Search

Magnetic measurements with an unmanned aerial vehicle are ideal for filling the gap between ground and airborne magnetic surveying. However, to obtain accurate aeromagnetic data, the compensation of magnetic effects of the unmanned aerial vehicle is a challenge. Typically, scalar magnetometers are towed several metres under the unmanned aerial vehicle to minimize its magnetic field. In this study, a fluxgate three‐component magnetometer is attached 42 cm in front of the unmanned aerial vehicle at the tip of a composite pipe. Using a scalar calibration, the sensor can be calibrated, and the permanent and induced magnetic fields of the unmanned aerial vehicle can be compensated. The contributions of the magnetic measurements at different altitudes to the unmanned aerial vehicle results were tested over an area of 1 km² in the Northern Vosges Mountains. The area is located in a hamlet surrounded by a forest where few geological outcrops are observed. Three magnetic surveys of the same area are obtained at different altitudes: 100, 30 and 1 m above the ground. The unmanned aerial vehicle magnetic data are compared with a helicopter aeromagnetic survey at 300 m above the ground and a ground magnetic survey using upward continuations of the maps to compare the results. The magnetic maps (300, 100, 30 and 1 m above the ground) show very different magnetic anomaly patterns (e.g. amplitude, shape, wavelength and orientation). The magnetic data at different altitudes improve the understanding of the geology from the local to more general scales.

Objective In the emergency department (ED), the early identification of patients suspected of infection is a challenge for emergency physicians. Sepsis prevalence among patients with suspected infection in the ED remains uncertain. Our objective was to determine how many cases of sepsis occurred among patients with suspected infections in the ED. Methods This multi-center, prospective, observational study was conducted in 19 EDs in France. For 1 week, all consecutive ED patients with suspected infection (according to the emergency physician) were included. The primary endpoint was the prevalence of sepsis in the ED according to the 'sepsis-3' definition. Secondary endpoints involved comparisons among patients with and without sepsis. Results During the study period, 13 904 patients were screened; 494 (3.6%) consulted for suspected infection and were included in the study. Among them, 172 patients [39%, 95% confidence interval (CI) (34-44)] were diagnosed with sepsis. The total hospital mortality for patients with a suspected infection was 4.7% and the hospital mortality for sepsis patients was 9.9%. Conclusion In the ED, among patients with a suspected infection, the prevalence of sepsis as per the 'sepsis-3' definition was 39% [95% CI (34-44)].

Deeply buried sandstone reservoirs are targeted in the Upper Rhine Graben (URG) for geothermal and hydrocarbon resources. These reservoirs are affected by a convective heat flow along fault zones and have a complex diagenetic and deformation history recorded in their paragenetic sequence. Here, the focus is made on siderite and barite cementation characterisation, which trace paleo geothermal circulations within the fracture network affecting the Buntsandstein Gp. sandstones. A double approach on geochemistry and fracture network features is used to characterise fluid-flow episodes in the rift basin and on its shoulders. Barite sulphur isotopic signature suggests a common source for all the locations. However, Rare Earth Elements distribution patterns, oxygen isotopic ratios, and fluid inclusion study suggest two distinct flow regimes for fluids associated with barite precipitation along the shoulders and at depth in the middle of the graben. The barite has a higher content in total REE and contains non-saline fluid inclusions on the graben shoulders, suggesting that fluid circulations within the border faults interact with sulphate rich layers and precipitate at temperature above 150 °C. In deep-seated samples from the central part of the basin, barite fluid inclusions show a wide range of salinities, suggesting a higher contribution of sedimentary brines and precipitation at lower temperatures (

International audience; Airborne magnetic surveys are common in geosciences. High precision surveys are usually performed at a low altitude, draping the topography, using scalar absolute magnetometers and active compensation systems to correct the disturbances generated by the carrier. Another solution is to measure the total magnetic intensity using vector magnetometers, which allows compensation for aircraft fields to be calculated directly, without compensation systems. This study uses data of an industrial airborne survey and of a vector magnetometer survey with a small overlapping area in the Vosges (France) to compare both datasets and shows that both solutions provide results of the same overall precision. This paper also addresses the issue of combining fixed altitude and draped level datasets as well as topographic effect management by proposing an equivalent source interpolator based on a set of simple dipole sources. A synthetic case shows that the equivalent source interpolator allows to compute grids of the magnetic anomaly as well as potential field transforms from a draped dataset with an error level a few orders of magnitude lower than could be obtained with minimum curvature, a classicaly applied interpolator. The interpolator is also tested on a case study in the Vosges massif of which geological interpretation is presented in Bertrand et al. (2020). The results confirm the observations made on the synthetic case and show that the equivalent source interpolator is more tolerant to navigation errors (altitude) than minimum curvature and allows more rigorous computation of potential field transforms of draped datasets.

