Comment on “Design of PID controllers for interval plants with time delay”

In [1] three theorems are presented which relate to the problem of stabilizing PID controller design for interval time-delay plants. We present a counterexample for these results.     

Travelling with Linux malware: Is Linux security for real?

Linux, is an Unix-like operating system. Although it is used mainly as a server operating system, it is slowly gaining more acceptance amongst end users. It has integrated security features and has the potential to help users protect themselves against malware. However, as we have seen, even Linux is not immune from such attacks.While the number of Windows worms has been increasing exponentially, to date there have only been a handful of malware programs directed at Linux. But as the number of workstation users running Linux increases, and as home users start to be connected via leased lines to the Internet, the situation may change. One indication of such progress was seen earlier this year, when Ramen was spreading Linux systems.This paper concentrates on current Linux malware, and describes the most typical malware seen on a Linux host.

Worms

The first Linux worm found in the wild, namely ADMworm, was reported by CERT®/CC[1] in 1998. It propagated in a fully automated fashion using a buffer overflow vulnerability in bind Domain Name Service server [1], and as such was very similar to the Internet Worm created by Robert Morris. The Morris worm almost shut down the entire Internet in November 1998. It was a VAX/VMS and SunOS based worm that exploited known vulnerabilities in sendmail’s debugging mode, fingerd and rsh/rexec. Within few hours the worm spread allegedly to more than half of the computers on the Internet at that time.This worm is similar to almost all Linux worms today — it is fully automatic, requires no user innovation and uses known vulnerabilities of the host operating system for its replication.[2]Table 1     

Parameter-dependent Lyapunov functional for systems with multiple time delays

The separation of the Lyapunov matrices and system matrices plays an important role when one use sparameter-dependent Lyapunov functional handling systems with polytopic type uncertainties. The delay-dependent robust stability problem for systems with polytopic type uncertainties is discussed by using parameter-dependent Lyapunov functional. The derivative term in the derivative of Lyapunov functional is reserved and the free weighting matrices are employed to express the relationship between the terms in the system equation such that the Lyapunov matrices are not involved in any product terms with the system matrices. In addition, the relationships between the terms in the Leibniz Newton formula are also described by some free weighting matrices and some delay-dependent stability conditions are derived. Numerical examples demonstrate that the proposed criteria are more effective than the previous results.     

Design of Fighter Flight Formation for Aerial Refueling Racetrack Mission with Drogue-Hose Configuration

The flying of aircraft information necessitates the extension of the theory of formation flight control to allow for three dimensional formation maneuvers. A leader and wingman formation is considered. A rotating reference frame attached to the wingman is used and special attention is given to the motion of the leader relative to the wingman. A thirteen state, three inputs, and three disturbances signal control system which models the dynamics of a two aircraft formation in three dimensional spaces is developed. The theory of formation control was applied to KC-130J tanker and F-16 receiver configuration to study the availability of performing such mission on a large scale. Three formation flight control concepts are investigated. A proportional, integral, and derivative automatic control system to maintain the wing aircraft in the specified formation geometry despite the leader＇s maneuvers is designed, and its performance is examined in simulation experiments. By adding special compensation to each control law to maintain the design damping ratio and gain margin, it is possible to reach the desired performance satisfying the predefined relative distances boundaries.     

A digital authentication watermarking scheme for JPEG images with superior localization and security

The drawbacks of the current authentication watermarking schemes for JPEG images, which are inferior localization and the security flaws, are firstly analyzed in this paper. Then, two counterferiting attacks are conducted on them. To overcome these drawbacks, a new digital authentication watermarking scheme for JPEG images with superior localization and security is proposed. Moreover, the probabilities of tamper detection and false detection are deduced under region tampering and collage attack separately. For each image block, the proposed scheme keeps four middle frequency points fixed to embed the watermark, and utilizes the rest of the DCT coefficients to generate 4 bits of watermark information. During the embedding process, each watermark bit is embedded in another image block that is selected by its corresponding secret key. Since four blocks are randomly selected for the watermark embedding of each block, the non-deterministic dependence among the image blocks is established so as to resist collage attack completely. At the receiver, according to judging of the extracted 4 bits of watermark information and the corresponding 9-neighbourhood system, the proposed scheme could discriminate whether the image block is tampered or not. Owing to the diminishing of false detection and the holding of tamper detection, we improve the accuracy of localization in the authentication process. Theoretic analysis and simulation results have proved that the proposed algorithm not only has superior localization, but also enhances the systematic security obviously. Supported by the National Natural Science Foundation of China (Grant No. 60572027), the Program for New Century Excellent Talents in University of China (Grant No. NCET-05-0794), the Sichuan Youth Science & Technology Foundation (Grant No. 03ZQ026-033), the National Defense Pre-research Foundation of China (Grant No. 51430804QT2201) and the Application Basic Foundation of Sichuan Province, China (Grant No. 2006 J13-10)     

