Study of the Photocrosslinking of Ethylene Propylene Diene Monomer Terpolymer Under UV Irradiation

The photocrosslinking of thick samples of 5-ethylidene-2-norbornene–ethylene propylene diene monomer (ENB-EPDM) under air at room temperature was investigated. First, a model study was carried out on low-molecular weight oligomers: squalene, 1,2-polybutadiene, and 1,4-polybutadiene. Several crosslinking agents (meth(acrylics), bismaleimide, and thiol) combined with various photoinitiators were tested to improve the reactivity of these oligomers under UV irradiation. Gel contents, crosslinking densities, viscosities, and viscoelastic properties were measured in order to characterize the extent of crosslinking. Acrylate-based crosslinking agents appeared to be the most reactive species and these results were then applied to a low-molecular weight EPDM. Several photoinitiators were tested and benzophenone turned out to be the most efficient photoinitiator when combined with trimethylolpropane triacrylate. Finally, a commercial EPDM was subsequently photocrosslinked and high gel content and crosslinking density were obtained after only 2 min of irradiation. POLYM. ENG. SCI., 60:95–103, 2020. © 2019 Society of Plastics Engineers     

Study of ITER equatorial port plug handling system and vacuum sealing interface

In the field of the ITER port plug engineering and integration task, CEA has contributed to define proposals concerning the port plugs vacuum sealing interface with the vessel flange and the equatorial plug handling.The 2001 baseline vacuum flange sealing consisted of TIG welding of a 316L strip plate on to U shapes. This arrangement presented some issues like welding access, implementation of tools, lip consumption, complex local leak test, continuous leak checking. Therefore, an alternate sealing solution based on the use of metallic gaskets is proposed. The different technical aspects are discussed to explain how this design can simplify the maintenance and deal with safety and vacuum requirements.The design of the mechanical attachment and vacuum sealing of the plug has constantly evolved, but the associated remote handling equipment was not systematically reviewed. An update of the cask and maintenance procedure was studied in order to design it in accordance with the last generic plug flange design. This includes a concept of a gripping system that uses the plug flange bolting area and, to help the remote handling process, a cantilever assisting system is suggested to increase the reliability of the transfer operation between vacuum vessel and cask.     

Effect of initial powder type on the hydrogen storage properties of high-pressure torsion consolidated Mg

While severe plastic deformation (SPD) on bulk samples has been widely applied for modifying the H-sorption properties, there has been little attention towards the use of SPD on powder materials. In this context, the aim of the present work was to compare the H-storage properties of high-pressure torsion (HPT) consolidated products obtained from two distinct Mg powder precursors: atomized micro-sized and condensed ultrafine powder particles. The results showed that the nature of the initial powder precursor had a pronounced effect on the H-sorption behavior. The HPT product obtained from the condensed ultrafine powder showed faster absorption kinetics than the consolidated product obtained from the atomized powder. However, the HPT product obtained from atomized powder could absorb more hydrogen and showed faster desorption kinetics corresponding to a lower activation energy. These results are discussed by taking into account the effectiveness of the HPT process to refine the grain sizes and differences in the dispersion of fine MgO oxide particles.     

Numerical modelling of geothermal vertical heat exchangers for the short time analysis using the state model size reduction technique

According to the introduction of a dynamic operating mode in ground-coupled heat pump systems, a short time analysis within and around borehole heat exchangers is required in the modern geothermal system simulation. A numerical modelling could be a proper answer for this challenge. However, the numerical model is time consuming and necessitates a large memory particularly in such large systems. Therefore, the state model size reduction technique has been applied in this paper with various numerical techniques particularly in the finite elements method. As a result, the reduced model developed is: (a) relevant with a validation using a traditional analytical model (using 100% modes) and (b) efficient in calculation time, only using 6% modes and consequently reducing time consumption up to 95%.     

Cohesive model approach to the nucleation and propagation of cracks due to a thermal shock

This paper studies the initiation of cohesive cracks in the thermal shock problem through a variational analysis. A two-dimensional semi-infinite slab with an imposed temperature drop on its free surface is considered. Assuming that cracks are periodically distributed and orthogonal to the surface, at short times we show that the optimum is a distribution of infinitely close cohesive cracks. This leads us to introduce a homogenized effective behavior which reveals to be stable for small times, thanks to the irreversibility. At a given loading cracks with a non-cohesive part nucleate. We characterize the periodic array of these macro-cracks between which the micro-cracks remain. Finally, for longer times, the cohesive behavior converges towards that from Griffith’s evolution law. Numerical investigations complete and quantify the analytical results.     