International audience; In many grabens of the West European Rift System, several drilling projects are targeting fluid conductive faults to produce electricity with geothermal energy. In order to reach the adequate temperatures, the targeted faults are located in the basement rocks or at the basement/cover interface. Unfortunately, the basement rock facies and structural data useful for reservoir modelling are often poorly constrained because of the lack of boreholes deeper than 2000 m and seismic information on the deep subsurface. With the aim to outline the basement structure in the Upper Rhine Graben, two aeromagnetic surveys were conducted where the basement outcrops in the Northern Vosges, with different flight parameters and types of magnetometers. An interpolator using equivalent sources for gridding these two surveys is described by Gavazzi et al. (this issue). Here, we describe the geological interpretation of these surveys. We demonstrate the consistency between the total magnetic field intensity and the outcropping lithological units organized in ENE‐WSW subvertical bands. In detail, three main blocks were delineated, separated by N‐S faults linked to the graben formation and ENE‐WSW inherited Hercynian faults. The latter faults, together with more local NE‐SW and NW‐SE faults compartmentalize the N‐S oriented basement rocks. This is relevant for geothermal prospection where the N‐S faults are the main targets because fluid flow through other fault systems is deemed restricted. With a focus on the interface between the Northern Vosges and the Upper Rhine Graben, we also demonstrate considerable segmentation on the main graben boundary faults.

Introduction Le 2 juillet 2017, les 182 km de ligne nouvelle entre Connerré (25 km à l’est du Mans) et Rennes constituant la Ligne à Grande Vitesse Bretagne-Pays de la Loire (LGV BPL) ont été mis en service après cinq ans de travaux. Le même jour, les passagers du TGV entre Paris et Bordeaux empruntaient pour la première fois les 340 km de la Ligne à Grande Vitesse Sud Europe Atlantique (LGV SEA) entre Tours et la capitale de la région N...

International audience; In fractured reservoirs in the basement of extensional basins, fault and fracture parameters like density, spacing and length distribution are key properties for modelling and prediction of reservoir properties and fluids flow. As only large faults are detectable using basin-scale geophysical investigations, these fine-scale parameters need to be inferred from faults and fractures in analogous rocks at the outcrop. In this study, we use the western shoulder of the Upper Rhine Graben as an outcropping analogue of several deep borehole projects in the basement of the graben. Geological regional data, DTM (Digital Terrain Model) mapping and outcrop studies with scanlines are used to determine the spatial arrangement of the faults from the regional to the reservoir scale. The data shows that: 1) The fault network can be hier-archized in three different orders of scale and structural blocks with a characteristic structuration. This is consistent with other basement rocks studies in other rifting system allowing the extrapolation of the important parameters for modelling. 2) In the structural blocks, the fracture network linked to the faults is linked to the interplay between rock facies variation linked to the rock emplacement and the rifting event.

In continental extension settings like the West European Rift, the main target for high-temperature geothermal drillings is the fault zones in basement rocks of the grabens. However, the reservoir properties of these structures remain almost unknown during the predrilling resource evaluations. This study shows the petrophysical evolution in fault zones on three outcropping areas at the basins’ shoulders. We highlight three petrographical groups with different petrophysical evolution in the fault zones: granites and granodiorites, metamorphic rocks with schistosity, and massive metamorphic or magmatic facies. It provides a first estimation of their reservoir properties that can be used for dual-porosity modeling.

The effect of family presence during cardiopulmonary resuscitation (CPR) on the family members themselves and the medical team remains controversial.We enrolled 570 relatives of patients who were in cardiac arrest and were given CPR by 15 prehospital emergency medical service units. The units were randomly assigned either to systematically offer the family member the opportunity to observe CPR (intervention group) or to follow standard practice regarding family presence (control group). The primary end point was the proportion of relatives with post-traumatic stress disorder (PTSD)-related symptoms on day 90. Secondary end points included the presence of anxiety and depression symptoms and the effect of family presence on medical efforts at resuscitation, the well-being of the health care team, and the occurrence of medicolegal claims.In the intervention group, 211 of 266 relatives (79%) witnessed CPR, as compared with 131 of 304 relatives (43%) in the control group. In the intention-to-treat analysis, the frequency of PTSD-related symptoms was significantly higher in the control group than in the intervention group (adjusted odds ratio, 1.7; 95% confidence interval [CI], 1.2 to 2.5; P=0.004) and among family members who did not witness CPR than among those who did (adjusted odds ratio, 1.6; 95% CI, 1.1 to 2.5; P=0.02). Relatives who did not witness CPR had symptoms of anxiety and depression more frequently than those who did witness CPR. Family-witnessed CPR did not affect resuscitation characteristics, patient survival, or the level of emotional stress in the medical team and did not result in medicolegal claims.Family presence during CPR was associated with positive results on psychological variables and did not interfere with medical efforts, increase stress in the health care team, or result in medicolegal conflicts. (Funded by Programme Hospitalier de Recherche Clinique 2008 of the French Ministry of Health; ClinicalTrials.gov number, NCT01009606.).

