Narrow Results

We have performed a new analysis on the dynamics and structure to investigate the aluminum-silicate melt under pressure. It is shown that the low-pressure configuration of the melt exhibits dynamic heterogeneity. The mobile and immobile atoms tend to reside in regions which have extremely high or low density. We reveal two moving types: the simply hopping or collective moving via supermolecule. The latter type is responsible for the positive pressure dependence on diffusivity. The structure is analyzed via SC-particle and SC-cluster. Our simulation reveals the structural heterogeneity in local environment and chemical composition. The densification of the melt is accompanied with the decreasing of the radius of core of SC-particle and the number of large SC-particles. We found that the liquid comprises two types of SC-particles. The SC-clusters of second type form large space regions which represent the diffusion pathway for aluminum.

This study reported a simulation of structural transition and correlation between structural and dynamical heterogeneity (DH) for liquid Al₂O₃. Structural characteristics of liquid Al₂O₃ were clarified through the pair radial distribution functions, the distribution of ${\text{AlO}}_x$ and ${\text{OAl}}_y$ ($x=3$, 4, 5, 6; $y=1$, 2, 3) basic structural units, angle and bond length distribution and 3D visualization. Simulation results revealed that network structure of liquid Al₂O₃ is built mainly by AlO₃, AlO₄, AlO₅ and AlO₆ units that are linked to each other through common oxygen atoms. We found the existence of separate AlO₄-, AlO₅- and AlO₆-phases where the mobility of atoms can be determined. The atoms in AlO₄-phase are more mobile than the ones in AlO₅- and AlO₆-phases. The existence of separate phases is evidence of DH in liquid Al₂O₃. Moreover, the self-diffusion of Al and O atoms was also discussed via characteristics of separate AlO₄-, AlO₅- and AlO₆-phases.

By the potential method, it was determined that regardless of the nature of the liquid, the surface tension coefficient is determined by $\sigma =2q\frac{(T_K-T)}{(T_K+T)}$. In this expression, $q$ is the specific heat of the surface formation, $T_k$ is the critical temperature. According to our approach, the specific heat of the surface formation (SHS) also depends on temperature: $q=q_m+\alpha \cdot (T-T_m)$ ($q_m$ — the specific heat of the surface formation at the mealting temperature, $\alpha$ — thermal coefficent of SHS). In this research work, the temperature dependence of the surface tension coefficient was calculated for seven dissimilar liquids. It was revealed that the calculated values of $\sigma$ are in satisfactory agreement with the available experimental values.

The nature of excitations in liquids has been a subject of debate for a long time. In liquids, phonons are extremely short-lived and marginalized. Instead, recent research results indicate that local topological or configurational excitations (anankeons) are the elementary excitations in high temperature metallic liquids. Local topological excitations are those which locally alter the atomic connectivity network by cutting or forming atomic bonds, and are directly tied to the atomistic origin of viscosity in the liquid. The local potential energy landscape (PEL) of anankeons represents the probability weighted projection of the global PEL to a single atom. The original PEL is an insightful concept, but is highly multi-dimensional and difficult to characterize or even to visualize. A description in terms of the local PEL for anankeons appears to offer a simpler and more effective approach toward this complex problem. At the base of these advances, is the recognition that atomic discreteness and the topology of atomic connectivity are the most crucial features of the structure in liquids, which current nonlinear continuum theories cannot fully capture. These discoveries could open the way to the explanation of various complex phenomena in liquids, such as atomic transport, fragility, and the glass transition, in terms of these excitations.

We perform a simulation of the structural phase-transition pathway under compression and dynamic properties in liquid germania (GeO₂). The structure of liquid GeO₂ is clarified through the pair radial distribution function (PRDF), distribution of GeO${}_x$$(x=4,5,6)$ units, bond angle and length distribution, and three-dimensional (3D) visualization. The result shows that the structure of liquid GeO₂ is built by GeO₄, GeO₅ and GeO${}_6$units, which are linked to each other via common oxygen atoms. The GeO${}_x$ units lead to form into the separate GeO₄-, GeO₅- and GeO₆-phases. The existence of separate phases is evidence of dynamical heterogeneity (DH) in liquid GeO₂. The atoms in GeO₅-phase are more mobile compared to other ones. The variation of the self-diffusions of Ge and O atoms under pressure is examined via the characteristics of separate GeO₄-, GeO₅- and GeO₆-phases. We found that under compression, there is diffusion anomaly in liquid GeO₂. This is suggested to be related to the very high mobility of Ge and O atoms in the GeO₅-phase compared to GeO₄- and GeO₆-phase.

The instability of longitudinally variable speed viscoelastic plates in contact with ideal liquid is studied for the first time. The effect of free surface waves is taken into account in the present study. The viscoelasticity is considered by using the Kelvin–Voigt viscoelastic constitutive relations. The classical theory of thin plate is utilized to derive the governing equation of variable speed plates. The fluid is assumed to be incompressible, inviscid and irrotational. Additionally, the velocity potential and Bernoulli’s equation are utilized to describe the fluid pressure acting on the vibrating plates. The fluid effect on the vibrational plates is described as the added mass of the plates which can be formulated by the kinematic boundary conditions at the structure–fluid interfaces. Parametric instability is analyzed by directly applying the method of multiple scales to the governing partial-differential equations and boundary conditions. The unstable boundaries are derived from the solvability conditions and the Routh–Hurwitz criterion for principal parametric, sum-type and difference-type combination resonances. Based on the numerical simulation, the effects of some key parameters on the unstable boundaries are illustrated in the excitation frequency and excitation amplitude plane in detail.

Correlated Density Matrix (CDM) theory permits formal analyses of microscopic properties of strongly correlated quantum fluids and liquids at nonzero temperatures. Equilibrium properties, thermodynamic potentials, correlation and structure functions can be studied formally as well as numerically within the CDM algorithm. Here we provide the essential building blocks for studying the radial distribution function and the single-particle momentum distribution of the ingredients of the quantum systems. We focus on the statistical properties of correlated fluids and introduce the concept of renormalized bosons and fermions. These entities carry the main statistical features of the correlated systems such as liquid ⁴He through their specific dependence on temperature, particle number density, and wavenumber encapsulated in their effective masses. The formalism is developed for systems of bosons and of fermions. Numerical calculations for fluid ⁴He in the normal phase demonstrate the power of the renormalization concept. The formalism is further extended to analyze the Bose-Einstein condensed phases and gives a microscopic understanding of Tisza's two-fluid model for the normal and superfluid density components.