bluuebunny/crossref_metadata_2025 huggingface dataset:
Preconditioned iterative algorithms for large sparse unsymmetric problems
Authors: Pini G. , Zilli G.
Published: August 2005

A numerical study of the efficiency of the generalized conjugate residual methods (GCR) is performed using three different preconditioners all based upon an incomplete LU factorization. The GCR behavior is evaluated in connection with the solution of large, sparse unsymmetric systems of equations, arising from the finite element integration of the diffusion‐convection equation for 2‐dimensional (2‐D) and 3‐D problems with different Peclet and Courant numbers. The order of the test matrices ranges from 450 to 1700. Results from a set of numerical experiments are presented and comparisons with preconditioned GCR methods and with direct method are carried out.
Approximating solutions to linear and nonlinear differential equations by the method of maximum entropy
Authors: Baker‐Jarvis James , Schultz Dwight , Alamendine Jihad
Published: August 2005

A technique to approximate the solution to linear and nonlinear boundary value problems is developed and numerical examples are presented. The technique is based on the method of maximum entropy with moments of the differential equation used as constraints. The method is very general and has the advantage that additional information can be fed into the solution, such as the function's domain or the positivity or negativity of the solution. The technique should find applications in approximating solutions to equations which may or may not contain noise and as an alternative to finite difference and Fourier series solutions and may have applications to large scale simulations.
A finite difference approach to the equations of age‐dependent population dynamics
Authors: Kannan R. , Ortega R.
Published: August 2005

We establish the convergence of the finite difference scheme for the nonlinear equations of population dynamics proposed by Guertin and MacCamy. The applicability of the discrete equations to establish qualitative properties of the solution to the continuous problem is also illustrated.
Mixed‐hybrid finite elements and streamline computation for the potential flow problem
Authors: Kaasschieter E. F. , Huijben A. J. M.
Published: August 2005

An important class of problems in mathematical physics involves equations of the form −∇ · (A∇ϕ) = f. In a variety of problems it is desirable to obtain an accurate approximation of the flow quantity u = −A∇ϕ. Such an accurate approximation can be determined by the mixed finite element method. In this article the lowest‐order mixed method is discussed in detail. The mixed finite element method results in a large system of linear equations with an indefinite coefficient matrix. This drawback can be circumvented by the hybridization technique, which leads to a symmetric positive‐definite system. This system can be solved efficiently by the preconditioned conjugate gradient method. After approximating u by the lowest‐order mixed finite element method, streamlines and residence times can be determined easily and accurately by computations at the element level.
Probabilistic viscosity algorithm for the scalar conservation law
Authors: Korzeniowski Andrzej
Published: August 2005

We derive an algorithm for solving the initial value problem for ut = ½σ2uxx + f(u)ux. The approach is based on the representation of the solution to the above equation in the form of the functional of Brownian motion. For small σ we get the approximation for ut = f(u)ux. A comparison with the random choice method is illustrated by the numerical example.
Box‐spline–based approach to the formulation of numerical methods for partial differential equations
Authors: Diamond Harvey , Raphael Louise Arakelian , Williams Daniel A.
Published: August 2005

A multivariate box spline framework for the formulation of numerical methods for partial differential equations has been constructed. In particular, a fourth‐order Galerkin method and a second‐order collocation method were derived and applied to a test problem (classical Poisson equation on a square). The examples indicate that accuracy compares favorably with standard methods and the success of iterative schemes suggests an underlying stabilizing effect.
Error estimates for a discretized Galerkin method for a boundary integral equation in two dimensions
Authors: Penzel F.
Published: August 2005

We present a priori and a posteriori estimates for the error between the Galerkin and a discretized Galerkin method for the boundary integral equation for the single layer potential on the square plate. Using piecewise constant finite elements on a rectangular mesh we study the error coming from numerical integration. The crucial point of our analysis is the estimation of some error constants, and we demonstrate that this is necessary if our methods are to be used. After the determination of these constants we are in the position to prove invertibility and quasioptimal convergence results for our numerical scheme, if the chosen numerical integration formulas are sufficiently precise. © 1992 John Wiley & Sons, Inc.
Unified symmetric finite element and boundary integral variational coupling methods for linear fluid–structure interaction
Authors: Zeng Xiaogang , Bielak Jacobo , Maccamy Richard C.
Published: August 2005

This article concerns the development of energy‐based variational formulations and their corresponding finite element–boundary element Rayleigh–Ritz approximations for solving the time‐harmonic vibration and scattering problem of an inhomogeneous penetrable fluid or solid object immersed in a compressible, inviscid, homogeneous fluid. The resulting coupled finite element and boundary integral methods (FEM‐BEM) have the following attractive features: (1) Separate direct and complementary variational principles lead naturally to several alternative structure variable and fluid variable methodologies. (2) The solution in the exterior region is represented by a combined single‐ and double‐layer potential which ensures the validity of the methods for all wave numbers; even though this representation introduces hypersingular integrals, for actual computations the hypersingular operator may be rewritten in terms of single‐layer potentials, which can be integrated by standard techniques. (3) Since the discretized equations for the interior region and for the boundary are derived from the first variation of bilinear functionals the resulting algebraic systems of equations are always symmetric. In addition, the transition conditions across the interface are natural. This allows one to approximate the solutions within the interior and exterior regions independently, without imposing any boundary constraints.
Defect correction and Galerkin's method for second‐order boundary value problems
Authors: Chibi Ahmed‐Salah , Moore Gerald
Published: August 2005

