Showing papers by "Russian Academy of Sciences published in 1968"

Linear and Quasi-linear Equations of Parabolic Type

Abstract: Introductory material Auxiliary propositions Linear equations with discontinuous coefficients Linear equations with smooth coefficients Quasi-linear equations with principal part in divergence form Quasi-linear equations of general form Systems of linear and quasi-linear equations Bibliography.

Self-oscillations in glycolysis. 1. A simple kinetic model.

Abstract: The paper describes a simple kinetic model of an open monosubstrate enzyme reaction with substrate inhibition and product activation. A comparison between the model and the phosphofructokinase reaction shows a close resemblance between their dynamical properties. This makes it possible to explain qualitatively most experimental data on single-frequency oscillations in glycolysis. A mathematical analysis of the model has shown the following. 1In the model, at a definite relationship between the parameters, self-oscillations arise. 2The condition of self-excitation is satisfied more readily with a lower source rate, larger product sink rate constants, lower product-enzyme affinity and higher enzyme activity. 3Self-oscillations exist only in a certain range of values of the parameter determining the degree of substrate inhibition. This range increases with decreasing source rate. Too strong or, conversely, too weak substrate inhibition leads to damped oscillations. 4The period of self-oscillations depends on the degree of substrate inhibition, the source rate, the sink rate constant, the enzyme activity, the affinity of the substrate and the product for the enzyme; it decreases with an increase in these values. 5With an increase in the relative sink rate constant the steady state amplitude of self-oscillations initially increases until a definite maximum is reached and then drops to zero. 6A self-oscillatory state in the phosphofructokinase reaction exists only when the maximum rate of this reaction is essentially higher than the source rate, and lower than the maximum rate of the reactions controlling the sink of the products. 7An experimental investigation of self-oscillations in the phosphofructokinase reaction may be considerably simplified by using a reconstituted system consisting of a small number of reactions with an irreversible sink of the products and artificial substrate supply. In this case the above relationship (section 6) should hold.

The theory of metasomatic zoning

Abstract: The main features of the theory of metasomatic zoning, developed by the author, are here exposed. The basic differential equations of metasomatic zoning, of the infiltration as well as of the diffusion type, are deduced for the conditions of local equilibrium, the kinetic phenomena being neglected. The sharpness of the fronts of replacement and other regularities of metasomatic columns are established and the differences between infiltration and diffusion columns are shown. The mathematical model of the “outstripping wave of acidic components” in the flow of postmagmatic solutions is discussed, in relation with the “acidic filtration effect”, i.e., with the higher filtration rate of acidic components as compared with basic ones. The passage of this acidity wave causes the acid leaching of metals out of rocks and their subsequent concentrated redeposition in veins. One may therefore speak of a lateral and vertical hydrothermal acid-base differentiation.

Very high frequency radiowave scattering by a disturbed sea surface Part I: Scattering from a slightly disturbed boundary

Abstract: This paper considers the scattering of very high frequency (VHF) electromagnetic waves from a random weakly corrugated surface by the perturbation method. The calculations show that the scattering has a resonant nature, i.e., only certain Fourier components of the surface shape are responsible for scattering in every given direction. Experiments carried out in a water basin confirmed the results of the calculations. The backscattered intensity is proportional to the spectral density of those Fourier components of the surface oscillation that have a resonant space period. In these experiments, resonant maxima of the reflected signal corresponding to the second-order approximation of the perturbation method were also observed. The frequency spectrum of the scattered electromagnetic field is also investigated. It is shown that the spectrum of the scattered radiation is shifted from the incident frequency by a certain value related to the phase velocity of the resonantly scattering Fourier component of the surface shape. The experimentally observed dependence of the scattered intensity on frequency and the theoretically predicted one are very much alike.

Very high frequency radiowave scattering by a disturbed sea surface Part II: Scattering from an actual sea surface

Abstract: A two-scale model of rough surfaces is considered which permits theoretical interpretation of the features of very high frequency (VHF) scattering from such surfaces (say, from a sea surface). The scattering surface is assumed to be a superposition of small-scale ripple and large waves (swell). Reflection from the latter may he considered by the Kirchhoff approximation. The spatial spectrum of corrugations is taken into consideration; the calculations based on this model help to give an explanation of the behavior of the scattered intensity as a function of the angle of incidence \psi , and to establish which factors affect this dependence at various values of \psi - Theoretically predicted dependence of the scattered intensity upon radio wavelength \lambda , depolarization of the scattered signal, and other features of the scattered radiation are in good agreement with the experimental data obtained from direct measurements. Frequency spectra of the backscattered signal were also investigated (experimental measurements were carried out at wavelengths 3.2 cm, 10 cm, 50 cm, 1.5 m, and 4 m). Observed shifts of the central frequency agree with results of other authors (for the range of \lambda = 3 cm to 200 m). The measured values of the spectrum width appeared approximately twice those theoretically calculated. This may be explained by the influence of dissipative processes and of fluctuations of the skin-deep layer drift velocities. Space correlation of the backscattered signal was also investigated (both theoretically and experimentally). 50 percent decorrelation occurs at distances compared with dimensions of a wave slope.

The Theory of Elastic Media with Microstructure and the Theory of Dislocations

Abstract: Different phenomenological theories of generalized Cosserat continua have been developed in the well-known works of Aero, Eringen, Green, Grioli, Gunther, Koiter, Kuvshinski, Mindlin, Naghdi, Noll, Palmov, Rivlin, Toupin, Truesdell and others. These theories approximately take into account the inner degrees of freedom and the existence of a scale parameter in a medium. From this point of view the classical theory of elasticity may be considered as an asymptotic theory and the above mentioned ones as next order approximations1.

