bluuebunny/crossref_metadata_2025 huggingface dataset:
On the dynamics of a discrete reaction‐diffusion system
Authors: Azmy Y. Y. , Protopopescu V.
Published: August 2005

We investigate various aspects of the dynamics of a discrete reaction‐diffusion system. First, we examine the effect of the boundary conditions on the spatially uniform fixed point at locations far from the boundaries by using an asymptotic expansion. We show that, except for a few computational cells adjacent to the boundary, the fixed point practically coincides with the one calculated by using reflective boundary conditions (equivalent to an infinite domain). Next, we introduce a classification of the fixed points based on the wavelength in the infinite‐medium approximation of the system. We use the symbolic manipulator MACSYMA to analytically calculate the amplitude of several such classes of fixed points and we generate bifurcation diagrams for their members. Also, we consider two special classes of periodic solutions; we calculate their amplitude analytically in the infinite‐medium approximation, and generate bifurcation diagrams that shed new light on some previous confusing results. Finally, we present an analysis of fictitious periodic solutions that have been previously reported and incorrectly interpreted.
Numreical solutoin of a class of parabolic partial differential equation arising in optimal control problems with uncertainty
Authors: Dahleh M. , Perice A. P.
Published: August 2005

In this paper the optimal control of uncertain parabolic systems of partial differential equations is investigated. In order to search for controllers that are insensitive to uncertainties in these systems, an iterative optimization procedure is proposed. This procedure involves the solution of a set of operator valued parabolic partial differential equations. The existence and uniqueness of solutions to these operator equations is proved, and a stable numerical algorithm to approximate the uncertain optimal control problem is proposed. The viability of the proposed algorithm is demonstrated by applying it to the control of parabolic systems having two different types of uncertainty.
Analysis of numerical integration in p‐version finite element eigenvalue approximation
Authors: Banerjee Uday , Suri Manil
Published: August 2005

We study the effect of numerical integration when the p‐version of the finite element method is used to approximate the eigenpairs of elliptic partial differential operators. We obtain optimal orders of convergence for approximate eigenvalues and eigenvectors under a certain set of requirements on the quadrature rules employed. This is the same set of conditions that has been shown (in an earlier work) to be sufficient for the optimal approximation of the solutions of the corresponding source problems.
Direct numerical method for an inverse problem of hyperbolic equations
Authors: Lin Tao , Ewing Richard E.
Published: August 2005

A coefficient inverse problem of the one‐dimensional hyperbolic equation with overspecified boundary conditions is solved by the finite difference method. The computation is carried out in the x direction instead of the usual t direction. The original boundary condition and the overspecified boundary data are used as the new initial conditions, and the original data at t = 0 are used to compute the coefficient directly. The computation time used by this scheme is almost equal to that for solving the hyperbolic equation in the same region once, even though the inverse problem is essentially nonlinear and hence more difficult to solve. An error estimate is obtained that guarantees the stability of the scheme marching in the x direction. Several numerical experiments are carried out to show the convergence and other properties of the scheme. © 1992 John Wiley & Sons, Inc.
Method of separation of variables and Hamiltonian system
Authors: Wanxie Zhong , Xiangxiang Zhong
Published: August 2005

In the theory of mechanics and/or mathematical physics problems in a prismatic domain, the method of separation of variables ususally leads to the Sturm–Liouville‐type eigenproblems of self‐adjoint operators, and then the eigenfunction expansion method can be used in equation solving. However, a number of important application problems cannot lead to self‐adjoint operator for the transverse coordinate. From the minimum potential energy variational principle, by selection of the state and its dual variables, the generalized variational principle is deduced. Then, based on the analogy between the theory of structural mechanics and optimal control, the present article leads the problem to the Hamiltonian system. The finite‐dimensional theory for the Hamiltonian system is extended to the corresponding theory of the Hamiltonian operator matrix and adjoint symplectic spaces. The adjoint symplectic orthonormality relation is proved for the whole state eigenfunction vectors, and then the expansion of an arbitrary whole state function vector by the eigenfunction vectors is established. Thus the range of classical method of separation of variables is considerably extended. The eigenproblem derived from a plate bending problem in a strip domain is used for illustration. © 1993 John Wiley & Sons, Inc.
Domain‐imbedding alternating direction method for linear elliptic equations on irregular regions using collocation
Authors: Cooper K. D.
Published: August 2005

A new method is presented for solving elliptic partial differential equations over two‐dimensional irregular regions. The scheme imbeds the irregular region in a rectangle, and then uses an alternating direction iteration to solve the resulting system of linear equations. Collocation with cubic Hermite splines is used for discretization. The method is shown to be equivalent to a multiboundary alternating direction method. A theory of convergence for a simplified case is given, details of implementation are discussed, and two numerical illustrations are presented. © 1993 John Wiley & Sons, Inc.
Existence and C0, α regularity of minima of a functional related to the grid‐generation problem
Authors: Liao G. , Liu H.
Published: August 2005

The existence of C0,α regularity of minima of a functional arising from the grid‐generation problem are provided in the case of n‐dimensional domains. The functional studied in this article is a linear combination of the length functional, the volume functional, and a higher‐order term. The inclusion of the latter guarantees the existence and regularity of a minimum via the direct method for calculus of variations. © 1993 John Wiley & Sons, Inc.
Linearized stability analysis of staggered‐grid difference schemes for multidimensional viscous incompressible flows
Authors: Kwok Yue‐Kuen , Tam Kin‐Kiu
Published: August 2005

