Molecular dynamics simulations of oxide memristors: thermal effects

We have extended our recent molecular-dynamic simulations of memristors to include the effect of thermal inhomogeneities on mobile ionic species appearing during operation of the device. Simulations show a competition between an attractive short-ranged interaction between oxygen vacancies and an enhanced local temperature in creating/destroying the conducting oxygen channels. Such a competition would strongly affect the performance of the memristive devices.     

Kinetics of Iodous Acid Disproportionation

The iodous acid disproportionation is autocatalytic, and it is not easy to measure the rate constant of the step 2IO₂H → IO₃^? + IOH + H⁺ separately. Hg(II) was used previously to suppress the autocatalytic pathway, but this method presents difficulties discussed in this work. A more effective method is the use of crotonic acid, an effective IOH scavenger. It suppresses side reactions, and a purely second‐order rate law is obtained. The rate constant decreases from 5 to 0.2 M^?1 s^?1 when the sulfuric acid concentration increases from 0.08 to 0.60 M. The observed decrease could be explained if IO₂^? reacts faster than IO₂H. This may have consequences for the mechanism of the oscillating Bray–Liebhafsky reaction.     

Republication of: The dynamics of general relativity

This article—summarizing the authors’ then novel formulation of General Relativity—appeared as Chap. 7, pp. 227–264, in Gravitation: an introduction to current research, L. Witten, ed. (Wiley, New York, 1962), now long out of print. Intentionally unretouched, this republication as Golden Oldie is intended to provide contemporary accessibility to the flavor of the original ideas. Some typographical corrections have been made: footnote and page numbering have changed–but not section nor equation numbering, etc. Current institutional affiliations are encoded in: arnowitt@physics.tamu.edu, deser@brandeis.edu, misner@umd.edu. An editorial note to this paper and biographies of the authors can be found via doi:. Original paper   R. Arnowitt, S. Deser and C. W. Misner, in Gravitation: an introduction to current research (Chap. 7). Edited by Louis Witten. John Wiley & Sons Inc., New York, London, 1962, pp. 227–265. Reprinted with the kind permissions of the editor, Louis Witten, and of all three authors     

Perturbations of an Acetone‐Based Briggs–Rauscher System by α‐Tocopherol (Vitamin E)

The malonic acid (MA)‐based oscillating Briggs–Rauscher reaction (BR) in batch mode has been shown to be sensitive to various hydrophilic polyphenol antioxidants. Several of these have been shown to cause cessation of oscillations for a period of time before a restart occurs. The length of time before oscillations restart is related to the type of antioxidant and its concentration. Procedures have been devised to use this method as a tool for measuring antioxidant activity from pure compounds and from extracts of natural sources. The antioxidant activity has been related to the reaction of the antioxidants with HOO^. radicals present in the oscillating system. Vitamin E (α‐tocopherol), a typical highly lipophilic antioxidant containing an phenolic OH group, is soluble in acetone that also is a suitable substrate for the BR reaction. Perturbations of a highly concentrated acetone‐based BR oscillator by acetonic solutions of vitamin E were studied. The inhibitory effects were found similar to those provoked by hydrophilic polyphenols in the MA‐based oscillator, but to obtain reasonable inhibition times, the concentration of vitamin E must be at the mM level instead μM . However, there is a region of concentrations where there is a nearly linear relation between concentration and inhibition time. A comparison with a hydrophilic diphenol (2,6‐dihydroxybenzoic acid) in the acetone‐based oscillator showed that the inhibitory reaction is much slower in this system than in the MA one. We were able to model the perturbations by vitamin E assuming its reaction with HOO^. radicals by using the FCA mechanism previously reported with some little modifications.     

Probing shear-banding transitions of the VCM model for entangled wormlike micellar solutions using large amplitude oscillatory shear (LAOS) deformations

We explore the use of large amplitude oscillatory shear (LAOS) deformation to probe the dynamics of shear-banding in soft entangled materials, primarily wormlike micellar solutions which are prone to breakage and disentanglement under strong deformations. The state of stress in these complex fluids is described by a class of viscoelastic constitutive models which capture the key linear and nonlinear rheological features of wormlike micellar solutions, including the breakage and reforming of an entangled network. At a frequency-dependent critical strain, the imposed deformation field localizes to form a shear band, with a phase response that depends on the frequency and amplitude of the forcing. The different material responses are compactly represented in the form of Lissajous (phase plane) orbits and a corresponding strain-rate and frequency-dependent Pipkin diagram. Comparisons between the full network model predictions and those of a simpler, limiting case are presented.     

47th Session of the ISI: Gastronomie et Paris

Abstract

The Skeptical Environmentalist: Measuring the Real State of the World, by Bjorn Lomborg. Cambridge University Press, 2001. Reviewed by Thomas Wonnacott     

μ3-ethylidyne-triphenylphosphine-octacarbonyltricobalt: a re-determination from diffractometer data

The structure of the title compound was originally reported from film data (Brice et al., Inorg Chem 9:362, 1970) and comprises a triangle of cobalt atoms capped by an ethylidyne substituent to form an approximately tetrahedral cluster unit. The triphenylphosphine ligand lies in an equatorial position with respect to the plane of the cobalt triangle. Two carbonyl groups, one axial the other equatorial, complete the coordination sphere of the cobalt atom bound to phosphorus. The other two cobalt atoms each carry two equatorial and one axial carbonyl ligand. The Co–Co bond cis to the phosphine substituent is significantly longer than the other two Co–Co distances. The crystal structure is stabilised by C—H···π interactions and C—H···O hydrogen bonds. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A comparison of the properties of two structurally equivalent but regiochemically different mono‐alkylated polybithiophenes prepared through AABB‐type stille polycondensation

Previous routes to polymers with mono‐alkylated bithiophenes have proceeded through polymerization of monoalkyl‐2,2′‐bithiophene monomers through oxidative or AB‐type cross‐coupling polymerizations. The resulting polymer regiochemistry affects both the location and orientation of the polymer side‐chains. In contrast, AABB‐type cross‐coupling polymerizations can control the location and in some cases the orientation of the side‐chains. To study how this control can impact polymer properties, two poly(monodecyl‐2,2′‐bithiophene) polymers have been synthesized through Stille AABB‐type polycondensations of 2,5‐bis(trimethylstannyl)thiophene with different monomers. The alkyl side‐chains are located on every other thiophene, but polymer 1 consists of both head‐to‐tail and head‐to‐head dyads, whereas polymer 2 is made up of only head‐to‐head dyads. ¹H NMR, ¹³C NMR, and heteronuclear single quantum correlation spectroscopy are used to confirm and contrast the polymer regiochemistries. The physical properties of the two polymers are analyzed using UV–vis spectroscopy, differential scanning calorimetry, and grazing‐incidence X‐ray diffraction. Polymer 2 is found to display significantly more aggregation in solution than 1, and it displays different thermal properties. The film properties of polymers 1 and 2, however, are very similar, with nearly identical UV–vis profiles and d‐spacing values as determined by grazing incidence X‐ray diffraction. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013