Several studies have been conducted to determine the frequency and characteristics of adverse drug reactions (ADRs) in elderly populations, focusing on those leading to hospital admission. However, most of these studies have been limited in their ability to assess risk factors, particularly the renal status of patients. Thus, the aim of this prospective study was to assess the incidence of ADRs and associated factors leading to hospital admissions in the elderly population.All patients agedor =65 years admitted to the Toulouse University Hospital through the Emergency Department during four non-consecutive weeks in 2002-3 were included in this study except for patients in ambulatory care or admitted for intentional overdoses. The characteristics of patients admitted for a suspected ADR were compared with those of patients admitted for other reasons.The incidence of hospital admissions for ADRs was 8.37 per 100 admissions (95% CI 6.52, 10.52), corresponding to 66 patients with ADRs among 789 admissions. The most important factors associated with ADRs were the number of drugs being taken (odds ratio [OR] 1.18; 95% CI 1.08, 1.29), self-medication (OR 2.34; 95% CI 1.18, 4.66), use of antithrombotics (Anatomic Therapeutic and Chemical [ATC] classification B01; OR 2.26; 95% CI 1.33, 3.88) and use of antibacterial drugs (ATC J01; OR 4.04; 95% CI 1.50, 10.83). Surprisingly, exposure to drugs for acid-related disorders was associated with a low risk of ADRs (OR 0.26; 95% CI 0.09, 0.76).A significant incidence of ADRs leading to hospital admissions was found among elderly people. Our study showed that there is a need to increase the availability of information for the general public concerning potential ADRs due to self-medication and for prescribers concerning ADRs due to drug-drug interactions and polypharmacy.

International audience; The in-depth investigation of fractured reservoirs is mainly limited to geophysical data that is in 3D and mostly on the scale of hundred meters to several kilometers or boreholes data that is in 1D and at meter to lower scale. The study of outcropping analogues of buried reservoirs is therefore a key tool for the characterization of the fault and fracture network at the reservoir scale. Tamariu granite has been the subject of this study with the aim to analyse faults and fractures from seismic to borehole scale. With the combination of satellite picture at different resolution and field study, we perform a statistical analysis focused of the length and orientation from infra centimeter crack to hundred kilometer length fault. On the whole range of scale studied, i.e. on 7 orders of magnitude, we have defined a length distribution following a power-law with an exponent a ¼ À2. On the contrary to the length that can be modelled with a unique law, the orientation data shows a variation depending on the scale of observation: as the fault and fracture sets are suitable from the regional faults to the centimeter crack, the proportion of the sets varies at each scale of observation.

To evaluate the psychological consequences among family members given the option to be present during the CPR of a relative, compared with those not routinely offered the option. Prospective, cluster-randomized, controlled trial involving 15 prehospital emergency medical services units in France, comparing systematic offer for a relative to witness CPR with the traditional practice among 570 family members. Main outcome measure was 1-year assessment included proportion suffering post-traumatic stress disorder (PTSD), anxiety and depression symptoms, and/or complicated grief. Among the 570 family members [intention to treat (ITT) population], 408 (72 %) were evaluated at 1 year. In the ITT population (N = 570), family members had PTSD-related symptoms significantly more frequently in the control group than in the intervention group [adjusted odds ratio, 1.8; 95 % confidence interval (CI) 1.1–3.0; P = 0.02] as did family members to whom physicians did not propose witnessing CPR [adjusted odds ratio, 1.7; 95 % CI 1.1–2.6; P = 0.02]. In the observed cases population (N = 408), the proportion of family members experiencing a major depressive episode was significantly higher in the control group (31 vs. 23 %; P = 0.02) and among family members to whom physicians did not propose the opportunity to witness CPR (31 vs. 24 %; P = 0.03). The presence of complicated grief was significantly greater in the control group (36 vs. 21 %; P = 0.005) and among family members to whom physicians did not propose the opportunity to witness resuscitation (37 vs. 23 %; P = 0.003). At 1 year after the event, psychological benefits persist for those family members offered the possibility to witness the CPR of a relative in cardiac arrest.

International audience; The laser thermoelastic generation of ultrasound is a promising technique with many potential applications, but it is also a complicated process with many physical phenomena involved. Contrary to a conventional piezoelectric transducer generation, which is a surface phenomenon, a laser generation can activate acoustic sources within the material by optical penetration of the excitation wavelength, resulting in asynchronous wave arrivals at a given point. More generally, in the ideal case of a nondispersive isotropic material, the laser-ultrasonics displacement signals result from temporal convolutions between optical penetration, laser pulse duration, and laser spot extension effects. In this paper, a deconvolution technique is presented that extracts the laser pulse duration contribution from the experimental displacement signals. This deconvolution scheme applied to one-dimensional experiments, in which the laser excitation is spread over a sufficiently large area on the front side of the sample, allows the measurement of the optical absorption coefficient of the material at the excitation wavelength and also a precise evaluation of its longitudinal acoustic velocity.