This paper presents a systematic linearized (frozen coefficient) von Neumann stability analysis for various staggered‐grid marker‐and‐cell (MAC) finite difference schemes for solving viscous incompressible fluid flows. These schemes employ the primitive variables formulation and require the velocity field to be divergent free at every time step. It is illustrated that the stability results for staggered‐grid MAC schemes are similar to that for the multidimensional convective‐diffusion equation with constant coefficients. © 1993 John Wiley & Sons, Inc.
Characteristic‐based schemes for dispersive waves I. The method of characteristics for smooth solutions
Authors: Roe Philip L. , Arora Mohit
Published: August 2005

In order to embark on the development of numerical schemes for stiff problems, we have studied a model of relaxing heat flow. To isolate those errors unavoidably associated with discretization, a method of characteristics is developed, containing three free parameters depending on the stiffness ratio. It is shown that such “decoupled” schemes do not take into account the interaction between the wave families and hence result in incorrect wave speeds. We also demonstrate that schemes can differ by up to two orders of magnitude in their rms errors even while maintaining second‐order accuracy. We show that no method of characteristics solution can be better than second‐order accurate. Next, we develop “coupled” schemes which account for the interactions, and here we obtain two additional free parameters. We demonstrate how coupling of the two wave families can be introduced in simple ways and how the results are greatly enhanced by this coupling. Finally, numerical results for several decoupled and coupled schemes are presented, and we observe that dispersion relationships can be a very useful qualitative tool for analysis of numerical algorithms for dispersive waves. © 1993 John Wiley & Sons, Inc.
Dual finite element analysis of three‐dimensional axisymmetric elliptic problems. Part II
Authors: Hlaváček Ivan , Křížek Michal
Published: August 2005

In Part II we derive a priori error estimates for the second type of a pure dual finite element model of a three‐dimensional axisymmetric elliptic problem with mixed boundary conditions. Convergence is proved for both types of model without any regularity assumption upon the solution. An algorithm for finding a particular solution is presented. © 1993 John Wiley & Sons, Inc.
Superconvergence phenomena in nonlinear two‐point boundary‐value problems
Authors: Chow S. S. , Carey G. F.
Published: August 2005

Superconvergence estimates are derived for a class of strongly nonlinear two‐point boundary‐value problems. The analysis considers solution and gradient superconvergence points as well as flux postprocessing formulas. Finally, the extension to parabolic problems is considered. © 1993 John Wiley & Sons, Inc.
Fourth‐order schemes for the wave equation, Maxwell equations, and linearized elastodynamic equations
Authors: Tuomela Jukka
Published: August 2005

With simple finite‐difference operators we construct fourth‐order schemes in space and in time for the wave equation, Maxwell equations, and linearized elastodynamic equations using the modified equation approach. The schemes remain stable for arbitrary heterogeneous mediums because the relevant difference operators are always positive definite. We also present some dispersion curves to show the accuracy of the schemes. © 1994 John Wiley & Sons, Inc.
Two‐dimensional modeling of microscale transport and biotransformation in porous media
Authors: Chen B. , Cunningham A. , Ewing R. , Peralta R. , Visser E.
Published: August 2005

We develop a model for simulating the growth of a biofilm in a tortuous tube. The solutions to the Navier‐Stokes equations and the advection‐diffusion equation are calculated numerically using finite differences. These solutions are then coupled with a biofilm growth model. © 1994 John Wiley & Sons, Inc.
Multidomain direct method and its applicability to the local time‐step concept
Authors: Jelen Jaroslaw A.
Published: August 2005

A new multidomain direct (noniterative) method for solving boundary‐value problems is presented. Using this method, the solution is expressed by a linear combination of auxiliary functions and unknowns which pertain to the boundaries of a subdomain. This approach enables us to solve problems independently and exactly, without any iterations between subdomains. As a consequence, different types of equations and coordinate systems may be considered in different subdomains. Moreover, different boundary conditions and variable (in space) time steps may be imposed on the subdomains as well. Applications are given for initial boundary‐value problems with known analytical solutions, including a highly nonlinear porosity equation. © 1994 John Wiley & Sons, Inc.
Improved error estimates for mixed finite‐element approximations for nonlinear parabolic equations: The continuous‐time case
Authors: Garcia Sonia M. F.
Published: August 2005

L2‐error estimates are computed for mixed finite‐element methods for second‐order quasilinear (and linear, variable coefficient) parabolic equations. Results are given for the continuous‐time case. The convergence of the values for both the scalar function and the flux is demonstrated. The technique used here covers the lowest‐order Raviart‐Thomas spaces, as well as the higher‐order spaces. A second paper will present the analysis of a fully discrete scheme. © 1994 John Wiley & Sons, Inc.
Finite‐difference methods for one‐dimensional hyperbolic conservation laws
Authors: Berkenbosch A. C. , Kaasschieter E. F. , ten Thije Boonkkamp J. H. M.
Published: August 2005

