43 research outputs found
The phonon theory of liquid thermodynamics
Heat capacity of matter is considered to be its most important property
because it holds information about system's degrees of freedom as well as the
regime in which the system operates, classical or quantum. Heat capacity is
well understood in gases and solids but not in the third state of matter,
liquids, and is not discussed in physics textbooks as a result. The perceived
difficulty is that interactions in a liquid are both strong and
system-specific, implying that the energy strongly depends on the liquid type
and that, therefore, liquid energy can not be calculated in general form. Here,
we develop a phonon theory of liquids where this problem is avoided. The theory
covers both classical and quantum regimes. We demonstrate good agreement of
calculated and experimental heat capacity of 21 liquids, including noble,
metallic, molecular and hydrogen-bonded network liquids in a wide range of
temperature and pressure.Comment: 7 pages, 4 figure
A unified hyperbolic formulation for viscous fluids and elastoplastic solids
We discuss a unified flow theory which in a single system of hyperbolic
partial differential equations (PDEs) can describe the two main branches of
continuum mechanics, fluid dynamics, and solid dynamics. The fundamental
difference from the classical continuum models, such as the Navier-Stokes for
example, is that the finite length scale of the continuum particles is not
ignored but kept in the model in order to semi-explicitly describe the essence
of any flows, that is the process of continuum particles rearrangements. To
allow the continuum particle rearrangements, we admit the deformability of
particle which is described by the distortion field. The ability of media to
flow is characterized by the strain dissipation time which is a characteristic
time necessary for a continuum particle to rearrange with one of its
neighboring particles. It is shown that the continuum particle length scale is
intimately connected with the dissipation time. The governing equations are
represented by a system of first order hyperbolic PDEs with source terms
modeling the dissipation due to particle rearrangements. Numerical examples
justifying the reliability of the proposed approach are demonstrated.Comment: 6 figure
Liquid heat capacity in the approach from the solid state: anharmonic theory
Calculating liquid energy and heat capacity in general form is an open
problem in condensed matter physics. We develop a recent approach to liquids
from the solid state by accounting for the contribution of anharmonicity and
thermal expansion to liquid energy and heat capacity. We subsequently compare
theoretical predictions to the experiments results of 5 commonly discussed
liquids, and find a good agreement with no free fitting parameters. We discuss
and compare the proposed theory to previous approaches.Comment: 8 pages, 6 figure
Graphene-based modulation-doped superlattice structures
The electronic transport properties of graphene-based superlattice structures
are investigated. A graphene-based modulation-doped superlattice structure
geometry is proposed and consist of periodically arranged alternate layers:
InAs/graphene/GaAs/graphene/GaSb. Undoped graphene/GaAs/graphene structure
displays relatively high conductance and enhanced mobilities at elevated
temperatures unlike modulation-doped superlattice structure more steady and
less sensitive to temperature and robust electrical tunable control on the
screening length scale. Thermionic current density exhibits enhanced behaviour
due to presence of metallic (graphene) mono-layers in superlattice structure.
The proposed superlattice structure might become of great use for new types of
wide-band energy gap quantum devices.Comment: 5 figure