Improved initial vertex ordering for exact maximum clique search

This paper describes a new initial vertexordering procedure NEW_SORT designed to enhance approximate-colour exact algorithms for the maximum clique problem (MCP). NEW_SORT considers two different vertex orderings: degree and colour-based. The degree-based vertex ordering describes an improvement over a well-known vertex ordering used by exact solvers. Moreover, colour-based vertex orderings for the MCP have been traditionally considered suboptimal with respect to degree-based ones. NEW_SORT chooses the “best” of the two orderings according to a new evaluation function. The reported experiments on graphs taken from public datasets show that a leading exact solver using NEW_SORT —and further enhanced with a strong initial solution— can improve its performance very significantly (sometimes even exponentially).     

On relationships among passivity,positive realness,and dissipativity in linear systems

The notions of passivity and positive realness are fundamental concepts in classical control theory, but the use of the terms has varied. For LTI systems, these two concepts capture the same essential property of dynamical systems, that is, a system with this property does not generate its own energy but only stores and dissipates energy supplied by the environment. This paper summarizes the connection between these two concepts for continuous and discrete time LTI systems. Beyond that, relationships are provided between classes of strictly passive systems and classes of positive real systems. The more general framework of dissipativity is introduced to connect passivity and positive realness and also to survey other energy-based results. The frameworks of passivity indices and conic systems are discussed to connect to passivity and dissipativity. After surveying relevant existing results, some clarifying results are presented. These involve connections between classes of passive systems and finite-gain _L2$L_2$ stability as well as asymptotic stability. Additional results are given to clarify some of the more subtle conditions between classes of these systems and stability results. This paper surveys existing connections between classes of passive and positive real systems and provides results that clarify more subtle connections between these concepts.     

An adaptive inverse controller for explicit rate congestion control with guaranteed stability and fairness

This paper examines explicit rate congestion control for data networks. The available bit rate (ABR) service category of asynchronous transfer mode (ATM) networks serves as an example explicit rate system. However, the results of this paper are applicable to other systems as well. After a plant model is established, a control strategy based on approximate inverse concepts is introduced. The control process includes a linear digital filter (with a DC or drift tap) that uses normalized least mean square (NLMS) adaptation. The convergence, stability and fairness properties of this control scheme are discussed. This work differentiates itself from the other contributions in the area of rate-based congestion control in its balanced approach of retaining enough complexity as to afford attractive, analytically-proven performance properties, but not so much complexity as to make implementation prohibitively expensive.     

Investigating remanufacturing competition with yield uncertainty on market share,profit, and consumer surplus

Remanufacturing has been recognized both in literature and practice because of its greenness and cost saving. Since the reproduction processes could be affected by uncertain factors, remanufacturing is much more complex than producing new products. To investigate how yield uncertainty and market competition affect remanufacturing decisions, we compare the results under three classical market scenarios with random yield, that is, (a) Nash–Cournot, (b) monopoly, and (c) Stackelberg–Cournot. On comparing the expected remanufacturing scale, expected profit, and consumer surplus, it shows that as the number of remanufacturers increases, the planned collection quantity of a single remanufacturer decreases, while the total expected market output increases. Furthermore, we find that the largest expected profit and expected consumer surplus brought by market scenarios depend on a threshold remanufacturer number. We also relax the assumptions and extend our model to consider the scenario of m leaders and followers in a Stackelberg game. It is interesting to find that the first‐mover advantage in profit and market share of the leader remanufacturer would be challenged when the number of leader remanufacturers is no less than 2. The results can be potentially useful for managerial decisions and environmental administrations.     

Efficient multi-level design optimization using analytical target cascading and sequential quadratic programming

Decomposition-based optimization techniques are attractive for designing complex systems in industrial practice, such as design of structural, aerospace or automotive systems. Decomposition is attractive when a possibly intractable problem can be converted to a set of smaller, simpler problems; it also helps to understand better relationships and tradeoffs among subsystems which determine the overall behavior of the system to be optimized. A practical drawback is the increased computational cost for coordinating subproblem solutions and linking variable values to achieve overall system consistency and optimality. In this article, we exploit the problem partitioning structure to improve coordination efficiency when using analytical target cascading to solve multilevel problems. A simple modification in the coordination process allows for reduced function evaluations, as demonstrated in a structural and an automotive suspension example.     

