Showing papers by "Bulgarian Academy of Sciences published in 1986"
TL;DR: Various properties are proved, which are connected to the operations and relations over sets, and with modal and topological operators, defined over the set of IFS's.
13,376 citations
TL;DR: In this paper, the zero-order diffraction efficiency anomalies of a corrugated dielectric waveguide were studied theoretically in detail and a new and surprising phenomenon was observed: the efficiency changes from 0 to 100 per cent in the vicinity of the excitation of guided waves.
Abstract: The zero-order diffraction efficiency anomalies of a corrugated dielectric waveguide are studied theoretically in detail. A new and surprising phenomenon is observed: the efficiency changes from 0 to 100 per cent in the vicinity of the excitation of guided waves. The fundamental parameters of the system are found in the case where only one order is propagating and some of their properties are shown. The behaviour of the efficiency curves is explained by a phenomenological theory and a comparison with numerical rigorous results is made.
244 citations
TL;DR: In this paper, the characteristics of rigid solutions of organic dyes suitable for holographic recording were investigated, including fluorescein/orthoboric acid, methyl red/polymethylmetacrylate, and methyl orange/polyvinylalcohol.
Abstract: The characteristics of rigid solutions of organic dyes suitable for holographic recording-fluorescein/orthoboric acid, methyl red/polymethylmetacrylate, and methyl orange/polyvinylalcohol-are investigated. All of the three systems allow real-time recording and do not exhibit fatigue up to more than 104cycles of recording erasure. The system fluorescein/orthoboric acid possesses a faster response time than the other two systems-around 0.1 s. The phase character of the recording in the system methyl orange/polyvinylalcohol explains the high diffraction efficiency-up to 35 percent-in polarization holographic recording. New experimental results on the kinetics of the photoinduced anisotropy are presented and the mechanisms which could possibly speed up the processes, repeated periodically, are discussed.
95 citations
78 citations
TL;DR: In this paper, the atomic arrangement of a zinc-tellurite glass with composition 80% TeO2 + 20 mol% ZnO has been studied by means of the neutron diffraction method.
75 citations
TL;DR: It was shown that the changes in the shape of the extracellular action potentials around the end of the fibres were mainly due to the existence of the fibre end though a better correspondence of the experimentally recorded and the calculated extraceocytes was obtained when the morphology of the fiber end was taken into consideration.
Abstract: Intra- and extracellular action potentials of isolated frog muscle fibres were recorded at different distances to the end of the fibre. The first and second time derivatives of the intracellular action potentials were also recorded. The intracellular action potentials and their first and second time derivatives were almost the same regardless of the place of recording. With the decrease in the axial distance to the end the extracellular action potentials changed gradually in a complicated manner from a shape similar to the second time derivative into a shape similar to the first time derivative. Extracellular potentials, having two negative maxima, were recorded over the terminal taper part of the fibres. These alterations were simulated by a mathematical model. It was shown that the changes in the shape of the extracellular action potentials around the end of the fibres were mainly due to the existence of the fibre end though a better correspondence of the experimentally recorded and the calculated extracellular action potentials was obtained when the morphology of the fibre end was taken into consideration.
56 citations
TL;DR: In this paper, the authors attributed this phenomenon to a displacement current due to the oscillating flexoelectric polarization, which is proportional to the membrane curvature and depends on the lipid dipole moment and surface charge.
Abstract: Upon periodical bending of a BLM, by means of oscillating hydrostatic pressure with sound frequency, the generation of an a.c. electric current with the same frequency can be observed under short circuit conditions. Previously, this phenomenon was attributed by us to a displacement current due to the oscillating flexoelectric polarization. The latter is proportional to the membrane curvature and depends on the lipid dipole moment and surface charge.
55 citations
TL;DR: A total of thirty-eight water buffalo cows were treated in four experiments simultaneously either with FSH (first group) or PMSG (second group) within a 4-day period as mentioned in this paper.
54 citations
TL;DR: Protoplasts were isolated from seedling roots, hypocotyls, and cotyledons of four cultivars of Helianthus annuus and from leaves of axenic shoot cultures of the wild species H. rigidus to induce protoplast division, which could be induced to produce roots and organised meristematic regions in the presence of NAA and 6-BAP.
