Search results for "Transition point"

Theories of the Structural Glass Transition

2005

A neutron tomography study: Probing the spontaneous crystallization of randomly packed granular assemblies

2018

We study the spontaneous crystallization of an assembly of highly monodisperse steel spheres under shaking, as it evolves from localized icosahedral ordering towards a packing reaching crystalline ordering. Towards this end, real space neutron tomography measurements on the granular assembly are carried out, as it is systematically subjected to a variation of frequency and amplitude. As expected, we see a presence of localized icosahedral ordering in the disordered initial state (packing fraction around 0.62). As the frequency is increased for both the shaking amplitudes (0.2 and 0.6 mm) studied here, there is a rise in packing fraction, accompanied by an evolution to crystallinity. The ext…

Coexistence of periods in a bifurcation

2012

Abstract A particular type of order-to-chaos transition mediated by an infinite set of coexisting neutrally stable limit cycles of different periods is studied in the Varley–Gradwell–Hassell population model. We prove by an algebraic method that this kind of transition can only happen for a particular bifurcation parameter value. Previous results on the structure of the attractor at the transition point are here simplified and extended.

High-pressure polymorphs of gadolinium orthovanadate: X-ray diffraction, Raman spectroscopy, and ab initio calculations

2019

We present a study of the different high-pressure polymorphs of $\mathrm{GdV}{\mathrm{O}}_{4}$ and its stability. Powder x-ray diffraction and Raman experiments show a phase transition from a zircon- to a scheelite-type structure taking place at 6.8(4) GPa. Ab initio density functional theory calculations support this conclusion. The equations of state of these two phases are reported. In addition, we studied the pressure evolution of the Raman modes for the zircon and scheelite phases, showing good agreement between calculations and experiments. For the sake of completeness, we performed optical-absorption measurements up to 16 GPa, showing a band-gap collapse at the transition point. Beyo…

Crystallographic, electronic structure and magnetic properties of the GdTAl; T=Co, Ni and Cu ternary compounds

2000

Abstract Single phase GdCoAl, GdCuAl and single crystal GdNiAl samples of good quality were synthesized. The electrical resistivity, magnetization and AC susceptibility as a function of temperature revealed in all these compounds a ferromagnetic ordering at 100, 83 and 60 K, respectively. A magnetic transition, probably to a non-colinear structure was observed in GdNiAl at 31 K as well as the presence of the third magnetic transition at 14 K, while in the GdCuAl compound an evidence of similar transition was found at 23 K. In GdNiAl a transition between two different crystallographic phases of ZrNiAl-type was observed at 220 K. The transition was accompanied by rapid jumps of crystal lattic…

Cavitation in 3He-4he Liquid Mixtures

2002

Phase transitions under equilibrium conditions are experimentally well determined and take place in the coexistence regime. However, phase transitions do not always occur under equilibrium conditions. As the new phase forms, the free energy of the system is lowered, but the original phase can be held in a metastable state close to the equilibrium transition point. Although they are internally stable, in each case there exists another configuration that has a lower thermodynamical potential. The metastable state is separated from the stable state by a thermodynamic barrier. Due to statistical fluctuations in density or concentration, this barrier can be overcome as the result of the formatio…

Monte-Carlo Study of Pure-Phase Cumulants of 2D q-State Potts Models

1997

We performed Monte Carlo simulations of the two-dimensional q-state Potts model with q=10, 15, and 20 to study the energy and magnetization cumulants in the ordered and disordered phase at the first-order transition point $\beta_t$. By using very large systems of size 300 x 300, 120 x 120, and 80 x 80 for q=10, 15, and 20, respectively, our numerical estimates provide practically (up to unavoidable, but very small statistical errors) exact results which can serve as a useful test of recent resummed large-q expansions for the energy cumulants by Bhattacharya `et al.' [J. Phys. I (France) 7 (1997) 81]. Up to the third order cumulant and down to q=10 we obtain very good agreement, and also the…

Anomalous critical slowdown at a first order phase transition in single polymer chains

2017

Using Brownian Dynamics, we study the dynamical behavior of a polymer grafted onto an adhesive surface close to the mechanically induced adsorption-stretching transition. Even though the transition is first order, (in the infinite chain length limit, the stretching degree of the chain jumps discontinuously), the characteristic relaxation time is found to grow according to a power law as the transition point is approached. We present a dynamic effective interface model which reproduces these observations and provides an excellent quantitaive description of the simulations data. The generic nature of the theoretical model suggests that the unconventional mixing of features that are characteri…

Finite-size scaling for a first-order transition where a continuous symmetry is broken: The spin-flop transition in the three-dimensional XXZ Heisenb…

2019

Finite-size scaling for a first-order phase transition where a continuous symmetry is broken is developed using an approximation of Gaussian probability distributions with a phenomenological ``degeneracy'' factor included. Predictions are compared with data from Monte Carlo simulations of the three-dimensional, $XXZ$ Heisenberg antiferromagnet in a field in order to study the finite-size behavior on a $L\ifmmode\times\else\texttimes\fi{}L\ifmmode\times\else\texttimes\fi{}L$ simple cubic lattice for the first-order ``spin-flop'' transition between the Ising-like antiferromagnetic state and the canted, $XY$-like state. Our theory predicts that for large linear dimension $L$ the field dependen…

Study of the confined Ising magnet with long-range competing boundary fields

2005

We present extensive Monte Carlo simulations of the Ising film confined in an L × M geometry () in the presence of long-range competing magnetic fields h(n) = h1/n3(n = 1,2,...,L) which are applied at opposite walls along the M-direction. Due to the fields, an interface between domains of different orientations that runs parallel to the walls forms and can be located close to one of the two surfaces or fluctuate in the centre of the film (localization–delocalization transition). This transition is the precursor of the wetting phase transition that occurs in the limit of infinite film thickness () at the critical curve Tw(h1). For T<Tw(h1) (T≥Tw(h1)) such an interface is bound to (unbound fr…