"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:b501ee35-170e-4b3f-b1e9-0087cc995c49","http://resolver.tudelft.nl/uuid:b501ee35-170e-4b3f-b1e9-0087cc995c49","Interoperable Protection and control of multi-terminal HVDC systems","Liu, L. (TU Delft Intelligent Electrical Power Grids)","Popov, M. (promotor); Lekić, A. (copromotor); Delft University of Technology (degree granting institution)","2024","The MMC-based MTDC systems are considered a promising solution for long-distance power transmission, integration of renewable energy sources, and interconnection of power grids. Nowadays, MMC-based MTDC systems have been successfully developed in various projects worldwide and are expected to play a significant role in future electrical power transmission systems.
Despite the benefits provided by the MMC-based MTDC system, various technical problems emerge. For example, in case of a DC fault on HVDC transmission lines, the DC voltage suffers a deep sag, and the fault current increases to the peak value after several milliseconds, the system stability is seriously affected. The fault currents will easily damage the power electronics and may lead to a collapse of the entire system if the faults are not cleared promptly. Thus, it is crucial to implement a fast, selective, and reliableDC fault protection technology in the system for fault detection. Once the fault is cleared, it is important to know the exact fault location to repair the faulty sections and to restore the system. Hence, an accurate DC fault location technique is of utmost importance for the MTDC system, which would significantly minimize electricity loss and expedite the system restoration process in the event of power outages. In addition, there is a lack of standardization in MMC control, and the majority of HVDC projects are constructed in a vendor-specific manner. As of today, it is unclear how MMC converters from different manufacturers will interoperate with each other. These pose new challenges to the performance of HVDC protection and MMC control and need to be addressed to manage, safeguard, and accelerate the practical feasibility of this system.
The research in this thesis aims to address the shortcomings that have not been addressed in the state of the art, mainly related to the challenges arising when DC faults occur in the MMC MTDC systems and, as such, could provide promising solutions for future practicalMTDCapplications. The main topics areMMC control&interoperability, Protection, and Fault location for the MMC-based MTDC system. The thesis deals with designing a robust protection scheme, a fault location method, and an investigation of the interoperableMMC controllers...
The computational design of knitting attracted increased attention in recent years. In this dissertation, we consider the customized design and fabrication of 3D and 4D garments as knitwears. The 3D knitwear fits the target human body, and the 4D knitwear also considers comfort during body movement. The main research question (RQ) is: How to design customized 3D and 4D knitwear and generate instructions for a digital knitting machine?
In this dissertation, we researched computational knitwear design methods. We considered not only 3D fitting but also comfort during motion (4D). Our research can be applied in garment production (especially mass customization) or other knitting applications. Garment designers and other industrial designers can use the proposed methods to generate knitting instructions for free-form 3D surfaces. Our 4D design method helps designers place elastic or other varied knitting structures while keeping the intended 3D shape. This dissertation presents new perspectives on computational approaches to existing manufacturing techniques. It also provides enough details to further develop such design systems to be applied in practice.","knitting; computational design; computational fabrication; 3D garment; 4D garment","en","doctoral thesis","","978-94-6384-423-9","","","","","","","","","Emerging Materials","","",""
"uuid:291baefe-c4b9-46ea-b250-a6c8f4e6ece8","http://resolver.tudelft.nl/uuid:291baefe-c4b9-46ea-b250-a6c8f4e6ece8","Pressure-assisted CU sintering for SiC Die-attachment application","Liu, X. (TU Delft Electronic Components, Technology and Materials)","Zhang, Kouchi (promotor); Ye, H. (copromotor); Microelectronics (degree granting institution); Delft University of Technology (degree granting institution)","2023","","nano Cu sintering; Silicon carbide power electronics packaging; Shear Strength; Mechanical reliability; Thermal conductivity; Molecular dynamics; Static and dynamic test; Nanoindentation","en","doctoral thesis","","978-94-6473-018-0","","","","","","2025-01-30","","","Electronic Components, Technology and Materials","","",""
"uuid:3762e136-0fbf-4e7a-b701-36399a3c2cd0","http://resolver.tudelft.nl/uuid:3762e136-0fbf-4e7a-b701-36399a3c2cd0","The hydrocarbon-pool chemistry of methanol conversions in zeolite catalysts","Liu, C. (TU Delft ChemE/Inorganic Systems Engineering)","Pidko, E.A. (promotor); Kapteijn, F. (promotor); Uslamin, E. (copromotor); Delft University of Technology (degree granting institution)","2022","The MTH process is recognized as one of the key ingredients of the methanol (MeOH) economy concept enabling the production of crucial hydrocarbon building blocks, such as light olefins and aromatics, starting from CO2 as the primary carbon source. Besides the driving force of reducing reliance on fossil fuels, the highly tunable nature of this process in response to rapidly changing market demands attracts continuous process development by industry. In academia, proposing comprehensive structure-performance relationships relying on a deeper understanding of the complex reaction pathways makes MTH a perfect model reaction system for new porous material synthesis and catalyst design...","","en","doctoral thesis","","978-94-6384-379-9","","","","","","","","","ChemE/Inorganic Systems Engineering","","",""
"uuid:7e395294-c8da-4f71-8422-7d0f8a2be9c8","http://resolver.tudelft.nl/uuid:7e395294-c8da-4f71-8422-7d0f8a2be9c8","Catalysts and Operating Conditions for Electrochemical Reduction of Carbon Dioxide","Liu, K. (TU Delft ChemE/Materials for Energy Conversion and Storage)","Smith, W.A. (promotor); Dam, B. (promotor); Burdyny, T.E. (promotor); Delft University of Technology (degree granting institution)","2022","The urgent threat of global warming and the demand for sustainable fuels have made the electroreduction of CO2 a priority, due to its possibility in closed-loop cycle of carbon. The energy conversion and strategy can diminish the content of CO2 in the atmosphere, convert renewable electricity into chemical energy and store it in chemical bonds, and gain high-value fuels or chemicals formed from CO2 conversion. However, there is much room for the improvement of the efficiency of electrocatalytic reduction of CO2. The inertness of CO2 determines a large negative potential needed for sufficient electron and proton transfer. Hence, this thesis focuses on research how the catalysts and operating conditions electrochemical influence the electrochemical CO2 reduction...","","en","doctoral thesis","","978-94-6458-605-3","","","","","","","","","ChemE/Materials for Energy Conversion and Storage","","",""
"uuid:9d70c96d-7a7e-4b8d-98d6-d7b0ffaf6812","http://resolver.tudelft.nl/uuid:9d70c96d-7a7e-4b8d-98d6-d7b0ffaf6812","Application of advanced seismic techniques for archaeological investigations","Liu, J. (TU Delft Applied Geophysics and Petrophysics)","Ghose, R. (promotor); Draganov, D.S. (promotor); Delft University of Technology (degree granting institution)","2022","At different places in the world, the local climate conditions have helped the preservation of archaeological sites to a very high degree. This has helped us understand better our history. This situation, however, is quickly changing due to the climate change we are now facing. The condition at an increasing number of ancient sites around the world is now deteriorating due to the warming climate. Obtaining high-resolution images of the subsurface of the archaeological sites without excavation can help us make better strategies for conserving these sites. Such possibilities are provided by the application of geophysical exploration methods. Among all available geophysical approaches, high-resolution reflection seismic using transverse (S-) waves is one of the few options that can provide detailed information regarding the subsurface structure beneath archaeological sites for depths up to several meters. However, most unexcavated sites are covered by soil. Near-surface seismic data acquired in such soil-covered sites are dominated by source-generated, dispersive surface waves, and sometimes surface waves caused by other anthropogenic sources, e.g., traffic and human activities in the vicinity of the seismic line. Both of these strong events can camouflage the very shallow reflections. The conventional techniques for suppression of surface waves, e.g., muting or spatial filtering, are ineffective or even detrimental to the target reflections, especially at near offsets. This is especially challenging in surveys where the available source-receiver offset range is often quite limited, and the velocity and frequency content of the surface waves largely overlap with those of the target S-wave reflections. In chapter 2, we aim to develop a data-driven way to suppress surface-wave noise and thus reveal the very shallow reflections. We make use of seismic interferometry (SI) to retrieve both source-coherent and source-incoherent surface-wave parts of the data. The retrieved surface waves are then adaptively subtracted (AS) from the recorded data, thereby exposing the hidden reflections. We apply our schemes to both synthetic and field seismic data. We show that artifacts caused by stacking surface-wave noise are greatly reduced and that reflectors, especially at very shallow depth, can be much better imaged and interpreted. The dominance of surface waves also make it impossible to identify weak diffraction signals, which is the seismic response of buried objects of small size. The diffraction events can be used to detect and locate the distribution of shallow objects. Revealing the hidden diffraction signals from under the dominant surface waves and using them for locating objects constitute another goal of this thesis. In chapters 3 and 4, we introduce an interferometric workflow for imaging subsurface objects using masked diffractions. This workflow includes three main steps. We first reveal masked diffractions by suppression of the dominant surface waves through a combination of SI and nonstationary AS. The revealed weak diffraction signal is then enhanced by cross coherence-based super virtual interferometry (SVI). Finally, we produce a diffraction image by a multipath summation approach, which can be used to interpret the locations of subsurface diffractors. We apply our method to field data acquired at an archaeological site using two different active sources. Two shallow anomalies were detected in our sections, whose locations agree well with burial burnt stones. These burnt stones have also been detected in an independent magnetic survey and in corings. The limitation of our workflow is that it can only be applied with desired resolution to S-wave data when seismic sources and receivers polarized in the cross-line direction.","","en","doctoral thesis","","978-94-6423-855-6","","","","","","","","","Applied Geophysics and Petrophysics","","",""
"uuid:9f380f03-5842-45a0-87d4-4a8372e88dd5","http://resolver.tudelft.nl/uuid:9f380f03-5842-45a0-87d4-4a8372e88dd5","nD-PointCloud Data Management: continuous levels, adaptive histograms, and diverse query geometries","Liu, H. (TU Delft GIS Technologie)","van Oosterom, P.J.M. (promotor); Meijers, B.M. (copromotor); Delft University of Technology (degree granting institution)","2022","In the Geomatics domain, a point cloud refers to a data set which records the coordinates and other attributes of a huge number of points. Conceptually, each of these attributes can be regarded as a dimension, representing a specific type of information. Apart from routinely concerned spatio-temporal dimensions for coordinates, other dimensions such as intensity and classification are also widely used in spatial applications. In fact, more dimensions can be involved. For instance, a point in the hydraulic modelling grid also records the flow direction, speed, sediment concentration, and other related attributes. As these point cloud data can be directly collected, computed, stored and analyzed, this thesis proposes the term – nD-PointCloud, as a general spatial data representation to cover them.
At present, drastically increasing production of nD-PointCloud data raises essential demand for smart and highly efficient data management and querying solutions. However, we lack effective tools. Prevalent software for nD-PointCloud processing, analyzing and rendering are built on file-based systems, requiring substantial development of data structures and algorithms. To make things worse, when other data types are involved, multiple formats, libraries and systems need enormous effort to be integrated. Aimed at generic support for diverse applications, DataBase Management Systems (DBMSs) on the other hand avoid these issues to a large extent. However, since they are initially developed to resolve 2D or 3D issues, they do not provide native support for nD data indexing and operations. Yet the 2D and 3D operators cannot be easily extended to nD.
