bluuebunny/crossref_metadata_2025 huggingface dataset:
A semi‐discrete convergent scheme for a quasilinear hyperbolic equation
Authors: Kannan R. , Ortega R.
Published: August 2005

We establish here the convergence (thereby proving the existence) of a semi‐discrete scheme for the quasilinear hyperbolic equation
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where x ∈ Rn, t ∈ [0,T], and ϕ ∈ L∞ (Rn). It is well known that the above problem does not necessarily have global classical solutions and the usual concepts of weak solution. do not lead to a unique solution The existence of a unique solution to the above problem in a suitable sense was established in [3], where a parabolic problem obtained by introducing the term −ϵΔu was studied and then the behavior as ϵ → 0 was discussed. A difference scheme approach to a problem of the above type where ϕi does not depend on x and t and Ψ does not depend on u was also studied in [2]. The aim of this paper is to present a proof for the case when ϕ depends on x, Ψ depends on u, and the technical complications in this case are nontrivial. The discussions in this paper my be considered as continuation of the ideas in the above papers.
A spline interpolation method for solving boundary value problems of potential theory from discretely given data
Authors: Freeden Willi
Published: August 2005

An interpolation procedure using harmonic splines is described and analyzed for solving (exterior) boundary value problems of Laplace's equation in three dimensions (from discretely given data). The theoretical and computational aspects of the method are discussed. Some numerical examples are given.
Solution of the advection‐dispersion equation with free exit boundary
Authors: Frind Emil O.
Published: August 2005

I investigated the exit boundary condition for the advection‐dispersion equation and found that in numerical solutions of this equation, using Galekin finite elements, a free exit boundary condition requiring no a priori information is possible, provided the advective component in the numerical equations is of sufficient magnitude relative to the dispersive component. Since the relationship between these two components is controlled by the spatial discretization through the grid Peclet number, the free exit boundary condition can in fact be applied whenever there is a non‐zero advective component. The numerical solution in a finite domain with free exit boundary, using a correctly proportioned spatial discrezation, behaves like an infinite‐domain solution.
Stability improvement of the Euler forward method for initial value problems
Authors: Kujawski Jerzy
Published: August 2005

The Euler forward method is transformed into a highly stable two‐step explicit algorithm by use of a relaxation paramenter α. The stability of the new explicit family can be very high and linearly proportional to the absolute value of α. An adaptive stability approach with a matrix of parameters α is used that strongly increases the effeciency of the method. The one‐dimensional finite element solutions for linear and nonlinear transient heat conduction problems show the stability, accuracy, and computational efficiency characteristics of the proposed algorithms.
A finite element method for a two‐sex model of population dynamics
Authors: Milner Fabio A.
Published: August 2005

A finite element scheme is described to approximate the solution of a nonlinear and non‐local system of integro‐differential equations that models the dynamics of a two‐sex population. Crank‐Nicolson time discretization is used and error estimates are derived for the appoximation.
Super‐computer simulation of a multichambered muffler
Authors: Cooke Charlie H.
Published: August 2005

The problem of attenuating muzzle blast noise produced by firing a gun weapon is studied. A multichambered muffler is attached to a M242 25mm cannon. For this weapons configuration, the transitional ballistics problem is solved numerically using the CRAY XMP computer. The second‐order accurate total variation diminishing (TVD) shock capturing scheme of Harten is used to solve the Euler equations of compressible flow. The simulation yields a detailed picture of the flow field, as displayed by pressure and Mach contours. Pressure time histories at selected field locations are recorded for future comparison with experiment. Energy efflux time history, from which predictions of noise attenuation can be made, is also recorded. Noise reduction levels so obtained are seen to compare well with experimental data. From this evidence it appears that the simulation method can become an effective aid in muffler design.
On the accuracy and convergence of conjugate flux approximations
Authors: Rachowicz W. , Oden J. Tinsley
Published: August 2005

We prove that the L2‐projections of derivatives of piecewise bilinear or linear finite element approximations of smooth solutions of elliptic boundary‐value problems on the interior of uniform meshes, converge in L2 and L∞ at a rate faster than that of derivatives of the approximations themselves.
Regularization procedures of mixed finite element approximations of the stokes problem
Authors: Pierre Roger
Published: August 2005

We propose a theoretical framework for the study of regularization of the Stokes problem. This enables us to perform a general error analysis and to apply it to known schemes as well as to a new one pertaining to the use of the P1‐P1 element. Finally we show that in the P1‐case the theory can also be used to get convergence results for elements obtained by addition of bubble functions, without using the usual mixed finite element machinery.
Exact solutions to a finite‐difference model of a nonlinear reaction‐advection equation: Implications for numerical analysis
Authors: Mickens Ronald E.
Published: August 2005

This article gives exact solutions to a finite‐difference model of a nonlinear reaction‐advection equation. We show that this partial difference equation and the corresponding stationary and spatially independent difference equations derived from this model give the best representation of the original partial differential equation. The relevance of this work to the elimination of chaotic behavior in numerical solutions of differential equations is discussed.
Superconvergence of recovered gradients of piecewise quadratic finite element approximations. Part I: L2‐error estimates
Authors: Goodsell G. , Whiteman J. R.
Published: August 2005

