Showing papers by "University of Twente published in 2005"

A Tutorial on the Cross-Entropy Method

Abstract: The cross-entropy (CE) method is a new generic approach to combinatorial and multi-extremal optimization and rare event simulation. The purpose of this tutorial is to give a gentle introduction to the CE method. We present the CE methodology, the basic algorithm and its modifications, and discuss applications in combinatorial optimization and machine learning.

Electrowetting: from basics to applications

Abstract: Electrowetting has become one of the most widely used tools for manipulating tiny amounts of liquids on surfaces. Applications range from 'lab-on-a-chip' devices to adjustable lenses and new kinds of electronic displays. In the present article, we review the recent progress in this rapidly growing field including both fundamental and applied aspects. We compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high. We discuss in detail the origin of the electrostatic forces that induce both contact angle reduction and the motion of entire droplets. We examine the limitations of the electrowetting equation and present a variety of recent extensions to the theory that account for distortions of the liquid surface due to local electric fields, for the finite penetration depth of electric fields into the liquid, as well as for finite conductivity effects in the presence of AC voltage. The most prominent failure of the electrowetting equation, namely the saturation of the contact angle at high voltage, is discussed in a separate section. Recent work in this direction indicates that a variety of distinct physical effects?rather than a unique one?are responsible for the saturation phenomenon, depending on experimental details. In the presence of suitable electrode patterns or topographic structures on the substrate surface, variations of the contact angle can give rise not only to continuous changes of the droplet shape, but also to discontinuous morphological transitions between distinct liquid morphologies. The dynamics of electrowetting are discussed briefly. Finally, we give an overview of recent work aimed at commercial applications, in particular in the fields of adjustable lenses, display technology, fibre optics, and biotechnology-related microfluidic devices.

Ammonia sensors and their applications - a review

Abstract: Many scientific papers have been written concerning gas sensors for different sensor applications using several sensing principles. This review focuses on sensors and sensor systems for gaseous ammonia. Apart from its natural origin, there are many sources of ammonia, like the chemical industry or intensive life-stock. The survey that we present here treats different application areas for ammonia sensors or measurement systems and different techniques available for making selective ammonia sensing devices. When very low concentrations are to be measured, e.g. less than 2 ppb for environmental monitoring and 50 ppb for diagnostic breath analysis, solid-state ammonia sensors are not sensitive enough. In addition, they lack the required selectivity to other gasses that are often available in much higher concentrations. Optical methods that make use of lasers are often expensive and large. Indirect measurement principles have been described in literature that seems very suited as ammonia sensing devices. Such systems are suited for miniaturization and integration to make them suitable for measuring in the small gas volumes that are normally available in medical applications like diagnostic breath analysis equipment.

Career success in a boundaryless career world.

Abstract: This paper compares contemporary career theory with the theory applied in recent career success research. The research makes inconsistent use of career theory, and in particular neglects the interdependence of the objective and subjective careers, and boundaryless career issues of inter-organizational mobility and extra-organizational support. The paper offers new guidelines for bringing about a rapprochement between career theory and career success research. These guidelines cover adequacy of research designs, further dimensions of career success, broader peer group comparisons, deeper investigation of the subjectively driven person, and seeing new connections between boundaryless career theory and career success research.

Requirements engineering paper classification and evaluation criteria: a proposal and a discussion

Abstract: In recent years, members of the steering committee of the IEEE Requirements Engineering (RE) Conference have discussed paper classification and evaluation criteria for RE papers. The immediate trigger for this discussion was our concern about differences in opinion that sometimes arise in program committees about the criteria to be used in evaluating papers. If program committee members do not all use the same criteria, or if they use criteria different from those used by authors, then papers might be rejected or accepted for the wrong reasons. Surely not all papers should be evaluated according to the same criteria. Some papers describe new techniques but do not report on empirical research; others describe new conceptual frameworks for investigating certain RE problems; others report on industrial experience with existing RE techniques. Other kinds of papers can also be easily recognized. All of these types of papers should be evaluated according to different criteria. But we are far from a consensus about what classes of paper we should distinguish, and what the criteria are for each of these classes.

