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Two-scale models for reinforced concrete, where the large-scale problems are defined in terms of Euler-Bernoulli beam and Kirchhoff-Love plate models, are constructed. The subscale problem on the Representative Volume Element (RVE) is correspondingly outlined as finding the response of the three-dimensional RVE comprising plain concrete continuum, reinforcement bars and the bond between them. The boundary region of the periodic mesh is modelled with special solid elements, which allow for prescribing the macroscopic input via strongly periodic boundary conditions in an effective way. The effective response of the reinforced concrete RVEs of different sizes subjected to tension and pure bending is investigated for both effective beam and plate models. A series of experiments on reinforced concrete panels subjected to bending and membrane loads is simulated, and the effective moment–curvature response is studied. Within the developed framework, an arbitrary macroscopic loading in terms of membrane strains and curvatures can be prescribed on the RVE, and the corresponding effective response is obtained, making the proposed formulation feasible for future use in an FE2 scheme.

Structural batteries consist of carbon fibres embedded in a porous structural battery electrolyte (SBE), which is composed of two continuous phases: a solid polymer skeleton and a liquid electrolyte containing Li-salt. In this paper we elaborate on a computational modelling framework to study the electro-chemo-mechanical properties of such structural batteries while accounting for the combined action from migration as well as stress-assisted diffusion and convection in the electrolyte. Further, we consider effects of lithium insertion in the carbon fibres, leading to insertion strains. The focus is placed on how the convective contribution to the mass transport within the SBE affects the general electro-chemo-mechanical properties. The numerical results indicate that the convective contribution has only minor influence on the multifunctional performance when the mechanical loading is caused by constrained deformation of constituents during electro-chemical cycling. However, in the case of externally applied mechanical loading that causes severe deformation of the SBE, or when large current pulses are applied, the convective contribution has noticeable influence on the electro-chemical performance. In addition, it is shown that the porosity of the SBE, which affects the effective stiffness as well as the mobility and permeability, has significant influence on the combined mechanical and electro-chemical performance.

Aloe barbadensis Mill. (Aloe) with potential prebiotic effects has been suggested to reduce symptoms in patients with irritable bowel syndrome (IBS). We therefore aimed to determine the effects of an Aloe extract on symptoms of IBS, and evaluate whether effects may be mediated by fecal microbiota and metabolites in a randomized, double-blind, controlled trial.Patient with IBS diagnosed according to the ROME III criteria (all subtypes), received Aloe or control treatment (inulin) for 4 weeks. IBS Symptom Severity Score (IBS-SSS) was assessed, and fecal samples collected before and at end of treatment. Fecal microbiota composition and metabolomic profile were determined.In total, 160 IBS patients completed the study. The overall severity of IBS symptoms was reduced in both Aloe and control treatment groups (P .001, both groups, comparing baseline vs end of treatment), without difference between groups (P = .62). The frequency of responders (IBS-SSS reduction ≥ 50) did not differ between Aloe treatment (n = 33, 39%) and control (n = 34, 45%) (P = .49). However, fecal microbiota and metabolite profiles differed between Aloe, but not control treatment responders and non-responders both before and after treatment.In a mixed group of IBS patients, Aloe was not superior to control treatment, although it showed potential to reduce IBS symptom severity in subsets of IBS patients which could be predicted by fecal microbiota and metabolite profiles. ClinicalTrials.gov no: NCT01400048.

Amorphous tin-gallium oxide (a-SGO) grown with atomic layer deposition was evaluated as a buffer layer in (Ag,Cu)(In,Ga)Se2 thin-film solar cells in search for a new material that is compatible with a variety of absorber band gaps. Hard and soft X-ray photoelectron spectroscopy on absorber/a-SGO stacks combined with J–V characterization of solar cells that were fabricated, showed that the conduction band alignment at the absorber/a-SGO interface can be tuned by varying the cation composition and/or growth temperature. Here, the surface band gap was 1.1 eV for the absorber. However, optical band gap data for a-SGO indicate that a suitable conduction band alignment can most likely be achieved even for wider absorber band gaps relevant for tandem top cells. A best efficiency of 17.0% was achieved for (Ag,Cu)(In,Ga)Se2/a-SGO devices, compared to η = 18.6% for the best corresponding CdS reference. Lower fill factor and open-circuit voltage values were responsible for lower cell efficiencies. The reduced fill factor is explained by a larger series resistance, seemingly related to interface properties, which are yet to be optimized. Some layer constellations resulted in degradation in fill factor during light soaking as well. This may partly be explained by light-induced changes in the electrical properties of a-SGO, according to analysis of Al/SGO/n-Si metal-oxide-semiconductor capacitors that were fabricated and characterized with J–V and C–V. Moreover, the introduction of a 1 nm thick Ga2O3 interlayer between the absorber and a-SGO improved the open-circuit voltage, which further indicates that the absorber/a-SGO interface can be improved.

