Showing papers by "Bulgarian Academy of Sciences published in 1976"
TL;DR: In this article, a group-theoretical derivation of the vacuum operator-product expansion undertaken by Mack in 1973 is presented, where the Green's functions of the corresponding Gell-Mann-Low limit theory are expanded in conformal partial waves.
Abstract: An expansion of the type ${〈\ensuremath{\phi}({x}_{1})\ensuremath{\cdots}\ensuremath{\phi}({x}_{n})〉}_{0}={〈\ensuremath{\phi}({x}_{1})\ensuremath{\phi}({x}_{2})〉}_{0}{〈\ensuremath{\phi}({x}_{3})\ensuremath{\cdots}\ensuremath{\phi}({x}_{n})〉}_{0}+\ensuremath{\Sigma}\stackrel{}{{\ensuremath{\chi}}_{l}}{C}^{2}({\ensuremath{\chi}}_{l})\ensuremath{\int}(\mathrm{dp}){Q}^{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{l}}({x}_{1},{x}_{2};\ensuremath{-}p){w}_{{\ensuremath{\chi}}_{l}} (p){Q}^{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{l}}(p;{x}_{1},\dots{},{x}_{4})$ is derived, where ${\ensuremath{\chi}}_{l}=[l,{c}_{l}]$ are labels for infinite-dimensional symmetric tensor representations of the Euclidean conformal group ${\mathrm{O}}^{\ensuremath{\uparrow}}(2h+1,1)$,${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{l}=[l,\ensuremath{-}{c}_{l}]$, the constants $C ({\ensuremath{\chi}}_{l})$ are real, and ${Q}^{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}$ and ${w}_{\ensuremath{\chi}}$ have the properties of vacuum expectation values of field products. The starting point is an infinite set of coupled nonlinear integral equations for Euclidean Green's functions in $2h$ space-time dimensions of the type written some 15 years ago by Fradkin and Symanzik. The Green's functions of the corresponding Gell-Mann-Low limit theory are expanded in conformal partial waves. The dynamical equations imply the existence of poles and factorization of residues in the partial waves as functions of the representation parameters. In proving the validity of the expansion we use some differential relations between partially equivalent exceptional representations of ${\mathrm{O}}^{\ensuremath{\uparrow}}(2h+1,1)$, established in an earlier paper. This work completes the group-theoretical derivation of the vacuum operator-product expansion undertaken by Mack in 1973.
226 citations
TL;DR: The result suggests the existence of a mechanism for processing a high spatial frequency stimulus which demands more time than that forprocessing a low spatial frequency.
160 citations
TL;DR: In this article, it has been established that qualitative agreement between the experimental data and either the classical or the atomistic model cannot be considered as a reliable criterion for the validity of either of the two theoretical concepts.
88 citations
TL;DR: In this article, the kinetics of mobility coalescence in a thin discontinuous film are investigated provided that the deposition is completed and the process proceeds in a pure form, and the analysis is made on the basis of the mathematical formalism developed by Smoluchowski for description of the colloid rapid coagulation.
67 citations
53 citations
TL;DR: The accuracy and precision of the method were evaluated on a standard mixture and on sunflower oil, olive oil, lard, cocoa butter, and beef tallow.
Abstract: A method has been developed for the quantitative thin layer chromatographic determination of the triglyceride groups, differing in unsaturation, based on densitometry of the charred bands. Complete separation was achieved by continuous development in an open glass jar. The need for correction coefficients was avoided through addition of bromine to the double bonds prior to charring in the presence of sulphuryl chloride. The accuracy and precision of the method were evaluated on a standard mixture and on sunflower oil, olive oil, lard, cocoa butter, and beef tallow. The method is applicable for triglyceride group analysis of the most common fats and oils which contain saturated, monoene, and diene acids.
51 citations
TL;DR: In this article, the tensor product decomposition of two unitary class I representations of the generalized Lorentz group is studied and conditions are found under which only principal series representations contribute to the decomposition Normalized Clebsch-Gordan kernels are evaluated which satisfy a completeness and orthogonality relation.
