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  • 2010-2014
  • 1990-1994  (701)
  • 1920-1924
  • 1890-1899
  • 1850-1859
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  • 101
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990) 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 102
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. ii 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
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  • 103
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 247-257 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The MMP (multiple multipole) code, that is based on the generalized multipole technique (GMT), offers several features to overcome problems occurring in computations of guided waves and waveguide discontinuities. The most important problems and the corresponding MMP solutions are outlined. The procedure is illustrated with different examples which demonstrate the wide range of applications of the code.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 104
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 229-234 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A new time-domain approach based on the frequency-domain transverse resonance method is proposed to solve guided wave problems. This new method is capable of solving both the two-dimensional and the three-dimensional propagation problems. The structure under investigation is cut into individual substructures. Time-domain Green's functions of each substructure are computed via the analytical inverse Laplace transform of the frequency-domain Green's functions. The original problem is reconstructed by connecting the cut-out substructures together through the interface boundary conditions. In order to verify the present approach, the empty rectangular waveguide is used as a comparison. With accurately calculated time-domain Green's functions, the data obtained are in good agreement with the analytical results.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 105
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 235-246 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: There are two major difficulties in applying the finite element method to the analysis of microwave devices in three dimensions. One is to obtain a stable vector finite element which does not generate spurious modes, or non-physical solutions, in the numerical analysis. The other is to model efficiently the coupling of port regions and the discontinuity region. In this paper, we describe the application of two new finite element techniques, the tangential vector finite element method and the transfinite element method, for modelling three-dimensional microwave devices. The tangential vector finite element method, unlike the conventional nodal finite element methods, imposes only the tangential continuity of the vector unknown across elements' boundaries. As a result, there would be no spurious modes, and reliable solutions are obtained. The transfinite element method, which combines the modal basis functions and the finite element basis functions through the variational technique, provides an efficient way to model the open boundary nature of the device. To validate the current analysis, a low VSWR waveguide connector and two microstrip low-pass filters are analysed. Numerical results agree very well with the measurements or those obtained by other methods.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 106
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 91-97 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The diffusion of Zn into a GaAs crystal is modelled using numerical techniques similar to those of Zahari and Tuck.1 This technique does not directly solve any differential equations, the physical processes are directly modelled. The diffusion of Zn is assumed to be by the kick-out mechanism. In this mechanism the Zn atoms diffuse into the crystal interstitially with a constant diffusion coefficient. The interstitial Zn atoms transfer to the substitutional lattice site by kicking out a Ga atom. The incorporation of the Zn atoms on to the lattice sites is assumed to take place at a rate much greater than the diffusion of the interstitial Zn. The diffusion of the generated Ga interstitial is also contained in the model. The effect on the Zn concentration profile and Ga interstitial concentration of varying both the Ga interstitial diffusivity and equilibrium concentration has been examined. Finally, the implications of these results on Zn induced disordering of GaAs/AlAs superlattices is discussed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 107
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 157-169 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper is concerned with the theoretical determination of the amount of atomic mixing which accompanies the erosion of a solid surface exposed to an energetic ion beam. The work is relevant to sputter depth profiling where such mixing complicates the deduction of the initial depth distributions from the measured ion yields.A mathematical model, which considers the effects of incident ion accumulation, ballistic relocation and diffusion is described. The governing integro-differential equations are solved numerically.Results for a GaAs-AlGaAs multi-layer structure bombarded with O2+ ions are compared with results obtained experimentally.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 108
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 171-182 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Wave scattering from an aperture coupled system is studied using a new method which combines the hybrid ray-mode method and method of moments. The latter is used to formulate the coupling process and the former to provide the Green's function of a parallel plate waveguide. Following standard procedures of the method of moments, we first formulate a system equation for field distributions across the aperture. By expressing these unknown distributions in terms of appropriate basis functions and choosing appropriate weighting functions, the system equation is then reduced to a matrix equation which is solved numerically. In the system of equations, one needs to compute the Green's function of the waveguide for various arrangements of locations of source and receiver. The hybrid ray-mode formulation is best suited for this purpose because it combines rays and modes self-consistently to optimize the advantages of each. The efficiency of the ray-mode Green's function makes use of the moment method practical in waveguides, and the flexibility of the moment method permits application of the Green's function considered to arbitrarily shaped and placed apertures. Numerical implementation illustrates these aspects.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 109
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 183-193 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Analysis of transients in integrated circuits is performed with the use of highly specialized computer programs. The transient responses are computed using time-marching integration methods and require a substantial amount of computer time. A new method based on spectral analysis and waveform relaxation is proposed. The method results in a substantial saving in computing time without compromising the accuracy. A basic algorithm utilizing the spectral technique in a relaxation framework is described. A prototype simulator based on the algorithm was developed and used to simulate certain types of CMOS circuits. The results showed a significant time savings in comparison with the widely used circuit simulator ‘SPICE’. Example circuits and relevant results are provided.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 110
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 207-214 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A simple method is described for spatial substructuring of meshes used in TLM diffusion routines in such a way as to enable discontinuous mesh lines to be used. A method of operating TLM diffusion routines using different timesteps in different spatial regions is also described. For both aspects, results are compared with those derived using standard TLM techniques.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 111
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 259-268 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Accurate full-wave analysis of shielded microstrip discontinuities, based on a mode-matching technique and employing Kühn's method is presented. Finite thickness of the strip metallization is taken into account. Examples include bends, T-junctions, and crossings.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 112
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 287-315 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The fundamentals of computer-aided noise analysis of linear noisy microwave circuits are presented. The method is based on the description of noisy networks by correlation matrices, and allows the noise analysis of linear circuits of general topology exhibiting arbitrary correlations between the noise sources. The description of linear noisy networks by correlation matrices in different representations, the interconnection of noisy networks and the nodal analysis of noisy networks are treated. The correlation matrices of circuits or subcircuits exhibiting thermal noise may be calculated directly from its admittance matrix. The application of the method for the noise analysis of linear microwave amplifiers is discussed.
    Zusätzliches Material: 24 Ill.
    Materialart: Digitale Medien
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  • 113
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 269-285 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The transmission-line matrix (TLM) method enables simulation of interior electromagnetic field propagation problems. With the use of absorbent walls, we can simulate exterior problems such as the radiaition of a microstrip antenna. The input impedance is deduced from the standing wave observed in the feedline. The radiation pattern is determined from the field over a plane located in the immediate vicinity of the antenna, using the theory of radiating apertures. However, the CPU time and memory space involved are excessive. Since the radiating structure has several resonant frequencies, it is convenient to apply classical digital signal processing techniques such as finite impulse response filtering associated with a linear prediction method. The present paper focuses on a Prony-Pisarenko method to improve on the TLM method in terms of both computation time and precision of the frequency-domain analysis of the results. In this case, overall CPU time is reduced by a factor of 2 to 3. The paper discusses the results obtained for radiation patterns. This represents a new field of application for the TLM method whose drawbacks are reduced by using appropriate signal processing methods.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 114
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 27 (1990), S. 168-172 
    ISSN: 1040-452X
    Schlagwort(e): Motility ; Genetics ; Sex chromosome ratio ; Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: In this study, we address the relationship between motility and genetic content of mouse sperm. The chromosome complements of highly motile mouse sperm, selected using the swim-up technique, were analyzed after in vitro fertilization, at the first cleavage state. They were compared to those of unselected sperm. Identification of male and female chromosome sets was possible because of their differential condensation at the first mitotic division. In vitro fertilization, swim-up separation, chromosome preparation, and staining were carried out using standard techniques. The results indicate that highly motile mouse sperm did not differ in types and frequencies of chromosomal abnormalities from those not selected for motility. Moreover, separation of motile sperm does not deviate the sex ratio from the theoretical 1:1.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 115
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990) 
    ISSN: 0271-2091
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
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  • 116
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 47-77 
    ISSN: 0271-2091
    Schlagwort(e): Finite element ; Convection ; Centrifugal ; Gravitation ; Cylinder ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The performance of the Galerkin finite element method when applied to time-dependent convection involving rotation, self-gravitation and the normal gravity field in a horizontal cylinder is discussed in this paper. The governing equations, the parameters of the problem and our implementation of the numerical schemes are presented. The accuracy, spatial scale of resolution, flexibility and robustness of the resulting code show the element method as a valuable tool for research in this area or in related problems in astrophysical fluid dynamics. The numerical difficulties in large-amplitude flows are associated with an error-control scheme for time integration and the ‘short-time’ wiggles in transient Dirichlet problems. Coarse grids give the correct qualitative picture in most simulations, but the type of solution at short time (and hence grid refinement) presumably resolves the degeneracy in the azimuthal orientation of convection cells in flows driven by self-gravitation and (perhaps) centrifugal buoyancy. The final state in transient flows is a motionless isothermal fluid. However, residual motions can be nullified only in the limit of zero grid size in flows driven by centrifugal buoyancy (self-gravitation), while a fairly coarse grid is sufficient for this purpose in normal gravity-driven flows.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 117
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 161-178 
    ISSN: 0271-2091
    Schlagwort(e): Euler equations ; Finite volumes ; Cell vertex storage ; Zonal approach ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A zonal grid methodology has been developed for the calculation of compressible fluid flows. The domain subdivision is based on patched grid systems composed of zones or blocks within which a distinct curvilinear grid is generated. The flow simulation is then carried out with a modified scheme based on the Euler finite volume solver of Ni. This scheme uses a distribution procedure that provides an easy and accurate way for the transfer of information from one block to another. This method results in a naturally conservative computation at the interfaces. It is analysed and developed for the treatment of embedded grids with a grid point common to more than four blocks.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
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  • 118
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 213-222 
    ISSN: 0271-2091
    Schlagwort(e): Jet flow ; Variational inequality ; Finite element method ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The numerical analysis of plane and axially symmetric jet flows of an incompressible inviscid fluid is treated. A new formulation of the variational inequality type is developed from the variational principle associated with jet problems. A successive approximation method is formulated by the combined use of variational inequality and the finite element method. Numerical examples based on the iterative method are presented. The results obtained agree well with those by other methods.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 119
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990) 
    ISSN: 0271-2091
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 120
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 227-246 
    ISSN: 0271-2091
    Schlagwort(e): Adaptive ; Finite element method ; p-version ; Unsaturated flow ; Hierarchic ; Non-linear ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The advantages associated with the use of self-adaptive methods for the solution of problems which require the prediction of a frontal position in time are well known. In this paper a self-adaptive finite element solution for the non-linear unsaturated flow equation is developed using hierarchic p-version enrichment of the interpolating space. Additional computational advantages are demonstrated for an iteration scheme in which iterations after enrichment are performed only over a subdomain. Numerical solutions are presented for a one-dimensional infiltration scenario.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 121
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 327-351 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Taylor-Galerkin algorithm ; Fractional step method ; Cavity flow ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: In this paper the development and behaviour of a new finite element algorithm for viscous incompressible flow is presented. The stability and background theory are discussed and the numerical performance is considered for some benchmark problems. The Taylor-Galerkin approach naturally leads to a time-stepping algorithm which is shown to perform well for a wide range of Reynolds numbers (1 ≤ Re ≤ 400).A conventional definition for Re is assumed. Various modifications to the algorithm are investigated, particularly with respect to their effects on stability and accuracy.