White etching layers (WELs) in the form of thermally induced martensite spots are often associated to so-called stud defects on rail surfaces and so-called rolling contact fatigue clusters on wheel treads. These defects might promote further material deterioration of rails and wheels and it is thus of importance to deepen the knowledge regarding their initiation mechanisms. The aim of this study is to gain insight into the problem by making qualitative assessments of different operational scenarios, involving various axle loads and amount of friction. To this end, this paper considers crack initiation, quantified through the Jiang–Sehitoglu low cycle fatigue criterion, in the vicinity of pre-existing WELs (in the form of martensite spots) subjected to varying contact load conditions. Three-dimensional finite element analyses are conducted to model phase transformations as well as the resulting residual stresses. It is seen that the contact pressure magnitude and WEL thickness affect the results only moderately, while the traction coefficient has a significant detrimental influence. It is furthermore seen that occasional wheel passages that are off-set in the lateral direction with respect to the WEL spot’s centre might be responsible for crack initiation on the gauge corner side of the rail surface.

A single-scale model for reinforced concrete, comprising the plain concrete continuum, reinforcement bars and the bond between them, is used as a basis for deriving a two-scale model. The large-scale problem, representing the “effective” reinforced concrete solid, is enriched by an effective reinforcement slip variable. The subscale problem on a Representative Volume Element (RVE) is defined by Dirichlet boundary conditions. The response of the RVEs of different sizes was investigated by means of pull-out tests. The resulting two-scale formulation was used in an FE $$^2$$ analysis of a deep beam. Load–deflection relations, crack widths, and strain fields were compared to those obtained from a single-scale analysis. Incorporating the independent macroscopic reinforcement slip variable resulted in a more pronounced localisation of the effective strain field. This produced a more accurate estimation of the crack widths than the two-scale formulation neglecting the effective reinforcement slip variable.

A two-scale model is derived from a fully resolved model where the response of concrete, steel reinforcement, and bond between them are considered. The pertinent “effective” large-scale problem is derived from selective homogenisation in terms of the equilibrium of reinforced concrete considered as a single-phase solid. Variational formulations of the representative volume element problem are established in terms of the subscale displacement fields for the plain concrete continuum and the reinforcement bars. Dirichlet and Neumann boundary conditions (BCs) are imposed on the concrete (pertaining to uniform boundary displacement and constant boundary traction, respectively) and on the reinforcement bars (pertaining to prescribed boundary displacement and vanishing sectional forces, respectively). Different representative volume element sizes and combinations of BCs were used in FE 2 analyses of a deep beam subjected to four-point bending. Results were compared with those of full resolution (single-scale). The most reliable response was obtained for the case of Dirichlet-Dirichlet BCs, with a good match between the models in terms of the deformed shape, force-deflection relation, and average strain. Even though the maximum crack widths were underestimated, the Dirichlet-Dirichlet combination provided an approximate upper bound on the structural stiffness.

Tandem solar cell structures require a high-performance wide band gap absorber as top cell. A possible candidate is CuGaSe2, with a fundamental band gap of 1.7 eV. However, a significant open-circuit voltage deficit is often reported for wide band gap chalcopyrite solar cells like CuGaSe2. In this paper, we show that the open-circuit voltage can be drastically improved in wide band gap p-Cu(In,Ga)Se2 and p-CuGaSe2 devices by improving the conduction band alignment to the n-type buffer layer. This is accomplished by using Zn1−xSnxOy, grown by atomic layer deposition, as a buffer layer. In this case, the conduction band level can be adapted to an almost perfect fit to the wide band gap Cu(In,Ga)Se2 and CuGaSe2 materials. With an improved buffer band alignment for CuGaSe2 absorbers, evaporated in a 3-stage type process, we show devices exhibiting open-circuit voltages up to 1017 mV, and efficiencies up to 11.9%. This is to the best of our knowledge the highest reported open-circuit voltage and efficiency for a CuGaSe2 device. Temperature-dependent current-voltage measurements show that the high open-circuit voltage is explained by reduced interface recombination, which makes it possible to separate the influence of absorber quality from interface recombination in future studies.