The defect correction technique, based on the Galerkin finite element method, is analyzed as a procedure to obtain highly accurate numerical solutions to second‐order elliptic boundary value problems. The basic solutions, defined over a rectangular region Ω, are computed using continuous piecewise bilinear polynomials on rectangles. These solutions are O(h2) accurate globally in the second‐order discrete Sobolev norm. Corrections to these basic solutions are obtained using higher‐order piecewise polynomials (Lagrange polynomials or splines) to form defects. An O(h2) improvement is gained on the first correction. The lack of regularity of the discrete problems (beyond the second‐order Sobolev norm) makes it impossible to retain this order of improvement, but for problems satisfying certain periodicity conditions, straightforward arbitrary accuracy is obtained, since these problems possess high‐order regularity. © 1992 John Wiley & Sons, Inc.
On parallel algorithms for semidiscretized parabolic partial differential equations based on subdiagonal Padé approximations
Authors: Khaliq A. Q. M. , Twizell E. H. , Voss D. A.
Published: August 2005

It is well known that methods for solving semidiscretized parabolic partial differential equations based on the second‐order diagonal [1/1] Padé approximation (the Crank–Nicolson or trapezoidal method) can produce poor numerical results when a time discretization is imposed with steps that are “too large” relative to the spatial discretization. A monotonicity property is established for all diagonal Padé approximants from which it is shown that corresponding higher‐order methods suffer a similar time step restriction as the [1/1] Padé. Next, various high‐order methods based on subdiagonal Padé approximations are presented which, through a partial fraction expansion, are no more complicated to implement than the first‐order implicit Euler method based on the [0/1] Padé approximation; moreover, the resulting algorithms are free of a time step restriction intrinsic to those based on diagonal Padé approximations. Numerical results confirm this when various test problems from the literature are implemented on a Multiple Instruction Multiple Data (MIMD) machine such as an Alliant FX/8. © 1993 John Wiley & Sons, Inc.
Some results on the stability and dynamics of finite difference approximations to nonlinear partial differential equations
Authors: Choudhury S. Roy
Published: August 2005

A miscellany of results on the nonlinear instability and dynamics of finite difference discretizations of the Burgers and Kortweg de Vries equations is obtained using a variety of phase‐plane, functional analytic, and regularity methods. For the semidiscrete (space‐discrete, time‐continuous) schemes, large‐wave‐numer instabilities occurring in special exact solutions are investigated, and parameter values for which the semidiscrete scheme is monotone are considered. For fully discrete schemes (space and time discrete), large‐wave‐number instabilities introduced by various time‐stepping schemes such as forward Euler, leapfrog, and Runge–Kutta schemes are analyzed. Also, a time step restriction for the monotonicity of the forward‐Euler time‐stepping scheme, and regularity of a 4‐stage monotone/conservative Runge–Kutta time stepping are investigated. The techniques used here may be employed, in conjunction with bifurcation‐theoretic and weakly nonlinear analyses, to analyze the stability of numerical schemes for other nonlinear partial differential equations of both dissipative and dispersive varieties. © 1993 John Wiley & Sons, Inc.
An organization of sparse gauss elimination for solving partial differntial equations on distributed memory machines
Authors: Mu Mo , Rice John R.
Published: August 2005

A computational arrangement of Gauss elimination is presented for solving sparse, nonsymmetric linear systems arising from partial differential equation problems. It is particularly targeted for use on distributed memory message passing multiprocessor computers and it is presented and analyzed in this context. The objective of the algorithm is to exploit the sparsity (i.e., reducing computation, communication, and memory requirements) and to optimize the data structure manipulation overhead. The algorithm is based on the nested dissection approach, which starts with a large set of very sparse, completely independent subsystems and progresses in stages to a single, nearly dense system at the last stage. The computational efforts of each stage are roughly equal (almost exactly equal for model problems), yet the data structures appropriate for the first and last stages are quite different. Thus we use different types of data structures and algorithm components at different stages of the solution. The new organization is a combination of previous techniques including nested dissection, implicit block factorization, domain decomposition, fan‐in, fan‐out, up‐looking, down‐looking, and dynamic data structures. © 1993 John Wiley & Sons, Inc.
Numerical solution of partial differential equations on curved domains by collocation
Authors: Van Blerk J. J. , Botha J. F.
Published: August 2005

The application of the finite element collocation method to two‐ and three‐dimensional partial differential equations is hampered by the fact that its accuracy depends largely on the position of the collocation points. The method has, in the past, thus mainly been applied to two‐dimensional differential equations defined on rectangular domains. In this case the method yields an optimal global convergence rate, when the Gauss‐Legendre quadrature points are used as collocation points. It is shown in this paper that the same accuracy can also be achieved in the case of differential equations defined on nonrectangular domains. The only prerequisite for this is to solve the differential equation on a rectangular domain, mapped onto the nonrectangular domain of the differential equation by a bilinear blended map. © 1993 John Wiley & Sons, Inc.
Studies of an interface relaxation domain decomposition technique using finite elements on a parallel computer
Authors: Wang K. P. , Bruch J. C.
Published: August 2005

