Showing papers by "Sofia University published in 1976"
TL;DR: In this article, a hydrodynamic theory of the process of thinning of one-sided and symmetrical emulsion films is presented, and the complete set of Navier-Stokes equations for the dispersion phase is solved.
38 citations
TL;DR: In this article, the reproducibility of the iodide-selective electrode was shown to be 2.3% for 10-5N solutions, and the limits of determination were 33 ng NaAsO2, 32 ng Na2SO3, 44 ng C6H8O6, 13 ng N2H4·2 HCl and 17 ng NH2OH·HCl per ml.
34 citations
TL;DR: In this paper, a qualitative dependence of polytype structures 6H, 15R, and 3C on the partial pressure of nitrogen in the interval 4 to 760 Torr is obtained by optical and X-ray studies of SiC epitaxial layers, grown by recrystallization in the gaseous phase at 1900 to 2300°C.
Abstract: A qualitative dependence of polytype structures 6H, 15R, and 3C on the partial pressure of nitrogen in the interval 4 to 760 Torr is obtained by optical and X-ray studies of SiC epitaxial layers, grown by recrystallization in the gaseous phase at 1900 to 2300°C. The morphological peculiarities of β-SiC epitaxial layers, grown on the (0001) and (0001) faces of the α-SiC substrate are determined. The strained regions of the α-SiC monocrystals, due to inhomogeneous nitrogen-doping, are established by optical and X-ray methods. The effect of nitrogen on the polytype stability of SiC is the basis of the discussion of the experimental data.
[Russian Text Ignored]
23 citations
TL;DR: In this article, Mitiagin and Zobin constructed an example of nuclear Frechet space without basis, and the essential modification of their constructions gives the following results: (1) there exists such a nuclear Freche space X that for any nuclear frechet space Y the space X × Y has no basis (Sections 1 and 2).
22 citations
TL;DR: The second-order intensity correlation function of a laser beam passing through a nonlinear medium has been experimentally found to be a decreasing function of the power density in the medium as discussed by the authors.
21 citations
TL;DR: In this paper, the spectral dependence of the photoconductance in the ferromagnetic semiconductor CdCr 2 Se 4 was found to be a direct evidence for magnetic-order-induced band splitting.
18 citations
TL;DR: A simple and sélective extraction spectrophotometric determination of zinc is described, where PAR is the 4-(2-pyridylazo)resorcinol anion and CDBA is cetyldimethylbenzylammonium ion.
17 citations
TL;DR: The polymeric form in which long-chain aliphatic aldehydes are present in rose flower waxes has been established as the 2,4,6-trialkyl 1,3,5-trioxane.
12 citations
TL;DR: In this article, a simple and very sensitive new catalytic method is proposed for determination of copper(II), based on the oxidation of sulphanilic acid with H2O2 at pH 7 in the presence of pyridine as activator.
Abstract: A simple and very sensitive new catalytic method is proposed for determination of copper(II). The method is based on the oxidation of sulphanilic acid with H2O2 at pH 7 in the presence of pyridine as activator. The sensitivity of the method is 5 ng/ml. Cobalt(II) interferes at concentrations of the same order as copper(II). The method is suitable for determination of copper in biological materials.
10 citations
TL;DR: In this article, a Markov chain based equation for the composition of copolymers in binary, ternary, and K-component copolymerization with depropagation is developed by means of Markov chains.
Abstract: Equations for the composition of the copolymers in binary, ternary, and K-component copolymerization with depropagation developed by means of Markov chains. The mole fractions of the different monomers in the copolymers are determined as components of the limit vector α = (a1, …, an), the latter being obtained as an eigenvector of the transition matrix P. The elements of this matrix are so defined that they reflect the possibility of slipping one, two, or K types of monomer units off the growing chain in the K-component copolymerization (K = 2, 3, …, n). We take the case in which the monomer units slip off if they are attached to a chain, ending with one or more monomer units of the same type. Calculated and experimental data for the composition of the copolymers of o-methylstyrene and methyl methacrylate obtained by radical copolymerization are given. These data agree very well. It is shown that after small simplifications, the equations developed can also be used for common copolymerization (wi...
9 citations
TL;DR: In this paper, the cyclization of sulfonamide derivatives of alkylated 2-hydroxyphenylthioureas in the presence of an ammoniacal solution of silver oxide gives 2-alkylaminobenzoxazole-5-sulfonamides or the corresponding 3-alkyl-2-alkyliminobensoxazolines.