50 citations
TL;DR: It is shown that under optimal conditions the presence of urea decreases markedly the band width of RNA fractions and improves the resolving power of the method.
49 citations
TL;DR: The phase composition, microstructure, porosity, density and consistency of positive plate pastes prepared at 35 and 80° C were determined as functions of the amount of H2SO4 as discussed by the authors.
Abstract: The phase composition, microstructure, porosity, density and consistency of positive plate pastes prepared at 35 and 80° C were determined as functions of the amount of H2SO4. It was found that the phase composition of the paste is determined by the H2SO4 oxidized lead powder ratio and by the temperature at which the paste is mixed. The paste density is determined by the liquid powder ratio. The total pore volume is controlled by the paste density while the average pore radius and the consistency are determined by the phase composition. Stoichiometric calculations were made for the phase composition of the pastes. It is concluded that the paste represents a non-equilibrium system consisting of crystalline basic lead sulphates and oxides and amorphous sulphate-containing components.
41 citations
TL;DR: In this paper, it is shown that the supersaturation plays a significant role in determining the growth mode in addition to already discussed interrelation between the specific surface energies of the substrate, deposit and the substrate-deposit interface.
Abstract: The thermodynamic criterion of the mechanism of growth of thin films is reconsidered. It is shown that the supersaturation plays a significant role in determining the growth mode in addition to already discussed interrelation between the specific surface energies of the substrate, deposit and the substrate-deposit interface. The conclusions are in good agreement with experimental observations in deposition of f.c.c. metals on f.c.c. metal substrates that at positive surface energy change the island growth is favoured at supersaturations lower than some critical one while at higher supersaturations a layer growth takes place. The STRANSKI-KRASTANOV mechanism consisting in formation of threedimensional nuclei on top of previously deposited layers of the overgrowth is considered in more details. It is concluded that its occurrence depends on the sign and the value of the lattice misfit between the substrate and the overgrowth, on the interaction forces between them and on the thermodynamic stability of the deposit. The validity of the classical nucleation theory for explanation of the growth mode transition is also discussed.
Das thermodynamische Kriterium fur den Wachstumsmechanismus von dunnen Schichten wurde nachgepruft. Es wurde gezeigt, das neben den schon diskutierten Zusammenhangen zwischen den spezifischen Oberflachenenthalpien der Unterlage, des Niederschlags und der Phasengrenze Niederschlag-Unterlage auch die Ubersattigung bei der Bestimmung des Wachstumsmechanismus eine bedeutende Rolle spielt. Die Schlusfolgerungen sind in guter Ubereinstimmung mit den experimentellen Befunden im Falle der Abscheidung von k.f.z.-Metallen auf k.f.z.-Metallunterlagen, wonach bei positiven Anderungen der Oberflachenenthalpie bei Ubersattigungen niedriger als die kritische das Inselwachstum, und bei Ubersattigungen hoher als die kritische das Schichtenwachstum bevorzugt wird. Der STRANSKI-KRASTANOV Mechanismus, gekennzeichnet durch Bildung dreidimensionaler Keime auf zuvor abgeschiedenen Schichten, wurde ausfuhrlicher betrachtet. Es wurde die Schlusfolgerung gezogen, das seine Verwirklichung von dem Vorzeichen und der Grose des relativen Unterschieds der Gitterkonstanten der Metalle der Unterlage und des Niederschlags, von den Wechselwirkungskraften zwischen ihnen und von der thermodynamischen Stabilitat des Niederschlags abhangig ist. Die Gultigkeit der klassischen Keimbildungstheorie wurde in Hinblick auf die Deutung der Ubergange der Wachstumsmechanismen ineinander diskutiert.
39 citations
TL;DR: The inhibitory effect of some pyrazole derivatives on purine biosynthesis was studied in a pigeon liver cell-free system and it was demonstrated that 3-amino-4-carbethoxypyrazole and 3-(3′3′-bis-β-chloroethyltriazenyl-1′)-4- carbohydrate-based derivatives were inhibitors.
