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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 77 (1973), S. 313-329 
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The portion of the life cycle ofAcetabularia mediterranea from cyst formation to gamete release is described. During maturation, the cyst nucleus undergoes a series of mitoses in which the nuclear membrane remains intact, and the spindle microtubules are confined to the intranuclear space. There is a dark requirement for the completion of cyst maturation at the end of which the nuclei are in groups and centrioles are present. The final migration of the nuclei, cleavage of the cytoplasm into gametes, and the development of flagella is cxtremely rapid, taking six to twelve hours. Cysts which fail to germinate are blocked at a late stage in the maturation process, either before or after the final nuclear division. The observations are related to mitosis in other green algae (Chlorophyceae) and to gametogenesis inBryopsis hypnoides. Changes in the amount and distribution of heterochromatin in the nuclei are discussed in relation to the life cycle ofA. mediterranea.
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  • 2
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Jahn-Teller Distortions of Transition Metal Ions in Tetrahedral Coordination  -  The Structures of Cat[MII(NCS)4]II (MII: Co, Ni, Cu) and of Mixed Crystals MIICr2O4(MII: Zn—Ni, Zn—Cu, Cu—Ni) of the Spinel TypeThe structure determination of compounds Cat[MII(NCS)4] with Cat = p-xylylenebis(triphenylphosphonium)2+ and MII = Co, Ni, Cu [space group P21/n, Z = 4] yielded pseudotetrahedral MIIN4-polyhedra, which are distorted by packing forces and vibronic coupling effects of the Jahn-Teller type. Spinel mixed crystals with MII = Zn—Ni, Zn—Cu, Ni—Cu in the tetrahedral sites exhibit phase transition to tetragonal and o-rhombic structures, induced by cooperative Jahn-Teller interactions. The distortion symmetries of the MIIN4 and MIIO4 tetrahedra are analysed on the basis of the respective electronic groundstate and the possible Jahn-Teller active vibrational modes.
    Notes: Die Strukturbestimmung von Verbindungen Cat[MII(NCS)4] mit Cat = p-Xylylen-bis(triphenylphosphonium)2+ und MII = Co, Ni, Cu [Raumgruppe P21/n, Z = 4] ergab pseudo-tetraedrische MN4-Polyeder, die als Folge von Packungseinflüssen und vibronischen Kopplungseffekten vom Jahn-Teller-Typ verzerrt sind. Bei Spinell-Mischkristallen MIICr2O4 mit normaler Kationenverteilung und MII = Zn—Ni, Zn—Cu, Ni—Cu werden Phasenübergänge zu tetragonalen und o-rhombischen Gittern als Folge kooperativer Jahn-Teller-Effekte beobachtet. Die auftretenden Verzerrungssymmetrien der MN4- und MO4-Tetraeder werden gruppentheoretisch auf der Grundlage der elektronischen Grundzustände und der möglichen Jahn-Teller-aktiven Normalschwingungen analysiert.
    Additional Material: 6 Ill.
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  • 3
    ISSN: 0044-2313
    Keywords: Rare earth hydride halides ; ir, uv/vis, photoelectron spectra ; magnetism ; electrical properties ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: LnHal2Hn - New Phases in the Ternary System Ln/Hal/H (Ln = Lanthanoid, Hal = Br, I) 111. Physical PropertiesIR and diffuse reflectance spectra, magnetic susceptibility and electrical resistance as well as photo-electron spectra of GdI2Hn and CeI2Hn (n ≦ 1) are reported. GdI2Hn samples with 0 〈 n 5 1 are insulators or semiconductors. Compounds with n = 1 are colourless, with n 〈 1 blue transparent. Phases with n 〈 0.9 show metallic lustre. This feature and the electrical properties can be understood on the basis of the electronic structure (Extended Hückel calculations, photoelectron- and reflectance spectroscopy). For n ≠ 1, in contrast to the stoichiometric hydride halides, bands approx. 1 eV below the Fermi edge are populated. With decreasing H content they broaden and the density of states increases. CeI2Hn exhibits a metal-to-semiconductor transition for n = 0.33. According to the susceptibility measurements the ferromagnetic order of GdI2 successively is suppressed by the incorporation of hydrogen. Simultaneously, correlated regions with spontaneous magnetization are maintained. Temperature dependent X-ray diffraction measurements also indicate the existance of such clusters.
