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  • 1995-1999  (980)
  • 1965-1969
  • 1920-1924
  • 1996  (980)
  • Engineering General  (686)
  • Theoretical, Physical and Computational Chemistry  (294)
  • 101
    Electronic Resource
    Electronic Resource
    EDDY CURRENT AND TEMPERATURE SIMULATION IN THIN MOVING METAL STRIPS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 141-163 
    Details
    ISSN: 0029-5981
    Keywords: induction heating ; coupled problem ; three-dimensional analysis ; eddy current temperature analysis ; thin conducting sheet model ; eddy current boundary condition ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents a special finite element formulation for the computer simulation of an inductive heating device for thin moving metal strips. The calculation includes both the electromagnetic field and the temperature distribution resulting from the losses of the induced currents. The electromagnetic field is described by an electric vector potential and a magnetic scalar potential, the induced eddy currents are represented by a special boundary condition for the magnetic scalar potential along the surface of the current-carrying strip. This avoids the necessity to discretize the thin secondary region. The thermal model includes the movement of the strip as well as convection and radiation as its surfaces. The field equations are discretized using the Galerkin variant of the Method of Weighted Residuals. The mutually coupled electromagnetic and temperature fields are then calculated using an iterative, staggered solution scheme. Comparisons between calculated and measured temperature profiles show the validity of the presented approach.
    Additional Material: 17 Ill.
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  • 102
    Electronic Resource
    Electronic Resource
    OPTIMAL DESIGN FOR NON-STEADY-STATE METAL FORMING PROCESSES - I. SHAPE OPTIMIZATION METHOD (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 33-50 
    Details
    ISSN: 0029-5981
    Keywords: finite element method ; shape optimization ; sensitivity analysis ; forming process ; optimal design ; forging ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We suggest a shape optimization method for a non-linear and non-steady-state metal forming problem. It consists in optimizing the initial shape of the part as well as the shape of the preform tool during a two-step forging operation, for which the shape of the second operation is known. Shapes are described using spline functions and optimal parameter values of the splines are searched in order to produce, at the end of the forging sequence, a part with a prescribed geometric accuracy, optimal metallurgical properties and for a minimal production cost. The finite element method, including numerous remeshing operations, is used for the simulation of the process. We suggest using a least-squares-type algorithm for the unconstrained optimization method (based on external penalty) for which we describe the calculation of the derivatives of the objective function. We show that it can reduce to calculations which are equivalent to the derivative calculations of steady-state processes and to evolution equations. Therefore, the computational cost of such an optimization is quite reasonable, even for complex forging processes. Lastly, in order to reduce the errors due to the numerous remeshings during the simulation, we introduce error estimation and adaptive remeshing methods with respect to the calculation of derivatives.
    Additional Material: 6 Ill.
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  • 103
    Electronic Resource
    Electronic Resource
    A FRICTIONAL CONTACT ELEMENT FOR STRONGLY CURVED CONTACT PROBLEMS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 165-184 
    Details
    ISSN: 0029-5981
    Keywords: curved unilateral contact ; augmented Lagrangian ; frictional contact element ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Based on a mixed formulation approach, a frictional contact element is proposed for the numerical solution of contact problems including strongly curved rigid obstacles. The implementation of the frictional contact element is analogous to that of a finite element. This feature facilitates its implementation in implicit finite element programmes, since the structure of the code need not be modified.For efficient modelling of the forming tool geometries by Computer Aided Geometric Design techniques and in order to achieve a high performance of the contact search, the numerical schemes of the frictional contact element operate directly on parametric polynomial surface patches. Thus, no discretization of curved contact surfaces is performed.Numerical simulations of deep drawing processes demonstrate the performance of the method in the case of large sliding increments upon curved tools and in the case of elasto-plasticity.
    Additional Material: 8 Ill.
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  • 104
    Electronic Resource
    Electronic Resource
    FORMULATION AND EXPERIMENTAL VERIFICATION OF A PNEUMATIC FINITE ELEMENT (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1097-1114 
    Details
    ISSN: 0029-5981
    Keywords: finite elements ; pneumatics ; air springs ; containers ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Many engineering structures completely surround and enclose gas filled volumes. The enclosed gas adds additional stiffness to the surrounding structure. This paper shows how to account for this effect by means of an augmented virtual work principle. The additional term augmenting the virtual work equilibrium statement for the structure is the virtual boundary work done by the pressure of the enclosed gas. The augmented equations are discretized using standard finite element methods, and the additional terms are discussed. The resulting ‘pneumatic’ finite element is shown to be analogous to regular structural finite elements. To assess the accuracy and efficiency and also to illustrate the applicability of the present formulation, a series of four examples was selected. In two of the examples, the behaviour of the end cap of a partially filled plastic food product container is studied. The numerical results using the pneumatic element compare well with an alternative Rayleigh-Ritz solution of the end cap behaviour. The other two examples represent the behaviour of a double bellows air spring shock absorber under static isothermal and dynamic adiabatic conditions. For the static isothermal case, an experimental study was performed with results in good agreement with the pneumatic element solutions. For the dynamic adiabatic loading case, the dynamic stiffness of the air spring was predicted using the pneumatic element. The numerical results agree with experimental data published in an air spring application guide. The examples illustrate that the pneumatic element formulation can be applied to the large deflection analysis of structures that enclose gas filled volumes.
    Additional Material: 9 Ill.
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  • 105
    Electronic Resource
    Electronic Resource
    A PARTICLE TRACKING TECHNIQUE FOR THE LAGRANGIAN-EULERIAN FINITE ELEMENT METHOD IN MULTI-DIMENSIONS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1115-1136 
    Details
    ISSN: 0029-5981
    Keywords: particle tracking ; Lagrangian-Eulerian finite element methods ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a multi-dimensional particle tracking technique for applying the Lagrangian-Eulerian finite element method to solve transport equations in transient-state simulations. In the Lagrangian- Eulerian approach, the advection term is handled in the Lagrangian step so that the associated numerical errors can be considerably reduced. It is important to have an adequate particle tracking technique for computing advection accurately in the Lagrangian step. The particle tracking technique presented here is designed to trace fictitious particles in the real-world flow field where the flow velocity is either measured or computed at a limited number of locations. The technique, named ‘in-element’ particle tracking, traces fictitious particles on an element-by-element basis. Given a velocity field, a fictitious particle is traced one element by one element until either a boundary is encountered or the available time is completely consumed. For the tracking within an element, the element is divided into a desired number of subelements with the interpolated velocity computed at all nodes of the subelements. A fictitious particle, thus, is traced one subelement by one subelement within the element. The desired number of subelements can be determined based on the complexity of the flow field being considered. The more complicated the flow field is, the more subelements are needed to achieve accurate particle tracking results. A single-velocity approach can be used to efficiently perform particle tracking in a smooth flow field, while an average-velocity approach can be employed to increase the tracking accuracy for more complex flow fields.
    Additional Material: 15 Ill.
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  • 106
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    Electronic Resource
    HIGH-PERFORMANCE PCG SOLVERS FOR FEM STRUCTURAL ANALYSIS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1313-1340 
    Details
    ISSN: 0029-5981
    Keywords: iterative methods for linear systems ; preconditioning ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The preconditioned conjugate gradient algorithm is a well-known and powerful method used to solve large sparse symmetric positive definite linear systems. Such systems are generated by the finite element discretization in structural analysis but users of finite elements in this context generally still rely on direct methods. It is our purpose in the present work to highlight the improvement brought forward by some new preconditioning techniques and show that the preconditioned conjugate gradient method performs better than efficient direct methods.
    Additional Material: 8 Ill.
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  • 107
    Electronic Resource
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    FEASIBLE DESCENT CONE METHODS FOR INEQUALITY CONSTRAINED OPTIMIZATION PROBLEMS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1341-1356 
    Details
    ISSN: 0029-5981
    Keywords: constrained optimization ; feasible descent ; mathematical programming ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new Feasible Descent Cone (FDC) method for constrained optimization, previously restricted to linear objectives, is here generalized to include non-linear objective functions as well. In the basic and exact algorithm a sequence of descent steps is taken through the interior of the feasible region along the central lines of mathematically defined descent cones, constructed at successive boundary points. Here the basic algorithm is modified to allow for a minimum to occur within the interior, along a central descent ray in the case of non-linear objectives. A special interior procedure, with desirable mathematical properties, is adopted should the latter occur. To ensure economic implementation, the new generalized and exact algorithm, referred to as SSOPT2, is successively applied to a sequence of approximate quadratic subproblems. The overall generalized procedure that includes the successive application of SSOPT2 to the approximate subproblems, is referred to as the successive approximation version 2 algorithm (SAM2). The practical performance of SAM2 is assessed through its application to a number of small but otherwise representative test problems.
    Additional Material: 2 Ill.