    Zusätzliches Material: 23 Ill.
    Materialart: Digitale Medien
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  • 122
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 357-372 
    ISSN: 0271-2091
    Schlagwort(e): Singular finite elements ; Die swell ; Sudden expansion ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The singular finite element method is used to solve the sudden-expansion and the die-swell problems in order to improve the accuracy of the solution in the vicinity of the singularity and to speed up the convergence. The method requires minor modifications to standard finite element schemes, and even coarse meshes give more accurate results than refined ordinary finite element meshes. Improved normal stress results for the sudden-expansion problem have been obtained for various Reynolds numbers up to 100 using the singular elements constructed for the creeping flow problem. In addition, the normal stresses at the walls appear to be insensitive to the singularity powers used in the construction of the singular basis functions. The die-swell problem is solved using the singular elements constructed for the stick-slip problem. The singular elements accelerate the convergence of the free surface dramatically.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 123
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 411-428 
    ISSN: 0271-2091
    Schlagwort(e): Proper orthogonal decomposition ; Karhunen-Loève expansion ; Data compression ; Large-scale structure ; Supersonic shear flow ; Flux-corrected transport ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The Karhunen-Loève procedure is applied to the analysis of an ensemble of snapshots obtained from a conditionally sampled localized shear layer simulation. The computed set of optimal basis functions is used to economically characterize sampled flow realizations. Pictorially it is seen that the essential features (and roughly 80% of the energy) of typical flows are captured by retaining roughly 10-20 parameters in the expansion. Smaller-scale features are resolved by retaining more terms in the series.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 124
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 481-517 
    ISSN: 0271-2091
    Schlagwort(e): Spectral methods ; Chebyshev polynomials ; Navier-Stokes equations ; Time-dependent convection ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Pseudospectral methods are used for the computation of the time-dependent convective flows which arise in shallow cavities filled with low-Prandtí-number liquids when submitted to a horizontal temperature gradient. In similar situations several former numerical results have been shown to disagree about the determination of the threshold of oscillations and about the subsequent supercritical regimes. Two different tau-Chebyshev methods based on the vorticity-streamfunction formulation and using multistep time schemes are considered. Their results are discussed to assess the validity of the solutions. The physical problems concern rectangular cavities which involve either a rigid or a stress-free top wall and either conducting or insulating horizontal walls. Aside from the prediction of the onset of oscillations, which is discussed in the various situations with respect to the results of linear and non-linear analyses and to other computational results, the present study exhibits some bifurcation sequences and a hysteresis cycle at moderate Grashof numbers which are associated to the occurrence of multiple solutions.
    Zusätzliches Material: 24 Ill.
    Materialart: Digitale Medien
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  • 125
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 603-606 
    ISSN: 0271-2091
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
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  • 126
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 623-636 
    ISSN: 0271-2091
    Schlagwort(e): Least-squares method ; Optimal control problem ; Conjugate gradient ; Advection-diffusion equation ; Perturbation series ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: In this paper a least-squares formulation associated with a conjugate gradient algorithm is proposed for the solution of transport problems. In this procedure the advection-diffusion equation is first discretized in time using an implicit scheme. At each time step the resulting partial differential equation is replaced by an optimal control problem. This minimization problem involves the minimization of a functional defined via a state equation. This functional is chosen in order to force the numerical solution of the advection-diffusion equation to be equal to the hyperbolic advective part of this equation. The effectiveness of the method is shown through a one-dimensional example involving advective and diffusive transport. No oscillation and high accuracy have been obtained for the entire range of Peclet numbers with a Courant number well in excess of unity.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 127
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 713-721 
    ISSN: 0271-2091
    Schlagwort(e): Boundary node correction ; Pressure smoothing ; Finite element method ; Superconvergence ; Posterior error analysis ; Multiple mesh extrapolation ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Convergence improvement and superconvergence behaviour, obtained by the simple boundary node correction (BNC) procedure for certain stress-like variables of smoothed FEM solutions, are reported in this paper. The effectiveness of BNC is shown through three examples of steady flow problems, and a posterior error analysis based on the multiple-mesh extrapolation technique has been used for estimating the convergence rates.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 128
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 651-681 
    ISSN: 0271-2091
    Schlagwort(e): Porous media ; Two-phase flow ; Oil recovery ; Finite elements ; Preconditioning ; Conjugate gradients ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The equations governing immiscible, incompressible, two-phase, porous media flow are discretized by generalized streamline diffusion Petrov-Galerkin methods in space and by implicit differences in time. Systems of non-linear algebraic equations are solved by Newton-Raphson iteration employing ILU-preconditioned conjugate-gradient-like methods to the non-symmetric matrix system in each iteration. The resulting solution methods are robust, enable complex grids with irregular nodal orderings and allow capillary effects.Several numerical formulations are tested and compared for one-, two- and three-dimensional flow cases, with emphasis on problems involving saturation shocks, heterogeneous media and curved boundaries. For reservoirs consisting of multiple rock types with differing capillary pressure properties, it is shown that traditional Bubnov-Galerkin methods give poor results and the new Petrov-Galerkin formulations are required. Investigations regarding the behaviour of several preconditioned conjugate-gradient-like methods in these type of problems are also reported.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 129
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 791-809 
    ISSN: 0271-2091
    Schlagwort(e): Stokes flow ; Hydrodynamic interactions ; Suspension flows ; Two-phase ; flows ; Boundary element method ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A numerical method for the dynamic simulation of the hydrodynamic interaction among particles in Stokes flow is developed. The method couples the quasi-static Stokes equations for the fluid with the equilibrium equations for the particles. The boundary element method is used to represent the velocity at a general field point in terms of surface velocities and stresses. However, neither the stresses nor the velocities are assumed to be known on the surface of the particles. Kinematic equations relating the linear and angular velocities at the centroids of the particles to the surface velocities are combined with the discretized boundary element equations and the equilibrium equations to generate a system of linear equations. The associated coefficient matrix is correspondent to the grand resistance matrix which relates the velocities of the particles to a given geometry.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 130
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990) 
    ISSN: 0271-2091
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
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  • 131
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 889-905 
    ISSN: 0271-2091
    Schlagwort(e): Computational fluid dynamics ; Parallel computing ; Parallel processing ; Domain decomposition ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A concurrent algorithm for the solution óf the Navier-Stokes equations expressed in curvilinear co-ordinates has been developed for execution on a distributed memory parallel computer. This algorithm offers the ultimate promise of near-supercomputer performance on relatively low-cost parallel computers. The new algorithm is based on an existing serial pressure-correction-based algorithm, and uses domain decomposition to partition the problem onto the processors. The algorithm is demonstrated on an Intel iPSC for a complicated two-dimensional laminar flow problem, for various grid sizes and numbers of processors. Initial results based on straightforward domain decomposition showed that the speed-up per iteration approached 100% parallel efficiency as the grid size was increased, but that the convergence rate of the algorithm deteriorated relative to the original serial algorithm as the number of processors was increased, limiting the speed-up achieved. This degradation in convergence rate was traced to a poorer solution of the pressure correction equation in the concurrent procedure. The addition of a global block correction procedure, implemented via efficient global communications routines, remedied this problem, making the convergence rate of the concurrent procedure equivalent to the serial algorithm. The maximum speed-up achieved with the revised concurrent algorithm was a factor of 12·3 with 16 processors, representing a parallel efficiency of 77%.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 132
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 849-865 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Navier-stokes ; Rotating cylinders ; Viscous dissipation ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A computational study of viscous flow between two eccentrically rotating cylinders is presented in which the effect of viscous dissipation is taken into account. The space discretization is based on piecewise linear finite elements with velocity stabilization, while the method of characteristics is used for time integration. Numerical results illustrate the efficiency of the adopted approach.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 133
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 445-446 
    ISSN: 0271-2091
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
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  • 134
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 453-477 
    ISSN: 0271-2091
    Schlagwort(e): Finite element method ; Lagrangian description ; Velocity correction method ; Sloshing analysis ; Waves in a container ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Two dimensional sloshing analysis has been carried out by the Lagrangian finite element method. For the integration in time, the velocity correction method with the same interpolation functions for velocity and pressure is successfully used. The Lagrangian treatment to pursue the free surface position is presented. The comparison with the experiments shows extremely good agreement. It is shown that the large amplitude sloshing waves in a container can be analyzed by the present method.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 135
