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  • 1
    Electronic Resource
    Electronic Resource
    Variation of Permeability with Porosity in Sandstone Diagenesis Interpreted with a Fractal Pore Space Model (2000)
    Springer
    Pure and applied geophysics 157 (2000), S. 603-619 
    Details
    ISSN: 1420-9136
    Keywords: Key Words: Permeability, sandstone, fractals, diagenesis.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Permeability is one of the key rock properties for the management of hydrocarbon and geothermal reservoirs as well as for aquifers. The fundamental equation for estimating permeability is the Kozeny-Carman equation. It is based on a capillary bundle model and relates permeability to porosity, tortuosity and an effective hydraulic pore radius which is defined by this equation. Whereas in clean sands the effective pore radius can be replaced by the specific surface or by the grain radius in a simple way, the resulting equations for permeability cannot be applied to consolidated rocks. Based on a fractal model for porous media, equations were therefore developed which adjust the measure of the specific surface and of the grain radius to the resolution length appropriate for the hydraulic process. These equations are calibrated by a large data set for permeability, formation factor, and porosity determined on sedimentary rocks. This fractal model yields tortuosity and effective pore radius as functions of porosity as well as a general permeability-porosity relationship, the coefficients of which are characteristic for different rock types. It can be applied to interpret the diagenetic evolution of the pore space of sedimentary rocks due to mechanical and chemical compaction with respect to porosity and permeability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00001110
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  • 2
    Electronic Resource
    Electronic Resource
    Stoffwechselprodukte von Mikroorganismen (1973)
    Springer
    Archives of microbiology 88 (1973), S. 25-35 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Ein zellfreier Extrakt aus Streptomyces rimosus katalysiert die Synthese von TDP-Mycarose aus TDP-d-Glucose und S-Adenosyl-l-methionin. Die Reaktion benötigt NADPH. Das Reaktionsprodukt enthält einen weiteren methylierten TDP-Zucker unbekannter Struktur. Die Reaktion verläuft über TDP-4-Keto-6-desoxy-d-glucose als Zwischenprodukt.
    Notes: Summary A cell-free extract from mycelium of Streptomyces rimosus producing the antibiotic tylosin, catalyses the formation of TDP-mycarose from TDP-d-glucose and S-adenosyl-l-methionine. The reaction requires NADPH. The product contains a second methylated TDP-sugar with a presently unknown structure. TDP-4-Keto-6-deoxy-d-glucose is an intermediate in the reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00408838
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  • 3
    Electronic Resource
    Electronic Resource
    Stoffwechselprodukte von Mikroorganismen (1972)
    Springer
    Archives of microbiology 85 (1972), S. 233-238 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Die Biosynthese der Makrotetrolide Monactin, Dinactin und Trinactin wurde in Kulturen von Streptomyces griseoflavus untersucht. Markierungsversuche mit radioaktivem Acetat, Propionat und l-Methionin sowie Abbau der Antibiotica und homologen Untereinheiten zeigen, daß die Kohlenstoffatome 8–10 der Homononactinsäure einer Propionateinheit entstammen, die wahrscheinlich als Startereinheit fungiert.
    Notes: Summary The biosynthesis of the macrotetrolides monactin, dinactin, and trinactin, which differ from nonactin by substitution of one to three homononactinic acid units for nonactinic acid, was studied in cultures of Streptomyces griseoflavus. Labelling experiments with radioactive acetate, propionate, and l-methionine, and degradation of the antibiotics and homologous subunits, showed that the carbon atoms 8 to 10 arise from a propionate residue which probably acts as the starter unit of the carbon chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00408848
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  • 4
    Electronic Resource
    Electronic Resource
    Stoffwechselprodukte von Mikroorganismen (1972)
    Springer
    Archives of microbiology 85 (1972), S. 239-248 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Nonactinsäure und Homononactinsäure, die bisher nicht als freie Stoffwechselprodukte bekannt waren, wurden aus Kulturlösungen von Streptomyces griseus isoliert. Beide Hydroxysäuren wurden als Methylester gereinigt und chromatographisch und spektroskopisch identifiziert. Die optischen Drehwerte zeigen, daß die Nonactinsäure überwiegend als (-)-Isomer, Homononactinsäure dagegen praktisch einheitlich als (+)-Isomer vorliegt. In produzierenden Kulturen konnten die freien Nonactinsäuren bereits vor Beginn der Makrotetrolidsynthese nachgewiesen werden. (+,-)-Nonactinsäure-8-3H wurde synthetisiert und mit Kulturen von Streptomyces griseus und Streptomyces griseoflavus inkubiert; 6 bis 52% der markierten Verbindung wurden in die Makrotetrolide eingebaut. Die Spezifität des Einbaus wurde durch chemischen Abbau bewiesen. Die Ergebnisse zeigen, daß die chiralen Hydroxysäuren direkte Vorstufen der Makrotetrolide sind.