This thesis aims at developing a generic yet efficient solution for managing and querying nD-PointCloud data. The work is based on an existing solution called PlainSFC, which maps nD data into 1D space. PlainSFC is implemented in the DBMS, adopting space filling curve based clustering and B+-tree indexing strategies. Besides, PlainSFC applies an advanced querying mechanism which recursively refines hypercubic nD spaces to 1D ranges to approach the query geometry for primary filtering. This achieves high querying efficiency. However, the solution still has drawbacks, and this research focuses on resolving them by developing and using novel methods:
• A continuous Level of Importance (cLoI) method for data organization to eliminate visual artifacts of density shocks in points' rendering, which is introduced by conventional tree structures such as Quadtree or Octree. The cLoI method computes an importance value for every point according to an ideal distribution generalized from the discrete distributions of those tree structures. This forms an additional cLoI dimension, and each point actually represents a level. By integrating the cLoI dimension into PlainSFC, smooth and efficient rendering is realized.
• An nD-histogram approach to improve querying efficiency on non-uniformly distributed data. PlainSFC decomposes the nD space into sub-spaces recursively to approach the query geometry without considering point distribution. This is not optimal when the distribution of points is severely skewed. To improve this, an nD-histogram which records the number of points inside each nD sub-space is established as a representation of data distribution. The developed solution called HistSFC decomposes and refines the nD space more smartly, which improves the accuracy and efficiency of primary filtering.
• A convex polytope querying function. Besides orthogonal window queries, the polytope query, which is the extension of the widely adopted polygonal query in 2D, also plays a critical role in many nD spatial applications. To address this type of query, an easy-to-use polytope formulation for querying is firstly proposed. Then, based on PlainSFC and HistSFC, efficient intersection algorithms are developed for convex polytope querying on nD point clouds. These algorithms are tested through experiments with up to 10D point data. Using this newly developed function, applications including perspective view selections and flood risk queries are resolved more efficiently, achieving sub-second performance.
Additionally, other optimization techniques such as parallelization are developed and experimented with, which also bring performance gain. To verify the whole framework, several benchmark tests devised by considering real applications are conducted, and comparisons with different state-of-the-art solutions are performed. The result shows that the newly developed solution outperforms the others, overall. In certain cases, the solution can be applied without further optimizations. However, this will not be the end. Rapidly arising high tech such as cloud computing platforms can boost the solution further to incorporate more data and users. Potential nD-PointCloud based applications still need to be explored, prototyped and tested to serve the society in practice.
and investigated the possibility that using the radiation power as a trigger for drug release from the micelles. In the second part, we focus more on the cooperation of radionuclides and PCL-PEO micelles. So far we developed a chelator-free method to radiolabel micelles for determining their in vivo behavior, as well as evaluated the possibility to combine chemotherapy with radionuclide therapy using the micelles as a nanoplatform. In both parts we attempted to unravel mechanisms behind the observed phenomena to be able to adjust the
nano-carriers accordingly.
extended the traditional signal processing tools to the graph domain. Under
these circumstances, the emergence of graph signal processing has offered a
brand new framework for dealing with complex data. In particular, the graph
Fourier transform (GFT) lets us analyze the spectral components of a graph signal in the graph frequency domain. Based on the GFT, graph filters provide useful tools to modify or extract spectral parts in terms of different objectives, e.g., using a low-pass graph filter to construct graph signals without noise. This thesis mainly focuses on designing and implementing graph filters. Similar to traditional signal processing, we investigate two types of graph filters: finite impulse response (FIR) and infinite impulse response (IIR) graph filters. Moreover, this thesis takes both undirected and directed graphs into account for the design methods and implementations.
This thesis presents a series of studies focusing on wind induced hydrodynamic circulation in large shallow lake, with the implication of Taihu Lake from lake scale hydrodynamic study, to lake scale water quality implication, and to basin scale implication. The proposed modelling approach could serve as a basis and provide information on lake scale wind effects on hydrodynamic circulation and catchment scale urbanization implication on water environment for management and planning of Taihu Lake and Taihu Basin.
Our first main contribution is related to temporal correlations. In most of the studies, the influence of time in the SIS spreading process is omitted because the specific value of the infection and curing rates does not influence the first-moment metastable properties, such as the infection probability of each node. Only the ratio between the two rates matters. In this dissertation, we show that the temporal correlation can be analyzed with the mean-field approaches, although mean-field methods are meant to only analyze first-moment properties. We derive the autocorrelation of the nodal infection state both in the steady and transient states under the mean-field approximation. By analyzing the autocorrelation, we indicate the influence of the underlying network and the value of the infection and curing rates on the temporal properties of the spreading process. We also show that the infection and curing rates can be calculated by measuring the infection state of each node.
Second, we relax the Markovian assumption in the SIS process by extending the Poisson infection process to a Weibull renewal process. The Poisson infection process is just a special case of the Weibullian renewal process. Under this Weibullian framework, we can parameterize the non-Markovian infection behavior and show some new features raised by it. We specifically focus on an extreme (limiting) case of the Weibullian SIS process where the distribution of the infection time is a Dirac delta function. The analysis of the extreme case leads to the largest possible epidemic threshold for non-Poissonian infection processes. We further discuss the epidemic threshold for different infection processes with Weibull, lognormal and Gamma distributed infection time, which fit realistic spreading phenomena well, under a previous non-Markovian mean-field method based on renewal theory. We show consistency between our results and previous theory and that those different infection processes behave similarly.
Third, we dive into the localization phenomena in networks from the viewpoint of SIS spreading processes. Localization of the spreading process appears just above the epidemic threshold in networks whose principal eigenvector of the adjacency matrix is localized. In the localized spreading, the prevalence (order parameter), which is the expected fraction of infected nodes, converges to zero with the increase of network size but the number of infected nodes is non-zero. Thus, the localized spreading forms an interesting phase different from the all-healthy phase (no infection) and the endemic phase (non-zero prevalence). We evaluate the above-mentioned extreme case of the Weibullian SIS process where the time-dependent prevalence is periodic in the long-run. Near the epidemic threshold, the ratio between the steady-state maximum and minimum prevalence, which equals to the largest eigenvalue of the adjacency matrix, diverges in some networks, but the spreading process is still localized. In other words, the divergent ratio of prevalence, determined by the largest eigenvalue of the network, cannot amplify a zero-prevalence to a non-zero one in the thermodynamic limit. The result indicates that the localization of spreading processes may be only determined by the network structure but not the specific infection process.
Finally, we study the curing strategy for the control of the spreading process, specifically, the pulse curing strategy. Compared to the classical asynchronous curing strategy (for instance Poissonian), pulse strategy is an optimized method of suppressing the spreading and applied broadly in disease control. Here, we study the model which is composed of a susceptible-infected process and a periodical pulse curing process with a successful curing probability below one. We derive the mean-field epidemic threshold. Based on our analysis, the pulse strategy reduces the number of curing operations by $36.8\%$ compared to traditional asynchronous curing strategies in the Markovian SIS model.
All the above-mentioned theoretical analyses are verified by directly simulating SIS processes.","Spreading Process; Complex Networks; Stochastic Simulation","en","doctoral thesis","","978-94-6384-074-3","","","","","","","","","Network Architectures and Services","","",""
"uuid:1f879b34-73f1-42e1-96c0-92f85289e13e","http://resolver.tudelft.nl/uuid:1f879b34-73f1-42e1-96c0-92f85289e13e","Multi-functional LED Module Integration and Miniaturization for Solid State Lighting Applications","Liu, P. (TU Delft Electronic Components, Technology and Materials)","Zhang, Kouchi (promotor); van Zeijl, H.W. (copromotor); Delft University of Technology (degree granting institution)","2019","Solid State Lighting (SSL) develops towards small size, high lumen output, high working temperature, and multi-functional applications. These trends are more desirable in miniaturized LED applications such as retrofit G4 LED devices. Retrofit G4 LEDs were chosen in this work as a technical carrier due to the miniaturized size challenge and high lumen requirements. The solutions for miniaturized retrofit G4 can also be extended to other applications of consumer lighting applications with similar requirements.","Solid State Lighting; Miniaturization; Wafer Level Integration","en","doctoral thesis","","978-94-6380-220-8","","","","","","","","","Electronic Components, Technology and Materials","","",""
"uuid:40873d8a-b698-4bd1-a9a5-4803989ba537","http://resolver.tudelft.nl/uuid:40873d8a-b698-4bd1-a9a5-4803989ba537","Indoor Semantic Modelling for Routing: The Two-Level Routing Approach for Indoor Navigation","Liu, L. (TU Delft Urban Data Science)","van Oosterom, P.J.M. (promotor); Zlatanova, S. (copromotor); Delft University of Technology (degree granting institution)","2017","Humans perform many activities indoors and they show a growing need for indoor navigation, especially in unfamiliar buildings such as airports, museums and hospitals. Complexity of such buildings poses many challenges for building managers and visitors. Indoor navigation services play an important role in supporting these indoor activities. Indoor navigation covers extensive topics such as: 1) indoor positioning and localization; 2) indoor space representation for navigation model generation; 3) indoor routing computation; 4) human wayfinding behaviours; and 5) indoor guidance (e.g., textual directories). So far, a large number of studies of pedestrian indoor navigation have presented diverse navigation models and routing algorithms/methods. However, the major challenge is rarely referred to: how to represent the complex indoor environment for pedestrians and conduct routing according to the different roles and sizes of users. Such complex buildings contain irregular shapes, large open spaces, complicated obstacles and different types of passages. A navigation model can be very complicated if the indoors are accurately represented. Although most research demonstrates feasible indoor navigation models and related routing methods in regular buildings, the focus is still on a general navigation model for pedestrians who are simplified as circles. In fact, pedestrians represent different sizes, motion abilities and preferences (e.g., described in user profiles), which should be reflected in navigation models and be considered for indoor routing (e.g., relevant Spaces of Interest and Points of Interest)...","","en","doctoral thesis","A+BE | Architecture and the Built Environment","978-94-92516-93-0","","","","A+BE | Architecture and the Built Environment No. 17 (2017)","","","","","Urban Data Science","","",""
"uuid:71da5266-8d7a-4143-91de-d2284fb02639","http://resolver.tudelft.nl/uuid:71da5266-8d7a-4143-91de-d2284fb02639","Materials aspects of hydro-abrasive wear in the dredging industry","Liu, Y. (TU Delft Micro and Nano Engineering)","Janssen, G.C.A.M. (promotor); Delft University of Technology (degree granting institution)","2017","A better understanding of the wear mechanism of materials is essential to selecting suitable materials to prolong service time and reduce costs. Wear resistance is not an intrinsic material property but a response to a system including multiples parameters determined by the material, the counter body, the load condition, and the environment. Wear is a common cause of materials degradation, as well as Corrosion. When mechanical wear and corrosion co-exist, they interact with each other and, often, enhance each other, resulting in faster material failure than the situation where only a single factor exists. This thesis presents the study of the interaction between corrosion and wear with the goal of obtaining a better understanding of the wear mechanism to guide the material selection. To study the wear mechanism, a pin on disc tribometer was employed to precisely control the load, rotational speed, and corrosion environment. A potentiostat was also used to provide well-defined corrosion environment (corrosion is quantified by the current and potential). By connecting the pin on disc with a potentiostat, a well-controlled mechanical and chemical (electrochemical) system was employed to perform wear experiments. Results show that the influence of corrosion on wear is found to be much more complex than simply enhancing, as proposed at the onset of my PhD research. The new findings in this thesis show that the influence of corrosion is highly dependent on the specific situation and the corresponding wear mechanism. Corrosion may increase wear rate when the process is governed by cyclic formation and removal of surface corrosion products. Corrosion may decrease wear rate when the process is governed by the galvanic micro coupling effect. Corrosion may not influence wear rate when the process is dominated by impacting.","Wear; Corrosion; Surface roughness; Micro coupling; Carbon enrichment; Cathodic protection","en","doctoral thesis","","978-94-91909-46-7","","","","","","","","","Micro and Nano Engineering","","",""
