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  • 2
    Publication Date: 2002-01-01
    Description: Development of the rifted continental margins and subsequent seafloor spreading in the North Atlantic was dominated by interaction between the Iceland mantle plume and the continental and oceanic rifts. There is evidence that at the time of breakup a thin sheet of particularly hot asthenospheric mantle propagated beneath the lithosphere across a 2500 km diameter region. This event caused transient uplift, massive volcanism and intrusive magmatism, and a rapid transition from continental stretching to seafloor spreading. Subsequently, the initial plume instability developed to an axisymmetric shape, with the c. 100 km diameter central core of the Iceland plume generating 30-40 km thick crust along the Greenland-Iceland-Faroes Ridge. The surrounding 2000 km diameter region received the lateral outflow from the plume, causing regional elevation and the generation of thicker and shallower than normal oceanic crust. We document both long-term (10-20 Ma) and short-term (3-5 Ma) fluctuations in the temperature and/or flow rate of the mantle plume by their prominent effects on the oceanic crust formed south of Iceland. Lateral ridge jumps in the locus of rifting are frequent above the regions of hottest asthenospheric mantle, occurring in both the early history of seafloor spreading, when the mantle was particularly hot, and throughout the generation of the Greenland-Iceland-Faroes Ridge.
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  • 3
    ISSN: 1615-6102
    Keywords: Microtubules ; Protoplasts ; Mougeotia ; Polarity ; Electric fields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Initially non-polar protoplasts of the green algaMougeotia will regenerate to re-establish their original cylindrical cell shape. The orientation of the growth axis of regenerating protoplasts held in agarose was independent of both the direction of incident white light and gravity. Protoplasts elongated parallel to applied DC electric fields of approx. 0.2 Vcm−1 (1 mV/protoplast) and greater, with an increasing percentage oriented with increasing field strength. At the maximum field strength used (10 mV/cell), 53% of protoplasts were oriented within +- 10° of the 0/180° axis of the field. In untreated controls, the orientation of elongation was random. Protoplast survival was unaffected by field treatment. Some protoplasts (up to 37% in 10 mV/cell fields) formed outgrowths towards the cathode and occasionally towards the anode. Regenerating protoplasts in fields displayed the normal sequence of microtubule reorganization. This means that the positioning of the ordered symmetrical array of microtubules centred on two foci that appears within 3 to 4 h, and the subsequent organization of microtubules by 8 to 12 h into a band that intersects both foci and which is transverse to the axis of elongation (Galway and Hardham 1986), may be controlled by externally applied electric fields. In the region of this microtubule band, the applied field causes the plasma membrane to be stretched parallel to the field (Bryant and Wolfe 1987). We suggest that microtubules may become oriented perpendicular to the direction of field-induced membrane stretching, and that membrane stretching may be one of the orienting mechanisms for membrane-linked microtubules in elongating plant cells.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 180 (1994), S. 169-184 
    ISSN: 1615-6102
    Keywords: Actin ; Cell-cell communication ; Plasmodesmata ; Regulation ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have used several methods to localise actin associated with plasmodesmata. In meristematic plant material fixed in 0.1% glutaraldehyde/1% paraformaldehyde and embedded in LR White resin, actin was localised (in TEM using 5 nm gold-labelled secondary antibody to C4 anti-actin primary antibody) in the neck region by the plasma membrane and endoplasmic reticulum, and also down the length of the plasmodesma, deep in the cell wall. When the chemical fixation was replaced by rapid freezing in liquid propane (without cryoprotectants) and substitution in acetone, the plasmodesmata were labelled in similar positions, but with less background label on sections. While only 8–20% of plasmodesmata were labelled, the label was 10 to 100 fold denser over plasmodesmata than over the surrounding wall indicating specific association with plasmodesmata. We presume the apparent extracellular location of some label was due to the size of the antibodies between the site of attachment and the observed position of the gold particle. Gold label was found in similar locations in material fixed in 3% paraformaldehyde, infiltrated with sucrose, frozen, sectioned (10–12 μm thick), then labelled with antibodies before resin embedding. Furthermore, cell walls in epidermal peels stained with