Search

This paper presents the results of an experimental research aimed at assessing the material performance of adobe bricks in compression for a wide range of induced strain rates, from statics to high velocity impact. Adobe connotes a traditional masonry whose bricks are made of sundried soil mixtures possibly reinforced with natural fibres and joined together using mud mortar. The inclusion of fibre and the presence of water in the mixture have a dominant effect on the mechanical performance of adobe bricks and masonry. Their influence on the dynamic behaviour of this material is quantified and interpreted in this study at high strain rates also with data produced through Hopkinson bar testing. Appropriate dynamic increase factors and constitutive equations for adobe materials in dynamics are also investigated. The paper presents the experimental campaign, shows the main results and offers qualitative and quantitative interpretations for the principal damage patterns observed. © 2019 The Author(s)

In this paper, a distributed consensus control approach for vehicular platooning systems is proposed. In formalizing the underlying consensus problem, a realistic vehicle dynamics model is considered and a velocity-dependent spacing policy between two consecutive vehicles is realized. As a particular case, the approach allows to consider bidirectional vehicle interaction, which improves the cohesion between vehicles in the platoon. Exponential stability of the platoon dynamics is evaluated, also in the challenging scenario in which a limitation on the velocity of one of the vehicles in the platoon is introduced. The theoretical results are experimentally validated using a three-vehicle platoon consisting of (longitudinally) automated vehicles equipped with wireless intervehicle communication and radar-based sensing.

Design decisions are made in an early-design phase of system development. These decisions have a big impact on the resulting system design and realization. Making design decisions in this stage is a complex and risky task, because there are a lot of uncertainties regarding their impact on the system qualities. Moreover, in many cases, trade-offs have to be made when there are conflicting objectives. This paper presents a methodology to support decision making for evolutionary systems, to decide on the most suitable design. The focus is on the embedded part of a system. Information is structured with explicit relations, such that the realization of a design can be traced towards the concerns a stakeholder has for the system. This structure enables architects and designers to understand and reason about the impact of a design with a system-wide perspective. The method consists of a calibration step which imports a current design, a design exploration step in which designs are selected, and a decision step where the most suitable design is chosen. The methodology is demonstrated by exploring and revealing the trade-offs for platooning designs from the automotive domain.

Interaction of ultrasonic waves with partially-closed surface-breaking cracks in concrete structures has been studied. Measurements have been conducted on a reinforced concrete beam containing various mechanical-load-induced cracks and compared with the baseline measurements at those locations. Influence of crack width, incident angle of waves with cracks, and distance from the cracks on travel time and amplitude of the waves have been investigated when the beam was unloaded. It has been observed that a measurable part of the waves propagate through the cracks due to the acoustic coupling between the crack faces, although attenuation can be relatively high. The travel time has shown a nearly independent behavior from remaining crack opening in the measured range of 0.05 mm to 3 mm. Measurements in directions orthogonal and parallel to the crack suggest that there is substantial anisotropy in the cracking zone. Furthermore, an effective width of the micro-cracking area around the cracks has been estimated from the measurements.

Thermochemical heat storage in salt hydrates is a promising method to improve the solar fraction in the built environment. The major concern at this stage is liquefaction followed by washing out of active material and agglomeration into large chunks of salt, thus deteriorating the diffusive properties of the porous salt hydrate structure. In this work, specific attention is given to the methods to stabilize a sample salt hydrate. Attempts have been made to stabilize calcium chloride by impregnation in expanded natural graphite and vermiculite, and by microencapsulation with ethyl cellulose. The effect of these stabilization methods on the performance of the material, such as kinetics and energy density, is investigated. Characterization of the materials is carried out with combined Thermo-Gravitational Analysis (TGA) and Differential Scanning Calorimetry (DSC) methods and microscopic observation, in order to evaluate the improvements on the basis of three subjects: reaction kinetics, heat storage density and stability. Within the boundary conditions for thermochemical energy storage as presented in this work, microencapsulated calcium chloride showed high multicyclic stability, compared with pure and impregnated materials, that liquefy upon hydration under the given conditions. Microencapsulated material remains stable over multiple cycles and at the same time shows the faster kinetics, but has a lower volumetric energy storage density.

The need for personalised and smart products drives the development of structural electronics with mass-customisation capability. A number of challenges need to be overcome in order to address the potential of complete free form manufacturing of electronic devices. One key challenge is the integration of conductive structures and components into 3D printed devices by combining different materials and printing techniques that have nearly incompatible printing conditions. In this paper, several methods to integrate electronic circuits and components into a 3D printed structure are discussed. The functional performance of the resulting structures is described. Structural parts were manufactured with a stereolithography-based 3D printing technique, which was interrupted to pick and place electronic components, followed by either direct writing or squeegee filling of conductive material. A thermal curing step was applied to enhance the bonding and improve the electrical performance. Optical micrography, 4-point resistance measurement and cross-sectional analysis were performed to evaluate functionality.

