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Austenite grain size is an important microstructure parameter when processing steels as it provides the initial condition for the austenite decomposition that determines the final microstructure and thus properties of the steel. In low-carbon steels it is frequently difficult if not impossible to quantify the austenite grain size using conventional metallographic techniques. Laserultrasonics provides an attractive alternative to quantify the grain size in-situ during thermomechanical processing of a steel sample. The attenuation of the laser generated ultrasound wave is a function of the grain size. The present paper gives an overview on the state-of-the-art of this novel measurement technique. Using isothermal and non-isothermal grain growth tests in low-carbon steels the advantages and limitations of laser-ultrasonic measurements will be demonstrated. Further, their application for deformed samples will be presented to quantify austenite grain sizes during and after recrystallization. The in-situ measurements provide significantly new insights into the austenite microstructure evolution during thermo-mechanical processing of low-carbon steels. The implications on expediting the development of improved process models will be discussed. © (2012) Trans Tech Publications, Switzerland., Fourth International Conference on Recrystallization and Grain Growth, July 4-9, 2010, Sheffield, England, Series: Materials Science Forum

Using a novel laser ultrasonics technique in situ measurements of austenite grain growth were conducted during continuous heating (10 °C s−1) and subsequent isothermal holding at various temperatures in the range 950–1250 °C in a microalloyed linepipe steel. Based on the experimental results, a grain growth model was developed, which includes the pinning effect of precipitates present in the steel. Analyzing the grain growth behaviour and using the advanced thermo-kinetic software MatCalc, an approach was developed to estimate the initial distribution of precipitates in the as-received material and their dissolution kinetics. The evolution of the volume fractions and mean particle sizes of NbC and TiN leads to a time-dependent pinning pressure that is coupled with the proposed grain growth model to successfully describe the observed kinetics of austenite grain growth. The predictive capabilities of the model are illustrated by its application to independent grain growth data for rapid heat treatment cycles that are typical of the weld heat affected zone.

Etching patterns displayed on the surfaces of near-alpha titanium forgings (alloy IMI834) were quantified in terms of sizes and orientations using a two-dimensional (2-D) autocorrelation method. These patterns, which can be associated with local variations of microstructure and further related to regions of specific crystallographic orientations, are known to play a significant role in fatigue and dwell fatigue life predictions. It is then necessary to quantify their dimensions in a manufactured part in order to build a better statistical approach for life prediction in titanium forgings. These distributions of macroregion size and shape were examined on forging cross sections. A data analysis methodology based on a 2-D autocorrelation was used to process sample image data and quantify the macroregion characteristics. The results are more precise than those obtained using a mean linear intercept (MLI) method and additional useful information can be gathered., available, unlimited, public

available, unlimited, public

Chez l’enfant, le syndrome des voies aero-digestives superieures qui entraine des apnees du sommeil et des difficultes de deglutition, peut egalement avoir des repercussions neurologiques staturo-ponderales, ainsi que des modifications notables de la croissance maxillofaciale. L’examen ORL approfondi permet d’en determiner l’etiologie et de proposer la therapeutique adaptee.

Ultrasonic velocity and attenuation measurements are powerful tools to infer much information about the microstructure and properties of aluminum and its alloys. Laser-ultrasonics is a technology that enables doing these measurements remotely, in-situ or inline and in a fraction of a second. Therefore, it is possible to characterize the thermomechanical processing of aluminum alloys with unprecedented time resolution. This paper reviews the physical principles that allow relating velocity and attenuation measurements to various materials properties and microstructural features such as elastic moduli, crystallographic distribution orientation (texture), residual stresses, recrystallization and dislocations. In-situ (in laboratory furnaces) and in-line measurement examples from the Industrial Materials Institute research group are reviewed and presented.

