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University of Twente Publications (47,497 recursos)
University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.

Type = Article

Mostrando recursos 1 - 20 de 21,688

1. Ultra Small-angle X-ray Scattering Study of Flocculation in Silica-filled Rubber - Mihara, S.; Datta, R.N.; Dierkes, W.K.; Noordermeer, J.W.M.; Amino, N.; Ishikawa, Y.; Nishitsuji, S.; Takenaka, M.

2. Deployment versus data retrieval costs for caches in the plane - Mitici, Mihaela; Goseling, Jasper; Graaf, Maurits de; Boucherie, Richard J.
We consider the problem of finding the Pareto front of the expected deployment cost of wireless caches in the plane and the expected retrieval cost of a client requesting data from the caches. The data is stored at the caches according to partitioning and coding strategies. We show that under coding, it is optimal to deploy many caches with low storage capacity. For partitioning, we derive a simple relation between the cost of the cache deployment and the cost of retrieving the data from the caches. We quantify the improvements offered by optimal coding in comparison to partitioning, i.e., we...

3. Erbium-doped spiral amplifiers with 20 dB of net gain on silicon - Vázquez-Córdova, Sergio A.; Dijkstra, Meindert; Bernhardi, Edward H.; Ay, Feridun; Wörhoff, Kerstin; Herek, Jennifer L.; Garcia-Blanco, Sonia M.; Pollnau, Markus
Spiral-waveguide amplifiers in erbium-doped aluminum oxide on a silicon wafer are fabricated and characterized. Spirals of several lengths and four different erbium concentrations are studied experimentally and theoretically. A maximum internal net gain of 20 dB in the small-signal-gain regime is measured at the peak emission wavelength of 1532 nm for two sample configurations with waveguide lengths of 12.9 cm and 24.4 cm and concentrations of 1.92 × 10^20 cm^-3 and 0.95 × 10^20 cm^-3, respectively. The noise figures of these samples are reported. Gain saturation as a result of increasing signal power and the temperature dependence of gain are...

4. Software defined radio receivers exploiting noise cancelling: a tutorial review - Klumperink, Eric; Nauta, Bram
Traditional radio receivers were narrowband and dedicated to a single frequency band exploiting LC tanks, whereas software defined radios target a flexibly programmable frequency. The broadband noise cancelling circuit technique has proven useful to achieve this target, as it breaks the traditional trade-off between low noise and broadband impedance matching. Different variants exist, with noise cancellation in the voltage or current domain, either at RF or after frequency translation to baseband. This article reviews the development of the noise cancelling technique and its role in inductorless interference robust software defined radio receivers.

5. On the Physical Interpretation of the Saleh-Valenzuela Model and the definition of its power delay profiles - Meijerink, Arjan; Molisch, Andreas F.
The physical motivation and interpretation of the stochastic propagation channel model of Saleh and Valenzuela are discussed in detail. This motivation mainly relies on assumptions on the stochastic properties of the positions of transmitter, receiver and scatterers in the propagation environment, and on the frequency range that is covered by the model. Some of these assumptions break down when the application of the model is extended from wideband to ultra-wideband propagation channels. Another important difference between these application contexts is the spatial scale over which the stochastic properties of the channel fluctuate when the transmitter or receiver is moved. This...

6. Application of a conceptual framework for the modelling and execution of clinical guidelines as networks of concurrent processes - Fung, Nick Lik San; Widya, Ing; Broens, Tom; Larburu, Nekane; Bults, Richard; Shalom, Erez; Jones, Val; Hermens, Hermie
We present a conceptual framework for modelling clinical guidelines as networks of concurrent processes. This enables the guideline to be partitioned and distributed at run-time across a knowledge-based telemedicine system, which is distributed by definition but whose exact physical configuration can only be determined after design-time by considering, amongst other factors, the individual patient's needs. The framework was applied to model a clinical guideline for gestational diabetes mellitus and to derive a prototype that executes the guideline on a smartphone. The framework is shown to support the full development trajectory of a decision support system, including analysis, design and implementation.

7. Design and fabrication of in-plane AFM probes with sharp silicon nitride tips based on refilling of anisotropically etched silicon moulds - Geerlings, J.; Sarajlic, E.; Berenschot, J.W.; Siekman, M.H.; Jansen, H.V.; Abelmann, L.; Tas, N.R.
In this paper a micromachining method for batch fabrication of in-plane atomic force microscope (AFM) probes that consist of a sharp silicon nitride tip on a monocrystalline silicon cantilever is presented. The tips are realized by conformal deposition of silicon nitride inside an anisotropically etched cavity inside a silicon wafer. The best measured radius of the sharp tips was 8 nm. Our fabrication method is fully compatible with silicon-on-insulator (SOI) micromachining, allowing a straightforward monolithic integration of the AFM probes with high-aspect-ratio monocrystalline silicon MEMS. The fabrication method allows for lateral cantilevers, which oscillate in the plane of the fabrication...

