E-Delay Systems letter

Issue: 1, December 2006


I would like to start with wishing you Happy Holidays and Happy New Year !!

The idea of establishing an electronic letter reaching the audience working on time delayed systems has been circulating among our colleagues in the past years. At the last IFAC Time Delay Systems Workshop in L’Aquila, Italy in July 2006, our discussions on this idea evolved into an effort of bringing this e-letter to life. I volunteered to take this responsibility, for the time being, to initiate the start-up of the letter.

The spirit of this e-letter is to create an open platform informing researchers among our community about forthcoming events on the topics, such as, recent publications, conference announcements, available positions all of which overlap on the core topic of delay systems. Furthermore, the e-letter will serve to our colleagues to share their preliminary results/internal reports with the community. In this way, the letter may help establish network among the researchers that are physically distanced.

Although the e-letter is around the topic of delay systems, its scope is not strictly limited to delay keyword. Topics that may inspire delays systems community are regarded as an important component of the scope of this e-letter. We believe that this maintains a flexible framework where new ideas, topics and comments emerging from various disciplines may intersect. It is believed that this flexibility will enrich the e-letter by enabling it to encompass multi-disciplinary research topics.

The first issue starts with recent publications, conference announcements and abstracts of recently defended PhD theses related with time delay systems. In order to add some flavor of entertainment, a pixel gallery section is devoted to share with you the photo gallery of IFAC TDS Workshop held in L'Aquila, Italy as well as some stabiltiy pictures of various dynamics obtained by our colleagues. The issue finishes with three open position announcements.

I gratefully thank Silvi-Iulian Niculescu for his idea of initiating, constructing and structuring this e-letter and many colleagues who showed their support. Contributions – which formed this first issue – from Jean Jacques Loiseau, Jean-Francois Lafay, Rabah Rabah, Jean-Pierre Richard, Pierdomenico Pepe, Leonid Shaikhet, Insperger Tamas, Gabor Orosz, Elias Jarlebring, Dimitri Breda, Sarah Spurgeon, Alexandre Seuret, Francois Veysset, Nima Yeganefar, Michael Di Loreto, Lotfi Belkoura are sincerely acknowledged.

It is our pleasure to share with you the first issue, and we will be waiting for your contributions for the upcoming issues.

Rifat Sipahi & Silviu-Iulian Niculescu



Recent Publications


Contributed by: Jean-Pierre Richard, Jean-Pierre.richard "AT" ec-lille.fr

• T. Ogushi, J.P. Richard - "Sliding-mode control of retarded nonlinear systems via finite spectrum assignment approach", IEEE Trans. Aut. Control, Vol. 51, No 9, pp. 1527-1531, Sept. 2006.


Contributed by: Leonid Shaikhet, leonid.shaikhet "AT" usa.net

• Shaikhet L., Roberts J. Reliability of difference analogues to preserve stability properties of stochastic Volterra integro-differential equations. Advances in Difference Equations. 2006. V.2006, Article ID 73897, 22 pages.

• Shaikhet L. Some new aspect of Lyapunov type theorems for stochastic difference equations with continuous time. Asian Journal of Control, 2006, Vol.8, N.1, p.76-81.

• Shaikhet L. A new view on one problem of asymptotic behavior of solutions of delay difference equations. Discrete Dynamics in Nature and Society. 2006. V.2006, Article ID 74043, 16 pages.

• Shaikhet L. About stability of a difference analogue of a nonlinear integro-differential equation of convolution type. Applied Mathematics Letters, 2006. V 19, N. 11, p.1216-1221.


Contributed by: Rifat Sipahi, rifat "AT" coe.neu.edu

• Sipahi, R., Olgac, N., 2006, A Unique Methodology for the Stability Robustness of Multiple Time Delay Systems, Systems & Control Letters, 55(10), 819-825.

• Sipahi, R., Olgac, N., 2006, Stability Robustness of Retarded LTI Systems with Single Delay and Exhaustive Determination of Their Imaginary Spectra, SIAM Journal on Control and Optimization, Volume 45 Issue 5, Pages 1680-1696.


