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The scale-free ideal gas (SFIG) is a physical model assuming a collection of non-interacting elements with an stochastic proportional growth. It is the scale-invariant version of an ideal gas. Some cases of city-population, electoral results and cites to scientific journals can be approximately considered scale-free ideal gases. In a one-dimensional discrete model with size-parameter ''k'', where ''k''1 and ''k''''M'' are the minimum and maximum allowed sizes respectively, and ''v'' = ''dk''/''dt'' is the growth, the bulk probability density function ''F''(''k'', ''v'') of a scale-free ideal gas follows : where ''N'' is the total number of elements, Ω = ln ''k''1/''k''''M'' is the logaritmic "volume" of the system, is the mean relative growth and is the standard deviation of the relative growth. The entropy equation of state is : where is a constant that accounts for dimensionality and is the elementary volume in phase space, with the elementary time and ''M'' the total number of allowed discrete sizes. This expression has the same form as the one-dimensional ideal gas, changing the thermodynamical variables (''N'', ''V'', ''T'') by (''N'', Ω,''σ''''w''). Zipf's law may emerge in the external limits of the density since it is a special regime of scale-free ideal gases. == References == 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Scale-free ideal gas」の詳細全文を読む スポンサード リンク
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