Structure and stability of helices in square-well homopolymers

Recently, it has been demonstrated [Magee et al., Phys. Rev. Lett. 96, 207802 (2006)] that isolated, square-well homopolymers can spontaneously break chiral symmetry and freeze into helical structures at sufficiently low temperatures. This behavior is interesting because the square-well homopolymer is itself achiral. In this work, we use event-driven molecular dynamics, combined with an optimized parallel tempering scheme, to study this polymer model over a wide range of parameters. We examine the conditions where the helix structure is stable and determine how the interaction parameters of the polymer govern the details of the helix structure. The width of the square well (proportional to lambda) is found to control the radius of the helix, which decreases with increasing well width until the polymer forms a coiled sphere for sufficiently large wells. The helices are found to be stable for only a window of molecular weights. If the polymer is too short, the helix will not form. If the polymer is too long, the helix is no longer the minimum energy structure, and other folded structures will form. The size of this window is governed by the chain stiffness, which in this model is a function of the ratio of the monomer size to the bond length. Outside this window, the polymer still freezes into a locked structure at low temperature, however, unless the chain is sufficiently stiff, this structure will not be unique and is similar to a glassy state.Comment: Submitted to Physical Review

Exact on-event expressions for discrete potential systems

The properties of systems composed of atoms interacting though discrete potentials are dictated by a series of events which occur between pairs of atoms. There are only four basic event types for pairwise discrete potentials and the square-well/shoulder systems studied here exhibit them all. Closed analytical expressions are derived for the on-event kinetic energy distribution functions for an atom, which are distinct from the Maxwell-Boltzmann distribution function. Exact expressions are derived that directly relate the pressure and temperature of equilibrium discrete potential systems to the rates of each type of event. The pressure can be determined from knowledge of only the rate of core and bounce events. The temperature is given by the ratio of the number of bounce events to the number of disassociation/association events. All these expressions are validated with event-driven molecular dynamics simulations and agree with the data within the statistical precision of the simulations

Transport properties of highly asymmetric hard-sphere mixtures

The static and dynamic properties of binary mixtures of hard spheres with a diameter ratio of sigma(B)/sigma(A)= 0.1 and a mass ratio of m(B)/m(A)= 0.001 are investigated using event driven molecular dynamics. The contact values of the pair correlation functions are found to compare favorably with recently proposed theoretical expressions. The transport coefficients of the mixture, determined from simulation, are compared to the predictions of the revised Enskog theory using both a third-order Sonine expansion and direct simulation Monte Carlo. Overall, the Enskog theory provides a fairly good description of the simulation data, with the exception of systems at the smallest mole fraction of larger spheres (x(A)=0.01) examined. A "fines effect" was observed at higher packing fractions, where adding smaller spheres to a system of large spheres decreases the viscosity of the mixture; this effect is not captured by the Enskog theory

Mapping continuous potentials to discrete forms

The optimal conversion of a continuous inter-particle potential to a discrete equivalent is considered here. Existing and novel algorithms are evaluated to determine the best technique for creating accurate discrete forms using the minimum number of discontinuities. This allows the event-driven molecular dynamics technique to be efficiently applied to the wide range of continuous force models available in the literature, and facilitates a direct comparison of event-driven and time-driven molecular dynamics. The performance of the proposed conversion techniques are evaluated through application to the Lennard-Jones model. A surprising linear dependence of the computational cost on the number of discontinuities is found, allowing accuracy to be traded for speed in a controlled manner. Excellent agreement is found for static and dynamic properties using a relatively low number of discontinuities. For the Lennard-Jones potential, the optimized discrete form outperforms the original continuous form at gas densities but is significantly slower at higher densities

A Role for Dorsal and Ventral Hippocampus in Inter-Temporal Choice Cost-Benefit Decision Making

Previous studies suggest a preferential role for dorsal hippocampus (dHPC) in spatial memory tasks, whereas ventral hippocampus (vHPC) has been implicated in aspects of fear and/or anxiety. In this study, we tested the hypothesis that vHPC may be a critical subregion for performance on a delay-based, cost-benefit decision making task. Rats chose between the two goal arms of a T maze, one containing an immediately available small reward, the other containing a larger reward that was only accessible after a delay. dHPC, vHPC, and complete hippocampal (cHPC) lesions all reduced choice of the delayed high reward (HR) in favor of the immediately available low reward (LR). The deficits were not due to a complete inability to remember which reward size was associated with which arm of the maze. When an equivalent 10-s delay was introduced in both goal arms, all rats chose the HR arm on nearly all trials. The deficit was, however, reinstated when the inequality was reintroduced. Our results suggest an important role for both dHPC and vHPC in the extended neural circuitry that underlies intertemporal choice

A Dental Student Perspective on the Impacts of an Inter-professional Engagement Module

Community engagement, defined as the process of getting communities involved in decisions that affect them (NICE, 2008), is paramount to the development and governance of services and activities that promote health and target inequalities (Buck, Baylis, Dougall, &amp; Robertson, 2018; NICE, 2008). The inter-professional engagement module is an integral part of the curriculum of Peninsula Dental School, University of Plymouth, United Kingdom. It enables second-year undergraduate dental and dental therapy and hygiene students to develop and deliver an oral health intervention targeted at disadvantaged groups in the community. These groups commonly experience higher levels of dental disease (Public Health England, 2018; Office of the Director of Public Health, Plymouth City Council, 2018). As part of this module, we, a second-year group of undergraduate dental students, worked alongside the Family Intensive Intervention Project (FIIP) and its beneficiaries to improve vulnerable families’ awareness of oral and general health, and to break down barriers toward accessing dental care. FIIP provides holistic support to families with complex needs who may have difficulties with issues such as substance misuse, mental health and evidence of neglectful parenting (W. Kirby, personal communication, 2018).</jats:p

Reflections on a degree initiative: the UK's Birmingham Royal Ballet dancers enter the University of Birmingham

This paper provides an opportunity to share experiences and perceptions of the first 5 years of a degree programme for professional dancers. A partnership developed in the mid-1990s between the UK's Birmingham Royal Ballet and the University of Birmingham, Westhill (now School of Education), to provide a part-time, post-experience, flexible study programme for full-time Company dancers. This is the first 'company customised' higher education programme to dovetail studies around rehearsal, performance and touring schedules. Methodology is based on a narrative by the author, informed by ongoing internal and external evaluations, in-depth interviews with dancers and Company managers, documentation and secondary sources. Outcomes indicate that the programme has made a positive difference to the Company, to the dancers and to the wider education and dance/arts world