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University of Twente Publications (46,904 recursos)
University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.

Group = KEUR

Mostrando recursos 1 - 20 de 6,690

1. Stub resonators for online monitoring early stages of corrosion - Hoog, N.A.; Mayer, M.J.J.; Miedema, H.; Wagterveld, R.M.; Snaakes, M.; Tuinstra, J.; Olthuis, W.; Berg, A. van den
Here we demonstrate the proof-of-principle of a new type of sensor to assess effects due to corrosion of metal surfaces. The method can be applied to all situations where metals are exposed to a corrosive (fluidic) environment, including, for instance, the interior of pipes and tubes. The sensing device is based on the operating principle of a quarter wave length open-ended stub resonator. In the absence of corrosion, inner and outer conductors of the resonator are separated by a single dielectric, i.e., a fluid. Oxidation of the metal surface of inner and/or outer conductor changes the properties of the dielectric...

2. Modeling and simulations of the amplitude–frequency response of transmission line type resonators filled with lossy dielectric fluids - Mayer, M.J.J.; Miedema, H.; Olthuis, W.; Leferink, F.B.J.; Berg, A. van den
Stub resonators can be used to assess the dielectric properties of fluids. The resonance frequencies, determined from the amplitude versus frequency (AF) response of such resonators, are mainly determined by the permittivity of the fluid while damping arises from dielectric losses. Even though this methodology has been extensively reported in the literature, without almost any exception these studies refer to (near) ideal behavior regarding for example, geometry and negligibly low conductivity of the fluid studied. Online stub resonator-based sensors (i.e., flow-through) in use for industrial applications, however, quite often suffer from high dielectric losses, non-ideal material choice of the conductors...

3. De inhoud van het beleid - Bressers, J.T.A.; Klok, P.J.

4. Imaging of the ejection process of nanosecond laser-induced forward transfer of gold - Pohl, R.; Visser, C.W.; Römer, G.R.B.E.; Sun, C.; Huis in 't Veld, A.J.; Lohse, D.
Laser-induced forward transfer is a direct-write process suitable for high precision 3D printing of several materials. However, the driving forces related to the ejection mechanism of the donor ma-terial are still under debate. So far, most of the experimental studies of nanosecond LIFT, are based on post process analysis of either the donor layer and/or the deposits, which were transferred to the receiving substrate. To gain further insights into the ejection dynamics, this article presents results of a series of imaging experiments of the release process of nanosecond LIFT of a 200 nm thick gold donor layer. Images were obtained...

5. High-resolution imaging of ejection dynamics in laser-induced forward transfer - Pohl, R.; Visser, C.W.; Römer, G.R.B.E.; Sun, C.; Huis in 't Veld, A.J.; Lohse, D.
Laser-induced Forward Transfer (LIFT) is a 3D direct-write method suitable for precision printing of various materials. As the ejection mechanism of picosecond LIFT has not been visualized in detail, the governing physics are not fully understood yet. Therefore, this article presents an experimental imaging study on the ejection process of gold-based LIFT. The LIFT experiments were performed using a 6.7 picosecond Yb:YAG laser source equipped with a SHG. The beam was focused onto a 200 nm thick gold donor layer. The high magnification images were obtained using bright field illumination by a 6 ns pulsed Nd:YAG laser source and a...

6. An Open FOAM-based electro-hydrodynamical model - Roghair, I.; Ende, H.T.M. van den; Mugele, F.G.

7. Design and analysis of a high-efficiencyv high-voltage class-D power output stage - Ma, Haifeng; Zee, Ronan van der; Nauta, Bram
The analysis and design of a highly-efficient 80 V class-D power stage design in a 0.14 μm SOI-based BCD process is described. It features immunity to the on-chip supply bounce, realized by internally regulated floating supplies, variable driving strength for the gate driver, and an efficient 2-step level shifter design. Fast switching transition and low switching loss are achieved with 94% peak efficiency for the complete class-D power stage in the realized chip.

