bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Helmholtz equation in disturbed half‐spaces
Authors: Willers A. , Werner P. 
Published: March 2007

AbstractWe consider boundary value problems for the Helmholtz equation in domains with boundaries coinciding with a plane outside a sufficiently large sphere. As opposed to the method of Gartmeier [6] (see also [12]) our analysis leads to an integral equation of the second kind with a compact operator. In the last chapter we study the set of far field patterns which are generated by entire incident fields.
A free boundary problem for three‐dimensional harmonic vector fields
Authors: Wegmann R. , Martensen E. 
Published: March 2007

AbstractWe study in this paper a free boundary value problem (FB), where a region Go in R3 is determined by the condition that there exists a vector field vo in Go which satisfies div vo = eo, curl vo = go in Go and vo = E on the boundary ∂Go with a given scalar function eo and given vector fields go and E. We give two equivalent formulations for this problem. Then we characterize the solutions by a non‐linear integral equation. In order to solve the latter by a Newton method we linearize this equation. We investigate the ensuing linear integral equation. In case of axisymmetric configurations this is a singular integral equation whose index can be easily determined from the given data. We obtain a related equation, if we try to construct a field v in a region G which is on the boundary perpendicular to a given field B. Finally we use this method to investigate an astrophysical problem, which arises in the theory of pulsar magnetospheres.
An ecoepidemiological model with disease in predator: the ratio‐dependent case
Authors: Haque Mainul , Venturino Ezio 
Published: March 2007

AbstractWe propose a ratio‐dependent demographic predator–prey model in which also a disease spreads among predators via homogeneous mixing. Equilibria of the system are analysed, numerical evidence shows limit cycles to arise. The disease effects on the model are discussed. Comparisons of these findings with results of some related investigations allow the general conclusion that an infection in either species, prey or predator, may act as a biological control. Copyright © 2007 John Wiley & Sons, Ltd.
Analytical and numerical solution of the elastodynamic strip load problem
Authors: Verruijt A. , Brinkgreve R. B. J. , Li S. 
Published: March 2007

AbstractAnalytical and numerical solutions of the elastodynamic problem of an instantaneous strip load on a half space are presented and compared. The analytical solution is obtained using the De Hoop–Cagniard method, and the numerical solution is obtained using the dynamic module of the finite element package Plaxis. The purpose of the paper is to validate the numerical solution by comparison with a completely analytical solution, and to verify that the main characteristics of the analytical solution are also obtained in the numerical solution. Particular attention is paid to the magnitude, the velocity, and the shape of the Rayleigh wave disturbances. Copyright © 2007 John Wiley & Sons, Ltd.
Randomized, double‐blind, sham‐controlled evaluation of the effect of functional continuous magnetic stimulation in patients with urgency incontinence
Authors: Suzuki Tsuneki , Yasuda Kosaku , Yamanishi Tomonori , Kitahara Satoshi , Nakai Hideo , Suda Shin , Ohkawa Hiromi 
Published: March 2007

AbstractAimsTo evaluate the effect of functional continuous magnetic stimulation (FCMS) on urgency incontinence in randomized, sham‐controlled manner.MethodsThirty‐nine patients with urgency incontinence, 16 males and 23 females (aged 66.0 ± 16.5 years), who were refractory to pelvic floor muscle training (PFMT), were randomly assigned either to the treatment schedule performing 10‐week active treatment, followed by 4‐week non‐treatment interval and then by 10‐week sham treatment (A–S, n = 20) or to that performing the sham treatment first followed by 10‐week active treatment (S–A, n = 19).ResultsAt 10 weeks, the number of leaks/week, the total score of the International Consultation on Incontinence‐Questionnaire: Short Form (ICIQ‐SF), and maximum cystometric capacity (MCC) were significantly improved as compared with the initial levels (P < 0.001, P < 0.001, and P = 0.003, respectively) in the former group, but not in the latter group. Four (20.0%) patients were cured in the A–S group, while no patient was cured in the S–A group.At the end of the A–S schedule (24 weeks of study), the effect of the active treatment was still maintained at a significantly improved level, as compared with the initial level. At the end of the S–A schedule, the number of leaks/week was significantly improved as compared with the initial level and with its 10‐week level (P < 0.001 and P = 0.049, respectively), as well as ICIQ‐SF total score (P = 0.001 and P = 0.006, respectively). MCC significantly increased from its initial level (P = 0.030).ConclusionMagnetic stimulation was effective on urgency incontinence in comparison to sham stimulation in this small patient group. Neurourol. Urodynam. 26:767–772, 2007. © 2007 Wiley‐Liss, Inc.
Stability and error analysis for spectral Galerkin method for the Navier–Stokes equations with L2 initial data
Authors: He Yinnian 
Published: March 2007

