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Biomedical subjects

C Gourdon

Publications and source records attributed to C Gourdon.

At least 19 recordsLinked to original sources
PubMed2006

Effect of mass transfer on the film drainage between colliding drops.

The influence of mass transfer on the drainage behaviour of the thin liquid film between two drops immersed in another liquid colliding at constant approach velocity has been studied experimentally. The liquid-liquid system used is glycerol in silicone oil. The transferred solute is acetone and the volume concentration difference across the interface ranges from 1 to 5%. The film thickness evolution has been measured using a laser interferometry technique. The direction of mass transfer (from the drops towards the film phase and inversely) has been investigated and the results compared to the case with no mass transfer. When the solute transfers from the drops towards the continuous phase, the drainage rate is significantly higher than in the case with no mass transfer. This result is interpreted as a consequence of the mass transfer induced surface mobility in the film region (the so-called Marangoni effect) due to localized surface tension differences. This effect has been demonstrated by the visualization of the flow patterns in the drops and in the film phase (using a particle tracer technique). In this case, the slope of the film height as a function of time seems to be independent of the approach velocity condition imposed on the drop and appears to be controlled by the interfacial tension gradient. In the opposite case, when the solute transfers from the continuous phase towards the drops, the film drainage rate is lowered with respect to the case of no mass transfer, goes to zero or even changes its sign depending on the mass transfer intensity. The results also show that in the range of solute concentration studied, the effect of mass transfer on the film drainage process takes place at large distances compared to the scales at which lubrication theory is valid.

Journal Article↗
PubMed2006

Nucleation and collapse of the superconducting phase in type-I superconducting films.

The phase transition between the intermediate and normal states in type-I superconducting films is investigated using magneto-optical imaging. Magnetic hysteresis with different transition fields for collapse and nucleation of superconducting domains is found. This is accompanied by topological hysteresis characterized by the collapse of circular domains and the appearance of lamellar domains. Magnetic hysteresis is shown to arise from supercooled and superheated states. Domain-shape instability resulting from long-range magnetic interaction accounts well for topological hysteresis.

Journal Article↗
PubMed2004

Impeded growth of magnetic flux bubbles in the intermediate state pattern of type I superconductors.

Normal state bubble patterns in type I superconducting indium and lead slabs are studied by the high resolution magneto-optical imaging technique. The size of bubbles is found to be independent of the long-range interaction between the normal state domains. Under bubble diameter and slab thickness proper scaling, the results gather onto a single master curve. We calculate the equilibrium diameter of an isolated bubble resulting from the competition between the Biot-and-Savart interaction of the Meissner current encircling the bubble and the superconductor-normal interface energy. A good quantitative agreement with the master curve is found over two decades of the magnetic Bond number. The isolation of each bubble in the superconductor and the interface energy are shown to preclude any continuous size variation of the bubbles after their formation, contrary to the prediction of mean-field models.

Journal Article↗
PubMed2004

Extraction of valerenic acids from valerian (Valeriana officinalis L.) rhizomes.

Extraction of valerenic acids (valerenic, acetoxyvalerenic and hydroxyvalerenic) from dry ground rhizomes of valerian (Valeriana officinalis L.) was studied. The effect of ethanol concentration in the solvent, extraction temperature and drug particle size on extraction kinetics were investigated and the optimum values of these process parameters were determined for the case of intensively stirred two-phase dispersion. It was found that increased processing temperature favors extraction kinetics, but provokes moderate degradation of valerenic acids.

Ethanol↗
PubMed2000

Film Drainage between Colliding Drops at Constant Approach Velocity: Experiments and Modeling.

Experiments and modeling of the drainage of the thin liquid film between two deformable spherical drops approaching each other at constant velocity in another liquid are being presented. Two numerical models based on the lubrication theory have been developed considering the cases of immobile or mobile drop interfaces. The absolute film thickness and the thinning rate have been measured using laser interferometry for a wide range of capillary numbers. In all studied cases, the model with immobile interfaces was found to give the best predictions of the experimental time evolution of the film thickness and radial expansion. These results made it possible to derive a typical time scale of the drainage process. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Emulsification processes: on-line study by multiple light scattering measurements.

The use of ultrasound in various processes of the chemical industry has been a subject of research and development for many years. As regards in emulsification, apart from formulation variables, power is the most important parameter. Efficiency of emulsification processes may be followed and evaluated by measuring particle size distribution, which mainly governs the kinetic stability of such dispersions. Unfortunately, this kind of measurement must be performed at high dilution (low volume fraction of dispersed phase). The present work is devoted to the on-line study of ultrasound emulsification by means of a newly developed apparatus based on multiple light scattering, which allows us to determine average droplet diameter and its variations directly on concentrated media. The model system was an oil (kerosene)-in-water emulsion stabilized by a polyethoxylated sorbitan monostearate.

Journal Article↗
PubMed1999

Emulsification by ultrasound: drop size distribution and stability.

The aim of this work is to compare the oil-in-water emulsions produced by mechanical agitation (Ultra-Turrax, 10,000 rpm, P = 170 W) or power ultrasound (ultrasound horn, 20 kHz, 130 W) using the same model system: water/kerosene/polyethoxylated (20 EO) sorbitan monostearate. The following parameters were varied: emulsification time, surfactant concentration, consumed power and volume fraction of oil. With ultrasound, the drop size (Sauter diameter, d32) is much smaller than that given by mechanical agitation under the same conditions, which makes insonated emulsions more stable. For a given drop size (d32), less surfactant is required.

Journal Article↗
PubMed1998

A comparative study of local sensors of power ultrasound effects: electrochemical, thermoelectrical and chemical probes.