Biomass gasification in near- and super-critical water: Status and prospects

Abstract: The current status of biomass gasification in near- and supercritical water (SCWG) is reviewed. There are two approaches to biomass gasification in supercritical water. The first: low-temperature catalytic gasification, employs reaction temperature ranging from 350 to 600 °C, and gasifies the feedstock with the aid of metal catalysts. The second: high-temperature supercritical water gasification, employs reaction temperatures ranging from 500 to 750 °C, without catalyst or with non-metallic catalysts. Reviews are made on reaction mechanism, catalyst, and experimental results for these two approaches. Engineering technologies for SCWG gasification, and an example of process analysis are also introduced. Finally, the authors’ prognostications on the future prospects of this technology are offered.

Measuring orientation of human body segments using miniature gyroscopes and accelerometers

Abstract: In the medical field, there is a need for small ambulatory sensor systems for measuring the kinematics of body segments. Current methods for ambulatory measurement of body orientation have limited accuracy when the body moves. The aim of the paper was to develop and validate a method for accurate measurement of the orientation of human body segments using an inertial measurement unit (IMU). An IMU containing three single-axis accelerometers and three single-axis micromachined gyroscopes was assembled in a rectangular box, sized 20×20×30 mm. The presented orientation estimation algorithm continuously corrected orientation estimates obtained by mathematical integration of the 3D angular velocity measured using the gyroscopes. The correction was performed using an inclination estimate continuously obtained using the signal of the 3D accelerometer. This reduces the integration drift that originates from errors in the angular velocity signal. In addition, the gyroscope offset was continuously recalibrated. The method was realised using a Kalman filter that took into account the spectra of the signals involved as well as a fluctuating gyroscope offset. The method was tested for movements of the pelvis, trunk and forearm. Although the problem of integration drift around the global vertical continuously increased in the order of 0.5°s −1, the inclination estimate was accurate within 3° RMS. It was shown that the gyroscope offset could be estimated continuously during a trial. Using an initial offset error of 1 rads −1, after 2 min the offset error was roughly 5% of the original offset error. Using the Kalman filter described, an accurate and robust system for ambulatory motion recording can be realised.

Nanofluidics: what is it and what can we expect from it?

Abstract: Starting from the background of nanofluidics in other disciplines, this paper describes the present state of research in this field and discusses possible directions of development. Emphasis is put on the very diverse background of nanofluidics in biology, chemistry, physics and engineering and the valuable knowledge available in these disciplines. First, the forces that play a role on the nanoscale are discussed and then a summary is given of some different theoretical treatments. Subsequently, an overview is given of the different phenomena occurring on the nanoscale and their present applications. Finally, some possible future applications are discussed.

A model for large amplitude oscillations of coated bubbles accounting for buckling and rupture

Abstract: We present a model applicable to ultrasound contrast agent bubbles that takes into account the physical properties of a lipid monolayer coating on a gas microbubble Three parameters describe the properties of the shell: a buckling radius, the compressibility of the shell, and a break-up shell tension The model presents an original non-linear behavior at large amplitude oscillations, termed compression-only, induced by the buckling of the lipid monolayer This prediction is validated by experimental recordings with the high-speed camera Brandaris 128, operated at several millions of frames per second The effect of aging, or the resultant of repeated acoustic pressure pulses on bubbles, is predicted by the model It corrects a flaw in the shell elasticity term previously used in the dynamical equation for coated bubbles The break-up is modeled by a critical shell tension above which gas is directly exposed to water

Compensation of magnetic disturbances improves inertial and magnetic sensing of human body segment orientation

Abstract: This paper describes a complementary Kalman filter design to estimate orientation of human body segments by fusing gyroscope, accelerometer, and magnetometer signals from miniature sensors. Ferromagnetic materials or other magnetic fields near the sensor module disturb the local earth magnetic field and, therefore, the orientation estimation, which impedes many (ambulatory) applications. In the filter, the gyroscope bias error, orientation error, and magnetic disturbance error are estimated. The filter was tested under quasi-static and dynamic conditions with ferromagnetic materials close to the sensor module. The quasi-static experiments implied static positions and rotations around the three axes. In the dynamic experiments, three-dimensional rotations were performed near a metal tool case. The orientation estimated by the filter was compared with the orientation obtained with an optical reference system Vicon. Results show accurate and drift-free orientation estimates. The compensation results in a significant difference (p<0.01) between the orientation estimates with compensation of magnetic disturbances in comparison to no compensation or only gyroscopes. The average static error was 1.4/spl deg/ (standard deviation 0.4) in the magnetically disturbed experiments. The dynamic error was 2.6/spl deg/ root means square.