Tamariu’s granite has been studied with the aim to characterize the fracture network and the porosity through the analysis of cementation associated to paleo-fluids circulation. With the help of regional and outcrop studies (Le Garzic 2010, Place 2010), we could interest on the fracture network over 8 orders of magnitudes. We used 1D scan lines and 2D fracture mapping on outcrop pictures to precisely define the fracture network and the organization of the flow in this network. The data acquired on our maps show a power law distribution of the cumulative fractures numbers and faults lengths between the centimeter scale and the hundred kilometers scale. This homogenous length distribution over a large range of scales contrasts with the fracture orientation distribution that highly depends on the scale observation and on their location relative to the larger structures. The volume of paleo-fluids associated cementation has been quantified using calcimetry and mapping of different parts of the porous network: the veins, breccias cemented by carbonates, fractured granite and poorly fractured granite. The percentage of percolated rock volume reaches to 3% of the total granitic body, and the main part of them are localized in fractured corridors composed of mains veins and breccias.

Study objectivesFamily presence during cardiopulmonary resuscitation (CPR) of a loved one remains controversial. Our study aimed to determine if offering a relative the choice to observe CPR of a family member might reduce his psychological impact 90 days later.MethodsA multicenter, cluster randomized, controlled trial. We enrolled 570 relatives of patients who were in cardiac arrest in 17 prehospital emergency medical services. Centers were randomized either to 1) systematically offer the family member the opportunity to observe CPR (intervention group) or 2) to the habitual practice regarding family presence (control group). The primary endpoint was the proportion of relatives having post-traumatic stress disorder (PTSD)-related symptoms by an Impact of Event Scale (IES)>30 at 90 days. Secondary endpoints were the presence of anxiety and depression symptoms and impact of family presence on medical efforts at resuscitation, wellbeing of the healthcare team, and on the occurrence of medicolegal claims. Analyses used the Generalized Estimating Equations (GEE).Results211/266 (79%) relatives witnessed CPR (intervention group) compared to 131/304 (43%) relatives (control group). In the intention-to-treat analysis, family members had PTSD-related symptoms significantly more frequently in the control group (adjusted odds ratio, 1.7; 95% confidence interval [CI], 1.2-2.5; P=0.004) and when they did not witness CPR (adjusted odds ratio, 1.6; 95% CI, 1.1–2.5; P=0.02). According to family presence, relatives who did not witness CPR had more frequently symptoms of anxiety and depression. Family-witnessed CPR did not affect resuscitation characteristics, patient survival, medical team stress or result in medicolegal claims.ConclusionsOur results promote family presence during CPR. This experience was associated with positive results on psychological parameters and neither interfered with medical efforts or health care team stress nor resulted in medicolegal conflicts.

To evaluate the association between emergency tracheal intubation difficulty and the occurrence of immediate complications and mortality, when standardised airway management is performed by emergency physicians.The present study was a substudy of the KETAmine SEDation (KETASED) trial, which compared morbidity and mortality after randomisation to one of two techniques for rapid sequence intubation in an emergency setting. Intubation difficulty was measured using the intubation difficulty scale (IDS) score. Complications recognised within 5 min of endotracheal intubation were recorded. We used multivariate logistic regression analysis to determine the factors associated with the occurrence of complications. Finally, a Cox proportional hazards regression model was used to examine the association of difficult intubation with survival until 28 days.A total of 650 patients were included, with mean age of 55 ± 19 years. Difficult intubation (IDS5) was recorded in 73 (11%) patients and a total of 248 complications occurred in 192 patients (30%). Patients with at least one complication had a significantly higher median IDS score than those without any complications. The occurrence of a complication was independently associated with intubation difficulty (odds ratio 5.9; 95% confidence interval (CI) [3.5;10.1], p0.0001) after adjustment on other significant factors. There was a positive linear relationship between IDS score and complication rate (R(2) = 0.83; p0.001). The Cox model for 28-day mortality indicated that difficult intubation (hazard ratio 1.59; 95%CI [1.04;2.42], p = 0.03) was a significant independent predictor of death.Difficult intubation, measured by the IDS score, is associated with increased morbidity and mortality in patients managed under emergent conditions.