Studies are presented for an interface relaxation domain decomposition technique using finite elements on an iPSC/2 D5 Hypercube Concurrent computer. The general type of problem to be solved is one governed by a partial differential equation. The application of the approach, however, will be extended to a free boundary value problem by appropriate modification of the numerical scheme. Using the domain decomposition technique, the computation domain is subdivided into several subdomains. In addition, on the interfaces between two adjacent subdomains are imposed a continuity condition on one side and an equilibrium condition on the other side. Successive overrelaxation iterative processes are then carried out in all subdomains with a relaxation process imposed on the interfaces. With this domain decomposition technique, the problem can be solved parallelly until convergence is reached both in the interiors and on the interfaces of all subdomains. Moreover, the formulation includes a simple domain decomposer that automatically divides a finite element mesh into a list of subdomains to guarantee load balancing. Furthermore, it is shown, through numerical experiments performed on an example problem of free surface seepage through a porous dam, how the values of the relaxation parameters, the choice of imposed boundary conditions, and the number of subdomains (i.e., the number of processors used) affect the solution convergence in this parallel computing environment. © 1993 John Wiley & Sons, Inc.
Numerical approximation of bounded solutions for semilinear elliptic equations in an unbounded cylindrical domain
Authors: Fuming Ma
Published: August 2005

We consider the approximation of bounded solutions for a class of semilinear elliptic equations in an unbounded cylindrical domain. On certain conditions, the existence of approximate solutions for the semidiscretization of the problem is proved. Error estimates, applications, and a numerical example are also given. © 1993 John Wiley & Sons, Inc.
Error analysis of the finite‐strip method for parabolic equations
Authors: Smith Stanley S. , Allen Myron B.
Published: August 2005

The finite‐strip method (FSM) is a hybrid technique which combines spectral and finite‐element methods. Finite‐element approximations are made for each mode of a finite Fourier series expansion. The Galerkin formulated method is set apart from other weighted‐residual techniques by the selection of two types of basis functions, a piecewise linear interpolating function and a trigonometric function. The efficiency of the FSM is due in part to the orthogonality of the complex exponential basis: The linear system which results from the weak formulation is decoupled into several smaller systems, each of which may be solved independently. An error analysis for the FSM applied to time‐dependent, parabolic partial differential equations indicates the numerical solution error is O(h2 + M−r). M represents the Fourier truncation mode number and h represents the finite‐element grid mesh. The exponent r ≥ 2 increases with the exact solution smoothness in the respective dimension. This error estimate is verified computationally. Extending the result to the finite‐layer method, where a two‐dimensional trigonometric basis is used, the numerical solution error is O(h2 + M−r + N−q). The N and q represent the trucation mode number and degree of exact solution smoothness in the additional dimension. © 1993 John Wiley & Sons, Inc.
Superconvergence of recovered gradients of discrete time/piecewise linear Galerkin approximations for linear and nonlinear parabolic problems
Authors: Wheeler Mary F. , Whiteman J. R.
Published: August 2005

Superconvergent error estimates in l2(H1) and l∞(H1) norms are derived for recovered gradients of finite difference in time/piecewise linear Galerkin approximations in space for linear and quasinonlinear parabolic problems in two space dimensions. The analysis extends previous results for elliptic problems to the parabolic context, and covers problems in regions with nonsmooth boundaries under certain assumptions on the regularity of the solutions. © 1994 John Wiley & Sons, Inc.
Crank‐Nicolson method for the numerical solution of models of excitability
Authors: López‐Marcos J. C.
Published: August 2005

We analyze a Crank‐Nicolson scheme for a family of nonlinear parabolic partial differential equations. These equations cover a wide class of models of excitability, in particular the Hodgkin Huxley equations. To do the analysis, we have in mind the general discretization framework introduced by López‐Marcos and Sanz‐Serna [in Numerical Treatment of Differential Equations, K. Strehemel, Ed., Teubner‐Texte zur Mathematik, Leipzig, 1988, p. 216]. We study consistency, stability and convergence properties of the scheme. We use a technique of modified functions, introduced by Strang [Numer. Math. 6, 37 (1964)], in the study of consistency. Stability is derived by means of the energy method. Finally we obtain existence and convergence of numerical approximations by means of a result due to Stetter (Analysis of Discretization Methods for Ordinary Differential Equations. Springer‐Verlag, Berlin, 1973). We show that the method has optimal order of accuracy in the discrete H1 norm. © 1994 John Wiley & Sons, Inc.
Viscous stress relaxation, characteristics, and numerical boundary conditions
Authors: Trapp John A. , Ransom Victor H.
Published: August 2005

The anomalous infinite propagation speeds in the classical parabolic flow equations are removed by the inclusion of a small amount of fluid elasticity or viscous stress relaxation. The inclusion of such effects results in a hyperbolic system of equations with a complete set of characteristic equations. The directional characteristic equations are used to give insights into the appropriate boundary molecules to be used in finite difference numerical schemes. © 1994 John Wiley & Sons, Inc.
A fourth‐order finite difference scheme for two‐dimensional nonlinear elliptic partial differential equations
Authors: Saldanha Godfrey , Ananthakrishnaiah U.
Published: August 2005

