Long-term material balance of iron in aluminum reduction cells

The distribution of iron was evaluated using the total material balance of iron in aluminum cells. The data on the Fe₂O₃ content in primary and secondary alumina, in aluminum fluoride, and in melted and crushed baths, and the data on the iron content in prebaked anodes, anode butts, and produced aluminum in the period 1998 through 2002 were determined using statistical analysis. The average content for the standard deviation of iron oxide, with respect to the iron in each material, was studied for each year, and a trend was calculated for the entire period. From a statistical point of view, the content of Fe in aluminum systematically increased during the years 1998 through 2002. Conversely, it was observed that the content of Fe₂O₃ in the crushed bath decreased during the same period. The crushed bath seems to be a very important flow in the process, since it accumulates most of the iron content. One can expect that a substantial part of the iron is distributed directly into the aluminum and the dry scrubbers. Based on the statistical analysis, the material balance of the iron in the prebaked anode cells resulted in the production of 1 t of aluminum. The total iron material balance (for both input and output materials) in the whole period of investigation totaled −642 g Fe. This value was approximately the same for each year. The higher content of Fe in the output materials is most probably caused by secondary sources of iron, which were not incorporated into the balance.     

Urolithiasis in dogs. II: Breed prevalence, and interrelations of breed, sex, age, and mineral composition

OBJECTIVE: To analyze selected breed-related data for canine urinary calculi. SAMPLE POPULATION: 11,000 specimens: 5,781 from female dogs, 5,215 from males, and 4 from dogs of unrecorded sex. PROCEDURE: Information was compiled for all canine urinary calculi submitted between July 1981 and January 1994. Results for a mixed-breed group and 26 of the most common breeds of stone-forming dogs were analyzed. Interrelations of breed, sex, and age of affected dogs and mineral composition of the specimens were determined. RESULTS: Prevalence of 5 specific mineral types was significantly correlated between the sexes of 27 common breed groups: struvite, calcium phosphate (apatite), calcium oxalate, brushite, and urate. Struvite-containing calculi were seen in high proportions in both sexes of 7 breeds, and in low proportions in both sexes of 7 other breeds. Male and female Lhasa Apsos, Cairn Terriers, and 5 other breeds had high proportions of oxalate-containing calculi; values in males were substantially higher. Low numbers of oxalate-containing calculi were seen in both sexes of 7 breeds; Dalmatians had the lowest numbers. Males and females of 6 breeds had high numbers of urate-containing calculi, Dalmatians and English Bulldogs had the highest numbers. Low amounts of urate were found in calculi from males and females of 6 breeds, Samoyeds had the lowest numbers. Highest proportions of cystine-containing calculi were seen in male Dachshunds, English Bulldogs, and Chihuahuas. Males of 8 breeds had no specimens that contained cystine; only 2 such specimens were obtained from females. CONCLUSIONS: Prevalence of uroliths differs among breed, age, and sex of affected dogs. CLINICAL RELEVANCE: Breed, sex, and age of dogs; mineral types of calculi in males versus females; and their anatomic location within the tract are important considerations for clinicians when evaluating risk in dogs with urolithiasis and in identifying areas that need further in-depth applied or clinical investigation, or both.     

Conditional independence structures examined via minors

The notion of minor from matroid theory is adapted to examination of classes of conditional independence structures. For the classes of semigraphoids, pseudographoids and graphoids, finite sets of their forbidden minors are found. The separation graphoids originating from simple undirected graphs and triangulated graphs are characterized in this way neatly as well. Semigraphoids corresponding to the local Markov property of undirected graphs and to the d-separation in directed acyclic graphs are discussed. A new class of semimatroids, called simple semimatroids, is introduced and an infinite set of its forbidden minors constructed. This class cannot be characterized by a finite number of axioms. As a consequence, the class of all semimatroids and the classes of conditional independence structures of stochastic variables and of linear subspaces have infinite sets of forbidden minors and have no finite axiomatization. The closure operator of semimatroids is examined by linear programming methods. All possibilities of conditional independences among disjoint groups of four random variables are presented. This revised version was published online in June 2006 with corrections to the Cover Date.     