    Notes: Summary Nonacting and homononactinic acid which were not previously known as free metabolic products, were isolated from culture broths of a macrotetrolide producing strain of Streptomyces griseus. Both hydroxy acids were purified and identified as their methyl esters by chromatographic and spectroscopic methods. The optical rotation values indicated that the free nonactinic acid is mainly the (-)-isomer whereas homononactinic acid appears to be pure (+)-isomer. In producing cultures the nonactinic acids could be detected prior to the beginning of macrotetrolide synthesis. (+,-)-Nonactinic acid-8-3H was synthesized and incubated with cultures of Streptomyces griseus and Streptomyces griseoflavus (the latter producing mainly monactin and dinactin); between 6 and 52% of the labeled acid were incorporated into the macrotetrolides. Chemical degradation showed that no randomization of tritium had occurred. The results suggest that the chiral hydroxy acids are direct biosynthetic precursors of the macrotetrolides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00408849
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  • 5
    Electronic Resource
    Electronic Resource
    Stoffwechselprodukte von Mikroorganismen (1972)
    Springer
    Archives of microbiology 82 (1972), S. 254-264 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Die Biosynthese des Makrotetrolids Nonactin in Streptomyces griseus wurde mit Hilfe radioaktiv markierter Substrate untersucht. Acetat, Propionat und Succinat erwiesen sich als gute Vorstufen; C1- und isoprenoide Einheiten wurden nur in geringem maß eingebaut. Die Verteilung der Radioaktivität in der Nonactinsäure wurde durch chemischen Abbau ermittelt. Versuche mit Essigsäure-1-14C,-2-14C, Propionsäure-1-14C,-2-14C, Bernsteinsäure-1,4-14C und 2,3-14C lieferten die folgenden ergebnisse: 1. Zwei Acetateinheiten werden in die C-Atome 6–9 eingebaut. 2. Eine Propionateinheit ist Vorstufe der C-Atome 1, 2 und 2′. 3. Bernsteinsäure ist sehr wahrscheinlich Vorläufer einer C3-Einheit, die in die C-Atome 3, 4 und 5 eingebaut wird. Dieser Befund wird durch den Einbau von Succinat-1,4-14C/2,3-3H gestützt.
