Showing papers by "Delft University of Technology published in 2003"
05 Nov 2003
TL;DR: T-MAC, a contention-based Medium Access Control protocol for wireless sensor networks, introduces an adaptive duty cycle in a novel way: by dynamically ending the active part of it to handle load variations in time and location.
Abstract: In this paper we describe T-MAC, a contention-based Medium Access Control protocol for wireless sensor networks. Applications for these networks have some characteristics (low message rate, insensitivity to latency) that can be exploited to reduce energy consumption by introducing an activesleep duty cycle. To handle load variations in time and location T-MAC introduces an adaptive duty cycle in a novel way: by dynamically ending the active part of it. This reduces the amount of energy wasted on idle listening, in which nodes wait for potentially incoming messages, while still maintaining a reasonable throughput.We discuss the design of T-MAC, and provide a head-to-head comparison with classic CSMA (no duty cycle) and S-MAC (fixed duty cycle) through extensive simulations. Under homogeneous load, T-MAC and S-MAC achieve similar reductions in energy consumption (up to 98%) compared to CSMA. In a sample scenario with variable load, however, T-MAC outperforms S-MAC by a factor of 5. Preliminary energy-consumption measurements provide insight into the internal workings of the T-MAC protocol.
2,844 citations
TL;DR: In this paper, the authors provide a conceptual basis for the systematic treatment of uncertainty in model-based decision support activities such as policy analysis, integrated assessment and risk assessment, and propose an uncertainty matrix as a heuristic tool to classify and report the various dimensions of uncertainty, thereby providing a conceptual framework for better communication among analysts as well as between them and policymakers and stakeholders.
Abstract: The aim of this paper is to provide a conceptual basis for the systematic treatment of uncertainty in model-based decision support activities such as policy analysis, integrated assessment and risk assessment. It focuses on the uncertainty perceived from the point of view of those providing information to support policy decisions (i.e., the modellers’ view on uncertainty) – uncertainty regarding the analytical outcomes and conclusions of the decision support exercise. Within the regulatory and management sciences, there is neither commonly shared terminology nor full agreement on a typology of uncertainties. Our aim is to synthesise a wide variety of contributions on uncertainty in model-based decision support in order to provide an interdisciplinary theoretical framework for systematic uncertainty analysis. To that end we adopt a general definition of uncertainty as being any deviation from the unachievable ideal of completely deterministic knowledge of the relevant system. We further propose to discriminate among three dimensions of uncertainty: location, level and nature of uncertainty, and we harmonise existing typologies to further detail the concepts behind these three dimensions of uncertainty.We propose an uncertainty matrix as a heuristic tool to classify and report the various dimensions of uncertainty, thereby providing a conceptual framework for better communication among analysts as well as between them and policymakers and stakeholders. Understanding the various dimensions of uncertainty helps in identifying, articulating, and prioritising critical uncertainties, which is a crucial step to more adequate acknowledgement and treatment of uncertainty in decision support endeavours and more focused research on complex, inherently uncertain, policy issues.
1,835 citations
TL;DR: In this article, the pore size distributions derived from adsorption isotherms of micro- and mesoporous materials are identified and discussed based on new results and examples reported in the recent literature.
1,775 citations
TL;DR: In this article, the applicability and perspectives of various desulfurization technologies are evaluated taking into account the requirements of the produced fuels, and the progress achieved during recent years in catalysis-based HDS technologies (synthesis of improved catalysts, advanced reactor design, combination of distillation and HDS) and in non-HDS processes of sulfur removal (alkylation, extraction, precipitation, oxidation, and adsorption) is illustrated through a number of examples.
1,531 citations
TL;DR: A new technique for fabricating silicon oxide nanopores with single-nanometre precision and direct visual feedback, using state-of-the-art silicon technology and transmission electron microscopy is reported.