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  • 108
    Electronic Resource
    Electronic Resource
    NUMERICAL REDUCED MINIMIZATION THEORY FOR BEAM ELEMENTS UNDER NON-UNIFORM ISOPARAMETRIC MAPPING (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1357-1382 
    Details
    ISSN: 0029-5981
    Keywords: numerical reduced minimization ; non-uniform isoparametric mapping ; unmatched coefficient ; spurious constraint ; optimal minimization ; locking ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, the effects of various numerical integrations on the behaviour of C0-continuous beam elements under non-uniform isoparametric mapping are investigated by using numerical reduced minimization theory. The theory shows that stress recovery can be achieved by sampling stresses at the optimal integration points once a reduced integration is employed. It rationalizes the continued acceptance of the conventional reduced integration of constrained strain energy as one of remedies for locking due to spurious constraint.
    Additional Material: 12 Ill.
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  • 109
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    APPLICATION OF TOPOLOGICAL OPTIMIZATION TECHNIQUES TO STRUCTURAL CRASHWORTHINESS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1383-1403 
    Details
    ISSN: 0029-5981
    Keywords: crashworthiness ; homogenization ; topology design ; automotive structure optimization ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The topological optimization of components to maximize crash energy absorption for a given volume is considered. The crash analysis is performed using a DYNA3D finite element analysis. The original solid elements are replaced by ones with holes, the hole size being characterized by a so-called density (measure of the reduced volume). A homogenization method is used to find elastic moduli as a function of this density. Simpler approximations were developed to find plastic moduli and yield stress as functions of density.Optimality criteria were derived from an optimization statement using densities as the design variables. A resizing algorithm was constructed so that the optimality criteria are approximately satisfied. A novel feature is the introduction of an objective function based on strain energies weighted at specified times. Each different choice of weighting factors leads to a different structure, allowing a range of design possibilities to be explored.The method was applied to an automotive body rear rail. The original design and a new design of equal volume with holes were compared for energy absorption.
    Additional Material: 25 Ill.
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  • 110
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    ANALYSIS OF THREE-DIMENSIONAL TRANSIENT ACOUSTIC WAVE PROPAGATION USING THE BOUNDARY INTEGRAL EQUATION METHOD (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1419-1431 
    Details
    ISSN: 0029-5981
    Keywords: integral equations ; scattering ; boundary elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes a boundary integral equation (boundary element) method for the solution of a variety of transient acoustic problems. The spatial and temporal discretization employs quadratic isoparametric elements with high-order Gauss quadrature, and the ensuing equations are implicit. The implicit formulation both eliminates the instabilities reported in explicit treatments, and permits a freedom of choice of timestep which can reduce costs dramatically. The accuracy of the approach is demonstrated by comparison with the analytical solution for a sphere. Results for more demanding sphere-cone-sphere geometries extending to seven wavelengths long are presented, and compared to those obtained from a related frequency domain approach.
    Additional Material: 7 Ill.
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  • 111
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    A FAST NUMERICAL METHOD FOR ISOTHERMAL RESIN TRANSFER MOLD FILLING (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1405-1417 
    Details
    ISSN: 0029-5981
    Keywords: RTM ; control volume ; free surface ; porous medium ; sparse matrix ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient numerical scheme is presented for simulating isothermal flow in resin transfer molding. The problem involves transient, free surface flow of an incompressible fluid into a non-deforming porous medium. A new variant of the Control Volume Finite Element (CVFE) algorithm is explained in detail. It is shown how the pressure solutions at each time step can be obtained by adding a single row and column to the Cholesky factorization of the stiffness matrix derived from a finite element formulation for the pressure field. This approach reduces the computation of a new pressure solution at each time step to essentially just two sparse matrix back-substitutions. The resulting performance improvement facilitates interactive simulation and the solution of inverse problems which require many simulations of the filling problem. The computational complexity of the calculation is bounded by O(n2⋅5), where n is the number of nodes in the finite element mesh. A 100-fold speedup over a conventional CVFE implementation was obtained for a 2213-node problem.
    Additional Material: 4 Ill.
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  • 112
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    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996) 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620390801
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  • 113
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    Publisher's annoucement (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1436-1436 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620390803
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  • 114
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    Conference diary (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1433-1435 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620390802
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  • 115
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    A FORMULATION OF THE QS6 ELEMENT FOR LARGE ELASTIC DEFORMATIONS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1437-1454 
    Details
    ISSN: 0029-5981
    Keywords: large elastic deformations ; enhanced strain method ; finite elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The numerical simulation of processes undergoing finite deformations requires robust elements. For a broad range of applications these elements should have a good performance in bending dominated situations as well as in the case of incompressibility. The element should be insensitive against mesh distortions which frequently occurs during finite deformations. Furthermore, due to efficiency reasons a good coarse mesh accuracy in required in non-linear analysis. The QS6 element, developed in this paper, tries to fulfil the above-mentioned requirements. The performance is depicted by means of numerical examples.
    Additional Material: 10 Ill.
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  • 116
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    PETROV-GALERKIN METHODS FOR THE TRANSIENT ADVECTIVE-DIFFUSIVE EQUATION WITH SHARP GRADIENTS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1455-1473 
    Details
    ISSN: 0029-5981
    Keywords: transient loads ; advective-diffusive equations ; Petrov-Galerkin ; Galerkin Leask-Square ; boundary layers ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A Petrov-Galerkin formulation based on two different perturbations to the weighting functions is presented. These perturbations stabilize the oscillations that are normally exhibited by the numerical solution of the transient advective-diffusive equation in the vicinity of sharp gradients produced by transient loads and boundary layers. The formulation may be written as a generalization of the Galerkin Least-Square method.
    Additional Material: 8 Ill.
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  • 117
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    GENERALIZED 3-D PAVING: AN AUTOMATED QUADRILATERAL SURFACE MESH GENERATION ALGORITHM (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1475-1489 
    Details
    ISSN: 0029-5981
    Keywords: meshing ; three-dimensional ; surfaces ; quadrilateral ; finite element ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper discusses the extension of the paving algorithm for all quadrilateral mesh generation to arbitrary three-dimensional trimmed surfaces. Methods of calculating angles, projecting elements, and detecting collisions between paving boundaries, for general surfaces are presented. Extensions of the smoothing algorithms for three dimensions are set forth. Advances in the use of scalar sizing functions are presented. These functions can be used to better approximate internal mesh density from boundary densities and surface characteristics.
    Additional Material: 16 Ill.
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  • 118
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    HIGH-ORDER ELEMENT FOR PREBUCKLING AND BUCKLING ANALYSIS OF LAMINATED PLANE FRAMES (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2155-2168 
    Details
    ISSN: 0029-5981
    Keywords: buckling ; composite laminated structures ; high-order element ; locking ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new high-order element for prebuckling and buckling of any laminated plane frame is developed. The kinematic approach involves a variety of high-order models with different powers of the thickness co-ordinate, and the derived stiffness matrix is based on a special power series, without a numerical process. It yields an exact formulation for high-order (first) models and improved formulations for higher-order (second and third) ones. A parametric study of the ‘locking’ phenomenon and the shear deformation effects was carried out for isotropic and laminated structures. It was found that the first-order model with an appropriate shear correction factor yielded results close to its higher-order counterparts.
    Additional Material: 10 Ill.
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  • 119
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    AN ENERGY-CONSERVING CO-ROTATIONAL PROCEDURE FOR THE DYNAMICS OF PLANAR BEAM STRUCTURES (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2265-2282 
    Details
    ISSN: 0029-5981
    Keywords: energy-conservation ; dynamics ; beams ; co-rotation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper describes an energy-conserving procedure for the implicit non-linear dynamic analysis of planar beam structures. The method is based on a form of co-rotational technique which is ‘external to the element’. A range of numerical results are presented which clearly demonstrate the improved numerical performance in comparison with more conventional techniques.
    Additional Material: 8 Ill.
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  • 120
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    EVALUATION OF THE STRESS TENSOR IN 3-D ELASTOPLASTICITY BY DIRECT SOLVING OF HYPERSINGULAR INTEGRALS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2555-2573 
    Details
    ISSN: 0029-5981
    Keywords: 3-D boundary element method ; elastoplastic analysis ; hypersingular formulation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A 3-D hypersingular Boundary Integral Equation (BIE) of elastoplasticity is derived. Using this formulation the displacement rate gradients and the complete stress tensor on the boundary can be evaluated directly as opposed to the classical approach, where the shape functions derivatives are to be calculated. The regularization of strongly singular and hypersingular boundary integrals, as well as strongly singular domain integrals for a source point positioned on the boundary is carried out in a general manner. Arbitrary types of elements and arbitrary positions of the source point with respect to continuity requirements can be used. Numerical 3-D elastoplastic examples (notch and crack problems) illustrate the advantages of the proposed method.
    Additional Material: 16 Ill.
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  • 121
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    HIGH-ACCURACY LOW-ORDER THREE-DIMENSIONAL BRICK ELEMENTS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2337-2361 
    Details
    ISSN: 0029-5981
    Keywords: elastoplastic ; high-accuracy ; locking-free ; low-order ; nonlinear ; three-field functional ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a family of low-order high-accuracy three-dimensional brick elements. The elements are formulated via a three-field variational principle. The assumed (independent) strain field is constructed from two disjointed distributions. The first contains the lower-order distribution and its dimension is the minimum required to satisfy stability requirements. An energy constraint, which is enforced weakly at the element level, is used to relate the second distribution to the first. The stress field is chosen to a priori satisfy a similar energy constraint. As a result, internal constraints (e.g. incompressibility) are automatically satisfied by these fields, and locking behaviour is avoided. A J2-plasticity model illustrates the proposed elements' performance in nonlinear solids. The excellent performance of the proposed elements is demonstrated with numerous challenging examples, including many that are usually modelled by shell elements.
