A Lie-Group Adaptive Method for Imaging a Space-Dependent Rigidity Coefficient in an Inverse Scattering Problem of Wave Propagation

We are concerned with the reconstruction of an unknown space-dependent rigidity coefficient in a wave equation. This problem is known as one of the inverse scattering problems. Based on a two-point Lie-group equation we develop a Lie-group adaptive method (LGAM) to solve this inverse scattering problem through iterations, which possesses a special character that by using onlytwo boundary conditions and two initial conditions, as those used in the direct problem, we can effectively reconstruct the unknown rigidity function by aself-adaption between the local in time differential governing equation and the global in time algebraic Lie-group equation. The accuracy and efficiency of the present LGAM are assessed by comparing the imaged results with some postulated exact solutions. By means of LGAM, it is quite versatile to handle the wave inverse scattering problem for the image of the rigidity coefficient without needing any extra information from the wave motion.     

On the parameterization of algebraic curves

In this paper, by using the concept of resolvents of a prime ideal introduced by Ritt, we give methods for constructing a hypersurface which is birational to a given irreducible variety and birational transformations between the hypersurface and the variety. In the case of algebraic curves, this implies that for an irreducible algebraic curveC, we can construct a plane curve which is birational toC. We also present a method to find rational parametric equations for a plane curve if it exists. Hence we have a complete method of parameterization for rational algebraic curves.The work reported here was supported in part by the NSF Grants CCR-8702108 and 9117870On leave from Institute of Systems Science, Academia Sinica, Beijing 100080, P.R. China     

盘形滚刀垂向振动特性分析与试验

盘形滚刀的垂向振动对于全断面隧道掘进机的贯入度和破岩效率有一定的影响,为了研究影响滚刀垂向振动的因素,首先建立盘形滚刀垂向三自由度振动模型,得到盘形滚刀刀圈与刀体、圆锥滚子轴承和刀轴的等效质量和刚度,利用MATLAB软件对该振动模型进行仿真,得到滚刀各部分的振动位移,并通过试验得到滚刀各部分振动位移与仿真的结果趋势一致。结果表明:滚刀的刀圈加刀体的最大振动位移量为2.8×10^-4 m,轴承最大振动位移为2.1×10^-4 m,当滚刀的轴承刚度增大3倍时,各部分最大振动位移减少约50%,增大刀圈刀体刚度时,各部分最大振动位移减少约12%,盘形滚刀减振需要增加轴承和刀圈刀体的刚度。研究结果为盘形滚刀的振动测量提供了一种有效方法,对滚刀的设计具有重要的指导意义。     

New secondary constructions of Bent functions

In this paper, we first present a novel secondary construction of bent functions (building new bent functions from two already defined ones). Furthermore, the algebraic degree and algebraic immunity of the constructed functions are analysed. Finally, we apply the construction using as initial functions some specific bent functions and then specify sufficient conditions for the resulting bent functions not to be contained in the completed Maiorana–McFarland class. In the second part of the paper, we present a corrigendum of “Constructions of bent–negabent functions and their relation to the completed Maiorana–McFarland Class” (IEEE Trans Inf Theory 61(3):1496–1506, 2015).     

对称布尔函数的代数免疫性

在流密码和分组密码的加密体制中,需要构作具有各种密码学性质的布尔函数,用来作为密钥,以抵抗已有的各种有效攻击方法。近年来,人们提出了代数攻击方法,为了抵抗这种攻击方式,构作代数免疫度很大的布尔函数,成为近五年来信息安全领域一个研究热点。本文综述布尔函数代数免疫性方面的重要问题和主要进展,其中包括中国学者在对称布尔函数代数免疫性的研究成果。     

Torsional rigidity of a circular bar with multiple circular inclusions using the null-field integral approach

In this article, a systematic approach is proposed to calculate the torsional rigidity and stress of a circular bar containing multiple circular inclusions. To fully capture the circular geometries, the kernel function is expanded to the degenerate form and the boundary density is expressed into Fourier series. The approach is seen as a semi-analytical manner since error purely attributes to the truncation of Fourier series. By collocating the null-field point exactly on the real boundary and matching the boundary condition, a linear algebraic system is obtained. Convergence study shows that only a few number of Fourier series terms can yield acceptable results. Finally, torsion problems are revisited to check the validity of our method. Not only the torsional rigidities but also the stresses of multiple inclusions are also obtained by using the present approach.     

Building strategic agility through user-driven innovation: the case of the Finnish public service sector

This paper investigates how to build strategic agility through the lens of user-driven innovation. Drawing on survey data collected in the public service sector in Finland, our study suggests that the strategic rigidity of public service organisations, assessed according to their strategic sensitivity, resource fluidity and leadership unity, can hamper their effective adoption of the user-driven innovation approach to build strategic agility. We propose a 4C model of building strategic agility through user-driven innovation, addressing the need of taking actions in four areas: commitment, competences, communications and climate. Our research highlights that actions in the four dimensions, which are closely interlinked and reinforce each other, should involve actors at different levels both internally and externally.     