Superconvergence properties in the L2 norm are derived for the recovered gradients of piecewise quadratic finite element approximations on triangular partitions for two‐dimensional elliptic problems and systems, including the case of linear elasticity. The analysis covers problems defined on polygonal domains, where the solutions have low regularity. The effects of numerical integration are treated.
Mixed methods and the marriage between “mixed” finite elements and boundary elements
Authors: Bossavit Alain
Published: August 2005

When fields that describe a physical situation extend over the whole space, but with complex behavior (nonlinearity, coupling, etc.) only in a bounded region and simple behavior in the rest of space, it may be worthwhile to treat the inner field by a finite elements procedure and the outer field by boundary elements. We address this “marriage” problem in the case of mixed elements. The model problem adopted for this discussion is magnetostatics. A new approach to the question of mixed elements is used, which emphasizes their parenthood with a classical concept of differential geometry, Whitney forms.
Penalty‐combined approaches to the Ritz‐Galerkin and finite element methods for singularity problems of elliptic equations
Authors: Li Zi‐Cai
Published: August 2005

Penlty coupling techniques on an interface boundary, artificial or material, are first presented for combining the Ritz–Galerkin and finite element methods. An optimal convergence rate first is proved in the Sobolev norms. Moreover, a significant coupling strategy, L + 1 = O(|ln h|), between these two methods are derived for the Laplace equation with singularities, where L + 1 is the total number of particular solutions used in the Ritz–Galerkin method, and h is the maximal boundary length of quasiuniform elements used in the linear finite element method. Numreical experiments have been carried out for solving the benchmark model: Motz's problem. Both theoretical analysis and numreical experiments clearly display the importance of penalty‐combined methods is solving elliptic equations with singularities.
Optimal convergence rates for the combined methods of different finite element methods
Authors: Li Zi‐Cai
Published: August 2005

Coupling techniques are essential to combining different numerical methods together for the purpose of solving an elliptic boundary value problem. By means of nonconforming constraints, the combinations of various Lagrange finite element methods often cause reduced rates of convergence. In this article, we present a method using penalty plus hybrid technique to match different finite element methods such that the optimal convergence rates in the ‖ · ‖h and zero norms of errors of the solution can always be achieved. Also, such a coupling technique will lead to an optimal asymptotic condition number for the associated coefficient matrix. Moreover, this study can easily be extended for combining the finite difference method with the finite element method to also yield the optimal rate of convergence.
Mathematical model of coupled plates meeting at an angle 0 < θ < π and its finite element method
Authors: Lie‐heng Wang
Published: August 2005

A mathematical model of coupled plates meeting at an arbitrary angle 0 < θ < π is established. The finite element approximation for the mathematical model is considered, and the optimal error bound is obtained, which shows that the convergence of the approximation is reciprocally proportional to the sine of the angle θ between the two plates. © 1993 John Wiley & Sons, Inc.
On the relationship between nodal schemes and mixed‐hybrid finite elements
Authors: Hennart J. P. , Valle E. Del
Published: August 2005

The relationships between a general family of nodal schemes [J.P. Hennart, SIAM J. Sci. Stat. Comput. 3, 264 (1986)] and primal nonconforming as well as mixed‐hybrid finite element formulations are explored in this paper. It is shown in particular that the nodal schemes proposed are quite natural extensions in rectangular geometry of the Raviart‐Thomas‐Nédélec mixed‐hybrid finite elements. This paper is a revised and extended version with new numerical results of part of a previous research report [J.P. Hennart, Rapports de Recherche INRIA Vol. 386 (1985)]. © 1993 John Wiley & Sons, Inc.
Improved error estimates for mixed finite‐element approximations for nonlinear parabolic equations: The discrete‐time case
Authors: Garcia Sonia M. F.
Published: August 2005

This article treats mixed finite‐element methods for second‐order quasilinear parabolic equations. A fully discrete scheme is presented and L2‐error estimates are established. The convergence of both the function value and the flux is demonstrated. In a previous paper, Part I the author introduced powerful numerical methods for dealing with parabolic problems. The technique used here is an extension of the continuous‐time results for the discrete‐time case. © 1994 John Wiley & Sons, Inc.
Steady incompressible flow around objects in general coordinates with a multigrid solution method
Authors: Oosterlee C. W. , Wesseling P.
Published: August 2005

Steady incompressible flow around objects in general coordinates is investigated. First, an overview of the popular approaches to discretize incompressible flow problems in general coordinates is given. It has been chosen to solve the equations on a staggered grid with contravariant flux unknowns and pressure as primitive variables. A solution method multigrid is used, with a line smoother able to deal with stretched cells. For flow problems around objects solved with a single block discretization periodic boundary, conditions are prescribed and adaptations for the discretization and the multigrid method are given. Steady flow around a circular cylinder and around an ellipse are presented. © 1994 John Wiley & Sons, Inc.
Analysis of the Kleiser‐Schumann method for a family of mixed finite elements for the Stokes equations
Authors: Chinosi Claudia , Comodi Maria I.
Published: August 2005

