University of Chemical Technology and Metallurgy
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Item Über das Kriechen kristallisierender Salze, 3. Mitt. - Einige Besonderheiten in der Verteilung der Verunreinigung bei der kriechenden Kristallisation(1963-05-01) Kolarow N.; Bontschewa Z.Item Extraction-spectrophotometric determination of niobium in steels using sulphochlorophenol S and high-molecular amines(1969-01-01) Ivanov N.; Borissova R.; Veselinova E.Item A possibility of nitration of elastomers in solid state(1971-01-01) Mladenov I.; Dimov A.Item Investigation of the Active Center of Porcine‐Pancreatic Amylase(1972-01-01) Elödi P.; Móra S.; Krysteva M.The effect of maltose was studied in porcine pancreatic amylase. At neutral pH 1% (29 mM) maltose produced with amylase a difference spectrum characteristic of the perturbation of tryptophan. The molar absorption difference at the maximum wavelength was Δ290= 1200. The difference spectrum appeared to be specific for maltose. Perturbation difference spectra measurements in 20% polyethylene glycol indicated that one tryptophyl side chain per mol amylase was involved in the interaction with maltose. The dissociation constant of the amylase · maltose complex calculated from the concentration dependence of the absorption difference at 290 nm was Ks= 13 mM. Maltose inhibited amylase activity competitively and an inhibition constant of Ki= 25 mM was obtained, a similar value to that found spectrophotometrically. It is assumed that the tryptophyl side chain interacting with maltose may be involved in the binding of substrate by pancreatic amylase. Copyright © 1972, Wiley Blackwell. All rights reservedItem HIGH RESISTANCE ANODIC FILM FORMATION ON BISMUTH WITH OR WITHOUT APPEARANCE OF INDUCTION PERIOD.(1972-01-01) Ikonopisov S.; Nikolov T.The galvanostatic oxidation of bismuth in aqueous oxalic acid solutions has been studied at various anodic current densities, J, electrolyte concentrations, N, and temperatures, T. An induction period was found to appear always when, J is lower than a critical value, specific for given N and T. Relations considering the duration of the induction period as a function of J, N, and T, and the dependence of the linear potential rise on time in absence of induction period or after its expiration have been established. These relations are explained on the basis of a model considering the precipitation of crystals of a slightly soluble bismuth compound which isolates a part of electrode surface. When the current density on the rest (uncovered) surface reaches the critical value, an anodic film begins to grow on it, causing corresponding increase in the anodic potential.Item Vibrational Spectra of the Hydrates of LiBF4 Die Schwingungsspektren der Hydrate des LiBF4(1972-10-01) Manewa M.; Fritz H.P.Item Studies on Tyrosine Environments of Chicken Ovomucoid: The Environment of the Most‐Exposed Tyrosine(1973-01-01) Krysteva M.; Mancheva I.; Dobrev I.The particular environments of tyrosine side chains were suggested to be responsible for the non‐denaturation acidic difference spectra of ovomucoid as well as of abnormal ionization of its phenolic groups. The micro environment of the most exposed tyrosine in ovomucoid was studied. The tyrosine was first labelled by means of tetranitromethane. Nitrotyrosine peptide was isolated. The study of the nine steps of nitrotyrosine peptide degradation results in the following amino acid sequence: Ala‐Gly‐Ala‐Lys‐Thr‐Gln‐NO2Tyr‐Gly‐Gly. The analysis of neutral sugars as well as glycosamine gave negative results. The presence of sialic acid however was detected. On the basis of evidence obtained, the existence of a glycosidic bond formed from the hydroxyl group of tyrosine and the glycosidic hydroxyl group of sialic acid was suggested. The spectral behaviour of the tyrosine studied was discussed in the light of above assumption. Copyright © 1973, Wiley Blackwell. All rights reservedItem Comparative study on histidine modification by diethylpyrocarbonate in human serotransferrin and lactotransferrin(FEBS Letters, 1975-01-01) Krysteva M.A.; Mazurier J.; Spik G.; Montreuil J.Item Comparative study on histidine modification by diethylpyrocarbonate in human serotransferrin and lactotransferrin(1975-01-01) Krysteva M.A.; Mazurier J.; Spik G.; Montreuil J.Item Structural Studies on Periodate‐Oxidized Chicken Ovomucoid: Spectral Behaviour of the Tyrosine Residues(1977-01-01) KRYSTEVA M.; DOBREV I.About 50% of the carbohydrate moiety of ovomucoid was destroyed by periodate oxidation. The oxidation was carried out for 6 h or 24 h. The data obtained showed that in the carbohydrate chain 2–5 glucosamines and 1–2 neutral sugar residues were decomposed with the consumption of 16 mol and 29 mol of periodate respectively. Periodate oxidation slightly changed the inhibitory activity of the ovomucoid, but altered its spectral properties. An increase of the absorption maximum at 278 nm was noted, as well as a tendency for normalization of phenolic ionization and an increase of the re‐lative fluorescence. The reactivity of tyrosine residues towards tetranitromethane is also changed. It was suggested that even in native ovomucoid the tyrosines could be regarded as ‘dissolved’ in the ‘carbohydrate solvent’. This contact could be achieved by the hydrogen bonds in the formation of which the NHCOCH3 groups of the glucosamine residues play an essential role. Peroxidate oxidation seems to lead to an alteration of the nature of the ‘sugar solvent’ and disturbs the conformation of the sugar chain. Copyright © 1977, Wiley Blackwell. All rights reservedItem Kinetics of nitration of cis-1,4-polybutadiene rubber in solution with nitrogen dioxide.