Abstract: The cyclization of sulfonamide derivatives of alkylated 2-hydroxyphenylthioureas in the presence of an ammoniacal solution of silver oxide gives 2-alkylaminobenzoxazole-5-sulfonamides or the corresponding 3-alkyl-2-alkyliminobenzoxazolines. Alkyl-substituted 2-aminobenzoxazole-5-sulfonamides were also obtained by the reaction of benzoxazolylthione with secondary amines and aniline.
TL;DR: A new catalytic method is proposed for determination of copper in blood serum, based on the oxidation of sulphanilic acid with H2O2, catalysed by copper(II), suitable for routine serial analyses in clinical practice.
Abstract: A new catalytic method is proposed for determination of copper in blood serum, based on the oxidation of sulphanilic acid with H2O2, catalysed by copper(II). Because of its high sensitivity the method requires a serum sample of only 0.10 ml. Using the fixed-time method reduces the procedure to that of an ordinary photometric determination. The method shows reasonable precision and accuracy and is suitable for routine serial analyses in clinical practice.
TL;DR: In this paper, the properties of high concentrated (40-60 %) sodium lauryl sulphate solutions with the aid of a special conductance cell are compared with the black foam films, showing that at low temperatures a complete analogy between the electroconductivity properties of the second black film and the surfactant-water gel on the other is evident.
Abstract: The analogy between the properties of the high concentrated surfactant solutions and the black foam films is discussed. Measurements of the specific electric conductance ϰ of high concentrated (40–60 %) sodium lauryl sulphate solutions are carried out with the aid of a special conductance cell (fig. 1). The temperature dependence of ϰ for several surfactant concentrations is compared on fig. 3 with the temperature dependence of the specific electric conductance ϰf of the black foam films. The results show that at low temperatures a complete analogy between the electroconductivity properties of the second black film on one hand and the surfactant-water gel on the other is evident, which indicates an analogy between the structures of these two systems. A further analogy is available between the electroconductivities and respectively the structures of the first black film and the liquid crystal phase surfactant-water, both being stable at higher temperatures.
TL;DR: In this article, it was shown that the elements of the matrix of the average times for first approach M (mij), represent the average number of units occupying places between the units mi and mj in the macromolecules.
Abstract: A regular Markov chain is set equivalent to n-component copolymerization (n ≥ 2) with depropagation. It is shown that the elements of the matrix of the average times for first approach M (mij), represent the average number of units mk (k = 1, 2, …, n; k ± j), occupying places between the units mi and mj in the macromolecules. These are the average lengths of the blocks, beginning with any monomer unit mi and ending with any unit mj, which however do not meet further in the block. For n = 2, the composition of these blocks is fully determined, because they are composed only of one type of units. When, however, n ≥ 3, two or more types of monomer units are included in these blocks. By means of the absorbing Markov chains, expressions for the composition of these blocks when n ≥ 3 are also obtained. In binary copolymerization the diagonal elements of the matrix M (mij) give the average lengths of the homoblocks ∼ mi-mi-…-mi ∼ in the macromolecules. For the n-component copolymerizatior. (n ≥ 3), the ...
TL;DR: In this article, the scattering on potentials containing δ-function terms is discussed and a method of resolving this ambiguity is proposed which applies equally well to the non-relativistic Schrodinger equation and to the Todorov quasipotential equation.
TL;DR: There are no detectable differences in the Ribosomal protein complement and accessibility of the ribosomal proteins to phosphorylation between ribosomes isolated by this procedure and those prepared by classical ultracentrifugation methods.
TL;DR: In this article, a methode for le dosage du mercure and de lor dans l'eau de mer, basee sur la preconcentration de ces elements par retention sur le sulfure du plomb en colonne a pH l (HNO3 + H2SO4).
TL;DR: In this article, the influence of ring strain on certain characteristic vibrational frequencies of carbonyl derivatives of oxazoline and imidazoline is analyzed on the basis of experimental results and approximate molecular orbital calculations.
TL;DR: In this paper, an exact solution of Vlasov and Maxwell's equations for a bounded hot plasma is proposed to derive the dispersion relation of the axially-symmetric surface waves propagating along a plasma column.