Contributed by: Insperger Tamas, inspi "AT" mm.bme.hu

• Insperger,T., Act-and-wait concept for time-continuous control systems with feedback delay, IEEE Transactions on Control Systems Technology, 14(5) (2006), pp. 974-977.

• Stépán, G., Insperger,T., Stability of time-periodic and delayed systems - a route to act-and-wait control, Annual Reviews in Control, 30 (2006), pp. 159-168.


Contributed by: Fatihcan Atay, atay "AT" member.ams.org

• F. M. Atay. Oscillator death in coupled functional differential equations near Hopf bifurcation. J. Differential Equations, 221:190-209, 2006.

• F. M. Atay and A. Hutt. Neural fields with distributed transmission speeds and long-range feedback delays. SIAM J. Appl. Dynamical Systems, 5:670-698, 2006.

• F. M. Atay and O. Karabacak. Stability of coupled map networks with delays. SIAM J. Appl. Dynamical Systems, 5:508-527, 2006.

• A. Hutt and F. M. Atay. Effects of distributed transmission speeds on propagating activity in neural populations. Physical Review E, 73(2):021906, 2006.


Contributed by: Gabor Orosz, g.orosz "AT" exeter.ac.uk

• G. Orosz and G. Stepan, Subcritical Hopf bifurcations in a car-following model with reaction-time delay, Proceedings of the Royal Society of London A 462(2073), 2643-2670, (2006)


Conference Announcements



October 17 - 19, 2007, Iguassu Falls, Brazil

Main topics include: Time delay systems

Important dates

Submission of manuscript and proposal of invited session: January 31th, 2007
Notification of acceptance: April 17th, 2007
Receipt of paper in camera-ready form: June 17th, 2007

For further information, please visit: http://sssc07.ece.ufrgs.br

Contributed by: Rifat Sipahi, rifat "AT"coe.neu.edu

Symposium on Time Delay in Complex Networks, Stability and Stabilization

(click to view announcement)

21st Biennial Conference on Mechanical Vibration and Noise (VIB) Conference,

An Integral Part of the 2007 ASME International Design Engineering Technical Conferences (2007 IDETC),

September 4-7, 2007, Rio All-Suite Hotel and Casino, Las Vegas, Nevada


Abstract/Full-length Paper: Feb. 19, 2007
Acceptance Notification: April 20, 2007
Final Paper Submission: May 28, 2007

13th IEEE IFAC International Conference on Methods and Models in Automation and Robotics

27 August - 30 August 2007, Szczecin, POLAND

Optimization of Infinite Dimensional Systems

Abstract submission: March 1, 2007

For further information, please visit: http://www.mmar.ps.pl

Contributed by: Jean Jacques Loiseau, Jean-Francois Lafay, Rabah Rabah (Jean-Francois.Lafay "AT" irccyn.ec-nantes.fr)

7th Workshop on Time Delay Systems

2007, Nantes, IRCCYN , 1 rue de la Noë, BP 92101, F-44321 Nantes, France


This IFAC Workshop on Time-Delay –Systems is the seventh in a series. The previous workshops were held in Grenoble (France, 1998), Ancona (Italy, 2000), Santa Fe (USA, 2001), Rocquencourt (France, 2003), Leuven (Belgium, 2004), and L’Aquila (Italy, 2006).

The objective is to bring together the specialists in the field of Time Delay Systems. High level contributions on the many aspects of this research area ranging from theory over numerics to various applications, are awaited. Contributions on related domains will be considered with great interest, provided they contain relations with Time Delay Systems. Industrial participants and junior researchers are particularly welcome.

