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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Entomologia experimentalis et applicata 57 (1990), S. 9-16 
    ISSN: 1570-7458
    Schlagwort(e): Aphid ; alder ; food quality ; temperature ; ovariole number ; Pterocallis alni
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Beschreibung / Inhaltsverzeichnis: Résumé P. alni DeGeer (Homopt. Callaphididae) vit sur Alnus glutinosa Gaertner pendant toute l'année. L'aulne étant un arbre fixant l'azote, cette étude a été entreprise pour examiner la croissance et la reproduction de ce puceron sur cet arbre afin d'expliquer les changements de la dynamique de sa population. 6 générations successives estivales ont été élevées dans la nature et en température constante au laboratoire. La qualité de l'aliment a été mesurée chaque semaine par une microkjeldahl analyse des concentrations foliaires en azote soluble. La qualité de l'aliment varie saisonnière, mais ne diminue que de 23%; elle semble n'avoir que peu d'effets sur le puceron, puisque la fécondité dans la nature n'est réduite que pendant une génération. Quand la température est maintenue constante, il n'y a pas de différences entre les performances des différentes générations de pucerons. Ainsi, les changements saisonniers dans la croissance et la reproduction des pucerons sont provoqués par la température et non par la qualité de l'aliment.
    Notizen: Abstract Six successive summer generations of the alder aphid (Pterocallis alni (DeGeer) (Homoptera: Callaphididae)) were reared simultaneously in the field and under controlled temperature conditions in the laboratory. The growth and reproduction of each generation were recorded. The available food quality for the aphids was measured by weekly analysis of foliar soluble nitrogen concentrations. Although there was a significant change in leaf soluble nitrogen during the season, the decline was only 23% and this did not appear to have an adverse effect on the performance of this aphid. Instead, the major environmental factor affecting the aphid is temperature. This is evidenced by the facts that when aphids were reared at constant temperatures, there were no differences in generation performance, even though food quality varied seasonally. In addition, all generations of the aphid posess the same number of ovarioles, indicating that there is no pre-programmed anticipation of a seasonal deterioration in food quality in this aphid species.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Entomologia experimentalis et applicata 85 (1997), S. 231-236 
    ISSN: 1570-7458
    Schlagwort(e): Glossina fuscipes fuscipes ; vegetation ; biconical trap ; temperature ; light ; relative humidity ; monitor lizard
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Glossina fuscipes fuscipes Newstead was sampled in isolated thickets and forest patches near Lake Victoria, Kenya using unbaited biconical traps, between March 1992 and June 1993. Traps set at 1 m from the forest edge caught 3.3 times as many males and 5 times as many females as those set inside or 10 m away. The corresponding figures at 1 m from the edge of thicket were about 1.43 and 1.64 times, respectively. Hourly catches of males and females were positively correlated with temperature, light intensity and host (monitor lizard) prevalence, and negatively correlated with relative humidity. Light intensity and temperature were the most important variables affecting the catches of each sex. The results are discussed in relation to control and monitoring of G. f. fuscipes using traps.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Entomologia experimentalis et applicata 83 (1997), S. 171-180 
    ISSN: 1570-7458
    Schlagwort(e): within-plant heterogeneity ; tent caterpillars ; temperature ; circular statistics ; Lepidoptera ; Yponomeutidae
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The caterpillars of Yponomeuta mahalebella Latr. (Lepidoptera: Yponomeutidae) are monophagous on Prunus mahaleb (Rosaceae) leaves. Adult females deposit eggs in batches, which determines larval gregarious behaviour. Coupled with gregarious behaviour, caterpillars spin silk tents within they will feed until pupation. Distribution of tents in the field, their effect in microenvironmental larval growth conditions and the consequences for adult body mass and survival of larvae were studied. There was a significant trend for tents to be placed with a southward orientation. Within-plant tent orientation was related to the sun-shade pattern experienced, which was the main effect determining thermal differences between the inside and the outside of the tent. These differences appeared to affect larval growth and survival, with higher survival of larvae and heavier adults emerging from tents oriented to the south-east and east, respectively.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Fire technology 33 (1997), S. 195-213 
    ISSN: 1572-8099
    Schlagwort(e): point of fire origin ; fire ; temperature ; plaster ; concrete ; thermal ; damage ; biotite ; magnetization ; susceptibility ; N-rays ; P-rays ; X-rays
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung
    Notizen: Abstract Magnetic susceptibility (MS) measurements were taken to determine fire exposure patterns on noncombustible structural members and compartment boundaries. These measurements led on-site fire investigators to the cause of combustion and the point of fire origin. Thermal damage to walls and to ceilings was estimated quantitatively by measuring MS and two-valent Fe ion concentration in building materials such as concrete and plaster. It was shown that these effects are preconditioned by thermochemical transformations in the mineral biotite, which is present as a component of common building materials. For the first time, the effect of a substantial and irreversible increase in biotite magnetization exposed to powerful flows of N- and P-rays was found. It is hoped that the presence of this “magnetic trace” of radiation in building materials will allow investigators to use the magnetometric method at nuclear power plant catastrophes such as that in Chernobyl. It was also shown that the influence of N- and P-rays on biotite's magnetic properties greatly differs from the thermal influence on biotite.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Entomologia experimentalis et applicata 82 (1997), S. 159-166 
    ISSN: 1570-7458
    Schlagwort(e): Diaeretiella rapae ; reproduction ; life-tables ; temperature ; Diuraphis noxia ; biological control
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Diaeretiella rapae (M'Intosh), a polyphagous and cosmopolitan parasite of aphids, was imported from China to the USA for biological control of Diuraphis noxia (Mordwilko), a pest of small grains. We studied several aspects of its biology on D. noxia hosts in the laboratory at 3 constant temperatures, 10.0, 21.1, and 26.7 °C. Females lived significantly longer than males at all 3 temperatures, and longevity was greatest at 10 °C, followed by 21.1 and 26.7 °C. Fecundity (= number of mummies) did not differ significantly among the 3 temperatures studied. The ovarian egg-load was 129.1 ± 9.3, and was significantly affected by the size of adult females. A pre-oviposition period ± 0.26 days) was detected at 10 °C, but not at the other temperatures. Pre-imaginal survivorship was similar among temperatures, while R o and T c decreased with temperature, and r m increased with temperature. The offspring sex ratio (proportion females) was lowest at 26.7 °C, and similar between 10.0 and 21.1 °C. In addition, the offspring sex ratio significantly declined with the age of the female parent. The suitability of D. rapae for colonization against D. noxia in North America is discussed in relation to its responses to temperature and the climate of its home range.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Entomologia experimentalis et applicata 82 (1997), S. 319-333 
    ISSN: 1570-7458
    Schlagwort(e): chlorogenic acid ; light availability ; Lycopersicon esculentum ; Manduca sexta ; protein ; rutin ; temperature ; tomatine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We examined how light availability influenced the defensive chemistry of tomato (Lycopersicon esculentum: Solanaceae). Tomato plants were grown either in full sunlight or under shade cloth rated at 73%. Leaves from plants grown in full sunlight were tougher, had higher concentrations of allelochemicals (chlorogenic acid, rutin and tomatine), and had less protein than leaves from plants grown in shade. We determined how these differences in host plant quality due to light availability affected the behavior and growth of a Solanaceae specialist, Manduca sexta. Both in the greenhouse and in the field, caterpillars on shade-grown plants grew heavier in a shorter amount of time than those on plants that had previously been grown in full sunlight. In contrast, the effects of previous light availability to plants on caterpillar behavior appeared to be minor. To further investigate how light availability to plants influenced herbivore growth, we examined the effects of leaf-powder diets made from tomato leaves of different ages (new, intermediate, or mature) grown in full sunlight or shade on caterpillar performance. Caterpillars fed diets made from plants grown in shade consumed less but grew faster than larvae fed diets made from tomato plants grown in full sunlight. Caterpillars fed diets made from new leaves grew larger in less time than caterpillars fed diets made from intermediate aged leaves. Caterpillars did not survive on the mature leaf powder diets. There were plant-light treatment by larval thermal regime interactions. For example, at 26:15 °C , plant-light treatment had no effect on stadium duration, but at 21:10 °C, stadium duration was prolonged with the full sunlight-new leaf diet compared with the shaded-new leaf diet. In a second diet experiment, we examined the interactive effects of protein and some tomato allelochemicals (rutin, chlorogenic acid and tomatine) on the performance of caterpillars. There were food quality by thermal regime interactions. For instance, at 26:15 °C , neither protein nor allelochemical concentration influenced stadium duration, whereas at 21:10 °C, stadium duration was prolonged with the low protein-high allelochemical diet, which simulated full sunlight leaves. In sum, light availability to plants affected defensive chemistry and protein concentration. The difference in food quality was great enough to influence the growth of a specialist insect herbivore, but the effects were temperature-dependent.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Entomologia experimentalis et applicata 84 (1997), S. 255-265 
    ISSN: 1570-7458
    Schlagwort(e): Delia radicum ; postdiapause development ; temperature ; Diptera ; Anthomyiidae
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Canadian populations of D. radicum differ in their response to temperature during postdiapause development. Populations that are primarily of the early-emerging type ( $$\left( { \leqslant 256DD_{04} } \right)$$ ) (St-Jean, Quebec; London, Ontario) have high values for the parameters describing this response: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOuamaaBa% aaleaacaWGTbaabeaakiabg2da9aaa!38F2!$$R_m = $$ 12.7–13.3; $$T_m = $$ 28.0–31.8 °C ; Tσ = 10.3–14.2 ( $$R_m $$ , the maximum developmental rate at the temperature, $$T_m $$ [ °C ] where the developmental rate is highest, and Tσ , the parameter which gives the shape of the truncated normal curve fitted to the data), a low degree-day requirement for emergence (160–232 $$DD_{04} $$ ), and may lack a developmental delay at temperatures above ca. 21 °C . Populations of the late-emerging type (Kildare, Prince Edward Island) have low parameter values ( $$ R_m = 2.5$$ , $$T_m = 19.3$$ °C ; Tσ = 6.4), high degree-day requirements (530 $$DD_{04} $$ ), and a developmental delay at high temperatures. The parameters for the early-emergers in the population from Winnipeg, Manitoba (74% early) were intermediate ( $$R_m = 9.1$$ , $$T_m = 27.1$$ °C , Tσ = 10.7, $$ DD_{04} = 246 $$ ), but resembled the early rather than the late type. This population varied from 31 to 90% early type over a 10-year period and the rate of postdiapause development at 20 °C was directly related to the percentage early. In the year with the most rapid development (90% early), development was significantly slower than in the populations from other locations with predominantly early populations, and the year with the slowest development (31% early) showed significantly faster development than that from Kildare, Prince Edward Island (100% late). Therefore the parameters for early and late types of development will not be accurate for use in mixed populations, and the parameters in mixed populations will change among years. Populations of D. radicum in North America and Europe (67 locations by years) varied from 0–100% early. At Winnipeg, the percentage early was directly related to the annual temperature accumulation ( $$DD_{05} $$ ) during the growing season. The calculation of developmental parameters for the early-emergers of mixed populations provides a more accurate basis for estimating the times of first emergence and the first peak of emergence than parameters based on the whole population. Since postdiapause developmental rates vary both among and annually within locations, developmental models should be designed to include such variations.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Journal of solution chemistry 19 (1990), S. 1137-1151 
    ISSN: 1572-8927
    Schlagwort(e): Ethylbenzene ; excess entalphy ; excess volume ; experimental ; heat capacity ; isobaric expansibility ; isentropic and isothermal compressibility ; liquid mixtures ; mixing function ; n-alkanes ; n-hexadecane ; n-tetradecane ; pressure ; temperature ; theory
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Isobaric expansibilities α P and isothermal compressibilities κ T have been determined at 25 and 45°C for binary mixtures of ethylbenzene + n-tetradecane and + n-hexadecane and the corresponding excess functions (∂V E /∂T)P and (∂V E /∂P)T have also been obtained. With these data and supplementary literature values, the following second order mixing properties are also reported at 25°C: κ S E , (∂V E /∂P)T, ΔCV and Δ(ΔγVT). All mixing quantities have been compared with the results obtained at 25°C by using the Prigogine-Flory-Patterson theory of liquid mixtures. The predicted values suggest that the ability of ethylbenzene as a breaker of the pure n-Cn orientations is similar to what we found for toluene and higher than for p-xylene.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Journal of applied electrochemistry 27 (1997), S. 1275-1282 
    ISSN: 1572-8838
    Schlagwort(e): Carbon monoxide ; Pt-Ru/C catalyst ; Tafel slopes ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract CO electrooxidation on a Pt–Ru/C catalyst was investigated in sulphuric acid electrolyte. The physico-chemical properties of the Pt–Ru/C catalyst were studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The influence of temperature, CO partial pressure and proton concentration on the electrochemical oxidation rate was investigated by steady-state galvanostatic polarization measurements. The apparent activation energy decreased from 70 to 30kJmol−1 as the overpotential increased from 0.5 to 0.9V vs NHE. The reaction order with respect to carbon monoxide increased, passing from 0.4 to 1, with the increase of the overpotential from 0.5 to 0.7V vs NHE; a reaction order close to −1 with respect to the protonic concentration was observed, irrespective of the potential. Tafel slopes of about 136mVdec−1 were determined for oxidation of CO and CO/N2 mixtures.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Journal of applied electrochemistry 27 (1997), S. 1328-1332 
    ISSN: 1572-8838