This article contains a survey of some important finite‐difference methods for one‐dimensional hyperbolic conservation laws. Weak solutions of hyperbolic conservation laws are introduced and the concept of entropy stability is discussed. Furthermore, the Riemann problem for hyperbolic conservation laws is solved. An introduction to finite‐difference methods is given for which important concepts such as, e.g., conservativity, stability, and consistency are introduced. Godunov‐type methods are elaborated for general systems of hyperbolic conservation laws. Finally, flux limiter methods are developed for the scalar nonlinear conservation law. © 1994 John Wiley & Sons, Inc.
A principle of images for absorbing boundary conditions
Authors: Ha Duong T. , Joly P.
Published: August 2005

When one uses high‐order finite difference schemes for the wave equation, for instance fourth order schemes, the treatment of boundary conditions poses a real difficulty since one needs several additional equations (for the nodes close to the boundary), while one single scalar boundary condition is available. In the case of perfectly reflecting boundary conditions, namely the homogeneous Neumann or Dirichlet conditions, this difficulty can be overcomed by the use of the well‐known image principle, which permits the extension of the equation outside of the domain of calculation by an appropriate symmetrization of the data. We propose in this article a generalization of this principle to the absorbing boundary conditions. Through a symmetrization process, we are led to introduce a damped wave equation with a damping term supported by the boundary. The treatment of the boundary condition is then replaced by the approximation of this new damped wave equation in the whole space. The theoretical justification of our approach is based on new energy estimates for the wave equation (when high‐order absorbing boundary conditions are used), and constitutes an alternative to the use of the well‐known Kreiss criterion to prove the stability of the associated initial boundary value problems. © 1994 John Wiley & Sons, Inc.
Finite‐difference methods for solving the reaction‐diffusion equations of a simple isothermal chemical system
Authors: Twizell E. H. , Wang Yigong , Price W. G. , Fakhr F.
Published: August 2005

Numerical methods are proposed for the numerical solution of a system of reaction‐diffusion equations, which model chemical wave propagation. The reaction terms in this system of partial differential equations contain nonlinear expressions. Nevertheless, it is seen that the numerical solution is obtained by solving a linear algebraic system at each time step, as opposed to solving a nonlinear algebraic system, which is often required when integrating nonlinear partial differential equations. The development of each numerical method is made in the light of experience gained in solving the system of ordinary differential equations, which model the well‐stirred analogue of the chemical system. The first‐order numerical methods proposed for the solution of this initialvalue problem are characterized to be implicit. However, in each case it is seen that the numerical solution is obtained explicitly. In a series of numerical experiments, in which the ordinary differential equations are solved first of all, it is seen that the proposed methods have superior stability properties to those of the well‐known, first‐order, Euler method to which they are compared. Incorporating the proposed methods into the numerical solution of the partial differential equations is seen to lead to two economical and reliable methods, one sequential and one parallel, for solving the travelling‐wave problem. © 1994 John Wiley & Sons, Inc.
Solving multivariable mathematical models by the quadrature and cubature methods
Authors: Civan Faruk
Published: August 2005

The utilization and generalization of quadrature and cubature approximations for numerical solution of mathematical models of multivariable transport processes involving integral, differential, and integro‐differential operators, and for numerical interpolation and extrapolation, are presented. The methodology for determination of the quadrature and cubature weights for composite operators is developed to accommodate for general functional representations. Application of these methods is demonstrated by solving two‐dimensional steady‐state and one‐dimensional transient‐state problems. The solutions are compared with exact‐analytical solutions to evaluate the performance of these methods. It is demonstrated that the quadrature and cubature approximations are simple and universal; i.e., the same formula is applicable irrespective of the order of accuracy of the numerical approximation, the type of linear operator, and the number of temporal and/or spatial variables. Since the quadrature and cubature methods can produce solutions with sufficient accuracy even when using fewer discrete points, both the programming task and computational effort are reduced considerably. Therefore, the quadrature and cubature methods appear to be very practical in solving the mathematical models of a variety of transport processes. © 1994 John Wiley & Sons, Inc.
Spectral Lanczos decomposition method for solving single‐phase fluid flow porous media
Authors: Knizhnerman Leonid , Druskin Vladimir , Liu Qing‐Huo , Kuchuk Fikri J.
Published: August 2005

A three‐dimensional well model (r − θ − z) for the simulation of single‐phase fluid flow in porous media is developed. Rather than directly solving the 3‐D parabolic PDE (partial differential equation) for fluid flow, the PDE is transformed to a linear operator problem that is defined as u = f(A)σ, where A is a real symmetric square matrix and σ is a vector. The linear operator problem is solved by using the spectral Lanczos decomposition method. This formulation gives continuous solutions in time. A 7‐point finite difference scheme is used for the spatial discretization. The model is useful for well testing problems as well as for the simulation of the wireline formation tester tool behavior in heterogeneous reservoirs. The linear operator formulation also permits us to obtain solutions in the Laplace domain, where the wellbore storage and skin can be incorporated analytically. The infinite‐conductivity (uniform pressure) wellbore condition is preserved when mixed boundary conditions, such as partial penetration, occur. The numerical solutions are compared with the analytical solutions for fully and partially penetrated wells in a homogeneous reservoir. © 1994 John Wiley & Sons, Inc.
A mixed finite element method for the Stokes equations
Authors: Farhloul Mohamed
Published: August 2005