    Additional Material: 20 Ill.
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  • 122
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    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996) 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620391401
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  • 123
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    Conference diary (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2507-2508 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620391402
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  • 124
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    ELASTOHYDRODYNAMIC LUBRICATION ANALYSIS OF LAYERED LINE CONTACT BY THE BOUNDARY ELEMENT METHOD (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2531-2554 
    Details
    ISSN: 0029-5981
    Keywords: boundary element method ; elastohydrodynamic lubrication ; layered contact ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a numerical routine to compute the contact characteristics of elastomer layered cylinders lubricated by isoviscous liquids. The indentation of the elastic layer is calculated from boundary integral equations which are solved by linear and quadratic boundary element methods for a finite plane model and a circular representation of the junction. The hydrodynamic equation is also transformed into a boundary integral equation and solved by Simpson's rule. Some factors which possibly affect numerical accuracy are examined. Examples for finite plane and circular layer are analysed with reference to parameters for printing press roller contact, in which results are obtained for the indentation, film thickness and liquid pressure, as well as internal stresses through the simultaneous solution of the elasticity and hydrodynamic equations. The results show that high precision is easily achieved and the method is efficient for such layered problems.
    Additional Material: 10 Ill.
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  • 125
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    A SET OF HYBRID EQUILIBRIUM FINITE ELEMENT MODELS FOR THE ANALYSIS OF THREE-DIMENSIONAL SOLIDS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2789-2802 
    Details
    ISSN: 0029-5981
    Keywords: finite elements ; three-dimensional elasticity ; equilibrium formulations ; hybrid finite elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper an approach to the formulation of equilibrium elements for the analysis of three-dimensional elasticity problems is presented.This formulation is an extension of the approach previously proposed for the analysis of two-dimensional elasticity problems. The general aspects of the formulation remain unchanged when applied to the new problem, but new points are considered, namely the way to perform volume integrations for general elements and the techniques used to obtain the self-equilibrated three-dimensional stress approximation functions.The numerical behaviour of such elements is presented and discussed.
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    SENSITIVITY ANALYSIS FORMULATION FOR THREE-DIMENSIONAL CONDUCTION HEAT TRANSFER WITH COMPLEX GEOMETRIES USING A BOUNDARY ELEMENT METHOD (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2837-2862 
    Details
    ISSN: 0029-5981
    Keywords: special boundary integral formulation ; design sensitivity analysis (DSA) ; direct differentiation approach (DDA) ; three-dimensional conduction heat transfer ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A special boundary integral formulation had been proposed to analyse many engineering problems of conduction heat transfer in complex three-dimensional geometries (closely spaced surface and circular hole in infinite domain or simple modification of it) by Rezayat and Burton. One example of such geometries is the mold sets in the injection molding process. In this paper, an efficient and accurate approach for the design sensitivity analysis (DSA) is presented for these kinds of problems in the similar complex geometries using the direct differentiation approach (DDA) based on the above special boundary integral formulation. The present approach utilizes the implicit differentiation of the boundary integral equations with respect to the design variables (radii and locations of circular holes) to yield the sensitivity equations. A sample problem (heat transfer of injection molding cooling system) is solved to demonstrate the accuracy of the present sensitivity analysis formulation. Although the techniques introduced here are applied to a particular problem in heat transfer of injection molding cooling system, their potential application is quite broad.
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    THE COMPUTATION OF WAVELET-GALERKIN APPROXIMATION ON A BOUNDED INTERVAL (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2921-2944 
    Details
    ISSN: 0029-5981
    Keywords: wavelet orthogonal bases ; wavelet-Galerkin method ; Burgers' equation ; numerical method ; approximation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes exact evaluations of various finite integrals whose integrands involve products of Daubechies' compactly supported wavelets and their derivatives and/or integrals. These finite integrals play an essential role in the wavelet-Galerkin approximation of differential or integral equations on a bounded interval.
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    AN ALGORITHM FOR INTEGRATING THE SPIN ON CONVECTED BASES (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2973-2985 
    Details
    ISSN: 0029-5981
    Keywords: co-rotational frame ; convected bases ; integration of the spin ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new algorithm is proposed for integrating the spin in the frame of large deformation analysis. The method is based on the integration of a matrix relation, obtained from an adapted decomposition of the deformation gradient, and directly written in convected co-ordinates. The input of this algorithm is either the Gram matrix at any time (if a kinematical method is used, for instance) or more generally, the incremental deformation gradient, and the output is the required rotation matrix on convected bases. The result takes a very simple form in the important case of classical shells.
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    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996) 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620391701
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    A MODIFIED EFFECTIVE CAPACITANCE METHOD FOR SOLIDIFICATION MODELLING USING LINEAR TETRAHEDRAL FINITE ELEMENTS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3195-3215 
    Details
    ISSN: 0029-5981
    Keywords: modified effective capacitance ; solidification ; tetrahedral elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper a new formulation for modelling solidification is discussed. The formulation has similar features to both the apparent and effective heat capacitance methods used for solidification problems where conduction predominates over other heat transfer mechanisms. The main feature of the new method is that a modified form of effective heat capacitance is calculated from the solution of non-linear equations that describe the energy loss for linear tetrahedral finite elements. This approach ensures that the predicted temperature field corresponds exactly with the energy loss and so providing an extremely stable formulation. The method is tested against a range of problems including some with non-linear liquid fractions. The predictions are compared against known analytical solutions and the method is shown to provide reasonable accuracy even for relatively large time-steps. A comparison is made between the method and the well-known temporal and spatial approximations of apparent heat capacitance, and effective capacitance. Accuracy is maintained over a greater variation in time-step and mesh density with comparable computational requirements. In addition, the method lends itself to the use of relatively simple bisection techniques for the solution of the non-linear finite element equations. Also demonstrated is the method's innate ability to predict energy loss to a high degree of accuracy for large time steps.
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    THREE-DIMENSIONAL TRANSIENT MOLD COOLING ANALYSIS BASED ON GALERKIN FINITE ELEMENT FORMULATION WITH A MATRIX-FREE CONJUGATE GRADIENT TECHNIQUE (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3049-3064 
    Details
    ISSN: 0029-5981
    Keywords: mold cooling ; injection molding ; finite element method ; three-dimensional ; Jacobi conjugate gradient ; matrix-free algorithm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A methodology is presented to simulate the three-dimensional heat transfer within a mold during the injection molding process. The mold cooling analysis assists cooling channel design and paves the way for part shrinkage and warpage analysis. The transient temperature distributions in the mold and the polymer part are simultaneously computed by Galerkin Finite Element Method (GFEM) using a matrix-free Jacobi Conjugate Gradient (JCG) scheme. The numerical method presented here is efficient and has shown to require a fraction of the memory and computing time required by conventional methods. The matrix-free algorithm is initially validated using an injection mold designed to produce a plaque with a molded-in hole. Subsequently, the method is further applied to a representative automotive plastic component.
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  • 132
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    SENSITIVITY ANALYSIS FOR BOUNDARY ELEMENT ERROR ESTIMATION AND MESH REFINEMENT (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2907-2920 
    Details
    ISSN: 0029-5981
    Keywords: sensitivity analysis ; error estimates ; mesh refinement ; hypersingular integrals ; boundary element method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The subject of this paper is the sensitivity analysis of approximate boundary element solutions with respect to the positions of the collocation points. The direct differentiation approach is considered here and the analysis is performed analytically. Since only the collocation points are perturbed, the shape of the body and the corresponding discretization remain unaltered. This aspect makes the present work quite different in spirit with respect to earlier analyses on shape sensitivities. Sensitivities of approximate BEM solutions with respect to the positions of collocation points are shown to be related to the residual of hypersingular integral equations. Numerical results confirm that the present approach can be seen as the analytical counterpart of an adaptive scheme for mesh refinement presented by the same author in some recent papers. Some other advantages of the present approach over the former one are also outlined.
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    Conference diary (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3217-3217 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620391802
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    THE WHISKER WEAVING ALGORITHM: A CONNECTIVITY-BASED METHOD FOR CONSTRUCTING ALL-HEXAHEDRAL FINITE ELEMENT MESHES (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3327-3349 
    Details
    ISSN: 0029-5981
    Keywords: mesh generation ; hexahedral ; whisker weaving ; duality ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper introduces a new algorithm called whisker weaving for constructing unstructured, all-hexahedral finite element meshes. Whisker weaving is based on the Spatial Twist Continuum (STC), a global interpretation of the geometric dual of an all-hexahedral mesh. Whisker weaving begins with a closed, all-quadrilateral surface mesh bounding a solid geometry, then constructs hexahedral element connectivity advancing into the solid. The result of the whisker weaving algorithm is a complete representation of hex mesh connectivity only: Actual mesh node locations are determined afterwards.The basic step of whisker weaving is to form a hexahedral element by crossing or intersecting dual entities. This operation, combined with seaming or joining operations in dual space, is sufficient to mesh simple block problems. When meshing more complex geometries, certain other dual entities appear such as blind chords, merged sheets, and self-intersecting chords. Occasionally specific types of invalid connectivity arise. These are detected by a general method based on repeated STC edges. This leads into a strategy for resolving some cases of invalidities immediately.The whisker weaving implementation has so far been successful at generating meshes for simple block-type geometries and for some non-block geometries. Mesh sizes are currently limited to a few hundred elements. While the size and complexity of meshes generated by whisker weaving are currently limited, the algorithm shows promise for extension to much more general problems.
