Showing papers by "University of Twente published in 1992"

Micro resonant force gauges

Abstract: A review of micro resonant force gauges is presented. A theoretical description is given of gauges operating in a flexural mode of vibration, including a discussion of non-linear effects. Gauge factor and quality factor are defined and their relevance is discussed. Performance issues such as sensitivity, stability and resolution are addressed. Design aspects, including the means for excitation and detection of the vibration, and examples of silicon microfabrication technologies are described.

Reduced light-scattering properties for mixtures of spherical particles: a simple approximation derived from Mie calculations

Abstract: The reduced scattering cross section per unit of volume Σs′ ≡ Σs(1 − g) is an important parameter to describe light propagation in media with scattering and absorption. Mie calculations of the asymmetry factory g for nonabsorbing spheres and Qsca, the ratio of the scattering cross section Σs and the particle cross section, show that Qsca(1 − g) = 3.28x0.37(m − 1)2.09 is true to within a few percent, when the Mie parameters for relative refractive index m and size x are in the ranges of 1 < m ≤ 1.1 and 5 < x < 50, respectively. A ratio of reduced scattering cross sections for radiation at two wavelengths is also independent of the size within the range mentioned, even for mixtures of different size spheres. The results seem promising for biomedical applications.

Training for Reflective Expertise: A Four-Component Instructional Design Model for Complex Cognitive Skills.

Abstract: This article presents a four-component instructional design model for the training of complex cognitive skills. In the analysis phase, the skill is decomposed into a set of recurrent skills that remain consistent over problem situations and a set of nonrecurrent skills that require variable performance over situations. In the design phase, two components relate to the design of practice; they pertain to the conditions under which practice leads either to rule automation during the performance of recurrent skills or to schema acquisition during the performance of nonrecurrent skills. The other two components relate to the design of information presentation; they pertain to the presentation of information that supports the performance of either recurrent or nonrecurrent skills. The basic prediction of the model is that its application leads to “reflective expertise” and increased performance on transfer tasks. Applications of the model that support this prediction are briefly discussed for the training of fault management in process industry, computer programming, and statistical analysis.

Strategies for computer-based programming instruction: program completion vs. program generation

Abstract: Two instructional strategies were implemented in a two-and-a-half hour computer-based training program that was designed to teach elementary turtle graphics programming techniques to novice undergraduate students (N = 40). Learning activities that either emphasized the completion of existing programs or the generation of new programs were studied for the two strategies. In the completion group, the information needed to perform the program completion tasks appeared to be largely available in the to-be-completed programs; in the generation group, students frequently had to search for useful examples while they were performing their program generation tasks. It is hypothesized that during practice, the direct availability of examples in the form of incomplete computer programs facilitates the acquisition of programming language templates, especially because students cannot complete a program without carefully studying it so that “mindful abstraction” is explicitly provoked. Data in this study on learning ou...

The Shapley value for cooperative games under precedence constraints

Abstract: Cooperative games are considered where only those coalitions of players are feasible that respect a given precedence structure on the set of players. Strengthening the classical symmetry axiom, we obtain three axioms that give rise to a unique Shapley value in this model. The Shapley value is seen to reflect the expected marginal contribution of a player to a feasible random coalition, which allows us to evaluate the Shapley value nondeterministically. We show that every exact algorithm for the Shapley value requires an exponential number of operations already in the classical case and that even restriction to simple games is #P-hard in general. Furthermore, we outline how the multi-choice cooperative games of Hsiao and Raghavan can be treated in our context, which leads to a Shapley value that does not depend on pre-assigned weights. Finally, the relationship between the Shapley value and the permission value of Gilles, Owen and van den Brink is discussed. Both refer to formally similar models of cooperative games but reflect complementary interpretations of the precedence constraints and thus give rise to fundamentally different solution concepts.

An Object-Oriented Language-Database Integration Model: The Composition-Filters Approach

Abstract: This paper introduces a new model, based on so-called object-composition filters, that uniformly integrates database-like features into an object-oriented language. The focus is on providing persistent dynamic data structures, data sharing, transactions, multiple views and associative access, integrated with the object-oriented paradigm. The main contribution is that the database-like features are part of this new object-oriented model, and therefore, are uniformly integrated with object-oriented features such as data abstraction, encapsulation, message passing and inheritance. This approach eliminates the problems associated with existing systems such as lack of reusability and extensibility for database operations, the violation of encapsulation, the need to define specific types such as sets, and the incapability to support multiple views. The model is illustrated through the object-oriented language Sina.

