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  • 2005-2009  (116)
  • 1995-1999  (84)
  • 1965-1969  (16)
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  • 21
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 312 (June 2006), p. 9-14 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An advanced finite-element model for the complete failure process of a double notched specimen with crack tip blunting caused by yielding and subsequent crack propagation is used for the simulation of realistic specimens. Cracks in a homogeneous material and bimaterial cracks are studied. The calculated load-displacement curves show generally the shape known from experiments and theoretical considerations. The simulation allows determination of a working rangeof set up parameters like geometry, test speed or clamping conditions.The numerical model simulates crack propagation on the basis of a criterion which is similar to the energy release rate. The essential work of interfacial fracture method provides a method to determine the fracture toughness from load-displacement curves. This method is well suited to check the numerical simulation because both use an energy based failure criterion. If applied to simulated load-displacement curves the resulting essential work of interfacial fracture shoulddirectly match the fracture criterion used as input for the simulation.In fact, the data reduction of the simulated curves results in values for the fracture toughness that almost perfectly match the input values of the simulation. This agreement is a strong argument for the consistency of the simulation and the data reduction scheme
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  • 22
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 10 (1997), S. 101-106 
    ISSN: 1432-2145
    Keywords: Key words Pollen ; Pollen competition ; Pollen performance ; Microgametophyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We examined the influence of pollen competitive environment on pollen performance in Mirabilis jalapa. We used the number of pollen grains and the number of pollen tubes per pistil as measures of pollen competition. Pollen germination, pollen tube penetration into the style, and pollen tube growth rates were used as measures of pollen performance. All three measures of pollen performance were affected by the competitive environment. Pollen germination was greatest at intermediate pollen load sizes. The percentage of germinated pollen grains that penetrated the stigma and grew into the style decreased with pollen load size. Pollen tube growth rate in the style was greater and more variable with larger numbers of pollen tubes in the style. Controlling for the degree of selection at the stigma indicated that pollen-pollen or pollen-style interactions were the likely causes of increased growth rates.
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  • 23
    ISSN: 1432-0983
    Keywords: Key words Transcriptional regulation ; Phospholipid biosynthesis ; Saccharomyces cerevisiae ; INO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Expression of structural genes of phospholipid biosynthesis in yeast is mediated by the inositol/choline-responsive element (ICRE). ICRE-dependent gene activation, requiring the regulatory genes INO2 and INO4, is repressed in the presence of the phospholipid precursors inositol and choline. INO2 and, to a less extent, INO4 are positively autoregulated by functional ICRE sequences in the respective upstream regions. However, an INO2 allele devoid of its ICRE functionally complemented an ino2 mutation and completely restored inositol/choline regulation of Ino2p-dependent reporter genes. Low-level expression of INO2 and INO4 genes, each under control of the heterologous MET25 promoter, did not alter the regulatory pattern of target genes. Thus, upstream regions of INO2 and INO4 are not crucial for transcriptional control of ICRE-dependent genes by inositol and choline. Interestingly, over-expression of INO2, but not of INO4, counteracted repression by phospholipid precursors. Possibly, a functional antagonism between INO2 and a negative regulator is the key event responsible for repression or de-repression.
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  • 24
    ISSN: 1617-4623
    Keywords: Prolidase ; Metalloprotease ; Lactobacillus delbrueckii subsp. lactis ; Nucleotide sequence analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract From a genomic library of Lactobacillus delbrueckii subsp. lactis (DSM7290) DNA, in the low-copy-number vector pLG339, a recombinant clone was selected, which complemented a mutation in the prolidase gene (pepQ) of Escherichia coli UK173. Nucleotide sequence analysis revealed an open reading frame of 1104 nucleotides corresponding to a protein of 368 amino acids with a calculated pI of 4.64 and a molecular mass of 41087 Da. The start site of pepQ transcription was determined by primer extension analysis with mRNA prepared from L. delbrueckii. Based on homology of the gene product to various peptidases and on the substrate specificity determined, the peptidase was designated PepQ. The influence of various protease inhibitors and cations on peptidase activity indicated that PepQ is a metalloprotease. The absence of a membrane-spanning domain and a signal peptide sequence argues for a cytoplasmic localization of the enzyme.