Robust multi-branch space–time beamforming for OFDM system with interference

Space–time receive beamforming is a promising technique to suppress co-channel multiuser interference for orthogonal frequency division multiplexing (OFDM) systems. However, the performance of existing receive beamforming methods is highly sensitive to the memory length of time–domain equalizer. In this paper, we propose a new robust solution of space–time receive beamforming to combat co-channel multiuser interference for OFDM systems. The proposed method performs subspace analysis for the received space–time snapshots from both the training block and few data blocks, and constrains the space–time beamforming vectors to lie in the corresponding signal subspace. A few beamforming vectors are then carefully designed to suppress interference as well as provide the potential multi-branch diversity gain. The numerical results are provided to corroborate the proposed studies. We show that the proposed method not only can outperform the exiting competitors but also has the advantage of being quite insensitive to the memory length of time–domain equalizer.     

Observer theory in optimal control for systems with time delay†

An observer theory for estimating the state variables of deterministic linear time-invariant dynamic forced system is presented. The variation in the cost performance when some of the state variables are estimated by using a linear observer system is evaluated.     

Comment on “Stability of linear stationary systems with time delay”

Quadratic programming (QP) has previously been applied to the computation of optimal controls for linear systems with quadratic cost criteria. This paper extends the application of QP to non-linear problems through quasi-linearization and the solution of a sequence of linear-quadratic sub-problems whose solutions converge to the solution of the original non-linear problem. The method is called quasi-linearization-quadratic programming or Q-QP.

The principal advantage of the Q-QP method lies in the ease with which optimal controls can be computed when saturation constraints are imposed on the control signals and terminal constraints are imposed on the state vector. Use of a bounded-variable QP algorithm permits solution of constrained problems with a negligible increase in computing time over the corresponding unconstrained problems. Numerical examples show how the method can be applied to certain problems with non-analytic objective functions and illustrate the facility of the method on problems with constraints. The Q-QP method is shown to be competitive with other methods in computation time for unconstrained problems and to be essentially unaffected in speed for problems having saturation and terminal constraints     

Are learning styles useful indicators to discover how students use Scrum for the first time?

Teaching agile practices is in the cutting-edge of Software Engineering education since agile methodologies are widely used in the industry. An effective strategy to teach agile practices is the use of a capstone project, in which students develop requirements following an agile methodology. To improve students’ learning experience, professors have to keep track and analyze the information generated by the students during the capstone project development. The problem here arises from the large amount of information generated in the learning process, which hinders professors to meet each student’s learning profile. Particularly, to know the students skills and preferences are key aspects on a learner-centered approach of education in order to personalize the teaching. In this work, we aim to discover the relationships between students’ performance along a Scrum-based capstone project and their learning style according to the Felder–Silverman model, towards a first step to build the profiles. To address this issue, we mined association rules from the interaction of 33 Software Engineering students with Virtual Scrum, a tool that supports the development of the capstone project in the course. In the present work we describe promising results in experiments with a case-study.     

Asynchronous H∞ filtering for linear switched systems with average dwell time

This paper is concerned with the H_∞ filtering problem for a class of continuous-time linear switched systems with the asynchronous behaviours, where ‘asynchronous’ means that the switching of the filters to be designed has a lag to the switching of the system modes. By using the Lyapunov-like functions and the average dwell time technique, a sufficient condition is obtained to guarantee the asymptotic stability with a weighted H_∞ performance index for the filtering error system. Moreover, the results are formulated in the form of linear matrix inequalities that are numerical feasible. As a result, the filter design problem is solved. Finally, an illustrative numerical example is presented to show the effectiveness of the results.     

A self-tuning controller for systems with unknown or varying time delays†

A SISO self-tuning controller with a Smith-predictor type of time delay compensator (STC-TDC) is proposed to handle open-loop stable processes with unknown or varying time delays. Two numerical examples comparing PI control, the standard STC of Clarke and Gawthrop, the self-tuning Dahlin algorithm of Vogel and Edgar, and the STC-TDC show that the new approach performs best for both set-point and load changes when process time delay changes occur. A third example shows that the STC-TDC matches the extended stability characteristics of the alternative approach due to Kurz and Goedecke but is computationally much simpler.     

