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Showing papers by "Sofia University published in 1985"


Journal ArticleDOI
TL;DR: Mecanisme de formation des complexes de Cr(V). Structure et liaison. Photochimie de la reduction of Cr(VI) as discussed by the authors, and the reduction de Cr

113 citations


Journal ArticleDOI
TL;DR: Femtosecond transform limited light pulse propagation in vacuum is described in scalar approximation of diffraction theory in this article, where evolution of the spatial and temporal characteristics of the pulse are presented.

84 citations


Journal ArticleDOI
TL;DR: In this article, the role of a soluble surfactant with diffusion-controlled surface transfer onto the surface is analyzed and analytical solutions are obtained for the limiting cases of small and large deformations of the bubbles' caps.

75 citations


Journal ArticleDOI
TL;DR: Combinatory PDL is obtained, a conservative extension of Propositional Dynamic Logic that captures the ‘identity of states’ in CPDL, and its expressive power, as compared to PDL, strongly increases.

56 citations



Journal ArticleDOI
TL;DR: In this article, the motion of the three-phase contact line upon entrainment or drainage of glycerol and glycerols on hydrophobic substrates is studied and it is established that the relative speed of the perimeter of wetting with respect to the solid surface remains constant under these conditions, regardless of the changes in film thickness and length due to variations in withdrawal velocity and time.

37 citations



Journal ArticleDOI
TL;DR: In this article, generalized Laplace equations, accounting for the variations of the surface tension and the disjoining pressure in the transition region, were derived and used to obtain integral expressions for the line and transversal tensions.

28 citations


Book ChapterDOI
S. Panchev1
01 Jan 1985
TL;DR: In this article, the Earth's atmosphere, precisely the lower part, including the troposphere and the stratosphere, represents a continuous medium, and in the problems of dynamic meteorology we can ignore the discrete molecular structure of the atmosphere and apply the general methods of fluid dynamics for its description.
Abstract: A system of material points is called a continuous medium if these points entirely fill some volume of space. In this case the substance, as well as the physical characteristics of its state or motion, have a continuous distribution. The Earth’s atmosphere, precisely the lower part, including the troposphere and the stratosphere, represents a continuous medium. Therefore, in the problems of dynamic meteorology we can ignore the discrete molecular structure of the atmosphere and apply the general methods of fluid dynamics for its description.

28 citations



Journal ArticleDOI
TL;DR: In this paper, a variational procedure for deriving the conditions for mechanical equilibrium between a planar film of finite thickness and the external meniscus is formulated, and it is shown that the normal condition can be satisfied only if a new transversal tension is introduced.

Journal ArticleDOI
TL;DR: In this article, the complex formation between creatinine and Cu(II) was studied by means of electronic, IR and EPR spectroscopy, and spectral data showed the formation of a four-membered chelate with distorted rhombic structure.

Journal ArticleDOI
TL;DR: In this paper, the attenuated total reflection infrared spectroscopy (ATR-IR) method was used to compare the transmission spectra of the corresponding skimmed monolayers collected at pH 4.5, 7.5 and 9.5.

Journal ArticleDOI
TL;DR: This paper deals with, prepositional calculi with strong negation (N-logics) in which the Craig interpolation theorem holds.
Abstract: This paper deals with, prepositional calculi with strong negation (N-logics) in which the Craig interpolation theorem holds. N-logics are defined to be axiomatic strengthenings of the intuitionistic calculus enriched with a unary connective called strong negation. There exists continuum of N-logics, but the Craig interpolation theorem holds only in 14 of them.

Journal ArticleDOI
TL;DR: In this article, the melting properties of nascent and thermally treated super-high molecular weight polyethylene (SHMWPE) were investigated by means of differential scanning calorimetry (DSC).
Abstract: The melting of nascent and thermally treated super-high molecular weight polyethylene (SHMWPE) is investigated by means of differential scanning calorimetry (DSC) Higher melting temperatures and enthalpies of the nascent and annealed samples are observed The melting temperatures and enthalpies of melt crystallized SHMWPE is lower and depends on the temperature of thermal treatment All melting properties are explained by presuming that the lamellar structure contains a high concentration of entangled tie macromolecules in amorphous regions formed during polymerization It was supposed that the concentration of the entanglements and the stressed tie molecules are changed with the temperature of the thermal pretreatment

Journal ArticleDOI
Ts. G. Tsvetkov1
TL;DR: In this paper, a radial pulsation mode of 83 Delta Scuti stars is estimated in two ways: 1H and 2H, and 3H and 4H and 5H.
Abstract: On the basis of observational data (Breger, 1979), a radial pulsation mode of 83 Delta Scuti stars is estimated in two ways. These stars can pulsate in four lowest modes—F, 1H, 2H, 3H— and, perhaps, in 4H and 5H. Our earlier suggestion—that the apparent heterogeneity of these objects in both the period-luminosity plane and the period-frequency distribution may be explained by means of pulsations in various modes—is confirmed. Semi-empirical period-luminosity relations for the four lowest modes are derived and the semi-empirical period ratios are compared with the theoretical ones.