We study the Stokes problem by using a mixed finite element method introduced by Stenberg [Numer. Math. 56, 827 (1990)] and adapt it to the splitting introduced by Canuto and Sacchi Landriani [Numer. Math. 50, 217 (1986)] and Chinosi and Comodi [Numer. Methods Partial Different. Equations 7, 363 (1991)], by using the incompressibility condition to implicitly define a boundary condition for the pressure. © 1994 John Wiley & Sons, Inc.
Numerical solutions of the Dirichlet problem via a density theorem
Authors: Whitley Robert , Hromadka T. V.
Published: August 2005

Under mild conditions a certain subspace M, consisting of functions which are analytic in a simply connected domain Ω and continuous on the boundary Gamma;, is shown to have real parts which are dense, in the sup norm, in the set of all solutions to the Dirichlet problem for continuous boundary data. Similar results hold for Lp boundary data. Numerical solutions of sample Dirichlet problems are computed. © 1994 John Wiley & Sons, Inc.
Convergence of the lines method for first‐order partial differential‐functional equations
Authors: Zubik‐Kowal Barbara
Published: August 2005

Initial‐boundary value problems for nonlinear differential‐functional equations are considered. A general class of lines method is investigated. The Perron‐type estimation for the right‐hand side of the equation with respect to the functional argument is assumed. The proof of the convergence is based on a comparison theorem for differential‐difference inequalities. A numerical example is given. © 1994 John Wiley & Sons, Inc.
Optimal‐order convergence rates for Eulerian‐Lagrangian localized adjoint methods for reactive transport and contamination in groundwater
Authors: Wang Hong , Ewing R. E.
Published: August 2005

Eulerian–Langrangian localized adjoint methods (ELLAM) were developed to solve convection–diffusion–reaction equations governing contaminant transport in groundwater flowing through a porous medium, subject to various combinations of boundary conditions. In this article, we prove optimal‐order error estimates and some superconvergence results for the ELLAM schemes. In contrast to many existing estimates for a variety of numerical methods, which often contain the temporal derivatives of the exact solution, our error estimates contain the total derivatives of the exact solution but do not involve any temporal derivatives of the exact solution. © 1995 John Wiley & Sons, Inc.
A primal hybrid finite element method for a strongly nonlinear second‐order elliptic problem
Authors: Park E.‐J.
Published: August 2005

The Neumann problem for a strongly nonlinear second‐order elliptic equation in divergence form is approximated by primal hybrid finite element methods defined by Raviart and Thomas. Existence and uniqueness of the approximation are proved, and optimal order error estimates are established in various norms. © 1995 John Wiley & Sons, Inc.
Interpolation for solutions of the Helmholtz equation
Authors: González–Casanova Pedro , Wolf Kurt Bernardo
Published: August 2005

We study the interpolation problem for solutions of the two‐dimensional Helmholtz equation, which are sampled along a line. The data are the function values and the normal derivatives at a discrete set of point sensors. A wave transform is used, analogous to the common Fourier transform. The inverse wave transform defines the Hilbert space for oscillatory Helmholtz solutions. We thereby introduce an interpolant that has some advantages over the usual sinc x in the Whittaker–Shannon sampling in one dimension; in particular, coefficients of the two‐dimensional solution are invariant under translations and rotations of the sampling line. The analysis is relevant for the optical sampling problem by sensors on a screen. © 1995 John Wiley & Sons, Inc.
The stability of finite element methods
Authors: Verfürth Rüdiger
Published: August 2005

We give an abstract stability result for finite element methods. It provides a general guideline for establishing the stability of finite element methods for a given norm once it is established with respect to another norm. The abstract result yields stability estimates of natural norms for finite element methods, which have recently been developed to stabilize effects like dominant convection, incompressibility constraints, or boundary conditions. These stability results simplify the error analysis of the discretizations and are helpful fin the convergence analysis of multigrid methods for the solution of the corresponding discrete problems. © 1995 John Wiley & Sons, Inc.
Least‐squares finite element approximation of Fisher's reaction–diffusion equation
Authors: Carey G. F. , Shen Yun
Published: August 2005

Fisher's equation is a classical diffusion–reaction type of problem describing diffusion and nonlinear reproduction of a species. In the present study we develop a least‐squares finite element formulation of Fisher's equation and carry out supporting numerical studies. Of particular interest are questions associated with the approximation of progressive wave solutions with minimum speed and the viability of the least‐squares approach for this class of problem. © 1995 John Wiley & Sons, Inc.
Expanding stability regions of explicit advective‐diffusive finite difference methods by Jacobi preconditioning
Authors: Rodrigue Garry , Wolitzer Donald
Published: August 2005

Explicit time differencing methods for solving differential equations are advantageous in that they are easy to implement on a computer and are intrinsically very parallel. The disadvantage of explicit methods is the severe restrictions that are placed on stable time‐step intervals. Stability bounds for explicit time differencing methods on advective–diffusive problems are generally determined by the diffusive part of the problem. These bounds are very small and implicit methods are used instead. The linear systems arising from these implicit methods are generally solved by iterative methods. In this article we develop a methodology for increasing the stability bounds of standard explicit finite differencing methods by combining explicit methods, implicit methods, and iterative methods in a novel way to generate new time‐difference schemes, called preconditioned time‐difference methods. A Jacobi preconditioned time differencing method is defined and analyzed for both diffusion and advection–diffusion equations. Several computational examples of both linear and nonlinear advective‐diffusive problems are solved to demonstrate the accuracy and improved stability limits. © 1995 John Wiley & Sons, Inc.
A conservative semi‐Lagrangian method for multidimensional fluid dynamics applications
Authors: Scroggs J. S. , Semazzi F. H. M.
Published: August 2005

