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HELIUM II [4 records]

Record 1 2013-01-15

English

Subject field(s)
  • Astronomy
OBS

"Population II stars"... are relatively aged objects of low metal content, i. e. they are mainly hydrogen and perhaps helium, with little or no gas and dust; orbits have a high eccentricity(often outside of the galactic plane).... Examples include the globular star clusters of our own galaxy. These stars are on the average one hundred times less luminous than population I stars. Masses do not exceed 1 1/2 times that of our sun. Ages approach 1010 years.

French

Domaine(s)
  • Astronomie
CONT

Il semble donc exister deux types de populations stellaires : celle des parages solaires, dans la Voie Lactée, que Baade appelle la «population I» et celle des amas globulaires que Baade appelle la «population II» [...]

Spanish

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Record 2 2003-02-11

English

Subject field(s)
  • Chemistry
  • Cryogenics
  • Petroleum Cracking
DEF

Liquid helium existing as a superfluid below the transition point of approximately 2.2°K at 1 atmosphere and having extremely low viscosity and extremely high thermal conductivity.

CONT

Superfluid Helium What Is It? As the temperature of helium gas is lowered to approximately 5. 2°K, a phase transition to ordinary liquid helium(He I) takes place. The latter is unremarkable and its behavior is identical to any other liquid. As temperature is lowered further(at moderate pressures) helium does not solidify. Rather, it undergoes a phase change to a second liquid phase He II at temperature of about 2. 17°K.... the He II phase persists all the way to absolute zero.... The He II phase is referred to as superfluid helium because of its remarkable properties, including the ability to flow through microscopic passages [holes as small as 10-7 centimeters in diameter] with no apparent friction; the quantization of vortices; and the ability to support four wave modes : first sound which is analogous to sound in ordinary gases and liquids, second sound which carries temperature and entropy perturbations with virtually no pressure variations, third sound which are waves on thin films, and fourth sound which are acoustic-like waves in the "superfluid" component of He II.

CONT

Superfluid Helium(He II, Superfluidity). Superfluid or Helium II technology has been developed quite successfully in the past decades in both aerospace and magnet cooling systems.... Other strange properties of superfluid include the Rollin film, mechanocaloric effect and fountain effect.

Key term(s)
  • super-fluid helium
  • super fluid helium

French

Domaine(s)
  • Chimie
  • Cryogénie
  • Craquage (Pétrole)
CONT

On désigne par Hélium II, l'hélium en dessous de Tlambda. L'hélium superfluide a la propriété bien connue d'avoir une viscosité nulle (il peut traverser de très fins capillaires sans frottement; il a la capacité de pouvoir remonter le long des parois, etc.).

CONT

En refroidissant sous la pression atmosphérique de l'hélium ordinaire [...], on constate qu'il se liquéfie à 4,2 K. Le liquide ainsi produit (hélium I) n'a rien de particulier, sa viscosité est faible, mais il se comporte comme tous les liquides usuels. En refroidissant ce liquide au-dessous de 2,17 K, on voit apparaître une phase liquide aux propriétés exceptionnelles (hélium II) souvent désignée sous le nom d'hélium superfluide en raison de sa viscosité pratiquement nulle. L'hélium II est également caractérisé par une résistivité thermique pratiquement nulle, on dit que c'est un supraconducteur thermique.

Spanish

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Record 3 2000-06-14

English

Subject field(s)
  • Petroleum Cracking
DEF

Designation for helium II existing below 2. 17 K and exhibiting zero viscosity.

French

Domaine(s)
  • Craquage (Pétrole)
CONT

Hélium superfluide.

Spanish

Save record 3

Record 4 1980-01-02

English

Subject field(s)
  • Conductivity and Superconductivity (Electricity)
DEF

the unusual properties of liquid helium when it is cooled below 2. 18 K °(...). The term was coined [to show] that in this state of helium, called helium II(He II), there is an apparent enormous rise in heat conductivity, rapid flow through capillaries or over the rim of its containment vessel as a thin film, and that a number of other unusual properties also appear(...)

French

Domaine(s)
  • Conductivité et supraconductivité (Électricité)
DEF

Propriété présentée par la phase liquide 4He II, ou état II de l'hélium-4, à basse température, qui traduit la possibilité pour ce liquide de s'écouler dans des capillaires très fins sans viscosité aucune.

Spanish

Save record 4

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