Singularity-free simulation of closed loop multibody systems by using null space of Jacobian matrix

Numerical simulation of closed loop multibody systems is associated with numerical solution of equations of motion which are, in general, in the form of DAE’s index-3 systems. For assuring continuous simulation, one should overcome some difficulties such as stabilization of the constraint equations, singular configuration of the system. In this paper, the system equations of motion with the Lagrange multipliers is rewritten by introducing generalized reaction forces. The combination with the condition of ideality of constraints leads to the system of equations which can be solved by numerical techniques smoothly, even over singular positions. Based on the new criterion of ideality of constraints, which relates generalized reaction forces and the null space matrix of Jacobian matrix, it is possible also to remove reaction forces and use only the reduced system of equations with null space matrix for passing singular positions. In order to prevent the constraint equations from the accumulated errors of integral time, the method of position and velocity projection has been exploited. Some numerical experiments are carried out to verify the proposed approach.     

On Constrained MMVC of Discrete‐Time First‐Order Linear Stochastic Systems with PSI I: The Critically Stable Case

This paper is devoted to the study of the modified minimal variance control (MMVC) of discrete‐time first‐order linear critically stable stochastic systems with prospective strong intervention (PSI) and control input constraints. Due to different evolutionary characteristics of systems with PSI, that is, the two modes of tending to infinity and having bounded oscillations, the discrete‐time first‐order linear critically stable systems can be partitioned into two types regarding the signs of a key system parameter a. A necessary and sufficient condition for the state mean convergence of a system with a = 1 is derived and the corresponding design of MMVC is formulated. For the critical stable system with a =? 1, its oscillation amplitudes of state means can be effectively suppressed or the means can converge under control. Finally, the effectiveness and advantages of the proposed control strategies comparing with MVC are confirmed by numerical simulations.     

On the nature and impact of self-similarity in real-time systems

In real-time systems with highly variable task execution times simplistic task models are insufficient to accurately model and to analyze the system. Variability can be tackled using distributions rather than a single value, but the proper characterization depends on the degree of variability. Self-similarity is one of the deepest kinds of variability. It characterizes the fact that a workload is not only highly variable, but it is also bursty on many time-scales. This paper identifies in which situations this source of indeterminism can appear in a real-time system: the combination of variability in task inter-arrival times and execution times. Although self-similarity is not a claim for all systems with variable execution times, it is not unusual in some applications with real-time requirements, like video processing, networking and gaming.     

An efficient and accurate short-characteristics solver for radiative transfer problems

Summary  In Turek (Computing 54, 27–38, 1995), the concept of the generalized mean intensity has been proposed as a special numerical approach to the (linear) radiative transfer equations which can result in a significant reduction of the dimension of the discretized system, without eliminating any information for the specific intensities. Moreover, in combination with Krylov-space methods (CG, Bi-CGSTAB, etc.), robust and very efficient solvers as extensions of the classical approximate Λ-iteration have been developed. In this paper, the key tool is the combination of special renumbering techniques together with finite difference-like discretization strategies for the arising transport operators which are based on short-characteristic upwinding techniques of variable order and which can be applied to highly unstructured meshes with locally varying mesh widths. We demonstrate how such special upwinding schemes can be constructed of first order, and particularly of second order accuracy, always leading to lower triangular system matrices on general meshes. As a consequence, the global matrix assembling can be avoided (“on-the-fly”) so that the storage cost is almost optimal, and the solution of the corresponding convection-reaction subproblems for each direction can be obtained very efficiently. As a further consequence, this approach results in a direct solver in the case of no scattering, while in the case of non-vanishing absorption and scattering coefficients the resulting convergence rates for the full systems depend only on their ratio and the absolute size of these physical quantities, but only weakly on the grid size or mesh topology. We demonstrate these results via prototypical configurations and we examine the resulting accuracy and efficiency for different computational domains, meshes and problem parameters. This paper is based on research which was supported in part by DFG grant No. TU102/16-1.     

Multiple level orthogonal codes and their application in MC-CDMA systems

This paper proposes the use of multiple level orthogonal (MLO) codes in multicarrier CDMA (MC-CDMA) systems. It is extremely challenging to improve system error probability performance of MC-CDMA systems with binary spreading codes in multi-user conditions, since attainable-diversity performance is severely degraged by multi-user interference (MUI) in frequency-selective fading channel conditions, even with the use of optimum multi-user detection (MUD) methods. MLO codes are shown to improve system error probability performance in heavily-loaded or fully-loaded systems, in comparison to binary codes. Some widely used MLO code generation methods are summarized, and a new generation method is also provided. The performance advantage of MLO codes over binary codes is analyzed by treating the spreading process in MC-CDMA as a coding process and via analysis of pair-wise sequence error probability. Rules for choosing desirable MLO codes for multi-user MC-CDMA are also given. Numerical results show that MLO codes can provide a substantial performance improvement in fully-loaded systems. For example, for a K = 4 user system with spreading gain L = 4, our system can obtain a diversity order of 3, whereas the binary code system diversity order is only slightly larger than 1. The MLO code application provides a new way to compensate for multi-user interference (MUI) and makes MC-CDMA more attractive for future high data-rate transmission systems.     

