Heterogeneous distribution of chain mobility in nascent UHMWPE in the less entangled state

The structure of chain entanglements in the solid state is important for revealing the relationship of structure and properties of polyolefin. In this work, low-field solid-state ¹H NMR is used to study the chain dynamics of ultra-high molecular weight polyethylene (UHMWPE) in the solid state. It has been found that the relaxation distribution, analyzed by a multi-exponential inversion program, is an effective method to characterize the heterogeneous chain mobility. It is evidenced from the results that the UHMWPE in a less entangled state presents an obviously heterogeneous distribution of chain mobility in the non-crystalline phase, corresponding to its heterogeneous distribution of entangled points. In comparison, the commercial UHMWPE with a large number of entanglements shows a much more uniform mobility of the non-crystalline components. This heterogeneous distribution of chain mobility becomes even more critical after annealing the samples below the melting point, especially for the less entangled UHMWPE.     

Manufacture and measurement of combinatorial libraries of dielectric ceramics: Part II. Dielectric measurements of Ba1−xSrxTiO3 libraries

Applying combinatorial methods to materials science offers the opportunity to accelerate the discovery of more efficient dielectric ceramics. High-throughput methods have the potential to investigate the effects of a wide range of dopants on the dielectric properties, and to optimise existing systems, encouraging the short innovation cycles that the communications technology industry requires. The London University Search Instrument (LUSI) is a fully automated, high-throughput combinatorial robot that has the potential capability to produce large numbers of sintered bulk ceramic samples with varying composition in 1 day, as combinatorial libraries on alumina substrates. Ba_1−xSr_xTiO₃ (BST) libraries were produced by LUSI as a proof-of-principle, with x = 0–1 in steps of 0.1, and fired to 1350 and 1400 °C for 1 h. Part I of this paper described the manufacture and physical characterisation of BST libraries, showing a regular change in composition with x across the libraries. In this second part, the dielectric properties of BST libraries produced by LUSI are assessed at frequencies between 100 Hz and 1 MHz, and at temperatures between 150 and 500 K. Local piezoelectric properties were also characterised by scanning probe microscope (SPM). All measurements showed evidence of a clear functional gradient varying with x across the library, with measured _r corresponding to expected values for BST.     

Prediction of Ferroalloy Properties for Expert Evaluation of the Efficiency of their Use During Addition to Steel in a Ladle Furnace Unit

Metallurgist - A procedure is developed for calculating criteria for estimation and evaluation of chemical and structural micro-inhomogeneity of ferroalloy production melts. Models are proposed for...     

Optimizing the cross section of continuous-cast slab

New designs are proposed for the narrow mold walls in continuous slab-casting machines at OAO MMK, so as to reduce the incidence of defects at the corner of the slabs and enhance the quality of hot-rolled sheet.     

Modeling the influence of the Chelyabinsk meteorite’s bow shock wave on the Earth’s surface

The influence of the Chelyabinsk meteorite’s bow shock wave on the Earth’s surface is modeled. For solving the problem, a 3D statement is considered for its gas-dynamic and seismic parts. The determining equations of a gas-dynamic model and a seismic model are Euler equations with respect to the radiation heat exchange and the equations of linear elasticity theory, respectively. Two parts of the problem are matched by the direct mechanism of the disturbance transmission. A model seismic signal is compared with the real data. Modeling a seismic effect makes it possible to specify the estimate of the typical parameters of the phenomenon (height of the explosion, and the density and characteristic sizes of the meteorite).     

Producing hardfacing composite materials for ecologically safe technologies

The application of hardfacing materials for producing high-strength coatings on components working in abrasive wear conditions is one of the important directions of research into increasing the service life of road construction, agricultural and other types of equipment. However, in producing this equipment, the ecological safety requirements are sometimes ignored and this results in negative effects on the environment and the health of personnel. This article describes the results of scientific and research investigations of the team of authors to develop a cladding powder by the method of chemical gas phase deposition of nickel tetracarbonyl on the surface of aluminium oxide particles and application of the powder for producing wear-resistant coatings. The powder materials are deposited in a closed cycle excluding contact of the personnel with toxic substances and emission of contaminants into the atmosphere, resulting in a safe process. Plasma coatings with the required physical–mechanical properties have been produced. This confirms the efficiency of the approaches used in this case and increases the service life of working sections of machines subjected to abrasive wear.     

Nonlinear filtering of statistically connected video sequences based on hidden Markov chains

A method for the synthesis of algorithms for nonlinear filtering of statistically connected (correlated) video sequences of digital halftone images distorted by a white Gaussian noise is proposed. The method is based on the use of hidden Markov chains as a mathematical model for video sequences of digital halftone images, which, in limited observation intervals, can be represented by multidimensional Markov chains.