A new mixed finite element for the Stokes equations is considered. This new finite element is based on a mixed formulation of the Stokes problem in which the gradient of the velocity is introduced and the velocity is approximated by the Raviart‐Thomas element [1]. Optimal error estimates are derived. The number of degrees of freedom, for this element, is the lowest possible, and the local conservation of the mass is assured. A hybrid version of the mixed method is also considered. Finally, some numerical results for the incompressible Navier‐Stokes equations are presented. © 1994 John Wiley & Sons, Inc.
A solution of the convection‐conduction heat‐transfer equation in porous media by the von Rosenberg finite‐difference scheme
Authors: Ginosar Daniel M. , Green Don W.
Published: August 2005

von Rosenberg developed an explicit finite‐difference scheme for solution of the linear convection‐conduction partial differential equation in one space dimension. The method is stable and accurate when a dimensionless ratio of dispersion to convection is between zero and one. In this work, the von Rosenberg method was applied to a linear, one space dimensional set of coupled convection‐conduction equations. The system examined involves the change in temperature resulting from a fluid flowing through a stationary porous solid with heat transfer between the fluid and solid phases. The equations, which describe heat transfer in each phase, were solved simultaneously and, thus, the solution method was required to be implicit rather than explicit. It was observed that when the interphase convective heat‐transfer rate was small relative to the fluid velocity, an implicit solution of the von Rosenberg weighted equations provided a good solution, but when the interphase convective heat‐transfer rate was relatively large, a modified weighting on the equations provided a more accurate, stable solution. © 1994 John Wiley & Sons, Inc.
Nonlinear Poisson‐Boltzmann equation in a model of a scanning tunneling microscope
Authors: Chan Kwong‐Yu , Henderson Douglas , Stenger Frank
Published: August 2005

The nonlinear Poisson‐Boltzmann equation is solved in the region between a sphere and a plane, which models the electrolyte solution interface between the tip and the substrate in a scanning tunneling microscope. A finite difference method is used with the domain transformed into bispherical coordinates. Picard iteration with relaxation is used to achieve convergence for this highly nonlinear problem. An adsorbed molecule on the substrate can also be modelled by a superposition of a perturbing potential in a small region of the plane. An approximate analytical solution using a superposition of individual solutions for plane, the adsorbed molecule, and the sphere is also attempted. Results for cases of different potential values on the boundary surfaces and different distances of the sphere from the plane are presented. The results of the numerical method, the approximate analytical method, as well as the previous solutions of the linearized equation are compared. © 1994 John Wiley & Sons, Inc.
Time‐dependent boundary conditions for the 2‐D linear anisotropic‐viscoelastic wave equation
Authors: Carcione José M.
Published: August 2005

Wave propagation simulation requires a correct implementation of boundary conditions to avoid numerical instabilities. A boundary treatment based on characteristics, which includes as special cases more simple rheologies involving isotropy and elastic behavior, is applied to the anisotropic‐viscoelastic wave equation. The method introduces the boundary conditions by specifying the values of the incoming variables, which depend on the solution outside the model volume. The formulation ends up with a wave equation for the boundaries that implicitly includes the boundary conditions. The examples illustrate common problems in geophysical modeling, including free surface and nonreflecting conditions. © 1994 John Wiley & Sons, Inc.
An error estimate for a finite volume scheme for a diffusion–convection problem on a triangular mesh
Authors: Herbin Raphaèle
Published: August 2005

We study here a finite volume scheme for a diffusion‐convection equation on an open bounded set Ω of ℝ2, using a triangular mesh for the discretization of Ω. The 4‐point numerical scheme is presented along with the geometrical assumptions on the mesh. An error estimate of order h on the discrete L2 norm is obtained, where h denotes the “size” of the mesh. The proof uses an estimate of order h of the consistency error on the fluxes and an estimate of the number of edges of the mesh between one given triangle and the boundary Ω. © 1995 John Wiley & Sons, Inc.
A modified method of characteristics incorporating streamline diffusion
Authors: Allen Myron B. , Liu Biyue
Published: August 2005

A hybrid finite‐element method, combining ideas from a modified method of characteristics and the streamline diffusion method, delivers accurate solutions to the advection–diffusion equation. An error analysis for the case of tensorial diffusion shows that the lowest‐order version of the scheme, which allows one to use a symmetric linear solvers at each time step, possesses first‐order accuracy in time and space. Numerical experiments demonstrate the scheme's ability to model advection‐dominated transport of solute plumes without distorting sharp fronts. © 1995 John Wiley & Sons, Inc.
Truncation error in grid generation: A case study
Authors: Knupp P. , Luczak R.
Published: August 2005

Theoretical proofs state that the planar Winslow or homogenous Thompson–Thames–Mastin (hTTM) map is a diffeomorphism, yet numerical solutions to the hTTM equations produce folded grids on the so‐called “horseshoe” domain. A quasi‐analytic solution to the horseshoe problem is constructed to demonstrate that folding is due to truncation error effects. Higher‐order difference methods are also explored. © 1995 John Wiley & Sons, Inc.
A computer science approach for solving elliptic differential equations
Authors: Peralta R. , Chen B.
Published: August 2005

