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This paper presents an experimental validation of an in situ ultrasound technique for tracking the solid-liquid interface during directional solidification of photovoltaic silicon. Ultrasound bursts are introduced from the top into the melt via the tip of a carbon glass waveguide directly plunged into the liquid. Several runs of solidification have been conducted using the same waveguide thus demonstrating its reusability, its mechanical resilience and its appropriate acoustical and chemical compatibility with the melt. We present the times of flight analysis to track the location of the solid-liquid interface. As part of the signal crosses the solidifying ingot, we also measure $c_s$ , the average celerity of sound waves in the solid. Since $c_s$ exhibits a significant dependance on crystal orientation, we consider the possibility to use the echoes to extract some information on the crystalline orientation in the ingot. By quantifying the uncertainties and their dependence with the duration of the experiment in particular, we outline the conditions necessary to detect accurately the average orientation in the solid.

PurposeTrust is one of the main pillars of many communication and interaction domains. Computing is no exception. Fog computing (FC) has emerged as mitigation of several cloud computing limitations. However, selecting a trustworthy node from the fog network still presents serious challenges. This paper aims to propose an algorithm intended to mitigate the trust and the security issues related to selecting a node of a fog network.Design/methodology/approachThe proposed model/algorithm is based on two main concepts, namely, machine learning using fuzzy neural networks (FNNs) and the weighted weakest link (WWL) algorithm. The crux of the proposed model is to be trained, validated and used to classify the fog nodes according to their trust scores. A total of 2,482 certified computing products, in addition to a set of nodes composed of multiple items, are used to train, validate and test the proposed model. A scenario including nodes composed of multiple computing items is designed for applying and evaluating the performance of the proposed model/algorithm.FindingsThe results show a well-performing trust model with an accuracy of 0.9996. Thus, the end-users of FC services adopting the proposed approach could be more confident when selecting elected fog nodes. The trained, validated and tested model was able to classify the nodes according to their trust level. The proposed model is a novel approach to fog nodes selection in a fog network.Research limitations/implicationsCertainly, all data could be collected, however, some features are very difficult to have their scores. Available techniques such as regression analysis and the use of the experts have their own limitations. Experts might be subjective, even though the author used the fuzzy group decision-making model to mitigate the subjectivity effect. A methodical evaluation by specialized bodies such as the security certification process is paramount to mitigate these issues. The author recommends the repetition of the same study when data form such bodies is available.Originality/valueThe novel combination of FNN and WWL in a trust model mitigates uncertainty, subjectivity and enables the trust classification of complex FC nodes. Furthermore, the combination also allowed the classification of fog nodes composed of diverse computing items, which is not possible without the WWL. The proposed algorithm will provide the required intelligence for end-users (devices) to make sound decisions when requesting fog services.

International audience; The aim of this experimental and numerical work is to determine the mass transfer at the wall of a steel cylinder rotating within liquid Lead-Bismuth blend. This is a crucial parameter for the analysis of corrosion tests performed in the CICLAD experimental setup for the investigation of flow assisted corrosion of steel by liquid metals. As a reliable numerical modelling must rely on experimental validation, and since no direct wall mass transfer measurement is possible in CICLAD, a scaled electrochemical model has been achieved. Modelling the turbulence in this rotating configuration is shown to require the use of a Reynolds-Stress Model. A sensitivity to the Schmidt number is observed in the numerical simulations representing the measured mass transfer in the electrochemical model. Simulations dedicated to liquid Pb-Bi are thus presented in addition to those dedicated to the aqueous solution used in the electrochemical model. Following correlations are proposed for the prediction of Fe mass transfer at the wall of a steel rotating cylinder in liquid Pb-Bi: Sh=1.9x10-1 (Re 2 Sc) 0.31 for 2x10 9

