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  • 1
    ISSN: 1432-2242
    Keywords: Key words Abies alba ; Organic nitrogen ; Somatic embryogenesis ; Somaclonal variation ; Trisomic karyotype
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Karyological studies were made on a 6-year-old embryogenic cell line of Abies alba. Embryogenic cells were obtained from a mature zygotic embryo cultivated on modified MCM-medium and subcultured every 3 weeks. Three years after induction, part of the cell line was transferred to media supplemented with 500 or 1000 mg l-1 caseine hydrolysate and 500 mg l-1 L-glutamine. Approximately 3 years after addition of the organic nitrogen to the medium, morphological changes such as malformation of the suspensor cells and a loss of maturation capacity occurred. Chromosome counts revealed that all cells cultivated on medium with organic nitrogen were trisomic. Fluorescent-banding methods and comparison with an euploid cell line showed that the additional chromosome belonged to the group of long, metacentric chromosomes of Abies alba without secondary constriction. Those cells cultured on medium not supplemented with caseine hydrolysate and L-glutamine retained a stable chromosome number of 2n=24. Both normal and deformed suspensor cells were observed. The maturation frequency was very low. The emergence of aneuploidy within one cell line could be the consequence of high selection pressure caused by the different culture conditions.
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  • 2
    ISSN: 1615-6102
    Keywords: DNA content ; Embryo sac development ; Endosperm ; Facultative heterochromatin ; Fertilization ; Gagea lutea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Facultative heterochromatin occurs not only in certain animals in connection with sex determination but also in members of at least one plant genus,Gagea (Liliaceae s. str.), but here in the course of embryo sac development, fertilization, and endosperm formation. The present contribution intends to provide undebatable photographic and cytometric evidence, previously not available, for the events in the course of which three whole genomes in the pentaploid endosperm nuclei ofGagea lutea become heterochroma-tinized. In this plant, embryo sac formation usually follows the Fritillaria type, i.e., the embryo sac is tetrasporic, and a “1 + 3 position” of the spore nuclei is followed by a mitosis in which the three chalazal spindles fuse and two triploid nuclei are formed. A triploid chalazal polar nucleus is derived from one of these, which contributes to the pentaploid endosperm. These nuclei in the chalazal part of the embryo sac show stronger condensation compared with the micropylar ones. The pycnosis of the triploid polar nucleus is maintained and even enhanced during endosperm proliferation, while the micropylar polar nucleus and the sperm nucleus maintain their euchromatic condition. The origin of the heterochromatic masses in the endosperm nuclei from the three chalazal genomes of the central cell is unambiguously evident from the distribution of heterochromatic chromosomes in the first endosperm mitosis and the following interphase. DNA content measurements confirm a 3 ∶ 2 relationship of heterochromatic and euchromatic chromosome sets, which is usually maintained up to the cellularized endosperm. Pycnotic nuclei in the chalazal part of megagametophytes are characteristic of several embryo sac types, but only forGagea spp. it is documented that such nuclei can take part in fertilization and endosperm formation.
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  • 3
    ISSN: 1573-8205
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Physics
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  • 4
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract BET, scanning electron microscopy, X-ray photoelectron, infrared, X-ray diffraction and Mössbauer spectroscopy methods were used to identify changes in surface, structural and spectroscopic properties of sphalerite produced by mechanical activation. Activated samples exhibit amorphization of crystallographic structure of the mineral, as well as of hyperfine structure of the accessory manganese. The presence of a new magnetic phase was disclosed in the samples activated for longer periods of time. Changes in structure are accompanied by mechanochemical oxidation of the surface layer of sphalerite.
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  • 5
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract BET, scanning electron microscopy, X-ray photoelectron, infrared, X-ray diffraction and Mössbauer spectroscopy methods were used to identify changes in surface, structural and spectroscopic properties of sphalerite produced by mechanical activation. Activated samples exhibit amorphization of crystallographic structure of the mineral, as well as of hyperfine structure of the accessory manganese. The presence of a new magnetic phase was disclosed in the samples activated for longer periods of time. Changes in structure are accompanied by mechanochemical oxidation of the surface layer of sphalerite.
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  • 6
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Fibres of boron-silicate-glass are destructed at the surface by ion bombardment from plasma of a radio-frequency glow discharge. The alkaline elements are sputtered away, but partly readsorbed as hydroxides. The strength of fibres decreases strongly on shorttime of plasma exposition. In a plasma of ammonia N-containing groups are formed on the surface of fibres.