An important reason to apply coatings on wood is to protect wood against moisture. As a result of regulations and ecological concerns, there has been a shift towards waterborne coatings, which make coatings intrinsically more sensitive to water. As a consequence of the higher sensitivity to water, the durability of both wood and coatings can be negatively affected. In order to use waterborne coatings for woodcare, the main factors influencing transport through these coatings have to be understood. The aim of this study is to elucidate the influence of the wooden substrate on the water permeability of the coating applied to it. Pine sapwood, oak and teak were selected as the wood types, covering a whole range of low to high density wood. Three types of coatings were formulated: a solventborne alkyd, a waterborne alkyd and a waterborne acrylic. NMR imaging was used to measure the moisture distribution and quantify the changes in bound and free water in coated wood during drying. For all wood-coating combinations that were investigated, water transport appeared to be externally (i.e. coating) limited. The loss of bound water started only after evacuation of free water, which showed a local thermodynamic equilibrium associated with bound and free water. We furthermore compared water permeability of free films and wood supported films to understand the influence of the wood-coating interactions. The permeability of free coating films has been determined by the wet-cup method, followed by investigating the solubility and diffusion of water in order to understand the differences in the permeability. We found that the interaction of the coating with the wood has no influence on the water permeability for the considered combinations. Furthermore, the permeability is largely determined by the water solubility. © 2017 Elsevier B.V.

There is limited knowledge on deriving the strength of an explosion based on the observed explosion effects. Existing methods are based primarily on the effects of blast overpressure on surrounding structures. Window breakage and structural damage are well studied and are widely used to derive most probable explosion strengths. Other explosive effects such as debris throw are usually left out of such forensic analyses. In this paper, a quantitative method is presented that can be used to obtain the explosion strength based on debris throw. When the method is applied together with analysis of other evidence at a post blast scene, more accurate predictions of the original amount of explosive can be obtained. An overview of the required information that has to be collected from a post-blast scene is outlined, which will aid in the backward calculations that will be carried out in the next stage. This calculation method is applied to two case studies, which illustrate that it is applicable to events involving both low and high order accidental explosion events. Besides accidents, the method is also applicable to intentional explosion scenarios such as terrorist attacks. It is shown that the added value of such a method to forensic investigation depends on the precision of the data collected. Therefore, it is recommended that first responders not only register the impact locations but also attempt to identify the part of the donor installation from which the debris originated. Furthermore, estimates should be made of the launch height and ballistic properties of the debris and information should be recorded on obstructions and terrain properties in the vicinity. In this way, the quality of the backward calculations can be optimized. © 2017 Elsevier Ltd

In design against fatigue, a lower bound stress range vs. endurance curve (S-N curve) is employed to characterize fatigue resistance of plain material and structural details. With respect to the inherent variability of the fatigue life, the S-N curve is related to a certain probability of exceedance, a percentile of the fatigue life. This paper is concerned with modelling and estimating uncertainties in fatigue resistance of welded joints under constant amplitude loading. A new S-N curve format is proposed and fitted to fatigue test data by using the Maximum Likelihood Method. The results have been compared with the Random Fatigue Limit Model and the Bilinear Random Fatigue Limit Model. The proposed S-N curve appears to be more accurate in describing the S-N relation in high-cycle fatigue: it presents a smooth transition from finite to infinite-life regions and, differently from previous non-linear S-N relations with fatigue limit, this transition is controlled by an independent model parameter. Thereby it provides more flexibility for statistical fitting. In addition, a Bayesian framework is defined to fit the proposed relation including informative and non-informative prior distributions. © 2017 Elsevier Ltd

Personal monitors based on unipolar diffusion charging (miniDiSC/DiSCmini, NanoTracer, Partector) can be used to assess the individual exposure to nanoparticles in different environments. The charge acquired by the aerosol particles is nearly proportional to the particle diameter and, by coincidence, also nearly proportional to the alveolar lung-deposited surface area (LDSA), the metric reported by all three instruments. In addition, the miniDiSC/DiSCmini and the NanoTracer report particle number concentration and mean particle size. In view of their use for personal exposure studies, the comparability of these personal monitors was assessed in two measurement campaigns. Altogether 29 different polydisperse test aerosols were generated during the two campaigns, covering a large range of particle sizes, morphologies and concentrations. The data provided by the personal monitors were compared with those obtained from reference instruments: a scanning mobility particle sizer (SMPS) for LDSA and mean particle size and a ultrafine particle counter (UCPC) for number concentration. The results indicated that the LDSA concentrations and the mean particle sizes provided by all investigated instruments in this study were in the order of ± 30% of the reference value obtained from the SMPS when the particle sizes of the test aerosols generated were within 20–400 nm and the instruments were properly calibrated. Particle size, morphology and concentration did not have a major effect within the aforementioned limits. The comparability of the number concentrations was found to be slightly worse and in the range of ± 50% of the reference value obtained from the UCPC. In addition, a minor effect of the particle morphology on the number concentration measurements was observed. The presence of particles > 400 nm can drastically bias the measurement results of all instruments and all metrics determined. © 2016 Elsevier B.V.

Restrictions on the carriage of liquids, aerosol, and gels (LAGs) by airline passengers have been in place since November 2006, following the discovery of a terrorist plot involving homemade liquid explosives to be used on transatlantic flights (Wikipedia, 2006). Restrictions on the carriage of LAGs remain today, and the operational impact of introducing further screening of liquids is subject to ongoing debate. This paper addresses one of the concerns, namely that the false alarm rates of liquid explosive detection systems (LEDS) are adversely affected by the filling level of LAGs containers. Our study contributes to a better understanding of the operational impact of screening partially full containers, based on a large number of screening repetitions under laboratory conditions and robust statistical analysis. False alarm rates were observed for 39 LAGs screened with 5 different LEDS. For each combination, four different container filling levels (100%, 75%, 50% and 25%) were studied. These observations were used to model the impact of partially filling for sequential combinations of equipment. Three possible scenarios were considered, namely passengers being allowed to carry (1) only water, (2) water & soft drinks, and (3) all LAGs. The results show that, for a sequential combination of two equipment types, the impact of partially filled containers on the overall false alarm rate is negligible. Nevertheless, partially filled containers do result in an approximate two-fold increase in the number of items requiring level-two screening, which may be significant for airports when managing their screening processes. © 2017, The Auhtor(s).

