Showing papers by "Eindhoven University of Technology published in 2007"

The endothelial glycocalyx: composition, functions, and visualization

Abstract: This review aims at presenting state-of-the-art knowledge on the composition and functions of the endothelial glycocalyx. The endothelial glycocalyx is a network of membrane-bound proteoglycans and glycoproteins, covering the endothelium luminally. Both endothelium- and plasma-derived soluble molecules integrate into this mesh. Over the past decade, insight has been gained into the role of the glycocalyx in vascular physiology and pathology, including mechanotransduction, hemostasis, signaling, and blood cell–vessel wall interactions. The contribution of the glycocalyx to diabetes, ischemia/reperfusion, and atherosclerosis is also reviewed. Experimental data from the micro- and macrocirculation alludes at a vasculoprotective role for the glycocalyx. Assessing this possible role of the endothelial glycocalyx requires reliable visualization of this delicate layer, which is a great challenge. An overview is given of the various ways in which the endothelial glycocalyx has been visualized up to now, including first data from two-photon microscopic imaging.

Plant oil renewable resources as green alternatives in polymer science

Abstract: The utilization of plant oil renewable resources as raw materials for monomers and polymers is discussed and reviewed. In an age of increasing oil prices, global warming and other environmental problems (e.g. waste) the change from fossil feedstock to renewable resources can considerably contribute to a sustainable development in the future. Especially plant derived fats and oils bear a large potential for the substitution of currently used petrochemicals, since monomers, fine chemicals and polymers can be derived from these resources in a straightforward fashion. The synthesis of monomers as well as polymers from plant fats and oils has already found some industrial application and recent developments in this field offer promising new opportunities, as is shown within this contribution. (138 references.)

Chapter 3: MHD stability, operational limits and disruptions

Abstract: Progress in the area of MHD stability and disruptions, since the publication of the 1999 ITER Physics Basis document (1999 Nucl. Fusion 39 2137-2664), is reviewed. Recent theoretical and experimental research has made important advances in both understanding and control of MHD stability in tokamak plasmas. Sawteeth are anticipated in the ITER baseline ELMy H-mode scenario, but the tools exist to avoid or control them through localized current drive or fast ion generation. Active control of other MHD instabilities will most likely be also required in ITER. Extrapolation from existing experiments indicates that stabilization of neoclassical tearing modes by highly localized feedback-controlled current drive should be possible in ITER. Resistive wall modes are a key issue for advanced scenarios, but again, existing experiments indicate that these modes can be stabilized by a combination of plasma rotation and direct feedback control with non-axisymmetric coils. Reduction of error fields is a requirement for avoiding non-rotating magnetic island formation and for maintaining plasma rotation to help stabilize resistive wall modes. Recent experiments have shown the feasibility of reducing error fields to an acceptable level by means of non-axisymmetric coils, possibly controlled by feedback. The MHD stability limits associated with advanced scenarios are becoming well understood theoretically, and can be extended by tailoring of the pressure and current density profiles as well as by other techniques mentioned here. There have been significant advances also in the control of disruptions, most notably by injection of massive quantities of gas, leading to reduced halo current fractions and a larger fraction of the total thermal and magnetic energy dissipated by radiation. These advances in disruption control are supported by the development of means to predict impending disruption, most notably using neural networks. In addition to these advances in means to control or ameliorate the consequences of MHD instabilities, there has been significant progress in improving physics understanding and modelling. This progress has been in areas including the mechanisms governing NTM growth and seeding, in understanding the damping controlling RWM stability and in modelling RWM feedback schemes. For disruptions there has been continued progress on the instability mechanisms that underlie various classes of disruption, on the detailed modelling of halo currents and forces and in refining predictions of quench rates and disruption power loads. Overall the studies reviewed in this chapter demonstrate that MHD instabilities can be controlled, avoided or ameliorated to the extent that they should not compromise ITER operation, though they will necessarily impose a range of constraints.