Abstract: Protoplasts were isolated from seedling roots, hypocotyls, and cotyledons of four cultivars of Helianthus annuus and from leaves of axenic shoot cultures of the wild species H. praecox, H. scaberimus and H. rigidus. Optimal culture conditions were established for the respective protoplast systems, using the agarose bead method of culture. Protoplast division was induced for all the species examined. In the case of the cultivars of H. annuus, hypocotyl and cotyledon protoplast division was sustained leading to callus formation, which in turn, could be induced to produce roots and organised meristematic regions in the presence of NAA and 6-BAP.
53 citations
TL;DR: In this article, a possible solution of the solar neutrino problem is that electron neutrinos decay in transit from the sun, and the phenomenological consequences of this hypothesis are discussed for the experiments with detectors of 2 H, 40 Ar, 71 Ga, 98 Mo, and electron-neutrino scattering.
53 citations
TL;DR: The results are discussed in terms of the possible role of C synapses in the regulation of AChE synthesis in postsynaptic cholinergic neurons and/or in theregulation of A ChE release into the extracellular space as well as in the establishment of new synaptic contacts.
Abstract: Using the electron-microscope technique of Lewis and Shute, we studied the localization of the acetylcholinesterase (AChE) activity in the hypoglossal, facial and spinal-cord motor nuclei of rats. The technique used selectively detects synapses with subsynaptic cisterns (type C synapses) as well as heavy deposits of reaction products in the rough endoplasmic reticulum, in fragments of the nuclear envelope, in some Golgi zones and on parts of the pericaryal plasma membrane, the axolemma and the dendritic membrane. In C synapses, AChE activity was located in the synaptie cleft and on the membrane of presynaptic boutons. Some C synapses exhibited distinct synaptic specialization in the form of multiple ‘active zones’. These zones were characterized by dense presynaptic projections, short dilations of the synaptic cleft, and postsynaptic densities localized between the postsynaptic membrane and the outer membrane of the subsynaptic cistern. Within the postsynaptic densities, rows of rod- or channel-like structures were observed. The subsynaptic cisterns were continuous with the positive rough endoplasmic reticulum. The results are discussed in terms of the possible role of C synapses in the regulation of AChE synthesis in postsynaptic cholinergic neurons and/or in the regulation of AChE release into the extracellular space as well as in the establishment of new synaptic contacts.
TL;DR: In this article, Voltammetric measurements were taken on electrolytically grown Ag(111) and Ag(100) electrodes to reveal new features of the Pb-adsorbates.
TL;DR: It is proved by use of the classification of the doubly even (32, 16) codes, that in addition to the design formed by the planes in PG(4, 2), there are exactly four other nonisomorphic quasi-symmetric 2-(31, 7, 7) designs, and they all have 2-rank 16.
TL;DR: In this article, the short range atomic order of a 20 mol% WO3-TeO2 glass has been investigated and correlation with the model RDFpartial (radial distribution function) and RDFtotal (RDFtotal) has been carried out.
Abstract: The short range atomic order of a 20 mol% WO3-TeO2 glass has been investigated. The alteration of the stereochemical polyhedra characteristics have been studied and correlation with the model RDFpartial (radial distribution function) and RDFtotal for TeO2 and WO3 glass has been carried out. A structural interpretation of the influence of the modifier on the P1, P2 and P3 peaks location has also been carried out. A comparison of RDFpartial, and RDFtotal, with RDFexp curve of the glass has been accomplished. Stability of the 0-0 distances (peak P2) has been established as well as a broadening effect at Te-Te, Te-second 0 distances (peak P3). The Te-Te atomic distances are most sensitive towards glass transition. A structural model based on TeO4, WO4 and WO6 polyhedra has been presented.
TL;DR: In this paper, it was shown that certain processes of random fragmentation called "uniform random fragmentation" lead to particle size distributions identical with the Weibull extremal probability distribution.
TL;DR: In this article, the authors dealt with a discontinuous control system that consists of two finite-dimensional linear systems; the first describes the motion in a given half-space, the second in the complementary half-Space Necessary and sufficient conditions for local controllability are obtained.
TL;DR: In this paper, the authors investigated the effect of Ag and As on anodic oxidation of lead in H 2 SO 4 solutions, and found that Ag reduces the oxidation rate of Pb significantly, while As enhances it.