Summary Background Critically ill patients often require emergency intubation. The use of etomidate as the sedative agent in this context has been challenged because it might cause a reversible adrenal insufficiency, potentially associated with increased in-hospital morbidity. We compared early and 28-day morbidity after a single dose of etomidate or ketamine used for emergency endotracheal intubation of critically ill patients. Methods In this randomised, controlled, single-blind trial, 655 patients who needed sedation for emergency intubation were prospectively enrolled from 12 emergency medical services or emergency departments and 65 intensive care units in France. Patients were randomly assigned by a computerised random-number generator list to receive 0·3 mg/kg of etomidate (n=328) or 2 mg/kg of ketamine (n=327) for intubation. Only the emergency physician enrolling patients was aware of group assignment. The primary endpoint was the maximum score of the sequential organ failure assessment during the first 3 days in the intensive care unit. We excluded from the analysis patients who died before reaching the hospital or those discharged from the intensive care unit before 3 days (modified intention to treat). This trial is registered with ClinicalTrials.gov, number NCT00440102. Findings 234 patients were analysed in the etomidate group and 235 in the ketamine group. The mean maximum SOFA score between the two groups did not differ significantly (10·3 [SD 3·7] for etomidate vs 9·6 [3·9] for ketamine; mean difference 0·7 [95% CI 0·0–1·4], p=0·056). Intubation conditions did not differ significantly between the two groups (median intubation difficulty score 1 [IQR 0–3] in both groups; p=0·70). The percentage of patients with adrenal insufficiency was significantly higher in the etomidate group than in the ketamine group (OR 6·7, 3·5–12·7). We recorded no serious adverse events with either study drug. Interpretation Our results show that ketamine is a safe and valuable alternative to etomidate for endotracheal intubation in critically ill patients, and should be considered in those with sepsis. Funding French Ministry of Health.

International audience; This work compares the effects induced by polysaccharides on the hydration of cement. It also brings new insights into the interaction mechanisms between these two components. Several parameters such as structure, concentration, average molecular weight, and the soluble fraction value of the polysaccharides were examined. The hydration of cement was monitored by conductivity measurement, and ionic chromatography. The influence of polysaccharide structure on the kinetics of cement hydration was revealed. The extent of retardation increases when polysaccharide concentration rises. Dextrins with lower average molecular weights compared with starches favor a higher soluble fraction value and further retard hydration. The growth of hydrates seemed to be more affected by the presence of these admixtures than did the dissolution of anhydrous particles or the nucleation of former hydrates

Virtual laboratories are used to help teaching a course on lasers. The spectral emission of a laser, the Zeeman effect on the laser frequencies, the frequency stabilisation of a laser and the Lamb dip are the subjects chosen to virtually illustrate the properties of a laser. All the laboratories are very close to reality, including possible experimental missteps. The student is under the conditions he can find in the real laboratory and can spend as long as he wishes, at any time. The teacher can track the student via a data base that includes the eventual missteps which the student would have committed.

The use of a visual 3D display and a virtual spectrometer for the teaching of a course in molecular spectroscopy presents new possibilities. All the movements of the molecules are shown along with their relations with their characteristic spectra. The virtual laboratory simulates a true commercial spectrometer as well as a software of recognition. All the students simultaneously follow the laboratory under conditions very close to the reality of a modern industrial laboratory.

International audience; We present a numerical model that calculates the surface displacements generated by the absorption of a laser pulse by an orthotropic medium. This model solves the heat and acoustic wave equations using temporal Laplace and spatial two-dimensional Fourier transformations. This model allows us to calculate the normal and in-plane displacements on the front or back surface of an orthotropic plate over a complete area and for virtually any time and beam profiles of the laser excitation. Numerical simulations are compared to experimental results obtained on an aluminum sample and on a graphite-eppxy plate. The experimental and numerical results are in good agreement. Laser generation of ultrasound, especially when coupled to optical detection, has been recognized to be a powerful tool for nondestructive materials evaluation.'-3 In the thermoelastic generation regime, a localized temperature elevation in the sample induced by the absorption of a laser pulse results in a localized thermal expansion which, in turn, generates ultrasonic waves. Several approaches were proposed for modeling this thermoelastic process, essentially using Green functions4-7 or Laplace and Hankel transformations.8'9 However, the use of Green functions or Hankel transformations for modeling this process cannot be easily extended to the case of anisotropic materials such as materials with an orthotropic symmetry. Other numerical techniques, like the finite element technique, " are not suitable for the resolution of the laser generation of ultrasound. In this letter, we present a model based on temporal Laplace and spatial two-dimensional (2D) Fourier transformations that allows us to describe the thermoelastic generation of ultrasound in the case of an orthotropic sample. In our model, we consider an infinite plate of finite thickness L made of an orthotropic material. The coordinate =es XI, x2, and x3 correspond to the principal axes of the medium, with x3 being the optical axis of the incident laser radiation. The stiffness tensor [C] of the orthotropic medium has then only nine different nonzero components when the abbreviated notation is used.'r To describe the laser generation of ultrasound in the ther-moelastic regime, one must solve simultaneously the heat equation and the acoustic wave equation. In our model, we neglect the mechanical heat sources in the heat equation. This assumption is valid for the time scales of our simulations.7~gP12 We use the hyperbolic heat equation' even if in the cases studied, the classical one would be adequate. The temperature elevation field 6 is then given by d6 Bs v([k]w)=pc, at +7x-%dxlkk-l " 3f(t>, i 1 (1)

Laser-generated ultrasonic waves were produced in the ablation regime at the surface of three steel samples, each having a different grain size. We show that the “noise” following the first longitudinal pulse behaves, with respect to frequency, as if it was the result of the scattering of the incident waves by the inhomogeneities in the material. We show that the grain size is related to the level of the relative “noise” spectrum, i.e. the “noise” spectrum compared to the first longitudinal pulse spectrum.

