The decentralized Markov parameters and the selection of control structures

The properties of the decentralized pole placement map under constant output feedback are investigated and they are linked to known invariants of the decentralized pole assignment problem. A new expression of the differential of this map allows the derivation of relationships between the decentralized Plucker matrix invariant and the Markov parameters and leads to the definition of the Decentralized Markov Parameters (DMP). The matrix associated with the DMPs provides a new simple test for selection of decentralization schemes using as criteria the avoidance of formation of fixed modes and the preconditioning of the decentralized problem to be linearly assignable which excludes also almost fixed modes and it is a necessary condition for solution of the decentralized control problem. The natural link of this test to the Markov parameters and state space parameters of the models provides the means for affecting the shaping of properties of Plucker matrices by design, redesign of the input, and output structure of the system model. The results which are originally presented for the decentralized constant output feedback are subsequently extended to the case of decentralized PI feedback.     

Approximating distributional behaviour of LTI differential systems using Gaussian function and its derivatives

This article is concerned with the approximation of the distributional behaviour of linear, time-invariant (LTI) systems. First, we review the different types of approximations of distributions by smooth functions and explain their significance in characterising system properties. Second, we consider the problem of changing the state of controllable LTI differential systems in a very short time. Thus, we establish an interesting relation between the time and volatility parameters of the Gaussian function and its derivatives in the approximation of distributional solutions. An algorithm is then proposed for calculating the distributional input and its smooth approximation which minimises the distance to an arbitrary target state. The optimal choice of the volatility parameter for the state transition is also derived. Finally, some complementary distance problems are also considered. The main results of this article are illustrated by numerous examples.     

A two-folded impact analysis of schema changes on database applications

Database applications are becoming increasingly popular, mainly due to the advanced data management facilities that the underlying database management system offers compared against traditional legacy software applications. The interaction, however, of such applications with the database system introduces a number of issues, among which, this paper addresses the impact analysis of the changes performed at the database schema level. Our motivation is to provide the software engineers of database applications with automated methods that facilitate major maintenance tasks, such as source code corrections and regression testing, which should be triggered by the occurrence of such changes. The presented impact analysis is thus two-folded： the impact is analysed in terms of both the affected source code statements and the affected test suites concerning the testing of these applications. To achieve the former objective, a program slicing technique is employed, which is based on an extended version of the program dependency graph. The latter objective requires the analysis of test suites generated for database applications, which is accomplished by employing testing techniques tailored for this type of applications. Utilising both the slicing and the testing techniques enhances program comprehension of database applications, while also supporting the development of a number of practical metrics regarding their maintainability against schema changes. To evaluate the feasibility and effectiveness of the presented techniques and metrics, a software tool, called DATA, has been implemented. The experimental results from its usage on the TPC-C case study are reported and analysed.     

A matrix pencil based numerical method for the computation of theGCD of polynomials

The paper presents a new numerical method for the computation of the greatest common divisor (GCD) of an m-set of polynomials of R[s], P _m,d, of maximal degree d. It is based on a previously proposed theoretical procedure (Karcanias, 1989) that characterizes the GCD of P_m,d as the output decoupling zero polynomial of a linear system S(Aˆ,Cˆ) that may be associated with P_m,d . The computation of the GCD is thus reduced to finding the finite zeros of the pencil sW-AW, where W is the unobservable subspace of S(Aˆ,Cˆ). If k=dim W, the GCD is determined as any nonzero entry of the kth compound C_k(sW-AˆW). The method defines the exact degree of GCD, works satisfactorily with any number of polynomials and evaluates successfully approximate solutions     

The fundamental subspace sequences of matrix pencils: A toeplitz matrix unified characterization

The geometric theory of the domain of an ordered pair (F, G) of matrices or the geometry associated with matrix pencils provides a unifying framework for the study of algebraic, dynamic and feedback properties of linear singular systems. The key concepts and tools of the geometry are the notions of the (F, G)-, (G, F)-invariance and a set of subspace sequences. In this paper, an alternative characterization of these sequences is given based on the properties of the partitioned null spaces of appropriate sequences of Toeplitz matrices defined by the (F, G) pair. The results provide a simple procedure for the computation of the limit spaces of these sequences and clearly cover corresponding problems of the singular, implicit systems theory.     

The pole placement map, its properties, and relationships to systeminvariants

A number of properties of the complex and real pole placement map (PPM) which relate to the dimensions of their images and relate them to known system invariants are derived. It is shown that the two dimensions are equal and that their computation is equivalent to determining the rank of the corresponding differential. A new expression for the differential of the PPM allows the derivation of relationships between the Markov parameters and the Plucker matrix invariant of the system. Conditions for pole assignability are derived, based on the relationships between the rank of the Plucker matrix and the rank of the differential of the PPM     

Plastic Torsional Buckling of Cruciform Compression Members

In this paper the plastic torsional buckling of a cruciform column is revisited. The interest in this classical problem resurfaced from a practical application in the area of seismic protection of structures. The theoretical challenges associated with this problem emerge from the “paradoxial” differences between the plastic buckling strength that results from the total deformation and the incremental theories of plasticity. The paper shows that when the flanges of the column are not perfectly straight, the incremental theory of plasticity predicts that at the onset of plastic torsional buckling, the shear stress and the shear strain are related with the tangent shear modulus. The analysis presented herein involves a small-strain theory, examines the column at its slightly deformed configuration, and results are obtained with hand calculations. Experimental evidence supporting the theoretical findings is presented.     

开放创新与互操作性推动开放标准

信息技术（IT）行业正处于一个前所未有的互操作性和创新的时代。在不断增加的选择机会和创新产品中,用户是直接受益人。本文针对当今的IT行业,简要地论述了一些关键性问题,包括：（1）IT行业（以及其它行业）从“封闭创新”向“开放创新”转型;（2）在实现互操作性的过程中,互操作性的类型和行业、政府应起的作用;（3）“开放标准”公平的定义的重要性是确保知识产权（IP）所有者和使用者都有积极性,并一起努力开发和实施创新技术的解决方案。在本文的第四部分提出了一些建议,以期政府和决策者在制定影响这些重要领域的政策时,予以考虑。     

Passive vibration control of an offshore floating hydrostatic wind turbine model

We propose to make use of the hydraulic reservoir of a floating barge hydrostatic wind turbine (HWT) to suppress the pitch and roll motions of the barge by making the reservoir into a shape of an annular rectangular to serve as a bidirectional tuned liquid column damper (BTLCD). This means that we have made a barge‐motion damper with negligible extra costs as an HWT needs a reservoir for fluid storage anyway. The barge HWT simulation model is transformed from the NREL (National Renewable Energy Laboratory) 5‐MW geared equipped ITI Energy barge wind turbine model within the FAST (fatigue, aerodynamics, structures, and turbulence) code by replacing its drivetrain with a hydrostatic transmission drivetrain and incorporating the coupled dynamics of the barge‐reservoir system. We use 2 simplified turbine‐reservoir models to optimize the parameters of the BTLCD reservoir, which describe the pitch and roll motions of the turbine‐reservoir system, respectively. Simulation results based on the transformed NREL 5‐MW barge HWT model show that the optimal BTLCD reservoir is very effective in mitigating pitch and roll motions of the barge under realistic wind and wave excitations, which reduces the tower load and improves the power quality.