bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the stability and convergence of the finite section method for integral equation formulations of rough surface scattering
Authors: Meier A. , Chandler‐Wilde S. N. 
Published: January 2005

AbstractWe consider the Dirichlet and Robin boundary value problems for the Helmholtz equation in a non‐locally perturbed half‐plane, modelling time harmonic acoustic scattering of an incident field by, respectively, sound‐soft and impedance infinite rough surfaces.Recently proposed novel boundary integral equation formulations of these problems are discussed. It is usual in practical computations to truncate the infinite rough surface, solving a boundary integral equation on a finite section of the boundary, of length 2A, say. In the case of surfaces of small amplitude and slope we prove the stability and convergence as A→∞ of this approximation procedure. For surfaces of arbitrarily large amplitude and/or surface slope we prove stability and convergence of a modified finite section procedure in which the truncated boundary is ‘flattened’ in finite neighbourhoods of its two endpoints. Copyright © 2001 John Wiley & Sons, Ltd.
Analysis of a time discretization for an implicit variational inequality modelling dynamic contact problems with friction
Authors: Ricaud Jean‐Marc , Pratt Elaine 
Published: January 2005

AbstractSome dynamic contact problems with friction can be formulated as an implicit variational inequality. A time discretization of such an inequality is given here, thus giving rise to a so‐called incremental solution. The convergence of the incremental solution is established, and then the limit is shown to be the unique solution of the variational inequality. This paper contains therefore not only some new results concerning the numerical aspect of some models of contact and friction but also a constructive existence result. Copyright © 2001 John Wiley & Sons, Ltd.
1H NMR studies of copper binding by histidine‐containing peptides
Authors: Gaggelli Elena , D'Amelio Nicola , Valensin Daniela , Valensin Gianni 
Published: January 2005

AbstractWe review recent developments in the studies of Cu(II) complexes with histidine‐containing peptides in solution by NMR. An overview of the theoretical background of the effects of the paramagnetic metal on the NMR properties (relaxation and shift) of nearby nuclei is given. Particular attention is paid to the effect of exchange rates between free and metal‐bound forms of the ligand on detection of paramagnetic relaxation rates. General methods are underlined to determine the structure of the complexes (and thus the donor set to the metal) and to distinguish between the binding of copper(II) to either N‐1 or N‐3 of the imidazole ring of histidine. Examples are reported dealing with fragments of the amyloid precursor protein (a protein related to Alzheimer's disease) and of the prion protein (related to Creutzfeldt–Jakob disease) in which the binding of copper may be relevant for subsequent redox activities, protein aggregation or metal‐catalyzed protein damage. Copyright © 2003 John Wiley & Sons, Ltd.
A 19F relaxometric study of the competition of Gd(III) and Lu(III) towards DTPA in water
Authors: Bonnet Célia S. , Fries Pascal H. 
Published: January 2005

AbstractBecause of its strong Coulomb attraction by the positive Gd(III) aqua ion and its strong repulsion by the negative gadolinium diethylenetriaminepentaacetate (Gd‐DTPA) complex, the trifluoroacetate anion CF3COO− has very different relative spatial dynamics with respect to these two species. Therefore, the Gd(III) aqua ion and Gd‐DTPA complex cause very different longitudinal relaxivities of the trifluoroacetate 19F nuclei. In the presence of competitor Lu(III) ions, the relaxivity difference makes it possible to assay the concentrations of Gd(III) aqua ion and Gd‐DTPA complex from the measured paramagnetic relaxation rate enhancement of the trifluoroacetate 19F nuclei. This experimental method allows one to characterize the present transmetallation equilibrium and it can be easily generalized to other systems. Copyright © 2003 John Wiley & Sons, Ltd.
Solution NMR methods for quantitative identification of chemical exchange in 15N‐labeled proteins
Authors: Wang Chunyu , Palmer Arthur G. 
Published: January 2005

