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  • Engineering General  (12)
  • Cell & Developmental Biology  (9)
  • Organic Chemistry  (9)
  • 1990-1994  (30)
  • 1
    Electronic Resource
    Electronic Resource
    Morphological changes in the oocyte and its surrounding vestments during in vivo fertilization in the dasyurid marsupial sminthopsis crassicaudata (1990)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 204 (1990), S. 177-196 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: This light and transmission electron microscopical study shows that the first polar body is given off before ovulation and that part of its cell membrane and that of the surrounding oocyte have long microvilli at the time of its ejection. Several layers of cumulus cells initially surround the secondary oocyte and first polar body, but the ovulated oocytes in the oviducts in the process of being fertilized do not have cumulus cells around them. Partly expelled second polar bodies occur in the oviduct; they are elongated structures that lack organelles and have electron-dense nuclei. A small fertilization cone appears to form around the sperm tail at the time of sperm entry into the egg and an incorporation cone develops around the sperm head in the egg cytoplasm. In three fertilized eggs a small hole was seen in the zona, which was presumably formed by the spermatozoon during penetration. Cortical granules, present in ovarian oocytes, are not seen in fertilized tubal or uterine eggs; release of their contents probably reduces the chances of polyspermy, although at least one polyspermic fertilized egg was seen and several other fertilized eggs had spermatozoa within the zona pellucida. In the zygote the pronuclei come to lie close together, but there was no evidence of fusion. A “yolk mass,” which becomes eccentric before ovulation, is extruded by the time the two-cell embryos are formed, but many vacuoles remain in the non-yolky pole of the egg. A shell membrane of variable thickness is present around all uterine eggs but its origin remains undetermined.
    Additional Material: 51 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1052040207
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  • 2
    Electronic Resource
    Electronic Resource
    Marsupial fertilization: Some further ultrastructural observations on the dasyurid Sminthopsis Crassicaudata (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 32 (1992), S. 277-292 
    Details
    ISSN: 1040-452X
    Keywords: Oocyte maturation ; Sperm - egg interaction ; Sperm incorporation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Various morphological aspects of in vivo egg maturation and sperm - egg interaction were investigated in the Australian marsupial Sminthopsis crassicaudata with the transmission and scanning electron microscopes. Cortical granules invariably occurred in primary oocytes, with the number increasing after resumption of the first meiotic division. They generally occurred close to the oolemma, including the region near the oocyte nucleus. After mating, spermatozoa with intact acrosomes, which had a homogeneous electron-dense matrix, were found on the outer zona surface, but loss of acrosomal contents had occurred by the time of zona penetration. Sperm incorporation into the egg took place at the metaphase II stage of meiosis, and, at this time, cortical granules disappeared from the egg cortex. Sperm heads with condensed chromatin in the egg cytoplasm had an electron-dense layer of subacrosomal material over part of the dorsal nuclear surface, but no membranes were present around these incorporated spermatozoa. Sperm chromatin decondensation resulted in an elevation of egg cytoplasm, and the cell membrane over this area lacked microvilli. The pronuclear envelope was not laid down until after chromatin decondensation had occurred. By this time the fertilized egg had reached the uterus, and a smooth, electron-dense, shell membrane had been deposited. These observations, together with our previous findings, indicate that some of the processes of sperm - egg interaction are similar to those in eutherian mammals, whereas others appear highly divergent.
    Additional Material: 47 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080320314
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  • 3
    Electronic Resource
    Electronic Resource
    Unusual nuclear structure of the spermatozoon in a marsupial, Sminthopsis crassicaudata (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 37 (1994), S. 78-86 
    Details
    ISSN: 1040-452X
    Keywords: Marsupial ; Sperm head ; Chromatin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The organization of sperm chromatin in the dasyurid marsupial, Sminthopsis crassicaudata, was investigated using various morphological techniques. Transmission electron microscopy indicates two quite distinct chromatin regions became evident late in spermiogenesis with an outer globular region containing blocks of very electron-dense chromatin. Fluorescent light microscopical studies after staining with DNA dyes and 7-amino actinomycin D of testicular, caput, and cauda epididymal spermatozoa showed that this region fluoresced less brightly than the rest of the nucleus, indicating the presence of fewer DNA binding sites. Freeze fracture showed that the chromatin in most of the nucleus had randomly arranged particles of various sizes, but that of the outer region was composed entirely of small particles. This outer region was more resistant to low concentrations of the ionic detergent, SDS, whereas both guanidine hydrochloride and urea together with sodium chloride generally dispersed all the chromatin except that in the outer globular region and in a localized area of the nucleus beneath the acrosome. This study has thus revealed that the outer globular chromatin of these spermatozoa responds differently to ionic detergents and protein denaturing agents and has a different chromatin organization than most of the rest of the nucleus. The significance of these differences remains, however, to be determined. © 1994 Wiley-Liss, Inc.