In order to propose standard methods for the local measurement of the effects of power ultrasound inside a reactor, we compare three methods: a chemical dosimeter (Weissler reaction), a thermal sensor (embedded thermocouple) and an electrochemical probe (developed in our laboratory). The same emission device, i.e. the resonant tube (Sonitube-Sodeva), was used for all these methods. Similar trends were observed using various measurements: ultrasound effects vary significantly along the tube axis (due to standing waves in the resonant tubular emitter), but only slightly from the tube axis to the wall. More reliable and reproducible results were obtained with the thermal and electrochemical probes than with the chemical dosimeter.

Journal Article↗
PubMed1997

Predictive Model for the Calculation of Interfacial Tension in Nonideal Electrolytic Systems

A new model is proposed for the calculation of the interfacial tension between an organic solvent and concentrated aqueous solutions of electrolytes. The interfacial tension is derived from the isothermal Gibbs equation. The increase or decrease of interfacial tension with concentrations are modeled using a Langmuir-type adsorption equation and the strong non-ideality of the mixtures is taken into account through the Mikulin equation. The model parameters are first determined with binary water-electrolyte solutions and are kept constant in the case of mixtures. The model has been applied to chloride solutions-chloride salts of various metals and hydrochloric acid-and compared with experimental data obtained by using the pendant drop technique and a Wilhelmy tensiometer. In all cases investigated, good agreement is observed, even in the case of stiff variations of interfacial tension with the electrolyte concentration and also at high concentrations of electrolytes.

Journal Article↗
PubMed1997

Experimental study of the ultrasound attenuation in chemical reactors.

Ultrasound is used in different domains, and in sonochemistry particularly, for different purposes and in various flow configurations: monophasic, two-phase and polyphasic reactors. In order to optimize and to design sonochemical reactors, it is important to describe the ultrasonic intensity space and time distribution. In addition, it is important to study the different parameters influencing the intensity profiles of the ultrasonic wave. In this work, a thermoelectric probe has been used to measure the ultrasonic intensity. This procedure has shown that the ultrasound propagation is influenced by the presence of cavitation bubbles, the flow regime and the presence of solid particles.

Journal Article↗
PubMed1993

[Viral infections and asthma].

Respiratory tract viruses have been held responsible for the genesis and aggravation of asthma in both children and adults. The relationship between asthma and viruses is looser in adults than in children, but it has been demonstrated that viral infections can generate a peripheral obstructive disorder on the one hand, and a transient non-specific bronchial hyperreactivity in healthy subjects on the other hand. Current data are insufficient to define clearly the alterations induced by viral infections and responsible for bronchial inflammation and non-specific bronchial hyperreactivity. Numerous studies have concluded to a complex mechanism involving bronchial epithelium lesions, imbalance of the autonomic nervous system in bronchial tone regulation, occurrence of immediate hypersensitivity reaction with facilitation of its delayed component, and cytokines produced during viral infection.

Adolescent↗
PubMed1993

Recurrent interlobar pneumothorax in an asthmatic patient.

We report a case of spontaneous interlobar pneumothorax, an uncommon condition. The diagnosis was suspected from the frontal chest X-ray, which showed an incompletely circumscribed air-containing space, with a fluid level. The diagnosis was confirmed by the lateral projections of standard X-ray and tomography, and by thoracic computed tomography (CT). Such air-fluid levels should not be confused with pneumatocele, cystic or cavitary diseases.

Asthma↗
PubMed1992

[Occupational asthma].

The diagnosis of occupational asthma requires the integration of a multiplicity of data; the history, cutaneous skin tests, biological tests, respiratory function tests and non-specific tests of bronchial hyperreactivity and specific bronchial provocation test. The history search for the presence of an atopic state, the occurrence of similar disorders in members of the same firm and also the timing of symptoms in relation to the occupational activities. Cutaneous tests are particularly helpful in IgE-mediated asthma in relation to the inhalation of animal or vegetable materials of glycoprotein origin. For haptens, the need for their prior coupling to a protein carrier causes problems which have not been entirely resolved. Laboratory tests run into the same snags. Respiratory function and non-specific bronchial provocation tests, confirm the diagnosis of asthma and enable the medium and long term prognostic to be assessed. Specific bronchial provocation tests are the most appropriate tests to establish an aetiological diagnosis in occupational asthma. Different technical methods are possible: quantitative administration of allergen aerosols, realistic tests, and tests using exposure chambers to achieve true test doses. The products responsible for occupational asthma are multiple. The different substances are characterised in a simplified manner: first animal matter (mammalian and arthropod allergens), secondly substances of vegetable origin (roots, leaves, flowers, grain and flour, wood and its derivates) and finally chemical products. The chemical products are primarily from the pharmaceutical and metal industries and above all from the plastics industry.

Allergens↗
PubMed1990

[Endobronchial aspergillosis associated with a carcinoid tumor].

We report a case of a 62 year old man who presented with effort dyspnoea accompanied by a cough and haemoptysis. The chest radiograph of the thorax showed atelectasis of the right upper lobe. Bronchoscopy showed evidence of a tumour like mass obstructing the right bronchus and this revealed itself to be a mass of organised fibrinous deposit in granulation tissue containing numerous colonies of Aspergillus. In fact it appeared to be an obstructive Aspergillus bronchitis, with a pseudo-tumour appearance attached to a carcinoid tumour which was obstructing the apical segment of the right upper lobe. Obstructive Aspergillus bronchitis makes up only a small percentage of overall respiratory disease caused by Aspergillus. They pose a problem of differential diagnosis with bronchopulmonary aspergillosis which is much more frequent.

Aspergillosis↗