We have developed a 2 layer Laser-Ultrasonics model with interfacial conditions that describes the cohesion of materials. Different materials made with Schott’s BG18 and KG3 glass plates glued on aluminum plates were studied. Our model allows us to fit nicely the experimental results: the reflections coming from the interfacial medium are seen giving us information on the bonding of the two plates.

We present a numerical modelling of a laser ultrasonic process, which can be applied to the visualisation of near surface defects in composite materials. To this aim, the laser generation and propagation of ultrasound are described by a one-dimensional thermoelastic model and the detection of ultrasound is simulated by modelling the response of the Fabry-Perot receiver. Results have been compared to experimental data obtained on test samples with good agreement.

International audience; We present three all-optical methods that were used for the determination of the physical properties of a carbon-epoxy composite. The pulsed photothermal method, the photoacoustic method and the laser-ultrasonics method were used for the determination of, respectively, the thermal diffusivity, the optical penetration length, the thickness and the elastic coefficients of a carbon-epoxy composite covered with a 75 µm paint film at its surface.

There is now a growing interest in the use of laser-generated ultrasound for nondestructive evaluation of materials [1,2]. In the case of nonmetals, the laser-ultrasonic displacement signals result from temporal convolution between the optical penetration, the laser pulse duration and the laser spot extension [3,4]. The temporal information present in the first longitudinal arrival called “the precursor” depends on this three parameters [4,5 ]. A temporal broadening of the precursor with increasing the optical penetration have been already observed experimentally [6]. It has been shown that a measurement of the full width at half maximum (FWHM) of the precursor allows an evaluation of the optical absorption coefficient of the material at the excitation wavelength [7]. To evaluate this coefficient with a good reliability one needs to take into consideration the two other parameter effects (the extension spot size effect and the pulse duration effect). In this paper, first we present experimental and theoretical studies of the optical penetration on the acoustic waveforms. As the laser wavelength was fixed (1064 nm), we have used Schott glasses with identical thermomecanic properties and different optical absorption coefficients. Characteristic curves (in the 1-d and the 2-d regimes) that relates the FWHM of the precursor to the optical absorption coefficient have been plotted. Llinear variation regions have been identified on these curves. We have shown that it is possible to deduce the optical absorption coefficient in these regions by fitting the curves. Optical absorption coefficients of the Schott glasses have been deduced using this approach. Results were in good agreement with data given by the manufacturer and data calculated using a theoretical approach [5].

International audience; In this article, we concentrate on the optical penetration and laser pulse duration effects on the features of the ultrasonic waves generated in a solid by a laser impact. We consider the simple case of a uniform irradiation of the sample, which we describe with the help of a simple analytical one-dimensional model. In spite of its simplicity, this model clearly highlights the competition that occurs between two temporal convolution sources, related to the optical penetration and the laser pulse duration, respectively, to produce the longitudinal arrivals on the rear side of the sample. The model is also used for an accurate description of the features of the longitudinal precursor.

We previously reported the performances of a numerical simulation model [1] that calculates the mechanical displacements induced within a sample by the absorption of a laser pulse. This model solves the heat diffusion and acoustic wave propagation equations over an orthotropic slab of finite thickness with the help of temporal Laplace and spatial 2D Fourier transformations. The parallel and normal displacements predicted by the model were found to be in generally very good agreement with experimental data obtained on various samples in various excitation conditions. Among these experiments, one consisted in the CO2 laser excitation of a graphite-epoxy sample. We performed an optical study of the graphite-epoxy composite using FTIR photoacoustic spectroscopy [2] to determine the optical penetration depth spectrum of this material. This study revealed that a thin (≈ 30 μm thick) epoxy layer covered the top graphite fiber sheet of the composite, and that the optical penetration depth of the CO2 radiation in the epoxy was about 20 μm. Consequently, when a CO2 laser pulse impinges on the composite, all the radiation is absorbed in the epoxy layer, and it is easy to simulate this situation with the model, using the rigidity-expansion tensor [λ] of the epoxy for the generation and the rigidity tensor [C] of the composite for the propagation (see [1]).

International audience; We present an analytical one-dimensional model of the laser generation of ultrasound that takes the optical penetration effect into account. This model leads to a simple expression relating the full width at half maximum of the precursor to the product of the optical absorption coefficient by the longitudinal velocity, and establishes the conditions under which this expression is valid. The results of this model are compared to those provided by a more sophisticated semianalytical three-dimensional model and to experimental data obteined under various experimental conditions. The agremment is very good.

