Showing papers by "Bulgarian Academy of Sciences published in 1979"
TL;DR: In this paper, the behavior of light beams in nonlinear media (self-focussing of optical beams as well as self-modulation and transmission of optical pulses) is considered in the case when the nonlinear polarization contains susceptibilities of third-and fifth-order.
Abstract: The behaviour of light beams in nonlinear media (self-focussing of optical beams as well as self-modulation and transmission of optical pulses) is considered in the case when the nonlinear polarization contains susceptibilities of third- and fifth-order. The soliton solutions are obtained for the nonlinear equations deduced.
170 citations
TL;DR: In this article, it was shown that the Higgs is unlikely to be detected at LEP if its mass is greater than 150 GeV, which is the threshold for the existence of a heavy Weinberg-salam-type neutral Higgs boson.
126 citations
TL;DR: In this paper, the effect of the surfactant concentration on the equilibrium thickness of foam films and the potential of the diffuse electric layer is studied in a wide concentration range (including cmc).
Abstract: The effect of the surfactant concentrationc
s
on the equilibrium thicknessh
r
, of foam films and the potentialϕ
0 of the diffuse electric layer is studied in a wide concentration range (including cmc). The cell for investigation of thin liquid films is improved and a good reproducibility of the measuredh
r
is obtained. The possibilities for determination of the capillary pressureP
σ
in.the cell for investigation of microscopic thin liquid films are discussed. The values ofP
σ
can be measured with sufficient accuracy by the capillary-rise method, using a tube, identical with the tube of the cell for thin liquid films. The dependenceh
r
(c
s
) is studied for nonionic surfactants (decylmethyl sulphoxide, nonyl-phenol 20-glycol ether and dodecyl 11-ethylene oxide) and the ionic sodium dodecyl sulphate. After reaching a steady value (a plateau in theh
r
(c
s
) curve) at high concentrations (about cmc) a decrease in the equilibrium thickness of nonionic surfactants is found. The possible reasons for this decrease are discussed. It is shown that this effect probably is due to the electrostatic disjoining pressure. The values of theϕ
o-potential at the plateau of theh
r
(c
s
) curves are determined by the DLVO-theory using theh
r
, values. The so determinedϕ
0-values are more correct than the obtained earlier by this method because of the more precise measurement of the equilibrium thickness and the direct experimental determining of the capillary pressure. A qualitative interpreting of theϕ
0(c
s
) dependence is made on the basis of the surfactant adsorption at the solution/air interface and it is found that for nonionic surfactants the surface charge saturation is very near to the saturation in the adsorption layer, and for the ionic surfactants the adsorption layer saturation is at higher concentration.
122 citations
TL;DR: In this article, AlB2-type (C32 structure) boron compounds were examined for superconductivity down to 0.42 K and none of these compounds proved to be superconducting above 0. 42 K.
Abstract: We examined some AlB2-type (C32 structure) boron compounds for superconductivity down to 0.42 K; the compounds have the formula MeB2(MeTi,Zr,Hf,V,Nb,Ta,Cr,Mo) (the atomic ratio of metal to boron was 0.5). Only NbB2 was found to be superconducting with Tc = 0.62 K and a surprisingly high value of Hc(0), about 1600 Oe. Other transition metal as well as non-transition metal boron phases were also tested for superconductivity down to 0.42 K; these compounds were MeB6 (MeCa,Sr,Ba), W2B5, CrB, Cr5B3, UB2, UB4 and UB12. None of these compounds proved to be superconducting above 0.42 K; nor was any trace of superconductivity down to 0.42 K observed in MoB and NbB.
88 citations
TL;DR: These studies cover a number of plants growing in Bulgaria that have a healing effect in hypertension, atherosclerosis and ischemic heart disease according to the data of traditional medicine and conventional experimental methods in pharmacology are often unsuitable for revealing the real biological activity of one or another medicinal plant.
