Showing papers by "Bulgarian Academy of Sciences published in 1993"
TL;DR: According to this model, the rapid deacetylation of distinct lysines in especially H2A and H2B would facilitate the association of anionic protein domains of regulatory proteins to specific nucleosomes and may represent a unique regulatory mechanism in the early steps of gene activation.
326 citations
TL;DR: In this article, the effect of Co substitution on the Ni 3+ content and long-range order in Li x Ni 2− x O 2 (0.8≤ y ≤ 1) was investigated.
235 citations
TL;DR: In this paper, experimental data on the activity of nucleating catalysts in various organic and inorganic glass-forming melts are summarized and discussed in terms of the theoretical approach developed in Part I of the present investigation.
Abstract: Methods for determining the nucleating activity of substrates are considered. Experimental data on the activity of nucleating catalysts in various organic and inorganic glass-forming melts are summarized and discussed in terms of the theoretical approach developed in Part I of the present investigation. The nucleation of the same melt induced by different substrates is analysed. In this respect, the data for sodium metaphosphate, lithium metaphosphate, poly(ethylene terephthalate), poly(vinyl chloride), sodium tetraborate nucleated with noble metal cores, for poly(decamethylene terephthalate), lithium disilicate, poly(ethylene) and water initiated by oxide and halide catalysts give a direct proof for the validity of the concepts, developed in Part I.
229 citations
TL;DR: In this article, the nucleating activity of different insoluble additives in the heterogeneous nucleation of organic and inorganic glass-forming melts is treated from a generalized thermodynamic standpoint.
Abstract: The nucleating activity of different insoluble additives in the heterogeneous nucleation of organic and inorganic glass-forming melts is treated from a generalized thermodynamic standpoint. The activity of a nucleating catalyst is defined through the adhesion energy and calculated from the forces of cohesion in the substrate and in the overgrowing crystal. An estimate is also made of the relative contribution of structure mismatch to the bonding energy by evaluating the total energy of misfit dislocations at the deposit/substrate interface. This approach extends and specifies the limits of application of existing concepts of crystallographic matching and mismatching. By this generalized method, there is a possibility of predicting the nucleating activity of various crystallization cores in the induced crystallization of glass-forming melts by using data on the heat of sublimation (or the temperature of melting) of the respective nucleation catalyst or the value of its thermal expansion coefficient.
203 citations
TL;DR: In this paper, strong converse inequalities for various linear approximation processes are established. But these results are restricted to trigonometric polynomial approximation processes, on holomorphic semigroups, on Bernstein polynomials and on other commonly used approximation processes.
Abstract: Techniques are developed to obtain strong converse inequalities for various linear approximation processes. This will establish equivalence between the approximating rate of a certain linear process and the appropriate PeetreK-functional. Approximation processes that will be treated have to be saturated asK-functionals are saturated. These general methods will lead to new results on the various trigonometric polynomial approximation processes, on holomorphic semigroups, on Bernstein polynomials and on other commonly used approximation processes.
165 citations
TL;DR: In this paper, the effect of the starting products and the synthesis temperature on electrochemical parameters of Li 1− x Mn 2 O 4 (0 x 2 O4 spinel) for lithium cells operating at low and medium discharge rates is not essentially affected by the nature of starting products.
134 citations
TL;DR: In this article, the authors investigated the kinetics of complete catalytic oxidation of benzene by ozone on MnO2 in gradientless conditions and established that the decomposition of ozone and the oxidation process for benzene can proceed within the same temperature range (10 − 80 °C ), and the apparent activation energies are 32 kJ/mol and 30 kJ /mol, respectively.
Abstract: The kinetics of complete catalytic oxidation of benzene by ozone on MnO2 in gradientless conditions has been investigated. It was established that the decomposition of ozone and the oxidation of benzene on MnO2 proceed within the same temperature range (10–80 °C ), and the apparent activation energies are 32 kJ/mol and 30 kJ/mol, respectively. The complete oxidation of benzene by molecular oxygen takes place at temperatures above 160°C with an apparent activation energy of 88 kJ/mol. It has been assumed that the rate-determining step of complete oxidation by ozone is the ozone decomposition.
