University of Twente Publications
University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.
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Electrochemical actuator with a short response time: A new actuation regime - Svetovoy, Vitaly B.; Uvarov, Ilia; Postnikov, Alexander V.; Sanders, Remco G.P.; Krijnen, Gijs
The lack of fast and strong microactuators is a well-recognized problem in the MEMS community. Electro- chemical actuators can develop high pressure but they are notoriously slow. Water electrolysis produced by short voltage pulses of alternating polarity can overcome the problem of slow gas termination due to spontaneous ignition of the reaction between hydrogen and oxygen in nanobubbles. An actuation regime with the termination time as short as 100 s was demonstrated previously. Here we describe a new actuation regime, for which the gas pressure is relaxed just in 10 s and a minimal degradation of the electrodes is observed....
3D printing of functional structures - Krijnen, G.J.M.
The technology colloquial known as ‘3D printing’ has developed in such diversity in printing technologies and application fields that meanwhile it seems anything is possible. However, clearly the ideal 3D Printer, with high resolution, multi-material capability, fast printing, etc. is yet to be developed. Nevertheless, one can al- ready start to wonder what possibilities for electrical engineering applications will become available in the near future. Here I try to give a brief and balanced overview of current developments and a few examples of the first small steps towards 3D printed transducers.
Using PLS path modeling in new technology research: updated guidelines - Henseler, Jörg; Hubona, Geoffrey; Ray, Pauline Ash
– Partial least squares (PLS) path modeling is a variance-based structural equation modeling (SEM) technique that is widely applied in business and social sciences. Its ability to model composites and factors makes it a formidable statistical tool for new technology research. Recent reviews, discussions, and developments have led to substantial changes in the understanding and use of PLS. The paper aims to discuss these issues.
– This paper aggregates new insights and offers a fresh look at PLS path modeling. It presents new developments, such as consistent PLS, confirmatory composite analysis, and the heterotrait-monotrait ratio of correlations.
– PLS path...
Heat and mass transfer over slippery, superhydrophobic surfaces - Haase, A. Sander; Lammertink, Rob G.H.
The classical Graetz-Nusselt problem is extended to describe heat and mass transfer over heterogeneously slippery, superhydrophobic surfaces. The cylindrical wall consists of segments with a constant temperature/concentration and areas that are insulating/impermeable. Only in the case of mass transport do the locations of hydrodynamic slip and mass exchange coincide. This makes advection near the mass exchanging wall segments larger than near the heat exchanging regions. Also the direction of radial fluid flow is reversed for heat and mass transport, which has an influence on the location where the concentration or temperature boundary layer is compressed or extended. As a result,...
Pitchfork–Hopf bifurcations in 1D neural field models with transmission delays - Dijkstra, K.; Gils, S.A. van; Janssens, S.G.; Kouznetsov, I.A.; Visser, S.
Recently, local bifurcation theory for delayed neural fields was developed. In this paper, we show how symmetry arguments and residue calculus can be used to simplify the computation of the spectrum in special cases and the evaluation of the normal form coefficients, respectively. This is done hand in hand with an extensive study of two pitchfork–Hopf bifurcations for a 1D neural field model with ‘Wizard hat’ type connectivity.
Center of mass velocity based predictions in balance recovery following pelvis perturbations during human walking - Vlutters, M.; Asseldonk, E.H.F. van; Kooij, H. van der
In many simple walking models foot placement dictates the center of pressure location and ground reaction force components, whereas humans can modulate these aspects after foot contact. Because of the differences, it is unclear to what extend predictions made by models are valid for human walking. Yet, both model simulations and human experimental data have previously indicated that the center of mass (COM) velocity plays an important role in regulating stable walking.
Here, perturbed human walking was studied for the relation of the horizontal COM velocity at heel strike and toe-off with the foot placement location relative to the COM, the...
Enhancement of turbulent flame speed of V-shaped flames in fractal-grid-generated turbulence - Verbeek, A.A.; Willems, P.A.; Stoffels, G.G.M.; Geurts, B.J.; Meer, T.H. van der
A variety of fractal grids is used to investigate how fractal-grid-generated turbulence affects the turbulent flame speed for premixed flames. The grids are placed inside a rectangular duct and a V-shaped flame is stabilized downstream of the duct, using a metal wire. This flame is characterized using OH-LIF. The turbulent flow is characterized by means of hot-wire anemometry. In total 24 grids containing variation in grid patterns, blockage ratio and range of embedded scales were assessed. The results quantify in detail the relation between grid parameters and the turbulence downstream of the different grids. The increase in turbulent flame speed...
An assessment of a days off decomposition approach to personnel shift scheduling - Veldhoven, Sophie van; Post, Gerhard; Veen, Egbert van der; Curtois, Tim
This paper studies a two-phase decomposition approach to solving the personnel scheduling problem. The first phase creates a days-off-schedule, indicating working days and days off for each employee. The second phase assigns shifts to the working days in the days-off-schedule. This decomposition is motivated by the fact that personnel scheduling constraints are often divided into two categories: one specifies constraints on working days and days off, while the other specifies constraints on shift assignments. To assess the consequences of the decomposition approach, we apply it to public benchmark instances, and compare this to solving the personnel scheduling problem directly. In...
