Search results for "GLASS"
showing 10 items of 1153 documents
Microscopic theory for the glass transition in a system without static correlations
2002
We study the orientational dynamics of infinitely thin hard rods of length L, with the centers-of-mass fixed on a simple cubic lattice with lattice constant a.We approximate the influence of the surrounding rods onto dynamics of a pair of rods by introducing an effective rotational diffusion constant D(l),l=L/a. We get D(l) ~ [1-v(l)], where v(l) is given through an integral of a time-dependent torque-torque correlator of an isolated pair of rods. A glass transition occurs at l_c, if v(l_c)=1. We present a variational and a numerically exact evaluation of v(l).Close to l_c the diffusion constant decreases as D(l) ~ (l_c-l)^\gamma, with \gamma=1. Our approach predicts a glass transition in t…
Ideal glass transitions for hard ellipsoids
2000
For hard ellipsoids of revolution we calculate the phase diagram for the idealized glass transition. Our equations cover the glass physics in the full phase space, for all packing fractions and all aspect ratios X$_0$. With increasing aspect ratio we find the idealized glass transition to become primarily be driven by orientational degrees of freedom. For needle or plate like systems the transition is strongly influenced by a precursor of a nematic instability. We obtain three types of glass transition lines. The first one ($\phi_c^{(B)}$) corresponds to the conventional glass transition for spherical particles which is driven by the cage effect. At the second one ($\phi_c^{(B')}$) which oc…
Strain pattern in supercooled liquids
2016
Investigations of strain correlations at the glass transition reveal unexpected phenomena. The shear strain fluctuations show an Eshelby-strain pattern ($\,\sim \cos{(4\theta)}/r^2\,$), characteristic for elastic response, even in liquids at long times [1]. We address this using a mode-coupling theory for the strain fluctuations in supercooled liquids and data from both, video microscopy of a two-dimensional colloidal glass former and simulations of Brownian hard disks. We show that long-ranged and long-lived strain-signatures follow a scaling law valid close to the glass transition. For large enough viscosities, the Eshelby-strain pattern is visible even on time scales longer than the stru…
Nonlinear active micro-rheology in a glass-forming soft-sphere mixture.
2013
We present extensive molecular dynamics computer simulations of a glass-forming Yukawa mixture, investigating the nonlinear response of a single particle that is pulled through the system by a constant force. Structural changes around the pulled particle are analyzed by pair correlation functions, measured in the deeply supercooled state of the system. A regime of intermediate force strengths is found where the structural changes around the pulled particle are small, although its steady-state velocity shows a strong nonlinear response. This nonlinear response regime is characterized by a force-temperature superposition principle of a Peclet number and anisotropic diffusive behavior. In the …
Fluctuating hydrodynamics and diffusion in amorphous solids
1994
The fluctuating hydrodynamic description for an isotropic fluid is extended to include the displacement field u, reflecting the freezing of the local structures in an amorphous solid. The fluctuating nonlinear equations for the set of hydrodynamic variables including u has been obtained. The role of u is manifested through its longitudinal part, i.e., \ensuremath{\nabla}\ensuremath{\cdot}u, in terms of which we define the variable c(x,t). It refers to the diffusion of the free volume or vacancies, signifying configurational rearrangements in the amorphous solid. The analysis here shows that one recovers the earlier result obtained by Das and Mazenko [Phys. Rev. A 34, 2265 (1986)] for mode c…
Transverse nonlinear optics in heavy-metal-oxide glass
2008
6 pags. ; 9 figs.
What can be learned from the rotational motion of single molecules in a polymer melt near the glass transition?
2007
We develop a framework for the interpretation of single-molecule (SM) spectroscopy experiments of probe dynamics in a complex glass-forming system. Specifically, from molecular dynamics simulations of a single probe molecule in a coarse-grained model of a polymer melt, we show the emergence of sudden large angular reorientations (SLARs) of the SM as the mode coupling critical temperature is closely approached. The large angular jumps are intimately related to meta-basin transitions in the potential energy landscape of the investigated system and cause the appearance of stretched exponential relaxations of various rotational observables, reported in the SM literature as dynamic heterogeneity…
Glassy dynamics in confinement: planar and bulk limits of the mode-coupling theory.
2014
We demonstrate how the matrix-valued mode-coupling theory of the glass transition and glassy dynamics in planar confinement converges to the corresponding theory for two-dimensional (2D) planar and the three-dimensional bulk liquid, provided the wall potential satisfies certain conditions. Since the mode-coupling theory relies on the static properties as input, the emergence of a homogeneous limit for the matrix-valued intermediate scattering functions is directly connected to the convergence of the corresponding static quantities to their conventional counterparts. We show that the 2D limit is more subtle than the bulk limit, in particular, the in-planar dynamics decouples from the motion …
Implementing consistent NLO factorization in single inclusive forward hadron production
2017
Single inclusive forward hadron production in high-energy hadron collisions can provide an important test of the Color Glass Condensate picture at small $x$. Recent studies of this process at next-to-leading order have led to problematic results, with cross sections becoming negative at large transverse momenta. We study a new formulation of this quantity proposed recently by Iancu et al. We show that it leads to physical results up to large transverse momenta at fixed coupling. Taking into account running coupling effects in a way that is consistent with existing DIS calculations still poses a challenge.
Glass physics: still not transparent
1999
Glass is a commonplace word. One immediately thinks of windows or bottles and of properties like brittleness or transparency. However, for a glass blower another feature is more important: glass does not melt abruptly, as a crystal does, but gradually over a range of temperatures. This means that he or she can alter the temperature at which glass solidifies or becomes a liquid by changing the rate at which it is cooled or heated. This is in stark contrast to the behaviour observed when the crystalline form of a material is heated: it will always melt at the same temperature.