8. Coaxial stub resonator for online monitoring early stages of corrosion - Hoog, Natalia A.; Mayer, Mateo J.J.; Miedema, Henk; Olthuis, Wouter; Berg, Albert van den
Here we demonstrate the proof-of-principle of a new type of flow-through sensor to assess the corrosion rate of metal surfaces. The method can be applied to all situations where metals are exposed to a corrosive (fluidic) environment, including, for instance, the interior of pipes and tubes. Our sensing device is based on the operating principle of a quarter wave length open-ended coaxial stub resonator. The method described here can be applied for on-line monitoring corrosion.

9. Surface-enhanced Raman Spectroscopy of self-assembled monolayer conformation and spatial uniformity on silver surfaces - Wiedemair, Justyna; Le Thi Ngoc, Loan; Berg, Albert van den; Carlen, Edwin T.
We apply well-characterized silver nanowire grating (Ag-NWG) plasmonic surfaces as a Raman surface spectroscopy tool, which is based on surface-enhanced Raman scattering (SERS), to study the surface conformation characteristics of amine terminated alkanethiol self-assembled monolayers (SAMs). The surface conformation has implications for amine group availability, which is important when SAMs are used as linking layers for the binding of secondary molecules. Two different alkanethiols with different alkane chain lengths, namely 2-aminoethanethiol (cysteamine, CEA) and 11-aminoundecanethiol (AUT), are investigated. It is shown that both alkanethiols bind to Ag surfaces forming corresponding Ag-thiolates, however surface conformations, which are related to the ordering...

10. A novel side electrode configuration integrated in fused silica microsystems for synchronous optical and electrical spectroscopy - Sukas, Sertan; Schreuder, Erik; Wagenaar, Bjorn de; Swennenhuis, Joost; Berg, Albert van den; Terstappen, Leon; Le Gac, Séverine
We present a novel electrode configuration consisting of coplanar side electrode pairs integrated at the half height of the microchannels for the creation of a homogeneous electric field distribution as well as for synchronous optical and electrical measurements. For the integration of such electrodes in fused silica microsystems, a dedicated microfabrication method was utilized, whereby an intermediate bonding layer was applied to lower the temperature for fusion bonding to avoid thereby metal degradation and subsequently to preserve the electrode structures. Finally, we demonstrate the applicability of our devices with integrated electrodes for single cell electrical lysis and simultaneous fluorescence and...

11. Quantum oscillations and subband properties of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface - McCollam, A.; Wenderich, S.; Kruize, M.K.; Guduru, V.K.; Molegraaf, H.J.A.; Huijben, M.; Koster, G.J.; Blank, D.H.A.; Rijnders, A.J.H.M.; Brinkman, A.; Hilgenkamp, H.; Zeitler, U.; Maan, J.C.

12. Globalization, Representation, and Attitudes Towards Democracy - Aarts, Kees; Thomassen, Jacques; Ham, Carolien van

13. A 4-element phased-array system with simultaneous spatial- and frequency-domain filtering at the antenna inputs - Ghaffari, Amir; Klumperink, Eric A.M.; Vliet, Frank van; Nauta, Bram
To reject strong interference in excess of 0 dBm, a 4- element LO-phase shifting phased-array receiver with 8-phase passive mixers terminated by baseband capacitors is presented. The passive mixers upconvert both the spatial and frequency domain filtering from baseband to RF, hence realizing blocker suppression directly at the antenna inputs. A comprehensive mathematical model provides a set of closed-form equations describing the spatial and frequency domain filtering including imperfections. A prototype is realized in 28 nm CMOS. It exploits third harmonic reception to achieve a wide RF-frequency range from 0.6–4.5 GHz at 34–119 mW power dissipation, while also providing impedance...