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    EXPONENTIAL MAP ALGORITHM FOR STRESS UPDATES IN ANISOTROPIC MULTIPLICATIVE ELASTOPLASTICITY FOR SINGLE CRYSTALS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3367-3390 
    Details
    ISSN: 0029-5981
    Keywords: finite plasticity ; single crystals ; multisurface plasticity ; active set search ; exponential map ; stress update algorithm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a new stress update algorithm for large-strain rate-independent single-crystal plasticity. The theoretical frame is the well-established continuum slip theory based on the multiplicative decomposition of the deformation gradient into elastic and plastic parts. A distinct feature of the present formulation is the introduction and computational exploitation of a particularly simple hyperelastic stress response function based on a further multiplicative decomposition of the elastic deformation gradient into spherical and unimodular parts, resulting in a very convenient representation of the Schmid resolved shear stresses on the crystallographic slip systems in terms of a simple inner product of Eulerian vectors. The key contribution of this paper is an algorithmic formulation of the exponential map exp: sl(3) → SL(3) for updating the special linear group SL(3) of unimodular plastic deformation maps. This update preserves exactly the plastic incompressibility condition of the anisotropic plasticity model under consideration. The resulting fully implicit stress update algorithm treats the possibly redundant constraints of single-crystal plasticity by means of an active set search. It exploits intrinsically the simple representation of the Schmid stresses by formulating the return algorithm and the associated consistent elastoplastic moduli in terms of Eulerian vectors updates. The performance of the proposed algorithm is demonstrated by means of a representative numerical example.
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    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996) 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620391901
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    A WELL-CONDITIONED MATRIX FOR (kuX)X WITH DISCONTINUOUS k (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3663-3677 
    Details
    ISSN: 0029-5981
    Keywords: matrix condition ; heat equation ; discontinuous coefficients ; error stability ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The traditional tridiagonal matrix approximating the one-dimensional heat equation is ill-conditioned when heat conductivity changes radically. An algebraic reformulation of the tridiagonal produces a well-conditioned matrix. Additional variables are rates q=-kux at interfaces between radical changes in k. A reduced matrix amounts to a coarse approximation.
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    MODELLING OF 3-D MIXED-MODE FRACTURES NEAR PLANAR BIMATERIAL INTERFACES USING SURFACE INTEGRALS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3679-3703 
    Details
    ISSN: 0029-5981
    Keywords: 3-D fracture ; interface ; boundary element ; singular integration ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Mixed-mode fractures of arbitrary orientation with respect to a planar bimaterial interface have been effectively modelled using a surface integral approach. By requiring only that the surface of the fracture be discretized, the surface integral method circumvents the practical difficulties associated with having to mesh the interacting dual singularities in stress along the three-dimensional (3-D) crack front and at the interface. The key elements of this numerical capability are discussed in detail. These include: the derivation of the fundamental solutions for a generalized fracture event near a planar bimaterial interface, formulation of the governing integral equation including its decomposition into singular and non-singular terms, development of analytical and numerical techniques for performing the singular integrations, and efficient numerical integration of the non-singular terms using non-dimensionalized surface approximations of the dipole solutions. The problem of a pressurized planar crack near a bimaterial interface was used to assess convergence. The effect of material contrast and crack shape on tendencies for crack growth were also examined.
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    A C0 EIGHT-NODE MEMBRANE-SHEAR-BENDING ELEMENT FOR GEOMETRICALLY NON-LINEAR (STATIC AND DYNAMIC) ANALYSIS OF LAMINATES (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3453-3474 
    Details
    ISSN: 0029-5981
    Keywords: plate ; finite element ; locking ; non-linear ; buckling ; vibrations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new eight-node C0 membrane-plate quadrilateral finite element is presented to analyse static and dynamic moderately large deflections of moderately thick laminates. The finite element is based on the Reissner- Mindlin plate theory and on previous works for the shear-bending (plate) part, which has been described in a previous paper, Reference 10. In the paper, the novelty is in the way of improving isoparametric membrane response without adding zero-energy modes, and the moderately large deflection static and dynamic analysis of laminates based on von Karman's assumptions. Finally, some numerical simulations are presented in statics and in dynamics for laminates, including buckling analysis and membrane-plate coupling effects. Among a large variety of finite elements which have been proposed during the two last decades, interest in the present element lies in its simplicity implementation, its efficiency without any correction factors and spurious energy modes, and (also) the fact it is fully standard from an engineering view point.
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    UNCONDITIONALLY STABLE HIGHER-ORDER ACCURATE HERMITIAN TIME FINITE ELEMENTS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3475-3495 
    Details
    ISSN: 0029-5981
    Keywords: structural dynamics ; time finite elements ; Hermitian shape functions ; unconditionally stable algorithms ; higher-order accurate algorithms ; time-step integration ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, single step time finite elements using the cubic Hermitian shape functions to interpolate the solution over a time interval are considered. The second-order differential equations are manipulated directly. Both the effects of modal damping and external excitation are considered. The accuracy of the solutions at the end of the time interval and the interpolated solutions within the time interval is investigated. The weighted residual approach is adopted to derive the time-integration algorithms. Instead of specifying the weighting functions, the weighting parameters are used to control the characteristics of the time finite elements. The weighting parameters are chosen to eliminate the higher-order truncation error terms or to enforce the asymptotic annihilation condition. A one-parameter family of third-order accurate asymptotically annihilating algorithms and another one-parameter family of fourth-order accurate non-dissipative algorithms are presented. The ranges of the weighting parameters for unconditionally stable algorithms are given. It is found that one of the members in each family corresponds to the Padé approximants of the exponential function in solving the first-order differential equations. Some of the existing unconditionally stable higher-order accurate algorithms are re-derived by the present unified approach.
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    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996) 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620392001
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    FREQUENCY-INDEPENDENT INFINITE ELEMENTS FOR ANALYSING SEMI-INFINITE PROBLEMS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3553-3569 
    Details
    ISSN: 0029-5981
    Keywords: finite/infinite element method ; infinite element ; semi-infinite problem ; soil-structure interaction ; wave propagation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Two drawbacks exist with the infinite elements used for simulating the unbounded domains of semi-infinite problems. The first is the lack of an adequate measure for calculating the decay parameter. The second is the frequency-dependent characteristic of the finite/infinite element mesh used for deriving the impedance matrices. Based on the properties of wave propagation, a scheme is proposed in this paper for evaluating the decay parameter. In addition, it is shown that by the method of dynamic condensation, the far-field impedance matrices for waves of lower frequencies can be obtained repetitively from the one for waves of the highest frequency, using exactly the same finite/infinite element mesh. Such an approach ensures that accuracy of the same degree can be maintained for waves of all frequencies within the range of consideration. Effectiveness of the proposed method is demonstrated in the numerical examples through comparison with previous results.
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    A FLAT TRIANGULAR SHELL ELEMENT WITH LOOF NODES (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3867-3887 
    Details
    ISSN: 0029-5981
    Keywords: discrete Kirchhoff theory ; shell element ; semiloof element ; non-linear shell analysis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the formulation of flat shell elements it is difficult to achieve inter-element compatibility between membrane and transverse displacements for non-coplanar elements. Many elements lack proper nodal degrees of freedom to model intersections making the assembly of elements troublesome. A flat triangular shell element is established by a combination of a new plate bending element DKTL and the well-known linear membrane strain element LST, and for this element the above-mentioned deficiencies are avoided. The plate bending element DKTL is based on Discrete Kirchhoff Theory and Loof nodes. The nodal configuration of the element is similar to the SemiLoof element, and the formulation is an improvement of a previous formulation. The element is used for both linear statics, linear buckling and geometrical non-linear analysis, and numerical examples are presented to show the robustness, accuracy and quick convergence of the element.
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    Conference diary (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3931-3931 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620392203
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    A TIME-STEPPING PROCEDURE FOR STRUCTURAL DYNAMICS USING GAUSS POINT COLLOCATION (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3985-3998 
    Details
    ISSN: 0029-5981
    Keywords: structural dynamics ; time stepping ; collocation ; Gauss points ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: When a cubic function is interpolated between the prescribed initial displacement and velocity and the exact displacement and velocity at the end of a time step for a single degree of freedom system, the error, or residual, in the governing equation is zero at a number of times. It is shown that for a general undamped system, in the limit as the time step approaches zero these times correspond to Gauss points. This observation is verified by considering a general collocation procedure in which the displacement in any time step is approximated as a cubic function of time, with two coefficients chosen to satisfy the displacement and velocity at the beginning of the time step with the other two coefficients being chosen to satisfy the governing differential equation at any two times. It is shown that optimum accuracy is obtained if these points are the Gauss points. Detailed expressions are then presented for this particular case, and stability of the algorithm is investigated showing that the procedure is conditionally stable. For time steps which are a small proportion of the least period of vibration of the structure, the algorithm is considered to be the most accurate possible procedure based on cubic approximation of the displacement.