The Shapley value for cooperative games under precedence constraints

Abstract: Cooperative games are considered where only those coalitions of players are feasible that respect a given precedence structure on the set of players. Strengthening the classical symmetry axiom, we obtain three axioms that give rise to a unique Shapley value in this model. The Shapley value is seen to reflect the expected marginal contribution of a player to a feasible random coalition, which allows us to evaluate the Shapley value nondeterministically. We show that every exact algorithm for the Shapley value requires an exponential number of operations already in the classical case and that even restriction to simple games is #P-hard in general. Furthermore, we outline how the multi-choice cooperative games of Hsiao and Raghavan can be treated in our context, which leads to a Shapley value that does not depend on pre-assigned weights. Finally, the relationship between the Shapley value and the permission value of Gilles, Owen and van den Brink is discussed. Both refer to formally similar models of cooperative games but reflect complementary interpretations of the precedence constraints and thus give rise to fundamentally different solution concepts.

An intrinsic Hamiltonian formulation of network dynamics: Non-standard Poisson structures and gyrators

Abstract: The aim of this paper is to provide an intrinsic Hamiltonian formulation of the equations of motion of network models of non-resistive physical systems. A recently developed extension of the classical Hamiltonian equations of motion considers systems with state space given by Poisson manifolds endowed with degenerate Poisson structures, examples of which naturally appear in the reduction of systems with symmetry. The link with network representations of non-resistive physical systems is established using the generalized bond graph formalism which has the essential feature of symmetrizing all the energetic network elements into a single class and introducing a coupling unit gyrator. The relation between the Hamiltonian formalism and network dynamics is then investigated through the representation of the invariants of the system, either captured in the degeneracy of the Poisson structure or in the topological constraints at the ports of the gyrative type network structure. This provides a Hamiltonian formulation of dimension equal to the order of the physical system, in particular, for odd dimensional systems. A striking example is the direct Hamiltonian formulation of electrical LC networks.

Synthesis of ceramic membranes

Abstract: Non-supported γ-alumina films are prepared from a boehmite colloidal suspension. After calcination at 600°C, the microstructure is characterized by a mean pore diameter of 3 nm, a porosity of 50% and a tortuosity of 5.5. The structure is formed by card packed, plate-shaped particles, giving rise to slit-shaped pores. Supported γ-alumina films, made by a slipcasting process using the same boehmite precursor, have a similar structure as the non-supported films. The slipcasting process is very sensitive to support characteristics and frequently yields defect films. Polyvinylalcohol (PVA) (molecular weight 72000 g mol−1) is added to the boehmite precursor (0.25 gg−1 film) to improve this process. This addition results in a less critical and better controllable drying and calcining procedure. The addition of PVA is necessary to slipcast defect free γ-alumina films on supports with pore diameters of 0.4 μm or smaller and on multi-layer supports. It has no significant effect on the resultant microstructure of the γ-alumina film, provided all PVA is removed by appropriate thermal treatment. The slipcasting rate is slower, resulting in thinner films of 3–5 μm at identical slipcasting times.

Nitrocalix [4]arenes as Molecules for Second-Order Nonlinear Optics

Abstract: The frequency-doubling of 820 nm laser light is o­ne of the properties of a series of nitrocalix-[4]arenes making them suitable, in principle, for the construction of a blue laser. Derivative 1 is the most promising, since it displays the greatest hyperpolarizability and the largest dipole moment and is stable as a film in a polymer matrix for long periods.

Relations between in vitro cytotoxicity and crosslinked dermal sheep collagens

Abstract: Collagen-based biomaterials have found various applications in the biomedical field. However, collagen-based biomaterials may induce cytotoxic effects. This study evaluated possible cytotoxic effects of (crosslinked) dermal sheep collagen (DSC) using a 7-d-methylcellulose cell culture with human skin fibroblasts. Noncrosslinked DSC (NDSC), hexamethylene-diisocyanate-crosslinked DSC (HDSC), and glutaraldehyde-crosslinked DSC (GDSC), their extracts (1 x 10 d to 4 x 10 d extracts), or the corresponding extracted DSC samples were tested. Cell growth was evaluated by cell counting, while cell morphology was assessed by light microscopy and transmission-electron microscopy. Both GDSC and, to a lesser extent, HDSC, induced cytotoxicity, observed as inhibited cell growth and deviant cell morphology. The deviant morphology consisted of extensive accumulations of lipid, reduction in the amount and dilatation of rough endoplasmatic reticulum, increased inclusions of cell remnants, and relatively rounded cell membranes. With HDSC, both primary cytotoxicity, due to extractable products from the material, and secondary cytotoxicity, possibly due to a release of cytotoxic products resulting from enzymatic cell-biomaterial interactions, could be discriminated. With GDSC, however, no clear distinction between primary and secondary cytotoxicity could be made. With NDSC, only primary cytotoxicity, measured as low inhibition of cell proliferation, but without deviant morphology, was observed. These remarkable differences in cytotoxicity are discussed in relation to residual agents and specific crosslinks present in DSCs as a consequence of processing and the crosslinking agents used. The residual agents and the specific crosslinks give rise to differences in direct release of products and in sensitivity to hydrolysis and enzymatic breakdown.

