Modeling Termination Kinetics of Non‐Stationary Free‐Radical Polymerizations

Pulsed‐laser induced polymerization is modeled via an approach presented in a previous paper.^[1] An equation for the time dependence of free‐radical concentration is derived. It is shown that the termination rate coefficient may vary significantly as a function of time after applying the laser pulse despite of the fact that the change in monomer concentration during one experiment is negligible. For the limiting case of t ≫ c^–1 (k_pM)^–1, where c is a dimensionless chain‐transfer constant, k_p the propagation rate coefficient and M the monomer concentration, an analytical expression for k_t is derived. It is also shown that time‐resolved single pulse‐laser polymerization (SP–PLP) experiments can yield the parameters that allow the modeling of k_t in quasi‐stationary polymerization. The influence of inhibitors is also considered. The conditions are analyzed under which M (t) curves recorded at different extents of laser‐induced photo‐initiator decomposition intersect. It is shown that such type of behavior is associated with a chain‐length dependence of k_t.     

Magnetoresistance of a Ferromagnet/Superconductor/Ferromagnet Trilayer Microbridge Based on Diluted PdFe Alloy

JETP Letters - A negative magnetoresistive effect has been observed for ferromagnet/superconductor/ferromagnet (FSF) microbridges based on diluted ferromagnetic PdFe alloy containing as small as 1%...     

Spectral Characteristics of Half-Ring Quantum-Cascade Lasers

Optics and Spectroscopy - A cavity scheme based on a half-ring with different radii is proposed and fabricated for 7–8 μm quantum-cascade lasers. A quantum-cascade laser with a half-ring...     

A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of Calculations

For a tetrabutylammonium-selective electrode with a ion-exchange membrane, in the real-work scenario corresponding to the determination of selectivity coefficients by the IUPAC-recommended method of separate solutions, it is shown that of the results of calculations obtained within the framework of the dynamic diffusion model based on the use of the finite-difference technique substantially depend on of the chosen boundary conditions and the values of arbitrarily set simulation parameters. The key parameter that determines the quality of simulation results is the thickness of the elementary layer in the membrane phase, especially for low diffusion coefficients. It is found that the use of thin elementary layers in membranes and thick elementary layers in the aqueous phase makes it possible to combine the high quality with the high calculation rate. In simulating the long-term experiments, account should be taken of the accumulation of the potential-determining ion in the aqueous solution volume as a result of its displacement by a foreign ion from the membrane. A good correspondence between calculation data and experimental results is demonstrated.     

Ion-Beam and X-Ray Methods of Elemental Diagnostics of Thin Film Coatings

Physics of the Solid State - We show how the combined use of the methods of Rutherford backscattering of ions and X-ray fluorescence analysis under conditions of total external reflection of the...     

Replica neutron guides for experiments with ultracold neutrons

Technical Physics - The method for producing neutron guides for ultracold neutrons based on the replica method has been described. A comparative analysis of the quality of replica neutron guides,...     

Effect of phase transitions on the kinetic parameters of polytetrafluoroethylene deformation

The effect of solid-state phase transitions on the kinetic parameters of creep deformation in polytetrafluoroethylene has been studied by differential scanning calorimetry and a laser-interferometric creep rate meter. It has been shown that the deformation activation volumes and the elementary phase transition volume differ from each other by more than an order of magnitude. The crystalline component of this polymer becomes a liquid-crystal phase coexisting with an amorphous phase.

     

The Riemann–Roch theorem for the Dynnikov–Novikov discrete complex analysis

We prove an analog of the Riemann–Roch Theorem for the Dynnikov–Novikov discrete complex analysis.     

Bone cements in the calcium phosphate–chitosan systems containing magnesium and zinc

Based on studying the possibility of the introduction of physiologically important cations into a cementing system, technology of fabrication of highly deformable calcium phosphate cements has been developed for bone tissue reconstruction in medicine. It has been elucidated that the method of introduction of metal cations (magnesium, zinc) into the cementing system has an effect on the formation of the microstructure and properties. The in vitro degradation of composite cements in simulated body fluids has been studied. Results have been obtained for the development of cements with tailored properties, which can be varied in different ranges.