Showing papers by "University of Twente published in 1999"

Aspect-Oriented Programming

Abstract: We have found many programming problems for which neither procedural nor object-oriented programming techniques are sufficient to clearly capture some of the important design decisions the program must implement. This forces the implementation of those design decisions to be scattered throughout the code, resulting in “tangled” code that is excessively difficult to develop and maintain. We present an analysis of why certain design decisions have been so difficult to clearly capture in actual code. We call the properties these decisions address aspects, and show that the reason they have been hard to capture is that they cross-cut the system's basic functionality. We present the basis for a new programming technique, called aspect-oriented programming, that makes it possible to clearly express programs involving such aspects, including appropriate isolation, composition and reuse of the aspect code. The discussion is rooted in systems we have built using aspect-oriented programming.

Principles and Methods of Development Research

Abstract: This chapter discusses the role of research in relation to educational design and development activities. The first part of the chapter focuses on the rationale and basic principles of development research by outlining motives for conducting formative research, analyzing definitions and aims of various types of development research, and discussing several of its key characteristics. The second part of the chapter deals with methods of development research, exploring some of its typical problems and dilemmas, and discussing several challenges for further action and reflection.

Field-Effect Flow Control for Microfabricated Fluidic Networks

Abstract: The magnitude and direction of the electro-osmotic flow (EOF) inside a microfabricated fluid channel can be controlled by a perpendicular electric field of 1.5 megavolts per centimeter generated by a voltage of only 50 volts. A microdevice called a "flowFET," with functionality comparable to that of a field-effect transistor (FET) in microelectronics, has been realized. Two flowFETs integrated with a channel junction have been used to generate opposite flows inside a single EOF-pumped channel, thus illustrating the potential of the flowFET as a controlling and switching element in microfluidic networks.

Transparent Nanocomposites with Ultrathin, Electrospun Nylon-4,6 Fiber Reinforcement

Abstract: Transparent sheets of epoxy resin reinforced with nylon-4,6 nanofibers are described. The 30-200 nm diameter fibers, obtained by electrospinning from formic acid solutions, are reported to provide significant improvement in strength and stiffness to the epoxy film. The Figure is a scanning electron microscopy image of the electrospun nanofibers.

Dynamics and control of a class of underactuated mechanical systems

Abstract: This paper presents a theoretical framework for the dynamics and control of underactuated mechanical systems, defined as systems with fewer inputs than degrees of freedom. Control system formulation of underactuated mechanical systems is addressed and a class of underactuated systems characterized by nonintegrable dynamics relations is identified. Controllability and stabilizability results are derived for this class of underactuated systems. Examples are included to illustrate the results; these examples are of underactuated mechanical systems that are not linearly controllable or smoothly stabilizable.

A recursive technique for tracking control of nonholonomic systems in chained form

Abstract: The authors address the tracking problem for a class of nonholonomic chained form control systems. A recursive technique is proposed which appears to be an extension of the currently popular integrator backstepping idea to the tracking of nonholonomic control systems. Conditions are given under which the problems of semiglobal tracking and global path-following are solved for a nonholonomic system in chained form and its dynamic extension. Results on local exponential tracking are also obtained. Two physical examples of an articulated vehicle and a knife edge are provided to demonstrate the effectiveness of our algorithm through simulations.

Complete asymmetric chirality in a hydrogen-bonded assembly

Abstract: Chirality at the supramolecular level involves the non-symmetric arrangement of molecular components in a non-covalent assembly1,2. Supramolecular chirality is abundant in biology, for example in the DNA double helix3, the triple helix of collagen4 and the α-helical coiled coil of myosin5. These structures are stabilized by inter-strand hydrogen bonds, and their handedness is determined by the configuration of chiral centres in the nucleotide or peptide backbone. Synthetic hydrogen-bonded assemblies have been reported that display supramolecular chirality in solution6,7,8 or in the solid state9,10,11,12. Complete asymmetric induction of supramolecular chirality—the formation of assemblies of a single handedness—has been widely studied in polymeric superstructures13,14. It has so far been achieved in inorganic metal-coordinated systems15,16,17, but not in organic hydrogen-bonded assemblies18,19,20. Here we describe the diastereoselective assembly of enantio-pure calix[4]arene dimelamines and 5,5-diethylbarbituric acid (DEB) into chiral hydrogen-bonded structures of one handedness. The system displays complete enantioselective self-resolution: the mixing of homomeric assemblies (composed of homochiral units) with opposite handedness does not lead to the formation of heteromeric assemblies. The non-covalent character of the chiral assemblies, the structural simplicity of the constituent building blocks and the ability to control the assembly process by means of peripheral chiral centres makes this system promising for the development of a wide range of homochiral supramolecular materials or enantioselective catalysts.