This study addresses cumulative damage and its evolution during the cold dwell fatigue of a near-α titanium alloy. An experimental study was undertaken to examine the evolution of life, strain, strength and damage of 13 titanium IMI 834 samples cut from a single disk forging. The samples were tested in the same dwell-fatigue loading conditions. In the dwell phase, the load is maintained at 80% of ultimate tensile strength (824 MPa, 90% of yield strength) for 30 s. The secant Young’s modulus and inelastic strain at minimum load were measured in order to document the evolution of the irreversible damage against the number of cycles for all specimens. Experimental observations show significant differences in dwell-fatigue life and damage behavior. This mechanical analysis and an analysis of the cumulative Weibull reliability distribution suggest a bimodal dwell-fatigue failure process. Some features of the mechanical behavior can be used to sort the samples according to each of the two failure modes and improve the reliability of the fatigue test campaign.

Ultrasonic velocity and attenuation measurements for three different semi-solid (SS) aluminum (Al) alloy billets (A356, A357 and 86S) and one dendritic sample (A356) were performed in the temperature range between room temperature and ~575 °C using a non-contact laser-ultrasonic technique. It was found that there are measurable differences in ultrasonic velocity and attenuation between SS and dendritic samples and these differences are larger as the temperature becomes closer to the complete melt state. In a laboratory setup simulating the barrel section of a thixomoulding or a rheomoulding machine, a clad buffer rod (high temperature probe) was used to perform real time ultrasonic monitoring. We have observed 10 MHz ultrasonic signals of 30 dB signal-to-noise ratio reflected from a rotating screw with a distance of 5.5 mm between the probe end and the root of the screw in a viscous liquid Al alloy (A356) at 610 °C. This information should enable us to determine whether the processed part has the desired thixotropic structure or not, and then to properly adjust heating and other process parameters.

The ferrite-austenite transformations in A36 and in IF steels were monitored using laser-ultrasonics. Sudden variations of ultrasonic attenuation were observed at transformation temperatures. Dilatometry and standard metallographic observations support an interpretation of these attenuation variations in terms of nucleation and growth of the new phase. Laser-ultrasonics is a new technique to monitor microstructural changes that take place during phase transformations. This information is obtained in real-time and may greatly facilitate laboratory studies on phase transformations. Using ultrasonic scattering models, and with reliable values of the austenite elastic constants as a function of temperature, laser-ultrasonics could provide a quantitative evaluation of grain sizes during phase transformations.

International audience; Titanium alloys are known to have texture heterogeneities, i.e. regions much larger than the grain dimensions, where the local orientation distribution of the grains differs from one region to the next. The electron backscattering diffraction (EBSD) technique is the method of choice to characterize these macro regions, which are called macrozones. Qualitatively, the images obtained by EBSD show that these macrozones may be larger or smaller, elongated or equiaxed. However, often no well-defined boundaries are observed between the macrozones and it is very hard to obtain objective and quantitative estimates of the macrozone dimensions from these data. In the present work, we present a novel, non-destructive ultrasonic technique that provides objective and quantitative characteristic dimensions of the macrozones. The obtained dimensions are based on the spatial autocorrelation function of fluctuations in the sound velocity. Thus, a pragmatic definition of macrozone dimensions naturally arises from the ultrasonic measurement. This paper has three objectives: 1) to disclose the novel, non-destructive ultrasonic technique to measure macrozone dimensions, 2) to propose a quantitative and objective definition of macrozone dimensions adapted to and arising from the ultrasonic measurement, and which is also applicable to the orientation data obtained by EBSD, and 3) to compare the macrozone dimensions obtained using the two techniques on two samples of the near-alpha titanium alloy IMI834. In addition, it was observed that macrozones may present a semi-periodical arrangement.

Acoustic second harmonic generation in solids is difficult to measure and often requires careful sample preparation. In this paper, a heterodyne interferometer modified to measure acoustic fundamental and second harmonics is presented. It requires relatively little sample preparation and it provides noncontact, wideband, absolute, and pointlike measurements. It is shown that the output of an ideal heterodyne interferometer does not contain any even harmonics of a single‐frequency acoustic signal. Odd harmonics, however, are produced in calculable amounts. A detailed model of the interferometer is introduced to account for various sources of spurious second harmonics and the model is experimentally verified. Three methods of calibration for the absolute measurement of surface displacement are presented. Measurements of the nonlinearity parameter, β, of a fused quartz sample are shown to agree with literature values.