Light-on-bias effects were investigated in multiple Cu(In, Ga)Se2 solar cells with varying absorber layer compositions. A strong link between deformations caused by red-on-bias treatments in current–voltage ( IV ) and capacitance–voltage ( CV ) characteristics was demonstrated. Similarly to red-on-bias, blue-on-bias leads to a local increase in static negative charge, but in samples with CdS buffers this increase is shifted away from the interface and has no impact on device performance. IV characteristics of samples with Cd-free buffers are not affected by any light-on-bias treatments, suggesting that CdS plays a vital role in the decreased performance after red-on-bias. A statistical approach was used to search for compositional trends in red-on-bias behavior. Deformation factors were defined for IV and CV characteristics before and after the treatment. While there is a strong relationship between the deformations observed in both types of measurements, the degree to which red-on-bias affects IV and CV curves can vary dramatically. These variations cannot be attributed to changes in composition, since no clear compositional trends were found. Rather, other factors related to sample manufacturing and to the buffer layer seem to have major impact on red-on-bias behavior.

A wide range of applications benefit from transparent semiconducting oxides with tunable electronic properties, for example, electron transport layers in solar cell devices, where the electron affinity is a key parameter. Presently, a few different ternary oxides are used for this purpose, but the attainable electron affinity range is typically limited. In this study, the authors develop a low-temperature atomic layer deposition (ALD) process to grow amorphous Sn1-xGaxOy thin films from dimethylamino-metal complexes and water. This oxide is predicted to provide a wide selection of possible electron affinity values, from around 3 eV for pure Ga2O3 to 4.5 eV for pure SnO2. The ALD process is evaluated for deposition temperatures in the range of 105-195 degrees C by in situ quartz crystal microbalance and with ex situ film characterization. The growth exhibits an ideal-like behavior at 175 degrees C, where the film composition can be predicted by a simple rule of mixture. Depending on film composition, the growth per cycle varies in the range of 0.6-0.8 angstrom at this temperature. Furthermore, the film composition for a given process appears insensitive to the deposition temperature. From material characterization, it is shown that the deposited films are highly resistive, fully amorphous, and homogeneous, with moderate levels of impurities (carbon, nitrogen, and hydrogen). By tailoring the metal cation ratio in films grown at 175 degrees C, the optical bandgap can be varied in the range from 2.7 eV for SnO2 to above 4.2 eV for Ga2O3. The bandgap also varies significantly as a function of deposition temperature. This control of properties indicates that Sn1-xGaxOy is a promising candidate for an electron transport layer material in a wide electron affinity range. Published by the AVS.

Background: Aloe barbadensis Mill. (Aloe) extract was found to be well-tolerated, safe and showed beneficial effects in subsets of irritable bowel syndrome (IBS) patients in two randomized, double-blind, controlled studies. However, the individual studies were underpowered to perform subgroup analyses. We therefore determined the effect of Aloe extract in IBS subgroups in a post hoc analysis combining the results from the two studies. Methods: Data from the two controlled studies comparing Aloe and control treatment taken orally for 4 weeks, were pooled. Both studies included IBS patients fulfilling the ROME III criteria and IBS Symptom Severity Score (IBS-SSS) was assessed. We analysed the effect of Aloe extract on IBS symptom severity and the proportion of responders (IBS-SSS reduction ⩾ 50) in IBS subgroups. Results: In total, 213 IBS patients were included in the post hoc subgroup analyses. A reduction in overall symptom severity, primarily driven by effect on pain severity and frequency, comparing baseline versus end of treatment, was recorded in IBS patients with diarrhoea (IBS-D) receiving Aloe ( n = 38, p Conclusion: Aloe extract improves symptom severity in IBS-D patients and can be regarded as a safe and effective treatment option for this patient group.

Batteries, in particular lithium-ion (Li-ion) batteries, are seen as an alternative to fossil fuels in the automotive sector. Li-ion batteries, however, have some safety issues including possible emissions of toxic fluorine-containing compounds during fire and other abuse situations. This paper demonstrates the possibilities to use the Fourier transform infrared technique to assess some of the most important compounds, including hydrogen fluoride and the far less often measured POF3 and PF5. The study is conducted in the cone calorimeter with different solvents used in Li-ion batteries. The measurements show that, in addition to hydrogen fluoride, with a known high toxicity, POF3 is emitted and can be quantified using Fourier transform infrared.