Surface and grain boundary analysis of doped zirconia ceramics studied by AES and XPS

Abstract: The surface- and grain boundary composition of Y, Ce and Ti doped zirconia were studied by X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy/Scanning Auger Microscopy. The grain boundaries and free surfaces showed the same enrichment levels. After heat treatment ≥ 1000 ‡C all yttria doped samples showed yttrium enrichment. In the ZrO2-Y2O3 system the yttrium enrichment did not depend on the bulk concentration and amounted 30–34 mol% YO1.5 in all cases. As a consequence the segregation factor increases with decreasing solute concentration in the bulk. The thickness of the segregation layer was about 2–4 nm. In the ternary Y doped systems yttrium is the main segregant. In ceria-doped tetragonal zirconia polycrystals (Ce-TZP) systems significant segregation of cerium starts atT≥1300‡C and is mainly attributed to Ce3+. In Y,Ti-TZP systems also strong segregation of Ti4+ occurs. The absolute value of the increase of the surface concentration in fine grained material is smaller than in coarse grained material. This is mainly due to depletion of the bulk.

CMOS low-voltage operational amplifiers with constant-G/sub m/ rail-to-rail input stage

Abstract: Two 3-V CMOS low-voltage operational amplifiers (op-amps) with constant transconductance (g/sub m/) rail-to-rail input stages are presented. The constant g/sub m/ ensures a constant unity-gain frequency within the whole common-mode input range. Two new methods to control the g/sub m/ of the input stage are introduced. The op-amps contain the same class-AB output stage with rail-to-rail output swing. The common-mode input voltage swing extends the positive supply rail by 600 mV and the negative supply rail by 200 mV. The output voltage can reach the supply rails within 130 mV. The output current of the op-amps was limited to +or-2 mA, voltage gain was 85 dB, and the unity-gain frequency was 165 kHz. The op-amps were integrated in a semicustom CMOS process with transistor lengths of 10 mu m. >

Laser Doppler velocimeter based on the self-mixing effect in a fiber-coupled semiconductor laser: theory

Abstract: A laser Doppler velocimeter that consists of a semiconductor laser coupled to a fiber and that uses the self-mixing effect is presented. The velocimeter can be used for solids and fluids. A theoretical model is developed to describe the self-mixing signals as a function of the amount of feedback into the laser and the distance from the laser to the moving object. Good agreement is found between this theory and measurements.

Instructional Models in Computer-Based Learning Environments

Abstract: For over thirty years, there has been a vast research interest in computer-based learning environments However, the last decade is characterized by rapid developments in the field On the surface level, these changes largely pertain to the constitution of the research community, in which more and more cognitive scientists and Artificial Intelligence (AI) specialists are operating, and to the type of learning environments which are developed The term Computer Assisted Instruction (CAI) quickly became old-fashioned and is replaced by the term ICAI, where the “I” denotes the assumed intelligence built in the learning environment; for example, its knowledge of the domain to be taught, its knowledge of the learner’s cognitive processes, its knowledge of instruction and communication, and — last but not least — its inference capabilities to use one or more of these knowledge bases in order to control the learning process A whole new family of computer-based learning environments appeared under the label ICAI, including microworlds, Intelligent Tutoring Systems (ITS), (intelligent) hypermedia, adaptive help systems, and so further

Order acceptance strategies in a production-to-order environment with setup times and due-dates

Abstract: SUMMARY A production situation is considered in which different items are produced on one machine. Setup times are incurred between the production of orders of different items. Production is driven by customer orders; each order concerns a batch of one product type and is furthermore completely characterized by its batchsize and (customer determined) due-date. Acceptance of orders may be refused if these orders are likely to cause late deliveries. The problem is to determine good acceptance strategies which naturally raises the question on what information such acceptance decisions have to be based. Three basic approaches are explored in this paper. In the monolithic approach, the acceptance decision is based on detailed information on a current production schedule for all formerly accepted orders. In the hierarchic approach, the acceptance strategy is based on global capacity load profiles only, while detailed scheduling of accepted orders takes place at a lower level (possibly later in time). In the myo...