Lattice-Boltzmann simulations of low-Reynolds-number flow past mono- and bidisperse arrays of spheres: results for the permeability and drag force

Abstract: We report on lattice-Boltzmann simulations of slow fluid flow past mono- and bidisperse random arrays of spheres. We have measured the drag force on the spheres for a range of diameter ratios, mass fractions and packing fractions; in total, we studied 58 different parameter sets. Our simulation data for the permeability agrees well with previous simulation results and the experimental findings. On the basis of our data for the individual drag force, we have formulated new drag force relations for both monodisperse and polydisperse systems, based on the Carman?Kozeny equations; the average deviation of our binary simulation data with the new relation is less than 5%. We expect that these new relations will significantly improve the numerical modelling of gas?solid systems with polydisperse particles, in particular with respect to mixing and segregation phenomena. For binary systems with large diameter ratios (1:4), the individual drag force on a particle, as calculated from our relations, can differ by up to a factor of five compared with predictions presently favoured in chemical engineering.

Analog circuits in ultra-deep-submicron CMOS

Abstract: Modern and future ultra-deep-submicron (UDSM) technologies introduce several new problems in analog design. Nonlinear output conductance in combination with reduced voltage gain pose limits in linearity of (feedback) circuits. Gate-leakage mismatch exceeds conventional matching tolerances. Increasing area does not improve matching any more, except if higher power consumption is accepted or if active cancellation techniques are used. Another issue is the drop in supply voltages. Operating critical parts at higher supply voltages by exploiting combinations of thin- and thick-oxide transistors can solve this problem. Composite transistors are presented to solve this problem in a practical way. Practical rules of thumb based on measurements are derived for the above phenomena.

Water saving through international trade of agricultural products

Abstract: Many nations save domestic water resources by importing water-intensive products and exporting commodities that are less water intensive. National water saving through the import of a product can imply saving water at a global level if the flow is from sites with high to sites with low water productivity. The paper analyses the consequences of international virtual water flows on the global and national water budgets. The assessment shows that the total amount of water that would have been required in the importing countries if all imported agricultural products would have been produced domestically is 1605 Gm3/yr. These products are however being produced with only 1253 Gm3/yr in the exporting countries, saving global water resources by 352 Gm3/yr. This saving is 28 per cent of the international virtual water flows related to the trade of agricultural products and 6 per cent of the global water use in agriculture. National policy makers are however not interested in global water savings but in the status of national water resources. Egypt imports wheat and in doing so saves 3.6 Gm3/yr of its national water resources. Water use for producing export commodities can be beneficial, as for instance in Cote d'Ivoire, Ghana and Brazil, where the use of green water resources (mainly through rain-fed agriculture) for the production of stimulant crops for export has a positive economic impact on the national economy. However, export of 28 Gm3/yr of national water from Thailand related to rice export is at the cost of additional pressure on its blue water resources. Importing a product which has a relatively high ratio of green to blue virtual water content saves global blue water resources that generally have a higher opportunity cost than green water.

Practical biometric authentication with template protection

Abstract: In this paper we show the feasibility of template protecting biometric authentication systems In particular, we apply template protection schemes to fingerprint data Therefore we first make a fixed length representation of the fingerprint data by applying Gabor filtering Next we introduce the reliable components scheme In order to make a binary representation of the fingerprint images we extract and then quantize during the enrollment phase the reliable components with the highest signal to noise ratio Finally, error correction coding is applied to the binary representation It is shown that the scheme achieves an EER of approximately 42% with secret length of 40 bits in experiments

Morphological Muscle and joint parameters for musculoskeletal modelling of the lower extremity