© 2016 John Wiley and Sons, Ltd. The effective response of microstructures undergoing crack propagation is studied by homogenizing the response of statistical volume elements (SVEs). Because conventional boundary conditions (Dirichlet, Neumann and strong periodic) all are inaccurate when cracks intersect the SVE boundary, we herein use first order homogenization to compare the performance of these boundary conditions during the initial stage of crack propagation in the microstructure, prior to macroscopic localization. Using weakly periodic boundary conditions that lead to a mixed formulation with displacements and boundary tractions as unknowns, we can adapt the traction approximation to the problem at hand to obtain better convergence with increasing SVE size. In particular, we show that a piecewise constant traction approximation, which has previously been shown to be efficient for stationary cracks, is more efficient than the conventional boundary conditions in terms of convergence also when crack propagation occurs on the microscale. The performance of the method is demonstrated by examples involving grain boundary crack propagation modelled by conventional cohesive interface elements as well as crack propagation modelled by means of the extended finite element method in combination with the concept of material forces.

A model is presented for predicting the cell-to-cell propagation of a thermal runaway/fire in a lithium-ion battery cell to neighboring cells by simulating the temperature development in neighboring cells. The modelling work comprises of two major steps; setting up a model of the cells including the thermal properties of the cells, and then validating the model through experiments where the boundary conditions in the validation test must be determined carefully. The model is developed to allow a fast evaluation of several different preventive means of thermal insulation, it is not modelling the pack and cells to a great detail. Still the experimental validation indicates that the model is good enough to fulfil its purpose of the model. A feasibility study using the model is conducted assessing two different types of fire walls between battery modules of 10 cells. The results show that there is a substantial risk for a cascading of thermal events in a battery pack, although cooling systems and fire walls may mitigate these risks.

A two-dimensional computational model for assessment of rolling contact fatigue induced by discrete rail surface irregularities, especially in the context of so-called squats, is presented. Dynamic excitation in a wide frequency range is considered in computationally efficient time-domain simulations of high-frequency dynamic vehicle–track interaction accounting for transient non-Hertzian wheel–rail contact. Results from dynamic simulations are mapped onto a finite element model to resolve the cyclic, elastoplastic stress response in the rail. Ratcheting under multiple wheel passages is quantified. In addition, low cycle fatigue impact is quantified using the Jiang–Sehitoglu fatigue parameter. The functionality of the model is demonstrated by numerical examples.

A strategy for macroscale modeling adaptivity in fully nested two-scale computational (first-order) homogenization based on assumed scale separation is proposed. The representative volume element (RVE) for a substructure pertinent to duplex stainless steel is considered with its typical phase morphology, whereby crystal plasticity with hardening is adopted for the subscale material modeling. The quality of the macroscale constitutive response depends on, among the various assumptions regarding the modeling and discretization, the choice of a prolongation condition defining the deformation mapping from the macro- to the subscale This is the sole source of model error discussed in the present contribution. Two common choices are (in hierarchical order) (1) a "simplified" model based on homogeneous (macroscale) deformation within the RVE, that is the Taylor assumption, and (2) a "reference" model employing Dirichlet boundary conditions on the RVE, which is taken as the exact model in the present context. These errors are assessed via computation of the pertinent dual problem. The results show that both the location and the number of qudrature points where the reference model is employed depend on the chosen goal function.

The effect of initial rail surface irregularities on promoting further surface degradation is investigated. The study concerns rolling contact fatigue formation, in particular in the form of the so-called squats. The impact of surface irregularities in the form of dimples is quantified by peak magnitudes of dynamic contact stresses and contact forces. To this end simulations of two-dimensional (later extended to three-dimensional) vertical dynamic vehicle–track interaction are employed. The most influencing parameters are identified. It is shown that even very shallow dimples might have a large impact on local contact stresses. Peak magnitudes of contact forces and stresses due to the influence of rail dimples are shown to exceed those due to rail corrugation.

Lithium-ion batteries offer great energy and power densities but the thermal stability is an issue of concern compared to other battery technologies. In this study different types of abuse testing have been performed in order to compare the battery safety for different types of commercial lithium-ion battery cells. The results show large differences in abuse response for different cells. Exposed to external heating laptop cells with cobalt based cathode developed a thermal runaway resulting in pressure release, fire and temperatures over 700°C. Lithium iron phosphate (LFP) is known to be a very thermally stable cathode material and LFP-cells showed a significantly lower thermal response, a thermal runaway could, however, be detected for some of the cells in the external heating test. The overcharge tests of LFP-cells were in most cases uneventful but in one case the test resulted in a violent fire. The short circuit tests showed modest temperature increases of the cells in spite of high currents peaking at around 1000 A. Although the development of safer lithium-ion battery cells has been successful thermal runaway events may still occur under extreme conditions.

