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  • General Chemistry  (9)
  • Sex steroids  (3)
  • ball milling  (2)
  • ball-milling  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Comparative study of nanocrystalline Ti2RuFe and Ti2RuFeO2 electrocatalysts for hydrogen evolution in long-term chlorate electrolysis conditions (1999)
    Springer
    Journal of applied electrochemistry 29 (1999), S. 551-560 
    Details
    ISSN: 1572-8838
    Keywords: ball-milling ; electrocatalyst ; hydrogen evolution ; nanocrystalline alloy ; sodium chlorate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Ti2RuFe and Ti2RuFeO2 nanocrystalline alloys were prepared by high energy ball-milling and used as cathodes for the hydrogen evolution reaction (HER) in the process of sodium chlorate synthesis. Ti2RuFe is almost single phase with the B2 structure. In contrast, Ti2RuFeO2 is made of a mixture of Ti2RuFe and TiOx phases. Tests in chlorate electrolysis conditions did not show any sign of degradation of Ti2RuFeO2 over a 300 h period, while Ti2RuFe breaks down after less than 100 h. The degradation of Ti2RuFe occurs because of hydrogen absorption and desorption during alternating hydrogen discharge and open-circuit conditions. Various hypotheses to explain the increase stability of the O containing alloy are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026441532352
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  • 2
    Electronic Resource
    Electronic Resource
    Large specific surface area nanocrystalline Ti–Ru–Fe cathode materials for sodium chlorate (1999)
    Springer
    Journal of applied electrochemistry 29 (1999), S. 627-635 
    Details
    ISSN: 1572-8838
    Keywords: ball-milling ; electrocatalyst ; hydrogen evolution ; leaching ; lixiviation ; nanocrystalline alloys ; sodium chlorate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Ball-milled nanocrystalline Ti3RuFe powders were mixed with 1, 2, 4, 10 and 20 equivalents of Al and the mixtures were milled again for 20 h. The amount of Al atoms dissolved into the B2 structure of Ti3RuFe does not exceed 8–9 at %, the remaining being present as elemental Al into the powder mixture. During a subsequent treatment of the composite powder in alkaline solutions, the elemental Al is leached out, while Al solutes in the B2 structure are not affected. An examination of the surface by scanning electron microscopy reveals that the leached powder has a highly porous surface structure. Surface area measurements performed by BET measurements show that there is a tenfold increase in the effective surface area. Activated electrodes made from these porous materials show a significant decrease of the cathodic overpotential for hydrogen evolution in typical chlorate electrolysis conditions of about 80 mV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026408502373
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of oxygen and titanium contents on the stability of nanocrystalline Ti–Ru–Fe–O cathode materials for chlorate electrolysis (2000)
    Springer
    Journal of applied electrochemistry 30 (2000), S. 491-498 
    Details
    ISSN: 1572-8838
    Keywords: ball milling ; chlorate electrolysis ; electrocatalysis ; hydrogen evolution ; nanocrystalline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Electrodes made from nanocrystalline Ti:Ru:Fe (2−y:1+y/2:1+y/2), with y varying from 0 to 1 by step of 0.25, and Ti:Ru:Fe:O (2:1:1:w), with w varying from 0 to 2 by step of 0.5, were prepared and tested as activated cathodes for the hydrogen evolution reaction in typical chlorate electrolysis conditions. These electrodes were subjected to an accelerated aging test, consisting of a succession of cycles of hydrogen discharge (HER) and open-circuit (OCP) conditions. In addition to monitoring the cathodic overpotential value during the aging test, visual inspection and mass loss measurements were performed on the electrodes at the end of the test to assess their stability. In the case of Ti:Ru:Fe (2:1:1), a large increase of the cathodic overpotential value is observed after 20 cycles. Adding O to the formulation causes a remarkable improvement of the long-term stability of the electrodes. As little as [O] = 10 at.% in nanocrystalline Ti:Ru:Fe:O (2:1:1:w) materials is sufficient for the electrode to show absolutely no sign of degradation after 50 cycles of HER/OCP, the longest accelerated test conducted. Adding more O to the formulation of the material does not lead to further stability improvement. A better stability under the conditions of the accelerated aging test can also be observed for nanocrystalline Ti:Ru:Fe (2−y:1+y/2:1+y/2) materials with y 〉 0. In that case however, the level of improvement is dependent on the value of y. The best results are obtained for y = 0.75. A hypothesis is proposed to explain the improved stability obtained by lowering the Ti content and/or by adding O. The similarity and difference between both ways of improving the stability of the nanocrystalline Ti:Ru:Fe materials are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003961417762
