Showing papers by "Eindhoven University of Technology published in 2005"

The prom framework: a new era in process mining tool support

Abstract: Under the umbrella of buzzwords such as “Business Activity Monitoring” (BAM) and “Business Process Intelligence” (BPI) both academic (e.g., EMiT, Little Thumb, InWoLvE, Process Miner, and MinSoN) and commercial tools (e.g., ARIS PPM, HP BPI, and ILOG JViews) have been developed. The goal of these tools is to extract knowledge from event logs (e.g., transaction logs in an ERP system or audit trails in a WFM system), i.e., to do process mining. Unfortunately, tools use different formats for reading/storing log files and present their results in different ways. This makes it difficult to use different tools on the same data set and to compare the mining results. Furthermore, some of these tools implement concepts that can be very useful in the other tools but it is often difficult to combine tools. As a result, researchers working on new process mining techniques are forced to build a mining infrastructure from scratch or test their techniques in an isolated way, disconnected from any practical applications. To overcome these kind of problems, we have developed the ProM framework, i.e., an “pluggable” environment for process mining. The framework is flexible with respect to the input and output format, and is also open enough to allow for the easy reuse of code during the implementation of new process mining ideas. This paper introduces the ProM framework and gives an overview of the plug-ins that have been developed.

Hybrid zinc oxide conjugated polymer bulk heterojunction solar cells.

Abstract: Bulk heterojunction photovoltaic devices based on blends of a conjugated polymer poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) as electron donor and crystalline ZnO nanoparticles (nc-ZnO) as electron acceptor have been studied. Composite nc-ZnO:MDMO-PPV films were cast from a common solvent mixture. Time-resolved pump-probe spectroscopy revealed that a photoinduced electron transfer from MDMO-PPV to nc-ZnO occurs in these blends on a sub-picosecond time scale and produces a long-lived (milliseconds) charge-separated state. The photovoltaic effect in devices, made by sandwiching the active nc-ZnO:MDMO-PPV layer between charge-selective electrodes, has been studied as a function of the ZnO concentration and the thickness of the layer. We also investigated changing the degree and type of mixing of the two components through the use of a surfactant for ZnO and by altering the size and shape of the nc-ZnO particles. Optimized devices have an estimated AM1.5 performance of 1.6% with incident photon to current conversion efficiencies up to 50%. Photoluminescence spectroscopy, atomic force microscopy, and transmission electron microscopy have been used to gain insight in the morphology of these blends.

Case handling: a new paradigm for business process support

Abstract: Case handling is a new paradigm for supporting flexible and knowledge intensive business processes. It is strongly based on data as the typical product of these processes. Unlike workflow management, which uses predefined process control structures to determine what should be done during a workflow process, case handling focuses on what can be done to achieve a business goal. In case handling, the knowledge worker in charge of a particular case actively decides on how the goal of that case is reached, and the role of a case handling system is assisting rather than guiding her in doing so. In this paper, case handling is introduced as a new paradigm for supporting flexible business processes. It is motivated by comparing it to workflow management as the traditional way to support business processes. The main entities of case handling systems are identified and classified in a meta model. Finally, the basic functionality and usage of a case handling system is illustrated by an example.

Unified Description of Charge-Carrier Mobilities in Disordered Semiconducting Polymers

Abstract: From a numerical solution of the master equation for hopping transport in a disordered energy landscape with a Gaussian density of states, we determine the dependence of the charge-carrier mobility on temperature, carrier density, and electric field. Experimental current-voltage characteristics in devices based on semiconducting polymers are excellently reproduced with this unified description of the mobility. At room temperature it is mainly the dependence on carrier density that plays an important role, whereas at low temperatures and high fields the electric field dependence becomes important. Omission in the past of the carrier-density dependence has led to an underestimation of the hopping distance and the width of the density of states in these polymers.