We have developed a scanning tunneling microscope capable of detecting high frequency (1.8–12.5 MHz) acoustic waves. Acoustic pulses arriving at a conducting surface are detected as a high frequency perturbation of the tunneling current. Near and below the rolloff frequency of the current to voltage amplifier, the instantaneous displacement of the surface can be reconstructed. For higher frequencies, the nonlinear (rectifying) properties of the tunneling behavior allow the detection of the envelope (and hence the time of arrival and total amplitude) of the acoustic burst. The technique’s sensitivity is comparable to that of optical detection schemes but offers much better lateral resolution.

The amplitudes of backscattered ultrasound were measured at 10 MHz on different samples of the near-a titanium alloy Ti–5.8Al– 4Sn–3.5Zr–0.7Nb–0.5Mo–0.3Si. Orientation imaging maps (OIMs) of these samples were also determined by electron backscatter diffraction. The backscattered amplitude appears to be related to the microstructure, notably to the orientations, volume fractions and spatial distribution of specific zones. These zones, named macrozones, are formed with a majority of primary ap grains and secondary as colonies having nearly a common crystallographic axis. To illustrate the role of the microstructure on wave propagation, the local elastic constants determining the velocities of the longitudinal ultrasonic waves were deduced from the OIMs. The analysis of the spatial distribution and variations of the elastic constants explains the observed variations in backscattered ultrasound amplitude., available, unlimited, public

Cet article a pour objet d’étude la représentation de l’idéal féminin présenté, par le biais d’un symbolisme médical et lapidaire, dans le Livre de la vertu du sacrement de mariage rédigé par Philippe de Mézières entre 1385 et 1389. La première partie consiste en l’analyse des liens entre la médecine, les péchés et la passion amoureuse dans la culture chrétienne européenne du xive siècle. Appuyée sur cette contextualisation, la suite de l’article porte plus directement sur l’œuvre de Mézières. Dans la deuxième section sont analysés les comportements que les épouses doivent éviter afin de maintenir leur santé. Cette section est suivie par une analyse de l’idéal féminin et du rôle qui lui est associé dans l’obtention sotériologique de la vie éternelle. The purpose of this article is to study the representation of the feminine ideal presented, through a medical and lapidary symbolism, in the Livre de la vertu du sacrement de mariage written by Philippe de Mézières between 1385 and 1389. The first part consists of an analysis of the links between medicine, sins and love passion in the European Christian culture of the fourteenth century. Based on this contextualization, the rest of the article deals more directly with the work of Mézières. In the second section are analyzed the behaviors that brides must avoid in order to maintain their health. This section is followed by an analysis of the feminine ideal and its associated role in the soteriological attainment of eternal life.

The authors have developed a novel technique for measuring the phase velocity of elastic waves in self-supporting thin films. One edge of the film is fixed to an interdigital transducer (IDT) acting as a transmitter, while another IDT, the receiver, moves freely above the film. The coupling between the receiver and the film is made through a liquid bond. This allows a continuous variation of the path length, and the resulting change in phase and amplitude of the received continuous-wave (CW) signal permits a simultaneous and accurate measurement of the phase velocities of the different vibrational modes present in the foil., 1988 Ultrasonics Symposium, October 2-5 1988, Chicago IL, USA

Laser-ultrasonics is a non-destructive and non-contact technique to generate and detect ultrasound in materials. The measured ultrasonic velocity depends on the orientation distribution of the crystallites and may be used to infer the lowest order texture coefficients. Recrystallization generally involves texture changes and can thus be monitored using ultrasonics. In this paper, cold-rolled samples of an Al-Mg alloy (AA5754) and an Al-Si-Mg-Cu alloy (AA6111) are annealed in a Gleeble thermomechanical simulator at various temperatures. The recrystallization kinetics is monitored in-situ and in real time by laser-ultrasonics. It is found that the longitudinal and shear velocity variations correlate well with the recrystallized fraction, as evaluated by metallography and by the softening behaviour of samples submitted to similar thermal cycles. it is also found that the ultrasonic behaviour is consistent with the randomization of texture and a reduction of the W400 and W420 texture coefficients., Thermec 2003 International Conference on Processing and Manufacturing of Advanced Materials, Series: Materials Science Forum; no. Vol. 426-432