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    ELEMENT RESEQUENCING FOR USE WITH A MULTIPLE FRONT ALGORITHM (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3999-4020 
    Details
    ISSN: 0029-5981
    Keywords: sparse matrices ; frontal methods ; Gaussian elimination ; finite-element equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The multiple front algorithm is an extension of the frontal method to allow parallelism to be exploited in the solution process. The finite-element domain is partitioned into a number of subdomains and a frontal decomposition is performed on each subdomain separately. For a given partitioning of the domain, the efficiency of the multiple front algorithm depends on the ordering of the elements within each subdomain. We look at the limitations of existing element reordering algorithms when applied to a subdomain and consider how these limitations may be overcome. Extensive numerical experiments are performed on a range of practical problems and, on the basis of the results, we propose a new element resequencing algorithm for use with a multiple front algorithm.
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    CRITERIA TO ACHIEVE NEARLY OPTIMAL MESHES IN THE h-ADAPTIVE FINITE ELEMENT METHOD (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 4039-4061 
    Details
    ISSN: 0029-5981
    Keywords: finite element method ; optimal mesh ; strategy ; refinement ; error estimation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Five Adaptive Modification Strategies (AMSs) are studied as means to obtain nearly optimal meshes using an adaptive finite element modelling system based on the h-version of the FEM. These strategies include the method traditionally seem in the literature as well as four additional methods. The five strategies are tested over five numerical examples, one of them producing convergence oscillations in one example. The principal characteristic of our system is that it permits the user to control certain parameters of the adaptive process, which contributes to an improvement in the results.
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    Preconditioning Mixed Finite Element Saddle-point Elliptic Problems (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 1-20 
    Details
    ISSN: 1070-5325
    Keywords: preconditioning saddle-point problems ; eigenvalue estimation ; mixed finite element method ; minimum residual method ; second-order elliptic problems ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We consider saddle-point problems that typically arise from the mixed finite element discretization of second-order elliptic problems. By proper equivalent algebraic operations the considered saddle-point problem is transformed to another saddle-point problem. The resulting problem can then be efficiently preconditioned by a block-diagonal matrix or by a factored block-matrix (the blocks correspond to the velocity and pressure, respectively). Both preconditioners have a block on the main diagonal that corresponds to the bilinear form(δ is a positive parameter) and a second block that is equal to a constant times the identity operator. We derive uniform bounds for the negative and positive eigenvalues of the preconditioned operator. Then any known preconditioner for the above bilinear form can be applied. We also show some numerical experiments that illustrate the convergence properties of the proposed technique.
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    Masthead (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996) 
    Details
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nla.1680030101
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  • 150
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    A Parallel Preconditioned Iterative Realization of the Panel Method in 3D (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 65-80 
    Details
    ISSN: 1070-5325
    Keywords: boundary value problem ; boundary element method ; preconditioning ; iterative method ; fast Fourier transform ; parallel algorithm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The parallel version of precondition iterative techniques is developed for matrices arising from the panel boundary element method for three-dimensional simple connected domains with Dirichlet boundary conditions. Results were obtained on an nCube-2 parallel computer showing that preconditioned iterative methods are very well suited also in three-dimensional cases for implementation on an MIMD computer and that they are much more efficient than usual direct solution techniques.
    Additional Material: 6 Ill.
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  • 151
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    Conference diary (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 91-93 
    Details
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nla.1680030102
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  • 152
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    Two-stage Multisplitting Methods with Overlapping Blocks (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 113-124 
    Details
    ISSN: 1070-5325
    Keywords: iterative methods ; linear systems ; multisplittings ; overlap ; parallel algorithms ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Parallel two-stage multisplitting methods with overlap for the solution of linear systems of algebraic equations are studied. It is shown that, under certain hypotheses, the method with overlap is asymptotically faster than that without overlap. Experiments illustrating this phenomenon are presented.
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  • 153
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    On Fast Computations with the Inverse to Harmonic Potential Operators via Domain Decomposition (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 91-111 
    Details
    ISSN: 1070-5325
    Keywords: boundary integral operators ; domain decomposition ; interface operators ; fast elliptic problem solvers ; parallel algorithms ; preconditioning ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this paper a method for fast computations with the inverse to weakly singular, hypersingular and double layer potential boundary integral operators associated with the Laplacian on Lipschitz domains is proposed and analyzed. It is based on the representation formulae suggested for above-mentioned boundary operations in terms of the Poincare-Steklov interface mappings generated by the special decompositions of the interior and exterior domains. Computations with the discrete counterparts of these formulae can be efficiently performed by iterative substructuring algorithms provided some asymptotically optimal techniques for treatment of interface operators on subdomain boundaries. For both two- and three-dimensional cases the computation cost and memory needs are of the order O(N logp N) and O(N log2 N), respectively, with 1 ≤ p ≤ 3, where N is the number of degrees of freedom on the boundary under consideration (some kinds of polygons and polyhedra). The proposed algorithms are well suited for serial and parallel computations.
    Additional Material: 2 Ill.
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  • 154
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    Short Communication: Two Properties of Diagonally Dominant Matrices (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 173-177 
    Details
    ISSN: 1070-5325
    Keywords: diagonally dominant matrix ; determinant ; norm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A property of strictly diagonally dominant matrices and a generalization of a Varga's bound for ∥ A-1∥∞ to the case ∥ A-1B∥∞ are given and the two-sided bounds for the determinants of strictly diagonally dominant matrices are derived
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  • 155
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    Analysis of Algorithms for Orthogonalizing Products of Unitary Matrices (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 125-145 
    Details
    ISSN: 1070-5325
    Keywords: orthogonalization ; QR factorization ; polar decomposition ; subspace tracking ; error analysis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We consider the problem of computing Uk = QkUk-1(where U0 is given) in finite precision (εM = machine precision) where U0 and theQi are known to be unitary. The problem is that Ûk, the computed product may not be unitary, so one applies an O(n2) orthogonalizing step after each multiplication to(a) prevent Ûk from drifing too far from the set of untary matrices(b) prevent Ûk from drifting too far from Uk the true product.Our main results are1. Scaling the rows to have unit length after each multiplication (the cheaptest of the algorithms considered) is usually as good as any other method with respect to either of the criteria (a) or (b).2. A new orthogonalization algorithm that guarantees the distance of Ûk (k = 1, 2, …) to the set of unitary matrices is bounded by n3.5εM for any choice of Qi.
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  • 156
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    Masthead (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996) 
    Details
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nla.1680030201
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  • 157
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    The Potential Fluid Flow Problem and the Convergence Rate of the Minimal Residual Method (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 525-542 
    Details
    ISSN: 1070-5325
    Keywords: potential flow problem in porous media ; mixed-hybrid formulation trilateral prismatic elements ; symmetric indefinite linear systems ; minimal residual method ; rate of convergence ; asymptotic convergence factor ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In the paper the potential fluic flow problem in porous media using Darcy's law and the continuity equation is solved. Mixed-hybrid finite element formulation based on general trilateral prismatic elements is considered. Spectral properties of resulting symmetric indefinite system of linear equations are examined. Minimal residual method for the solution of systems with a symmetric indefinite matrix is applied. The rate of convergence and the asymptotic convergence factor which depend on the eigenvalue distribution of the system matrix are estimated.
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  • 158
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    Masthead (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996) 
    Details
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nla.1680030301
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  • 159
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    Globalization of Newton's Method for Solving Non-linear Equations (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 239-249 
    Details
    ISSN: 1070-5325
    Keywords: non-linear equations ; global convergence ; Lagrangians ; non-linear programming ; Lagrangian globalization ; detour potentials ; homotopy methods ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The Lagrangian globalization (LG) method for non-linear equation-solving proposed in [10] is developed through theoretical analysis, the formulation of a particular LG algorithm, and a numerical illustration. New merit functions (termed detour potentials) for non-linear equation-solving, which broaden the LG concept, are also defined.
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  • 160
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    Conference diary (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 251-254 
    Details
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nla.1680030302
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  • 161
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    Toeplitz Preconditioners with Block Structure for First-order PDEs (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 21-44 
    Details
    ISSN: 1070-5325
    Keywords: first-order PDEs ; iterative methods ; preconditioners ; Toeplitz ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Preconditioners to nonsymmetric, nondiagonally dominant systems of equations are constructed and examined numerically. The preconditioners are based on a Toeplitz approach with a certain symmetry that we define. The inversion of the preconditioners is defined through a Fast Modified Sine Transform. As a model problem we study the systems of equations arising from a implicit time-discretization with a large time-step of a scalar hyperbolic PDE.
