Dynamic adhesive strength of fiber-polymer systems

A new device for studying the dynamic adhesive strength is created. A procedure for determining the dynamic adhesive strength in fiber—polymer systems under impact loading (pull-out technique) is developed. The adhesive strength of the interface of polymer—steel wire joints formed by polymers of different chemical nature (epoxy resin, polysulfone, and polypropylene) is examined. It is shown that the dynamic adhesive strength grows as the loading rate increases for all the systems under investigation and that the relationship between the adhesive strength and the loading rate, , over a wide range of rates can be described by two straight lines corresponding to the quasi-static and impact loading, respectively. When passing from the quasi-static to dynamic loading, the character of scale relations of the adhesive strength does not change.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 6, pp. 689–700, November–December, 1999.     

Relativistic precession of a gyroscope. I. Circular orbits

The relativistic precession of the rotation axis of a spherical gyroscope is treated in the framework of monadic specification of the frame of reference. It is found that the precession in the comoving frame compensates the rotation of the frame of reference itself. An exact expression is derived for the angular velocity of precession for motion of a gyroscope in circular epiequatorial orbits in the Kerr field. The results are compared with the approximate expression obtained by Schiff. Numerical examples are considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 64–68, March, 1981.     

Phase equilibria in water-protein-polysaccharide systems

Summary Phase separation and thermodynamic stability of water (W) — casein (C) — neutral polysaccharide (NPS) systems have been studied. Dextrans of different molecular weights D40, D150, D500 and D2000 (10^–3 M _w =40, 150, 500, 2000), ficoll (10^–3 M _w =400) and amylopectin (10-^–6 M _w = 38) have been used as neutral polysaccharides. Phase diagrams of W-C-NPS systems, as well as their effect on the thermodynamic stability of the molecular weight and structural features of polysaccharides, low-molecular salts, pH and temperature have been considered. There has been shown the similarity of conditions under which the stability of W-C-NPS systems is disturbed, resulting in their separation, as well as conditions favorable to self-association of casein. A decrease in the pH value, an increase in the ionic strength and a rise in temperature are favorable both to self-association of casein and separation of W-C-NPS systems. Proceeding from this fact and from the results obtained earlier for W-C-acidic polysaccharide and W-albumin-D-glucan systems, a conclusion is drawn as to the common nature of the relationship between self-association of polymers and their compatibility. At constant temperature and pH, the stability limit of W-C-NPS systems is determined by the concentrations of polymers (w ₂ andw ₃) and salt (C₄). The totality of cloud points C ₄ ^* (pH) at givenw ₂ andw ₃ being considered as the stability limit. It is also shown that the relationship C ₄ ^* (pH) is an increasing function within the range of pH values from 6.5 to 11.5 and in all cases where lim C ₄ ^* (pH)=0. The sequence of values 947-1PHPH IEP C ₄ ^* is determined by the nature of the low-molecular salt (Na₂SO₄ NaCl KSCN) and the specific nature of the polysaccharides (D2000 amylopectin < D 150 < ficoll < D 40).W-C-NPS-NaCl have been found to possess a lower critical point in a system of coordinates: temperature-composition. W-C-NPS-urea (6M) systems feature, in a system of coordinates: pH-polymer concentration, two areas of separation, overlapping at sufficiently high total concentrations. This fact is indicative of the specific nature of interaction of casein macromolecules capable of association near the isoelectric point due to interaction of charge fluctuations and, in the acid region, due to interaction of non-ionized carboxyl groups. The obtained results are discussed with the stability limit being expressed in terms of second virial coefficients.With 13 figures and 2 tables     

Effective excitation cross section and lifetime of Er<Superscript>3+</Superscript> ions in Si: Er light-emitting diodes fabricated by sublimation molecular-beam epitaxy

A series of Si: Er electroluminescent diode structures is fabricated by sublimation molecular-beam epitaxy. The diode structures efficiently emit at a wavelength of 1.5 μm under conditions of p-n junction breakdown at room temperature. The effective cross section of excitation of Er³⁺ ions with hot carriers heated by the electric field of a reverse-biased p-n junction and the lifetime of Er³⁺ ions in the first excited state ⁴I_13/2 are determined for structures that emit in a mixed breakdown mode and are characterized by the maximum intensity and excitation efficiency of the Er³⁺ electroluminescence.     

In memory of Sergei A. Kornilov

Orbituary

In memory of Sergei A. Kornilov     

Selective synthesis of the C3v isomer of C60h18

[chemical structure: see text]. C60H18 has been produced by hydrogenation of C60 at 100 bar H2 pressure and 673 K for 10 h. We have investigated the crude material without any purification by use of 1H NMR, 13C NMR, and IR spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. We show that the crude material consists of 95% of the C3v isomer of C60H18.