Abstract: Background: To assist in the treatment of gait disorders, an inverse and forward 3D musculoskeletal model of the lower extremity will be useful that allows to evaluate if–then scenarios. Currently available anatomical datasets do not comprise sufficiently accurate and complete information to construct such a model. The aim of this paper is to present a complete and consistent anatomical dataset, containing the orientations of joints (hip, knee, ankle and subtalar joints), muscle parameters (optimum length, physiological cross sectional area), and geometrical parameters (attachment sites, ‘via’ points). Methods: One lower extremity, taken from a male embalmed specimen, was studied. Position and geometry were measured with a 3D-digitizer. Optotrak was used for measurement of rotation axes of joints. Sarcomere length was measured by laser diffraction. Findings: A total of 38 muscles were measured. Each muscle was divided in different muscle lines of action based on muscle morphology. 14 Ligaments of the hip, knee and ankle were included. Interpretation: The presented anatomical dataset embraces all necessary data for state of the art musculoskeletal modelling of the lower extremity. Implementation of these data into an (existing) model is likely to significantly improve the estimation of muscle forces and will thus make the use of the model as a clinical tool more feasible.

Role of shape and localized resonances in extraordinary transmission through periodic arrays of subwavelength holes: Experiment and theory

Abstract: The effect of the aspect ratio of rectangular holes on the transmissivity of periodic arrays of subwavelength holes in optically thick metal films is investigated. The transmissivity is found to be highly dependent on the aspect ratio of the holes. Moreover, the wavelengths of maximum transmissivity show a monotonous shift as a function of the aspect ratio of the holes. We attribute the enhanced transmission of the periodic arrays to an interplay of surface plasmons at the surface of the metal and shape resonances (also known as localized modes) inside the holes. The importance of the shape resonances was confirmed by a comparison of transmission through periodic hole arrays and through randomly distributed holes. Dispersion curves of periodic and random hole arrays confirmed the existence of shape resonance as well. We suggest that the localized modes effectively act as waveguides and increase the coupling efficiency of surface plasmons between both sides of the film, which results in a higher transmissivity. The shift of the maxima of the transmissivity may in part be explained by the spectral position of the localized modes in the individual holes. Finally measurements on similar patterns in Ni and Ag revealed that the occurrence of shape resonances is independent of the material of the film.

Single-cell Raman and fluorescence microscopy reveal the association of lipid bodies with phagosomes in leukocytes

Abstract: Cellular imaging techniques based on vibrational spectroscopy have become powerful tools in cell biology because the molecular composition of subcellular compartments can be visualized without the need for labeling. Using high-resolution, nonresonant confocal Raman microscopy on individual cells, we demonstrate here that lipid bodies (LBs) rich in arachidonate as revealed by their Raman spectra associate with latex bead-containing phagosomes in neutrophilic granulocytes. This finding was corroborated in macrophages and in PLB-985 cells, which can be induced to differentiate into neutrophil-like cells, by selective staining of LBs and visualization by confocal fluorescence microscopy. We further show that the accumulation of LBs near phagosomes is mediated at least in part by the flavohemoprotein gp91phox (in which “phox” is phagocyte oxidase), because different LB distributions around phagocytosed latex beads were observed in WT and gp91phox-deficient PLB-985 cells. gp91phox, which accumulates in the phagosomal membrane, is the catalytic subunit of the leukocyte NADPH oxidase, a critical enzyme in the innate immune response. Finally, time-lapse fluorescence microscopy experiments on neutrophils revealed that the LB-phagosome association is transient, similar to the “kiss-and-run” behavior displayed by endosomes involved in phagosome maturation. Because arachidonic acid (AA) has been shown to be involved in NADPH oxidase activation and phagosome maturation in neutrophils and macrophages, respectively, the findings reported here suggest that LBs may provide a reservoir of AA for local activation of these essential leukocyte functions.

