Multiscale Coarse-Graining with Effective Polarizabilities: A Fully Bottom-Up Approach.

Coarse-grain (CG) models offer a way to estimate the behavior of larger systems, for longer times than possible in fine-grain calculations by eliminating fine detail. For most atomistic models this often involves eliminating electrostatic interactions, yet, in many calculations, the dielectric properties of a material may be too important to ignore. In this work, we expand upon a previous CG representation which preserves the instantaneous center of mass (CoM), charge, and dipole of clusters of atoms by representing them with charged dimers.

Multiscale Coarse-Graining of Polarizable Models through Force-Matched Dipole Fluctuations.

An extension of the multiscale coarse-graining method (MS-CG) to polarizable coarse-grain (CG) models is presented. In the extension, force matching is used to derive charged dimers that mimic the dipole behavior, including electronic polarizability, of fine resolution systems. The extended MS-CG method separates short-range and electrostatic forces and treats the polarization interactions by representing dipole fluctuations with a harmonic bond reminiscent of the Drude oscillator.

Observation of interstitial molecular hydrogen in clathrate hydrates.

The current knowledge and description of guest molecules within clathrate hydrates only accounts for occupancy within regular polyhedral water cages. Experimental measurements and simulations, examining the tert-butylamine + H2 + H2O hydrate system, now suggest that H2 can also be incorporated within hydrate crystal structures by occupying interstitial sites, that is, locations other than the interior of regular polyhedral water cages. Specifically, H2 is found within the shared heptagonal faces of the large (4(3)5(9)6(2)7(3)) cage and in cavities formed from the disruption of smaller (4(4)5(4)) water cages.

Orifice jamming of fluid-driven granular flow.

The three-dimensional jamming of neutrally buoyant monodisperse, bidisperse, and tridisperse mixtures of particles flowing through a restriction under fluid flow has been studied. During the transient initial accumulation of particles at the restriction, a low probability of a jamming event is observed, followed by a transition to a steady-state flowing backlog of particles, where the jamming probability per particle reaches a constant. Analogous to the steady-state flow in gravity-driven jams, this results in a geometric distribution describing the number of particles that discharge prior to a jamming event.

Remote magnetic navigation and arrhythmia ablation.

Radiofrequency treatment is the first-choice treatment for arrhythmias, in particular complex arrhythmias and especially atrial fibrillation, due to the greater benefit/risk ratio compared with antiarrhythmic drugs. However, complex arrhythmias such as atrial fibrillation require long procedures with additional risks such as X-ray exposure or serious complications including tamponade. Given this context, robotic magnetic navigation is a technique well suited to the treatment of complex arrhythmias, on account of its efficacy and reliability, the significant reduction in X-ray exposure for both patient and operator, and the very low risk of perforation.

The cages, dynamics, and structuring of incipient methane clathrate hydrates.

Interest in describing clathrate hydrate formation mechanisms spans multiple fields of science and technical applications. Here, we report findings from multiple molecular dynamics simulations of spontaneous methane clathrate hydrate nucleation and growth from fully demixed and disordered two-phase fluid systems of methane and water. Across a range of thermodynamic conditions and simulation geometries and sizes, a set of seven cage types comprises approximately 95% of all cages formed in the nucleated solids.

Prevalence and risk factors related to infections of cardiac resynchronization therapy devices.

Aims: Device-related infections (DRI) are not well understood in patients implanted with a cardiac resynchronization therapy (CRT) device. The aims of this study were: (i) to evaluate the prevalence of CRT DRI; (ii) to establish the factors predictive of CRT DRI.

Methods And Results: Between January 2001 and May 2007, CRT implantation was performed in 303 patients (247 men, 82%).