Soft Condensed Matter
The failure of the Classical Nucleation Theory at low temperatures resolved (1902.03193v1)
Daniel Roberto Cassar, André Hofmeister Serra, Oscar Peitl, Alisson Mendes Rodrigues, Edgar Dutra Zanotto
2019-02-08
A relevant observation about crystal nucleation kinetics in glass-forming substances has been a matter of intense debate for several decades. The Classical Nucleation Theory (CNT) allegedly fails to describe the temperature dependence of the homogeneous crystal nucleation rates below the temperature of maximum nucleation rate. This failure was reported for several glass-forming substances and is known as nucleation "breakdown". Some reasonable explanations for this apparent break have been advanced in the literature, however, the simplest hypothesis has never been tested: that this break is a byproduct of nucleation datasets that have not reached the steady-state regime. In this work, we tested this hypothesis by thoroughly analyzing new and published nucleation data for supercooled Li2Si2O5, BaSi2O5, Na4CaSi3O9, and Na2Ca2Si3O9 liquids, using only datasets for which steady-state conditions (likely) have been reached. For that purpose, we used three restraining conditions: i) Nucleation and diffusion data were measured in the same glass batch, and each batch was individually analyzed; ii) only nucleation rate data that passed a steady-state regime test were used in the analysis; iii) the uncertainty and regression confidence bands were computed and considered. With this strategy, we proved that the alleged nucleation break is indeed an experimental artifact! This result ends a four decade-old dilemma and corroborates the use of CNT for analyses of crystal nucleation rates.
Efficient sliding locomotion with isotropic friction (1902.03163v1)
Silas Alben
2019-02-08
Snakes' bodies are covered in scales that make it easier to slide in some directions than in others. This frictional anisotropy allows for sliding locomotion with an undulatory gait, one of the most common for snakes. Isotropic friction is a simpler situation (that arises with snake robots for example) but is less understood. In this work we regularize a model for sliding locomotion to allow for static friction. We then propose a robust iterative numerical method to study the efficiency of a wide range of motions under isotropic Coulomb friction. We find that simple undulatory motions give little net locomotion in the isotropic regime. We compute general time-harmonic motions of three-link bodies and find three local optima for efficiency. The top two involve static friction to some extent. We then propose a class of smooth body motions that have similarities to concertina locomotion (including the involvement of static friction) and can achieve optimal efficiency for both isotropic and anisotropic friction.
Escape rate of transiently active Brownian particle in one dimension (1902.03148v1)
A. Scacchi, A. Sharma, J. M. Brader
2019-02-08
Activity significantly enhances the escape rate of a Brownian particle over a potential barrier. Whereas constant activity has been extensively studied in the past, little is known about the effect of time-dependent activity on the escape rate of the particle. In this paper we study the escape problem for a Brownian particle that is transiently active; the activity decreases continuously during the escape process. Using the effective equilibrium approach we analytically calculate the escape rate, under the assumption that the particle is either completely passive or fully active when crossing the barrier. We perform numerical simulations of the escape process in one dimension and find good agreement with the theoretical predictions.
Fractal nature of protein structures affects their Vibrational Energy Exchange (1902.03063v1)
Luca Maggi
2019-02-08
Recent vibrational energy exchange experiments on a protein have been explained employing the relation, not new in itself, between protein and fractal structure. The differnce in the scaling exponent of specific part of the protein entails a distinct vibrational localization property and consequentely a discrepancy in the vibrational energy exchange
Diffusion of Colloidal Rods in Corrugated Channels (1902.03059v1)
Xiang Yang, Qian Zhu, Chang Liu, Wei Wang, Yunyun Li, Fabio Marchesoni, Peter Hänggi, Hepeng Zhang
2019-02-08
In many natural and artificial devices diffusive transport takes place in confined geometries with corrugated boundaries. Such boundaries cause both entropic and hydrodynamic effects, which have been studied only for the case of spherical particles. Here we experimentally investigate diffusion of particles of elongated shape confined into a corrugated quasi-two-dimensional channel. Elongated shape causes complex excluded-volume interactions between particle and channel walls which reduce the accessible configuration space and lead to novel entropic free energy effects. The extra rotational degree of freedom also gives rise to a complex diffusivity matrix that depends on both the particle location and its orientation. We further show how to extend the standard Fick-Jacobs theory to incorporate combined hydrodynamic and entropic effects, so as, for instance, to accurately predict experimentally measured mean first passage times along the channel. Our approach can be used as a generic method to describe translational diffusion of anisotropic particles in corrugated channels.
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