rhodamine-phalloidin showed localised patches of fluorescence, presumably at the site of plasmodesmata (or primary pit-fields), which were connected on either side to fluorescent strands of actin in the cytoplasm. Suspension cultured cells ofNicotiana plumbaginifolia similarly stained showed very faint, narrow fluorescent strands crossing the walls of sister cells, which may indicate actin associated with individual plasmodesmata, shown in TEM to be sparsely distributed in these walls. In addition, the neck regions of cytochalasin-treated plasmodesmata were greatly enlarged and lacked the normal extracellular ring of particles. We propose that actin associated with plasmodesmata stabilizes the neck region and possibly also the cytoplasmic sleeve, and may be actively involved in regulating cell-to-cell transport.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-966X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Analysis mathematica 7 (1981), S. 217-233 
    ISSN: 1588-273X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract ПустьР - линейный диф ференциальный опера тор с достаточно гладкими коэффициентами. По определению,P явля ется оператором внут ренней регулярности на ω ⊂R n т огда и только тогда, когда $$u \in B_{p,k_{ - N} }^{loc} (\Omega )$$ и ω′⊂ω из условия $$Pu \in B_{p,k_s }^{loc} (\Omega ')$$ вытекает, что $$u \in B_{p,k_s k}^{loc} (\Omega ')$$ , где −N+1≦s≦N. Соотве тствующий пример: $$Pu = - \Delta u + u c k(\xi ) = \xi _1^2 + \ldots + \xi _n^2 + 1.$$ Указанные операторы характеризуются в ра боте в терминах априорных н еравенств. До− казывается также сущ ествование локальны х фундаментальных реш ений для оператора, со пряженного кP, а также его гладкос ть вне диагонали. Эти результаты являются аналогами соответствующих рез ультатов для гипоэлл иптических операторов.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-8469
    Keywords: Nicotiana tabacum ; tobacco mosaic virus ; polyacrylamide gel electrophoresis ; enzyme-linked immunosorbent assay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This review describes the discovery and identification of the pathogenesis-related proteins (PRs) from tobacco. In crude leaf extracts the PRs are distinguished from the proteins in uninfected plants by their solubility at pH 3, resistance to a range of proteases, and mobility in polyacrylamide gels upon electrophoresis (PAGE) in non-denaturing conditions. PAGE has been used as a qualitative and semi-quantitative assay for PRs, and their migration in gels made from different acrylamide concentrations has been used to identify charge and size isomers and electrophoretically identical PRs in different tobacco cultivars. The subunit composition and molecular weight (mol. wt) of the four PRs identified first in ‘Xanthi-nc’ were determined by SDS-PAGE; staining the gels has shown that these same four proteins in ‘Samsun NN’ did not contain carbohydrate, lipid or nucleic acid, nor were they isozymic forms of twenty five enzymes known to increase in activity following infection with TMV. Evidence suggests that most of the PRs in ‘Xanthi-nc’ and ‘Samsun NN’ are extracellular. The purification of several PRs from ‘Xanthi-nc’, ‘Samsun NN’ and other tobaccos is described, as well as their mol. wt, subunit and amino acid composition. PRs 1a, b and c consist of a single polypeptide and have similar mol. wt and amino acid compositions. Antisera prepared against purified ‘Xanthi-nc’ b1 protein have been used to determine serological relationships between PRs and form the basis of a very sensitive quantitative assay using ELISA. The regulation of synthesis of some PRs has been shown to involve translational control.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 18 (1983), S. 1021-1027 
    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 The substitution of the end-member oxides in the ternary glass forming sodium borosilicate system was studied. The replacement of SiO2 with combinations of La2O3 and Ta2O52 was found to produce glasses which, after heat treatment decomposed to form a leachable sodium borate phase and an insoluble ceramic phase. The mode of phase decomposition is sensitive to impurities: the importance of crucible selection, e.g. Al2O3 or Pt/Rh is demonstrated by resulting differences in pore size, surface area, chemical resistance and structure of the insoluble phase for a series of La2O3-Ta2O5 and La2O3-Ta2O3-Al2O3 glass ceramic. These new materials have a specific surface area of up to 145 m2 g−1 and average pore radii ranging between 0.7 and 28.6 nm and show a varying degree of chemical resistance.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    European journal of plant pathology 89 (1983), S. 311-311 
    ISSN: 1573-8469
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-8469
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
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