Showing papers by "Sofia University published in 1971"
166 citations
TL;DR: In this paper, thin-layer chromatography on silica gel is proposed as a method for assigning the relative configurations of diastereomeric pairs of compounds of the above type.
30 citations
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TL;DR: A model of fatigue is proposed based on permeability changes in the synaptic membranes and a feedback regulation due to metabolicChanges in the working organ as well as in the whole organism.
Abstract: A model of fatigue is proposed based on permeability changes in the synaptic membranes and a feedback regulation due to metabolic changes in the working organ as well as in the whole organism. The model is described by mathematical equations which permit its quantitative study by means of a digital computer.
16 citations
TL;DR: In this article, a biogenetic relationship between paraffins, olefins, secondary alcohols and ketones in rose flower wax was suggested, compared with those by other authors.
14 citations
TL;DR: The structures of talatisamine and cammaconine were established by correlation with isotalatizidine as discussed by the authors, a diterpenoid alkaloid with known structure and stereochemistry.
13 citations
TL;DR: In this article, the fragmentation of six substituted 10-alkylphenothiazines is discussed and the dominant expulsion of OH, SO and O occurs from the molecular ions of the molecular ion of 10-ALKYL-PHENTHIA-5-oxide derivatives, the relative extent depending upon the configuration of the 10substituent.
Abstract: The fragmentation of six substituted 10-alkylphenothiazines is discussed. Predominant expulsion of OH, SO and O occurs from the molecular ions of 10-alkylphenothiazine-5-oxide derivatives, the relative extent depending upon the configuration of the 10-substituent. The simultaneous elimination of two OH radicals from the molecular ion of 10-alkylphenothiazine-5-sulphone derivative is also observed.
11 citations
TL;DR: A review of some Russian-language papers published as early as 1952-1954 that are unknown to most English-speaking readers is presented in this paper, where the influence of an abrupt change in the surface friction velocityv*, surface roughnessz0 and surface temperature or heat flux on the wind velocity profile and vertical motions has been investigated analytically and numerically.
Abstract: A review is presented of some Russian-language papers published as early as 1952–1954 that are unknown to most English-speaking readers. In these papers the influence of an abrupt change in the surface friction velocityv*, surface roughnessz0 and surface temperature or heat flux on the wind velocity profile and vertical motions has been investigated analytically and numerically. Most of the theories are based on the exchange-coefficient approximation for momentum and heat. In terms of this approximation, further generalization and development of the problem is discussed.
11 citations
TL;DR: The specific surface energy at the crystal-solution interface was calculated from the induction period and the Volmer relationship, while the critical nuclei dimension was found by means of the Thomson-Gibbs equation as mentioned in this paper.
Abstract: The kinetics of crystallisation of ZnC2O4 · 2 H2O was investigated at 25°C and at different supersaturations. Zinc oxalate was prepared from pure zinc sulphate and oxalic acid solutions. The specific surface energy at the crystal-solution interface was calculated from the induction period and the Volmer relationship, while the critical nuclei dimension was found by means of the Thomson-Gibbs equation. With the decrease in supersaturation the size of the nuclei does not increase to infinity, but changes by 1–2 unit cells within a given supersaturation range.
[Russian Text Ignored]
10 citations
TL;DR: In this paper, the activation energies of crystal growth on the faces of KCl, KBr, and KI crystals in water solutions were determined and compared with the respective crystal lattice energies according to Sletter and Mayer, as well as with experimental ones.
Abstract: The effective activation energies of crystal growth on the faces (100) of KCl, KBr, and KI crystals in water solutions have been determined. The values obtained have been compared with the respective crystal lattice energies according to Sletter and Mayer, as well as with the experimental ones. The activation energies of crystal growth are in strictest linear dependence on the heats of dehydration of the ions. This shows that the dehydration of the ions is most probably the rate-controlling stage of the process of crystal growth in solutions. This concept is supported by the results of an experimental study of the rates of growth on the faces (111) and (100) of NaClO3 crystals.
[Russian Text Ignored]
10 citations
TL;DR: In this paper, the influence of temperature on the polarity of the liquid phase in gas chromatography was investigated for twenty-one liquid phases of various types of structure, and it was found that the liquid polarity depends on the temperature linearly, and its temperature coefficient can be negative, positive or zero.
