Showing papers by "Sofia University published in 1974"
TL;DR: In this article, the influence of surface viscosity on the rate of thinning and on the critical thickness of rupture of foam films has been studied and it is shown that this effect depends strongly on the length-scale of the flow.
Abstract: The influence of surface viscosity on the rate of thinning and on the critical thickness of rupture of foam films has been studied. It is shown that this effect depends strongly on the length-scale of the flow. Therefore it is possible to neglect it when calculating the rate of thinning, but to assume for the wave motion, caused by the thermic fluctuations, that the surface viscosity is infinitely great. The expression for the critical thickness, obtained in this way, agrees relatively well with the experimental results. A possible explanation of the dependence of critical thickness on surfactant concentration is suggested.
144 citations
TL;DR: In this paper, a theory of the effect of the surfactant on the rate of thinning of foam films is presented and the formulae obtained for the separately treated cases of low and high concentrations cover the whole concentration range.
Abstract: A theory of the effect of the surfactant on the rate of thinning of foam films is presented. The formulae obtained for the separately treated cases of low and high concentrations cover the whole concentration range. The effect of both bulk and surface diffusion is taken into consideration and it is demonstrated that the relative importance of the latter increases with the decrease of the film thickness. The role of the surface diffusion for the stability of foam films is discussed. It is shown that films stabilized with soluble surfactants never strictly obey Reynolds'eq. [19] so that the actual velocity of thinning can be substantially higher than that calculated by the quoted equation.
114 citations
TL;DR: In this paper, it is shown that an increase in surfactant concentration at first causes the critical thicknesses of rupture on microscopic films to decrease but gradually a nearly constant value is reached.
Abstract: It is shown that an increase in surfactant concentration at first causes the critical thicknesses of rupture on microscopic films to decrease but gradually a nearly constant value is reached. With films of aqueous solutions of fatty acids (valeric, caproic, caprylic and capric acids), this dependence correlates well with the effect of the surfactant concentration on the damping of capillary waves. With surfactants of the detergent type (OPE-7, OPE-20) in addition to the change of the critical thickness, the transition from rupture to formation of black spots is described, as the surfactant concentration exceedsC
bl. The remarkable fact in the latter case is the independence of the critical thickness of the final state, be it rupture or formation of first or second black films. On the basis of the experimental data the assumption is put forward that the critical thickness of rupture or the critical thickness of formation of black spots is substantially affected by macroscopic non-uniformities in the film thickness. Thus the conclusion is reached that the critical thickness of an ideally plane parallel film which is the object of the theory, must be obtained by extrapolation of the measured value toward extremely small radii.
73 citations
TL;DR: In this paper, the conditional stability constants of the zinc(II)- and cadmium-II-arsenazo III complexes are given, and they show that with iodide and allyl alcohol, molar absorptivities increase to 42,800 and 38,500 respectively.
25 citations
TL;DR: Arsenazo III is used as a spectrophotometric reagent for alkaline-earth metals and the stability constants have been measured and the structure of the complexes is discussed.
19 citations
TL;DR: In this article, the reaction in liquid ammonia of magnesium naphtalenide with the ethyl esters of 2-bromoproionic and 2bromobutyric acid gives after hydrolysis the corresponding 2,2′ -dialkylsuccinic acids, whereas calcium naphthalenide reacts to give in the former case 2, 2′ -dimethyl anhydride, and 2-hexene-3,4-dicarboxylic acid in the latter.
13 citations
12 citations
TL;DR: A highly sensitive method for determination of iron in blood serum is proposed, based on the catalytic action of iron on the oxidation ofp-phenetidine with hydrogen peroxide with hydrogenperoxide, suitable for serial clinical analysis.
Abstract: A highly sensitive method for determination of iron in blood serum is proposed, based on the catalytic action of iron on the oxidation ofp-phenetidine with hydrogen peroxide. The method permits very small serum samples (0.05–0.1 ml) to be analysed without previous deproteination and even with turbid lipoid serums. The procedure is very simple and suitable for serial clinical analysis.
10 citations
TL;DR: In this paper, the damping rates of low-frequency quasistatic surface waves propagating on the boundary surface between a nonisothermal plasma and a dielectric were investigated on the basis of kinetic plasma description.
Abstract: The spectra and the damping rates of low-frequency quasistatic surface waves propagating on the boundary surface between a non-isothermal plasma and a dielectric are investigated on the basis of kinetic plasma description. The spectra obtained coincide with the spectra of ion-acoustic and ion plasma surface waves derived by a hydrodynamical plasma model with cold ions. It is shown that the influence of the thermal motion of the ions on the spectra and the damping rates of the waves is essential for the propagation of the short-wavelength surface ion plasma waves only.
9 citations
TL;DR: The presence of seven members of the homologous series of γ-lactones in wax of the Bulgarian oil-bearing rose (Rosa damascena mill) was established by means of mass spectrometry of a fraction isolated by chromatography as discussed by the authors.