We describe a finite volume semi‐Lagrangian method for the numerical approximation of conservation laws arising in fluid‐dynamic applications. A discrete conservation relation is satisfied by using conservative interpolation for the material (or property) being conserved. The method was developed with a view to application in climate prediction. © 1995 John Wiley & Sons, Inc.
Solution domain decomposition with finite difference methods for partial differential equations
Authors: Nguyen Hoa D. , Paik Seungho
Published: August 2005

The Solution Domain Decomposition method of Nguyen and Paik [J. Sci. Comput. 4, 357 (1993)] originally developed in a pseudospectral context is extended for use with finite difference techniques to solve partial differential equations. The essential idea behind this method lies in an application of the superposition principle, which allows interactions between adjacent subdomains to be decoupled and the resulting equations to be solved in parallel. Several tests are performed to assess its accuracy and efficiency based on a model problem arising from thermal convection inside a fluid‐saturated porous cavity with heating from a side. The results reveal a well adaptation of the methodology into the framework of finite differences. © 1995 John Wiley & Sons, Inc.
Coupling of FEM and BEM for a nonlinear interface problem: The h–p version
Authors: Carstensen C. , Stephan E. P.
Published: August 2005

This article presents some numerical examples for coupling the finite element method (FEM) and the boundary element method (BEM) as analyzed in [11]. This coupling procedure combines the advantages of boundary elements (problems in unbounded regions) and of finite elements (nonlinear problems with inhomogeneous data). In [28], experimental rates of convergence for the h version are presented, where the accuracy of the Galerkin approximation is achieved by refining the mesh. In this article we treat the h–p version, combining an increase of the degree of the piecewise polynomials with a certain mesh refinement. In our model examples, we obtain theoretically and numerically exponential convergence, which indicates a great efficiency in particular if singularities appear. © 1995 John Wiley & Sons, Inc.
Expression of NOX1, a superoxide‐generating NADPH oxidase, in colon cancer and inflammatory bowel disease
Authors: Szanto I , Rubbia‐Brandt L , Kiss P , Steger K , Banfi B , Kovari E , Herrmann F , Hadengue A , Krause K‐H
Published: August 2005

Reactive oxygen species (ROS) are at the centre of many physiological and pathological processes. NOX1, a ROS‐producing NADPH oxidase, is highly expressed in the colon but its function in colonic physiology or pathology is still poorly understood. It has been suggested to play a role in host defence, but also in cell growth and possibly malignant transformation. In this study we characterized NOX1 expression in human colon samples derived from healthy control subjects and patients with colon cancer or inflammatory bowel disease (IBD). NOX1 mRNA expression was assessed by dot‐blot hybridization, real‐time PCR and in situ hybridization, using samples derived from surgical specimens from patients undergoing colon resection. In normal tissues, NOX1 expression was low in the ileum, intermediate in the right colon, and high in the left colon (p = 0.0056 right vs. left colon). NOX1 mRNA levels were not influenced by factors linked to colon tumourigenesis, such as age or sex. Moreover, there was no statistical difference in NOX1 expression between samples derived from adenomas, well differentiated or poorly differentiated colon adenocarcinomas. At a cellular level, NOX1 was highly expressed in colon epithelial cells, both within the crypts and on the luminal surface. In addition, a population of lymphocytes, particularly in the appendix, showed NOX1 expression. Lymphocytes in lesions of Crohn's disease and ulcerative colitis were also strongly positive for NOX1. In conclusion, NOX1 is an enzyme that is constitutively expressed in colon epithelium and is not associated with tumourigenesis. Its distribution in crypts and on the luminal surface, as well as its left‐to‐right gradient in the colon, suggests a role in host defence function. In addition to the known epithelial localization, we define lymphocytes as a novel site of NOX1 expression, where it may potentially be involved in the pathogenesis of inflammatory bowel diseases. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Prenatal diagnosis in a family with X‐linked hydrocephalus
Authors: Panayi Maria , Gokhale David , Mansour Sahar , Elles Rob
Published: August 2005

The neural cell adhesion molecule L1 is a transmembrane glycoprotein belonging to the immunoglobulin superfamily of cell adhesion molecules (CAMs). Its expression is essential during embryonic development of the nervous system and it is involved in cognitive function and memory. Mutations in the L1CAM gene are responsible for four related L1 disorders; X‐linked hydrocephalus/HSAS (Hydrocephalus as a result of Stenosis of the Aqueduct of Sylvius), MASA (Mental retardation, Aphasia, Shuffling gait, and Adducted thumbs) syndrome, X‐linked complicated spastic paraplegia type I (SPG1) and X‐linked Agenesis of the Corpus Callosum (ACC). These four disorders represent a clinical spectrum that varies both between and within families. The main clinical features of this spectrum are Corpus callosum hypoplasia, mental Retardation, Adducted thumbs, Spastic paraplegia and Hydrocephalus (CRASH syndrome). Since there is no biochemically assayed disease marker, molecular analysis of the L1CAM gene is the only means of confirming a clinical diagnosis. Most L1CAM mutations reported to date are point mutations (missense, nonsense, splice site) and only a few patients with larger rearrangements have been documented. We have characterised a rare intragenic deletion of the L1CAM gene in a sample of DNA extracted from a chorionic villus biopsy (CVB) performed at 12 weeks' gestation. Copyright © 2005 John Wiley & Sons, Ltd.
The influence of maternal insulin‐dependent diabetes on fetal nuchal translucency thickness and first‐trimester maternal serum biochemical markers of aneuploidy
Authors: Spencer Kevin , Cicero Simona , Atzei Alessia , Otigbah Chineze , Nicolaides Kypros H.
Published: August 2005

