Showing papers by "Bulgarian Academy of Sciences published in 1994"
TL;DR: In vivo O2 increases the supply of free iron by oxidatively attacking the [4Fe-4S] clusters of dehydratases such that they release Fe(II), which can then reduce H2O2.
415 citations
TL;DR: In this article, a series of activated carbons has been prepared by steam pyrolysis of apricot and cherry stones, almond shells, and grape seeds at relatively low temperatures of 600, 650, and 700°C for 1-3 h at each temperature.
220 citations
TL;DR: It was demonstrated that there are striking differences in the morphology of fibroblasts adhering to hydrophilic and hydrophobic surfaces, judged by the overall cell shape, the organization of FN receptors and actin filaments, which suggest that the method of adsorption and reorganization of FN may be critical for the biocompatibility of materials.
Abstract: It is a general trend that mammalian cells interact better with wettable surfaces than with non-wettable surfaces. The basis for this difference is still poorly understood. In this study hydrophilic clean glass and hydrophobic octadecyl glass have been used as model surfaces. We show that fibroblasts on hydrophilic surfaces may reorganize fluorescent fibronectin (FN) in an extracellular matrix-like structure whereas on hydrophobic surfaces no rearrangement of FN occurs. This was accompanied by a high proliferation of fibroblasts on clean glass whereas on octadecyl glass no cell growth occurred. Moreover, it was demonstrated that there are striking differences in the morphology of fibroblasts adhering to hydrophilic and hydrophobic surfaces, judged by the overall cell shape, the organization of FN receptors and actin filaments. Indeed, the preadsorption of FN on these surfaces could almost abolish morphological differences between hydrophilic and hydrophobic surfaces. However, preadsorption of FN could not restore the proliferation of fibroblasts on the hydrophobic surface. Taken together, the results suggest that the method of adsorption and reorganization of FN may be critical for the biocompatibility of materials.
191 citations
TL;DR: In this paper, LiMnyCo1−yO2 has been obtained by a solid state reaction between lithium hydroxide and manganese-cobalt spinels in air (0.1−4.2 V) or under nitrogen ( 0.2 < y<1).
128 citations
TL;DR: In this paper, the glass formation region in the V2O5, MoO3, and Bi2O3 systems was investigated by the roller-quenching method, based on X-ray diffraction, differential thermal analysis (DTA), and IR spectroscopy.
Abstract: The glass formation region in the V2O5MoO3Bi2O3 system was investigated by the roller-quenching method. Low melting glasses were obtained in the MoO3- and V2O5-rich compositions. Characterization of the glasses was made by X-ray diffraction, differential thermal analysis (DTA) and IR spectroscopy. According to the DTA data, the glass transformation temperature, Tg, for the different compositions varied between 200 and 290°C and the cystallization temperature, TX, was within the interval of 225–330°C. Structural models for glasses of th MoO3Bi2O3 and V2O5Bi2O3 systems were suggested on the basis of IR spectral investigations, by comparing with known crystalline structures. It was shown that the glasses possess [MoO4], [MoO6], [VO4], and [BiO6] groups as basic structural units.
127 citations
TL;DR: The results suggest that the chloroplasts under saline conditions in the leaves of salt tolerant wheat cultivars, are not exposed to excess Na + , in contrast to those in the sensitive ones.
111 citations
TL;DR: The growth and carotenoid biosynthesis of the yeast Rhodotorula glutinis was studied by cocultivation with Lactobacillus helveticus in cheese ultrafiltrate containing 3.9% and 7.1% lactose, and a maximum production was reached at an early stationary phase.
Abstract: The growth and carotenoid biosynthesis of the yeast Rhodotorula glutinis was studied by cocultivation with Lactobacillus helveticus in cheese ultrafiltrate containing 3.9% and 7.1% lactose. By growing this mixed culture in a 15-L fermentor MBR AG (Switzerland) at an air flow rate of 0.5 L/L min and agitation at 220 rpm for 6 days, a total yield of carotenoids of 268 μg/g dry cells wasobtained. Carotenoids were formed almost parallel with the cell growth, anda maximum production was reached at an early stationary phase. A high-performance liquid chromatographic system (HPLC) permitting simultaneous determination of major carotenoid pigments was used. The three main pigments (torularhodin, β-carotene, and torulene) were formed in Rhodotorula glutinis, and reached a maximum concentration as follows: 182.0, 43.9, 23.0 μg,g dry cells. © 1994 John Wiley & Sons, Inc.