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  • 4
    Electronic Resource
    Electronic Resource
    A novel method to produce nanocrystalline metastable supported catalysts (1995)
    Springer
    Catalysis letters 35 (1995), S. 89-106 
    Details
    ISSN: 1572-879X
    Keywords: supported catalyst ; nanocrystalline alloys ; metastable alloys ; ball milling ; mechanical alloying ; surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The high energy ball-milling technique has been used to produce metastable Ni(Ru) alloys supported on alumina. This catalyst has potential application for the hydrogenation of the C=O bond. The active species are first formed by mechanical alloying pure Ni and Ru powders. The alumina support is ground independently until no structural transformation occurs. Finally, the supersaturated Ni(Ru) powder is milled with the alumina support to produce highly dispersed individual Ni(Ru) nanocrystals on the surface of Al2O3. This supported catalyst has been characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and thermal desorption spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807007
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  • 5
    Electronic Resource
    Electronic Resource
    Androgen-induced changes in Leydig cell ultrastructure and steroidogenesis in juvenile African catfish, Clarias gariepinus (1999)
    Springer
    Cell & tissue research 297 (1999), S. 291-299 
    Details
    ISSN: 1432-0878
    Keywords: Key words Teleost fish ; Puberty ; Testes ; Sex steroids ; Ultrastructure ; Steroidogenesis ; Clarias gariepinus (Teleostei)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The present report focuses on the mechanism(s) involved in the steroid-induced decrease of androgen production in immature African catfish testes that was observed in previous studies. Juvenile animals were implanted with Silastic pellets containing different 11-oxygenated androgens (11-ketotestosterone, KT; 11β- hydroxyandrostenedione, OHA; 11-ketoandrostenedione, KA), testosterone (T) or estradiol-17β (E2). Control groups received steroid-free pellets. Two weeks later, testis tissue fragments were either incubated with increasing concentrations of catfish luteinizing hormone (LH), or incubated with [3H]-pregnenolone ([3H]-P5) or [3H]-androstenedione ([3H]-A). Tissue fragments were also prepared for the quantitative assessment of Leydig cell morphology. Most of the parameters studied were not affected significantly by implantation of E2. Implantation of all androgens inhibited both the basal and the LH-stimulated androgen secretory capacity in vitro. This was associated with a reduced size of the Leydig cells and loss of half of their mitochondria. The studies on the metabolism of tritiated steroid hormones indicated that steroidogenic steps prior to 11β-hydroxylation, probably C17–20 lyase activity, were affected by all androgens. Although the effects of 11-oxygenated androgens and T on Leydig cells were mostly similar, previous work showed that only the 11-oxygenated androgens stimulated spermatogenesis, suggesting that distinct mechanisms of action are used by 11-oxygenated androgens and T. These mechanisms, however, seem to merge on the same target(s) to impair Leydig cell androgen production. Such a negative feedback mechanism may be of relevance in the context of the decline in androgen secretion per milligram testis tissue that accompanies the first wave of spermatogenesis in pubertal African catfish.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051357
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  • 6
    Electronic Resource
    Electronic Resource
    Sexual steroids during puberty in male African catfish (Clarias gariepinus): serum levels and gonadotropin-stimulated testicular secretion in vitro (1994)
    Springer
    Journal of comparative physiology 164 (1994), S. 195-205 
    Details
    ISSN: 1432-136X
    Keywords: Sex steroids ; Blood levels ; Testicular in vitro secretion ; Pubertal development ; African catfish (Clarias gariepinus)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Blood serum and testicular tissue samples were collected from 3 to 13-month-old African catfish (groups A-G) in order to study their pubertal development. The sampling covered the period from before the beginning of spermatogenesis until full maturity. Testes of fish in group A contained spermatogonia alone. In testes of group B, spermatogonia, spermatocytes and spermatids were present. Spermatozoa were first observed in group C and became predominant as the fish attained full maturity (group G). Several sex steroids were determined in the blood samples. Testosterone was the quantitatively dominating androgen in the blood serum (3–5 ng·ml-1) in groups B and C (fish in group A were too small to collect blood samples). In group D, the concentrations of 11-ketotestosterone and 