The wheel–rail contact force is an essential parameter in many aspects in railway mechanics, for instance, in rolling contact fatigue analysis. Since the wheel–rail contact force cannot be measured directly, instrumented wheelsets have been developed to collect the radial strains at certain positions on the wheel web. In this paper, an inverse method to estimate the wheel–rail contact force history based on strain measurements is discussed. In the proposed method, the contact force is determined by minimizing the least-squares discrepancy between measured radial strains and corresponding computed strains from a three-dimensional finite-element model of the wheel. The inverse method is compared with the existing method based on direct extraction of the contact force from combinations of measured strains using Wheatstone bridges. Using synthetic data, it is found that the proposed inverse method is insensitive to the eigenmodes of the wheel, as opposed to the existing method. In addition, noise reduction by using Tikhonov regularization and by choosing proper sampling rates are discussed.

We propose a novel method for iterative learning of point correspondences between image sequences. Points moving on surfaces in 3D space are projected into two images. Given a point in either view, the considered problem is to determine the corresponding location in the other view. The geometry and distortions of the projections are unknown as is the shape of the surface. Given several pairs of point-sets but no access to the 3D scene, correspondence mappings can be found by excessive global optimization or by the fundamental matrix if a perspective projective model is assumed. However, an iterative solution on sequences of point-set pairs with general imaging geometry is preferable. We derive such a method that optimizes the mapping based on Neyman's chi-square divergence between the densities representing the uncertainties of the estimated and the actual locations. The densities are represented as channel vectors computed with a basis function approach. The mapping between these vectors is updated with each new pair of images such that fast convergence and high accuracy are achieved. The resulting algorithm runs in real-time and is superior to state-of-the-art methods in terms of convergence and accuracy in a number of experiments. funding agencies|EC|215078247947|ELLIIT||Strategic Area for ICT research||CADICS||Swedish Government||Swedish Research Council||CUAS||FOCUS||Swedish Foundation for Strategic Research|| DIPLECS GARNICS ELLIIT ETT CUAS FOCUS CADICS

Along with technological developments and increasing competition there is a major incentive for companies to produce and market high quality products before their competitors. In order to conquer a bigger portion of the market share, companies have to ensure the quality of the product in a shorter time frame. To accomplish this task companies try to automate their test processes as much as possible. It is critical to investigate and understand the problems that occur during different stages of test automation processes. In this paper we report on a case study on automatic analysis of non-functional test results. We discuss challenges in the face of continuous integration and deployment and provide improvement suggestions based on interviews at a large company in Sweden. The key contributions of this work are filling the knowledge gap in research about performance regression test analysis automation and providing warning signs and a road map for the industry.

A theoretical and numerical framework to evaluate rolling contact using an arbitrary Lagrangian–Eulerian (ALE) formulation is established. A finite element formulation is implemented featuring cylinder–plate contact, automated mesh refinement, non-reflecting boundary conditions, and the ability to incorporate surface roughness through user-defined gap functions. Presented examples include rolling contact on a corrugated surface and negotiation of a surface discontinuity. Sensitivity and validation analyses are presented and show the model to be robust and the trends in parametric responses to be reasonable as compared to results in literature. Owing to the ALE formulation, the model can be kept very compact and the computational demands very modest.

For many applications, direct measurement of forces in mechanical systems is difficult or even impossible, and indirect measurement involving inverse analysis must be adopted. One such application of major industrial relevance is the accurate measurement of contact forces acting on rolling bodies. In this paper, a newly proposed strategy for load identification is applied to an example problem of a rolling disc. Based on strain gauge measurements, the contact force is estimated using finite element analysis. A virtual calibration procedure is introduced in order to reduce the dependency of the results on the spatial discretization. In particular, the sensitivity of the results with respect to finite element discretization, sensor placement and noise is discussed. Numerical results based on synthetic data illustrate the behavior and accuracy of the proposed strategy.

This paper presents a computational framework for the simulation of planar crack growth (including kinking) driven by "material forces". An evolution law for the crack tip position is formulated, which is shown to give rise to different propagation strategies when subjected to certain assumptions on regularity. Three such strategies, that previously have been proposed in the literature in principle: Explicit Proportional Extension (EPE), Implicit Proportional Extension (IPE) and Maximum Parallel Release Rate (MPRR), are outlined and assessed. Based on the results of two numerical examples, it is concluded that the presented propagation strategies produce almost identical results and are robust with respect to time discretization.