New Trends in the Use of Transition Metal–Ligand Complexes for Applications in Electroluminescent Devices

Abstract: The advantage of using phosphorescent transition metal-ligand complexes in optoelectronic applications such as organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs) are described and evaluated. Additionally, different device constructions utilizing phosphorescent transition-metal complexes like iridium(III) mixed-ligand complexes and ruthenium(II) systems are reviewed and specified. Diverse host materials in which the phosphorescent emitters can be placed are discussed, such as small organic molecules and a few polymeric systems, and alternative processing technologies are briefly compared. Recent developments in the synthesis of iridium(III) triplet emitters are discussed. Different device architectures require different kinds of metal-ligand complexes. The different synthetic routes leading to charged and non-charged complexes are briefly discussed.

Management Research as a Design Science: Articulating the Research Products of Mode 2 Knowledge Production in Management

Abstract: The relevance problem of academic management research in organization and management is an old and thorny one. Recent discussions on this issue have resulted in proposals to use more Mode 2 knowledge production in our field. These discussions focused mainly on the process of research itself and less on the products produced by this process. Here the focus is on the so-called field-tested and grounded technological rule as a possible product of Mode 2 research with the potential to improve the relevance of academic research in management. Technological rules can be seen as solution-oriented knowledge. Such knowledge may be called Management Theory, while more description-oriented knowledge may be called Organization Theory. In this article the nature of technological rules in management is discussed, as well as their development, their use in actual management practice and the potential for cross-fertilization between Management Theory and Organization Theory.

Superhydrophobic Films from Raspberry-like Particles

Abstract: We report a robust procedure for preparing superhydrophobic hybrid films on which the advancing contact angle for water is about 165° and the roll-off angle of a 10-μL water droplet is 3 ± 1°. Dual-size surface roughness, which mimics the surface topology of self-cleaning plant leaves, originates from well-defined silica-based raspberry-like particles that are covalently bonded to an epoxy-based polymer matrix. The roughened surface is chemically modified with a layer of poly(dimethylsiloxane) (PDMS). The robustness and simplicity of this procedure may make widespread applications of so-prepared superhydrophobic films possible.

Funology: from usability to enjoyment

Abstract: Theories and Concepts.- to Section 1.- Let's Make Things Engaging.- The Engineering of Experience.- The Thing and I: Understanding the Relationship Between User and Product.- Making Sense of Experience.- Enjoyment: Lessons from Karasek.- Fun on the Phone: The Situated Experience of Recreational Telephone Conferences.- The Enchantments of Technology.- The Semantics of Fun: Differentiating Enjoyable Eeperiences.- Methods and Techniques.- User Empowerment and the Fun Factor.- to Section 2.- Measuring Emotion: Development and Application of an Instrument to Measure Emotional Responses to Products.- That's Entertainment!.- Designing for Fun: User-Testing Case Studies.- Playing Games in the Emotional Space.- Deconstructing Experience: Pulling Crackers Apart.- Designing Engaging Experiences with Children and Artists.- Building Narrative Experiences for Children Through Real Time Media Manipulation: Pogo World.- Case Studies in Design.- to Section 3.- The Joy of Telephony: Designing Appealing Interactions.- From Usable to Enjoyable Information Displays.- Fun for All: Promoting Engagement and Paraticipation in Community Programming Projects.- Storytelling & Conversation to Improve the Fun Factor in Software Applications.- Deconstructing Ghosts.- Interfacing the Narrative Experience.- Whose Line is It Anyway? Enabling Creative Appropriation of Television.- The Interactive Installation ISH: In Search of Resonant Human Product Interaction.- Fun with Your Alarm Clock: Designing for Engaging Experiences Through Emotionally Rich Interaction.

Contrasting the Theory of Planned Behavior With the Value‐Belief‐Norm Model in Explaining Conservation Behavior1

Abstract: In this paper, we contrast the value-belief-norm (VBN) model and the theory of planned behavior (TPB) for the first time regarding their ability to explain conservation behavior. The participants represent a convenience sample of 468 university students. Using survey data and adopting previously established compound measures, structural equation analyses revealed a remarkable explanatory power for both theories: TPB's intention accounted for 95% of people's conservation behavior and VBN's personal norms accounted for 64%. Compared to the VBN model, the TPB covered its concepts more fully in terms of proportions of explained variance. More importantly, the fit statistics revealed that only the TPB depicts the relations among its concepts appropriately, whereas the VBN model does not.