AbstractChemical exchange phenomena in NMR spectra reveal protein motions on microsecond to millisecond time scales that are associated with biological functions, including catalysis, ligand binding, allosteric conformational changes and protein folding. This review surveys solution NMR methods for identifying chemical exchange in proteins by measuring transverse relaxation rate constants for backbone 15N spins. The relaxation‐compensated‐IzSz and in‐phase Hahn echo methods are suitable for small‐ to medium‐sized proteins. The transverse relaxation optimized spectroscopy method is suitable for large, deuterated proteins. Differential multiple quantum relaxation is also a signature of chemical exchange and provides unique information about exchange processes. The various methods are illustrated by application to basic pancreatic trypsin inhibitor and triosephosphate isomerase. Copyright © 2003 John Wiley & Sons, Ltd.
Conformational analysis of N‐arachidonylethanolamide (anandamide) using nuclear magnetic resonance and theoretical calculations
Authors: Bonechi C. , Brizzi A. , Brizzi V. , Francioli M. , Donati A. , Rossi C. 
Published: January 2005

AbstractThe conformational properties of cis‐5,8,11,14‐eicosatetraenoylethanolamide (anandamide) were analysed by the combined use of NMR experimental results plus molecular simulations. The structure of anandamide was found to be a predominantly linear with a seven‐atom ring of the ethanolamine group having a hydrogen bond which stabilizes the molecule. The vinylic group present has a cis conformation in solution. The terminal chain has a linear conformation and undergoes isotropic fast motion typical of this structure. Copyright © 2001 John Wiley & Sons, Ltd.
Identifying environmental contributions to autism: Provocative clues and false leads
Authors: Lawler Cindy P. , Croen Lisa A. , Grether Judith K. , Van de Water Judy 
Published: January 2005

AbstractThe potential role of environmental factors in autism spectrum disorders (ASD) is an area of emerging interest within the public and scientific communities. The high degree of heritability of ASD suggests that environmental influences are likely to operate through their interaction with genetic susceptibility during vulnerable periods of development. Evaluation of the plausibility of specific neurotoxicants as etiological agents in ASD should be guided by toxicological principles, including dose–effect dependency and pharmacokinetic parameters. Clinical and epidemiological investigations require the use of sufficiently powered study designs with appropriate control groups and unbiased case ascertainment and exposure assessment. Although much of the existing data that have been used to implicate environmental agents in ASD are limited by methodological shortcomings, a number of efforts are underway that will allow more rigorous evaluation of the role of environmental exposures in the etiology and/or phenotypic expression of the disorder. Surveillance systems are now in place that will provide reliable prevalence estimates going forward in time. Anticipated discoveries in genetics, brain pathology, and the molecular/cellular basis of functional impairment in ASD are likely to provide new opportunities to explore environmental aspects of this disorder. © 2004 Wiley‐Liss, Inc. MRDD Research Reviews 2004;10:292–302.
Strength of two structured soils in triaxial compression
Authors: Wong Ron C. K. 
Published: January 2005

AbstractOil sands are dense granular materials with interlocked structure and clay shales are heavily overconsolidated clays. They are classified as structured soil or weak rock, exhibiting high peak strength with severe softening and dilation, particularly at low confining stress. The triaxial compression test results indicate that both materials yield linear Mohr–Coulomb envelopes with an apparent cohesion for peak and residual strengths. However, the strength components mobilized from these two materials are very different. This paper investigates if these strength parameters are intrinsic properties or responses derived in triaxial compression conditions. Computer tomography scanning technique is used to aid in examining the micro‐structural features of the sheared specimens such as shear banding pattern, shear band thickness, spatial porosity distributions inside and outside shear bands. These micro‐structural features are used to explain the macro‐deformation response observed in the triaxial compression tests. Mobilization of strength components derived from interlocked structure, cementation, dilation, rolling and critical state are analysed for pre‐, post‐peak softening and residual stages. It is found that the empirical correlation such as Mohr–Coulomb failure criterion based on triaxial compression test results does not necessarily reflect the intrinsic properties of the test materials. Testing conditions are embedded in the empirical correlation. Copyright © 2001 John Wiley & Sons, Ltd.
Finite element analysis of land subsidence above depleted reservoirs with pore pressure gradient and total stress formulations
Authors: Gambolati Giuseppe , Ferronato Massimiliano , Teatini Pietro , Deidda Roberto , Lecca Giuditta 
Published: January 2005

