Erfahrungen bei der Isolierung von Schnellarbeitsstahlcarbiden sowie der Trennung von MC und M6C

Elektrolytwahl, Isolierungsbedingungen, Trennungsmöglichkeit in röntgenreine Einzelphasen MC und M₆C. Phasenverteilung in den Werkstoffen S 3-3-2, S 6-5-2, S 6-5-3, S 7-4-2-5 und S 10-4-3-10 und Einfluß unterschiedlicher Härtetemperaturen. Chemische Zusammensetzung der röntgenreinen Einzelphasen. Mathematische Problemlösung, Einfluß der Elemente Kohlenstoff und Silicium auf den Ausscheidungsverlauf, die Phasenverteilung und die Phasenzusammensetzung. Störung durch M₂₃C₆, Ermittlung des M₂C-Anteils in Dreiphasengemischen durch Differenzverfahren. Selektive Phasenanreicherung.     

Short-chain aliphatic acids in the interdigital gland secretion of reindeer (Rangifer tarandus L.), and their discrimination by reindeer

Interdigital gland secretion from reindeer (Rangifer tarandus L.) was analyzed by thin-layer chromatography and gas chromato-graphy. The short-chain acid fraction consisted of acetic, propionic, isobutyric,n-butyric, isovaleric, 2-methylbutyric,n-valeric, isocaproic, andn-caproic acids. The short-chain acids were produced by sterol esters when hydrolyzed in the gland-probably by microorganisms. Triglycerides present did not contain any short-chain acids. By testing isovaleric acid and isobutyric acid applied on small filter papers placed in a pen and measuring the number of sniffings on and towards the samples, we elicited good response at 1 ng application compared with the blanks, while pivalic acid gave no response under the same conditions.     

Desaturation of saturated fatty acids by rat liver microsomes

A method was developed for the rapid determination of the initial velocity of the desaturation of saturated fatty acids. In the reaction, DPNH was a more efficient electron donor than TPNH. Fatdeficient rats have a 2.5-fold greater level of acyl desaturase per milligram of liver microsomal protein than did animals fed lab chow. Increasing the chain length of the acyl substrate from 10∶0 to 18∶0 increases the rate of monoene formation, but 19∶0 is desaturated at a rate lower than that for 15∶0. The energy of activation (Ea) for the overall desaturation reaction has been determined for 12∶0 through 19∶0. The Ea values for desaturation of 13∶0 and 16∶0 are markedly lowr than for the other acids. An interaction between the alkyl chain of the substrate and polyunsaturated acids of the microsomal membrane-bound phospholipids is postulated to explain the recurring 3-carbon pattern of the relative reaction rates of the various acyl substrates.     

Oxidative activation of guanylate cyclase by prostaglandin endoperoxides and fatty acid hydroperoxides

Purified prostaglandin endoperoxides (PGG₂ and PGH₂) and hydroperoxides (15-OOH-PGE₂) as well as fatty acid hydroperoxides (12-OOH-20∶4, 15-OOH-20∶4, and 13-OOH-18∶2) were examined as effectors of soluble splenic cell guanylate cyclase activity. The procedures employed for the preparation and purification of these components circumvented the use of diethyl ether which obscured effects of lipid effectors because of contaminants presumed to be ether peroxides which were stimulatory to the cyclase. Addition of prostaglandin endoperoxides or fatty acid hydroperoxides to the reaction mixture led to a time-dependent activation of guanylate cyclase activity; 2.5-to 5-fold stimulation was seen during the first 6 min. The degree of stimulation and rate of activation were dependent on the concentration of the fatty acid effector; when initial velocities (6 min) were assessed, half maximal stimulation was achieved in the range of 2 to 3 μM. However, by extending the incubation time to 90 min, similar maximal increases in specific activity could be achieved with 3 or 10 μM PGG₂ or PGH₂. Activation of guanylate cyclase upon addition of prostaglandin endoperoxides or fatty acid hydroperoxides was prevented or reversed by the thiol reductants dithiothreitol (3 to 5 mM) or gluthathione (10 to 15 mM). Na₂S₂O₄, not known as an effective reducing agent of disulfieds, prevented but was relatively ineffective in reversing activation after it had been induced by PGG₂. Pretreatment of the enzyme preparation with increasing concentrations of N-ethyl-maleimide in the range of 0.01 to 1.0 mM prevented activation by PGG₂ without effecting basal guanylate cyclase activity. These observations indicate that fatty acid hydroperoxides and prostaglandin endoperoxides promote activation of the cyclase by oxidation of enzyme-related thiol functions. In contrast, PGE₂, PGF_2α, hydroxy fatty acids (13-OH-18∶2, 12-OH-20∶4) as well as saturated (18∶0), monoenoic (18∶1), dienoic (18∶2), and tetraenoic (20∶4) fatty acids were ineffective in promoting cyclase activation in the range of 1 to 10 μM. Studies to identify the species of the rapidly metabolized prostaglandin endoperoxides that serve as effectors of the cyclase indicated that PGG₂ but not 15-OOH-PGE₂ (the major buffer-rearrangement product of PGG₂) is most likely an activator. In the case of PGH₂ a rapidly generated (30 sec) metabolite of PGH₂ was found which contained a hydroperoxy or endoperoxy functional group and was equally as effective as PGH₂ as an apparent activator of the enzyme. The combined effects of PGG₂ and dehydroascorbic acid, another class of activator, exhibited additivity with respect to the rate at which the time-dependent activation was induced. These results suggest that activation of soluble guanylate cyclase from splenic cells can be achieved by the oxidation of sulfhydryls that may be associated with specific hydrophobic sites of the enzyme or a related regulatory component.     

Statische und kinetische Instabilitäten bei Bauwerken

In der Bautechnik treten oft, z. B. bei windbelasteten oder meerestechnischen Konstruktionen, statische oder dynamische Instabilitäten auf – manchmal auch ein Zusammenwirken (Interaktion) beider Mechanismen, wobei die Knick‐ oder Beuleigenformen durchaus verschieden von den entsprechenden Schwingungseigenformen sein können. Es soll dargestellt werden, wann die Stabilitätsuntersuchungen der Strukturen statisch durchgeführt werden dürfen und in welcher Form sich die Ergebnisse bei einer zusätzlichen dynamischen Belastung verändern. Static and dynamic instabilities of structures. In structural design e. g. under wind loads or offshore structures we often have static or dynamic instabilities sometimes also an interaction of both mechanisms, where the buckling modes may be different from the vibration modes. We want to recognize, whether the investigations may be static and how the results may alter by dynamic loads.