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  • 162
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    Generalization of Strang's Preconditioner with Applications to Toeplitz Least Squares Problems (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 3 (1996), S. 45-64 
    Details
    ISSN: 1070-5325
    Keywords: Toeplitz least squares problems ; circulant preconditioned conjugate gradient method ; deconvolution ; image restoration ; atmospheric imaging ; medical imaging ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this paper, we propose a method to generalize Strang's circulant preconditioner for arbitrary n-by-n matrices An. The th column of our circulant preconditioner Sn is equal to the th column of the given matrix An. Thus if An is a square Toeplitz matrix, then Sn is just the Strang circulant preconditioner. When Sn is not Hermitian, our circulant preconditioner can be defined as . This construction is similar to the forward-backward projection method used in constructing preconditioners for tomographic inversion problems in medical imaging. We show that if the matrix An has decaying coefficients away from the main diagonal, then is a good preconditioner for An. Comparisons of our preconditioner with other circulant-based preconditioners are carried out for some 1-D Toeplitz least squares problems: min ∥ b - Ax∥2. Preliminary numerical results show that our preconditioner performs quite well, in comparison to other circulant preconditioners. Promising test results are also reported for a 2-D deconvolution problem arising in ground-based atmospheric imaging.
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  • 163
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996) 
    Details
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1640120101
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  • 164
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    Conference diary (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 75-76 
    Details
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1640120102
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  • 165
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    The displacement bound estimation for structures with an interval description of uncertain parameters (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 1-11 
    Details
    ISSN: 1069-8299
    Keywords: interval parameters ; interval static responses ; interval linear equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A structure subjected to interval parameters and interval loads which are unknown, except for the fact that they belong to given intervals, is studied and the displacement bound estimation is given. These parameters are uncertain, and yet they are not treated as being random since no information is available on their probabilistic characteristics. A set of possible states of the system is described by interval matrices. The perturbation method is employed as a simple analytical tool for determining static responses - interval displacements of finite element equilibrium equations with interval parameters. The numerical results show that the proposed method is extremely effective.
    Additional Material: 1 Ill.
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  • 166
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    Super-time-stepping acceleration of explicit schemes for parabolic problems (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 31-42 
    Details
    ISSN: 1069-8299
    Keywords: explicit scheme ; implicit scheme time-stepping ; acceleration ; Chebyshev parabolic ; heat equation ; Stefan problem ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The goal of the paper is to bring to the attention of the computational community a long overlooked, very simple, acceleration method that impressively speeds up explicit time-stepping schemes, at essentially no extra cost. The authors explain the basis of the method, namely stabilization via wisely chosen inner steps (stages), justify it for linear problems, and spell out how simple it is to incorporate in any explicit code for parabolic problems. Finally, we demonstrate its performance on the (linear) heat equation as well as on the (non-linear) classical Stefan problem, by comparing it with standard implicit schemes (employing SOR or Newton iterations). The results show that super-time-stepping is more efficient than the implicit schemes in that it runs at least as fast, it is of comparable or better accuracy, and it is, of course, much easier to program (and to parallelize for distributed computing).
    Additional Material: 1 Ill.
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  • 167
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996) 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610090701
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  • 168
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    Hydrocarbon oxidation with Ph4PHSO5 catalyzed by manganese(III) porphyrins in homogeneous solution (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 539-544 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The oxidation of ethylbenzene with Ph4PHSO5 catalyzed by Mn(TMP)Cl in the presence of 4-tert-butylpyridine was studied in 1,2-dichloroethane. The reaction affords acetophenone together with minor amounts of 1-phenylethyl alcohol. The oxidation of 1-phenylethyl alcohol to acetophenone was studied under identical experimental conditions. In both cases, the oxidation rates are independent of the concentration of the substrates whereas they depend linearly on catalyst concentration. By increasing the concentration of 4-tert-butylpyridine, which acts as an axial ligand of the catalyst, saturation behavior is observed. The observations reported above, together with the chemoselectivity observed, the fact that the reactivities of the alkane and of the alcohol are similar and the activation parameters of ethylbenzene oxidation (ΔH
    Additional Material: 2 Ill.
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  • 169
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    1,3-Elimination in 2-(Tert-alkyl)adamantan-2-ols: An easy synthesis of bridgehead-substituted 2,4-dehydroadamantanes (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 588-591 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: When 2-(tert-alkyl)adamantan-2-ols (where the substituent is bi- or tricyclic) are thermolysed or the corresponding bromide is refluxed in pyridine, an unusual 1,3-elimination occurs, leading to 2,4-dehydroadamantanes bearing the tert-alkyl substituent on the cyclopropane system.
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  • 170
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    Zwitterionic pyridinecarboxylic acids (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 593-597 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A study of the acid-base behaviour of the three isomeric pyridinecarboxylic acids (picolinic, nicotinic and isonicotinic acid) was carried out using spectrophotometric and potentiometric measurements. The cationic form of picolinic acid converts partially into the corresponding zwitterion (pK1) within a borderline acidity range where neither the pH scale nor the acidity functions work satisfactorily. Protonation of the carboxyl groups (pK33) occurred at the highest acidity levels employed. The medium effects observed on the spectral curves were corrected by factor analysis. The potentiometric measurements gave values for pK1 and pK2 only, which were in good agreement with those determined spectrophotometrically.
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  • 171
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    A long-lived iminoxyl radical by electrooxidation of 1-nitroso-2-naphtholPresented in part at the 29th Middle Atlantic Regional ACS Meeting, Washington, DC, May 24-26, 1995. (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 695-700 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cyclic voltammetry of 1-nitroso-2-naphthol in the potential region 0 to 1·0 V vs Ag/AgCl using glassy carbon and platinum electrodes shows a reversible redox couple. The electrode process is diffusion controlled and corresponds to an EC mechanism. The one-electron oxidation product, an iminoxyl radical, is characterized by a triplet ESR signal at g = 2·0067 further split by three ring hydrogens. This radical is unusually long-lived, with half-life times of 150 s in water and 3600 s in acetonitrile.
    Additional Material: 2 Ill.
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    Bimolecular nucleophilic displacement at tertiary carbon centers: Aminolyses of 2-cyano-2-propyl and 1-cyanocyclooctyl arenesulfonatesDetermination of Reactivity by MO Theory, Part 100. For Part 99, see Ref. 1. (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 683-688 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic studies were carried out on the reactions of anilines with 2-cyano-2-propyl and 1-cyanocyclooctyl arenesulfonates in acetonitrile at 50·0°C. The second-order rate constants for the former are in general greater than those for the latter but the rates of the two become comparable for a strong nucleofuge. The cross-interaction constants, ρXZ (and βXZ), are considerably smaller (ca -0·04) than those for the primary (ca 0·33) and secondary (ca 0·12) compounds. The negative sign and small magnitude are consistent with a dissociative SN2 mechanism with a loose transition state structure. The ab initio MO theoretical results for Cl- + RCl ClR + Cl- at the MP2 level (MP2/6-31 + G*//MP2/6-31 + G*) confirm the looseness of the transition state for the tertiary (R) alkyl compounds. The average r(Cl…Cl) value is 47middot;88 ± 0·03 Å, which is larger than those for the reactions at primary (4·68 ± 0·02 Å) and secondary (4·80 ± 07middot;02 Å) carbon centers. Thus a looser transition state with a smaller magnitude of ρXZ for the tertiary carbon centers has a larger theoretical r(Cl…Cl) value.
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  • 173
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    The predominance of axial conformers for trans-4-substituted cyclohexene oxides (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 706-710 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A 1H NMR conformational study of cis- and trans-4-substituted cyclohexene oxides revealed an increased predominance, as compared with the parent 4-substituted cyclohexenes, of the equatorial conformer for cis-isomers and a preference of the axial conformer for trans-isomers. These conformational shifts can be rationalized in terms of intramolecular dipole-dipole and/or steric interactions. However, molecular mechanics calculations failed to reproduce the relative stability of the axial conformer in trans-4-substituted cyclohexene oxides.
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996) 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610091001
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    Computational investigations of carbonyl reactions: Comparison between nucleophilic addition versus enolate formation in the reaction of acetaldehyde with hydroxide ion (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 711-716 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reaction pathways leading to nucleophilic addition and enolate formation were investigated for the reaction between acetaldehyde and hydroxide anion. Ab initio calculations predict small activation barriers for both reactions in the gas phase. Monte Carlo simulations were performed to assess the effects of aqueous solvation. It was found that both reaction pathways involve significant solvent-induced activation barriers, in addition to effecting some structural changes in the transition state.
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  • 176
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    Aminolysis of O-(2,4-dinitrophenyl)-p,p′-disubstituted benzophenone oximes in benzene: Evidence for Hirst's mechanism (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 770-776 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of O-(2,4-dinitrophenyl)-substituted p,p′-dimethoxybenzophenone oxime, p,p′-fluorobenzophenone oxime and p,p′-dichlorobenzophenone oxime with pyrrolidine and piperidine in benzene were found to be third order in amine, with no uncatalytic route. The overall rate is a combined effect of rates of two routes, one of which increases and the other decreases with rise in temperature. The relative contribution of the two routes to overall rate varies with temperature, nucleofugicity of the substrate, nucleophilicity and concentration of amine. As a result, the effect of temperature on the overall rate for some reactions is positive and for others negative. This unusual temperature effect on the overall rate supports Hirst's mechanism.