Plasmonic color generation offers several advantages but is also limited by the cost and availability of noble metals like gold. In this work, we present color-tunable metasurfaces with high chromaticity and reflectivity consisting of an aluminum mirror, a dielectric spacer, and a plasmonic nanohole array in copper. Copper is shown to be an excellent alternative to gold when properly protected from oxidation and makes it possible to generate a wide RGB gamut covering 27% of the standard RGB. By patterning the metasurfaces into microscale pixel triplets, color photos can be well reproduced with high resolution over wafer-sized areas. Further, we demonstrate active modulation of the reflected intensity using an electrochromic conductive polymer deposited on top of the nanostructures by screen printing. This technology opens up for ultrathin and flexible reflective displays in full color, that is, plasmonic electronic paper, compatible with large-scale sustainable production. Funding agencies: Swedish Foundation for Strategic Research [RMA11-0037]; Wenner-Gren Foundations; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Chalmers Nanoscience and Nanotechnology Area of

Stimulated by the growing demand for greener and more sustainable polymer systems we have studied thermoreversible polymer networks composed largely (> 83% w/w) of diethylitaconate of bio-based origin. A series of coating materials has been synthesized consisting of linear chains of diethylitaconate copolymerized with furfurylmethacrylate moieties enabling the formation of reversible crosslinks between the chains through the Diels-Alder reaction upon addition of a bismaleimide. The ability to reversibly crosslink these materials can be used to improve the sustainability of the coatings by elongation of the lifetime through enhancement of mechanical properties (glass transition temperature, hardness and susceptibility towards abrasive wear as well as solvent resistance have been quantified). The thermoreversibility of the network makes this kind of crosslinked coatings mendable after a damaging event during the coating life-time and ultimately recyclable. Heat induced decrosslinking of the coating materials through the retro-Diels Alder reaction has been analyzed with differential scanning calorimetry and self-healing has been demonstrated.

A literature review is performed in order to collect and analyse the thermodynamic data of an utmost number of salt hydrate reactions (i.e., 563 reactions are reviewed). These data allow us to evaluate the theoretical possibilities and limitations of salt hydrates as thermochemical materials (TCMs) for seasonal heat storage in the built environment (1 GJ/m3 on system level). Two filters are used for evaluation. Filter 1 including three criteria i.e., an ideal hydration reaction with a capacity larger than 2 GJ/m3, a hydration temperature of 65 °C (suitable for domestic hot water) or higher, a dehydration temperature below 100 °C to profit as much as possible from the solar heat that can be harvested. Only four of the studied hydrates fit with these demands. For selecting a larger number of hydrates, a second filter is introduced with less demanding constraints. It is expected that modifications on heat storage system level are needed to reach an acceptable system performance with the hydrates selected through filter 2 (hydration reaction with a capacity larger than 1.3 GJ/m3, a hydration temperature of 50 °C or higher, a dehydration temperature below 120 °C). Based on this filter, a shortlist of 25 TCM hydrate reactions are identified, including the four of filter 1. The shortlist is analyzed by considering price, chemical stability, reaction kinetics and safety for domestic environment. Based on this additional analysis with the used constraints, K2CO3 is determined to be the most promising candidate for open or closed systems, but has a low energy density. Based on the review of 563 hydrate reactions, we concluded that no ideal salt exists for seasonal heat storage under the considered boundary conditions. With the current concept of seasonal heat storage, including closed and open systems, whereby only one dehydration cycle per year is performed under a system energy density of 1 GJ/m3, it is not realistic for large scale implementation to use pure salt hydrates as heat storage material. By adjusting the constraints, such as multiple cycles per year or higher water vapor pressures, salt hydrates can still be used as TCMs. It should be mentioned that MgSO4·7H2O, MgSO4·6H2O and CaCl2·6H2O are not listed in our shortlist of 25 TCMs, although these hydrates are commonly suggested in the literature as promising TCM for seasonal heat storage. The present study on pT-characteristics shows, however, that these salts are not fitting the demands of such a heat storage system.

Accurate link quality estimation is a fundamental building block in quality aware multi hop routing. In an inherently lossy, unreliable and dynamic medium such as wireless, the task of accurate estimation becomes very challenging. Over the years ETX has been widely used as a reliable link quality estimation metric. However, more recently it has been established that under heavy traffic loads ETX performance gets significantly worse. We examine the ETX metric's behavior in detail with respect to the MAC layer and UDP data; and identify the causes of its unreliability. Motivated by the observations made in our analysis, we present the design and implementation of our link quality measurement metric xDDR – a variation of ETX. This article extends xDDR to support network mobility. Our experiments show that xDDR substantially outperforms minimum hop count, ETX and HETX in terms of end-to-end packet delivery ratio in static as well as mobile scenarios.

Tri-phase PZT-porous polyurethane (PU) composites are investigated with the aim of developing conformable, highly sensitive tactile sensors for application in Human-Machine Interactions. The main goal is to reduce the dielectric constant of the polymer matrix, and improve flexibility of traditional diphase piezo-composites, consisting of ceramic particles in a dense polymeric matrix, by adding a third (gaseous) phase to the system. The presence of the gaseous component in the polymer matrix in the form of well-distributed spherical inclusions effectively decreases the polymer dielectric permittivity, which improves the piezoelectric voltage coefficient of the composites significantly. The unique combination of dielectrophoretic structuring of PZT particles and the addition of a gaseous phase to the polymer resin results in the highest performance of the particulate composite sensors reported in the literature so far. The g33 values of the newly developed triphase composites are twice that of the structured di-phase PZT-dense PU composites (80 mV.m/N) and more than five times the g33 value of bulk PZT ceramics (24-28 mV.m/N).

