摘要:

The glass transition of a hard sphere system is investigated within the framework of the density functional theory (DFT). Molecular dynamics (MD) simulations are performed to study dynamical behavior of the system on the one hand and to provide the data to produce the density field for the DFT on the other hand. Energy landscape analysis based on the DFT shows that there appears a metastable (local) free energy minimum representing an amorphous state as the density is increased. This state turns out to become stable, compared with the uniform liquid, at some density, around which we also observe sharp slowing down in MD simulations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764272

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A framework to calculate the specific heat near the glass transition point is presented within the energy landscape picture. This framework gives the characteristics of the glass transition that the glass transiton a transition from annealed to quenched system and the glass transition point is decreased with increasing observation time. We apply this framework to classic model and one constructed with Debye oscillators, and they shows the characteristics of the glass transition. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764273

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

NearTgthe dynamics in glass‐formers vary by orders of magnitude from one region to another. The existence of such spatially heterogenous dynamics is now well established, both through simulation and experiment. However, it remains unclear to what extent this dynamic heterogeneity is a reflection of some underlying structural properties of the glass‐former. Here we provide a general theoretical tool for establishing the connection between a particle configuration and the spatial heterogeneity of the dynamics that originates from that configuration, and apply this to a model soft‐disk glass. We find that the dynamic heterogeneity in a trajectory is not completely determined by the initial configuration and establish a rigorous causal connection between a given configuration and the propensity of particles to move. Finally, we discuss a number of generalisations of this tool. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764274

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

I have two configurations constracted by the model short polymers. That polymers have the internal structure by means of it’s potentials and the systems also have the internal structures. One system has some small crystalline domains and the long time relaxation. The another system has no long time relaxation. I think that the long displacement of polymers in short time distinguishes the two system’s dynamics. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764275

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In this study, we conducted anab initiocalculation of Al which contains self‐interstitials with concentration up to 6&percent; and an empirical molecular dynamics simulation of an ionic crystal Ca1−xLaxF2+xwith the concentration of charge balanced interstitials up to 50&percent;. For Al, we find that the shear modulus decreases with the concentration of self‐interstitials and becomes unstable when interstitialcy concentration reaches about 6&percent;, a trend agrees with that predicted by an interstitialcy model. For the ionic crystal, the shear modulus changes very little with the interstitialcy concentration and shows a dip as the concentration is about 13&percent;. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764276

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We have performed molecular dynamics simulations for a model two‐dimensional soft‐core mixture in a supercooled state. The mixture exhibits a slow structural relaxation in a quiescent state, however, the relaxation is much enhanced in sheared states. There observed surprisingly small anisotropy both in the coherent and incoherent density correlation functions even under extremely strong shear which is 103times faster than the structural relaxation rate. The present simulation results agree well with predictions of the recently developed mode‐coupling theory in shear. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764277

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The atomic dynamics of hyperquenched glasses proceeds in basins in a different region of the 3N‐dimensional energy surface than are the basins of slow cooled glasses. As has been shown by computer simulations and experiments very recently, the atomic dynamics can be different in these basins in different regions of the energy surface. Using neutron inelastic scattering this question is here investigated on the basis of the total dynamic structure factor of a bulk metallic glass and the same glass after melt spinning, leading to a difference in quenchrate of approximately three orders of magnitude. The investigation of the wavelength dependence of the atomic dynamics demonstrates that the additional modes found in the dynamic structure factor of the hyperquenched glass show no momentum transfer dependence and are therefore most likely due to non‐ propagating modes. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764278

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

An artificial lipid bilayer in planar form, well known as bilayer lipid membrane (BLM), spontaneously forms from a lipid droplet (diphytanoyl phosphatidylcholine in n‐decane and chloroform in this work) in an aperture of a thin partition in aqueous solution. The thinning dynamics of the lipid droplet or membrane has been studied by simultaneous capacitance and image recording. The simultaneous measurements have revealed the two‐step thinning of the lipid membrane from its specific capacitance value: first, the initial droplet thins to yield a membrane of 60 nm thickness (0.03 &mgr;F/cm2), and second, within this thin lipid membrane, a lipid bilayer of 4 nm thickness (0.45 &mgr;F/cm2) suddenly emerges and grows with keeping a bilayer structure. The revealed dynamics provides a quantitative support for a “zipper” mechanism proposed by Tien and Dawidowicz; in the mechanism, the first thinning results in a sandwich consisting of the organic solvent between two adsorbed lipid monolayers whose distance is the order of 100 nm, and then a chance contact of both monolayers initiates the formation and growth of a lipid bilayer in a zipper‐like manner. However, because of the existence of the two solvent‐water interfaces containing surface‐active molecules, phospholipids, this work claims that the zipper mechanism should be modified in view of the Marangoni effect. The present formation and growth of a lipid bilayer can be explained by the classic nucleation theory of two‐dimensional crystallization. BLM systems with the simultaneous measurements can be considered as a useful environment for the study of soft‐matter chemical physics. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764279

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Slow dynamics of energy transfer between different phonon modes under the resonance conditions is considered. It may result in new effects in the inelastic and quasielastic neutron scattering spectra. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764280

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Dynamic behavior and its stability of Boltzmann‐machine learning algorithm for Bayesian gray scale image restoration are investigated. We derive the differential equations by which we attempt to maximize the marginal likelihood function with respect to hyper‐parameters. Average‐case performance and linear stability of the algorithm are evaluated exactly at the mean‐field level. We conclude that the solution of the Boltzmann‐machine learning equation isasymptotically stableas long as the solution is identical to the correct value of the hyper‐parameters. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1764281

出版商:AIP    

年代:1904

数据来源: AIP