Wall Slip of Soft-Jammed Systems: A Generic Simple Shear Process

International audienceFrom well-controlled long creep tests we show that the residual apparent yield stress observed with soft-jammed systems along smooth surfaces is an artefact due to edge effects. By removing these effects we can determine the stress solely associated with steady state wall slip below the material yield stress. This stress is found to vary linearly with the slip velocity for a wide range of materials whatever the structure, the interaction types between the elements and with the wall, and the concentration. Thus wall slip results from the laminar flow of some given free liquid volume remaining between the (rough) jammed structure formed by the elements, and the smooth wall. This phenomenon may be described by the simple shear flow in a Newtonian liquid layer of uniform thickness. For various systems this equivalent thickness varies in a narrow range (35 ± 15 nm)

Wideband Mid Infrared Absorber using surface Doped Black Silicon

Black silicon (BSi) is a synthetic nanomaterial with high aspect ratio nano protrusions inducing several interesting properties such as a very large absorptivity of incident radiation. We have recently shown that heavily doping the BSi in volume enables to significantly enhance its mid infrared absorptivity and tune its spectral range of interest up to 20 micrometer. In the present letter, we explore the effect of surface doping on BSi radiative properties and it absorptance, in particular since surface doping enables reaching even larger dopant concentrations than volume doping but at more limited penetration depths. We considered 12 different wafers of BSi, fabricated with cryogenic plasma etching on n and p-type silicon wafers and doped using ion-implantation with different dopant types, dosages and ion beam energies leading to different dopant concentrations and profiles. The different wafers radiative properties, reflectance, transmittance and absorptance, are measured using Fourier transform infrared spectroscopy. We show that doping an n-type BSi wafer with Phosphorous with a dose of 10^17 atm/cm2 and an energy of 100 keV increases its absorptivity up to of 98% in the spectral range of 1-5 micrometer. We propose a simple phenomenological explanation of the observed results based on the dopant concentration profiles and the corresponding incident radiation penetration depth. Obtained results provide simple design rules and pave the way for using ion-implanted BSi for various applications such as solar energy harvesting, thermo-photovoltaics and infrared radiation sensing where both high absorptance and variable dopant concentration profiles are required

Optimization and AMS Modeling for Design of an Electrostatic Vibration Energy Harvester’s Conditioning Circuit with an Auto-Adaptive Process to the External Vibration Changes

Electrostatic transducers for vibration energy scavenging have been an object to numerous studies, but are still facing major issues relating to their conditioning circuit. One of the most popular ones uses a charge pump and a flyback circuit based on a Buck DC-DC converter (Fig. 1). A commutation between the energy accumulation in the charge pump and the recharge of the buffer capacitor Cres is assured by a switch which is the major bottleneck in the energy harvester circuit. The commutation timing of the switch determines the efficiency of the energy harvesting. In previous papers [1] the switch commutates periodically with some fixed duty ratio. However, this solution is not appropriate when the environment parameters, e.g. the vibration frequency, change. We found that the switching should be ordered by the internal state of the circuit, an not by some fixed timing scenario. We presents how to find the optimal operation mode of the harvester. To validate the study, the system was modeled using a mixed VHDL-AMS - ELDO model

Operationalising emission and toxicity modelling of pesticides in LCA: the OLCA-Pest project contribution

Purpose Current field emission modelling and toxicity characterisation of pesticides suffer from several shortcomings like mismatches between LCI databases and LCIA methods, missing characterisation factors, missing environmental compartments, and environmental impact pathways. The OLCA-Pest project was implemented to address these aspects and to operationalise the assessment of pesticides in LCA. Based on this effort, we propose an approach to integrate pesticide emissions into LCI databases. Methods The PestLCI Consensus Model has been developed in order to estimate emission fractions to different environmental compartments. The initial distribution fractions should be linked to the compartments air, agricultural soil, natural soil, and freshwater. Emissions to off-field surfaces are hereby distributed between agricultural soil, natural soil, and freshwater by using surface cover data. Deposition on the crop surface should be recorded in an emission compartment crop with 13 sub-compartments for crop archetypes for both food and non-food uses. Default emission fractions are provided to calculate the emission fractions for different pesticide application scenarios. Results and discussion A sensitivity analysis shows the effects of the application technique, drift reduction, crop and development stage, field width, and buffer zone on the initial distribution fractions of field-applied pesticides. Recommendations are given for the implementation of a set of default initial distribution fractions into LCI databases, for the organisation of metadata, and for the modelling of pesticide residues in food along the supply chain (processing, storage). Priorities for further research are: improving the modelling of pesticide secondary emissions, further extending emission modeling (e.g. additional application techniques, including cover crops), considering metal-based pesticides in emission models, and systematically assessing human health impacts associated with pesticide residues in food crops. Conclusions The proposed approach allows to preserve the mass balance of the pesticide emitted after application, to make a consistent assessment of ecotoxicity and human toxicity, to define a clear and consistent interface between the LCI and LCIA phases, to estimate initial emission distribution fractions based on existing data, to document metadata transparently and efficiently within crop datasets, and to model the removal of pesticide residues in food during processing.info:eu-repo/semantics/publishedVersio

Optimisation-driven design of sliding mode triboelectric energy harvesters

With the increasing demand of emerging technologies for autonomous sensing, the modelling and optimisation of complete energy harvesting systems are essential to achieve efficient power output. To date, most of the optimisation efforts in enhancing the performance of triboelectric energy harvesters have been focused on the improvement of material properties and on the establishment of figures of merit to assist in the definition of parameters. However, these efforts do not consider the complex relationship between the device structure and power output, physical constraints in place, and varying excitation conditions. This paper fills that gap for the first time by applying an optimisation algorithm to establish mechanisms for optimisation-driven design of sliding-mode triboelectric energy harvesters. A global optimisation methodology is developed to improve its performance, having experimentally validated the numerical model adopted. This work highlights the need for a more robust design framework for applications of triboelectric energy harvesting and proposes a hybrid approach combining the finite element method with analytical models to consider different energy harvesting parameters including the degradation of the charge transfer efficiency due to the edge effect. A novel high-power output sliding-mode triboelectric energy harvesting concept is proposed and its performance is optimised, using the proposed methodology