    Schlagwort(e): metal hydride ; capacity ; temperature ; performance ; enthalpy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The effect of temperature on the performance of a LaNi4.76Sn0.24 metal hydride electrode was investigated in the temperature range of 0 to 50°C. The electrode showed a maximum discharge capacity at 25°C. The total resistance increases with a decrease of temperature from 50°C to 0°C. The apparent activation enthalpies at different states of charge were determined by evaluating the polarization resistance at different temperatures. It was found that the apparent activation enthalpy is an indicator of the relative reaction rate of the charge-transfer reaction and hydrogen absorption.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 11
    ISSN: 1572-8757
    Schlagwort(e): porous carbons ; activation ; oxidation ; surface oxygen groups ; LTPD
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Physik , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract A styrene/divinylbenzene copolymer has been used as precursor for making porous carbons with bimodal pore size distributions (i.e., with both microporosity and mesoporosity). Pretreatment of the as-received copolymer by mild oxidation in air, significantly increased the carbon yield after carbonization. Reactivity studies of the polymer-based chars to CO2 clearly show the influences of some important factors such as carbonization temperature, heating rate, soak time on char reactivities. Bimodal porous carbons were prepared by carbonization of the preoxidized styrene/divinylbenzene copolymer in N2, followed by activation in CO2 at different temperatures to different levels of burnoff. The pore structures of the porous carbons produced have been characterized by various techniques such as gas adsorption and mercury porosimetry. The surfaces of the porous carbons produced, and a commercial carbon adsorbent, have been modified with HNO3 and H2O2 treatment at various conditions. Characterization of the surface oxygen functionality, both quantitatively and qualitatively, has been achieved using techniques such as Linear Temperature Programed Desorption (LTPD) and selective neutralization of bases.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 12
    ISSN: 1572-8765
    Schlagwort(e): carbonado ; diamond ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of carbonado type synthesized polycrystalline diamonds produced from graphite together with catalytic Ni-Mo alloy doped with TiB2 and BNcub was investigated. It was found that the addition of these boron compounds increases the oxidation resistance of the carbonado type synthesized polycrystalline diamonds. The oxidation mechanism acting on the carbonado type synthesized polycrystalline diamonds and the role of boron compounds in increasing the resistance to the oxygen reaction are discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 13
    ISSN: 1572-879X
    Schlagwort(e): fluorination ; alumina ; platinum catalysts ; oxidation ; oxidation of benzene
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Platinum supported on fluorinated alumina is more active for the total oxidation of benzene than is the catalyst with the same Pt loading supported on hydrophilic unfluorinated alumina. The Pt-F/alumina catalyst contains well-dispersed small Pt particles, in contrast to Pt/alumina. The high dispersion is a consequence of a strong metal-support interaction.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Catalysis letters 7 (1990), S. 241-251 
    ISSN: 1572-879X
    Schlagwort(e): Fischer-Tropsch synthesis ; iron based catalysts ; Fe ; Co ; Ru catalysts ; fixed bed reactors ; fluidized bed reactors ; sulfur poisoning ; oxidation ; coke fouling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Because of the decreased profitability of making synthetic fuels, Sasol intends expanding its production of the higher valued chemicals, in particular waxes and olefins. The advantages and disadvantages of using Fe, Co and Ru catalysts are discussed from the point of view of costs, availability, product selectivity, activity and sensitivity to poisons. The loss of activity and selectivity of iron based catalysts in both fixed and fluidized bed reactors is discussed. The main contributing factors are sulfur poisoning, oxidation and coke fouling. In fixed bed reactors sulfur poisoning and “coke” laydown deactivates the front end of the bed while hydrothermal sintering/oxidation deactivates the back end. In fluidized beds the deposition of large amounts of Boudouard carbon doesnot markedly lower the activity. The smaller catalyst particles end up consisting of small iron carbide entities embedded in a matrix of carbon. The larger catalyst particles consist of cores of inert magnetite surrounded by the carbide/carbon matrix. FT reactor development at Sasol is briefly reviewed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 46 (1990), S. 579-585 
    ISSN: 1420-9071
    Schlagwort(e): Lipids ; phospholipids ; galactolipids ; fatty acids ; transfer ; binding ; membranes ; mitochondria ; chloroplasts ; biogenesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary Plant cells contain cytosolic proteins, called lipid transfer proteins (LTP), which are able to facilitate in vitro intermembrane transfer of phospholipids. Proteins of this kind from three plants, purified to homogeneity, have several properties in common: molecular mass around 9 kDa, high isoelectric point, lack of specificity for phospholipids, and binding ability for fatty acids. The comparison of their amino acid sequences revealed striking homologies and conserved domains which are probably involved in their function as LTPs. These proteins could play a major role in membrane biogenesis by conveying phospholipids from their site of biosynthesis to membranes unable to form these lipids. Immunochemical methods were used to establish an in vivo correlation between membrane biogenesis and the level of LTP or the amount of LTP synthesized in vitro from mRNAs. The recent isolation of a full-length cDNA allows novel approaches to studying the participation of LTPs in the biogenesis of plant cell membranes.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 46 (1990), S. 586-592 
    ISSN: 1420-9071
    Schlagwort(e): Phospholipids ; bacterial membranes ; yeast membranes ; phospholipid transfer proteins ; mitochondria
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary Microorganisms are useful model systems for the study of intracellular transport of lipids. Eukaryotic microorganisms, such as the yeastSaccharomyces cerevisiae, are similar to higher eukaryotes with respect to organelle structure and membrane assembly. Experiments in vivo showed that transport of phosphatidylcholine between yeast microsomes and mitochondria is energy independent; transfer of phosphatidylinositol to the plasma membrane and the flux of secretory vesicles take place by different mechanisms. Linkage of transfer and biosynthesis of phospholipids was demonstrated in the case of intramitochondrial phospholipid transfer. A yeast phosphatidylinositol/phosphatidylcholine transfer protein, which is essential for cell viability, was isolated and characterized. Another phospholipid transfer protein present in yeast cytosol, which has a different specificity, is currently under investigation. Transfer of phospholipids between cellular membranes was also demonstrated with prokaryotes. The cytoplasm and the periplasma of the gram-negative facultative photosynthetic bacteriumRhodopseudomonas sphaeroides contain phospholipid transfer proteins; these seem to be involved in the biosynthesis of prokaryotic membranes.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 46 (1990), S. 101-104 
    ISSN: 1420-9071
    Schlagwort(e): Genetic variability ; mitochondria ; allozymes ; Drosophila sechellia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary Genetic variability ofD. sechellia is investigated at both mitochondrial and nuclear levels. The results reveal the existence of a single main type of mtDNA with very few variants and a very low enzyme polymorphism. This situation is consistent with the small population size of this specialized species.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Catalysis letters 6 (1990), S. 181-186 
    ISSN: 1572-879X
    Schlagwort(e): Metals for catalysis “syngas” ; oxidation ; nickel ; platinum group metals
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Partial oxidation of methane to synthesis gas has been carried out over a number of transition metal catalysts under a range of conditions. It is found that the metals Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium. The yield of CO and H2 improves with increasing temperature in the range 650–1050 K, and decreases with increasing pressure between 1 and 20 atm. An excellent yield (∼92%) is obtained with a 4∶2∶1 N2∶CH4∶O2 ratio at 1050 K and atmospheric pressure, with a space velocity of 4×104 hour−1.
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  • 19
    ISSN: 1572-879X
    Schlagwort(e): Ultraviolet heterogeneous photocatalysis ; oxidation ; trichloroethylene ; titania ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Kinetics of the gas/solid heterogeneous photocatalytic oxidation of dilute trichloroethylene (TCE) vapors by ultraviolet-illuminated titanium dioxide have been determined using a fixed-bed dynamic photoreactor. Reaction rate dependences on inlet TCE, oxygen and water vapor concentrations were found to consist of both reactant sensitive and insensitive regions. In the reactant sensitive regions, measured limiting apparent reaction rate orders for TCE, oxygen and water vapor are 0.8, 1.7 and — 3, respectively. Water vapor in the reactant stream lowersinitial reaction rates relative to corresponding water free conditions, but is required to sustain photocatalytic activity for extended periods of time.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Entomologia experimentalis et applicata 55 (1990), S. 161-168 
    ISSN: 1570-7458
    Schlagwort(e): Tephritidae ; Dacus oleae ; olive fruit fly ; ovarian maturation ; olive fruit ; diapause ; photoperiod ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Beschreibung / Inhaltsverzeichnis: Résumé La maturation ovarienne des femelles adultes agées de 7, 22–23 et 28 jours de D. oleae ayant accompli leur développement embryonnaire, larvaire et nymphal en LD 12:12, 19±1°C et maintenues en LD 16:8, 26±1°C, sans accès à des olives, est inhibée. Dans les mêmes conditions, mais avec accès permanent à des olives, 54% des femelles ont des ovocytes mûrs à 7 jours, 87% à 22–23 jours et 100% à 28 jours. Avec des femelles ayant accès à des domes de paraffine, les pourcentages d'individus ayant des ovocytes mûrs sont intermédiaires entre ceux des deux situations précédentes. Dans les conditions cidessus défavorables à la maturation ovarienne, 50% des femelles de 28 jours ont des ovocytes mûrs si elles sont en présence d'olives durant leur première semaine de vie imaginale et 91% si elles sont en présence la 4éme semaine. Les pourcentages respectifs concernant les femelles pourvues de dômes de paraffine sont encore intermédiaires entre ceux des femelles avec olives et ceux de femelles privées de tout substrat. La présence d'olives a aussi un effet fortement positif sur la maturation ovarienne de femelles ayant accompli leur développement pre-imaginal et maintenues aussi à l'etat adulte en conditions LD 16:8, 26±1°C, favorisant la maturation ovarienne. L'accès à des dômes de paraffine a, là encore, un effet intermédiaire. On conclut par conséquent que la non maturation ovarienne des femelles de D. oleae qui est causée par une photopériode à jour court pendant la vie pre-imaginale accompagné par une photopériode à jour long et une augmentation de la température pendant la vie imaginale persiste au moins jusqu'à la fin de la quatrième semaine de la vie imaginale en absence d'olives, mais ne se produit pas si on met les femelles adultes en présence d'olives.
    Notizen: Abstract Ovarian maturation was prevented in 7-, 22-, 23- and 28-day-old females of Dacus oleae (Gmelin) (Diptera: Tephritidae), developed in the pre-imaginal stages at LD 12:12, 19±1°C and kept as adults at LD 16:8, 26±1°C without access to olive fruits. In females of the above ages having continuous access to olive fruits and held under the same photoperiod and temperature conditions, 54, 87 and 100%, respectively, had mature oocytes. When the females had access to domes of paraffin wax, the percentages of females with mature oocytes were intermediate between those with and those without access to olive fruits. Under the above photoperiod and temperature conditions unfavorable for maturation, 50% of 4-week-old females had mature oocytes if exposed for one week to olive fruits during their first week and 91% if exposed during their 4th week of adult life. The respective percentages with wax domes in the cages were again intermediate between those with olives and those without olives or wax domes. The presence of olive fruits had also a strong positive effect on the ovarian maturation of females which developed from egg through the adult stage at LD 16:8, 26±1°C, a condition favoring ovarian maturation. Access to wax domes had again an intermediate effect on maturation. It is concluded therefore that the lack of ovarian maturation of D. oleae females which is observed under a short photophase during the pre-imaginal stages if followed by a long photophase and an increase of temperature during the adult stage, continues at least till the end of the 4th week of adult life in the absence of olive fruits but is averted when such fruits are offered to the adult flies.
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Archive of applied mechanics 67 (1997), S. 331-338 
    ISSN: 1432-0681
    Schlagwort(e): Key words frictional heating ; wear ; contact pressure ; temperature ; brake system
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Summary A transient contact problem with frictional heating and wear for two nonuniform sliding half-spaces is considered. One of the two half-spaces is assumed to be slightly curved to give a Hertzian initial pressure distribution: the other is a rigid nonconductor. Under the assumption that the contact pressure distribution could be described by Hertz formulas during all the process of interaction, the problem is formulated in terms of one integral equation of Volterra type with unknown radius of contact area. A numerical solution of this equation is obtained using a piecewise-constant presentation of an unknown function. The influence of operating parameters on the contact temperature and the radius of the contact area is studied.
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    European journal of nutrition 36 (1997), S. 336-339 
    ISSN: 1436-6215
    Schlagwort(e): Amino acids ; protein ; metabolism ; meal feeding ; oxidation ; breath test ; Aminosäuren ; Protein ; Stoffwechsel ; Fütterung ; Oxidation ; Atemtest
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die aktuellen Mengen an freien Aminosäuren im Blut reichen nur aus, um die Ganzkörper-Proteinsynthese für einige Minuten aufrecht zu erhalten. Das zeigt, daß die freien Aminosäurenkonzentrationen in der Zirkulation klein und konstant gehalten werden im Vergleich zu den Mengen der Aminosäuren, die täglich aufgenommen und über die Körperproteine umgesetzt werden. Das Verschwinden der Aminosäuren exogenen oder endogenen Ursprungs aus dem freien Aminosäuren-Pool, findet hauptsächlich durch die Proteinsynthese und den Aminosäurenabbau statt. Die Partitionierung der Nahrungs-Aminosäuren zwischen diesen beiden Prozessen im Kurzzeitbereich werden als bedeutsam für die Ökonomie der Ganzkörper-Aminosäuren angesehen. Eine Verbesserung der Aminosäurenökonomie könnte durch solche nutritiven Maßnahmen erreicht werden, welche die Clearance der Nahrungsaminosäuren durch die Proteinsynthese anstelle des Aminosäurenabbaus begünstigen. Diese nutritiven Maßnahmen sollten sich an den „Schwellenwerten“ des Abbaus der individuellen Aminosäuren orientieren.