109 citations
TL;DR: In this paper, the adsorption of Pb 2+, Cu 2+, Zn 2+ and Cd 2+ from aqueous solution at 293 K by activated carbons obtained from different raw materials was studied.
Abstract: The adsorption of Pb 2+ , Cu 2+ , Zn 2+ and Cd 2+ from aqueous solution at 293 K by activated carbons obtained from different raw materials was studied. These carbons were prepared by water vapour pyrolysis of the raw materials-apricot stones, coconut shells and lignite coal. The influence of the solution pH on the adsorption processes has been studied. The presence of other metal ions in the solution decreases the adsorption of each of the ions. The selective adsorption of the metal ions is observed but the ones preferentially adsorbed do not completely prevent the adsorption of other ions. The chemical nature of the carbon surface and metal ions have great significance for the adsorption process
107 citations
TL;DR: It is shown that the first intermediate host is a lymnaeid snail and the second intermediate hosts are various pulmonate and prosobranch snails, mussels, frogs and freshwater turtles, and the final hosts are birds.
Abstract: The life-cycle of Echinostoma revolutum (Froelich, 1802) Dietz, 1909 has been completed experimentally beginning with infected snails collected at the type-locality, near Erlangen, Germany. Based on the specimens obtained, each stage of the life-cycle has been redescribed. Important taxonomic features are discussed and hitherto unknown characteristics are described. Synonyms for E. revolutum are: Fasciola revoluta Froelich, 1802; Echinostoma paraulum Dietz, 1909; E. audyi Lie & Umathevy, 1965; and E. ivaniosi Mohandas, 1973. Adults and larvae described as E. revolutum in other works are found to be identical with Echinostoma echinatum (Zeder, 1803), E. trivolvis (Cort, 1914), E. jurini (Skvortsov, 1924), E. caproni Richard, 1964, Moliniella anceps (Molin, 1859), Echinochasmus beleocephalus (Linstow, 1873) and other echinostome species. For nearly a century, incorrect morphological, biological, life-cycle and host information has been attributed to E. revolutum, and at times these data have contributed to the diagnoses of the species. Occasionally, authors actually working with E. revolutum have ascribed their results to other species. Based on extensive experimental life-cycle studies beginning with infected snails from type-localities, it is shown that (1) the first intermediate host is a lymnaeid snail; (2) the second intermediate hosts are various pulmonate and prosobranch snails, mussels, frogs and freshwater turtles; (3) the final hosts are birds; (4) E. revolutum cercariae and adults have 37 collar spines; (5) the species occurs only in Europe and Asia; (6) Cercaria echinata Siebold, 1937, Echinostoma echinatum (Zeder, 1803) and E. jurini (Skvortsov, 1924) are the closely related 37-spined allies in Europe; and (7) species specific characteristics are expressed only in the larvae and the host-parasite relationships. The adults of E. revolutum cannot be identified using morphological criteria and it is proposed that worms with 37 collar spines belonging to the genus Echinostoma and occurring in naturally infected birds in Europe and Asia be referred to an “E. revolutum group.”
101 citations
TL;DR: The polysaccharide isolated from the green marine algae Ulva lactuca was studied for antiviral activity in vitro against a number of human and avian influenza viruses and showed considerable inhibition of the viral reproduction.
Abstract: A polysaccharide from the green marine algae Ulva lactuca has been isolated. The substance has been investigated after acid hydrolysis by thin-layer and gas chromatography. The following carbohydrate components have been found: arabinose-xylose-rhamnose-galactose-mannose-glucose in ratio 1:1:9:5:2.5:16 respectively. One unidentified sugar has been demonstrated too. The polysaccharide has been studied for antiviral activity in vitro against a number of human and avian influenza viruses. A considerable inhibition of the viral reproduction was found. The effect was dose-dependent, strain-specific and selective.