AbstractThe solution of the poroelastic equations for predicting land subsidence above productive gas/oil fields may be addressed by the principle of virtual works using either the effective intergranular stress, with the pore pressure gradient regarded as a distributed body force, or the total stress incorporating the pore pressure. In the finite element (FE) method both approaches prove equivalent at the global assembled level. However, at the element level apparently the equivalence does not hold, and the strength source related to the pore pressure seems to generate different local forces on the element nodes. The two formulations are briefly reviewed and discussed for triangular and tetrahedral finite elements. They are shown to yield different results at the global level as well in a three‐dimensional axisymmetric porous medium if the FE integration is performed using the average element‐wise radius. A modification to both formulations is suggested which allows to correctly solve the problem of a finite reservoir with an infinite pressure gradient, i.e. with a pore pressure discontinuity on its boundary. Copyright © 2001 John Wiley & Sons, Ltd.
A note on formulas for localized failure of frictional materials in compression and biaxial loading modes
Authors: Lambrecht Matthias , Miehe Christian 
Published: January 2005

AbstractThe paper investigates aspects of the localization analysis of frictional materials. We derive closed formulas and diagrams for the inclination angle of critical discontinuity surfaces which develop in homogeneous compression and biaxial loading tests. The localization analysis is based on a Drucker–Prager‐type elastoplastic hardening model for non‐associated plastic flow at small strains, which we represent in spectral form. For this type of constitutive model, general analytical formulas for the so‐called critical hardening modulus and the inclination angle of critical discontinuity surfaces are derived for the plane strain case. The subsequent treatment then specializes these formulas for the analysis of compression and biaxial loading modes. The key contribution here is a detailed analysis of plane strain deformation modes where the localized failure occurs after subsequent plastic flow. The derived formulas and diagrams can be applied to the checking of an accompanying localization analysis of frictional materials in finite‐element computations. Copyright © 2001 John Wiley & Sons, Ltd.
A modified Jacobi preconditioner for solving ill‐conditioned Biot's consolidation equations using symmetric quasi‐minimal residual method
Authors: Chan S. H. , Phoon K. K. , Lee F. H. 
Published: January 2005

AbstractThis paper identifies imbalanced columns (or rows) as a significant source of ill‐conditioning in the preconditioned coefficient matrix using the standard Jacobi preconditioner, for finite element solution of Biot's consolidation equations. A simple and heuristic preconditioner is proposed to reduce this source of ill‐conditioning. The proposed preconditioner modifies the standard Jacobi preconditioner by scaling the excess pore pressure degree‐of‐freedoms in the standard Jacobi preconditioner with appropriate factors. The performance of such preconditioner is examined using the symmetric quasi‐minimal residual method. To alleviate storage requirements, element‐by‐element iterative strategies are implemented. Numerical experiment results show that the proposed preconditioner reduces both the number of iteration and CPU execution time significantly as compared with the standard Jacobi preconditioner. Copyright © 2001 John Wiley & Sons, Ltd.
Linear coupled analysis of desiccation shrinkage in a double‐layer partially saturated medium: semi‐explicit solutions
Authors: Thouvenin G. , Giraud A. , Homand F. 
Published: January 2005