112 citations
TL;DR: In this paper, the characteristics of a capacitor in the form of trilayer structure YBa2Cu9O7−x/(BaxSr1−x)TiO9/YBa2cu9O 7−x are discussed.
Abstract: The initial success in high-T c superconductivity applications at microwaves leads to the creation of new branch in microwave electronics operating at liquid nitrogen temperature. In this connection one should reconsider the behaviour of nonlinear dielectrics at microwaves. The characteristics of a capacitor in the form of trilayer structure YBa2Cu9O7−x/(BaxSr1−x)TiO9/YBa2Cu9O7−x are discussed. The crucial influence of oxygen stoichiometry on the structure properties is assumed. The layered structures including non-linear dielectrics could be used as a basis for devices with voltage control of the microwave circuit parameters.
106 citations
TL;DR: The results obtained, together with the already established neuronspecific enolase-, substance P-, methionine-enkephalinand proopiomelanocortin (POMC)-derived peptide-like immunoreactivity, provide strong evidence for the neuroendocrine (paraneuronal, APUD-like) nature of the Leydig cells of the human testis.
Abstract: A number of marker substances for neuronal and neuroendocrine cells have been demonstrated in the cytoplasm of the interstitial Leydig cells of human testes using basic immunocytochemical methods and some of their modifications. We were able to reveal immunoreactivity for enzymes involved in the synthesis of the catecholamines dopamine and noradrenaline (tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine-beta-hydroxylase), for the indolamine 5-hydroxytryptamine (serotonin), as well as for a number of well-known neuronal markers such as the neurofilament protein 200, synaptophysin, chromogranin A + B, the neural cell-adhesion molecule (N-CAM), the microtubule-associated protein (MAP-2), and the calcium-binding proteins: S-100, calbindin and parvalbumin. Immunoreactivity for these substances was found in the majority of the interstitial cells although differences in the staining intensity among the individual Leydig cells and among Leydig cells from different patients were observed. At the electron-microscopic level the Leydig cell cytoplasm was seen to contain microtubules, intermediate- and microfilaments as well as clear (40-60 nm) and dense-core (100-300 nm) vesicles, providing a morphological correlate for some of the immunocytochemical results. Although individual marker substances are not absolutely specific for nerve and neuroendocrine cells, the results obtained, together with the already established neuron-specific enolase-, substance P-, methionine-enkephalin- and proopiomelanocortin (POMC)-derived peptide-like immunoreactivity, provide strong evidence for the neuroendocrine (paraneuronal, APUD-like) nature of the Leydig cells of the human testis.
102 citations
Journal Article•
99 citations
TL;DR: In this paper, a method for producing membranes for optical pH sensors is described, where pH indicators (neutral red and Congo red) are covalently bonded to a transparent acetylcellulose film.
TL;DR: The aim of this study was first to specify the morphology and neuronal environment of the large cholinergic neurons, and second to determine the distribution and mode of termination of the corticostriatal and dopaminergic inputs on these neurons in the rat striatum.
TL;DR: In this article, the influence of elastic strain on devitrification processes in glasses is investigated, and it is shown that elastic strain can be considered as the origin both for the absence of bulk deformation and preferential surface crystallization of glasses in systems with different specific volumes of the vitreous and crystalline states.
Abstract: The influence of elastic strains on devitrification processes in glasses is investigated. It is known that in the vicinity and below the vitrification temperature, Tg, thermodynamic inhibition of crystallization has to be taken into account in addition to kinetic inhibition of crystallization connected with the extremely low values of the mobility (large values of the viscosity). This thermodynamic inhibition results from the evolution of elastic fields due to a difference in the specific volumes of the vitreous and crystalline states of the substance. The inhibiting term is of the same order of magnitude as the thermodynamic driving force of crystallization (and may even exceed it). It is considerably diminished for devitrification at the surface of a glass. In this way, elastic strains can be considered as the origin both for the absence of bulk devitrification and for preferential surface crystallization of glasses in systems with different specific volumes of the vitreous and crystalline states.
