bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reflection/refraction of SH-waves at a corrugated interface between two different anisotropic and vertically heterogeneous elastic solid half-spaces
Authors: Kumar Rajneesh , Tomar Sushil K. , Chopra Asha 
Published: February 2009

AbstractWe investigate the reflection and transmission of SH-waves at a corrugated interface between two different anisotropic, heterogeneous elastic solid half-spaces. Both the media are assumed to be transversely isotropic and vertically heterogeneous. Rayleigh's method is followed and expressions for the reflection and transmission coefficients are obtained in closed form for the first-order approximation of the corrugation. It is found that these coefficients depend on corrugation and are affected by the anisotropy and heterogeneity of the media. Numerical computations for a particular model have been performed.
The time fractional diffusion equation and the advection-dispersion equation
Authors: Huang F. , Liu F. 
Published: February 2009

AbstractThe time fractional diffusion equation with appropriate initial and boundary conditions in an n-dimensional whole-space and half-space is considered. Its solution has been obtained in terms of Green functions by Schneider and Wyss. For the problem in whole-space, an explicit representation of the Green functions can also be obtained. However, an explicit representation of the Green functions for the problem in half-space is difficult to determine, except in the special cases α = 1 with arbitrary n, or n = 1 with arbitrary α. In this paper, we solve these problems. By investigating the explicit relationship between the Green functions of the problem with initial conditions in whole-space and that of the same problem with initial and boundary conditions in half-space, an explicit expression for the Green functions corresponding to the latter can be derived in terms of Fox functions. We also extend some results of Liu, Anh, Turner and Zhuang concerning the advection-dispersion equation and obtain its solution in half-space and in a bounded space domain.
Stochastic stability of linear systems with semi-Markovian jump parameters
Authors: Hou Zhenting , Luo Jiaowan , Shi Peng 
Published: February 2009

AbstractOver the past two decades considerable effort has been devoted to problems of stochastic stability, stabilisation, filtering and control for linear and nonlinear systems with Markovian jump parameters, and a number of results have been achieved. However, due to the exponential distribution of the Markovian chain, there are many restrictions on existing results for practical applications. In the present paper, we study systems whose jump parameters are semi-Markovian rather than fully Markovian. We consider only linear systems with semi-Markovian jump parameters, and also study systems with phase-type semi-Markovian jump parameters, because the family of phase-type distributions is dense in the families of all probability distributions on [0, +∞). Some stochastic stability results are obtained. An example is given to show the potential of the proposed techniques.
A convolution back projection algorithm for local tomography
Authors: Sastry Challa S. , Das P. C. 
Published: February 2009

AbstractThe present work deals with the problem of recovering a local image from localised projections using the concept of approximation identity. It is based on the observation that the Hilbert transform of an approximation identity taken from a certain class of compactly supported functions with sufficiently many zero moments has no significant spread of support. The associated algorithm uses data pertaining to the local region along with a small amount of data from its vicinity. The main features of the algorithm are simplicity and similarity with standard filtered back projection (FBP) along with the economic use of data.
Queueing systems for multiple FBM-based traffic models
Authors: Matache Mihaela T. , Matache Valentin 
Published: February 2009

AbstractA multiple fractional Brownian motion (FBM)-based traffic model is considered. Various lower bounds for the overflow probability of the associated queueing system are obtained. Based on a probabilistic bound for the busy period of an ATM queueing system associated with a multiple FBM-based input traffic, a minimal dynamic buffer allocation function (DBAF) is obtained and a DBAF-allocation algorithm is designed. The purpose is to create an upper bound for the queueing system associated with the traffic. This upper bound, called a DBAF, is a function of time, dynamically bouncing with the traffic. An envelope process associated with the multiple FBM-based traffic model is introduced and used to estimate the queue size of the queueing system associated with that traffic model.
The stability of a curved, heated boundary layer: linear and nonlinear problems
Authors: Watson C. E. , Otto S. R. 
Published: February 2009

