220 research outputs found
Nucleation in a Fermi liquid at negative pressure
Experimental investigation of cavitation in liquid helium 3 has revealed a
singular behaviour in the degenerate region at low temperature. As the
temperature decreases below 80 mK, the cavitation pressure becomes
significantly more negative. To investigate this, we have extrapolated the
Fermi parameters in the negative pressure region. This allowed us to calculate
the zero sound velocity, which we found to remain finite at the spinodal limit
where the first sound velocity vanishes. We discuss the impact on the
nucleation of the gas phase in terms of a quantum stiffness of the Fermi
liquid. As a result we predict a cavitation pressure which is nearer to the
spinodal line than previously thought.Comment: 6 pages, 2 figures. To be published in Journal of Low Temperature
Physics, Proceedings of the International Symposium on Quantum Fluids and
Solids QFS200
Effects of compressibility and wetting on the liquid-vapor transition in a confined fluid
When a fluid is constrained to a fixed, finite volume, the conditions for
liquid-vapor equilibrium are different from the infinite volume or constant
pressure cases. There is even a range of densities for which no bubble can
form, and the liquid at a pressure below the bulk saturated vapor pressure
remains indefinitely stable. As fluid density in mineral inclusions is often
derived from the temperature of bubble disappearance, a correction for the
finite volume effect is required. Previous works explained these phenomena, and
proposed a numerical procedure to compute the correction for pure water in a
container completely wet by the liquid phase. Here we revisit these works, and
provide an analytic formulation valid for any fluid and including the case of
partial wetting. We introduce the Berthelot-Laplace length
, which combines the liquid isothermal compressibility
and its surface tension . The quantitative effects are fully
captured by a single, non-dimensional parameter: the ratio of to the
container size.Comment: 13 pages, 13 figure
Non-linear effects and shock formation in the focusing of a spherical acoustic wave : Numerical simulations and experiments in liquid helium
The focusing of acoustic waves is used to study nucleation phenomena in
liquids. At large amplitude, non-linear effects are important so that the
magnitude of pressure or density oscillations is difficult to predict. We
present a calculation of these oscillations in a spherical geometry.
We show that the main source of non-linearities is the shape of the equation
of state of the liquid, enhanced by the spherical geometry. We also show that
the formation of shocks cannot be ignored beyond a certain oscillation
amplitude. The shock length is estimated by an analytic calculation based on
the characteristics method. In our numerical simulations, we have treated the
shocks with a WENO scheme. We obtain a very good agreement with experimental
measurements which were recently performed in liquid helium. The comparison
between numerical and experimental results allows in particular to calibrate
the vibration of the ceramics used to produce the wave, as a function of the
applied voltage.Comment: 20 pages, 26 figures. Submitted to The European Physical Journal
Minimal microscopic model for liquid polyamorphism and water-like anomalies
Liquid polyamorphism is the intriguing possibility for a single component
substance to exist in multiple liquid phases. We propose a minimal model for
this phenomenon. Starting with a binary lattice model with critical azeotropy
and liquid-liquid demixing, we allow interconversion of the two species,
turning the system into a single-component fluid with two states differing in
energy and entropy. Unveiling the phase diagram of the non-interconverting
binary mixture gives unprecedented insight on the phase behaviors accessible to
the interconverting fluid, such as a liquid-liquid transition with a critical
point, or a singularity-free scenario, exhibiting thermodynamic anomalies
without polyamorphism. The model provides a unified theoretical framework to
describe supercooled water and a variety of polyamorphic liquids with
water-like anomalies.Comment: 15 pages, 11 figure
Les flux d'hydrocarbures entre le Niger et le Nigéria : formes, estimation, déterminants et impact sur l'économie du Niger
Compressibility anomalies in stretched water and their interplay with density anomalies
Water keeps puzzling scientists because of its numerous properties which
behave oppositely to usual liquids: for instance, water expands upon cooling,
and liquid water is denser than ice. To explain this anomalous behaviour,
several theories have been proposed, with different predictions for the
properties of supercooled water (liquid at conditions where ice is more
stable). However, discriminating between those theories with experiments has
remained elusive because of spontaneous ice nucleation. Here we measure the
sound velocity in liquid water stretched to negative pressure, and derive an
experimental equation of state, which reveals compressibility anomalies. We
show by rigorous thermodynamic relations how these anomalies are intricately
linked with the density anomaly. Some features we observe are necessary
conditions for the validity of two theories of water.Comment: 17 pages, 3 figures, 24 reference
Politique d'ouverture commerciale et instabilité de la croissance économique : Le cas des pays du Moyen Orient et d’Afrique du Nord
This paper studies the impact of trade openness policy on economic growth volatility in Middle Eastern and North African countries. The observed trade openness is divided into natural openness and trade openness policy. Natural openness is determined by a country’s structural and geographical characteristics while trade openness policy depends on policy makers’ decisions. First, a specific indicator is elaborated for the trade openness policy. Then, the impact of trade openness policy is econometrically tested on 13 countries of the Middle East and North Africa over 1960-1999. The results show that countries with a more open trade policy are less volatile.Middle East and North Africa., economic growth volatility, Trade openness policy
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