Journal ArticleDOI
TL;DR: In this paper, hydrogen desorption in mischmetal intermetallics MmNi5−xFex (x = 0.3−0.7, 0.85, 1.0) prepared by arc melting were studied in the range 0 −40 °C.
Abstract: Hydrogen desorption in mischmetal intermetallics MmNi5−xFex (x = 0.3, 0.5, 0.7, 0.85, 1.0) prepared by arc melting were studied in the range 0–40 °C. The substitution of iron for nickel causes a decrease in the hydrogen dissociation pressure. This substitution does not, in practice, change the maximum hydrogen capacity (6.1−5.8 H atoms per formula unit) in the range x = 0.3−0.7, but for x > 0.7 it decreases considerably.

Journal ArticleDOI
TL;DR: There was no correlation between the number of infused nucleated cells and granulocyte recovery and there were significant differences between the day of engraftment in patients with clinically documented HSV infection compared to patients without infection.
Abstract: The possible interrelation between infused bone marrow CFU-GM and peripheral granulocyte recovery was studied in 16 patients transplanted for acute leukemia. The influence of several clinical events that could modify the graft fate were also analysed. Our results show that: 1) There was no correlation between the number of infused nucleated cells and granulocyte recovery. 2) There was no correlation between the number of infused CFU-GM and granulocyte regeneration. 3) There were significant differences between the day of engraftment in patients with clinically documented HSV infection compared to patients without infection.

Journal ArticleDOI
TL;DR: In this paper, the 13C NMR chemical shifts, one-bond and some long-range 13C-1H coupling constants and the 1H chemical shifts for isoquinolinone, phthalazinone, quinazolinone and their derivatives containing CH3, COOH, cOOCH3 and CH2COOH substituents in the hetero-ring are reported.
Abstract: The 13C NMR chemical shifts, one-bond and some long-range 13C–1H coupling constants and the 1H NMR chemical shifts for isoquinolinone, phthalazinone, quinazolinone and their derivatives containing CH3, COOH, COOCH3 and CH2COOH substituents in the hetero-ring are reported. The NMR data are in agreement with the lactam structure for all compounds studied; no evidence for the detectable presence of other tautomers was obtained.

Journal ArticleDOI
TL;DR: Superoxide dismutase activity of 4 strains of methylotrophic yeasts of the genera Candida, Torulopsis, Hansenula and Pichia was demonstrated.
Abstract: Superoxide dismutase (SOD) activity of 4 strains of methylotrophic yeasts of the genera Candida, Torulopsis, Hansenula and Pichia was demonstrated. Strains tested were grown on glucose or methanol. Yeasts grown on methanol possessed considerably higher levels of SOD- and catalase activity than cells cultivated on glucose.

Journal ArticleDOI
TL;DR: The steric and electronic effects of acyl substituents COR (R = Me, i-Pr, Ph and t-Bu) upon conformational and keto-enol equilibria in 3-acyl-3,4-dihydrocoumarins have been studied by 1 H and 13 C NMR spectroscopy as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, quantum chemical SCC-Xα calculations have been performed on a M[Si3Al3O6(OH)12] cluster (M  Ca2+, Na+), modelling the favored sorption site in front of S1 cations.
Abstract: In order to get more detailed information on the adsorbed state of carbon monoxide in zeolites A, quantum chemical SCC-Xα calculations have been performed on a M[Si3Al3O6(OH)12] cluster (M  Ca2+, Na+), modelling the favoured sorption site in front of S1 cations. Evaluation of the electronic structure gave several well-separated energy bands. CO bonding to the cluster is predicted for linear MCO as well as MOC arrangements. From the total electronic energies an equilibrium distance CaC of 2.7 A can be inferred. Both findings are in agreement with results from classical calculations of the interaction of CO with zeolite Na4Ca4A and are able to explain the observed IR band pattern. Ascribing the partial charges from Xα calculations to the atoms of the cluster in the classical model leads to improvement of the electric field strength values inside the zeolite skeleton from which frequency shifts more consistent with the observed spectrum are expected.