March 15, 2007: Submission of papers and invited sessions.
April 15, 2007: Notification of acceptance



Control and observation of systems with variable delays - Theory and applications

Alexandre Seuret (PhD defended Oct. 4th, 2006), Contact: as389 "AT" leicester.ac.uk

This work deals with the control and the observation of linear or nonlinear systems with time-varying delays, as well as some related experimentations: sampling, networked control systems and control with visual feedback. For such so-called "hereditary" systems, the behavior depends not only on current information but also depends on past times. The first chapter deals with the presentation of the context and of theoretical grounds of this work. The second chapter concerns the problem of exponential stability and stabilization of systems with time-varying delays. Here, the speed performance is then taken into account in the control design. The third chapter generalizes these results to disturbed systems the behavior of which do not amount to the linear and time invariant models. We consider in particular two practical problems: uncertainties due to parameter variations and saturated control inputs. In the fourth chapter, we focuss on continuous systems subject to sampled-data control. An input-delay approach is proposed which allows one to apply classical in "continuous-time" results. The fifth chapter is devoted to the observation of delay systems. The worked-out results hold for systems with known delays (which case often appears in the literature), as well as for unknown delays (which is a sensitive and less explored case) The last chapter presents some applicative problems where the theoretical results find their justification. We specially focuss on remote control trough an internet network and on a visual feedback control of mechanical benchmark.

Modelling and identification of aircraft behaviours in turbulent flight using time delay models

Francois Veysset (PhD defended Nov. 17th, 2006), Contact: francois.veysset "AT" onera.fr

This study relates to the mathematical representation of the behaviour of the aircraft in atmospheric turbulence as well as the identification of the dynamics induced by the gust. The approach falls under a prospect for identification from tests carried out in the Flight Analysis Laboratory of the DCSD of ONERA in Lille. To achieve this, the plane is considered into various elements which consist in the fuselage, the wing and the tail. The obtained model incorporates unsteady effects, modelled via Küssner functions, and clearly clarified delays. Results in simulation confronting our model with recent work on modelling highlight the fact that these phenomena have to be taken into account in the modelling. The comparison with experimental data shows that the tendencies observed during the tests are confirmed for our model. The algebraic identification method initiated by Fliess and Sira-Ramirez in 2003 was extended to time delay systems. This technique based on the distributional framework allows to identify some delays and parameters of our model.

Definitions and analysis of stabilities for nonlinear time-delay systems

Nima Yeganefar (PhD defended Nov. 24th, 2006), Contact: nimnima "AT" gmail.com

Currently at ATER in Ecole Centrale de Lille

The focus of this work is the notion of stability for nonlinear time-delay systems using the Lyapunov time-domain approach. Five different chapters are devoted to stability properties. After a general introduction, the second chapter proposes an unconventional approach --- based on Lyapunov-Krasovskii functionals --- to the problem of input-output stability. The descriptor form is used to guaranty this stability by solving linear matricial inequalities (LMI). The next chapter, finite-time stability, is, as far we know, the first work on this topic for time-delay systems. Specifically several results are given for the stabilization problem on linear systems with delayed input. The first examples of finite-time stable delayed systems are also given. The fourth chapter is devoted to the input-to-state stability, which is generalized to the delay case. Sufficient conditions are given to check this stability using Lyapunov-Krasovskii methodology. The interest of the study based on perturbation problems is highlighted and some interesting perspectives for further research are given. The last part of the work is devoted to the study of practical stability used in solving the so-called chattering problem in sliding mode control. As the control is rapidly switching, chattering may appear on the state space --- for instance in practical applications when the control dynamics can no longer be neglected. The chattering problem is carefully analyzed and many simulations are given to demonstrate the advantages of the proposed solution.

Methodology for the analysis and the control of time-delay systems

Michael Di Loreto, IRCCyN, UMR CNRS 6597, Nantes, France, Contact: michael.di-loreto"AT" insa-lyon.fr

