Application of phased array techniques to coarse grain components inspection

Ultrasonic inspection of cast stainless steel components from primary and auxiliary cooling circuits of French Nuclear Power Plant has to face with major difficulties due to the coarse grained structure of these materials. Attenuation losses and structural noise are encountered, which limits the performances of defect detection ability, mostly in terms of degraded signal-to-noise ratio and poor sensitivity. To overcome such problems, theoretical and experimental studies have been achieved at the French Atomic Energy Commission, with support from the French Institute for Radiological Protection and Nuclear Safety. Experimental studies have been performed over stainless steel specimen of known coarse structure (equiaxial grains and/or elongated grains), containing artificial reflectors (cylindrical holes and electro-eroded surface breaking notches). Those mock-ups have been inspected using contact probes of different array designs (linear or matrix splitting), and using pulse echo or dual-element techniques. Such arrays allow to control the ultrasonic beam so as to investigate different inspection angles and focusing depths. Experiments were carried out using oblique longitudinal waves, using delay laws computed by a specific model, taking account of acoustical and geometrical properties of the probes and the inspected component. In addition, specific reconstruction techniques have been investigated to enhance the signal-to-noise ratio as well as spatial resolution. These techniques are based on beam-forming summation and multi-angle inspections. Experimental results show that such techniques allow to reduce the speckle noise and to optimise the beam resolution. Those increased performances allow to detect and to size small planar defects located at the inner wall of a thick specimen, using corner and tip diffraction echoes.     

At-sea measurements of sound penetration into sediments using a buried vertical synthetic array

Acoustic bottom penetration experiments were carried out in a medium-grain sandy bottom at a site in St. Andrews Bay, Florida. These investigations used a new buried, vertical, one-dimensional synthetic array system where a small hydrophone was water-jetted into the sediment to a depth of approximately 2 m. Once buried, this hydrophone was mounted to a vertical robotics stage that translated the hydrophone upward in 1-cm increments. A broadband (3 to 80 kHz) spherical source, positioned 50 cm above the sediment-water interface, was used to insonify the sediment. Measurements were made with insonification angles above and below the critical angle by changing the horizontal distance of the source relative to the insertion point. This new measurement system is detailed, and results are presented that include temporal, frequency, and wavenumber analysis for natural and roughened interfaces. The measured compressional sound speed and attenuation are shown to be self-consistent using the Kramers-Kronig relation. Furthermore, only a single fast compressional wave was observed. There was no observation of a second slower compressional wave as predicted by some applications of the Biot model to unconsolidated water-saturated porous media.     

Solvent-stabilized molecular capsules

Pyrrogallolarenes 2 were prepared by acid-catalyzed condensation of pyrrogallol with aldehydes. Compound 2a crystallizes from a methanol solution of quinuclidine hydrochloride to give a dimeric molecular capsule surrounding one disordered quinuclidinium cation. The molecules of 2a are connected by direct hydrogen bonds and by bridging methanol and water molecules. The chloride anion is positioned outside the capsule and is hydrogen bonded to the hydroxy groups of 2a. The shortest distance between the cation and anion was found to be 6.7 A. Crystallization of 2b from aqueous acetonitrile resulted in a dimeric capsule linked by a polar belt of 16 hydrogen bonding water molecules. Four acetonitrile molecules occupy the cavity of this dimeric capsule and assume two binding sites that differ in hydrogen bonding and electronic environment. Compounds 2 also form hydrogen-bonded dimeric molecular capsules in alcohols and aqueous acetonitrile solutions. These assemblies readily encapsulate tetramethylammonium, tetramethylphosphonium, quinuclidinium, and tropylium cations to give complexes stable on the NMR time scale at 233 K.     

