Machining of reproducible flaws corresponding to fatigue cracks for fracture mechanics tests of components and welded joints

In connection with the analysis and the development of failure concepts in fracture mechanics for quasistatic loaded components and elastic-plastic behaviour of the material, tests are also carried out with welded and/or complex shaped specimens or structures. Thereby the difficulty arises of generating reproducible flaws in the form of fatigue precracks in definite positions in the components, respectively in the welded joint. It is reported exemplarily about experiments on different CT25 and CCT specimens and on a pressure vessel which contained a fatigue pre-crack, a 0.2 mm saw cut or notches with notch root radius ≤ ≥ 0.1 mm as flaws. The comparison of the results with regard to J-integral at initiation of stable crack, J_i, and J_R curves shows that under certain conditions the 0.2 mm saw cut (notch root radius ≤ ≤ 0.02 mm) is a useful alternative, if reproducible generation of a fatigue pre-crack will not be successful or too expensive. The tests were carried out on StE 460 and on a welded joint of this steel at 25 ± 2°C.     

Investigation of the stability of tablets prepared from sucrose and citric acid anhydride utilizing response surface methodology

Inversion of sucrose is a stability problem particularly of candies with acidic taste that contain sucrose and small amounts of organic acids such as citric acid, since the free d-fructose produced by hydrolysis is hygroscopic. The following possibilities were investigated for preventing the hydrolysis of sucrose in tablets containing sucrose and citric acid: Adding various amounts of tri-sodium citrate to the formulation to neutralize the citric acid, (Hot) melt coating of citric acid and tri-sodium citrate with a vegetable fat at different coating ratios, variation of the ratio of coated citric acid and tri-sodium citrate in formulations, and compressing the formulations with different compression forces. After tablet processing and storage of tablets, the concentration of d-fructose was determined on the basis of enzymatic reactions. A response surface central composite design was used. The above-mentioned variations were chosen as independent variables and the amount of d-fructose was chosen as response variable. The lowest rates of inversion could be achieved by increasing the content of tri-sodium citrate and the ratio of coating material and decreasing the ratio of coated citric acid and tri-sodium citrate in the tablet formulations. The compression force had no significant effect on the inversion of sucrose.     

Induced free liquid surface oscillations in a visco-elastic liquid column due to angular temperature fluctuations

The response due to time-fluctuating temperature distribution applied at the free surface of a viscoelastic cylindrical liquid column with no axial dependency has been determined analytically. The amplitude of the radial- and angular velocity as well as the free liquid surface elevation has been presented as a function of the “reduced” forcing frequency of the oscillatory temperature and has numerically been evaluated for an angular temperature field proportional to sin 2φ. It was found, that visco-elasticity as described by the Maxwell model has quite some influence upon the liquid behavior. It shows for larger relaxation times besides the enlarged resonance peak additional peaks below and above resonance. This is particularly evident inside the liquid column, indicating a more pronounced elastic behavior of the liquid.     

Untersuchungen an Caramel Curiepunkt-Pyrolyse von Caramelzuckersirupen und andere strukturspezifische Untersuchungen

Zusammenfassung Es wird über die Curiepunkt-Pyrolyse handelsüblicher Caramelzuckersirup-Proben und die Identifizerung von über 80 Pyrolysefragmenten durch kombinierte Capillargaschromatographie/ Massenspektrometrie berichtet. Mit dieser Methode sind die Proben untereinander and gegenüber Couleuren differenzierbar. Mittels Ultrafiltration wurden die Komponenten einer intensiv braunen Probe in Fraktionen unterschiedlicher Molekülmasse getrennt and nach Pyrolyse miteinander verglichen. In einer niedermolekularen Fraktion wurden nach Permethylierung Laevoglucosan, 1,6-Anhydro--d-glucofuranose, Trehalose, Cellobiose, Maltose, Isomaltose und Gentiobiose Bowie einige Difructosedianhydride nachgewiesen.

---

Investigations of caramel. Curiepoint pyrolysis of caramel syrups and other investigations of structure

Summary A report is given on the investigation of commercial caramel syrups by Curiepoint pyrolysis and the identification of more than 80 pyrolysis products by capillary gas chromatography mass spectrometry. This method enables the differentiation between different caramel syrups and, additionally, between caramel syrups and caramel colours. Compounds of different molecular masses have been examined in the same manner after they have been isolated from an intense brown caramel sample by ultrafiltration. In a fraction consisting of compounds with low molecular masses laevoglucosan, 1,6-anhydro--d-glucofuranose, trehalose, cellobiose, maltose, isomaltose, gentiobiose and some difructosedianhydrides were identified by GC/MS after permethylation.

