Search results for "Condensed Matter::Disordered Systems and Neural Networks"
showing 10 items of 107 documents
Aging and the fluctuation dissipation ratio in a Lennard-Jones fluid
1999
We discuss numerically the relaxation dynamics of a simple structural glass which has been quenched below its (computer) glass transition temperature. We demonstrate that time correlation functions show strong aging effects and compute the fluctuation dissipation ratio of this non-equilibrium system.
Glass Transition and Glass Dynamics
2014
The transition from an undercooled liquid towards a glass (glass transition) is introduced and discussed in terms of mode-coupling theory. It is demonstrated that mode-coupling theory leads to a two-step relaxation scenario near the transition with time-critical exponents, which characterize the two relaxation steps (beta and alpha relaxation). The anomalous vibrational properties of a disordered solid (glass) is explained in terms of a model with spatially fluctuating harmonic force constants.
Disorder-induced single-mode transmission.
2017
Localized states trap waves propagating in a disordered potential and play a crucial role in Anderson localization, which is the absence of diffusion due to disorder. Some localized states are barely coupled with neighbours because of differences in wavelength or small spatial overlap, thus preventing energy leakage to the surroundings. This is the same degree of isolation found in the homogeneous core of a single-mode optical fibre. Here we show that localized states of a disordered optical fibre are single mode: the transmission channels possess a high degree of resilience to perturbation and invariance with respect to the launch conditions. Our experimental approach allows identification…
Defects in glasses
1995
Abstract The absence of long range order in the glass structure allows to define only point defects in these materials. They are: 1) intrinsic defects—atomic size local deviation from short range order; 2) impurity defects—isolated impurity atoms or ions in the glass network; 3) intrinsic impurity defects—complexes consisting of the impurity atoms chemically bonded to one of the intrinsic defect atoms. The latter defects are characteristic for the doped glasses. Presence of point defects in glasses introduces new spectroscopic properties of these solid materials. Defect generation, interaction and recombination reactions resulting from the external influence causes the glass spectroscopic p…
Spin Glasses on Thin Graphs
1995
In a recent paper we found strong evidence from simulations that the Isingantiferromagnet on ``thin'' random graphs - Feynman diagrams - displayed amean-field spin glass transition. The intrinsic interest of considering such random graphs is that they give mean field results without long range interactions or the drawbacks, arising from boundary problems, of the Bethe lattice. In this paper we reprise the saddle point calculations for the Ising and Potts ferromagnet, antiferromagnet and spin glass on Feynman diagrams. We use standard results from bifurcation theory that enable us to treat an arbitrary number of replicas and any quenched bond distribution. We note the agreement between the f…
Effect of the milling conditions on the degree of amorphization of selenium by milling in a planetary ball mill
2007
The effect of the milling parameters (rotation speed of the milling device and duration of milling) on the phase composition of the products of milling of fully crystalline selenium has been investigated. The milling was conducted using a planetary micromill and the phase composition of the milling products was determined by differential thermal analysis. It has been found that ball milling leads to the partial amorphization of the starting crystalline material. The content of amorphous phase in the milling products depends, in a rather complicated way, on the milling parameters. At the milling parameters adopted in the present study, the milling product was never fully amorphous. The compl…
Devitrification of the Kob-Andersen glass former: Competition with the locally favored structure
2018
Abstract Supercooled liquids are kinetically trapped materials in which the transition to a thermodynamically more stable state with long-range order is strongly suppressed. To assess the glass-forming abilities of a liquid empirical rules exist, but a comprehensive microscopic picture of devitrification is still missing. Here we study the crystallization of a popular model glass former, the binary Kob-Andersen mixture, in small systems. We perform trajectory sampling employing the population of the locally favored structure as order parameter. While for large population a dynamical phase transition has been reported, here we show that biasing towards a small population of locally favored s…
Critical phenomena without “hyper scaling”: How is the finite-size scaling analysis of Monte Carlo data affected?
2010
Abstract The finite size scaling analysis of Monte Carlo data is discussed for two models for which hyperscaling is violated: (i) the random field Ising model (using a model for a colloid-polymer mixture in a random matrix as a representative) (ii) The Ising bi-pyramid in computing surface fields.
Slow and fast methyl group rotations in fragile glass-formers studied by NMR
2000
Abstract The spin-lattice relaxation times of the selectively ring deuterated, fragile glass-formers propylene carbonate and toluene were compared with those measured for species which were specifically labeled at the methyl groups. It was found that the dynamics of the CD 3 group is strongly decoupled from that associated with the primary response of toluene, while for propylene carbonate the degree of decoupling is relatively weak. The experimental results could be described successfully using a model which takes into account the ring dynamics as well as those of the methyl group.
The Ultimate Fate of Supercooled Liquids
2010
In recent years it has become widely accepted that a dynamical length scale {\xi}_{\alpha} plays an important role in supercooled liquids near the glass transition. We examine the implications of the interplay between the growing {\xi}_{\alpha} and the size of the crystal nucleus, {\xi}_M, which shrinks on cooling. We argue that at low temperatures where {\xi}_{\alpha} > {\xi}_M a new crystallization mechanism emerges enabling rapid development of a large scale web of sparsely connected crystallinity. Though we predict this web percolates the system at too low a temperature to be easily seen in the laboratory, there are noticeable residual effects near the glass transition that can account …