"uuid:8736e6df-f2fb-48ac-aa28-7d61a214507e","http://resolver.tudelft.nl/uuid:8736e6df-f2fb-48ac-aa28-7d61a214507e","Reduction of uncertainty in stability calculations for slopes under seepage","Liu, K. (TU Delft Geo-engineering)","Hicks, M.A. (promotor); Vardon, P.J. (copromotor); Delft University of Technology (degree granting institution)","2017","br","Data assimilation; ensemble Kalman filter; heterogeneity; inverse analysis; seepage; slope stability; uncertainty reduction; unsaturated soil","en","doctoral thesis","","9789461868442","","","","","","2017-09-22","","","Geo-engineering","","",""
"uuid:074d4f96-e7bf-4dde-a7b4-86c9dd2e214f","http://resolver.tudelft.nl/uuid:074d4f96-e7bf-4dde-a7b4-86c9dd2e214f","Increasing the Feasibility of Superconducting Generators for 10 MW Direct-Drive Wind Turbines","Liu, D. (TU Delft DC systems, Energy conversion & Storage)","Ferreira, Jan Abraham (promotor); Polinder, H. (copromotor); Abrahamsen, Asger Bech (copromotor); Delft University of Technology (degree granting institution)","2017","In recent years, superconducting synchronous generators (SCSGs) have been proposed as an alternative to permanent magnet synchronous generators (PMSGs). They are expected to reduce the top head mass and the nacelle size for such large wind turbines. In 2012, the INNWIND.EU project initiated this research to investigate SCSGs for 10-20MWdirect-drive offshore wind turbines. However, the feasibility of SCSGs was limited by a few critical issues, such as high costs, AC losses in the superconducting winding and excessive short circuit torque. Furthermore, SCSG designs proposed in the literature were various but all less competitive than PMSGs.","Feasibility; superconducting generator; direct-drive; wind turbine","en","doctoral thesis","","978-94-6299-627-4","","","","","","","","","DC systems, Energy conversion & Storage","","",""
"uuid:3cb7ded7-4308-4199-8afa-7027d2991076","http://resolver.tudelft.nl/uuid:3cb7ded7-4308-4199-8afa-7027d2991076","Analysis and Design of Low-Power Receivers: Exploiting Non-50 Ω Antenna Impedance and Phase-Only Quantization","Liu, Y. (TU Delft Bio-Electronics)","Serdijn, W.A. (promotor); Delft University of Technology (degree granting institution)","2017","Reducing the power consumption of low-power short-range receivers is of critical importance for biomedical and Internet-of-Things applications. Two interesting degrees of freedom (or properties) that have not been fully exploited in the pursuit of low power consumption are the antenna impedance and the phase-only modulation property of FSK/PSK signals. This dissertation explores the possibility of reducing the power consumption of the receiver by utilizing these two degrees of freedom.","","en","doctoral thesis","","978-94-028-0627-4","","","","","","","","","Bio-Electronics","","",""
"uuid:bef6c12f-5804-407b-a4c6-f7949541f21c","http://resolver.tudelft.nl/uuid:bef6c12f-5804-407b-a4c6-f7949541f21c","Impacts of rudder configurations on inland vessel manoeuvrability","Liu, J. (TU Delft Ship Design, Production and Operations)","Hopman, J.J. (promotor); Hekkenberg, R.G. (copromotor); Delft University of Technology (degree granting institution)","2017","Ship manoeuvrability is fundamental for the navigation safety of ships. Furthermore, through the equipment used for manoeuvring, it also affects investment, operation, and maintenance cost of these ships. Ships are primarily designed from an economic point of view. To ensure and improve the maritime efficiency, research on inland vessel manoeuvrability deserves more attention than the present situation. Most of the research on manoeuvrability has been performed for seagoing ships. Since sailing conditions and ship particulars between seagoing ships and inland vessels are different, the impacts of these differences on manoeuvring prediction and evaluation should be carefully considered.
Inland vessels should be designed in such a way that they should always be capable of manoeuvring without significantly harming the cost-effectiveness of operations. One of the biggest differences between seagoing ships and inland vessels is the rudder configuration. Conventionally, seagoing ships have similar single-rudder configurations while inland vessels have more complex multiple-rudder configurations. Although multiple-rudder configurations can have a positive effect on manoeuvrability, they often have a negative effect on resistance and, therefore, also a negative effect on the fuel consumption.
Quantitative impacts of the rudder configuration on ship manoeuvrability have not been fully understood, especially for multiple-rudder configurations with complex rudder profiles. These differences in the rudder configuration may significantly change the ship manoeuvring behaviours and, therefore, should require further research. Moreover, to compare and evaluate the manoeuvring performance of inland vessels with different configurations, the existing manoeuvring tests and standards for inland vessels are less elaborate than those for seagoing ships. The above-mentioned considerations formulate the following main research question: What are the proper rudder configurations to achieve well manoeuvrable inland vessels without significant loss of navigation efficiency?
The main research question of this thesis can be answered through resolving four key research questions as follows:
Q1. What are the practical manoeuvres to evaluate and compare the manoeuvring performance of inland vessels?
Q2. How does the rudder configuration affect the rudder hydrodynamic characteristics?
Q3. How do changes in the rudder configuration affect the ship manoeuvrability in specific manoeuvres?
Q4. How to choose a proper rudder configuration according to the required manoeuvring performance?
An accurate estimation of rudder forces and moments is needed to quantify the impacts of the rudder configurations on ship manoeuvring performance. This thesis applied Reynolds-Averaged Navier-Stokes (RANS) simulations to obtain rudder hydrodynamic characteristics and integrated the RANS results into manoeuvring models. Additionally, new manoeuvres and criteria have been proposed for prediction and evaluation of inland vessel manoeuvrability. Simulations of ships with various rudder configurations were conducted to analyse the impacts of rudder configurations on ship manoeuvrability in different classic and proposed test manoeuvres. Accordingly, guidance on rudders for inland vessel manoeuvrability has been summarised for practical engineers to make proper design choices.
Through the research presented in this thesis, it is clear that different rudder configurations have different hydrodynamic characteristics, which are influenced by the profile, the parameters, and the type of a specific configuration. New regression formulas have been proposed for naval architects to quickly estimate the rudder induced forces and moments in manoeuvring. Furthermore, an integrated manoeuvring model has been proposed and validated for both seagoing ships and inland vessels. Using the proposed regression formulas and manoeuvring model, the impacts of rudder configurations on inland vessel manoeuvrability have been studied.
The manoeuvring performance of a typical inland vessel can be improved by 5% to 30% by changing the rudder configuration. The rudder configuration should be capable of providing sufficient manoeuvring forces and then optimised to reduce the rudder induced resistance. In general, well-streamlined profiles are good for efficiency but not as good as high-lift profiles for effectiveness. As a summary, the ship manoeuvring performance can be improved by using effective profiles, enlarging the total rudder area, accelerating the rudder inflow velocity, increasing the effective rudder aspect ratios, and enlarging the spacing among multiple rudders.","inland vessels; inland vessel manoeuvrability; ship manoeuvrability; rudder configurations; manoeuvring simulations; rudder profiles; rudder prarameters; rudder design; rudder hydrodynamic characteristics; Computational Fluid Dynamics (CFD)","en","doctoral thesis","","978-94-6233-5622","","","","","","2021-08-27","","","Ship Design, Production and Operations","","",""
"uuid:2a1f0bd2-ac41-4707-8d3a-b7f2c74d8ad4","http://resolver.tudelft.nl/uuid:2a1f0bd2-ac41-4707-8d3a-b7f2c74d8ad4","Impacts of rudder configurations on inland vessel manoeuvrability","Liu, Jialun","Hopman, H. (promotor)","2017","","hydrodynamics","","doctoral thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Marine and Transport Technology","Ship Design, Production and Operation","","",""
"uuid:a30f03a2-ea65-44fe-9e63-1551e2722450","http://resolver.tudelft.nl/uuid:a30f03a2-ea65-44fe-9e63-1551e2722450","Self-organizing energy-autonomous systems","Liu, Q. (TU Delft Embedded Systems)","Brazier, F.M. (promotor); Langendoen, K.G. (promotor); Warnier, Martijn (copromotor); Pawełczak, Przemysław (copromotor); Delft University of Technology (degree granting institution)","2016","With the rapid development of mobile technology, more and more devices connect to the Internet of Things (IoT). The management of such large-scale networks becomes a challenge. Firstly, a large number of heterogeneous devices are distributed over a wide area, leading to a variation of the requirements of users, the performance of mobile devices, and the application scenarios. As the size of the IoT increases, the complexity of controlling such systems becomes a challenge. Most existing solutions choose global control, and are designed for a specific type of application scenario. However, any changes in the network, e.g. topology, node density, etc., affect the control schedule of the central node. Once the context changes beyond the adaptation ability, the system can hardly function anymore. Furthermore, the center node is the single break point in the control structure. Therefore, it is critical to find a solution with autonomous management, in which networks are organized and controlled by the local management of each node. Secondly, maintaining the power supply for a large number of battery-operated mobile devices in the IoT becomes a challenge. The most direct solution is to replace batteries of devices periodically. However, this costs much money, time, and human resources. Increasing the size of the battery is another commonly used approach, but this enlarges the formand weight of devices, which is unsuitable for application scenarios where size and weight of devices should be minimized. Therefore, we need an approach where devices have autonomous energy, in which batteries of mobile devices can be wirelessly charged. Based on the motivation above, the research of this dissertation is positioned in the area of autonomic computing. The proposed systems are self-adaptive self-organized and use radio-frequency based wireless power transfer. Specifically, nodes in the network can achieve global operation, based on local information exchange and control of each node, and increase battery lifetime by harvesting energy from transmitted radio waves and decreasing the duty cycle of radio in the communication protocol. In the area of self-adaptive self-organization systems, we explore controlling networks based on local information exchange. The global operation of the whole network is controlled by local management of each node. The advantage is that nodes do not need to collect a large amount of global information, which largely decreases the communication complexity of the network. We leverage this mechanism in two case studies. First, we target data aggregation in mobile networks. Our algorithmuses evolutionary dynamics to select and spread the configuration of each node, and the network automatically adapts to the variation of application scenarios. The network can optimize configurations without predesigned setup for a specific scenario. In the second case study, we design an algorithmto achieve distance estimation with self-organization in large-scale mobile networks. The algorithm uses messages collected by local information exchange for statistical calculation, and the network collectively estimates distances between nodes in the network. This improves the accuracy and extends the application area of the existing distance estimation approaches. In the area of wireless power transfer systems, the main contribution is based on the exploration of increasing the efficiency of energy transmission and utilization in mobile devices using radio-frequency based wireless power transfer. First of all, we exploit the properties of active and backscatter radio for increasing the energy efficiency of harvesters. We demonstrate the world’s first hybrid radio platformthat combines the strengths of active radio (long range and robustness to interference) and backscatter radio (low power consumption). We design a switching mechanism that selects active radio or backscatter radio for different radio channel qualities. The measurement results onmobile devices prove that harvesting and saving radio energy is not the only choice to provide autonomous energy, and that backscatter radio for communication is more energy efficient for some applications on mobile devices. Second, we save energy on the charger side to make wireless power transfer green. Wireless power transfer based on radio frequency radiation and rectification is fairly inefficient due to power decaying with distance, antenna polarization, etc. To save energy in chargers, we monitor the idle charging state in wireless power transfer networks and switch off the energy transmitters when the received energy is too lowfor rectification. Although this systemdoes not directly increase the efficiency of the radio harvesting process, the saved energy in chargers largely boosts the energy efficiency of the whole wireless power transfer network. The system is especially valuable for increasing the lifetime ofmobile chargers powered by batteries. Finally, to demonstrate the value of energy autonomy in real applications, we select indoor localization using wireless power transfer as a case study. We design a battery-less indoor localization system that can operate perpetually under wireless power transfer. The novel localization method operates at energy levels that are within the energy budget provided by wireless power transfer today, and the communication schedule is well-designed to minimize the amount of idle listening. We use off-the-shelf devices to implement and deploy the system. It proves the feasibility of using long-range wireless power transfer for mobile systems.","SELF-ORGANIZING; ENERGY-AUTONOMOUS","en","doctoral thesis","","978-94-6186-762-9","","","","This work was carried out in the ASCI graduate school of TUDelft. ASCI dissertation series number: 363","","","","","Embedded Systems","","",""