    Notes: Es wird über IR- und diffuse Reflexionsspektroskopie, magnetische Suszeptibilitäts- und elektrische Widerstandsmessungen sowie Photoelektronenspektroskopie an GdI2Hn und Cel2Hn und Cel2Hn (n ≦ 1) berichtet. GdI2Hn-Proben mit 0 〈 n ≦ 1 sind Isolatoren bzw. Halbleiter. Verbindungen mit n = 1 sind farblos, mit n 〈 1 blau transparent und n 〈 0,9 zunehmend metallisch glänzend. Dies und die elektrischen Eigenschaften sind mit der elektronischen Struktur (Extended-Hückel-Rechnungen, Photoelektronen- und Reflexionsspektren) interpretierbar: Gegenüber den stöchiometrischen Hydridhalogeniden werden bei n ≠ 1 ca. 1 eV unterhalb der Fermikante Bänder besetzt, die sich mit sinkendem H-Gehalt zunehmend verbreitern und deren Zustandsdichte sich erhöht. CeI2Hn zeigt einen Metall-Halbleiter-Übergang bei n ∼ 0,33.Suszeptibilitätsmessungen zufolge wird die ferromagnetische Ordnung in GdI2 durch den Einbau von Wasserstoff sukzessive unterdrückt. Dies geschieht unter Erhalt von korrelierten Bereichen, die ferromagnetische Spontanmagnetisierung aufweisen. Für die Existenz solcher Cluster sprechen auch die Ergebnisse temperaturabhängiger Röntgendiffraktometrie.
    Additional Material: 11 Ill.
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  • 4
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Near threshold photoproduction ofη-mesons from the proton has been measured at the MAMI accelerator with the TAPS spectrometer. The mass of theη-meson was deduced from the threshold energy forη-photoproduction. The result of m η =(547.12 ± 0.06 ± 0.25) MeV supports the low value of theη-mass reported from a dp →3Heη measurement at SATURNE in 1992. Theη-decay branching ratio Γ3π0/Γγγ was measured to be (0.832±0.005±0.012).
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  • 5
    ISSN: 1434-601X
    Keywords: 25.20.Dc ; 25.85.Jg ; 27.90.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The total photofission cross section σγ,F for235U and238U has been measured in the energy range 50≤E γ≤800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4π arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section σγF , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections σγ,F normalized to the atomic numberA for both isotopes coincide, and agree in theΔ-resonance region, within the systematic errors, with the socalled“Universal Curve” σγ,T /A of the total photon absorption cross section σγ,T . At higher energies the cross sections exhibit a smooth behaviour. In particular, it is shown for the first time that there isno resonance-like shape near the D13 resonance (at ≈710 MeV) as observed for the free proton. This complete suppression of the D13 resonance in complex nuclei is not yet understood on a microscopic level. The fragment mass distributions show a predominantly mass symmetric fission. However, contributions from mass asymmetric fission at some photon energies may give a hint of an increased mass asymmetric fission after the onset of the pion and two pion channels.
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  • 6
    ISSN: 1573-5117
    Keywords: dune lakes ; acidic freshwaters ; chlorophyll-phosphorus ; eutrophication ; Australia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This study provides the most comprehensive physico-chemical and phytoplankton data yet available for Australian dune lakes, which are among the world's most naturally acidic and oligotrophic freshwaters. Seasonal and spatial variations were examined in Blue Lagoon and Lake Freshwater, two ‘water-table window’ lakes in south-east Queensland. Like other dune lakes, they are acidic (minimum pH 4.20 and 4.55, respectively), polymictic water bodies with low concentrations of marine-derived major ions and almost undetectable levels of trace metals. While linmologically similar in winter, during spring-summer Lake Freshwater has significantly higher levels of chlorophyll-a, total phosphorus (TP) and turbidity than Blue Lagoon and other dune lakes, indicating seasonal mesotrophy. The key nutrient is TP, which has recently increased to a maximum of 17 μ· l−1, due either to inputs from recreational sources, or to the death and decomposition of littoral vegetation resulting from falling water levels over the last decade. Inorganic nitrogen, though present only in small amounts, does not appear to limit the eutrophication process because of a shift in phytoplankton dominance from the usual desmids and dinoflagellates to N2-fixing blue-green algae. A chlorophyll - TP linear regression derived for dune lakes indicates that at TP 〈 20 µg · l−1 chlorophyll ‘yield’ is higher than in other lake types represented by regressions from the literature. This may be due to a more efficient utilization of the limited available phosphorus by dune lake algae which have adapted to the naturally oligotrophic environment. The implications of these findings for lake management are discussed.