Lasing in metallic-coated nanocavities

Abstract: Metallic cavities can confine light to volumes with dimensions considerably smaller than the wavelength of light. It is commonly believed, however, that the high losses in metals are prohibitive for laser operation in small metallic cavities. Here we report for the first time laser operation in an electrically pumped metallic-coated nanocavity formed by a semiconductor heterostructure encapsulated in a thin gold film. The demonstrated lasers show a low threshold current and their dimensions are smaller than the smallest electrically pumped lasers reported so far. With dimensions comparable to state-of-the-art electronic transistors and operating at low power and high speed, they are a strong contender as basic elements in digital photonic very large-scale integration. Furthermore we demonstrate that metallic-coated nanocavities with modal volumes smaller than dielectric cavities can have moderate quality factors.

Controller Area Network (CAN) schedulability analysis: Refuted, revisited and revised

Abstract: Controller Area Network (CAN) is used extensively in automotive applications, with in excess of 400 million CAN enabled microcontrollers manufactured each year. In 1994 schedulability analysis was developed for CAN, showing how worst-case response times of CAN messages could be calculated and hence guarantees provided that message response times would not exceed their deadlines. This seminal research has been cited in over 200 subsequent papers and transferred to industry in the form of commercial CAN schedulability analysis tools. These tools have been used by a large number of major automotive manufacturers in the design of in-vehicle networks for a wide range of cars, millions of which have been manufactured during the last decade. This paper shows that the original schedulability analysis given for CAN messages is flawed. It may provide guarantees for messages that will in fact miss their deadlines in the worst-case. This paper provides revised analysis resolving the problems with the original approach. Further, it highlights that the priority assignment policy, previously claimed to be optimal for CAN, is not in fact optimal and cites a method of obtaining an optimal priority ordering that is applicable to CAN. The paper discusses the possible impact on commercial CAN systems designed and developed using flawed schedulability analysis and makes recommendations for the revision of CAN schedulability analysis tools.

Fuzzy mining: adaptive process simplification based on multi-perspective metrics

Abstract: Process Mining is a technique for extracting process models from executionlogs. This is particularly useful in situations where people have an idealizedview of reality. Real-life processes turn out to be less structured than peopletend to believe. Unfortunately, traditional process mining approaches haveproblems dealing with unstructured processes. The discovered models are often"spaghetti-like", showing all details without distinguishing what is important andwhat is not. This paper proposes a new process mining approach to overcome thisproblem. The approach is configurable and allows for different faithfully simplifiedviews of a particular process. To do this, the concept of a roadmap is used asa metaphor. Just like different roadmaps provide suitable abstractions of reality,process models should provide meaningful abstractions of operational processesencountered in domains ranging from healthcare and logistics to web servicesand public administration.

Clicking polymers: a straightforward approach to novel macromolecular architectures

Abstract: Living/controlled polymerization techniques have enabled the synthesis of a large variety of different well-defined (co)polymer structures. In addition, the use of click chemistry in polymer science is a quickly emerging field of research since it allows the fast and simple creation of well-defined and complex polymeric structures in yields that were previously unattainable. In this critical review, the application of the azide–alkyne 1,3-dipolar cycloaddition for the construction of well-defined polymer architectures will be discussed in detail, providing a comprehensive overview for all disciplines related to polymeric materials.

Amplification of chirality in dynamic supramolecular aggregates

Abstract: The quest to understand the origin of chirality in biological systems has evoked an intense search for nonlinear effects in catalysis and pathways to amplify slight enantiomeric excesses in racemates to give optically pure molecules. The amplification of chirality in polymeric systems as a result of cooperative processes has been intensely investigated. Ten years ago, this effect was shown for the first time in noncovalent dynamic supramolecular systems. Since then, it has become clear that a subtle interplay of noncovalent interactions such as hydrogen-bonding, pi-pi stacking, and hydrophobic interactions is also sufficient to observe amplification of chirality in small molecules. Here we summarize the results obtained over the past decade and the general guidelines we can deduce from them. Predicting amplification of chirality is still impossible, but it appears to be a balance between different types of interactions, the formation of an intrinsically chiral object, and cooperative aggregation processes.

