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University of Twente Publications (43.882 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 6.571

1. Chronopotentiometric chloride sensing using transition time measurement - Abbas, Y.; de Graaf, D.B.; Olthuis, W.; van den Berg, A.
Detection of chloride ions is crucial to accurately access the concrete structure durability[1]. The existing electrochemical method of chloride ions detection in concrete, potentiometry[1], is not suitable for in-situ measurement due to the long term stability issue of conventional reference electrode (RE) inside concrete.

2. Stability and Interactions in Mixed Monolayers of Fatty Acid Derivatives on Artificial Sea Water - Brzozowska, A.M.; Mugele, F.; Duits, M.H.G.

3. Method for manufacturing a single crystal nanowire - Berg, Albert van den; Bomer, Johan; Carlen, Edwin Thomas; Chen, Songyue; Kraaijenhagen, Roderik Adriaan; Pinedo, Herbert Michael
A method for manufacturing a single crystal nano-structure is provided comprising the steps of providing a device layer with a 100 structure on a substrate; providing a stress layer onto the device layer; patterning the stress layer along the 110 direction of the device layer; selectively removing parts of the stress layer to obtain exposed parts of the device layer; plane dependent etching of the exposed parts of the device layer to obtain an exposed 111 faces of the device layer; thermally oxidizing the exposed 111 face of the device layer and forming a lateral oxidation layer at an interface...

4. Point of care creatinine measurement for diagnosis of renal disease using a disposable microchip - Ávila Muñoz, Mónica; Floris, Arjan; Staal, Steven; Ríos, Ángel; Eijkel, Jan; Berg, Albert van den
A point-of-care device for the determination of elevated creatinine levels in blood is reported. This device potentially offers a new and simple clinical regime for the determination of creatinine that will give huge time savings and removal of several steps of determination. The test employs a disposable prefilled microchip and the handheld Medimate Multireader®. By optimizing the analytical conditions it was found that the LOD of the proposed method was 87 μM creatinine, close to the normal human serum levels that are in the range of 60 to 100 μM. A statistical analysis of the residual shows a normal distribution,...

5. Lactate biosensors: current status and outlook - Rassaei, Liza; Olthuis, Wouter; Tsujimura, Seiya; Sudhölter, Ernst J.R.; Berg, Albert van den
Many research efforts over the last few decades have been devoted to sensing lactate as an important analytical target in clinical care, sport medicine, and food processing. Therefore, research in designing lactate sensors is no longer in its infancy and now is more directed toward viable sensors for direct applications. In this review, we provide an overview of the most immediate and relevant developments toward this end, and we discuss and assess common transduction approaches. Further, we critically describe the pros and cons of current commercial lactate sensors and envision how future sensing design may benefit from emerging new technologies.

6. Sample preconcentration inside sessile droplets using electrowetting - Mampallil, Dileep; Tiwari, D.; Ende, H.T.M. van den; Mugele, F.G.

7. Stability and interactions in mixed monolayers of fatty acid derivatives on artificial sea water - Brzozowska, A.M.; Mugele, F.; Duits, M.H.G.
We studied the formation and stability of fatty acid and derivatives films on aqueous sub-phases by means of Langmuir trough experiments. Films were prepared from pure stearic acid (SA), stearyl amine (SAm) and 12-phenyldodecanoic acid (PDA), and from binary systems of SA with either SAm or PDA. For the aqueous sub-phase, multicomponent salt solutions (‘Artificial Sea Water’) at various concentrations (cASW, 0–100%) and pH values (3–7) were explored. SAm and SA differ most strongly at pH 7, where they can dissociate into oppositely charged species. For SA:SAm mixtures at this pH, pressure-area isotherms indicate mixing on a molecular scale. Increase...

8. Sample preconcentration inside sessile droplets using electrowetting - Mampallil, Dileep; Tiwari, D.; Ende, H.T.M. van den; Mugele, F.

