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University of Twente Publications (49,892 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 22,670

1. Utilising the 3D aspects of micro array technologies - Vulto, Paul; Joore, J.; Walsh, Steven

2. An overview of systems for CT- and MRI-guided percutaneous needle placement in the thorax - Arnolli, Maarten M.; Hanumara, Nevan C.; Franken, Michel; Brouwer, Dannis M.; Broeders, Ivo A.M.J.
Minimally invasive biopsies, drainages and therapies in the soft tissue organs of the thorax and abdomen are typically performed through a needle, which is inserted percutaneously to reach the target area. The conventional workflow for needle placement employs an iterative freehand technique. This article provides an overview of needle-placement systems developed to improve this method. An overview of systems for needle placement was assembled, including those found in scientific publications and patents, as well as those that are commercially available. The systems are categorized by function and tabulated. Over 40 systems were identified, ranging from simple passive aids to fully actuated...

3. Robotic transanal total mesorectal excision for rectal cancer: experience with a first case - Verheijen, P.M.; Consten, E.C.J.; Broeders, I.A.M.J.
Background: A transanal approach for total mesorectal excision (TME) using a single incision port is feasible. The disadvantages are technical difficulties associated with limited manoeuvrability. Methods: We present our first experience with robotic-assisted transanal total mesorectal excision. A 48 year-old woman with a tumour 8 cm from the anal verge was successfully operated using a transanal approach. A complete mesorectal excision was performed through a single incision port, using two robot arms. Results: TME was performed successfully and the patient recovered quickly without any complications. The histological report showed a complete mesorectal excision with free distal and circumferential margins. A sigmoidoscopy showed an intact anastomosis...

4. Robotics: the next step? - Broeders, Ivo A.M.J.
Abstract: Robotic systems were introduced 15 years ago to support complex endoscopic procedures. The technology is increasingly used in gastro-intestinal surgery. In this article, literature on experimental- and clinical research is reviewed and ergonomic issues are discussed. Methods: literature review was based on Medline search using a large variety of search terms, including e.g. robot(ic), randomized, rectal, oesophageal, ergonomics. Review articles on relevant topics are discussed with preference. Results: There is abundant evidence of supremacy in performing complex endoscopic surgery tasks when using the robot in an experimental setting. There is little high-level evidence so far on translation of these merits to clinical practice. Discussion: Robotic systems...

5. Laparoscopic resection rectopexy versus laparoscopic ventral rectopexy for complete rectal prolapse - Formijne Jonkers, H.A.; Maya, A.; Draaisma, W.A.; Bemelman, W.A.; Broeders, I.A.; Consten, E.C.J.; Wexner, S.D.
Background: Laparoscopic resection rectopexy (LRR) and laparoscopic ventral rectopexy (LVR) are favored for the treatment for rectal prolapse (RP) in the USA and Europe, respectively. This study aims to compare these two surgical techniques. Methods: All patients who underwent LRR because of RP between January 2000 and January 2012 at Cleveland Clinic Florida (Weston, FL, USA) were identified, and all relevant characteristics were entered in a database. This same analysis was also conducted for all patients who underwent LVR in the Meander Medical Center (Amersfoort, the Netherlands) between January 2004 and January 2012. These two cohorts were retrospectively compared with regard...

6. Successive interference cancellation in heterogeneous networks - Wildemeersch, Matthias; Quek, Tony Q.S.; Kountouris, Marios; Rabbachin, Alberto; Slump, Cornelis H.
At present, operators address the explosive growth of mobile data demand by densification of the cellular network so as to reduce the transmitter-receiver distance and to achieve higher spectral efficiency. Due to such network densification and the intense proliferation of wireless devices, modern wireless networks are interference-limited, which motivates the use of interference mitigation and coordination techniques. In this work, we develop a statistical framework to evaluate the performance of multi-tier heterogeneous networks with successive interference cancellation (SIC) capabilities, accounting for the computational complexity of the cancellation scheme and relevant network related parameters such as random location of the access...

7. Impact of image processing in the detection of ischaemia using CZT-SPECT/CT - Koopman, Daniëlle; Dalen, Jorn A.; Slump, Cornelis H.; Lots, Dimitri; Timmer, Jorik R.; Jager, Pieter L.
Background: The new multipinhole cardiac single photon emission computed tomography/computed tomography (SPECT/CT) cameras with cadmium–zinc–telluride (CZT) detectors are highly sensitive and produce images of high quality but rely on complex dedicated reconstruction algorithms. The aim of this study was to determine the impact of various processing steps on image formation and in the detection of ischaemia in CZT-SPECT/CT both with and without attenuation correction (AC). Materials and methods: Data on 20 consecutive patients who underwent a 1-day protocol stress–rest SPECT/CT using 99mTc-tetrofosmin were processed twice by three experienced operators, yielding 120 AC and 120 noncorrected (NC) data sets. Processing steps included selection and...

