Conical Interfaces between Two Immiscible Fluids Induced by an Optical Laser Beam.

We demonstrate the existence of conical interface deformations induced by a laser beam that are similar to Taylor cones in the electrical regime. We show that the cone morphology can be manipulated by fluid and laser parameters. A theory is proposed to quantitatively describe these dependences in good agreement with experimental data obtained for different fluid systems with low interfacial tensions. Counterintuitively, the cone angle is proved to be independent of the refractive index contrast at leading order. These results open a new optofluidic route towards optical spraying technology-an analogue of electrospraying-and more generally for the optical shaping of interfaces.

Viscoelastic Drag Forces and Crossover from No-Slip to Slip Boundary Conditions for Flow near Air-Water Interfaces.

The "free" water surface is generally prone to contamination with surface impurities, be they surfactants, particles, or other surface active agents. The presence of such impurities can modify flow near such interfaces in a drastic manner. Here we show that vibrating a small sphere mounted on an atomic force microscope cantilever near a gas bubble immersed in water is an excellent probe of surface contamination. Both viscous and elastic forces are exerted by an air-water interface on the vibrating sphere even when very low doses of contaminants are present. The viscous drag forces show a crossover from no-slip to slip boundary conditions while the elastic forces show a nontrivial variation as the vibration frequency changes. We provide a simple model to rationalize these results and propose a simple way of evaluating the concentration of such surface impurities.

Excitation of fountain and entrainment instabilities at the interface between two viscous fluids using a beam of laser light.

We report on two instabilities, called viscous fountain and viscous entrainment, triggered at the interface between two liquids by the action of bulk flows driven by a laser beam. These streaming flows are due to light scattering losses in turbid liquids, and can be directed either toward or forward the interface. We experimentally and numerically investigate these interface instabilities and show that the height and curvature of the interface deformation at the threshold and the jet radius after interface destabilization mainly depend on the waist of the laser beam. Analogies and differences between these two instabilities are characterized.

Universal morphologies of fluid interfaces deformed by the radiation pressure of acoustic or electromagnetic waves.

We unveil the generation of universal morphologies of fluid interfaces by radiation pressure regardless of the nature of the wave, whether acoustic or optical. Experimental observations reveal interface deformations endowed with steplike features that are shown to result from the interplay between the wave propagation and the shape of the interface. The results are supported by numerical simulations and a quantitative interpretation based on the waveguiding properties of the field is provided.

Optohydrodynamics of soft fluid interfaces: optical and viscous nonlinear effects.

Recent experimental developments showed that the use of the radiation pressure, induced by a continuous laser wave, to control fluid-fluid interface deformations at the microscale, represents a very promising alternative to electric or magnetic actuation. In this article, we solve numerically the dynamics and steady state of the fluid interface under the effects of buoyancy, capillarity, optical radiation pressure and viscous stress. A precise quantitative validation is shown by comparison with experimental data. New results due to the nonlinear dependence of the optical pressure on the angle of incidence are presented, showing different morphologies of the deformed interface going from needle-like to finger-like shapes, depending on the refractive index contrast. In the transient regime, we show that the viscosity ratio influences the time taken for the deformation to reach steady state.

Influence of contact angle on slow evaporation in two-dimensional porous media.

We study numerically the influence of contact angle on slow evaporation in two-dimensional model porous media. For sufficiently low contact angles, the drying pattern is fractal and can be predicted by a simple model combining the invasion percolation model with the computation of the diffusive transport in the gas phase. The overall drying time is minimum in this regime and is independent of contact angle over a large range of contact angles up to the beginning of a transition zone. As the contact angle increases in the transition region, the cooperative smoothing mechanisms of the interface become important and the width of the liquid gas interface fingers that form during the evaporation process increases. The mean overall drying time increases in the transition region up to an upper bound which is reached at a critical contact angle thetac. The increase in the drying time in the transition region is explained in relation with the diffusional screening phenomenon associated with the Laplace equation governing the vapor transport in the gas phase. Above thetac the drying pattern is characterized by a flat traveling front and the mean overall drying time becomes independent of the contact angle. Drying time fluctuations are studied and are found to be important below thetac, i.e., when the pattern is fractal. The fluctuations are of the same order of magnitude regardless of the value of contact angle in this range. The fluctuations are found to die out abruptly at thetac as the liquid gas interface becomes a flat front.