    Notes: Summary The biosynthesis of the macrotetrolide antibiotic nonactin in Streptomyces griseus was studied with the aid of radioactive labelled substrates. Acetate, propionate and succinate proved to be good precursors of nonactin; C1- and isoprenoid units were incorporated into the antibiotic only in negligible amounts. The distribution of the radioactivity in nonactinic acid was studied by chemical degradation. Experiments with acetic acid-1-14C,-2-14C, propionic acid-1-14C,-2-14C, succinid acid-1,4-14C and 2,3-14C gave the following results: 1. two acetate units are incorporated into carbon atoms 6–9. 2. A propionate unit is the precursor of carbon atoms 1, 2 and 2′. 3. Succinate appears to be the precursor of a C3-unit which forms the carbon atoms 3, 4 and 5 of the tetrahydrofurane ring. The latter finding is supported by the incorporation of succinic acid-1,4-14C-2,3-3H; the increase of the 3H/14C-ratio is in agreement with the assumption that one carboxyl group of the succinic acid is lost without loss of hydrogen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00412197
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  • 6
    Electronic Resource
    Electronic Resource
    Stoffwechselprodukte von Mikroorganismen (1973)
    Springer
    Archives of microbiology 88 (1973), S. 37-48 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung TDP-d-Glucose-oxidoreduktase wurde aus einem Tylosin produzierenden Stamm von Streptomyces rimosus 30 fach angereichert. Das Reaktionsprodukt wurde als TDP-4-Keto-6-desoxy-d-glucose identifiziert. Einige Eigenschaften des Enzyms wurden untersucht. Die Enzymaktivität steigt in Kulturen von S. rimosus in der stationären Phase etwa gleichzeitig mit der Tylosinkonzentration und dem TDP-Mycarose synthetisierenden System an; TDP-d-Glucose-oxidoreduktase ist daher als ein am Sekundärstoffwechsel beteiligtes Enzym anzusehen.
    Notes: Summary TDP-d-glucose oxidoreductase was purified 30 fold from a tylosin producing strain of Streptomyces rimosus. The product of the enzymatic reaction is TDP-4-keto-6-deoxy-d-glucose as shown by spectral properties, chromatographic mobilities of the products obtained by chemical reduction of the nucleotide, and susceptibility of one of the reduction products to d-glucose oxidase. The enzyme has a pH-optimum of 7.2. The apparent Michaelis constant is 9.3 · 10-5 M for TDP-d-glucose. The enzyme is competetively inhibited by TMP (K i=5 · 10-3 M) and TDP (K i=6.5 · 10-5 M). Enzymatic activity is stimulated by NAD. TDP-d-glucose oxidoreductase activity increases during the stationary phase of S. rimosus together with tylosin and the TDP-mycarose synthesizing system; it is therefore regarded to be an enzyme with a function in the secondary metabolism of this organism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00408839
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  • 7
    Electronic Resource
    Electronic Resource
    Queer Current and Pacemaker: The Hyperpolarization-Activated Cation Current in Neurons (1996)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 58 (1996), S. 299-327 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ph.58.030196.001503
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of the transfer region of the Streptomyces plasmid SCP2* (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 10 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: plJ903, a bifunctional derivative of the 31.4 kb low-copy number, conjugative Streptomyces plasmid SCP2, was mutagenized in Streptomyces lividans using Tn4560. Mutant plasmids differing in their transfer frequencies, chromosome mobilization abilities, pock formation, and complementation properties were isolated. The mutations defined five transfer-related genes, traA, traB, traC, traD and spd, clustered in a region of 9 kb. The deduced sequences of the putative TraA and TraB proteins showed no overall similarity to known protein sequences, but the phenotype of traA mutant plasmids and sequence motifs in the putative TraA protein suggested that it might be a DNA helicase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb00912.x
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  • 9
    Electronic Resource
    Electronic Resource
    Kontaktschwellen bei der Eiskernbildung einiger lichtempfindlicher Oberflächen (1979)
    Springer
    Colloid & polymer science 257 (1979), S. 911-911 
    Details
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01383371
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  • 10
    Electronic Resource
    Electronic Resource
    The inheritance of the piebald spotting pattern and its variation in Holstein-Friesian cattle and in Landseer-Newfoundland dogs (1990)
    Springer
    Genetica 80 (1990), S. 115-128 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The black and white spotting patterns of Landseer dogs are divided into qualitatively recognizable phenotypic classes. Breeding data were obtained from the Swiss Dog Stud Book (SHSB) and from breeders' recent records. A plausible interpretation assumed qualitative inheritance of the generally accepted piebald spotting genes 1 p with at least two modifiers,s 2 ands 3. The modifier genes are regarded as minor spotting genes and may be responsible for white markings in the related Newfoundland breed which has been cross-bred with Landseers. The proposed scheme of polygenic inheritance can also be applied to the piebald spotting pattern of Holstein-Friesian cattle, using breeding data from literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00127132
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