Most research of texturization of solar cells has been devoted to Si based cells. For perovskites, it was assumed that texturization would not have much of an impact because of the relatively low refractive indexes lead to relatively low reflection as compared to the Si based cells. However, our optical modeling shows that a significant gain in perovskite (1.55 Ev) absorption from 84.6% to 93.5% for the wavelength range of 400 nm up to 800 nm. The largest gain in absorption is achieved between wavelengths of 700 nm and 800 nm. Because this is a range with a high photon density, the current density increases up to 10rel.%. We have modeled different sine texture sizes and show generic trends in performance with texture. Moreover, by introducing a texture, the light is locally concentrated, depending on the texture configuration. This offers new cell architectures with optimized front and back contacts.

Creating a driving cycle (DC) for the design and validation of new vehicles is an important step that will influence the efficiency, functionality and performance of the final systems. In this work, a DC synthesis method is introduced, based on multi-dimensional Markov Chain, where both the velocity and road slope are investigated. Particularly, improvements on the DC synthesis method are proposed, to reach a more realistic slope profile and more accurate fuel consumption and CO2 emission estimates. The effects of using synthesized DCs on fuel consumption are investigated considering three different vehicle models: conventional ICE, and full hybrid and mild hybrid electric vehicles. Results show that short but representative synthetic DCs will results in more realistic fuel consumption estimates (e.g. in the 5%-10% range) and in much faster simulations. Using the results of this proposed method also eliminates the need to use very simplified DCs, as the New European Driving Cycle(NEDC), or long, measured DCs.

In the context of model-free optimization of dynamic nonlinear multiple-input-single-output (MISO) systems using extremum-seeking (ES), accurate and fast derivative estimation of the systems steady-state performance map is essential. This paper presents a generalized derivative estimator (DE) framework for unknown MISO static maps. To this extent, the map input is perturbed with sinusoidal dither signals with different frequencies. Using the proposed framework, the derivatives can be estimated up to an arbitrary order, for maps with an arbitrary number of inputs. Conditions on the dither frequencies are provided, which optimize the DE time-scale, such that derivative estimation is as fast as possible. Simulation examples are provided to demonstrate the effectiveness of the proposed framework.

In mesostructured perovskite solar cell devices, charge recombination processes at the interface between the transparent conductive oxide, perovskite and hole transport layer are suppressed by depositing an efficient compact TiO2 blocking layer. In this contribution we investigate the role of the atomic layer deposited TiO2 on ITO-PET substrates in hybrid halide (CH3NH3PbI3−xClx) perovskite solar cells. In the absence of the TiO2 layer, very low open circuit voltage (VOC = 35 mV) and efficiency (η = 0.02%) values are observed. The analysis of JV dark current reveals the lack of rectifying behaviour at the above-mentioned interface. The introduction of ultra-thin ALD layers (from 2.5 to 44 nm) leads to an increment in all the photovoltaic parameters and, consequently, in the photovoltaic conversion efficiency. A maximum power conversion efficiency of 9.2% is achieved, much higher than the 4% obtained when a low temperature conventional sol gel TiO2 compact layer is used. The higher quality of the ALD layer in terms of low defect density and low level of impurities with respect to the solution processed approach has been highlighted by electrochemical characterization and XPS analysis.

Cobalt based driers are the most commonly used primary catalysts in alkyd coatings as they promote fast drying and lead to hard coatings. However, several studies have suggested potential reclassification of cobalt-based alkyd driers. Therefore, cobalt based driers are being replaced by alternatives, e.g. based on iron or manganese. In practice primary driers (Co, Mn, or Fe) are used in combination with secondary driers (e.g. Ca, Zr) to enhance drying of the film. Coating formulators aim for a high drying speed and hardness development. However, each combination of primary and secondary driers leads to a different oxidative drying pattern resulting in variations in the crosslink density and hardness development. In this study we have systematically investigated the effect of two secondary driers, Calcium (Ca) and Zirconium (Zr), on curing behavior when added to different primary driers (Co, Mn, and Fe) using a high spatial resolution NMR set-up. As expected, we observed increased drying speed and higher crosslink densities when adding these secondary driers. While calcium showed to promote the front speed, zirconium showed to increase the measured crosslink density. The behavior seems to be generic as this was seen for all three the primary driers. © 2017 Elsevier Ltd

