University of Twente Publications
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 20.781
Process Control of Stainless Steel Laser Welding using an Optical Spectroscopic Sensor - Konuk, A.R.; Aarts, R.G.K.M.; Huis in 't Veld, A.J.; Sibillano, T.; Rizzi, D.; Ancona, A.
The in-process monitoring and real-time control of the penetration depth during laser welding is evaluated. An optical collimator collects the optical emission for measurement with a fast spectrometer. The sensor data are used to calculate the electron temperature and subsequently to determine the weld quality of overlap welds in AISI 304 stainless steel sheets performed both with CW Nd:YAG and CO2 lasers. A PI-controller adjusts the laser power aiming at a constant penetration depth and has been tested for Nd:YAG laser welding. Optical inspection of the weld verifies the results obtained with the proposed closed-loop system of spectroscopic sensor and...
Study on the correlation between plasma electron temperature and penetration depth in laser welding processes - Sibillano, T.; Ancona, A.; Rizzi, D.; Saludes Rodil, S.; Rodriguez Nieto, J.; Konuk, A.R.; Aarts, R.; Huis in 't Veld, A.J.
The plasma electron temperature has been estimated starting from the spectroscopic analysis of the optical emission of the laser-generated plasma plume during quite diverse stainless steel welding procedures (c.w. CO2 and pulsed Nd:YAG). Although the optical emissions present different spectral features, a discrete contribution of several iron lines can be highlighted in both types of welding. We have found that the electron temperature decreases as the laser power is enhanced, in static as well as dynamic conditions. Such a result could be useful to develop a closed loop control system of the weld penetration depth.
Fluid-Structure Interaction in Combustion System of a Gas Turbine—Effect of Liner Vibrations - Pozarlik, A.K.; Kok, J.B.W.
Prediction of mutual interaction between flow, combustion, acoustic, and vibration phenomena occurring in a combustion chamber is crucial for the reliable operation of any combustion device. In this paper, this is studied with application to the combustion chamber of a gas turbine. Very dangerous for the integrity of a gas turbine structure can be the coupling between unsteady heat release by the flame, acoustic wave propagation, and liner vibrations. This can lead to a closed-loop feedback system resulting in mechanical failure of the combustor liner due to fatigue and fatal damage to the turbine. Experimental and numerical investigations of the...
Pulse-analysis-pulse investigation of femtosecond laser-induced periodic surface structures on silicon in air - Obona, J.V.; Skolski, J.Z.P.; Römer, G.R.B.E.; Huis in 't Veld, A.J.
A new approach to experimentally investigate laser-induced periodic surface structures (LIPSSs) is introduced. Silicon was iteratively exposed to femtosecond laser pulses at λ = 800 nm and normal incidence in ambient air and at a fluence slightly over the single-pulse modification threshold. After each laser pulse, the topography of the surface was inspected by confocal microscopy. Subsequently, the sample was reproducibly repositioned in the laser setup, to be exposed to the next laser pulse. By this approach, the initiation and spatial evolution (“growth”) of the LIPSSs were analyzed as function of the number of pulses applied. It was found that,...
The value of quantitative patient preferences in regulatory benefit-risk assessment - Oude Egbrink, Mart; IJzerman, Maarten
Quantitative patient preferences are a method to involve patients in regulatory benefit-risk assessment. Assuming preferences can be elicited, there might be multiple advantages to their use. Legal, methodological and procedural issues do however imply that preferences are currently at most part of the solution on how to best involve patients in regulatory decision making. Progress is recently made on these issues.
Parents’ decision for helmet therapy in infants with skull deformation - Wijk, Renske M. van; Til, Janine A. van; Groothuis-Oudshoorn, Catharina G.M.; L'Hoir, Monique P.; Boere-Boonekamp, Magda M.; IJzerman, Maarten J.
Helmet therapy is regularly prescribed in infants with positional skull deformation. Evidence on the effectiveness is lacking, which complicates decision making. This study aims to assess the relation between parents’ decision for treatment of skull deformation in their infant and their level of anxiety, decisional conflict, expectations of treatment effect, perceived severity of deformation and perceived side effects.
Parents of 5-month-old infants with skull deformation were invited to participate in a survey. Data collection included background characteristics, anthropometric assessment, parent-reported outcomes, decision for treatment (helmet therapy or awaiting natural course), decisional conflict scale and questions about perceived (side) effects of helmet...