"uuid:e813298e-93d8-4a76-a7ab-72b327bcde4b","http://resolver.tudelft.nl/uuid:e813298e-93d8-4a76-a7ab-72b327bcde4b","Prediction of belt conveyor idler performance","Liu, X. (TU Delft Transport Engineering and Logistics)","Lodewijks, G. (promotor); Pang, Y. (copromotor); Delft University of Technology (degree granting institution)","2016","","bulk material; condition monitoring; maintenance; belt conveyor; idler; reliability","en","doctoral thesis","TRAIL Research School","978-90-5584-207-0","","","","TRAIL Thesis Series T2016/14, The Netherlands TRAIL Research School","","","","","Transport Engineering and Logistics","","",""
"uuid:2d1d6e46-f90d-4d73-8021-aa6b6437c46d","http://resolver.tudelft.nl/uuid:2d1d6e46-f90d-4d73-8021-aa6b6437c46d","Modeling, robust and distributed model predictive control for freeway networks","Liu, S. (TU Delft Team Bart De Schutter)","De Schutter, B.H.K. (promotor); Hellendoorn, J. (promotor); Delft University of Technology (degree granting institution)","2016","In Model Predictive Control (MPC) for traffic networks, traffic models are crucial since they are used as prediction models for determining the optimal control actions. In order to reduce the computational complexity of MPC for traffic networks, macroscopic traffic models are often used instead of microscopic traffic models. These macroscopic traffic models can be divided into homogeneous, single-class models and heterogeneous, multi-class models. In general, multi-class models are more accurate than single-class models, without increasing the computational complexity significantly. In MPC a more accurate model in general implies a better prediction of the controlled system, providing the controller more accurate information for determining the control actions. Therefore, developing and using multi-class traffic models is one way to improve the effectiveness of MPC. Apart from the above characteristics of traffic models, other factors such as uncertainties in external inputs and model parameters can also affect the accuracy of predictions. Thus another way for improving the effectiveness of MPC is to take into account the effects of these uncertainties and to develop robust MPC approaches for handling these uncertainties. Apart from improving the effectiveness of MPC, making MPC feasible for large-scale traffic networks is also important, due to the rapid increase of the computational complexity of the MPC optimization problem with the size of the controlled system. For large-scale systems, Distributed Model Predictive Control (DMPC) is often considered for making the control approach computationally feasible. Moreover, robust DMPC can be developed for ensuring both feasibility and robustness.","freeway networks; model predictive control; multi-class macroscopic traffic models; scenario-based receding-horizon parameterized control; scenario-based distributed model predictive control","en","doctoral thesis","","978-90-5584-199-8","","","","","","","","","Team Bart De Schutter","","",""
"uuid:2ee2b93d-d3e9-41e7-888a-a52f231070c8","http://resolver.tudelft.nl/uuid:2ee2b93d-d3e9-41e7-888a-a52f231070c8","Self-healing supramolecular nanocomposites","Liu, Z.","Picken, S.J. (promotor); Besseling, N.A.M. (promotor)","2015","The aim of this thesis is to execute a bottom-up design of the intrinsically self-healing nanocomposites. We briefly introduced the self-healing materials in chapter 1, covering classification and basic self-healing mechanism. In chapter 2, we have synthesized polyborosiloxane (PBS) according to the last century recipe as the self-healing supramolecular matrix. Additionally, we provided the long existing recipe with exclusive supplementary details, such as reaction kinetics, structural refinement and characterization, mechanical performance, glass transition temperature, etc. We have denoted the refined PBS, in which the end groups of PBS primarily exhibit in the well-defined borono structure (B(OH)2), rPBS. In chapter 3, the molecular interaction of PBS molecules that leads to the self-healing behavior was investigated with modern techniques. Besides the well-known physically cross-linked H-bonds, PBS molecules also cross-link via forming reversible covalent boroxane structures (B-O-B). Chapter 4 and 5 focus on the reinforcing effects of rigid nanoclay particles (Cloisite 20A) and flexible graphene oxide (GO), respectively. As PBS molecules bear the hydrophilic borono end groups, the incorporation of natural clay and graphene oxide leads to softened nanocomposites due to their hydrophilic surfaces. GO platelets efficiently drive the GO/rPBS nanocomposite into thixotropic material readily at a mass fraction of 0.001. However, natural clay surface is not as hydrophilic as GO. The softening effect is not only less pronounced, but also quickly compensated due to the formation of the particle network. Nevertheless, it results in a paste-like thixotrope when the mass fraction of natural clay reaches 0.6. Cloisite 20A and OMGO are surface modified natural clay and GO, with almost the same alkyl modifier. They behave as ordinary reinforcement additives and may efficiently enhance the rheological properties of the nanocomposites.","self-healing; mechanism; nanocomposites; particle network; graphene oxide; thixotropic","en","doctoral thesis","","","","","","","","","Applied Sciences","Chemical Engineering","","","",""
"uuid:f6a61773-4173-4728-a2e3-ce320228753a","http://resolver.tudelft.nl/uuid:f6a61773-4173-4728-a2e3-ce320228753a","Optical Coherence Tomography for Material Characterization","Liu, P.","Benedictus, R. (promotor)","2014","Optical coherence tomography (OCT) is a non-invasive, contactless and high resolution imaging method, which allows the reconstruction of two or three dimensional depth-resolved images in turbid media. In the past 20 years, OCT has been extensively developed in the field of biomedical diagnostics, while OCT in the non-destructive testing (NDT) field is lagging far behind. The aim of this thesis is to use OCT as a novel NDT technique for material structure characterization and damage detection. Besides an overview of the OCT fundamentals and developments, the thesis is mainly driven by three tasks: instrument design, signal processing, and applications. An integrated OCT system working at a wavelength of 1550 nm has been built. It combines time domain (TD) and Fourier domain (FD) OCT to make the both types of measurement available in one instrument. TD-OCT has the advantage of a large A-scan range and high SNR, while FD-OCT system has tremendous superiority in fast imaging due to no movement of the reference mirror. These two kinds of measurement can be implemented based on the user request in the developed hybrid OCT system, e.g. improved imaging depth or speed. In TD-OCT, the envelope detector was selected as the ideal method for the demodulation of each axial signal. A bandpass filter and 2D median filter are applied before and after demodulation, respectively, to reduce OCT system and speckle noise. In FD-OCT, raw data was first processed to remove the influence from the optical source and dark noise of the CCD detectors. It was then linearly resampled to convert to evenly spaced intervals of wavenumber, instead of wavelength. With an inverse Fourier transform, one depth profile was recovered and a cross-sectional image was constructed by accumulating a series of depth profiles. The quality of cross-sectional images can be further improved by merging multiple images with different pathlength offsets. The application of the designed OCT system was mainly focused on glass fiber composites and the microstructure of the specimens was displayed by either cross-sectional or volumetric images. Special attention was given to delamination growth in a glass fiber composite for wind turbine blade applications. The glass fiber composite was tested by incremental loading. Volumetric images obtained by OCT were further processed to reconstruct 3D crack surface profiles, from which a full field view of the delamination crack was given, providing substantial information for the study of crack growth in the composites. Additionally, the study explored the use of optical coherence elastography (OCE) for the deformation measurement of glass fiber composites, for the first time to the best of our knowledge. The developed OCE system based on speckle tracking was first evaluated by a test of ridge body translation. Then experiments were implemented for a set of glass fiber composites under tensile testing and three point bending. The results show that OCE can measure the internal displacements of a glass fiber composite in the range from a few micrometers to hundreds of micrometers. Besides, other applications are also presented in the thesis. These include defects and thickness measurement of polymer coating and the microstructure characterization of a wooden-panel painting. The results show the designed OCT system also has high potential for these alternative applications. Recommendations for further improvement to the OCT design and the applications are presented at the end of the thesis.","Optical Coherence Tomography; Non-destructive Testing; Glass Fiber Composites; Delamination","en","doctoral thesis","","","","","","","","","Aerospace Engineering","Aerospace Structures and Materials","","","",""
"uuid:90df47f1-197b-4ae4-a759-3f9796f2784a","http://resolver.tudelft.nl/uuid:90df47f1-197b-4ae4-a759-3f9796f2784a","A Method for Transmission Network Expansion Planning: A Monte-Carlo and Lagrangian Multiplier-based Optimisation Approach","Liu, Z.","Van der Sluis, L. (promotor); Papaefthymiou, G. (promotor)","2014","Power systems conventionally have been designed and operated to facilitate electrical energy transportation from large centralised power plants to distant load centres. It is currently under development towards the purpose of being able to facilitate more distributed generation from renewable energy sources (RES), for instance wind and solar energy. Increasing the share of RES would allow us to replace carbon-intensive energy sources and achieve significant reduction of the greenhouse gas emissions, establish vast and inexhaustible energy supply, and offer more affordable electricity price amongst others. On the other hand, the integration of RES to the existing power systems brings additional challenges to system planners and operators. Transmission system operators (TSOs) are already facing operational challenges of high power flows starting in the areas with large wind power installations in Germany to the remote load centres, observing substantial loop flows through Poland and the Czech Republic. As a consequence, the daily operation of Europe's electricity system is increasingly threatened by the risks of blackouts or component failures with wide-reaching impact. According to ENTSO-E the changing generation mix will contribute to upcoming congestion situations, resulting in a limitation in possible exports. The Commission's Priority Interconnection Plan also points out the danger arising from the operation of networks closer to their physical limits. It is of utmost importance to develop a methodology that is able to identify transmission network bottlenecks, i.e. those components with a high potential to be the origin of a major blackout or cascading event, meanwhile incorporating the uncertainties caused by the RES integration as well as the diversified energy policies in terms of future generation mixes. The improvement of the transmission and distribution infrastructure begins with the identication of its current shortcomings. Another aspect of power system assessment is to investigate transmission congestions, which is labelled as the 'symptom' of the insufficient transfer capacity when the existing capacity cannot facilitate the desired electricity demand. The reduction of congestions is an indicator of social and economic welfare assuming equitable distribution of benefits under the goal of the European Union to develop an integrated market as stated in the ENTSO-E Ten Year Development Plan. A relative small number of additional capacity could lead to major economic benefits for many consumers, as advised by US Department of Energy. For such demanding requests on the power system assessment, there is strong need to translate the explained challenges into an engineering problem, which requires a clear technical vision of the aforementioned challenges in the power system operation and planning, in addition to a clear understanding of power system modelling with substantial supporting material of mathematics. To substantiate the knowledge of both engineering and mathematics, the thesis provides a structured way of elaborating the engineering background of power systems as well as the mathematical formulations that are essential for understanding the novelty of the proposed methods (Chapters 2, 3 and 4 of this thesis). Chapter 5 provides a method for the transmission network assessment taking into account the wind stochasticity using a unified Monte-Carlo method and Copula approach. Two main reasons of using the Monte-Carlo method are a) the anti-aliasing property and b) the ability to quickly approximate the answer that otherwise would be very computation-intensive. The methodology is firstly elaborated and applied to a single scenario study, and further enhanced to a more general approach that allows taking into account multiple scenarios caused by uncertainties raised from energy policy perspectives. The solution set of the multiple scenario study captures the impact of uncertainties of all energy policy perspectives without increasing the size of stochastic infeed inputs. A new method for the transmission expansion planning problem is presented in Chapter 6 and 7, which separate the topic into snapshot-based and multi-stage expansion planning methods. Actively optimising Lagrangian multipliers as 'primal' variables in the optimization problem is used as a tool for the network expansion, providing the copper-plate topology from either a congested or an infeasible grid configuration. The method also emphasizes the over-investment issues by introducing a maximum allowable overloading factor, to prevent a large amount of inefficient investment on 'minor' congestions. The multi-stage expansion planning method further strengthens the snapshot-based method by proposing the optimal network topology at different time horizon chronologically, taking into account the possible scenarios of conventional generation mix, load and wind energy infeed at each stage. The modular approach of functionally partitioning the multi-stage planning methodology offers additional advantages including a) reducing computational effort, b) allowing easy modification of the existing modules, and c) allowing adaptation of other modules for enhancement, etc. The final optimal expansion plan at each stages guarantees the copper-plate network structure subject to various scenarios and wind generation infeeds at the lowest operational and investment costs.","","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Power Engineering","","","",""