A strategy for macroscale modeling adaptivity in fully nested two-scale computational (first order) homog- enization based on assumed scale separation is proposed. The Representative Volume Element (RVE) for a quite complex substructure pertinent to Duplex Stainless Steel (DSS) is considered, whereby crystal plasticity is adopted for the subscale material modeling. The choice of the pertinent prolongation condition defining the deformation mapping from the macro- to the subscale is the sole source of model error discussed here. Two common choices are (in hierarchical order): (1) ”simplified” model based on homogeneous (macroscale) deformation within the RVE, i.e., the Taylor assumption, (2) ”reference” model employing Dirichlet boundary conditions on the RVE.

The objective of this paper is to investigate geometric and material parameters that affect the interaction of multiple pre-existing (initiated) cracks due to rolling contact fatigue (RCF) loading conditions. In particular, the behaviour of short cracks (head checks) in railway rail is studied. Parameters of interest are initial crack angle and spacing, distribution of initial crack lengths, width of the load/contact zone, and the material properties (in particular, the friction coefficient). Furthermore, the sensitivity of the finite element (FE)-mesh density is investigated. An open question of particular interest is the effect of crack interaction, e.g. shielding, on the prevailing crack spacing. In view of all uncertainties of the material model as well as the three-dimensional geometric complexity of the RCF problem, it is important to obtain a good understanding of the sensitivity of parameter changes. This is achieved in the presented investigation, although it is carried out using simplifying assumptions such as plane strain, linear elasticity, and Hertzian pressure distribution.

At the development of commercial vehicles, it is necessary to develop cost-optimized components with respect to their entire lifetime. This requires a product development process that utilizes the possibility to simulate the product performance using modeling of different degrees of sophistication at any predefined level-of-detail (LOD). For example, the mechanical properties of a cast component depend strongly on the casting process, the simulation of which requires complex modeling at a high LOD. In this article, we propose an optimization strategy that is based on the LOD concept to develop cost-effective components. A sizing optimization of a cast model component is carried out with respect to both the mechanical and thermal response to exemplify the process. In particular, a (novel) global measure of the temperature in energy norm is introduced as an indicator of the “production fitness” to ensure high quality of the material properties. This measure is the thermal counterpart of the well-accepted mechanical strain energy.

Cu2ZnSnS4 (CZTS) solar cells typically include a CdS buffer layer in between the CZTS and ZnO front contact. For sulfide CZTS, with a bandgap around 1.5 eV, the band alignment between CZTS and CdS is not ideal ("cliff-like"), which enhances interface recombination. In this work, we show how a Zn1-xSnxOy (ZTO) buffer layer can replace CdS, resulting in improved open circuit voltages (V-oc) for CZTS devices. The ZTO is deposited by atomic layer deposition (ALD), with a process previously developed for Cu(In,Ga)Se-2 solar cells. By varying the ALD process temperature, the position of the conduction band minimum of the ZTO is varied in relation to that of CZTS. A ZTO process at 95 degrees C is found to give higher Voc and efficiency as compared with the CdS reference devices. For a ZTO process at 120 degrees C, where the conduction band alignment is expected to be the same as for CdS, the Voc and efficiency is similar to the CdS reference. Further increase in conduction band minimum by lowering the deposition temperature to 80 degrees C shows blocking of forward current and reduced fill factor, consistent with barrier formation at the junction. Temperature-dependent current voltage analysis gives an activation energy for recombination of 1.36 eV for the best ZTO device compared with 0.98 eV for CdS. We argue that the Voc of the best ZTO devices is limited by bulk recombination, in agreement with a room temperature photoluminescence peak at around 1.3 eV for both devices, while the CdS device is limited by interface recombination.

Full system simulation seeks to strike a balance between accuracy and performance. Many of its possibilities have been obvious to practitioners in both academia and industry for quite some time, perhaps decades, but Simics supports more of these possibilities within a single framework than other tools do. Simics is a platform for full system simulation that can run actual firmware and completely unmodified kernel and driver code. It is sufficiently abstract to achieve tolerable performance levels, and it provides both functional accuracy for running commercial workloads and sufficient timing accuracy to interface to detailed hardware models. Simics can also run a heterogeneous network of systems from different vendors within the same framework. Exceptionally fast, Simics can easily add new components and leverage older ones within a practical abstraction level. It offers a platform with a rich API and a powerful scripting environment for use in a broad range of applications.