3-Dimensional Bag of Visual Words Framework on Action Recognition

Human motion recognition plays a crucial role in the video analysis framework. However, a given video may contain a variety of noises, such as an unstable background and redundant actions, that are completely different from the key actions. These noises pose a great challenge to human motion recognition. To solve this problem, we propose a new method based on the 3-Dimensional (3D) Bag of Visual Words (BoVW) framework. Our method includes two parts: The first part is the video action feature extractor, which can identify key actions by analyzing action features. In the video action encoder, by analyzing the action characteristics of a given video, we use the deep 3D CNN pre-trained model to obtain expressive coding information. A classifier with subnetwork nodes is used for the final classification. The extensive experiments demonstrate that our method leads to an impressive effect on complex video analysis. Our approach achieves state-of-the-art performance on the datasets of UCF101 (85.3%) and HMDB51 (54.5%).     

Analysis of Elastic-PlasticWaves in a Thin-Walled Tube By a Novel Lie-Group Differential Algebraic Equations Method

In this paper, we adopt the viewpoint of a nonlinear complementarity problem (NCP) to derive an index-one differential algebraic equations (DAEs) system for the problem of elastic-plastic wave propagation in an elastic-plastic solid undergoing small deformations. This is achieved by recasting the pointwise complementary trio in the elastic-plastic constitutive equations into an algebraic equation through the Fischer-Burmeister NCP-function. Then, for an isotropicallyhardening/ softening material under prescribed impulse loadings on a thin-walled tube with combined axial-torsional stresses, we can develop a novel algorithm based on the Lie-group differential algebraic equations (LGDAE) method to iteratively solve the resultant DAEs at each time marching step, which converges very fast. The one-dimensional axial-torsional wave propagation problems under different imposed dynamical loading conditions and initial conditions are solved, to assess the performance of the LGDAE.     

Interaction of free-surface waves with floating flexible strips

The method developed by the author to derive a set of algebaic equations to solve the interaction of free-surface waves with a single floating rigid or flexible two-dimensional platform with small draft is extended to the case that the platform consists of strips with different constant flexural rigidity and mass. The method is based on the application of Green's theorem, with a specific choice of the Green function to arrive at a differential-integral equation along the platform. This equation can be solved exactly by means of superposition of exponential functions, a standard method to solve a set of linear differential equations. After integration with respect to the space coordinate the residue theorem leads to both the dispersion relation along each individual strip and an algebraic equation for the coefficients. Due to very fast convergence with respect to the number of coefficients taken into account the series are truncated. Depending on the water-depth, in each series three to ten terms are taken into account. Results are shown for a structure consisting of several strips that are tightly connected and for disjoint strips. In the latter case the computation of the water level between the strips is also computed. The water level and the reflection and transmission coefficients are not unknowns in the algebraic equation, but are computed afterwards by means of Green's theorem.     

Insights into a mixed Chinese postman problem

Abstract

In this study, we consider a Mixed Chinese Postman Problem in the form of an Integer Program and investigate its properties with both algebraic solutions and geometric configurations. The insights this study provides into their relationship have paved a way toward designing more efficient structural algorithm for finding an exact solution. Theoretical proofs are provided with numerical illustrations.     

Accident investigation: keep asking "why?"

Finding the causes of an accident or operating problem and deciding what actions to take to prevent it happening again is rather like dismantling a set of Russian dolls (Fig. 1). Each time we ask "why?" (or a similar searching question) we find another cause besides the ones we have found already and another action (or set of actions) we can take to prevent similar accidents occurring again. Many investigators stop too soon. This occurred at Flixborough, at Bhopal and in the investigation of many lesser-known accidents. We are more likely to find the deeper causes and the more original actions if groups of people with wide interests and experience are able to take part in the investigations or discuss the investigation reports. We should never look at an accident report as "closing out" a problem. As we read it, we should ask ourselves, "what else could be done?"     

Polynomial parametrization of nonsingular complete intersection curves

In this paper we give a new method to compute a polynomial parametrization, in case it exists, of an affine nonsingular complete intersection curve. Our method is based on the study of vector fields on nonsingular algebraic curves. In contrast to the existing methods, our algorithm does not use any projection, and no sample point on the curve is needed. It is also important to stress the fact that the algorithm produces a parametrization with coefficients in the ground field.     

Impact of the alignment between the strategic and operational levels of a manufacturing enterprise

In today's economic environment, manufacturing organisations compete against each other as part of supply chains (SC). As both the SC strategic level and production floor operational level are interdependent, a misalignment between them has a deep impact on the performance of the manufacturing organisation. For this reason, in this paper we develop an analytical expression of the impact such misalignment has on the manufacturing organisation performance, specifically, its demand fulfillment ability. The usefulness of the analytical expression is illustrated via the development, for the case of a local furniture company, of a system dynamics (SD) simulation model. The SD simulation model is tested under different operational conditions, so the case study company can derive conclusions regarding actions to improve its demand fulfillment ability.     

