Incremental viscosity by non-equilibrium molecular dynamics and the Eyring model

2018 Author(s). The viscoelastic behavior of sheared fluids is calculated by Non-Equilibrium Molecular Dynamics (NEMD) simulation, and complementary analytic solutions of a time-dependent extension of Eyring’s model (EM) for shear thinning are derived. It is argued that an “incremental viscosity,” ηi, or IV which is the derivative of the steady state stress with respect to the shear rate is a better measure of the physical state of the system than the conventional definition of the shear rate dependent viscosity (i.e., the shear stress divided by the strain rate). The stress relaxation function, Ci(t), associated with ηi is consistent with Boltzmann’s superposition principle and is computed by NEMD and the EM. The IV of the Eyring model is shown to be a special case of the Carreau formula for shear thinning. An analytic solution for the transient time correlation function for the EM is derived. An extension of the EM to allow for significant local shear stress fluctuations on a molecular level, represented by a gaussian distribution, is shown to have the same analytic form as the original EM but with the EM stress replaced by its time and spatial average. Even at high shear rates and on small scales, the probability distribution function is almost gaussian (apart from in the wings) with the peak shifted by the shear. The Eyring formula approximately satisfies the Fluctuation Theorem, which may in part explain its success in representing the shear thinning curves of a wide range of different types of chemical systems.D.D. would like to acknowledge the support received from the EPSRC under the Established Career Fellowship Grant No. EP/N025954/1

Viscuit and the fluctuation theorem investigation of shear viscosity by molecular dynamics simulations: The information and the noise

Engineering and Physical Sciences Research Council (EPSRC) Established Career Fellowship Grant No. EP/N025954/1

Single trajectory transport coefficients and the energy landscape by molecular dynamics simulations

EPSR

Non-equilibrium molecular simulations of thin film rupture

Data availability: The data that support the findings of this study are available from the corresponding author upon reasonable request.Codes to reproduce and analyze the data reported in this work can be found at https://github.com/MuhammadRRahman/Thin-Film-Rupture-NEMD.git.Supplementary data are available online at https://pubs.aip.org/aip/jcp/article/158/15/151104/2882242/Non-equilibrium-molecular-simulations-of-thin-film#supplementary-data .Copyright © Author(s) 2023. The retraction of thin films, as described by the Taylor–Culick (TC) theory, is subject to widespread debate, particularly for films at the nanoscale. We use non-equilibrium molecular dynamics simulations to explore the validity of the assumptions used in continuum models by tracking the evolution of holes in a film. By deriving a new mathematical form for the surface shape and considering a locally varying surface tension at the front of the retracting film, we reconcile the original theory with our simulation to recover a corrected TC speed valid at the nanoscale.M.R.R. acknowledges Shell and the Beit Trust for Ph.D. funding through a Beit Fellowship for Scientific Research. L.S. acknowledges the Engineering and Physical Sciences Research Council (EPSRC) for a Postdoctoral Fellowship (Grant No. EP/V005073/1). J.P.E. was supported by the Royal Academy of Engineering (RAEng) through their Research Fellowships scheme. B.C. was supported by Shell and the EPSRC via an iCASE Ph.D. studentship (Grant No. EP/T517690/1). D.D. acknowledges a Shell/RAEng Research Chair in Complex Engineering Interfaces and the EPSRC for an Established Career Fellowship (Grant No. EP/N025954/1)

Explaining why simple liquids are quasi-universal

It has been known for a long time that many simple liquids have surprisingly similar structure as quantified, e.g., by the radial distribution function. A much more recent realization is that the dynamics are also very similar for a number of systems with quite different pair potentials. Systems with such non-trivial similarities are generally referred to as "quasi-universal". From the fact that the exponentially repulsive pair potential has strong virial potential-energy correlations in the low-temperature part of its thermodynamic phase diagram, we here show that a liquid is quasi-universal if its pair potential can be written approximately as a sum of exponential terms with numerically large prefactors. Based on evidence from the literature we moreover conjecture the converse, i.e., that quasi-universality only applies for systems with this property

Aesthetic sense and social cognition: : a story from the Early Stone Age

Human aesthetic practices show a sensitivity to the ways that the appearance of an artefact manifests skills and other qualities of the maker. We investigate a possible origin for this kind of sensibility, locating it in the need for co-ordination of skill-transmission in the Acheulean stone tool culture. We argue that our narrative supports the idea that Acheulean agents were aesthetic agents. In line with this we offer what may seem an absurd comparison: between the Acheulean and the Quattrocento. In making it we display some hidden complexity in human aesthetic responses to an artefact. We conclude with a brief review of rival explanations—biological and/or cultural—of how this skills-based sensibility became a regular feature of human aesthetic practices

Contingency and contiguity of imitative behaviour affect social affiliation

Actions of others automatically prime similar responses in an agent’s behavioural repertoire. As a consequence, perceived or anticipated imitation facilitates own action control and, at the same time, imitation boosts social affiliation and rapport with others. It has previously been suggested that basic mechanisms of associative learning can account for behavioural effects of imitation, whereas a possible role of associative learning for affiliative processes is poorly understood at present. Therefore, this study examined whether contingency and contiguity, the principles of associative learning, affect also the social effects of imitation. Two experiments yielded evidence in favour of this hypothesis by showing more social affiliation in conditions with high contingency (as compared to low contingency) and in conditions of high contiguity (compared to low contiguity)

The predictive mirror: interactions of mirror and affordance processes during action observation

An important question for the study of social interactions is how the motor actions of others are represented. Research has demonstrated that simply watching someone perform an action activates a similar motor representation in oneself. Key issues include (1) the automaticity of such processes, and (2) the role object affordances play in establishing motor representations of others’ actions. Participants were asked to move a lever to the left or right to respond to the grip width of a hand moving across a workspace. Stimulus-response compatibility effects were modulated by two task-irrelevant aspects of the visual stimulus: the observed reach direction and the match between hand-grasp and the affordance evoked by an incidentally presented visual object. These findings demonstrate that the observation of another person’s actions automatically evokes sophisticated motor representations that reflect the relationship between actions and objects even when an action is not directed towards an object

Harnessing learning biases is essential for applying social learning in conservation

Social learning can influence how animals respond to anthropogenic changes in the environment, determining whether animals survive novel threats and exploit novel resources or produce maladaptive behaviour and contribute to human-wildlife conflict. Predicting where social learning will occur and manipulating its use are, therefore, important in conservation, but doing so is not straightforward. Learning is an inherently biased process that has been shaped by natural selection to prioritize important information and facilitate its efficient uptake. In this regard, social learning is no different from other learning processes because it too is shaped by perceptual filters, attentional biases and learning constraints that can differ between habitats, species, individuals and contexts. The biases that constrain social learning are not understood well enough to accurately predict whether or not social learning will occur in many situations, which limits the effective use of social learning in conservation practice. Nevertheless, we argue that by tapping into the biases that guide the social transmission of information, the conservation applications of social learning could be improved. We explore the conservation areas where social learning is highly relevant and link them to biases in the cues and contexts that shape social information use. The resulting synthesis highlights many promising areas for collaboration between the fields and stresses the importance of systematic reviews of the evidence surrounding social learning practices.BBSRC David Phillips Fellowship (BB/H021817/1