Laser-ultrasound resonance spectroscopy, a non-contact ultrasonic technique, was used to determine reliably and rapidly the crystallographic texture, the average plastic strain ratio, and the thickness of sheet metal on the production line. As with laser-ultrasonics, a short laser pulse is used to generate a wide-band pulse of ultrasound and a laser interferometer is used for its detection. In this paper, a large number of echoes are collected and analyzed together using Fourier techniques to measure the natural resonance frequencies in the thickness of the sheet. One longitudinal and two shear resonance frequencies were measured together with their harmonics. From these frequencies, two crystallographic orientation distribution coefficients, W(400) and W(420), are obtained, as well as a highly accurate measurement of the sheet thickness that is corrected for changes in ultrasonic velocity caused by texture variations. Using these coefficients, the average and in-plane twofold and fourfold variations of the plastic strain ratio, respectively r delta(2)r, and delta(4)r, can be evaluated. These parameters are indications of the formability of metals sheets, which is of industrial interest. Measurements on 1 mm thick, low carbon steel sheets have shown the following measurement accuracies: r to within +/-0.08, delta(2)r, and delta(4)r to within +/-0.1, and thickness to better than +/-1 microm. On-line tests at LTV Steel Company showed that the sensitivity of the apparatus is sufficient to detect systematic variations in texture along the length of similar production coils and that the on-line repeatability for r was of order +/-0.02.

Laser-ultrasound spectroscopy, a non-contact ultrasonic technique was used to characterize the Lame coefficients ((lambda) ,(mu) ) and thickness (h) of a zinc layer on a steel substrate. This characterization is based on fitting the measured velocity dispersion curve of surface acoustic waves (SAW) to the dispersion calculated one using the conjugates gradients algorithm (C.G). A short laser pulse was used to generate a wideband pulse of ultrasound and a laser interferometer was used for its detection. From a large number of echoes we identified the one corresponding to the SAW. Furthermore other useful information were obtained from these data like attenuation and surface skimming longitudinal wave. Measurements of the velocity dispersion of the Rayleigh wave were achieved up to 50 MHz. The evaluation of layer's parameters performed for similar cases, on a pseudo-experimental model, were obtained with accuracy better then 1% for (h, (mu) ) and about 4% to 6% for (lambda) .© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The goal of this project was to demonstrate the feasibility to measure the mechanical properties, such as yield strength, tensile strength, elongation, strain hardening exponent and plastic strain ratio parameters, of low carbon steel sheets on the production line using laser ultrasound. The ultrasound generated by the developed apparatus travels mostly back and forth in the thickness of the steel sheet. By measuring the time delay between two echoes, and the relative amplitude of these two echoes, one can measure ultrasound velocity and attenuation. These are governed by the microstructure: grain size, crystallographic texture, dislocations, etc. Thus, by recording the time behavior of the ultrasonic signal, one can extract microstructural information. These microstructural information together with the modified Hall-Petch equation allow measurement of the mechanical properties. Through laboratory investigations with a laboratory laser ultrasound system, followed by the installation of a prototype system at LTV Steel Company's No.1 Inspection Line in Cleveland, all target mechanical properties of ultra low carbon (ULC), low carbon (LC) and high strength low alloy (HSLA) steel sample lots were measured meeting or nearly meeting all the target accuracies. Thus, the project realized its goal to demonstrate that the mechanical properties of low carbon steel sheets can be measured on-line using laser ultrasound