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 515-539 
    ISSN: 0271-2091
    Schlagwort(e): Vorticity-streamfunction ; Unsteady incompressible flows ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A review of our solution techniques for the vorticity-streamfunction formulation of two-dimensional incompressible flows is presented. While both the viscous and inviscid cases are considered, the derivation of the proper finite element formulations for multiply connected domains is emphasized. In all formulations associated with the vorticity transport equation, the streamline upwind/Petrov-Galerkin method is used. The adaptive implicit-explicit and grouped element-by-element solution strategies are employed to maximize the computational efficiency. The solutions obtained in all test cases compare well with solutions from previously published investigations. The convergence and benchmark studies performed in this paper show that the solution techniques presented are accurate, reliable and efficient.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 136
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 661-675 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Navier-Stokes ; Velocity-vorticity ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: 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.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 137
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 719-749 
    ISSN: 0271-2091
    Schlagwort(e): Compressible Navier-Stokes ; FEM ; Non-linear solver ; Compatible approximations ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: We discuss in this paper the numerical simulation of compressible viscous flows by a combination of finite element methods for the space approximation, an implicit second-order multistep scheme for the time discretization and GMRES iterative methods for solving the non-linear problems encountered at each time step. Numerical results corresponding to flows around aerofoils and aerospace vehicles illustrate the possibilities of these methods.
    Zusätzliches Material: 38 Ill.
    Materialart: Digitale Medien
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  • 138
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 791-809 
    ISSN: 0271-2091
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Axisymmetric, ideal MHD configurations with steady flow are computed by the finite-element method. Rectangular elements with four to nine nodes are used. The equilibria are obtained in flux co-ordinates by mesh rearrangement. The properties of the linearized motions around an equilibrium state are studied by a normal-mode analysis. Dissipation is taken into account. Applying the Galerkin method leads to a large-scale complex eigenvalue problem Ax = λ Bx, which is solved by inverse iteration and by the Lanczos algorithm.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 139
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 835-847 
    ISSN: 0271-2091
    Schlagwort(e): Higher-order Godunov method ; Mixed finite element method ; Immiscible displacement ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The immiscible displacement problem in reservoir engineering can be formulated as a system of partial differential equations which includes an elliptic pressure-velocity equation and a degenerate parabolic saturation equation. We apply a sequential numerical scheme to this problem where time splitting is used to solve the saturation equation. In this procedure one approximates advection by a higher-order Godunov method and diffusion by a mixed finite element method. Numerical results for this scheme applied to gas-oil centrifuge experiments are given.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 140
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 88-96 
    ISSN: 0192-253X
    Schlagwort(e): Pattern formation ; segmentation ; gap genes ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: L(1)giant is a zygotic lethal mutation which affects the embryonic development of both the labial/thoracic segments and a subset of posterior abdominal segments. Using antibodies specific for proteins encoded by several Drosophila genes to identify the compartmental origin of the defects, we show that the requirement of giant activity is different in these two embryonic domains. Anteriorly, the posterior compartment of the labial segment is missing at the blastoderm stage. Posteriorly, cells are specifically deleted by cell death within the anterior compartments of abdominal segments 5-7 during germ band elongation. In mature embryos, posterior compartment structures of the peripheral nervous system of A5-7 are fused. In addition to a different pattern of defect in the two parts of the embryo, the kind of action appears different. Anteriorly, giant resembles a gap mutation in that a particular region is missing from the blastoderm fate map, whereas in the abdominal domain, giant affects the development of anterior compartment-specific structures.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 141
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 123-123 
    ISSN: 0192-253X
    Schlagwort(e): Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Materialart: Digitale Medien
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  • 142
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990) 
    ISSN: 0192-253X
    Schlagwort(e): Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Materialart: Digitale Medien
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  • 143
    ISSN: 0192-253X
    Schlagwort(e): Heat shock promoters ; HSP70-CAT ; microinjection ; linker-scanner mutations ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Microinjected human HSP70 promoter-chloramphenicol acetyl transferase (CAT) chimeric genes are constitutively expressed immediately after the midblastula transition of Xenopus embryogenesis. Analysis of a series of 5′-deletion mutants in the HSP70 promoter revealed that sequences within 74 bases of the transcriptional start site were sufficient for strong basal activity. We investigated the role of specific sequences in the basal promoter by injecting HSP70-CAT vectors containing linker-scanner mutations in the basal elements (CCAAT, purine-rich element, GC-element, ATF/AP1, and 1ATA). Our data reveal that deletion of any of these cis-acting elements in the basal promoter prevents expression after the midblastula stage of development. Furthermore, we have identified specific binding activities in embryonic nuclear extracts that complex with basal promoter elements (CCAAT, ATF, and GC) of the heterologous HSP70 promoter. These trans-acting factors are detectable in nuclear extracts of early blastula embryos, and their respective binding activity increases dramatically after the midblastula transition. The expression of the human HSP70 gene after the midblastula transition of Xenopus embryogenesis requires an array of cisacting elements, which interact with specific Xenopus transcription factors.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 144
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 110-122 
    ISSN: 0192-253X
    Schlagwort(e): Embryonic cell surface ; glycoconjugates ; monoclonal antibodies ; developmental expression of glycoconjugates ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Molecular markers for specific cell lineages would be useful in studies of cellular differentiation. To isolate such markers monoclonal antibodies (MoABs) were raised against plasma membranes isolated from gastrulating Xenopus embryos. Those antibodies that recognized subsets of cells within the embryo were selected by indirect immunofluorescence. The analysis of eight such MoAbs is presented. Western blot analysis showed that all but one MoAb recognized a complex pattern of glycoconjugates associated with glycoproteins. All the antigens recognized by the MoAbs were maternal in origin and displayed similar spatial patterns of pregastrular expression. This pattern of immunoreactivity at the apical surface was inherited passively during cleavage by the resulting superficial blastomeres suggesting that ectodermal specific markers of maternal origin are pre-localized to the cortical ooplasm in mature oocytes. We suggest that these maternal components may be specific glycosyl transferases. Three different patterns of expression were observed during gastrulation as exemplified by MoAbs 1F10C1, 3A4D1, and 6F10B6. MoAb 6F10B6 was specific for both neural and non-neural epithelium. MoAb 3A4D1 was specific for non-neural epidermis. MoAb 1F10C1 appeared to recognize a protein epitope on an extracellular component expressed by the superificial and involuting epithelial cells. The pattern of expression for the 1F10C1 antigen suggests that it may play a role in facilitating the movement of the involuting cells during gastrulation.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 145
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 125-132 
    ISSN: 0192-253X
    Schlagwort(e): Flow cytometry ; polytenization ; C value ; fluorescence ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Multiparametric flow cytometry was used to analyze the development of the endosperm in Zea mays L. during the period from 8 to 20 days after pollination (dap). Nuclear size, DNA content per nucleus, and frequencies of nuclei with varying properties were measured in preparations that included all of the endosperm nuclei of single kernels of the inbred strain Al88. Characteristics of nuclear populations from different kernels on the same ear showed minimal variation. The dynamic changes of non-mitotic cells involved in endosperm development consisted of alternating periods of DNA replication with non-replication. Seven rounds of DNA replication had occurred in some nuclei in the later developmental stages with the rate averaging approximately one round per 24-hour period. Analysis of the DNA levels in the nuclei showed an exact doubling pattern indicating an endoreduplication process, that is, replication of the entire genome during each round. The loosely organized polytenization of the chromatin occurred to varying extents among the nuclei within an endosperm. A weak positive correlation existed between DNA content and size of nuclei suggesting that DNA increases and nuclear growth may not be highly coordinated in this tissue. Increased proportions of the larger nuclei occurred in the later stages of endosperm development. Considering the entire endosperm, the average DNA content per nucleus at the 15-dap peak level was approximately 12.8 C constituting a 2.7-fold overall increase from 8 dap.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 146
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 176-181 
    ISSN: 0192-253X
    Schlagwort(e): Direct gene transfer ; transgenic plants ; expression of transgenes ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Direct gene transfer to protoplasts is one of several methods developed for the production of transgenic plants. This method utilizes the efficient uptake of DNA from the surrounding medium by protoplasts (cell wall-less plant cells). Where a suitable protoplast system exists large numbers of transformant clones can be efficiently produced and often regenerated to normal fertile plants. This review concentrates on the fate of the DNA which is taken up into the protoplasts. Particular emphasis is given to the factors which can influence the integration and form of the transferred DNA, the expression of transferred genes, and the inheritance in further generations of those genes. The information available suggests (1) that DNA is taken up by a large proportion of the cells in a transformation mixture, (2) that this DNA forms complexes sometimes involving carrier DNA, (3) that fewer cells actually take up DNA into the nucleus, and (4) that the complex may be rearranged and/or amplified and then integrated into the genome. If the DNA is arranged in such a way that a gene can be expressed it does so in a normal manner and is stably inherited both mitotically and meiotically.