8. Acquisition of GNSS signals in urban interference environment - Wildemeersch, Matthias; Slump, Cornelis H.; Rabbachin, Alberto
In urban environment Global Navigation Satellite System (GNSS) signals are impaired by strong fading and by the presence of several potential sources of interference that can severely affect the acquisition. The work presented here evaluates the acquisition performance for the most common acquisition strategies in terms of receiver operating characteristics (ROC) and studies the impact of fading and interference on the acquisition performance. Two different interference scenarios are considered: a single interferer and a network of interferers. We present a framework to evaluate the GNSS acquisition performance with respect to all relevant system parameters that jointly considers the acquisition method,...

9. GEM: A distributed goal evaluation algorithm for trust management - Trivellato, Daniel; Zannone, Nicola; Etalle, Sandro
Trust management is an approach to access control in distributed systems where access decisions are based on policy statements issued by multiple principals and stored in a distributed manner. In trust management, the policy statements of a principal can refer to other principals' statements; thus, the process of evaluating an access request (i.e., a goal) consists of finding a “chain” of policy statements that allows the access to the requested resource. Most existing goal evaluation algorithms for trust management either rely on a centralized evaluation strategy, which consists of collecting all the relevant policy statements in a single location (and...

10. Thermo-Chemical Modelling Strategies for the Pultrusion Process - Baran, Ismet; Hattel, Jesper H.; Tutum, Cem C.
In the present study, three dimensional (3D) numerical modeling strategies of a thermosetting pultrusion process are investigated considering both transient and steady state approaches. For the transient solution, an unconditionally stable alternating direction implicit Douglas-Gunn (ADI-DG) scheme is implemented as a first contribution of its kind in this specific field of application. The corresponding results are compared with the results obtained from the transient fully implicit scheme, the straightforward extension of the 2D ADI and the steady state approach. The implementation of the proposed approach is described in detail. The calculated temperature and cure degree profiles at steady state are...

11. An ultra low energy FSK receiver with in-band interference robustness exploiting a 3-Phase chirped LO - Dutta, Ramen; Zee, Ronan van der; Kokkeler, André B.J.; Bentum, Mark J.; Klumperink, Eric; Nauta, Bram
An ultra-low-energy Binary Frequency Shift Keying (BFSK) receiver is proposed. It features improved in-band interference tolerance by chirping the transmission frequency. To reduce the receiver power consumption, a novel three-phase passive mixer along with a three stage digitally controlled ring oscillator is proposed, while still allowing quadrature detection. A mixer-first direct conversion receiver architecture moves the required gain to lowest frequency and lowest bandwidth to reduce power consumption. A low power flip-flop based BFSK demodulator is proposed that reduces the baseband power further. The receiver is designed and fabricated in a 65 nm complementary metal-oxide-semiconductor process. It consumes 219 μW...

12. Effective coastal boundary conditions for tsunami wave run-up over sloping bathymetry - Kristina, W.; Bokhove, O.; Groesen, E.W.C. van
An effective boundary condition (EBC) is introduced as a novel technique for predicting tsunami wave run-up along the coast, and offshore wave reflections. Numerical modeling of tsunami propagation in the coastal zone has been a daunting task, since high accuracy is needed to capture aspects of wave propagation in the shallower areas. For example, there are complicated interactions between incoming and reflected waves due to the bathymetry and intrinsically nonlinear phenomena of wave propagation. If a fixed wall boundary condition is used at a certain shallow depth contour, the reflection properties can be unrealistic. To alleviate this, we explore a...

13. Quick detection of nodes with large degrees - Avrachenkov, Konstatin; Litvak, Nelly; Sokol, Marina; Towsley, Don
Our goal is to find top-$k$ lists of nodes with the largest degrees in large complex networks quickly. If the adjacency list of the network is known (not often the case in complex networks), a deterministic algorithm to find the top-$k$ list of nodes with the largest degrees requires an average complexity of $\mathcal{O}(n)$ , where $n$ is the number of nodes in the network. Even this modest complexity can be very high for large complex networks. We propose to use a random-walk-based method. We show theoretically and by numerical experiments that for large networks, the random-walk method finds good-quality...

14. The Relation Between Residential Property and its Surroundings and Day- and Night-Time Residential Burglary - Montoya, Lorena; Junger, Marianne; Ongena, Yfke
This article examines how residential property and its surroundings influence day- and night-time residential burglary. Crime Prevention Through Environmental Design (CPTED) principles of territoriality, surveillance, access control, target hardening, image maintenance, and activity support underpin the study. Data were collected by observing 851 houses in the city of Enschede, half of which were burgled and half representing a random selection of houses not burgled. Multilevel multinomial regression models were estimated for predicting day- and night-time burglaries. The findings show that territoriality and access control predict daytime burglary while access control and target hardening predict night-time burglary. The analysis controls for...