A laser ultrasonic system has been used to measure backscattered waves with the intention of evaluating microstructures of steels. The frequency spectrum of the backscattered signal from samples with different grain sizes is evaluated and compared with a simple model that accounts for single scattering and a first order correction to multiple scattering. This model predicts a maximum in the spectrum of the backscattered signal at the frequency near the transition between the single and multiple scattering. Accordingly, the experimental results show that for larger grain sizes, the scattered signal has a lower frequency content. A good quantitative correlation between the grain size and a spectrum parameter is presented., Review of Progress in Quantitative Nondestructive Evaluation, July 16-20 2000, Ames, Iowa USA, Series: AIP Conference Proceedings; no. 557

This article presents accurate laser-ultrasonic measurements of longitudinal velocity in the 500–1000 °C temperature range in carbon steel samples for different conditions known to affect phase transformations such as cooling rate, carbon concentration, and rolling. Measurements were performed during continuous heating and cooling at rates varying between 0.1 and 20 °C/s. Carbon concentrations ranged from 0.0% to 0.72%. Hot-rolled and cold-rolled samples were measured. For the hot-rolled samples, a reproducible hysteresis was observed in the dependence of the ultrasonic velocity versus temperature of samples having a significant carbon concentration. This hysteresis is attributed to the combined effects of the phase transformation and of the ferromagnetic–paramagnetic transition. In particular, the rate of change of velocity with temperature during heating suddenly diminishes at the Curie temperature, and the velocity behavior during cooling shows clearly the start and end of phase transformations, even allowing discrimination between ferrite and pearlite nucleations. For the cold-rolled samples, significant drops in ultrasonic velocity were observed at the transformation temperatures when the samples were heated for the first time. However, the magnitude of these drops decreased for subsequent heating. These drops are attributed to irreversible crystallographic orientation changes caused by phase transformations. This effect was modeled using the Kurdjumov–Sach transformation relationship. The model calculation agrees well with the experimental data.

In this paper we explore laser induced breakdown spectroscopy (LIBS) at relatively low energies in the range 10 - 350 tJ. We present measurements ofthe threshold laser energy needed for LIBS and the scaling of plasma size and crater size with energy. The effects of the laser pulse length and gating of the detector on the LIB spectra are studied and we also assess the use of microjoule LIBS for the identification of Al alloys., SPIE International Conference on the Applications of Photonic Technology (ICAPT) 4, June 12 2000, Quebec City, Canada

A new technique to measure quantitatively grain growth kinetics at high temperatures was presented in this article. This technique, based on the generation and detection of ultrasound using lasers, called laser-ultrasonics, measures the scattering of ultrasonic echoes propagating in a sample to evaluate grain size. A quantitative evaluation was obtained by comparing ultrasonic attenuation with quantitative metallographic size measurements of austenite grains. Results obtained using this new technique during the austenitization of A36, DQSK, and IF steel samples were presented. The results presented showed that this new technique provides the austenite grain growth kinetics at a given austenitization temperature in a single experiment with a time resolution far superior to the resolution obtained using lengthy conventional metallographic techniques. In the present study, very few metallographic measurements of austenite grain size smaller than 100 {micro}m were available for comparison with laser-ultrasonic measurements. This small number of points is essentially due to abnormal growth of the austenite grains in the A36 steel which is associated with the dissolution of pinning A1N particles. The laser-ultrasonic technique should therefore be validated for grain sizes smaller than 100 {micro}m using materials and thermal treatments showing a low tendency for abnormal grain growth. Furthermore, systematic testsmore » should be performed to delineate the sensitivity of the technique to steel chemistry, and ultrasonic scattering models should be improved to include the effects of grain shape and of grain size distribution in the calibration.« less

Recent developments in laser-ultrasonic technology have made it possible to remotely inspect large and complex aeronautic structures for structural integrity as well as gauge hot steel products on the production line. These developments based on laser and interferometer technology have also resulted in a powerful tool for characterizing materials and their microstructure. In fact the same features that make laser-ultrasonics attractive for the inspection of complex structures, such as relaxed requirements of the normalcy of the transducer, a broad frequency bandwidth, and large standoff distances make this technology unique and extremely useful for characterizing materials both in the laboratory and on the production line. Examples of recent developments and applications are presented. These relate to the measurement of microstructural features such as texture, grain size, degree of cold deformation in metals, solid-liquid-interfaces. In particular, the real-time measurement of grain size during thermal processing is presented., The Ninth International Symposium on Nondestructive Characterization of Materials, June 28 - July 2, 1999, Sydney, Australia, Series: AIP Conference Proceedings; no. 497