    Materialart: Digitale Medien
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  • 147
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 197-204 
    ISSN: 0192-253X
    Schlagwort(e): Light-regulated genes ; transgenic plants ; enhancer ; silencer ; regulatory elements ; trans-acting factors ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Transgenic plants have been particularly useful in studying nuclear genes encoding for photosynthetic functions. The expression of these genes and their chimeric constructs in transgenic plants faithfully mimics their natural counterparts. The use of sensitive chimeric reporter genes has enabled localizing the activity of genes encoding photosynthetic proteins to individual cells. Cab and rbcS transgenes have been shown to retain sensitivity to light quality, which is modulated by phytochrome. Conditional light activation under the influence of a circadian rhythm has been shown for Cab transgenes. Transgenic plants containing truncated promoters have helped delineate cis-regulatory positive and negative elements involved in light-mediated transcriptional induction and tissue specificity.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 148
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 182-196 
    ISSN: 0192-253X
    Schlagwort(e): nodulins ; leghemoglobin ; glutamine synthetase ; Enod2 ; cis-acting elements ; transacting factors ; Agrobacterium turnefaciens ; A. rhizogenes ; binary vectors ; plant transformation ; chimeric genes ; chloramphenicol acetyltransferase ; glucuronidase ; cytokinin induction ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Nodulin genes are plant genes specifically activated during the formation of nitrogen-fixing nodules on leguminous plants. These genes are interesting to study since they are not only induced in a specific developmental fashion by signals coming directly or indirectly from the rhizobial symbiont, but are also expressed in a tissue-specific manner. By examining the expression of chimeric nodulin-reporter genes in transgenic legume plants it has been shown that nodule specific expression is mediated by DNA sequences present in the 5′upstream region of several nodulin genes. Here we summarize the available data on these cis-acting elements and the trans-acting factors interacting with them. We also review experiments designed to identify rhizobial “signals” which may play a role in nodule specific gene expression.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 149
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 205-213 
    ISSN: 0192-253X
    Schlagwort(e): cauliflower mosaic virus 35S RNA ; cell cycle gene expression ; cis-acting element ; wheat histone H3 gene ; trnas-acting factor ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: A majority of histone genes are expressed in the S phase during the cell cycle. Using the gene expression system of transformed sunflower cells into which wheat histone H3 gene was introduced by the Ti-plasmid gene transfer technique, we determined three cis-acting control sequences (hexameric, octameric, and nonameric motifs) which seemed to confer the S-phase-specific transcription of wheat histone genes. Furthermore, as candidates for regulatory transcription factors, three nuclear DNA-binding proteins HBP-la, HBP-lb, and HBP-2 that interact with the hexameric and nonameric motifs were identified. The structural analysis of the cDNA of HBP-la revealed that a nuclear protein has the leucine-zipper structure and a DNA-binding motif. The hexameric motif in the H3 gene was also seen in cauliflower mosaic virus 35S (CaMV 35S) promoter and shown to function as a regulatory element of this promoter. The wheat HBP-1b can interact with the hexameric motif of the CaMV 35S promoter. Much attention has been paid to the significance of the hexameric sequences within the H3 and CaMV 35S promoters and the DNA-binding proteins HBP-la and HBP-lb.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 150
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990) 
    ISSN: 0192-253X
    Schlagwort(e): Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 151
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 224-232 
    ISSN: 0192-253X
    Schlagwort(e): lux ; luc reporter genes ; light emission ; gene expression ; single photon imaging in vivo ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Genes encoding light-emitting luciferase were recently isolated from luminous marine bacteria and fireflies. Expression of luciferase genes in diverse organisms is a unique way for studying gene expression by simple and sensitive measurement of light. Recent advances in application of luciferase reporter genes are reviewed and documented by examples of in vivo visualization of their expression in transgenic plants.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 152
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 214-223 
    ISSN: 0192-253X
    Schlagwort(e): Gene interactions ; cytosine methylation ; epigenetic variation ; transgenic plants ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Unusual gene interactions were observed in several doubly transformed tobacco plants which were obtained following sequential transformation steps using two T-DNAs encoding different selection and screening markers. The expression of T-DNA-I, which encoded kanamycin resistance (Kanr) and nopaline synthase (NOS), was suppressed in some, but not all, of the double transformants after the introduction of T-DNA-II, which encoded hygromycin resistance (Hygr) and octopine synthase (OCS). Double transformants in which T-DNA-I had been inactivated could produce KanrNOS+ progeny, but these were shown to lack T-DNA-II, thus establishing the role of this T-DNA in the suppression of T-DNA-I. Reversible cytosine methylation of the promoters of T-DNA-I genes was shown to correlate with their activation/inactivation cycle. In this paper we pursue further the questions of the mechanism of suppression of T-DNA-I genes by T-DNA-II, and also the timing and extent of demethylation of T-DNA-I promoters in Kanr progeny following the loss of T-DNA-II. We propose that the suppression is due to the competition between homologous regions on each T-DNA for binding to nuclear sites with fixed locations. We further suggest that incomplete demethylation patterns of T-DNA-I promoters in Kanr progeny reflect the existence in the shoot apex meristem of two cell populations, which have either methylated or unmethylated T-DNA-I promoters, respectively. Thus, Kanr progeny are epigenetic chimeras with respect to the expression of T-DNA-I genes.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 153
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 233-247 
    ISSN: 0192-253X
    Schlagwort(e): Chromatin structure ; foreign gene expression ; transgenic plants ; Nicotiana tabacum ; position effect ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The chromatin structure of foreign genes in transgenic tobacco plants was investigated by digestion of nuclei with DNase I and micrococcal nuclease, respectively, followed by restriction and Southern analysis of the digestion products. The results were compared to the differential expression of the different transgenes. Two model systems were used: plants harbouring vector DNA derived from the disarmed vector pGV 3850 and plants harbouring the light-regulated and organ-specifically expressed potato ST-LS1 gene and the cotransferred ncpaline synthase (nos) reporter gene. Our results show that transferred genes are located in DNase l-sensitive domains in all transformants. Slight variations of DNase l-sensitivity of the transferred ST-LS1 constructs in different transformants neither reflected the between-transformant variability of expression nor the organ-specific activity of the transgenes. A deletion event was found responsible for silencing the ST-LS1 gene but not the nos gene in one of the transformants. Whereas no DNase l-hypersensitive sites were found within the 3850-T-DNA and the ST-LS1 gene, one prominent site was mapped to the nos promoter within the ST-LS1 construct in all transformants. Digestion of chromatin harbouring 3850-T-DNA with micrococcal nuclease resulted in a blurred nucleosomal pattern as compared to nucleolar and bulk chromatin, the extent of blurring being independent of the expression of transferred genes. The present results favour the “permissive domain” hypothesis which capitalizes on the chromatin surrounding the integration site as the determining factor for the chromatin structure of incoming alien genes. However, between-transformant variability of expression is not reflected by differential sensitivity to DNase I. Hence, other factors than chromatin structure must be involved in creating “position effects”.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 154
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 249-253 
    ISSN: 0192-253X
    Schlagwort(e): Drosophila ; embryonic development ; sex differentiation ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: We report the first practical application of a genetic scheme devised for the purpose of obtaining large quantities of embryos of a specific sex. The scheme, which is based on the meiotic drive system Segregation Distorter, results in the production of populations of zygotes that are almost exclusively of one sex. We have used this scheme to determine that the steady-state levels of transcripts of X-linked genes are the same in early male and female embryos, establishing that these genes are dosage compensated.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 155