We introduce a new way to look at the combined lateral and longitudinal control problem for platooning vehicles by studying these problems separately. The lateral control problem is approached as a path following problem in the spatial domain: based on the path of the preceding vehicle we determine a path for the following vehicle which converges to the given path of its predecessor. In particular if the following vehicle happens to be on the path of its predecessor, the generated path of the follower equals the path of its predecessor. This approach not only overcomes the problem of corner cutting, but also achieves appropriate following behavior in case of large initial errors. As a by-product of solving the lateral control problem, we obtain a mapping from the path of the follower to the path of its predecessor. Using this mapping we can consider the longitudinal control problem as controlling two points on the same path towards a required inter-vehicle distance, which is comparable to CACC, i.e., the problem of controlling two points on a straight line towards a required inter-vehicle distance. We illustrate our approach by means of simulation. We introduce a new way to look at the combined lateral and longitudinal control problem for platooning vehicles by studying these problems separately. The lateral control problem is approached as a path following problem in the spatial domain: based on the path of the preceding vehicle we determine a path for the following vehicle which converges to the given path of its predecessor. In particular if the following vehicle happens to be on the path of its predecessor, the generated path of the follower equals the path of its predecessor. This approach not only overcomes the problem of corner cutting, but also achieves appropriate following behavior in case of large initial errors. As a by-product of solving the lateral control problem, we obtain a mapping from the path of the follower to the path of its predecessor. Using this mapping we can consider the longitudinal control problem as controlling two points on the same path towards a required inter-vehicle distance, which is comparable to CACC, i.e., the problem of controlling two points on a straight line towards a required inter-vehicle distance. We illustrate our approach by means of simulation.

For conventional buses, based on the decades of their operational knowledge, public transport companies are able to optimize their cost of operation. However, with recent trend in the usage of electric buses, cost optimal operation can become challenging. In this paper an offline optimal charging strategy is developed to minimize the energy cost. This is done by exploiting the periodicity and predictable operation of the city buses. For effective usage of the developed offline strategy, the actual energy demand of the electric bus must be known a-priori, which can be demanding. In order to address this issue, a predictor is designed. The neural network based predictor is able to estimate the energy demand for the next day. Using this, three different optimal charging strategies are implemented. Initially, only the operational constraints are considered to ensure the completion of a trip, later, a more involved problems consisting of battery state of charge (SoC) constraints and temperature constraints are included for the second and third optimization problems, respectively. All the three approaches result in significant energy cost minimization when compared to the non-optimal strategy of charging the electric bus to the full capacity at every available opportunity. Additionally, for the second and third formulations, namely, SoC and temperature constraints, by using a qualitative aging approach, some enhancements in the battery health is observed when compared to the non-optimal charging strategy.

In this paper a Vehicle State Estimator is developed and validated on experimental data from a 2012 Toyota Prius. The estimator is capable of estimating both planar vehicle velocities and the tyre-road friction parameter. Emphasis is placed on the comparison of the commonly used Extended Kalman Filter and a novel application of the State Dependent Riccati Equation technique. The State Dependent Riccati based estimator relies on a factorization compared to linearization in the case of the Extended Kalman Filter. This factorization is non-unique, therefore the construction of this factorization, is also presented. A comparison is for both estimators is presented for experimental data. For estimation of the tyre-road friction parameter, simulations are used, due to absence of a reference value in the experimental set-up.

Nowadays, there is an increasing societal demand for smart mobility solutions which can increase the throughput, comfort, and safety of driving on a road. As one of these solutions, vehicle following technologies like cooperative adaptive cruise control (CACC) are introduced. with the help of vehicle-to-vehicle (V2V) communication, CACC can reduce the safe minimal inter-vehicular distance. Additionally, sharing the vehicle intentions through V2V, enables multi-vehicle maneuvers to be cooperatively executable. In this paper, using the concept of artificial potential fields, a longitudinal control scheme for performing a cooperative merging maneuver will be suggested. Artificial potential fields are powerful enough for modeling and solving such a complex problem, where in addition to vehicle following other objectives such as merging should be addressed. The designed algorithms for vehicle cooperative maneuvering are verified through simulations.

Backside ventilation is one of the most common passive cooling methods of PV modules in the built environment, but might be under constraint when integrating PV in the building envelope. To investigate the short and long term effect of backside ventilation on Building Integrated PV (BIPV) performance and lifespan, a comparative BIPV field test is conducted in a real life lab located in the Netherlands. The field test includes 24 modules in 4 segments with different levels of backside ventilation. PV energy output, module backside temperature, relative humidity in the air gap, and air velocity in the air gap have been monitored for three years in the period January 2013–December 2015. At the end of the monitoring period Electric Luminescence (EL) images were made and Standard Testing Condition (STC) power was determined. The ventilated segments show a similar behaviour (6% difference) in PV energy output, but the non-ventilated segment shows a strong decrease of 86% in output after three years. A maximum temperature of 72 °C is reached in the ventilated segments and a maximum temperature of 83 °C in the non-ventilated segment. Relative humidity (RH) levels reach a maximum of 100% in all segments. Air velocity in the non-ventilated segment is 13–39% of the air velocity in the ventilated segments. STC power determination and EL imaging show lower peak power and more defects in the non-ventilated modules, and modules placed at vertical higher positions in the non-ventilated segment have a lower power output of 50–60%. The results indicate that, considering the first generation Metal Wrap Through (MWT) modules investigated, the non-ventilated BIPV modules exposed to the highest temperatures show the lowest power output, lowest STC power and show the most damaged cells in the EL imaging. Even though PV module manufacturing shows continuous technological advances, the methodology and results of this work has added value for the prediction of BIPV operating aspects and lifespan when designing and realizing a BIPV installation. Moreover, the BIPV field test presented in this study has been a very illustrative BIPV demonstration project for manufacturers, installers and designers.