A finite difference scheme for the two‐dimensional, second‐order, nonlinear elliptic equation is developed. The difference scheme is derived using the local solution of the differential equation. A 13‐point stencil on a uniform mesh of size h is used to derive the finite difference scheme, which has a truncation error of order h4. Well‐known iterative methods can be employed to solve the resulting system of equations. Numerical results are presented to demonstrate the fourth‐order convergence of the scheme. © 1995 John Wiley & Sons, Inc.
Efficient computation of a mathematical model for the damping of pressure waves in tubes of circular form
Authors: Kroller M.
Published: August 2005

A computational method for a system of partial integrodifferential equations of Volterra type is developed. These equations describe the damping of pressure waves in tubes of circular form, taking into account the nonstationary increase of friction. The analytical solution of the model equations is given. A rapidly convergent expansion as well as sharp error estimates for the approximate solutions are obtained. Finally an efficient algorithm using recursion formulas is presented and the algorithm is compared numerically with the method of characteristics. © 1995 John Wiley & Sons, Inc.
Finite element approximation of optimal control problems for the von Kármán equations
Authors: Hou L. Steven , Turner James C.
Published: August 2005

This article is concerned with optimal control problems for the von Kármán equations with distributed controls. We first show that optimal solution exist. We then show that Lagrange multipliers may be used to enforce the consstraints and derive an optimality system from which optimal states and controls may be deduced. Finally, we define finite element approximations of solutions for the optimality system and derive error estimate for the approximations. © 1995 John Wiley & Sons, Inc.
Finite difference reaction diffusion equations with nonlinear boundary conditions
Authors: Pao C. V.
Published: August 2005

This article is concerned with numerical solutions of finite difference systems of reaction diffusion equations with nonlinear internal and boundary reaction functions. The nonlinear reaction functions are of general form and the finite difference systems are for both time‐dependent and steady‐state problems. For each problem a unified system of nonlinear equations is treated by the method of upper and lower solutions and its associated monotone iterations. This method leads to a monotone iterative scheme for the computation of numerical solutions as well as an existence‐comparison theorem for the corresponding finite difference system. Special attention is given to the dynamical property of the time‐dependent solution in relation to the steady‐state solutions. Application is given to a heat‐conduction problem where a nonlinear radiation boundary condition obeying the Boltzmann law of cooling is considered. This application demonstrates a bifurcation property of two steady‐state solutions, and determines the dynamic behavior of the time‐dependent solution. Numerical results for the heat‐conduction problem, including a test problem with known analytical solution, are presented to illustrate the various theoretical conclusions. © 1995 John Wiley & Sons, Inc.
Fractional step algorithm for solving a multi‐dimensional diffusion‐migration equation
Authors: Kwok Yue‐Kuen , Wu Charles C. K.
Published: August 2005

The earlier fractional step algorithm for solving the diffusion–migration equation in electrochemistry is extended to a multi‐dimensional multi‐species system with second‐order spatial accuracy. For each time‐step increment, the algorithm consists of three stages: (i) diffusion, (ii) satisfaction of the electroneutrality constraint, and (iii) migration. Each stage accounts for one individual physical process. Exact analytical solutions are derived for a two‐species system and comparisons between exact and numerical results are made. Numerical results are also obtained for a two‐dimensional three‐species electrochemical model. © 1995 John Wiley & Sons, Inc.
A numerical study of a spectral problem in solid‐fluid type structures
Authors: Conca Carlos , Durán Mario
Published: August 2005

This article presents a numerical study of a spectral problem that models the vibrations of a solid–fluid structure. It is a quadratic eigenvalue problem involving incompressible Stokes equations. In its numerical approximation we use Lagrange finite elements. To approximate the velocity, degree 2 polynomials on triangles are used, and for the pressure, degree 1 polynomials. The numerical results obtained confirm the theory, as they show in particular that the known theoretical bound for the maximum number of nonreal eigenvalues admitted by such a system is optimal. The results also take account of the dependence of vibration frequencies with respect to determined physical parameters, which have a bearing on the model. © 1995 John Wiley & Sons, Inc.
High resolution upwind‐mixed finite element methods for advection‐diffusion equations with variable time‐stepping
Authors: Dawson Clint
Published: August 2005

Numerical methods for advection‐diffusion equations are discussed based on approximating advection using a high‐resolution upwind finite difference method, and incorporating diffusion using a mixed finite element method. In this approach, advection is approximated explicitly and diffusion implicitly. We first describe the basic procedure where each advection time‐step is followed by a diffusion step. Because the explicit nature of the advective scheme requires a CFL time‐step constraint, the basic procedure may be expensive, especially if the CFL constraint is severe. Two alternative time‐stepping approaches are presented for improving computational efficiency while preserving accuracy. In the first approach, several advective time‐steps are computed before taking a diffusion step. In the second approach, the advective time‐steps are also allowed to vary spatially. Numerical results for these three procedures for a model problem arising in flow through porous media are given. © 1995 John Wiley & Sons, Inc.
Synthesis, characterization and water absorbency properties of poly(acrylic acid)/sodium humate superabsorbent composite
Authors: Li An , Zhang Junping , Wang Aiqin
Published: August 2005