Probable changes in the composition of sea water during the course of geological time1

Abstract: SUMMARY The initial geological facts are considered on which the author bases on of the possible variants of the evolutionary scheme of the stratisphere, ocean and atmosphere composition from the Early Precambrian to the Recent. Some general tendencies and causal relationships in the development of these external shells of the earth are traced. The object of this paper is to trace the evolution of the compositions of the sedimentary shell, the world ocean and the atmosphere from the Early Precambrian to the Recent period. Further, an attempt is made to elucidate some general tendencies in the development of these outer shells of the earth, in the changes of magmatic rock composition and in the history of tectonic movements and to establish causal relationships between them. The solution suggested is one of the possible variants, as the data used and the assumptions that have been made are not uniformly reliable for the different stages of geological history.

Electromagnetic waves in metals in a magnetic field

Abstract: (1968). Electromagnetic waves in metals in a magnetic field. Advances in Physics: Vol. 17, No. 69, pp. 605-747.

The role of neurohumors in early embryogenesis. II. Acetylcholine and catecholamine content in developing embryos of sea urchin.

Abstract: In a previous paper (Buznikov, Chudakova & Zvezdina, 1964) it has been reported that serotonin (5-hydroxytryptamine, 5-HT) may be involved in early embryogenesis in various groups of animals. This conclusion was confirmed by Baker9s recent publication (Baker, 1965) concerning 5-HT synthesis in Xenopus laevis embryos. Some other low molecular weight substances, neurohumors or related compounds, are known to be synthesized in fertilized eggs as well. Acetylcholine (ACh) synthesis in sea-urchin eggs and embryos was demonstrated by Numanoi (1953, 1955, 1959, 1961). It seems possible that ACh can be synthesized in fertilized insect eggs as well (Morley & Schachter, 1963; Schachter, 1964). The synthesis of another neurohumor, dopamine (DA), in early insect embryos seems to be indisputable (Furneaux & McFarlane, 1965). However, in most cases changes in the level of neurohumors with age have not been studied. In the present paper data concerning the change of concentration with age of ACh and catecholamines (adrenaline (A) and noradrenaline (NA)) in early sea-urchin embryos will be presented.

Recent studies on the role of microorganisms in the cycling of substances in lakes1

Abstract: This paper presents a review of current trends in research in the Soviet Union on the ecology of aquatic bacteria. The paper shows an increasing emphasis on in situ measurements of the rate or extent of conversion of carbon, nitrogen, sulfur, and iron from one form to another and on the bacteria responsible for these conversions. Theoretical considerations and results of several studies are summarized. These include measurement of bacterial biomass production and nitrogen fixation with isotopes, factors affecting decomposition of water humus in bog lakes, annual succession of iron bacteria in relation to the cycling of iron, nitrogen exchange between bottom sediment and benthic waters, the concept and calculation of nitrogen balance in a lake, and the bacteria responsible for the oxidation of sulfur. An attempt is made to incorporate this information into flow diagrams showing the dynamics of the cycling of the four elements discussed.

Optical Absorption by Polarons in Rutile (TiO2) Single Crystals

Abstract: The optical absorption in rutile single crystals doped with Nb and other impurities as well as partially reduced is investigated in the temperature range 10 to 900°K. It is shown that the spectrum and the magnitude of the optical absorption by current carriers can be satisfactorily explained in terms of the small polaron theory. The oscillator strength for the absorption band studied as well as the polaron binding energy, the mean electron-phonon coupling constant, and the nearest neighbour overlap integral are estimated from the experimental data.

Adsorption properties of hydrophobic surfaces

Abstract: Completely hydrophobic adsorbents such as graphitized thermal carbon blacks, BN, and many sulfides are nonspecific, provided that the structural defects are largely eliminated. Their surfaces carry no π-bonds or groups with lone electron pairs, ions, or free radicals. The adsorption isotherms of water vapor on such surfaces are convex towards the pressure axis and the maount of adsorption is very low. Adsorbates capable of forming intermolecular hydrogen bonds are adsorbed on such surfaces at first as isolated molecules with a heat of adsorption much below the heat of condensation, but, with increasing surface coverage, they become associated, and the heat of adsorption abruptly increases. Certain porous polymers, for instance, chromosorb 102, are also fairly hydrophotic, although the presence on their surfaces of aromatic π-bonds and possibly oxygen-containing groups impart to them a slight specificity, especially in relation to adsorbate molecules containing OH or NH groups. Specific adsorbents may be made nonspecific by chemical modification, grafting saturated groups to their surface, or adsorption of a dense layer of saturated macromolecules. Conversely, the deposition on th carbon black surface of dense layer of macromolecules or high melting organic substances, containing π-bonds or functional groups with lone electron pairs, imparts specificity to the surface. the heats of adsorption on modified adsorbents are usually lower than the heats of condensation. The oxidation in liquid media of carbon blacks makes them as hydrophilic as hydroxylated silicas.

Some peculiar features of the hydrochemical regime and the fauna of mesohaline waters

Abstract: The information available reveals pronounced changes in the ion ratio when marine and fresh waters are mixed. The critical salinity has been shown to be about 5%. in the Kara, White, Baltic, Azov, Black and, probably, Caspian Seas, and British Columbia. Corresponding results were obtained in experimental mixings of White Sea waters with a variety of fresh waters. A close connection is suggested between mixed water hydrochemistry and the existence of an eco-physiological barrier. This barrier divides, at salinities of 5 to 8%., the two basic types of aquatic animals into marine and freshwater representatives.