The electricity production and distribution is facing two major changes. First, the production is shifting from classical energy sources such as coal and nuclear power towards renewable resources such as solar and wind. Secondly, the consumption in the low voltage grid is expected to grow significantly due to expected introduction of electrical vehicles. The first step towards more efficient operational capabilities is to introduce an observability of the distribution system and allow for leveraging the flexibility of end connection points with manageable consumption, generation and storage capabilities. Thanks to the advanced measurement devices, management framework, and secure communication infrastructure developed in the FP7 SUNSEED project, the Distribution System Operator (DSO) now has full observability of the energy flows at the medium/low voltage grid. Furthermore, the prosumers are able to participate pro-actively and coordinate with the DSO and other stakeholders in the grid. The monitoring and management functionalities have strong requirements to the communication latency, reliability and security. This paper presents novel solutions and analyses of these aspects for the SUNSEED scenario, where the smart grid ICT solutions are provided through shared cellular LTE networks., Accepted for publication in IEEE Wireless Communications Magazine, special issue on Smart Grids, to be published April 2017

Integrated Emission Management (IEM) is a supervisory control strategy that minimises operational costs (consisting of fuel and AdBlue) for diesel engines with an aftertreatment system, while satisfying emission constraints imposed by legislation. In most work on IEM, a suboptimal heuristic real-time implementable solution is used, which is based on Pontryagin's Minimum Principle (PMP). In this paper, we compute the optimal solution using both PMP and Dynamic Programming (DP). As the emission legislation imposes a terminal state constraint, standard DP algorithms are sensitive to numerical errors that appear close to the boundary of the feasible sets. Therefore, we propose two extensions to existing DP methods, which use an approximation of the forward reachable sets to reduce the grid size over time and an approximation of the backward reachable sets to avoid the aforementioned numerical errors. Using a simulation study of a cold-start World Harmonised Transient Cycle for a Euro-VI engine, we show that the novel extension to the DP algorithm yields the best approximation of the optimal cost, when compared to existing DP methods. Furthermore, we show that PMP yields almost the same results as DP, and that the real-time implementable solution only deviates approximately 0.08–0.16% from the optimal solution.

For the preparation of electrically conductive composites, various combinations of cellulose and conducting materials such as polymers, metals, metal oxides and carbon have been reported. The conductivity of these cellulose composites reported to date ranges from 10−6 to 103 S cm−1. Cellulose nanocrystals (CNCs) are excellent building blocks for the production of high added value coatings. The essential process steps for preparing such coatings, i.e. surface modification of CNCs dispersed in water and/or alcohol followed by application of the dispersion to substrate samples using dip coating, are low cost and easily scalable. Here, we present coatings consisting of Ag modified CNCs that form a percolated network upon solvent evaporation. After photonic sintering, the resulting coatings are electrically conductive with an unprecedented high conductivity of 2.9 × 104 S cm−1. Furthermore, we report the first colloidal synthesis that yields CNCs with a high degree of Ag coverage on the surface, which is a prerequisite for obtaining coatings with high electrical conductivity.

Piezoelectric composites made from soft and hard lead zirconium titanate (PZT) particles as filler and an epoxy as the matrix were prepared by dielectrophoresis and studied for their piezoelectric properties. It was found that the dielectric constant of the piezoelectric filler plays a significant role in determining the final piezoelectric properties of the composites. Composites with lower dielectric constant for the PZT filler material showed better piezoelectric properties compared to the composites with high dielectric constant filler. This can be ascribed to a more efficient poling of the piezoelectric filler particles. The aging behaviour of these composites was compared to that reported for monolithic ceramics.

In this article we evaluate context-aware recommendation systems for information re-finding by knowledge workers. We identify 4 criteria that are relevant for evaluating the quality of knowledge worker support: context relevance, document relevance, prediction of user action, and diversity of the suggestions. We compare 3 different context-aware recommendation methods for information re-finding in a writing support task. The first method uses contextual prefiltering and content-based recommendation (CBR), the second uses the just-in-time information retrieval paradigm (JITIR), and the third is a novel network-based recommendation system where context is part of the recommendation model (CIA). We found that each method has its own strengths: CBR is strong at context relevance, JITIR captures document relevance well, and CIA achieves the best result at predicting user action. Weaknesses include that CBR depends on a manual source to determine the context and in JITIR the context query can fail when the textual content is not sufficient. We conclude that to truly support a knowledge worker, all 4 evaluation criteria are important. In light of that conclusion, we argue that the network-based approach the CIA offers has the highest robustness and flexibility for context-aware information recommendation.

Atomic layer deposition (ALD), a gas-phase thin film deposition technique based on repeated, self-terminating gas-solid reactions, has become the method of choice in semiconductor manufacturing and many other technological areas for depositing thin conformal inorganic material layers for various applications. ALD has been discovered and developed independently, at least twice, under different names: atomic layer epitaxy (ALE) and molecular layering. ALE, dating back to 1974 in Finland, has been commonly known as the origin of ALD, while work done since the 1960s in the Soviet Union under the name "molecular layering" (and sometimes other names) has remained much less known. The virtual project on the history of ALD (VPHA) is a volunteer-based effort with open participation, set up to make the early days of ALD more transparent. In VPHA, started in July 2013, the target is to list, read and comment on all early ALD academic and patent literature up to 1986. VPHA has resulted in two essays and several presentations at international conferences. This paper, based on a poster presentation at the 16th International Conference on Atomic Layer Deposition in Dublin, Ireland, 2016, presents a recommended reading list of early ALD publications, created collectively by the VPHA participants through voting. The list contains 22 publications from Finland, Japan, Soviet Union, United Kingdom, and United States. Up to now, a balanced overview regarding the early history of ALD has been missing; the current list is an attempt to remedy this deficiency.

