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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.

Group = KEUR

Mostrando recursos 1 - 20 de 6,839

1. 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...

2. RF transconductor linearization technique robust to process, voltage and temperature variations - Kundur Subramaniyan, Harish; Klumperink, Eric A.M.; Nauta, Bram; Venkatesh, Srinivasan; Kiaei, Ali
A new reconfigurable linearized low noise transconductance amplifier (LNTA) design for a software-defined radio receiver is presented. The transconductor design aims at realizing high linearity at RF in a way that is robust for Process, Voltage and Temperature variations. It exploits resistive degeneration in combination with a floating battery by-pass circuit and replica biasing to improve IIP3 in a robust way. The LNTA with current domain mixer is implemented in a 45nm CMOS process. Compared to an inverter based LNTA with the same transconductance, it improves PIIP3 from 2 dBm to a robust PIIP3 of 8 dBm at the cost...

3. 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

4. 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...

5. A Brush-Gel/Metal-Nanoparticle Hybrid Film as an Efficient Supported Catalyst in Glass Microreactors - Costantini, Francesca; Benetti, Edmondo M.; Tiggelaar, Roald M.; Gardeniers, Han J.G.E.; Reinhoudt, David N.; Huskens, Jurriaan; Vancso, Julius; Verboom, Willem
A polymer-brush-based material was applied for the formation and in situ immobilization of silver and palladium nanoparticles, as a catalytic coating on the inner wall of glass microreactors. The brush film was grown directly on the microchannel interior by means of atom-transfer radical polymerization (ATRP), which allows control over the polymer film thickness and therefore permits the tuning of the number of nanoparticles formed on the channel walls. The wide applicability of the catalytic devices is demonstrated for the reduction of 4-nitrophenol and for the Heck reaction

6. A capillary micro-reactor as a tool to study pressurised reactions: The influence of pressure on the stereoselectivity of the Diels-Alder reaction of 2- and 3-Furylmethanol with maleimides - Benito-Lopez, Fernando; Kettelarij, Albert J.; Egberink, Richard J.M.; Velders, Aldrik H.; Tiggelaar, Roald M.; Gardeniers, Han J.G.E.; Reinhoudt, David N.; Verboom, Willem
The influence of a pressure of 60 MPa on theconversion and the stereoselectivity of the Diels-Alderreaction of 2- and 3-furylmethanol with methyl-, benzyl-, andphenylmaleimide was studied in a capillary micro-reactor. Inthe case of 2-furylmethanol, a 1.7-fold higher conversion wasobtained at 60 MPa with respect to 0.1 MPa experiments.Pressure positively affects the formation of the exo isomer,whereas in the case of 3-furylmethanol pressure does notaffect the reaction.

7. Pathway Study on Dielectric Barrier Discharge Plasma Conversion of Hexane - Agiral, Anil; Boyadjian, Cassia; Seshan, K.; Lefferts, Leon; Gardeniers, J.G.E. (Han)
A plasma reactor based on dielectric barrier discharge has been developed for oxidative cracking of hexane to yield olefins at atmospheric pressure. Dissociation of hexane in the presence of oxygen with nonequilibrium plasma state represents complex chemistry, and both conversion and product selectivities differ significantly from the thermodynamic equilibrium state. In order to understand plasma chemistry initiated by electron impact processes, the Boltzmann equation is solved to determine the average electron energy and energy fractions in collision processes. Activation of oxygen in the plasma brings a new route with electron impact dissociation yielding atomic oxygen radicals and initiates oxidative cracking...

8. Ruthenium catalyst on carbon nanofiber support layers for use in silicon-based structured microreactors, Part II: Catalytic reduction of bromate contaminants in aqueous phase - Thakur, D.B.; Tiggelaar, R.M.; Weber, Y.; Gardeniers, J.G.E.; Lefferts, L.; Seshan, K.
Catalyst layers were synthesized inside a structured channel of silicon based microreactor and used to remove bromate contaminants in water. It is demonstrated that Ru/CNF based catalyst is active for bromate reduction, resulting in turn over frequencies (TOFs) higher than conventional powdered catalyst, i.e. activated carbon (AC). This enhanced catalytic performance can be attributed to improve mass transfer properties of entangled CNF layers with macroporous (open) structure, which offer enhanced accessibility to all the Ru active sites in contrast to the poor accessibility of active sites in the case of AC support material. Although promising catalytic activity of Ru/CNF catalyst was...

9. Ruthenium catalyst on carbon nanofiber support layers for use in silicon-based structured microreactors, Part I: Preparation and characterization - Thakur, D.B.; Tiggelaar, R.M.; Hoang, T.M.C.; Gardeniers, J.G.E.; Lefferts, L.; Seshan, K.
The preparation and characterization of ruthenium catalytic nanoparticles on carbon nanofiber (CNF) support layers via homogeneous deposition precipitation (HDP) and pulsed laser deposition (PLD) is presented. Prior to ruthenium deposition the CNF layers were functionalized via liquid phase oxidation treatment using nitric acid at 90 °C. This acid treatment not only effectively removed accessible CNF-growth catalyst, but also resulted in the formation of oxygen containing functional groups on the external surface of CNFs. A variety of characterization techniques, viz. TEM, XRD, XRF, XPS, and point-of-zero-charge (PZC) measurements were used to analyze the influence of the oxidation pretreatment on physico-chemical properties...