Rethinking the science-policy nexus: from knowledge utilization and science technology studies to types of boundary arrangements

Abstract: The relationship between political judgment and science-based expertise is a troubled one. In the media three cliche images compete. The business-as-usual political story is that, in spite of appearances to the contrary, politics is safely ‘on top’ and experts are still ‘on tap’. The story told by scientists is that power-less but inventive scholars only ‘speak truth to power’. But there is plenty of room for a more cynical interpretation. It sees scientific advisers as following their own interests, unless better paid by other interests, and politicians as asking for advice only to support and legitimize their pre-formed political decisions. To the extent this cynical perspective gains ascendancy, politics and science lose credibility. If we think the three cliches cloak a more complex reality, we should embark upon a quest for other, possibly better models of the science/politics nexus. That is exactly the purpose of this article. Its claim is that a mutual transgression of the knowledge utilization strand of research in policy studies and the study of science, technology and society will provide us with more sophisticated images of science/politics boundary arrangements. Building upon Habermas’ well-known distinctions and Wittrock’s historical-institutional approach in the construction of a property space, eight models are presented. We should try to discover the conditions under which some of these models may claim greater verisimilitude. This may allow us to rethink the role of scientific expertise in policymaking and generate a model that guides experts and policymakers (and perhaps other stakeholders as well) in their day-to-day boundary work.

Polymer Scaffolds Fabricated with Pore-Size Gradients as a Model for Studying the Zonal Organization within Tissue-Engineered Cartilage Constructs

Abstract: The zonal organization of cells and extracellular matrix (ECM) constituents within articular cartilage is important for its biomechanical function in diarthroidal joints. Tissue-engineering strategies adopting porous three-dimensional (3D) scaffolds offer significant promise for the repair of articular cartilage defects, yet few approaches have accounted for the zonal structural organization as in native articular cartilage. In this study, the ability of anisotropic pore architectures to influence the zonal organization of chondrocytes and ECM components was investigated. Using a novel 3D fiber deposition (3DF) technique, we designed and produced 100% interconnecting scaffolds containing either homogeneously spaced pores (fiber spacing, 1 mm; pore size, about 680 µm in diameter) or pore-size gradients (fiber spacing, 0.5–2.0 mm; pore size range, about 200–1650 µm in diameter), but with similar overall porosity (about 80%) and volume fraction available for cell attachment and ECM formation. In vitro cell seeding showed that pore-size gradients promoted anisotropic cell distribution like that in the superficial, middle, and lower zones of immature bovine articular cartilage, irrespective of dynamic or static seeding methods. There was a direct correlation between zonal scaffold volume fraction and both DNA and glycosaminoglycan (GAG) content. Prolonged tissue culture in vitro showed similar inhomogeneous distributions of zonal GAG and collagen type II accumulation but not of GAG:DNA content, and levels were an order of magnitude less than in native cartilage. In this model system, we illustrated how scaffold design and novel processing techniques can be used to develop anisotropic pore architectures for instructing zonal cell and tissue distribution in tissue-engineered cartilage constructs.

State-of-the-art of battery state-of-charge determination

Abstract: From the early days of its discovery, humanity has depended on electricity, a phenomenon without which our technological advancements would not have been possible. With the increased need for mobility, people moved to portable power storage—first for wheeled applications, then for portable and finally nowadays wearable use. Several types of rechargeable battery systems, including those of lead–acid, nickel–cadmium, nickel–metal hydride, lithium ion and lithium-ion polymer exist in the market. The most important of them will be discussed in this review. Almost as long as rechargeable batteries have existed, systems able to give an indication about the state-of-charge (SoC) of a battery have been around. Several methods, including those of direct measurements, book-keeping and adaptive systems (Bergveld et al 2002 Battery Management Systems, Design by Modelling (Philips Research Book Series) vol 1 (Boston: Kluwer)) are known in the art for determining the SoC of a cell or battery of cells. An accurate SoC determination method and an understandable and reliable SoC display to the user will improve the performance and reliability, and will ultimately lengthen the lifetime of the battery. However, many examples of poor accuracy and reliability can be found in practice (Bergveld et al 2002, cited above). This review presents an overview on battery technology and the state-of-the-art of SoC methods. The goal of all the presented SoC indication methods is to design an SoC indication system capable of providing an accurate SoC indication under all realistic user conditions, including those of spread—in both battery and user behaviour, a large temperature and current range and ageing of the battery.