Abstract: Single nanometre-sized pores (nanopores) embedded in an insulating membrane are an exciting new class of nanosensors for rapid electrical detection and characterization of biomolecules. Notable examples include α-hemolysin protein nanopores in lipid membranes1,2 and solid-state nanopores3 in Si3N4. Here we report a new technique for fabricating silicon oxide nanopores with single-nanometre precision and direct visual feedback, using state-of-the-art silicon technology and transmission electron microscopy. First, a pore of 20 nm is opened in a silicon membrane by using electron-beam lithography and anisotropic etching. After thermal oxidation, the pore can be reduced to a single-nanometre when it is exposed to a high-energy electron beam. This fluidizes the silicon oxide leading to a shrinking of the small hole due to surface tension. When the electron beam is switched off, the material quenches and retains its shape. This technique dramatically increases the level of control in the fabrication of a wide range of nanodevices.
1,375 citations
TL;DR: This first demonstration of nanotube-based biosensors provides a new tool for enzymatic studies and opens the way to biomolecular diagnostics.
Abstract: We demonstrate the use of individual semiconducting single-wall carbon nanotubes as versatile biosensors. Controlled attachment of the redox enzyme glucose oxidase (GOx) to the nanotube sidewall is achieved through a linking molecule and is found to induce a clear change of the conductance. The enzyme-coated tube is found to act as a pH sensor with large and reversible changes in conductance upon changes in pH. Upon addition of glucose, the substrate of GOx, a steplike response can be monitored in real time, indicating that our sensor is also capable of measuring enzymatic activity at the level of a single nanotube. This first demonstration of nanotube-based biosensors provides a new tool for enzymatic studies and opens the way to biomolecular diagnostics.
1,242 citations
TL;DR: Evidence for bacteria that anaerobically oxidize ammonium with nitrite to N2 in the world's largest anoxic basin, the Black Sea is provided and anammox bacteria have been identified and directly linked to the removal of fixed inorganic nitrogen in the environment.
Abstract: The availability of fixed inorganic nitrogen (nitrate, nitrite and ammonium) limits primary productivity in many oceanic regions. The conversion of nitrate to N2 by heterotrophic bacteria (denitrification) is believed to be the only important sink for fixed inorganic nitrogen in the ocean. Here we provide evidence for bacteria that anaerobically oxidize ammonium with nitrite to N2 in the world's largest anoxic basin, the Black Sea. Phylogenetic analysis of 16S ribosomal RNA gene sequences shows that these bacteria are related to members of the order Planctomycetales performing the anammox (anaerobic ammonium oxidation) process in ammonium-removing bioreactors. Nutrient profiles, fluorescently labelled RNA probes, 15N tracer experiments and the distribution of specific 'ladderane' membrane lipids indicate that ammonium diffusing upwards from the anoxic deep water is consumed by anammox bacteria below the oxic zone. This is the first time that anammox bacteria have been identified and directly linked to the removal of fixed inorganic nitrogen in the environment. The widespread occurrence of ammonium consumption in suboxic marine settings indicates that anammox might be important in the oceanic nitrogen cycle.
1,172 citations
TL;DR: In this article, the aerodynamic properties of wind turbine wakes are studied, focusing on the physics of power extraction by wind turbines, and the main interest is to study how the far wake decays downstream in order to estimate the effect produced in downstream turbines.
1,161 citations
TL;DR: The observed coherent time evolution between two quantum states of a superconducting flux qubit comprising three Josephson junctions in a loop is promising for future solid-state quantum computing.
Abstract: We have observed coherent time evolution between two quantum states of a superconducting flux qubit comprising three Josephson junctions in a loop. The superposition of the two states carrying opposite macroscopic persistent currents is manipulated by resonant microwave pulses. Readout by means of switching-event measurement with an attached superconducting quantum interference device revealed quantum-state oscillations with high fidelity. Under strong microwave driving, it was possible to induce hundreds of coherent oscillations. Pulsed operations on this first sample yielded a relaxation time of 900 nanoseconds and a free-induction dephasing time of 20 nanoseconds. These results are promising for future solid-state quantum computing.
