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71.
The thermal nonlinearity of superconducting films in an electromagnetic field is investigated theoretically. It is shown that the transition of the superconductor from the superconducting to the normal state as a result of Joule heating exhibits hysteresis, corresponding to the onset of a bistable state in the film. It is shown that as a result of the nonuniformity of the amplitude of the electromagnetic field along the surface of the superconducting film, above some threshold a normal-phase domain forms in the superconductor. It is ascertained that the temporal evolution of the domain walls exhibits the character of thermal autowaves of heating or cooling. The nonlinear radio-frequency characteristics (reflection and transmission coefficients and frequency responses) of a stripline resonator under conditions of thermal nonlinearity are calculated. Zh. Tekh. Fiz. 67, 81–89 (October 1997)  相似文献   
72.
New solutions of the problem of describing hyperbolic surfaces of specified negative Gaussian curvature are obtained. The answer is given in terms of 9 functions.Translated from Matematicheskie Zametki, Vol. 52, No. 3, pp. 78–88, September, 1992.The first author (D. A. K.) wishes to express his appreciation to A. I. Bobenko for useful discussion.  相似文献   
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Tarnish layers are formed in the heat affected zone during the welding of steels and nickel based alloys. They commonly consist of oxides of the alloying elements. The corrosion behaviour of welded components is generally influenced by the thickness and composition of the oxide films. In the following the corrosion behaviour of annealed samples cut from NiMo28 and NiMo16Cr16Ti is investigated, correlating XPS, SNMS and SEM/EDX data to their pitting corrosion potentials.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday  相似文献   
75.
The acid-base properties of 4,6-dimethyl- and 4,6-diamino-2(1H)-pyrimidinethiones (1 and2) were investigated by potentiometric titration. Dissosiation of1 and protonation of its anion occur in two steps, the first of which affords the deprotonated dimer [HA2). The relative stability of the dimer depends on the nature of the solvent. The effect of kinetic factors on the acid-base behavior of1 was elucidated by comparing the results of potentiometric titrations carried out under various kinetic conditions. It was concluded that the difference between the acid-base properties of1 and2 results from the electron-donating effect of the amino groups.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2145–2148, December, 1994.  相似文献   
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The reactions of 1,3-bis(-bromobutyl- or -pentyl)-6-methyluracil with 1,3-bis(-ethylaminobutyl- or -pentyl)-6-methyluracil afforded pyrimidinophanes containing N atoms in bridging polymethylene chains. Individual geometric isomers of pyrimidinophanes were isolated. The structure of one of these isomers was established by X-ray diffraction analysis. Quaternization of the bridging N atoms with o-nitrobenzyl bromide gave rise to water-soluble pyrimidinophanes.  相似文献   
79.
A new macrocycle including pyrimidine fragments, 12,23,36-trimethyl-24,40-dioxo-15,33-dithia-2,9,13,22,26,35,38,39-octaazatetracyclo[32.3.1.110,14.122,26]tetraconta-1(38),10(39),11,13,23,34,36-heptaene, was synthesized. According to the data of IR and UV spectroscopy and HF/6-31G** quantum-chemical calculations, macrocyclic compounds of this series in crystal exist in the amino form, one NH group of which is likely to be involved in intramolecular hydrogen bond, and the other, in intermolacular hydrogen bond. The strength of the latter depends on the macroring size. In solution, the above structures are supplemented by conformers containing both intramolecularly H-bonded and free amino groups, predominantly with trans structure of the HÄNÄCÍN fragment. The imino form of the aminopyrimidine moieties is hardly probable.  相似文献   
80.
A procedure for thermal-vacuum tests for elements of real rod structure in spaces is presented. The procedure makes it possible to determine the heat conductivity of polymer-composite materials in a wide range of temperatures. According to the procedure, the tested samples are cooled by liquid nitrogen and heated by a contact method. The experimental data are processed by solving the coefficient inverse problem of heat conductivity.  相似文献   
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