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    Dimethyldioxirane reactions: Rate acceleration due to intramolecular H-bondingChemistry of Dioxiranes, Part 32. For Part 31, see Ref. 1. (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 751-758 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Absolute rate studies were carried out on a series of C(SINGLE BOND)H insertion reactions of dimethyldioxirane (1a). The substrates were chosen so that the distance between a single tertiary C(SINGLE BOND)H bond and an OH group could be varied. The measured rate constants indicate that a rate acceleration occurs when the distance between the reacting C(SINGLE BOND)H bond and the OH group permits intramolecular H-bonding stabilization of the transition state. A similar study in related compounds without the OH group showed no effect of chain length on the rate of the C(SINGLE BOND)H insertion reaction. A related study of the epoxidation reaction of la also found an increased rate when chain length permitted intramolecular H-bonding by an OH group.
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996) 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610091101
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  • 179
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    Nitrogen-15 NMR studies of hydrogen bonding and proton transfer in complexes of pyridine N-oxides with dichloroacetic acid in CDCl3 (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 746-750 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 15N NMR chemical shifts of eight substituted pyridine N-oxides (B) and their complexes (AHB) with methanol and dichloroacetic and trifluoromethanesulfonic acids were measured in chloroform-d at the natural abundance level. The measured chemical shifts are strongly affected by substituents, hydrogen bond strength and protonation. The plot of the relative chemical shifts, Δδ(15N) = δ(AHB) - δ(B), against ΔpKa gives a titration curve that reflects the variation of the hydrogen bond strength and the proton moves from the acid to the N-oxide. According to previous IR data, in the complexes from the inversion region (ΔpKa = 1·26), the proton is either delocalized (B…H…A) or more likely the lifetime is so short (≤10-13 s) that the method does not recognize the B…H-A and B+H…A- species. Protonation of pyridine N-oxides shifts the nitrogen signal ca 50 ppm to lower frequencies compared with the ca 123 ppm for pyridines.
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  • 180
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    15N and 13C NMR study of two adducts containing NHN+ and NHN- hydrogen bonds (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 781-786 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 13C and 15N NMR data are reported for two substituted nitronaphthalenes 1,8-bis(4-toluenesulphonamido)-2,4,7-trinitronaphthalene and 1,8-bis(4-toluenesulphonamido)-2,4,5,7-tetranitronaphthalene and their salts with 1,8-dimethylaminonaphthalene. The salts are shown to contain NHN+ and NHN- intramolecular hydrogen-bonded systems in CD3CN solutions, in agreement with x-ray diffraction data on solid samples and 1H NMR studies on solutions. Examples are given of both a symmetrical and an unsymmetrical bonding system for the NHN atoms. 15N NMR is shown to be particularly helpful in these studies, both 15N shielding and 1J(15N, 1H) couplings are of value. Additional assistance is obtained from 3J(13C9, N1H) data. © 1996 John Wiley & Sons, Ltd.
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  • 181
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    Elimination kinetics and mechanisms for several 2-alkoxyacetic acids in the gas phase (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 787-794 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the gas-phase elimination of three 2-alkoxyacetic acids were investigated in a static system, seasoned with allyl bromide, and in the presence of the free chain radical inhibitor cyclohexene. The working temperature and pressure range were 350·4-410·8°C and 57-261·5 torr, respectively. The reactions proved to be homogeneous and unimolecular and to follow a first-order rate law. The temperature dependence of the rate coefficients is given by the following equations: for 2-methoxyacetic acid, log k1 (s-1) = (12·10 ± 0·22)-(193·3 ± 2·8) kJ mol-1 (2·303RT)-1; for 2-ethoxyacetic acid, log k1 (s-1) = (12·76 ± 0·29)-(199·6 ± 3·7) kJ mol-1 (2·303RT)-1; and for 2-isopropoxyacetic acid, log k1 (s-1) = (12·40 ± 0·32)-(193·7 ± 3·9) kJ mol-1 (2·303RT)-1. The alkyl group R in ROCH2COOH does not seem to exert a significant effect on the rates. It is postulated that the predominant mechanism for the decomposition of the alkoxy acids involves a five-membered cyclic transition state, where the elimination of the RO substituents is assisted by the acidic proton of the COOH group. © 1996 John Wiley & Sons, Ltd.
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  • 182
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    Theoretical study of the thermal isomerization of fulvene to benzene (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 801-810 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The potential energy surface for the thermal isomerization of fulvene to benzene was studied by modified Gaussian-2 (G2M) and the bond additivity-corrected fourth-order perturbation Møller-Plesset (BAC-MP4) methods. Three isomerization pathways were investigated. One involves the intermediate prefulvene by a concerted mechanism, which has a significantly higher barrier. The second, also involving prefulvene and cyclopenta-1,3-dienylcarbene intermediates, has a barrier of 84·0 kcal mol-1. The third, a multi-step pathway, includes bicyclo[3.1.0]hexa-1,3-diene and cyclohexadiene carbene intermediates. The activation energy of the multi-step pathway was calculated to be 74·3 kcal mol-1, which is 7-11 kcal mol-1 higher than the experimental value obtained by a brief very low-pressure pyrolysis (VLPP) study. RRKM calculations were performed on the multi-step pathway in order to determine the rate of isomerization. These theoretical results cast doubt on the validity of the VLPP data. © 1996 John Wiley & Sons, Ltd.
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  • 183
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996) 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610091201
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  • 184
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    Mechanism of solid-solid resolution of pantolactone (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 795-800 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The enantioselective solid-solid clathration of (S)-pantolactone (1) into (R,R)-trans-2,3-bis(diphenylhydroxymethyl)-1,4-dioxaspiro[4·4]nonane (2) and -[4·5]decane (3) was studied preparatively and mechanistically using atomic force microscopy (AFM) measurements and crystal packing data. Short-distance solid-to-solid sublimation mechanisms occur in both cases with initial formation of epitaxial floes along the b-axis in 2 and random craters in 3. The bulk control in the phase rebuilding stage is understood from the particular crystal packings. Bulk control was largely lost in the phase transformation stage when passivation of the surfaces occurred in both cases. The host lattices of 2 and 3 exhibit closed molecular double layers with all hydroxyl groups inside and lacking access for intercalation of 1. The reaction has to start at isolated surface defects. Once started, new doors for further entrance of guest molecules (S)-1 are opened in the double layer. For practical use, both the crystallographic difficulties and the passivation have to be overcome. A slurry technique involving addition of stoichiometric amounts of water to the solids provided useful conditions for the preparative resolution of (R/S)-1 or further racemates exhibiting passivation, whereas heating alone speeded up the resolution of 2-methylpiperazine with 2. © 1996 John Wiley & Sons, Ltd.
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  • 185
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    Conformational analysis of 2-cyano-1,1-dihydroxyethane in solution (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 119-127 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The conformational space of the 2-cyano-1,1-dihydroxyethane molecule was studied at the semi-empirical PM3 level and ab initio MP2/6-31G**//6-31G level in the gas phase and in a low-polarity medium. This system has been chosen as a model compound for 2-cyanocyclohexanone propylene and ethylene acetals. This has allowed the study of the role of polar groups on the relative conformation of two adjacent OH groups, which is of interest also in relation to the anomeric effect in carbohydrate chemistry. Solvent effects are taken into account using a continuum model with general cavity shapes.
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  • 186
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996) 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610090201
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  • 187
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    Apotransferrin proton dissociation and interactions with hydrogencarbonate in neutral media (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 111-118 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A spectrofluorimetric titration analysis of the proton dissociation and the interactions of human serum transferrin with hydrogencarbonate was performed at pH 7·0-9·0. Apotransferrin loses a single proton probably per binding site with Ka = (6·80 ± 0·35) × 10-9 M. This proton dissociation is independent of the hydrogencarbonate concentration. Apotransferrin does not interact with CO32-. However, it interacts with two HCO3-, exhibiting two different affinity constants; the dissociation constant presumably for the C-site is KC = (4·40 ± 0·15) × 10-3 M and that for presumably the N-site is KN = (3·60 ± 0·30) × 10-2 M. These interactions are independent of pH and occur with the unprotonated and protonated apotransferrin species with the same low affinities. Such affinities are probably induced by ionic interactions involving the side chain of the arginine residues in each of the two binding sites. As for the proton dissociation, it can occur with one of the other side-chains of the amino acid residues of these binding sites.
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  • 188
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    MM3 calculations on sulfoxides (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 159-167 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structures of several sulfoxides, including dimethyl sulfoxide and pentamethylene sulfoxide, were fitted with the MM3 force field to existing experimental data from electron diffraction and microwave spectroscopy. The vibrational spectra were also fitted for dimethyl sulfoxide. The torsional parameters could not be determined from existing experimental data, so the torsional profile for methyl ethyl sulfoxide was fitted to ab initio values.