TL;DR: The optimum conditions of starch hydrolysis, catalysed by a thermostable α-amylase (EC 3.2.1) produced by the strain Bacillus licheniformis (MB 80), were determined in this paper.
TL;DR: In this paper, a classification scheme of epitaxy is proposed, which relates the order of the epitaxy to the hierarchy of the coinciding reciprocal lattice vectors of the substrate surface and the monolayer.
TL;DR: In this article, self-organization phenomena are observed during electrodeposition of silver-antimony alloys and the width of the black and white regions depends on the current density and the antimony content in the electrolyte.
Abstract: Self-organization phenomena are observed during electrodeposition of silver-antimony alloys. On increasing the current density, black regions (assumed to be an antimony-richer phase) appear on the electrode surface. Under certain conditions these black regions are shaped as spirals with different topological charges. The width of the black and white regions depends on the current density and the antimony content in the electrolyte. Quantitative characterization of the phase composition in the black regions is a problem which still remains to be solved.
TL;DR: In this article, it was shown that magnetic ordering at finite temperatures occurs when interchain interactions in a quasi-dimensional nonclassical polymers are taken into account, and the two-dimensional alternant polymers display magnetic order at finite temperature.
Abstract: Within the Ising model, the two-dimensional alternant nonclassical polymers display magnetic order at finite temperatures and are characterized by a nonzero critical point Tc.
It is shown that magnetic ordering at finite temperatures occurs when interchain interactions in a quasi- dimensional nonclassical altemant polymer are taken into account.
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.
TL;DR: The phospholipid composition of ram spermatozoa plasma membranes has been investigated and an exclusively high participation of the choline- and ethanolamine-plasmalogens in the phosphatidylcholine and phosph atidylethanolamine fractions has been established.
TL;DR: Analysis of the response distributions suggests the existence of two-independent mechanisms for evaluating temporal interrelations: one for detecting simultaneity and the other for identifying temporal order.
Abstract: Temporally overlapping, spatially separated visual stimuli were used for studying perception of simultaneity and temporal order. Pairs of flashes each of 100 ms duration were presented with stimulus onset asynchronies of 0, 30, 50, and 70 ms. Three spatial arrangements of flash presentation were tested: both flashes were presented foveally; one flash was presented foveally and the other at 8 deg in the left visual hemifield; one flash was presented foveally and the other at 8 deg in the right visual hemifield. Onset asynchronies of 30 and 50 ms were not sufficient for correct identification of temporal order although the flashes were not perceived as simultaneous. Analysis of the response distributions suggests the existence of two-independent mechanisms for evaluating temporal interrelations: one for detecting simultaneity and the other for identifying temporal order. A better detection of simultaneity was found when synchronous flashes were presented together with pairs of flashes separated by larger onset asynchronies. Reading habits may explain only part of the left-right asymmetries of the response distributions. The possible lateralization of the two suggested mechanisms within the cerebral hemispheres is discussed.
TL;DR: In this article, the authors describe the process of accumulation of the new archaeointensity results from Bulgaria after 1978 and discuss the methods of laboratory treatments are discussed, and the results are given in terms of the ratio FA/FD, where FD is the geomagnetic field intensity at the site due to an axial geocentric dipole with the present day moment.
Abstract: This paper describes the process of accumulation of the new archaeointensity results from Bulgaria after 1978. The methods of laboratory treatments are discussed. Beside the difficulties connected with the experimental determination of the ancient intensity, the main obstacle for a better elucidation of its variations is inaccurate dating, especially in the prehistoric past. The conclusion is drawn that the relative chronology of prehistoric cultures has to be preserved.The revised archaeointensity results are systematized as site averages and a weight is given to each individual result. Data are given in terms of the ratio FA/FD, where FD is the geomagnetic field intensity at the site due to an axial geocentric dipole with the present-day moment.A first attempt for computer processing of the experimental data is shown. A second order polynomial is taken as a local model in a running window of 5 points. In the Appendix the theoretical basis is described and the weights given to experimental site mean values are explained. To obtain the continuous curve of smooth values of the intensity a spline cubic interpolation with a step of 10 years is used.
TL;DR: In this article, the diffraction efficiency curves of planar waveguides with corrugation on the waveguide-air boundary or on the substrate boundary were calculated as a function of the angle of incidence.