8. The persuasion and security awareness experiment: reducing the success of social engineering attacks - Bullee, Jan-Willem H.; Montoya, Lorena; Pieters, Wolter; Junger, Marianne; Hartel, Pieter
Objectives: The aim of the current study is to explore to what extent an intervention reduces the effects of social engineering (e.g. the obtaining of access by persuasion) in an office environment. In particular, we study the effect of authority during a `social engineering' attack. Methods: 31 different `offenders' visited the offices of 118 employees and on the basis of a script, asked them to hand over their office keys. Authority, one of the six principles of persuasion, was used by half of the offenders to persuade a target to comply with his/her request. Prior to the visit, an intervention was randomly administered...

9. Preliminary results using a newly developed projection method to visualize vascular anatomy prior to DIEP flap breast reconstruction - Hummelink, S.; Hameeteman, M.; Hoogeveen, Y.; Slump, C.H.; Ulrich, D.J.O.; Schultze Kool, L.J.
Introduction: In a deep inferior epigastric perforator (DIEP) flap breast reconstruction, computed tomography angiography (CTA) is currently considered as the gold standard in preoperative imaging for this procedure. Unidirectional Doppler ultrasound (US) is frequently used; however, this method does not distinguish the main axial vessels from perforator arteries at the height of the fascia, it has a limited penetration depth, and it cannot assess the branching patterns of the deep inferior arteries. A new method and system were developed, which consisted of a video projector preoperatively displaying the location and intramuscular course of the artery perforators and subcutaneous branching on the...

10. Nanostructure Based on Polymer Brushes for Efficient Heterogeneous Catalysis in Microreactors - Costantini, Francesca; Bula, Wojciech P.; Salvio, Riccardo; Huskens, Jurriaan; Gardeniers, Han J.G.E.; Reinhoudt, David N.; Verboom, Willem
PGMA polymer brushes are successfully grown on the inner wall of a microreactor to give a nanostructure. The oxirane groups of the brushes are used for the anchoring of a catalyst. The utility of the combination of catalyst-functionalized brushes and a microreactor is clearly demonstrated for the TBD-catalyzed Knoevenagel condensation reaction of benzaldehyde and malononitrile

11. Effect of the presence of an ordered micro-pillar array on the formation of silica monoliths - Detobel, Frederik; Eghbali, Hamed; De Bruyne, Selm; Terryn, Herman; Gardeniers, Han; Desmet, Gert
We report on the synthesis of siloxane-based monoliths in the presence of a two-dimensional, perfectly ordered array of micro-pillars. Both methyltrimethoxysilane- and tetramethoxysilane-based monoliths were considered. The obtained structures were analyzed using scanning-electron microscopy and can be explained from the general theory of surface-directed phase separation in confined spaces. The formed structures are to a large extent nearly exclusively determined by the ratio between the bulk domain size of the monolith on the one hand and the distance between the micro-pillars on the other hand. When this ratio is small, the presence of the pillars has nearly no effect on...

12. Room-temperature intermediate layer bonding for microfluidic devices - Bart, Jacob; Tiggelaar, Roald; Yang, Mengjong; Schlautmann, Stefan; Zuilhof, Han; Gardeniers, Han
In this work a novel room-temperature bonding technique based on chemically activated Fluorinated Ethylene Propylene (FEP) sheet as an intermediate between chemically activated substrates is presented. Surfaces of silicon and glass substrates are chemically modified with APTES bearing amine terminal groups, while FEP sheet surfaces are treated to form carboxyl groups and subsequently activated by means of EDC–NHS chemistry. The activation procedures of silicon, glass and FEP sheet are characterized by contact angle measurements and XPS. Robust bonds are created at room-temperature by simply pressing two amine-terminated substrates together with activated FEP sheet in between. Average tensile strengths of 5.9...

13. A Microfluidic High-Resolution NMR Flow Probe - Bart, Jacob; Kolkman, Ard J.; Oosthoek-de Vries, Anna Jo; Koch, Kaspar; Nieuwland, Pieter J.; Janssen, Hans (J.W.G.); Bentum, Jan (P.J.M.) van; Ampt, Kirsten A.M.; Rutjes, Floris P.J.T.; Wijmenga, Sybren S.; Gardeniers, Han (J.G.E.); Kentgens, Arno P.M.
A microfluidic high-resolution NMR flow probe based on a novel stripline detector chip is demonstrated. This tool is invaluable for the in situ monitoring of reactions performed in microreactors. As an example, the acetylation of benzyl alcohol with acetyl chloride was monitored. Because of the uncompromised (sub-Hz) resolution, this probe holds great promise for metabolomics studies, as shown by an analysis of 600 nL of human cerebrospinal fluid

14. Catalyst Activation by Microplasma for Carbon Nanofiber Synthesis in a Microreactor - Agiral, Anil; Lefferts, Leon; Gardeniers, J.G.E.
A dielectric barrier discharge is generated by flowing helium and hydrogen through a microreactor capillary which contains a coating of Ni/alumina catalyst to activate carbon nanofiber (CNF) synthesis. Optical and electrical measurements have been done to characterize the discharge during catalyst treatment. A sinusoidal voltage of 6 kV (peak) with a frequency of 50 kHz has been applied to a high-voltage electrode, and a helium gas flow stabilizes the discharge to have a uniform and high-power-density surface treatment. Cold-plasma operation for 15 min is simple and audiovisual, increases the CNF yield significantly compared to nonactivated samples, and can compete with...