Toward High-Performance Polymer Solar Cells: The Importance of Morphology Control

Abstract: Polymer solar cells have the potential to become a major electrical power generating tool in the 21st century. R&D endeavors are focusing on continuous roll-to-roll printing of polymeric or organic compounds from solution-like newspapers-to produce flexible and lightweight devices at low cost. It is recognized, though, that besides the functional properties of the compounds the organization of structures on the nanometer level-forced and controlled mainly by the processing conditions applied-determines the performance of state-of-the-art polymer solar cells. In such devices the photoactive layer is composed of at least two functional materials that form nanoscale interpenetrating phases with specific functionalities, a so-called bulk heterojunction. In this perspective article, our current knowledge on the main factors determining the morphology formation and evolution is introduced, and gaps of our understanding on nanoscale structure-property relations in the field of high-performance polymer solar cells are addressed. Finally, promising routes toward formation of tailored morphologies are presented.

DECLARE: Full Support for Loosely-Structured Processes

Abstract: Traditional workflow management systems (WFMSs) are not flexible enough to support loosely-structured processes. Furthermore, flexibility in contemporary WFMSs usually comes at a certain cost, such as lack of support for users, lack of methods for model analysis, lack of methods for analysis of past executions, etc. DECLARE is a proto-type of a WFMS that uses a constraint-based process modeling language for the development of declarative models describing loosely-structured processes. In this paper we show how DECLARE can support loosely-structured processes without sacrificing important WFMSs features like user support, model verification, analysis of past executions, changing models at run-time, etc.

Genetic process mining: an experimental evaluation

Abstract: One of the aims of process mining is to retrieve a process model from an event log. The discovered models can be used as objective starting points during the deployment of process-aware information systems (Dumas et al., eds., Process-Aware Information Systems: Bridging People and Software Through Process Technology. Wiley, New York, 2005) and/or as a feedback mechanism to check prescribed models against enacted ones. However, current techniques have problems when mining processes that contain non-trivial constructs and/or when dealing with the presence of noise in the logs. Most of the problems happen because many current techniques are based on local information in the event log. To overcome these problems, we try to use genetic algorithms to mine process models. The main motivation is to benefit from the global search performed by this kind of algorithms. The non-trivial constructs are tackled by choosing an internal representation that supports them. The problem of noise is naturally tackled by the genetic algorithm because, per definition, these algorithms are robust to noise. The main challenge in a genetic approach is the definition of a good fitness measure because it guides the global search performed by the genetic algorithm. This paper explains how the genetic algorithm works. Experiments with synthetic and real-life logs show that the fitness measure indeed leads to the mining of process models that are complete (can reproduce all the behavior in the log) and precise (do not allow for extra behavior that cannot be derived from the event log). The genetic algorithm is implemented as a plug-in in the ProM framework.

Digital game design for elderly users

Abstract: The current paper reviews and discusses digital game design for elderly users. The aim of the paper is to look beyond the traditional perspective of usability requirements imposed by age-related functional limitations, towards the design opportunities that exist to create digital games that will offer engaging content combined with an interface that seniors can easily and pleasurably use.

Microscopic understanding of the anisotropic conductivity of PEDOT:PSS thin films

Abstract: The anisotropic conductivity of spin-coated poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films by temperature-dependent conductivity measurements, has been analyzed. A detailed 3D morphological model was derived from topographic scanning tunneling microscopy (STM) and cross-sectional atomic force microscopy (AFM) images, which correlated the anisotropy, both in conductivity magnitude and in the conduction mechanism. Spin coated films of PEDOT:PSS formed a reasonably homogenous material in terms of electrical conductivity. It was observed that the vertical conductivity that is perpendicular to the substrate, can be up to three orders of magnitude lower than the lateral conductivity in the plane of the film. The macroscopic in-plane conductivity was found to be completely isotropic, and the ordering was found to be confined to randomly oriented micrometer-size domains.

