Flexible organic P3HT:PCBM bulk-heterojunction modules with more than 1 year outdoor lifetime

Flexible organic solar cells and modules based on P3ht:PCBM bulk-heterojunctions were fabricated and their lifetime was investigated under laboratory and outdoor conditions. In the laboratory cells were exposed to 1 sun illumination at 65 °C in order to accelerate the degradation. The outdoor behavior of modules was investigated at the Konarka rooftop testing setup in Lowell, MA (USA). We show that these flexible polymer solar cells have a good light stability, passing 1000 h under accelerated light soaking conditions in the laboratory, and that flexible modules survived over 1 year of outdoor exposure without performance losses.     

On the reliability of scanning probe based electrostatic force measurements

The dimensions of semiconductor devices rapidly decreasing, the detection and control of spatial inhomogeneities of material properties on a sub-μm scale becomes essential.For mapping various electrical properties with nearly nm-resolution, scanning probe techniques appear to be ideally suited. However, data evaluation always involves a transfer from measured to real properties by a device depending convolution procedure.We report on our results for different modes of electrical measurements, namely scanning Kelvin probe microscopy (SKM) and scanning capacitance microscopy (SCM) on various sample systems discussing the influence of experimental parameters. In addition, results of finite element simulations on this topic are presented.It turns out that the averaging function correlating real and measured data may appear quite simple, thus making a reliable reconstruction possible. On the other hand, the existence of surface charges can drastically change the results.     

Combining Scan Test and Built-in Self Test

For digital chips containing functional logic and embedded memories, these are usually tested separately: Scan test is used for testing functional logic; Memory Built-in Self Test (MBIST) is run for embedded memories. A new approach is proposed to exercise scan test and MBIST in parallel in order to reduce production test time and improve stress tests. It requires only small additional logic and allows to simultaneously run both test modes. In general, the approach can be used to control simultaneously scan test and any Built-in Self Test (BIST) providing a simple pass/fail result.     

An overview of state of the art and research in the fields of sensible, latent and thermo-chemical thermal energy storage

Due to the increase in volatile renewable power and heat generation (wind or solar), thermal energy storage (TES) has obtained growing importance and interest. The technology can be distinguished into three main types: sensible, latent and thermochemical storage. Apart from low and medium temperature heat applications, high temperature TES also is an attractive means to store power in the form of heat (before the thermodynamic transformation process). Thermochemical storage allows for long duration seasonal storage of energy.     

Instability during cohesive zone growth

Tensile microcracking of quasi-brittle materials is studied by means of micromechanics, based on (i) an elasto-damaging cohesive zone model accounting for cohesive softening and (ii) a dilute distribution of non-interacting microcracks of uniform orientation and size. Considering virgin microcracks (initially without cohesive zones), macroscopic tensile load increase results in growth of cohesive zones ahead of stationary (non-propagating) cracks and, subsequently, in crack propagation which, notably, will be encountered before the cohesive zones are fully developed i.e. onset of instable cohesive zone growth will be encountered at a load level (i) at which tractions are still transmitted across the inner edges of the cohesive zones and (ii) at which the separation at the inner edges of the cohesive zones is smaller than its critical value. Focusing on onset of instable cohesive zone growth, the chosen approach allows for accessing quantities characterizing the stability limit (e.g., the intensity of the macroscopic loading and the opening at the inner edges of the cohesive zones), without raising the need for non-linear Finite Element analyses. It is shown that the tensile macrostrength of materials containing virgin microcracks is larger than the one related to cracks with already initially fully developed cohesive zones, and related strength differences are quantified for a wide class of cohesive softening behavior. The proposed model is validated by comparing model predictions with an exact solution (available for the special case of constant cohesive tractions) and with results from reliable Finite Element analyses. The paper will be of interest for engineers involved in testing and/or in modeling of quasi-brittle media including cementitious materials and rock.     

Rupture Mechanics of Vimentin Intermediate Filament Tetramers

Together with the globular proteins, microtubules and microfilaments, intermediate filaments are one of the three major components of the cytoskeleton in eukaryotic cells. They consist of a dimeric coiled-coil building block, assembled in a very precise, hierarchical fashion into tetramers, forming filaments with characteristic dimensions on the order of several micrometers. Here we focus on the theoretical analysis of the deformation mechanics of vimentin intermediate filaments, a type of intermediate filament expressed in leukocytes, blood vessel endothelial cells, some epithelial cells, and mesenchymal cells such as fibroblasts. The main contribution of this paper is the study of the rupture mechanics of intermediate filament tetramers, representing an assembly of two dimers, by utilizing a statistical Bell model adapted to describe the rupture dynamics of intermediate filaments. Possible deformation mechanisms, including interdimer sliding and uncoiling of the dimer, are illustrated in light of the interdimer adhesion and dimer stability. The analysis reveals that the dominating deformation mechanism depends critically on the interdimer adhesion, solvent condition, and deformation rate.     

Canonical views of dynamic scenes.

The visual recognition of dynamic scenes was examined. The authors hypothesized that the notion of canonical views, which has received strong empirical support for static objects, also holds for dynamic scenes. In Experiment 1, viewpoints orthogonal to the main axis of movement in the scene were preferred over other viewpoints, whereas viewpoints in line with the main axis were least preferred. Experiment 2 provided no empirical evidence for a recognition advantage of canonical viewpoints when presented during the initial learning phase, but Experiment 3 showed a cognitive advantage for canonical viewpoints if they were presented as test stimuli during the recognition test. Overall, the findings suggest that on a phenomenological level, viewers are consciously aware of such viewpoints, and, on a cognitive level, viewers benefit from canonical viewpoints in terms of recognition accuracy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Embedded Multicore Processors and Systems

Unlike desktop PC or server applications, multicore devices used in embedded systems are many and diverse. There are many potential approaches to solving the numerous multicore-related issues. The articles in this issue on embedded multicore processors and systems represent a small sampling of these issues.     

Dissolution of Alumina, Sintering, and Crystallization in Glass Ceramic Composites for LTCC

Sintering and microstructure evolution of alkali-free calcium–alumo–borosilicate glass/α-Al₂O₃ composites (mean particle size ca. 2 μm) for low-temperature cofired ceramics were studied during heating at 5 K/min by heating microscopy, thermal analysis (DTA), X-ray diffraction (XRD), and electron microscopy (SEM). Composites fully densify at ≈830°C, not essentially influenced by the dissolution of alumina and glass crystallization. Thus wollastonite, as first crystalline phase, was detectable at 840°C. Above 900°C, a pronounced crystallization of anorthite is evident, reaching 60 wt% at 1050°C. Rietveld analyses of XRD data revealed that anorthite precipitates at the expenses of alumina, which declines from ≈33 to <10 wt%, and wollastonite, which fully declines from its maximum of ≈19 wt%. Based on XRD, we discuss the evolution of crystal mass fractions, the residual glass composition, the glass viscosity, and the effective shear viscosity of the composites under study during heating.