A model for 3D Statistical Volume Elements (SVEs) of mesoscale concrete is presented and employed in the context of computational homogenization. The model is based on voxelization where the SVE is subdivided into a number of voxels (cubes) which are treated as solid finite elements. The homogenized response is compared between 3D and 2D SVEs to study how the third spatial dimension influence the over-all results. The computational results show that the effective diffusivity of the 3D model is about 1.4 times that of the 2D model.

In railway mechanics, the wheel-rail contact force is an important measure in the analysis of different kinds of rolling contact fatigue as well as being used for track condition monitoring. As the contact force cannot be measured directly in the field, one approach is to measure the strain at certain points on an instrumented wheel and upon employing signal processing techniques, extract an estimation of the contact force. However, the obtained force is restricted in terms of frequency content, i.e. the results are not accurate close to certain resonance frequencies of the wheel, [2]. In order to investigate and overcome the experienced problems, a 3-D Finite Element model of the wheel is used in an inverse identification procedure [7], whereby the proper dynamics of the system is taken into account. The method of signal processing using two Wheatstone bridges is compared with the inverse identification scheme by means of synthetic data.

Traffic sign recognition is important for the development of driver assistance systems and fully autonomous vehicles. Even though GPS navigator systems works well for most of the time, there will always be situations when they fail. In these cases, robust vision based systems are required. Traffic signs are designed to have distinct colored fields separated by sharp boundaries. We propose to use locally segmented contours combined with an implicit star-shaped object model as prototypes for the different sign classes. The contours are described by Fourier descriptors. Matching of a query image to the sign prototype database is done by exhaustive search. This is done efficiently by using the correlation based matching scheme for Fourier descriptors and a fast cascaded matching scheme for enforcing the spatial requirements. We demonstrated on a publicly available database state of the art performance. Original Publication: Fredrik Larsson and Michael Felsberg, Using Fourier Descriptors and Spatial Models for Traffic Sign Recognition, SCIA konferens, 23-27 May 2011, Ystad Sweden, 2011, Lecture Notes in Computer Science, Image Analysis, 238-249. http://dx.doi.org/10.1007/978-3-642-21227-7_23 Copyright: Springer

The Fourier descriptors (FDs) is a classical but still popular method for contour matching. The key idea is to apply the Fourier transform to a periodic representation of the contour, which results in a shape descriptor in the frequency domain. FDs are most commonly used to compare object silhouettes and object contours; the authors instead use this well-established machinery to describe local regions to be used in an object-recognition framework. Many approaches to matching FDs are based on the magnitude of each FD component, thus ignoring the information contained in the phase. Keeping the phase information requires us to take into account the global rotation of the contour and shifting of the contour samples. The authors show that the sum-of-squared differences of FDs can be computed without explicitly de-rotating the contours. The authors compare correlation-based matching against affine-invariant Fourier descriptors (AFDs) and WARP-matched FDs and demonstrate that correlation-based approach outperforms AFDs and WARP on real data. As a practical application the authors demonstrate the proposed correlation-based matching on a road sign recognition task. This paper is a postprint of a paper submitted to and accepted for publication in IET Computer Vision and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital Library Fredrik Larsson, Michael Felsberg and Per-Erik Forssen, Correlating Fourier descriptors of local patches for road sign recognition, 2011, IET Computer Vision, (5), 4, 244-254.http://dx.doi.org/10.1049/iet-cvi.2010.0040Copyright: Iethttp://www.theiet.org/ DIPLECS, GARNICS, ELLIIT

A common computer vision task is navigation and mapping. Many indoor navigation tasks require depth knowledge of flat, unstructured surfaces (walls, floor, ceiling). With passive illumination only, this is an ill-posed problem. Inspired by small children using a torchlight, we use a spotlight for active illumination. Using our torchlight approach, depth and orientation estimation of unstructured, flat surfaces boils down to estimation of ellipse parameters. The extraction of ellipses is very robust and requires little computational effort. DIPLECS GARNICS ELLIIT CADICS

This work presents a novel object tracking approach, where the motion model is learned from sets of frame-wise detections with unknown associations. We employ a higher-order Markov model on position space instead of a first-order Markov model on a high-dimensional state-space of object dynamics. Compared to the latter, our approach allows the use of marginal rather than joint distributions, which results in a significant reduction of computation complexity. Densities are represented using a grid-based approach, where the rectangular windows are replaced with estimated smooth Parzen windows sampled at the grid points. This method performs as accurately as particle filter methods with the additional advantage that the prediction and update steps can be learned from empirical data. Our method is compared against standard techniques on image sequences obtained from an RC car following scenario. We show that our approach performs best in most of the sequences. Other potential applications are surveillance from cheap or uncalibrated cameras and image sequence analysis. DIPLECS

