphere packing. We found that the larger the difficulty to rotate, the larger the final shear strength of the sample. Other micro-mechanical variables, like the structural anisotropy and the distribution of forces, are also influenced by the threshold. These results reveal the key role of rotations on the critical behavior of soils and suggest the inclusion of rotational variables into their constitutive equations.Comment: 9 pages, 8 figures, Accepted for publication in Computer Physics Communication

Online Self-Healing Control Loop to Prevent and Mitigate Faults in Scientific Workflows

Scientific workflows have become mainstream for conducting large-scale scientific research. As a result, many workflow applications and Workflow Management Systems (WMSs) have been developed as part of the cyberinfrastructure to allow scientists to execute their applications seamlessly on a range of distributed platforms. In spite of many success stories, a key challenge for running workflow in distributed systems is failure prediction, detection, and recovery. In this paper, we present a novel online self-healing framework, where failures are predicted before they happen, and are mitigated when possible. The proposed approach is to use control theory developed as part of autonomic computing, and in particular apply the proportional-integral-derivative controller (PID controller) control loop mechanism, which is widely used in industrial control systems, to mitigate faults by adjusting the inputs of the mechanism. The PID controller aims at detecting the possibility of a fault far enough in advance so that an action can be performed to prevent it from happening. To demonstrate the feasibility of the approach, we tackle two common execution faults of the Big Data era—data footprint and memory usage. We define, implement, and evaluate PID controllers to autonomously manage data and memory usage of a bioinformatics workflow that consumes/produces over 4.4TB of data, and requires over 24TB of memory to run all tasks concurrently. Experimental results indicate that workflow executions may significantly benefit from PID controllers, in particular under online and unknown conditions. Simulation results show that nearly-optimal executions (slowdown of 1.01) can be attained when using our proposed control loop, and faults are detected and mitigated far in advance

Diffusion-weighted imaging for evaluating inflammatory activity in Crohn's disease: comparison with histopathology, conventional MRI activity scores, and faecal calprotectin

PURPOSE: To evaluate whether the extent of enteric diffusion-weighted imaging (DWI) signal abnormality reflects inflammatory burden in Crohn's disease (CD), and to compare qualitative and quantitative grading. METHODS: 69 CD patients (35 male, age 16-78) undergoing MR enterography with DWI (MRE-D) and the same-day faecal calprotectin (cohort 1) were supplemented by 29 patients (19 male, age 16-70) undergoing MRE-D and terminal ileal biopsy (cohort 2). Global (cohort 1) and terminal ileal (cohort 2) DWI signal was graded (0 to 3) by 2 radiologists and segmental apparent diffusion coefficient (ADC) calculated. Data were compared to calprotectin and a validated MRI activity score [MEGS] (cohort 1), and a histopathological activity score (eAIS) (cohort 2) using nonparametric testing and rank correlation. RESULTS: Patients with normal (grades 0 and 1) DWI signal had lower calprotectin and MEGS than those with abnormal signal (grades 2 and 3) (160 vs. 492 μg/l, p = 0.0004, and 3.3 vs. 21, p  120 μg/l) were 83% and 52%, respectively. There was a negative correlation between ileal MEGS and ADC (r = -0.41, p = 0.017). There was no significant difference in eAIS between qualitative DWI scores (p = 0.42). Mean ADC was not different in those with and without histological inflammation (2077 vs. 1622 × 10(-6)mm(2)/s, p = 0.10) CONCLUSIONS: Qualitative grading of DWI signal has utility in defining the burden of CD activity. Quantitative ADC measurements have poor discriminatory ability for segmental disease activity