Flaw detection close to the interface using ultrasonic echography

The detection of flaws by ultrasonic echography becomes difficult when the flaw is at a shallow depth. The time delay between the interface and flaw echos is less than the width of the impulse-response time of the transducer, and the flaw echo generally has an amplitude much smaller than the dominating interface echo. When the surface is not too rough, the interface echo can be assumed to be known, and its comparison with the signal interface and flaw echo permits the detection of the flaw. In this article it is shown that signal processing techniques allow small flaws to be detected very close to the surface (0.5 mm). Two methods are proposed, the first one is based on the minimization of the mean-square error, and the second on the spectral substraction of the two echos.This work has been supported by the French Ministry of Defense.     

Study of Nano-Porous Silicon with Low Thermal Conductivity as Thermal Insulating Material

Recently discovered phenomenon of extremely low thermal conductivity of nano-porous silicon (nano-PS) is discussed in detail. A theoretical model describing specific mechanisms of heat transport in as-prepared and oxidized nano-PS layers is described. The theoretical estimations are in a good agreement with experimental data obtained earlier. The low thermal conductivity values allow to use this promising material as thermal insulator in microsensors and microsystems. To ensure an efficient thermal isolation, a nano-PS layer has to be as thick as possible and mechanically stable. We describe here the procedures to form thick (up to 200 m) and stable nano-PS layers. Distribution of Si oxidized fraction along the layer thickness after thermal oxidation in dry O₂ atmosphere at 300°C during 1 h is studied.     

The analysis of scientometric matrices for policy implications

A method is explained for analysing matrices of statistics where each element should be approximately proportional to some column coefficient and also to some row coefficient. Using U. S. patent data as an example it is shown that entries are usually proportional to country size and patent category size. Deviations from proportionality expectations when tabulated often suggest policy implications.     

Mechanisms of cyclic softening in precipitation-hardening alloys—A ball model approach and tests at 78 K

Tests of random, alternating cuts on a ball-model of in Al–Cu alloy have been run to check the kinetics at which disordering occurs in an initially ordered precipitate subject to cyclic strain. In addition, fatigue tests at low temperature (78 K) and various microscopical observations have been made on Al–Ag alloy containing GP zones to check whether a structure containing an initially disordered precipitate will cyclically soften or not. It was thus found that the ball model disorders as a function of accumulated plastic strain consistently with the kinetics of cyclic softening in actual material. Further, Al–Ag alloy was found not to soften at 78 K. Both of these results supoort the disordering hypothesis of cyclic softening over the dissolution or shearing-off mechanisms, although other systems may be subject to these mechanisms. In spite of the low temperature at which the Al–Ag alloy was tested, small / precipitates were found to have formed in the longest lived test; however, this result did not interfere with the validity of the experiment as it did previously at room temperature. The fatigue lives at 78 K were much longer than those previously measured at room temperature although the failure mechanisms were not affected at high strain and only somewhat affected at low strain (there was increased incidence of transgranular crack nucleation and propagation).

---

Résumé Des essais d'application de coups alternés et aléatoires sur un modèle de simulation par des billes de la phase dans les alliages de Cu–Al ont été effectués en vue de vérifier la cinétique suivant laquelle se produisent des désordres dans un précipité initialement ordonné et soumis à des déformations cycliques. En outre, des essais de fatigue à basse température (78°K) ainsi que diverses observations microscopiques ont été effectués sur un alliage Al–Ag comportant des zones GP en vue de vérifier si une structure comportant un précipité initialement en désordre subirait un adoucissement cyclique ou non. On a donc trouvé que le modèle de utilisant des billes fait état de désordres en fonction de l'accumulation de la déformation plastique et ce en rapport avec la cinétique d'adoucissement cyclique dans le matériau réel. En outre, l'alliage Al–Ag s'est révélé ne pas s'adoucir à 78°K. Ces deux résultats soutiennent l'hypothèse suivant laquelle un adoucissement cyclique s'accompagne de désordres plutôt que de mécanismes de disolution ou de séparation par cisaillement, bien que d'autres systèmes puissent être sujets à ces mécanismes. En dépit de la basse température à laquelle l'alliage Al–Ag a été essayé, on a trouvé de petits précipités / qui se sont formés au cours des essais, les plus longs. Cependant, ce résultat ne gène pas la validité de l'expérience comme c'était le cas précédemment à température ambiante. Les vies en fatigue à 78°K ont été trouvées bien plus longues que celles mesurées précédemment à température ambiante, en dépit du fait que le mécanisme de rupture n'ait pas été affecté sous les déformations élevées et ne l'a été que quelque peu sous les déformations faibles, auxquelles apparait une incidence croissante d'une nucléation et d'une propagation d'une fissure transgranulaire.

