Development and application of a particle-particle particle-mesh Ewald method for dispersion interactions

For inhomogeneous systems with interfaces, the inclusion of long-range dispersion interactions is necessary to achieve consistency between molecular simulation calculations and experimental results. For accurate and efficient incorporation of these contributions, we have implemented a particle-particle particle-mesh (PPPM) Ewald solver for dispersion ($r^{-6}$) interactions into the LAMMPS molecular dynamics package. We demonstrate that the solver's $\mathcal{O}(N\log N)$ scaling behavior allows its application to large-scale simulations. We carefully determine a set of parameters for the solver that provides accurate results and efficient computation. We perform a series of simulations with Lennard-Jones particles, SPC/E water, and hexane to show that with our choice of parameters the dependence of physical results on the chosen cutoff radius is removed. Physical results and computation time of these simulations are compared to results obtained using either a plain cutoff or a traditional Ewald sum for dispersion.Comment: 31 pages, 9 figure

Self-propelled Worm-like Filaments: Spontaneous Spiral Formation, Structure, and Dynamics

Worm-like filaments that are propelled homogeneously along their tangent vector are studied by Brownian dynamics simulations. Systems in two dimensions are investigated, corresponding to filaments adsorbed to interfaces or surfaces. A large parameter space covering weak and strong propulsion, as well as flexible and stiff filaments is explored. For strongly propelled and flexible filaments, the free-swimming filaments spontaneously form stable spirals. The propulsion force has a strong impact on dynamic properties, such as the rotational and translational mean square displacement and the rate of conformational sampling. In particular, when the active self-propulsion dominates thermal diffusion, but is too weak for spiral formation, the rotational diffusion coefficient has an activity-induced contribution given by $v_c/\xi_P$, where $v_c$ is the contour velocity and $\xi_P$ the persistence length. In contrast, structural properties are hardly affected by the activity of the system, as long as no spirals form. The model mimics common features of biological systems, such as microtubules and actin filaments on motility assays or slender bacteria, and artificially designed microswimmers

Fund Jurisdiction Over Capital Movements Comments, Panel On Preventing Asian Type Crises: Who If Anyone Should Have Jurisdiction Over capital Movement?

Within the last two years, the Fund has given extensive consideration to the questions of whether the liberalization of capital movements should be pursued through an amendment of its Articles of Agreemen

Heard but Not Seen: Instructor-Led Video and its Effect on Learning

Educators and instructional designers are seeking ways to increase levels of learning. One of the ways this is being done is through cognitive load theory which attempts to reduce cognitive load through a better understanding of working memory and the factors that impact its function. Past studies have found that working memory processes visual and auditory information using separate and non-sharable resources (dual coding theory) and that by properly utilizing multimedia elements, information processing in working memory is more efficient (multimedia learning). What is not known is the effect that instructor-led video, which uses the visual channel but delivers no information, has on the cognitive load of the learner. Further, will the introduction of multimedia elements make the information processing of the learner more efficient? This study examined three ways in which instructional designers may create a more efficient learning environment through a better understanding of multimedia learning. First, by using the theories of multimedia learning, I examined a more efficient use of sensory memory. By minimizing extraneous load, which communication theory calls noise, on working memory through increased utilization of the visual and auditory channels, the effectiveness of instruction was increased. Secondly, the multimedia effect, defined as using visual helps and guides with spoken and written text, was shown to assist working memory in processing new information into existing schema. Last, by using the personalization principle set forth by Clark and Mayer (2008), I used both the video feed and multimedia together to foster a more social or conversational presentation to the learner