Curved OLED microdisplays

Technical background for CMOS substrate thinning of CEA‐LETI (historically developed for through silicon via technology as well as for more recent activity to provide curved image sensors, for IR as well as for visible spectra) has been applied to realize curved OLED‐based microdisplays. It will be shown that test OLEDs made onto silicon wafers as well as 873 × 500 WVGA, 0.38″ diagonal, and an innovative 1920 × 1200 WUXGA, 1″diagonal, CMOS‐based microdisplays can be curved at R = 45 mm radius of curvature (1D) with no negative impact onto the circuit electrical characteristics. This feature can allow significant innovation on the system and application because it can help to redesign simpler and lighter optical engine systems, in the same manner as for curved image sensors. These results can be obtained owing to the integration of a new protective hard coat layer that has been used in conjunction with a robust thin‐film encapsulation to protect OLEDs from mechanical ingress (from process steps and handling) and oxidizing gas of the atmosphere, respectively. Results have been produced within the framework of the EU‐funded, H2020 project, called L arge cost‐effective O LED MI cro D isplays (LOMID and their applications).     

Investigating the usability of real-time scheduling theory with the Cheddar project

This article deals with real-time critical systems modelling and verification. Real-time scheduling theory provides algebraic methods and algorithms in order to make timing constraints verifications of these systems. Nevertheless, many industrial projects do not perform analysis with real-time scheduling theory even if demand for use of this theory is large and the industrial application field is wide (avionics, aerospace, automotive, autonomous systems, …). The Cheddar project investigates why real-time scheduling theory is not used and how its usability can be increased. The project was launched at the University of Brest in 2002. In Lecture Notes on Computer Sciences, vol. 5026, pp. 240–253, 2008, we have presented a short overview of this project. This article is an extended presentation of the Cheddar project, its contributions and also its ongoing works.     

Synchronization of multi-agent systems without connectivity assumptions

Multi-agent systems arise from diverse fields in natural and artificial systems, such as schooling of fish, flocking of birds, coordination of autonomous agents. In multi-agent systems, a typical and basic situation is the case where each agent has the tendency to behave as other agents do in its neighborhood. Through computer simulations, Vicsek et al. (1995) showed that such a simple local interaction rule can lead to a certain kind of cooperative phenomenon (synchronization) of the overall system, if the initial states are randomly distributed and the size of the system population is large. Since this model is of fundamental importance in understanding the multi-agent systems, it has attracted much research attention in recent years. In this paper, we will present a comprehensive theoretical analysis for this class of multi-agent systems under a random framework with large population, but without imposing any connectivity assumptions as did in almost all of the previous investigations. To be precise, we will show that for any given and fixed model parameters concerning with the interaction radius r and the agents’ moving speed v, the overall system will synchronize as long as the population size n is large enough. Furthermore, to keep the synchronization property as the population size n increases, both r and v can actually be allowed to decrease according to certain scaling rates.     

Integration of behavioural feedback in web‐based systems nutrition learning among university students

This study evaluated whether nutrition knowledge and healthy eating patterns can be achieved through web‐based systems, a secondary analysis of learning activities and assessment records. Students used online dietary recording systems to capture food intake data for 2 weeks. The first cohort used a food photo‐upload method and the second cohort used a food text‐searching (TS) method. We compared nutrient intake profiles, nutrition knowledge, and reflective journals of the 2 groups. Interaction effects were tested by 1‐way multivariate ANOVA on outcomes between groups (p < .05). More reflective and action statements in reflective journals were observed in the TS group. The photo‐upload group exhibited significant improvement in saturated fat, sodium, cholesterol, and fat consumption (p < .001), as compared with TS group. Web‐based dietary systems can be adopted in nutrition education to effectively enhance students' nutrition knowledge and help them to reflect on their dietary patterns.     