TL;DR: In this paper, the number of nuclei grown as a function of time, overpotential and eletrolyte concentration have been investigated experimentally during the electrodeposition of Hg from an aqueous solution of HO 2 (NO 3 ) 2 onto a plane structureless platinum electrode and a hemispherical single-crystal electrode.
TL;DR: In this paper, the influence of the electrolyte concentration on the induction period, the steady state nucleation rate and the saturation nucleus density is analyzed in two timiting cases where the saturation nuclei density is determined by the number of energetically preferred active centers on the electrode surface and the overlapping of nucleation exclusion zones.
TL;DR: An EPR study of the reaction of copper(II) dithiocarbamate and acetylacetonate complexes with CuCl 2, CuBr 2, CuNO 3 ) 2 and Cu(ClO 4 ) 2 in solution has shown the formation of mixed-ligand copper-II complexes as mentioned in this paper.
TL;DR: In this article, in-beam measurements of nanosecond lifetimes applying the method of delayed γ-γ coincidences were performed in the (p, n) reaction.
TL;DR: In this paper, a qualitative physical model is proposed to explain the influence of the oxygen content in the gas flow on the discharge current for reactive cathode sputtering in a d.c. diode system.
TL;DR: Analysis of the melting profile of DNA stripped of non-histone proteins and histone H1 allows definite structural conclusions to be drawn, and it is possible to calculate what a particular chromatin model's melting curve will look like.
Abstract: Analysis of the melting profile of DNA stripped of non-histone proteins and histone H1 allows definite structural conclusions to be drawn; conversely, it is possible to calculate what a particular chromatin model's melting curve will look like.
TL;DR: In this article, the influence of molecular asymmetry on the elastic and flexoelectric properties of bilayer lipid membranes is studied and an expression for the elastic energy of a monolayer of asymmetrical molecules is proposed.
Abstract: The influence of the molecular asymmetry on the elastic and flexoelectric properties of bilayer lipid membranes is studied. At first a definition of the lipid asymmetry is introduced. Then an expression for the elastic energy of a monolayer of asymmetrical molecules is proposed and the curvature elasticity of bilayer lipid membrane is studied on such a basis. Formulas for the equilibrium curvature of a membrane are obtained at equal and different asymmetries of the two monolayers. After that the lipid distribution between two monolayers of a deformed membrane is studied and expressions for curvature-induced polarization are obtained. Finally the flexoelectric coefficient of a lecithin-cholesterol membrane is determined.
TL;DR: In this article, the EPR spectra of bis(8-quinolinethiolato) copper(II) and bis( 8-quinoline) copper (II) complexes are recorded both at 300 K and 77 K. The EPR parameters are obtained and the coefficients of the MO of the unpaired electron are calculated.
TL;DR: In this article, the structural units predicted by Myuller and coworkers to form the continuous network of As-S-Ge glasses were investigated and the variation with x of several physical properties (density, microhardness, electrical dark conductivity, photoconductivity, optical gap and first-neighbour coordination) in the whole series of As 2 S 3 Ge x glasses can be either understood qualitatively or even calculated quantitatively with the aid of additivity laws.
Abstract: Spectroscopical and structural investigations directly reveal the presence of those structural units which were predicted by Myuller and coworkers to form the continuous network of As-S-Ge glasses. After refining Myuller's model to some extent, the variation with x of several physical properties (density, microhardness, electrical dark conductivity, photoconductivity, optical gap and first-neighbour coordination) in the whole series of As 2 S 3 Ge x glasses can be either understood qualitatively or even calculated quantitatively with the aid of additivity laws.
TL;DR: The neuronal fraction was found to contain mainly H forms of LDH, and the glial fraction also contained H forms but its M/H ratio was higher than that of the neuronal fraction.
TL;DR: Changes in the potentials from separate motor units in human m.
TL;DR: In this article, the surface conductance of epitaxial layers of pure AgBr is measured and the temperature dependence of the conductivity of layers with varying thickness is measured, and the bulk conductivity is found to be practically identical with that of pure large single crystals of AgBr.