10. Polymer relaxations in thin films in the vicinity of a penetrant or a temperature induced glass transition - Ogieglo, W.; Wessling, M.; Benes, N.E.
The transient properties of thin glassy polymer films in the vicinity of the glass transition are investigated. We compare the differences and similarities between sorption and temperature induced glass transitions, referred to as Pg and Tg, respectively. The experimental technique used is in situ spectroscopic ellipsometry, which allows for a very precise dynamic measurement of the changes in the thickness and the refractive index of the thin films. It is shown that significant differences exist between the penetrant- and temperature-induced transitions. The Tg is relatively well-defined with a sharp change in polymer dynamics, causing a well-known curvature change, a kink,...

11. Hybrid Polyhedral Oligomeric Silsesquioxanes-Imides with Tailored Intercage Spacing for Sieving of Hot Gases - Raaijmakers, M.J.T.; Wessling, M.; Nijmeijer, A.; Benes, N.E.
Macromolecular network rigidity of synthetic membranes is essential for sieving of hot gases. Hyper-cross-linked polyPOSS−imide membranes with tailored intercage spacing are presented. The length and flexibility of their imide bridges enables tuning of gas permeability and selectivity in a broad temperature range. The facile synthesis allows for large-scale production of membranes designed for specific process conditions.

12. Effects of time, temperature, and pressure in the vicinity of the glass transition of a swollen polymer - Ogieglo, W.; Upadhyaya, L.; Wessling, M.; Nijmeijer, A.; Benes, N.E.
In-situ spectroscopic ellipsometry is used for the dynamic study of thermally perturbed thin polystyrene films, swollen with n-octane or n-decane. The thermal evolution of the swollen films reveals pronounced changes both in equilibrium and kinetic properties. Upon vitrification, a kinetically arrested swollen matrix isobserved. This phenomenon is related to the excess energy term in the chemical potential of the solvent, associated with the non-equilibrium status of the swollen polymer matrix. The swollen polystyrene – n-decane system shows no measurable compression when exposed to hydrostatic pressures up to 50 bar, neither above or below the glass transition temperature. A slight compression...

13. Sieving of Hot Gases by Hyper-Cross-Linked Nanoscale-Hybrid Membranes - Raaijmakers, M.J.T.; Hempenius, M.A.; Schön, P.M.; Vancso, G.J.; Nijmeijer, A.; Wessling, M.; Benes, N.E.
Macromolecular networks consisting of homogeneously distributed covalently bonded inorganic and organic precursors are anticipated to show remarkable characteristics, distinct from those of the individual constituents. A novel hypercross-linked ultrathin membrane is presented, consisting of a giant molecular network of alternating polyhedral oligomeric silsesquioxanes and aromatic imide bridges. The hybrid characteristics of the membrane are manifested in excellent gas separation performance at elevated temperatures, providing a new and key enabling technology for many important industrial scale applications.

14. Oxidative Conversion of Hexane to Olefins-Influence of Plasma and Catalyst on Reaction Pathways - Boyadjian, C.; Agiral, A.; Gardeniers, J.G.E.; Lefferts, L.; Seshan, K.
An integrated plasma-Li/MgO system is efficient for the oxidative conversion of hexane. In comparison to the Li/MgO catalytic system, it brings considerable improvements in the yields of light olefins (C 2 = –C 5 = ) at relatively low temperatures indicating synergy from combination of plasma and catalyst. The study on the influence of temperature on the performance of the integrated plasma-Li/MgO system shows dominancy of plasma chemistry at the lower temperature (500°C), while contribution from the catalyst both in hexane activation and in enhancing olefin formation becomes significant at the higher temperature (600°C). At 500°C significant amount of acetylene...

15. Detection of ion adsorption at solid–liquid interfaces using internal reflection ellipsometry - Wang, Lei; Zhao, Cunlu; Duits, Michel H.G.; Mugele, Frieder; Siretanu, Igor
We use imaging internal reflection ellipsometry (IRE) in combination with a microfluidic device to study the adsorption of inorganic salt ions to silica–water interfaces. In our data analysis, the measured polarization-dependent reflectivity is compared to calculations from a layer stack model, where the electric double layer is modeled as a separate layer. Due to the high resolution of our technique, we are able to quantify the adsorption of Na+ and Ca2+ ions from aqueous solutions of their chloride salts as a function of their bulk concentrations at pH 3 and 10. Our measurements demonstrate a preferential adsorption of Ca2+ counterions....

16. Design of wave breaking experiments and A-Posteriori Simulations - Kurnia, R.; Groesen, E. van
This report presents results of 30 wave breaking experiments conducted in the long wave tank of TU Delft, Department of Maritime and Transport Technology (6,7 and 10-12 March 2014), together with simulations performed before the experiment to determine the required wave maker motion and a-posteriori simulations that use a measured time trace as influx for calculation further downstream.

17. Impact of the Internet on higher education in the Netherlands - Boezerooy, Petra; Beerkens, Eric; Collis, Betty; Huisman, Jeroen; Moonen, Jef

18. Tools and strategies for engaging the supervisor in technology-supported work-based learning : evaluation research - Bianco, Manuela; Collis, Betty
This study reports the results of the formative evaluations of two computer-supported tools and the associated strategies for their use. Tools and strategies embedded in web-based courses can increase a supervisor’s involvement in helping employees transfer learning onto the workplace. Issues relating to characteristics of the tools and strategies as well as factors influencing their likelihood of use are identified via summaries of the two evaluation studies.

19. BE COOL!: a digital learning environment to challenge and socially include gifted learners - Eysink, T.H.S.; Dijk, A.M. van; Jong, T. de

20. The role of curiosity triggering events in game-based learning for mathematics - Wouters, P.; Oostendorp, H. van; Vrugte, J. ter; Vandercruysse, S.; Jong, T. de; Elen, J.

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