Step semantics for “true” concurrency with recursion

We present a variety of denotational linear time semantics for a language with recursion and true concurrency in a form of synchronous co-operation, which in the literature is known as step semantics. We show that this can be done by a generalization of known results for interleaving semantics. A general method is presented to define semantical operators and denotational semantics in the Smyth powerdomain of streams. With this method, first a naive and then more sophisticated semantics for synchronous co-operation are developed, which include such features as interleaving and synchronization. Then we refine the semantics to deal with a bounded number of processors, subatomic actions, maximal parallelism and a real-time operator. Finally, it is indicated how to apply these ideas to branching-time models, where it becomes possible to analyze deadlock behaviour as well as a form of true concurrency. John-Jules Meyer received his Master's degree in Mathematics in 1979 from the University of Leiden, and his Ph.D. degree in 1985 from the Free University Amsterdam. He is currently a Professor of Theoretical Computer Science, both at the Free University Amsterdam and at the University of Nijmegen. His current research interests include semantics of programming languages and logics for computer science, in particular artifical intelligence. Erik de Vink received the M.S. degree in Mathematics from the University of Amsterdam. He is currently a Junior Researcher at the Department of Mathematics and Computer Science of the Free University Amsterdam. At the moment his main research concerns the semantics of concurrent and logic programming languages.     

An imperfect production process for time varying demand with inflation and time value of money – An EMQ model

The paper deals with an economic manufacturing quantity (EMQ) model for time-dependent (quadratic) demand pattern. Every manufacturing sector wants to produce perfect quality items. But in long run process, there may arise different types of difficulties like labor problem, machinery capabilities problems, etc., due to that the machinery systems shift from in-control state to out-of-control state as a result the manufacturing systems produce imperfect quality items. The imperfect items are reworked at a cost to become the perfect one. The rework cost may be reduced by improvements in product reliability i.e., the production process depend on time and also the reliability parameter. We want to determine the optimal product reliability and production rate that achieves the biggest total integrated profit for an imperfect manufacturing process using Euler–Lagrange theory to build up the necessary and sufficient conditions for optimality of the dynamic variables. Finally, a numerical example is discussed to test the model which is illustrated graphically also.     

“Standardizing information security – a structurational analysis”

Given that there are an increasing number of information security breaches, organizations are being driven to adopt best practice for coping with attacks. Information security standards are designed to embody best practice and the legitimacy of these standards is a core issue for standardizing organizations. This study uncovers how structures at play in de jure standard development affect the input and throughput legitimacy of standards. We participated as members responsible for standards on information security and our analysis revealed two structures: consensus and warfare. A major implication of the combination of these structures is that legitimacy claims based on appeals to best practice are futile because it is difficult to know which the best practice is.     

The complexity of the temporal logic with “until” over general linear time

It is shown that the decision problem for the temporal logic with the strict until operator over general linear time is PSPACE-complete. This shows that it is no harder to reason with arbitrary linear orderings than with discrete linear time temporal logics. New techniques are used to give a PSPACE procedure for the logic.     

μ-Dependent model reduction for uncertain discrete-time switched linear systems with average dwell time

In this article, the model reduction problem for a class of discrete-time polytopic uncertain switched linear systems with average dwell time switching is investigated. The stability criterion for general discrete-time switched systems is first explored, and a μ-dependent approach is then introduced for the considered systems to the model reduction solution. A reduced-order model is constructed and its corresponding existence conditions are derived via LMI formulation. The admissible switching signals and the desired reduced model matrices are accordingly obtained from such conditions such that the resulting model error system is robustly exponentially stable and has an exponential H _∞ performance. A numerical example is presented to demonstrate the potential and effectiveness of the developed theoretical results.     

Discontinuous Galerkin time stepping with local projection stabilization for transient convection–diffusion-reaction problems

A time-dependent convection–diffusion-reaction problem is discretized in space by a continuous finite element method with local projection stabilization and in time by a discontinuous Galerkin method. We present error estimates for the semidiscrete problem after discretizing in space only and for the fully discrete problem. Numerical tests confirm the theoretical results.     

Fuzzy robust H ∞ filter design for nonlinear discrete-time systems with interval time delays

This article deals with the problem of H _∞ filter design for nonlinear discrete-time systems with norm-bounded parameter uncertainties and time-varying delays. A new Lyapunov function and free-weighting matrix method are used for filtering design, consequently, a delay-dependent design method is first proposed in terms of linear matrix inequalities, which produces a less conservative result. Finally, numerical examples are given to demonstrate the effectiveness and the benefits of the proposed method.