    Notizen: Summary Actual amounts of free amino acids in the blood are sufficient to support whole body protein synthesis for some minutes only. This indicates that the levels of free amino acids in the circulation are kept small and constant relative to the amounts of amino acids supplied by daily intake and turnover of body proteins. The clearance of the amino acids originating from either endogenous or exogenous sources is mainly due to protein synthesis and metabolic degradation. The partitioning of dietary amino acids between these processes, on the short term, is supposed to play an important role in whole body amino acid economy. Therefore whole body amino acid economy could be improved by nutritional measures that favour the clearance of dietary amino acids by protein synthesis instead of by metabolic degradation. These nutritional measures should to be focused on threshold values for metabolic degradation of individual amino acids.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Microchimica acta 102 (1990), S. 271-276 
    ISSN: 1436-5073
    Schlagwort(e): mercaptans ; oxidation ; disulphide ; Chlorobenzotriazole ; potentiometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A simple but accurate potentiometric method for the estimations of mercaptans in 0.01M perchloric acid has been developed, based on their oxidation with 1-Chlorobenzotriazole. Quantitative oxidation solely to the disulphide stage is ensured by using critical amounts of methanol, acetonitrile and potassium iodide. Chloride, mercury(II) and copper(II) interfere. A back-titration procedure can also be used. The oxidation products have been identified.
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Microchimica acta 125 (1997), S. 401-406 
    ISSN: 1436-5073
    Schlagwort(e): fullerenes ; intercalation ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The investigation of structural and electronic properties of the novel family of fullerenes depends on the existence of pure reference materials. Sublimation of the van-der Waals solids is a suitable purification method. Little attention has been paid to the question about the air stability of such sublimed samples in form of crystals or thin films. A combination of thermal desorption spectroscopy, thermal analysis and diffuse reflectance FT-IR spectroscopy is used to show the extent to which oxygen from dry air is intercalated into fullerenes and which detrimental reactivity occurs from attempts to thermally remove („nneal”) air-exposed samples. The conclusion is that any fullerene sample exposed to air will be transformed in part into a polymeric non-fullerene carbon upon thermal treatment to above 400 K irrespective of its initial purity.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 25
    ISSN: 1573-0832
    Schlagwort(e): DNA ; mitochondria ; restriction profiles ; Sporothrix schenckii ; sporotrichosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract TwoSporothrix schenckii strains of different mitochondrial DNA restriction profiles were isolated from different cutaneous lesions in a 53 year-old woman with sporotrichosis. These results suggest that sporotrichosis can be simultaneously caused by two or more genetically differentS. schenckii strains.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Mycopathologia 110 (1990), S. 107-112 
    ISSN: 1573-0832
    Schlagwort(e): DNA ; Exophiala dermatitidis ; Exophiala gougerotii ; Exophiala jeanselmei ; mitochondria ; restriction profiles ; taxonomy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Mitochondrial DNA (mtDNA) analysis with Hae III, Hind. III and Msp I was performed in 45 Exophiala jeanselmei strains (30 Phialophora jeanselmei and 15 Phialophora gougerotii strains) and 31 Exophiala dermatitidis strains. The results were as follows, 1) P. jeanselmei and P. gougerotii are identical, 2) E. jeanselmei is classified into 18 types based on restriction profiles, 3) two strains of E. jeanselmei CBS 577.76 and CBS 578.76 are identified as E. dermatitidis, 4) E. dermatitidis has no intraspecific variation and is definitely distinct from E. jeanselmei, 5) E. jeanselmei is suggested to be a complex organism because of extensive mtDNA polymorphism.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 27
    ISSN: 1573-0832
    Schlagwort(e): Anthracnose ; guava ; Colletotrichum glososporioides ; temperature ; free moisture ; inoculum density
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The influence of environmental factors (temperature and humidity), inoculum density on infection by Colletotrichum glososporioides and development of anthracnose lesions were determined on uninjured, sand-injured and punctured fruits. The optical temperature for severe infection was 30 °C, whereas the disease incidence was less at 20 and 35 °C. Inoculated guavas that received 1–60 h of continuous free moisture developed lesions, but the disease was minimal (0–7%) after 1–6 h free moisture. Infection rates of uninjured, sand-injured and punctured fruits receiving 60 h of free moisture were 34, 70 and 100%, respectively. Disease incidence increased as inoculum density increased from 101 to 106 conidia/ml. In field conditions, the development of anthracnose lesions was greater on punctured guavas than on uninjured or sand-injured ones, in both rainy and winter seasons. In general, the number of lesions was highest in sand-injured fruits, followed by punctured and uninjured fruits. In rainy season the number of lesions on injured and uninjured fruits was greater than similarly treated guavas in winter.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Mycopathologia 139 (1997), S. 151-155 
    ISSN: 1573-0832
    Schlagwort(e): Antagonism ; biocontrol ; ginger ; postharvest rot ; Sclerotium rolfsii ; Trichoderma ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Sclerotium rolfsii is a destructive soil-borne and postharvest plant pathogen. Use of the antagonistic fungus Trichoderma sp. has been earlier reported by us to successfully control this pathogen under postharvest conditions. In the present paper we report on the effects of temperature on the growth and biocontrol potential of Trichoderma sp. on S. rolfsii. Experimental results indicated that S. rolfsii and Trichoderma sp. have different temperature optima for growth: 30–35 °C for the pathogen and 25–30 °C for the antagonist. In dual culture, Trichoderma overgrew S. rolfsii at 25 °C and 30 °C, but at 35 °C and 37 °C, S. rolfsii overgrew the colony of Trichoderma. Trichoderma produced higher concentration of fungitoxic metabolites in broth culture at higher temperatures. In bioassays using ginger slices and whole rhizomes, it has been demonstrated that Trichoderma is not very effective in suppressing S. rolfsii at temperatures above 30 °C. In light of these results, possible mechanisms of biocontrol of S. rolfsii as a postharvest pathogen has been discussed. Storage temperature has been suggested as a critical factor in biocontrol of S. rolfsii.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Nutrient cycling in agroecosystems 23 (1990), S. 97-103 
    ISSN: 1573-0867
    Schlagwort(e): Carbon ; mineralization ; nitrogen ; organic fertilizer ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The C and N mineralization characteristics of two organic N fertilizers were determined in a soil-less incubation system at three temperature regimes. Protox (derived from activated sewage sludge) initially degraded more rapidly by microbial action compared with dried blood. However, dried blood released more CO2-C and inorganic N towards the end of the incubation periods. The rate of microbial degradation increased with temperature. Mineralization characteristics of protein-based N sources are discussed in relation to organic N nutrition of vegetable crops.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Nutrient cycling in agroecosystems 49 (1997), S. 91-95 
    ISSN: 1573-0867
    Schlagwort(e): greenhouse effect ; land use ; methane ; oxidation ; soils
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Intact core samples from soils with different textures and land use were tested for their capacity to oxidise methane. The soil cores were taken from arable land, grassland and forest. It was found that coarse textured soils (6.74–16.38 µg CH4 m-2 h-1) showed a higher methane uptake rate than fine textured soils (4.66–5.34 µg CH4 m-2 h-1). Increasing soil tortuosity was thought to reduce the methane oxidation rate in fine textured soils. The oxidation rate of forest soils (16.32–16.38 µg CH4 m-2 h-1), even with a pH below 4.5, was very pronounced and higher than arable land (11.40–14.47 µg CH4 m-2 h-1) and grassland (6.74–9.30 µg CH4 m-2 h-1). Within the same textural class arable land showed a faster methane uptake rate than grassland. In grassland with a fine texture, even methane production was observed. Nitrogen availability and turnover in these land use systems were thought to cause the different oxidation rates. Decreasing the moisture content slowed down the oxidation rate in all soils. This could be caused by an increased N turnover and a starvation of the methanotrophic bacteria.
    Materialart: Digitale Medien
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Nutrient cycling in agroecosystems 49 (1997), S. 59-70 
    ISSN: 1573-0867
    Schlagwort(e): land use ; methane ; nitrogen fertilizer ; oxidation ; soil
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Aerobic soils are an important sink for methane (CH4) contributing up to 15% of annual global CH4 destruction. However, the sink strength is significantly affected by land management, nitrogen (N) fertilizers and acidity. We tested these effects on samples taken from the Broadbalk Continuous Wheat, Park Grass permanent grassland and Broadbalk and Geescroft Wilderness experiments at Rothamsted. The rates of uptake from the atmosphere of both enhanced (10 ppmv) and ambient (2 ppmv) concentrations of CH4 were measured in laboratory incubations of soil cores under controlled conditions. The most rapid rates of uptake were measured in soil from deciduous woodland at pH 7 (measured in water); acidic (pH 4) woodland soil showed no net CH4 oxidation. While disturbance of the cores used in the experiments did not affect the rate of CH4 uptake, extended (150 years) cultivation of land for arable crops reduced uptake rate by 85% compared to that in the soil under calcareous woodland. The long-term application of ammonium- (NH4) based fertilizer, but not nitrate- (NO3) based fertilizer, completely inhibited CH4 uptake, but the application for the same period of farmyard manure that contained more N than the fertilizer had no inhibitory effect. Although the effects of agricultural practice on the oxidation of CH4 in soil are significant, the differences in oxidation rates between land use types are even greater. The likely effects of forest clearance, agricultural intensification and anthropogenic emissions of CH4 over the last 2500 years have been estimated for the United Kingdom. The calculations indicate that 54% of the current CH4 uptake by UK soils is the result of increased CH4 mixing ratio. They also indicate that land use change has decreased the potential sink strength by 62% or 37 kt CH4 g-1. In countries with much larger land areas than the UK, such as China, aerobic soil is likely to be a more significant factor in calculating net fluxes of CH4. It is important that the impacts of different agricultural managements and land use systems are understood and quantified so that the best possible estimate of CH4 sinks is calculated for comparison with sources.
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  • 32
    ISSN: 1572-9508
    Schlagwort(e): X-ray ; calibration ; filters ; interference ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We report on UV/Visible transmission measurements of aluminum coated Lexan filters designed as UV blocking filters for soft x-ray detectors. Transmission of the filters in the 2300-8000 Å wavelength range is significantly higher than expected. It cannot be accounted for applying a simple slab model of the transmission and adopting material properties reported in the literature. We show that this is due to interference effects which are strongly dependent on the filter geometry, and to oxidation of exposed aluminum surfaces and/or chemical interaction with the plastic support. The results of this work have led to the redesign of the Advanced X-ray Astrophysics Facility High Resolution Camera UV blocking filters.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Pure and applied geophysics 133 (1990), S. 251-267 
    ISSN: 1420-9136
    Schlagwort(e): Heat flow ; sediments ; temperature ; gradients ; conductivity ; industrial data ; scientific data ; hydrodynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract Temperature, temperature gradient and heat flow, derived from four wells in the Western Canada Sedimentary Basin have been compared with similar quantities derived from maps constructed from industrial data. Individual industrial temperature data may differ from the high-resolution temperature log by up to 30 K, but linear regression of the collected data agrees within 10 K at all points observed. Some evidence suggests that measured conductivities, using drill-cuttings, are biased toward average values. Derived heat flows show agreement of heat flow within 10% within the Mesozoic section. In the Paleozoic section differences are greater, and more varied, with insufficient data for general conclusions. Both styles of measurement provide opportunities for interpretation, each contributing to thermal analysis of sedimentary basins.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 46 (1990), S. 1117-1126 
    ISSN: 1420-9071
    Schlagwort(e): Genetic code ; mitochondria ; evolution ; organelles
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The universal genetic code is used without changes in chloroplasts and in mitochondria of green plants. Non-plant mitochondria use codes that include changes from the universal code. Chloroplasts use 31 anticodons in translating the code; a number smaller than that used by bacteria, because chloroplasts have eliminated 10 CNN anticodons that are found in bacteria. Green plant mitochondria (mt) obtain some tRNAs from the cytosol, and genes for some other tRNAs have been acquired from chloroplast DNA. The code in non-plant mt differs from the universal code in the following usages found in various organisms: UGA for Trp, AUA for Met, AGR for Ser and stop, AAA for Asn, CUN for Thr, and possibly UAA for Tyr. CGN codons are not used byTorulopsis yeast mt. Non-plant mt, e.g. in vertebrates, may use a minimum of 22 anticodons for complete translation of mRNA sequences. The following possible causes are regarded as contributing to changes in the non-plant mt: directional mutation pressure, genomic economization, changes in charging specificity of tRNAs, loss of release factor RF2, changes in RF1, changes in anticodons, loss of lysidine-forming enzyme system, and disappearance of codons from coding sequences.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 46 (1990), S. 1149-1157 
    ISSN: 1420-9071
    Schlagwort(e): Genetic code ; amino acid code ; evolution of code ; mitochondria ; codon capture ; directional mutation pressure ; selenocysteine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The genetic code is evolving as shown by 9 departures from the universal code: 6 of them are in mitochondria and 3 are in nuclear codes. We propose that these changes are preceded by disappearance of a codon from coding sequences in mRNA of an organism or organelle. The function of the codon that disappears is taken by other, synonymous codons, so that there is no change in amino acid sequences of proteins. The deleted codon then reappears with a new function. Wobble pairing between anticodons and codons has evolved, starting with a single UNN anticodon pairing with 4 codons. Directional mutation pressure affects codon usage and may produce codon reassignments, especially of stop codons. Selenocysteine is coded by UGA, which is also a stop codon, and this anomaly is discussed. The outlook for discovery of more changes in the code is favorable, and open reading frames should be compared with actual sequential analyses of protein molecules in this search.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 46 (1990), S. 1180-1185 
    ISSN: 1420-9071
    Schlagwort(e): Oxygen transfer ; tissue hypoxia ; mitochondria ; respiration, cellular ; diffusion, intracellular ; adaptation to hypoxia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary Studies of O2 supply in freshly isolated adult mammalian cells provide new insight into the factors that limit mitochondrial oxygenation in vivo. Of particular importance, mitochondria are present at high densities and often in apparent clusters, both of which contribute to local O2 gradients under hypoxic conditions. Current evidence indicates that the mitochondrial distribution is a component of the differentiated phenotype of adult mammalian cells and that specific motors and anchoring mechanisms are present to allow redistribution in response to developmental, physiological and pathological challenges. To compare the importance of resistance to O2 transfer under different conditions and at different sites along the supply path in vivo, a simple mathematical expression of relative resistance to O2 supply is introduced. Under various pathophysiological conditions, this resistance increases in specific regions of the pulmonary, circulatory of cellular supply path and results in O2 deficiency in the mitochondria. Regardless of cause, the relative resistance increases dramatically in the vicinity of mitochondrial clusters during hypoxia.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 46 (1990), S. 1097-1106 
    ISSN: 1420-9071
    Schlagwort(e): Genetic code ; directional mutation pressure ; GC-content ; unassigned codon ; tRNA ; codon capture ; codon usage ; Mycoplasma ; mitochondria ; Micrococcus ; methanogens
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The prokaryotic genetic code has been influenced by directional mutation pressure (GC/AT pressure) that has been exerted on the entire genome. This pressure affects the synonymous codon choice, the amino acid composition of proteins and tRNA anticodons. Unassigned codons would have been produced in bacteria with extremely high GC or AT genomes by deleting certain codons and the corresponding tRNAs. A high AT pressure together with genomic economization led to a change in assignment of the UGA codon, from stop to tryptophan, inMycoplasma.