9 citations
TL;DR: In this article, the interfering effect of the γ-radiation of radioactive isotopes of the rare earths on the non-destructive neutron activation analysis of μg amounts of uranium, using the 106 KeV-γ-line of 239Np and NaI (Tl). detector, is estimated.
Abstract: The interfering effect of the γ-radiation of radioactive isotopes of the rare earths on the non-destructive neutron activation analysis of μg amounts of uranium, using the 106 KeV-γ-line of 239Np and NaI (Tl). detector, is estimated. The errors introduced by the interfering isotope in the analysis of uranium, are determined as a function of the ratio of the concentration in the sample of the interfering element and uranium. In addition, the possibilities of determining the quantitative effect of these elements are described. The use of the proposed method is demonstrated by the analysis of some geological samples.
TL;DR: A wide range of anomalies is found in the basal cell nevus syndrome (BCNS), and mental and neurologic abnormalities such as mental retardation, aberrations and partial agenesis of the corpus callosum are anomalies of the nervous system.
Abstract: In 1951, Binkley and Johnson^ reported hereditary multiple basal cell epitheliomas in mother and daughter; they also found other developmental defects in these patients. Subsequent studies of such patients confirmed that this combination of the anomalies constitutes a distinct syndrome.i' "• 12,13 A wide range of anomalies is found in the basal cell nevus syndrome (BCNS). Cutaneous anomalies include basal cell epitheliomas, milia, epithelial and sebaceous cysts, lipomas and dyskeratoses of the palms and soles. Some osseous anomalies are mandibular cysts, rib anomalies, brachymetacarpalism, spina bifida occulta, sclerosis and defective dentition. Soft-tissue anomalies are calcification of the falx cerebri, ovarian fibromas with calcification and lymphatic mesenteric cysts. Mental and neurologic abnormalities such as mental retardation, aberrations and partial agenesis of the corpus callosum are anomalies of the nervous system. Ocular anomalies are hypertelorism, dystopia canthi, cataracts, and congenital blindness. In addition, this condition sometimes is associated with visceral carcinoma23. s, 13 or with hereditary or congenital syndromes.
TL;DR: The influence of phenol on the habit of sodium chloride crystals was studied quantitatively in this paper, showing that at small concentrations, phenol has no influence whatsoever on the growth rate of the (100) face.
Abstract: The influence of phenol on the habit of sodium chloride crystals was studied quantitatively. At small concentrations the presence of phenol has no influence whatsoever on the growth rate of the (100) face. At greater concentrations this growth rate increases. Spiral growth was observed on the (100) face by surface dissolution. Phenol slows down the growth rate of the (111) face, the energy barrier being about 600 cal/mole. Roughening of this face is observed when crystallization takes place from pure solutions and in the presence of small amounts of phenol. At a phenol concentration of 0.065 mole/l the growth rates of the (100) and (111) faces become equal.
[Russian Text Ignored]
TL;DR: In this article, the effect of the adsorption of water vapor on the conductivity of thin copper films has been investigated, the films being obtained by vacuum evaporation and condensation on a glass support at different temperatures.
TL;DR: In this article, the formation of charge transfer complex (CTC) between p -phenetidine and vanadium(V) species existing in acid medium at low vanadium (V) concentrations was studied.
TL;DR: In this article, a new analytical approximation, concerning the integral of the WT (p ) dp in the spectral equations (3), (4) is suggested based on the physical idea about natural realization of the degree of interaction between the mean and fluctuating fields and is analytically expressed by the formulae (10, (12) and (13).
Abstract: In this paper a new analytical approximation, concerning the integral ?? k ? WT ( p ) dp in the spectral equations (3), (4) is suggested. It is based on the physical idea about natural realization of the degree of interaction between the mean and fluctuating fields and is analytically expressed by the formulae (10, (12) and (13). In the extreme cases of strong and weak interaction the general expression (13) has (11) as its asymptotes. The system of spectral equations (14), (15) is solved numerically and the result is presented in the figure. It is seen that in case of stable stratification, a general inertial range exists, in the middle of which a buoyancy subrange appears with slopes of the spectral curves as shown in the figure. The results eliminate the so far unresolved contradiction between the theories of Bolgiano and Lumley. Shur and agree well with the experimental data. DOI: 10.1111/j.2153-3490.1971.tb00597.x
Abstract: Galvanomagnetic effect was used for studying the magnetization reversal processes in thin NiFe-NiFeMn films with the unidirectional anisotropy. The experimental results were compared with the simple coherent magnetization rotation model. A large contribution of rotation of the magnetization vectorM s to the reversal process in easy direction was found (around 22°). The dependence of angular dispersionα45 on external fieldH‖ was also measured.