Abstract: However great the success in the therapy of hypertension, atherosclerosis and ischemic heart disease has been gained today by recent efficient drugs, the definite healing of patients is not yet attained. The late discovery of reserpine, such an efficient drug of plant origin against hypertension, convinced so far reluctant scientists to consider the chemical compounds of the plant world. With respect to this traditional medical knowledge, it seems necessary to define more accurately the specificity of these healings-sometimes recommended unspecifically for a whole branch of medicine. This experimental verification should not use inconsiderately the present-day classification of diseases; there should be an awareness that conventional experimental methods in pharmacology are often unsuitable for revealing the real biological activity of one or another medicinal plant. The interest in the millennial empirical field of health care is acknowledged by the World Health Organization which promotes research and development of traditional medicine, along with investigations into its psychosocial and ethnographic aspects. These studies cover a number of plants growing in Bulgaria that have a healing effect in hypertension, atherosclerosis and ischemic heart disease according to the data of traditional medicine. Using screening methods, extracts and chemically pure substances were investigated; extraction was done with solvents such as water, ether, chloroform, dichloretan, ethanol, methanol, and acetone. Most of the experiments were carried out on anesthetized cats, rabbits and dogs. The substances tested were applied mainly intravenously, and in some experiments orally. Chronic experiments were also carried out on wakeful dogs with induced hypertension, on animals fed on an atherogenic diet, and on animals with induced arrhythmia and coronary spasm. Data are presented of clinical examination of some plants or of active substances isolated from them. Major results of these studies are presented for the following plants: Garlic, Geranium; Hellebore; Mistletoe; Olive; Valerian; Hawthorn; Pseucedanum arenarium; Periwinkle; Fumitory. For another 50 plants growing in Bulgaria and in other countries the author presents his and other investigators' experimental and clinical data about hypotensive, antiatheromatous and coronarodilatating action.
85 citations
TL;DR: Data obtained from reaction time (RT) measurements as well as from experiments employing masking paradigms suggest that high spatial frequency gratings are perceived with some delay in comparison with low spatial frequency ones, supported by records of human visually evoked response (VER) to sinusoidal gratings.
78 citations
TL;DR: In this paper, the bands of stretching and deformation vibrations of CH 2, CCH 3 and OCH 3 groups in the infrared and Raman spectra were assigned.
77 citations
TL;DR: The notion of a sequential program machine @p-machine) tram+ forming strings to trees is introduced and some results on the equivalence problem for sp-machines and sp machine languages are presented.
76 citations
TL;DR: Results suggest that HMG14 and HMG17 might be interacting with the 15 base pair linker DNA, suggesting an involvement of these two proteins with transcribed sequences.
Abstract: Two methods have recently been described for the isolation of monomer nucleosomes enriched in transcribed sequences which depend on their solubility in 0.1 M NaCl (Levy, W.B. and Dixon (1978), Nucleic Acid Res., 5, 4155-4163) or solutions containing divalent metal ions (Bloom, K.S. and Anderson, J.N. (1978), Cell, 15, 141-150). Using these procedures the proteins associated with such nucleosomes from rabbit thymus, calf liver and hen oviduct nuclei were isolated and analysed. Increased amounts of proteins HMG14 AND HMG17 and small amounts of HMG1 and HMG2 were found associated with the four core histones H2A, H2B, H3 and H4 in these nucleosomes. HMG14 and HMG17 were found to be enriched 2 - 7 fold, suggesting an involvement of these two proteins with transcribed sequences. 0.1 M NaCl-soluble monomer nucleosomes prepared by the method of Levy and Dixon were analysed by polyacrylamide gel electrophoresis and found to be composed of principally two types of particle: 1. Core particles of 145 base pairs of DNA associated with the four core histones only. 2. Nucleosomes with 160 base pairs of DNA associated with the four core histones, increased amounts of HMG14 and 17, and no H1. Small amounts of HMG1 and HMG2 are also detected. These results suggest that HMG14 and HMG17 might be interacting with the 15 base pair linker DNA. A model is presented for the structure of transcriptionally active chromatin.
71 citations
TL;DR: Two further strains of acute avian leukemia viruses, OK10 and E26, have been found to be able to transform chicken hematopoietic cells in vitro, suggesting that their hematobiology targets are nonerythroid cells.
