Abstract. In atmospheric chemistry, a parameter called residence time is defined for each gas as T=M/F, where M represents the mass of the gas in the atmosphere and F is the total average influx or outflux, which in time averages are equal. In this brief communication, we extend this concept from matter to energy which is also a conservative quantity and estimate the average residence time of energy in the atmosphere, which amounts to about 58 d. A similar estimation for the residence time of energy in the Sun is of the order of 107 years, which agrees with the Kelvin–Helmholtz timescale.
The symmetry of self-duality (Savit 1980 Rev. Mod. Phys. 52 453) of some models of statistical mechanics and quantum field theory is discussed for finite spin blocks of the Ising chain in a transverse magnetic field. The existence of this symmetry in a specific type of these blocks, and not in others, is manifest by the degeneracy of their energy levels. This illustrates the fact that in quantum mechanics, more symmetry in the Hamiltonian induces more degeneracy in the energy spectrum.
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