A method that combines computer science and numerical analysis techniques for the solution of elliptic partial differential equations in domains consisting of the union of rectangles is presented. It is applied to Laplace's equation and to the Navier–Stokes equations in several domains. The method is very flexible and can be easily modified to solve other equations. © 1995 John Wiley & Sons, Inc.
Monotone method and convergence acceleration for finite‐difference solutions of parabolic problems with time delays
Authors: Lu Xin
Published: August 2005

In this article we study a finite‐difference system, which is a discrete version of a class of nonlinear reaction‐diffusion systems with time delays. Existence‐comparison and uniqueness theorem are first established for the discretized problem by the method of upper and lower solutions. A monotone iterative scheme is also developed for the solution of the finite‐difference system. Under a convergence acceleration scheme, it is shown that the monotone sequences converge quadratically to the solution of the finite‐difference system. At last, numerical results on some model problems are demonstrated to substantiate our theorems. © 1995 John Wiley & Sons, Inc.
An operator‐splitting algorithm for the three‐dimensional diffusion equation
Authors: Khan Liaqat Ali , Liu Philip L.‐F.
Published: August 2005

A second‐order‐accurate and unconditionally stable operator‐splitting algorithm for the three‐dimensional diffusion equation is presented in this article. The governing equation is split into three one‐dimensional equations, and the split equations are solved by a finite‐element method. The simulation characteristics of the algorithm are demonstrated by numerical experiments. © 1995 John Wiley & Sons, Inc.
AKT activation predicts outcome in breast cancer patients treated with tamoxifen
Authors: Kirkegaard Tove , Witton Caroline J , McGlynn Liane M , Tovey Sian M , Dunne Barbara , Lyon Alison , Bartlett John MS
Published: August 2005

Oestrogen receptor (ERα) expression is a strong predictor of response to endocrine therapy. The PI3K/AKT/mTOR signal transduction pathway has been implicated in endocrine resistance in vitro. The present study was carried out to test the hypothesis that AKT activation mediates tamoxifen resistance in clinical breast cancer. Immunohistochemistry (IHC) using AKT1‐3, pan‐AKT, pAKT (Thr‐308), pAKT (Ser‐473), pER (Ser‐167), and pHER2 antibodies was performed on 402 ERα‐positive breast carcinomas from patients treated with tamoxifen. High pAKT (Ser‐473) activity (p = 0.0406) and low AKT2 expression (p = 0.0115) alone, or in combination [high pAKT (Ser‐473)/low AKT2; ‘high‐risk’ patient group] (p = 0.0014), predicted decreased overall survival in tamoxifen‐treated patients with ERα‐positive breast cancers. There was no significant association between tumour levels of AKT expression or activity and disease‐free survival (DFS); however, the ‘high‐risk’ patient group was significantly more likely to relapse (p = 0.0491). During tamoxifen treatment, neither AKT2 nor pAKT predicted DFS. Finally, activation of AKT, via phosphorylation, was linked to activation of both HER2 and ERα in this patient cohort. The data presented here show that the PI3K/AKT/mTOR pathway is associated with relapse and death in ERα‐positive breast cancer patients treated with tamoxifen, supporting in vitro evidence that AKT mediates tamoxifen resistance. Patients with a ‘high‐risk’ expression profile were at increased risk of death (hazard ratio 3.22, p = 0.002) relative to ‘low‐risk’ patients, highlighting the potential that tumour profiling, with multiple IHC markers predictive of therapeutic response, may improve patient selection for endocrine therapies, eg tamoxifen or aromatase inhibitor‐based treatments. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
The concept of the ‘percent wasted patients’ in preventive health strategies
Authors: Cardinal Héloise , Monfared Amir Abbas Tahami , Dorais Marc , LeLorier Jacques
Published: August 2005

Purpose

To better communicate the impact of poor persistence when preventive therapies are initiated, we propose a new measure that is intuitively understandable for clinicians. This measure is the percent wasted patients (PWP).

Methods

The PWP is the percentage of patients, out of the new users of a given preventive treatment, who have discontinued therapy before the time point at which clinical benefits become apparent on the cumulative incidence curves in randomized controlled trials (RCTs) comparing active treatment to placebo. To calculate the PWP, the RCTs that demonstrated the efficacy of the therapy under study must be identified from a MEDLINE search. The point at which the cumulative incidence curves for the main outcome in the experimental and placebo group start diverging is identified and is called the point of visual divergence (PVD). Then, using pharmaceutical claims databases, the percent persistence at the PVD in new users of the therapy is determined. The PWP is then calculated as 100% persistence at PVD.

Results

For primary prevention with statins, in the province of Quebec, the PWP is 44%. Of 100 patients starting statins for the primary prevention of coronary events, 44 will represent a waste in health resources because they will have discontinued therapy before any clinical benefit can be expected.