Abstract: Carefully controlled conditions of evaporation allow the preparation of epitaxial layers of pure AgBr. The temperature dependence of the conductivity of layers with varying thickness is measured. This in principle makes possible the splitting of the conductance into surface and bulk components. The bulk conductivity of the layers is found to be practically identical with that of pure large single crystals of AgBr, which until now has not been observed. For the first time considerable surface conductance is directly observed not only for {111} but for {200} layers too. All parameters characterizing the Frenkel disorder in the subsurface region are evaluated from 150 °C down to room temperature.
Dunne Epitaxieschichten aus reinem Silberbromid werden unter sorgfaltig kontrollierten Bedingungen hergestellt. Die Temperaturabhangigkeit der Leitfahigkeit wird fur verschiedene Schichtdicken gemessen. Dies erlaubt im Prinzip, die Leitfahigkeit in eine Oberflachen- und eine Volumenkomponente zu trennen. Es wird gefunden, das die Volumenleitfahigkeit der Schichten mit der von grosen, reinen Silberbromideinkristallen identisch ist, was bis jetzt noch nicht beobachtet wurde. Zum ersten Mal wird eine betrachtliche Oberflachenleitfahigkeit nicht nur fur die {111}-sondern auch fur die {200}-Schichten direkt festgestellt. Alle Parameter, die die Frenkel-Fehlordnung in den oberflachennahen Gebieten charakterisieren, werden in einem Temperaturintervall von 150 °C bis Zimmertemperatur ausgewertet.
TL;DR: It appears that the post-transcriptional degradation of pre-rRNA and poly(A)+-RNA caused by actinomycin D is not connected with the action of the drug on transcription.
TL;DR: The parameters of the single contraction and the size of the summated equivalent potential determined through location of motor units in human opponens pollicis muscles upon electrical stimulation and during voluntary activity were studied.
TL;DR: It is found that the visual threshold elevation caused by jerk movements of a vertical grating in the visual field is due to the movement of the grating and not to its displacement from one retinal locus to another one; the masking range is about 4° and only the parts of thegrating near to the stimulus produce an essential masking effect.
TL;DR: The relationship between the appearance of large and active mitochondria in the initial part of the axon and the elevated axonal transport during regeneration of the peripheral nerve is discussed.
Abstract: The initial part of the axon including the axon hellock, the initial unmyelimated segment and the beginning of myelinated axon was studied electron microscopically during regeneration, 1--30 days following a crush lesion of the rat hypoglossal nerve. Large mitochondria reaching 1.1 mum in diameter, with abundant cristae and dense granules in the matrix were observed between days 3--21. They formed clusters in the initial myelinated segment of the axon. End-to-end contacts and ribosomes around them were very often visible. The large mitochondria exhibited strong succinate dehydrogenase and NAD - H2 diaphorase activities. The relationship between the appearance of large and active mitochondria in the initial part of the axon and the elevated axonal transport during regeneration of the peripheral nerve is also discussed.
TL;DR: In this paper, the experimental conditions for obtaining hollow crystals are discussed and presented systematically in tables Some inferences concerning the effect of impurities, supersaturation, type of substrate and other factors on the growth of hollow crystals were made.
Abstract: Published data on hollow crystals of II–VI compounds are reviewed The experimental conditions for obtaining hollow crystals are discussed and presented systematically in tables Some inferences concerning the effect of impurities, supersaturation, type of substrate and other factors on the growth of hollow crystals are made Particular attention is paid to the structure, form and defects of hollow crystals and it is established that they can be classified in the following groups: hollow hexagonal columns and prisms, hollow pyramids, hollow crystals with spiral-like hexagonal form and hollow crystals with a more complex structure consisting of whisker-pyramid-prism The mechanism and kinetics of the growth of hollow crystals as presented by different authors are discussed
TL;DR: In this paper, the effect of platinum and polymeric phthalocyanines as promoters on the overall electrochemical characteristics of oxygen and air electrodes was investigated when working with air and oxygen, and the extent of mass transport hindrances was estimated in terms of ΔE(i) curves.
TL;DR: In this article, the authors derived an equation for the dependence of the concentration of the H 2 SO 4 in the Pb−PbSO 4 zone on the thickness of this zone.