"uuid:bacef458-dc8a-49b3-bfd9-609517b0ef49","http://resolver.tudelft.nl/uuid:bacef458-dc8a-49b3-bfd9-609517b0ef49","Generation Y Interactions: Making the Office Catch Up","Liu, W.","Stappers, P.J. (promotor)","2014","The rapid development of information technology in the past decade has enabled the introduction of a number of new communication tools and platforms in everyday life, such as instant messaging, podcasting, blogging and social networking. These tools offer people new ways of interacting, enabling them to create, retrieve and broadcast large amounts of digital information, using a great variety of devices, techniques and media. As a result of this constant stream of information, people have become more socially active as well as become more capable and ready to integrate their virtual world with their physical world, using highly interactive devices, such as mobile phones, laptops and multi-touch tablets. So far, however, this kind of interactive behavior has mainly manifested itself in people’s private context, while in the more public work context the rich interactions that all these new technologies are offering do not seem to be supported to a great extent yet. Whereas office applications have increased sometimes dramatically in functionality, the ways of interacting with all these functionalities have evolved much more slowly. As a consequence, most office work is thus still done through the ubiquitous, almost 40-year old, set-up of keyboard, display and mouse, which only supports limited behaviors, such as keyboard tapping and mouse clicking. This lack of richness in interaction is becoming more evident, now that a new generation of workers is quickly entering the market. This so-called Generation Y, born in the 1980s and early 90s, are digital natives, who have experienced digital technology their entire lives. Thus they have developed new ways and habits of interacting with their (digital) world, putting very high demands on the applications, services, devices and networks that enable and support these interactions. An interesting challenge therefore presents itself to designers and researchers: How to bring the qualities of the interactions that people currently experience in the private context of their homes and friends into the more public context of their offices and colleagues? In this thesis this challenge is taken on through a number of studies, in which the following research questions were addressed: 1. What are Generation Y styles of interaction in home life and office work? 2. What are the interaction qualities that make up Generation Y styles of interaction? 3. How are these interaction qualities experienced within home and office context? 4. What are opportunities to design office tools or services that support Generation Y styles of interaction? 5. How are the interaction qualities of these new designs experienced? The research framework of this thesis distinguishes three major components: 1) people (Generation Y), 2) technology and 3) context (home vs. work). On the intersections of these three components are the interactions that are at the core of the research. From the beginning and throughout the whole research, prototypes that are rich in aesthetic, expressive and experiential quality were built and tested in real contexts. In the first phases of the project emphasis was in the exploration of new ways of interacting, while later on in the project the focus shifted to applying these new interactions within the office context. Chapter 2 addresses research questions 1 and 2 through literature review, as well as a qualitative study, aimed at exploring Generation Y styles of interaction, behaviors and interaction qualities. In a series of contextual interviews with office workers, we found that they put very high demands on the applications, services, devices, and networks that enable and support collaborative work. A set of examples of activities representative of what people currently do in their home and office context was gathered and grouped into a style of interaction, which we have labeled as ‘Generation Y’. This style of interaction seemed to be more prominent in the home situation than in the office context. Six interaction qualities (instant, expressive, playful, collaborative, responsive and flexible) were identified to make up the Generation Y style of interaction. The interviews strengthened the impression that these qualities were better represented in the home context, through activities such as gaming or chatting, than in the office context. Chapter 3 focuses on interactive technology design, designing and developing a number of experiential prototypes as a first exploration. It explores how to use interaction qualities to guide the design of Generation Y styles of interaction by combining functional, experience and technology approaches. In an educational setting a number of interactive prototypes were built by students in which specific interaction qualities were explored and demonstrated. From designing, building and testing these prototypes, we learned to use interaction qualities to explicitly guide and constrain the design process. Interaction qualities were found to be able to integrate all three design approaches, and thus can be introduced as a possible new principle into design research and education. Chapter 4 addresses research question 3. In follow-up interviews, we explored how office workers experienced and judged the interaction qualities in their home and the office situations in order to develop interaction design guidelines. The interviews and discussions showed that the six interaction qualities made sense to users and designers alike. Designers are more used to talk about interactions and qualities as abstract things, whereas other people will refer to their direct experiences. The six interaction qualities, together with their corresponding guidelines were subsequently used by the author and by design students, to design new types of interactions in the work context. Chapter 5 deals with research question 4 by implementing the interaction qualities into a new design, which uses the knowledge and experience gained from the previous chapters and integrates them into a working prototype. An office phone was chosen as the product to bring the Generation Y interaction qualities into an office context. The YPhone prototype was developed to demonstrate the interaction qualities with new ways of working, e.g., pushing down hard on a contact to send an urgent mood while calling. YPhone prototype is being developed using Max/MSP, Phidgets sensors and Arduino. A pair of prototypes was built to demonstrate and to evaluate the Generation Y interaction style in office work. Chapter 6 focuses on synthesis again to answer research question 5. This chapter presents findings on the prototype’s performance on the interaction qualities in a lab setup and in a real office work context. The YPhone prototype was demonstrated, evaluated and discussed at a series of venues, with respondents trying out scenarios such as placing an urgent call, or relaying an incoming message. The prototype worked in demonstrating the intended Generation Y interaction qualities. Moreover, the evaluation results indicated that the interactions would fit into work contexts and enrich people’s work situations. These findings indicate that the interaction qualities can give guidance in designing Generation Y type of interactions. Chapter 7 starts by reflecting on the answers on the five research questions. This is followed by a general discussion of the research: what has been learned and what are the possible impact of its results. The aim of this research was to contribute to the existing body of knowledge in the domains of interaction design and design research. By taking interaction qualities as a driver in the design and research process, the intention was to bring Generation Y interaction qualities from the home context to the work context. We believe and hope that interaction qualities can serve as a tool to guide the design process, and that the six interaction qualities will become a valuable instrument to guide designers in developing new office tools and applications that are rich and engaging in interaction.","generation Y; interaction qualities; work context; design research","en","doctoral thesis","","","","","","","","","Industrial Design Engineering","Industrial Design","","","",""
"uuid:3db90695-a6cb-475a-aa87-6a33d874996c","http://resolver.tudelft.nl/uuid:3db90695-a6cb-475a-aa87-6a33d874996c","Whole Body Activity Retentions in the Peptide Receptor Radionuclide Therapy with Lu-177","Liu, B.","Wolterbeek, H.T. (promotor)","2013","The patients with the neuroendocrine tumours (liver, spleen, etc.) often need treatment by the Peptide Receptor Radionuclide Therapy with 177Lu. The amount of 177Lu activity in the body of patients has to be known accurately for assessment of the dosimetry and for evaluation of the effectiveness of the therapy. Whole-body activities at the given time after administration can be derived from measurements of the activity of a sub-sample from the excreted urine, collected by the patient him/herself. This approach has to be abandoned because it increases the radiation dose of analysts and nurses involved. Moreover, the collection is patient unfriendly; there is a high risk of contamination by spills, and therefore, a risk of incomplete collection. As such, it is not unlikely that the urine collection method results in an underestimated indication of the total amount of activity actually excreted. As a consequence, the urine collection method may render an overestimated value of the whole-body activity. On the other hand, it is an intrinsic problem that the measurement uncertainty of the whole-body activity derived from the urine collection method increases when the whole-body activity decreases with time. As an example, the expanded uncertainties of the whole-body activity were about ±4% (the coverage factor k=2) shortly after administration and up to >±20% at 24 h; however all expanded uncertainties of the activity of the collected urine were about ±3.4%. The objective of the research described in this thesis was to develop a patient friendly technique for an accurate estimate of the whole-body activity of 177Lu as an alternative for the collection of the excreted urine by patient themselves. Two methods, (i) direct measurement of the activity of the excreted urine in the toilet pot and (ii) paired whole-body measurements, have been developed to overcome the concerns. In the first method, the activity of the excreted urine was measured in the toilet pot itself. A small CeBr3 detector is positioned on the side wall of the toilet room, aligned to centre of the water in the toilet pot. The patient uses the toilet as normal but does not need to flush it. The only modification for the current toilet system is to replace the mechanical flushing by a delayed flushing. The activity of the excreted urine is measured directly in the toilet pot after the patient has left the room. This approach is friendly and comfortable for patients and does not lead to an enhanced radiation dose to the staff that otherwise need handling the collected urine. The effects of urine volume and the voiding flow rate were investigated with 177Lu mock-up urine solutions. The expanded uncertainty varied from ±5 to ±10 %, dependent on the occurrence of diarrhea or extreme voiding styles. Therefore measurement uncertainties of the derived whole-body activity were equivalent to the values derived from the urine collection method or even a little bit worse. As an alternative, a radiation measurement system was designed by which the activity in the patient’s body can be measured directly by positioning the patient between two CeBr3 detectors for simultaneous measurements. Whole-body activities during subsequent measurements are commonly normalized to the administered activity before the first voiding. The detector responses of the measurement system are affected by the fully filled bladder during this measurement before the first voiding and by activity redistributions in between subsequent measurements. This was confirmed by measurements with patients, in which the geometric mean value of the count rates of the two detectors after voiding differed from that before the next voiding and by comparison with the results from the urine collection method. This problem could be largely overcome by a series of paired measurements before and after each voiding consecutively, from which time-dependent detector responses were derived. The whole-body activities were then determined accurately using these time-dependent responses, with measurement uncertainties of about ±7%. The results around 1 h after administration have been validated by measurements of the collected first excreted urine from 5 patients. The uncertainty of the whole-body dose is an essential quantity in the individual dosimetry of radionuclide therapy and is mainly dependent on the time-integrated activity coefficient, which is calculated by the bi-exponential regression of the time-activity curve. Using the trapezoidal area under the measurement curve as a reference, the uncertainty of the time-integrated activity coefficient was estimated from the three components, e.g. the uncertainty of the trapezoidal area under the measurement curve, the sum of squares of fitting residuals and the bias between the fitting and trapezoidal areas. The expanded uncertainty in measurement is about ±4% for the new paired measurements method. The toilet measurement set-up is in principle ready for implementation but requires additional modifications of the logistics in the use of the toilet, such as a delayed flushing and blocking of the access during the measurements. The whole-body measurement system is ready for implementation. Handling of radioactive urine is not needed any more. The approaches meet the objective: a reduction of the burden to radiotherapy patients and analysts in the assays of the amount of activity in the patient body.","PRRT; whole-body dose; activity in the excreted urine; activity in the whole-body; whole-body measurements; uncertainty in measurement","en","doctoral thesis","IOS Press","","","","","","","","Applied Sciences","Radiation, Radionuclides & Reactors","","","",""