A novel poly(acrylic acid)/sodium humate superabsorbent composite was synthesized by aqueous solution polymerization of acrylic acid using N, N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator in the presence of sodium humate. The effects on water absorbency such as initial monomer concentration, degree of neutralization of acrylic acid, amount of crosslinker, initiator and sodium humate, etc. were investigated. The water absorbency of the superabsorbent composite synthesized under optimal synthesis conditions with a sodium humate content of 20% exhibited an absorption of 1268 g H2O/g sample and 93 g H2O/g sample in distilled water and in 0.9 wt% NaCl solution, respectively. Swelling rate and water retention tests were also carried out. The results show that sodium humate, as a kind of functional filler, can enhance comprehensive properties of superabsorbent composite and reduce the product cost significantly. Copyright © 2005 John Wiley & Sons, Ltd.
Expression and localization of Reg IV in human neoplastic and non‐neoplastic tissues: Reg IV expression is associated with intestinal and neuroendocrine differentiation in gastric adenocarcinoma
Authors: Oue Naohide , Mitani Yoshitsugu , Aung Phyu Phyu , Sakakura Chouhei , Takeshima Yukio , Kaneko Mayumi , Noguchi Tsuyoshi , Nakayama Hirofumi , Yasui Wataru
Published: August 2005

Regenerating islet‐derived family, member 4 (Reg IV) is a candidate marker for cancer and inflammatory bowel disease. In the present study, immunohistochemical analysis of Reg IV was performed in various human neoplastic (n = 289) and non‐neoplastic tissues. In the stomach, foveolar epithelium was negative for Reg IV, whereas goblet cells of intestinal metaplasia and neuroendocrine cells at the base of intestinal metaplasia expressed Reg IV. Neuroendocrine cells of the small intestine and colon showed strong expression of Reg IV, whereas goblet cells of the small intestine and colon showed weak or no expression of Reg IV. Insulin‐producing beta cells of the endocrine pancreas were positive for Reg IV. Among 143 gastric adenocarcinomas, Reg IV expression was detected in 42 (29.4%) and was associated with both the intestinal mucin phenotype and neuroendocrine differentiation. No association was found between Reg IV expression and clinical characteristics such as tumour stage and patient prognosis. Of 36 colorectal adenocarcinomas, 13 (36.1%) were positive for Reg IV, which was associated with tumour stage (p = 0.0379, Fisher's exact test). Expression of Reg IV was detected in 14 (93.3%) of 15 colorectal carcinoid tumours. Reg IV expression was also detected in 5 (21.7%) of 23 ductal adenocarcinomas of the pancreas. In contrast, lung cancers (n = 30) and breast cancers (n = 30) did not express Reg IV. This is the first immunohistochemical analysis of the expression and distribution of Reg IV protein in human tumours. These data suggest that Reg IV is expressed by gastrointestinal and pancreatic tumours, including adenocarcinomas and carcinoid tumours, and that Reg IV is associated with intestinal and neuroendocrine differentiation of the stomach and gastric carcinoma. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Second trimester ultrasound prenasal thickness combined with nasal bone length: a new method of Down syndrome screening
Authors: Maymon Ron , Levinsohn‐Tavor Orna , Cuckle Howard , Tovbin Yosef , Dreazen Eli , Wiener Yifat , Herman Arie
Published: August 2005

Objective

To evaluate ultrasound prenasal thickness (PT) as a way of enhancing the Down syndrome (DS) screening performance of second‐trimester nasal bone (NB) length measurement.

Methods

Twenty‐one DS and 500 normal fetuses were scanned at 14–27 weeks' gestation. The affected karyotype was known to the person performing the scan. Both PT and NB were measured in a mid‐sagittal position and results were expressed in multiples of the normal gestation‐specific median (MoM). Gaussian modelling was used to predict the performance of routine screening.

Results

Among DS fetuses, the PT median was 1.35 MoM, a highly statistically significant increase compared with the unaffected pregnancies (p < 0.0001, Wilcoxon Rank Sum Test, two‐tailed). The NB median was 0.87 MoM (p < 0.0005) and the ratio PT/NB median was 1.51 MoM (p < 0.0001). In the normal fetuses, the two markers were positively correlated (0.25, p < 0.0001), whereas in the DS fetuses there was a non‐significant negative correlation (−0.24, p = 0.33). For a 5% false‐positive rate, the model predicted detection rate was 70% for PT and NB compared with 43% for NB alone.

Conclusion

In the second trimester, PT is increased on average in DS fetuses. Combining PT and NB measurement could yield a higher screening detection rate than NB alone. Confirmation of our findings in a series of women scanned before the karyotype was known is needed before the method can be clinically implemented. Copyright © 2005 John Wiley & Sons, Ltd.
Trisomy 2 due to a 3:1 segregation in an abortion studied by QF‐PCR and CGH
Authors: Lorda‐Sánchez Isabel , Diego‐Alvarez Dan , Ayuso Carmen , de Alba Marta Rodríguez , Trujillo Maria Jose , Ramos Carmen
Published: August 2005