In this paper, we present a visual servoing method based on a learned mapping between feature space and control space. Using a suitable recognition algorithm, we present and evaluate a complete method that simultaneously learns the appearance and control of a low-cost robotic arm. The recognition part is trained using an action precedes perception approach. The novelty of this paper, apart from the visual servoing method per se, is the combination of visual servoing with gripper recognition. We show that we can achieve high precision positioning without knowing in advance what the robotic arm looks like or how it is controlled. Original Publication:Fredrik Larsson, Erik Jonsson and Michael Felsberg, Simultaneously learning to recognize and control a low-cost robotic arm, 2009, Image and Vision Computing, (27), 11, 1729-1739.http://dx.doi.org/10.1016/j.imavis.2009.04.003Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com/

Fourier descriptors (FDs) is a classical but still popular method for contour matching. The key idea is to apply the Fourier transform to a periodic representation of the contour, which results in a shape descriptor in the frequency domain. Fourier descriptors have mostly been used to compare object silhouettes and object contours; we instead use this well established machinery to describe local regions to be used in an object recognition framework. We extract local regions using the Maximally Stable Extremal Regions (MSER) detector and represent the external contour by FDs. Many approaches to matching FDs are based on the magnitude of each FD component, thus ignoring the information contained in the phase. Keeping the phase information requires us to take into account the global rotation of the contour and shifting of the contour samples. We show that the sum-of-squared differences of FDs can be computed without explicitly de-rotating the contours. We compare our correlation based matching against affine-invariant Fourier descriptors (AFDs) and demonstrate that our correlation based approach outperforms AFDs on real world data. ©2009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Fredrik Larsson, Michael Felsberg and Per-Erik Forssén, Patch Contour Matching by Correlating Fourier Descriptors, 2009, Digital Image Computing: Techniquesand Applications (DICTA), Melbourne, Australia, December 2009. IEEE Computer Society.

In this paper we investigate the possibility for, and characteristics of, reliable and efficient a posteriori error computation at the integration of the constitutive relations pertinent to large strain viscoplasticity. An important feature is the possibility to select “goal-oriented” error measures with great freedom. A key task is to identify and solve the pertinent dual problem.

A major problem in model-checking timed systems is the huge memory requirement. In this paper, we study the memory-block traversal problems of using standard operating systems in exploring the state-space of timed automata. We report a case study which demonstrates that deallocating memory blocks (i.e. memory-block traversal) using standard memory management routines is extremely time-consuming. The phenomenon is demonstrated in a number of experiments by installing the UPPAAL tool on Windows95, SunOS 5 and Linux. It seems that the problem should be solved by implementing a memory manager for the model-checker, which is a troublesome task as it is involved in the underlining hardware and operating system. We present an alternative technique that allows the model-checker to control the memory-block traversal strategies of the operating systems without implementing an independent memory manager. The technique is implemented in the UPPAAL model-checker. Our experiments demonstrate that it results in significant improvement on the performance of UPPAAL. For example, it reduces the memory deallocation time in checking a start-up synchronisation protocol on Linux from 7 days to about 1 hour. We show that the technique can also be applied in speeding up re-traversals of explored state-space.

Uppaal is a tool suite for automatic verification of safety and bounded liveness properties of real-time systems modeled as networks of timed automata. It includes: a graphical interface that supports graphical and textual representations of networks of timed automata, and automatic transformation from graphical representations to textual format, a compiler that transforms a certain class of linear hybrid systems to networks of timed automata, and a model-checker which is implemented based on constraint-solving techniques. Uppaal also supports diagnostic model-checking providing diagnostic information in case verification of a particular real-time systems fails.

In this paper we apply the tool Uppaal1 to an automatic analysis of a version of the Philips Audio Control Protocol with two senders and bus collision handling. This case study is significantly larger than the real-time/hybrid systems previously analysed by automatic tools. During the case study the tool Uppaal was extended with a new feature, committed locations, allowing efficient modelling of broadcast communication.

A methodology for evaluation of stress intensity factors from the asymptotic displacement (or stress) fields at a crack front is proposed. The methodology strives to be of practical use in conjunction with commercial FE-codes, also when approaches such as XFEM are employed. To this end, the matching of the fields is carried out through a minimalistic, low order, ansatz of the displacement and stress fields. As demonstrated, the proposed methodology can deal with multiaxial loading of curved crack fronts in three-dimensional bodies. The methodology shows good accuracy also for compressive loading when crack face friction can be neglected.