Engineers'' CAx education—it''s not only CAD

The general product development can be divided into three phases: creative, conceptual and engineering phase. All phases of the complete life cycle of a product are supported by various IT-systems often called ‘CAx’¹-systems. Therefore CAD-education should be extended to ‘CAx-education’ and pay attention to all phases of the life cycle.

When looking at today's process chain many different jobs related to CAx can be identified. All of them require different levels of knowledge about subjects like information technology, design procedures or CAGD^{, 2}-functionalities.

The methods to teach those subjects vary from simple autodidactic, via computer supported training methods to interactive person to person training. In industry, the training methods are primarily depending on the company's size and branch. The bigger the company is, the more complex are the training methods and the more specialized is the CAx-education.

Enterprises specialised on CAx-training but also in-house education departments are concerned. Other possibilities for CAx-education are internships, technical colleges and universities. All of those suffer from the complexity of the subject and result often in broad but superficial education.

Apart from knowledge about CAx-systems and their usage, the students have to learn also about the organisation of the CAx-process and its structures including the cooperation of enterprises.

Following these experiences the students or employees will at first be trained in fundamental CAS/CAD/CAM. In a second step they will attend special courses for PDM, Data exchange, FEM, or others. On higher level there will be courses dealing with PLM^{, 3}, process- and company networks, with future trends and techniques. During the whole education the application aspect has to be dominant.     

Oscillation criteria for second-order quasi-linear neutral difference equations

In this paper, we obtain some oscillation criteria for the second-order quasi-linear neutral delay difference equation

Full-size image

, where > 0, τ ≥ 0, and σ ≥ 0 are constants, {a_n}, {p_n}, {q_n} are nonnegative sequences and f ε C(R,R).     

Integral averages and oscillation of second-order nonlinear differential equations

We present some criteria for the oscillation of the second-order nonlinear differential equation

Full-size image

where a ε C¹([t₀, ∞)) is a nonnegative function, q ε C ([t₀, ∞)) are allowed to change sign on [t₀, ∞), ψ, f ε C¹ , ψ(x) > 0, xf(x) > 0, f′(x) ≥ 0 for x ≠ 0. These criteria are obtained by using a general class of the parameter functions H(t,s) in the averaging techniques and represent extension, as well as improvement of known oscillation criteria of Philos and Purnaras for the generalized Emden-Fowler equation.     

Optimal bounds for the approximation of boolean functions and some applications

This paper presents an optimal bound on the Shannon function L(n,m,) that gives the worstcase circuit-size complexity to approximate, within an approximation degree at least , partial boolean functions having n inputs and domain size m. That is

Full-size image

. Our bound applies to any partial boolean function and any approximation degree, and thus completes the study of boolean function approximation introduced by Pippenger (1977).

Our results give an upper bound for the hardness function h(ƒ), introduced by Nisan and Wigderson (1994), which denotes the minimum value l for which there exists a circuit of size at most l that approximates a boolean function ƒ with degree at least 1/l. Indeed, if H(n) denotes the maximum hardness value achieved by boolean functions with n inputs, we prove that for almost every nH(n)n/3 + n² + O(1). The exponent n/3 in the above inequality implies that no family of boolean functions exists which has ‘full’ hardness. This fact establishes connections with Allender and Strauss' (1994) work that explores the structure of BPP.

Finally, we show that for almost every n and for almost every boolean function ƒ of n inputs we have h(ƒ)2^{n/3−2 log n}. The contribution in the proof of the upper bound for L(n, m, ) can be viewed as a set of technical results that globally show how boolean linear operators are ‘well’ distributed on the class of 4-regular domains. This property is then applied to approximate partial boolean functions on general domains using a suitable composition of boolean linear operators.     

Interpolation by periodic radial functions

Let d be the natural (geodesic) metric on the circle S¹. We study the interpolation of arbitrary data on a set of equally-spaced nodes Y_i ε S¹ by means of functions having the form

Full-size image

, in which φ is a function at our disposal. A cardinal function is found, and convergence questions can be answered with the aid of it.     

