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What is Liquid? [in two dimensions]

Travis K. P., Hoover Wm. G., Hoover C. G., Hass A. B.

Computational Methods in Science and Technology

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2021

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Vol. 27, No. 1

5--23

EN

We consider the practicalities of defining, simulating, and characterizing “Liquids” from a pedagogical standpoint based on atomistic computer simulations. For simplicity and clarity we study two-dimensional systems throughout. In addition to the infinite-ranged Lennard-Jones 12/6 potential we consider two shorter-ranged families of pair potentials. At zero pressure one of them includes just nearest neighbors. The other longer-ranged family includes twelve additional neighbors. We find that these further neighbors can help stabilize the liquid phase. What about liquids? To implement Wikipedia’s definition of liquids as conforming to their container we begin by formulating and imposing smooth-container boundary conditions. To encourage conformation further we add a vertical gravitational field. Gravity helps stabilize the relatively vague liquid-gas interface. Gravity reduces the messiness associated with the curiously-named “spinodal” (tensile) portion of the phase diagram. Our simulations are mainly isothermal. We control the kinetic temperature with Nosé-Hoover thermostating, extracting or injecting heat so as to impose a mean kinetic temperature over time. Our simulations stabilizing density gradients and the temperature provide critical-point estimates fully consistent with previous efforts from free energy and Gibbs ensemble simulations. This agreement validates our approach.

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Numerical analysis of the onset of condensation in the IMP PAN nozzle for cases without the appearance of shock waves in the steam ﬂow

Kornet S., Banaszkiewicz M., Badur J.

Transactions of the Institute of Fluid-Flow Machinery

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2017

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nr 138

107--123

EN

The present paper focuses on the prediction of the spontaneous condensation phenomena in the wet steam ﬂow depending on the inlet temperature. The basic tests including comparison with experimental data have been performed using the planar symmetrical nozzle with the de Laval geometry (IMP PAN nozzle). It was assumed in calculations that steam is pure and does not contain heterogeneous sources of condensation. Numerical analysis was performed for boundary conditions which correspond to the ﬂow regime without the shock wave. The present work includes simulations results of the onset of condensation and shows whether initiation of phase transition is located in the region between a spinodal and a binodal. Numerical results along the nozzle axis are presented on thermodynamic diagrams for all considered ﬂow conditions.

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Metamaterials with negative compressibility – a novel concept with a long history

Imre A R

Materials Science Poland

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2014

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Vol. 32, No. 2

126--129

EN

Metamaterials with negative compressibility are a very promising group of novel materials with a wide variety of potential application. A recent model proposed construction of the structures with three-dimensional negative compressibility by utilizing successive destabilization of stable or metastable states and inducing phase transitions mimicking negative compressibility. Here, we would like to show that similar concept is used by the nature and a nice example of this kind of metamaterial can be seen even in a glass of water.