15. Ambulatory estimation of relative foot positions by fusing ultrasound and inertial sensor data - Weenk, Dirk; Roetenberg, Daniel; Beijnum, Bert-Jan F. van; Hermens, Hermie J.; Veltink, Peter H.
Relative foot position estimation is important for rehabilitation, sports training and functional diagnostics. In this paper an extended Kalman filter fusing ultrasound range estimates and inertial sensors is described. With this filter several gait parameters can be estimated ambulatory. Step lengths and stride widths from 54 walking trials of three healthy subjects were estimated and compared to an optical reference. Mean ( standard deviation) of absolute difference was 1.7 cm (1.8 cm) and 1.2 cm (1.2 cm) for step length and stride width respectively. Walking with a turn and walking around in a square area were also investigated and resulted...

16. Motives to mentor: Self-focused, protégé-focused, relationship-focused, organization-focused, and unfocused motives - Janssen, Suzanne; Vuuren, Mark van; Jong, Menno D.T. de
This study examines the motives mentors have for providing developmental support to their protégés. Based on qualitative interviews with 20 informal mentors, we show five broad categories of mentor motives: self-focused motives (based on individual reasons), protégé-focused motives (directed at the protégé), relationship-focused motives (directed at the relationship between the mentor and the protégé), organization-focused motives (benefiting the organization), and unfocused motives (mentoring as the result of unconscious information processing). Furthermore, based on self-determination theory, we show five subcategories of self-focused motives, ranging from extrinsic motivations to intrinsic motivations. Implications of the findings and suggestions for future research are presented

17. Investigation of process induced warpage for pultrusion of a rectangular hollow profile - Baran, Ismet; Hattel, Jesper H.; Akkerman, Remko
A novel thermo-chemical–mechanical analysis of the pultrusion process is presented. A process simulation is performed for an industrially pultruded rectangular hollow profile containing both unidirectional (UD) roving and continuous filament mat (CFM) layers. The reinforcements are impregnated with a commercial polyester resin mixture (Atlac 382). The reactivity of the resin is obtained from gel tests performed by the pultruder. The cure kinetics parameters are estimated from a fitting procedure against the measured temperature. The cure hardening instantaneous linear elastic (CHILE) model is adopted for the evolution of the resin elastic modulus using the temperature-dependent elastic response provided by the resin...

18. Present it like it is here: Creating local presence to improve online product experiences - Verhagen, Tibert; Vonkeman, Charlotte; Feldberg, Frans; Verhagen, Plon W.
Advanced online product presentation technologies such as virtual mirrors enable consumers to experience products like they are actually present with them in the real world. This study is one of the first to address the mechanism underlying this phenomenon. Inspired by literature on media technology the concept of local presence is put forward and applied to the online consumer behavior domain. A key objective of this paper is to examine whether local presence adds to our understanding of how emerging product presentation formats influence online product experiences. To this end, a laboratory experiment (N = 366) was conducted with product...

19. Clusters of supernova stars in knowledge-based spaces: Value creation through cooperation - Kourtit, K.; Nijkamp, P.; Vught, F.A. van
The process of value creation out of the acquisition, transfer and exploitation of scientific knowledge has become a major challenge for developed economies. Knowledge institutions like universities and R&D centres are important actors in this context. This paper offers a novel contribution to the assessment of the regional-economic importance of local and regional knowledge centres in the Eastern part of the Netherlands (provinces Gelderland and Overijssel) by exploring the potential benefits of supra-regional synergy that may arise through an alliance of three important distinct regional knowledge clusters (a 'supernova star'), viz. the technology valley, the food valley and the health...

20. A Systematic Review to Identify the Use of Preference Elicitation Methods in Healthcare Decision Making - Weernink, Marieke G.M.; Janus, Sarah I.M.; Til, Janine A. van; Raisch, Dennis W.; Manen, Jeannette G. van; IJzerman, Maarten J.
Introduction Preference elicitation methods help to increase patient-centred medical decision making (MDM) by measuring benefit and value. Preferences can be applied in decisions regarding reimbursement, including health technology assessment (HTA); market access, including benefit–risk assessment (BRA); and clinical care. These three decision contexts have different requirements for use and elicitation of preferences. Objectives This systematic review identified studies using preference elicitation methods and summarized methodological and practical characteristics within the requirements of the three contexts. Methods The search terms included those related to MDM and patient preferences. Only articles with original data from quantitative preference elicitation methods were included. Results The selected articles (n...

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