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 263-269 
    ISSN: 0192-253X
    Schlagwort(e): Penetrance ; reciprocal effects ; suppressor genes ; developmental cycle in mammals ; initialization ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The phenomenon of gametic imprinting in mammals has raised developmentally relevant questions concerning the manifestation and inheritance of genes with variable penetrance. The dominant fused (Fu) gene located on chromosome 17 is one of the few good cases demonstrating the phenomenon in mice. The Fu mutation has a maternal effect.We have previously shown that the † 12 haplotype significantly lowers the penetrance of Fuin ♀ ♀ Fu/†12 offspring. Results of recipiocal matings of the heterozygotes for Fu indicated that the Fu of maternal origin has a lowered level of penetrance. The dominant suppressors locotad outside chromosome 17, in contrast to †12 residing in it, had stronger effects on the manifestation of Fu, decreasing its penetrance to 8-17%. Experimental evidence is presented that the pathway via which Fu passes to the zygote nucleus during gametogenesis through successive generations has a marked effect on its penetrance. Based on this evidence, patterns of genetic imprinting are described. A survey of genetic imprinting allowed us to distinguish two developmental phases, gametic and zygotic. The hypothesis for the gametic phase of the development of multicellular organisms suggests that it proceeds from initialization, a process thought to ensure the freeing of chromosomes from redundant epigenetic information and their preparation for the consecutive developmental cycle.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 156
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 318-325 
    ISSN: 0192-253X
    Schlagwort(e): Mice ; housekeeping genes ; liver ; tissue specificity ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: In situ hybridization using nucleic acid probes was used to detect cell- and tissue-specific transcript(s) of embryonic genes during development and differentiation. This highly sensitive technique has the potential to provide valuable information on the regulation of low-abundance housekeeping genes during development. We have determined the experimental conditions required to detect the catalase message in adult mouse liver. Catalase effects the breakdown of H2O2 to O2 and H2O and offers protection against the toxic effects of oxygen radicals. We used a cloned 550 bp BamHI-Pstl fragment from a mouse catalase cDNA (pMCT-1) to generate 35S-labeled sense and antisense riboprobes. The experimental conditions used were sensitive enough to quantitate the abundance of silver grains generated by the antisense riboprobe on the adult liver, a tissue known to be positive for this message. The hybridization protocol was applied to serial sections of 13- and 18-day-old mouse embryos. The results suggest that the catalase expression in the liver and brain begins with somite formation and increases with development and differentiation. On the other hand, this message appears to be absent in mesenchyme, particularly in day 13 embryos. The message in positive tissues appears evenly distributed throughout the cell. The observed expression of the catalase message in the adult liver is approximately six times that in the embryonic liver. It is compatible with the enzyme activity results and emphasizes the sensitivity of the in situ hybridization method (over northern blot, etc.) used in this study.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 157
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 328-332 
    ISSN: 0192-253X
    Schlagwort(e): Cellular slime molds ; cytoskeleton ; actin-binding proteins ; review ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The cellular slime mold Dictyostelium discoideum is becoming the premier system for the explication of the biochemical and cellular events that occur during motile processes. Proteins associated with the actin cytoskeleton, in particular, appear to play key roles in cellular responses to many external stimuli. This review summarizes our present understanding of the actin-associated proteins in Dictyostelium, including their in vitro activities and their structural and/or functional analogues in mammalian cells.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 158
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 333-340 
    ISSN: 0192-253X
    Schlagwort(e): Dictyostelium discoideum ; actin ; ABP-120 ; elongation factor 1 alphc ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: In this work we evaluate the cartical expansion model for amoeboid chemo-taxis with regard to new information about molecular events in the cytoskeleton following chemo-tactic stimulation of Dictyostelium amoebae. A rapid upshift in the concentration of chemoattrac-tant can be used to synchronize the motile behavior of a large population of cells. This synchrony presents an opportunity to study the biochemical basis of morphological changes such as pseudopod extension that are required for amoeboid chemotaxis. Changes in the composition and activity of the cytoskeleton following stimulation can be measured with precision and correlated with important morphological changes. Such studies demonstrate that activation of actin nucleation is one of the first and most crucial events in the actin cytoskeleton following stimulation. This activation is followed by incorporation of specific actin cross-linking proteins into the cytoskeleton, which are implicated in the extension of pseudopods and filopods. These results, as well as those from studies with mutants deficient in myosin, indicate that cortical expansion, driven by focal actin polymerization, cross-linking and gel osmotic swelling, is an important force for pseudopod extension.It is concluded that whereas three forces, frontal sliding, tail contraction, and cortical expansion may cooperate to produce amoeboid movement, the cortical expansion model offers the simplest explanation of how focal stimulation with a chemoat-tractant causes polarized pseudopod extension.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 159
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 362-368 
    ISSN: 0192-253X
    Schlagwort(e): Dictyostelium ; filopodia ; actin binding proteins ; calcium ; cell motility ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The Dictyostelium discoideum 30,000 dalton actin-binding protein is an actin cross-linking protein that organizes formation of parallel bundles of actin filaments in vitro, and is present in filopodia in living cells. This protein binds calcium directly and exhibits a decreased affinity for actin filaments in the presence of micromolar calcium. In this work, the existence of antigenic homologs of the 30,000 dalton protein in Physarum polycephalum, Schistosoma mansoni, Chara carolina, and Drosophila melanogaster is detected by use of affinity purified antibody and electrophoretic blotting methods. The expression of this protein during development of Dictyostelium is also analyzed, revealing a progressive 3-fold decrease in the level of this protein in amoebae between the vegetative and slug stages. A highly ordered structure of bundles of actin and the 30,000 dalton protein formed in vitro is inferred from the presence of transverse striations on the bundles with a minor periodicity at 11.4 nm and a major periodicity at 33.9 nm. Finally, we propose a working model of the interaction of this actin cross-linking protein with actin filaments to form bundles.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 160
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 369-376 
    ISSN: 0192-253X
    Schlagwort(e): Cytoskeleton ; capping proteins ; genamic structure ; Dictyostelium ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The two subunits of the het-erodimeric protein cop32/34, an actin-binding protein, are encoded by separate single-copy genes. We have established the genomic structure of both genes. A sequence comparison of cap32/34 with capZ from chicken skeletal muscle and two partially known sequences from Saccharomyces cerevisiae and Xenopus laevis show that heterodimeric capping proteins belong to a highly conserved group of actin-binding proteins. This conclusion is supported by the cross-reaction of polyclonal antibodies against cap32 and cap34 with proteins from lower and higher eukaryotes. In addition, a system is presented that allows the expression of truncated cap34 polypeptides under the control of the cap34 promoter.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 161
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 388-390 
    ISSN: 0192-253X
    Schlagwort(e): Transformation ; electroporotion ; gene targetting ; antisense RNA ; complementation ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: DNA mediated transformation is a critical technique for uniting genetic, molecular genetic and reverse genetic approaches to a wide range of problems in cell and molecular biology. In Dictyostelium, there is now the capability not only to manipulate DNA sequences in vitro and put them back into the cell, but also to alter the sequences of endogenous chromosomal genes through high frequency homologous recombination. This means that the range of gene manipulation techniques that have made yeast such a useful system should now be applicable in Dictyostelium. For studying problems such as cellular motility, morphogenesis, and gene regulation, few organisms have the combination of features offered by Dictyostelium.