1,109 citations
TL;DR: This paper compares three distributed localization algorithms (Ad-hoc positioning, Robust positioning, and N-hop multilateration) on a single simulation platform and concludes that no single algorithm performs best.
1,106 citations
TL;DR: A solid-state nanopore microscope capable of observing individual molecules of double-stranded DNA and their folding behaviour is demonstrated and extensions of the nanopore telescope concept to alternative probing mechanisms and applications are discussed, including the study of molecular structure and sequencing.
Abstract: A nanometre-scale pore in a solid-state membrane provides a new way of electronically probing the structure of single linear polymers, including those of biological interest in their native environments. Previous work with biological protein pores wide enough to let through and sense single-stranded DNA molecules demonstrates the power of using nanopores, but many future tasks and applications call for a robust solidstate pore whose nanometre-scale dimensions and properties may be selected, as one selects the lenses of a microscope. Here we demonstrate a solid-state nanopore microscope capable of observing individual molecules of double-stranded DNA and their folding behaviour. We discuss extensions of the nanopore microscope concept to alternative probing mechanisms and applications, including the study of molecular structure and sequencing.
TL;DR: In this paper, the authors present a re-analysis of the FD-excitation, absorption, reflection, and emission spectra of Eu2+ in inorganic compounds.
08 Sep 2003
TL;DR: It is argued that next-generation human-computer interaction (HCI) designs need to include the essence of emotional intelligence - the ability to recognize a user's affective states- in order to become more human-like, more effective, and more efficient.
Abstract: The ability to recognize affective states of a person we are communicating with is the core of emotional intelligence. Emotional intelligence is a facet of human intelligence that has been argued to be indispensable and perhaps the most important for successful interpersonal social interaction. This paper argues that next-generation human-computer interaction (HCI) designs need to include the essence of emotional intelligence - the ability to recognize a user's affective states-in order to become more human-like, more effective, and more efficient. Affective arousal modulates all nonverbal communicative cues (facial expressions, body movements, and vocal and physiological reactions). In a face-to-face interaction, humans detect and interpret those interactive signals of their communicator with little or no effort. Yet design and development of an automated system that accomplishes these tasks is rather difficult. This paper surveys the past work in solving these problems by a computer and provides a set of recommendations for developing the first part of an intelligent multimodal HCI-an automatic personalized analyzer of a user's nonverbal affective feedback.
TL;DR: In this article, the authors demonstrate that hole transport and electron transport are both generic properties of organic semiconductors and combine the organic ambipolar transistors into functional CMOS-like inverters.
Abstract: There is ample evidence that organic field-effect transistors have reached a stage where they can be industrialized, analogous to standard metal oxide semiconductor (MOS) transistors. Monocrystalline silicon technology is largely based on complementary MOS (CMOS) structures that use both n-type and p-type transistor channels. This complementary technology has enabled the construction of digital circuits, which operate with a high robustness, low power dissipation and a good noise margin. For the design of efficient organic integrated circuits, there is an urgent need for complementary technology, where both n-type and p-type transistor operation is realized in a single layer, while maintaining the attractiveness of easy solution processing. We demonstrate, by using solution-processed field-effect transistors, that hole transport and electron transport are both generic properties of organic semiconductors. This ambipolar transport is observed in polymers based on interpenetrating networks as well as in narrow bandgap organic semiconductors. We combine the organic ambipolar transistors into functional CMOS-like inverters.
TL;DR: The experimental hole mobilities extracted from both types of devices, although based on a single polymeric semiconductor, can differ by 3 orders of magnitude, demonstrating the strong dependence of the hole mobility on the charge carrier density in disordered semiconducting polymers.
