Prognostication of aging of polymeric composite materials

Experimental data demonstrate that a study of accelerated aging can enable prognostication of the working capacity and storage life of polymeric formulations used in aircraft components on the basis of changes in thermogravimetric constants of these polymeric formulations.     

Morphology of dispersed zinc deposited by pulsed current in a ZnCl<Subscript>2</Subscript>–NH<Subscript>4</Subscript>Cl electrolyte

Morphology of dispersed zinc deposits produced by pulsed electrolysis from aqueous ZnCl₂–NH₄Cl solutions was studied.     

Phase problem in three-beam X-ray diffraction

It is shown that, apart from the purely elastic scattering of X-rays, their inelastic coherent scattering by phonons can play, in some cases, a significant part in the formation of reflection curves for multiple X-ray diffraction. This process may affect the interference pattern for weak reflection, and it must be taken into account when extracting the triplet phase, as was demonstrated by an analysis of the experimental rocking curves obtained for the coplanar three-beam diffraction by a KDP crystal.     

Calculating Helix-to-Coil Transitions of Duplexes Formed by Phenazine-Conjugated Oligonucleotide, Using Flourescence Melting Data

A novel intercalating phenazine derivative (Pzn) was covalently linked to the 3-end of decathymidylate via a ribose residue of the dye. A fluorescence technique was used to study double helix formation by this conjugate with poly(rA) in aqueous solutions of neutral pH, at the presence of 0.1 and 1 M sodium ions. Proportionality between thermally induced changes in the fluorescence intensity of the free conjugate and bound one was revealed, that made it possible to calculate the helix-to-coil transition from fluorescence melting data using a simple equation. The transition curves were found to be in well conformity with those constructed from absorption measurements. It was shown that the attachment of Pzn significantly enhanced the stability of poly(rA) · (dT)₁₀ duplex due to intercalation of the dye chromophore into the adenine strand. The temperature of half-dissociation was increased by 12°C, and the stabilizing increment of standard free energy was 3.2–3.6 kcal/mol at 37°C.     

Contact interaction of the edges of a crack in a plane under harmonic loading

Kharkov Road Institute, Kharkov Aviation Institute, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 30, No. 12, pp. 75–79, December, 1994.     

Analysis of the film condensation process of vapor on a vertical finely serrated surface

The process of film condensation of vapor on vertical finely serrated surfaces is investigated. The analysis shows that owing to the specific conditions under which the distribution of the condensed film along the cooling surface is in the main affected by surface tension, the effectiveness of such surfaces may be several times higher than that of plain tubes.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol. 10, No. 3, pp. 93–97, May–June, 1969.     

Contact Interaction of the Faces of a Rectangular Crack under Normally Incident Tension–Compression Waves

A three-dimensional problem on the contact interaction between the faces of a rectangular crack under a normally incident harmonic tension–compression wave is considered. The problem is solved by using the method of boundary integral equations and an iterative algorithm. The contact forces and the discontinuity in the displacement of the crack faces are studied. The results obtained are compared with those for a finite plane crack.     

Three-Dimensional Dynamic Contact Problem for an Elliptic Crack Interacting with a Normally Incident Harmonic Compression–Expansion Wave

The paper deals with the three-dimensional dynamic problem for an elliptic crack interacting with a normally incident harmonic compression–expansion wave, considering the contact interaction of the crack faces. An asymmetric solution is obtained using an iteration algorithm developed earlier. Numerical results are presented     

Surface contact of elliptical crack under normally incident tension–compression wave

Surface contact interaction of a plane elliptical crack under normally incident tension–compression wave is solved by the method of boundary integral equations. The contact forces and the displacement discontinuity of the crack edges are examined. The dependence of the mode I stress intensity factor on the wave number is studied. The solution is compared with the results obtained for an elliptical crack without allowance for crack edges contact interaction.     

Nature of the silver precipitation obtained by cementation from thiosulphate solutions

The morphology and composition of the deposits formed on the surface of magnesium disk during cementation from thiosulphate solutions (0.0025–0.1M) [Ag(S₂O₃)₂]³⁻ + 0.5M S₂O₃ ²⁻ have been studied. A porous deposit with low adhesion is formed on the surface of the magnesium metal substrate. Within a wide range of [Ag(S₂O₃)₂]³⁻ ion concentrations, sulfur as well as silver are constituents of the deposit at the initial stages of cementation and at the end of the reaction. This is attributed to the electrochemical behaviour of magnesium in thiosulphate solutions resulting in the exceeding of current limit on cathode for pure silver reduction. Hence, parallel electrochemical reactions take place that are very close in their values to the standard redox potentials of reduction of [Ag(S₂O₃)₂]³⁻ ions to Ag⁰ and S₂O₃2− ions to S²⁻. Sulfur content in the cement deposits increases with the decrease in [Ag(S₂O₃)₂]³⁻ ion concentration and increase in cementation time. This tendency is also observed with the decreasing solution temperature.