69 citations
TL;DR: Diploid homo- and heterokaryotypes of barley translocation lines with only one satellite chromosome pair containing two nucleolus organizer regions (NORs) in opposite arms were found to show represseducleolus formation by the transposed NOR as evident from the formation of only micronucleoli.
Abstract: Diploid homo- and heterokaryotypes of barley translocation lines with only one satellite chromosome pair containing two nucleolus organizer regions (NORs) in opposite arms were found to show repressed nucleolus formation by the transposed NOR as evident from the formation of only micronucleoli. The same was true for auto-tetraploid homokaryotypes and for translocation lines with all NORs tandemly arranged into the same chromosome arm. When NORs were transposed to chromosomes without NOR in the standard karyotype, the normal pattern of nucleolus formation remained unaffected. The modified mode of nucleolus formation after the combination of all NORs in one chromosome pair is interpreted to be due to intrachromosomal nucleolar dominance analogous to interchromosomal nucleolar dominance observed in certain interspecific hybrids.
TL;DR: In this article, the structure characteristics of glasses in the TeO 2 Fe 2 O 3 system have been studied by means of Moessbauer and IR spectroscopy and positron annihilation.
TL;DR: In this article, a catalytic epoxidation of propylene with tert-butyl hydroperoxide in the presence of a modified weakly acidic cation-exchange resin, Amberlite IRC-50, is carried out.
TL;DR: To what extent the overtracking and the mislocation of a disappearing moving target are interrelated and whether the misIocation can be determined by the ocutomotor behavior during performance of the localization task is revealed.
TL;DR: The effect of the pressure in the Plateau-Gibbs borders of the foam upon its drainage and its stability has been investigated in this paper, where the principle of the method and the apparatus for applying pressure gradient in the plateau-gibbs border of foam are described.
Abstract: The effect of the pressure in the Plateau-Gibbs borders of the foam upon its drainage and its stability has been investigated. The principle of the method and the apparatus for applying pressure gradient in the Plateau-Gibbs borders of the foam are described. The kinetics of establishing of the capillary pressure in the Plateau-Gibbs borders of the foam in dependence of the height of the foam column, the applied pressure difference and the type of the surfactant has been studied. The obtained results are qualitatively confirmed by an investigation of the foam water content change (calculated by measurements of its specific conductivity) at the same experimental conditions. The influence of the increased drainage rate and respectively the decreased foam water content on the foam stability when a pressure gradient is applied in its Plateau-Gibbs borders is discussed. It is shown that the time for the foam destruction when a pressure gradient is applied in the foam Plateau-Gibbs borders can be used for characterising the foam stability at definite conditions.
TL;DR: In this paper, a review of the recent progress in the theory of thin film coalescence due to crystal-lite surface migration is reviewed and the theoretical analysis applies to thin discontinuous films for which the mass of the deposit remains constant.
TL;DR: In this article, the same problem was studied by Monte Carlo simulation and the results showed asymmetric adsorption isotherms with respect to a degree of coverage of 0.5.
TL;DR: The influence of PbO modification on the formation of 4PbO·PbSO4 paste was determined by X-ray diffraction analysis and scanning electron microscopy as discussed by the authors.
Abstract: The influence of PbO modification on the formation of 4PbO·PbSO4 paste is determined by X-ray diffraction analysis and scanning electron microscopy. The paste was prepared from tetragonal PbO, orthorhombic PbO and several mixtures of both oxides at 80° C and a H2SO4/PbO ratio of 6 wt%.
TL;DR: The influence of temperature on the morphology of ice crystals grown from pure vapour is studied in this paper, where it is found that at temperatures close to the melting point non-singular (rounded) regions exist on the growth form of ice on the more loosely packed portions in contact with the basal face.
TL;DR: In this article, a new way of preparing homogeneous chalcogenide electrodes is discussed with the example of copper-selective electrodes, which are electrolytically plated on a conducting Pt basis, conveniently shaped and sized as an electrode.
