Efficient frequency-domain sample selection for recovering limited-support images

An image whose region of support is smaller than its bounding rectangle can, in principle, be reconstructed from a subset of the Nyquist samples. However, determining such a sampling set that gives a stable reconstruction is a difficult and computationally intensive problem. An algorithm is developed for determining periodic nonuniform sampling patterns that is orders of magnitude faster than existing algorithms. The speedup is achieved by using a sequential selection algorithm and heuristic metrics for the quality of sampling sets that are fast to compute, as opposed to the more rigorous linear algebraic metrics that have been used previously. Simulations show that the sampling sets determined using the new algorithm give image reconstructions that are of accuracy comparable with those determined by other slower algorithms.     

Asymptotically efficient order selection in nonstationary AR processes

In this paper we investigate the issue of asymptotic efficiency in nonstationary AR(∞) processes. Since the inverse of the autocovariance matrix of the underlying process cannot be evaluated due to the fact that the matrix is singular, traditional methods and techniques (Karagrigoriou 1995, 1997; Bhansali 1996) cannot be applied. Here we attempt to reduce the nonstationary case to a stationary one so that known results can then be applied to the reduced process. Asymptotic results regarding the overestimation of the order of an AR process with several unit roots are presented and the asymptotic efficiency of the order selected is established in the case whered (d>0) unit roots are present.     

Integrated order selection and production scheduling under MTO strategy

We consider an integrated order selection and production scheduling problem where a make-to-order (MTO) manufacturer has to select a subset of the orders to process so as to maximise the total profit, and sequence-dependent setup times and costs are incurred between the manufacturing of different classes of products. The problem is formulated as the resource-constrained profitable tour problem (RCPTP) where many variants of the traveling salesman problem (TSP) are its special cases. We model the problem as an integer program and develop an efficient algorithm to solve the problem. Computational results show the efficiency as well as effectiveness of the algorithm. The benefit of the integration is shown and managerial insights are discussed with the computational experiments as well.     

基于互信息的顺序向前特征选择算法

特征选择是水声目标识别领域的重要环节之一。提出基于互信息的顺序向前特征选择算法,通过计算特征之间的互信息和特征与类别间的互信息对所有特征的分类能力进行排序。提取了实测4类水声目标进行特征选择和分类实验,结果表明:该算法能够选择有效特征子集,得到较高的正确识别率,并且运行速度快,稳定性强。     

Higher order tip enrichment of eXtended Finite Element Method in thermoelasticity

An eXtended Finite Element Method (XFEM) is presented that can accurately predict the stress intensity factors (SIFs) for thermoelastic cracks. The method uses higher order terms of the thermoelastic asymptotic crack tip fields to enrich the approximation space of the temperature and displacement fields in the vicinity of crack tips—away from the crack tip the step function is used. It is shown that improved accuracy is obtained by using the higher order crack tip enrichments and that the benefit of including such terms is greater for thermoelastic problems than for either purely elastic or steady state heat transfer problems. The computation of SIFs directly from the XFEM degrees of freedom and using the interaction integral is studied. Directly computed SIFs are shown to be significantly less accurate than those computed using the interaction integral. Furthermore, the numerical examples suggest that the directly computed SIFs do not converge to the exact SIFs values, but converge roughly to values near the exact result. Numerical simulations of straight cracks show that with the higher order enrichment scheme, the energy norm converges monotonically with increasing number of asymptotic enrichment terms and with decreasing element size. For curved crack there is no further increase in accuracy when more than four asymptotic enrichment terms are used and the numerical simulations indicate that the SIFs obtained directly from the XFEM degrees of freedom are inaccurate, while those obtained using the interaction integral remain accurate for small integration domains. It is recommended in general that at least four higher order terms of the asymptotic solution be used to enrich the temperature and displacement fields near the crack tips and that the J- or interaction integral should always be used to compute the SIFs.     

