Coiling Instability of Multilamellar Membrane Tubes with Anchored Polymers

We study experimentally a coiling instability of cylindrical multilamellar stacks of phospholipid membranes, induced by polymers with hydrophobic anchors grafted along their hydrophilic backbone. Our system is unique in that coils form in the absence of both twist and adhesion. We interpret our experimental results in terms of a model in which local membrane curvature and polymer concentration are coupled. The model predicts the occurrence of maximally tight coils above a threshold polymer occupancy. A proper comparison between the model and experiment involved imaging of projections from simulated coiled tubes with maximal curvature and complicated torsions.Comment: 11 pages + 7 GIF figures + 10 JPEG figure

Scaling Reliably: Improving the Scalability of the Erlang Distributed Actor Platform

Distributed actor languages are an effective means of constructing scalable reliable systems, and the Erlang programming language has a well-established and influential model. While the Erlang model conceptually provides reliable scalability, it has some inherent scalability limits and these force developers to depart from the model at scale. This article establishes the scalability limits of Erlang systems and reports the work of the EU RELEASE project to improve the scalability and understandability of the Erlang reliable distributed actor model. We systematically study the scalability limits of Erlang and then address the issues at the virtual machine, language, and tool levels. More specifically: (1) We have evolved the Erlang virtual machine so that it can work effectively in large-scale single-host multicore and NUMA architectures. We have made important changes and architectural improvements to the widely used Erlang/OTP release. (2) We have designed and implemented Scalable Distributed (SD) Erlang libraries to address language-level scalability issues and provided and validated a set of semantics for the new language constructs. (3) To make large Erlang systems easier to deploy, monitor, and debug, we have developed and made open source releases of five complementary tools, some specific to SD Erlang. Throughout the article we use two case studies to investigate the capabilities of our new technologies and tools: a distributed hash table based Orbit calculation and Ant Colony Optimisation (ACO). Chaos Monkey experiments show that two versions of ACO survive random process failure and hence that SD Erlang preserves the Erlang reliability model. While we report measurements on a range of NUMA and cluster architectures, the key scalability experiments are conducted on the Athos cluster with 256 hosts (6,144 cores). Even for programs with no global recovery data to maintain, SD Erlang partitions the network to reduce network traffic and hence improves performance of the Orbit and ACO benchmarks above 80 hosts. ACO measurements show that maintaining global recovery data dramatically limits scalability; however, scalability is recovered by partitioning the recovery data. We exceed the established scalability limits of distributed Erlang, and do not reach the limits of SD Erlang for these benchmarks at this scal

Tight-binding parameters for chemisorptive bonds of transition metals with hydrogen, oxygen and sulfur

Calculations of the tight-binding parameters have been worked out for Fe, Co, Ni, Cu, Pd, Pt bonds either in metal-metal bonds or in chemisorptive bonds with oxygen, sulfur, hydrogen, nitrogen, etc. Parameters are extracted from Herman-Skillman atomic self-consistent Hartree-Fock-Slater calculations with α-Schwartz correlation values. Variations of these parameters with adsorption distances are established. Surface crystal field effects and the role of three-centre integrals are discussed.Les paramètres de liaisons fortes ont été calculés pour les métaux de transition Fe, Co, Ni, Cu, Pd, Pt, soit pour décrire le métal pur (liaisons métal-métal), soit pour décrire un couplage avec des atomes légers, azote, carbone, hydrogène, oxygène, soufre. Pour cela, on utilise un calcul atomique self-consistent Hartree-Fock-Slater de type Herman-Skillman avec une correction de potentiel type Slater pour tenir compte des effets d'échange et corrélation. L'étude des variations des paramètres avec les distances interatomiques montre que ceux-ci décroissent exponentiellement avec la distance. Finalement les effets des intégrales de champ cristallin et des intégrales à trois centres sont discutés