Abstract: The diffraction efficiency curves are calculated as a function of the angle of incidence for planar waveguides with corrugation on the waveguide-air boundary or on the waveguide-substrate boundary, respectively. It is shown that the reflectance of the system is increased up to 100% because of the excitation of the waveguide mode. A detailed phenomenological study is carried out taking into account the influence of the waveguide thickness and the corrugation depth. Possible applications of these waveguides as a narrow-band reflection filter and selective mirror are discussed.
TL;DR: In this article, a quasi-liquid layer on a crystal surface was investigated by considering it as a thin liquid layer and the following thermodynamic quantities: chemical potential, vapour pressure, pressure tensor components and disjoining pressure of the layer were derived.
TL;DR: Acetone washes of leaves and stems of A. kotschyi, A. umbellata and A. spinulifolia yielded methyl ethers of 6-hydroxyflavones and 6- Hydroxyflavonols, which were confirmed by spectroscopic methods and by co-chromatography with authentic standards.
TL;DR: Data show that the rat rDNA NTS regions flanking the rRNA transcription unit are characterized by a combination of short interspersed (B2-superfamily) and various simple sequences.
Abstract: We investigated the organization of the rat rDNA non-transcribed spacer (NTS) by determining the sequence of large NTS segments located upstream (2501 bp) and downstream (4025 bp) from the rRNA transcription unit. We identified four B2-like and two ID mobile elements. They may be grouped in three pairs with the members of each pair located in the upstream and downstream NTS. The ID sequences are identical to the consensus sequence, while the pairs of B2-like elements show 85% and 50/65% homology to the consensus B2 sequence. The proximal part of the downstream NTS contains a region of widely diverged SalI tandem repeats. A considerable part of the analyzed upstream and downstream NTS sequences is constituted by different types of simple sequences and long poly(purine) X poly(pyrimidine) tracts. These data show that the rat rDNA NTS regions flanking the rRNA transcription unit are characterized by a combination of short interspersed (B2-superfamily) and various simple sequences.
TL;DR: In immature erythroblasts erythropoietin acts via a receptor and a guanine nucleotide-binding protein with high affinity for GTP (EC50 less than 10 nM), whereas haemin appears to activate adenylate cyclase indirectly, as a consequence of progressive perturbations of the plasma membrane.
Abstract: The effect of two agents of erythroid cell differentiation on the adenylate cyclase activity of fractionated rabbit bone marrow erythroblasts has been investigated. Addition of 0.2U/ml erythropoietin to cell cultures causes a transient increase in the activity of plasma membrane adenylate cyclase, which is maximal by 20 min and disappears within 4 h. The magnitude of the response to hormonal stimulation depends on the stage of erythroid cell development and is greater in the more immature cells. Addition of 50 microM haemin to cultures of erythroblasts also causes an increase in the activity of adenylate cyclase, which differs from the effect of erythropoietin in kinetics and specificity of target cells. With immature cells the haemin-induced stimulation starts after the first hour and continues to increase up to 20 h of culture. Erythropoietin but not haemin can stimulate the basal activity of adenylate cyclase in an in vitro assay containing plasma membranes of immature erythroid cells. The degree of activation depends on the concentration of erythropoietin and is maximal with 0.2-0.5 U/ml hormone (5-12 nM). In the presence of guanine nucleotides the activation of adenylate cyclase by erythropoietin is increased further but the effect is not additive. With respect to the basal and the guanine-nucleotide-stimulated activities of adenylate cyclase erythropoietin acts differently from the beta-agonist l-isoprenaline. The in vitro effect of erythropoietin is abolished by the beta-thio analogue of GDP, GDP[beta S], and extensive washing of membranes makes hormone action GTP-dependent. The stimulation of adenylate cyclase by the addition of erythropoietin to the reaction mixture is inversely related to the extent of previous hormonal stimulation of the cells from which the membranes were prepared. This loss of hormonal responsiveness is due to desensitization or receptor down-regulation and persists for up to 20 h. We conclude that in immature erythroblasts erythropoietin acts via a receptor and a guanine nucleotide-binding protein with high affinity for GTP (EC50 less than 10 nM), whereas haemin appears to activate adenylate cyclase indirectly, as a consequence of progressive perturbations of the plasma membrane.