(1978-01-01) Mladenov I.; Kostov G.; Rashev V.The kinetics of nitration of cis-1,4-polybutadiene rubber dissolved in dichloroethane in the range of concentrations up to 2.2% was studied in a stirred cell. It was found that diffusion of nitrogen dioxide is not important and the reaction is of the first order with respect to both reactants. The overall second-order reaction rate constant was found to be about 1.1×10−5l/(gmol sec) at 303K. The obtained value for the activation energy corresponds to kinetic regime. Based on these results a reaction mechanism is proposed. © 1978, The Society of Polymer Science, Japan. All rights reserved.Item Fluidisation of polydisperse systems(1979-01-01) Doichev K.; Akhmakov N.Item Relationship Between New Structural Data on Clinoptilolite and Its Behaviour in Ion-Exchange and Heating(1979-02-01) Galabova I.Low degrees of removal of K in ion-exchange as well as alterations of relative intensities of (0k0) X-ray reflections under heating have been found for clinoptilolite. These observations are in good accord with the newly provided structural data of clinoptilolite. © 1979, Walter de Gruyter. All rights reserved.Item The influence of experimental design on robustness to nonnormality of the f test in regression analysis(1980-12-01) Vuchkov I.; Solakov E.The robustness to nonnormality of the F test for model adequacy depends essentially on the distribution of repeated trials over the support points of the design.The influence of the regression design matrix upon robustness is more limited. © 1980 Biometrika Trust.Item PROCESS OPTIMIZATION FOR HOT STRIP MILL.(1986-01-01) Koinov T.; Kihara J.The authors propose an economic-mathematical model in which production cost is a function of technological parameters such as threading speed, thickness of transfer bar and extraction temperature from a reheating furnace. The optimization of these parameters is performed for a hot strip mill in Bulgaria and Japan. With use of the code, a new rolling schedule in which the transfer bar thickness decreased with length of strip reduced production cost and improved gage accuracy.Item Continuous Dependence on the Initial Condition of the Solution of a System of Differential Equations with Variable Structure and with Impulses(1987-01-01) Dishliev A.; Bainov D.Item Continuous Dependence on the Initial Condition of the Solution of a System of Differential Equations with Variable Structure and with Impulses(1987-01-01) Dishliev A.; Bainov D.Item Continuous dependence of the solution of a system of differential equations with impulses on the impulse hypersurfaces(1988-11-01) Dishliev A.; Bainov D.In the present paper the initial value problem is considered for systems of ordinary differential equations with impulses where the impulses are realized in the moments when the integral curve of the system meets some of previously given hypersurfaces called impulse hypersurfaces. Sufficient conditions for the continuous dependence of the solution on the impulse hypersurfaces are found. © 1988.Item Continuous dependence of the solution of a system of differential equations with impulses on the impulse hypersurfaces(1988-11-01) Dishliev A.; Bainov D.In the present paper the initial value problem is considered for systems of ordinary differential equations with impulses where the impulses are realized in the moments when the integral curve of the system meets some of previously given hypersurfaces called impulse hypersurfaces. Sufficient conditions for the continuous dependence of the solution on the impulse hypersurfaces are found. © 1988.Item Population dynamics control in regard to minimizing the time necessary for the regeneration of a biomass taken away from the population(1990-01-01) Bainov D.; Dishliev A.The dynamics of a population whose mathematical model is the equation of Verhulst is considered. From the population, by discrete external effects (in the form of impulses), a certain quantity of biomass is taken away (or added). This process is described by means of differential equations with impulses at fixed moments. The moments and the magnitudes of the impulses are determined so that the time of regeneration of the quantity of biomass taken away from the population be minimal. © 1990.