AbstractIn this article we consider the spectral Galerkin method with the implicit/explicit Euler scheme for the two‐dimensional Navier–Stokes equations with the L2 initial data. Due to the poor smoothness of the solution on [0,1), we use the the spectral Galerkin method based on high‐dimensional spectral space HM and small time step Δt2 on this interval. While on [1,∞), we use the spectral Galerkin method based on low‐dimensional spectral space Hm(m = O(M1/2)) and large time step Δt. For the spectral Galerkin method, we provide the standard H2‐stability and the L2‐error analysis. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2007
Efficient numerical methods for pricing American options under stochastic volatility
Authors: Ikonen Samuli , Toivanen Jari 
Published: March 2007

AbstractFive numerical methods for pricing American put options under Heston's stochastic volatility model are described and compared. The option prices are obtained as the solution of a two‐dimensional parabolic partial differential inequality. A finite difference discretization on nonuniform grids leading to linear complementarity problems with M‐matrices is proposed. The projected SOR, a projected multigrid method, an operator splitting method, a penalty method, and a componentwise splitting method are considered. The last one is a direct method while all other methods are iterative. The resulting systems of linear equations in the operator splitting method and in the penalty method are solved using a multigrid method. The projected multigrid method and the componentwise splitting method lead to a sequence of linear complementarity problems with one‐dimensional differential operators that are solved using the Brennan and Schwartz algorithm. The numerical experiments compare the accuracy and speed of the considered methods. The accuracies of all methods appear to be similar. Thus, the additional approximations made in the operator splitting method, in the penalty method, and in the componentwise splitting method do not increase the error essentially. The componentwise splitting method is the fastest one. All multigrid‐based methods have similar rapid grid independent convergence rates. They are about two or three times slower that the componentwise splitting method. On the coarsest grid the speed of the projected SOR is comparable with the multigrid methods while on finer grids it is several times slower. ©John Wiley & Sons, Inc. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007
A new alternating‐direction finite element method for hyperbolic equation
Authors: Zhang Zhiyue , Deng Dingwen 
Published: March 2007

AbstractA modified backward difference time discretization is presented for Galerkin approximations for nonlinear hyperbolic equation in two space variables. This procedure uses a local approximation of the coefficients based on patches of finite elements with these procedures, a multidimensional problem can be solved as a series of one‐dimensional problems. Optimal order H01 and L2 error estimates are derived. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007
A stabilized method for a secondary consolidation Biot's model
Authors: Gaspar F.J. , Gracia J.L. , Lisbona F.J. , Vabishchevich P.N. 
Published: March 2007

AbstractThis work deals with the numerical solution of a secondary consolidation Biot's model. A family of finite difference methods on staggered grids in both time and spatial variables is considered. These numerical methods use a weighted two‐level discretization in time and the classical central difference discretization in space. A priori estimates and convergence results for displacements and pressure in discrete energy norms are obtained. Numerical examples illustrate the convergence properties of the proposed numerical schemes, showing also a non‐oscillatory behavior of the pressure approximation. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007
A remark on the coercivity for a first‐order least‐squares method
Authors: Ku Jaeun 
Published: March 2007