Balanced reciprocal translocation is one of the known causes of recurrent spontaneous abortions. Cytogenetic studies of unbalanced miscarriages are difficult due to the growth failure of early loss and usually macerated abortions. We present a molecular study of an abortion in which the father carries a balanced reciprocal translocation t(2;17)(q32.1;q24.3) using QF‐PCR and CGH techniques. DNA analysis showed the presence of a trisomy 2 due to a 3:1 interchange segregation. Recombinant events could also be investigated by comparing DNA samples from the family. We propose QF‐PCR in addition to CGH as an efficient diagnostic method to improve our knowledge of unbalanced offspring in balanced translocation carriers. Copyright © 2005 John Wiley & Sons, Ltd.
Prenatal diagnosis of del(9)(p24): a sex reverse case
Authors: Privitera Orsola , Vessecchia Graziella , Bernasconi Barbara , Bettio Daniela , Stioui Sabine , Giordano Giovanna
Published: August 2005

Background

We report on a fetus with sex reversal and del(9)(p24) consequent to a malsegregation of a maternal balanced complex translocation involving chromosomes 7, 9 and 11.

Methods

Fluorescence in situ hybridization (FISH) was performed in order to verify the presence of the SRY gene and the absence of DMRT1 and DMRT2 genes located in 9p24.3 region and frequently associated with sex reversal.

Results and Conclusions

The prenatal karyotype revealed an unbalanced male fetus. The postmortem examination showed a malformed fetus with female external genitalia. Lack of DMRT1‐2 genes established by FISH. Copyright © 2005 John Wiley & Sons, Ltd.
Pyroelectric and dielectric properties of side‐chain liquid crystal polymers
Authors: Mehl Georg H. , Nordmann Ina , Lacey David , Goodby John W. , Hogg J. H. Christopher , Das‐Gupta Dilip K.
Published: August 2005

Liquid crystal side‐chain polymers (LCP), where the polymer architecture consists of a polymer backbone, flexible spacers, and mesogenic groups, are of considerable interest as they promise desirable electro‐active properties, including pyroelectricity and electro‐optic display phenomena. Induced polarization in the LCP system remains stable at ordinary temperatures, and therefore these systems are suitable for sensor materials for pyroelectric applications where switching times are less important. The dielectric applications of the polarized LCP system are also of importance if they are to be used as thin film electro‐active devices. This paper reports the results of the dielectric and pyroelectric characterizations of six different polymers over a wide range of frequencies and temperatures. To elucidate the effect of a variation of chemical structure on the macroscopic properties, the structure of the mesogenic moiety was kept constant, and the length of the spacer and the size of the polymer backbone were varied.
Thermodynamic characterization of interpenetrating polymer networks
Authors: Privalko Valery P. , Azarenkov Vassily P. , Baibak Alexander V. , Korskanov Valery V. , Titov Georgy V. , Frisch Harry L. , Zhou Peiguang
Published: August 2005

Crosslinked poly(methyl methacrylate) (PMMA‐c), poly(carbonate‐urethane) (PCU‐c), poly(vinyl pyridine) (PVP‐c), and full, simultaneous interpenetrating polymer networks (IPNs) based on the above polymers were characterized by precise heat capacity (Cp) measurements in the temperature interval 4.2–450 K. The raw values of Cp scaled with temperature (T) as Cp ∼ Td with d = 2 and 5/3, as expected for a fracton‐like vibration regime, in the temperature intervals 8–10 and 10–30 K, respectively. A single glass transition temperature (Tg) and two Tg's were observed for apparently homogeneous and microphase‐separated IPNs, respectively. Judged by the positive sign of the excess Gibbs free energy, the apparently single‐phase state of homogeneous IPNs is thermodynamically unstable; however, its kinetic stability is ensured by permanent topological constraints (network junctions) prohibiting the incipient phase separation.
Complex dielectric permittivity of an ion‐containing polymer in the microwave region
Authors: Dabek Roman
Published: August 2005

A method for determination of the complex dielectric permittivity of polar, non‐polar and ion‐containing polymers at microwave frequencies is presented. Disk‐shaped samples are employed in a radial‐line configuration at the end of a coaxial‐line structure. An equivalent circuit, established by admittance measurements, is used to relate the capacitance at the sample face to the impedance measured on the slotted line preceding the coaxial sample holder. The method has been applied first to determine the frequency spectrum of polyethylene (PE) and poly(tetrafluoroethylene) (PTFE) between 80 MHz and 4 GHz at 293 K. The results agree with those reported in the literature, demonstrating the reliability of the method as well as usability of PE and PTFE as standards at high frequencies. Subsequently, the AMF C‐311 cation exchange membrane (polyfluorocarbon backbone chains with grafted polystyrene side chains containing sulfonate groups) was studied in the same frequency range. Values of dielectric permittivity and dielectric losses for AMF C‐311 samples in the dry and swollen hydrated states are reported and compared.
Dielectric spectroscopy of polyethylene in the frequency range of 10−5 Hz to 106 Hz
Authors: Scarpa P. C. N. , Svatík A. , Das‐Gupta D. K.
Published: August 2005