94 citations
TL;DR: In this article, the authors present a review of quantitative EPR spectrometer results available in the literature in order to focus the attention of the world EPR community and thus to stimulate their activity on solving the problems of quantitative epr spectrometry.
Abstract: The purpose of the present review is to collect some results available in the literature in order to focus the attention of the world EPR community and thus to stimulate their activity on solving the problems of quantitative EPR spectrometry.
TL;DR: The 3‐dimensional optimization of the electrostatic interactions between the charged amino acid residues was studied by Monte Carlo simulations on an extended representative set of 141 protein structures with known atomic coordinates to conclude that the charge‐charge interactions are better optimized in the enzymes than in the proteins without enzymatic functions.
Abstract: The 3-dimensional optimization of the electrostatic interactions between the charged amino acid residues was studied by Monte Carlo simulations on an extended representative set of 141 protein structures with known atomic coordinates. The proteins were classified by different functional and structural criteria, and the optimization of the electrostatic interactions was analyzed. The optimization parameters were obtained by comparison of the contribution of charge-charge interactions to the free energy of the native protein structures and for a large number of randomly distributed charge constellations obtained by the Monte Carlo technique. On the basis of the results obtained, one can conclude that the charge-charge interactions are better optimized in the enzymes than in the proteins without enzymatic functions. Proteins that belong to the mixed alpha beta folding type are electrostatically better optimized than pure alpha-helical or beta-strand structures. Proteins that are stabilized by disulfide bonds show a lower degree of electrostatic optimization. The electrostatic interactions in a native protein are effectively optimized by rejection of the conformers that lead to repulsive charge-charge interactions. Particularly, the rejection of the repulsive contacts seems to be a major goal in the protein folding process. The dependence of the optimization parameters on the choice of the potential function was tested. The majority of the potential functions gave practically identical results.
TL;DR: In this article, the antioxidant properties of p-hydroxybenzoic, vanillic, syringic, 3,4-dihydroxybenzosic, p-coumaric, ferulic, sinapic and caffeic acids were studied in the concentration range 0.02-0.20 wt% during autoxidation at 100°C of lard and sunflower oil methyl esters (MEL and MESO, respectively).
Abstract: Antioxidative properties ofp-hydroxybenzoic, vanillic, syringic, 3,4-dihydroxybenzoic,p-coumaric, ferulic, sinapic and caffeic acids were studied in the concentration range 0.02–0.20 wt% during autoxidation at 100°C of lard and sunflower oil methyl esters (MEL and MESO, respectively). In both lipid systems, the derivatives of benzoic acid had weaker inhibiting properties than did the corresponding analogues of cinnamic acid. The effectiveness and strength of the antioxidative action were considerably lower in the lipid system MESO, which was rich in linoleic acid and was more easily oxidized. Thep-hydroxybenzoic, vanillic, syringic andp-coumaric acids in this system exercised no inhibiting effect. We established that the molecules of the investigated phenolic acids initiated the chain radical process of autoxidation, and the formed antioxidant radicals propagated the chains as a result of the reaction with the lipid substrate. These reactions proceeded at a higher rate in MESO than in MEL.
TL;DR: The mineralogy, elemental composition, and modes of occurrence of 49 elements in nine composite samples of Bobov Dol high-ash coals were studied by optical microscopy, scanning and transmission electron microscopy and chemical analysis as discussed by the authors.
TL;DR: In this paper, the authors introduce two new concepts for efficient and weakly efficient point sets and investigate the relationship between the efficient and the weakly efficiency point sets under the following aspects: (1) What are the relationships between the Efficient and the Weakly Efficient point sets? (2) If the sequence (v) of Efficient points converges for ρ 0, is the limit efficient, or weakly EH? (3) Can the distance between the -efficient and EH point set be estimated in terms of ρ?
Abstract: We introduce two new concepts forź-efficiency and investigate these and some known concepts under the following aspects: (1) What are the relationships between the efficient and theź-efficient point set? (2) If the sequence (vź) ofź-efficient points converges forź ź 0, is the limit efficient, or weakly efficient? (3) Can the distance between theź-efficient and the efficient point set be estimated in terms ofź?