TL;DR: The results identify the 37 S r RNA precursor molecules as the primary transcripts of ribosomal RNA genes in S. cerevisiae and suggest also that processing of the primary rRNA precursor cannot Start normally before transcription of its 25 S rRNA segment is completed.
TL;DR: The genetic analysis of VY1160 sorbitol dependent, osmotic sensitive yeast mutant led to the identification of three different nuclear recessive mutations, designated sorb- and ts1 and ts2, which confers the sensitivity of Vy1160 mutant cells towards rifampicin.
Abstract: The genetic analysis of VY1160 sorbitol dependent, osmotic sensitive yeast mutant led to the identification of three different nuclear recessive mutations. Two of them, designated sorb- and ts1 are closely linked to one another. The mutation sorb- determines the lysis, while the mutation tsl increases the ability for lysis of the sorbitol dependent cells. The third mutation ts2 segregates independently from the other two and confers the sensitivity of VY1160 mutant cells towards rifampicin.
TL;DR: In this article, the dependence of spherulite dimensions, degree of crystallinity and other structure parameters of nascent polyethylene on polymerization time and temperature are discussed, and both the endo-and exothermal transitions occurring in the nascent and annealed structures after heating to 250°C were studied by means of DTA and DSC.
Abstract: Nascent polyethylene with high molecular mass (Mn ≈ 105, Mw ≈ 106) produced in hydrocarbon medium in presence of TiCl4/(C2H5)2AlCl/(C6H5)2Mg catalyst was studied by means of X-ray diffraction, electron and light microscopy, and low-angle light scattering. It consists of porous spherulite-fibril aggregates indicating a not very high degree of crystallinity α(α≈). Data, concerning the dependence of spherulite dimensions, degree of crystallinity and other structure parameters of nascent polyethylene on polymerization time and temperature are discussed. Using the same structure-analytical methods some samples of nascent polyethylene were studied after annealing them in nitrogen atmosphere at different temperatures between 110–250°C with successive cooling to room temperature. Furthermore both the endo- and exothermal transitions occurring in the nascent and annealed structures after heating to 250°C were studied by means of DTA and DSC. The experimental information leads to the conclusion that nascent polyethylene structures consist of crystalline folded chain lamellae with an increased amount of tie molecules between them as well as of extended chain crystals.
TL;DR: In this article, the catalytic activity of tungsten carbide for the oxidation of hydrogen in an acid medium has been investigated on sedimented powder electrodes by taking current density values at a given potential in the straight line portion of Tafel curves.
TL;DR: In this article, the interaction between aromatic compounds and the binary potassium-graphite intercalation compound-KC 24 -in solvating solvents (tetrahydrofuran or dimethoxyethane) was investigated.
TL;DR: The comparison of the gel electrophoresis patterns of nuclear and nucleolar matrix proteins reveals marked differences between these structures and it is suggested that theucleolar matrix has a distinct structure participating in selective interactions.
TL;DR: In this paper, the surface conductivity versus coverage curves successively pass through a minimum and a maximum and the decreasing parts of these curves are attributed to the appearance of alkali-metal-induced extrinsic surface states, whereas the increasing one is ascribed to the disappearance of the intrinsic states of the clean Ge(111) surface.
TL;DR: The protease from Fasciola hepatica belongs to the carboxyl group of proteases and probably plays an important role in helminth nutrition.
Abstract: A new protease, detected in an extract of Fasciola hepatica, was isolated and partly purified. The pH optimum for the cleavage of denaturated haemoglobin by the enzyme is pH 3.0. This proteolytic activity is inhibited by diazoacetylnorleucine methyl ester, pepstatin, the pepsin inhibitor from Ascaris suum, and phenylalanine. The cathepsin D inhibitor from potatoes, EDTA, mercaptoethanol and the inorganic salts tested have no inhibitory effect. The cleavage of the B-chain of oxidized insulin by enzyme was studied and compared with the digestion of the same substrate by chicken and pig pepsin. The protease from Fasciola hepatica belongs to the carboxyl group of proteases and probably plays an important role in helminth nutrition.