Conclusions

The PWP is a simple measure that can be used by clinicians to select the therapies that need the most reinforcement concerning the importance of persistence. Copyright © 2005 John Wiley & Sons, Ltd.
Fluorescence polarization measurements of orientation in labeled polyisoprene networks
Authors: Jarry J. P. , Monnerie L.
Published: August 2005

Fluorescence polarization was used to measure segmental orientation in stretched polyisoprene networks. Stress and orientation of chemically bonded fluorescent labels were simultaneously recorded during stretching. Two deviations from the classical theory of rubber elasticity were observed: (i) an extra orientation of dry networks, which was interpreted by assuming the existence of weak nematiclike interactions between segments, and (ii) a saturation of orientation at high elongation which could be due to local conformational changes.
Hydrodynamic studies on model branched polystyrenes
Authors: Roovers J. , Toporowski P. M.
Published: August 2005

The measurement of the sedimentation velocity coefficient of narrow distribution linear, four‐arm and six‐arm star and comb polystyrenes in a theta solvent permits the experimental determination of h, i.e., the ratio of the translational friction coefficients of the branched polymer to that of its linear homolog. A comparison of experimental h/g1/2 values with theoretical predictions can then be made. It was observed that the equivalent hydrodynamic radii derived from sedimentation and intrinsic viscosity measurements are identical within experimental error.
Order in poly(N‐(10‐n‐alkyloxycarbonyl‐n‐decyl)‐maleimides)
Authors: De La Campa J. I. Gonzalez , Barrales‐Rienda J. M.
Published: August 2005

Wide‐angle and small‐angle x‐ray diffraction patterns of 11 poly(N‐(10‐n‐alkyloxycarbonyl‐n‐decyl)maleimides) (PEMI) (including only even members of the series) have been obtained on unoriented samples. They show major maxima at two diffraction angles. The one at the larger angles is due to the interaction of neighboring n‐alkyl side‐chains. The smaller one (which shows second and third orders of diffraction in higher members of the series, n = 14 to n = 22, where n is the number of methylene groups in the external n‐alkyl sequence in the side chain) is related to the distance between lamellar planes formed by the main chains. In all cases, the measured layer separation di is higher than the structural unit length L of the side‐chain in the most extended conformation, and lower than the length corresponding to two side‐chains. On the basis of the experimental results reported here, a model is proposed for the packing of these comblike polymers in the solid state. The mode of packing is also supported by infrared spectra in the 720 cm−1 region for the CH2 rocking mode of vibration of the n‐alkyl side‐chain.
A fourier‐transform infrared spectroscopic study of the hydrolytic stability of silane coupling agents on E‐glass fibers
Authors: Ishida Hatsuo , Koenig Jack L.
Published: August 2005

Fourier‐transform (FT) infrared spectroscopy has been applied to the study the hydrothermal degradation of various coupling agents on E‐glass fibers. The coupling agents studied include γ‐methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, and cyclohexyltrimethoxysilane. The amount of coupling agents on E‐fibers was measured as a function of immersion time in water at 80°C. Structural changes were also followed by obtaining FT‐IR difference spectra of the coupling agent on the glass fiber surface. Silanes desorb quite differently depending on the organofunctional groups. The resistance to desorption is strongly influenced by the organization of the silane interphase as well as the solubility of the silane in water.
The occurrence of head‐to‐head butene units in ethylene‐butene copolymers and corresponding ethyl branches in low‐density (branched) polyethylenes
Authors: Dechter James J. , Mandelkern Leo
Published: August 2005

A high resolution carbon‐13 NMR study of an ethylene‐butene copolymer has yielded a spectrum whose resonances could be assigned to isolated ethyl branches, 1,3‐diethyl branching as well as 1,2‐diethyl branches resulting from head‐to‐head butene polymerization. All these structures are present in the same sample. An examination of all the published spectra of low‐density (branched) polyethylenes has revealed many examples of heretofore unassigned resonances which can be associated with this latter type of diethyl branching in these polymers. Spin‐lattice relaxation times have been determined, when feasible, for the carbon atoms in each of the three branched structures.
Radical polymerizations of 4‐pentamethyldisilylstyrenes
Authors: Saigo Kazuhide
Published: August 2005

Radical polymerization of 4‐pentamethyldisilylstyrene (1) and 4‐pentamethyldisilyl‐α‐methylstyrene (2) have been conducted. Monomer reactivity ratious (r1 and r2) of 1 and 2 with styrene (M1) were measured with Fineman‐Ross plots. The resonance factor (Q) and polar factor (e) of a Q–e scheme for 1 were conculated with the r1 and r2 values. The inductive effect (σI) resonance effect (σ) of the pentamethyldisily group were monitored with the 1H‐ and 13C‐NMR spectra of 1. The magnitudes of σI and σ were found to be analogous to those of the trimethylsilyl group, indicating that the disilyl group shows a net electron‐withdrawal effect
Cationic polymerization of α‐methylstyrene in dichloromethane initiated with system 2,5‐dichloro‐2,5‐dimethylhexane‐BCl3. I. Molecular weight distribution and stereoregularity of poly (α‐methylstyrene)
Authors: Toman L. , Pokorný S. , Spěváček J.
Published: August 2005