AbstractThis study present a short proof concerning the coercivity of a first‐order least‐squares finite element method for general second‐order elliptic problems proposed by Cai, Lazarov, Manteuffel and McCormick (Cai et al. J Numer Anal 31 (1994), 1785–1799). Our proof is based on a priori estimate and the technique can be applied to prove L2‐norm error estimate for the primary function u. After establishing the coercivity bound from the assumed a priori estimate, we observe that the coercivity bound is actually equivalent to the a priori estimate. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007
Dynamic infrared measurements of poly(vinyl chloride) in the vicinity of the glass transition
Authors: Ogura Katsuyuki 
Published: March 2007

AbstractThe temperature dependences of some selected infrared bands of poly(vinylchloride) in the vicinity of the glass transition were examined. The intensities of 1333 and 1427 cm−1 bands changed discontinuouly at Tg; on the other hand, 2920 cm−1 did not show any significant changes at this temperature. From these results, the nature of the temperature dependence of infrared intensity of the polymer was discussed. The procedure introduced in this work offers a rapid method for the determination of the Tg as compared with the conventional infrared methods.
Effect of formulation on properties and morphology of polyurethane elastomers
Authors: Fulcher Keith U. , Corbett Gerald E. 
Published: March 2007

AbstractA model polyurethane elastomers system has been used to study the relationships between chemical formulation, polymer physical structure and mechanical properties. The elastomers were made from formulations comprising a polyether polyol blend (diol plus triol), a chain extender blend (1,4 butane diol plus 1,1,1‐trimethylol propane) and 4,4′‐di‐isocyanate diphenylmethane. The morphologies of the elastomers were investigated in detail, mainly by means of small angle X‐ray scattering techniques. It was confirmed that the polyurethane systems examined comprised domains 50 to 100 Å in size and spaced around 100 to 200 Å apart. A complete decription of the polyurethane morphology has been made in terms of the volume fraction of domains present, the average domain size and the average domain–domain separation. The results suggest that, whilst it is possible to correlate, in general, formulation changes with variations in the elastomer morphology, it seems that direct correlations between physical structure and mechanical properties are not very meaningful in the present model system. However, it is clear that knowledge of the morphology is of considerable importance in interpreting the effects of formulation on observed properties.
Ionomer cements
Authors: Wilson Alan D. , Crisp Stephen 
Published: March 2007

AbstractThe chemistry and properties of the ionomer cements are reviewed. These cements are defined by the acid‐base interaction between metal oxides or silicates with aqueous solutions of organic polymeric acids. the cements formed both from ion‐leachable aluminosilicates and from zinc oxide are of practical importance and characterised by their ability to bond to active substrates under moist conditions. The polymer solutions used in these formulations tend to gel slowly over a period of several months. This phenomenon can be avoided by partial methylation of the polymer or by the use of a suitable copolymer. The role of the anoins present in the system and those, such as tartrate, added to improve rheological properties, is discussed. The nature of the bonding in these cement gels is considered in terms of ion‐binding of polyanions of polyvalent cations. The function of water in the cement and hydrolysis of cations is discused. In the final section the long‐term development of surface hardness and compressive strenght is reported. The modulus of elasticity and stress relaxation properties of these cements are compared to those of the brittle dental silicate cement.
Physical and mechanical properties of glass—ionomer cements
Authors: Elliott Joseph , Holliday Leslie , Hornsby Peter R. 
Published: March 2007

AbstractA comparison is made of the mechanical properties of ionic polymer cements, prepared by reacting an aqueous poly(acrylic acid) solution with ion‐leachable inorganic powders. Out of the wide range of powders investigated, specially formulated aluminosilicate glasses gave the most promising results, and the properties of cements made from them are discussed in greater detail. In particular, the dependence of compressive strength on cement age is described, and the loss of water from the material when exposed to atmospheres of low relative humidity is shown to be related to property changes which occur under these conditions. An interpretation of these detrimental effects is presented in terms of variation in the cement microstructure, and methods of minimising the effects by various modifications to the basic system are reviewed.
Electrical conductivity in ionic complexes of poly(ethylene oxide)
Authors: Wright Peter V. 
Published: March 2007