Parametric quadratic stabilizability of uncertain nonlinear systems

The objective of this paper is to introduce the notion of parametric quadratic stabilizability (PQ-stabilizability) of nonlinear control systems

Full-size image

. When we consider nonlinear systems, reference inputs and disturbances may alter dynamics in an essential way by moving the equilibrium to a new location, or destroying it altogether. For this reason, when we consider quadratic stabilizability (Q-stabilizability) of nonlinear systems, we need to combine the two concepts of parametric stability and Q-stabilizability, and consider PQ-stabilizability. When nonlinear function φ belongs to a subclass of passive functions, it is shown that the necessary and sufficient condition for quadratic stabilizability (Q-stabilizability) of linear systems via dynamic state feedback, which was derived by Zhou and Khargonekar, is also a necessary and sufficient condition for that of nonlinear systems considered in this paper. Moreover, when nonlinear function φ belongs to a subclass of incresing functions and when ΔB = 0, it shown that the necessary and sufficient condition for Q-stabilizability of linear systems via static state feedback, which was derrived by Petersen, is also a necessary and sufficient condition for that of nonlinear systems considered in this paper.     

A multi-model reference control approach for bandwidth-on-demand protocols in satellite networks

This paper presents a multi-model reference control (MMRC) approach for queue-based bandwidth-on-demand (BoD) procedures in geostationary satellite networks. BoD access protocols address the problem of guaranteeing a high exploitation of the valuable satellite bandwidth while offering acceptable end-to-end delays to the traffic accessing the network. In queue-based protocols, the controller objective is to drive the buffer queue length to a certain target queue length; in the proposed scheme, model references (MRs) are used to address the problem of adapting the target queue length to the statistical characteristics of the traffic. The reference queue length is computed as a weighted sum of the outputs of the different MRs; the weights are computed on-line by evaluating the network utilization achieved by each MR, in response to the actual traffic feeding the system. Moreover, the target network utilization is dynamically varied based on the estimated network load. The BoD performances are evaluated via simulations. The work underlying this paper is based on the results of the GEOCAST,¹ SATIP6² and SATSIX³ projects, financed by European Union.     

Edge coloring of bipartite graphs with constraints

A classical result from graph theory states that the edges of an l-regular bipartite graph can be colored using exactly l colors so that edges that share an endpoint are assigned different colors. In this paper, we study two constrained versions of the bipartite edge coloring problem.

Full-size image

Heterogeneous system level co-simulation for the design of telecommunication systems

The advanced complexity and heterogeneity of modern telecommunication systems mostly lead to the incorporation of heterogeneous implementation technologies and design styles. Consequently, the design representation of such systems often requires the mixed use of distinct model of computations at different abstraction layers. Therefore, heterogeneous co-simulation is needed in order to enable the effective communication and interaction among the involved models of computation. This paper resolves this issue by proposing the heterogeneous co-modelling of telecom systems based on the combination of SDL semantics with C language running on an instruction set simulator, coupling in that way the specification and the first refinement steps of the co-design flow. The missing test link between the corresponding tools that support the SDL-C co-model is addressed by proposing a heterogeneous co-simulation scheme through the development of a mediator. Finally, the proposed methodology and the efficiency of the built environment are evaluated through a case study associated with the design of the MAC layer of the DECT telecom system.^1,2     

Some remarks on uniform asymptotic expansions for Bessel functions

The uniform asymptotic expansion of the modified Bessel function of the first kind I_ν(νz), except for an auxiliary multiplier, is in the form

Full-size image

is a polynomial in u² of degree k and U_k(u) is determined by use of a recurrence equation which is in the form of a difference–differential–integral equation. As a consequence these coefficients are not easily evaluated and the calculation becomes more cumbersome as k increases. In this paper, we show that the above series can be rearranged as where c_k(ν) satisfies a difference equation of order three, but there are only three terms as the coefficient of one of the terms is always zero. We also show how K_ν(νz), the Hankel functions, etc. can be handled in a similar fashion.     