14. A Survey of Provably Secure Searchable Encryption - Bösch, Christoph; Hartel, Pieter; Jonker, Willem; Peter, Andreas
We survey the notion of provably secure Searchable Encryption (SE) by giving a complete and comprehensive overview of the two main SE techniques: Searchable Symmetric Encryption (SSE) and Public Key Encryption with Keyword Search (PEKS). Since the pioneering work of Song, Wagner and Perrig (IEEE S&P ’00), the field of provably secure SE has expanded to the point where we felt that taking stock would provide benefit to the community. The survey has been written primarily for the non-specialist who has a basic information security background. Thus, we sacrifice full details and proofs of individual constructions in favor of an overview...

15. Failing Political Representation or a Change in Kind? Models of Representation and Empirical Trends in Europe - Thomassen, J.J.A.; Ham, C.T. van
This article reviews Peter Mair’s argument on the failure of political parties and the subsequent failure of representative democracy in Europe. It develops a conceptual framework to test the validity of Mair’s argument against competing interpretations of the development of representative democracy. It identifies three ideal typical models of representative democracy that seem to have succeeded each other over time: cleavage-based democracy, competitive democracy, and audience democracy. The article proposes specific empirical hypotheses for political parties and voters in each of these periods and provides empirical evidence to test the validity of these hypotheses. It concludes with a discussion of...

16. The Effects on Students’ Conceptual Understanding of Electric Circuits of Introducing Virtual Manipulatives Within a Physical Manipulatives-Oriented Curriculum - Zacharia, Zacharias C.; Jong, Ton de
This study investigates whether Virtual Manipulatives (VM) within a Physical Manipulatives (PM)-oriented curriculum affect conceptual understanding of electric circuits and related experimentation processes. A pre–post comparison study randomly assigned 194 undergraduates in an introductory physics course to one of five conditions: three experimental conditions with different PM and VM sequences and two control conditions with only PM or VM. Conceptual tests assessed students’ understanding. Instructors’ journals, video data, and interviews provided process-related data. Results showed interplay between manipulative and circuit types. For simple circuits, PM and VM use similarly impacted students’ understanding. However, VM better facilitated understanding than PM for...

17. Effective medium approximations for penetrant sorption in glassy polymers accounting for excess free volume - Ogieglo, Wojciech; Wormeester, Herbert; Wessling, Matthias; Benes, Nieck E.
An accurate determination of a penetrant volume fraction in a swollen polymer is of crucial importance in a range of different technologies. Using optical methods, such as in-situ spectroscopic ellipsometry, it is possible to extract the thickness and refractive index of dry and swollen polymer films. The volume fraction of the penetrant can then be calculated from the change in thickness, or from the refractive index using effective medium approximations. For thermodynamically equilibrated and ideal swollen rubbery polymers, these calculations yield accurate results. However, for glassy polymers the influence of the excess free volume trapped within the polymer network during...

18. Estimating aeolian sand supply from the intertidal beach using video imagery - Duarte Campos, L.A.; Wijnberg, K.M.; Reim, E.; Hulscher, S.J.M.H.

19. Electrostatic potential wells for manipulations of drops in microchannels - Ruiter, R. de; Pit, A.M.; Martins de Oliviera, V.; Wijnperle, D.; Duits, M.H.G.; Ende, H.T.M. van den; Mugele, F.

20. Electrostatic potential wells for on-demand drop manipulation in microchannels - Ruiter, R. de; Pit, A.M.; Martins de Oliviera, V.; Duits, M.H.G.; Ende, H.T.M. van den; Mugele, F.G.
Precise control and manipulation of individual drops are crucial in many lab-on-a-chip applications. We present a novel hybrid concept for channel-based discrete microfluidics with integrated electrowetting functionality by incorporating co-planar electrodes (separated by a narrow gap) in one of the microchannel walls. By combining the high throughput of channel-based microfluidics with the individual drop control achieved using electrical actuation, we acquire the strengths of both worlds. The tunable strength of the electrostatic forces enables a wide range of drop manipulations, such as on-demand trapping and release, guiding, and sorting of drops in the microchannel. In each of these scenarios, the...

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