AbstractThe temperature dependence of d.c. conductivity of poly(ethylene oxide) complexes with sodium iodide and the thiocyanates of sodium, potassium and ammonium has been investigated. In each case a transition to a lower activation energy at higher temperatures was observed. For the sodium complexes this transition occurs at ca 55°C which is well below the crystalline melting points at 200°C. For the potassium and ammonium complexes however, the transitions coincide with the melting points at ca 100 and 70°C respectively. It is proposed that at the transitions, thermal disintegration of complexes in the amorphous regions occurs. The complexes involve coordination of the cations to the ether oxygen atoms in the polymer backbone.
Thermal and mechanical properties of block copolymers of poly(hexamethylene terephthalate) and poly(oxyethylene) units
Authors: Goodman Isaac , Peters Raymond H. , Schenk Victor T. J. 
Published: March 2007

AbstractBlock copolyetheresters of poly(hexamethylene terephthalate) (6GT) with poly(oxyethylene) terephthalate (POET) units have been prepared by polycondensation and certain of their thermal, morphological and mechanical properties have been determined. The copolymers rich in 6GT or POET units show the crystalline characteristics of the single respective homopolymers, whereas in the middle of the composition range crystalline phases of both types coexist. Increase in the proportion of POET units causes a decrease in the melting and glass transition temperatures and in the crystallisation rates whilst concomitantly the mechanical properties change from fibrous to elastomer in type. The results are interpreted in terms of a polycrystallite model in which the compostion‐dependent nature of the crystallites and tie bars determines the overall mechanical properties of the copolymers.
The thermal degradation of some poly(fluorethers)
Authors: Cotter John L. , Knight Graham J. , Wright Walter W. 
Published: March 2007

AbstractA series of poly(fluoroethers) has been studied by thermogravimetry, pyrolysisgas chromatography–mass spectrometry and fluoride ion analysis. The thermal stabilities are lower than those of a vinylidene fluoride/hexafluoropropene copolymer. Primary chain scission occurs at O—CH2 links. Rearrangement processes giving rise to cyclic compounds are important for polymers containing aromatic or heterocyclic rings in the chain.
Phase equilibria and phase separation proceedings of the 5th polymer meeting point at the university of essex. Phase equilibria and phase separation
Authors: Koningsveld R. 
Published: March 2007

AbstractPhase separations in condensed systems are reviewed on the basis of the still valid considerations of Gibbs, Van der Waals and Schreinemakers, formulated many years ago. Examples are taken from more recent data on mixtures containing macromolecules, which appear to obey phase‐rule theory in great detail and subtlety. The phase rule sets limits to the maximum possible number of phases, the actual number being governed by the precise dependence of the free enthalpy (Gibbs free energy) of mixing on temperature, concentration, molecular weight, etc. Accurate knowledge of the free enthalpy function allows prediction of phase behaviour with great precision. Methods are described which permit sufficiently accurate determination of the necessary parameters.
Effect of natural ageing on the dielectric properties of natural rubber—channel black mixtures
Authors: Bishai Augenie M. , Hanna Faika F. 
Published: March 2007

AbstractA systematic dielectric study over the frequency region from 60 Hz to 107 Hz has been carried out on natural rubber samples mixed with channel black after being subjected to natural ageing for nine years. The results are compared with those obtained before8 and the differences are interpreted.
Bis‐4,9‐diazapyrenium dications: synthesis of the methylenedibenzyl‐analogue, interactions with nucleotides, DNA, RNA. The antitumour activity of all till now prepared analogues
Authors: Piantanida Ivo , Žinić Mladen , Marczi Saška , Glavaš‐Obrovac Ljubica 
Published: March 2007