Comparison of nonparametric methods in nonlinear mixed effects models

During the drug development, nonlinear mixed effects models are routinely used to study the drug’s pharmacokinetics and pharmacodynamics. The distribution of random effects is of special interest because it allows to describe the heterogeneity of the drug’s kinetics or dynamics in the population of individuals studied. Parametric models are widely used, but they rely on a normality assumption which may be too restrictive. In practice, this assumption is often checked using the empirical distribution of random effects’ empirical Bayes estimates. Unfortunately, when data are sparse (like in patients phase III clinical trials), this method is unreliable. In this context, nonparametric estimators of the random effects distribution are attractive. Several nonparametric methods (estimators and their associated computation algorithms) have been proposed but their use is limited. Indeed, their practical and theoretical properties are unclear and they have a reputation for being computationally expensive. Four nonparametric methods in comparison with the usual parametric method are evaluated. Statistical and computational features are reviewed and practical performances are compared in simulation studies mimicking real pharmacokinetic analyses. The nonparametric methods seemed very useful when data are sparse. On a simple pharmacokinetic model, all the nonparametric methods performed roughly equivalently. On a more challenging pharmacokinetic model, differences between the methods were clearer.     

Experimental study of a mechanically ventilated double-skin façade with venetian sun-shading device: A full-scale investigation in controlled environment

The aim of this article is to present results of an experimental campaign performed on a full-scale facility provided with a double-skin façade. The behaviour of this architectural concept is tested under controlled climatic conditions. A summer case is scrutinised under different configurations: variation of the airflow through the double-skin façade and different angle of the solar shading device. This paper describes the experimental conditions, as well the test facility and the tested façade element. The results show the temperatures of the test cell and the façade and how they depend on the climatic conditions and the sun-shading device blade angles. One objective of this research was to measure and provide extensive data set detailing air and surface temperatures on the double-skin façade, together with airflow rates and air velocities. The experiments are fully described so that the results can be used for the validation of numerical models dealing with ventilated double-skin façades with venetian sun-shading device.     

Improving light absorption in organic solar cells by plasmonic contribution

Plasmonic phenomenon inside the materials composing an organic solar cell based on a photoactive poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene):(6,6)-phenyl-C₆₁-butyric-acid-methyl ester (MEH-PPV:PCBM) bulk heterojunction is studied using Finite Difference Time Domain (FDTD) method calculations and the modeling results are compared with experimental results.Enhanced absorptance of light up to 50% is experimentally obtained in a 50-nm-thick blend layer including spin-coated silver nanospheres with a diameter of 40 nm. FDTD calculations based on the design of 2D-grating of nanoparticles confirm the high values of absorptance. Spatial distributions of electromagnetic field power density in the structures show confinement of the power at the interface or in the vicinity of the nanoparticles depending on the wavelength and on the preferential directions.     

Isochronism defect for various doubly rotated cut quartz resonators

It has been shown in earlier works that the amplitude-frequency effect [also called isochronism defect (ID) or anisochronism] could be a limitation factor on ultrastable oscillators. Theoretical studies based on the nonlinear theory of piezoelectricity have already been developed to explain the amplitude-frequency effect. So, it is possible to estimate the dependence of the ID versus various parameters of the resonator design (overtone rank, radius of curvature, electrodes diameter, etc.). However, because of the lack of available fourth-order elastic coefficients, it is not possible to predict the ID of any resonant frequency of a given trapped energy resonator. To tentatively find orientations of plates exhibiting a quasi- ID, we have realized electroded resonators with different orientations and curvatures. We present results that verify, particularly, the R/sup -1/2/ dependence of the amplitude-frequency effect versus radius of curvature. Moreover, we show that the ID can be positive or negative, that it can vary from one orientation to other one of about one order of magnitude, and that there exists a thermal compensated mode for which the amplitude-frequency effect is .     

Helicoidal vortex model for steady and unsteady flows

A helicoidal vortex model is used to predict the flow past the blades of a wind turbine. As the tip speed ratio (TSR) varies, the environment in which the blades operate varies, and for low enough TSR, the local angle of attack α will be larger than (α)_Clmax, the incidence of maximum lift. The problem becomes highly nonlinear and it is shown that adding an artificial viscosity term to the equation allows the iterative algorithm to converge toward a smooth solution that is physically acceptable.The introduction of unsteady effects is useful to understand the cyclic forces and moments due to yaw or tower interaction, both for the design of blades to account for fatigue and for power output prediction. The 2-D impulsively plunging plate problem is solved with a semi-implicit scheme and the integral and numerical solutions compared and shown to be in excellent agreement. A 2-D test case to study the convection of a periodic shedding of vorticity downstream of a blade element is analyzed using the same semi-implicit algorithm and a stretched mesh similar to that used to model a turbine vortex sheet. The scheme captures accurately the vorticity distribution in the wake. Finally, the scheme is applied to the simulation of the NREL two-bladed rotor in yaw to assess the validity of the approach.