A Taxonomy of Systems of Corporate Governance

Abstract: This paper argues that debate on corporate governance in an international context is hampered by the lack of a coherent framework. A taxonomy of systems of corporate governance is proposed as a remedy. The taxonomy is based upon eight characteristics: the prevailing concept of the firm, the board system, the salient stakeholders able to exert influence on managerial decision-making, the importance of stock markets in the national economy, the presence or absence of an external market for corporate control, the ownership structure, the extent to which executive compensation is dependent on corporate performance, and the time horizon of economic relationships. Four types of systems of corporate governance emerge: the Anglo-Saxon systems, the Germanic systems, the Latin systems and the Japanese system.

Remote opto-chemical sensing with extreme sensitivity: design, fabrication and performance of a pigtailed integrated optical phase-modulated Mach-Zehnder interferometer system

Abstract: This paper describes the design, fabrication and testing of a pigtailed integrated optical (IO) phase-modulated Mach–Zehnder interferometer (MZI) including both the optical chip and the electronics. The optical chip is realised in SiON technology. The IO components (the sensing function, the straight waveguiding channels, the phase modulator, the polariser, the splitter, the combiner and the fibre-to-chip connection unit) are individually optimised and interconnected by using transversal adiabatic tapers. To obtain a high waveguide evanescent field sensitivity, the sensor is designed for — but not limited to — a wavelength of 632.8 nm. The integrated MZI is actively phase-modulated by virtue of the electro-optic effect of the incorporated material zinc oxide (ZnO). The electro-optical voltage–length product Vπ is 16 V cm at frequencies above 10 Hz. The polariser is a distributed function, that effectively filters TM-polarised light (TE/TM polarising ratio >30 dB). The fibre pigtail, affording remote optical sensing, is based on a cheap, easy-to-use fibre-to-chip connection with a typical coupling efficiency of 50%, while the device throughput (“insertion loss”) is −20 dB. The drive- and demodulation electronics enable a phase resolution 5×10−5×2π, corresponding to a refractive index resolution of 2×10−8. The sensing system as has been realised up to now shows a phase resolution of 1×10−4×2π, its long-term stability (hours) being ≤3×10−4×2π. This corresponds to a refractive index resolution of 5×10−8, and a long-term stability of 10−7.

Prototyping to Reach Product Quality

Abstract: This chapter provides a framework for product quality consisting of the following three criteria: validity, practicality and effectiveness, and provides insight into the applicability of the framework in various domains of educational product development.

A multisensory integration model of human stance control.

Abstract: A model is presented to study and quantify the contribution of all available sensory information to human standing based on optimal estimation theory. In the model, delayed sensory information is integrated in such a way that a best estimate of body orientation is obtained. The model approach agrees with the present theory of the goal of human balance control. The model is not based on purely inverted pendulum body dynamics, but rather on a three-link segment model of a standing human on a movable support base. In addition, the model is non-linear and explicitly addresses the problem of multisensory integration and neural time delays. A predictive element is included in the controller to compensate for time delays, necessary to maintain erect body orientation. Model results of sensory perturbations on total body sway closely resemble experimental results. Despite internal and external perturbations, the controller is able to stabilise the model of an inherently unstable standing human with neural time delays of 100 ms. It is concluded, that the model is capable of studying and quantifying multisensory integration in human stance control. We aim to apply the model in (1) the design and development of prostheses and orthoses and (2) the diagnosis of neurological balance disorders.

Testing Concurrent Systems: A Formal Approach

Abstract: This paper discusses the use of formal methods in testing of concurrent systems. It is argued that formal methods and testing can be mutually profitable and useful. A framework for testing based on formal specifications is presented. This framework is elaborated for labelled transition systems, providing formal definitions of conformance, test execution and test derivation. A test derivation algorithm is given and its tool implementation is briefly discussed.

Governmental policies and organisational change in higher education

Abstract: In this article a theoretical framework designed for a comparative research project on organisational change in higher education is presented. In the project the main focus is on how organisational change in universities and colleges is affected by governmental policies and programmes. The framework is based upon two major theoretical perspectives, resource dependency and neo-institutionalism. It is argued that for examining changes in universities and colleges both the relationship between these organisations and the government, as well as their internal dynamics are of importance. In addition to integrating the two main theoretical perspectives in the project also attempts to do justice to the complexities of the concept of (governmental) steering by attempting to incorporate general models on the role of the state. The article suggests that these models offer a meaningful insight into how and why governmental steering approaches have been changed over time.

Approximative Symbolic Model Checking of Continuous-Time Markov Chains

Abstract: This paper presents a symbolic model checking algorithm for continuous-time Markov chains for an extension of the continuous stochastic logic CSL of Aziz et al [1]. The considered logic contains a time-bounded until-operator and a novel operator to express steadystate probabilities. We show that the model checking problem for this logic reduces to a system of linear equations (for unbounded until and the steady state-operator) and a Volterra integral equation system for timebounded until. We propose a symbolic approximate method for solving the integrals using MTDDs (multi-terminal decision diagrams), a generalisation of MTBDDs. These new structures are suitable for numerical integration using quadrature formulas based on equally-spaced abscissas, like trapezoidal, Simpson and Romberg integration schemes.

