3/5/2023 0 Comments Earman and norton 1998![]() Other researchers have implemented forms of Maxwell's demon in experiments, though they all differ from the thought experiment to some extent and none have been shown to violate the second law. Most scientists argue, on theoretical grounds, that no practical device can violate the second law in this way. ![]() It stimulated work on the relationship between thermodynamics and information theory. The concept of Maxwell's demon has provoked substantial debate in the philosophy of science and theoretical physics, which continues to the present day. This would decrease the total entropy of the two gases, without applying any work, thereby violating the second law of thermodynamics. Because the kinetic temperature of a gas depends on the velocities of its constituent molecules, the demon's actions cause one chamber to warm up and the other to cool down. ![]() As individual gas molecules (or atoms) approach the door, the demon quickly opens and closes the door to allow only fast-moving molecules to pass through in one direction, and only slow-moving molecules to pass through in the other. In the thought experiment, a demon controls a small massless door between two chambers of gas. In his first letter Maxwell called the demon a "finite being", while the Daemon name was first used by Lord Kelvin. It was proposed by the physicist James Clerk Maxwell in 1867. Maxwell's demon is a thought experiment that would hypothetically violate the second law of thermodynamics. The article concludes with a brief review of our present theoretical understanding of turbulent structures, and with a list of open problems and future perspectives.Schematic figure of Maxwell's demon thought experiment While the waves require a wall to determine their length scale, the bursts are essentially independent from it. ![]() Conversely, bursts exist at all scales, are characteristic of the logarithmic layer, and interact almost linearly with the shear. Although they are shear-driven, these waves have enough internal structure to maintain a uniform advection velocity. The former are found in the viscous layer near the wall, and as very large structures spanning the entire boundary layer. In wall-bounded turbulence, they can be classified into coherent dispersive waves and transient bursts. In particular, it is shown that coherent structures larger than the Corrsin scale are a natural consequence of the shear. Intense eddies are examined next, including their temporal evolution, and shown to satisfy many of the properties required for coherence. After briefly reviewing the underlying low-order statistics of flows at moderate Reynolds numbers, the article examines what two-point statistics imply for the decomposition of the flow into individual eddies. The guiding principle is that randomness is not a property, but a methodological choice of what to ignore in the flow, and that a complete understanding of turbulence, including the possibility of control, requires that it be kept to a minimum. This article discusses the description of wall-bounded turbulence as a deterministic high-dimensional dynamical system of interacting coherent structures, defined as eddies with enough internal dynamics to behave relatively autonomously from any remaining incoherent part of the flow.
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