Improving light harvesting in polymer photodetector devices through nanoindented metal mask films

To enhance light harvesting in organic photovoltaic devices, we propose the incorporation of a metal (aluminum) mask film in the system’s usual layout. We fabricate devices in a sandwich geometry, where the mask (nanoindented with a periodic array of holes of sizes d and spacing s) is added between the transparent electrode and the active layer formed by a blend of the semiconducting polymer P3HT and substituted fullerene. Its function is to promote trapping of the incident light into the device’s cavity (the region corresponding to the active layer). For d, we set a value that allows light diffraction through the holes in the relevant absorption range of the polymer. To optimize the mask structure, we consider a very simple model to determine the s leading to trapped fields that are relatively intense and homogeneous within the device. From measurements of the action spectra, we show that, indeed, such architecture can considerably improve the resulting photocurrent efficiencies—one order of magnitude in the best situation studied.

Return of the Great Spaghetti Monster : Learnings from a Twelve-Year Adventure in Web Software Development

The widespread adoption of the World Wide Web has fundamentally changed the landscape of software development. Only ten years ago, very few developers would write software for the Web, let alone consider using JavaScript or other web technologies for writing any serious software applications. In this paper, we reflect upon a twelve-year adventure in web development that began with the development of the Lively Kernel system at Sun Microsystems Labs in 2006. Back then, we also published some papers that identified important challenges in web-based software development based on established software engineering principles. We will revisit our earlier findings and compare the state of the art in web development today to our earlier learnings, followed by some reflections and suggestions for the road forward.Peer reviewe

Depth-Sensing Indentation on REBa2Cu3O(7-\delta) Single Crystals obtained from Xenotime Mineral

A natural mixture of heavy rare earths oxides extracted from xenotime mineral have been used to prepare large single crystals of high-temperature REBa2Cu3O(7-\delta) superconductor grown using the CuO-BaO self-flux method. Its mechanical properties along the ab-plane were characterized using instrumented indentation. Hardness and elastic modulus were obtained by the Oliver and Pharr method and corresponds to 7.4 \pm 0.2 GPa and in range 135-175 GPa at small depths, respectively. Increasing the load promotes the nucleation of lateral cracks that causes a decrease in hardness and the measured elastic modulus by instrumented indentation at higher loads. The indentation fracture toughness was estimated by measuring the radial crack length from cube-corner indentations at various loads and was 0.8 \pm 0.2 MPa.m1/2. The observed slip systems of REBa2Cu3O(7-\delta) single crystals were [100](001) and [010](001), the same as for YBa2Cu3O(7-\delta) single crystals. The initial stages of deformation and fracture in the indentation process were investigated. The hardness and elastic modulus were not strongly modified by the crystallographic orientation in the ab-plane. This was interpreted in terms of the resolved shear stresses in the active slip systems. Evidence of cracking along the {100} and {110} planes on the ab-plane was observed. As a conclusion, the mechanical properties of REBa2Cu3O(7-\delta) single crystals prepared from xenotime are equivalent to those of YBa2Cu3O(7-\delta) single crystals produced by conventional rare earths oxides.Comment: The paper will appear in Volume 42 (2012) of the Brazilian Journal of Physic

Mechanical and tribological properties of a sintered glass-ceramic compared to granite and porcelainized stoneware

a b s t r a c t Mechanical and tribological properties of a partially crystallized sintered glass-ceramic were compared to two commercial floor tiles: black granite and porcelainized stoneware. Mechanical properties, hardness and elastic modulus were evaluated by instrumented indentation. Friction coefficient and wear characterization were evaluated using a reciprocating ball-on-flat tribometer in two controlled environments: air with relative humidity of 53% and under running water at 23 • C. The sintered glass-ceramic and porcelainized stoneware presented similar mechanical and tribological properties. Regarding the mechanical and tribological properties, the results suggest that this glass-ceramic is suitable to be used as industrial tile

