Showing papers by "Sofia University published in 1986"
01 Jan 1986
106 citations
01 Jul 1986
TL;DR: In this article, it was shown that Young's equation for solid particles does not follow from force balance, which is due to the difference between the surface tension and the specific surface free energy of the solid.
Abstract: A general variational approach has been applied to derive the conditions for mechanical equilibrium of fluid and solid particles at an interface in the presence of an external field. It is shown that Young's equation for solid particles does not follow from force balance, which is due to the difference between the surface tension and the specific surface free energy of the solid. The correct definition of the contact angles in the presence of an external field is discussed.
92 citations
TL;DR: In this paper, the film and line tension appearing when a bubble is pressed against a liquid-gas interface are measured with solutions of dodecyl sodium sulfate at two electrolyte concentrations.
49 citations
TL;DR: In this article, the spectral dependence of the free carriers relaxation time is determined directly by using only the envelopes of the reflectance extrema of a semiconductive thin film.
48 citations
TL;DR: By using the method of matched asymptotic expansions analytical equations for the shapes of a sessile (pendant) bubble or drop and the external meniscus around it are derived.
44 citations
TL;DR: In this paper, the theory of a grating-pair compressor is developed, taking account of the cubic term into the expansion of the phase shift with the frequency, as well as the finite aperture of the input beam.
41 citations
TL;DR: In this paper, the existence and uniqueness of canonical points for best L1-approximation from an Extended Tchebycheff (ET) system, by Hermite interpolating polynomials with free nodes of preassigned multiplicities, are proved.
39 citations
TL;DR: In this paper, the elemental content of the leaves correlated with the extent of anthropogenic pollution of the region where the plant developed, and the dependence of the element concentrations on the distance from the source has been evaluated.
39 citations
TL;DR: In this paper, the propagation of light pulses with partial spatial and temporal coherence is analyzed and it is shown that the introduction of the second-order coherence function enables the description of both spatial and time radiation characteristics to be described in the angular spectrum approach.
Abstract: The propagation of light pulses with partial spatial and temporal coherence is analysed. It is shown that the introduction of the second-order coherence function enables the description of both spatial and temporal radiation characteristics to be described in the angular spectrum approach. A strong correlation between the spatial and temporal parameters is obtained.
35 citations
TL;DR: In this paper, the CO 2 − radicals in the interstitials of the aragonite lattice of SrCO 3 are most probably responsible for the self-activated luminescence.
35 citations
TL;DR: In this article, a differential interferometric method for experimental determination of the shapes of the bubble cap and the external meniscus is described, and a method for thermodynamic definition of the contact line and experimental measurement of its radius is proposed.
TL;DR: In this article, the effect of 2,2′-oxydiethanol (diethylene glycol, DEG) content and of the annealing temperature on the density, calorimetric, dynamic- and static-mechanical and small angle X-ray scattering (SAXS) behavior of undrawn and drawn samples (granules, films, and bristles) of poly(ethylene terephthalate) (PET) has been studied.
Abstract: The effect of 2,2′-oxydiethanol (diethylene glycol, DEG) content (ranging from 2 to 15 mol %) and of the annealing temperature (in the range from 100 to 260°C) on the density, calorimetric, dynamic- and static-mechanical and small angle X-ray scattering (SAXS) behavior of undrawn and drawn samples (granules, films, and bristles) of poly(ethylene terephthalate) (PET) has been studied. The known dependences on the annealing temperature are confirmed. Some discrepancies with earlier investigations of the dependences on the DEG content are established: constant values for the SAXS intensity and long spacing, for the lamellar thickness and for the volume fraction crystallinity ac. These discrepancies are explained by the variation of the glass transition temperature (Tg) and melting temperature (Tm) of the materials with different DEG contents. The previous hypothesis of the segregation of the comonomer (DEG) units into the amorphous regions is confirmed.
TL;DR: In this article, a new type of superfield fusion rules (even, odd and even-odd) are found in the case of the discrete series of unitary representations of the N = 1 Neveu-Schwarz algebra.
TL;DR: The radius of curvature at the top of small liquid drops has been determined both visually and by means of differential interferometry in reflected light (microscope Epival Interphako, Carl Zeiss-Jena) as discussed by the authors.
Abstract: The radius of curvature at the top of small liquid drops has been determined both visually and by means of differential interferometry in reflected light (microscope Epival Interphako, Carl Zeiss-Jena) Systematic errors in the interferometric measurements have not been found within the investigated interval of curvatures A comparison between the data for aqueous and mercury drops showed that there is no pronounced effect of the reflectivity of the surface on the accuracy of the interferometric measurements
TL;DR: Using a series of ZSM-5 zeolites with different Si:Al ratios (11, 50, 140, 250 and 500), the disproportionation and alkylation of toluene with methanol was investigated in the temperature range 593-743 K.
TL;DR: In this article, a spray hydrolysis method was used to obtain transparent and conductive films of In2O3 doped with tellurium by spraying an alcoholic solution of InCl3 and TeCl4 in an open-air atmosphere.