Abstract: In this paper we propose an exact solution of Vlasov and Maxwell's equations for a bounded hot plasma in order to derive the dispersion relation of the axially-symmetric surface waves propagating along a plasma column. Assuming specular reflexion of plasma particles from the boundary, expressions for the components of the electric displacement vector are obtained on the basis of the Vlasov equation. Their substitution in Maxwell's equations, neglecting the spatial dispersion in the transverse plasma dielectric function, allows us to determine the plasma impedance. The equating of plasma and dielectric impedances gives the wave dispersion relation which, in different limiting cases, coincides with the well-known results.
TL;DR: In this paper, the results of the kinetic study of the thermal decomposition of ammonium thiocarbamate in vacuum (ca. 10−2 torr) in the temperature range 303-353 K are presented.
Abstract: Results of the kinetic study of the thermal decomposition of ammonium thiocarbamate in vacuum (ca. 10−2 torr) in the temperature range 303–353 K are presented. Under these conditions ammonium thiocarbamate decomposes into gaseous products (NH4COSNH2→2 NH3 + COS). Fifteen general equations for the kinetics of thermal decomposition of solids were taken into consideration. The following equation describes the experimental results over the whole range of the degree of decomposition:
$$\alpha = \frac{{2k_2 }}{{ab}}(t - t_0 )[a + b - 2k_2 (t - t_0 )]$$
whereα=degree of decomposition,t=time,t
0=time required to attain constant growth rate of nuclei, anda andb are the dimensions of the crystal. The temperature-dependence of the rate constantk
2 was determined and the activation energy was found to be 10.7 kcal/mole. An experiment planning scheme was adopted in this study: in a series of experiments, each one was followed by statistical analysis in order to plan successive experiments depending on the results of the previous one.
TL;DR: It has been found that five ribosomal proteins incorporate γ- 32 P from ATP during the incubation of wheat ribosomes with wheat protein kinase, confirming the suggestion that the Ribosomal structure affects the phosphorylation.
TL;DR: In this paper, a method of determining the recoilless absorption probability of Mossbauer radiation with the use of a control absorber is presented, by means of which the influence of the background on the value of the effect and on the resonance curve area, measured experimentally, is being eliminated.
TL;DR: The method is rather simple and permits rapid determination of cephalexin with satisfactory precision and accuracy — coefficient of variation 0.91–1,36%, relative error of the determination 0.66-1,19% (95% confidence limits).
Abstract: A photometric extraction method is developed for determination of cephalexin. Cephalexin is hydrolysed for 5 min in sulphuric acid medium on a steam-bath, the hydrolytic product forming a coloured compound with ninhydrin in 25% H2SO4. This compound is extracted with CHCl3 and its absorbance measured at 520 nm. The reaction is selective — it is negative for the initial reagents in the cephalexin synthesis and for most other antibiotics. The only two antibiotics giving a similar reaction — ampicillin and cephalotin — do not interfere in the determination of cephalexin. The method is rather simple and permits rapid determination of cephalexin with satisfactory precision and accuracy — coefficient of variation 0.91–1,36%, relative error of the determination 0.66–1,19% (95% confidence limits).
TL;DR: In this paper, the authors measured the reflectance of thin Cd, Ga and In films with various thicknesses during isochronal annealing above 77 K. The irreversibility of temperature dependence of reflectance factor is related to annihilation of lattice defects, growth of crystallites and granulation.
TL;DR: A highly sensitive method for detection of gold, almost free from interferences, is described in this article, where the reaction is performed on a short column of anion exchange resin Dowex 1 X8 (100-200 mesh) in iodide form.
Abstract: A highly sensitive method for detection of gold, almost free from interferences, is described The reaction is performed on a short column of anion-exchange resin Dowex 1 X8 (100–200 mesh) in iodide form To the test solution containing 013μg/ml of gold(III) is added Sb-solution (weight ratio Au: Sb=1 ∶ 200) and the mixture is then passed through the resin, followed by 1N NaOH A crimson colour appearing within 2–3 min indicate gold Many metal ions, including Pt-metals, Tl(I), Tl(III), Ir(IV), In (III), Ga(III), Cu(II), Cd(II), Zn(II), Pb(II), Fe(III), Mn(II), Co(II), Ni(II), Hg(II), As(III) do not interfere In the presence of 50-fold excess of Ag(I) or Bi(III) there is no colour because of the formation of a precipitate on the resin