"uuid:e8a46e6a-542f-4da3-8be0-bf0742aba538","http://resolver.tudelft.nl/uuid:e8a46e6a-542f-4da3-8be0-bf0742aba538","Microbiological water quality in drinking water distribution systems: Integral study of bulk water, suspended solids, loose deposits, and pipe wall biofilm","Liu, G.","Van Dijk, J.C. (promotor); Medema, G. (promotor)","2013","","","en","doctoral thesis","Delft University of Technology","","","","","","","","Civil Engineering and Geosciences","Water Management","","","",""
"uuid:ed6f1b38-e29e-4e84-b536-12a096e587fc","http://resolver.tudelft.nl/uuid:ed6f1b38-e29e-4e84-b536-12a096e587fc","Biomass-powered Solid Oxide Fuel Cells: Experimental and Modeling Studies for System Integrations","Liu, M.","Verkooijen, A.H.M. (promotor)","2013","Biomass is a sustainable energy source which, through thermo-chemical processes of biomass gasification, is able to be converted from a solid biomass fuel into a gas mixture, known as syngas or biosyngas. A solid oxide fuel cell (SOFC) is a power generation device that directly converts the chemical energy of a fuel to electricity. Therefore, biomass-powered SOFCs could be highly efficient. Typically, in addition to carbon dioxide and water vapor, the major components of syngas produced from biomass gasification include hydrogen, carbon monoxide and methane which are potential fuels for SOFCs, which make integration possible between SOFCs and biomass gasifiers. However, the syngas is also comprised of trace species such as tars, H2S, HCl, and alkali compounds, among others, which could be detrimental to SOFCs if they are contained within the feeding syngas stream. Therefore, the syngas must be pretreated in order to reduce these trace species to a level that SOFCs are able to tolerate. With various gas treatments, the overall system performance would fluctuate, and therefore, the influence of the gas treatment methods on the system performance must be understood. The most prominent among the trace species is tar. The effect of tars on the performance of SOFCs has yet to be studied, however, it is known that, even though tar can possibly poison the fuel cell through carbon deposition, it may also become a fuel for SOFCs. Furthermore, SOFC systems are currently designed in general for employing natural gas. Due to the fact that SOFC systems are very sensitive to the fuel types, it is necessary to completely understand the system response when switching from natural gas to biosyngas to enable a better controllability for future experiments. The research scope of this thesis is limited to the aforementioned issues. The objective of this thesis is to provide a fundamental study to ensure a safe and efficient system integration. The study is limited to an existing downdraft fixed-bed gasifier and a 5 kWe SOFC CHP system due to these two units entering the commercial market. The approach utilized, however, could be further adopted for the large scale power plants based on biomass gasifiers and SOFCs. The research begins with the evaluation of technologies involved biomass-powered SOFCs in chapter 2. Technologies regarding biomass gasification, gas cleanup and fuel cells are discussed based on literature surveys. The review begins by briefly summarizing conventional gasifiers including fixed-bed and fluidized bed gasifiers, which are implented for biomass gasification. Following that, details are indicated for SOFC performance affected by the trace species such as particulates, H2S and available cleaning technologies. The combination of biomass gasifiers with fuel cells including proton exchange membrane fuel cells (PEMFC), molten carbonate fuel cells (MCFC), and SOFCs is then reviewed with an emphasis on the development of SOFC technology and the study of integration between biomass gaisifers and SOFCs. Chapter 3 presents a thermodynamic study of the influence of cleaning technology on the energetic and exergetic performance of the integrated gasifier–SOFC system with distinctive system configurations. Two gas cleaning systems, specifically, a combined high and low temperature gas cleaning system and a high temperature gas cleaning system are considered to connect the gasifier with the SOFC system. The influence of the steam addition for the suppression of carbon deposition and various heat sources for steam generation on the system performance is evaluated. The performance of the SOFC system operating with natural gas and biosyngas is also compared. The installed SOFC system, particularly the embedded pre-reformer and anode off-gas recirculation was initially designed for natural gas. This design is desirable as it effectively uses the steam in the anode off-gas and the heat generated in the stack. As SOFC performance is very sensitive to gas composition and operating conditions, both of which are affected by the anode recirculation, an evaluation of the recirculation behavior on safety issues regarding carbon deposition and nickel oxidation and system performance are presented in chapter 4. An important finding is that, by not implementing the recirculation, the biosyngas-fueled SOFC system effectuates a much higher net electrical efficiency, less initial investment and simpler system configuration in comparison to that when recirculation is implemented. Tolerance of SOFCs to the trace species from biomass gasification is not yet fully understood. The influence of biomass gasification tars on SOFC performance and mitigation of carbon deposition are experimentally evaluated in chapter 5&6. Well-controlled operational conditions assist in the suppression of carbon deposition. Chapter 5 presents the influence of operating conditions including steam levels, current density and time on stream on the performance of SOFCs with Ni–YSZ anodes fueled by tar-containing biosyngas at 800 °C. Changes in impedance spectra and polarization curves of SOFCs following tar exposure were analyzed to assess the cell performance. The biosyngas composition and the tar concentration employed in these measurements were identical to those measured from the commercial air-blown biomass gasifier that is to be connected to the studied SOFC system. Operating this type of SOFC with the tar concentrations could result in severe damage to the cell due to carbon formation on the anodes. Scanning Electron Microscopy (SEM) indicated carbon deposition which affected the performance of the SOFC, as is exhibited by the impedance spectra and anode polarization curves of the cells after exposure to tars. However, the risk of carbon deposition could be alleviated by increasing steam levels and current loads. Chapter 6 presents a similar study of the effects of tar on SOFC performance, but possesses a focus on Ni–GDC anodes and various operating temperatures levels (700, 800 and 900 °C) under both dry and wet conditions. Polarization behavior, electrochemical impedance spectroscopy, and cell voltage degradation were analyzed to evaluate the cell performance. It is most likely that the cells with Ni–GDC anodes did not suffer from carbon deposition under the wet conditions studied. Dry tar-containing syngas for SOFCs is unlikely to cause carbon formation under a mild current load; however, it may induce carbon formation at open circuit. The effect of carbon dioxide that is capable of suppressing carbon deposition was experimentally investigated, and an enhanced performance was observed under the conditions studied. Under carbon risk-free operating conditions, the cell voltage increases when raising the feeding tar concentration, indicating that tar performs as fuel for SOFCs. Numerical simulation is an efficient tool for the evaluation of SOFCs’ response when switching fuels. Chapter 7 presents such a numerical study with the focus on the evaluation of kinetic models for methane steam reforming for SOFCs operation with multiple fuels. Three frequently employed kinetic models were selected in order to examine their impacts on the performance of a tubular SOFC. The resulting thermo-electrochemical behaviors derived from these models were compared. It was discovered that all three kinetic models are reasonably accurate in terms of the polarization behavior, but they significantly affected the local thermo-electrochemical performance. A more rapid kinetic model was adopted based on the evaluation of these three kinetic models in order to evaluate the performance of the tubular SOFC in terms of local electrochemical performance, anode oxygen partial pressure and overall SOFC performance when performing with multiple fuels. Chapter 8 draws the conclusions regarding the work presented in this dissertation, and recommendations are suggested for future research activities.","SOFC; biomass gasification; renewable energy; power plant","en","doctoral thesis","Delft University of Technology","","","","","","","2013-04-18","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:7a2dcf0b-e88e-4da6-baa9-59cfc4cc63ad","http://resolver.tudelft.nl/uuid:7a2dcf0b-e88e-4da6-baa9-59cfc4cc63ad","Robustness and Optimization of Complex Networks: Reconstructability, Algorithms and Modeling","Liu, D.","Van Mieghem, P. (promotor)","2013","The infrastructure networks, including the Internet, telecommunication networks, electrical power grids, transportation networks (road, railway, waterway, and airway networks), gas networks and water networks, are becoming more and more complex. The complex infrastructure networks are crucial to our human society, and it has been a hot research
eld to make our complex infrastructure networks more robust and optimize the performance of them. Besides man-designed infrastructure networks, complex networks also cover many natural networks, such as social networks, ecological networks, and biological networks. In order to tackle some of the di¢ cult social issues, ecological problems, and unsolved medical problems, we must learn how these natural complex networks organize, operate, and function. Complex networks can be represented by graphs. A graph consists of a collection of nodes and a collection of links that connect the nodes. A graph is uniquely described by its adjacency matrix, of which the entry on row i and column j is one only if node i and node j in the graph is connected by a link, otherwise the entry is zero. Each adjacency matrix is associated to a unique set of eigenvalues and corresponding eigenvectors. The eigenvalues and corresponding eigenvectors of a graph, also called the spectrum of the graph, contains all the information of the graph, and the topological/physical meanings of some eigenvalues and eigenvectors are already known. The knowledge on the spectra of networks is of crucial importance to the many aspects of the researches on complex network, such as connectivity of networks and virus spreading in networks. The line graph l (G) of a graph G has a set of nodes mapping the set of links in G, and two nodes in l (G) are adjacent if and only if the corresponding links in G have a node in common. Some problems of graphs can be transformed to much easier ones in the domain of line graphs. For example, partitioning the nodes to
nd the overlapping communities in a graph can be done by partitioning the links in the line graph of the concerned graph. Moreover, the line graphs often share common features with real-world complex networks, like highly clustered and assortative mixing. Hence, the line graphs are considered by many to model real-world complex networks. The robustness and optimization of complex network is a rather broad research fi
eld. We focus on the reconstruction of complex networks from the spectral domain and the line graph domain. This thesis is organized as follows. We
first study the reconstruction of networks from their eigenvalues and eigenvectors and the spectral properties of networks. In the second part of this thesis, we present two algorithms which reconstruct networks from the line graph domain, the properties of the line graphs, and a random line graph model. We at last give the research results on two types of real-world networks. The adjacency matrix of a graph can be computed with its eigenvalues and eigenvectors. When some of the eigenvalues are set to zero, the adjacency matrix can still be correctly computed. We propose a measure, the reconstructability coefficient, de
fined as the maximum number of eigenvalues that can be removed. We
find that the reconstructability coefficient is linear function of the size of the network for all networks that we have studied. We give some results on the spectral metric, the energy of a graph, which is de