    Materialart: Digitale Medien
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  • 162
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 391-395 
    ISSN: 0192-253X
    Schlagwort(e): Lipofectin ; slime mould ; transformation ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: We have studied the transient expression, in Dictyostelium cells growing on a bacterial food source, of a construct containing the coding region of the firefly luciferase gene inserted downstream of a Dictyosteliumactin promoter. The fusion gene is not detectably expressed when DNA is introduced by calcium phosphate precipitation or by electroporation, but it is expressed when introduced using cationic liposomes (lipofectin). Using this latter procedure, we are able to transform cells with a G418 resistance vector and select stable, drug-resistant transformants at a relatively low, but workable, efficiency. This technique will allow molecular genetics to be applied to the many important nonaxenic Dictyostelium strains.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 163
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 377-387 
    ISSN: 0192-253X
    Schlagwort(e): Cell-cell ; adhesion molecule ; cell binding site ; cell aggregation ; development ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: During development of Dictyostelium discoideum, cells acquire EDTA-resistant cell-cell adhesion at the aggregation stage. The EDTA-resistant cell binding activity is associated with a cell surface glycoprotein of Mr 80,000 (gp80), which mediates cell-cell binding via ho-mophilic interaction. Analysis of the structure of gp80 deduced from cDNA sequence reveals the presence of three internally homologous segments in the NH2-terminal domain, which also contains regions with homology to the neural cell adhesion molecule. Secondary structure predictions show an abundance of β-structures and very few α-helices. This is confirmed by circular dichroism measurements. It is likely that the homologous segments are organized into globular structures, extended from the cell surface by a Pro-rich stalk domain. The cell binding activity of gp80 resides within the first globular repeat of the NH2-terminal domain and has been mapped to a 51 amino acid region between Val123 and Leu 173. Synthetic oligopeptides corresponding to sequences within this region have been prepared and assayed for their ability to bind to cell surface gp80. Results lead to identification of the homophilic binding site to an octapeptide sequence within this region. Synthetic peptides containing this octapeptide sequence and univalent antibodies directed against this site block the formation of organized cell streams during aggregation. Although cell aggregates are eventually formed, most fail to undergo further development to give rise to slugs and fruiting bodies, indicating that cell-cell adhesion involving gp80 is an important step in normal morphogenesis.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 164
    ISSN: 0192-253X
    Schlagwort(e): Transformation ; Dictyostelium discoideum ; UMP-synthase/ura-complementation ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Whereas transformation ofDictyostelium discoideum now can be done routinely and reliably, there is increasing demand for a system that allows selection of cells that have gone through repeated transformation cycles. Such a system is presented here. Selection is based on resistance to 5-fluoro-orotic-acid (5-FOA). D. discoi-deum is highly sensitive to this drug, and cells can survive only in the presence of 5-FOA if they carry a defective UMP-synthase gene. After transformation with a plasmid carrying a cloned version of the UMP-synthase gene, 5-FOA resistant cells are obtained at high frequency. Because 5-FOA-resistant cells depend on exogenously added uracil, these cells can be taken through a second round of transformation. A plasmid-borne UMP-synthase gene renders 5-FOA-resistant cells phenotypically ura +. Finally, cells can be further transformed using the standard G418 selection system.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 165
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 425-426 
    ISSN: 0192-253X
    Schlagwort(e): Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Materialart: Digitale Medien
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  • 166
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 403-409 
    ISSN: 0192-253X
    Schlagwort(e): Electroporation ; soft-agarose ; G418 ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: A new method for clonal growth of Dictyostlium axenic amoebae has been developed. Cells are plated in growth medium containing 1% ultra-low gelling temperature agarose. Cells grow normally in the agarose and form colonies up to several millimeters in diameter. When the colonies have grown to a sufficient size, they begin multicellular development. Pseudoplasmodia are formed, migrate to the surface of the agar, and then undergo fruiting body formation. Cells can be removed from the soft agarose colonies with a toothpick or by picking spores from the fruiting bodies. This method should be useful for drug, auxotrophic, and temperature selections where clonal maintenance of axenic colonies is important.This method has been used in combination with a selection for resistance to G418 to isolate independent colonies following DNA-mediated transformation. Several parameters in the calcium phosphate and electroporation transformation protocols have been optimized and the transformation frequency qualified. Independent transformed colonies are obtained at a frequency of 1 in 104 to 1 in 105 cells when integrating plasmids are introduced using calcium phosphate coprecipitation. The frequency is about tenfold higher when extrachromosomal shuttle vectors are introduced into cells.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 167
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 410-417 
    ISSN: 0192-253X
    Schlagwort(e): Suppressor †RNA genes ; yeast ; lacZ expression in D. discoideum ; †RNATrp genes ; †RNAGlu genes ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: We describe the generation of Dictyostelium discoideum cell lines that carry different suppressor †RNA genes. These genes were constructed by primer-directed mutagenesis changing a †RNATrp(CCA) gene from D. discoideum to a †RNATrp(amber) gene and changing a †RNAGlu(UUC) gene from D. discoideum to a †RNAGlu(ochre) as well as a †RNAGlu(amber) gene. These genes were stably integrated into the D. discoideum genome together with a reporter gene. An actin 6::lacZ gene fusion carrying corresponding translational stop signals served as a reported. Active β-galactosidase is expressed only in D. discoideum strains that contain, in addition to the reporter, a functional suppressor †RNA. Both amber suppressors are active in D. discoideum without interfering significantly with cell growth and development. We failed, however, to establish cell lines containing a functional †RNAGlu(ochre) suppressor. This may be due to the fact that nearly every message from D. discoideum known so far terminates with UAA. Therefore a †RNA capable of reading this termination codon may not be compatible with cell growth.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 168
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 418-424 
    ISSN: 0192-253X
    Schlagwort(e): Transcription ; development ; cAMP ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Genetic studies have revealed a network of three unlinked regulatory genes that control the developmental expression of the family of endogenous lectins in Dictyostelium discoideum. Mutations in the disA and disB loci have a null phenotype and do not express the discoidin I or II lectins. The third mutation, drsA, is a second-site suppressor of the disB mutation, which restores expression of all lectin species. Cells carrying this mutation express the discoidin lectins during growth, which is in contrast to wild-type cells in which lectin synthesis is developmentally regulated. In addition to this basic level of genetic control, the conditions of growth dramatically influence the patterns of discoidin expression. Growth-phase wild-type cells do not express lectin if the cells are grown on plates in association with bacteria. However, wild-type cells growing in bacterial suspensions express high levels of lectin during growth. Synthesis of the discoidin lectins in growing cells is sensitive to the levels of extracellular cyclic adenosine monophosphate (cAMP) and folic acid. These results suggest that the drsA mutation renders cells insensitive to cAMP and/or folate and thus allows expression of lectin during growth.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 169
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 439-441 
    ISSN: 0192-253X
    Schlagwort(e): Cellular slime molds ; timing of differentiation ; differentiation ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Vital dyes have been extensively used in many laboratories to distinguish the prestalk and prespore zones of a migrating slug in Dictyostelium discoideum. Here we present evidence that the two zones do not form immediately following aggregation, as is sometimes assumed, but only after 1-4.5 hr of migration. When the transition to the two-toned state occurs, it changes very quickly, in a matter of approximately 10 min. Furthermore, it can be rapidly induced by submerging the slug in mineral oil. The time of appearance of the zones is correlated with previously reported changes in the distribution of cyclic AMP secretion and with changes in regulation properties along the axis of the slug.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 170
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 442-446 
    ISSN: 0192-253X
    Schlagwort(e): Prestalk cells ; prespore cells ; slugs ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Ammonia appears to be an important regulatory signal for several aspects of the Dictyostelium life cycle. The postulated role of ammonia in the determination of the prespore pathway in cells of the slug stage has led us to examine the effect of ammonia on the prestalk/prespore ratio of migrating slugs. In the presence of 10-3 M ammonium chloride, the volume of the prestalk region decreases by 40.8%. The kinetics of the process make it unlikely that this is due to a shift in the differentiation pathway. A test of the hypothesis that the decrease in volume of the prestalk region is due to the conversion of prestalk cells to anterior-like cells shows that the percent of anterior-like cells in the posterior region increases by the amount predicted by the hypothesis. This suggests that ammonia may be the molecular signal, produced by the tip, that prevents anterior-like cells from chemotactically migrating to the tip and thereby becoming anterior cells. The effect of enzymatic removal of ammonia from vitally stained migrating slugs is the appearance of a series of dark stripes beginning at the posterior end and progressing forward. We interpret this as a result of progressive removal of anterior-like cells from tip dominance and essentially as the formation of new potential tips. Indeed, in a few cases one or even two of the stripes separate from the posterior of the cell mass and form small fruiting bodies. We consider the phenomenon of stripe formation further evidence that the tip acts on anterior-like cells through ammonia.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 171
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 427-438 
    ISSN: 0192-253X