Objective

To evaluate the influence of maternal insulin dependent diabetes mellitus (IDDM) on maternal serum free β‐hCG, PAPP‐A and fetal nuchal translucency (NT), thickness at 11 to 13+6 weeks of gestation in a large cohort of women screened prospectively for chromosomal anomalies.

Methods

Information on maternal IDDM status, maternal serum biochemical marker levels and fetal NT were collected from the prenatal screening computer records in two first‐trimester screening centres. In total the control group included 33 301 pregnancies of which 16 366 had NT and maternal serum biochemistry results and 16 305 with NT only. The IDDM group included 195 pregnancies of which 79 had NT and maternal serum biochemistry results and 127 with NT only. The median maternal weight corrected free β‐hCG and PAPP‐A, expressed as multiple of the median (MoM), and fetal NT, expressed as delta values, in the IDDM and non‐IDDM groups were compared.

Results

There were no significant differences between the IDDM and non‐IDDM groups in median maternal weight corrected free β‐hCG (IDDM 0.87 MoM, 95% Confidence Interval 0.75 to 1.16 MoM, non‐IDDM 1.00 MoM), median maternal weight corrected PAPP‐A (IDDM 1.02 MoM, 95% Confidence Interval 0.83 to 1.05 MoM, non‐IDDM 1.01 MoM), or mean delta NT (IDDM 0.0358 mm, non‐IDDM 0.0002 mm).

Conclusions

In pregnancies with maternal IDDM, first‐trimester screening for chromosomal defects does not require adjustments for the measured fetal NT. However, more data are required before the possible reduction in maternal serum free β‐hCG and the reduction of PAPP‐A suggested by the published world series can be considered sufficiently important to take into account in the calculation of risks for chromosomal defects. Copyright © 2005 John Wiley & Sons, Ltd.
A semi‐quantitative microarray method to detect fetal RNAs in maternal plasma
Authors: Ge Qinyu , Liu Quanjun , Bai Yunfei , Wen Tian , Lu Zuhong
Published: August 2005

Objectives

To set up a semi‐quantitative microarray method for the detection of fetal RNAs in maternal plasma.

Methods

We developed a semi‐quantitative microarray method for the detection of placental RNA in maternal plasma. Firstly, the selected fetal RNAs were linearly amplified from the maternal plasma and then fluorescently labeled as the target DNAs. Finally, the targets were hybridized and detected by capturing DNA probes on a microarray slide. Two genes of beta subunit of human chorionic gonadotrophin (β‐hCG) and zinc finger gene on the Y chromosome (ZFY) were assayed with the microarray, and beta actin gene was used as an internal standard. Eighty‐five pregnant women in the first trimester and the third trimester of gestation joined in this experiment, 14 of them also sampling in 36 h after delivery for the same assay. Real‐time quantitative PCR was performed for comparison.

Results

It was found that the mRNA level of β‐hCG decreased with the increasing of gestation age, and it was much higher in the carriers of the female fetus than in the carriers of the male fetus in the first trimester of gestation, which was consistent with the real‐time quantitative PCR results. The results also reveal that delivery would result in the clearance of fetal mRNA in maternal plasma.

Conclusions

The results suggest that the semi‐quantitative microarray method has great potential as a high‐throughput assay in prenatal diagnosis and clinical laboratory. Copyright © 2005 John Wiley & Sons, Ltd.
The effect of compatibilization on the behavior of a polycarbonate/polymer liquid crystal blend
Authors: Singer Michelle , Simon George P. , Varley Russell , Nobile M. Rossella
Published: August 2005

Polymer liquid crystalline materials (PLC) blended with engineering plastics (EP) have the potential to reduce viscosity and increase the modulus of the EP, particularly if the PLC is in a favorable fibrillar morphology. A major deficiency in these blends—as with many other immiscible polymeric systems—is poor failure properties. In this paper, polycarbonate (PC) and a rigid, all‐aromatic commercial PLC are blended and a third resin, a copolymer of methyl methacrylate and N‐methyl‐dimethyl‐glutarimide is included as a compatibilizing agent. Characterization of the binary and ternary blends is carried out using rheological, mechanical, morphological, and dynamic mechanical characterization techniques. Binary blends of PLC in a PC matrix result in an immiscible, nodular morphology with low failure stresses. The addition of the copolymeric compatibilizer—particularly one with reactive functionalities—is found to improve tensile strength and yield a fibrillar blend morphology. It is proposed that this may be due to the compatibilizer reducing interfacial tension and adhering to the blend phases, rather than by causing a major change in blend viscosity.
Polymers from renewable resources. VII: Thermal properties of the semi‐interpenetrating polymer networks composed of castor oil polyurethanes and cardanol‐furfural resin
Authors: Mishra D. K. , Mishra B. K. , Lenka S. , Nayak P. L.
Published: August 2005