Currently at Insa-Lyon, LAI 69621, Villeurbanne, France

This thesis deals with methodologies for the analysis and the control of linear time-delay systems. The first is the geometric approach. The linear time-delay systems can be modelled by a quadruple of matrices with entries over a ring. Then the geometric approach makes it possible to analyze a system with the properties of the modules over a ring. In this part, we develop a well argued analysis of invariance concepts for application in system control. Some logical relationships among various classes of controlled and conditioned invariant modules are established. The second approach is based on algebraic concepts. In this approach, the use of pseudo-polynomials, which are operators with a finite number of derivatives, pointwise and distributed delays, is fundamental. More precisely, the ring of proper and stable fractions of pseudo-polynomials is used in the stabilization problem. The solution gives us a parameterization of all stabilizing controllers and closed-loop transfer matrices. Then, various control problems are addressed, like the disturbance rejection, the disturbance attenuation, the exact or approximated model matching, or the optimal l1 control. Finally, the last approach is about numerical calculus. In this part, the interval analysis is used to solve hard numerical problems, like the robust stability, the stabilization, or the verification of a gauge for performances and robustness.

Habilitation thesis, French "Habilitation à diriger des recherches", University of Lille 1, 3 October 2006.

Contribution to the Identification of Delay Systems

Lotfi Belkoura, Associate Professor at the University of Lille, Contact: Lotfi.Belkoura "AT" univ-lille1.fr

In the first part of this thesis, parameter identifiability is studied for a class of finite and infinite dimensional systems described by convolution equations. The notion of sufficiently rich input which enforces identifiability is also addressed and the results are obtained assuming knowledge of solutions on a bounded time interval. The second part deals with on-line identification of delay systems. It is based on new non-asymptotic algebraic estimation techniques. A concrete case-study and an application to transmission delays are discussed. Several successful numerical simulations are provided even with noisy data.


Time Delay Systems Pixel Gallery


Open Positions

Research Associate and Research Studentship (Two posts)

Contributed by: Professor Sarah Spurgeon, eon "AT" le.ac.uk , Head of Department of Engineering University of Leicester.

This EPSRC funded research programme within the Control and Instrumentation Research Group at the University of Leicester, UK is concerned with the development of novel, theoretically sound sliding mode control techniques for application to nonlinear, complex and uncertain industrial processes. The research will focus on extending the existing sliding mode control design paradigm to enable the application of the methodology, with its proven robustness properties, to systems with after effect, otherwise known as time-delay systems and only given output signals are available for measurement. The applied research will focus on the production of two significant implementation studies relating to control of autonomous and semi-autonomous vehicles and also the control of satellites to demonstrate the efficacy of the underlying philosophy and the new design algorithms. These are pertinent design studies to inform the development of the theoretical research programme as well as being used as vehicles to illustrate the research outcomes. The broad objectives are

1. To provide practical yet theoretically rigorous solutions to the problem of robust sliding mode control for uncertain nonlinear systems in the presence of time-delay based upon knowledge of the measured system output (s). The problem will be considered from both a continuous and discrete time perspective.

2. To produce significant implementation studies relating to control of satellites and autonomous and semi-autonomous vehicles which demonstrate the relevance of the theoretical results to industry.

Post 1: Research Associate Grade 7: £27,193 to £31,525 per annum (Ref: R3053):

Applicants for this post should have a good honours degree and hold a PhD in a relevant area of control engineering. Expertise in sliding mode control and the analysis of systems in the presence of time delay would be an advantage.

Downloadable application forms and further particulars are available by following the link below, or in hardcopy from Personnel Services, tel: 0116 223 1341, fax: 0116 252 5140, email: recruitment3 "AT" le.ac.uk, http://www.le.ac.uk/personnel/jobs. Please note that CVs will only be accepted in support of a fully completed application form.

Post 2: Research Studentship: Full fees and maintenance are available to the successful candidate.

Applicants for the Research Studentship should have a good honours degree, or internationally recognised equivalent, in engineering or mathematics.

Please send a full CV to Professor Sarah Spurgeon, Department of Engineering University of Leicester, University Road, Leicester LE1 7RH. Tel: 0116 252 2531, fax: 0116 252 2619, email: eon "AT" le.ac.uk


PhD assistantship immediately available at Northeastern University, Mechanical and Industrial Engineering Department. Click for details.



Prepared by Rifat Sipahi, December 20th, 2006.