1,720,980 research outputs found
Extended law of corresponding states in short-range square wells: a potential energy lands study
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Arrested phase separation in a short-ranged attractive colloidal system: A numerical study
No full textWe numerically investigate the competition between phase separation and dynamical arrest in a colloidal system interacting via a short-ranged attractive potential. Equilibrium fluid configurations are quenched at two different temperatures below the critical temperature and followed during their time evolution. At the lowest studied T, the phase-separation process is interrupted by the formation of an attractive glass in the dense phase. At the higher T, no arrest is observed and the phase-separation process proceeds endlessly in the simulated time window. The final structure of the glass retains memory of the interrupted phase-separation process in the form of a frozen spinodal decomposition peak, whose location and amplitude is controlled by the average packing fraction. We also discuss the time evolution of the nonergodicity parameter, providing evidence of a progressively decreasing localization length on increasing the packing fraction. Finally, we confirm that the reported results are independent of the microscopic dynamics
Scaling of dynamics with the range of interaction in short-range attractive colloids
No full textWe numerically study the dependence of the dynamics on the range of interaction Delta for the short-range square well potential. We find that, for small Delta, dynamics scale exactly in the same way as thermodynamics, both for Newtonian and Brownian microscopic dynamics. For interaction ranges from a few percent down to the Baxter limit, the relative location of the attractive-glass line and the liquid-gas line does not depend on Delta. This proves that, in this class of potentials, disordered arrested states (gels) can be generated only as a result of a kinetically arrested phase separation
Star polymers: A study of the structural arrest in the presence of attractive interactions
No full textSimulations and mode-coupling theory calculations, for a large range of the arm number f and packing fraction eta have shown that the structural arrest and the dynamics of star polymers in a good solvent are extremely rich: the systems show a reentrant melting of the disordered glass nested between two stable fluid phases that strongly resemble the equilibrium phase diagram. Starting from a simple model potential we investigate the effect of the interplay between attractive interactions of different range and ultrasoft core repulsion, on the dynamics and on the occurrence of the ideal glass transition line. In the two cases considered so far, we observed some significant differences with respect to the purely repulsive pair interaction. We also discuss the interplay between equilibrium and nonequilibrium phase behavior. The accuracy of the theoretical tools we utilized in our investigation has been checked by comparing the results with molecular dynamics simulations
Gaussian density fluctuations and mode coupling theory for supercooled liquids
No full textThe equations of motion for the density modes of a fluid, derived from Newtons equations, are written as a linear generalized Langevin equation. The constraint imposed by the fluctuation-dissipation theorem is used to derive an exact form for the emory function. The resulting equations, solved under the assumption that the noise, and consequently density fluctuations, of the liquid are Gaussian distributed, are equivalent to the random phase approximation for the static structure factor and to the well-known ideal mode coupling theory (MCT) equations for the dynamics. This finding suggests that MCT is a theory of fluid dynamics that becomes exact in a mean-field limit
Ideal glass in attractive systems with different potentials
No full textWe discuss the ideal glass transition for two types of potential model of attractive colloidal systems, i.e. the square-well system and the Yukawa hard-sphere fluid. We use the framework of the ideal mode-coupling theory and we mostly focus our attention on the nature of the singularities predicted by the theory. We also study the phenomena that arise by varying the range of the attraction, since this parameter has been identified as one of the key parameters in colloidal systems
Inertial effects in diffusion-limited reactions
No full textDiffusion-limited reactions are commonly found in biochemical processes such as enzyme catalysis, colloid and protein aggregation and binding between different macromolecules in cells. Usually, such reactions are modeled within the Smoluchowski framework by considering purely diffusive boundary problems. However, inertial effects are not always negligible in real biological or physical media on typical observation time frames. This is all the more so for non-bulk phenomena involving physical boundaries, that introduce additional time and space constraints. In this paper, we present and test a novel numerical scheme, based on event-driven Brownian dynamics, that allows us to explore a wide range of velocity relaxation times, from the purely diffusive case to the underdamped regime. We show that our algorithm perfectly reproduces the solution of the Fokker-Planck problem with absorbing boundary conditions in all the regimes considered and is thus a good tool for studying diffusion-guided reactions in complex biological environments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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