    Schlagwort(e): Cellular slime molds ; patterning ; development ; immunoblotting ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: A series of monoclonal antibodies were previously raised against developing Polysphondylium pallidum cells. In this work, six of these antibodies have been used as probes to identify and characterize antigens regulated during development. Soluble and membrane fractions of P. pallidum cells at six stages of development or three stages of cyclic adenosine monophosphate (cAMP)-induced development were run in sodium dodecyl sulfate (SDS)-polyacrylamide gels and subjected to Western blot analysis. Three of the monoclonals, anti-Tp200, anti-Tp423, and antiPg 101, stain sorogen tips. Tp423 and Tp200 are membrane-associated antigens; both are stable to urea extraction, and Tp200 remains in the membrane after NaOH extraction. Tp423 is present in starved cells but is more prominent in sorogens and particularly in cAMP-developed cells. In contrast, Tp200 is first detected in early to mid-aggregation and is more abundant late in development. Pg101, which is expressed as a gradient with its highest concentration in tips, first appears in tight aggregates but is much more abundant in sorogens; unlike the Tp antigens, Pg101 is not greatly induced in cAMP-developed cells. All three of these antigens undergo changes in apparent molecular weight at the tight aggregate or sorogen stage: The gel mobilities of Tp200 and Pg101 increase, whereas that of Tp423 decreases. In addition to the tip-specific monoclonals, two monoclonals that stain all but the tips of sorogens have been used for analysis. One of these, anti-3D 10Pnk stains most cells within secondary tips, whereas anti-3D 10Dif does not. 3D 10Dif is membrane associated; it is present very early in development, increasing two- to threefold through the sorogen stage and diminishing in late cAMP-developed cells. 3D 10Pnk is a mostly soluble species first detected in late streaming. Anti-1c3, a sixth monoclonal, which stains nuclei uniformly throughout sorogens, is also developmentally expressed. 1c3 is mainly membrane associated and is expressed from late streaming through the sorogen stage.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 172
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 453-453 
    ISSN: 0192-253X
    Schlagwort(e): Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Materialart: Digitale Medien
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  • 173
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 11 (1990), S. 447-452 
    ISSN: 0192-253X
    Schlagwort(e): Pattern regulation ; cell sorting ; transplantation ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: In classical transplantation experiments, we have attempted to distinguish between cell sorting and position-dependent mechanisms of pattern formation during the regulation of amputated prespore regions of Dictyostelium slugs. Host and transplanted tissue were distinguished by prior labelling with 14C and 3H, and their distributions in the manipulated slugs were determined by double-label scintillation counting of serial sections of the slugs. First, we showed that the regenerated prestalk region is formed predominantly from the anterior of a prespore isolate. This disproves extreme cell sorting models, which hold that the new prestalk cells arise at random in the prespore mass, before sorting to the prestalk zone. Second, we showed that a proportion of posterior cells, which are not normally recruited into the new prestalk region, can be recruited into it if they are transplanted into the anterior of the prespore isolate. Recruitment of these cells occurs only during the first hour of regulation. We believe that these experiments prove a position-dependent mechanism of pattern formation during slug regulation. This in turn implies the existence of localized inductive signals in the regulating fragments. Although cell sorting occurs efficiently when cells are misplaced in the slug, it does not appear to play a major role in reforming the prestalk/prespore pattern.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 174
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 123-139 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: In this paper there is presented an alternative numerical procedure for obtaining approximations to non-linear conservation laws like those that describe the dynamical behaviour of elastic rods (composed of materials whose stress-strain relation is non-linear). The above-mentioned procedure consists of approximating the solution of the Riemann problem (associated with the considered conservation law) by a piecewise constant function (satisfying the jump conditions) and using Glimm's scheme for advancing in time, step by step. The proposed numerical approach eliminates the necessity of solving (in a complete way) the associated Riemann problem, easing and cheapening its computational implementation. This procedure is employed for simulating the dynamical response of an elastic-non-linear rod, fixed at its edges, that is left in a non-equilibrium state. There is presented a comparison between results obtained through a classical procedure and through the procedure proposed in this work.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 175
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Thermal stresses developed in a dendritic silicon crystal ribbon have been shown to cause plastic deformation and residual stresses in the ribbon. This paper presents an implementation of a numerical model proposed for thermo-elasto-plastic behaviour of a material. The model has been used to study the effects of plasticity of silicon on the residual stresses. The material properties required to implement this model are all assumed, and the response of the material to the variations in these assumed parameters of the constitutive law and in the finite element mesh is investigated. The steady state growth process is observed to be periodic with non-zero residual stresses. Numerical difficulties are also encountered in the computer solution process, resulting in sharp jumps and large oscillations in the stress responses.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 176
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990) 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Materialart: Digitale Medien
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  • 177
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 275-290 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A new higher order explicit one step scheme is presented for use in the solution of a certain class of non-linear problems in structural dynamics. The generalized scheme covers some recently developed multistep algorithms as well as some new one step methods with improved numerical properties. A weighted residual approach is used which contains new aspects for design of single step algorithms. Accuracy and stability are investigated for linear and non-linear systems. Algorithms with higher accurary than the central difference method are developed and optimized to minimize the reduction in the stability limit.
    Zusätzliches Material: 2 Tab.
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  • 178
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 315-336 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Algorithms based upon the notion of return mapping have been developed for the Hill yield function of anisotropic plasticity. The relative accuracy of two algorithms is assessed by means of iso-error maps. The choice of the algorithm turns out to be much more critical for the orthotropic Hill criterion than for the underlying isotropic von Mises plasticity model. A tangent operator that is consistent with the developed integration algorithm is formulated and its efficiency is assessed compared with the classical continuum tangent operator. The model has been applied to three shell/plate structures.
    Zusätzliches Material: 17 Ill.
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  • 179
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 371-390 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A direct Boundary Element formulation and its numerical implementation for inelastic transient dynamic analysis of three-dimensional solids is presented. The formulation is based on an initial stress approach and is the first ever of its kind in the field of the Boundary Element Method. This formulation employs the Navier-Cauchy equation of motion, Graffi's dynamic reciprocal theorem, Stokes' fundamental solution and the Divergence theorem, together with Kinematical and Constitutive equations to obtain the pertinent integral equations of the problem in the time domain within the context of small displacement theory of elastoplasticity. The boundary integral equations are cast in an incremental form, in which elastoplastic relations of the incremental type are used for the material description. These equations are then solved using a time-stepping algorithm in conjunction with an iterative solution scheme to satisfy the constitutive relations. Higher order shape functions are used to approximate the field quantities in space as well as in time. Finally, the applicability of this methodology is demonstrated by presenting a few example problems.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 180
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: This paper presents a flexible approach to domain decomposition preconditioning for problems expressed in terms of local stiffness matrices of subdomains. Evaluation of the preconditioner requires fully parallelizable local computations and the solution of a global auxiliary problem with few variables per subdomain. Convergence factors can be bounded using properties of the local stiffness matrices only. The method is applied to the p-version finite element method for three-dimensional elasticity. We treat each element as a subdomain and compute explicit convergence bounds.
    Zusätzliches Material: 5 Tab.
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  • 181
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 1177-1192 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: An embedding method is considered for the numerical determination of the cathode shape for a given anode shape in a two-dimensional electrolytic cell. Reference is made to an analytic solution to illustrate the difficulties which have to be overcome by any numerical method applied to this ill-posed problem. The embedding method searches amongst the direct solutions (i.e. anodes for given cathodes) since these, resulting from a well-posed problem, are less troublesome to compute. For anodes of the form βG(x), x the transverse direction, the embedding method gives good results for β less than 30-60 percent of the β for which the cathode first contains cusps or becomes triple-valued. It is shown that the embedding method performs better than some other numerical methods in overcoming the error growth difficulties associated with the illposedness of the problem.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 182
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 1421-1440 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: In this paper, a new formulation for two-dimensional time-domain transient elastodynamic analysis by the Boundary Element Method (BEM) is presented. The traction kernel is derived by using the causality of the waves and the resulting kernel is explicit and much simpler than the ones that have appeared in the recent literature. An appropriate set of linear time interpolation functions together with quadratic spatial variations are incorporated. Moreover, the algorithm has a capability of handling problems with multiply connected regions. All of these advanced features have resulted in an efficient formulation capable of producing very accurate results and represent significant improvements over the present level of sophistication in this area. This above algorithm is now a part of the general purpose BEM code known as GPBEST.
    Zusätzliches Material: 9 Ill.
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  • 183
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 1455-1471 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: The axisymmetric behaviour of geometrically non-linear elastic shells of revolution with finite rotations is discussed. In contrast to the approach of Reissner and to standard classical shell theories a new straightforward strategy is derived for the formulation of fully non-linear strain measures in the axisymmetric case. Within this approach the computation of the deformed director vector d is a main assumption which is essential to describe the fully non-linear bending behaviour. A Total Lagrangian Description is chosen to represent the large displacements. As an illustrative example the finite element formulation for a simple two-node conical element is given. A consistent linearization of the weak form leads to a quadratically convergence behaviour. The discussed shell examples under proportional loading show the good performance of the derived finite element formulation.
    Zusätzliches Material: 9 Ill.