A number of semi‐interpenetrating polymer networks (semi‐IPNs) were synthesized by reacting polyurethanes (prepared from castor oil and various diisocyanates) and a phenolic resin (prepared from cardanol and furfural) The physico‐chemical properties of the semi‐IPNs have been investigated. The thermogravimetric analysis of polymers was followed using a computer analysis method for assigning the kinetic mechanism. Various kinetic equations have been used to evaluate the kinetic parameters. The suggested mechanism of degradation of the semi‐IPNs is based on the kinetic parameters.
Nonlinear behavior of linear low‐density polyethylene
Authors: Rand James L. , Henderson John K. , Grant Debora A.
Published: August 2005

To predict the response of polyethylene thin films subjected to stress for a long time, it is necessary to understand the influence of stress on either the relaxation modulus or creep compliance. Extensive testing has been conducted on 20‐micron‐thick samples of a particular linear low‐density polyethylene film at temperatures from 23°C to −50°C. When reduced to creep compliance and compared with results from dynamic mechanical analysis (DMA), the influence of nonlinearities in the response function is apparent. However, the use of a two‐step loading procedure has produced sufficient data to discriminate between the effect of stress on amplitude and time on the creep compliance. It has been found that a master curve of compliance generated by DMA equipment may be used in conjunction with certain nonlinear functions to accurately predict the response of the polyethylene. Perhaps of more importance is the observation that the principles of simple time‐temperature superposition, commonly used with linear viscoelastic characterization, are insufficient for use with polyethylene films at most stress levels of interest.
Studies on the modification of interphase/interfaces by use of plasma in certain polymer composite systems
Authors: Akovali Güneri , Dilsiz Nursel
Published: August 2005

Calcium carbonate and carbon fiber surfaces were modified by use of a series of plasma polymers at different selected plasma conditions, and the effect of surface modification, mainly on the mechanical properties of composite systems prepared, was investigated. The matrices for the composite systems employed were polypropylene and epoxy, for the chalk and C fiber, respectively. Mechanical and thermal studies and scanning electron microscopy (SEM) pictures revealed that inclusion surfaces, being independent of their geometry and size, can be modified effectively by plasma. A polypropylene matrix with 30% modified chalk had better properties than composites with 10% unmodified chalk. Tensile strength and stress to failure values for single carbon fibers were found to be improved by plasma treatment. Surface‐treated carbon fibers yielded at composites with better interlaminar shear strength and flexural strengths.
On the role of electric forces in the processing of composites prepared with polymeric matrices
Authors: Yurkevich Oleg R.
Published: August 2005

Thermosetting and thermoplastic polymeric binders in the powder form and reinforcing carbon‐, glass‐, and organic fiber fillers were used to study the effects of electric forces on different stages of composites processing. Electric fields appear to uniformly distribute the powder binder across the filler surface as well as through its bulk. They favor stronger interaction of the components, leading to composites with better physical‐and‐mechanical performance properties. The optimal conditions provided for mixing of the components in an electrostatic field promote higher strength (by 1.5–1.8 times) and lower porosity (by 2–3 times) of carbon‐, and glass‐fiber reinforced plastics.
Conformation of polymer molecules at solid‐liquid interfaces by small‐angle neutron scattering
Authors: Forsman W. C. , Latshaw B. E.
Published: August 2005

A wide variety of physical‐chemical phenomena depend on the behavior of the polymer at solid‐liquid interfaces. The feature that distinguishes such phenomena from their small‐molecule counterparts is the long‐chain structure of the polymer molecules. Just as in solution and the bulk, the conformational statistics of the polymer molecules in the interface is an important determinant of interfacial properties. Conformational statistics of interfacial polymer is expressed in terms a function called the polymer density profile ϕ(Z), which is just the volume fraction of polymer as a function of Z, the distance from the solid surface out into the continuum liquid. There is only one experimental technique that is purported to be able to determine polymer density profiles of polymers confined to the interface between finely divided substrate and dispersant, and that technique is small‐angle neutron scattering (SANS). In this paper we present a protocol for the analysis of SANS data on spherical particles with adsorbed polymer for the determination of ϕ(Z). We give an example for nearly‐monodisperse chains of poly(n‐butyl methacrylate) with a molecular weight of 45,000 tethered to silica spheres with a diameter of 2150 Å. The polymer density profile demonstrates a deep depletion layer next to the surface with a maximum in ϕ(Z) of about 0.7 at about Z = 40 Å. Our experimental ϕ(Z) is compared with various theoretical predictions.
Low‐density polyethylene modified by thermal polymerization of 4‐vinylpyridine and methyl methacrylate: Structural studies
Authors: De Barros Glaucione Gomes , Sales Maria José Araújo , De Britto Ana Regina Feitosa
Published: August 2005