Abstract: A systematic study of the hole mobility in hole-only diodes and field-effect transistors based on poly(2-methoxy-5-(3('),7(')-dimethyloctyloxy)-p-phenylene vinylene) and on amorphous poly(3-hexyl thiophene) has been performed as a function of temperature and applied bias. The experimental hole mobilities extracted from both types of devices, although based on a single polymeric semiconductor, can differ by 3 orders of magnitude. We demonstrate that this apparent discrepancy originates from the strong dependence of the hole mobility on the charge carrier density in disordered semiconducting polymers.
TL;DR: Room temperature ionic liquids are non-volatile, thermally stable and highly polar; they are also moderately hydrophilic solvents; their use as reaction media for biocatalysis is discussed.
TL;DR: The main features of the implementation are it is based on a homogeneous and self-dual model, it handles rotated quadratic cones directly, it employs a Mehrotra type predictor-corrector extension and sparse linear algebra to improve the computational efficiency and it exploits fixed variables which naturally occurs in many conic Quadratic optimization problems.
Abstract: Based on the work of the Nesterov and Todd on self-scaled cones an implementation of a primal-dual interior-point method for solving large-scale sparse conic quadratic optimization problems is presented. The main features of the implementation are it is based on a homogeneous and self-dual model, it handles rotated quadratic cones directly, it employs a Mehrotra type predictor-corrector extension and sparse linear algebra to improve the computational efficiency. Finally, the implementation exploits fixed variables which naturally occurs in many conic quadratic optimization problems. This is a novel feature for our implementation. Computational results are also presented to document that the implementation can solve very large problems robustly and efficiently.
TL;DR: In this paper, the energy needed to transfer an electron from the valence band of an inorganic compound to a trivalent lanthanide impurity is presented, which is a measure of the location of the ground state of the divalent lanthanides relative to the top of the Valence band.
Abstract: Information on the energy that is needed to transfer an electron from the valence band of an inorganic compound to a trivalent lanthanide impurity is presented. The energy is a measure of the location of the ground state of the divalent lanthanide relative to the top of the valence band. A variation with type of lanthanide is found that is the same irrespective of the type of compound (fluorides, chlorides, bromides, iodides, oxides, sulfides). The variation is anti-correlated with the known variation in fd transition energies in divalent lanthanides. Because of the anti-correlation, the energy difference between the first 4fn−15d state and the bottom of the conduction band is relatively invariant with type of lanthanide ion. The difference is largest for Eu2+, and decreases gradually towards the end of the lanthanide series by 0.5 eV for Y b2+. Based on the systematic variation in charge transfer energy and fd energy, a three-parameter model is presented to position the energy levels for each divalent lanthanide relative to valence and conduction band states. Using a similar model the levels of trivalent lanthanides are positioned.
TL;DR: A new genus and species of anaerobic ammonium oxidizing planctomycetes, discovered in a wastewater treatment plant treating landfill leachate in Pitsea, UK, are described, making this genus the most widespread of all anammox bacteria described so far.
TL;DR: In this article, a unified view of nucleation in solutions is presented from a unified point of view, where the thermodynamics of the process is considered and expressions for the supersaturation, the nucleation work and the size of the nucleus in homogeneous or heterogeneous nucleation.
Abstract: Existing and new results in nucleation in solutions are outlined from a unified point of view. The thermodynamics of the process is considered and expressions are given for the supersaturation, the nucleation work and the size of the nucleus in homogeneous or heterogeneous nucleation. It is shown how the nucleation theorem can be used for a model-independent determination of the nucleus size from experimental data. The mechanism and kinetics of nucleation are also considered and formulae are presented for the supersaturation dependence of the monomer attachment frequency and the stationary rate of homogeneous or heterogeneous nucleation. General expressions for the induction time and the critical supersaturation ratio for crystallization are given. An approximate formula is derived for estimating the width of the metastable zone with the help of data for the solubility of the substance crystallized. Existing experimental data are used for verification of the validity of some of the presented theoretical dependences.
TL;DR: The thinkLet concept is proposed, a codified packet of facilitation skill that can be applied by practitioners to achieve predictable, repeatable patterns of collaboration, such as divergence or convergence, which may become a sine qua non for organizations to effectively support virtual work teams.