15. Design and evaluation of flow distributors for microfabricated pillar array columns - Vangelooven, Joris; De Malsche, Wim; Op de Beeck, Jeff; Eghbali, Hamed; Gardeniers, Han; Desmet, Gert
Five different flow distributors have been compared as a function of the flow rate for their ability to distribute small sample volumes over the entire width of flat rectangular microfabricated pillar array columns. The investigated designs can be divided in two major categories: (1) bifurcating, radially non-interconnecting distributors and (2) radially interconnecting distributors consisting of diamond-shaped pillars, elongated in the direction perpendicular to the flow, providing a high ratio of radial permeability over axial permeability. The quality of the flow distribution was evaluated experimentally by injecting equal volumes of fluorescent tracer into each of the tested designs and calculating the...

16. Novel shape and placement definitions with retention modeling for solid microfabricated pillar columns for CEC and HPLC - Sukas, Sertan; Desmet, Gert; Gardeniers, Han J.G.E.
A novel design approach for optimizing the shape of microfabricated pillar columns for LC is presented. 2-D flow simulations are performed with a focus on electrokinetically driven flow, in order to evaluate the performance of the new method. The proposed foil shape is compared with geometrical shapes known from the literature, for various arrangements. It yields a much more uniform velocity field distribution and a decrease in plate height values up to 25%. In addition to shape optimization, a new method for spatial arrangement of structures is presented. With the aim of conserving the hydrodynamic balance, the axial spacing of...

17. The interaction between nanoscale surface features and mechanical loading and its effect on osteoblast-like cells behavior - Prodanov, Ljupcho; Riet, Joost te; Lamers, Edwin; Domanski, Maciej; Luttge, Regina; Loon, Jack J.W.A.; Jansen, John A.; Walboomers, X. Frank
Osteoblasts respond to mechanical stimulation by changing morphology, gene expression and matrix mineralization. Introducing surface topography on biomaterials, independently of mechanical loading, has been reported to give similar effects. In the current study, using a nanotextured surface, and mechanical loading, we aimed to develop a multi-factorial model in which both parameters interact. Mechanical stimulation to osteoblast-like cells was applied by longitudinal stretch in parallel direction to the nanotexture (300 nm wide and 60 nm deep grooves), with frequency of 1 Hz and stretch magnitude varying from 1% to 8%. Scanning electron microscopy showed that osteoblast-like cells subjected to mechanical loading...

18. Gas–liquid dynamics at low Reynolds numbers in pillared rectangular micro channels - Loos, S.R.A. de; Schaaf, J. van der; Tiggelaar, R.M.; Nijhuis, T.A.; Croon, M.H.J.M. de; Schouten, J.C.
Most heterogeneously catalyzed gas–liquid reactions in micro channels are chemically/kinetically limited because of the high gas–liquid and liquid–solid mass transfer rates that can be achieved. This motivates the design of systems with a larger surface area, which can be expected to offer higher reaction rates per unit volume of reactor. This increase in surface area can be realized by using structured micro channels. In this work, rectangular micro channels containing round pillars of 3 μm in diameter and 50 μm in height are studied. The flow regimes, gas hold-up, and pressure drop are determined for pillar pitches of 7, 12,...

19. Experimental study of the retention properties of a cyclo olefin polymer pillar array column in reversed-phase mode - Illa, Xavi; De Malsche, Wim; Gardeniers, Han; Desmet, Gert; Romano-Rodriguez, Albert
Experimental measurements to study the retention capacity and band broadening under retentive conditions using micromachined non-porous pillar array columns fabricated in cyclo olefin polymer are presented. In particular, three columns with different depths but with the same pillar structure have been fabricated via hot embossing and pressure-assisted thermal bonding. Separations of a mixture of four coumarins using varying mobile phase compositions have been monitored to study the relation between the retention factor and the ratio of organic solvent in the aqueous mobile phase. Moreover, the linear relation between the retention and the surface/volume ratio predicted in theory has been observed,...

20. Experimental study of the depth influence on the band broadening effect in a cyclo-olefin polymer column containing an array of ordered pillars - Illa, Xavi; De Malsche, Wim; Gardeniers, Han; Desmet, Gert; Romano-Rodriguez, Albert
An experimental study of a micromachined non-porous pillar array column performance under non-retentive conditions is presented. The same pillar structure has been fabricated in cyclo-olefin polymer (COP) chips with three different depths via hot embossing and pressure-assisted thermal bonding. The influence of the depth on the band broadening along with the already known contribution arising from the top and bottom cover plates has been studied. The experimental results exhibit reduced plate heights as low as 0.2, which are in agreement with the previous experimental work. Moreover, the constant values of the reduced Van Deemter expression are also in accordance with...

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