The structures of low‐density polyethylene (LDPE) modified by in situ sorption and thermal polymerization of 4‐vinylpyridine (4VP) and of methyl methacrylate (MMA) were studied. The phase behavior of these materials was investigated by means of X‐ray diffraction, scanning electron microscopy (SEM), and by thermal measurements (DSC). The diffraction studies indicated that the polymerization occurs at the amorphous domains of the matrix, except for the case of 4VP (168.0%), in which polymerization at the crystalline domains of LDPE matrix was also observed. These materials showed at least two Tg values, indicating microphase separation. The morphology of LDPE‐P4VP was different from that of LDPE‐PMMA.
Comments and corrections on “crystallization during polymerization of diphenylsilylene by a chemical transport reaction”
Authors: Shu Hua‐Cheng , Wunderlich Bernhard
Published: August 2005

Needlelike crystals of a phenylsilicon compound synthesized on crystallization during polymerization in a transport reaction in a temperature gradient, which were thought earlier to be polymeric diphenylsilylene, are shown to be actually tetraphenylsilane. Similarly produced crystals of the germanium analog led, in contrast, to polydiphenylgermylene. An overall reaction scheme uniting both reactions is suggested.
Viscoelastic properties of ethyl acrylate ionomers. I. Stress relaxation
Authors: Eisenberg A. , Matsuura H. , Tsutsui T.
Published: August 2005

Ethyl acrylate ionomers were studied by stress relaxation. The results are compared with those for the styrene ionomers studied previously. The behaviour of the two systems is qualitatively similar, although significant quantitative differences exist. Specifically, the onset of thermorheological complexity is found here at 12–16 mole% of ions, while in styrene it is observed at ca. 6 mole%. Furthermore, the modulus‐temperature plots show great similarity if the present samples are compared with the styrenes containing about half as many ions. Other properties show similar trends. The increased dielectric constant of the acrylates is believed to be responsible for the observed differences in the two systems. The effect of a change in counterions was also studied to some extent. The onset of thermorheological complexity is seen to be qualitatively related to the size and charge of the cation.
Photoconductivity of poly(hexamethylene adipamide)
Authors: Guillaud G. , Rosenberg N. , Maitrot M.
Published: August 2005

Photocurrents induced by pulsed ultraviolet light in polyhexamethylene adipamide (nylon‐66) have been studied. Two transient photocurrents are observed for light wavelenghts shorter than 3000 Å;. The first one is weakly field and temperature dependent and has been ascribed to electron photoinjection. On the whole, the time dependence of the two photoresponses suggests the possible formation of a space charge in the material.
Coherent scattering law for dilute polymer solutions: Continued fraction formalism
Authors: John Myung S. , Fesciyan Sezar , Dahler John S.
Published: August 2005

The continued fraction formalism of Mori is adapted to study the coherent scattering law of dilute polymer solutions. Calculations are carried out for the Rouse chain to see the effects of the memory function. We find such effects to be significant.
Rubber networks containing unattached macromolecules. IV. Stress relaxation in end‐linked polybutadiene with unattached styrene‐butadiene copolymer
Authors: Nelb Gary W. , Pedersen Sven , Taylor Carl R. , Ferry John D.
Published: August 2005

Stress relaxation has been studied in networks of dihydroxy‐terminated polybutadiene (mostly cis:trans:vinyl = 34:40:26) crosslinked by triphenyl methane‐4,4′,4″‐triisocyanate and containing about 9.5% by weight of unattached linear random styrene‐butadiene copolymer with various molecular weights (from 1.4 to 3.3 × 105) and with styrene content and butadiene microstructure chosen to match the average solubility parameter of the end‐linked network. Stress relaxation measurements were made also on networks containing no unattached species and containing 9.3% hydrocarbon oil, and on the various uncrosslinked linear polymers. The stretch ratio was 1.25 and the Young's relaxation modulus was calculated from the neo‐Hookean stress‐strain relation. For the uncrosslinked linear polymers, the relaxation modulus E11(t) corresponds to a rather narrow distribution of relaxation times whose magnitudes were approximately proportional to the 3.4 power of viscosity‐average or weight‐average molecular weight; for one polymer, the time dependence agreed closely with the prediction of the Doi‐Edwards theory modified for a small degree of molecular weight distribution. The disengagement times calculated from the Doi‐Edwards theory as modified by Graessley appeared to be of the correct order of magnitude. The contribution of the unattached species in the networks E1(t) was calculated by difference; after multiplication by (1−v)−1, where v2 is the volume fraction of network, and correction for the difference in monomeric friction coefficient associated with the difference in fractional free volume in the two environments, E1(t) was compared with E11(t) for each linear polymer. The relaxation was slower in the network than in the uncrosslinked polymer by about an order of magnitude, but the form of the relaxation modulus was similar in both environments except for two linear polymers for which the relaxation in the network became very much slower at long times. This behavior appeared to be correlated with a broader molecular weight distribution.
Polyimidines. VIII. Condensation of 3,5‐dibenzylidenepyromellitide‐1,7‐dithione with m‐xylylenediamine
Authors: Johnson C. Greg , Cassidy Patrick E.
Published: August 2005