Influência da cristalização na dureza, módulo de elasticidade e tenacidade à fratura por indentação em vitrocerâmicas de dissilicato de lítio (Li2 O.2SiO2 )

Resumo O efeito da cristalização sobre as propriedades mecânicas (dureza, módulo de elasticidade e tenacidade à fratura por indentação) do vitrocerâmico dissilicato de lítio Li2O.2SiO2 foi investigado pela técnica de indentação (indentação instrumentada, microdurezas Vickers e Knoop). Os tratamentos térmicos para cristalização foram realizados em duas etapas: nucleação em 475 °C por 2, 5 e 10 h, e crescimento de cristais em 563 °C por 0,5, 1, 2, 3 e 24 h. Foram determinadas as frações cristalizadas, que foram correlacionadas com a dureza, o módulo de elasticidade e a tenacidade à fratura por indentação. Os testes de microdureza foram realizados utilizando-se penetradores Vickers e Knoop. O módulo de elasticidade das regiões amorfas e cristalinas foi medido por testes de indentação instrumentada com um indentador Berkovich, realizado em cada fase separadamente. A modificação da morfologia das trincas geradas por indentação com pontas piramidais foi avaliada para amostras com diferentes frações cristalinas utilizando microscopia óptica. Foi discutida a alteração dos padrões de trincas, para diferentes graus de cristalização, na forma de determinação da tenacidade à fratura por indentação. Os maiores valores de dureza e tenacidade foram obtidos em amostras com 100% de fração cristalina, sendo que maiores tempos de nucleação de cristais levaram a melhores valores nas propriedades mecânicas investigadas. Os valores obtidos para amostras 100% de fração cristalina foram: tenacidade à fratura por indentação de 1,8 MPa.m1/2, microdureza Knoop de 7,2 GPa e módulo de elasticidade de 155 GPa

Mechanical and tribological properties of a sintered glass-ceramic compared to granite and porcelainized stoneware

Mechanical and tribological properties of a partially crystallized sintered glass-ceramic were compared to two commercial floor tiles: black granite and porcelainized stoneware. Mechanical properties, hardness and elastic modulus were evaluated by instrumented indentation. Friction coefficient and wear characterization were evaluated using a reciprocating ball-on-flat tribometer in two controlled environments: air with relative humidity of 53% and under running water at 23 degrees C. The sintered glass-ceramic and porcelainized stoneware presented similar mechanical and tribological properties. Regarding the mechanical and tribological properties, the results suggest that this glass-ceramic is suitable to be used as industrial tile. (C) 2011 Elsevier B.V. All rights reserved.CNPqCAPESFAPESP[2007/08179-9

Designing a MOOC as an Agent-Platform Aggregating Heterogeneous Virtual Learning Environments

With the emergence of cloud technologies on the one hand and social networks on the other hand, the possibilities for e-learning have been considerably enhanced in the latest years. Virtual Learning Environments (VLE) can now indeed contain a huge amount of learning resources; in parallel large user communities are available in social networks. Nevertheless, these systems remain different but, by using these heterogeneous software environments together, the possibilities for interaction could be multiplied. That is why, this paper suggests building a Massive Open Online Course (MOOC) environment through a Multi-Agent System (MAS) working as a virtual abstraction layer over heterogeneous software platforms. The idea is to aggregate different traditional VLE to dispose of the learning objects they own as well as other platforms like social networks to furnish an easy access to the MOOC of their large user communities. The MAS design and implementation has been architectured around a real-life organizational pattern – the joint venture – allowing us to deal with the complexity of heterogeneous software environments in the fashion that real-life companies join governance and management. Communication scenarios issued from a field analysis are pointed out in the paper; these are supported by the MOOC platform in the native environment as well as in Facebook. The proposal is indeed validated through the development of a prototype using Facebook as a case study for third-party platform interfacing. We finally highlight the benefits for the user experience