Public stated preferences and predicted uptake for genome-based colorectal cancer screening - Groothuis-Oudshoorn, Catharina G.M.; Fermont, Jilles M.; Til, Janine A. van; IJzerman, Maarten J.
Emerging developments in nanomedicine allow the development of genome-based technologies for non-invasive and individualised screening for diseases such as colorectal cancer. The main objective of this study was to measure user preferences for colorectal cancer screening using a nanopill.
A discrete choice experiment was used to estimate the preferences for five competing diagnostic techniques including the nanopill and iFOBT. Alternative screening scenarios were described using five attributes namely: preparation involved, sensitivity, specificity, complication rate and testing frequency. Fourteen random and two fixed choice tasks, each consisting of three alternatives, were offered to 2225 individuals. Data were analysed using the McFadden...
Belief Elicitation to Populate Health Economic Models of Medical Diagnostic Devices in Development - Haakma, Wieke; Steuten, Lotte M.G.; Bojke, Laura; IJzerman, Maarten J.
Background and Objective
Bayesian methods can be used to elicit experts’ beliefs about the clinical value of healthcare technologies. This study investigates a belief–elicitation method for estimating diagnostic performance in an early stage of development of photoacoustic mammography (PAM) imaging versus magnetic resonance imaging (MRI) for detecting breast cancer.
Eighteen experienced radiologists ranked tumor characteristics regarding their importance to detect malignancies. With reference to MRI, radiologists estimated the true positives and negatives of PAM using the variable interval method. An overall probability density function was determined using linear opinion pooling, weighted for individual experts’ experience.
The most important tumor characteristics are mass...
Comparison of 3 biodegradable polymer and durable polymer-based drug-eluting stents in all-comers (BIO-RESORT): Rationale and study design of the randomized TWENTE III multicenter trial - Lam, Ming Kai; Sen, Hanim; Tandjung, Kenneth; Houwelingen, K. Gert van; Vries, Arie G. de; Danse, Peter W.; Schotborgh, Carl E.; Scholte, Martijn; Löwik, Marije M.; Linssen, Gerard C.M.; IJzerman, Maarten J.; Palen, Job van der; Doggen, Carine J.M.; Birgelen, Clemens von
To evaluate the safety and efficacy of 2 novel drug-eluting stents (DES) with biodegradable polymer-based coatings versus a durable coating DES.
Methods and Results
BIO-RESORT is an investigator-initiated, prospective, patient-blinded, randomized multicenter trial in 3540 Dutch all-comers with various clinical syndromes, requiring percutaneous coronary interventions (PCI) with DES implantation. Randomization (stratified for diabetes mellitus) is being performed in a 1:1:1 ratio between ORSIRO sirolimus-eluting stent with circumferential biodegradable coating, SYNERGY everolimus-eluting stent with abluminal biodegradable coating, and RESOLUTE INTEGRITY zotarolimus-eluting stent with durable coating. The primary endpoint is the incidence of the composite endpoint target vessel failure at 1 year, consisting of...
Explaining the non-implementation of health-improving policies related to solid fuels use in South Africa - Matinga, Margaret Nijrambo; Clancy, Joy S.; Annegarn, Harold J.
In 1998, the South African government developed an energy policy that focused on a pro-poor agenda. Its objectives included addressing the health impacts of solid fuel use in households. Fourteen years later, and with household electrification at over 80%, millions still use solid fuels and yet ambitious policy objectives to address this situation are not being met. Using three theoretical frameworks; institutional capacity, policy inheritance and the symbolic use of policy, this paper analyses the reasons why household energy policy objectives related to solid fuels and health, as stated in the 1998 South African energy policy, have not been implemented....
On the effect of numerical noise in approximate optimization of forming processes using numerical simulations - Wiebenga, J.H.; Boogaard, A.H. van den
The coupling of Finite Element (FE) simulations with approximate optimization techniques is becoming increasingly popular in forming industry. By doing so, it is implicitly assumed that the optimization objective and possible constraints are smooth functions of the design variables and, in case of robust optimization, design and noise variables. However, non-linear FE simulations are known to introduce numerical noise caused by the discrete nature of the simulation algorithms, e.g. errors caused by re-meshing, time-step adjustments or contact algorithms. The subsequent usage of metamodels based on such noisy data reduces the prediction quality of the optimization routine and is known to...