[Cutaneous anthrax: seven cases]. / Maladie du charbon cutanée: sept cas.

BACKGROUND: Anthrax is an acute infection caused by the Gram-positive organism, Bacillus anthracis, which rarely affects humans under normal conditions. Depending on the mode of contamination, there are three distinct clinical forms: pulmonary, gastrointestinal and cutaneous. This type of infection is still common in the developing countries, a fact that should be borne in mind by examining doctors, and in particular by dermatologists. It is important to recognise the clinical aspects of this disease rarely encountered in clinical practice since any delay in treatment may have fatal consequences, as illustrated by our case reports. CASE REPORTS: Five men and two women of mean age 35years presented one or more cutaneous lesions of the upper limbs in all instances. All patients had a fever of 39-40 degrees C but none were presenting gastrointestinal or pulmonary signs. Neurological signs and/or disturbed consciousness were seen in three patients. Bacteriological diagnosis was based on isolation of B. anthracis in cultures of skin specimens. Treatment with parenteral or oral ciprofloxacin was initiated in six patients, and this therapy was combined with oral corticosteroids in three patients. A favourable outcome was achieved in four patients, while the remaining three patients died of their disease. DISCUSSION: Anthrax is an anthropozoonosis that has now become rare in the developed countries. The disease is contracted by humans through touching either animals killed by anthrax or the products thereof. The cases we report were subsequent to collective contamination of several members of a single family, probably due to contact with goats carrying the disease. If left untreated, cutaneous anthrax may progress in 5 to 20% of cases to septicaemia with potentially lethal central nervous system involvement. The only means of eradicating anthrax in animals, and thus in humans, is through animal vaccination.

[Eruptive pseudoangiomatosis in infant and newborns]. / Pseudoangiomatose éruptive du nourrisson et du nouveau-né.

INTRODUCTION: Eruptive pseudoangiomatosis was first described in children in the form of an acute non-pruritic macular or papular rash that fades on application of a glass test and resolves within several days. Viral aetiology is suspected but has never been demonstrated to date. OBSERVATIONS: We discuss seven cases of infants presenting this disease: 5 boys and 2 girls aged 8 days to 16 months. The rash presented typical clinical features in all cases and affected the face and limbs in 6 of the 7 subjects. In one child, involvement of the face and back was observed with sparing of the limbs. The rash occurred after an episode of rhinolaryngeal infection in 3 cases and after gastrointestinal infection in 1 case. Spontaneous resolution was seen within 3 to 10 days in 6 patients although a longer course lasting over 9 months was observed in one infant. In another patient, the rash appeared after surgery for mesoblastic nephroma. In one child, a similar rash was seen in both parents. Screening for infectious agents was negative for the two children from whom samples were obtained. DISCUSSION: This series of paediatric cases of eruptive pseudoangiomatosis is characterised by the very young age of one of the children, coexistence of the condition with a renal tumour in another child, the familial nature of the rash in a third child and unusually long disease duration in the final child. However, this series did not allow identification of the causative infectious agent or agents. Probably, as with other syndromes such as Giannotti-Crosti syndrome or "gloves and socks" syndrome, eruptive pseudoangiomatosis forms a clinical picture common to a non-specific viral infection.

The diagnosis and treatment of carcinomas occurring at the sites of chronic pressure ulcers.

Tumours that develop at the sites of pressure ulcers are very aggressive. Removal is thus crucial, but such cases are difficult to diagnose. This paper discusses a rare case of Marjolin's ulcer, which was treated with excision and radiotherapy.

[American histoplasmosis: a case with cutaneous presentation in Morocco]. / Histoplasmose américaine: une observation marocaine à forme cutanée.

Histoplasmosis Histoplasma capsulatum is a common systemic mycosis in immunocompromised subjects. It has not been reported in Maghreb countries. The purpose of this report is to describe a case with cutaneous presentation involving a Moroccan woman undergoing long-term corticosteroid therapy for systemic inflammatory diseases (rheumatoid polyarthritis and scleroderma). In addition to the main pathophysiological features of the disease, the authors present the causal agent and clinical manifestations. They stress the importance of laboratory findings in the diagnosis of this fungal disease.