Plasmonic crystal demultiplexer and multiports

Artificially built periodic optical structures in dielectric and metallic media have generated considerable interest due to their potential for optical device miniaturization. In this context plasmonics, i.e., optics based on surface plasmon polaritons (SPPs) offers new exciting prospects. SPPs are hybrid light/electron surface waves at the interface between a dielectric and a metal and as such hold the potential for 2D optical functionality. Indeed, SPP elements as mirrors, splitters and interferometers have been recently demonstrated. However, for plasmonics to qualify at the information technology level requires necessarily the realization of wavelength division (demultiplexing) which constitutes a fundamental ingredient of optical communication. In the following we experimentally demonstrate 2D SPP demultiplexing in the visible spectral range by using photonic crystals for SPPs (plasmonic crystals). In addition, we demonstrate that plasmonic crystal are capable of realizing integrated linear multiports which could constitute building blocks of analog or quantum optical computing.Comment: Nano Lett.7, 1697 (2007

Spherical nanoindentation – advancements and prospects towards its application as a multifunctional testing technique

With the development of modern high-performance materials and components, cases increase where conventional testing techniques used for the mechanical characterization miss their target. Material fabrication at a bench scale, miniaturization and not least cost-effectiveness yearn for a highly reliable, fast and highly automatable testing technique. Even though uniaxial micromechanical tests on micro-pillars or -tensile samples are well suitable for the extraction of flow curves, they face the problem of elaborate specimen manufacturing. Spherical nanoindentation could be a candidate technique to overcome the mentioned drawbacks, since time needed for sample preparation is tremendously reduced. The present study will outline solutions of existing problems, which may lay the foundation for spherical nanoindentation to become a widely-used testing technique. Main objections concerning tip imperfections will be resolved by modifying the calibration procedure, and validated on a broad spectrum of materials independent of the indenter tip radius. Once the actual tip shape is available, displacement-time profiles can be designed to guarantee constant strain-rates during testing and thus permit the determination of the strain-rate sensitivity for rate-dependent materials. Finally, the comparison between nanoindentation flow curves and uniaxial tests will evidence that spherical indentation is a highly reliable technique for the extensive mechanical characterization of modern high-performance materials and show its high potential as a multifunctional standard testing technique. Please click Additional Files below to see the full abstract

A comprehensive study on the deformation behavior of ultra-fine grained and ultra-fine porous Au at elevated temperatures

Modern design and engineering of highly efficient devices and machines demand innovative materials to satisfy requirements such as high strength at low density. The purpose of this study was to compare mechanical properties and deformation behavior of ultra-fine grained Au and its ultra-fine porous counterpart, both fabricated from the same base material. Microstructural investigations of the foam surrendered a ligament size of approximately 100 nm consisting of ~60 nm grains in average. The ultra-fine grained Au features a mean grain size of 250 nm. Nanoindentation is a convenient technique to obtain materials properties at ambient but also at non-ambient conditions and elevated temperatures. In this work, a broad indentation test series was performed in order to determine hardness, Young’s modulus, strain-rate sensitivity, and activation volume between room and elevated temperatures up to 300 °C for both materials. Due to the small characteristic dimensions, high hardness values were noted for both materials, which rapidly drop at elevated temperatures. In addition, an enhanced strain-rate sensitivity accompanied by low activation volumes was determined, increasing with elevated temperatures for both states. This can clearly be associated with interactions between dislocations and interphases. Moreover, for ultra-fine porous Au, a considerable increase of hardness was observed after annealing, which potentially can be attributed to starvation of mobile dislocations not occurring in the ultra-fine grained state. Cross-sections of indentations in ultra-fine porous Au combined with quantitative analysis of the resulting porosity maps allow visualizing the occurring deformation of the foam properly, showing distinct differences for tests at varying conditions. While the as-fabricated material exhibits distributed plasticity underneath the indent, this changes to strongly localized failure events in the annealed condition. At increased temperature, the deformation morphology reverts to more distributed deformation favored by the additional thermal activation

Learning Arbitrary-Goal Fabric Folding with One Hour of Real Robot Experience

Manipulating deformable objects, such as fabric, is a long standing problem in robotics, with state estimation and control posing a significant challenge for traditional methods. In this paper, we show that it is possible to learn fabric folding skills in only an hour of self-supervised real robot experience, without human supervision or simulation. Our approach relies on fully convolutional networks and the manipulation of visual inputs to exploit learned features, allowing us to create an expressive goal-conditioned pick and place policy that can be trained efficiently with real world robot data only. Folding skills are learned with only a sparse reward function and thus do not require reward function engineering, merely an image of the goal configuration. We demonstrate our method on a set of towel-folding tasks, and show that our approach is able to discover sequential folding strategies, purely from trial-and-error. We achieve state-of-the-art results without the need for demonstrations or simulation, used in prior approaches. Videos available at: https://sites.google.com/view/learningtofol

Thermally activated processes in materials probed by nanoindentation - challenges, solutions, and insights

