Rate constants for some reactions of inorganic radicals with inorganic ions. Temperature and solvent dependence

Rate constants for several reactions of inorganic radicals with inorganic anions in aqueous and aqueous/acetonitrile solutions have been measured as a function of temperature by laser flash photolysis. The reactions studied were (1) Cl₂^? + N₃^?, (2) Br₂^? + N₃^?, (3) Cl₂^? + SCN^?, (4) Br₂^? + SCN^?, (5) SO₄^? + Cl^?, (6) SO₄^? + CO₃^2?, and (7) N₃? + I^?. The rate constants were corrected for ionic strength and ranged from 10⁶ to 10⁹ L mol^?1 s^?1. The Arrhenius activation energies varied from 2 to 12 kJ mol^?1 for the first 4 reactions, were higher for reaction 6, and negative for reaction 5. The pre-exponential factors also varied considerably with log A ranging from 5 to 14. The values of k₂₉₈ decreased in most cases by more than an order of magnitude upon increasing the acetonitrile (ACN) fraction from 0 to 70%. For most reactions, this decrease in k₂₉₈ was due to changes in log A with little regularity in the small changes observed in E_a. For reaction 7, k₂₉₈ was practically unchanged due to compensating effects of the changes in E_a and log A with ACN mol fraction, giving an isokinetic relationship. An isokinetic relationship was also observed in the case of reaction 6; E_a and log A change in parallel while changing ACN mol fraction. Reaction 3 (Cl₂^? + SCN^?) was also studied in water/t-butanol and water/acetic acid mixtures. Linear correlation was found between log k and the dielectric constant of the medium for water/ACN and water/t-BuOH but the lines for the two solvent mixtures had different slopes, suggesting specific solvation effects in addition to the primary solvent polarity effects. With water/acetic acid, k decreased and then increased upon addition of acetic acid. © 1993 John Wiley & Sons, Inc.     

Region of Magnetic Dominance near a Rotating Black Hole

Processes of collimation of electrically charged particles near a rotating black hole are discussed. It is assumed that the black hole is immersed in a weak magnetic field aligned with rotation axis. This situation is relevant for understanding pre-collimation of astrophysical jets. The magnetic field affects the motion of material and restricts the validity of various scenarios which use the test-particle (cold plasma) approximation. A simplified criterion to estimate the relevance of this approximation is discussed in connection with the mechanism of the dissipative collimation, as proposed by de Felice and Curir.     

Dung’s Argumentation is Essentially Equivalent to Classical Propositional Logic with the Peirce–Quine Dagger

In this paper we show that some versions of Dung’s abstract argumentation frames are equivalent to classical propositional logic. In fact, Dung’s attack relation is none other than the generalised Peirce–Quine dagger connective of classical logic which can generate the other connectives ?, ù, ú, ?{\neg, \wedge, \vee, \to} of classical logic. After establishing the above correspondence we offer variations of the Dung argumentation frames in parallel to variations of classical logic, such as resource logics, predicate logic, etc., etc., and create resource argumentation frames, predicate argumentation frames, etc., etc. We also offer the notion of logic proof as a geometrical walk along the nodes of a Dung network and thus we are able to offer a geometrical abstraction of the notion of inference based argumentation. Thus our paper is also a contribution to the question:     

Dynamic fracture instabilities in brittle crystals generated by thermal phonon emission: Experiments and atomistic calculations

Dynamic cleavage fracture experiments of brittle single crystal silicon revealed several length scales of surface and path instabilities: macroscale path selection, mesoscale crack deflection, and nanoscale surface ridges. These phenomena cannot be predicted or explained by any of the continuum mechanics based equations of motion of dynamic cracks, as presumably critical energy dissipation mechanisms are not fully accounted for in the theories. Experimentally measured maximum crack speed, always lower than the theoretical limit, is another phenomenon that is as yet not well understood.We suggest that these phenomena depend on velocity dependent and anisotropic material property that resists crack propagation. The basic approach is that the bond breaking mechanisms during dynamic crack propagation vibrate the atoms at the crack front to generate thermal phonon emission, or heat, which provides additional energy dissipation mechanisms. This energy dissipation mechanism is a material property that resists crack propagation. To evaluate this property, we combined the continuum based elastodynamic Freund equation of motion with molecular dynamics atomistic computer “experiments”.We analyzed the above experimental dynamic fracture instabilities in silicon with the obtained velocity dependent and anisotropic material property and show its importance in cleavage of brittle crystals.     

Finite difference approximation of a nonlinear integro-differential system

Finite difference approximation of the nonlinear integro-differential system associated with the penetration of a magnetic field into a substance is studied. The convergence of the finite difference scheme is proved. The rate of convergence of the discrete scheme is given. The decay of the numerical solution is compared with the analytical results proven earlier.     

Optimization and method validation of determining polyphenolic compounds by UFLC-DAD system using two biphenyl and pentafluorophenylpropyl columns

The development of efficient analytical methods for the identification and quantification of polyphenols in natural products is needed. The present study was aimed to optimize the polyphenols by UFLC using two different Ascentis express columns. Chromatographic separation was performed using UFLC-DAD connected with Ascentis Express Biphenyl column (system I) and Ascentis Express F5 pentafluorophenylpropyl (PFP) column (system II). Multistep gradient elution program was used in both analytical instruments to detect 34 compounds of different classes (phenolic acids, flavonoids, isoflavones, flavanols, flavonols and flavanones). The detection wavelength, linear calibration range, theoretical plate, tailing factor, limits of detection and of quantification were determined. The results were validated and the optimized method was proven to be precise, revealing good separation in the UFLC system II using Ascentis Express F5 PFP column. In conclusion, this study shows analytical preciseness and is useful in determining polyphenols in natural products.     

Building analytical three-field cosmological models

A difficult task to deal with is the analytical treatment of models composed of three real scalar fields, as their equations of motion are in general coupled and hard to integrate. In order to overcome this problem we introduce a methodology to construct three-field models based on the so-called “extension method”. The fundamental idea of the procedure is to combine three one-field systems in a non-trivial way, to construct an effective three scalar field model. An interesting scenario where the method can be implemented is with inflationary models, where the Einstein–Hilbert Lagrangian is coupled with the scalar field Lagrangian. We exemplify how a new model constructed from our method can lead to non-trivial behaviors for cosmological parameters.