In the polymerization of α‐methylstyrene (α‐MeSt) in dichloromethane in the temperature interval between −60 and −20°C the polymer yield decreased with increasing temperature depending on the initiating system used (I‐IV) in the series II > I > IV > III, where I was a freshly prepared solution of 2,5‐dichloro‐2,5‐dimethylhexane (DDH) with BCl3 in dichloromethane, was the same solution as in the preceding case, but stored at room temperature one month and then used, III was a freshly prepared BCl3 solution in dichloromethane, and IV was the initiation system “H2O”/BCl3. The polymer samples synthesized at ≤ −30°C had a bimodal molecular weight distribution (MWD), which was attributed to the different participation of ionic pairs and free ions in the propagation reaction. The stereoregularity of the polymer observed (ca. 85% syndiotactic and ca. 15% heterotactic triads) determined from the 1H‐NMR spectra was not affected by the difference in the initiation system. MWD of the polymer samples was investigated by the GPC method
Peak area measurements of cross‐polarization magic‐angle‐spinning 13C‐NMR spectra of crosslinked polystyrenes
Authors: Ford Warren T. , Periyasamy M. , Mohanraj S. , McEnroe Frajk J.
Published: August 2005

Cross‐polarization magic‐angle‐spinning 13C‐NMR spectra of polystyrenes crosslinked with 1–20% of methine vinyl carbon 13C‐labeled p‐divinylbenzene and of Friedel–Crafts crosslinked poly(chloromethylstyrene)s have been obtained with both glossy solid and CDCl3‐swollen gel samples. The spectra of natural abundance, uncrosslinked, glassy polystyrene, and the spectra of the solid labeled networks give aliphatic and aromatic peak areas only 0.7 times as large per 13C atom as that of poly(oxymethylene). Similarly the crosslinked poly(chloromethylstyrene) gave peak areas about 0.6 times that of internal poly(oxymethylene). The labeled gels give peak areas 0.2–0.6 times as large per 13C atom as glassy polystyrene, and the peak areas in spectra of gels increase with the divinylbenzene content
Synthesis and properties of polyketones containing thiophene links
Authors: Yi Mi Hie , Choi Kil‐Yeong , Jung Jin Chul
Published: August 2005

A series of polyketones containing thiophene links was synthesized by the Friedel‐Crafts polymerization of these dithienylalkanes with aromatic diacid chlorides or dicarbonyl chlorides comprising thiophene links with diphenyl compounds. The resulting polymers had inherent viscosities in the range of 0.11–0.27 dL/g and showed poor solubilities to common organic solvents except strong acids. These thiophene‐based polyketones exhibited fairly good thermal stabilities. The TGA data revealed 5% weight losses at 375–450°C and residual weights at 500°C were 43–79% under nitorgen. It was found that the thermal stabilities of these polymers were superior to those of polymides or polysulfonamides containing thiophene links and almost comparable to common aromatic polyketones
Aqueous polymerization of methyl methacrylate initiated by Ce(IV)–alcohol redox systems: Effect of acid concentration and additives
Authors: Fernandez M. D. , Guzman G. M.
Published: August 2005

Polymerization of methyl methacrylate (MMA) initiated by ceric ammonium nitrate in combination with alcohols, isopropyl and, isobutyl alcohol, has been studied in aqueous nitric acid. The effect of nitric acid and nitrate ion concentrations on the initial rate of polymerization as well as on that of ceric ion consumption and on polymer molecular weight has been investigated. The rate of polymerization initially rapidly to a maximum with increasing nitric acid concentration at constant nitrate ion concentration, and then, decreased at higher acid concentrations. The rate of ceric ion consumption increased on increasing the acid concentration. A fall in both the rates was observed as the nitrate ion concentration increased, and when acid concentration was kept constant. Average‐molecular weights decreased with increasing the acid concentration; whereas they increased with increasing that of nitrate ion. The effect of certain water‐miscible organic solvents has also been studied. Both the rates increased in their presence, whereas the molecular weight underwent a decrease
Detection of Lymph Node Micrometastases and Isolated Tumor Cells in Sentinel and Nonsentinel Lymph Nodes of Colon Cancer Patients
Authors: Bembenek Andreas , Schneider Ulrike , Gretschel Stephan , Fischer Joerg , Schlag Peter M.
Published: August 2005

About 20% to 30% of colon cancer patients classified as node negative by routine hematoxylin‐eosin (H&E) staining are found to have micrometastases (MM) or isolated tumor cells (ITC) in sentinel lymph nodes (SLNs) if analyzed by step sections and immunohistochemistry (IHC). Whether SLNs are in this respect representative for all lymph nodes was addressed in this study. SLNs were identified using the intraoperative blue dye detection technique. If all lymph nodes (SLNs and non‐SLNs) of a patient were negative by routine H&E staining, they were step‐sectioned and analyzed by IHC using pancytokeratin antibodies. We identified at least one SLN in 47 of the 55 patients (85%) and examined a median of 26 lymph nodes per patient (range 10–59). By routine H&E staining, 14 of the 47 patients showed lymph node metastases (30%); the remaining 33 were classified as node‐negative. In this group (33 patients), 1011 lymph nodes were analyzed by step sections and IHC: 14 of 70 SLNs. (20%) but only 37 of 941 non‐SLNs (4%) had MM/ITC (p < 0.001). Furthermore, 13 of the 33 H&E‐negative patients were found to have MM/ITC (39%). In 11 of the 13 patients, MM/ITC were identified in both SLNs and non‐SLNs in 1 patient in the SLN only, and in 1 patient in a non‐SLN only (sensitivity for the identification of MM/ITC: 92%; negative predictive value: 95%). The SLN biopsy is a valid tool to detect, as well as exclude, the presence of MM/ITC in colon cancer patients. Our results may be of prognostic relevance and influence patient stratification for adjuvant therapy trials.
Normotensive Pheochromocytoma: Institutional Experience
Authors: Agarwal Amit , Gupta Sushil , Mishra Anand Kumar , Singh Nikhil , Mishra Saroj K.
Published: August 2005