TL;DR: Hydroulic loading rates above a critical value reduce the oxidation rat at influent Fe″>4g/L, and rotating speeds greater than 20 rpm did not affect the oxidation rate.
Abstract: Fe″ oxidation in rotating biological contactors has been studied over a range of influent Fe″ concentrations. Rotation speeds greater than 20 rpm did not affect the oxidation rate. Hydraulic loading rates above a critical value reduce the oxidation rat at influent Fe″>4g/L.
TL;DR: In this paper, the authors dealt with clustering of sea water samples from different sampling stations located at different distances from the polluting source, which allows a better understanding of the sampling strategy and a better interpretation of the interrelationships between the chemical variables of sampling objects.
Abstract: The present paper deals with clustering of sea water samples from different sampling stations located at different distances from the polluting source The information obtained by clustering allows a better understanding of the sampling strategy and a better interpretation of the interrelationships between the chemical variables of the sampling objects It is shown that the dynamic behaviour of the chemical variables near to the polluting source leads to some changes in the expected classification of the sampling stations Further, some interesting results in clustering of chemical compounds are also obtained: similarity between iron and phosphate as well as between fluoride and ammonia
TL;DR: In this paper, solvent strength and selectivity effects for twenty diastereoisomers compounds (ten threo and erythro pairs) were studied as a function of mobile phase composition, in thin-layer chromatography on silica.
TL;DR: In this article, the authors studied the contact line motion upon creation of Y-Langmuir-Blodgett multilayers under conditions of liquid-film entrainment.
TL;DR: Theoremes de representation integrale du type de Paley-Wiener for les fonctions des espaces de Bergman sur des domaines tubulaires as mentioned in this paper.
TL;DR: In this article, the Gibbs-Thomson equation was applied to determine the equilibrium melting temperature of polybutylenterephthalate (PBTP) films, which was found to be Tm 0 = 250 ± 4°C.
Abstract: An attempt is made for partial crosslinking (i.e., only in the amorphous regions) of films of poly(ethylene terephthalate) (PETP) and poly(butylene terephthalate) (PBTP) by diffusion of molten dicumyl peroxide. It is demonstrated that because of steric and structural reasons this technique is applicable only to PBTP. A series of crosslinked and non-crosslinked samples of drawn and undrawn PBTP films annealed at various temperatures were investigated. The average crystallite sizes have been determined by wide angle X-ray diffraction and the melting temperatures of crosslinked samples have been measured using DSC. Applying the Gibbs-Thomson equation, the equilibrium melting temperature of PBTP is found to be Tm0 = 250 ± 4°C.
Die Versuche, ein partielles Vernetzen (i. e. nur in den amorphen Bereichen) an Filmen aus Polyethylenterephthalat (PETP) und Polybutylenterephthalat (PBTP) mittels geschmolzenem Dicumylperoxid zu erreichen, zeigten, das aus sterischen und strukturellen Grunden diese Methode nur fur PBTP anwendbar ist. Untersucht wurde eine Serie aus bei verschiedenen Temperaturen getemperten, vernetzten und nicht vernetzten sowie aus verstreckten und nicht verstreckten Proben aus PBTP Filmen. Die mittleren Kristallitgrosen wurden anhand von Rontgenweitwinkelstreuexperimenten bestimmt. Die Schmelztemperaturen von vernetzten Proben wurden mittels DSC gemessen. Mit Hilfe der Gibbs-Thomson Gleichung wurde die Gleichgewichtsschmelztemperatur Tmo von PBTP berechnet (Tmo = 250 ± 4°C).
TL;DR: In this paper, the authors proposed a mechanism that includes absorption by molecular states, energy transfer to excited atomic levels and four-wave parametric generation enhanced by radiative decay of the excited states.
Abstract: A number of resonances have been observed in the excitation spectrum of the uv resonance lines of sodium. The mechanism proposed includes absorption by molecular states, energy transfer to excited atomic levels and four-wave parametric generation enhanced by radiative decay of the excited states.
TL;DR: In this paper, the reactivities of 3-acetyl-2H-1-benzo-pyran-2-one and 4-(2-arylvinyl)-3acetyl 2H 1-benzopyran 2-ones were compared in the condensation with aromatic aldehydes.
TL;DR: In this article, a method for the estimation of the effective kinetic diameter of complex molecules is proposed based on the construction of a geometrical model by using the known data for the internuclear distances and atomic radii.
Abstract: A method for the estimation of the effective kinetic diameter of the complex molecules is suggested. The method is based on the construction of a geometrical model by using the known data for the internuclear distances and atomic radii. On the basis of the suggested method the values of the effective kinetic diameter of some molecules for which there are no respective experimental data are calculated.
TL;DR: In this paper, a self-consistent mechanical model of the transition region between a thin soap film and its adjacent meniscus is presented, based on the approach of de Feijter and Vrij.
Abstract: A self-consistent mechanical model description is presented of the transition region between a thin soap film and its adjacent meniscus. As to the shape of this transition region our model yields numerical results that practically coincide with the corresponding calculations based on the approach of de Feijter and Vrij which relies upon the Derjaguin approximation.