We have observed that the infrared-active stretching modes of hydrogen in device-quality a-Si:H films are redshifted as the temperature increases. Over the range of temperatures studied, 100--600 K, the shift is approximately linear with temperature, 0.035 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ ${\mathrm{K}}^{\mathrm{\ensuremath{-}}1}$, and shows a totally reversible behavior. We have established that changes in the polarization of the material, via changes of the dielectric constant with temperature, can lead to small shifts, but cannot explain the magnitude of the experimentally observed effect. We compare our results with a similar observation made on well defined hydrogen-terminated Si surfaces. In that case, the shift was attributed to the coupling of the hydrogen stretching motion with lower-frequency phonons. We propose that an analogous coupling mechanism is present in the a-Si:H structure.

International audience; We have conducted both theoretical and experimental studies of the effect of the energy distribution of the ultrasound generating laser pulse on the amplitude of the longitudinal precursor and on the temporal profile of the displacement for single-point, two-points and line-of-points distributions. These preliminary studies show that the agreement between theory and experiment is generally good and that improvement of the amplitude of the precursor is possible.

International audience; We present an analytical 1D model of the laser generation of ultrasound that takes the optical penetration effect and the time profile of the laser pulse into account. This model leads to simple expressions for the time position and width of the precursor. The results of this model are compared to experimental data. We also present numerical and experimental directivity patterns of samples having various optical penetration depths.

The glass transition temperature Tg can be identified with a sharp increase of the thermal expansion coefficient X. We present photoacoustic and constrained photodeformation measurements of the glass transition in polystyrene in conditions of weak optical absorption. Since the thermoelastic contribution to the signal prevails in those conditions, we show both theoretically and experimentally that the signal amplitudes exhibit a sharp increase near Tg, allowing its clear identification and the observation of a viscoelastic behavior.

International audience; We present results of photoacoustics and laser-ultrasonics experiments that were performed on a ZnO ceramic sample and that led to optical, thermal and thermo-mechanical characterizations of this material.

International audience; Optical absorption is obviously of prime interest in the efficiency of laser generation of ultrasound in graphite-epoxy laminates. However, no quantitative spectrum of optical absorption in this composite material has yet been published in the literature. Transmission techniques are inefficient, and other techniques, like attenuated total reflectance or diffusive reflectance, do not give absolute values. The Fourier transform photoacoustic spectroscopy technique seems to be a good alternative that can analyze adequately and quantitatively a graphite-epoxy laminate. We used three different methods to compute the absolute optical absorption from the photoacoustic signal. The three methods are: the saturation of the real part of the photoacoustic spectrum, the comparison of the spectra obtained with two different mirror velocities, and the calibration of the photoacoustic cell with a transmission measurement. The spectra obtained in the IR band of 2.5 to 25 µm are presented, and the problems and limitations of each method are discussed. The results permit a better understanding of the absorption process in the composite laminate, and in this way, will help us enhance the efficiency of laser generation of ultrasound in graphite-epoxy.

By use of phase detection in Fourier transform infrared photoacoustic spectroscopy, we are able to obtain new information on materials difficult and often impossible to obtain otherwise. With our technique, a more precise and complete analysis is hereby possible. Applications of our approach to polyethylene, asbestos fibers and a thin layer of polymer illustrate well this capability.

Numerical simulations are performed to demonstrate the possibility to detect the glass transition of polymers by photoacoustic measurements and to deduce their viscoelastic properties.

We present a numerical study of the behavior of the signal in a photothermal experiment combining the mirage effect and a Jamin interferometer. Our analysis is limited to a square-pulse excitation by a weakly absorbed Gaussian pump laser beam with a large radius. We investigate the influence of three parameters: the time of illumination of the sample, the time of extinction of the pump beam, and the height of the probe-beam arm of the Jamin interferometer above the sample. We show that the path difference, which induces the variation of intensity at the output of the Jamin interferometer, is caused by both probe-beam deflection and temperature variation of the refractive index of air above the sample. The first effect is dominant for short times, and interferometry is a sensitive tool to monitor it.

International audience; The phase of the photoacoustic signal is of prime importance for obtaining accurate optical absorption coefficients using the photoa-coustic technique. Variations in the spectrometer or the photoacoustic cell parameters between the measurement of the sample spectrum and the carbon black reference spectrum are the main source of phase shifts. We reconsider a simple model that provides an accurate description of the photoacoustic effect—including photoacoustic saturation—for thermally thick, homogeneous samples. The model includes absorption from a thin layer at the sample surface. We propose a method for optimizing the photoacoustic phase for this model. The method is based on the internal calibration at the onset of the photoacoustic saturation, and on a simple analysis of the shape of the calculated surface absorption spectrum. Optimization is illustrated with a simulated spectrum and an experimental spectrum of ethylene-propylene-rubber.