Polyethylene, one of the most widely used electrical insulating materials, is known, despite its excellent physical properties, to exhibit structural degradation when submitted to a continued electrical (AC) stress in a humid environment. Although much work has been done to correlate the inception and growth of water trees with the breakdown in polyethylene, little attention appears to have been given to identify, through an appropriate model, the deterioration of the electrical and dielectrical parameters with the progressive aging of the insulator. This paper reports the results of a comprehensive study of electrical aging of both low‐density polyethylene (LDPE) and chemically crosslinked polyethylene (XLPE) aged in humid environment at an AC stress of 6 kV/mm for an extended time. For this study, dielectric spectroscopy in the frequency range of 10−5 Hz to 106 Hz has been employed to provide appropriate electrical analog models of the aging. An agreement, at least qualitative, is found with the dielectric and the thermally stimulated discharge current (TSDC) behavior.
Synthesis and characterization of new poly(butadiene‐co‐acrylic acid(g) acrylic acid) and poly(butadiene(g) acrylic acid)
Authors: Bertorello Héctor , Argüello Ricardo
Published: August 2005

Synthetic crosslinked polymers from oligomers of butadiene‐co‐acrylic acid (Mw 5000) or oligomers of butadiene (Mw 6000) and acrylic acids were obtained after grafting reactions using varying reactant ratios. Characterization of the new crosslinked polymers were carried out by use of FTIR, H‐NMR, and 13C‐NMR in the solid state and also with the swollen products in D2O, DMF D7, or DMSO D6. Determinations of swelling in distilled water for the different synthesized hydrogels showed increase in the V/Vo ratios as the concentrations of anions (carboxylate) became higher. These values were sensitive to different pH values and changes in the concentrations of electrolytes. Different behavior was observed for the polymers obtained from mass and from synthesis in benzene. SEM analysis of the surfaces of the polymers obtained in mass showed a fibrous structure (with lower contents of carboxylic groups, and more swellable and with greater capacity to retain albumin). A porous surface was observed for products obtained in benzene (with higher content of carboxyl groups and capacity to retain cations such as copper and malachite green).
Nonisothermal thermophysical evaluation of a polypropylene + ethylene propylene diene (EPDM) blend
Authors: Brostow Witold , D'Souza Nandika Anne , Galina Henryk , Ramamurthy A. C.
Published: August 2005

Recent theoretical evidence indicates that the rate effects of quenching seen in the isothermal crystallization kinetics can be eliminated through use of a nonisothermal method based on constant rate heating and cooling through inclusion of an activation energy. To investigate the potential of this method for polymers, we apply it to semicrystalline polymers: polypropylene (PP), a binary blend PP + ethylene propylene diene rubber (EPDM) and a ternary system PP + EPDM + high‐density polyethylene (PE). As opposed to traditional rubber‐modified systems such as high‐impact polystyrene (HIPS) wherein an amorphous component is blended with a rubbery one, the PP + EPDM system has a semicrystalline component. From the perspective of crystal lamellae growth or stress induced slip, the thermophysical properties are also a concern. Therefore, we use differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The results indicate that differences between isothermal and nonisothermal conditions must be taken into account since the latter conditions prevail in extrusion, injection molding, and in hot coating‐slow cooling processes. Our nonisothermal analysis of crystallization should assist in the optimization of cooling of semicrystalline polymers.
Rheology and morphology of poly(vinyl acetate) + calcite films
Authors: Kovacevic Vera , Lucic Sanja , Hace Drago , Glasnovic Antun
Published: August 2005

We have studied mechanical and rheological behavior of poly(vinyl acetate) (PVAC) composites filled with calcite as a function of filler particle geometry, particle size distribution, and active surface area. Detailed morphological characteristic were investigated. Tensile properties of PVAC composites were evaluated in the composition range 5–20 wt% calcite. The elongation at break decreases as consequence of matrix mobility restriction by filer particles. By contrast, the strength at break increases as a result of fewer stress concentration points produced by small calcite particles. Large calcite particles decrease the strength of the PVAC composite because of lack of structural continuity. Failure is then dominated by the dewetting. Understanding the deformation as it relates to structure, mechanism of failure, and strength of interactions makes development of improved PVAC composites for adhesives possible.
Conformational analysis and DFT calculations of 8α‐hydroxy‐germacradiene‐6,12‐olide derivatives
Authors: Maggio Antonella M. , Barone Giampaolo , Bruno Maurizio , Duca Dario , Rosselli Sergio
Published: August 2005

The Systematic Conformational Search Analysis (SCSA) code was employed to study the conformational properties of the 8α‐hydroxy‐germacradiene‐6,12‐olide isomers. This procedure was extended to the trans,cis‐ and trans,trans‐1(10),4‐isomers of 8α,15‐dihydroxy‐germacradiene‐6,12‐olides and 8α‐hydroxy‐15‐oxo‐germacradiene‐6,12‐olides, to investigate structural and energetic analogies between these and the 8α‐hydroxy‐germacradiene‐6,12‐olide species. The calculated 13C NMR spectra, at the hybrid DFT mPW1PW91 level, showed a sound correlation with the corresponding experimental spectra, providing a valid support to the reliability of the calculated structures and to the consistence of our conformational analysis. The results presented here allowed us to support our previous mechanistic interpretation on the oxidation of 8α,15‐dihydroxy‐trans,trans‐1(10),4‐germacradiene‐6,12‐olides to 8α‐hydroxy‐15‐oxo‐trans,cis‐1(10),4‐germacradiene‐6,12‐olides. Copyright © 2005 John Wiley & Sons, Ltd.
Chemical bonding in zwitterionic diamino‐meta‐quinonoids and their isomers
Authors: Höltzl Tibor , Veszprémi Tamás , Nguyen Minh Tho
Published: August 2005