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  • 25
    ISSN: 1617-4623
    Keywords: Key wordsSaccharomyces cerevisiae ; Gluconeogenesis ; Malate synthase ; Transcriptional regulation ; MLS1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The malate synthase gene, MLS1, of the yeast Saccharomyces cerevisiae is transcriptionally regulated by the carbon source in the growth medium. A MLS1-lacZ fusion gene, expressed at a basal level in the presence of 2% glucose, is derepressed more than 100-fold under conditions of sugar limitation. No evidence for MLS1 induction by oleic acid was found. By deletion analysis of the MLS1 control region, we identified two sites, UAS1 and UAS2, as important for efficient derepression of the gene. Both sites contain sequences that resemble the previously characterized carbon source-responsive element (CSRE) found in the promoter of the isocitrate lyase gene ICL1. Indeed, UAS1 and UAS2 in the MLS1 upstream region turn out to be functional CSRE sequence variants. This finding allowed us to define a modified version of the CSRE consensus sequence (CCRTYSRNCCG). Protein binding to UAS1MLS1 was observed with extracts from derepressed but not from repressed cells, and could be competed for by an excess of the unlabelled CSRE(ICL1) sequence. No competition was observed with a mutated CSRE variant. Site-directed mutagenesis of both CSREs in the MLS1 promoter reduced gene activation under derepressing conditions to 20% of the wild-type level. The same decrease was observed with the wild-type MLS1 promoter in a cat8 mutant, lacking an activator of CSRE-dependent transcription. The CSRE/Cat8p-independent activation of MLS1 is mediated by constitutive UAS elements. The pleiotropic transcription factor Abf1p, which binds to the MLS1 upstream region, may contribute to constitutive activation. Thus, in order to ensure the severe glucose repression of MLS1 observed, repressor elements that respond to the carbon source must counteract constitutive activation. In summary, ICL1 and MLS1 share common cis-acting elements, although a distinct mechanism of carbon source control also contributes to MLS1 regulation.
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  • 26
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 40 (1904), S. 385-399 
    ISSN: 0863-1778
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 27
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical methods of operations research 46 (1997), S. 287-307 
    ISSN: 1432-5217
    Keywords: Reliability-based optimization ; structural reliability ; cost function ; nonlinear programming ; Monte Carlo simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract A method to carry out a Reliability-Based Optimization (RBO) of especially nonlinear structural systems is introduced. Statistical uncertainties involving both structural and loading properties are considered. The concept is based on the separation of structural reliability analyses and the optimization procedures. Two approaches are discussed, depending on the interaction of reliability analysis and mathematical programming and the way of representation of the limit state functions (LSF) of the structure. As, for cases of practical significance, the LSF is known only pointwise it is approximated by Response Surfaces (RS). For the response calculations Finite Element (FE) procedures are utilized. Failure probabilities are determined by applying variance reducing Monte Carlo simulation (MCS) techniques such as Importance Sampling (IS). Following the reliability analysis, the optimization procedure is controlled by the NLPQL algorithm. A numerical example in terms of a template ocean platform exemplifies the procedures.
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  • 28
    Electronic Resource
    Electronic Resource
    Springer
    Plant foods for human nutrition 13 (1966), S. 137-149 
    ISSN: 1573-9104
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Description / Table of Contents: Summary The Federal Institute for Agricultural Chemistry in Vienna has for a number of years investigated the mineral composition of different varieties of wheat and the influence of the nutritional status and other chemical factors of the soil on the minerals in the wheat plant. In addition, the mineral composition of the wheat plants has been investigated as to how it is dependent on the developmental state and growth of the plants. To this end it was necessary to use a point of reference which is constant during all of the growing period. Dry matter and ash are therefore not suitable for this purpose. Useful points of reference were found to be “the average plant”, the “total nutrient uptake per unit area” or the mineral content of the seed used. The investigations are by no means yet completed but some of the many data so far obtained, have been analysed. They concern not only the major but also a number of minor elements and they are presented in a summarized form. It can be seen that comparatively little information can be obtained from data relating the mineral content of the plants to their dry matter content and that luxury consumption and varietal differences of nutrient uptake and nutrient storage come to light, using the suggested points of reference.