We report an audit of nine cases of subclinical or normotensive pheochromocytoma managed in our department. This is the first report from India of such a series. During the period 1990–2003 a total of 45 patients of pheochromocytoma were diagnosed and managed in the Department of Endocrine Surgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences. Among them, nine patients were diagnosed as having subclinical or normotensive pheochromocytoma. Inclusion criteria for normotensive pheochromocytoma were: no previous history of hypertension clinically and, in the previous treatment documents, any episode of symptoms suggesting high blood pressure. The demographic profile, clinical presentation, biochemical investigations, imaging results, surgical notes, and follow‐up record were reviewed retrospectively. All patients had a primary complaint of flank/abdominal pain and were normotensive. Seven had elevated urinary metanephrine levels, and one patient had normal values. One patient did not undergo the urinary metanephrine assay. Imaging of the abdomen showed seven adrenal and two extra‐adrenal masses (eight had computed tomography scans of the abdomen, and one underwent ultrasonography). After selective α‐adrenergic blockade (prazosin), surgery was performed. Six patients required infusion of sodium nitroprusside intraoperatively. The final histopathology was pheochromocytoma in all patients. Metanephrine levels were normal during the follow‐up. Normotensive pheochromocytomas are a distinct entity, and all adrenal incidentalomas should be investigated for catecholamine hypersecretion. We support the use of preoperative α‐adrenergic blockade, and these patients should be treated along the same lines as hypertensive pheochromocytoma.
Acute versus chronic pain treatment in Alzheimer's disease
Authors: Pickering Gisèle , Jourdan Didier , Dubray Claude
Published: August 2005

Several studies have suggested a lower consumption of analgesics in patients with Alzheimer's disease (AD) than in cognitively intact individuals (ND), but little attention has been paid to a distinction in analgesic consumption between acute and chronic pain treatment. The aim of this prospective and longitudinal study is a comparison in AD and ND residents at selection, and one year later, of analgesic consumption for acute and chronic pain, with an assessment of cognitive status (with the Mini Mental State Examination (MMSE)). Three hundred institution residents (150 AD and 150 ND), 20% male and 80% female (84.4 − 8.3 years old), were included in this study. Analgesic consumption and MMSE were reassessed at one year's distance (period 1 P1 and 2 (P2)). Analgesic consumption for acute pain was not significantly different for AD and ND at selection time or one year later, while MMSE declined significantly for AD (6 − 7 (P1) versus 4 − 6 (P2) p < 0.01, and ND individuals 23 − 5 (P1) versus 20 − 6 (P2), p < 0.01, respectively). Chronic pain analgesic consumption however was significantly lower in AD than in ND (p < 0.01). These findings may suggest a dissociation between sensory‐discriminative (lateral pain system) and motivational‐affective (medial pain system) aspects of pain in individuals with AD. This dissociation must be further investigated as it may have important consequences for pain evaluation and pain treatment in this vulnerable population.
The dinuclear iron‐oxo ferroxidase center of Pyrococcus furiosus ferritin is a stable prosthetic group with unexpectedly high reduction potentials
Authors: Tatur Jana , Hagen Wilfred R.
Published: August 2005

Recombinant ferritin from Pyrococcus furiosus expressed in Escherichia coli exhibits in EPR monitored redox titrations a mixed valence (Fe3+–Fe2+) S = 1/2 signal at intermediate potentials that is a high‐resolution homolog of the ferroxidase signal previously described for reconstituted horse spleen apo‐ferritin. P. furiosus reconstituted apo‐ferritin reduced to intermediate potentials exhibits the same mixed‐valence signal, which integrates to close to one spin per subunit. The reduction potentials of +210 and +50 mV imply that the iron dimer is a stable prosthetic group with three redox states.
Maturation of Borna disease virus glycoprotein
Authors: Eickmann Markus , Kiermayer Simone , Kraus Ina , Gössl Melanie , Richt Jürgen A. , Garten Wolfgang
Published: August 2005

The maturation of Borna disease virus (BDV) glycoprotein GP was studied in regard to intracellular compartmentalization, compartmentalization signal‐domains, proteolytic processing, and packaging into virus particles. Our data show that BDV‐GP is (i) predominantly located in the endoplasmic reticulum (ER), (ii) partially exists in the ER already as cleaved subunits GP‐N and GP‐C, (iii) is directed to the ER/cis‐Golgi region by its transmembrane and/or cytoplasmic domains in CD8‐BDV‐GP hybrid constructs and (iv) is incorporated in the virus particles as authentic BDV glycoprotein exclusively in the cleaved form decorated with N‐glycans of the complex type. Downregulation of BDV‐glycoproteins on the cell surface, their limited proteolytic processing, and protection of antigenic epitopes on the viral glycoproteins by host‐identical N‐glycans are different strategies for persistent virus infections.