Journal ArticleDOI
TL;DR: The variation of the transport coefficients at 300 K, Seebeck coefficient (α), specific resistivity or conductivity (ϱ = I/s), Hall coefficient (RH), and thermal conductivity with the composition (x) for solid solution (GeTe) 1−x((Ag2Te)1−y(Sb2Te3)y)x) with y = 0.60 is investigated in this article.
Abstract: The variation of the transport coefficients at 300 K, Seebeck coefficient (α), specific resistivity or conductivity (ϱ = I/s), Hall coefficient (RH), and thermal conductivity (K) with the composition (x) for solid solution (GeTe)1−x((Ag2Te)1−y(Sb2Te3)y)x) with y = 0.60 is investigated. The Hall coefficient decreases, reaches at x = 0.40 the minimal value and increases then up to x = 1, but the variation of the other transport coefficients are monotonous with composition: α and e increase but K decreases with composition. The results are interpreted qualitatively on the base of the band edge model of GeTe with splitting of the L- and ∑-valleys of the Brillouin zone (BZ) at the ferroelectric Oh–C3v phase transition and the complicated form of the surfaces of constant energy. [Russian Text Ignored].

Journal ArticleDOI
TL;DR: In this paper, the interaction of 3-(N,N-dimethylamino) propionitrile with aromatic 2-aminoketones is fulfilled successfully under the action of sodium amide in dry ether.

Journal ArticleDOI
TL;DR: In this paper, a method for simultaneous neutron activation determination of Al, Mg and Si using two irradiations in a nuclear reactor is proposed. But the applicability of the method is demonstrated by the analysis of standard reference materials (rocks, glass, as well as archaeological finds from medieval glass and sgraffito ceramics).
Abstract: A method for simultaneous neutron activation determination of Al, Mg and Si using two irradiations in a nuclear reactor—the first one with epithermal and the second one with pile neutrons is proposed. The applicability of the method is demonstrated by the analysis of standard reference materials—rocks, glass, as well as of archaeological finds from medieval glass and sgraffito ceramics.


Journal ArticleDOI
G. R. Ivanov1
TL;DR: In this article, the UAV photometry of 690 stars in the spiral arm S4 and the U magnitudes of 120 stars in S6 with the help of the 2 m RCC telescope of the Rozhen Observatory at the Bulgarian Academy of Sciences, has been used to obtain the colour-magnitude and colour-colour diagrams across the arms.
Abstract: TheUBV photometry of 690 stars in the spiral arm S4 and the U magnitudes of 120 stars in the spiral arm S6 with the help of the 2 m RCC telescope of the Rozhen Observatory at the Bulgarian Academy of Sciences, has been used to obtain the colour-magnitude and colour-colour diagrams across the arms. Our age estimations are compared with van den Bergh's (1964). The age gradient across the S4 arm has been found. The colour excessEB-V is highest at the inner edge of the arm S4. From the age we have evaluated the velocity of star formation propagation across the arm S4 ω⊥ ≈60 km s−1 , pattern frequency Ωp ≈14 km s−1 kpc−1 and corotation radiusRc≈20 kpc. The structure of S4 along the arm is complicated. In the OB 82 region an age gradient is absent. The young associationOB 79b is located near the outer edge of S4 and it has a large absorptionAv≈2m.5 contrary to the density wave prediction. This association bears no relation to the spiral density wave and it is probably, supernova events that stimulated the star formation in it. The colour excessER-V is randomly distributed and the youngest stars are concentrated in the middle of the S6 arm. A value of pattern frequency Ωp = 12km s−1 kpc−1 andRc=12 kpc of our Galaxy has been obtained from the age distribution of the open clusters and cepheids across the Carina-Sagittarius arm. The spiral structure of M31 is compared with that of the galaxy. There is a similarity between S4 in M31 and Carina-Sagittarius in the Galaxy, and also between the S6 and Perseus arms. The Orion arm in the Galaxy bears no relation to the wave density.


Journal ArticleDOI
TL;DR: In this paper, the authors used NAA followed by cluster analysis to find the local and chronological features of the investigated glasses, and proved that NAA is a successful approach to finding the local features of investigated glasses.
Abstract: The neutron activation analysis results from 30 glass samples were subjected to cluster analysis. The reliable localization of part of the medieval glass finds from Preslav enabled the evaluation of the variety of the production of a medieval glass workshop (ninth-tenth century), allowing conclusions to be made about the technological level of glass-making in Bulgaria during the Middle Ages. The work proved that NAA followed by cluster analysis is a successful approach to finding the local and chronological features of the investigated glasses.

Journal ArticleDOI
TL;DR: In this article, the retention characteristics of diatomaceous earth type supports are modified with a liquid phase, by high-temperature thermal treatment in a closed system, and the main advantage of this method is that liquid phase evaporation and possibility of oxydation during the process can be avoided.
Abstract: Diatomaceous earth type supports are modified with a liquid phase, by high-temperature thermal treatment in a closed system. It is shown that the retention characteristics of the support changes by this treatment. The main advantage of this method, as compared with modification in a flow-through system is that liquid phase evaporation and possibility of oxydation during the process can be avoided. This ensures a better uniformity of the modified support.