AbstractWe consider the stability of high Reynolds number flow past a heated, curved wall. The influence of both buoyancy and curvature, with the appropriate sense, can render a flow unstable to longitudinal vortices. However, conversely each mechanism can make a flow more stable; as with a stable stratification or a convex curvature. This is partially due to their influence on the basic flow and also due to additional terms in the stability equations. In fact the presence of buoyancy in combination with an appropriate local wall gradient can actually increase the wall shear and these effects can lead to supervelocities and the promotion of a wall jet. This leads to the interesting discovery that the flow can be unstable for both concave and convex curvatures. Furthermore, it is possible to observe sustained vortex growth in stably stratified boundary layers over convexly curved walls. The evolution of the modes is considered in both the linear and nonlinear régimes.
Cavities at atmospheric pressure behind two-dimensional bodies at an angle of attack
Authors: Haese P. M. 
Published: February 2009

AbstractThis paper presents an interior source method for the calculation of semi-infinite cavities behind two-dimensional bluff bodies placed at an angle of attack in a uniform stream. Aspects under consideration include the pressure distribution along the body, especially just ahead of the separation point, lift and drag forces, and how these quantities vary with the angle of attack. We include discussion of the physical conditions of separation, and identify critical angles of attack for which the cavitating flow past an airfoil may (a) become unstable, or (b) yield the greatest lift to drag ratio.
Elastic plastic analysis of shallow shells—a new approach
Authors: Mazumdar J. , Ghosh A. , Hewitt J. S. , Bhattacharya P. K. 
Published: February 2009

AbstractA simple and efficient method for the analysis of the elastic-plastic bending of shallow shells is presented. The method is based upon the concept of contour lines of equal deflection on the surface of the shell, and uses Illyushin's theory of plastic deformation. As an illustration of the method, a technically interesting example of a shallow elliptic elastic dome is examined. Results are obtained for increasing loads and varying aspect ratios, and are illustrated graphically. The application of the method to other shell geometries is quite straightforward.
Hyperelliptic parametrisation of the generalised order parameter of the N = 3 chiral Potts model
Authors: Baxter R. J. 
Published: February 2009

AbstractIt has been known for some time that the Boltzmann weights of the chiral Potts model can be parametrised in terms of hyperelliptic functions. but as yet no such parametrisation has been applied to the partition and correlation functions. Here we show that for N = 3 the function S(tp) that occurs in the recent calculation of the order parameters can he expressed quite simply in terms of such a parametrisation.
Including ionisation in a simple model of single-bubble sonoluminescence
Authors: Munro Angus I. S. , Forbes Larry K. 
Published: February 2009

AbstractA small gas bubble in a liquid, when driven by intense ultrasound, collapses and emits light in a process called Single-Bubble Sonoluminescence (SBSL). While the dynamics of driven bubbles are well studied, less is known of the physical conditions in the gas or whether it is necessary to include ionisation in simpler studies of bubble dynamics. In this study, a model was derived from Rayleigh-Plesset dynamics, a van der Waals equation of state and the first law of thermodynamics (including interfacial heat transfer and ionisation). Stronger model ionisation reduced the maximum collapse temperature, and altered other collapse characteristics. Chaotic parameter regions are proximal to, but not coincident with, known stable SL regions. Resonant behaviour was only markedly affected by ionisation close to these chaotic regions.
Guide expansions for the recursive parametric solution of polynomial dynamical systems
Authors: Duff G. F. D. , Leipnik R. B. , Pearce C. E. M. 
Published: February 2009

AbstractRecursive parametric series solutions are developed for polynomial ODE systems, based on expanding the system components in series of a form studied by Weiss. Individual terms involve first-order driven linear ODE systems with variable coefficients. We consider Lotka-Volterra systems as an example.
Saddle point criteria and duality in multiobjective programming via an η-approximation method
Authors: Antczak Tadeusz 
Published: February 2009

