Optimization of ultrasonic arrays design and setting using a differential evolution

Optimization of both design and setting of phased arrays could be not so easy when they are performed manually via parametric studies. An optimization method based on an Evolutionary Algorithm and numerical simulation is proposed and evaluated. The Randomized Adaptive Differential Evolution has been adapted to meet the specificities of the non-destructive testing applications. In particular, the solution of multi-objective problems is aimed at with the implementation of the concept of pareto-optimal sets of solutions. The algorithm has been implemented and connected to the ultrasonic simulation modules of the CIVA software used as forward model. The efficiency of the method is illustrated on two realistic cases of application: optimization of the position and delay laws of a flexible array inspecting a nozzle, considered as a mono-objective problem; and optimization of the design of a surrounded array and its delay laws, considered as a constrained bi-objective problem.     

Molecular Study of a Hoxa2 Gain-of-Function in Chondrogenesis: A Model of Idiopathic Proportionate Short Stature

In a previous study using transgenic mice ectopically expressing Hoxa2 during chondrogenesis, we associated the animal phenotype to human idiopathic proportionate short stature. Our analysis showed that this overall size reduction was correlated with a negative influence of Hoxa2 at the first step of endochondral ossification. However, the molecular pathways leading to such phenotype are still unknown. Using protein immunodetection and histological techniques comparing transgenic mice to controls, we show here that the persistent expression of Hoxa2 in chondrogenic territories provokes a general down-regulation of the main factors controlling the differentiation cascade, such as Bapx1, Bmp7, Bmpr1a, Ihh, Msx1, Pax9, Sox6, Sox9 and Wnt5a. These data confirm the impairment of chondrogenic differentiation by Hoxa2 overexpression. They also show a selective effect of Hoxa2 on endochondral ossification processes since Gdf5 and Gdf10, and Bmp4 or PthrP were up-regulated and unmodified, respectively. Since Hoxa2 deregulation in mice induces a proportionate short stature phenotype mimicking human idiopathic conditions, our results give an insight into understanding proportionate short stature pathogenesis by highlighting molecular factors whose combined deregulation may be involved in such a disease.     

Coupling of head and body movement with motion of the audible environment.

The authors asked whether standing posture could be controlled relative to audible oscillation of the environment. Blindfolded sighted adults were exposed to acoustic flow in a moving room, and were asked to move so as to maintain a constant distance between their head and the room. Acoustic flow had direct (source) and indirect (reflected) components. Participants exhibited strong coupling of postural motion with room motion, even when direct information about room motion was masked and was available only in reflected sound. Patterns of hip–ankle coordination closely resembled patterns observed in previous research involving coupling of sway with a visible moving room. The results demonstrate that blindfolded adults can control the dynamics of stance relative to motion of the audible environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of a Cooperative Beacon-Free MAC Layer for Body Area Networks

This paper discusses medium access control (MAC) issues for body area networks (BANs), relying on an Ultrawide Band Impulse radio (UWB-IR) physical layer. BANs are bound to be coordinated by a powerful device like a smart-phone, which manage the access of the nodes on a beaconed fashion. But in some particular situations, the coordinator may disappear and/or be not yet available. These transient situations shall be addressed and a beacon-free medium access control is desirable. We propose a beacon-free MAC layer, based on a collaborative version of the preamble sampling approach. This is designed to address the European regulatory low duty cycle (LDC) constraint, which UWB devices must comply to. A Markov chain model is given to describe the protocol. By means of simulations, we first show that the model is accurate and secondly that this protocol looks able to manage various BANs configurations.     

Single frequency electrochemical impedance investigation of zero charge potential for different surface states of Cu–Ni alloys

Adsorption of sulphate anions onto polycrystalline pure copper, pure nickel and two copper–nickel alloys was explored by performing zero charge potential E _PZC measurements. E _PZC measurements were performed by differential capacitance analysis using single?frequency electrochemical impedance spectroscopy. E _PZC and surface charge of the studied materials were analysed for different surface states: bare—immediately after cathodic polarisation and after 5 h of immersion in a 0.1 M Na₂SO₄ solution. According to the surface state and nature of the studied materials, the choice of the appropriate measuring frequency was investigated. Specific methodologies dedicated to the study of electrode/electrolyte interfaces are then presented for bare metal, metals covered by corrosion products and metals covered by passive film. In the presence of passive film, the space charge capacitance interferes with the differential capacitance measurements, and its influence is discussed in the framework of semiconductor electrochemistry.     