Luminescence properties of Eu2+ - activated alkaline-earth silicon-oxynitride MSi2O2-deltaN2+2/3delta (M = Ca, Sr, Ba) : A promising class of novel LED conversion phosphors

Abstract: The luminescence properties of Eu2+-activated alkaline-earth silicon-oxynitrides have been studied In the BaO−SiO2−Si3N4 system, a new BaSi2O2N2 compound was obtained having the monoclinic structure with lattice parameters a = 14070(4) A, b = 7276(2) A, c = 13181(3) A, β = 10774(6)° All MSi2O2-δN2+2/3δ:Eu2+ (M = Ca, Sr, Ba) materials can be efficiently excited in the UV to visible region (370−460 nm), making them attractive as conversion phosphors for LED applications A blue-green emission at 490−500 is observed for BaSi2O2N2:Eu2+, yellow emission at 560 nm for CaSi2O2-δN2+2/3δ:Eu2+ (δ ≈ 0), and a green-yellow emission peaking from 530 to 570 nm for SrSi2O2-δN2+2/3δ:Eu2+ (δ ≈ 1), the position depending on the exact value of δ BaSi2O2N2:Eu2+ is the most promising conversion phosphor for white-light LEDs due to its high conversion efficiency for blue light from InGaN-based LEDs related to its very small Stokes shift

Management Research as a Design Science: Articulating the Research Products of Mode 2 Knowledge Production in Management

Abstract: The relevance problem of academic management research in organization and management is an old and thorny one. Recent discussions on this issue have resulted in proposals to use more Mode 2 knowledge production in our field. These discussions focused mainly on the process of research itself and less on the products produced by this process. Here the focus is on the so-called field-tested and grounded technological rule as a possible product of Mode 2 research with the potential to improve the relevance of academic research in management. Technological rules can be seen as solution-oriented knowledge. Such knowledge may be called Management Theory, while more description-oriented knowledge may be called Organization Theory. In this article the nature of technological rules in management is discussed, as well as their development, their use in actual management practice and the potential for cross-fertilization between Management Theory and Organization Theory.

Best practices in business process redesign: an overview and qualitative evaluation of successful redesign heuristics

Abstract: To implement business process redesign several best practices can be distinguished. This paper gives an overview of heuristic rules that can support practitioners to develop a business process design that is a radical improvement of a current design. The emphasis is on the mechanics of the process, rather than on behavioral or change management aspects. The various best practices are derived from a wide literature survey and supplemented with experiences of the authors. To evaluate the impact of each best practice along the dimensions of cost, flexibility, time and quality, a conceptual framework is presented that synthesizes views from areas such as information systems development, enterprise modeling and workflow management. The best practices are thought to have a wide applicability across various industries and business processes. They can be used as a “check list” for process redesign under the umbrella of diverse management approaches such as Total Cycle Time compression, the Lean Enterprise and Constraints Management.

Foundations of attack trees

Abstract: Attack trees have found their way to practice because they have proved to be an intuitive aid in threat analysis. Despite, or perhaps thanks to, their apparent simplicity, they have not yet been provided with an unambiguous semantics. We argue that such a formal interpretation is indispensable to precisely understand how attack trees can be manipulated during construction and analysis. We provide a denotational semantics, based on a mapping to attack suites, which abstracts from the internal structure of an attack tree, we study transformations between attack trees, and we study the attribution and projection of an attack tree.