Quantum chemical calculations using molecular orbital (HF) and density functional (B3LYP) methods, in conjunction with the 6‐311 + + G(d,p) basis set, have been applied to investigate the electronic structure of a series of diamino‐meta‐quinonoid molecules, each containing a six‐membered ring coupled with two exocyclic CO bonds situated in ametaposition, along with two amino substituents (NH2and NHR). The chemical bonding phenomena in these zwitterions and isomers where one or two hydrogens are transferred from N to O are analyzed with the aid of the atoms‐in‐molecules (AIM) approach. The relative energies between zwitterionic and quinonoid isomers in both neutral and ionized states also have been evaluated. Substituents exert a strong effect that in many cases changes the energy ordering. Copyright © 2005 John Wiley & Sons, Ltd.
Nonlinear elasticity of rodlike macromolecules in condensed state
Authors: Doi Masao , Kuzuu Nobu Y.
Published: August 2005

The finite deformation elasticity of gels of stiff rodlike polymer chains is discussed theoretically. Unlike a rubber composed of flexible polymer chains, the elasticity of this system is energetic, and arises from the elastic deformation of the stiff chains which are forced to bend under macroscopic strain. The stress‐strain curve of this system is shown to be nonlinear even if the bending of the rods is small, and has a characteristic S‐shaped form which is unlike that of a rubber. The effect of orientational order is also discussed.
Interpretation of longitudinal‐acoustical‐mode spectra of polymers
Authors: Snyder Robert G. , Scherer James R.
Published: August 2005

The influence of temperature, frequency, and straight‐chain‐length distribution on the low‐frequency Raman‐active longitudinal‐acoustical‐mode (LAM) bands of polymers is discussed. Specifically, the effect of these factors on the intensity of LAM‐1, on the ratio of intensities of LAM‐1 to LAM‐k, and on peak position is computed or estimated. Band halfwidth and chain‐length‐distribution halfwidth are found not to be simply related. It is shown that the integrated intensity of LAM‐1 is very nearly proportional to the total length of straight chains.
Tensile properties and partial alignment of polyacetylene, (CH)x, films
Authors: Druy M. A. , Tsang C.‐H. , Brown N. , Heeger A. J. , Macdiarmid A. G.
Published: August 2005

The tensile properties of both cis‐ and trans‐polyacetylene, (CH)x, were investigated in order to determine the variables that influence that ultimate extension ratio (l/l0) of polyacetylene films. It was found that when cis‐films of polyacetylene were extended in an inert (argon) atmosphere, ultimate extension ratios as high as 3.3 were obtained and with subsequent isomerization at 160–200°C under stress, a final l/l0, of about 4 was obtained. The extension ratio is extremely sensitive to exposure to oxygen and decreases markedly after periods as short as 1 min. It appears as though crosslinking may occur in the polymer when it is exposed to air and this produces brittleness in the specimen. When (CH)x was isomerized from cis to trans, it became brittle, even in the absence of air.
Plastic deformation of polypropylene: Effect of molecular weight on drawing behavior and structural characteristics of ultra‐high‐modulus products
Authors: Wills A. J. , Capaccio G. , Ward I. M.
Published: August 2005

The influence of molecular weight and temperature on the tensile drawing behavior of polypropylene has been studied, with particular reference to the production of ultra‐high‐modulus oriented materials. It has been shown that the optimum draw temperature is molecular weight independent to a good approximation, and that high‐modulus products can be obtained for M̄w in the range 180,000–400,000, the highest modulus being achieved for polymer with M̄w = 181,000. As in the case of linear polyethylene, under optimum drawing conditions the Young's modulus relates only to the draw ratio. Low‐temperature moduli as high as 25–27 GPa were recorded, which compare favorably with a previously reported value of 42 GPa for the crystal‐lattice modulus. Although the drawing behaviour of the samples studied appeared comparatively insensitive to molecular weight, some of the properties of the draw materials, notably melting point and shrinkage at high temperature, showed a wide range of behavior.
Migration and blooming of waxes to the surface of rubber vulcanizates
Authors: Nah S. H. , Thomas A. G.
Published: August 2005

When certain substances, notably waxes, are incorporated into rubber during vulcanization, the surface of the vulcanized rubber may subsequently become covered by a film of the substance diffusing out. This phenomenon, known as blooming, depends on the substance being soluble at the vulcanization temperature but only partially soluble at the temperature of blooming. A study has been made using pure waxes in natural rubber vulcanizates with a range of crosslink densities. The mass of bloomed material has been determined as a function of time, and the expected dependence on the square root of the time has been found to hold over the anticipated range. It has been shown that the kinetics of the process cannot be explained simply in terms of the degree of supersaturation of the wax in the rubber, the observed rates being much too low. This appears to be related to the precipitation of the wax in the body of the material. A theory has been developed based on a calculation of the stresses set up around such a precipitated particle and the effect of the consequent free‐energy gradient on the rate of diffusion. Comparison with experiment shows satisfactory agreement with the theory.