AbstractIn this paper, Antczak's η-approximation approach is used to prove the equivalence between optima of multiobjective programming problems and the η-saddle points of the associated η-approximated vector optimisation problems. We introduce an η-Lagrange function for a constructed η-approximated vector optimisation problem and present some modified η-saddle point results. Furthermore, we construct an η-approximated Mond-Weir dual problem associated with the original dual problem of the considered multiobjective programming problem. Using duality theorems between η-approximation vector optimisation problems and their duals (that is, an η-approximated dual problem), various duality theorems are established for the original multiobjective programming problem and its original Mond-Weir dual problem.
Unsteady flow induced by a withdrawal point beneath a free surface
Authors: Stokes T. E. , Hocking G. C. , Forbes L. K. 
Published: February 2009

AbstractThe unsteady axisymmetric withdrawal from a fluid with a free surface through a point sink is considered. Results both with and without surface tension are included and placed in context with previous work. The results indicate that there are two critical values of withdrawal rate at which the surface is drawn directly into the outlet, one after flow initiation and the other after the flow has been established. It is shown that the larger of these values corresponds to the point at which steady solutions no longer exist.
A boundary value problem for second-order nonlinear difference equations on the integers
Authors: Dal F. , Guseinov G. Sh. 
Published: February 2009

AbstractIn this study, we are concerned with a boundary value problem (BVP) for nonlinear difference equations on the set of all integers Z. under the assumption that the left-hand side is a second-order linear difference expression which belongs to the so-called Weyl-Hamburger limit-circle case. The BVP is considered in the Hilbert space l2 and includes boundary conditions at infinity. Existence and uniqueness results for solution of the considered BVP are established.
Diversity sensitivity and multimodal Bayesian statistical analysis by relative entropy
Authors: Leipnik Roy B. , Pearce C. E. M. 
Published: February 2009

AbstractA list of recognised social diversities is assembled, including those used in social action programmes in the USA. Responses to diversity are discussed and diversity sensitivity defined as the derivative of response with respect to a defining parameter of a diversity distribution. Rewards (or penalties) for diversity are listed also; sensitivities to the responses to the rewards for diversity are called diversity sensitivities of the second kind. The statistics of bimodal and multimodal distributions are discussed, including the parametric estimation of such distributions by mixtures of multivariate normal distributions. An example is considered in detail.
On Parrondo's paradox: how to construct unfair games by composing fair games
Authors: Key E. S. , Kłosek M. M. , Abbott D. 
Published: February 2009

AbstractWe construct games of chance from simpler games of chance. We show that it may happen that the simpler games of chance are fair or unfavourable to a player and yet the new combined game is favourable—this is a counter-intuitive phenomenon known as Parrondo's paradox. We observe that all of the games in question are random walks in periodic environments (RWPE) when viewed on the proper time scale. Consequently, we use RWPE techniques to derive conditions under which Parrondo's paradox occurs.
Computational models satisfying relative angle constraints for 2-dimensional segmented bodies
Authors: Munzir S. , Jennings L. S. , Koh M. T. 
Published: February 2009

AbstractPlanar hinged segmented bodies have been used to represent models of biomechanical systems. One characteristic of a segmented body moving under gravitational acceleration and torques between segments is the possibility that the body's segments spin through more than a revolution or past a natural limit, and a computational mechanism to stop such behaviour should be provided. This could be done by introducing angle constraints between segments, and computational models utilising optimal control are studied here. Three models to maintain angle constraints between segments are proposed and compared. These models are: all-time angle constraints, a restoring torque in the state equations and an exponential penalty model. The models are applied to a 2-D three-segment body to test the behaviour of each model when optimising torques to minimise an objective. The optimisation is run to find torques so that the end effector of the body follows the trajectory of a half-circle. The result shows the behaviour of each model in maintaining the angle constraints. The all-time constraints case exhibits a behaviour of not allowing torques (at a solution) which makes segments move past the constraints, while the other two show a flexibility in handling the angle constraints which is more similar to what occurs in a real biomechanical system.
The molecular weight distribution problem and reptation mixing rules
Authors: Anderssen R. S. , Westcott M. 
Published: February 2009

