A Comprehensive Analysis of Macrosegregation Formation During Twin-Roll Casting

Metallurgical and Materials Transactions B - A two-phase Eulerian–Eulerian volume-averaged model is used to predict the formation of macrosegregation during the twin-roll casting of...     

Theory of chromatography of complex cyclic polymers: eight-shaped and daisy-like macromolecules

A theory of chromatography of eight-shaped, trefoil-shaped and daisy-like polymers is developed. For a model of an ideal chain in a slit-like pore exact equations and a number of approximate formulae for the distribution coefficient K of these polymers are derived. All modes of chromatography of complex macrocycles of arbitrary molar mass in both narrow and wide pores are covered by the theory. It is shown that complex macrocycles always elute after linear polymers and rings of the same contour length. The effective chromatographic radius of eight-shaped and daisy-like macromolecules, which determines retention in size-exclusion chromatography are calculated. The increase in the retention with molar mass is predicted for all types of macrocycles at the critical interaction condition. Non-monotonous molar mass dependences of K are found at pre-critical interaction. We simulate separation of complex cyclic polymers from linear and ring precursors, discuss possibilities to separate symmetric and asymmetric eights, and speculates on the use of chromatography for separating knotted and unknotted polymer rings. According to the theory, the chromatography under the critical and pre-critical interaction conditions is expected to be especially efficient in these and similar problems. Boundary conditions for the theory and its applicability to real systems are discussed.     

Peculiar electric properties of polarized layer in alkaline silicate glasses

Broadband dielectric spectroscopy (BDS) was applied to study polarization phenomena in alkaline silicate glasses, in particular, properties and structure of subsurface (anodic) polarized layers forming in poling with deposited film electrodes of different structures. A model of poled glasses which does not contradict experimental data is proposed. In accordance with the model, a poled glass is presented as two resistor-capacitor circuits in a series connection, one of which is the polarized layer and another is the rest of the sample. It is found that the electric properties of the layers essentially depend on the structure of the anodic electrode used in glass poling. It is also shown that the dielectric response of poled glass samples is mainly determined by the electric properties of the submicron polarized layers and this gives an opportunity to reveal specific properties of the layers rather than ones of the glass sample bulk. Revealed temperature dependence of DC conductivity of the polarized layers obeys Arrhenius's law, and determining activation energy does not depend on the electrode. Finally, it is noted that today above-mentioned information about polarized layers can be obtained only by BDS.     

Temperature-sensitive nanocapsules for methane storage

A nanocapsule is investigated for methane storage purposes. The nanocapsule is a dasiabucky shuttledasia (or a nanopeapod) with a hole in its structure. The bucky shuttle has a diameter of a nanotube (10, 10) and is 180dasiaAdasia in length. A K@C₆₀ ¹⁺ endohedral complex is encapsulated into the nanocapsule. Simulations are performed by a molecular dynamics method. The internal dynamics of the system are investigated - the nanocapsule, the K-C₆₀ ¹⁺ endohedral complex and methane molecules. The closing of the nanocapsule can be induced by the K@C₆₀ ¹⁺ ion transition as a result of applying an electric field. There is no need to keep the electric field at the storage stage, because the K@C₆₀ ¹⁺ ion cannot overcome the hole area owing to the effect of forces created in the hole of the nanocapsule. The opening of the nanocapsule takes place under the heating of the system. It is shown that this is a temperature-sensitive nanocapsule for methane molecule storage under zero external pressure and a temperature of 300 K. The nanocapsule retains 71 methane molecules (3.06 mass ) and releases gas at 350 K.     

Synthesis of mesostructured TiO2-based material and its functionalization with silver nanoparticles

We report the results of a template synthesis of a three-dimensional nanostructured material based on titanium(IV) oxide modified with silver nanoparticles. The chemical composition and structure of the material have been determined by scanning electron microscopy, IR spectroscopy, and X-ray diffraction.     

A theory of topological separation of linear and star-shaped polymers by two-dimensional chromatography

Topology influences the size of macromolecules, but polymers are usually distributed with respect to molar mass, which also results in the size distribution within a polymeric sample. Due to this fact size-exclusion chromatography (SEC) is not able to separate even moderately polydisperse polymers by topology; the same is also true for the adsorption chromatography (AC). The full separation by molar mass and topology is not possible by any single mode of chromatography. These problems can be solved by means of two-dimensional chromatography which combines SEC and AC mechanisms. A theory of interactive chromatography of linear and star-shaped ideal-chain polymers is used to analyze two-dimensional chromatographic separation of polydisperse linear and star polymers. Basing on this theory, we simulate 2D-chromatograms for model mixtures of polydisperse linear and star-shaped polymers of equal average molar mass, and demonstrate that 2D-separation of such polymers by topology is possible. A possibility to separate symmetric and very asymmetric stars by 2D-chromatography is predicted. The influence of the molar-mass heterogeneity, pore size and adsorption interaction parameter on the 2D chromatographic pattern is analysed, and the conditions for a good separation of linear and star polymers are formulated. The theoretical results are in a qualitative agreement with the experimental data, which have been reported previously by Gerber and Radke.     

Development and use of special measuring means for monitoring the equipment in nuclear power plants with VVÉR reactors

This article is devoted to the development, manufacture, and use of special measuring means for startup-adjustment and operational monitoring of equipment in nuclear power plants with VVéR reactors. The characteristics of the measuring means developed by the Experimental Design Office Gidropress are presented. __________ Translated from Atomnaya énergiya, Vol. 99, No. 6, pp. 466–470, December, 2005.