We have investigated the formation of helium droplets in two physical situations. In the first one, droplets are atomised from superfluid or normal liquid by a fast helium vapour flow. In the second, droplets of normal liquid are formed inside porous glasses during the process of helium condensation. The context, aims, and results of these experiments are reviewed, with focus on the specificity...

Helium-oxygen mixtures and pressure-support ventilation have been used to unload the respiratory muscles and increase exercise tolerance in COPD. Considering the different characteristics of these techniques, we hypothesized that helium-oxygen would be more effective in reducing exercise-induced dynamic hyperinflation than pressure-support. We also hypothesized that patients would experience gr...

This work reports on the evolution law of helium bubbles in Hastelloy N alloy on post-irradiation annealing conditions. After helium ion irradiation at room temperature and subsequent annealing at 600 °C (1 h), the transmission electron microscopy (TEM) micrograph indicates the presence of helium bubbles with size of 2 nm in the depth range of 0-300 nm. As for the sample further annealed at 850...

This paper presents results pertaining to the numerical modeling of the cryogenic system at the Canadian Light Source. The cryogenic system consists of the cryostat that houses a Radio Frequency (RF) Cavity used for boosting energy of an electron beam. For consistent operation of the RF Cavity, it must be kept immersed in liquid helium at a constant level with the pressure in the gas space main...

The best-known property of superfluid helium is the vanishing viscosity that objects experience while moving through the liquid with speeds below the so-called critical Landau velocity. This critical velocity is generally considered a macroscopic property as it is related to the collective excitations of the helium atoms in the liquid. In the present work we determine to what extent this concep...

Metal atoms have proved to be sensitive probes of the properties of superfluid helium nanodroplets. To date, all experiments on the doping of helium droplets have concentrated on the attachment of metal atoms in their ground electronic states. Here we report the first examples of metal atoms in excited states becoming attached to helium nanodroplets. The atoms in question are aluminum, and they...

The abundance of helium in the Sun's interior is estimated by the method of`model-oriented' helioseismic inversion of solar oscillation frequencies. In this method, the equations of state and thermal balance are used in addition to the hydrostatic equation. By inverting the observed p-mode frequencies, direct evidence for gravitational settling of helium has been obtained. However, the helium s...

We present an analysis of 40 cool helium-rich white dwarfs found in the Hamburg/ESO survey. They were selected for follow-up spectroscopy because of their U −B colour below -0.18, the absence of strong absorption lines, and a continuum shape similar to that of a quasar. Effective temperatures for individual stars were determined by fitting model atmospheres of nearly pure helium with a small ad...

The effect of helium implantation fluences in French nuclear borosilicate glass on He bubble nucleation and growth mechanisms was characterised using in-situ TEM experiments. Observations of implanted glass at 143K indicate that a helium concentration of around 3 at.% is required to nucleate a significant density of nanosized bubbles. He bubble growth is observed for He concentration higher tha...

High resolution spectra of the Hei587.6, 667.8 706.5 and 728.1 nm lines have been obtained to test the prediction (notably by Vauclair et al. 1991) that helium abundance should decrease with depth in helium rich stars and increase in helium weak stars. A sample of B-type main sequence stars, with expected solar abundances and non stratified atmospheres, have also been observed in order to compa...