In some photoacoustic experiments, thermoelastic bendings of solid samples produce strong signals which cannot be analyzed by usual photoacoustic calculations. We propose a model that, using the thermoelastic equations, analytically explains the effect of this bending. It is found that the model agrees well with data obtained from an experiment sensitive to thermoelastic deformations only. Furthermore, the model is also consistent with previous piezoelectric‐photoacoustic calculations. This experiment also leads to measurements of thermal diffusivities.

The ability to use the finite-element method to solve numerically the frequency-dependent coupled equations of the photoacoustic–thermal effect is demonstrated. Both solids and fluids are simulated by the same set of equations with temperature and displacement as variables. The main interest of this formulation lies in its great flexibility to deal with mixed fluid–solid systems. As a first application, we consider the influence of thermoacoustic coupling on the pressure in a photoacoustic cell. We show that with increasing frequency, a transition from an isothermal to an adiabatic process occurs. Subsequently, results obtained from a numerical simulation of the photoacoustic cell, which includes the effect of a residual volume, are in good agreement with existing experimental data.

Fourier transform infrared photoacoustic spectroscopy is greatly improved by the simultaneous measurement of the photoacoustic signal amplitude and phase. Saturation effects, sample dilation, and optical scattering, even in heterogeneous samples, can be easily corrected to give the absorption coefficient real value. Quantitative analyses without any special sample preparation or special photoacoustic cell are now possible. Moreover, the phase of the photoacoustic signal permits depth localization of the absorbing species within the thermal diffusion length. Surface analyses are thus possible that have a depth resolution at least one order of magnitude higher than that obtained by changing the thermal diffusion length. In this paper we illustrate the advantages of phase analysis in Fourier transform infrared photoacoustic spectroscopy with the detection of sorbed water in polyethylene.

A pulsed photothermal method is proposed for the detection of delaminations in layered materials. The surface of the material is heated by a focused laser pulse to a few degrees above the ambient temperature, and the induced thermoelastic displacement is detected by a laser interferometer. Unbonded areas are characterized by their thermoelastic bending behavior, in addition to their thermal expansion, because of the induced temperature gradients both in the radial and axial directions. A theoretical analysis and an experimental investigation of this behavior are described in order to point out the most significant parameters. An application of the nondestructive inspection of Al‐epoxy honeycomb panels is presented.

The photoacoustic detection of subsurface defects in metallic plasma coatings on metallic substrates has been achieved. The investigation is performed with samples that contain well-known artificial defects (Teflon, alumina or boron nitride) whose thermal properties are sufficiently different from those of the coatings (aluminium or Ni-Cr alloy) or the metallic substrates. The experimental results are interpreted in terms of a theoretical model for the layered structure of the sample. Moreover, the photoacoustic effects of the defect may be characterized by a thermal resistance at the coating-substrate interface. This study enables us to determine different characteristics of the coatings such as thermal properties, thickness and adherence to the substrate, in spite of the effects of the surface roughness on the photoacoustic signal.

A pulsed photothermoelastic technique for nondestructive testing of layered materials is described. A Fourier-transform signal analysis is presented for a quantitative characterization of subsurface defects. Discrepancies between the experimental results and the data obtained from the thin-plate analytical theory are interpreted through a finite-element numerical model. The effect of the vibrational properties of the whole structure is shown to be particularly important on the spectral features of the thermoelastic signal for small defects.

This paper sets forth a self‐contained theoretical description of the photoacoustic effect in a thick powdered or porous sample at low modulation frequencies where the sample medium can be considered homogeneous from the point of view of heat diffusion. It is shown that the photoacoustic signal results from two contributions: the heat flux from the sample to the gas plus the expansion of the interstitial gas and that the pressure is essentially uniform throughout the sample. Scattering effects are introduced with a Kubelka–Munk modified model and an expression is first given for the conventional partially filled cell. We discuss of these results and their application to the explanation of several texture effects and to the analysis of experimental data. Using a sample composed of chrysotile asbestos powder, we present experimental data and perform an approximate analysis to retrieve the absorption spectrum. Several experimental results are also presented and thoroughly discussed for a cell completely fill...

It has been previously shown that ultrasonic absorption in a solid material can be detected and, in some cases, measured by monitoring, with an infrared detector, the variation of temperature at the surface of the sample resulting from the periodic modulation of the ultrasonic intensity. Thermal-wave vignetting effects, which are caused by the finite ultrasonic beam size and the finite area viewed by the detector, and effects caused by the ultrasonic standing-wave pattern are analyzed in this paper by a theoretical derivation and by experiment. Satisfactory agreement is found between both.

Strong absorption bands of photoacoustic Fourier-transform spectra are often truncated relative to weaker bands owing to signal saturation. To correct this problem, we propose processing both the phase and the amplitude information in the photoacoustic signal. Under certain conditions, easily fulfilled in typical experiments, we are able to calculate the absolute absorption spectrum from the photoacoustic data. Experimental results are given for asbestos fibers (chrysotile).