Fractional‐order–dependent global stability analysis and observer‐based synthesis for a class of nonlinear fractional‐order systems

This paper focuses on proposing novel conditions for stability analysis and stabilization of the class of nonlinear fractional‐order systems. First, by considering the class of nonlinear fractional‐order systems as a feedback interconnection system and applying small‐gain theorem, a condition is proposed for L₂‐norm boundedness of the solutions of these systems. Then, by using the Mittag‐Leffler function properties, we show that satisfaction of the proposed condition proves the global asymptotic stability of the class of nonlinear fractional‐order systems with fractional order lying in (0.5, 1) or (1.5, 2). Unlike the Lyapunov‐based methods for stability analysis of fractional‐order systems, the new condition depends on the fractional order of the system. Moreover, it is related to the H_∞‐norm of the linear part of the system and it can be transformed to linear matrix inequalities (LMIs) using fractional‐order bounded‐real lemma. Furthermore, the proposed stability analysis method is extended to the state‐feedback and observer‐based controller design for the class of nonlinear fractional‐order systems based on solving some LMIs. In the observer‐based stabilization problem, we prove that the separation principle holds using our method and one can find the observer gain and pseudostate‐feedback gain in two separate steps. Finally, three numerical examples are provided to demonstrate the advantage of the novel proposed conditions with the previous results.     

Application of nonlinear dynamic analysis to the identification and control of nonlinear systems-III. n-Dimensional systems

In two previous publications, the authors have shown that normal form theory, a method used extensively in dynamic analysis, can be applied in the structure identification of nonlinear systems. In particular, normal form theory bridges the gap between structure of a nonlinear, low order polynomial dynamical system and the behavior it is able to predict or represent. This is important because knowing a system's dynamic behavior automatically leads to a simple nonlinear normal form model that can be used for (nonlinear) control. Previously, only two-dimensional normal form models were derived. For this paper, simple, n-dimensional, low order polynomial dynamical models will be derived that can represent a nonlinear system with multiple steady states or a limit cycle in the operating region of interest. Using as a plant the nonisothermal Continuous Stirred Tank Reactor with consecutive reactions (A→B→C), it is shown that identification and control of this three-dimensional system using the aforementioned normal form models is feasible.     

Bounded Real Lemmas for Fractional Order Systems

This paper derives the bounded real lemmas corresponding to L∞norm and H∞norm(L-BR and H-BR) of fractional order systems. The lemmas reduce the original computations of norms into linear matrix inequality(LMI) problems, which can be performed in a computationally efficient fashion. This convex relaxation is enlightened from the generalized Kalman-YakubovichPopov(KYP) lemma and brings no conservatism to the L-BR. Meanwhile, an H-BR is developed similarly but with some conservatism.However, it can test the system stability automatically in addition to the norm computation, which is of fundamental importance for system analysis. From this advantage, we further address the synthesis problem of H∞control for fractional order systems in the form of LMI. Three illustrative examples are given to show the effectiveness of our methods.     

The fundamental closed-form solution of control-related states of kth order S3PR system with left-side non-sharing resource places of Petri nets

Due to the state explosion problem, it has been unimaginable to enumerate reachable states for Petri nets. Chao broke the barrier earlier by developing the very first closed-form solution of the number of reachable and other states for marked graphs and the kth order system. Instead of using first-met bad marking, we propose ‘the moment to launch resource allocation’ (MLR) as a partial deadlock avoidance policy for a large, real-time dynamic resource allocation system. Presently, we can use the future deadlock ratio of the current state as the indicator of MLR due to which the ratio can be obtained real-time by a closed-form formula. This paper progresses the application of an MLR concept one step further on Gen-Left kth order systems (one non-sharing resource place in any position of the left-side process), which is also the most fundamental asymmetric net structure, by the construction of the system's closed-form solution of the control-related states (reachable, forbidden, live and deadlock states) with a formula depending on the parameters of k and the location of the non-sharing resource. Here, we kick off a new era of real-time, dynamic resource allocation decisions by constructing a generalisation formula of kth order systems (Gen-Left) with r^* on the left side but at arbitrary locations.     

Mobile agent systems and cellular automata

The purpose of this article (based on an earlier draft available as technical report: Gruner S, Mobile agent systems and cellular automata. LaBRI Research Reports, 2006) is to make a step towards uniting the paradigms of cellular automata and mobile agents, thus consequentially the fields of artificial life and multi agent systems, which have significant overlap but are still largely perceived as separate fields. In Chalopin et al. (Mobile agent algorithms versus message passing algorithms, pp. 187–201, 2006) the equivalent power of classical distributed algorithms and mobile agent algorithms was demonstrated for asynchronous systems with interleaving semantics under some further constraints and assumptions. Similar results are still being sought about mobile agent systems and distributed systems under other constraints and assumptions in search of a comprehensive general theory of these topics. This article investigates the relationship between mobile agent systems and a generalized form of cellular automata. With a particular notion of local equivalence, a cellular automaton can be translated into a mobile agent system and vice versa. The article shows that if the underlying network graph is finite, then the degree of pseudo-synchrony of the agent system simulating the cellular automaton can be made arbitrarily high, even with an only small number of active agents. As a possible consequence of this theoretical result, the Internet might be used in the future to implement large cellular automata of almost arbitrary topology.     