Energy management strategies for vehicular electric power systems

Abstract: In the near future, a significant increase in electric power consumption in vehicles is expected. To limit the associated increase in fuel consumption and exhaust emissions, smart strategies for the generation, storage/retrieval, distribution, and consumption of electric power will be used. Inspired by the research on energy management for hybrid electric vehicles (HEVs), this paper presents an extensive study on controlling the vehicular electric power system to reduce the fuel use and emissions, by generating and storing electrical energy only at the most suitable moments. For this purpose, both off-line optimization methods using knowledge of the driving pattern and on-line implementable ones are developed and tested in a simulation environment. Results show a reduction in fuel use of 2%, even without a prediction of the driving cycle being used. Simultaneously, even larger reductions of the emissions are obtained. The strategies can also be applied to a mild HEV with an integrated starter alternator (ISA), without modifications, or to other types of HEVs with slight changes in the formulation.

Discovering Social Networks from Event Logs

Abstract: Process mining techniques allow for the discovery of knowledge based on so-called "event logs", i.e., a log recording the execution of activities in some business process. Many information systems provide such logs, e.g., most WFM, ERP, CRM, SCM, and B2B systems record transactions in a systematic way. Process mining techniques typically focus on performance and control-flow issues. However, event logs typically also log the performer, e.g., the person initiating or completing some activity. This paper focuses on mining social networks using this information. For example, it is possible to build a social network based on the hand-over of work from one performer to the next. By combining concepts from workflow management and social network analysis, it is possible to discover and analyze social networks. This paper defines metrics, presents a tool, and applies these to a real event log within the setting of a large Dutch organization.

A modular and supramolecular approach to bioactive scaffolds for tissue engineering

Abstract: Bioactive polymeric scaffolds are a prerequisite for the ultimate formation of functional tissues. Here, we show that supramolecular polymers based on quadruple hydrogen bonding ureido-pyrimidinone (UPy) moieties are eminently suitable for producing such bioactive materials owing to their low-temperature processability, favourable degradation and biocompatible behaviour. Particularly, the reversible nature of the hydrogen bonds allows for a modular approach to gaining control over cellular behaviour and activity both in vitro and in vivo. Bioactive materials are obtained by simply mixing UPy-functionalized polymers with UPy-modified biomolecules. Low-molecular-weight bis-UPy-oligocaprolactones with cell adhesion promoting UPy-Gly-Arg-Gly-Asp-Ser (UPy-GRGDS) and the synergistic UPy-Pro-His-Ser-Arg-Asn (UPy-PHSRN) peptide sequences are synthesized and studied. The in vitro results indicate strong and specific cell binding of fibroblasts to the UPy-functionalized bioactive materials containing both UPy-peptides. An even more striking effect is seen in vivo where the formation of single giant cells at the interface between bioactive material and tissue is triggered.

Compositional dependence of the performance of poly(p-phenylene vinylene): Methanofullerene bulk-heterojunction solar cells

Abstract: The dependence of the performance of OC(1)C(10)-PPV:PCBM (poly(2-methoxy-5-(3',7'-dimethyloetyloxy)-p-phenylene vinylene):methanofullerene [6,6]-phenyl C(61)-butyric acid methyl ester)-based bulk heterojunction solar cells on their composition has been investigated. With regard to charge transport, we demonstrate that the electron mobility gradually increases on increasing the PCBM weight ratio, up to 80 wt.-%, and subsequently saturates to its bulk value. Surprisingly, the hole mobility in the PPV phase shows an identical behavior and saturates beyond 67 wt.-% PCBM, a value which is more than two orders of magnitude higher than that of the pure polymer. The experimental electron and hole mobilities were used to study the photocurrent generation of OC(1)C(10)-PPV:PCBM bulk-heterojunction (BHJ) solar cells. From numerical calculations, it is shown that for PCBM concentrations exceeding 80 wt.-% reduced light absorption is responsible for the loss of device performance. From 80 to 67 wt.-%, the decrease in power conversion efficiency is mainly due to a decreased separation efficiency of bound electron-hole (e-h) pairs. Below 67 wt.-%, the performance loss is governed by a combination of a reduced generation rate of e-h pairs and a strong decrease in hole transport.