9 citations
TL;DR: In this article, the propagation of axially symmetric high-frequency surface waves along gas discharge nonisothermal current plasma column, bounded by a dielectric, is investigated and the dispersion and the space damping rate of the downstream and upstream waves are measured and the results are compared with the theory.
TL;DR: In this paper, a new fraction has been isolated by chromatographic methods from the wax of the Bulgarian oil-bearing rose, which was characterized as an homologous series of γ-diols, from C 17 to C 33 with the major homologues those containing an odd number of carbon atoms.
TL;DR: In this article, a method for the determination of the content of the liquid phase in packings for gas was described, which is subject to an error due to the solubility of some inorganic compounds of the support.
TL;DR: A simple, rapid and sensitive method for the determination of iron in blood serum is proposed, which is compared with the bathophenantroline, nitroso-R-salt and flame atomic absorption methods.
01 Feb 1974
TL;DR: In this paper, the use of nonlinear optical phenomena at the boundary of a nonlinear medium for measuring the duration and the pulse shape of ultrashort light pulses is considered.
TL;DR: In this paper, the thresholds for four-phonon parametric amplification and generation in metal vapors and inert gases are calculated, and phase matching conditions for these processes in mixture of vapors, gases, and metal are considered.
TL;DR: In this paper, the ladder complete set and connected with it a classification scheme correspond to a rest system are introduced. And an intermediate complete set from commuting operators is formed from the latter (an analogy with the case of the ladder representation is at hand) and the manner for extract of the physical part of the considered space is shown.
TL;DR: In this paper, the influence of a high-frequency electric field, driving a semi-bounded nonisothermal plasma, on the propagation of surface ion-acoustic waves with sub-threshold values of the pump field is examined.
01 Mar 1974
TL;DR: In this article, a linear control of the acoustic radiation of a single-electrode section of a surface-wave transducer is described using the field effect transistor (FET).
Abstract: The field-effect transistor is used for a linear control of the acoustic radiation of single-electrode section of the surface-wave transducer. The electrically controlled surface-wave filters and delay lines, the characteristics of which may be specified by a set of constant control voltages, are described on this basis.
TL;DR: In this article, the effect of the anode surface area on the performance of self-quenching GM counters has been investigated, and it was shown that the change in the surface area is dependent on the momentum of the products attacking the anodes.
TL;DR: In this article, a method is proposed for neutron activation determination of U via 239Np, which is separated by coprecipitation of ZrO(H2PO4)2 and its 106 keV γ-peak measured.
Abstract: A method is proposed for neutron activation determination of U via239Np This is separated by coprecipitation of ZrO(H2PO4)2 and its 106 keV γ-peak measured The sensitivity of the determination is 10−9 g The method is based on the well-known ability of Np(IV) to coprecipitate with zirconium phosphate, while Np(VI) does not form insoluble phosphates or fluorides This permits elimination of elements interfering, with the determination of239Np via the 106 keV γ-peak: Sm, Nd, Yb, Lu, Pa (from Th) and Ta The rare earths are eliminated by coprecipitation on LaF3, and Pa and Ta as insoluble phosphates in an oxidizing medium The method is suitable for phosphorus-containing samples: phosphorites, apatites and their industrial treatment products The results obtained for the uranium content with the proposed method are in good agreement with the results of other methods and authors
01 Jan 1974
TL;DR: In this paper, the dependence of the elastical modulus in CdS on the wavelength and the intensity of the absorbed light was investigated, and the sensitivity of the sensitive modulation method was developed.
Abstract: The light influences the mechanical properties of semiconductors. With the sensitive modulation — interference method developed, the dependence of the elastical modulus in CdS on the wavelength and the intensity of the absorbed light was investigated.
01 Jan 1974
TL;DR: In this article, a linear relation between log ΔV and log ΔR for classical cepheids is found, which perhaps has a break at ΔR = 10 R⊙.
Abstract: On the basis of more numerous data a relation log P ΔV/log Δ R (P is the period, ΔR is the amplitude of the radius variation and ΔV is the amplitude of the V-magnitude variation) for cepheid variables (Fernie, 1965) has been established. A linear relation between log ΔV and log ΔR for classical cepheids is found, which perhaps has a break at ΔR = 10 R⊙.
TL;DR: In this paper, an asymmetric two-center shell model (ATCSM) was used for the description of the scission asymmetry of fissioning nuclei and the deformation energy surface was calculated by applying a modified shell-correction prescription due to Strutinsky.
Abstract: The asymmetry of the fragment mass distribution of fissioning nuclei is described by suitable parametrization of an asymmetric two-center shell model (ATCSM). The deformation energy surface is calculated by applying a modified shell-correction prescription due to Strutinsky. It is shown that the ATCSM is specially suited for the description of the scission asymmetry which turns out to be strongly dependent on the shell structure of the fragments. It is demonstrated that the mass asymmetry at scission is unaffected by whether or not the Strutinsky renormalization for the shell corrections is employed for the calculation of the deformation energy surface.