An active vision system for multitarget surveillance in dynamic environments.

This paper presents a novel agent-based method for the dynamic coordinated selection and positioning of active-vision cameras for the simultaneous surveillance of multiple objects-of-interest as they travel through a cluttered environment with a-priori unknown trajectories. The proposed system dynamically adjusts not only the orientation but also the position of the cameras in order to maximize the system's performance by avoiding occlusions and acquiring images with preferred viewing angles. Sensor selection and positioning are accomplished through an agent-based approach. The proposed sensing-system reconfiguration strategy has been verified via simulations and implemented on an experimental prototype setup for automated facial recognition. Both simulations and experimental analyses have shown that the use of dynamic sensors along with an effective online dispatching strategy may tangibly improve the surveillance performance of a sensing system.     

Chromium-oxide Growth on Fe–Cr–Ni Alloy Studied with Grazing-emission X-ray Fluorescence

Using grazing-emission X-ray fluorescence (GEXRF), isothermal oxidation of the alloys 55Fe–25Cr–20Ni and 55Fe–25Cr–20Ni(+0.3Y) (wt.%) were studied as a function of oxidation time at 750 °C in O₂. In addition, the effect of thermal cycling was studied. Using GEXRF, oxide thickness, the Cr-depletion zone in the substrate, and Fe and Ni concentrations in the oxide were monitored as a function of oxidation time. Scanning-electron microscopy was used to independently measure the Cr-depletion zone. Raman spectroscopy was used to measure the concentration of Fe₂O₃ appearing in the oxides in early oxidation (less than 2 h). Both GEXRF and Raman measurements show that the thermally-grown chromium oxide purifies with extended oxidation; initially abundant Fe₂O₃ became undetectable after 2 h of oxidation. However, the total Fe concentration was still ∼3% after 2 h but systematically decreased with further oxidation. Thermal cycling had no effect on these results.      

A complete chronicle discovery approach: application to activity analysis

Discovering temporal patterns hidden in a sequence of events has applications in numerous areas like network failure analysis, customer behaviour analysis, web navigation pattern discovery, etc. In this article, we present an approach to the discovery of chronicles hidden in the interaction traces of a human activity with the intention of characterizing some interesting tasks. Chronicles are a special type of temporal patterns, where temporal orders of events are quantified with numerical bounds. The algorithm we present is the first existing chronicle discovery algorithm that is complete. It is a chronicle discovery framework that can be configured to behave exactly as non‐complete algorithms existing in litterature with no reduction of performance, but it can also be extended to other useful chronicle discovery problems like hybrid episode discovery. We show that the complete chronicle discovery problem has a very high complexity but we argue and illustrate that this high complexity is acceptable when the knowledge discovery process in which our algorithm takes part is real time and interactive. The platform Scheme Emerger, also presented in this paper, has been developed in order to implement the algorithm and to support graphically the real time and interactive chronicle discovery process.     

Non-proportional Repartition Rules Optimize Environmental Flows and Energy Production

In order to meet the growing demand for energy, the development of hydropower leads to an increase of the river exploitation by human activities. Thereby, water management has become a major issue in the energy transition. A better definition of the flow release rules is now required to improve the Minimal Flow Requirement (MFR) concept, which has long been used in spite of its environmental inconsistency. In this work, we present a class of non-proportional redistribution rules that broadens the spectrum of dynamic flow releases based on proportional redistribution for run-of-the-river power plants. We adapt the mathematical form of the Fermi-Dirac statistical distribution to engineer a novel class of redistribution functions. In particular, such functions are used to define the fraction of water allocated to the environment depending on the inflow at the intake. The theoretical background as well as the economic interpretation is presented, and the ability to generate variable flow releases carefully discussed. MFR, proportional and non-proportional distribution policies are then applied to a real case study and their respective economic and environmental efficiencies quantitatively compared. We show that non-proportional distribution policies allow for operating conditions actually close to the Pareto frontier, which improve both efficiencies with respect to those obtained from some traditional MFR and proportional policies.