9. Building upon what is already there: The role of prior knowledge, background information, and scaffolding in inquiry learning - Wecker, C.; Lazonder, A.W.; Chiu, J.L.; Madeira, C.; Slotta, J.D.; Mulder, Y.G.; Jong, T. de; Rachel, A.; Wiesner, H.; Heran-Dorr, E.; Fischer, F.; Reimann, P.
Prior knowledge is one of the most important factors for learning. During the iterative cycles of inquiry learning, learners' prior domain knowledge is modified, refined, and further developed, provided that learners act upon self-assessments of their understanding and that they can actually think of appropriate hypotheses. Furthermore, knowledge about inquiry strategies influences the quality of the learners' inquiry activities, and the lack there of requires compensatory support. This symposium brings together recent work about the role of prior knowledge for inquiry learning and ways to compensate for the lack of it. The four papers focus on the role of learners'...

10. 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.

11. Zirconium and hafnium tert-butoxides and tert-butoxo-beta-diketonate complexes – Isolation, structrural characterization and application in the one-step synthesis of 3D metal oxide nanostructrures - Spijksma, G.I.; Seisenbaeva, G.A.; Bouwmeester, H.J.M.; Blank, D.H.A.; Kessler, V.G.
Long term storage of the pure commercial Zr(OtBu)4 in a sealed ampoule results in crystallization of a new high symmetry phase of Zr3O(OtBu)10 (1). Modification of Zr(OtBu)4 and Hf(OtBu)4 with 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) produces dependent on the stoichiometry two types of derivatives, M(OtBu)2(thd)2 (2, 3) and M(OtBu)(thd)3 (4, 5) M = Zr(2, 4), Hf(3, 5), which have all been characterized by NMR and mass-spectral studies and for 4 and 5 also by complete X-ray single crystal studies. The latter failed for 2 and 3 in the view of their poor X-ray reflectivity. Addition of minor amounts of n-C5H11OH to 3 resulted...

12. Buoyancy driven convection in vertically shaken granular matter: experiment, numerics, and theory - Eshuis, P.G.; Weele, J.P. van der; Alam, M.; Gerner, H.J. van; Hoef, M.A. van der; Kuipers, J.A.M.; Luding, S.; Meer, D. van der; Lohse, D.
Buoyancy driven granular convection is studied for a shallow, vertically shaken granular bed in a quasi 2D container. Starting from the granular Leidenfrost state, in which a dense particle cluster floats on top of a dilute gaseous layer of fast particles (Meerson et al. in Phys RevLett 91:024301, 2003; Eshuis et al. in Phys Rev Lett 95:258001, 2005), we witness the emergence of counter-rotating convection rolls when the shaking strength is increased above a critical level. This resembles the classical onset of convection—at a critical value of the Rayleigh number—in a fluid heated from below. The same transition, even quantitatively, is seen in molecular dynamics simulations, and explained by a hydrodynamic-like model...

13. Frequency limitations of first-order gm-RC all-pass delay circuits - Garakoui, Seyed Kasra; Klumperink, Eric A.M.; Nauta, Bram; Vliet, Frank E. van
All-pass filter circuits can implement a time delay but, in practice, show delay and gain variations versus frequency, limiting their useful frequency range. This brief derives analytical equations to estimate this frequency range, given a certain maximum allowable budget for variation in delay and gain. We analyze and compare two well-known gm - RC first-order all-pass circuits, which can be compactly realized in CMOS technology and relate their delay variation to the main pole frequency. Modeling parasitic poles and putting a constraint on gain variation, equations for the maximum achievable pole frequency and delay variation versus frequency are derived. These...

14. Towards minimum achievable phase noise of relaxation oscillators - Geraedts, Paul F.J.; Tuijl, Ed (A.J.M.) van; Klumperink, Eric A.M.; Wienk, Gerard J.M.; Nauta, Bram
A relaxation oscillator design is described, which has a phase noise rivaling ring oscillators, while also featuring linear frequency tuning. We show that the comparator in a relaxation-oscillator loop can be prevented from contributing to 1/f2 colored phase noise and degrading control linearity. The resulting oscillator is implemented in a power efficient way with a switched-capacitor circuit. The design results from a thorough analysis of the fundamental phase noise contributions. Simple expressions modeling the theoretical phase noise performance limit are presented, as well as a design strategy to approach this limit. To verify theoretical predictions, a relaxation oscillator is implemented...