TL;DR: In this article, it was shown that the lifetime of the excited state Δt always depends on ∣E−Er∣, where E is the energy of the incident and scattered photons.
Abstract: HEITLER1 showed that in the absorption and emission of photons in resonance fluorescence, the scattering system “remembers” how it was excited; it always emits photons with the same energy as the absorbed photon. When a monochromatic line (Γ ≪ Γ0) is scattered in the manner shown in Fig. 1, the intensity of the scattered photons is given by the Breit–Wigner equation illustration Ir is the intensity of the scattered photons at the resonance Er Γ0 is the line width of the scattering system and E is the energy of the incident (and scattered) photons. When resonance scattering takes place, the photon absorbed by the scatterer is delayed for a certain time before being emitted again. Messiah2 showed that the delay depends on the energy of the incident photons illustration where ħ is Planck's constant. No matter how the nuclei are excited, the lifetime of the excited state Δt always depends on ∣E−Er∣. In this work I report another relation which also depends on ∣E−Er∣ illustration and this equation can be verified experimentally.
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TL;DR: In this paper, experimental investigations on amplification of standing flexural waves in single crystal CdS platelets, both sides of which are rigidly attached, are given of experimental results.
Abstract: Results are given of experimental investigations on amplification of standing flexural waves in single crystal CdS platelets, both sides of which are rigidly attached. Experimentally obtained dependences of the amplification on the voltage and of the amplified vibration on the frequency coincide well with the theoretical calculations.
Es werden experimentelle Ergebnisse uber Verstarkung der Biegungswellen in CdS-Einkristallen, deren Enden starr befestigt sind, mitgeteilt. Die experimentell festgestellten Abhangigkeiten der Verstarkung von der Spannung sowie der verstarkten Schwingung von der Frequenz stimmen mit den berechneten theoretischen Abhangigkeiten gut uberein.
TL;DR: In this article, it was shown that in disordered systems there exist sound absorption due to electron hops, and the frequency dependence of the absorption coefficient was described, and it was also shown that sound absorption is due to the electron hops.
TL;DR: In this paper, the decay process of a Penning discharge was studied by means of the pulse technique and the discharge cell used had a flat anode and a cold cathode, in front of which control grids were placed.
Abstract: The decay process of a Penning discharge has been studied by means of the pulse technique. The discharge cell used had a flat anode and a cold cathode, in front of each of which control grids were placed. Constant negative cut-off voltage and periodical positive square pulse voltage were applied to the grids. In the absence of a pulse, the potential of the grids is lower than that of the cathodes, the secondary emission is eliminated and there is no discharge. In the presence of a pulse, there ia a normal secondary emission from the cathode surfaces and a firing of a self-sustained discharge.Oscillograms of the discharge current at pulsed Penning discharge and different values of the magnetic field, anode voltage and pressure are given. The character of the change of the discharge current after the secondary emission has been eliminated is explained qualitatively on the basis of a simplified discharge model. The average effective coefficient of secondary emission, the quantity of negative space c...
TL;DR: In this article, the mechanism of the reaction between aryloxazolones and amines was investigated in order to study the mechanism and structure of 2-(phenylsulfamido)phenyl esters.
Abstract: The reaction of N-phenylsulfonylbenzoxazolone with amines was investigated in order to study the mechanism of the reaction between aryloxazolones and amines. The sulfonyl group accelerates the reaction considerably. The structure of 2-(phenylsulfamido)phenyl esters of the corresponding N-substituted carbamic acids was assigned to the products on the basis of the IR spectra and alternative synthesis. The reaction with secondary aliphatic amines (dimethyl- and diethylamine)proceeds considerably more slowly and results in the formation of 2-(phenylsulfamido)phenol.
TL;DR: On the basis of a definite hypothesis about the material carrier of the electromagnetic field, a modified, free of divergences, Coulomb law, as well as an approximate value for the electron radius are obtained as discussed by the authors.