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    1,3-dioxenium cations: Synthesis, structure and topomerization (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 129-136 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Previously unknown 1,3-dioxenium perchlorates were obtained by coupling 1,3-diketones with aliphatic ketones in an acetic acid solution of perchloric acid. The dioxenium ring of 4,6-bis(p-methoxystyryl)-2,2-pentamethylenespiro-1,3-dioxenium perchlorate in the crystal possesses the envelope conformation, the geometry of the carbon triad being close to that of the allyl cations. Variable-temperature 1H NMR spectra of unsymmetrical 1,3-dioxenium cations revealed the occurrence of a sufficiently fast enantiotopomerization process governed by the C(SINGLE BOND)O bond dissociation-recombination mechanism.
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  • 190
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    Solvent effects on reactions of hydroxide ion with phosphorus(V) esters. A quantitative treatment (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 145-151 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Second-order rate constants of reactions of HO- with phosphate, phosphinate and thiophosphinate esters, (PhO)2PO.OC6H4NO2-p, Ph2PO.OC6H4NO2-p, Ph2PO.SPh, Ph2PO.SC6H4NO2-p and Ph2PO.SEt, go through minima with decreasing water content of H2O-MeCN or H2O-t-BuOH. The rate decrease is due to stabilization of the non-ionic ester on addition of organic solvent to H2O. This inhibition is partially offset by stabilization of the anionic transition states and in the drier solvents partial desolvation of HO- increases rates.
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  • 191
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    Kinetic and equilibrium studies of σ-adduct formation and nucleophilic substitution in the reactions of morpholine with 1,3,5-trinitrobenzene and some phenyl aryl ethers in dimethyl sulphoxide (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 152-158 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reactions of morpholine in dimethyl sulphoxide at unsubstituted ring positions of 1,3,5-trinitrobenzene, and phenyl 2,4,6-trinitrophenyl ether, yield anionic σ-adducts via zwitterionic intermediates. Reactions at the 1-position of phenyl 2,4,6-trinitrophenyl ether, phenyl 2,4-dinitronaphthyl ether, and phenyl 2,4-dinitrophenyl ether result in substitution of the phenoxy groups. In both these reaction types proton-transfer is rate-limiting. Comparison of kinetic and equilibrium data with those for corresponding reactions of piperidine shows that rate constants for proton transfer are similar for the two amines, but equilibrium constants for zwitterion formation have lower values for morpholine, the less basic amine. Implications for base catalysis are discussed.
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  • 192
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    Molecular mechanics calculations (MM3) on nitriles and alkynes (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 191-202 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The MM3 force field has been extended to include the nitriles and alkynes. Structures, heats of formation, dipole moments and conformational equilibria for aliphatic nitriles and alkynes compounds are fitted to within experimental error. The vibrational spectra for aliphatic nitriles and alkynes were studied, and the experimental values were fitted to an rms error of about 30 cm-1. Previous MM2 studies of nitriles and alkynes left unresolved the length of the Csp(SINGLE BOND)Csp3 bonds in isopropylnitrile, 3-methylbutyne, and tert-butylacetylene. In each of these compounds, previous MM2 results disagree with experiment. The present MM3 studies and quantum mechanical calculations (MP2/6-31G** and B3LYP/6-31G*) confirmed the previous MM2 results.
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    Studies on the nitrosation of N-silylated cyclopentenylamines (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 227-233 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The diazotization of N-silylated N-methyl- and N-phenylcyclopentenylamines affords products derived from intermediate methyl- and phenyldiazonium ions. However, when this method is applied to N,N-bissilylated cyclopentenylamines, the products obtained do not confirm the formation of a cyclopentenyl cation intermediate.
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  • 194
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    Theoretical and experimental analysis of properties in heterocycles containing the aminosulphonylamino moiety (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 203-211 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A theoretical and experimental analysis of the geometric and electronic properties of compounds containing the aminosulphonylamino moiety was carried out. The theoretical properties were calculated using molecular orbital ab initio methods at the Hartree-Fock (HF) and second order Möller-Plesset (MP2) levels of theory, local density functional (LDF) ab initio methods and the semi-ab initio method, SAM1, on sulphamide and seven heterocyclic compounds containing the aminosulphonylamino group. The experimental analysis has been performed using x-ray structures of related compounds gathered in the Cambridge Structural Database together with experimental dipole moments and 13CNMR shifts of some of the compounds studied. Comparison of the experimental analysis with the theoretical results indicates that none of the methods studied is the most adequate to describe the geometry and electronic distribution of these molecules. The use of the 6-31G* basis set to compute the geometry of these molecules and methods which include electronic correlation (MP2/61G*//RHF/6-31G*, MP2/6-31G* and LDF) to quantify their electronic distribution are proposed.
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  • 195
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    Photocyclization of 2-(dialkylamino)ethyl acetoacetates: Remote proton transfer and Stern-Volmer quenching kinetics in the system involving two reactive excited states (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 221-226 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Upon irradiation, 2-(dibenzylamino)ethyl and 2-(N-benzyl-N-methylamino)ethyl acetoacetate (1a and 1b) undergo photocyclization via remote proton transfer from the benzyl group to the acetyl carbonyl oxygen to give eight-membered azalactones. Irradiation of the corresponding (diisopropylamino)- and (dimethylamino)ethyl esters gave no azalactones. Introduction of the methyl group on C-2 of 1a brought about a complicated photoreaction, probably due to competition of α-cleavage. The Stern-Volmer plots for the photoreaction of 1a did not show the linear relationship, indicating that the photoreaction proceeds from two reactive excited states. The Stern-Volmer quenching equation for the system was obtained by applying the steady-state approximation and was used for the analysis of the photoreaction of 1a. The triplet lifetime was determined to be 1·6 × 10-8 s.
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    Benzamidines, alkamidines and formamidines formed by use of aryl- and alkyliminodimagnesium: Molar ratio and structure of reagent governing the reactionAryliminodimagnesium Reagents, Part XXVIII. For Part XXVII, see Ref. 3b. (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 212-220 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In order to extend the the method for preparation of amidines using N-Mg reagents, aryl- and alkyliminodimagnesium [IDMg, ArN(MgBr)2 and RN(MgBr)2] were reacted with esters, amides, ortho- esters, acetals, aminoacetal and arene- and alkane carbonitriles. Among the compounds used, aminoacetal and carbonitriles were proved to be useful as starting materials for amidine preparation; alkyl-IDMgs were successfully used for the first time. It was noted that an excess molar amount of IDMg is needed in the reported reaction of ArN(MgBr)2 with benzonitrile (aryl-aryl combination), whereas no excess is needed in aryl-alkyl, alkyl-aryl, and alkyl-alkyl combinations of reagent and substrate. From the viewpoint previously proposed in terms of relative efficiency of single electron transfer in the reactions of magnesium reagents, the most probable reason for the difference in the need for an excess molar amount of aryl and alkyl IDMg was ascribed to the difference in the electron-donating abilities of reagents. Additional minor reasons are discussed.
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996) 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610090401
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    ESR study of rotational motions of spin-labeled long-chain nitroxides in solution (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 234-240 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Information on the rotational motion of various types of spin-labelled long-chain nitroxides was obtained from the anisotropic ESR signals. By varying the position of the nitroxide moiety along the chain, the intrinsic flexibility of molecular chain was examined. The rotational correlation times (τc) of spin-labelled long-chain nitroxides were about 10-10 s. The activation parameters for rotational motion were estimated from the temperature and pressure dependences of τc. It was found that the activation entropy observed for methyl 16-doxyl stearate is obviously large compared with those for methyl 5- and methyl 12-doxyl stearates. The results suggest an increase in the molecular motions at the end of the hydrocarbon chain. The viscosity dependence of τc is discussed in terms of the difference in the strength between solute-solvent and solvent-solvent interactions.
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    Spectrophotometric determination of anionic micellar binding constants of ionized and non-ionized phenyl and methyl salicylates (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 295-300 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ionized (S-) and non-ionized (SH) phenyl (PSH) and methyl (MSH) salicylates exhibit strong and undetectable absorption at 350 nm, respectively. These molecular absorption properties were used to determine the binding constants of S- and SH with the micelles of sodium dodecyl sulphate in terms of the pseudophase model of micelles. The binding constants (K1) of S- are 4·0 ± 2·0 dm3 mol-1 for PSH and 5·7 ± 1·2 dm3 mol-1 for MSH and those (K2) of SH are 2350 ± 90 dm3 mol-1 for PSH and 100 ± 10 dm3 mol-1 for MSH at 30°C.
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    Oxidation of substituted phenethyl alcohols by sodium N-chlorobenzenesulphonamide: A kinetic study (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 279-286 
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    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the oxidation of six substituted phenethyl alcohols by sodium N-chlorobenzenesulphonamide or chloramine-B (CAB) in the presence of HCl was studied at 35°C. The rate shows a first order dependence on [CAB]0 and [H+] and is of fractional order in [PEA]0 and [Cl-]. Ionic strength variations, addition of the reaction product of benzenesulphonamide and variation of the dielectric constant of the medium have no effect on the rate. The solvent isotope effect k1H2O/k1D2O ≅ 0·78. Proton inventory studies were made in H2O-D2O mixtures. The rates correlate satisfactorily with Hammett's LFER. The reaction constant ρ was -3·5 for electron-releasing substituents and -0·30 for electron withdrawing groups at 35°C. Activation parameters ΔH
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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