Ferrite grain size strongly influences the mechanical properties of steels. In hot rolled steels, the ferrite grain size is determined by the austenite microstructure during the finish rolling, and by the rate of cooling through the transformation temperature range. A sensor to monitor phase transformations and grain sizes in strips during hot rolling would allow to control the process parameters, optimize the ferrite grain size, and better achieve the desired mechanical properties. Unfortunately, such a sensor is presently not available in hot strip mills.

In the CANDU™ (CANada Deuterium Uranium) nuclear reactor, the primary heat transport containment is a matrix of cold-worked Zr-2.5Nb pressure tubes containing pressurized heavy water, which extracts heat from the fuel bundles in the tube. In the last few years, periodical tests on removed tubes have established a significant tube-to-tube variability in fracture toughness due to variability in the as-installed tubes [1].

Laser-ultrasonics is a technique to remotely generate and detect acoustic waves using lasers. Being a truly remote technique, it is especially well suited for ultrasonic measurements at high temperatures, where conventional ultrasonic methods are impractical. Shear and longitudinal acoustic wave velocities were simultaneously measured in SiC reinforced alumina samples of varying porosity in the temperature range of 20°C to 1800°C. The temporal evolution of the velocities was also measured. Knowing the mass density and thermal expansion behavior of the samples, the measured velocities can be related to the average bulk elastic moduli. At room temperature, the elastic moduli vary linearly by one order or magnitude with mass density (porosity). At temperatures of up to 1300°C, the elastic moduli decrease linearly and independently of mass density (porosity). Above 1300°C, the elastic moduli may either increase or decrease depending on the sample mass density. Some time-dependence measurements at high temperatures were obtained. However, the samples sublimated and the condensate eventually blocked the furnace's optical ports, thus eliminating the time window to a few hours., Republished from Nondestructive Characterization of Materials VII.

The elastic and structural properties of Cu/Pd and Cu/Ni superlattices have been determined. Microstructurally the films have the same growth mechanisms, growth textures, and composition modulation amplitudes, as in past studies where the ``supermodulus effect'' was reported. Advanced techniques have been used to measure the flexural, shear, and Young's moduli of the thin films, and no significant anomalous elastic behavior has been observed.

We present three methods of measuring the velocity of ultrasound in self-supported thin films (1 μm or thicker). The first method involves time-of-flight measurements of sound pulses excited by a pulsed laser. These pulses are detected with a wide band laser interferometer and we measure the propagation delay time as a function of the path length. In the second method, we continuously excite the film using an interdigital transducer (IDT) while performing narrow band detection using the laser interferometer. The interferometer allows us to determine the position dependence of both the in-phase and the out-of-phase components of the film vibration (relative to the emitted signal). The third method is similar to the second, but both the generation and the detection of the ultrasonic wave are accomplished with IDTs. The receiving IDT is translated across the surface of the film and the ultrasonic continuity is maintained through a liquid bond. All three methods have been tested on the same film and yield similar values (within experimental limits) of the velocity of sound of the various modes excited. From these results, we deduce the shear and flexural moduli of the film and compare them with values quoted in the literature.

Using a new ultrasonic method which relies on the measurement of the in-phase and quadrature components of a continuous ultrasonic excitation as a function of position, we have measured the flexural modulus of composition modulated Cu-Ni self-supporting thin films. For some of the films, we have also observed the shear (S z ) modulus (allowing the calculation of the biaxial and Young’s moduli). No enhancement of these moduli was observed for composition wavelengths in the range of 17–40 Å.