fined by the sum of the absolute value of all the eigenvalues. We also explore the relations between graph energy and the topological metric, assortativity, for many different types of networks. For the reconstruction of networks from the line graph domain, we propose two algorithms Marinlinga and Iligra. While all previous algorithms rely on Whitney's theorem, Marinlinga is based on the principle of link relabeling and endnode recognition. Iligra reconstructs the graphs from the line graph domain with the linear time complexity. This thesis extends the researches in the line graph domain. We fi
nd that the number of links in a line graph with a fi
xed number of nodes can not take some consecutive natural numbers, and these numbers are called a bandgap of the line graph. We present the exact expressions of the bands and bandgaps of the number of links in line graphs. In order to facilitate the researches in the line graph domain, we propose a model which randomly generates line graphs. The essence of our model is to merge step by step a pair of nodes in cliques, subjecting to some rules to ensure that the resulting graphs are line graphs. Thanks to the random line model, a method to generate a serial of graphs of which the assortativity increases linearly has been invented. This thesis studies two types of real-world networks: social networks and human brain networks. We characterize the overlapping community structure of the social networks of ArXiv coauthorship, IMDB actors collaboration and SourceForge collaboration, and propose a growing hypergraph model, based on preferential attachment. The proposed hypergraph model captures the fundamental properties including the power-law distributions of group size, group degree, overlapping depth, individual degree and interest-sharing number of real-world affiliation networks, and reproduces the properties of high clustering, assortative mixing and short average path length of social networks. To study brain networks, we propose a spectral randomness metric to quantize the randomness of networks. Based on the randomness measuring method, we have found that the brain networks of Alzheimers disease are statistically more random than the healthy brain networks.","complex networks; graph spectra; reconstructability; line graphs; social networks; community structure; hypergraphs; brain networks; randomness","en","doctoral thesis","Next Generation Infrastructures Foundation","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Intelligent Systems","","","",""
"uuid:239b19f7-59d0-47b3-a3e3-dd1aeb19701f","http://resolver.tudelft.nl/uuid:239b19f7-59d0-47b3-a3e3-dd1aeb19701f","Diffusion in Liquids: Equilibrium Molecular Simulations and Predictive Engineering Models","Liu, X.","Vlugt, T.J.H. (promotor); Bardow, A. (promotor)","2013","The aim of this thesis is to study multicomponent diffusion in liquids using Molecular Dynamics (MD) simulations. Diffusion plays an important role in mass transport processes. In binary systems, mass transfer processes have been studied extensively using both experiments and molecular simulations. From a practical point of view, systems consisting more than two components are more interesting. However, experimental and simulation data on transport diffusion for such systems are scarce. Therefore, a more detailed knowledge on mass transfer in multicomponent systems is required. The presence of multiple components in a system introduces difficulties in studying diffusion in experiments. Investigating the concentration dependence of diffusion coefficients seriously increases the required experimental effort. In this thesis, we will use MD simulation based on classical force fields to study multicomponent diffusion in liquids. Diffusion can be described using both Fick and Maxwell- Stefan (MS) diffusion coefficients. Experiments provide Fick diffusion coefficients while simulations usually provide MS diffusion coefficients. Fick and MS diffusivities are related via the matrix of thermodynamic factors. A brief survey on methods for studying liquid diffusion and their limitations is presented in chapter 1 In chapter 2, we study the diffusion in the ternary system n-hexane-cyclohexanetoluene. The existing models for predicting MS diffusivities at finite concentrations (i:e: the Vignes equation) as well as the predictions at infinite dilution (i:e: predictions of Ðxk!1 i j using the so-called WK, KT, VKB, DKB and RS models) are tested using MD simulations. We find that (1) the Vignes equation only results in reasonable predictions for MS diffusivities yielding differences of 13% compared to the actual diffusion coefficients; (2) the best predictive model (the KT model) for calculating MS diffusivities at infinite dilution results in differences of 8% compared to the actual diffusion coefficients. It is important to note that the differences of 8% can be a coincidence since KT model is empirical and does not have a theoretical basis. This limitation makes KT model unreliable for other systems. To overcome the difficulties in predicting ternary MS diffusivities at infinite dilution (i:e: Ðxk!1 i j ), we derive the so-called LBV model based on the Onsager relations. MS diffusivities at infinite dilution can be expressed in terms of binary and pure component self-diffusivities and integrals over velocity cross-correlation functions. By neglecting the latter terms, we obtain the LBV model. In chapter 3, the LBV model is validated for WCA fluids and the ternary systems n-hexane-cyclohexane-toluene and methanol-ethanol-water. We find that: (1) for ideal mixtures i:e: the WCA system, as well as the n-hexane-cyclohexane-toluene system, the LBV model is accurate and superior compared to the existing models for predicting ternary MS diffusivities at infinite dilution (i:e: the WK, KT, VKB, DKB and RS models); (2) in mixtures containing associating components, i:e: the ethanol-methanol-water system, the LBV model indicates that in this system the integrals over velocity cross-correlation functions are important and cannot be neglected. Moreover, the LBV model provides an explanation why the MS diffusivity describing the friction between adsorbed components in a porous material is usually very large. In chapter 4, we focus on describing the values of MS diffusivities at finite concentration. A multicomponent Darken model for describing the concentration dependence of MS diffusivities is derived from linear response theory and the Onsager relations. In addition, a predictive model for the required self-diffusivities in the mixture is proposed leading to the so-called predictive Darken-LBV model. We compare our novel models to the existing generalized Vignes equation and the generalized Darken equation. Two systems are considered: (1) ternary and quaternary WCA systems; (2) the ternary system n-hexane-cyclohexane-toluene. Our results show that in all studied systems, our predictive Darken-LBV equation describes the concentration dependence better than the existing models. The physically-based Darken-LBV model provides a sound and robust framework for prediction of MS diffusion coefficients in multicomponent mixtures. In chapter 5, diffusion in more complex ionic liquid (IL) systems are investigated. Previous research reported in literature has largely focused on self-diffusion in ILs. For practical applications, mutual (transport) diffusion is by far more important than self-diffusion. We compute the MS diffusivities in binary systems containing 1-alkyl- 3- methylimidazolium chloride (CnmimCl), water and/or dimethyl sulfoxide (DMSO). The dependence of MS diffusivities on mixture composition are investigated. Our results show that: (1) For solutions of ILs in water and DMSO, self-diffusivities decrease strongly with increasing IL concentration. For the system DMSO-IL, an exponential decay is observed for this; (2) For both water-IL and DMSO-IL, MS diffusivities vary by a factor of 10 within the concentration range which is still significantly smaller than the variation of the self diffusivities; (3) The MS diffusivities of the investigated IL are almost independent of the alkyl chain length; (4) ILs stay in a form of isolated ions in CnmimCl-H2O mixtures, however, dissociation into ions is much less observed in CnmimCl-DMSO systems. This has a large effect on the concentration dependence of MS diffusivities; (5) The LBV model for predicting the MS diffusivity at infinite dilution described in chapter 3 suggests that velocity cross-correlation functions in ionic liquids cannot be neglected and that the dissociation of ILs into ion pairs has a very strong influence on diffusion. In experiments, Fick diffusion coefficients are measured and molecular simulation usually provides MS diffusivities. These approaches are related via the matrix of thermodynamic factors which is usually known only with large uncertainties. This leaves a gap between theory and application. In chapter 6, we introduce a consistent and efficient framework for the determination of Fick diffusivities in liquid mixtures directly from equilibrium MD simulations by calculating both the thermodynamic factor and the MS diffusivity. This provides the missing step to extract Fick diffusion coefficients directly from equilibrium MD simulations. The computed Fick diffusivities of acetone-methanol and acetone-tetrachloromethane mixtures are in excellent agreement with experimental values. The suggested framework thus provides an efficient route to model diffusion in liquids based on a consistent molecular picture. In chapter 7, we validate our method for computing Fick diffusivities using equilibrium MD simulations for the ternary system chloroform - acetone - methanol. Even though a simple molecular model is used (i:e: rigid molecules that interact by Lennard-Jones and electrostatic interactions), the computed thermodynamic factors are in close agreement with experiments. Validation data for diffusion coefficients is only available for two binary sub-systems. In these binary systems, MD results and experiments do agree well. For the ternary system, the computed thermodynamic factors using Molecular Dynamics simulation are in excellent agreement with experimental data and better than the ones obtained from COSMO-SAC calculations. Therefore, we expect that the computed Fick diffusivities should also be comparable with experiments. Our results suggest that the presented approach allows for an efficient and consistent prediction of multicomponent Fick diffusion coefficients from MD simulations. Now, a tool for guiding experiments and interpreting multicomponent mass transfer is available.","Diffusion","en","doctoral thesis","","","","","","","","2013-01-21","Mechanical, Maritime and Materials Engineering","Process & Energy","","","",""
"uuid:21b9ea98-b9f0-4520-9460-3cfdc14601f2","http://resolver.tudelft.nl/uuid:21b9ea98-b9f0-4520-9460-3cfdc14601f2","Satellite radar interferometry: Estimation of atmospheric delay","Liu, S.","Hanssen, R.F. (promotor)","2012","","satellite radar interferometry; atmospheric delay; numerical weather model; least-squares collocation; deformation","en","doctoral thesis","Delft University of Technology","","","","","","","","Aerospace Engineering","Geoscience and Remote Control","","","",""
"uuid:dea292f3-15ee-490a-a59c-5365df63bc16","http://resolver.tudelft.nl/uuid:dea292f3-15ee-490a-a59c-5365df63bc16","Induction Healing of Porous Asphalt Concrete","Liu, Q.","Schlangen, E. (promotor)","2012","Porous asphalt shows excellent performance in both noise reduction and water drainage. Although porous asphalt has these great qualities, its service life is much shorter (sometimes only half) compared to dense graded asphalt roads. Ravelling, which is the loss of aggregate particles from the surface layer, is the main damage mechanism of porous asphalt surface wearing courses. In this research, an induction healing approach (namely, activating the healing process of asphalt concrete through induction heating) was developed to enhance the durability of the porous asphalt roads. Steel fibers are added to a porous asphalt mixture to make it electrically conductive and suitable for induction heating. When micro cracks are expected to occur in the asphalt mastic of the pavement, the temperature of the mastic can be increased locally by induction heating of the steel fibers so that porous asphalt concrete can repair itself and close the cracks through the high temperature healing of the bitumen (diffusion and flow). The closure of micro cracks will prevent the formation of macro cracks. In such a way, ravelling can be avoided or delayed in the end. To make asphalt mastic and porous asphalt concrete electrically conductive and suitable for induction heating, steel (wool) fibers were incorporated into them. The electrical conductivity and induction heating speed of asphalt mastic and porous asphalt concrete were first studied in this research. Asphalt mastic and porous asphalt concrete with steel fibers can be heated with induction energy. There is an optimal volume content of steel fiber in asphalt mastic or porous asphalt concrete to obtain the highest induction heating speed. Adding more steel fiber above this optimal volume content does not increase the induction heating speed anymore. Furthermore, the highest induction heating speed corresponds to the minimum electrical resistivity. However, porous asphalt concrete does not need to be fully conductive for induction heating. Every single steel wool is a heating unit. Nonconductive samples with steel fiber can still be heated with induction heating, but at a low heating speed. The diameter, length and content of steel wool fiber are important for the conductivity and heating speed of asphalt concrete matrix. It is proven that induction heating does not cause extra ageing to bitumen. Addition of steel wool also reduces the binder drainage problem in porous asphalt concrete. The mechanical properties of porous asphalt concrete with steel wool fiber were studied in this research. Adding moderate percentage steel wool to porous asphalt concrete reinforce it by increasing its particle loss resistance, indirect tensile strength and fracture energy, water damage resistance, stiffness and fatigue resistance. The steel wool was optimized to obtain the best particle loss resistance in porous asphalt concrete. 