A study of incidents involving programmable electronic safety-related systems

This paper presents a study of 21 incidents¹ in small manufacturing enterprises involving electrical/electronic/programmable electronic (E/E/PE) safety-related systems, originally investigated by the Health and Safety Laboratory (HSL). The aim of this study is to highlight the causes of these incidents and suggest common solutions to those causes. A fault schema suitable for the classification of incidents of this nature is proposed. For each incident, identified faults are labelled according to the fault schema and are also denoted as primary, secondary or incidental. Examples of particular causes are given. The prominent faults are further discussed with the goal of highlighting the categories of faults most prominent in E/E/PE safety-related systems. This pinpoints the areas where future work on incident prevention should focus. Finally, mitigation techniques which could form part of an E/E/PE safety-related system development methodology suitable for small manufacturing enterprises are suggested.     

Input constrained funnel control with applications to chemical reactor models

Error feedback control (in the presence of input constraints) is considered for a class of exothermic chemical reactor models. The primary control objective is regulation of a setpoint temperature T^* with prescribed accuracy: given λ>0 (arbitrarily small), ensure that, for every admissible system and reference setpoint, the regulation error e=T−T^* is ultimately smaller than λ (that is, ||e(t)||<λ for all t sufficiently large). The second objective is guaranteed transient performance: the evolution of the regulation error should be contained in a prescribed performance funnel F around the setpoint temperature T^*. A simple error feedback control with input constraints of the form

Full-size image

, u^* an offset, is introduced which achieves the objective in the presence of disturbances corrupting the measurement. The gain k(t) is a function of the error e(t)=T(t)−T^* and its distance to the funnel boundary. The input constraints have to satisfy certain feasibility assumptions in terms of the model data and the operating point T^*.     

Constructing the Lyee method with a method engineering approach

This paper proposes an Evolution driven ME approach aiming to support the evolution of an existing method (the As–Is method) in order to obtain a new method (the To–Be method) better adapted to a given engineering situation and/or satisfying new methodogical requirements. The proposed approach is used in order to evolve the existing Lyee method into a Lyee user driven method.¹     

Facilitating simultaneous engineering in the automotive industry via high speed networks, control passing and face-to-face video: Results from the car project

The European automotive industry requires frequent interaction and transfer of data between geographically dispersed designers and engineers at all stages of the product introduction process. The RACE CAR project identified and demonstrated Integrated Broadband Communications (IBC)-supported applications to support this process and improve competitiveness. User requirements for workstation-based, multi-media facilities including conferencing were identified. Two experiments were designed to investigate the role of face-to-face video and the means by which participants organise and control their interactions. These are critical issues in the multi-cultural, international environment of the European automotive industry. In the first experiment groups of three users solved a cooperative, screen-based, object manipulation task supported by different levels of communication. ‘Linked computers plus an audio link’ resulted in significantly faster completion times than either ‘audio alone’ or ‘linked computer plus audio and face-to-face video’. ‘Linked computers plus audio’ was also perceived as the most effective communications media. The passage of cursor via verbal agreement was successfully managed. Video was generally considered beneficial for initial introductions, assessing understanding and facilitating a stronger feeling of group identity.

In the second experiment, subjects were grouped under ‘chaired’ or ‘free-for-all’ conditions and linked via (1) audio and linked computers or (2) audio, linked computers and face-to-face video. The task was similar to Experiment 1 and attempts to introduce contention were made through adding hidden, sub-goals. The task took significantly less time to complete in the ‘video chaired’ condition than the ‘non-video chaired’ or ‘video free-for-all’ conditions. This suggests that video has an important role in enabling a chairperson to control the meeting. Contention was not successfully achieved.

The results of the experiments suggest face-to-face video may be useful in chaired meetings and to develop ‘team’ feeling. A free-for-all method of control passing was seen as most appropriate although problems in achieving contention in Experiment 2 meant the impact of disagreement was not fully investigated. The results are discussed in relation to the European automotive industry and areas for further study identified. Relevance to industry

The European automotive industry, which maintains distinct engineering functions in disparate countries, is striving to reduce the length of its design life cycle by improving communications between designers and engineers. The studies described in this paper provide information of use to the developers and procurers of systems intended to support this process. In particular issues relating to the relevance of face-to-face video and use of control mechanisms for co-operative computer-mediated work.     

