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  • 1
    Electronic Resource
    Electronic Resource
    Male cytoplasmic diminution and male germ unit in young and mature pollen of Cymbidium goeringii: a 3-dimensional and quantitative study (1992)
    Springer
    Sexual plant reproduction 5 (1992), S. 169-181 
    Details
    ISSN: 1432-2145
    Keywords: Cymbidium goeringii ; Cytoplasmic diminution ; Generative cell ; Male germ unit ; Vegetative nucleus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pollinia of Cymbidium goeringii (Orchidaceae) were examined at a young stage (approx. 2 weeks before anthesis) and at anthesis using transmission electron microscopy, computer-assisted serial reconstruction and quantitative cytology. At the young stage, the generative cell (GC) has a spherically shaped main body with a large nucleus and 1 to 4 cytoplasmic extensions (up to 10 μm long) physically associated with a groove on one side of the vegetative nucleus (VN). By anthesis, some GCs lose their cytoplasmic extensions, becoming spherical. The GC surface becomes highly wrinkled, the distance between the GC and the VN increases and the two may separate completely. Enucleated cytoplasmic bodies (ECBs) are apparently generated by the GC, as evidenced by their similar ultrastructural appearance and distribution near the GC. ECBs are likely produced from two sites: the GC surface and the tips of cytoplasmic extensions of the GC. Vesicle-containing bodies (VCBs) may be generated from the lateral surface of the GC and may also represent a degeneration stage of ECBs, finally fusing with lipid bodies. Heritable organelles are rare and usually absent in the GC of Cymbidium: 0.176 mitochondria and 0.0042 plastids per GC were observed at the young stage and no mitochondria and 0.019 plastids at anthesis. Of 16 cellular parameters examined during GC development, all decreased with the exception of the surface area and volume of ECBs/ VCBs (which remained stable) and GC vacuoles (which increased). Significant decreases in 11 parameters presumably relate to dehydration of the pollen and male cytoplasmic diminution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189808
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  • 2
    Electronic Resource
    Electronic Resource
    Sperm cells in pollen tubes ofNicotians tabacum L.: three-dimensional reconstruction, cytoplasmic diminution, and quantitative cytology (1992)
    Springer
    Protoplasma 168 (1992), S. 172-183 
    Details
    ISSN: 1615-6102
    Keywords: Cytoplasmic inheritance ; Male cytoplasmic diminution ; Male gamete (angiosperm) ; Male germ unit ; Nicotiana ; Tobacco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The organization of the sperm cells and vegetative nucleus (male germ unit) ofNicotiana tabacum was examined 18 h after semivivo pollination using transmission electron microscopy, computerassisted serial section reconstruction and quantitative cytology. Based on a measurement of 11 cellular parameters in nine reconstructed sperm cell pairs, there are no statistically significant differences between the two cells. The Svn is characterized by a strapshaped cytoplasmic extension that is physically associated with the surface of the vegetative nucleus. The nucleus is located adjacent to the sperm crosswall, with sperm organelles being distributed between the nucleus and the extension. The Sua is a tapered cell with cytoplasmic areas at both poles and deep axial invaginations near the crosswall. This cell has a centrally-located nucleus and a largely polar distribution of organelles. Three mechanisms for cytoplasmic diminution were observed that appear to contribute actively to the loss of cytoplasmic volume and organelles: (1) enucleated cytoplasmic body production in the Sua; (2) vesiculation at the tip of the cytoplasmic projection of the Svn; and (3) vesicle-containing body accumulation in the periplasm of both the Svn and Sua.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01666263
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  • 3
    Electronic Resource
    Electronic Resource
    A novel isoparametric finite element displacement formulation for axisymmetric analysis of nearly incompressible materials (1993)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 36 (1993), S. 2453-2472 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: It is well accepted that severe numerical difficulties arise when using the conventional displacement method to analyse incompressible or nearly incompressible solids. These effects are caused by the kinematic constraints imposed on the nodal velocities by the constant volume condition. In elastic-plastic analysis, these effects are due to a conflict between the plastic flow rule and the finite element discretization. Although several methods have been proposed to cope with this problem, none has been based on the appropriate choice of displacement interpolation functions to minimize the constraints. The theoretical formulation of a new six-noded isoparametric displacement finite element, which is well suited for elastic-plastic analysis of axisymmetric constrained solids by using a rational displacement interpolation function, is presented in this paper. The proposed displacement interpolation function implies that the displacement in the axial direction and the product of the displacement in the radial direction and the radius should be treated as two independent basic variables. Alternatively, the proposed displacement interpolation function can also be implemented in a conventional displacement formulation simply by using a modified shape function matrix. The suitability of the proposed formulations is first studied theoretically by assessing the number of degrees of freedom per constraint and then verified by performing numerical experiments on typical boundary value problems which involve incompressible behaviour.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620361409
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  • 4
    Electronic Resource
    Electronic Resource
    Letter to the Editor (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 17 (1993), S. 205-207 
    Details
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nag.1610170306
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  • 5
    Electronic Resource
    Electronic Resource
    UNDRAINED CAVITY EXPANSIONS IN CRITICAL STATE SOILS (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 489-516 
    Details
    ISSN: 0363-9061
    Keywords: cavity expansion ; critical state models ; plasticity ; pile installation ; normally and overconsolidated clays ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Boundary value problems for hardening/softening soils, such as Cam-Clay, usually require the extensive use of finite element methods. Here analytical and semi-analytical solutions for the undrained expansion of cylindrical and spherical cavities in critical state soils are presented. The strain is finite, the initial cavity radius is arbitrary and the procedure applicable to any isotropically hardening materials. In all cases only simple quadratures are involved, and in the case of the original Cam-Clay a complete analytical solution can be found. In addition to providing models of the behaviour of displacement piles and pressuremeters these results also provide valuable benchmark solutions for verifying various numerical methods.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    A model for the ductile yield of porous rock (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 12 (1988), S. 679-688 
    Details
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A relatively simple yield model is developed for isotropic, porous rocks which yield in a ductile manner. The flow rule and yield function are derived using an adaptation of the work-balance approach of critical state soil mechanics. This adaptation allows for the dissipation of work by frictional and volume change mechanisms, including the dissipation of frictional work at sensibly constant plastic volumetric strain. The yield model uses two material parameters - a basic frictional parameter and a plastic volumetric strain adjustment parameter which is assumed to be constant for the yield locus corresponding to a particular specific volume. The model gives excellent fits to yield loci for two limestones, a chalk and gypsum plaster prepared at different initial void ratios.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nag.1610120608
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  • 7
    Electronic Resource
    Electronic Resource
    A large strain analytical solution for cavity contraction in dilatant soils (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 19 (1995), S. 793-811 
    Details
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: An infinite dilatant elastic-plastic soil mass contains a single cylindrical or spherical cavity within which a slowly increasing pressure is applied. The removal of the cavity pressure takes place after a partly plastic state of the soil has been reached. Closed form solutions for the stress and displacement fields in the soil during any stage of the unloading process are derived. The non-associated Mohr-Coulomb yield criterion is used to account for dilation of the soil during shearing. Large strains are taken into account by adopting an appropriate strain definition within the plastically deforming region.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nag.1610191104
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