Kinetic Solvation of Singly Charged Ions in Infinitely Dilute Solutions in Ethylene Glycol: Effect of Temperature

Journal of Solution Chemistry - To quantitatively describe the kind of interaction between ion and solvent, it is convenient to use the concept of negative or positive solvation. We have...     

Straw Chambers for the NA64 Experiment

Physics of Particles and Nuclei Letters - The aim of this work is to describe the characteristics and properties of the particle-tracking detectors created at the Joint Institute for Nuclear...     

Synthesis and physical chemical properties of isomers of vic-arylazonitro-1-methylpyrazoles

Taking account of special features of the diazotization of vic-aminonitro-1-methylpyrazoles, conditions have been found for synthesizing from them the isomers of arylazo-1-methylnitropyrazoles. The different behavior of these compounds under reducing conditions has been confirmed by polarographic data. The electronic absorption spectra of vic-arylazonitropyrazoles are interpreted.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 628–632, May, 1990.     

Mechanical properties of heterocyclic polymer networks

Heterocyclic networds prepared by copolymerization of oligomeric epoxy rubber (ER) with different amounts of hexamethylene diisocyanate (HMDI) were characterized by room-temperature static Young's and bulk moduli, as well as by measurements of dynamic Young's modulus and linear thermal expansivity in the temperature interval 293–503 K. It was concluded that the major factor affecting thermoelastic properties of these networks is the relative content of three-arm, six-membered isocyanoureate rings which determine the apparent overall network density, and of two-arm, five-membered oxazolidone rings which act as a sort of internal diluent.     

Measurement of the production cross section for charmed baryons in proton–nucleus interactions at 70 GeV

The results of an analysis of data from the SERP-Е-184 experiment devoted to studying mechanisms of the production of charmed particles in proton–nucleus interactions at 70 GeV and their decays are presented. The data in question were obtained upon irradiating the SVD-2 active target consisting of carbon, silicon, and lead plates with a beam of 70-GeV protons. A detailed simulation on the basis of the FRITIOF7.02 and GEANT3.21 code packages made it possible to optimize event-selection criteria and to calculate the detection efficiency for Λ_c⁺ baryons. After selecting a signal from the threebody decay of a Λ_c⁺ baryon, the inclusive cross section for its production at near-threshold energies, its lifetime, and the parameter of the A dependence of the cross section were found. The Λ_c⁺ -baryon yields are tabulated along with data from other experiments and theoretical predictions.     

Polymer micelles with hydrophobic core and ionic amphiphilic corona. 2. Starlike distribution of charged and nonpolar blocks in corona

Mixed polymer micelles with hydrophobic polystyrene (PS) core and ionic amphiphilic poly(4-vinylpyridine)/poly(N-ethyl-4-vinylpyridinium bromide) corona (P4VP/PEVP) spontaneously self-assembled from mixtures of PS-b-PEVP and PS-b-P4VP macromolecules in dimethylformamide/methanol/water selective solvent. The fraction of PEVP units in corona was β = [PEVP]/([PEVP] + [P4VP]) = 0.05-1.0. Micelles were transferred into pure water via dialysis technique and pH was adjusted to 9, where P4VP blocks are insoluble. Structural characteristics of micelles as a function of corona composition β were investigated. Methods of dynamic and static light scattering, electrophoretic mobility measurements, sedimentation velocity, transmission electron microscopy, and UV spectrophotometry were applied. Spherical morphology with core (PS)-shell (P4VP)-corona (PEVP) organization was postulated. Micelles demonstrated a remarkable inflection in structural characteristics near β ～ 0.5-0.7. Above this region, aggregation number (m), core and corona radii of mixed micelles coincided with those of individual PS-b-PEVP micelles. When β decreased below 0.5, dramatic growth of aggregation number was observed, accompanied by growth in micelle size and stretching PEVP chains. At β below 0.2, dispersions of mixed micelles were unstable and easily precipitated upon addition of NaCl. Scaling relationships between micelle characteristics and β were obtained via minimization the micelle free energy, taking into account electrostatic, osmotic, volume, and surface contributions. Theoretical estimations predicted dramatic influence of β on aggregation number, m ～ β(-3). This result is in general agreement with experimental data and confirms the correctness of the core-shell-corona model. The inflection in micelle characteristics entails drastic changes in micelle dispersion stability in the presence of oppositely charged polymeric (sodium polymethacrylate) or amphiphilic (sodium dodecyl sulfate) complexing agents.     

Ascorbate reacts with singlet oxygen to produce hydrogen peroxide

Singlet oxygen is a highly reactive electrophilic species that reacts rapidly with electron-rich moieties, such as the double bonds of lipids, thiols, and ascorbate (AscH-). The reaction of ascorbate with singlet oxygen is rapid (k = 3 x 10(8) M(-1) s(-1)). Here we have investigated the stoichiometry of this reaction. Using electrodes to make simultaneous, real-time measurements of oxygen and hydrogen peroxide concentrations, we have investigated the products of this reaction. We have demonstrated that hydrogen peroxide is a product of this reaction. The stoichiometry for the reactants of the reaction (1 1O2 + 1AscH--->1H2O2 + 1dehydroascorbic) is 1:1. The formation of H2O2 results in a very different oxidant that has a longer lifetime and much greater diffusion distance. Thus, locally produced singlet oxygen with a half-life of 1 ns to 1 micros in a biological setting is changed to an oxidant that has a much longer lifetime and thus can diffuse to distant targets to initiate biological oxidations.     

AB‐Block Copolymer with Moving B Blocks as a Model for Interpolymer Complexes

The conformational behavior of a single AB block copolymer is studied by Monte Carlo simulation. The A‐A and A‐B interactions have the character of excluded volume interactions while the B units attract each other; the attractive B blocks can move along the chain. The collapse transition of the chain with increasing attraction between the B units is analyzed. Intrachain separation of the A and B units takes place in the course of the chain collapse with the formation of “globule with a tail” conformations. The globule is formed by the attractive moving B blocks while the tail consists of the swollen A segments. The model of AB block copolymer with moving B blocks can describe the behavior of interpolymer complexes between a long macromolecule and shorter polymer chains.

     

Preconditioned iterative methods for diffusion problems with high‐contrast inclusions

This paper is concerned with robust numerical treatment of an elliptic PDE with high‐contrast coefficients, for which classical finite‐element discretizations yield ill‐conditioned linear systems. This paper introduces a procedure by which the discrete system obtained from a linear finite element discretization of the given continuum problem is converted into an equivalent linear system of the saddle‐point type. Three preconditioned iterative procedures—preconditioned Uzawa, preconditioned Lanczos, and preconditioned conjugate gradient for the square of the matrix—are discussed for a special type of the application, namely, highly conducting particles distributed in the domain. Robust preconditioners for solving the derived saddle‐point problem are proposed and investigated. Robustness with respect to the contrast parameter and the discretization scale is also justified. Numerical examples support theoretical results and demonstrate independence of the number of iterations of the proposed iterative schemes on the contrast in parameters of the problem and the mesh size.