Reducing MOSFET 1/f noise and power consumption by "Switched biasing"

Abstract: "Switched Biasing" is proposed as a new circuit technique that exploits an intriguing physical effect: cycling a MOS transistor between strong inversion and accumulation reduces its intrinsic 1/f noise. The technique is implemented in a 0.8µm CMOS sawtooth oscillator by periodically off-switching of the bias currents during time intervals that they are not contributing to the circuit operation. Measurements show a reduction of the 1/f noise induced phase noise by more than 8 dB, while the power consumption is reduced by more than 30% as well.

Business case Océ: Reverse logistic network re-design for copiers

Abstract: The introduction of extended producer responsibility forces Original Equipment Manufacturers to set up a logistic network for take back, processing and recovery of discarded products. In this paper, we discuss a business case study carried out at Oce, a copier firm in Venlo (NL). It concerns the installment of remanufacturing processes. There is a choice from two locations in Venlo (NL) and one in Prague (Czech Republic), where assignments are subjected to managerial constraints. The study is meant to verify whether the strategic decision of Oce to move remanufacturing activities to the Czech Republic is also economically feasible. We limit ourselves to an optimisation of the HV02-machine network. We follow our general approach, in which we first determine how return products are processed (recovery strategy) and subsequently optimise the reverse logistic network design. We optimise on total operational costs over all possibilities and also compare three pregiven managerial solutions (=network designs) with a Mixed Integer Linear Programming model. Differences in economic costs appear to be very small, hence installing recovery activities in Prague for the HV02-machine must be well motivated from a strategic point of view. Moreover, we argue that besides cost minimisation, Oce should include performance indicators, such as JIT, reliability, in logistic optimisation to support its quality oriented business strategy. In addition, we discuss aspects regarding specific modelling elements in this case situation, the definition of cost functions, the possibility of optimising the forward and reverse logistic network and the use of LP- versus MILP-models in this kind of situations.

A plastic micropump constructed with conventional techniques and materials

Abstract: A plastic micropump which can be produced using conventional production techniques and materials is presented. By applying well-known techniques and materials, economic fabrication of micropumps for various applications is feasible even at low production volumes. The micropump is capable of pumping both liquid and gas at a considerable high pump rate and is self-priming, which means that it can start pumping gas in a dry state and automatically fills with liquid. Pump rates, at actuation frequencies between 2 and 500 Hz, were around 2 ml/min for water and up to 50 ml/min for air. A differential pressure of 1.25×104 Pa (125 cm water column) was reached. Basically, the micropump consists of two parts, a flat valve assembly with two passive membrane valves and an actuator placed on top. The valves were made by sandwiching a punched thin polymer film between two plastic valve parts containing the valve seats. The latter parts are made by reactive injection molding of an epoxy resin. Two types of actuators have been applied to drive the pump; an electromagnetic actuator consisting of a magnet placed in a coil and secondly a disk. The first actuator, when combined with a flexible polymer pump membrane, showed a very large pump rate for gas, up to 40 ml/min at the resonant frequency of the actuator system. A disadvantage of the electromagnetic actuator was the relatively large volume occupied by the coil giving the micropump final dimensions of 10×10×8 mm3. Application of the piezoelectric actuator reduced these dimensions down to 12×12×2 mm3 with comparable performance.

R&D performance measurement: more than choosing a set of metrics

Abstract: In this article the results are presented of an empirical study focusing on the effectiveness of R&D performance measurement practices in the Netherlands. First, a theoretical examination of the subject ‘R&D performance measurement’ is given within the context of performance control. A distinction is made between feedback and feed forward control and between the R&D function and the R&D organisation. Subsequently, a description is given of the current practices of R&D performance measurement in terms of measurement purposes, metrics, measurement techniques, norms setting, etc. Furthermore, the influence of contingencies on measurement system design is explored. The data for this research were gathered by means of a survey and nine in‐depth interviews. Generally, managers evaluate their measurement systems as being quite valuable, having a positive impact on performance. The findings described in this paper can be used as references for managers to benchmark their R&D measurement procedures: in this respect we distinguish highly and hardly effective measurement procedures. The most important characteristic that seems to distinguish the most effective systems from the less effective ones is customer focus.

Principles and practice of the laser-Doppler perfusion technique

Abstract: This paper reviews the development and use of laser-Doppler perfusion monitors and imagers over the past two decades. The enormous interest in microvascular blood perfusion coupled with the ease of use of the technique has led to 1500+ publications citing its use. However, useful results can only be achieved with an understanding of the basic principles of the instrumentation and its application in the various clinical disciplines. The basic theoretical background is explored and definitions of blood perfusion and laser-Doppler perfusion are established. The calibration method is then described together with potential routes to standardisation. A guide to the limitations in application of the technique gives the user a clear indication of what can be achieved in new studies as well as possible inadequacy in some published investigations.

Sugar-Integrated Gelators of Organic Solvents—Their Remarkable Diversity in Gelation Ability and Aggregate Structure

Abstract: A drastic change in the solubility and gelation properties of 1-O-methyl-4,6-O-benzylidene derivatives of monosaccharides (see figure) results from the change in the configuration of only one carbon atom.