Liveness with invisible ranking

The method of invisible invariants was developed originally in order to verify safety properties of parameterized systems in a fully automatic manner. The method is based on (1) a project&generalize heuristic to generate auxiliary constructs for parameterized systems and (2) a small-model theorem, implying that it is sufficient to check the validity of logical assertions of a certain syntactic form on small instantiations of a parameterized system. The approach can be generalized to any deductive proof rule that (1) requires auxiliary constructs that can be generated by project&generalize, and (2) the premises resulting when using the constructs are of the form covered by the small-model theorem. The method of invisible ranking, presented here, generalizes the approach to liveness properties of parameterized systems. Starting with a proof rule and cases where the method can be applied almost “as is,” the paper progresses to develop deductive proof rules for liveness and extend the small-model theorem to cover many intricate families of parameterized systems.     

Enhanced abstract data types in object-relational databases

The explosion in complex multimedia content makes it crucial for database systems to support such data efficiently. This paper argues that the “blackbox” ADTs used in current object-relational systems inhibit their performance, thereby limiting their use in emerging applications. Instead, the next generation of object-relational database systems should be based on enhanced abstract data type (E-ADT) technology. An (E-ADT) can expose the semantics of its methods to the database system, thereby permitting advanced query optimizations. Fundamental architectural changes are required to build a database system with E-ADTs; the added functionality should not compromise the modularity of data types and the extensibility of the type system. The implementation issues have been explored through the development of E-ADTs in Predator. Initial performance results demonstrate an order of magnitude in performance improvements. Received January 1, 1998 / Accepted May 27, 1998     

Improving inter-block backtracking with interval Newton

Inter-block backtracking (IBB) computes all the solutions of sparse systems of nonlinear equations over the reals. This algorithm, introduced by Bliek et al. (1998) handles a system of equations previously decomposed into a set of (small) k ×k sub-systems, called blocks. Partial solutions are computed in the different blocks in a certain order and combined together to obtain the set of global solutions. When solutions inside blocks are computed with interval-based techniques, IBB can be viewed as a new interval-based algorithm for solving decomposed systems of nonlinear equations. Previous implementations used Ilog Solver and its IlcInterval library as a black box, which implied several strong limitations. New versions come from the integration of IBB with the interval-based library Ibex. IBB is now reliable (no solution is lost) while still gaining at least one order of magnitude w.r.t. solving the entire system. On a sample of benchmarks, we have compared several variants of IBB that differ in the way the contraction/filtering is performed inside blocks and is shared between blocks. We have observed that the use of interval Newton inside blocks has the most positive impact on the robustness and performance of IBB. This modifies the influence of other features, such as intelligent backtracking. Also, an incremental variant of inter-block filtering makes this feature more often fruitful.     

The RKHS method for numerical treatment for integrodifferential algebraic systems of temporal two-point BVPs

Many problems arising in different fields of sciences and engineering can be reduced, by applying some appropriate discretization, either to a system of integrodifferential algebraic equations or to a sequence of such systems. The aim of the present analysis is to implement a relatively recent computational method, reproducing kernel Hilbert space, for obtaining the solutions of integrodifferential algebraic systems of temporal two-point boundary value problems. Two extended inner product spaces W[0, 1] and H[0, 1] are constructed in which the boundary conditions of the systems are satisfied, while two smooth kernel functions R _t (s) and r _t (s) are used throughout the evolution of the algorithm in order to obtain the required grid points. An efficient construction is given to obtain the numerical solutions for the systems together with an existence proof of the exact solutions based upon the reproducing kernel theory. In this approach, computational results of some numerical examples are presented to illustrate the viability, simplicity, and applicability of the algorithm developed.

     

Matching high performance approximate inverse preconditioning to architectural platforms

In this paper we examine the performance of parallel approximate inverse preconditioning for solving finite element systems, using a variety of clusters containing the Message Passing Interface (MPI) communication library, the Globus toolkit and the Open MPI open-source software. The techniques outlined in this paper contain parameters that can be varied so as to tune the execution to the underlying platform. These parameters include the number of CPUs, the order of the linear system (n) and the “retention parameter” (δ l) of the approximate inverse used as a preconditioner. Numerical results are presented for solving finite element sparse linear systems on platforms with various CPU types and number, different compilers, different File System types, different MPI implementations and different memory sizes.