A molecular dynamics study of proton hopping in nafion membrane

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.We have investigated the transport phenomena of hydronium ions and water molecules in the nanostructure of hydrated Nafion membrane by systematically changing the hydration level using classical molecular dynamics simulations. The new empirical valence bond (EVB) model is developed in order to improve the description of proton mobility in both aqueous and Nafion environments. The new EVB model predicts a significantly enhanced transport in comparison with previous hopping models as well as the classical hydronium diffusion, which largely improves the agreement with the available experimental data. We have determined diffusion coefficients of hydronium ions and water molecules in hydrated Nafion membrane as a function of hydration level to investigate the impact of the Grotthuss mechanism on the proton transport property. Proton hopping mechanism was found to become more significant at higher hydration levels. It was also found that a proton-hopping mechanism has a small effect on the diffusivity of water molecules for various hydration levels

Molecular Model of the Contractile Ring

We present a model for the actin contractile ring of adherent animal cells. The model suggests that the actin concentration within the ring and consequently the power that the ring exerts both increase during contraction. We demonstrate the crucial role of actin polymerization and depolymerization throughout cytokinesis, and the dominance of viscous dissipation in the dynamics. The physical origin of two phases in cytokinesis dynamics ("biphasic cytokinesis") follows from a limitation on the actin density. The model is consistent with a wide range of measurements of the midzone of dividing animal cells.Comment: PACS numbers: 87.16.Ka, 87.16.Ac http://www.ncbi.nlm.nih.gov/pubmed/16197254 http://www.weizmann.ac.il/complex/tlusty/papers/PhysRevLett2005.pd

Real-time cavity QED with single atoms

We report the first measurement of the real-time evolution of the complex field amplitude brought on by single atom transits. We show the variation in time of both quadrature amplitudes (simultaneously recorded) of the light transmitted through the cavity, as well the resultant optical phase for a single atom transit event. In this particular measurement, the cavity and laser were both detuned by 10 MHz from the Cs resonance

Trapping of single atoms in cavity QED

By integrating the techniques of laser cooling and trapping with those of cavity quantum electrodynamics (QED), single Cesium atoms have been trapped within the mode of a small, high finesse optical cavity in a regime of strong coupling. The observed lifetime for individual atoms trapped within the cavity mode is $\tau \approx 28$ms, and is limited by fluctuations of light forces arising from the far-detuned intracavity field. This initial realization of trapped atoms in cavity QED should enable diverse protocols in quantum information science.Comment: 4 pages, 4 figure

Normal-mode spectroscopy of a single bound atom-cavity system

The energy-level structure of a single atom strongly coupled to the mode of a high-finesse optical cavity is investigated. The atom is stored in an intracavity dipole trap and cavity cooling is used to compensate for inevitable heating. Two well-resolved normal modes are observed both in the cavity transmission and the trap lifetime. The experiment is in good agreement with a Monte Carlo simulation, demonstrating our ability to localize the atom to within $\lambda/10$ at a cavity antinode.Comment: 4 pages, 4 figure

Processing and mechanical properties of hollow sphere aluminum foams

Hollow sphere metallic foams are a new class of cellular material that possesses the attractive advantages of uniform cell size distribution and regular cell shape. These result in more predictable physical and mechanical properties than those of cellular materials with a random cell size distribution and irregular cell shapes. In the present study, single aluminum hollow spheres with three kinds of sphere wall thickness as 0.1 mm, 0.3 mm and 0.5 mm were processed by a new pressing method. Hollow sphere aluminum foam samples were prepared by bonding together single hollow spheres with simple cubic packing (SC) and body-centered cubic packing (BCC). Compressive tests were carried out to evaluate the deformation behaviors and mechanical properties of the hollow sphere aluminum foams. Effects of the sphere wall thickness and packing style on the mechanical properties were investigated.<br /

Retroactive quantum jumps in a strongly-coupled atom-field system

We investigate a novel type of conditional dynamic that occurs in the strongly-driven Jaynes-Cummings model with dissipation. Extending the work of Alsing and Carmichael [Quantum Opt. {\bf 3}, 13 (1991)], we present a combined numerical and analytic study of the Stochastic Master Equation that describes the system's conditional evolution when the cavity output is continuously observed via homodyne detection, but atomic spontaneous emission is not monitored at all. We find that quantum jumps of the atomic state are induced by its dynamical coupling to the optical field, in order retroactively to justify atypical fluctuations in ocurring in the homodyne photocurrent.Comment: 4 pages, uses RevTex, 5 EPS figure

The co-existence of an aberrant origin of the right subclavian artery and a coronary myocardial bridge

We encountered the co-existence of an aberrant origin of the right subclavian artery and a myocardial bridge on the left anterior descending coronary artery in the cadaver of an 80-year-old Japanese woman during the course of educational dissection at Nagoya City University Medical School. We document the precise gross anatomical findings with some morphometric measurements. Neither an aberrant origin of the right subclavian artery nor the cardial myocardial bridge is a very rare anomaly, but a case of both anomalies being found in the same body is very rare. We believe this is the first report of the simultaneous occurrence of these two anomalies

Trapping of Single Atoms with Single Photons in Cavity QED

Two recent experiments have reported the trapping of individual atoms inside optical resonators by the mechanical forces associated with single photons [Hood et al., Science 287, 1447 (2000) and Pinkse et al., Nature 404, 365 (2000)]. Here we analyze the trapping dynamics in these settings, focusing on two points of interest. Firstly, we investigate the extent to which light-induced forces in these experiments are distinct from their free-space counterparts. Secondly, we explore the quantitative features of the resulting atomic motion and how these dynamics are mapped onto variations of the intracavity field. Not surprisingly, qualitatively distinct atomic dynamics arise as the coupling and dissipative rates are varied. For the experiment of Hood et al., we show that atomic motion is largely conservative and is predominantly in radial orbits transverse to the cavity axis. A comparison with the free-space theory demonstrates that the fluctuations of the dipole force are suppressed by an order of magnitude. This effect is based upon the Jaynes-Cummings eigenstates of the atom-cavity system and represents qualitatively new physics for optical forces at the single-photon level. By contrast, even in a regime of strong coupling in the experiment of Pinkse et al., there are only small quantitative distinctions between the free-space theory and the quantum theory, so it is not clear that description of this experiment as a novel single-quantum trapping effect is necessary. The atomic motion is strongly diffusive, leading to an average localization time comparable to the time for an atom to transit freely through the cavity and to a reduction in the ability to infer aspects of the atomic motion from the intracavity photon number.Comment: 19 pages, 22 figure files, REVTEX, corrected spelling, LaTeX now produces postscript which includes figures, minor changes to figures. Final version to be published in Physical Review A, expanded summary of results in introduction, minor changes to figures and tex