     

Correlations between blood pressure, blood volume and plasma renin during therapy with diuretics in essential hypertension. Comparison between the mineralocorticoid antagonist spironolactone and the "loop" diuretic mefruside

35 patients with benign essential hypertension were treated for 6 weeks with high doses of the mineralocorticoid-antagonist spironolactone (400 mg/day), or with the "loop-diuretic" mefruside (mean maximal dose 110 mg/day). Spironolactone caused greater reductions in blood pressure and blood volume and a more marked increase in plasma renin activity (PRA) than mefruside (p less than 0.05). It appears possible that he weaker antihypertensive effect of mefruside may relate partly to its lesser influence on circulatory volume. With both diuretics, mean decreases in blood pressure were greater in patients with low pre-therapeutic PRA than in patients with normal or high PRA. However, the diuretic-induced changes in blood pressure did not correlate with the associated variations in blood volume or PRA. Thus, the increased blood pressure sensitivity to diuretics in patients with low-renin essential hypertension did not appear to be volume or renin-dependent. Under normal conditions, the maintenance of a constant blood pressure during volume depletion may partly depend on compensatory activation of the sympathetic nervous system. Moreover, patients with low-renin essential hypertension have been found to have decreased adrenergic activity. It seems possible, therefore, that the marked blood pressure sensitivity to diuretic treatment in such patients may be the result of an impaired compensatory sympathetic response to sodium and volume depletion. Analysis of the literature suggests that the diuretic furosemide, a structural relative of mefruside, may also have less blood pressure lowering efficacy in patients with essential hypertension than the distally-acting thiazides, chlorthalidone or spironolactone. Consideration of possible differences in the blood pressure reducing potential of certain diuretics thus appears to be necessary in planning the pharmacotherapy of essential hypertension.     

Quasi-elastic light scattering of carnauba wax in the liquid phase: dynamics 2

Quasi-elastic light scattering of carnauba wax in the liquid phase is obtained in a heterodyne setup, and dynamic processes are analyzed through electrophoresis. Nonspherical polar clusters are found, containing a net electrical charge. An applied square-wave electric field induces drift and rotation of these clusters.These effects are dependent on strength and frequency of the applied electric field. At 373 K and in the low frequency limit the local electric field strength is approximately 70 times the strength of the applied one. This enhancement is believed to be caused by collective orientation of the clusters. The electrophoretic mobility is 1.1 X 10(-12) m2/V sec in the high frequency limit and 7.4 X 10(-11) m2/V sec in the low frequency limit. The electric dipole moment is 6.3 X 10(-16) N(-1/2) m(-1/2) where N is the cluster density/cubic meter and the net charge is about one or two elementary charges.     

An Investigation into Lubrication and Oxide Breakdown During Load-Carrying Capacity Testing

Changes occurring in the friction and wear mechanisms during a load-carrying capacity test, lubricated with cetane containing a carboxylic acid, were investigated. The changes in wear scar/track appearance and oxide coverage/composition were analyzed during every load stage.

The main conclusions were as follows:

• The breakdown in the protective oxide layer formed on the opposing steel surfaces was found to be the prerequisite for initiation of seizure.

• The seizure load achieved during load-carrying capacity testing quantifies the ability of the test fluid to prevent transition to the adhesive wear regime.

• The most severe surface damage was found to occur during the first few seconds after test initiation. Desorption of the adsorbed lubricant film and the subsequent removal of the naturally occurring thin oxide layer results in the initial period of adhesive wear.

• Partial recovery to a state of acceptable friction occurs after the period of initial seizure. During this period, the surface coverage by the adsorption lubricant molecules and the oxide coverage are sufficient to prevent severe adhesive wear from occurring. Wear is primarily a combination of oxidative, abrasive, and fatigue wear (all possible in the regions of mixed friction and boundary lubrication).

• Final lubricant breakdown and eventual seizure are initiated when the oxide removal rate exceeds the oxide formation rate resulting in severe adhesive wear followed by seizure.

     

An Investigation into the Use of Water by Portuguese Industry

ABSTRACT

The continuous increase in water demand for various uses underlines the importance of supply problems in the general context of water resources management.

In this domain it would clearly be useful to collect and make available all the data currently stored on different paper supports and kept by several regional agencies. This would provide an immediate overview of tbe resources, and also permit forecasting the future demand for tbe various utilizations.

This paper describes a project involving a database to be used for groundwater resources management, conceived not only as a support for research activity, but also as a contribution to developing new and more efficient managementprocedures. The database has been designed to be used on a personal computer, with software readily available on the market.     

Water network cost optimization in a paper mill based on a new library of mathematical models

The increasing costs associated with water supply and the disposal of wastewater has stimulated industries to seek more efficient water management systems. Mathematical modelling and simulation can be a very valuable tool for the study of the multiple alternatives available whilst assessing optimum solutions for water management in industry. This study introduces a new steady state model library able to reproduce industrial water circuits. It has been implemented in a novel software framework for the representation, simulation and optimization of industrial water networks. A water circuit representing a paper mill has been modelled and simulated showing the capability to reproduce real case studies. Alternative scenarios for the water network have also been tested to assess the capability of the models to optimize water circuits minimizing total cost.