Application of Ultrasonic Beam Modeling to Phased Array Testing of Complex Geometry Components

For several years, the French Atomic Energy Commission (CEA) has developed phased array techniques to improve defect characterization and adaptability to various inspection configurations [1]. Such techniques allow to steer and focus the ultrasonic beam radiated by a transducer split into a set of individually addressed elements, using amplitude and delay laws. For most conventional systems, those delay laws are extracted from geometric ultrasonic paths between each element of the array and a geometric focusing applied to perform beam-forming abilities [2] for simple geometry components (e.g. beam- steering over a plane specimen), whereas experimental delays can be supplied to the array at transmission and reception to optimally adapt the ultrasonic beam to the detected defect, in a so-called self-focusing process [3,4]. This method, relevant for complex material or geometry leading to phase distortion or complex paths that cannot be predicted by simple geometrical calculations, obviously requires the existence of a reflector and the ultrasonic beam radiated by the experimental delay law cannot be known. Therefore this technique is used to improve defect detection (optimal sensibility) rather than defect characterization. To assess complex geometry components inspection with an adaptive system, the CEA has developed new modeling devoted to predict the ultrasonic field radiated by arbitrary transducers through complex geometry and material specimen [5]. A model allows to compute optimized delay laws to preserve the characteristics of the beam through the complex surface, as well as the actual radiated field using those delays. This paper presents two applications of this model : the inspection of a misaligned specimen, and the inspection of an irregular surface

Low-energy helium ion irradiation-induced amorphization and chemical changes in olivine: Insights for silicate dust evolution in the interstellar medium

We present the results of irradiation experiments aimed at understanding the structural and chemical evolution of silicate grains in the interstellar medium (ISM). A series of He+ irradiation experiments have been performed on ultra-thin olivine, (Mg,Fe)2SiO4, samples having a high surface/volume (S/V) ratio, comparable to the expected S/V ratio of interstellar dust. The energies and fluences of the helium ions used in this study have been chosen to simulate the irradiation of interstellar dust grains in supernovae shock waves. The samples were mainly studied using Analytical Transmission Electron Microscopy (ATEM). Our results show that olivine is amorphized by low-energy ion irradiation. Changes in composition are also observed. In particular, irradiation leads to a decrease of the atomic ratios O/Si and Mg/Si as determined by X-ray Photoelectron Spectroscopy (XPS) and by X-ray Energy Dispersive Spectroscopy (EDS). This chemical evolution is due to the differential sputtering of atoms near the surfaces. We also observe a reduction process resulting in the formation of metallic iron. The use of very thin samples emphasizes the role of surface/volume ratio and thus the importance of the particle size in the irradiation-induced effects. These results allow us to account qualitatively for the observed properties of interstellar grains in different environments, i.e., at different stages of their evolution : chemical and structural evolution in the interstellar medium, from olivine to pyroxene-type and from crystalline to amorphous silicates, porosity of cometary grains as well as the formation of metallic inclusions in silicatesThe Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Effects of body weight, water temperature and ration size on ammonia excretion by the areolated grouper (Epinephelus areolatus) and mangrove snapper (Lutjanus argentimaculatus)

The effects of body weight, water temperature and ration size on ammonia excretion rates of the areolated grouper Epinephelus areolatus and the mangrove snapper Lutjanus argentimaculatus were investigated. Under given experimental conditions, L. argentimaculatus had a higher weight-specific ammonia excretion rate than E. areolatus. Weight-specific ammonia excretion rates of fasted individuals of both species showed an inverse relationship with body weight (W, g wet wt.), but a positive relationship with water temperature (t, °C). The relationships for total ammonia nitrogen (TAN) were: E. areolatus: TAN (mg N kg-1 d-1) = 21.4. exp(0.11t) · W-0.43 (r2 = 0.919, n = 60); L. argentimaculatus: TAN (mg N kg-1 d-1) = 121.5 · exp(0.12t) · W-0.55 (r2=0.931, n = 60). Following feeding, the weight-specific ammonia excretion rate of E. areolatus increased, peaked at 2 to 12 h (depending on temperature), and returned to pre-feeding levels within 24 h. A similar pattern was observed for L. argentimaculatus, with a peak of TAN excretion being found 6 to 12 h after feeding. Stepwise multiple regression analysis indicated that weight-specific TAN excretion rates of both species increased with increasing temperature and ration (R, percent body wt. d-1): E. areolatus: TAN (mg N kg-1 d-1) = 22.8 · t - 28.8 · R 378.2 (r2 = 0.832, n = 24); L. argentimaculatus: TAN (mg N kg-1 d-1) = 22.9 · t - 25.4 · R 216.4 (r2= 0.611, n = 24). The effect of body weight on weight-specific postprandial TAN excretion was not significant in either species (p > 0.05). This study provides empirical data for estimating ammonia excretion of these two species under varying conditions. This has application for culture management.link_to_subscribed_fulltex

Flexible variable-specific-impulse electric propulsion systems for planetary missions

Variable-specific-impulse electric propulsion systems can provide important advantages and cost reductions to any scale of planetary mission. The first part of this paper describes their potential benefits, with special emphasis on mission analysis aspects. The second part identifies the physical limitations of traditional electric propulsion technologies and presents some preliminary development results achieved within the frame of ongoing European activities

Flexible variable-specific-impulse electric propulsion systems for planetary missions

Variable-specific-impulse electric propulsion systems can provide important advantages and cost reductions to any scale of planetary mission. The first part of this paper describes their potential benefits, with special emphasis on mission analysis aspects. The second part identifies the physical limitations of traditional electric propulsion technologies and presents some preliminary development results achieved within the frame of ongoing European activitie

Flexible variable-specific-impulse electric propulsion systems for planetary missions

Variable-specific-impulse electric propulsion systems can provide important advantages and cost reductions to any scale of planetary mission. The first part of this paper describes their potential benefits, with special emphasis on mission analysis aspects. The second part identifies the physical limitations of traditional electric propulsion technologies and presents some preliminary development results achieved within the frame of ongoing European activities

Flexible variable-specific-impulse electric propulsion systems for planetary missions

Variable-specific-impulse electric propulsion systems can provide important advantages and cost reductions to any scale of planetary mission. The first part of this paper describes their potential benefits, with special emphasis on mission analysis aspects. The second part identifies the physical limitations of traditional electric propulsion technologies and presents some preliminary development results achieved within the frame of ongoing European activities

Harmattan, sea breeze, Nocturnal Low-Level Jet dynamics and aerosol variability in a coastal area of Senegal, Western Africa

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