A new pyromellitimidine‐forming monomer, 3,5‐dibenzylidenepyromellitide‐1,7‐dithione, was synthesized by thionation of 3,5‐dibenzylidenepyromellitide using phosphorus pentasulfide in boiling chloro‐ or bromobenzene. Polymerization of this monomer with m‐xylylenediamine (MXDA) in chlorobenezene at 95°C afforded poly(dihydroxydibenzylpyromellitimidinethione) with inherent viscosities of 0.23–0.51 dL/g in yields from 73 to 84%. Subsequent dehydration was accomplished by thermal methods or in a polar aprotic solvent such as dimethylformamide (DMF) using acid catalyst. Hydrated and dehydrated polymers were soluble in N‐methyl‐2‐pyrrolidinone (NMP), m‐cresol, and dioxane, and partially soluble in chloroform. Very brittle films could be cast from NMP solution. Thermogravimetric analysis of the dehydrated polymer showed a 10% weight loss in nitrogen atmosphere at 460°C
Synthesis and properties of polyesters of isomeric poly(oxynaphthyleneoxy‐2‐bromoterephthaloyl)s
Authors: Jin Jung‐Il , Choi E‐Joon , Kang Chung‐Seock , Chang Jin‐Hae
Published: August 2005

A series of aromatic polyesters were prepared from 2‐bromoterephthalic acid and naphthalenediol isomers. Only the polymers obtained from 1,4‐, and 1,5‐ and 2,6‐naphthalenediols were thermotropic nematogens and those from bent naphthalenediols were not liquid crystalline. Only the polyesters derived from 1,4‐, 1,5‐, and 2,6‐naphthalenediols were semicrystalline. The melting temperatures ranged from 319 to 374°C depending on the structure of naphthalenediol moiety. The glass transition temperature, Tg, ranged from 95 to 168°C. TGA studied revealed that the polyesters have fairly good thermal stability
NMR studies of the thermal decomposition and branching reactions of aromatic esters
Authors: Ting Su‐Jen , Noggle J. H.
Published: August 2005

Poly(chlorophydroquinone terephthalate) is an aromatic polyester containing mainly chlorohydroquinone and terephthalate. Thermal stability of this aromatic polyester has been a problem during the processing. In order to characterize the melt reactions of this polyester, the thermal degradation of the model compound chlorohydroquinone dibenzoate was studied. The chlorohydroquinone dibenzoate was characterized by high resolution 13C‐NMR. All experiments for studyng degradation of chlorohydroquinone dibenzoate were designed to test the following environmental parameters: (1) atmosphere, (2) temperature, (3) time, (4) additives, (5) container material. The analysis of the degradation products were carried out mainly using NMR; in some cases GC/MS and HPLC were also used to aid in separation and identification of the degradation products. The major degradation products produced in various experimental conditions were identified as chlorohydroquinone benzoates, hydroquinone dibenzoate, dichlorohydroquinone dibenzoate, 9‐fluorenone, benzoic acid, Fries products, and hydrogen chloride
13C‐NMR spectroscopic analysis of vinyl groups in styrene–divinylbenzene networks
Authors: Periyasamy M. , Ford Warren T. , McEnroe Frank J.
Published: August 2005

p‐Divinylbenzene (DVB) 13C‐labeled at the methine carbon of the vinyl group was copolymerized in suspension with styrene at 70, 70–95, and 135–155°C using 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. The number of unreacted vinyl groups in each copolymer was determined by 13C CP–MAS NMR analysis of solid samples, direct polarization 13C‐NMR analysis of CDCl3‐swollen gels, and bromination. Results from the three methods agree methods agree qualitatively. Even the 1% DVB‐crosslinked networks contained 40% unreacted DVB‐vinyl groups when prepared by high conversion polymerization at 70°C and 16% unreacted DVB‐vinyl groups when polymerization was finished at 95°C. The analyses were also applied to some commercial crosslinked polystyrenes. Every sample examined contained pendent vinyl groups
Characterization and thermal degradation studies on polyaniline‐intercalated montmorillonite nanocomposites prepared by a solvent‐free mechanochemical route
Authors: Yoshimoto Shoji , Ohashi Fumihiko , Kameyama Tetsuya
Published: August 2005

Polyaniline (PANI)‐montmorillonite (MMT) nanocomposites were prepared by direct intercalation of aniline molecules into MMT galleries, followed by in situ polymerization within the nano‐interlamellar spaces under solvent‐free conditions. The basal spacing of aniline‐intercalated MMT increased gradually up to 1.5 nm with increasing amounts of aniline loaded. This result suggests that aniline molecules were adsorbed by MMT clay and that intercalated aniline likely located perpendicular to the silicate sheets. After polymerization, X‐ray diffraction and Fourier transform infrared analyses confirmed the successful synthesis of PANI chains between the MMT nano‐interlayers. The scanning electron microscopy images indicated that the surface morphologies of PANI–MMTs were strongly different depending on the PANI content. The electrical conductivities of PANI nanocomposite particles in pressed pellets ranged in the order of between 10−3 and 10−2 S/cm. UV–vis spectroscopy and doping level measurement were further used to discuss the conductivities of nanocomposites. The thermal stabilities of PANI–MMT nanocomposites were examined by using thermogravimetric‐differential thermal analysis and derivative thermogravimetric analysis, and both analyses consequently demonstrated the improved thermal stabilities of the PANI chains in the nanocomposites as compared to pure PANI. The thermal stabilities of resulting nanocomposites were strongly related to the PANI content, which increased as the PANI content decreased in the nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2705–2714, 2005