TL;DR: The purified enzyme was strongly inhibited by N -bromosuccinimide (NBS) and by EDTA, and Dithiothreitol and iodacetamide had no inhibitory effect on the purified enzyme.
TL;DR: A review of numerical techniques for the solution of heat and mass transfer problems with solid/liquid phase change is presented in this paper, where two basic approaches with a free boundary (phase change interface) are considered.
TL;DR: The results suggest that the Panax ginseng G115 and the Ginkgo biloba GK501 extracts possess properties similar in every respect to those of nootropic drugs.
Abstract: In experiments on young (aged 3 months) and old (aged 26 months) rats, using some conditioned-reflex methods with punishment or positive reinforcement for active and passive avoidance (shuttle-box, step-down, step-through, and water maze), we studied the effects of the standardized extracts of Panax ginseng (G115), Ginkgo biloba (GK501) and their combination Gincosan (PHL-00701). The extracts were administered orally for 7 days before training at three increasing doses: 17, 50, and 150 mg/kg for G115; 10, 30, and 90 mg/kg for GK501; and 27, 80, and 240 mg/kg for PHL-00701. The two extracts and their combination improved the retention of learned behavior. This effect varied considerably with the extracts, with the dose and with the behavioral method used. The results suggest that the Panax ginseng G115 and the Ginkgo biloba GK501 extracts possess properties similar in every respect to those of nootropic drugs. The favorable effects on learning and memory of the combination of G115 plus GK501 and the other pharmacological activities inherent in the extracts characterize this combination, offered as Gincosan as a particularly promising drug in geriatric practice.
TL;DR: In this article, the effect of by-products obtained during the low-temperature synthesis of Mg, Al- hydrotalcite on further thermal decomposition of hydralcite material was studied by X-ray powder diffraction, scanning electron microscopy, transmission electron microscope and infrared spectroscopy.
Abstract: The effect of by-products obtained during the low-temperature synthesis of Mg, Al- hydrotalcite on further thermal decomposition of hydrotalcite material was studied by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and infrared spectroscopy. By-products, which thermally decomposed below 450°C, led to the formation of α-Al2O3 and MgO; by-products which completely decomposed above 500°C resulted in the formation of MgAl2O4 and a sharp increase in MgO dispersity.
TL;DR: In this article, the authors studied the kinetics of liquid membrane extraction of copper using LIX-860 as a carrier and found that the salicylaldoxime molecules are present in the organic (C 10 −C 13 normal paraffins) membrane solution in the form of dimmers and that the distribution coefficient of copper does not depend on temperature within the range of 273-293 K.
TL;DR: The aim of this investigation is to report the synthesis and fundamental photochemical properties of naphthalocyanines with potential interest for photodynamic therapy (PDT), as well as their pharmacokinetics and phototherapeutic effects in a tumor model.
Abstract: The aim of this investigation is to report the synthesis and fundamental photochemical properties of naphthalocyanines with potential interest for photodynamic therapy (PDT), as well as their pharmacokinetics and phototherapeutic effects in a tumor model. Four zinc naphthalocyanines (ZnNc), unsubstituted ZnNc 1 , tetraacetylamido-substituted ZnNc 2 , tetraamino-substituted ZnNc 3 and tetramethoxy-substituted ZnNc 4 absorbing around 760–770 nm, were synthesized. The dye-sensitized photo-oxidation of 1,3-diphenylisobenzofuran via 1 O 2 was studied in dimethylsulfoxide (DMSO). Quantum yields for this photoreaction are 0.135–0.164 and are relatively independent of the kind of substituent. In addition, the photoinduced electron transfer studied in N, N -dimethylformamide—water in the presence of methylviologen and mercaptoethanol is only slightly influenced by the kind of substituent. The pharmacokinetic properties of ZnNc 1 in hamsters bearing a transplanted rhabdomyosarcoma were studied using dipalmitoylphosphatidylcholine liposomes. Experimental PDT of rhabdomyosarcoma was carried out using liposome-delivered ZnNc 1–4 . The phototherapeutic effect was evaluated by tumor photonecrosis, the mean tumor diameter during the observation period and the percentage of cured animals. The best effect was found after PDT with ZnNc 2 (50% of the treated animals were cured). A slightly lower effect was observed after application of ZnNc 4 (40% cured animals). No effect at all was noted after PDT with ZnNc 3 and a very low efficiency was found after treatment with ZnNc 1 as photosensitizer. Obviously, the photodynamic effect depends on the biological characteristics as well as on the nature of the substituents.