Higher order ferroic properties of TGS monocrystals

It follows from symmetry consideration that ferroelectrics should possess ferroelastoelectric properties also. The form of ferroelastoelectric domains of uniaxial «pure» ferroelectric triglycine sulphate (TGS) is determined. The effects of the influence of uniaxial mechanical pressure on dielectric hysteresis loops of TGS single crystals are observed. Pressure applied in y-direction decreases height of saturated hysteresis loops (case of high ac-voltage) and increases height of non-saturated loops (case of low ac-voltage). In both cases coercitive field decreases with the pressure increase. Such a behavior may be connected with ferroelastoelectric properties of TGS crystals when uniaxial pressure produces favorable conditions on the domain wall motion.     

时变AR模型的一种定阶方法

自回归（AR）模型的定阶对其分析结果的准确性、效率和可靠性具有重要影响。对时变AR模型的定阶问题进行了深入研究,提出了一种基于采样频率以及分析频率之比的定阶方法。对一质量随时间变化的悬臂梁进行了有限元建模,运用计算所得到的振动响应建立了梁的时变AR模型,利用所提方法进行了该模型的定阶,采用递推最小二乘法对梁的模态频率进行了估计。对一质量时变的悬臂梁进行了试验,对采集的振动响应信号建立了时变AR模型并识别了其振动模态频率。模拟计算和试验结果都表明,提出的时变AR模型定阶方法是有效且可行的,且识别算法具有一定的抗噪性。     

Error performance of general order selection in correlated nakagami fading channels

A procedure for determining the probability distribution of the rth order statistic, Gr:L, r=1, 2, ==, L, among a set of L correlated Nakagami diversity branch gains G ₁, G ₂, , GL has been described in David and Nagaraja (2003) and Elkashlan et al. (2008). The results are used to evaluate the bit error rate (BER) of general order selection (GOS), a diversity method in which the rth order branch is selected for transmission, over correlated Nakagami fading branches. GOS can be used to improve system throughput and provide various levels of services, both of which are highly desirable in high-speed communication systems. Numerical and simulation results are presented and used to illustrate the effects of fading correlation on the BER associated with the rth order gain branch.     

Finite element analysis of plane couple-stress problems using first order stress functions

A complementary energy based variational principle, using first order stress functions, is developed for plane linear elastic couple-stress problems. The principle is analogous to that used in a total potential energy based Mindlin/Reissner thick plate bending analysis and as such is a generalization of the classical analogy between plate stretching and plate bending. Traction boundary conditions are enforced using a Lagrange multiplier technique. The resulting C⁰ finite element ‘equilibrium stress model’ is validated by investigating the reduction of the stress concentration factor associated with a small hole in a field of uniform tension.     

A note on testing independence by a copula-based order selection approach

We suggest a new consistent asymptotically distribution-free test for independence of the components of bivariate random variables. The approach combines methods of order-selection tests with nonparametric copula density estimation. We deduce the asymptotic distribution of the test statistic and investigate the small sample performance by means of a simulation study and a data application.     

Finite element methods for second order differential equations with significant first derivatives

Galerkin finite element methods based on symmetric pyramid basis functions give poor accuracy when applied to second order elliptic equations with large coefficients of the first order terms. This is particularly so when the mesh size is such that oscillations are present in the numerical solution. In the present note asymmetric linear and quadratic basis functions are introduced and shown to overcome this difficulty in an appropriate two point boundary value problem. In particular symmetric quadratic basis functions are oscillation free and highly accurate for a working range of mesh sizes.     

Simple large sample estimators of scale and location parameters based on blocks of order statistics

In this paper quite efficient large sample estimation procedures are derived for jointly estimating the parameters of the location-scale family of distributions. These estimators are linear combinations of the means of suitably chosen blocks of order statistics. For specific distributions, such as the extreme-value, normal, and logistic, little is to be gained by using more than three blocks. For these distributions we can obtain joint relative asymptotic efficiencies of 97–98% using the means of three blocks of ordered observations. The estimation procedures are also adapted for the estimation of the shape and scale parameters of the Weibull distribution.     