AbstractSolutions are presented for the problem of isothermal dessiccation shrinkage in a double‐layer porous partially saturated medium. The rheological model taken into account is linear poroelastic. Hence the analysis is mainly focused on hydromechanical coupling effects and contrasts of mechanical and hydraulic properties between two materials: a low thickness skin comprised between the outer boundary and the reference porous material. Three one‐dimensional ideal structures are taken into account: a wall of finite thickness (cartesian geometry), a thick cylinder and a thick sphere. The solution of the time‐dependent problem is arrived at by applying Laplace transforms to the field variables. Exact solutions are obtained in Laplace transform space using Mathematica© to solve the field equations whilst taking into account the continuity equations at the interface and the boundary conditions. The Talbot's modified algorithm has been performed to invert the Laplace transform solutions. A bibliographical and numerical study shows that this method is remarkably precise, stable and close to the analytical inversion. Results are presented using poroelastic data representative of a concrete material and involve a strong coupling effect between hydraulical and mechanical behaviours. A first approach elastic modelling of degradation process have been presented using a thin outer layer. Apart from emphasising the semi‐explicit solution utility due to accurate speed calculation, this paper deals with more complex problems than those which can be solved using purely analytical solutions. Copyright © 2001 John Wiley & Sons, Ltd.
The optimal feedback control of the linear‐quadratic control problem with a control inequality constraint
Authors: Mao Yunying , Liu Zeyi 
Published: January 2005

AbstractIn this paper, we consider the linear‐quadratic control problem with an inequality constraint on the control variable. We derive the feedback form of the optimal control by the agency of the unconstrained linear‐quadratic control systems. Copyright © 2001 John Wiley & Sons, Ltd.
The dynamic efficiency of the Ramsey model with endogenous labour participation rate
Authors: Faria João Ricardo 
Published: January 2005

AbstractThis paper incorporates the hypothesis of labour participation rate into the Ramsey model. It is shown that the economy can be dynamically inefficient if the average productivity of capital is greater than the sum of the rate of time preference, the population growth rate, the depreciation rate and the marginal rate of substitution between labour and consumption. The modified golden rule holds when the wage rate is equal to the marginal rate of substitution between labour and consumption. However, there is no guarantee that it will happen, since labour supply is driven by capital allocation decisions. Copyright © 2001 John Wiley & Sons, Ltd.
A suboptimal learning control scheme for non‐linear systems with time‐varying parametric uncertainties
Authors: Xu Jian‐Xin , Tan Ying 
Published: January 2005

AbstractIn this paper, learning control is integrated with non‐linear optimal control to enhance control performance of a class of non‐linear systems with time‐varying parametric uncertainties. A suboptimal control strategy based on a control Lyapunov function (CLF) and Sontag's formula provides suboptimal performance as well as stability along the time horizon for the nominal part of the non‐linear dynamic system. The proposed learning mechanism learns the unknown time‐varying parametric uncertainties so as to eliminate uncertain effects. System information both in time horizon and learning repetition horizon are incorporated in a composite energy function (CEF). The proposed control scheme achieves asymptotic convergence along the learning repetition horizon and boundedness and pointwise convergence of the tracking error (perfect tracking performance) along the time horizon. Copyright © 2001 John Wiley & Sons, Ltd.
Minimum effort dead‐beat control of linear servomechanisms with ripple‐free response
Authors: Mošna Jiří , Melichar Jiří , Pešek Pavel 
Published: January 2005

AbstractA new and systematic approach to the problem of minimum effort ripple‐free dead‐beat (EFRFDB) control of the step response of a linear servomechanism is presented. There is specified a set of admissible discrete error feedback controllers, complying with general conditions for the design of ripple‐free dead‐beat (RFDB) controllers, regardless of the introduced degree of freedom, defined as the number of steps exceeding their minimum number. The solution is unique for the minimum number of steps, while their increase enables one to make an optimal choice from a competitive set of controllers via their parametrization in a finite‐dimensional space. As an objective function, Chebyshev's norm of an arbitrarily chosen linear projection of the control variable was chosen. There has been elaborated a new, efficient algorithm for all stable systems of the given class with an arbitrary degree of freedom. A parametrized solution in a finite space of polynomials is obtained through the solution of a standard problem of mathematical programming which simultaneously yields the solution of a total position change maximization of servomechanism provided that a required number of steps and control effort limitation are given. A problem formulated in this way is consecutively used in solving the time‐optimal (minimum‐step) control of a servomechanism to a given steady‐state position with a specified limitation on control effort. The effect of EFRFDB control on the example of a linear servomechanism with torsion spring shaft, with the criterions of control effort and control difference effort, is illustrated and analysed. Copyright © 2001 John Wiley & Sons, Ltd.
A reduced‐order stochastic observer approach to optimal state estimation with noise‐free measurements
Authors: Yaz Edwin Engin , Yaz Yvonne Ilke 
Published: January 2005