Minimisation of the update response time in a distributed database system

This paper is concerned with the minimisation of the update response time in distributed database systems (DDBS) where resequencing algorithms are used to preserve the consistency of the databases. The authors proposed a novel resequencing technique, in reference [7], namely hop-by-hop resequencing with batch processing for connecting the first stage to the second stage of a two-stage DDBS. In this paper, a stochastic upper bound is calculated for the system response time and it is shown that the system response is smaller than that for a one-stage system of the same size and parameters.     

Probabilistic rebound Turing machines

This paper introduces a probabilistic rebound Turing machine (PRTM), and investigates the fundamental property of the machine. We first prove a sublogarithmic lower space bound on the space complexity of this model with bounded errors for recognizing specific languages. This lower bound strengthens a previous lower bound for conventional probabilistic Turing machines with bounded errors. We then show, by using our lower space bound and an idea in the proof of it, that

Full-size image

where £[PRTM(o(logn))] denotes the class of languages recognized by o(logn) space-bounded PRTMs with error probability less than . Furthermore, we show that there is an infinite space hierarchy for £[PRTM(o(logn))]. We finally show that £[PRTM(o(logn))] is not closed under concatenation, Kleene +, and length-preserving homomorphism. This paper answers two open problems in a previous paper.     

Operations planning for collect-and-place machines in PCB assembly

Collect-and-place machines represent one of the most popular types of placement machines in automated printed circuit board (PCB) assembly. For scheduling the operations of this type of machinery, a three-stage heuristic solution approach is presented. In the first stage, the feeders (component types) are assigned to locations in the magazine of the placement machine. In the second stage, based on the assignment of component feeders to magazine positions, the component placement sequence is determined. Apparently, for a collect-and-place machine, this problem is similar to the well-known vehicle-routing problem. Therefore, we adapt standard methods for vehicle-routing problems, namely savings heuristics introduced by Clark and Wright [Clark, G., & Wright, J. W. (1964). Scheduling vehicles from a central delivery depot to a number of delivery points. Operations Research Quarterly, 12, 568–581]. Finally, local search principles are applied in order to improve the feeder assignment and the component placement sequence obtained. Numerical experiments are performed in order to compare the performance of the various savings-based heuristics under different experimental settings.     

Using differentiated services to support Internet telephony

Internet telephony has been deemed as a promising candidate for the next generation telephone system. However, unstable voice quality is the main problem that prevents the Internet Telephone from competing with the traditional circuit switched telephone.

Current Internet supports only a best-effort service class, which does not provide any bandwidth or delay guarantee for the voice packets. During congestion, consecutive packets get lost or miss the deadlines, which results in severe degradation in voice quality. In this paper, we introduce the concept of using differentiated service model to solve the problem. First, we propose a class-based model to separate the voice streams from the best-effort traffic. Then we use a selective dropping model to further prevent consecutive packet losses to satisfy the (m, k) firm guarantee [9] requirement, and thereby enhance the voice quality in the Internet telephony services. The model is implemented using the ns simulator [18]. The performance of the proposed technique is evaluated through the simulator and the results justify the validity of using the model for Internet telephony.     

On the algebraic structure of combinatorial problems

We describe a general algebraic formulation for a wide range of combinatorial problems including

Full-size image

and In this formulation each problem instance is represented by a pair of relational structures, and the solutions to a given instance are homomorphisms between these relational structures. The corresponding decision problem consists of deciding whether or not any such homomorphisms exist. We then demonstrate that the complexity of solving this decision problem is determined in many cases by simple algebraic properties of the relational structures involved. This result is used to identify tractable subproblems of , and to provide a simple test to establish whether a given set of Boolean relations gives rise to one of these tractable subproblems.