Comparison of oxidation of cast and sintered magnesium materials in CO2

Properties of oxide films formed on cast and sintered magnesium materials during oxidation in CO₂ at 793 K were examined. The compactness and the strength of oxide films were determined from film resistance to magnesium evaporation from the basic metal matrix by means of thermogravimetric measurements. The oxide films are thick, porous on Mg-Mg_O and Mg-MgF₂ materials and thin and protective on Magnox Al2 and Mg 99.99. Incompact oxide films of Mg-Zr alloys facilitate the oxygen diffusion into the underlying layer of samples. The addition of dispersed beryllium into sintered materials results in the creation of two-component films with an inner protective BeO layer. The compact oxide films are resistant to evaporation of magnesium as well as to oxidation in CO₂. The incompact and less protective oxide films are characterized by the low temperature of the beginning of magnesium evaporation.The character of oxide films was influenced by the initial surface finishing and by the dispersed phase morphology.     

Minimizing Makespan in a Two-Machine Flow Shop with Delays and Unit-Time Operations is NP-Hard

One of the first problems to be studied in scheduling theory was the problem of minimizing the makespan in a two-machine flow shop. Johnson showed that this problem can be solved in O(n log n) time. A crucial assumption here is that the time needed to move a job from the first to the second machine is negligible. If this is not the case and if this delay is not equal for all jobs, then the problem becomes NP-hard in the strong sense. We show that this is even the case if all processing times are equal to one. As a consequence, we show strong NP-hardness of a number of similar problems, including a severely restricted version of the Numerical 3-Dimensional Matching problem.     

Toward a biotic ligand model for freshwater green algae: surface-bound and internal copper are better predictors of toxicity than free Cu2+-ion activity when pH is varied

The freshwater green microalgae Chlorella sp. and Pseudokirchneriella subcapitata (P. subcapitata) were chronically (48 and 72 h, respectively) exposed to copper at various pH levels, i.e., pH 6-7.5 and pH 5.9-8.5, respectively. Concentrations resulting in 50% inhibition of exponential growth rate (EC50) were determined as dissolved Cu, estimated chemical activity of the free Cu2+ ion (as pCu = - log{Cu2+ activity as molarity}), and as external (surface-bound) Cu and internal Cu in the algal cells. With increasing pH, EC50dissolved decreased from 30 to 1.1 microg of Cu L(-1) for Chlorella sp. and from 46 to 18 microg of Cu L(-1) for P. subcapitata. The pH effect on copper toxicity was even more obvious when expressed as Cu2+ activity. The EC50pCu increased on average 1.4 pCu unit per pH unit for Chlorella sp. and 1.1 pCu unit per pH unit for P. subcapitata, thus indicating a marked increase of Cu2+ toxicity at higher pH (more than 1 order of magnitude per pH unit). In contrast, it was found that EC50 values expressed as surface bound or external copper (EC50external) and as internal copper (EC50internal) did not vary substantially when pH was increased. External Cu was operationally defined as the Cu fraction removable from the algal cell by short-term contact with ethylenediaminetetraacetic acid; internal copper was defined as the nonremovable fraction. For Chlorella sp. the EC50external varied between 5 and 10 fg of Cu/ cell (factor of 2 difference) and the EC50internal between 25 and 40 fg of Cu/cell (factor of 1.6 difference). For P. subcapitata the EC50external varied between 10 and 28 fg of Cu/cell (factor of 2.8 difference) and the EC50internal between 42 and 71 fg of Cu/cell (factor of 1.7 difference). Because the observed variation in EC50external and EC50internal is much less than the variation in EC50Cu2+, it is concluded that both external and internal copper are better predictors of copper toxicity than Cu2+ when pH is varied. From the perspective of toxicity modeling, this observation is the first step toward considering the use of the cell surface as the algal biotic ligand for Cu in a similar way as fish gills fulfill this role in the biotic ligand model for predicting metal toxicity to fish species.     

The continuity of depression in clinical and nonclinical samples.