The rise of digitization in Industrial Control Systems (ICSs) using Commercial Off-The-Shelf software has stimulated the use of existing IT security solutions. This trend involves serious risks, due to the unsuitability of most existing IT security solutions to ICSs environments. The aim of this study is to prevent Intrusion Detection and Prevention Systems’ (IDPSs) behaviors from degrading the QoS of data transfers between time sensitive subsystems of ICSs. Facilities such as Nuclear Power Plants (NPPs) often have systems using Real Time Operating Systems (RTOS), which have to be response-time deterministic. A module is designed based on the utilization law, queuing theory, and a heuristic algorithm in order to evaluate and propose the optimal security policy and configuration for each role representing a machine. The crux of this approach is that the module integrated with the IDPS, solve an optimization problem using the Bat algorithm to generate a Pareto set of optimal solutions and propose the best one that will guarantee the security required for a role, while maintaining QoS (i.e. response time inferior to the Worst Case Execution Time (WCET)). MATLAB is used to simulate the proposed method. The results show that the IDPS efficiently selects the best security policies for all active roles and minimize the chances of WCET violations, thus, avoid any undesirable effects. As shown in the simulation scenarios, the module was able to propose a policy which represents an optimal solution where the security strength value is 0.68942 and the response time is 0.219015 s. Moreover, in the second scenario, even though the first run did not find any optimal solution, the improvement introduced using the urgency flag, solve the problem and propose a security policy for the role under evaluation. Therefore, the approach guarantees the maximum security possible without violating the WCET of roles. The study sheds light on the deficiencies and weaknesses of security systems in some demanding environments. Security policies might be a hindrance to these types of security systems when stringent constraints (e.g. real time response) are imposed. Consequently, the proposed method mitigating the issue would be a major contribution to the Information Communication Technology security field, if integrated with IDPSs designed to protect time sensitive ICSs using ROTSs. Moreover, it provides a much-needed approach to help guarantee real-time, deterministic performance, and security requirements needed by time sensitive systems.

Efficient numerical models are derived for problems of natural convection and material solidification in a horizontal differentially heated slender cavity. These 2D1/2 models are obtained by averaging the equations of momentum, heat, and mass conservation along the transverse direction assuming both a constant temperature and a well defined velocity profile in this direction. Based on our former works, the transverse velocity profile is assumed to be either a Poiseuille profile ( 2 D p 1 / 2 model), or Hartmann-type profiles featuring two boundary layers on the sides of a uniform bulk ( 2 D H 1 / 2 model). For this 2 D H 1 / 2 model, however, a parameter δ (giving the boundary layer thickness) has to be adjusted: optimal values have been found in a large range of the control parameters and expressed as a reliable fitted function of G r . The ability of the model to reproduce 3D results in a 2D framework is investigated in a large range of the control parameters (Prandtl number P r and Grashof number G r ); the validity domain of the model in this parameter space is also clarified and rigorously defined. A good precision is obtained for natural convection problems (intensity of the flow, temperature field) as well as for solid-liquid phase change problems (shape, position, and evolution of the front). A comparison with unpublished experimental data of solidification of pure tin is also conducted. The boundary conditions for the simulation are first defined after a post-treatment of the time-dependent experimental data in order for them to be representative of the experimental process despite a significant and time dependent thermal resistance between the walls of the crucible and the liquid. A very good agreement is observed between the 2 D H 1 / 2 model and the experimental measurements for this pure tin solidification experiment in the AFRODITE setup.

International audience

International audience; RESUME : Nous dressons ici une revue non-exhaustive des principales analogies relevées dans les différentes branches de la physique (mécanique, électrocinétique, électromagnétisme, thermodynamique, transferts thermiques, hydraulique). Ces analogies sont résumées sous forme de tableaux, où nous insistons notamment sur les différents élé-ments mis en jeu lors des échanges d'énergie, que ces éléments aient une fonction de dissipation, de stockage, ou d'inertie. Nous mettons également en parallèle certaines propriétés remarquables pour lesquelles des analogies peuvent aussi être identifiées, en l'occurrence les lois des mailles et des noeuds, les associations en série ou en parallèle, et les équivalents physiques au circuit R.L.C. Nous finissons par un focus sur l'analogie entre mécanique des fluides et élec-tromagnétisme, en présentant les équations hydrodynamiques de Maxwell, et en faisant correspondre grandeurs hydro-dynamiques et électromagnétiques.https://cetsis2018.sciencesconf.org/conference/cetsis2018/livre_des_actes.pdf

International audience; Most of the High Performance Research Reactors (HPRR) are made of plates undergoing a limited swelling during irradiation. Measuring the fuel thickness or the inter-plate distance is then a promissing way to obtain information on the fuel element irradiation history. The experimental constraints are however quite heavy due to the aimed resolution and the element geometry. In order to perform such measurements, a high resolution ultrasonic device was designed. It was thinned down to 1 mm in order to be inserted into the reactor water-channel. The system is then excited with a 120 MHz central frequency burst and the distance measurement is carried out through the ultrasonic waves' time of flight estimation. A series of experiments was performed on a full size irradiated fuel element of the "Institut Laue-Langevin" reactor proving the feasibility of real-time in-situ measurements.