Abstract: Field research and laboratory experiments suggest that, under certain circumstances, people using group support systems (GSS) can be significantly more productive than people who do not use them. Yet, despite their demonstrated potential, GSS have been slow to diffuse across organizations. Drawing on the Technology Transition Model, the paper argues that the high conceptual load of GSS (i.e., understanding of the intended effect of GSS functionality) encourages organizations to employ expert facilitators to wield the technology on behalf of others. Economic and political factors mitigate against facilitators remaining long term in GSS facilities that focus on supporting nonroutine, ad hoc projects. This especially hampers scaling GSS technology to support distributed collaboration. An alternative and sustainable way for organizations to derive value from GSS lies in an approach called "collaboration engineering": the development of repeatable collaborative processes that are conducted by practitioners themselves. To enable the development of such processes, this paper proposes the thinkLet concept, a codified packet of facilitation skill that can be applied by practitioners to achieve predictable, repeatable patterns of collaboration, such as divergence or convergence.A thinkLet specifies the facilitator'schoices and actions in terms of the GSS tool used, the configuration of this tool, and scripted prompts to accomplish a pattern of collaboration in a group. Using thinkLets as building blocks, facilitators can develop and transfer repeatable collaborative processes to practitioners. Given the limited availability of expert facilitators, collaboration engineering with thinkLets may become a sine qua non for organizations to effectively support virtual work teams.
TL;DR: The pros and cons of carrier-free versus carrier-bound immobilised enzymes and of each type of carriers-free enzyme are discussed.
TL;DR: In this paper, various mechanisms suggested to cause autogenous shrinkage are presented The mechanisms are evaluated from the point of view of their soundness and applicability to quantitative modeling of autogeneous shrinkage.
TL;DR: This survey paper considers linear structured systems in state space form, where a linear system is structured when each entry of its matrices, like A,B,C and D, is either a fixed zero or a free parameter.
TL;DR: In this article, a review examines 43 recent papers about factors behind success and failure of innovative projects and finds that most studies remain either inconsistent or inconclusive with respect to factors such as strength of competition, R&D intensity, the degree to which a project is "innovative" or "technologically advanced" and top management support.
Abstract: This review examines 43 recent papers about factors behind success and failure of innovative projects. Nine out of the 43 papers report a larger number of possible causes for success or failure and provide some rank ordering. Analyzing these rankings we find that the nine studies have a significant degree of similarity among the ten highest-ranking success factors; however, there is little similarity among lower ranking factors. The various studies remain either inconsistent or inconclusive with respect to factors such as strength of competition, R&D intensity, the degree to which a project is "innovative" or "technologically advanced" and top management support. Agreement exists, however, about the positive impact on innovative success of factors such as firm culture, experience with innovation, the multidisciplinary character of the R&D team and explicit recognition of the collective character of the innovation process or the advantages of the matrix organization.
TL;DR: These processes target the removal of ammonia from gases, and ammonium-bicarbonate from concentrated wastewaters (i.e. sludge liquor and landfill leachate) and the microbiology, its consequences for their application, the current status regarding application, and the future developments are addressed.
Abstract: Many countries strive to reduce the emissions of nitrogen compounds (ammonia, nitrate, NOx) to the surface waters and the atmosphere. Since mainstream domestic wastewater treatment systems are usually already overloaded with ammonia, a dedicated nitrogen removal from concentrated secondary or industrial wastewaters is often more cost-effective than the disposal of such wastes to domestic wastewater treatment. The cost-effectiveness of separate treatment has increased dramatically in the past few years, since several processes for the biological removal of ammonia from concentrated waste streams have become available. Here, we review those processes that make use of new concepts in microbiology: partial nitrification, nitrifier denitrification and anaerobic ammonia oxidation (the anammox process). These processes target the removal of ammonia from gases, and ammonium-bicarbonate from concentrated wastewaters (i.e. sludge liquor and landfill leachate). The review addresses the microbiology, its consequences for their application, the current status regarding application, and the future developments.