Simultaneous measurement of electric and magnetic properties of aspherical sample

A method using a solenoid coil for simultaneously estimating the electric and magnetic properties of a spherical conductor was studied. These properties are estimated by finding the difference in the complex impedance of the coil with and without a sample to find out the measuring value that best coincides with the theoretical value. A new formula applicable to a nonmagnetic, a magnetic or a superconductive spherical sample was derived. The conductivities a and permeabilities μ measured by this method and by the conventional methods were compared using various samples. The deviations were no larger than 3% for a nonmagnetic samples, and 1.5% for μ of magnetic samples     

Membrane selection — more than material properties alone

In this article, Dr Tony Franken from the Membrane Application Centre Twente (The Netherlands), discuss some important aspects of membrane selection. As the title indicates, selecting a membrane for a certain process involves much more than looking at membrane material properties. Certain separation problems can only be solved if the membrane is considered as part of the separation process as a whole. In addition to describing elements of membrane selection, Tony Franken illustrates examples from practical experiences with membrane and process selection at the Membrane Application Centre Twente, an independent and practically oriented expertise centre for membrane and separation technology.     

Uncertainties in the determination of dielectric properties in theinfinite sample method

In the infinite-sample method, the sample permittivity is found from the measured input reflection coefficient. The reflection coefficient domain of a traveling-wave system is transformed into the complex permittivity domain by two subsequent mappings which include the inverse bilinear and Schwarz-Christoffel transformations. The error bounds in permittivity measurements are derived. The dielectric properties and respective uncertainties are presented for a water sample in the form of the Cole-Cole diagram. The case presented represents the first step leading to a more general presentation of uncertainties in dielectric measurements     

Incorporating supplier selection and order allocation into the vehicle routing and multi-cross-dock scheduling problem

In the vehicle routing problem with cross-docking (VRPCD), it is assumed that the selected suppliers and the quantity of the products purchased from each supplier are known. This paper presents an MILP model which incorporates supplier selection and order allocation into the VRPCD in a multi-cross-dock system minimising the total costs, including purchasing, transportation, cross-docking, inventory and early/tardy delivery penalty costs. The sensitivity of the model on the key parameters of the objective function is analysed and the supply decisions are evaluated when the coefficients of the distribution cost are changed. A two-stage solution algorithm (TSSA) is proposed and the results of the TSSA for small-sized instances are compared with the exact solutions. Finally, a large-sized real case of an urban freight transport is solved using the TSSA.     

An integrated chance-constrained stochastic model for efficient and sustainable supplier selection and order allocation

Effective allocation of scarce resources across supply chain environments is an emerging issue, as enterprises face shortfalls in raw materials, human labour, budgetary resources, equipment, energy and capacity. We consider these related objectives in designing efficient and sustainable supply networks using a multi-objective mixed-integer non-linear programming (MINLP) model for efficient and sustainable supplier selection and order allocation with stochastic demand. Our approach considers sustainability dimensions including economic, environmental and social responsibility, but also seeks to design the most efficient supply network given constraints of the supply market. Enterprise efficiency is assessed using a bi-objective data envelopment analysis (DEA) whose inputs include raw materials, current expenses and labour force capacity. The resulting model is non-convex because of the presence of bilinear terms in DEA-related constraints, so we introduce a multi-stage solution procedure that first uses piecewise McCormick envelopes (PCM) to linearise the bilinear terms. Next, we introduce a set of valid inequalities in order to improve solution time of the problem whose dimension significantly increases after being linearised. We then exploit chance constrained programming approaches to deal with stochastic demand. Finally, a single aggregated objective function is derived using a fuzzy multi-objective programming approach. A manufacturing case study demonstrates the validity of the proposed approach, and its effectiveness in designing a supply network that addresses the ‘triple bottom line’ of people, profit and planet that comprises many sustainability initiatives in an efficient manner.