International audience; The present paper focuses on solute segregation occurring in directional solidification processes with sharp solid/liquid interface, like silicon crystal growth. A major difficulty for the simulation of such processes is their inherently multi-scale nature: the impurity segregation problem is controlled at the solute boundary layer scale (micrometers) while the thermal problem is ruled at the crucible scale (meters). The thickness of the solute boundary layer is controlled by the convection regime and requires a specific refinement of the mesh of numerical models. In order to improve numerical simulations, wall functions describing solute boundary layers for convecto-diffusive regimes are derived from a scaling analysis. The aim of these wall functions is to obtain segregation profiles from purely thermo-hydrodynamic simulations , which do not require solute boundary layer refinement at the solid/liquid interface. Regarding industrial applications, various stirring techniques can be used to enhance segregation, leading to fully turbulent flows in the melt. In this context, the scaling analysis is further improved by taking into account the turbulent solute transport. The solute boundary layers predicted by the analytical model are compared to those obtained by transient segregation simulations in a canonical 2D lid driven cavity configuration for validation purposes. Convective regimes ranging from laminar to fully turbulent are considered. Growth rate and molecular diffusivity influences are also investigated. Then, a procedure to predict concentration fields in the solid phase from a hydrodynamic simulation of the solidification process is proposed. This procedure is based on the analytical wall functions and on solute mass conservation. It only uses wall shear-stress profiles at the solidification front as input data. The 2D analytical concentration fields are directly compared to the results of the complete simulation of segregation in the lid driven cavity configuration. Finally, an additional output from the analytical model is also presented. We put in light the correlation between different species convecto-diffusive behaviour; we use it to propose an estimation method for the segregation parameters of various chemical species knowing segregation parameters of one specific species.

The main objective of this work is to study experimentally the primary instability of non-Newtonian film flows down an inclined plane. We focus on low-concentration shear-thinning aqueous solutions obeying the Carreau law. The experimental study essentially consists of measuring wavelengths in marginal conditions, which yields the primary stability threshold for a given slope. The experimental results for neutral curves presented in the $(Re,f_{c})$ and $(Re,k)$ planes (where $f_{c}$ is the driving frequency, $k$ is the wavenumber and $Re$ is the Reynolds number) are in good agreement with the numerical results obtained by a resolution of the generalized Orr–Sommerfeld equation. The long-wave asymptotic extension of our results is consistent with former theoretical predictions of the critical Reynolds number. This is the first experimental evidence of the destabilizing effect of the shear-thinning behaviour in comparison with the Newtonian case: the critical Reynolds number is smaller, and the ratio between the critical wave celerity and the flow velocity at the free surface is larger.

International audience; We combine an effective diffusivity model with a numerical approach initially proposed by Meyer (1981) to simulate transient heat and mass transfer phenomena in a directionally solidifying Sn-Bi rod. This particularly efficient 1D numerical model is light enough to be used within the frame of optimization methods at reasonable numerical cost. This approach is tested against reference in situ measurements obtained under microgravity conditions during the Mephisto program. We simulate the final homogenization transient of several experimental runs with different pulling velocities. The solid/liquid interface temperature evolution with time is extracted from the simulations and compared with that obtained by Seebeck in line measurements. After optimization of the model the observed discrepancy between the simulated and measured data is less than 1.5%. This validates both the proposed very efficient 1D numerical approach and the consistency of the set of thermophysical parameters values for dilute Sn-Bi alloys.

International audience; Acoustic streaming designates the ability to drive quasisteady flows by acoustic propagation in dissipative fluids and results from an acoustohydrodynamics coupling. It is a noninvasive way of putting a fluid into motion using the volumetric acoustic force and can be used for different applications such as mixing purposes. We present an experimental investigation of a kind of square flow driven by acoustic streaming, with the use of beam reflections, in a water tank. Time-resolved experiments using particle image velocimetry have been performed to investigate the velocity field in the reference plane of the experiments for six powers: 0.5, 1, 2, 4, 6, and 8 W. The evolution of the flow regime from almost steady to strongly unsteady states is characterized using different tools: the plot of time-averaged and instantaneous velocity fields, the calculation of presence density maps for vortex positions and for the maximal velocity and vorticity crest lines, and the use of spatiotemporal maps of the waving observed on the jets created by acoustic streaming. A transition is observed between two regimes at moderate and high acoustic forcing.