Nanoindentation experiments are widely used for assessing the local mechanical properties of materials. In recent years some new exciting developments were established for also analyzing thermally activated processes during deformation using indentation based techniques, namely nanoindentation strain rate jump and nanoindentation long term creep tests. For these different methods, control of the indenter tip movement as well as determination of the correct contact conditions are hugely important to assure reliable data. In fact, long term nanoindentation tests are prone to be strongly influenced by thermal drift, starting at room temperature but even more intensified for elevated temperatures. This talk will first focus on experimental issues and challenges, but also solutions during advanced nanoindentation testing to overcome thermal drift influences, as demonstrated for fused silica and ultra-fine grained (ufg) Au. Special focus will be on high temperature testing, different testing methodologies will be described, and it will be demonstrated how distinct indentation time and indentation depths related errors influence the basic results. In the second part different results on single crystal (sx) and ufg Cr but also on the intermetallic phase Mg17Al12 are presented. For Mg17Al12, it was observed that the deformation behavior, especially in terms of thermally activated processes, is significantly changing over temperature. While at room temperature up to 125°C deformation is dominated by jerky flow and a slight negative strain-rate sensitivity due to dislocation pinning and the Portevin - Le Chatelier effect, overcoming 150°C the material behaves remarkably different. In this regime the indentation data show significant ductile deformation behavior with large pile-up formation and a pronounced strain rate sensitivity in the superplastic regime, where the deformation is sustained by dislocation glide and climb. Sx and ufg Cr also show significant changes in deformation behavior with temperature. At ambient conditions, both microstructures show an enhanced strain-rate sensitivity due to the large thermally activated component in the flow stress. Overcoming the materials specific temperature Tc (~150°C for Cr) the behavior changes. For sx Cr the apparent strain-rate sensitivity diminishes completely, while for the ufg state the strain-rate sensitivity increases due to the increased importance of dislocation – grain boundary interactions paired with a change in the dominating deformation mechanism

Facilitating low-carbon living? A comparison of intervention measures in different community-based initiatives

The challenge of facilitating a shift towards sustainable housing, food and mobility has been taken up by diverse community-based initiatives ranging from ‘top-down’ approaches in low-carbon municipalities to ‘bottom-up’ approaches in intentional communities. This paper compares intervention measures of these two types, focusing on their potential of re-configuring daily housing, food and mobility practices. Taking up critics on dominant intervention framings of diffusing low-carbon technical innovations and changing individual behaviour, we draw on social practice theory for the empirical analysis of four case studies. Framing interventions in relation to re-configuring daily practices, the paper reveals differences and weaknesses of current low-carbon measures of community-based initiatives in Germany and Austria. Low-carbon municipalities mainly focus on introducing technologies and offering additional infrastructure and information to promote low-carbon practices. They avoid interfering into residents’ daily lives and do not restrict carbon-intensive practices. In contrast, intentional communities base their interventions on the collective creation of shared visions, decisions and rules and thus provide social and material structures, which foster everyday low-carbon practices and discourage carbon-intensive ones. The paper discusses the relevance of organisational and governance structures for implementing different types of low-carbon measures and points to opportunities for broadening current policy strategies

Investigating patterns of local climate governance: how low-carbon municipalities and intentional communities intervene into social practices

The local level has gained prominence in climate policy and governance in recent years as it is increasingly perceived as privileged arena for policy experimentation and social and institutional innovation. Yet, the success of local climate governance in industrialised countries has been limited so far. One reason may be that local communities focus too much on strategies of technology-oriented ecological modernisation (EM) and individual behaviour change and too little on strategies that target unsustainable social practices and their embeddedness in complex patterns of practices. In this paper we assess and compare the strategies of ‘low-carbon municipalities’ (top-down initiatives) and those of ‘intentional communities’ (bottom-up initiatives). We are interested to find out to what extent and in which ways each community type intervenes in social practices to curb carbon emissions and to explore the scope for further and deeper interventions on the local level. Employing an analytical framework based on social practice theory we identify characteristic patterns of intervention for each community type. We find that low-carbon municipalities face tenacious difficulties in transforming carbon-intensive social practices. While offering some additional low-carbon choices, their ability to reduce carbon-intensive practices is very limited. Their focus on efficiency and individual choice shows little transformative potential. Intentional communities, by contrast, have more institutional and organisational options to intervene into the web of social practices. Finally, we explore to what extent low-carbon municipalities can learn from intentional communities and propose strategies of hybridisation for policy innovation to combine the strengths of both models

Investigating patterns of local climate governance: How low-carbon municipalities and intentional communities intervene in social practices

The local level has gained prominence in climate policy and governance in recent years as it is increasingly perceived as a privileged arena for policy experimentation and social and institutional innovation. However, the success of local climate governance in industrialized countries has been limited. One reason may be that local communities focus too much on strategies of technology-oriented ecological modernization and individual behavior change and too little on strategies that target unsustainable social practices and their embeddedness in complex socioeconomic patterns. In this paper we assess and compare the strategies of "low-carbon municipalities" (top-down initiatives) and those of "intentional communities" (bottom-up initiatives). We were interested to determine to what extent and in which ways each community type intervenes in social practices to curb carbon emissions and to explore the scope for further and deeper interventions on the local level. Using an analytical framework based on social practice theory we identify characteristic patterns of intervention for each community type. We find that low-carbon municipalities face difficulties in transforming carbon-intensive social practices. While offering some additional low-carbon choices, their ability to reduce carbon-intensive practices is very limited. Their focus on efficiency and individual choice shows little transformative potential. Intentional communities, by contrast, have more institutional and organizational options to intervene in the web of social practices. Finally, we explore to what extent low-carbon municipalities can learn from intentional communities and propose strategies of hybridization for policy innovation to combine the strengths of both models