    Additional Material: 23 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080370111
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  • 4
    Electronic Resource
    Electronic Resource
    Distribution of filamentous actin in and around spermatids and in spermatozoa of Australian conilurine rodents (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 30 (1991), S. 369-384 
    Details
    ISSN: 1040-452X
    Keywords: F-actin ; Sperm head ; Australian rodents ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The distribution of filamentous actin around the maturing sperm head and in spermatozoa of four species of Australian conilurine rodents was investigated at the light and electron microscopic levels. Similar results were obtained for all the species studied. Mechanically isolated spermatids had NBD-phallacidin-positive longitudinal bands of fluorescence over the dorsolateral surface and, in late spermatids, bands of bright fluorescence passed perpendicularly from the dorsal convex to ventral concave surface. TEM observations indicated that these regions corresponded to filaments of ectoplasmic specializations and granular filamentous material around the tubulobulbar complexes, respectively. In testicular and cauda spermatozoa NBD-phallacidin fluorescent material was present in the two ventral processes that extended from the upper concave surface of the sperm head; also fainter material occurred along the concave border and as a dorsocaudal spur. Its distribution was identical for testicular and cauda spermatozoa. TEM of late spermatids showed that in the ventral process closest to the apical hook there were between 170 and 245 filaments, which attached to the inner surface of the postacrosomal dense lamina; in the more caudal ventral process about 70 filaments occurred. No filaments were, however, visible in the mature spermatozoon but, after immunocytochemical labelling for actin, deposition of gold particles was evident over ventral processes of both late spermatids and cauda spermatozoa. Within the female tract these ventral processes made contact with the zona matrix and were taken into the egg cytoplasm unchanged in morphology. The possible functional significance of the filamentous actin in these structures is discussed.
    Additional Material: 39 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080300412
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  • 5
    Electronic Resource
    Electronic Resource
    Finite element solution of the Navier-Stokes equations by a velocity-vorticity method (1990)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 661-675 
    Details
    ISSN: 0271-2091
    Keywords: Finite elements ; Navier-Stokes ; Velocity-vorticity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A velocity-vorticity formulation of the Navier-Stokes equations is presented as an alternative to the primitive variables approach. The velocity components and the vorticity are solved for in a fully coupled manner using a Newton method. No artificial viscosity is required in this formulation. The pressure is updated by a method allowing natural imposition of boundary conditions. Incompressible and subsonic results are presented for two-dimensional laminar internal flows up to high Reynolds numbers.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650110511
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  • 6
    Electronic Resource
    Electronic Resource
    Transonic viscous-inviscid interaction by a finite element method (1991)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 13 (1991), S. 309-319 
    Details
    ISSN: 0271-2091
    Keywords: Viscous-inviscid interaction ; Shock wave-boundary layer interaction ; Boundary layers ; Finite element method for flow problems ; Zonal methods ; Choked viscous flows ; Stream function-vorticity formulation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A method is outlined for solving two-dimensional transonic viscous flow problems, in which the velocity vector is split into the gradient of a potential and a rotational component. The approach takes advantage of the fact that for high-Reynolds-number flows the viscous terms of the Navier-Stokes equations are important only in a thin shear layer and therefore solution of the full equations may not be needed everywhere. Most of the flow can be considered inviscid and, neglecting the entropy and vorticity effects, a potential model is a good approximation in the flow core. The rotational part of the flow can then be calculated by solution of the potential, streamfunction and vorticity transport equations. Implementation of the no-slip and no-penetration boundary conditions at the walls provides a simple mechanism for the interaction between the viscous and inviscid solutions and no extra coupling procedures are needed. Results are presented for turbulent transonic internal choked flows.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650130304
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  • 7
    Electronic Resource
    Electronic Resource
    Finite element solution of the incompressible Navier-Stokes equations by a Helmholtz velocity decomposition (1991)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 13 (1991), S. 135-144 
    Details
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Finite element solution methods for the incompressible Navier-Stokes equations in primitive variables form are presented. To provide the necessary coupling and enhance stability, a dissipation in the form of a pressure Laplacian is introduced into the continuity equation. The recasting of the problem in terms of pressure and an auxiliary velocity demonstrates how the error introduced by the pressure dissipation can be totally eliminated while retaining its stabilizing properties. The method can also be formally interpreted as a Helmholtz decomposition of the velocity vector.The governing equations are discretized by a Galerkin weighted residual method and, because of the modification to the continuity equation, equal interpolations for all the unknowns are permitted. Newton linearization is used and at each iteration the linear algebraic system is solved by a direct solver. Convergence of the algorithm is shown to be very rapid. Results are presented for two-dimensional flows in various geometries.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650130202
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  • 8
    Electronic Resource
    Electronic Resource
    Trefftz method for Kirchhoff plate bending problems (1993)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 36 (1993), S. 765-781 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Kirchhoff plate bending problems were studied by both the Trefftz direct and indirect approximations in which non-singular, complete Trefftz functions are used as the weighting and/or trial functions. The Trefftz direct method involved only the quantities of engineering interest. Numerical results are given to show the efficiency and the excellent accuracy of the present method.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620360504
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  • 9
    Electronic Resource
    Electronic Resource
    Solution of Helmholtz equation by Trefftz method (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 32 (1991), S. 63-78 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The application of the Trefftz method for calculating wave forces on offshore structures is presented. Indirect and direct formulations using complete and non-singular systems of Trefftz functions for the Helmholtz equation are posed in this paper. An effective technique using different interpolation functions for the velocity potential and wave force are suggested to improve the computational accuracy of the wave force. The numerical examples show that the present method is highly efficient and accurate.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620320105
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  • 10
    Electronic Resource
    Electronic Resource
    Application of the Trefftz method in plane elasticity problems (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 30 (1990), S. 1147-1161 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Direct and indirect approximations using sets of non-singular, complete Trefftz functions, i.e. the complete systems of solutions, have been successfully applied to harmonic problems.1 In this paper, the procedure is applied to a more complex situation - plane elasticity problems.The examples show that the present method can avoid the difficulties relating to singular integration and has good accuracy compared with traditional boundary elements.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620300605
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