Competitive hydrogen bonding mechanisms underlying phase behavior of triple poly(N‐vinyl pyrrolidone)–poly(ethylene glycol)–poly(methacrylic acid‐co‐ethylacrylate) blends

Differential scanning calorimetry (DSC) of triple blends of high molecular weight poly(N‐vinyl pyrrolidone) (PVP) with oligomeric poly(ethylene glycol) (PEG) of molecular weight 400 g/mol and copolymer of methacrylic acid with ethylacrylate (PMAA‐co‐EA) demonstrates partial miscibility of polymer components, which is due to formation of interpolymer hydrogen bonds (reversible crosslinking). Because both PVP and PMAA‐co‐EA are amorphous polymers and PEG exhibits crystalline phase, the DSC examination is informative on the phase state of PEG in the triple blends and reveals a strong competition between PEG and PMAA‐co‐EA for interaction with PVP. The hydrogen bonding in the triple PVP–PEG–PMAA‐co‐EA blends has been established with FTIR Spectroscopy. To evaluate the relative strengths of hydrogen bonded complexes in PVP–PEG–PMAA‐co‐EA blends, quantum‐chemical calculations were performed. According to this analysis, the energy of H‐bonding has been found to diminish in the order: PVP–PMAA‐co‐EA–PEG(OH) > PVP–(OH)PEG(OH)–PVP > PVP–H₂O > PVP–PEG(OH) > PMAA‐co‐EA–PEG(? O? ) > PVP–PMAA‐co‐EA > PMAA‐co‐EA–PEG(OH). Thus, most stable complexes are the triple PVP–PMAA‐co‐EA–PEG(OH) complex and the complex wherein comparatively short PEG chains form simultaneously two hydrogen bonds to PVP carbonyl groups through both terminal OH‐groups, acting as H‐bonding crosslinks between longer PVP backbones. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Development of a Commercial Technology for Plasma Arc Remelting of a Nitrogen-Bearing 05Kh21AG15N8MF Steel

Steel 05Kh21AG15N8MF forgings 250 mm in diameter with a nitrogen content higher than 0.60%, which is necessary for a high-strength austenitic structure, are fabricated by plasma arc remelting. An experimental batch and strips are made of this steel. The chemical composition, the macrostructure, the mechanical properties, the intergranular corrosion resistance, and the hardness of the forgings are studied.     

Structure and properties of a high-temperature austenitic steel at high temperatures

The structure of a high-temperature austenitic 12Kh15N16M2TR steel, which is promising for manufacturing steam superheater tubes, is studied after long-term thermal holding under stress. The type, morphology, and matrix arrangement of excess-phase particles that form during thermal holding are found. The structure of the alloy correlates with its high-temperature strength, and the mechanical properties obtained during short-time tensile tests in the temperature range 20–730°C are compared to the results of high-temperature strength tests.     

Effect of alternating electric current on mechanical properties and structure of industrial accumulator alloys

The influence of alternating electric current on the mechanical properties and structure of industrial accumulator lead alloys during their crystallization is studied. The processes that evolve in the melt under the effect of electric current are described qualitatively and the results are explained.     

On optimum power allocation for the V-BLAST

A unified analytical framework for optimum power allocation in the unordered V-BLAST algorithm and its comparative performance analysis are presented. Compact closed-form approximations for the optimum power allocation are derived, based on average total and block error rates. The choice of the criterion has little impact on the power allocation and, overall, the optimum strategy is to allocate more power to lower step transmitters and less to higher ones. High-SNR approximations for optimized average block and total error rates are given. The SNR gain of optimization is rigorously defined and studied using analytical tools, including lower and upper bounds, high and low SNR approximations. The gain is upper bounded by the number of transmit antennas, for any modulation format and type of fading channel. While the average optimization is less complex than the instantaneous one, its performance is almost as good at high SNR. A measure of robustness of the optimized algorithm is introduced and evaluated. The optimized algorithm is shown to be robust to perturbations in individual and total transmit powers. Based on the algorithm robustness, a pre-set power allocation is suggested as a low-complexity alternative to the other optimization strategies, which exhibits only a minor loss in performance over the practical SNR range.     

Special Features of Steels Alloyed with Nitrogen

The role of nitrogen as an alloying element that stabilizes austenite in steels and makes it possible to replace nickel, manganese, and other austenization promoters without deterioration of mechanical and special properties of the metal is considered. Put into practice this could reduce the volume of mining of the mentioned elements. Methods for introducing nitrogen into iron alloys are described. The mechanical properties of nitrogen-bearing steels are considered. It is shown that such steels with a structure of nitrogen martensite possess a specific strength under static and cyclic loads no worse than the strength of light structural alloys and have better fracture toughness and technological properties than the latter. The replacement of light alloys by such steels should reduce the consumption of energy in the production.     

Thermal stability of the structure of a high-temperature nickel alloy fabricated by two different technologies

High-temperature treatment of the melt (HTTM) is a very simple and available technique for stabilizing and improving the service properties of parts. It tonsists in heating the melt to a certain critical temperature, a hold, and cooling. The present paper is devoted to the effect of HTTM, the standard heat treatment and long isotherm holds at the service temperatures on the structure and properties of castable high-temperature nickel alloy ZhS6U. Translated from Metallovedenic i Termicheskaya Obrabotka Metallov, No. 12, pp. 27–30, December, 1999.     

Phage mimotopes of monoclonal antibodies against plasma membrane Ca2+-ATPase

Libraries of random phage-displayed pentadeca- and hexapeptides were screened with the use of four monoclonal antibodies against the human plasma membrane Ca2(+)-ATPase. Bacteriophages specifically binding the antibodies were selected, and the amino acid sequences of the expressed peptides (mimotopes) were determined. Mimotopes for three antibodies (8B8, 2D8, F9) did not correspond to the Ca2(+)-ATPase sequence. Pentadecapeptides for the 7C8 antibodies displayed similarity to the fragment Glu1097-Arg1113 of the Ca2(+)-ATPase calmodulin-binding site. However, these antibodies failed to bind recombinant fragment Leu1069-Leu1220; therefore, the structure of this epitope remains obscure. This work opens a series of studies of the plasma membrane Ca2(+)-ATPase structure by means of monoclonal antibodies and the phage display method.     

Hydrazidation of fibres based on acrylonitrile copolymers

Conclusions A scheme has been suggested for the catalytic effect of carboxyl groups on the conversion of -CN groups in acrylonitrile copolymers in modification with hydrazine hydrate.It has been shown that the hydrazidation of acrylonitrile copolymers is accompanied by the appearance of stable free radicals, the rate of formation of these correlating with the rate of nitrile group conversion.The suggestion has been made that a three-dimensional chemical network which is formed during hydrazidation aids in stabilizing the radicals.A chemisorptive fibre with anion-exchange groups has been prepared, which has satisfactory physico-mechanical and sorptive properties.Translated from Khimicheskie Volokna, No. 4, pp. 10–12, July–August, 1988.