We have developed a new ultrasonic method for measuring the phase velocity of longitudinal and shear waves in self-supporting thin films. The film is bonded at one end to an interdigital transducer (IDT) which emits a continuous wave signal. The film is supported at the other end and maintained flat under a weak tension. A receiving IDT detects the in-phase and quadrature components of the sound waves as they propagate. A liquid bond is used between the receiving IDT and the film to allow a continuous variation of the path length. From the longitudinal and shear wavevelocities, we can deduce the flexural and shear moduli of the film. For films of uniaxial or higher symmetry, the Young’s and biaxial moduli can be expressed as combinations of the flexural and shear moduli. We applied this technique to Cu-Pd composition modulated thin films. Contrary to previous reports, we have not observed the supermodulus effect in either the flexural, shear, Young’s or biaxial moduli for modulation wavelengths between 13 and 36 Å.

We have investigated high frequency ultrasound generated by single laser pulses in thin 50m aluminum foils as a function of the laser fluence. Laser-pulse durations of 80 fs and 270 ps were used to compare the ultrasound generated in two very different regimes: thermoelastic and ablation. The measured rear-surface displacement induced by the ultrasound pulse is similar after 50-m propagation through the foils for the two laser-pulse durations in the fluence range of 0.1–0.7 J /cm2. For fluences greater than the ablation threshold 0.25 and 0.63J/cm2 for the 80 -fs and 270-ps pulses,respectively, the ultrasound amplitude generated by the 270-ps laser pulse is increased significantly due to absorption of laser energy by the ablating plasma. This is not observed for the 80-fs laser pulse since ablation is produced well after the laser-pulse irradiation of the target. The measured surface displacement as a function of laser fluence is compared to the calculations of a one-dimensional fluid code for both laser-pulse durations. The model calculations agree in many ways with the experimental results, but some discrepancies are observed.

Both ultrasonic attenuation and velocity as a function of temperature from 4.2 K to room temperature were measured on sinter-forged samples of YBa/sub 2/Cu/sub 3/O/sub 7- delta /, which have more than 80% alignment of the c-axis of the grains parallel to the forging axis. Strong anisotropy was found both in the attenuation and the velocity when propagating sound waves in different directions relative to the forging axis. Hysteresis was observed in the velocity changes. >

The ultrasound velocity in the sinter-forged YBa2Cu3O7 − δ superconductor was measured and the results showed evident anomalies as well as anisotropies. Both longitudinal and shear wave velocity along the c axis (the forging axis) showed a distinct thermal hysteresis from 65 K to 260 K. The velocity change ΔV V from room temperature to 4 K was 1.5%. The sound velocity along the “basal plane” reached a maximum around 160 K. No distinct thermal hysteresis was observed. ΔV V from room temperature to 4 K was 1%. All of these velocities were measured while sweeping the magnetic field up to 9 T at fixed temperatures of 4 K and 86 K respectively. No velocity change was observed. The shear wave velocity behaved similarly at 9 T during the thermal cycling between room temperature and 4 K.

We report ultrasonic attenuation measurements on sinter-forged YBa/sub 2/Cu/sub 2/O/sub 7-//sub delta/ material, which differs from ordinary sintered material in that the crystallites are preferentially oriented to form a uniaxial sample. Three peaks in attenuation, at temperatures of 250, 180, and 70 K, were observed for longitudinal waves propagating perpendicular to the forging axis, which is similar to that reported in ordinary (isotropic) polycrystalline samples. However, for both transverse and longitudinal sound propagated along the forging axis we have a different behavior, with only one peak at 180 K, showing a strong anisotropy. It is suggested that sound waves traveling parallel to and normal to the Cu-O planes may account for the anisotropic effect, and a relaxation mechanism may explain the increase in shear wave attenuation which was seen with decreasing temperature.

The velocity of ultrasound was measured on sinter-forged polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ samples with a superconducting transition temperature of 91 K. The forging process results in crystallites which are preferentially aligned with their c axis aligned parallel to the forging axis as confirmed from optical and x-ray measurements. Sound-velocity measurements show that the material is elastically anisotropic. The temperature dependence of the sound velocity shows distinct anomalies. For propagation parallel to the forging axis, both longitudinal and shear waves displayed a thermal hysteresis between 65 and 260 K; however the longitudinal sound velocity with q-circumflex in the basal plane showed a much smaller thermal hysteresis. No effect of a magnetic field was observed on sweeping the magnetic field to 7.2 T at temperatures of 4 and 86 K.