Historically, depression researchers have examined continuity in terms of whether the symptoms and characteristics of mild, moderate, and severe depression differ in degree along a continuum (i.e., a quantitative difference) or in kind (i.e., qualitative difference). The authors propose a differentiated framework that distinguishes 4 direct tests of continuity (i.e., phenomenological, typological, etiological, and psychometric continuity). They use this framework to suggest that most evidence is consistent with the continuity hypothesis. Moreover, they maintain that the findings of future research can be incorporated into a 2-factor model of depression that allows for both continuities and discontinuities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Respiratory inhibitors affect incorporation of glucose into Saccharomyces cerevisiae cells,but not the activity of glucose transport

Incubation of starved galactose-grown S. cerevisiae cells with cyanide reduced glucose uptake as measured over a 5-s period. The V_max for glucose uptake was decreased by over a factor of two but the apparent affinity for glucose doubled. When measured in the sub-second time scale, however, there was no significant inhibition of glucose uptake, by cyanide, up to 200-ms, clearly demonstrating that, in cyanide treated cells, glucose uptake was not linear for the first 5-s. After a 200-ms exposure of untreated cells to radio-labelled glucose, less than 10% of the intracellular label resided in soluble uncharged compounds. In cyanide-treated cells up to 43% of the labelled compounds were uncharged, with a concurrent reduction of intracellular label residing in anionic compounds. The results suggest that, in the presence of 10 mM cyanide when respiration is inhibited, a reduction in the cellular ATP concentration causes a reduction in hexose-kinase activity which results in an accumulation of internal free glucose, which in turn causes a reduction in net glucose transport.     

Reaction of histidine with methyl linoleate: Characterization of the histidine degradation products

Efforts have been made to characterize the products that result from interactions between L-histidine (free base) and peroxidizing methyl linoleate (ML) in a model system consisting of reactants dispersed on a filter paper. Imidazole lactic acid and imidazole acetic acid are identified as breakdown products when histidine is incubated with ML, methyl linoleate hydroperoxide (MLHPO), or n-hexanal over a period of 3 weeks. Two other reaction products are found to give back histidine upon acid hydrolysis. These products are though to be Schiff's base compounds which result from the condensation of the histidyl α-amino group and carbonyl groups of reactive aldehydes formed during ML peroxidation. Most of the detectable reaction products have the imidazole moiety intact indicating the high relative reactivity of the functional groups, especially the amino group, associated with the α-carbon. Such high reactivity provides an explanation for the low concentrations of ninhydrin-positive free amino compounds that are, at best, barely detectable on thin layer chromatography. Presented at the AOCS Meeting, Chicago, September 1976.     

Build-up of polymer networks by initiated polyreactions

Summary Theoretical treatment of network formation with participation of initiated reactions is to be based on the kinetic (coagulation) theory, because the application of the statistical network build-up from monomer units (cascade substitution) can be a source of serious deviations. This comparison is demonstrated by the degree-of-polymerization distribution obtained in the linear living polymerization and the gel point conversion in the multifunctional polymerization involving a monomer with two groups of independent reactivityDedicated to Dr. B. Sedláek on the occasion of his 60th birthday     

Features of network formation in the chain crosslinking (co)polymerization

Summary Analysis of experimental results on the chain (co) polymerization of bisunsaturated monomers suggests that cyclization plays a decisive role already at the onset of the reaction. At medium and elevated concentrations of the bisunsaturated compound, compact microgel-like particles are formed, which give rise to a gel mainly by participating in the polymerization reaction only with pendant double bonds in their surface layer, and not with double bonds in the interior. This mechanism is reflected in an apparent decrease in reactivity of the pendant double bonds.     

Quantitative Analyse der Heterogenität des Bruchvorganges von kohlenstoffarmem Stahl bei Kerbschlagbiegeversuchen

Aufnahme von Kerbschlagzähigkeit-Temperatur-Kurven eines unberuhigten Stahles mit 0,04% C für drei Zustände mit unterschiedlicher Korngröße. Elektronenfraktographische Analyse der Bruchflächen. Abhängigkeit der kennzeichnenden Bruchgefügearten von der Temperatur. Möglichkeiten der fraktographischen Analyse für die Beschreibung des Bruchverhaltens.