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  2. Negative temperature - Wikipedia

    en.wikipedia.org/wiki/Negative_temperature

    The two-dimensional systems of vortices confined to a finite area can form thermal equilibrium states at negative temperature, [17] [18] and indeed negative temperature states were first predicted by Onsager in his analysis of classical point vortices. [19]

  3. Two-dimensional quantum turbulence - Wikipedia

    en.wikipedia.org/wiki/Two-dimensional_quantum...

    Point vortices confined to finite area were predicted by Onsager to exhibit states of negative temperature. [11] [12] This possibility of negative absolute temperature can be traced to the finite phase space of the point vortex system: in contrast to a massive particle moving on a plane, each point vortex only has two degrees of freedom.

  4. Heat equation - Wikipedia

    en.wikipedia.org/wiki/Heat_equation

    The temperature is initially distributed over a one-dimensional, one-unit-long interval (x = [0,1]) with insulated endpoints. The distribution approaches equilibrium over time. The behavior of temperature when the sides of a 1D rod are at fixed temperatures (in this case, 0.8 and 0 with initial Gaussian distribution).

  5. Bose–Einstein condensate - Wikipedia

    en.wikipedia.org/wiki/Bose–Einstein_condensate

    In condensed matter physics, a Bose–Einstein condensate (BEC) is a state of matter that is typically formed when a gas of bosons at very low densities is cooled to temperatures very close to absolute zero, i.e., 0 K (−273.15 °C; −459.67 °F). Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which ...

  6. Ising model - Wikipedia

    en.wikipedia.org/wiki/Ising_model

    The Ising model (or Lenz–Ising model), named after the physicists Ernst Ising and Wilhelm Lenz, is a mathematical model of ferromagnetism in statistical mechanics. The model consists of discrete variables that represent magnetic dipole moments of atomic "spins" that can be in one of two states (+1 or −1). The spins are arranged in a graph ...

  7. Zero-point energy - Wikipedia

    en.wikipedia.org/wiki/Zero-point_energy

    The wave function of the ground state of a particle in a one-dimensional well is a half-period sine wave which goes to zero at the two edges of the well. The energy of the particle is given by: h 2 n 2 8 m L 2 {\displaystyle {\frac {h^{2}n^{2}}{8mL^{2}}}} where h is the Planck constant , m is the mass of the particle, n is the energy state ( n ...

  8. Bose gas - Wikipedia

    en.wikipedia.org/wiki/Bose_gas

    The thermodynamics of an ideal Bose gas is best calculated using the grand canonical ensemble.The grand potential for a Bose gas is given by: = ⁡ = ⁡ (). where each term in the sum corresponds to a particular single-particle energy level ε i; g i is the number of states with energy ε i; z is the absolute activity (or "fugacity"), which may also be expressed in terms of the chemical ...

  9. Laplace's equation - Wikipedia

    en.wikipedia.org/wiki/Laplace's_equation

    In mathematics and physics, Laplace's equation is a second-order partial differential equation named after Pierre-Simon Laplace, who first studied its properties.This is often written as = or =, where = = is the Laplace operator, [note 1] is the divergence operator (also symbolized "div"), is the gradient operator (also symbolized "grad"), and (,,) is a twice-differentiable real-valued function.