Charge-carrier concentration dependence of the hopping mobility in organic materials with Gaussian disorder

Abstract: It has recently been demonstrated that the hopping mobility in semiconducting organic materials depends on the charge-carrier concentration. We have analyzed this effect within the framework of six existing semianalytical models, for the case of a Gaussian density of states (DOS). These models were either not applied earlier to the case of a Gaussian DOS, or are shown to require a major modification. The mobility is constant below a certain concentration, which decreases with increasing ratio $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{s}$ of the width of the DOS over the thermal energy ${k}_{B}T$, and it increases for larger concentrations. At very high concentrations final state effects limit this increase or even give rise to a decrease. An analytical expression is given for the mobility, $\ensuremath{\mu}$, in the form of the product of the mobility in the low concentration limit times a concentration $(c)$ and $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{s}$-dependent enhancement factor. Depending on $c$, $\mathrm{ln}(\ensuremath{\mu})$ varies approximately linearly with $1∕T$ or with $1∕{T}^{2}$. This finding may lead to a solution for the long-standing controversy between polaron-based and disorder-based hopping models.

User-level performance of channel-aware scheduling algorithms in wireless data networks

Abstract: Channel-aware scheduling strategies, such as the Proportional Fair algorithm for the CDMA 1xEV-DO system, provide an effective mechanism for improving throughput performance in wireless data networks by exploiting channel fluctuations. The performance of channel-aware scheduling algorithms has mostly been explored at the packet level for a static user population, often assuming infinite backlogs. In the present paper, we focus on the performance at the flow level in a dynamic setting with random finite-size service demands. We show that in certain cases the user-level performance may be evaluated by means of a multiclass Processor-Sharing model where the total service rate varies with the total number of users. The latter model provides explicit formulas for the distribution of the number of active users of the various classes, the mean response times, the blocking probabilities, and the throughput. In addition we show that, in the presence of channel variations, greedy, myopic strategies which maximize throughput in a static scenario, may result in sub-optimal throughput performance for a dynamic user configuration and cause potential instability effects.

Unifying Ultrafast Magnetization Dynamics

Abstract: We present a microscopic model that successfully explains the ultrafast equilibration of magnetic order in ferromagnetic metals at a time scale tau(M) of only a few hundred femtoseconds after pulsed laser excitation. It is found that tau(M) can be directly related to the so-called Gilbert damping factor sigma that describes damping of GHz precessional motion of the magnetization vector. Independent of the spin-scattering mechanism, an appealingly simple equation relating the two key parameters via the Curie temperature T(C) is derived, tau(M) approximately c(0)h/k(B)T(C)sigma, with h and k(B) the Planck and Boltzmann constants, respectively, and the prefactor c(0) approximately 1/4). We argue that phonon-mediated spin-flip scattering may contribute significantly to the sub-ps response.

Flow of viscoelastic fluids past a cylinder at high Weissenberg number : stabilized simulations using matrix logarithms

Abstract: The log conformation representation proposed in [R. Fattal, R. Kupferman, Constitutive laws for the matrix-logarithm of the conformation tensor, J. Non-Newtonian Fluid Mech. 123 (2004) 281–285] has been implemented in a FEM context using the DEVSS/DG formulation for viscoelastic fluid flow. We present a stability analysis in 1D and identify the failure of the numerical scheme to balance exponential growth as a possible source for numerical instabilities at high Weissenberg numbers. A different derivation of the log-based evolution equation than in [R. Fattal, R. Kupferman, Constitutive laws for the matrix-logarithm of the conformation tensor, J. Non-Newtonian Fluid Mech. 123 (2004) 281–285] is also presented. We show numerical results for the flow around a cylinder for an Oldroyd-B and a Giesekus model. With the log conformation representation, we are able to obtain solutions beyond the limiting Weissenberg numbers in the standard scheme. In particular, for the Giesekus model the improvement is rather dramatic: there does not seem to be a limit for the chosen model parameter (α = 0.01). However, it turns out that although in large parts of the flow the solution converges, we have not been able to obtain convergence in localized regions of the flow. Possible reasons include artefacts of the model and unresolved small scales. More work is necessary, including the use of more refined meshes and/or higher order schemes, before any conclusion can be made on the local convergence problems. © 2005 Elsevier B.V. All rights reserved.