International audience; Over the last decade, various nanomaterial systems have been developed as important and powerful strategies to deliver conventional drugs, recombinant proteins, vaccines, aptamers, siRNA, nucleotides and genes. In particular, alongside polymeric, solid–lipid, magnetic and metal based nanoparticles, polymeric micelles and linear polymers, dendrimer nanostructures represent useful nano-carriers in medicine. Today's challenge to find safe and innovative drugs remains as critical as ever.In this review, for the first time, we define the term dendrimer space concept as an approach that affords a new paradigm of thought for medicinal chemists and opens new and promising avenues toward the identification of original dendrimer-based drugs. Thus, the dendrimer space defines a new ‘druggable’ cluster that is included within the vast volume of chemical space. The dendrimer space concept took its inspiration from both the concepts of ‘druglikeness’ and ‘druggability’, which are fully and practically integrated into the drug discovery process, and from different methods of exploration and navigation, such as the ‘chemography’ approach, in chemical space. It was further influenced by the large number of biomedical applications using dendrimers that were developed from only a handful existing in the early 1990s.To define the boundaries of the dendrimer space, this review first focuses on the recent progress in the exploration of specific sub-chemical spaces (clusters within the continuum of chemical space). Chemical space is defined as the entire collection of all meaningful chemical compounds, and its full examination is insuperable. The compounds included in these different clusters can be mapped onto the coordinates of a multidimensional descriptor space, with such variables as physicochemical properties or topological characteristics, and are based on the concepts of ‘druglikeness’ (drug-like space) and ‘leadlikeness’. In addition, the discrete areas occupied by specific biologically active compounds define the boundaries of the ‘target class’ clusters, which can overlap the drug-like space. Second, this review gives an overview of the nanopharmaceutical properties of dendrimers, both as biologically active derivatives per se and as drug delivery systems. Finally, several perspectives using dendrimers as new delivery platforms based on the concept of dendrimer space are presented.

International audience; Most high flux reactors possess for research purposes fuel elements composed of plates. Their relative distance is a crucial parameter, particularly concerning the irradiation history. For the High Flux Reactor (RHF) of the Institute Laue-Langevin (ILL), the measurement of this distance with a microscopic resolution becomes extremely challenging. To address this issue, a specific ultrasonic transducer, presented in a first paper, has been designed and manufactured to be inserted into the 1.8 mm width channel existing between curved fuel plates. It was set on a blade yielding a total device thickness of 1 mm. To achieve the expected resolution, the system is excited with frequencies up to 70 MHz and integrated into a set of high frequency acquisition instruments. Thanks to a specific signal processing, this device allows the distance measurement through the evaluation of the ultrasonic wave time of fight. One of the crucial points is then the evaluation of the local water temperature inside the water channel. To obtain a precise estimation of this parameter, the ultrasonic sensor is used as a thermometer thanks to the analysis of the spectral components of the acoustic signal propagating inside the sensor multilayered structure. The feasibility of distance measurement was proved during the December 2013 experiment in the RHF fuel element of the ILL. Some of the results will be presented as well as some experimental constraints identified to improve the accuracy of the measurement in future works.

International audience; Most high flux reactors for research purposes have fuel elements composed of plates and not pencils. The measure of inter-plate distance of a fuel element is tricky since a resolution of a micron is searched to measure plate swellings of about ten microns while the dimension between the plates is close to the millimeter. This measure should provide information about the fuel and particularly its history of irradiation. That is the reason why a solution has been considered: a robust device based upon high frequency ultrasonic probes adapted to the high radiation environment and thinned to 1 mm to be inserted into a 1.8 mm width water channel between two fuel plates. To achieve the expected resolution, the system is excited with frequencies up to 150 MHz. Thanks to a specific signal processing, this device allows the distance measurement through an ultrasonic wave's time of flight. The feasibility of such challenging distance measurement has already been proved with success on a full size irradiated fuel element of the RHF.