AbstractIn a continuous‐time Kalman filter, it is required that the measurement noise covariance be non‐singular. If the measurements are noise‐free, then this condition does not hold and, in practice, the measurement data are differentiated to define a derived measurement function to build what is known as Deyst filter. It is proposed here that a reduced‐order observer be used in deriving the linear minimum‐variance filter to construct state estimates based on the original measurement data with no need for differentiation. This filter is of dimension (n−p) wherenandpare the state and measurement vector dimensions, respectively. In this work, we consider both the finite‐time and infinite‐time results. The set of all assignable estimation error covariances are characterized and the set of all estimator gains are parametrized in addition to the linear minimum variance optimal results. The conditions for the existence of the optimal steady‐state filter are obtained in terms of the system theoretic properties of the original signal model. A simple example is included to illustrate the effectiveness of the proposed technique. Copyright © 2001 John Wiley & Sons, Ltd.
Model reduction for singular systems via covariance approximation
Authors: Jing Wang , Liu Wanquan , Zhang QingLing 
Published: January 2005

AbstractIn this paper, model reduction problem for singular systems will be investigated. To solve the problem, the covariance for singular systems will be defined. Then, a model reduction method based on covariance approximation will be presented for obtaining a stable and impulse controllable models for singular systems. Third, the error criterion was explicitly derived via a free parameter and the optimization procedure was presented in terms of gradient flow. Finally, illustrative examples are given to show the effectiveness of the proposed approach. Copyright © 2005 John Wiley & Sons, Ltd.
Constitution‐making in Africa: assessing both the process and the content
Authors: Ndulo M. 
Published: January 2005

AbstractThis article examines the relationship between governance and development, and concludes that underlying the litany of Africa's development problems is a crisis of governance. Good governance would result in institutions that are more likely to adopt economic policies that would resolve the constraints that hinder economic development. In addition, it would make a major contribution to the reduction of war and conflict. It would do this by creating an environment for sustainable development to take place and thereby reduce poverty, the root cause of war and conflict. This calls for a critical examination of the question of governance in Africa with a view to identifying the obstacles to its establishment and the possible approaches to the development of systems of governance that give political space to all groups. Since the most important legal instrument in the scheme of good governance is the national constitution, the article seeks to identify some of the key issues that must be considered in the process of developing a national constitution if it is to be durable. It also addresses the conditions under which such constitutions should be developed if they are to be acceptable to the people of the country they are intended to govern. Running through the article is the theme that the establishment of good governance in Africa depends on the development of political systems that give people a sense of ownership of the political process. Copyright © 2001 John Wiley & Sons, Ltd.
Governance for human development: the role of external partners
Authors: Cheema G. Shabbir , Maguire Linda 
Published: January 2005

AbstractThere is a positive correlation between democratic governance and human development. Democratic governance is governance infused with the principles of, inter alia, equity, participation, rule of law, transparency and accountability. Human development is at its very core the expansion of people's choices and their increased participation in decisions that affect their lives. Therefore democratic governance reinforces human development, and human development reinforces democratic governance. External partners—those actors outside of the national development process—can positively contribute to a country's transition to and consolidation of democratic governance (and, thereby, its human development) in a number of ways. External partners act through democratic governance entry points to deliver strategic services and use indicators to measure their relative progress. Indicators can be valuable tools in informing external partners and recipients of assistance of what works, what does not work and why. Copyright © 2001 John Wiley & Sons, Ltd.