Wir fuhren zwei neue Konzepte furź-Effizienz ein und untersuchen diese und einige bekannte Konzepte unter folgenden Gesichtspunkten: (1) Wie sind die Beziehungen zwischen den Mengen der effizienten und derź-effizienten Punkte? (2) Wenn eine Folge (vź) vonź-effizienten Punkten furź ź 0 konvergiert, welche Aussagen konnen uber den Limes gemacht werden (effizient, schwach effizient, ...)? (3) Kann der Abstand zwischen den Mengen derź-effizienten und effizienten Punkte bezuglichź abgeschatzt werden?
TL;DR: In this article, the authors summarized the archaeomagnetic determinations obtained from the collections of archaeological materials, dated in the last 2000 years, summarized the materials used, the methodology applied, the local database organization, the principles of data processing and smoothing procedures, and the errors evaluation at different levels of analysis of the experimental results are described.
Abstract: The archaeomagnetic determinations obtained from the collections of archaeological materials, dated in the last 2000 years are summarized The review describes the materials used, the methodology applied, the local database organization, the principles of data processing and smoothing procedures Errors evaluation at different levels of analysis of the experimental results are described Special attention is paid to the archaeointensity determinations Some rock magnetic properties studied in connection with the difficulties in the Thellier method are summarised The curves of geomagnetic field elements variations for the last 2000 years for Bulgaria are shown The Bauer plots, VGP path and VDM curve are also discussed, the latter confirming the general decrease in the strength of the geomagnetic field from the beginning of this era to the present Westward drift of the geomagnetic field non-dipole part cannot be considered proved yet for the time interval 7th to 13th Centuries AD from the Bulgarian directional data
TL;DR: CCK-8 exerted a favorable effect on learning and memory when injected into the left but not into the right amygdala, and increased locomotion at the lowest dose, while at the high doses it significantly decreased it.
TL;DR: In this paper, the level energies and transitions relevant to the members of quadrupole-oc-tupole and octupole-octupole two-phonon multiplets are calculated and compared to experiment in the case of 144 Sm.
TL;DR: Physical and biophysical mechanisms of mechano-sensitivity of cell membranes are reviewed, and possible applications in molecular electronics of mechanosensors employing some of the recognized principles of Mechano-electric transduction in natural membranes are discussed.
Abstract: Physical and biophysical mechanisms of mechano-sensitivity of cell membranes are reviewed. The possible roles of the lipid matrix and of the cytoskeleton in membrane mechanoreception are discussed. Techniques for generation of static strains and dynamic curvatures of membrane patches are considered. A unified model for stress-activated and stress-inactivated ion channels under static strains is described. A review of work on stress-sensitive pores in lipid-peptide model membranes is presented. The possible role of flexoelectricity in mechano-electric transduction, e.g. in auditory receptors is discussed. Studies of flexoelectricity in model lipid membranes, lipid-peptide membranes and natural membranes containing ion channels are reviewed. Finally, possible applications in molecular electronics of mechanosensors employing some of the recognized principles of mechano-electric transduction in natural membranes are discussed.
TL;DR: The reduced CO 2 fixation of protoplasts isolated from NaCl stressed plants indicated a direct effect of NaCl on the photosynthetic process, which was not dependent upon stomatal closure.
TL;DR: In this paper, the authors studied the stability of hollow fiber drawing based on quasi-one-dimensional equations of thin film dynamics and showed that the drawing process is unstable when the draw ratio E (that of output to input velocities) exceeds the critical value E*=20.22 when the viscosity force is dominating.
Abstract: Stability of hollow fiber drawing is studied, based on the quasi‐one‐dimensional equations of thin film dynamics. It is shown that the model isothermal drawing process is unstable when the draw ratio E (that of output to input velocities) exceeds the critical value E*=20.22 when the viscosity force is dominating. Under stable regimes with E
TL;DR: In this paper, the authors examined the infrared spectra of V2O5, MoO3, and Fe2O3 glasses and compared the results with the results of known crystals.
