Theoretical estimation of discontinuity flaw of adhesive contacts between multilayer elements of the liquid metal blanket in a fusion reactor

A technique developed for calculating the discontinuity flaw of an adhesive contact and the adhesion energy for two bodies makes it possible to take into account these effects in designing a multilayer cermet wall (insulating barrier) of the liquid-metal blanket in a fusion-type reactor. The technique is based on a model of a linearly elastic medium, in which strains are proportional to external forces, and on the assumption that any body in equilibrium possesses minimum internal potential energy. Expressions are derived for calculating the area of an adhesive contact between two bodies and their adhesion energy. Calculation data illustrate the dependence of these two parameters on the values of the Young modulus and Poisson’s ratio for various pairs of materials, including the most suitable materials for insulating barriers of liquid-metal blankets.     

Stereoselective synthesis of cis- and trans-2′,5′-disubstituted N-arylpyrrolo[3′,4′:1,9](C60-I h )[5,6]fullerenes by the 1,3-dipolar cycloaddition of azomethine ylides from dialkyl aziridinedicarboxylates to fullerene C60

A stereoselective method for the synthesis of 2′,5′-disubstituted N-arylpyrrolofullerenes from anilines, alkyl glyoxylates, alkyl diazoacetates, and fullerene C₆₀ was proposed. The key step of the synthesis is the 1,3-dipolar cycloaddition reaction of fullerene with azomethine ylides generated by heating of dialkyl aziridinedicarboxylates. The thermal opening of the aziridine ring to azomethine ylide and the cycloaddition of the latter to C₆₀ at 100 °C are nearly completely stereoselective: only trans-adducts are formed from cis-aziridines, whereas trans-aziridines give exclusively cis-adducts.     

Monofluorinated aziridines in asymmetric synthesis of chiral fluorinated prop-2-yn-1-amines

Nonracemic C-fluoroaziridines were synthesized for the first time by reaction of fluorocarbene with N-diphenylmethylidene-substituted natural amino acid esters. The products were shown to be used in asymmetric synthesis of chiral fluorinated prop-2-yn-1-amines via one-pot process involving isomerization of 2-fluoroaziridines into α-fluoro imines and subsequent reaction with alkynyldifluoroborane generated in situ.     

Ion exchange and redox reactions in metal-ion exchanger nanocomposites

The reducing sorption of oxygen dissolved in water with the use of metal-containing nanocomposites is considered taking into account the bifunctional nature of sorbents possessing both redox and ion exchange properties. A physicochemical model of the process including metal particle dispersity, their distribution over a grain, and the special features of the chemical oxidation of metals was used. Based on this model, a mathematical formulation of the problem including the stage of the interdiffusion of metal ions (metal oxidation products) and hydrogen ions (matrix counterions) is given.     

Muon Tomography of Large-Scale Objects

Physics of Atomic Nuclei - Cosmic ray muons arriving from the upper hemisphere to the Earth’s surface, are currently used to develop methods of muonography (analogous to radiography) of the...     

Correction to: Comments on the shape of voltammetric plots of reversible stoichiometric reactions for linear potential scan

Theoretical studies of the shape of the linear potential sweep voltammogram for a reversible electron-transfer reaction have been overviewed. Two different expressions for the current–potential dependences have been proposed therein. Our analysis has shown that this divergency originates from the implicit difference of the assumptions on the pretreatment procedure before the beginning of the potential sweep. Two principal variants of such pretreatment have been considered in detail: (1) potentiostatic exposure to the potential equal to the starting one for the subsequent sweep, E = E_i; (2) OCP (zero current) regime. In the former variant, the potentiostatic regime during the pretreatment period shifts the surface concentrations from their bulk values to the steady-state ones (dependent on E_i). It induces current passage of a diminishing amplitude due to the diffusion-layer expansion. If the pretreatment period is sufficiently long (well over 10 s in water) a time-independent distribution of the reactant and product concentrations is established across the steady-state diffusion layer accompanied by the current stabilization, i ≅ i_ss. At the starting moment of the potential sweep, t = t_i, both the potential and the surface concentrations are continuous as functions of time so that the amperometric response for t > t_i increases in time from its steady-state value, i ≅ i_ss, due to the potential sweep, with its gradual approach to a universal dependence which corresponds to the response of the system if the potential sweep starts very far from the half-wave potential where the equilibrium concentration of the reaction product is extremely low. In the latter variant of pretreatment there is a stepwise change of the potential and of the surface concentrations at t = t_i; it leads to a Cottrell-type contribution to voltammetric current which in the course of the potential sweep is supplemented by another contribution corresponding to the above universal response where the sweep starts very far from the half-wave potential. As a result, after a relatively short relaxation period the current responses in both variants approach its universal behavior. Method of a direct determination of the number of transferred electrons per consumed reactant species has been proposed. Approximate analytical expression for the dependence of current on time after passage of the current's peak has been derived. Predicted features have been verified with the use of a well-known reversible reaction: ferrocene oxidation in acetonitrile.

     

Hydrogen-Chlorate Electric Power Source: Feasibility of the Device,Discharge Characteristics and Modes of Operation

A power source based on the current-generating reaction of aqueous chlorate-to-chloride reduction by molecular hydrogen would provide as much as 1150 Wh per 1 L of reagent storage (for a combination of 700 atm compressed hydrogen and saturated aqueous solution of lithium chlorate) at room temperature, but direct electroreduction of chlorate only proceeds with unacceptably high overvoltages, even for the most catalytically active electrodes. In the present study, we experimentally demonstrated that this process can be performed via redox-mediator catalysis by intermediate products of chlorate reduction, owing to their participation in homogeneous com- and disproportionation reactions. A series of current–voltage and discharge characteristics were measured for hydrogen-chlorate membrane–electrode assembly (MEA) cells at various concentrations of chlorate and sulfuric acid under operando spectrophotometric monitoring of the electrolyte composition during the discharge. We established that chlorine dioxide (ClO₂) is the key intermediate product; its fraction in the electrolyte solution increases progressively, up to its maximum, equal to 0.4–0.6 of the initial amount of chlorate anions, whereas the ClO₂ amount decreases gradually to a zero value in the later stage. In most discharge experiments, the Faradaic yield exceeded 90% (maximal value: 99%), providing approximately 48% chemical energy storage-to-electricity conversion efficiency at maximal power of the discharge (max value: 402 mW/cm²). These results support prospect of a hydrogen-chlorate flow current generator as a highly specific energy-capacity source for airless media.     

On asymptotic normality of sequential LS-estimate for unstable autoregressive process AR(2)

For estimating parameters in an unstable AR(2) model, the paper proposes a sequential least squares estimate with a special stopping time defined by the trace of the observed Fisher information matrix. It is shown that the sequential LSE is asymptotically normally distributed in the stability region and on its boundary in contrast to the usual LSE, having six different types of asymptotic distributions on the boundary depending on the values of the unknown parameters. The asymptotic behavior of the stopping time is studied.