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 167 (1997), S. 106-111 
    ISSN: 1432-072X
    Schlagwort(e): Key wordsNitrosomonas ; Anaerobic ammonia ; oxidation ; Anaerobic cell growth ; Nitrogen dioxide ; Nitric oxide ; Nitrous oxide ; Dinitrogen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Nitrosomonas eutropha, an obligately lithoautotrophic bacterium, was able to nitrify and denitrify simultaneously under anoxic conditions when gaseous nitrogen dioxide (NO2) was supplemented to the atmosphere. In the presence of gaseous NO2, ammonia was oxidized, nitrite and nitric oxide (NO) were formed, and hydroxylamine occurred as an intermediate. Between 40 and 60% of the produced nitrite was denitrified to dinitrogen (N2). Nitrous oxide (N2O) was shown to be an intermediate of denitrification. Under an N2 atmosphere supplemented with 25 ppm NO2 and 300 ppm CO2, the amount of cell protein increased by 0.87 mg protein per mmol ammonia oxidized, and the cell number of N. eutropha increased by 5.8 × 109 cells per mmol ammonia oxidized. In addition, the ATP and NADH content increased by 4.3 μmol ATP (g protein)–1 and 6.3 μmol NADH (g protein)–1 and was about the same in both anaerobically and aerobically grown cells. Without NO2, the ATP content decreased by 0.7 μmol (g protein)–1, and the NADH content decreased by 1.2 μmol (g protein)–1. NO was shown to inhibit anaerobic ammonia oxidation.
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 49 (1997), S. 745-753 
    ISSN: 1572-8943
    Schlagwort(e): DSC ; kerogen ; oxidation ; pyrolysis ; type determination
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The rate of pyrolysis and oxidation of 8 different samples of oil shale kerogen concentrate (KC) were investigated using DSC analysis. Recently performed thermogravimetric studies (TG and DTG) with the same samples of KC indicated that the activation energy of the pyrolysis of specific KCs increases with increasing paraffinic structure in the KC. An opposite effect, i.e. a decrease of the activation energy with an increase of paraffinic structure was determined in the case of KC oxidation. In this study, using the standard ASTM E-698 method based on the determined temperature at which the maximum heat effect could be observed (exo in the case of oxidation and endo in the case of pyrolysis), an activation energy for the pyrolysis, as well as for the oxidation process was determined and also successfully correlated with the content of paraffinic structure of KC. Thus, the higher content of paraffinic structure in KCs indicates that higher values of the activation energy could be determined either in the case of pyrolysis or oxidation followed by DSC analysis.
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  • 40
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 49 (1997), S. 857-862 
    ISSN: 1572-8943
    Schlagwort(e): analytical methods ; kinetics ; powder milk ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract This work present comparative results on powder milk storage quality, obtained from analytical methods. Protein content was determined conventional (Kjeldahl) and colorimetric with biuret reagent at 540 nm and integral quality by thermogravimetric and biological methods. A method was developed for the protein separation of powder milk. Powder milk was submitted to degradation processes at 45, 60 and 80°C for 20 days. The results indicated that protein content values were inconsistent if determinations by Kjeldahl and colorimetric methods and biological tests were compared. There is evidence of thermal decomposition of powder milk as detected by biological and thermogravimetric methods.
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 49 (1997), S. 1017-1023 
    ISSN: 1572-8943
    Schlagwort(e): degradation ; microcalorimetry ; moisture ; oxidation ; permeability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The use of isothermal microcalorimetry (MC) as a sensitive monitor for slow reactions is demonstrated in a number of examples. In Example 1 the spontaneous decomposition of a nitrate ester propellant is studied and the absolute degradation rate estimated. Example 2 illustrates how MC can be used for comparing the rate of oxidative ageing at different O2 concentrations. Synergetic effects between oxygen and moisture in accelerated ageing of nitrile rubber are evaluated from a so-called 4-point test in Example 3. The last example shows a simple MC technique for rapid determination of moisture permeability through a polymeric sealant.
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 48 (1997), S. 657-664 
    ISSN: 1572-8943
    Schlagwort(e): nickel powders ; oxidation ; thermal analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Monodispersed fine metal nickel powders of uniform shape and high purity are increasingly required for specific uses in many technological areas, especially in the preparation of electronic materials such as the manufacture of conductive inks and pastes and the formation of catalysts. Metallic nickel powders were prepared in ethylene glycol by the reduction of a nickel solution. Hydrazine was used as a reducing agent. Metal powders were characterized by chemical analysis, scanning electron microscopy (SEM), thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). Particle size distributions were determined using laser light scattering. The reactivity and purity of these fine nickel powders were tested by repeated oxidation and reduction of nickel powders in oxidative and reductive atmospheres.
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  • 43
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 49 (1997), S. 1501-1507 
    ISSN: 1572-8943
    Schlagwort(e): calcium sulphide ; gypsum ; oxidation ; phosphogypsum ; reduction ; stability ; thermogravimetry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Using a heating rate of 2°C min−1, CaS reacts with oxygen in air from 700°C to form CaSO4, with a complete conversion at 1100°C. Synthesis of CaS from the reaction between CaSO4 containing compounds and carbon compounds in air would not be possible, as the carbon reacts from 600°C with oxygen in the air to give CO2. Heating stoichiometric amounts of carbon and pure CaSO4, synthetic gypsum or phosphogypsum in a nitrogen atmosphere, results in the formation of CaS from 850°C. Using a heating rate of 10°C min−1, the formation of CaS is completed at 1080°C. Addition of 5% Fe2O3 as a catalyst lowers the starting temperature of the reaction to 750°C. Activation energy values at different fraction reaction values (α) differ between 340 and 400 kJ mol−1. The relationship between the activation energy values and conversion (α) indicates that the reaction proceeds via multiple steps.
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  • 44
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 49 (1997), S. 1161-1170 
    ISSN: 1572-8943
    Schlagwort(e): basicity ; dinitramides ; kinetics ; oxidation ; tanδ ; transition temperatures
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The dinitramide salts of ammonia (ADN), hexamethylenetetramine (HDN), potassium (KDN), and sodium (NaDN) showed a linear relationship between the DSC rate of decomposition at the peak maximum and the DEA tanδ value at the low temperature transition peak. As the cation basicity increased in the series ADN〈HDN〈KDN〈NaDN, there was an increase in the low temperature transition peak, the energy barrier for relaxation, and the decomposition peak temperature, and a decrease in the tanδ value at the low temperature transition peak, specific heat capacity, and the rate and enthalpy of decomposition. The more basic salts were more thermally stable (i.e., higher decomposition temperature) and less energetic (i.e., lower enthalpy of decomposition). The more internal free volume (disorder) present in these salts, the higher the rates of relaxation and decomposition. Five aluminum powders of different surface areas were analyzed by DSC in platinum sample pans, and it was found that the enthalpy and rate of oxidation increased as the particle size of Al decreased while the enthalpy of the Al melt decreased. TG showed a two-step weight gain in the oxidation of Al with plateaus in the 650 and 1130°C regions and the percent weight gain increased as the particle size of Al decreased. Variable DSC and TG heating rate studies showed that the activation energies for the first step in the oxidation process increased as the particle size of Al increased.
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  • 45
    Digitale Medien
    Digitale Medien
    Springer
    Journal of nondestructive evaluation 16 (1997), S. 91-100 
    ISSN: 1573-4862
    Schlagwort(e): LASER ultrasound ; anisotropic material ; group velocity ; stiffness coefficients ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik
    Notizen: Abstract Ultrasonic waves are generated through a composite material by means of a noncontact technique. It uses a Nd:Yag LASER for the generation and an interferometric probe for the detection of acoustic waveforms. From a suitable set of experimental data, an inversion scheme is used for the recovering of four stiffness coefficients. They characterize the elasticity in a principal plane of symmetry of the material which exhibits an orthorhombic symmetry. The measurements are performed at various temperatures, elevated by steps up to 300°C for two specimen. The sensitivity of the method appears convenient to measure the temperature induced stiffness changes. The anisotropic degradation of the material properties are then pointed out.
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  • 46
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 47 (1997), S. 381-410 
    ISSN: 1573-4889
    Schlagwort(e): Ni-Base superalloys ; Astroloy ; Waspaloy ; Udimet 720 ; oxidation ; chromia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Several commercially available Ni-base superalloys were exposed isothermally in air at temperatures between 750° and 1000°C and also under cyclic conditions at 1000°C. The kinetics of oxidation were determined and the scales were analyzed by electron microscopy and X-ray diffraction. Thin adherent chromia-rich scales formed on the alloys at 750°C after 1000 hr. Although Waspaloy showed the lowest weight gain in this test, it also showed the deepest internal corrosion due to oxidation of the grain-boundary carbides. At temperatures up to 1000°C the external scales were also chromia-rich but there was greater internal corrosion. Titanium in the alloys oxidized, diffusing through the chromia scale to form faceted rutile (TiO2) grains at the surface as well as forming TiO2 and TiN internally. The amount of rutile at the oxide surface increased with temperature and alloy Ti concentration. Alumina formed as discrete internal oxides below the chromia scale, although Astroloy when oxidized isothermally at 1000°C developed a semicontinuous internal layer of alumina due to its higher Al content. Under cyclic conditions Astroloy formed a thicker, less-protective scale of transition oxides probably due to its lower Cr content.
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  • 47
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Incoloy 909 ; superalloy ; scale ; high temperature ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of an Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si superalloy (Incoloy 909 type alloy), was investigated at temperatures between 1000 K and 1400 K in Ar-(1, 10%)H20 atmosphere using metallographic, electron probe microanalysis, and X-ray diffraction techniques. The oxide scales consist of an external scale and an internal scale which has an intergranular scale (above 1200 K) and an intergranular scale. The oxide phases in each scale are identified asα-Fe2,O3 (below 1200 K) or FeO (above 1300 K) and CoO · Fe2O3 and FeO · Nb2O5, respectively. The morphologies, the oxide phases and the oxidation rates do not depend on the partial pressure of H2O in the range between one and ten percent in Ar gas. The rate constants for the intergranular-scale formation in this alloy are about one-tenth as large as those in Fe-36%Ni alloy reported previously. At all the temperatures the scales grow according to a parabolic rate law and the apparent activation energies for the processes are estimated.
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  • 48
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 47 (1997), S. 445-464 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Fe-Cr-Al alloy ; water vapor ; ESCA ; RHEED
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Fe-21.5 wt. %Cr-5.6 wt. %Al oxidation, at 1000°C, in dry or wet oxygen shows that steam has an influence on the oxide-scale growth mechanism. Steam modifies the kinetics of early-stage oxidation. In dry oxygen, an initial fast linear regime is observed during one hour. Under wet conditions, weight-gain curves follow the same parabolic regime over the entire oxidation test. The scale structure strongly depends on the presence of steam in the gaseous environment. With dry oxygen, the scale is composed mainly ofα-Al2O3 after the initial formation ofγ-Al2O3 identified by ESCA and RHEED. The kinetics transient stage corresponds to the necessary time for the internal part of the initialγ-Al2O3 scale to transform into a continuousα-Al2O3 diffusion barrier. Under wet oxygen conditions, transient oxides are identified as (Mg, Fe) (Cr, Al)2O4, MgAl2O4 (orthorhombic), Al2O3 (hexagonal), these oxides transform into MgAl2O4 (cubic), Cr3O4, Fe2O3,α-Al2O3, with time. When water vapor does not change drastically oxidation kinetics, the induced presence of iron and chromium in the oxide scale could be responsible for weakening the protectiveness of alumina scales.