    Abstract: Résumé Depuis plusieurs années à la station fédérale de chimie agricole de Vienne des recherches sont en cours pour déterminer dans quelle mesure la teneur en substances minérales du blé depend des variétés, de la fumure et des facteurs agropédologiques. Les variations taux de substances minérales dans les diverses parties de la plante, pendant de la phase de la développement de la végétation, ont également été suivies. Il est nécessaire pour cela de rapporter les résultats à une valeur de référence qui reste constante durant toute la période de végétation. Le poids sec le taux de cendres, ne peuvent servir de référence. Il s'est révélé objectif de rapporter les résultats à la plantule moyenne, et de ramener les prélèvements de minéraux à la surface cultivée; le taux de substances minérales d'un grain de semence est aussi une référence utilisable. Nos recherches ne sont nullement terminées; une partie de nos très nombreux résultats numériques, qui se rapportent aussi bien aux macroéléments qu'à divers oligoéléments, ont été exploités et présentés de facon synthétique. L'information pauvre de la valeur relative des taux rapportés au poids sec apparaît ainsi; on peut mettre en évidence une consommation de luxe, ainsi qu'une différence dans le pouvoir d'absorption et de stockage selon la variété.
    Notes: Zusammenfassung Seit mehreren Jahren sind an der Wiener Landw.-chemischen Bundesversuchsanstalt in Wien Untersuchungen im Gange, die zeigen sollen, ob und wie der Mineralstoffgehalt von Weizen sortenabhängig ist und wie der Mineralstoffgehalt verschiedener Sorten vom Düngungszustand und sonstigen bodenchemischen Faktoren abhängt. Auch wurde geprüft, wie sich der Mineralstoffgehalt in verschiedenen Teilen der Pflanze und in der ganzen Pflanze im Laufe der Vegetationsperiode verändert. Hierbei ist es notwendig, die Ergebnisse auf eine während der ganzen Vegetationszeit gleichbleibende Bezugsgröße zu beziehen. Trockengewicht oder Aschegehalt kommen daher nicht in Frage. Als geeignete Bezugsgrößen erwiesen sich die durchschnittliche Einzelpflanze, der Gesamtentzug pro Flächeneinheit, aber auch der Mineralstoffgehalt eines Saatkornes scheint brauchbar zu sein. Die Untersuchungen sind noch keineswegs abgeschlossen, ein Teil des vorhandenen außerordentlich umfangreichen Zahlenmaterials, das sich sowohl auf die Massenelemente als zum Teil auch auf die Spurenelemente bezieht, konnte aber schon ausgewertet werden und wird in übersichtlicher Form dargestellt. Der verhältnismäßig geringe Informationsgehalt der auf Trockensubstanz bezogenen Zahlen kommt hierbei deutlich zum Ausdruck und Luxuskonsum und sortenabhängiges Speicher- und Aufnahmevermögen werden deutlich.
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  • 29
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 30
    Electronic Resource
    Electronic Resource
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 20 (1969), S. 183-194 
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Investigations into the electrolytic-potentiostatic etching of stainless steels in 10 n NaOH, using a coulometerCurrent density/potential characteristics can only provide qualitative indications concerning the phenomena encountered with potentiostatic etching in 10 n NaOH. The process is best carried out in the trans-passive zone. Identification is based, not on the selective dissolution of certain standard components, but on the interference colours which can be observed as a result of the formation of cover layers of different thickness. The charge density/time characteristics also permit quantitative indications of the different phases. Current density/time curves permit a clarification of the mechanism govering the formation of cover layers. A ferritic steel (28 pC Cr) and a NiCr alloy (45 pC Cr) were found to follow a cubic law of growth, whilst CrNi steel 18-8 is initially governed by an approximately logarithmic law, followed by a zone extending over several hours where the growth begins to follow a parabolic law.
    Notes: Stromdichte-Potential-Kurven ermöglichen nur qualitative Aussagen über die Vorgänge beim potentiostatischen Ätzen in 10 n NaOH. Am günstigsten ist Ätzen im Transpassivbereich. Die Identifizierung erfolgt dabei nicht durch selektive Auflösung bestimmter Gefügebestandteile, sondern aufgrund der Interferenzfarben, die infolge der Bildung unterschiedlich starker Deckschichten zu beobachten sind. Die Ladungsdichte-Zeit-Kurven ermöglichen auch Aussagen über die Mengen der einzelnen Phasen. Stromdichte-Zeit-Kurven ermöglichen eine Aufklärung des Deckschichtbildungsmechanismus. Für einen ferritischen Stahl (28% Cr) und eine NiCr-Legierung mit 45% Cr gilt ein kubisches Wachstumsgesetz, während für CrNi-Stahl 18-8 zunächst ein annähernd logarithmisches Gesetz gilt, an das sich ein mehrstündiger Bereich anschließt, in dem übergang zu einem parabolischen Schichtwachstum erfolgt.
    Additional Material: 24 Ill.
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