The optimal design of a hybrid electric vehicle (HEV) can be formulated as a multiobjective optimization problem that spreads over multiple levels (technology, topology, size, and control). In the last decade, studies have shown that by integrating these optimization levels, fuel benefits are obtained, which go beyond the results achieved with solely optimal control for a given topology. Due to the large number of variables for optimization, their diversity, and the nonlinear and multiobjective nature of the problem, a variety of methodologies have been developed. This paper presents a comprehensive analysis of the various methodologies developed and identifies challenges for future research. Starting from a general description of the problem, with examples found in the literature, we categorize the types of optimization problems and methods used. To offer a complete analysis, we broaden the scope of the search to several sectors of transport, such as naval or ground.

Protecting groups are commonly applied in multi-step molecular syntheses to protect one or multiple functional groups from reacting. After the reaction, they are removed from the molecule. In full analogy to this concept, we report the practical and scalable colloidal synthesis of Au semishells using polyphenylsiloxane protecting patches to prevent part of the surface of polystyrene nanoparticles from being covered with Au. After Au deposition, the patches are removed yielding Au semishells. We anticipate that this strategy can be extended to the synthesis of other types of non-centrosymmetric nanoparticles.

Knowledge on moisture transport in wood is important for understanding its utilization, durability and product quality. Moisture transport processes in wood can be studied by Nuclear Magnetic Resonance (NMR) imaging. By combining NMR imaging with relaxometry, the state of water within wood can be identified, i.e. water bound to the cell wall, and free water in the cell lumen/vessel. This paper presents how the transport of water can be monitored and quantified in terms of bound and free water during water uptake and drying. Three types of wood from softwood to hardwood were selected covering a range of low to high density wood; pine sapwood and oak and teak. A calibration is performed to determine the different water states in each different wood type and to convert the NMR signal into moisture content. For all wood types, water transport appeared to be internally limited during both uptake and drying. In case of water uptake, free water was observed only after the cell walls were saturated with bound water. In case of drying, the loss of bound water starts only after vanishing of free water, irrespective of the position. Obviously, there is always a local thermodynamic equilibrium of bound and free water for both uptake and drying. Finally, we determined the effective diffusion coefficient (Deff). Experimentally determined diffusion constants were compared with those derived by the diffusion models for conceptual understanding of transport mechanism. We found that diffusion in the cell wall fibers plays a critical role in the transport process.

The threat of terrorists using CBRN agents continues to pose a risk of mass casualties and severe disruption of societal functions in Europe. Standardisation of crisis management activities is one important step towards effective national and international interoperability and increased resilience. Understanding which CBRN agents are involved in an incident is vital for appropriate response measures. We applied a system's view on the process of CBRN sample analysis and see three discrete applications; Immediate incident response, Forensics, Post incident monitoring. Together with laboratory experts and policy makers from across Europe we identified needs for quality assurance measures in these three areas. Here, we suggest various harmonisation activities that can facilitate interoperability between all stakeholders concerned with CBRN sample analysis. Foremost, we recommend purpose-oriented laboratory networks, but also minimum performance requirements for First Responders’ detection and sampling capabilities, best practices for sample transport and documentation.

Despite the great promise of printed flexible electronics from 2D crystals, and especially graphene, few scalable applications have been reported so far that can be termed roll-to-roll compatible. Here we combine screen printed graphene with photonic annealing to realize radio-frequency identification devices with a reading range of up to 4 meters. Most notably our approach leads to fatigue resistant devices showing less than 1% deterioration of electrical properties after 1000 bending cycles. The bending fatigue resistance demonstrated on a variety of technologically relevant plastic and paper substrates renders the material highly suitable for various printable wearable devices, where repeatable dynamic bending stress is expected during usage. All applied printing and post-processing methods are compatible with roll-to-roll manufacturing and temperature sensitive flexible substrates providing a platform for the scalable manufacturing of mechanically stable and environmentally friendly graphene printed electronics. (Figure presented.).

Ambipolar organic electronics offer great potential for simple and low-cost fabrication of complementary logic circuits on large-area and mechanically flexible substrates. Ambipolar transistors are ideal candidates for the simple and low-cost development of complementary logic circuits since they can operate as n-type and p-type transistors. Nevertheless, the experimental demonstration of ambipolar organic complementary circuits is limited to inverters. The control of the transistor polarity is crucial for proper circuit operation. Novel gating techniques enable to control the transistor polarity but result in dramatically reduced performances. Here we show high-performance non-planar ambipolar organic transistors with electrical control of the polarity and orders of magnitude higher performances with respect to state-of-art split-gate ambipolar transistors. Electrically reconfigurable complementary logic gates based on ambipolar organic transistors are experimentally demonstrated, thus opening up new opportunities for ambipolar organic complementary electronics.

Research funding was provided by the US Office of Naval Research and the Ministries of Defence of Norway, the Netherlands and France as well as the UK Natural Environmental Research Council. A key issue when investigating effects of anthropogenic noise on cetacean behavior is to identify the biological significance of the responses. Predator presence can be considered a natural high-level disturbance stimulus to which prey animals have evolved adaptive response strategies to reduce their risk of predation by altering behavior away from fitness-enhancing activities such as foraging. By contrasting the type and magnitude (duration, severity, consistency) of behavioral responses to anthropogenic noise and playback of killer whale (KW) sounds that simulated predator presence, this study aimed to provide a relative index of the disturbance level as an indication of the biological significance of responses to the anthropogenic stimulus. Using multi-sensor tags as well as visual observations of surface behavior of adult male sperm whales, we assessed a comprehensive range of behavioral metrics that could reduce individuals’ fitness if altered for a biologically relevant duration. Combining previously published results and new analyses, we showed that the responses to 1-2 kHz upsweep naval sonar and to KW playback were very similar, including horizontal avoidance, interruption of foraging or resting activities and an increase in social sound production. However, only KW playbacks elicited grouping behaviors, indicating that this social response component was specific to predator detection. Animals responded to a lesser extent to 6-7 kHz upsweep naval sonar, indicating weaker disturbance effects. Our study demonstrates the benefit of using anti-predator responses as a reference of disturbance when evaluating the relative impacts of anthropogenic stimuli, which can be of particular interest in studies of threatened species such as sperm whales. Publisher PDF