Abstract: Infrared spectra have been examined in V2O5MoO3Fe2O3 glasses, and the results were compared with infrared spectra of known crystals. This study has shown that structural units formed in the glasses include [VO5] groups (bands at 1020-930 cm−1), isolated [VO4] and [MoO4] tetrahedra (a band at 840 cm−1), [FeO4] tetrahedra and [FeO6] octahedra (bands at 660 cm− and 520-480 cm−1). Glass formation is discussed on the basis of glass structure. This study has established that the appearance of isolated tetrahedral groups in the network without MOM bridging bonds decreases the glass-formation ability.
TL;DR: In this article, the authors used an ansatz for the elliptic Baker-Akhiezer functions to describe the cover, which accentuated the work of Hermite and gave a description of elliptic solitons yielded by two-gap Lame and Treibich-Verdier potentials.
Abstract: We study special algebraic curves being a covering over tori and associated with elliptic solitons. To describe the cover, we use an ansatz for the elliptic Baker-Akhiezer functions which accentuates the work of Hermite. We give a description of the elliptic solitons yielded by two-gap Lame and Treibich-Verdier potentials; we also consider three and four-gap Lame potentials and the Halphen equation with n=4. Examples of elliptic solutions for integrable dynamical systems are constructed against the background of the developed approach.
TL;DR: In this paper, a comparative study has been carried out of the output characteristics, electric parameters, and main kinetic plasma processes concerning CuBr laser performance during the excitation pulse, and four electric circuits were used for CuBr vapor laser excitation.
Abstract: A comparative study has been carried out of the output characteristics, electric parameters, and main kinetic plasma processes concerning CuBr laser performance during the excitation pulse. Four electric circuits were used for CuBr vapor laser excitation: WPC (without peaking capacitor); OC (ordinary circuit, i.e., with a peaking capacitor); IPC (interacting peaking circuits), and IC (interacting circuits). The calculated and experimental values are in very good agreement. The improvement of the CuBr laser performance from WPC- to IC-excitation (the laser power and efficiency increase three times) is mainly attributed to the increased physical laser efficiency, which concerns the electrooptic energy conversion with regard to plasma kinetic processes. >
TL;DR: In this paper, a numerical model is developed for determination of the unsteady state temperature field in conductively heated canned foods of various shapes under boundary conditions of the third kind (surface convection) and at variable heating medium temperatures.
TL;DR: A description of the new version of the OASIS system for computer assisted quantitative structure-property analysis is presented, which is much more flexible and versatile than the version recently introduced.
TL;DR: The purpose of the present study was to establish the relationship between muscle architecture and H‐reflex recordings in quadriceps femoris muscle and monopolar recordings of the H‐potential were found to be preferable to bipolar recordings because of the reproducibility of shape and easier distinction between the M‐ andH‐potentials.
Abstract: The purpose of the present study was to establish the relationship between muscle architecture and H-reflex recordings in quadriceps femoris muscle. H-reflexes were elicited in human quadriceps femoris muscle over a broad area of skin to document the shape and amplitude of the H-potentials. This, in combination with recording monopolar and bipolar H-potentials, was performed to determine the location and method for measuring maximum-amplitude H-reflexes. The influence of neural and peripheral factors on the H-potential during passive length changes was studied by comparing the amplitude of H-potentials to motor unit action potentials. Monopolar recordings of the H-potential were found to be preferable to bipolar recordings because of the reproducibility of shape and easier distinction between the M- and H-potentials. The location for recording maximum H-potentials was in the distal one third of the quadriceps femoris muscle, over the border between vastus lateralis and rectus femoris. The inferred relationship between H-potential amplitude and reflex excitability must be made with caution in quadriceps femoris muscle because the amplitude of both the motor unit potential and H-potential change as a function of muscle length. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, the antioxidative effectivity and strength of different concentrations of ethanolic extract from Fraxinus ornus bark, as well as of esculetin, esculin, fraxetin and fraxin during the autoxidation at 100°C of kinetically pure triacylglycerols of lard (TGL) and triacyls of sunflower oil (TGSO) were determined.