163 research outputs found

### On the possible existence of crystallites in glass-forming liquids

We speculate that glass-forming liquids may contain fairly large and
well-defined crystallites. This is based on arguing that the slowly relaxing
"frozen-in" stresses characterizing ultraviscous liquids increase the barrier
for nucleation, thus allowing for larger unstable crystallites than otherwise
possible. The frozen-in stresses also deform the crystallites, making their
observation difficult; specifically it is argued that a situation where 1/N of
the molecules form N X N X N crystallites would be hard to detect by standard
X-ray or neutron scattering experiments

### Solidity of viscous liquids. III. Alpha relaxation

It is suggested that the $\omega^{-1/2}$ high-frequency decay of the alpha
loss in highly viscous liquids, which appears to be generic, is a manifestation
of a negative long-time tail as typically encountered in stochastic dynamics.
The proposed mechanism requires that the coherent diffusion constant is much
larger than estimated from the alpha relaxation time. This is justified by
reference to the solidity of viscous liquids in an argument which, by utilizing
the irrelevance of momentum conservation at high viscosity and introducing a
center of mass diffusion constant, implies that at high viscosity the coherent
diffusion constant is much larger than the incoherent diffusion constant

### NVU perspective on simple liquids' quasiuniversality

The last half century of research into the structure, dynamics, and
thermodynamics of simple liquids has revealed a number of approximate
universalities. This paper argues that simple liquids' reduced-coordinate
constant-potential-energy hypersurfaces constitute a quasiuniversal family of
compact Riemannian manifolds parameterized by a single number, from which
follows these liquids' quasiuniversalities

### Solidity of viscous liquids II: Anisotropic flow events

Recent findings on the displacements in the surroundings of isotropic flow
events in viscous liquids [Phys. Rev. E, to appear Feb. 1999] are generalized
to the anisotropic case. Also, it is shown that a flow event is characterized
by a dimensionless number reflecting the degree of anisotropy.Comment: Rev-tex file, no figures, submitted to Phys. Rev. E as a Brief Repor

### Elastic Models for the Non-Arrhenius Relaxation Time of Glass-Forming Liquids

We first review the phenomenology of viscous liquids and the standard models
used for explaining the non-Arrhenius average relaxation time. Then the focus
is turned to the so-called elastic models, arguing that these models are all
equivalent in the Einstein approximation (where the short-time elastic
properties are all determined by just one effective, temperature-dependent
force constant). We finally discuss the connection between the elastic models
and two well-established research fields of condensed-matter physics: point
defects in crystals and solid-state diffusion.Comment: Paper presented at the IWCS2005 (Nov. 2005, Sendai, Japan

### Isomorph theory beyond thermal equilibrium

This paper generalizes isomorph theory to systems that are not in thermal
equilibrium. The systems are assumed to be R-simple, i.e., have a potential
energy that as a function of all particle coordinates $\textbf{R}$ obeys the
hidden-scale-invariance condition $U(\textbf{R}_{\rm a})<U(\textbf{R}_{\rm
b})\Rightarrow U(\lambda\textbf{R}_{\rm a})<U(\lambda\textbf{R}_{\rm b})$.
"Systemic isomorphs" are introduced as lines of constant excess entropy in the
phase diagram defined by density and systemic temperature, which is the
temperature of the equilibrium state point with average potential energy equal
to $U(\textbf{R})$. The dynamics is invariant along a systemic isomorph if
there is a constant ratio between the systemic and the bath temperature. In
thermal equilibrium, the systemic temperature is equal to the bath temperature
and the original isomorph formalism is recovered. The new approach rationalizes
within a consistent framework previously published observations of isomorph
invariance in simulations involving nonlinear steady-state shear flows,
zero-temperature plastic flows, and glass-state isomorphs. The paper relates
briefly to granular media, physical aging, and active matter. Finally, we
discuss the possibility that the energy unit defining reduced quantities should
be based on the systemic rather than the bath temperature

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