15. Multi-Band linear chirp generation based on a type-III PLL - Velner, J.; Klumperink, E.A.M.; Nauta, B.; Vliet, F.E. van
A type-III PLL is used to generate linear frequency ramps with 386 kHz RMS frequency error in L-band (3088 kHz in X-band) and 10% fractional bandwidth. Pulse durations can be as low as 10 μs without performance degradation. The system covers the L-, S-, C- and X-bands. A programmable output driver delivering −17.9 to +4.9 dBm differentially is included on chip. The system is fully integrated using a 250 nm SiGe BiCMOS process.

16. A 12b 1.7GS/s two-times interleaved DAC with <-62dBc IM3 across nyquist using a single 1.2V supply - Olieman, Erik; Annema, Anne-Johan; Nauta, Bram; Bal, Ankur; Singh, Pratap Narayan
A two-times interleaved DAC using only a single supply voltage in a standard 65nm CMOS technology is presented. The interleaving architecture suppresses most of the non-idealities commonly found in high-speed DACs. Spurs generated by the interleaved architecture are suppressed by a novel calibration algorithm. The design achieves IM3 levels below -62dB across Nyquist with a clock frequency of 1.7GHz. The circuit’s active area is 0.4mm2 and the power consumption is 70mW from a nominal 1.2V supply.

17. Spectrum sensing with high sensitivity and interferer robustness using cross-correlation energy detection - Oude Alink, Mark S.; Kokkeler, André B.J.; Klumperink, Eric A.M.; Smit, Gerard J.M.; Nauta, Bram
Dynamic spectrum access relying on spectrum sensing requires reliable detection of signals in negative signal-to-noise ratio (SNR) conditions to prevent harmful interference to licensed users. Energy detection (ED) is a quite general solution, which does not require any knowledge of the signals to be detected. Unfortunately, it suffers from noise uncertainty in the receiver, which results in an SNR-wall below which signals cannot be reliably detected. Furthermore, distortion components originating from nonlinearity in the sensing receiver cannot be distinguished from true input signals, and is thus another effect that may obscure weak signals and cause false alarms or missed detections....

18. Wafer-scale fabrication of nanoapertures using corner lithography - Burouni, Narges; Berenschot, Erwin; Elwenspoek, Miko; Sarajlic, Edin; Leussink, Pele; Tas, Niels
Several submicron probe technologies require the use of apertures to serve as electrical, optical or fluidic probes; for example, writing precisely using an atomic force microscope or near-field sensing of light reflecting from a biological surface. Controlling the size of such apertures below 100 nm is a challenge in fabrication. One way to accomplish this scale is to use high resolution tools such as deep UV or e-beam. However, these tools are wafer-scale and expensive, or only provide series fabrication. For this reason, in this study a versatile method adapted from conventional micromachining is investigated to fabricate protruding apertures on...

19. An integrated 80-V class-D power output stage with 94% efficiency in a 0.14µm SOI BCD process - Ma, Haifeng; Zee, Ronan van der; Nauta, Bram
In this paper we present a highly-efficient 80V class-D power stage design in a 0.14μm SOI-based BCD process. Immunity to the on-chip supply bounce is 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 minimized switching loss are achieved with a 94% peak efficiency in the realized chip.

20. A 12GHz 210fs 6mW digital PLL with sub-sampling binary phase detector and voltage-time modulated DCO - Ru, Z.; Geraedts, P.; Klumperink, E.; He, X.; Nauta, B.
An integer-N digital PLL architecture is presented that simplifies the critical phase path using a sub-sampling binary (bang-bang) phase detector. Two power-efficient techniques are presented that can reduce DCO frequency tuning step by voltage-domain and time-domain (pulse-width) modulating the DCO LSB varactors. Measurement shows 210fs RMS jitter at 11.8GHz DCO frequency and 6mW power.

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