AbstractMixing rules model how the physical properties of a polymer, such as its relaxation modulusG(t), depend on the distributionw(m)of its molecular weightsm. They are of practical importance because, among other things, they allow estimates of the molecular weight distribution (MWD)w(m)of a polymer to be determined from measurements of its physical properties including the relaxation modulus. The two most common mixing rules are “single” and “double” reptation. Various derivations for these rules have been published. In this paper, a conditional probability formulation is given which identifies that the fundamental essence of “double” reptation is the discrete binary nature of the “entanglements”, which are assumed to occur in the corresponding topological model of the underlying polymer dynamics. In addition, various methods for determining the MWD are reviewed, and the computation of linear functionals of the MWD motivated and briefly examined.
Approximate evaluation of integrals
Authors: Hosking Roger J. 
Published: February 2009

AbstractAsymptotic and numerical analysis provides essential insight into the behaviour of Fourier integral solutions for the deflexion of an infinite continuously-supported flexible plate due to moving load. Thus we can define in detail how the plate deflexion depends upon the load speed, including (a) the wave patterns generated by a load moving steadily at various supercritical speeds; and (b) the time-dependent behaviour of the deflexion due to an impulsively-started load, where the two-dimensional response tends to a steady state except at the critical speed, when it grows continuously with time (in the absence of dissipation).
Aesthetic factors in geometric modelling
Authors: Pham Binh 
Published: February 2009

AbstractCAD systems have traditionally catered for architectural and mechanical engineering designs which are somewhat constrained in scope. Problems concerning other types of design such as art design, industrial design or sculpting, where creativity and aesthetic factors play an important role, are not adequately addressed. These types of design require much more flexibility in both geometric modelling capability and user-machine interaction. This paper first gives a brief overview of recent work which deals with creative activities, and analyses important issues that need to be addressed in object representations for 3D creative activities. We then discuss a scheme to categorise and represent aesthetic factors in geometric modelling.
Derivative-type ascent formulas for kernels of some half-space Dirichlet problems
Authors: Bragg L. R. 
Published: February 2009

AbstractDerivative-type ascent formulas are deduced for the kernels of certain half-space Dirichlet problems. These have the character of differentiation formulas for the Bessel functions but involve modifying variables after completing the differentiations. The Laplace equation and the equation of generalized axially-symmetric potential theory (GASPT) are considered in these. The methods employed also permit treating abstract versions of Dirichlet problems.
Conditions for permanence in well-known biological competition models
Authors: van Vuuren Jan H. , Norbury John 
Published: February 2009

AbstractReaction-diffusion systems are widely used to model the population densities of biological species competing for natural resources in their common habitat. It is often not too difficult to establish positive uniform upper bounds on solution components of such systems, but the task of establishingstrictly positiveuniform lower bounds (when they exist) can be quite troublesome. Two previously established criteria for the permanence (non-extinction and non-explosion) of solutions of general weakly-coupled competition-diffusion systems with diagonally convex reaction terms are used here as background to develop more easily verifiable and concrete conditions for permanence in various well-known competition diffusion models. These models include multi-component reaction-diffusion systems with (i) the by now classical Lotka-Volterra (logistic) reaction terms, (ii) higher order “logistic” interaction between the species, (iii) logistic-logarithmic reaction terms, (iv) Ayala-Gilpin-Ehrenfeld θ-interaction terms (which are used to modelDrosophilacompetition), (v) logistic-exponential interaction between the species, (vi) Schoener-exploitation and (vii) modified Schoener-interference between the species. In (i) a known condition for permanence (for the ODE-system) is recovered, while in (ii)–(vii) new criteria for permanence are established.
The best least squares approximation problem for a 3-parametric exponential regression model
Authors: Jukić D. , Scitovski R. 
Published: February 2009