Faster addition and doubling on elliptic curves

Abstract: Edwards recently introduced a new normal form for elliptic curves. Every elliptic curve over a non-binary field is birationally equivalent to a curve in Edwards form over an extension of the field, and in many cases over the original field. This paper presents fast explicit formulas (and register allocations) for group operations on an Edwards curve. The algorithm for doubling uses only 3M + 4S, i.e., 3 field multiplications and 4 field squarings. If curve parameters are chosen to be small then the algorithm for mixed addition uses only 9M + 1S and the algorithm for non-mixed addition uses only 10M + 1S. Arbitrary Edwards curves can be handled at the cost of just one extra multiplication by a curve parameter. For comparison, the fastest algorithms known for the popular "a4=-3 Jacobian" form use 3M + 5S for doubling; use 7M + 4S for mixed addition; use 11M + 5S for non-mixed addition; and use 10M + 4S for non-mixed addition when one input has been added before. The explicit formulas for non-mixed addition on an Edwards curve can be used for doublings at no extra cost, simplifying protection against side-channel attacks. Even better, many elliptic curves (approximately 1/4 of all isomorphism classes of elliptic curves over a non-binary finite field) are birationally equivalent--over the original field--to Edwards curves where this addition algorithm works for all pairs of curve points, including inverses, the neutral element, etc. This paper contains an extensive comparison of different forms of elliptic curves and different coordinate systems for the basic group operations (doubling, mixed addition, non-mixed addition, and unified addition) as well as higher-level operations such as multi-scalar multiplication.

Finite element analysis based on in vivo HR-pQCT images of the distal radius is associated with wrist fracture in postmenopausal women.

Abstract: BMD, bone microarchitecture, and bone mechanical properties assessed in vivo by finite element analysis were associated with wrist fracture in postmenopausal women. Introduction: Many fractures occur in individuals with normal BMD. Assessment of bone mechanical properties by finite element analysis (FEA) may improve identification of those at high risk for fracture. Materials and Methods: We used HR-pQCT to assess volumetric bone density, microarchitecture, and μFE-derived bone mechanical properties at the radius in 33 postmenopausal women with a prior history of fragility wrist fracture and 33 age-matched controls from the OFELY cohort. Radius areal BMD (aBMD) was also measured by DXA. Associations between density, microarchitecture, mechanical parameters and fracture status were evaluated by univariate logistic regression analysis and expressed as ORs (with 95% CIs) per SD change. We also conducted a principal components (PCs) analysis (PCA) to reduce the number of parameters and study their association (OR) with wrist fracture. Results: Areal and volumetric densities, cortical thickness, trabecular number, and mechanical parameters such as estimated failure load, stiffness, and the proportion of load carried by the trabecular bone at the distal and proximal sites were associated with wrist fracture (p < 0.05). The PCA revealed five independent components that jointly explained 86.2% of the total variability of bone characteristics. The first PC included FE-estimated failure load, areal and volumetric BMD, and cortical thickness, explaining 51% of the variance with an OR for wrist fracture = 2.49 (95% CI, 1.32–4.72). Remaining PCs did not include any density parameters. The second PC included trabecular architecture, explaining 12% of the variance, with an OR = 1.82 (95% CI, 0.94–3.52). The third PC included the proportion of the load carried by cortical versus trabecular bone, assessed by FEA, explaining 9% of the variance, and had an OR = 1.61 (95% CI, 0.94–2.77). Thus, the proportion of load carried by cortical versus trabecular bone seems to be associated with wrist fracture independently of BMD and microarchitecture (included in the first and second PC, respectively). Conclusions: These results suggest that bone mechanical properties assessed by μFE may provide information about skeletal fragility and fracture risk not assessed by BMD or architecture measurements alone and are therefore likely to enhance the prediction of wrist fracture risk.

Three-Port Bidirectional Converter for Hybrid Fuel Cell Systems

Abstract: The implementation of a hybrid fuel cell/battery system is proposed to improve the slow transient response of a fuel cell stack. This system can be used for an autonomous device with quick load variations. A suitable three-port, galvanic isolated, bidirectional power converter is proposed to control the power flow. An energy management method for the proposed three-port circuit is analyzed and implemented. Measurements from a 500-W laboratory prototype are presented to demonstrate the validity of the approach