8% steel wool type 00 (volume fraction of bitumen) was considered as the optimal content. The healing potential of porous asphalt concrete with steel wool fiber was also evaluated in this research with both cylinder and beam samples. Damaged porous asphalt concrete with steel wool fiber can greatly restore its stiffness, strength and fatigue life with induction heating, which proves that the healing capacity of porous asphalt concrete with steel wool fiber is enhanced by induction heating. The optimal induction heating temperature is 85 ºC for porous asphalt concrete to obtain the best healing rate. Reheating does not decrease the healing rate of porous asphalt concrete, which means that heating can be repeated when cracks appear again. To apply the induction healing technology in real porous asphalt road, a trial section was constructed on Dutch motorway A58 in December 2010. This trial section survived the past two winters perfectly. Experiments were done on the cores drilled from the trial section and the results coincided with those on the laboratory made samples. The field cores showed good particle loss resistance, high strength, good fatigue resistance and high induction healing capacity. Based on the laboratory experiments and field experiences, induction healing can be a very good approach to enhance the durability of porous asphalt pavement. Finally, some recommendations are given for further research. Steel fiber, mixing technology and induction generator need to be optimized. Modeling work is necessary to fully understand the mechanisms involved in induction healing.","healing; induction heating; steel fiber; porous asphalt concrete","en","doctoral thesis","","","","","","","","2012-10-02","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:bad09af1-fa51-445a-a575-9c429fae54ec","http://resolver.tudelft.nl/uuid:bad09af1-fa51-445a-a575-9c429fae54ec","Characterization and Identification of Bituminous Materials Modified with Montmorillonite Nanoclay","Liu, G.","Molenaar, A.A.A. (promotor); Wu, S.P. (promotor)","2011","Montmorillonite (Mt) nanoclay is a layered silicate mineral with a 2:1-type layer structure, two tetrahedrals sandwiching one octahedral. In recent decades, it is successfully introduced into polymer systems to form polymer-clay nanocomposites (PCN) in which the silicate layers of the Mt are randomly and homogeneously dispersed at a molecular level in the polymer matrix. Due to the addition of Mt, some properties of PCN, such as the mechanical, thermal and gas barrier properties, were superior to those of pristine polymers. Based on this idea, natural and organo Mts were used to modify bitumens with different penetration grades in this study. Some rheological, ageing and fatigue properties of the modified bitumens and mortars were characterized. High-shearing mixing method was used to prepare the modified bitumen; X-ray diffraction and micro-CT scanning were employed to observe structures of Mts in bitumen; DSR equipment was adopted to characterize the rheological properties; the rolling thin film oven (RTFO) and pressure ageing vessel (PAV) methods were used to simulate the short term and long term ageing on base and Mt modified bitumens, respectively. Fatigue tests were performed on bitumen and mortar samples which consisted of bitumen, filler and sand at a weight ratio of 0.34:0.30:0.36, as well as on a dense graded asphalt mixture. XRD results indicated an intercalated structure of organo Mts in the bituminous matrix. A phase separated structure of natural Mt was found in the base bitumen. Micro-CT images further proved that natural Mt acted like a conventional filler at micrometer level. The interaction between the Mts layers and bitumen changed its viscosity and dynamic response as characterized by means of the DSR. Reinforced shear thinning was observed on the modified bitumens at a liquid state, which implies a better drainage resistance of asphalt mixture during transportation. The results indicated that organo Mts improve the short term ageing resistance of base bitumen. The main reason for this improvement is that the barrier properties of Mt particles hinder the penetration of oxygen. Meanwhile, the reduction of volatilization of the oil components of bitumen due to these barrier properties can be another reason. However, a less effective improvement was observed for the long term ageing using the PAV. That is because organo Mt platelets automatically accumulated to reduce their surface area under tough testing conditions in the PAV. This accumulation weakened the barrier properties of the Mts. It is believed however that organo Mts will improve the long term ageing behaviour of bitumen in the field because the state of the Mt will be very stable and no accumulation as occurred in the PAV will happen. The addition of organo Mts can change the fatigue properties of bitumen and even mortar. This change was influenced by the type of the surfactant on the Mt which determined the interfacial interaction between the bitumen and the Mt. Because of the heterogeneous character of asphalt mixtures and their complicated failure mechanism, the fatigue test on the asphalt mixture with the modified bitumen only gave a limited improvement of this property. Finally, some important aspects are given for further research. Based on the present research results, the organo Mt can be an alternative to modifiers used in the bitumen to sustain the durability of asphalt pavements.","Bitumen; Montmorillonite; Ageing; Rheology; Fatigue","en","doctoral thesis","","","","","","","","2011-12-12","Civil Engineering and Geosciences","Design and Construction","","","",""
"uuid:d3a1fdd4-1b8e-4a3c-93bd-6e6c256c654e","http://resolver.tudelft.nl/uuid:d3a1fdd4-1b8e-4a3c-93bd-6e6c256c654e","Modeling Perceived Quality for Imaging Applications","Liu, H.","Heynderickx, I.E.J.R. (promotor)","2011","People of all generations are making more and more use of digital imaging systems in their daily lives. The image content rendered by these digital imaging systems largely differs in perceived quality depending on the system and its applications. To be able to optimize the experience of viewers of this content understanding and modeling perceived image quality is essential. Research on modeling image quality in a full-reference framework – where the original content can be used as a reference – is well established in literature. In many current applications, however, the perceived image quality needs to be modeled in a no-reference framework at real-time. As a consequence, the model needs to quantitatively predict perceived quality of a degraded image without being able to compare it to its original version, and has to achieve this with limited computational complexity in order to enable real-time application. Although human beings effortless judge image quality in a real-time no-reference framework, developing a model to simulate this perception is still an academic challenge partly due to our limited understanding of the human visual system. This thesis presents some achievements in designing no-reference objective quality metrics, which have the aim to automatically and quantitatively predict perceived image quality. Two different approaches are used. In one approach the perception of some specific image degradations is modeled. This approach is applied to the perception of blockiness and ringing, two degradations typically occurring as a consequence of signal compression. The resulting metrics are based on a two-steps framework: a first step, in which the artifacts are located and a second step, in which the local visibility of the artifact is estimated. Both components include aspects of human vision with which the reliability of the metrics in predicting perceived artifact annoyance is improved, while keeping the computational effort limited. In a second approach the overall perceived quality of images is predicted. An accurate and computationally efficient way to do so exists of combining a simplified feature extraction strategy – resulting in features based on aspects of the artifact specific metrics – with an adaptive neural network. After having trained the overall quality estimation system off-line, the metric can be very easily implemented in real-time devices. Whether the artifacts in an image attract the viewer’s attention also affect the viewer’s quality estimation. Hence, in a final study the improvement in quality prediction performance of various metrics by including visual attention is evaluated. In these metrics local quality information is weighted with the attention given locally by the averaged viewer. Results show that when using ground-truth attention obtained from eye-tracking recordings the degree to which the quality estimation is improved, depends on the type of metric and kind of image content.","","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Mediamatics","","","",""
"uuid:d333e02f-64a9-4ba0-8dde-4d46a5f996cc","http://resolver.tudelft.nl/uuid:d333e02f-64a9-4ba0-8dde-4d46a5f996cc","Quantum Dots and Andreev Reflections in Graphene","Liu, X.L.","Vandersypen, L.M.K. (promotor)","2010","Graphene is an exceptionally thin semiconductor that consists of only one atomic layer of carbon atoms. The electrons in graphene live in a strictly two-dimensional (2D) world. In addition to this remarkable 2Dness, it is also peculiar that the behavior of the electrons in graphene is governed by the Dirac equation rather than the well known Schrödinger’s equation, leading to the discovery of several new physics phenomena. Such unusual properties of graphene have stirred up great excitements since it was first isolated in the lab about five years ago. In this thesis, we investigate the low temperature transport properties of the electrons and holes in several graphene based nano-devices. Overall, two topics are explored in this thesis. First we engineer an energy gap in graphene, which is naturally a zero-gap semiconductor, and further form quantum dot devices on the gapped graphene. The low temperature electronic transport properties of the confined electrons are then studied experimentally in such graphene dots. In a second project,we fabricated Josephson junction devices on graphene using a high critical field superconductor as leads. Here the goal is to research on the interactions between the electrons from graphene and the Cooper pairs from the superconductor in the quantum Hall regime.","nano-devices; graphene; mesoscopic physics; quantum dots; double quantum dots; Andreev reflection; quantum Hall effect","en","doctoral thesis","","","","","","","","","Applied Sciences","Kavli Institute of Nanoscience Delft","","","",""
"uuid:af1f1ad0-2066-48e0-949a-6b17291c111d","http://resolver.tudelft.nl/uuid:af1f1ad0-2066-48e0-949a-6b17291c111d","Global gravity field recovery from satellite-to-satellite tracking data with the acceleration approach","Liu, X.","Klees, R. (promotor)","2008","","leo orbit dertermination; global gravity field modeling; kinematic orbit; kbr measurements; acceleration approach; water storage variation","en","doctoral thesis","","","","","","","","","Aerospace Engineering","","","","",""
"uuid:03cc13d9-6445-4fce-9185-8798dce1293a","http://resolver.tudelft.nl/uuid:03cc13d9-6445-4fce-9185-8798dce1293a","Travel time prediction for urban networks","Liu, H.","Van Zuylen, H.J. (promotor); Van Lint, H. (promotor)","2008","","travel time prediction; urban networks; state space neural networks","en","doctoral thesis","","","","","","","","","Trail","","","","",""
"uuid:6c2f1476-c703-431e-a573-42ead7a88f12","http://resolver.tudelft.nl/uuid:6c2f1476-c703-431e-a573-42ead7a88f12","On the prediction of damage and fracture strength of notched composites","Liu, C.","Marissen, R. (promotor); Ernst, L.J. (promotor)","2004","","","en","doctoral thesis","","","","","","","","","Design, Engineering and Production","","","","",""
"uuid:17e908d2-d4bb-4d59-90a1-9c4decd2ecde","http://resolver.tudelft.nl/uuid:17e908d2-d4bb-4d59-90a1-9c4decd2ecde","Numerical Modelling of Porous Media Response Under Static and Dynamic Load Conditions","Liu, X.","Blaauwendraad, J. (promotor)","2003","","","en","doctoral thesis","","","","","","","","","Civil Engineering and Geosciences","","","","",""
"uuid:e9562632-361f-4d36-b77f-5459d6123cf6","http://resolver.tudelft.nl/uuid:e9562632-361f-4d36-b77f-5459d6123cf6","A pattern directed approach towards an object adaptive decision support environment for water resources management","Liu, Y.","Kopperlaar, H. (promotor); Van der Veer, P. (promotor)","1996","","decision support system; geographical information system; object oriented design; pattern directed analysis; knowledge engineering; water management","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","",""
"uuid:940a2414-bfaf-402f-8d87-11cbe204d407","http://resolver.tudelft.nl/uuid:940a2414-bfaf-402f-8d87-11cbe204d407","On Chain Coding of Line Drawings","Liu, K.","Arnbak, J.C. (promotor)","1992","","","en","doctoral thesis","Delft University Press","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","",""
"uuid:4e48d7ca-1781-41a0-9911-14846eb2ec45","http://resolver.tudelft.nl/uuid:4e48d7ca-1781-41a0-9911-14846eb2ec45","Dynamics of elevated jack-up structures","Liu, P.","Wolters, J.G. (promotor); Blaauwendraad, J. (promotor)","1991","","","en","doctoral thesis","Delft University Press","","","","","","","","Civil Engineering and Geosciences","","","","",""
"uuid:1371861d-e39d-4bb1-8532-792526c9224d","http://resolver.tudelft.nl/uuid:1371861d-e39d-4bb1-8532-792526c9224d","Dynamics of elevated jack-up structures","Liu, Ping","","1991","","offshore","","doctoral thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Marine and Transport Technology","Ship Hydromechanics and Structures","","",""
"uuid:bbe1aa0b-a680-4d94-9ec9-b7ed33200b6e","http://resolver.tudelft.nl/uuid:bbe1aa0b-a680-4d94-9ec9-b7ed33200b6e","Phase transformations in iron-based interstitial martensites","Liu, C.","Mittemeijer, E.J. (promotor); Korevaar, B.M. (promotor)","1990","","","en","doctoral thesis","","","","","","","","","Mechanical Maritime and Materials Engineering","","","","",""
"uuid:121dda1b-2c69-497f-b9ce-33634ae12ded","http://resolver.tudelft.nl/uuid:121dda1b-2c69-497f-b9ce-33634ae12ded","Non-linear vibrations of imperfect thin-walled cylindrical shells","Liu, D.K.","Arbocz, J. (promotor)","1988","","","en","doctoral thesis","","","","","","","","","Aerospace Engineering","","","","",""