TL;DR: In this article, the Pitzer model is used to calculate the thermodynamic functions needed to plot the solubility isotherms of the systems and the free energies of formation of carnallite and bromcarnallite type double salts from simple salts are estimated.
Abstract: The solubility of the systems RbCl−MgCl2−H2O, RbBr−MgBr2−H2O and CsBr−MgBr2−H2O have been investigated by the physicochemical analysis method at 25°C and formation of carnallite type double salts was established. The Pitzer model is used to calculate the thermodynamic functions needed to plot the solubility isotherms of the systems. The results obtained are in good agreement with the experimental data. The free energies of formation of carnallite and bromcarnallite type double salts from simple salts and the standard molar energies of formation are estimated.
TL;DR: In this paper, electron absorption spectroscopy was used to study the dependence of the main polymerization steps (oxidation and reduction) on both the pH of the medium and the oxidation state of the chain.
TL;DR: In this article, the FT-IR polarization spectra of diphenylacethylene (tolane), pyrene and maleic anhydride, dissolved and oriented in a nematic liquid crystal mixture, were recorded and processed by means of the Thulstrup-Eggers procedure of stepwise reduction.
TL;DR: In this article, the buckling phenomenon characteristic of highly viscous liquid jets slowly impinging upon a plate was studied and the quasi-one-dimensional equations of the dynamics of thin liquid jets were used as the basis for the theoretical analysis of buckling.
Abstract: The present work deals with the buckling phenomenon characteristic of highly viscous liquid jets slowly impinging upon a plate. The quasi-one-dimensional equations of the dynamics of thin liquid jets are used as the basis for the theoretical analysis of buckling. With the problem linearized, the characteristic equation is obtained. Its solutions show that instability (buckling) sets in only in the presence of axial compression in the jet, and when the distance between the nozzle exit and the plate exceeds some critical value. The latter is calculated. It is shown that buckling instability corresponds to the rectilinear jet/folding jet bifurcation point. The value of the folding frequency is calculated at the onset of buckling. The theoretical results are compared with Cruickshank & Munson's (1981) and Cruickshank's (1988) experimental data and the agreement is fairly good.
TL;DR: In this article, a drop-shape analysis is used to investigate the relaxation of surfactant adsorption layers after transient interfacial area changes, e.g. square-pulse or step-type disturbances.
TL;DR: In this article, a theory is proposed and general expressions for the nucleation rate, the rate of crystal growth by two-dimensional nucleation and the introduction time in unseeded precipitation in the presence of additives.
TL;DR: In this paper, the catalytic activities in the oxidation of 2-mercaptoethanol of the different supported porphyrins are compared, and the influence of the substituents, correlating with their Hammett constants σp, and of the ligand types are discussed on the basis of the metal LUMO orbital energy.
TL;DR: In this article, the authors proposed a new approach to the structure of PAM, which seems to unite all above concepts and showed that antimony lowers the critical value of the density and thus prolongs the life of the plate.
TL;DR: In this paper, a chemical oxidative polymerization of aniline in aqueous dispersion stabilized by poly(vinyl alcohol coacetate) was studied by electron absorption spectroscopy and in situ pH measurements.
TL;DR: The penetration rate by boar spermatozoa of the zona pellucida can be used to predict fertility and/or as an in vitro standard for describing porcine semen characteristics.
TL;DR: The adsorption kinetics of human albumin (HA) at the aqueous solution/air interface and the surface relaxation behavior of HA adorption layers after transient area disturbances were studied using an axisymmetric drop shape technique (ADSA) as discussed by the authors.