AbstractNovel bis‐4,9‐diazapyrenium dication has shown reversible pH dependent formation of 4,9‐ diazapyrenium pseudobase in water characteristic for most 4,9‐diazapyrenium derivatives. The compound has formed non‐covalent complexes with nucleotides in water, whose stability is controlled dominantly by aromatic stacking interactions. No cooperativity between two 4,9‐diazapyrenium subunits was observed in binding of nucleotides. Novel bis‐4,9‐diazapyrenium dication formed mono‐intercalative complexes with studied double stranded DNA and RNA. Additional interactions of non‐intercalated part were found to depend significantly on the polynucleotide secondary structure, yielding strong DNA over RNA preference. Appearance of ICD band of3was found to be specific for DNA polynucleotides and together with observed destabilisation of double stranded RNA is attributed to the aggregation of compound in one of the RNA grooves. All bis‐4,9‐diazapyrenium dications prepared till now have shown considerable antiproliferative activity against five human tumour cell lines, which suggested mechanism of action by interacting with cell DNA. Copyright © 2007 John Wiley & Sons, Ltd.
Organocatalysis: quantum chemical modeling of nucleophilic addition to α,β‐unsaturated carbonyl compounds
Authors: Bruvoll Marius , Hansen Tore , Uggerud Einar 
Published: March 2007

AbstractOne of the successful transformations within the field of organocatalysis, the organocatalytic asymmetric addition of nitromethane to α,β‐unsaturated aldehydes and ketones, has been studied by quantum chemical modeling. The level of accuracy of the hybrid density functional theory method B3LYP/6‐31G(d) was compared to a high level ab initio benchmark for this reaction. It is concluded that B3LYP/6‐31G(d) performs very well for this reaction type, giving good estimates of critical energies. The reaction between acrolein and nitromethane was studied in detail. The reaction mechanism revealed an intermediate oxazolidin structure, which is currently unknown. Alkyl substitution in various positions on the amine catalyst or α,β‐unsaturated carbonyl compound influences the reactivity in a predictive fashion. The iminium ion, prop‐2‐en‐iminium, is less activated towards nucleophilic attack compared to protonated acrolein. Copyright © 2007 John Wiley & Sons, Ltd.
Swift hopping gallium over [AlO4]− tetrahedra in Ga/ZSM‐5: A DFT study
Authors: Kusmin Ilya V. , Zhidomirov Georgy M. , Solkan Vitaly N. 
Published: March 2007

AbstractDensity functional theory calculations were carried out to investigate gallium species (Ga+, [GaH2]+, and [GaO]+) stabilization in Ga‐exchanged HZSM‐5, using cluster modeling approach. Three isomeric gallium positions over [AlO4]− zeolite fragment at T12 position were found. These isomers are turning into each over with low activation energy barrier and gallium fragment revolves around [AlO4]− tetrahedron by hopping between cationic positions. Activation energies of gallium fragment hopping were computed and compared for different gallium containing cations. Those barriers were found to be times less than the activation energies of catalytic processes on gallium‐exchanged zeolite. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Predictive strength of Jonckheere's test for trend: an application to genotypic scores in HIV infection
Authors: Flandre Philippe , O'Quigley John 
Published: March 2007

AbstractA problem arising in studies on the human immunodeficiency virus (HIV) infection relate to one‐sided tests with ordered alternatives as opposed to the more classical two‐sided tests. Patients not having a resistance mutation may have a better virologic response to treatment than patients with a single mutation. In turn, those with a single mutation may have a better response to treatment than those patients having two mutations, and so on. In the presence of a continuous outcome, Jonckheere's test for ordered alternatives is well adapted to this situation. Such an analysis does not provide any measure of prediction or explained variation which can complement these results. A measure of strength of effect would be helpful in quantifying the degree of association between the genotypic score (number of mutations) and some continuous virological response. We suggest a simple measure of ‘goodness of split’ for Jonckheere's test for trend. Interestingly, the measure can be related to the non‐parametric measure of association known as gamma. The variance formula for the measure studied here can be seen to differ from the known variance estimate of the gamma measure, and simulations show it to be more accurate. Expectation and variance underH0of the measure are provided and a large simulation study is presented. Methods are applied to a recent clinical data set involving HIV‐1 infected patients where the number of resistance mutations are investigated as potential predictors of the amount of HIV‐1 RNA reduction at week 4. Copyright © 2007 John Wiley & Sons, Ltd.