AbstractGiven the data (pi, ti, fi), i = 1,…,m, we consider the existence problem for the best least squares approximation of parameters for the 3-parametric exponential regression model. This problem does not always have a solution. In this paper it is shown that this problem has a solution provided that the data are strongly increasing at the ends.
Bifurcation of positive solutions for a Neumann boundary value problem
Authors: Mays Laurence , Norbury John 
Published: February 2009

AbstractAnalytical, approximate and numerical methods are used to study the Neumann boundary value problem− uxx + q2u = u2(1 + sin x), for 0 < x < π,subject to ux(0) = 0, ux(π) = 0,for q2 ∈ (0,∞). Asymptotic approximations to (1) are found for q2 small and q2 large. In the case where q2 is large u(x) ≈ 3qδ(x − π/2). When q2 = 0 we show that the only possible solution is u ≡ 0. However, there exist non-zero solutions for q2 > 0 as well as the trivial solution u ≡ 0. To O(q4) in the q2 small case u(x) = q2π(π + 2)−1, so that bifurcation occurs about the trivial solution branch u ≡ 0 at the first eigenvalue λ0 = 0 and in the direction of the first eigenfunction ξ0 = constant.We obtain a bifurcation diagram for (1), which confirms that there exists a positive solution for q2 ∈ (0, 10). Symmetry-breaking bifurcations and blow-up behaviour occur on certain regions of the diagram. We show that all non-trival solutions to the problem must be positive.The formal outer solution u = q2û appears to satisfy û = û2(1 + sin x), so that û ≡ 0 and û = (1 + sin x)−1 are possible limit solutions. However, in the non-trivial case ûx(0) = −1 and ûx(π) = 1; this means that û does not satisfy the boundary conditions required for a solution of (1). This behaviour usually implies that for q2 large a boundary layer exists near x = 0 (and one near x = π), which corrects the slope. However, we find no evidence for such a solution structure, and only find perturbations in the direction of a delta function about u ≡ 0. We show using the monotone convergence theorem for quadratic forms that the inverse of the operator on the left-hand side of (1) is strongly convergent as q2 → ∞. We show that strong convergence of the operator is sufficient to stop outer-layer behaviour occurring.
Vector Lyapunov functions and conditional stability for systems of impulsive differential-difference equations
Authors: Bainov D. D. , Stamova I. M. 
Published: February 2009

AbstractBy means of piecewise continuous vector functions, which are analogues of the classical Lyapunov functions and via the comparison method, sufficient conditions are found for conditional, stability of the zero solution of a system of impulsive differential-difference equations.
Chaos in perturbed Lotka-Volterra systems
Authors: Christie J. R. , Gopalsamy K. , Li Jibin 
Published: February 2009

AbstractLotka-Volterra systems have been used extensively in modelling population dynamics. In this paper, it is shown that chaotic behaviour in the sense of Smale can exist in timeperiodically perturbed systems of Lotka-Volterra equations. First, a slowly varying threedimensional perturbed Lotka-Volterra system is considered and the corresponding unperturbed system is shown to possess a heteroclinic cycle. By using Melnikov's method, sufficient conditions are obtained for the perturbed system to have a transverse heteroclinic cycle and hence to possess chaotic behaviour in the sense of Smale. Then a special case involving a reduction to a two-dimensional Lotka-Volterra system is examined, leading finally to an application with a model for the self-organisation of macromolecules.
Extrapolation techniques and the collocation method for a class of boundary integral equations
Authors: Celorrio Ricardo , Sayas Francisco-Javier 
Published: February 2009

AbstractIn this paper we prove the existence of asymptotic expansions of the error of the spline collocation method applied to Fredholm integral equations of the first kind with logarithmic kernels. These expansions justify the use of Richardson extrapolation for the acceleration of convergence of the method. The results are stated and proven for a single equation, corresponding to the parameterization of a boundary integral equation on a smooth closed curve. As a byproduct we obtain the nodal superconvergence of the scheme. These results are then extended to smooth open arcs and to systems of integral equations. Finally we prove that such expansions also exist for the Sloan iteration of the numerical solution.