TL;DR: In this paper, the state-of-the-art for N2O control in the nitric acid manufacture is presented, and several options for reducing its emissions are discussed, depending on the position in the process.
Abstract: Nitric acid production represents the largest source of N2O in the chemical industry, with a global annual emission of 400 kt N2O. The high impact of N2O on the environment as greenhouse gas and stratospheric ozone depletor, and the ongoing agreements and prospective regulations calls for the development of efficient and economical systems for N2O mitigation, but no mature commercial technology is yet available. In this review, the current state-of-the-art for N2O control in the nitric acid manufacture is presented. The formation of N2O and the process are analyzed and several options for reducing its emissions are discussed, depending on the position in the process. Primary abatement options deals with modifications in the ammonia oxidation catalyst, secondary abatement with options between the ammonia converter and the absorber, tertiary abatement with options in the tail-gas upstream of the expander, and quaternary abatement with options in the tail-gas downstream of the expander. The abatement technologies are evaluated based on the technical advantages and disadvantages, and cost efficiency.
TL;DR: In this paper, an overview of the design and wind tunnel test results of the wind turbine dedicated airfoils developed by Delft University of Technology (DUT) is given.
Abstract: This paper gives an overview of the design and wind tunnel test results of the wind turbine dedicated airfoils developed by Delft University of Technology (DUT). The DU-airfoils range in maximum relative thickness from 15% to 40% chord. The first designs were made with XFOIL. Since 1995 RFOIL was used, a modified version of XFOIL, featuring an improved prediction around the maximum lift coefficient and capabilities of predicting the effect of rotation on airfoil characteristics. The measured effect of Gurney flaps, trailing edge wedges, vortex generators and trip wires on the airfoil characteristics of various DU-airfoils is presented. Furthermore, a relation between the thickness of the airfoil leading edge and the angle-of-attack for leading edge separation is given.Copyright © 2003 by Delft University of Technology
TL;DR: In this article, the authors explore the nature and functioning of trust in work teams and find that trust is defined as a multi-component variable with distinct but related dimensions, such as propensity to trust, perceived trustworthiness, co-operative and lack of monitoring behaviours.
Abstract: This article aims to explore the nature and functioning of trust in work teams. Trust is defined as a multi‐component variable with distinct but related dimensions. These include propensity to trust, perceived trustworthiness, co‐operative and lack of monitoring behaviours. A model was tested relating trust with perceived task performance, team satisfaction, and two dimensions of organisational commitment, i.e. attitudinal and continuance. Survey data from 112 teams(n=395) was collected in three social care institutions in The Netherlands. The results are supportive of a multi‐component structure for trust and of its importance to the functioning of teams and organisations. Work team trust appeared strongly related with team member's attitudes towards the organisation. Trust between team members was positively associated with attitudinal commitment and negatively with continuance commitment. Trust was also positively related with perceived task performance and with team satisfaction. In addition, perceived task performance appeared strongly related to team satisfaction.
TL;DR: This work has shown that the steadily increasing performance of computers again has become a driving force for new advances in flow visualisation, especially in techniques based on texturing, feature extraction, vector field clustering, and topology extraction.
Abstract: Flow visualisation is an attractive topic in data visualisation, offering great challenges for research. Very large data sets must be processed, consisting of multivariate data at large numbers of grid points, often arranged in many time steps. Recently, the steadily increasing performance of computers again has become a driving force for new advances in flow visualisation, especially in techniques based on texturing, feature extraction, vector field clustering, and topology extraction. In this article we present the state of the art in feature-based flow visualisation techniques. We will present numerous feature extraction techniques, categorised according to the type of feature. Next, feature tracking and event detection algorithms are discussed, for studying the evolution of features in time-dependent data sets. Finally, various visualisation techniques are demonstrated.