     

Single amino acid substitutions can further increase the stability of a thermophilic L-lactate dehydrogenase

Lactate dehydrogenases are of considerable interest as stereospecificcatalysts in the chemical preparation of enantiomerically pure-hydroxyacid synthons. For such applications in synthetic organicchemistry it would be desirable to have enzymes which tolerateelevated temperatures for prolonged reaction times, to increaseproductivity and to extend then applicability to poor substrates.Here, two examples are reported of significant thermostabilizations,induced by sitedirected mutagenesis, of an already thermostableprotein, the L-lactate dehydrogenase (EC 1.1.1.27 [EC] , 35 kDa permonomer subunit) from Bacillus stearothermophilus. Thermal inactivationof this enzyme is accompanied by irreversible unfolding of thenative protein structure. The replacement of Argl71 by Tyr stabilizesthe enzyme against thermal inactivation and unfolding. Thisstabilizing effect appears to be based on improved interactionsbetween the subunits in the core of the active dimeric or tetramericforms of the enzyme. The thermal stability of L-lactate dehydrogenasevariants with an active site Arg residue, either in the 171(wild-type) or in the 102 position, is further increased bysulfate ions. The two stabilizing effects are additive, as foundfor the Argl71Tyr/ Gln1O2Arg double mutant, for which the stabilityof the protein in 100 mM sulfate solution reaches that of L-lactatedehydrogenases from extreme thermophiles. All mutant proteinsretain significant catalytic activity, both in the presenceand absence of stnhilfoing salts, and are viable catalysts inpreparative scale reactions.     

Accumulation of nitrite and sulfite in yeast cells and synergistic depletion of the intracellular ATP content

Summary When nitrite or sulfite are applied to yeast cells below pH 5.0, an enormous intracellular accumulation occurs. It is assumed that nitrite and sulfite penetrate the cell membrane in their undissociated forms as nitrous acid (pK = 3.3) or sulfurous acid (pK =1.8), respectively. Due to the neutral intracellular pH they are trapped inside the cell in their anionic forms, which are impermeable to the cell membrane. It has previously been shown that sulfite causes a rapid depletion of the ATP content of yeast cells [Schimz, K. L. and Holzer, H. (1979) resp. Hinze et al. as above]. Similarly, millimolar concentrations of nitrite decrease the ATP level to less than 10% of the initial value. Nitrite and sulfite in combination deplete the ATP content of yeast cells much stronger than expected for the sum of the separate effects of these compounds (synergistic effect).

---

Akkumulation von Nitrit und Sulfit in Hefezellen und synergistischer Abfall des intrazellulären ATP-Gehalts

Zusammenfassung Wenn Hefezellen mit Nitrit oder Sulft bei pH-Werten unter 5,0 inkubiert werden, beobachtet man eine starke intracelluläre Akkumulation von Nitrit, bzw. Sulfit. Es ist anzunehmen, daß Nitrit und Sulfit in ihrer undissoziierten Form als salpetrige Säure (pK=3,3) bzw. schweflige Säure (pK=1,8) penetrieren und dann in den Zellen durch Neutralisation zu den anionischen Formen, die die Zellmembran nicht mehr permeieren können, abgefangen werden. Ähnlich dem früher beschriebenen raschen Abfall des ATP-Gehaltes nach Zusatz von Sulfit in Hefe [Schimz, KL und Holzer H (1979) Arch Microbiol 121:225–229] und in Bakterien [Hinze H, Maier K, Holzer H (1981) Z Lebensm Unters Forsch 172:389-392] verursacht auch Nitrit einen raschen Abfall des ATP-Gehaltes in Hefe auf weniger als 10 % des Anfangswertes. Werden Nitrit und Sulfit in Kombination verabreicht, so beobachtet man einen wesentlich stärkeren Abfall des ATP-Gehaltes als er aus der Summe der Einzeleffekte von Nitrit, bzw. Sulfit zu erwarten wäre (Synergistischer Effekt).