Predictive maintenance strategies which estimate remaining useful life of system components to prevent breakdowns and down-times by timely and well-scheduled maintenance ensures the reliable availability of assets and lowers total costs of ownership. The focus on the components’ life times falls short, however, to infer the system-level capability to achieve upcoming tasks, especially if these tasks vary either in the strain they cause for the system or in the environmental conditions in which the system needs to perform. Such an assessment of the health and mission readiness of a system is crucial for mobile assets like seafaring vessels undertaking long-term operations without the option to easily come in for repairs or for industrial assets that need to complete long production runs in one go under varying circumstances. We propose a multi-step methodology to achieve such assess­ments using both Bayesian reasoning for diagnosis and prognosis and physics-based simulation models. First, we construct an appropriate Bayesian network in an object-oriented way by fitting a pre-compiled library of network fragments to the system’s schematics using generative techniques. We then parameterize the obtained network using a combination of expert knowledge and machine learning to fine tune system-level interactions between components and their link to the system’s performance. The learning step uses past operational data that we augment or complement with synthetic data, created by a physics-based simulation model, where needed. Finally, we use the trained Bayesian network to assess the mission readiness of the system given the probabilistics of its diagnosed state, expected impact of possible maintenance interventions, and the estimated profile of the future use. We illustrate and verify our methodology on a cooling system with an active feedback control loop, but our approach for mission readiness assessment is domain-independent, universally applicable, and typically feasible where operational data and engineering knowledge can be brought together to solve its challenge.

De redactieraad vormt sinds de start van Solar Magazine het kloppend hart van de redactie. Het orgaan bevat onderzoeks- en koepelorganisaties uit de zonne-energiesector. De raad geeft de redactie gevraagd en ongevraagd advies over de redactionele koers die gevaren wordt. Voor deze jubileumeditie heeft Solar Magazine de redactieraadleden van het eerste uur gevraagd terug te blikken op 10 jaar Solar Magazine.

Alumina ceramic is often used in armour systems. This material is known to have a brittle response under tensile loading, while a ductile response is found when sufficiently high pressures are reached. During projectile impact a ceramic material experiences both tensile loading and high pressures, hence fails in both a brittle and ductile way. Properly capturing the ceramic failure in a single material model remains challenging. A viscosity regularized Johnson-Holmquist-2 model has been used to simulate dynamic loading on alumina ceramic. The simulations show that the brittle and ductile nature of the material can not be captured simultaneously in the current material model. A new failure strain formulation is proposed where the behaviour under tensile and compressive loading can be controlled independently. This allows to properly capture both the brittle and ductile response of the material in a single constitutive framework, with a single set of model parameters. © 2019 Elsevier Ltd

De redactieraad vormt sinds de start van Solar Magazine het kloppend hart van de redactie. Het orgaan bevat onderzoeks- en koepelorganisaties uit de zonne-energiesector. De raad geeft de redactie gevraagd en ongevraagd advies over de redactionele koers die gevaren wordt. Voor deze jubileumeditie heeft Solar Magazine de redactieraadleden van het eerste uur gevraagd terug te blikken op 10 jaar Solar Magazine.

Vibrational piezoelectric energy harvesters are being investigated to replace batteries in embedded sensor systems. The energy density that can be harvested depends on the figure of merit, d33g33, where d33 and g33 are the piezoelectric charge and voltage coefficient. Commonly used piezoelectric materials are based on inorganic ceramics, such as lead zirconium titanate (PZT), as they exhibit high piezoelectric coefficients. However, ceramics are brittle, leading to mechanical failure under large cyclic strains and, furthermore, PZT is classified as a Substance of Very High Concern (SVHC). To circumvent these drawbacks, we fabricated quasi 1–3 potassium sodium lithium niobate (KNLN) ceramic fibers in a flexible polydimethylsiloxane (PDMS) matrix. The fibers were aligned by dielectrophoresis. We demonstrate for the structured composites values of d33g33 approaching 18 pm3 J−1, comparable to that of state-of-the-art ceramic PZT. This relatively high value is due to the reduced inter-particle distance in the direction of the electric field. As a confirmation, the stored electrical energy for both material systems was measured under identical mechanical loading conditions. The similar values for KNLN/PDMS and PZT demonstrate that environmentally friendly, lead-free, mechanically compliant materials can replace state-of-the-art environmentally-less-desirable ceramic materials in piezoelectric vibrational energy harvesters.

De redactieraad vormt sinds de start van Solar Magazine het kloppend hart van de redactie. Het orgaan bevat onderzoeks- en koepelorganisaties uit de zonne-energiesector. De raad geeft de redactie gevraagd en ongevraagd advies over de redactionele koers die gevaren wordt. Voor deze jubileumeditie heeft Solar Magazine de redactieraadleden van het eerste uur gevraagd terug te blikken op 10 jaar Solar Magazine.