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  • 49
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 47 (1997), S. 507-524 
    ISSN: 1573-4889
    Schlagwort(e): alloys ; high temperature ; oxidation ; transient state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The initial transient high-temperature oxidation stage for binary alloys forming the most-stable oxide has been examined by means of a numerical procedure based on the finite-difference method. At variance with previous models, the present treatment takes into account the effect of the rate of the reaction at the scale/gas interface over the corrosion kinetics. The calculations concerning the transient stage are developed either using the general parabolic rate law to represent the overall scaling kinetics or using the rate law of the reaction at the scale/gas interface as a boundary condition without imposing any particular rate law to the overall process. A correct analysis of the oxidation behavior of binary alloys during the transient stage must take into account the kinetics effect of the rate of the surface reaction. The concentration of the most-reactive element at the alloy/scale interface changes regularly with time, decreasing gradually from the initial bulk value to its final steady-state value. The present results are in good agreement with those obtained by means of an approximate analytical model developed previously.
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  • 50
    ISSN: 1573-4889
    Schlagwort(e): high temperatures ; oxidation ; transient state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The transient state in the oxidation of solid solutions of a most-noble componentA in a most-reactive componentB (beta phase) for binaryA-B alloys presenting a limited reciprocal solubility of the two metals has been examined assuming that theirB content is sufficient for the exclusive growth of externalBO scales. Above a criticalB content of the alloy theBO scales may grow directly on the surface of the beta phase, while below this limit they can only form over a layer ofB-depleted solid solution ofB inA (alpha phase), which appears after a critical time. An approximate analytical expression for the profile of concentration ofB in the alloy has been adopted to calculate the flux ofB in the metal. Moreover, the effect of the reaction between the gas and the external oxide surface has been taken into account using a procedure developed by Wagner for the oxidation of pure metals. The corrosion kinetics as well as all the parameters involved, such as the concentration ofB at the alloy-scale interface, have been calculated as functions of the corrosion time. The results show that, as time proceeds, the instantaneous parabolic rate constant increases and the concentration ofB at the alloy-scale interface decreases, both tending gradually to their corresponding steady-state values. It is also predicted that if the rate of transformation of the beta phase in the alpha phase after the alloy reaches the composition of equilibrium at the interface with the oxide is lower than the corresponding rate of displacement of the alloy surface due to scale growth, the corrosion of beta phase alloys may eventually lead to the formation of two phase mixtures of alpha phase andBO which are expected to grow at much larger rates than in the presence of a uniform continuous alpha layer.
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  • 51
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 1-39 
    ISSN: 1573-4889
    Schlagwort(e): Ni-base ODS superalloys ; oxidation ; initial stages of oxidation ; alumina ; chromia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Mechanically-alloyed Ni-base ODS superalloys currently receive attention for application in future gas turbines because they exhibit outstanding mechanical properties at high temperatures. They also protect themselves against oxidation by forming chromia and/or alumina scales. However, little attention has been given so far to the initial stages of oxidation of Ni-base ODS superalloys, containing Cr as well as Al in considerable amounts. In the current work, oxidation at 1150°C was studied for different holding times up to 200 hr for the commercial materials MA6000 and PM3030 which contain. Al in increasing amounts. MA 754, a chromia former, was investigated as a reference. It was shown that for the potential alumina formers MA6000 and PM3030 the continuity and therefore protectiveness of the secondary Al2O3 at later stages is indeed determined by the initial stages of oxidation.
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  • 52
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 129-141 
    ISSN: 1573-4889
    Schlagwort(e): decarburization ; nickel ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A commercial-grade nickel containing small amounts of carbon, manganese, and silicon was exposed to air for periods up to 288 hr at 1050°C to study the effect of oxidation on the formation of oxides of these impurity elements. Exposure of nickel to air led to decarburization. The maximum amount of decarburization occurred during the initial period of air exposure and the loss in carbon was more in the metal with a smaller section size. Decarburization in the metal produced voids in the oxide scale due to the formation of CO2 gas. It has been shown further that CO and/or CO2 gas bubbles, which form in high purity nickel on grain boundaries during exposure to air at elevated temperatures, cannot exist in commercial-grade nickel where manganese is present as an impurity. Instead, oxides of manganese form in the grain boundaries as well as in the matrix. This is because manganese oxide is more stable than CO or CO2 gas.
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  • 53
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; kinetics ; iron ; iron-nitride
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of α-Fe and ɛ-Fe2N1−z at 573 K and 673 K in O2 at 1 atm was investigated by thermogravimetrical analysis, X-ray diffraction, light-optical microscopy, scanning electron microscopy and electron probe X-ray microanalysis. Upon oxidation at 573 K and 673 K, on α-Fe initially α-Fe2O3 develops, whereas on ɛ-Fe2N1−z initially Fe3O4 develops. In an early stage of oxidation the oxidation rate of ɛ-Fe2N1−z appears to be much larger than of α-Fe. This can be attributed largely to an effective surface area available for oxygen uptake, which is much larger for ɛ-Fe2N1−z than for α-Fe due to the porous structure of ɛ-Fe2N1−z as prepared by gaseous nitriding of iron. The development of a magnetite layer in-between the hematite layer and the α-Fe substrate, at a later stage of oxidation, enhances layer-growth kinetics. After 100 min oxidation at 673 K the (parabolic) oxidation rates for α-Fe and ɛ-Fe2N1−z become about equal, indicating that on both substrates the oxide growth is controlled by the same rate limiting step which is attributed to short-circuit diffusion of iron cations. Oxidizing ɛ-Fe2N1−z increases the nitrogen concentration in the remaining ɛ-iron nitride, because the outward flux of iron cations, necessary for oxide growth, leads to an accumulation of nitrogen atoms left behind.
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  • 54
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 201-214 
    ISSN: 1573-4889
    Schlagwort(e): titanium-aluminum alloys ; niobium ; intermetallics ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract In a recent study, CO2 has been reported to enhance the oxidation rate of binary titanium-aluminum alloys. The detrimental effect of CO2 was not, however, observed in a ternary alloy containing niobium. In this paper, possible explanations for these observations are examined. First, results from the literature regarding the effects of niobium in improving the resistance of titanium-aluminum alloys are briefly reviewed. Second, a thermodynamic analysis which offers a possible explanation for the beneficial effect of niobium in eliminating the CO2-enhanced oxidation of titanium-aluminum alloys is presented.
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  • 55
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 215-224 
    ISSN: 1573-4889
    Schlagwort(e): nanocrystallization ; oxidation ; mechanism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Many mechanisms for the effect of reactive elements on the selective oxidation and scale adhesion of alloys have been proposed. However, nanocrystallization (or microcrystallization) has recently been found to have almost the same effect as that of reactive elements. This note reviews the effect of nanocrystallization on the selective oxidation and adhesion of Al2O3 scale with particular reference to the author's own results.
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  • 56
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 289-302 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; titanium ; rutile ; scale ; high temperature ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of pure titanium has been investigated in the temperature range of 1000 K to 1300 K in CO2 or Ar-10%CO2. Optical microscopy, electron probe microanalyses, and X-ray measurements on the oxide scales formed during oxidation indicate that their structures are nearly independent of temperature and the corrosion atmosphere. The scales consisted of two layers, an external one and an internal one, having a rutile (TiO2) structure. The parabolic rate law was confirmed for growth of the external scale and the permeation depth of oxygen in titanium with apparent activation energies of 266 and 226 kJ/mol, respectively. The rate-determining diffusion species in the oxidation processes are discussed.
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  • 57
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 329-345 
    ISSN: 1573-4889
    Schlagwort(e): zirconium ; X-ray diffraction ; oxidation ; phase analysis ; texture
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of zirconium at high temperature (T〉 400°C) leads to reaction products of two allotropic oxide (ZrO2 monoclinic and ZrO2 tetragonal). The distribution and proportion of these two phases were studied as a function of time and space by X-ray diffraction techniques. Quantitative analyses are possible after some corrections, and we demonstrate the presence of a phase gradient in the oxide scale. The interest of this nondestructive method is then discussed.
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  • 58
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 357-380 
    ISSN: 1573-4889
    Schlagwort(e): chromium ; copper ; binary alloys ; two-phase alloys ; oxidation ; high temperatures
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation in air of three two phase Cu-Cr alloys with nominal Cr contents of 25, 50, and 75 wt. % was studied at 700–900°C. The alloys corroded nearly parabolically, except at 900°C, when the corrosion rates decreased with time more rapidly than predicted by the parabolic rate law. The corrosion rate decreased for higher Cr contents in the alloy under constant temperature and generally increased with temperature for the same alloy composition. The scales were complex and consisted in most cases of an outermost copper oxide layer free from chromium and an inner layer composed of a matrix of copper oxide or of the double oxide Cu2Cr2O4, often containing particles of chromium metal surrounded by chromia and then by the double oxide. Metallic copper was also frequently mixed with chromia. Cr-rich regions tended to form continuous chromia layers at the base of the scale, especially at the highest temperature. No chromium depletion was observed in the alloy.
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  • 59
    ISSN: 1573-4889
    Schlagwort(e): iron ; oxidation ; CeO2 coating ; in situ ; growth stress ; residual stress ; texture ; X ray diffraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract In situ XRD stress determinations have been performed during oxidation of pure iron (p(O2=2 × 10−3 Pa,T=800°C)). The compressive stress, initially present in the substrate due to surface preparation, is completely released at 400°C. Under the test conditions, the in situ compressive-stress level determined in the FeO scale during oxidation is not strongly dependent upon the presence of a ceria coating. On blank and coated specimens, the compressive stress varies from −400 ± 80 MPa to −150 ± 100 MPa during 30 hr oxidation. The decrease is quicker at the beginning of the test performed on blank specimens. Epitaxial relationships between the wüstite scale and iron (under low-pressure starting conditions) caused thein situ compressive stress in the oxide scale to be two times greater compared to the usual test conditions. This indicates that epitaxial relationships can be a source of stress in an oxide scale that ceria coatings may lower compressive stresses.
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  • 60
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 527-551 
    ISSN: 1573-4889
    Schlagwort(e): chloridation ; oxidation ; Fe-Cr alloys ; Ni-Cr alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The chloridation-oxidation behavior of Fe-Cr (0–25 wt. %Cr) and Ni-Cr (0–20 wt.%Cr) alloys was studied at 800°C in three different H2-HCl-H2O(ν) environments. In a low-HCI and low-H2O(ν) environment, where Cr2O3 is thermodynamically stable, the corrosion resistance of the Fe-Cr alloys increased with increasing Cr content in the alloys. In a high-HCl and high-H2O(ν) environment, where FeCr2O4 is stable and CrCl2 is metastable, the corrosion resistance of the Fe-Cr alloys depended similarly on the Cr content. Low-Cr-Fe-Cr alloys exhibited large weight losses, while Fe-Cr alloys with higher than 19 wt. %Cr showed good corrosion resistance. In an environment of high-HCl in the absence of H2O(ν), the evaporative corrosion rate was fast and limited by gas phase diffusion, and independent of the Cr content in the Fe-Cr alloys. Ni and Ni-Cr alloys generally showed good corrosion resistance in the environments of high H2O(ν) because of the low NiCl2 vapor pressure and formation of a protective Cr2O3 scale. However, in the environment of high HCl in the absence of H2O(ν), selective formation and evaporation of CrCl2 occur, which results in Cr depletion and networks of voids for even a high-Cr Ni-Cr alloy.
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  • 61
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 553-596 
    ISSN: 1573-4889
    Schlagwort(e): chloridation ; oxidation ; HCl ; high-temperature alloys ; high-temperature corrosion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Chloridation-oxidation studies of nine commercial high-temperature alloys were carried out at 800°C in three different H2-HCl-H2O(ν) environments: (A) both low HCl and H2O(ν) partial pressures, where either Cr2O3 or FeCr2O4 is stable, (B) both high HCl and H2O(ν) partial pressures, where FeCrO4 is stable and CrCl2 is metastable, and (C) high HCl partial pressure in the absence of H2O(ν), where either CrCl2 or Cr2O3 is stable. Although alloy 600 has the lowest Cr content of these nine alloys, it showed excellent corrosion resistance in all three environments because of its high Ni content. Alloy 304, with the lowest Ni content of the nine alloys, exhibited poor corrosion resistance in the environment C, fair resistance in the environment B and good resistance in the environment A. Alloy 800 showed very good resistance in Environment A, and fair corrosion resistance in Environment B; however, it suffered linear weight-loss kinetics when exposed to Environment C The alloys 617, 214, HR-160, X, 230 and 86 have good corrosion resistance in Environments A and B because of their relatively high contents of oxide-scale-forming elements Cr and/or Al. In Environment C, chlorine dramatically decreased the adhesion of the scale on the surface, and aluminum in alloys 617 and 214 hardly showed its usual beneficial effect in combating corrosion, nor does silicon in alloy HR-160. Different corrosion mechanisms are proposed for the alloys in the different environments.
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  • 62
    ISSN: 1573-4919
    Schlagwort(e): muscular diseases ; mitochondria ; MTDNA ; ATP synthase ; human
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The expression of several mitochondrial and nuclear genes involved in ATP production was examined in cells cultured from muscle biopsies of patients harboring mitochondrial pathologies. The transcript patterns in muscle cells from the patients affected by carnitine palmitoyl transferase II or 2-ketoglutarate dehydrogenase deficiencies were almost similar to control patterns. In the opposite, patterns were strikingly abnormal in all the other cell cultures from patients with defects in enzymatic complexes involved in oxidative phosphorylation: mitochondrial complex II and III deficiencies, two MELAS syndromes (myopathy, encephalopathy, lactic acidosis and stroke like episodes), a case of Kearns-Sayre syndrome and a case of chronic progressive external ophthalmoplegia. In cultured muscle cells from patients with mtDNA mutations, the percentage of mutated mtDNA was low as compared with those determined in the corresponding skeletal muscle biopsy. Moreover, the complex II defect resulting of a nuclear mutation was not expressed in the cell cultures. Thus, an undetermined transcriptional event, transmitted from muscle biopsies to cultured muscle cells, should be involved to account for such abnormal transcript patterns.