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  • 184
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 1527-1537 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: In this paper we present a method for numerically solving the Schrödinger equation for the problem of electron transmission through a quantum device defined on a two-dimensional domain. An important aspect of our formulation is the treatment of the boundary conditions at the contact-device interfaces, allowing the problem to be discretized on the device domain only. With the FEM aproach that we employ, the nature of the potential field does not effect the computational expense (for smoothly varying fields). We examine a sample problem of a symmetric cavity in a wave-guide structure.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 185
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990) 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 186
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 1653-1679 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: In a realistic analysis of thin-walled steel frames the warping of beam-columns of open cross-section must be considered. To model the behaviour of these structures up to collapse load, the plasticity of the material also has to be included in the analysis. This work presents the derivation of a new finite element for three-dimensional non-linear analysis of steel frames with bi-symmetrical cross-sections that models warping and elastic-plasticity. The displacement field is described by the Principle of Sectorial Areas and is modelled with Hermitian functions. For the material non-linearity the Incremental Plasticity Theory in a concentrated plasticity model has been used. The yield surfaces based on the natural stress resultants which include torsion and bimoment are used in the formulation of the element. The matrices of the proposed element are derived explicitly and implemented in a computer program which uses the Natural Approach. The implemented stress recovery process is insensitive to rigid-body motions. The accuracy of the finite element and the efficiency of the implementation are illustrated through examples.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 187
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 223-244 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A quantitative method of a posteriori error estimation based on finite element solutions is developed. The proposed method can estimate the error of solutions obtained by the finite element method for two-dimensional elastic problems with 4-node elements. Since the error is estimated element by element, the proposed method does not require a large memory or long computing time. Not only rectangular elements but also arbitrarily shaped 4-node elements can be used in this method for estimating the error in the finite element computation with high accuracy. The finite element solutions are improved by adding the estimated errors onto the original solutions. The proposed method can be utilized for any type of linear problem if an isoparametric finite element method is used.
    Zusätzliches Material: 27 Ill.
    Materialart: Digitale Medien
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  • 188
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 291-301 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A generalized explicit one step alogorithm developed in Part I of this paper is presented in the form of a predictor-corrector scheme suitable for arbitrary non-linear analyses of structural dynamics problems. Convergence results are checked through practical calculations on linear and non-linear systems. The generalized algorithm proposed is compared with other recently developed higher order one step algorithms. The slight amount of additional computational effort compared to second order methods pays off in linear and weakly non-linear systems. The behaviour of the methods is also tested on extreme stiffening and softening systems to investigate reliability and robustness of the algorithm.
    Zusätzliches Material: 9 Ill.
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  • 189
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 337-356 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: The dynamic stiffness method is extended to large amplitude free and forced vibrations of frames. When the steady state vibration is concerned, the time variable is replaced by the frequency parameter in the Fourier series sense and the governing partial differential equations are replaced by a set of ordinary differential equations in the spatial variables alone. The frequency-dependent shape functons are generated approximately for the spatial discretization. These shape functions are the exact solutions of a beam element subjected to mono-frequency excitation and constant axial force to minimize the spatial discretization errors. The system of ordinary differential equations is replaced by a system of non-linear algebraic equations with the Fourier coefficients of the nodal displacements as unknowns. The Fourier nodal coefficients are solved by the Newtonian algorithm in an incremental manner. When an approximate solution is available, an improved solution is obtained by solving a system of linear equations with the Fourier nodal increments as unknowns. The method is very suitable for parametric studies. When the excitation frequency is taken as a parameter, the free vibration response of various resonances can be obtained without actually computing the linear natural modes. For regular points along the response curves, the accuracy of the gradient matrix (Jacobian or tangential stiffness matrix) is secondary (cf. the modified Newtonian method). However, at the critical positions such as the turning points at resonances and the branching points at bifurcations, the gradient matrix becomes important. The minimum number of harmonic terms required is governed by the conditions of completeness and balanceability for predicting physically realistic response curves. The evaluations of the newly introduced mixed geometric matrices and their derivatives are given explicitly for the computation of the gradient matrix.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 190
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 30 (1990), S. 517-539 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: An improved boundary element formulation (BEM) for two-dimensional non-homogeneous biharmonic analysis of rectilinear plates is presented. A boundary element formulation is developed from a coupled set of Poisson-type boundary integral equations derived from the governing non-homogeneous biharmonic equation. Emphasis is given to the development of exact expressions for the piecewise rectilinear boundary integration of the fundamental solution and its derivatives over several types of isoparametric elements. Incorporation of the explicit form of the integrations into the boundary element formulation improves the computational accuracy of the solution by substantially eliminating the error introduced by numerical quadrature, particularly those errors encountered near singularities. In addition, the single iterative nature of the exact calculations reduces the time necessary to compile the boundary system matrices and also provides a more rapid evaluation of internal point values than do formulations using regular numerical quadrature techniques. The evaluation of the domain integrations associated with biharmonic forms of the non-homogeneous terms of the governing equation are transformed to an equivalent set of boundary integrals. Transformations of this type are introduced to avoid the difficulties of domain integration. The resulting set of boundary integrals describing the domain contribution is generally evaluated numerically; however, some exact expressions for several commonly encountered non-homogeneous terms are used. Several numerical solutions of the deflection of rectilinear plates using the boundary element method (BEM) are presented and compared to existing numerical or exact solutions.
    Zusätzliches Material: 15 Ill.
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  • 191
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 30 (1990) 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Materialart: Digitale Medien
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  • 192
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 30 (1990), S. 579-599 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A coupled finite element model is developed to simulate the metal casting process. We present a new method for capturing the solidification zone and obtaining the corresponding rate of phase change. The latent energy release is predicted by the heat conduction rate and introduced by following the enthalpy-temperature curve. The influence of mould-metal contact is considered in calculating the heat flux through the mould-metal interface. A viscoplastic model is employed to predict the gap opening and evolution of plastification.Four examples are presented to demonstrate certain numerical aspects and the capability of the model for industrial applications.
    Zusätzliches Material: 20 Ill.
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  • 193
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 211-215 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 194
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 219-222 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Materialart: Digitale Medien
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  • 195
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 533-557 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Simulation of turbulent swirling flows has been carried out to provide insight on streamline curvature effects. Numerical calculations were based on the control-volume method. Turbulence effects were represented by two-equation turbulence models. The analysis of steady flow between two concentric rotating cylinders showed that the most promising model which incorporates curvature effects is that based on mixing energy developed by Wilcox and Chambers, as opposed to the ad hoc modification to the standard k-∊ model. This model has also been used to simulate the decay of turbulent swirling flow in a short cylinder. A comparison between calculations and experimental results for such flow fields has been presented.
    Zusätzliches Material: 19 Ill.
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  • 196
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 619-632 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Three parallel iterative schemes to solve banded systems of equations are presented in this study. The techniques are special implementations of the theory of matrix multisplitting. The resulting algorithms are implemented on a Multiple Instruction Multiple Data (MIMD) grid architecture using 16 Transputer processors. Parametric analyses are performed to develop convergence criteria and examine the speed-up of solution. It is concluded that the algorithms make very efficient use of the parallel computer architecture, especially if this consists of a large number of nodes.
    Zusätzliches Material: 8 Ill.
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  • 197
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 665-678 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A mixed finite-element formulation is applied to solve the quasi-geostrophic equations in a two-layer ocean domain enclosed by solid boundaries. A combination of leap-frog and θ-schemes is used to integrate the equations in time. Wood's formula of the wall vorticity is derived in our formulation for the case of square elements adjacent to the boundaries. Long-term computations with and without lumping have been carried out.
    Zusätzliches Material: 6 Ill.
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  • 198
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 30 (1990), S. 207-231 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A new stiffness matrix for geometrically non-linear analysis of three-dimensional beam-columns with bisymmetrical, thin-walled, I-type cross-sections is presented. The displacement field is described in terms of natural and rigid-body displacements and both Cartesian and natural matrices are derived. A novelty of the resulting method is the use of this dual description in all aspects of the analysis including the computer implementation. A companion paper1 that introduces the plastic behaviour of the material also justifies the need for this dual approach as a means to separate nodal forces from stress resultants in the cross-section of the 3D beam-column element. The current development uses the updated Lagrangian formulation and corrections in the element matrix are made to properly consider the behaviour under finite rotation. It is shown that accuracy and convergence of the solution process can be improved if the natural matrices derived here are used in a new force recovery process that is insensitive to rigid-body displacements.
    Zusätzliches Material: 10 Ill.
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  • 199
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 1065-1077 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: In this study procedures for overcoming limit and bifurcation points in large-scale structural analysis problems are described and evaluated. The methods are based on Newton's method for the outer iterations, while for the linearized problem in each iteration the preconditioned truncated Lanczos method is employed. Special care is placed upon line search routines for accelerating the convergence properties and enhancing the stability of the outer method. The proposed methodology retains all characteristics of an iterative method by avoiding the factorization of the current stiffness matrix. The necessary eigenvalue information is retained in the tridiagonal matrix of the Lanczos approach.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 200
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990) 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
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