Effective line tension and contact angles between membrane domains in biphasic vesicles.

Inhomogeneities in membranes give rise to localized interactions at the interface between domains in two-component vesicles. The corresponding energy is expressed as a line tension between the two phases. In this paper we study the implications of the thickness mismatch between domains which has been experimentally reported to be of order 20-30% and the conditions under which the induced line tension can destabilize the domains in inhomogeneous vesicles.

Conical defects in growing sheets.

A growing or shrinking disc will adopt a conical shape, its intrinsic geometry characterized by a surplus angle phi(e) at the apex. If growth is slow, the cone will find its equilibrium. Whereas this is trivial if phi(e)0.

Dripping of a crystal.

Dripping is usually associated with fluid motion, but here we describe the analogous phenomenon of a 3He crystal growing and melting under the influence of surface tension and gravity. The pinch-off of the crystal is described by a purely geometric equation of motion, viscous dissipation or inertia being negligible. In analogy to fluid pinch-off, the minimum neck radius R{n} goes to zero like a power law, but with a new scaling exponent of 12 .

Cavitation in plants at low temperature: is sap transport limited by the tensile strength of water as expected from Briggs' Z-tube experiment?

Xylem cavitation in plants is thought to be caused by a loss of adhesion at the conduit wall surface because a rupture in the body of the water column was implicitly ruled out by an experiment by Lyman J. Briggs with Z-tube capillaries. However, Briggs reported a drastic increase in cavitation pressure of water below 5 degrees C which, if it were also true in xylem conduits, would suggest that water transport in plants could be limited by water cohesion at low temperature.

Cavitation pressure in water.

We investigate the limiting mechanical tension (negative pressure) that liquid water can sustain before cavitation occurs. The temperature dependence of this quantity is of special interest for water, where it can be used as a probe of a postulated anomaly of its equation of state. After a brief review of previous experiments on cavitation, we describe our method which consists in focusing a high amplitude sound wave in the bulk liquid, away from any walls.

Superfluidity of grain boundaries and supersolid behavior.

When two communicating vessels are filled to a different height with liquid, the two levels equilibrate because the liquid can flow. We have looked for such equilibration with solid (4)He. For crystals with no grain boundaries, we see no flow of mass, whereas for crystals containing several grain boundaries, we detect a mass flow.

Liquid-vapor interface, cavitation, and the phase diagram of water.

The study of the liquid-vapor interface and of the cavitation phenomenon in water can give deeper insight in its metastable phase diagram. We show how two different equations of state proposed for water, combined with the van der Waals-Cahn-Hilliard theory of a nonuniform system, lead to qualitatively different predictions. In particular, the thickness of the liquid-vapor interface is found either to increase with temperature or to exhibit a minimum.

Coalescence of crystalline drops.

We present the first experimental analysis of drop coalescence in a case where the dynamics is not governed by viscous dissipation in the bulk nor by the inertia of the fluid flow, only by the geometry and mobility of surfaces. We found such a situation in the physics of 3He crystals near 0.32 K where the latent heat of crystallization vanishes.

Critical casimir effect and wetting by helium mixtures.

We have measured the contact angle of the interface of phase-separated 3He-4He mixtures against a sapphire window. We have found that this angle is finite and does not tend to zero when the temperature approaches T(t), the temperature of the tricritical point. On the contrary, it increases with temperature.

Anomaly in the stability limit of liquid 3He.

We propose that the liquid-gas spinodal line of 3He reaches a minimum at 0.4 K. This feature is supported by our cavitation measurements.

Acoustic crystallization and heterogeneous nucleation.

By focusing a high-intensity acoustic wave in liquid helium, we have observed the nucleation of solid helium inside the wave above a certain threshold in amplitude. The nucleation is a stochastic phenomenon. Its probability increases continuously from 0 to 1 in a narrow pressure interval around P(m) + 4.