11β-hydroxyandrostenedione increased to levels similar to those of testosterone. Androstenedione that was undetectable before (below 0.4 ng·ml serum-1), also increased to 3–5 ng·ml-1 in group D. The levels of androgens kept increasing until the fish attained full maturity (group G). In order to monitor the responsiveness to gonadotropic hormone and the steroid secretion capacity, the in vitro secretion of two steroids (11β-hydroxyandrostenedione and 17α,20β-dihydroxy-4-pregnen-3-one) by testicular tissue was quantified at the different stages of development. Testicular maturation was accompanied by changes of both the steroid secretion capacities and of the sensitivity to gonadotropic hormone. The most important changes occurred just after the initiation of spermatogenesis, as spermatocyte/spermatid formation was associated with a drop of the secretory capacity (amount of steroid secreted per milligram of tissue incubated) and with a reduced sensitivity to gonadotropic hormone. At later stages, when the testicular weight substantially increased concurrently with the formation of numerous spermatozoa, both the secretory capacity and the responsiveness to gonadotropic hormone increased again to reach the levels typical of adult fish. The blood levels of androgens appeared to be positively related to the increasing testicular weight in the later phases of development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354080
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of salmon gonadotropic hormone on sex steroids in male rainbow trout: plasma levels and testicular secretion in vitro (1992)
    Springer
    Journal of comparative physiology 162 (1992), S. 224-230 
    Details
    ISSN: 1432-136X
    Keywords: Gonadotropic hormone ; Sex steroids ; Reproductive cycle ; Testis ; Rainbow trout, Oncorhynchus mykiss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Male rainbow trout were treated with salmon gonadotropic hormone (GTH) at different stages of the circannual reproductive cycle; spawning fish were also treated with an antiserum against salmon GTH. Injection of GTH led to a several-fold increase of plasma sex steroid levels during spermatogenesis and in the spawning season but was without effect at early stages of testicular development. GTH neutralization during the spawning season was followed by a several-fold decrease of plasma sex steroid levels. During spermatogenesis and in the spawning season, both treatment regimes resulted in an increased sensitivity of testicular explants in response to a subsequent stimulation of steroid secretion in vitro. This up-regulatory response may facilitate and maintain the high sex steroid plasma levels observed during the spawning season. It may also be necessary to allow for concomitant peak values of plasma GTH and sex steroids in the spawning season, a situation difficult to understand within the negative feedback concept. The adaptive capacities of the testicular steroidogenic system indicate that it is not only an effector site for GTH but also an active part of the endocrine system controling reproduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357528
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  • 8
    Electronic Resource
    Electronic Resource
    1 3C-NMR-Spektroskopie an Polyäthern (1974)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 86 (1974), S. 450-450 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19740861216
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  • 9
    Electronic Resource
    Electronic Resource
    Polymere mit atropisomeren Biphenyl-Grundbausteinen (1967)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 79 (1967), S. 422-422 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19670790936
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  • 10
    Electronic Resource
    Electronic Resource
    Synthetische makromolekulare Stoffe mit reaktiven Gruppen (1957)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 69 (1957), S. 153-171 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Es wird über Synthese, Eigenschaften und Reaktionen einiger makromolekularer Stoffe mit reaktiven Gruppen berichtet, und zwar über Derivate der Polyacrylsäure (Polyacrylsäure-hydrazid, Polyacrylhydroxamsäure, Polyacrylsäureamid), des Polyvinylalkohols, über Polyacrolein und Polymethacrolein, Polyvinylsulfonsäure und ihre Derivate sowie über Copolymere aus Styrol und Maleinsäureanhydrid. An den reaktiven Gruppen dieser polymeren Stoffe werden chemische Reaktionen ausgeführt. Dabei zeigt sich, daß unter Bedingungen, die dem makromolekularen Bau des Reaktionspartners angepaßt sind, eine Reihe von Reaktionen, die aus der niedermolekularen Chemie gut bekannt sind, auf solche Polymere übertragen werden können. Dadurch werden neue makromolekulare Stoffe zugänglich, die durch Polymerisation oder Polykondensation nicht zu erhalten sind.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19570690502
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