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  • 63
    ISSN: 1573-4919
    Schlagwort(e): porphyrin derivative ; mitochondria ; ascites ; singlet oxygen ; photosensitization ; lipid peroxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract With a view to locate porphyrins for use in photodynamic therapy (PDT), the new modality of cancer treatment we have evaluated the ability of a novel water soluble porphyrin meso-tetrakis[4-(carboxymethyleneoxy)phenyl]porphyrin (T4CPP) to induce damage to mitochondria during photosensitization. T4CPP, when exposed to visible light, induced lipid peroxidation in rat liver mitochondria as assessed by the formation of thiobarbituric acid reactive substances (TBARS), conjugated dienes (CD) and lipid hydroperoxides (LOOH). The effect on mitochondrial function was assessed by estimating the activity of succinate dehydrogenase (SDH). The peroxidation induced was observed to be time- and concentration- dependent. Analysis of product formation and selective inhibition by scavengers of reactive oxygen species showed that the oxidative damage observed was mainly due to singlet oxygen (1O2) and partly due to other reactive species. T4CPP plus light also caused significant lipid peroxidation in Sarcoma 180 ascites tumour mitochondria. Our studies indicate that T4CPP has the potential to photoinduce damage in hepatic and ascites mitochondria, a crucial site of damage in PDT. (Mol Cell Biochem 166: 25-33, 1997)
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  • 64
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 174 (1997), S. 325-328 
    ISSN: 1573-4919
    Schlagwort(e): ageing ; theory ; mitochondria ; respiratory chain ; mitochondrial DNA mutations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Mitochondria are believed to be involved in human ageing. Whilst it is clear that various mitochondrial DNA mutations do accumulate in human tissues with age, whether or not they interfere with respiratory chain function is uncertain. We question the results of previous studies which have measured respiratory chain function in human skeletal muscle with age. Whilst cytochrome c oxidase deficient fibres are a real finding in skeletal muscle, the contribution of mitochondrial DNA mutations to human ageing is still controversial. Our results show for mitochondria to be involved in ageing then it must be through a more subtle mechanism than a global decline in respiratory chain function. (Mol Cell Biochem 174: 325–328, 1997)
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  • 65
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 33 (1990), S. 19-30 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; segregation ; impurities ; CeO2-coated Fe-20Cr
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The interfacial segregation of sulphur and carbon during the oxidation in 1 torr O2 at 1173 K of Fe-20Cr alloy, which was either free of Ce, alloyed with 0.078 wt.% Ce, or sputter-coated with a 4 nm-thick CeO2 layer, was studied using polyatomic SIMS. Oxidation periods were up to 19 hr. During oxidation, sulphur and carbon accumulated at the alloy-oxide interface region of both uncoated and coated alloys. The amount of segregated sulphur did not vary appreciably with time, whereas carbon increased with time. The total amount of segregants was similar for both uncoated and coated alloys, although the scales formed on the sputter-coated alloy maintained adhesion and were about 10 times thinner than those on the uncoated alloys.
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  • 66
    ISSN: 1573-4889
    Schlagwort(e): Incoloy 800H ; oxidation ; sulphidation ; ion implantation ; CER
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Coatings, obtained by preoxidation of Incoloy 800H at low PO2 show good sulphidation resistance due to the higher chromia content in the oxide scale. Yttrium-ion implantation of Incoloy 800H has also a beneficial effect on sulphidation, if preoxidation is applied. The reason for this is presumably the segregation of yttrium to grain boundaries of the oxide. Furthermore, the oxidation kinetics of Incoloy 800H are independent of the partial pressure of the oxygen. Mechanical testing of the preformed oxide scale/substrate combinations in air at 600°C by means of constant-extension-rate experiments shows that preoxidation at low partial pressures of oxygen leads to earlier scalecracking.
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  • 67
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; sulphur ; manganese ; silicium ; precipitate ; cracks
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of presulphidized Ni-Cr alloys has been studied by taking into account the influence of the two distinct oxidation mechanisms described in part I of this article. Sulphur enters the Cr2O3 scale (in Ni-34Cr alloys) mainly as S2− species, which at high temperatures increases the V‴Cr content, and hence the oxidation kinetics. Sulphur is randomly distributed in the scale, except at the inner oxide-alloy interface, where intergranular microsulphides are analyzed in the oxide-scale zone. In the case of NiO, NiCr2O4, Cr2O3 oxide multilayers (in a Ni-20Cr alloy), sulphur in the S2− state is distributed in the oxide layers or at Si-precipitate interfaces. Such a distribution leads to crack formation, especially during cooling.
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  • 68
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 33 (1990), S. 301-308 
    ISSN: 1573-4889
    Schlagwort(e): Pb-In alloys ; oxidation ; oxide-inversion layer ; Auger analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of several single-phase Pb-In alloys has been studied in air at room temperature using AES (Auger electron spectroscopy) combined with sputter-depth profiling. Alloy samples with indium composition between 3 and 64 at.% In, which were prepared using a microtome, were oxidized in air. The oxidation of alloys with low In contents was found to be the same as that of Pb-2.9 at.% Sn.1 Increasing the bulk composition of In increased the ratio of oxidized In to oxidized Pb in the oxide mixture, although Pb oxide was observed even on the surface of the oxide for samples up to 64 at.% In. The oxidation behavior of Pb-In alloys can be explained in terms of preferential oxidation of In due to its much greater affinity for oxygen than Pb.
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  • 69
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 34 (1990), S. 47-70 
    ISSN: 1573-4889
    Schlagwort(e): erosion ; oxidation ; angle of incidence ; nickel ; cobalt
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The combined erosion-oxidation of cobalt and nickel at 600 and 780°C over a range of particle-impact angles has been studied by using weight change vs. time measurements and extensive morphological and microstructural characterization of exposed specimens. The oxidation process has been found to affect the angular dependence of the degradation rates. The effect is especially significant at low-impact angles where ripples and flakes are developed upon the surfaces of specimens.
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  • 70
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 34 (1990), S. 465-472 
    ISSN: 1573-4889
    Schlagwort(e): Al-Mg alloys ; oxidation ; MgO layers ; growth mechanism ; oxide morphology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of Al-5Mg alloy has been studied at 550°C in dry air. Morphological details of the MgO layers which develop on this alloy during hightemperature oxidation have been studied by scanning electron microscopy (SEM). A localized detachment of the protective, adherent MgO layer was found, which is caused by voids formed by vacancy condensation at the metal-oxide interface. The source of these vacancies was the outward diffusion of Mg through the oxide layer. Continuing growth of these voids was responsible for cracking of oxide ridges and nodules, as well as the growth of new MgO having a “cauliflower” morphology. A model describing the process of the outward diffusion is given.
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  • 71
    ISSN: 1573-4919
    Schlagwort(e): outlet obstruction ; bladder ; mitochondria ; transcription ; RNA
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Using the rabbit model, we showed that partial outlet obstruction of theurinary bladder causes significant changes in the status and expression ofthe mitochondrial (mt) genetic system in bladder smooth muscle immediatelyafter obstruction is initiated. Here we investigate quantitatively theseverity of the mt genetic response to partial outlet obstruction in bothshort- and long-term obstructed rabbits. Based on previous functionalstudies, bladders with mass 〈 6 fold greater than control were consideredcompensated; bladders with mass 〉 6 fold that of control were considereddecompensated. Analyses of DNA from compensated rabbit bladders showed thatrelative mt genome copy number decreased to 30% of control values.Transcript analyses for these samples showed that mt RNA levels increased 3fold to compensate for lower template copy number. Analysis of decompensatedbladders demonstrated that mt genome copy number increased to approximately90% of control levels; mt transcripts progressively decreased inthese samples by as much as 30 fold. In contrast, transcription of amt-related nuclear gene decreased 3-9 fold in compensated bladders butincreased 10-30 fold in decompensated bladders. Activity for the cytochromeoxidase complex, and for the mt enzyme citrate synthase, decreased steadilywith increasing bladder hypertrophy. These data suggest that bladderdysfunction following partial outlet obstruction is mediated partly by asignificant loss in mt and mt-related nuclear gene coordination.
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  • 72
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 174 (1997), S. 101-113 
    ISSN: 1573-4919
    Schlagwort(e): calorimetry ; cardiac muscle ; mitochondria ; oxidative phosphorylation ; atractyloside ; dinitrophenol ; ectonucleotidase ; respiratory control
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract A novel flow calorimetric technique was developed to study the energy turnover of myocardial mitochondria. Cylindrical strands of cardiac muscle (trabeculae) weighing 100–500 µg were isolated from guinea-pig heart and mounted in a tubular recording chamber which was continuously perfused with physiological salt solution at 37°C. The temperature difference between the upstream and the downstream side of the chamber, which is proportional to the rate of heat production of the trabecula, was measured at high resolution. In this way the rate of energy expenditure of isolated cardiac muscle could be recorded continuously for several hours. When the preparations were superfused with an 'intracellular' solution containing 5 mM pyruvate and 2 mM malate as substrates, permeabilization of the sarcolemma with 25 µM digitonin induced a marked increase in the measured heat rate in the presence of 2 mM ADP. The major fraction of the ADP sensitive heat production (83%) could be blocked with 400 µM at ractyloside, an inhibitor of the adeninenucleotide translocase, and by 600 µM α-cyano-4-hydroxycinnamate, an inhibitor of monocarboxylate/H+ co-transport. The atractyloside sensitive heat production was abolished in anoxic solution. These results suggest that the atractyloside-sensitive heat production (21.8 ± 3.5 mW cm-3 of tissue) was attributable to oxidative phosphorylation. The mitochondria apparently remained intact after treatment with digitonin, since application of the uncoupler 2,4-dinitrophenol (DNP) produced a very large increase in heat rate. A minor fraction of the heat rate induced by ADP in permeabilized cardiac muscle preparations (17%) was not sensitive to atractyloside. This component was also seen before application of digitonin and was probably related to ectonucleotidases. In conclusion, our calorimetric technique allows investigation of the energy metabolism of myocardial mitochondria 'in situ', i.e. without destroying the microarchitecture of cardiac muscle cells. (Mol Cell Biochem 174: 101–113, 1997)
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  • 73
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 174 (1997), S. 181-184 
    ISSN: 1573-4919
    Schlagwort(e): mitochondria ; cyclosporin ; cyclophilin ; channels ; permeability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Mitochondria possess an inner membrane channel, the permeability transition pore, which is inhibited by cyclosporin A (CBA) and by matrix protons. As suggested recently by our laboratory, pore closure by these inhibitors may be due to dissociation of mitochondrial cyclophilin (CyP-M), a matrix peptidyl-prolyl-cis-trans isomerase, from its putative binding site on the pore. Unbinding of CyP-M would follow a CsA-dependent or proton-dependent change in conformation of the CyP-M molecule. It is interesting that upon binding of CsA the enzymatic activity of CyP-M is inhibited, but it is not clear whether this event plays a role in pore inhibition. Here we report experiments designed to further test the role of CyP-M in pore function. Our results indicate that CyP-M-dependent and independent mechanisms of pore activation may exist, and that the peptidylprolyl-cis-trans-isomerase activity of CyP-M is not necessarily involved in pore modulation by CyP-M. (Mol Cell Biochem 174: 181–184, 1997)
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  • 74
    ISSN: 1573-4919
    Schlagwort(e): mitochondria ; calcium ; permeability transition ; vasopressin ; glucagon ; thapsigargin ; protein kineses and phosphatases ; rat hepatocytes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Ca2+ functions as an intracellular signal to transfer hormonal messages to different cellular compartments, including mitochondria, where it activates intramitochondrial Ca2+-dependent enzymes. However, excessive mitochondrial Ca2+ uptake can promote the mitochondrial permeability transition (MPT), a process known to be associated with cell injury. The factors controlling mitochondrial Ca2+ uptake and release in intact cells are poorly understood. In this paper, we investigate mitochondrial Ca2+ accumulation in intact hepatocytes in response to the elevation of cytosolic Ca2+ levels ([Ca2+]c) induced either by a hormonal stimulus (vasopressin), or by thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+ pump. After stimulation, cells were rapidly permeabilized for the determination of the mitochondrial Ca2+ content (Ca2+_m) and to analyze the susceptibility of the mitochondria to undergo the MPT. Despite very similar levels of [Ca2+]c elevation, vasopressin and thapsigargin had markedly different effects on mitochondrial Ca2+ accumulation. Vasopressin caused a rapid (〈 90 sec), but modest (〈 2 fold) increase in Ca2+m that was not further increased during prolonged incubations, despite a sustained [Ca2+]c elevation. By contrast, thapsigargin induced a net Ca2+ accumulation in mitochondria that continued for up to 30 min and reached Ca2+_m levels 10–20 fold over basal. Accumulation of mitochondrial Ca2+ was accompanied by a markedly increased susceptibility to undergo the MPT. Both mitochondrial Ca2+ accumulation and MPT activation were modulated by treatment of the cells with inhibitors of protein kineses and phosphatases. The results indicate that net mitochondrial Ca2+ uptake in response to hormonal stimulation is regulated by processes that depend on protein kinase activation. These controls are inoperative when the cytosol is flooded by Ca2+ through artificial means, enabling mitochondria to function as a Ca2+ sink under these conditions. (Mol Cell Biochem 174: 173–179, 1997)