纤维缠绕中的十字型管曲面的几何造型方法

管形曲面是在不同柱面间进行光滑过渡而生成的各种复合曲面。十字型管是管道工业中重要的连接元件。纤维缠绕要求十字型管曲面形状尽可能简单以便易于制作,文章提出了以低次曲面作为过渡曲面的十字型通管的造型方法,该方法采用简单明了的数学表示来生成过渡曲面,而且可以直观地控制过渡曲面的形状。     

A novel formulation leading to closed-form solutions for buckling of circular plates

Summary In this paper we study axisymmetric buckling of radially graded circular plates. The flexural rigidity is considered to be a suitably varying function of the radial coordinate. The problem is posed as a semi-inverse one. The buckling mode is selected first, then the variation of the flexural rigidity consistent with the buckling mode is determined. Apparently for the first time in the literature, closed-form solutions are found. Such solutions allow the design of a circular plate whose buckling load is at least the pre-specified one. Such a design appears to find much applications in various fields of engineering.     

Revisit of an elliptic hole problem by using complex variable method

In this paper, the problem of an elliptic hole embedded in an infinite plate interacting with an arbitrary point load is revisited by using the complex variable method. Based on analytical continuation theorem, the continuity conditions across the interface are automatically satisfied in a straightforward manner. It is shown that the solution for an infinite domain with an elliptic hole can be obtained from the solution of the corresponding homogeneous problem merely by a simple algebraic expression. This relation is universal in the sense of being independent of the loading considered. The solution of the corresponding homogeneous problem is considered as the principal part of the complex potentials while the complementary part of the complex potentials can be obtained by using analytical continuation theorem. Different expressions of the complementary part of the complex potentials are presented in this paper which are all proved to be the same result.     

Fuzzy programming for optimal product mix decisions based on expanded ABC approach

In sheet metal fabrication, bending is used in order to obtain rigidity and to obtain a part of desired shape and function. In analysing a sheet metal part, an important consideration is how to unfold the part after a bending operation or series of bending operations. The unfolding process is the first major step in process planning for generating NC paths for a sheet metal blank. This paper addresses the problem of determining whether or not a part can be unfolded. A graph-based approach using the face-edge of the sheet metal part is at the heart of the algorithm presented here. Using this algorithm one can determine which faces are unfoldable and which cannot be unfolded. This algorithm can be used to help facilitate the process of NC path generation. It also sheds some light on the kind of design practices that make a part easily unfoldable or otherwise.     

A coordination strategy for distributed multi-agent manufacturing systems

This paper proposes a distributed multi-agent approach for dynamic part routing in automated manufacturing systems. In particular, each part in the system is associated to an intelligent software agent that must select its next destination autonomously (i.e. ignoring the actions of the other agents) and in real time (i.e. at each time it completes an operation on a workstation). Differently from other existing approaches, we overcome the typical myopia of negotiation algorithms based on dispatching rules by allowing the part agents to take decisions not only about the imminent operation, but also for the subsequent ones. The anticipated decisions are transmitted to workstation agents, which are also designated to detect and resolve conflicts by modifying part agents’ decisions. To describe the single agents and their interaction schemes in a formal way, we take advantage of DEVS discrete-event modelling tools, which also allow us to develop a detailed simulation platform for our multi-agent system. The simulation experiments obtained on a detailed model of a manufacturing system derived from the literature confirm the effectiveness of the proposed approach.     

Numerical solutions of boundary detection problems using modified collocation Trefftz method and exponentially convergent scalar homotopy algorithm

In this paper, the boundary detection problem, which is governed by the Laplace equation, is analyzed by the modified collocation Trefftz method (MCTM) and the exponentially convergent scalar homotopy algorithm (ECSHA). In the boundary detection problem, the Cauchy data is given on part of the boundary and the Dirichlet boundary condition on the other part of the boundary, whose spatial position is unknown a priori. By adopting the MCTM, which is meshless and integral-free, the numerical solution is expressed by a linear combination of the T-complete functions of the Laplace equation. The use of a characteristic length in MCTM can stabilize the numerical procedure and ensure highly accurate solutions. Since the coefficients of MCTM and the position of part of the boundary are unknown, to collocate the boundary conditions will yield a system of nonlinear algebraic equations; the ECSHA, which is exponentially convergent, is adopted to solve the system of nonlinear algebraic equations. Several numerical examples are provided to demonstrate the ability and accuracy of the proposed meshless scheme. In addition, the consistency of the proposed scheme is validated by adding noise into the boundary conditions.