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  • 7
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The purpose of this pilot study was to evaluate surface-induced mineralization (SIM) as a potential technique to apply ceramic coatings to metal orthopaedic implants. Cylindrical titanium porous-coated implants were either coated by SIM or plasma-spray (PLS) techniques with calcium phosphate, or left uncoated (CTL). The implants were bilaterally implanted into the intramedullary canal of the proximal femur of 24 adult New Zealand white rabbits segregated into the following groups: PLS/CTL, SIM/CTL, and SIM/PLS. After 6 weeks in vivo, biomechanical and histologic evaluations were completed. Biomechanically, SIM had consistently greater mechanical interlock than PLS implants. However, CTL implants had greater mechanical interlock than both PLS and SIM. The small sample size prevented statistical evaluation and definitive biomechanical conclusions. Histologically, SIM and PLS had significantly greater ingrowth than CTL implants (p 〈 0.05). The SIM coating technique produced similar ingrowth characteristics as standard PLS coatings, yet may prevent osteolysis by providing a stronger, more reliable, covalent bond between the ceramic and metal. © 1997 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 8
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A series of squirrel monkeys received segmental femoral replacements in a study of the strength of the interface developed between the implant and bone. Implants were either made completely of bioglass-ceramic, or 316L stainless steel with a flame-prayed coating of bioglass. Fracture torque, energy at fracture, and shear stress at failure were compared to values obtained from a control group of pairs of tibias. Femurs containing bulk bioglassceramic implants showed about a 25% difference in strength compared to the opposite bone, while femurs containing flame-sprayed implants exhibited extremely low structural strength. While the strength of the metal-glass bond was very low (〈500 kgf/cm2), the bonebioglass bond was found to be at least as strong as the bioglass-ceramic, and at least 3/4 as strong as the host bone.
    Additional Material: 8 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 77 (1973), S. 331-341 
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Features of the cytology and ultrastructure of the life cycle ofAcetabularia mediterranea from events leading to the division of the primary nucleus to cysts formation are described. In agreement with the work ofBoloukhère (1969, 1970, 1972) the loss of the ramiform primary nucleolus, and striking changes in the rhizoid chloroplasts are observed. The development of the secondary nuclei, and their associated basophilic aggregates, the presence of cytoplasmic microtubules, and the process of cytoplasmic cleavage are described and discussed. Golgi bodies appear to be involved in cell wall synthesis.
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  • 10
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Uteroglobin, a secretory protein of rabbit uterine epithelium, was localized by the direct immunoperoxidase method in control and hCG-induced pseudopregnant rabbits. In control rabbits, uteroglobin was confined to the apical cytoplasm of nearly all cells of the endometrial epithelium. The induction of pseudopregnancy resulted in a pronounced continuing increase, through 4 days post-hCG administration, in the absolute number of epithelial cells engaged in uteroglobin synthesis. Furthermore, the endoplasmic reticulum was more intensely stained for uteroglobin than in the epithelial cells of control rabbit endometrium. Thus, the increased production of uteroglobin, in response to hormonal stimulation, appears to be achieved both through an increase in the amount of uteroglobin synthesized by a given cell as well as by an increase in the number of cells involved in uteroglobin synthesis. Concurrent with the increase in the number of cells synthesizing uteroglobin, an increase in the number of unstained cells first appeared at the second day of pseudopregnancy, during the period of maximal epithelial proliferation. However, within those cells containing uteroglobin on the second day following injection with hCG, most staining was limited to the perinuclear membrane. At various times following hCG administration, a number of scattered cells, intensely stained for uteroglobin, were observed in the uterine epithelium. Based upon ultrastructural studies, failure to exclude trypan blue, and the presence of intra-mitochondrial uteroglobin, they were identified as cither dead or dying cells.
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