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  • 75
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 174 (1997), S. 215-219 
    ISSN: 1573-4919
    Schlagwort(e): MERRF ; mitochondria ; mtDNA ; genetics ; tRNA
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract MERRF (myoclonic epilepsy with ragged-red fibers) is a severe, multisystem disorder characterized by myoclonus, seizures, progressive cerebellar syndrome, muscle weakness, and the presence of ragged-red fibers in the muscle biopsy. MERRF is associated with heteroplasmic point mutations, either A8344G or T8356C, in the gene encoding the mitochondrial tRNALys. The human ro cell system was utilized to examine the phenotypic consequences of these mutations, and to investigate their molecular genetic causes. Wild-type and mutant transmitochondrial cell lines harboring a pathogenic point mutation at either A8344G or T8356C in the human mitochondrial tRNALys gene were isolated and examined. Mitochondrial transformants containing 100% mutated mitochondrial DNAs (mtDNAs) exhibited severe defects in respiratory chain activity, in the rates of protein synthesis, and in the steady-state levels of mitochondrial translation products as compared with mitochondrial transformants containing 100% wild-type mtDNAs. In addition, both mutant cell lines exhibited the presence of aberrant mitochondrial translation products. These results demonstrate that two different mtDNA point mutations in tRNALys result in fundamentally identical defects at the cellular level, and that these specific protein synthesis abnormalities contribute to the pathogenesis of MERRF. (Mol Cell Biochem 174: 215–219, 1997)
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  • 76
    ISSN: 1573-4919
    Schlagwort(e): diabetes ; carbon tetrachloride ; liver toxicity ; glutathione ; mitochondria ; Schisandra chinensis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The streptozotocin-induced short-term (2 week) diabetic rats showed an increase in susceptibility to carbon tetrachloride (CCl4)-induced hepatocellular damage. This diabetes-induced change was associated with a marked impairment in the hepatic glutathione antioxidant/detoxification response to CCl4 challenge, as indicated by the abrogation of the increases in hepatic reduced glutathione (GSH) level, glucose-6-phosphate dehydrogenase and microsomal glutathione S-transferases (GST) activities upon challenge with increasing doses of CCl4. While the hepatic GSH level was increased in diabetic rats, the hepatic mitochondrial GSH level and Se-glutathione peroxidase activity were significantly reduced. Insulin treatment could reverse most of the biochemical alterations induced by diabetes. Both insulin and schisandrin B (Sch B) pretreatments protected against the CCl4 hepatotoxicity in diabetic rats. The hepatoprotection was associated with improvement in hepatic glutathione redox status in both cytosolic and mitochondrial compartments, as well as the increases in hepatic ascorbic acid level and microsomal GST activity. The ensemble of results suggests that the diabetes-induced impairment in hepatic mitochondrial glutathione redox status may at least in part be attributed to the enhanced susceptibility to CCl4 hepatotoxicity. Sch B may be a useful hepatoprotective agent against xenobiotics-induced toxicity under the diabetic conditions. (Mol Cell Biochem 175: 225–232, 1997)
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  • 77
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 95 (1990), S. 117-123 
    ISSN: 1573-4919
    Schlagwort(e): mitochondria ; carnitine ; CoQ10 ; carbon monoxide ; hypoxia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Summary The acute effects of carbon monoxide (CO) on cardiac metabolism at the mitochondrial level were investigated. Rats were exposed to 4% CO for 4 minutes in a closed chamber. Immediately after exposure, hearts were removed and frozen with a precooled clamp. Blood from the thoracic cavity was sampled for analysis. Gas analysis of arterial blood taken from the abdominal aorta demonstrated severe hypoxia with oxygen partial pressure less than 20 mmHg, metabolic acidosis and reduced pH value. There were no significant changes in the plasma level of glucose and non esterified fatty acids (NEFA). In the myocardium, ATP levels decreased significantly, and concomitantly, a significant increase in the plasma uric acid level was observed. Although no significant change was observed in short chain acyl carnitine, free carnitine levels decreased to one fourth of the control value. Long chain acylcarnitine increased 11-fold. Coenzyme Q9 (CoQ9) level decreased significantly, but there was no significant change in Coenzyme Q10 (CoQ10).
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  • 78
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 95 (1990), S. 177-182 
    ISSN: 1573-4919
    Schlagwort(e): periodate ; oxidation ; membrane ; cells ; interleukin-1
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Interleukin-1 (IL-1) production by periodic acid (H5IO6)-oxidized human peripheral blood mononuclear (PBMN) cells was assessed by the thymocyte co-mitogenesis assay. Maximum IL-1 levels (∼ 1.2 U/ml) in the conditioned media of PBMN cells were registered within the first 24 hrs post-oxidation, whereas no IL-1 was detected in the media from 24 hrs control cultures. Thymocyte proliferation, driven by periodic acid-induced IL-1, was abolished by an antibody to IL-1alpha and IL-1β. Quantitative analysis of IL-1-containing medium by radioimmunoassay (RIA) indicated that IL-1β comprised about 80% of total IL-1. Partial characterization of H5IO6-induced IL-1β indicated that it was identical to IL-1 produced by lipopolysaccharide-stimulated macrophages. It is concluded that oxidation of human PBMN cells by H5IO6 triggers synthesis and release of IL-1, most of which was in its IL-1β form.
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  • 79
    ISSN: 1573-4919
    Schlagwort(e): mitochondria ; adenine nucleotides ; purine metabolism ; compartmentation ; liver ; hypoxia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Summary The degradation of intramitochondrial adenine nucleotides to nucleosides and bases was investigated by incubating isolated rat liver mitochondria at 37°C under non-phosphorylating conditions in the presence of oligomycin and carboxyatractyloside. Within 30 min the adenine nucleotides were degraded by about 25 per cent. The main products formed were adenosine and inosine the contents of which increased five- to sevenfold. Compartmentation studies revealed that about 50 to 60 per cent of the adenosine formed remained inside the organelles whereas inosine was almost completely released into the surrounding medium. Outside the mitochondria only very small amounts of adenine nucleotides were detected. Similar incubations in the presence of [14C]-adenosine yielded no [14C]-inosine ruling out extramitochondrial adenosine deamination. It is concluded that endogenous adenine nucleotides can be degraded in mitochondria via AMP dephosphorylation and subsequent adenosine deamination. A purine nucleoside transport system mediating at least the efflux of inosine from the mitochondria is suggested.
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  • 80
    ISSN: 1573-4919
    Schlagwort(e): pyruvate dehydrogenase ; polyamines ; adipocyte ; mitochondria ; amino acids ; β-aminoketone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Summary The ability of polyamines and other cationic compounds including monoamines, amino acids, poly-L-arginine, poly-D-lysine and poly-L-lysine, to alter pyruvate dehydrogenase (PDH) activity in mitochondria from rat epididymal adipocytes was determined. PDH was assayed with the substrate [1-14C] pyruvate in the presence of 0.05 mM Ca2+ and Mg2+. Nine of the fourteen compounds tested at 0.1 mM caused a significant increase (procaine, 3-(β-morpholinopropionyl) benzo[b]thiophene [VII], spermine, spermidine, putrescine, lysine and tryptophan) or decrease (poly-L-arginine, 3-(β-piperidinopropionyl) benzo[b]thiophene) in PDH activity. None of these compounds nonenzymatically decarboxylated [1-14C] pyruvate to release 14CO2. NaF, a PDH phosphatase inhibitor, suppressed the stimulatory effects of those compounds tested: procaine, tryptophan, VII, spermine and spermidine. These results imply that these five compounds activate PDH activity through stimulation of the PDH phosphatase. When the Mg2+ concentration was increased from 0.05 to 4.5 mM, the stimulatory effect of spermine was increased, consistent with the finding by others that spermine lowers the Km of the enzyme for Mg2+. However, at Mg2+ concentrations greater than 0.3 mM, the stimulatory effect of VII was unaltered, procaine failed to alter PDH activity, lysine inhibited PDH activity, and poly-L-lysine stimulated PDH activity. Therefore, polyamines and other positively charged small molecules may be physiologic regulators of PDH activity.
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  • 81
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; carbon ; manganese ; nickel ; silicon ; Ni-Cr alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of Ni-Cr alloys (34 and 20 wt.% Cr) was investigated between 850 and 1200°C in oxygen for a maximum duration of about 70 hr. The oxide-growth mechanism is a diffusion process controlled by either outward diffusion of chromium in Cr2O3 (Ni-34Cr alloy) or by an increase in grain size (Ni-20Cr alloy). In the case of the Ni-34Cr alloy, low values of chromium diffusion were found for the growth of Cr2O3 by taking into account the general equation of Wagner. The influence of impurities (Si, C, Mn, Ni) diffusing from the underlying alloy is analyzed because of their doping effect in the outer oxide scales.
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  • 82
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 34 (1990), S. 23-45 
    ISSN: 1573-4889
    Schlagwort(e): erosion ; oxidation ; high-temperature corrosion ; interactions ; nickel ; cobalt
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The combined erosion-oxidation of nickel, cobalt, and the oxides of these metals have been studied at 780°C in air to examine two regimes of interactionnamely, a regime of erosion-enhanced oxidation during which an oxide scale of constant thickness covers metal specimens, and a regime of oxidation-affected erosion that is characterized by a composite surface layer of metal, oxide, and erodent. In the case of cobalt, these two regimes have been documented and the transition from one regime to another described. For the range of conditions examined, only the oxidation-affected erosion regime was observed for nickel due to its lower oxidation rate compared to cobalt.
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  • 83
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 34 (1990), S. 217-228 
    ISSN: 1573-4889
    Schlagwort(e): pack Cementation ; titanium aluminides ; activator ; diffusion ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The practical application of titanium aluminide metal-matrix composites (MMCs) at high temperatures requires suitable surface coatings to provide the needed oxidation resistance. Without a coating, the titanium aluminide alloys suffered from rapid oxidation attack at elevated temperatures, particularly under thermal cyclic conditions. The pack-cementation coating process was utilized to aluminize the surface region of a Ti3Al-base alloy to TiAl3, the most oxidation-resistant phase. With the existence of an adherent conversion coating, a thin protective alumina scale formed on the outer surface, and a significant improvement in the corrosion resistance was observed. Excellent coating efficiency and geometric flexibility were demonstrated in this study by the pack-cementation technique. Further development of the cementation process will focus on the elimination of surface cracking in the coating.
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  • 84
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 34 (1990), S. 229-258 
    ISSN: 1573-4889
    Schlagwort(e): nickel ; oxidation ; oxygen tracer ; SIMS ; duplex scale
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The effect of oxidation conditions on the penetration of oxygen into growing nickel oxide scales has been examined using oxygen isotope tracers and SIMS analysis. Depth profiles and cross-section images of oxide scales show that the proportion of oxygen penetration is increased as the temperature is reduced. At 600°C, the amount of oxygen tracer transported to the scale-metal interface is considerable, approaching that observed for a conventional “duplex” microstructure. The formation of healing oxide along numerous fissures through the oxide is directly observed in SIMS images. These fissures seem to coincide with grain boundaries in the preexisting oxide. As the oxidation temperature is increased, the oxygen transport becomes less uniform, some regions of the scale showing little or no transport. Reduction in the oxygen pressure reduces the amount of oxygen penetrating the scale.
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  • 85
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 34 (1990), S. 323-333 
    ISSN: 1573-4889
    Schlagwort(e): Al-Mg alloys ; oxidation ; high-temperature mechanisms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Surface-analysis techniques (x-ray photoelectron spectroscopy and Auger electron spectroscopy) and electron microscopy (SEM and TEM) have been used to study the mechanism of steady-state high-temperature oxidation of Al-Mg alloys. Two high-purity alloys containing 0.4 and 2.0 wt.% Mg were heat-treated in dry air at 550°C up to 90 hr. It was found that the oxide layer was composed of MgO and spinel (MgAl2O4), the major constituent being MgO. The molar concentration of MgO decreased with increasing depth, while that of spinel increased. The rate-controlling mechanism for the growth of the oxide layer in the Al-0.4Mg alloy was the solid-state diffusion of Mg in the MgO-spinel constituents. For alloys of higher-magnesium content, the growth of the oxide layer was controlled by solid-state diffusion of Mg through the adherent protective oxide areas and by the transport of Mg vapor across voids formed between the alloy substrate and the oxide layer.
    Materialart: Digitale Medien
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  • 86
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 33 (1990), S. 1-17 
    ISSN: 1573-4889
    Schlagwort(e): Ni-Cr-Al alloys ; alloy microstructure ; oxidation ; refractory-metal additions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior at 1023 and 1123 K in air has been followed for several Ni-Cr-Al ternary alloys and with small additions of refractory elements Nb, Mo, and Ta. Prior to testing, the alloys were characterized by microscopic and microanalytic methods. Microstructural observations have shown that the formation of oxide layers depends on the original microstructure. Discontinuous thermogravimetric tests were used to relate the behavior of different chromium, aluminum, and refractory-element additions, and eventually to service conditions in similar environments in which general oxidation takes place. The addition of refractory elements generally impaired the oxidation resistance.