Adoption of web-based group decision support systems: Experiences from the field and future developments - Hillegersberg, Jos van; Koenen, Sebastiaan
While organizations have massively adopted enterprise information systems to support business processes, business meetings in which key decisions are made about products, services and processes, are usually held without much support of information systems. This is remarkable as group decision support systems (GDSS) seems to fit for this purpose. They have existed for decades and modern versions benefit of web-based technologies, enabling low cost anyplace, any time and device independent meeting support. In this exploratory case research, we study nine organizations in four different adoption categories to learn more about the reasons for the relatively slow adoption of web-based GDSS....
Waiting Time from Diagnosis to Treatment has no Impact on Survival in Patients with Esophageal Cancer - Visser, E.; Leeftink, A.G.; Rossum, P.S.N. van; Siesling, S.; Hillegersberg, R. van; Ruurda, J.P.
Waiting time from diagnosis to treatment has emerged as an important quality indicator in cancer care. This study was designed to determine the impact of waiting time on long-term outcome of patients with esophageal cancer who are treated with neoadjuvant therapy followed by surgery or primary surgery.
Patients who underwent esophagectomy for esophageal cancer at the University Medical Center Utrecht between 2003 and 2014 were included. Patients treated with neoadjuvant therapy followed by surgery and treated with primary surgery were separately analyzed. The influence of waiting time on survival was analyzed using Cox proportional hazard analyses. Kaplan–Meier curves for short (<8...
Risk of regional recurrence in triple-negative breast cancer patients: a Dutch cohort study - Roozendaal, Lori M. van; Smit, Leonie H.M.; Duijsens, Gaston H.N.M.; Vries, Bart de; Siesling, Sabine; Lobbes, Marc B.I.; Boer, Maaike de; Wilt, Johannes H.W. de; Smidt, Marjolein L.
Triple-negative breast cancer is associated with early recurrence and low survival rates. Several trials investigate the safety of a more conservative approach of axillary treatment in clinically T1-2N0 breast cancer. Triple-negative breast cancer comprises only 15 % of newly diagnosed breast cancers, which might result in insufficient power for representative results for this subgroup. We aimed to provide a nationwide overview on the occurrence of (regional) recurrences in triple-negative breast cancer patients with a clinically T1-2N0 status. For this cohort study, 2548 women diagnosed between 2005 and 2008 with clinically T1-2N0 triple-negative breast cancer were selected from the Netherlands Cancer...
Problems experienced by informal caregivers with older care recipients with and without cognitive impairment - Bruggen, Sytske van; Gussekloo, Jacobijn; Bode, Christina; Touwen, Dorothea P.; Engberts, Dick P.; Blom, Janet W.
The care of older persons can have negative impact on the caregiver. The objective of this population-based observational study is to identify problems experienced by informal caregivers, and the extent of related difficulties, in their care of older care-dependent recipients with and without cognitive impairment. Caregivers (n = 2,704) caring for a home-dwelling person aged ≥ 75 years responded to a questionnaire with 23 questions on problems and related difficulties by mail. Prevalence of self-reported problems and related difficulties was calculated. The impact of the problem was estimated by weighing the percentage of problems reported as being difficult against the...
Performance evaluation using periodic system-state measurements - Ellens, W.; Mandjes, M.; Berg, H. van den; Worm, D.; Blaszczuk, S.
This paper deals with the problem of inferring short time-scale fluctuations of a system's behavior from periodic state measurements. In particular, we devise a novel, efficient procedure to compute four interesting performance metrics for a transient birth-death process on an interval of fixed length with given begin and end states: the probability to exceed a predefined (critical) level m , and the expectation of the time, area, and number of arrivals above level m . Moreover, our procedure allows to compute the variances and cross-correlations of the latter three metrics. The asymptotic behavior of the metrics for small and large...
Computation and dissipative dynamical systems in neural networks for classification - Velde, Frank van der
Foundational issues related to learning, processing and representation underlying pattern recognition have been discussed in history and in recent times. The scientific approach to pattern recognition could provide new tools to investigate these foundational issues, which in turn could inform the scientific approach to pattern recognition as well. One such tool could be the analysis of learning, processing and representation in connectionist (or neural) networks, which have been extensively used for pattern recognition. Based on a mathematical analysis of the classification behavior of feedforward networks an analysis is given of the empiricist vs. rationalist debate on the possibility or impossibility...
Cost-effectiveness of screening strategies to detect heart failure in patients with type 2 diabetes - Giessen, Anoukh van; Boonman-de Winter, Leandra J.M.; Rutten, Frans H.; Cramer, Maarten J.; Landman, Marcel J.; Liem, Anho H.; Hoes, Arno W.; Koffijberg, Hendrik
Heart failure (HF), especially with preserved ejection fraction (HFpEF) is common in older patients with type 2 diabetes (T2DM), but often not recognized. Early HF detection in older T2DM patients may be worthwhile because treatment may be initiated in an early stage, with clear beneficial treatment in those with reduced ejection fraction (HFrEF), but without clear prognostic beneficial treatment in those with HFpEF. Because both types of HF may be uncovered in older T2DM, screening may improve health outcomes at acceptable costs. We assessed the cost-effectiveness of five screening strategies in patients with T2DM aged 60 years or over.