L'etablissement d'un schema reactionnel de dissolution-passivation d'un metal, necessite en general la prise en compte d'un grand nombre de parametres : potentiel, concentration des constituants du milieu y compris l'oxygene dissous, temperature, temps, conditions hydrodynamiques…Nous nous proposons dans cette etude de definir un premier modele pour le titane T 40, en nous limitant a l'analyse des trois facteurs : conditions hydrodynamiques, potentiel, temperature, pour un meme milieu corrosif : l'acide chlorhydrique 8 M.l— 1 desaere.L'utilisation d’une electrode a disque tournant permet de constater que, dans le milieu etudie, le courant reste independant des conditions hydrodynamiques.L'influence du potentiel sur le courant stationnaire et sur la valence de dissolution, est interpretee par un modele reactionnel a une bifurcation defini precedemment.Enfin, nous etablissons que, dans l'intervalle de temperature [11,7 °C — 39 °C], les vitesses des etapes elementaires envisagees suivent une loi d'Arrhenius et que le schema de dissolution-passivation reste le meme.

La philosophie contemporaine a fait d'immenses progrès en introduisant dans la spéculation la préoccupation de la technique. La phénoménologie, entre autres, a cherché à faire coïncider ses découvertes avec les témoignages de la science. Merleau-Ponty, un des propagandistes français de la méthode phénoménologique, a contribué à rapprocher cette sorte de philosophie de la psychologie de la forme, des théories de l'organisme, des analyses expérimentales de la sensation. Sa conception de la perception illustre assez bien sa démarche. Chose étrange, c'est par des aspects typiquement représentatifs qu'elle se rapproche le plus à ce sujet de la pensée de Berkeley qui se rapporte pourtant au contexte scientifique d'une autre époque, spécialement en ce qui touche à l'optique géométrique.

We have measured ultrasonic absorption in sinter-forged high Tc YBa2Cu3O7 − δ. Owing to the anisotropic properties of the sinter-forged samples, longitudinal ultrasonic attenuation measurements showed very strong anisotropy when waves were propagated parallel and perpendicular to the forging axis. Sound absorption was found to increase with decreasing temperature for shear waves travelling parallel to the forging axis.

In einer fruheren Studie haben wir mittels eines Fragebogens, der einer Selbstbeurteilung diente, die Veranderungen untersucht, die nach der Weiterbildung in Balint-Gruppen auftraten. Es schien, das die Arzte zu einer verstandnisvolleren, sich besser einfuhlenden, weniger verurteilenden und lockereren Einstellung gelangten, einigermasen befreit von der Angst der Gegenubertragung. Diese Arzte waren offenbar toleranter geworden gegenuber Frustrationen im Zusammenhang mit der Ubertragungssituation sowie Frustrationen durch die relative Unkenntnis psychologischer Theorien und durch den Mangel an speziellen psychologischen Techniken. Die Arzte fuhlten sich vorurteilsfreier, weniger angstlich, selbstsicherer. Sie hatten bessere Kenntnisse ihrer Grenzen und zeigten sich bereit, von ihrem Podest herabzusteigen.

A heterodyne laser spectrometer has been used to detect the vibrations normal to the plane of a metallic self-supporting thin film (on the order of 1-μm thick or thicker) with a sensitivity on the order of 0.01 Å. The film is excited by attaching it to an interdigital transducer. With continuous scanning of the laser probe across the surface of the film and measuring the amplitude and phase of the vibrations at a fixed frequency, the propagation vector of the modes excited can be accurately determined. This makes it possible to calculate the sound velocity of the antisymmetric Lamb mode and to deduce either the thickness of the film or its elastic flexural modulus., 1989 IEEE Ultrasonic Symposium, October 3-6, 1989, Montreal, Canada