    Materialart: Digitale Medien
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  • 87
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 33 (1990), S. 309-320 
    ISSN: 1573-4889
    Schlagwort(e): manganese steels ; aluminum coatings ; oxidation ; thermogravimetry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Austenitic Mn-Al alloys (20–32 W/O Mn, 7–10 Al, 2–3 Si, 1C) were found to have satisfactory oxidation resistance up to 950°C under isothermal conditions in air. Surface enrichment of aluminum is a necessary condition for obtaining an almost pure alumina scale for uses at higher temperatures. Four different Mn-steels were Al-coated by the Capuano electroplating process. In all the steels there was an increase in the hot-oxidation resistance. The best results were obtained with steels containing both Al and Si, and this for temperatures up to 1100°C. No spalling was noticed during rapid cooling of the test pieces. Silicon was found to act as a diffusion barrier to outward iron diffusion. It appears that there is formation of a pure, thin film of alumina from the matrix which interacts with the aluminum diffusing from the superimposed, coating for the formation of good bonds.
    Materialart: Digitale Medien
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  • 88
    ISSN: 1573-4889
    Schlagwort(e): binary alloys ; oxidation ; transient state ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The initial transient stage in the oxidation of binary alloys forming scales exclusively composed of the most stable oxide is examined by means of a simplified approach which avoids the numerical integration of the diffusion equation for the transport of the metal components in the alloy. At variance with previous solutions to this problem obtained by means of numerical methods, this treatment takes into account also the effect of the gas-scale reaction at the outer surface of the oxide. The concentration of the most-reactive component at the alloy surface changes gradually with time from the initial bulk value towards the corresponding steady-state value without involving any minimum, while the overall rate of the reaction presents a gradual transition from an initial nearly linear towards final parabolic behavior.
    Materialart: Digitale Medien
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  • 89
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 47 (1997), S. 247-258 
    ISSN: 1573-4889
    Schlagwort(e): Ni3Al-base alloy ; sputtering ; nanocrystalline coating ; oxidation ; scale adhesion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Isothermal and cyclic oxidation resistance at 1000°C in air were investigated for a cast Cr-containing Ni3Al-base alloy and its sputtered nanocrystalline coating. The results indicated that both the cast Ni3Al alloy and its sputtered coating exhibit excellent isothermal oxidation resistance as a result of the formation of Al2O3 scales. However, the cast alloy possesses very poor cyclic oxidation resistance because of the spallation of the initially formed Al2O3 scale during cooling and subsequent formation of NiO. On the contrary, the sputtered Ni3(AlCr) nanocrystalline coating exhibits very good cyclic oxidation resistance due to the significant improvement of the adhesion of Al2O3.
    Materialart: Digitale Medien
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  • 90
    ISSN: 1573-4919
    Schlagwort(e): heart ; vascular endothelium ; vascular smooth muscle ; confocal microscopy ; pH ; calcium ; sodium ; voltage probe ; heart ; endothelin-1 ; Angiotensin II ; PAF ; nucleus ; mitochondria ; SR ; cardiomyopathy ; cells interaction ; R-type Ca2+ channel ; excitation-contraction coupling ; dystrophic mouse
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract In recent years, fluorescence microscopy imaging has become an important tool for studying cell structure and function. This non invasive technique permits characterization, localisation and qualitative quantification of free ions, messengers, pH, voltage and a pleiad of other molecules constituting living cells. In this paper, we present results using various commercially available fluorescent probes as well as some developed in our laboratory and discuss the advantages and limitations of these probes in confocal microscopy studies of the cardiovascular system.
    Materialart: Digitale Medien
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  • 91
    ISSN: 1573-4919
    Schlagwort(e): thiamine deficiency ; mitochondria ; energy metabolism ; necrosis ; neuroblastoma cells
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Culture of neuroblastoma cells in the presence of low thiamine concentration (6 nM) and of the transport inhibitor amprolium leads to the appearance of signs of necrosis: the chromatin condenses, the oxygen consumption decreases and is uncoupled, the mitochondrial cristae are disorganized, the thiamine diphosphate-dependent dehydrogenase activities are impaired. When 10 µM thiamine are added to these cells, the basal respiration increases, the coupled respiration is restored and mitochondrial morphology is recovered within 1 h. Addition of succinate, which is oxidized via a thiamine diphosphate-independent dehydrogenase, to digitonin-permeabilized cells immediately restores a coupled respiration. Our results suggest that the slowing of the citric acid cycle is the cause of the biochemical lesion induced by severe thiamine deficiency and that part of the mitochondria remain functional. (Mol Cell Biochem 174: 121–124, 1997)
    Materialart: Digitale Medien
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  • 92
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 174 (1997), S. 189-192 
    ISSN: 1573-4919
    Schlagwort(e): nitric oxide ; mitochondria ; inflammation ; respiration ; astrocytes ; cytochrome oxidase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Nitric oxide (NO) at high levels is cytotoxic, and may be involved in a range of inflammatory, neurodegenerative, and cardiovascular/ischaemic pathologies. The mechanism of NO-induced cytotoxicity is unclear. Recently we and others have found that low (nanomolar) levels of NO reversibly inhibit mitochondrial respiration by binding to the oxygen binding site of cytochrome oxidase in competition with oxygen. This raises the apparent Km for oxygen of mitochondrial respiration into the physiological range, potentially making respiration sensitive to the oxygen level. The NO inhibition of oxygen consumption was seen in isolated cytochrome oxidase, mitochondria, brain nerve terminals, and cultured cells. Cultured astrocytes activated to express the inducible form of NO synthase produced up to 1 µM NO and strongly inhibited their own cellular respiration rate. This respiratory inhibition was rapidly reversed by removing the NO, and was due to the inhibition of cytochrome oxidase. These results suggest that any cell producing high levels of NO will inhibit its own respiration and that of surrounding cells, and make the respiration rate sensitive to the oxygen level. This inhibition of energy metabolism may contribute to cytotoxity or cytostasis in some pathologies. (Mol Cell Biochem 174: 189–192, 1997)
    Materialart: Digitale Medien
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  • 93
    ISSN: 1573-4919
    Schlagwort(e): mitochondria ; mitochondrial myopathies ; oxidative phosphorylation ; principal component analysis (PCA) ; biplot
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The mitochondrial pathologies are a heterogeneous group of metabolic disorders that are characterized by anomalies of oxidative phosphorylation, especially in the respiratory chain. The diagnosis of these pathologies involves many investigations among which biochemical study is at present the main tool. However, the analysis of the results obtained during such study remains complex and often does not make it possible to conclude clearly if a patient is affected or not by a biochemical and/or bioenergetic deficiency. This arises from two main problems: 1. The determination of control values from the whole set of variable values (affected and unaffected people). 2. The small size of the population studied and the large number of variables collected which present a rather large variability. To cope with these problems, the principal component analysis method is applied to the results obtained during our biochemical studies. This analysis makes it possible for each respiratory chain complex, to distinguish clearly two subsets of the whole population (affected and unaffected people) as well as to detect the variables which are the most discriminative. (Mol Cell Biochem 174: 149–156, 1997)
    Materialart: Digitale Medien
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 175 (1997), S. 37-42 
    ISSN: 1573-4919
    Schlagwort(e): mitochondria ; peroxisomes ; fatty acids metabolism ; coenzyme A deficiency ; pantothenic acid
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Hepatic coenzyme A (CoA) plays an important role in cellular lipid metabolism. Because mitochondria and peroxisomes represent the two major subcellular sites of lipid metabolism, the present study was designed to investigate the specific impact of hepatic CoA deficiency on peroxisomal as well as mitochondrial β-oxidation of fatty acids. CoA deficiency (47% decrease in free CoA and 23% decrease in total CoA) was produced by maintaining weanling male Sprague-Dawley rats on a semipurified diet deficient in pantothenic acid (the precursor of CoA) for 5 weeks. Hepatic mitochondrial fatty acid oxidation of short-chain and long-chain fatty acids were not significantly different between control and CoA-deficient rats. Conversely, peroxisomal poxidation was significantly diminished (38% inhibition) in livers of CoA-deficient rats compared to control animals. Peroxisomal β-oxidation was restored to normal levels when hepatic CoA was replenished. It is postulated that since the role of hepatic mi tochondrial β-oxidation is energy production while peroxisomal β-oxidation acts mainly as a detoxification system, the mitochondrial pathway of β-oxidation is spared at the expense of the peroxisomal pathway when liver CoA plummets. The present study may offer an animal model to investigate mechanisms involved in peroxisomal diseases. (Mol Cell Biochem 175: 37–42, 1997)
    Materialart: Digitale Medien
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  • 95
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 177 (1997), S. 245-250 
    ISSN: 1573-4919
    Schlagwort(e): cataract ; crystalline ; glycation ; oxidation ; taurine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Modifications in lens protein structure and function due to nonenzymic glycosylation and oxidation have been suggested to play a significant role in the pathogenesis of sugar and senile cataracts. The glycation reaction involves an initial Schiff base formation between the protein NH2 groups and the carbonyl group of a reducing sugar. The Schiff base then undergoes several structural modifications, via some oxidative reactions involving oxygen free radicals. Hence certain endogenous tissue components that may inhibit the formation of protein-sugar adduct formation may have a sparing effect against the cataractogenic effects of sugars and reactive oxygen. The eye lens is endowed with significant concentration of taurine, a sulfonated amino acid, and its precursor hypotaurine. It is hypothesized that taurine and hypotaurine may have this purported function of protecting the lens proteins against glycation and subsequent denaturation, in addition to their other functions. The results presented herein suggest that these compounds are indeed capable of protecting glycation competitively by forming Schiff bases with sugar carbonyls, and thereby preventing the glycation of lens proteins per se. In addition, they appear to prevent oxidative damage by scavenging hydroxyl radicals. This was apparent by their preventive effect against the formation of the thiobarbituric acid reactive material generated from deoxy-ribose, when the later was exposed to hydroxyl radicals generated by the action of xanthine oxidase on hypoxanthine in presence of iron.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Springer
    Journal of chemical ecology 16 (1990), S. 1041-1058 
    ISSN: 1573-1561
    Schlagwort(e): Air velocity ; controlled release ; formulation ; pheromone ; release rate ; temperature ; tetradecen-1-ol acetates ; vapor collection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract An apparatus was developed for investigating the release rates of pheromone formulations at temperatures and air velocities that correspond with those in the field. Polyurethane foam proved an excellent adsorbent for the recovery of tetradecen-1-ol acetates, allowing high air flows at low differential pressure and without breakthrough of these compounds. The experimental setup and procedures are described. The release rates of all formulations investigated were almost proportional to the square root of air velocity, and their logarithms were proportional to the reciprocal of temperature (K). When temperature is increased from 15°C to 25°C, the release rates increase by about 2-2.5 ×. Both relationships were combined into one equation that allows a reliable estimate to be made of the actual release rates of a formulation, under varying conditions, on the basis of its specific parameters and the relevant meteorological data.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    Springer
    Journal of sol gel science and technology 8 (1997), S. 443-449 
    ISSN: 1573-4846
    Schlagwort(e): coatings ; protection of metals ; oxidation ; corrosion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Sol-gel derived films can be deposited on metals to improve their resistance to oxidation and corrosion or to modify their surface properties. However, practical applications are limited by problems intrinsic to sol-gel processing or specific of coating/metal systems. Coatings aimed to improve oxidation and wet corrosion resistance have been the most studied. The results published in the literature show that sol-gel coatings may offer good protection against oxidation. More difficult is to achieve a protection against wet corrosion. An important aspect of the application of the sol-gel method for coating metallic objects is also the deposition technique.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Springer
    Journal of sol gel science and technology 8 (1997), S. 443-449 
    ISSN: 1573-4846
    Schlagwort(e): coatings ; protection of metals ; oxidation ; corrosion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Sol-gel derived films can be deposited on metals to improve their resistance to oxidation and corrosion or to modify their surface properties. However, practical applications are limited by problems intrinsic to sol-gel processing or specific of coating/metal systems. Coatings aimed to improve oxidation and wet corrosion resistance have been the most studied. The results published in the literature show that sol-gel coatings may offer good protection against oxidation. More difficult is to achieve a protection against wet corrosion. An important aspect of the application of the sol-gel method for coating metallic objects is also the deposition technique.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 33 (1990), S. 177-189 
    ISSN: 1573-4889
    Schlagwort(e): kinetics ; oxidation ; titanium hydride ; rutile
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation kinetics of titanium-hydride powders were studied in the temperature range of 298–1378 K in air at atmospheric pressure. DTA, DSC, X-ray analysis, and scanning electron microscopy were used. Oxidation was found to take place by TiHxOy oxyhydride phases formation. The oxidation reaction rate at temperatures above 870 K was limited by diffusion of oxygen atoms through a rutile scale formed on the surface. The activation energy and preexponential values of the Arrhenius equation for different interaction stages as well as transformation enthalpies were calculated.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 33 (1990), S. 157-176 
    ISSN: 1573-4889
    Schlagwort(e): Fe-Ni-G-Al-S ; alloys ; Mo and Mn additions ; oxidation ; chromic scales
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Oxidation tests were conducted on a master alloy, Fe-16Ni-(5–8)Cr-3Si-lA1, to which (0–4) wt/o pct Mn and/or Mo were added. Tests were conducted at temperatures ranging from 1073–1273 K for times up to 1000 hr. Additions of Mn resulted in formation of a dual oxide structure and decreased oxidation protection. Addition of Mo significantly improved oxidation protection by formation of an intermetallic Fe(Mo)Si precipitate that eventually formed a protective SiO2 oxide sublayer. Increasing the Cr concentration in an alloy containing both Mn and Mo resulted in a slight increase in weight gain. To first order, the apparent oxidation activation energy for all the alloys was nearly constant, 121 kJ/mol, suggesting that the same mechanism controlled the oxidation for all compositions. The oxidation protection was related to the alloy components and concentration.
    Materialart: Digitale Medien
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