Bestimmung des Foulingfaktors an Wärmeübertragungsflächen mit Hilfe einer Fuzzy-Wissensbasis

Zusammenfassung Die Bestimmung des Foulingfaktors bei W?rmeübertragern ist objektiv nur bedingt m?glich. Aus diesem Grund wurden einige aus der Literatur entnommene Empfehlungen zur Bestimmung des Foulingfaktors mit den Methoden der Fuzzy-Heuristik aufgearbeitet. Durch wissensbasierte Methoden wurden diese prim?ren Erfahrungen als Fuzzy-Sets von einfachen bedingten Aussagen formuliert. Wegen der Vielfalt und Komplexit?t der Foulingproblematik war es nur m?glich, Regeln für den Foulingvorgang durch Sedimentation und den Foulingfaktor für Kohlenwasserstoffgemische aufzustellen. Anhand einer m?glichen Version des Fuzzy-Verfahrens werden zwei wirklichkeitsnahe Fragestellungen sowie deren Beantwortung detailliert beschrieben.     

Gaseous Products of Dinitromethane Decomposition Determined by DTA/FTIR

Gaseous products of the thermal decomposition of dinitromethane and potassium dinitromethanide were investigated by simultaneous DTA/FTIR analyses. Both isothermal and non-isothermal DTA regimes were applied. Nitrous oxide and carbon dioxide were detected by FTIR.     

Formation,Degradation, and Detoxification of Putrescine by Foodborne Bacteria: A Review

Biogenic amines (BAs) represent a considerable toxicological risk in some food products. Putrescine is one of the most common BAs in food. Its increased occurrence in food may lead to alimentary poisoning, due to enhancement of the toxic effects of other BAs, and also to lower quality of food, this amine is potentially carcinogenic. Increased occurrence of putrescine in food is mainly due to the bacterial metabolism of the Gram‐negative as well as Gram‐positive bacteria present. The bacterial metabolism of putrescine is very specific due to its complexity (in comparison with the metabolism of other BAs). There are 3 distinct known pathways leading toward the formation of putrescine, in some splices involving up to 6 different enzymes. The existence of more metabolic pathways and the possibility of their simultaneous use by different bacteria complicate the specification of the best conditions for food production and storage, which could lead to a lower content of putrescine. This review provides a summary of the existing knowledge about putrescine production and detection (mainly detection of specific genes for different enzymes using polymerase chain reaction) in both starter and contaminating microorganisms. Thus, this comprehensive review gives a useful overview for further research.     

Effect of gamma irradiation on properties of hardened cement paste

Carbonation of hydrated cement paste (HCP) under γ-irradiation is researched in this paper. It is supposed that radiation-induced carbonation takes part simultaneously with “natural” carbonation. “Natural” carbonation is governed by diffusion and therefore takes part in the material close to surface only, whereas radiation-induced carbonation manifests in all irradiated material. The hypothesis has been tested by means of three sets of experiments. Within these experiments the following changes were investigated: (a) changes of composition of hydrated cement paste (transformation of portlandite to calcite), (b) changes of porous space [changes of average pore diameter (APD)], (c) changes of mechanical properties (hardness). HCP was analysed in the surface layer as well as in the centre of samples. The results show clearly that radiation at least accelerates carbonation driven by diffusion and support a hypothesis that besides natural carbonation there is also independent carbonation caused by γ-irradiation.     

The Influence of Spraying Angle on Properties of HVOF Sprayed Hardmetal Coatings

The spraying angle is one of the deposition parameters that influence the quality of thermally sprayed coatings. In theory, decreasing the spraying angle results in lower process deposition efficiency, whereas the porosity of coatings increases, becoming a cause of poorer microstructure and mechanical properties. In this study, the dependence of microstructure together with the basic mechanical properties and wear of WC-Co and Cr₃C₂-NiCr high-velocity oxyfuel (HVOF) sprayed coatings on the spraying angle was investigated. For each coating, the maximum spraying angle was determined that can be used without significantly decreasing coating quality. Based on the changes in properties of coatings and requirements for the process deposition efficiency, a maximum 30° diversion from the normal spray direction is recommended for WC-Co and 15° diversion for Cr₃C₂-NiCr coatings.     

The amine modified acrylonitrile-divinylbenzene copolymers in the phase transfer catalysis

Summary Amine modified, macroporous acrylonitrile-divinylbenzene copolymers of various crosslinking degree were used as catalysts in the reaction of octylbromide with cyano anions.The dependence of their catalytic activity upon swelling and strongly basic amino groups content were discussed.The reaction rate constants were somewhat lower than those for the reactions catalysed by other polymers containing tributylammonium groups.lt was probably due to the presence of ordered regions in copolymers containing large amounts of acrylonitrile units.This work was presented in part at the 30th Microsymposium on Macromolecules, Prague, July 1987