Activation parameters for the reactive intermediates relevant to carbonylation catalysts based on cobalt carbonyls

Time-resolved spectroscopic techniques have been used to prepare and to interrogate transient species that are models for reactive intermediates in cobalt-catalyzed hydroformylation. Flash photolysis of acetylcobalt carbonyl complexes of the type RC(O)Co(CO)3(PR'3) (A; R = CH3, CD3, or C2H5; R' = Ph or nBu) leads to CO photodissociation to give the "unsaturated" intermediate [RC(O)Co(CO)2(PR'3)] (I), which decays by two competitive pathways, alkyl migration to the cobalt to give RCo(CO)3PR'3 (M) and reaction with CO to re-form A. With the perdeuterioacetyl complex (R = CD3, R' = Ph), rate constants both of CO trapping (kco) and of methyl migration (kM) were just slightly smaller than those of the perprotio analogue (kh/kd = 1.04 +/- 0.01 and 1.07 +/- 0.09, respectively). Thus, any stabilization of the "vacant" coordination site of I by agostic interactions with the acetyl methyl group appears to be kinetically insignificant, consistent with the previous conclusion (Inorg. Chem. 2000, 39, 3098-3106) that this site is stabilized by an eta 2-coordinated carbonyl. Changing the phosphine ligand has a greater influence on the kinetics of I. The species generated by the flash photolysis of the trialkyl phosphine complex CH3C(O)Co-(CO)3(P(nBu3)) exhibited a much larger kM than was the case for the PPh3 analogue, although there was little difference in the kco values. Similarly, kM proved to be sensitive to the nature of R as demonstrated by the slower alkyl migration (at 298 K) for the intermediate formed by CO photodissociation from the propionyl complex C2H5C(O)Co(CO)3PPh3 relative to the acetyl analogue. Nonetheless, all these intermediates displayed analogous time-resolved infrared spectra and general kinetics behavior in benzene solution (implying common mechanisms for decay), so it is concluded that all are present as the eta 2-chelated acyl structure under these conditions.     

Economy of proficiency testing: reference versus consensus values

Many proficiency tests are operated with a consensus value derived from the participants’ results. Apart from technical issues, one of the reasons often mentioned is that proficiency tests operated with consensus values would be cheaper than those using reference values obtained from a priori characterisation measurements. The economy of a proficiency test must of course be balanced by the need of the participants, and the quality of the comparison in general. The proficiency tests selected in this study had both a reference value and a consensus value, one of which was used for assessing the performance of the participating laboratories. In this work, both a technical and an economical assessment of how the comparisons were operated is made. From the evaluation, it follows that usually the use of consensus values does not necessarily reduce the costs of a proficiency test. However, frequently it may be observed that the quality of the assessment of the laboratories is better with a reference value. Received: 11 October 2000 Accepted: 3 January 2001     

Simplified method for concentration of mitochondrial membrane protein complexes

Extracting and concentrating mitochondrial protein complexes from gel strips after blue native PAGE (BN‐PAGE) can be daunting tasks using the traditional methods, such as electroelution, passive diffusion and centrifugal concentration. We present a simplified gel electrophoresis method to concentrate mitochondrial protein complexes with excellent recovery rate. Mitochondrial complex I present in a long gel strip from BN‐PAGE can be easily concentrated into a 0.8 cm gel strip when a second BN‐PAGE is performed with a Y‐shaped gel and the addition of 0.01% n‐dodecyl β‐D ‐maltoside and 0.001% SDS in the cathode buffer. Once completed, the concentrated protein complex in the gel strip is ready for SDS‐PAGE or proteomic studies.     

Second-order nonlinearities of lead borate glasses poled with different electrodes

The second-order nonlinearities in thermally poled lead borate glasses were studied. After poling with different electrodes, both bulk and near surface second-order nonlinearities were obtained. The second harmonic generation signal from near surface effect was two orders of magnitude larger than the bulk effect. By simulating the poling process with a multiple carrier model, we concluded that the bulk second-order nonlinearity was caused by the deficiency of Pb²⁺ in a thick layer after poling, and the near surface second-order nonlinearity was caused by the depletion of H⁺ in a thin layer when H⁺ injection from the atmosphere was blocked.