Representation of crack-tip plasticity in pressure sensitive geomaterials

This paper presents a model based on dislocation theory for representation of crack tip plasticity in a pressure sensitive material. The basic equations are derived from a simple model of the crack tip plasticity which represents the plasticity by superdislocations placed at the effective centres of the complete slip process distributed around the crack tip. The positions and strengths of the superdislocations are determined by imposing the following conditions:(i) the total stress-intensity factor at the crack tip is zero(ii) the total stress minus the self stress of the superdislocation acting at the superdislocation position is just equal to the friction stress due to the Mohr-Coulomb yield criterion and(iii) the total crack opening displacement produced by the model is maximized.Condition (iii) enables the angle of the slip band on which the superdislocation lies to be determined. The results are presented in a dimensionless form allowing the discussion of particular cases and the recognition of the dominant parameters. A series of parametric studies are carried out to demonstrate that the model can capture the essentials of the crack tip plasticity.     

Elementary function generators for neural-network emulators

Piecewise first- and second-order approximations are employed to design commonly used elementary function generators for neural-network emulators. Three novel schemes are proposed for the first-order approximations. The first scheme requires one multiplication, one addition, and a 28-byte lookup table. The second scheme requires one addition, a 14-byte lookup table, and no multiplication. The third scheme needs a 16-byte lookup table, no multiplication, and no addition. A second-order approximation approach provides better function precision; it requires more hardware and involves the computation of one multiplication and two additions and access to a 28-byte lookup table. We consider bit serial implementations of the schemes to reduce the hardware cost. The maximum delay for the four schemes ranges from 24- to 32-bit serial machine cycles; the second-order approximation approach has the largest delay. The proposed approach can be applied to compute other elementary function with proper considerations.     

Analytical modelling of plastic behaviour of uniformly FRP confined concrete members

A method is presented for the assessment and calibration of the elastoplastic behaviour of FRP confined concrete. The method is based on the evaluation of permanent deformations from observed experimental deformations and theoretical elastic response of confined concrete. The inelastic response of concrete and the parameters of its mathematical modelling are investigated. Closed form expressions are produced to relate the model parameters to the mechanical properties of the material. A strain-hardening Drucker–Prager model is developed which simulates both the hardening and softening material response with reasonable agreement to the experimental observations. The predictive ability of the model is verified through comparisons to numerous published experimental data and analytical models.     

Timed Petri Nets in Hybrid Systems: Stability and Supervisory Control

In this paper, timed Petri nets are used to model and control hybrid systems. Petri nets are used instead of finite automata primarily because of the advantages they offer in dealing with concurrency and complexity issues. A brief overview of existing results on hybrid systems that are based on Petri nets is first presented. A class of timed Petri nets named programmable timed Petri nets (PTPN) is then used to model hybrid systems. Using the PTPN, the stability and supervisory control of hybrid systems are addressed and efficient algorithms are introduced. In particular, we present sufficient conditions for the uniform ultimate boundness of hybrid systems composed of multiple linear time invariant plants which are switched between using a logical rule described by a Petri net. This paper also examines the supervisory control of a hybrid system in which the continuous state is transfered to a region of the state space in a way that respects safety specifications on the plant's discrete and continuous dynamics.     

Head Up Games: combining the best of both worlds by merging traditional and digital play

Current pervasive games are mostly location-aware applications, played on handheld computing devices. Considering pervasive games for children, it is argued that the interaction paradigm existing games support limits essential aspects of outdoor play like spontaneous social interaction, physical movement, and rich face-to-face communication. We present a new genre of pervasive games conceived to address this problem, that we call “Head Up Games” (HUGs) to underline that they liberate players from facing down to attend to screen-based interactions. The article discusses characteristics of HUG and relates them to existing genres of pervasive games. We present lessons learned during the design and evaluation of three HUG and chart future challenges.