    Notes: Borsilicatglasfasern werden durch den Beschuß mit Ionen aus dem Plasma einer Hochfrequenz-Glimmentladung oberflächlich umstrukturiert. Die Alkalielemente werden bevorzugt herausgesputtert und z. T. in Hydroxidform wieder abgelagert. Die Fasern verlieren auch nach nur kurzer Plasmabehandlungszeit stark an Eigenfestigkeit. Bei Behandlung im NH3-Plasma bilden sich an der Faseroberfläche N-haltige funktionelle Gruppen.
    Additional Material: 4 Ill.
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  • 7
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Light induced aging of the investigated photoconductors is studied by UV-VIS and EPR spectrometry. The reasons for the deterioration of the electrophotographic properties are discussed. It is supposed, that the holes generated by exposure are radical cations, which are able of R-abstraction and recombination with other free radicals.
    Notes: Die lichtinduzierten Alt erungsreaktionen der genannten Photoleiter werden durch UV-VIS- und EPR-Spektrometrie untersucht und die Ursachen für die Verschlechterung der elektrophotographischen Eigenschaften diskutiert. Es wird angenommen, daß die photogenerierten Defektelektronen sich chemisch wie Radikalkationen verhalten und zur R-Abstraktion sowie zur Rekombination mit anderen freien Radikalen befähigt sind.
    Additional Material: 6 Ill.
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  • 8
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: MgO/Cr2O3 mixed-oxide catalysts contain, depending on the preparation conditions and molar composition, in addition to a more or less ordered spinel phase the free starting oxides, small amounts of MgCrO4 (being important as an intermediate of the spinel formation), and Cr3+ on Mg2+ positions of different site symmetry.In the less complicated BeO/Cr2O3 system, besides BeCr2O4 and the starting oxides only small amounts of BeCrO4 occur which, however, is supposed to activate catalytically the spinel formation like MgCrO4.
    Notes: Es wird gezeigt, daß im System MgO/Cr2O3 unter den gewählten Darstellungsbedingungen je nach Zusammensetzung neben einer mehr oder weniger geordneten Spinellphase die freien Ausgangsoxide, sehr kleine Mengen an MgCrO4, das eine sehr entscheidende Rolle als Zwischenprodukt bei der Spinellbildung spielt, sowie auf Mg2+-Gitterplätzen befindliches Cr3+ mit verschiedener Punktsymmetrie existieren.Einfacher liegen die Verhältnisse im System BeO/Cr2O3. Neben BeCr2O4 und den Ausgangsoxiden BeO und Cr2O3 enthalten diese Substanzen nur geringe Mengen an BeCrO4, das bei der Spinellbildung sicherlich die gleiche katalytische Rolle wie das MgCrO4 bei der MgCr2O4-Bildung spielt, nämlich die Aktivierungsenergie der Spinellbildung herabzusetzen.
    Additional Material: 13 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 346 (1966), S. 66-75 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: 12 mixed-oxide specimens of different molar compositions have been prepared from CuO and Cr2O3 and investigated by chemical, X-ray and ESR methods. 5 phases were established: CuO, Cr2O3, CuCr2O4, Cu2ICr2O4, and basic copper chromate(VI). ESR spectra in combination with chemical analyses allow to distinguish quantitatively between Cu(I) and Cu(II) chromates(III).
    Notes: CuO, Cr2O3 und 12 verschiedene Mischungen dieser beiden Oxide wurden hergestellt. Die Struktur der so erhaltenen Katalysatoren wurde chemisch, röntgenographisch und mittels ESR-Spektroskopie untersucht. Es wurden 5 Phasen ermittelt: CuO, Cr2O3, CuCr2O4, Cu2Cr2O4 und basisches Kupferchromat. Es wird eine Möglichkeit gezeigt, durch ESR-Spektren in Verbindung mit chemischen Analysen die Chromite des Cu(I) und Cu(II) quantitativ zu unterscheiden.
    Additional Material: 3 Ill.
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  • 10
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The catalytic and electronic properties of Cr2O3—ZrO2 mixed oxides are dependent on the concentration of Cr5+ ions and the ratio Cr5+: Cr3+, respectively. The catalytic activity appears to be due to an electronic collision mechanism, while the observed lowering of the activation energy of electronic conductivity may be interpreted on the basis of a hopping-exchange process between Cr3+ and Cr5+.
    Notes: Die katalytischen und elektronischen Eigenschaften von Cr2O3—ZrO2-Mischoxiden werden von der Konzentration an Cr5+-Ionen bzw. von dem Verhältnis Cr5+/Cr3+ beeinflußt. Die katalytische Aktivität kann auf einen Elektronenstoßmechanismus zurückgeführt werden, während die Erniedrigung der Aktivierungsenergie der Leitfähigkeit durch einen Ladungsaustausch zwischen Cr3+ und Cr5+ interpretiert wird.
    Additional Material: 10 Ill.
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