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University of Twente Publications (57.695 recursos)

University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.

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  1. The softened heat-affected zone in resistance spot welded tailor hardened boron steel: a material model for crash simulation

    Eller, T.K.

  2. Plasticity and fracture modeling of the heat-affected zone in resistance spot welded tailor hardened boron steel

    Eller, T.K.; Greve, L.; Andres, M.T.; Medricky, M.; Geijselaers, H.J.M.; Meinders, V.T.; Boogaard, A.H. van den
    tFive hardness grades of 22MnB5 are considered, covering the full strength-range from 600 MPa in theferritic/pearlitic range to 1500 MPa in the fully hardened, martensitic state. These five grades form thebasis for a hardness-based material model for the heat-affected zone found around resistance spot weldsin tailor hardened boron steel. Microhardness measurements of resistance spot welds in all five gradesare used to determine the location and shape of the heat-affected zone and for mapping of the hardnessdistributions into FE-models of the specimens used for model calibration. For calibration of the strainhardening of the heat-affected zone, a specially designed asymmetric uni-axial tensile...

  3. Ultra-broadband Supercontinuum Generation at Telecommunication Wavelengths in Dispersion Engineered Stoichiometric Si3N4 Waveguides

    Schepers, F.; Porcel, M.A.; Epping, J.P.; Hellwig, T.; Hoekman, M.; Mateman, R.; Leinse, A.; Heideman, R.G.; Rees, A. van; Slot, P.J.M. van der; Lee, C.J.; Schmidt, R.; Bratschitsch, R.; Boller, K-J.; Fallnich, C.

  4. Modeling of tailor hardened boron steel for crash simulation

    Eller, Tom Karl
    The automotive industry is continuously working on the weight reduction of their vehicles, while maintaining or even improving the crashworthiness in accordance with increasing safety demands. This has favored the development of innovative materials and production processes. The hot stamping process, in which heated blanks are simultaneously formed and quenched in cooled dies, is one of these recent innovations. Due to the high cooling rates during quenching, an ultra high material strength of up to 1500 MPa can be obtained. By locally reducing the cooling rate during quenching, e.g. by using partially heated dies, regions of lower strength with increased...

  5. Pervaporation of ammonia solution with c-alumina supported organosilica membranes

    Yang, Xing; Ding, Lining; Wolf, M.J.; Velterop, F.; Bouwmeester, H.J.M.; Smart, S.; Costa, J.C.D. da; Liubinas, A.; Li, Jun-De; Zhang, Jianhua; Duke, Mikel
    In this work, pervaporation of ammonia-solution using c-alumina supported organosilica membrane (HybSi , Pervatech) was explored to understand ammonia removal performance and material stability in this unique high pH environment. During the testing of synthetic ammonia solution of 50 mg/L at 45 C (pH 10), the hybrid silica membrane showed a preference towards ammonia transport over water, with an ammonia separation factor up to 12 and flux of 4.3 kg m 2 h 1 stable in a continuous testing period of 7 h. At an ammonia concentration of 1000 mg/L (pH 11), the membrane initially exhibited separation preference towards ammonia...

  6. Oxygen nonstoichiometry and defect chemistry of perovskite-structured SrFe1−xMoxO3−δ solid solutions

    Merkulov, O.V.; Naumovich, E.N.; Patrakeev, M.V.; Markov, A.A.; Bouwmeester, H.J.M.; Leonidov, I.A.; Kozhevnikov, V.L.
    The oxygen nonstoichiometry ofmixed-conducting perovskite-structured SrFe1−xMoxO3−δ (x=0, 0.07, 0.15 and 0.25) was measured by oxygen coulometric titration in the range of oxygen partial pressure 10−20–0.5 atm and temperature 800–950 °C. Based upon a defect chemical analysis of the non-stoichiometry data it is shown that significant reduction of Mo6+ occurs under reducing conditions. The trend observed in the oxidation enthalpy suggests a weakening of the Fe\\O bond strength along with the degree of substitution of Fe by Mo, which behavior is consistent with the concomitant increase in lattice constant. Atomistic simulations were carried out to support the defect chemical analysis, showing...

  7. High-Pressure Sorption of Carbon Dioxide and Methane in All-Aromatic Poly(etherimide)-Based Membranes

    Ogieglo, Wojciech; Madzarevic, Z.P.; Raaijmakers, M.J.T.; Dingemans, T.J.; Benes, N.E.
    The sorption of compressed carbon dioxide and methane in a series of all-aromatic poly(etherimide) (PEI) thin films is presented. The polymer films are derived from the reactions between an arylether diamine (P1) and four different dianhydrides [3,30,4,40-oxydiphthalic dianhydride (ODPA), 3,30,4,40 biphenyltetra-carboxylic dianhydride (BPDA), 3,30,4,40-benzo-phenonetetracarboxylic dianhydride (BTDA), and pyromellitic dianhydride (PMDA)] that have been selected to systematically change the flexibility of the polymer backbone, the segmental mobility, and the nonequilibrium excess free volume (EFV) of the polymer. The EFV, gas sorption capacities, and sorption- and temperature-induced dynamic changes in film thickness and refractive index have been investigated by spectroscopic ellipsometry. The...

  8. Hybrid Polycaprolactone/Alginate Scaffolds Functionalized with VEGF to Promote de Novo Vessel Formation for the Transplantation of Islets of Langerhans

    Marchioli, G.; Luca, A.D.; Koning, E. de; Engelse, M.; Blitterswijk, C.A. van; Karperien, H.B.J.; Apeldoorn, A.A. van; Moroni, L.
    Although regarded as a promising treatment for type 1 diabetes, clinical islet transplantation in the portal vein is still hindered by a low transplantation outcome. Alternative transplantation sites have been proposed, but the survival of extra-hepatically transplanted islets of Langerhans critically depends on quick revascularization after engraftment. This study aims at developing a new 3D scaffold platform that can actively boost vascularization and may find an application for extra-hepatic islet transplantation. The construct consists of a 3D ring-shaped polycaprolactone (PCL) scaffold with heparinized surface to electrostatically bind vascular endothelial growth factor (VEGF), surrounding a hydrogel core for islets encapsulation. Heparin...

  9. Opening the ‘‘White Box’’ in Tissue Engineering: Visualization of Cell Aggregates in Optically Scattering Scaffolds

    Groot Nibbelink, M.; Daoudi, K.; Slegers, S.; Grootendorst, D.C.; Dantuma, M.; Steenbergen, W.; Karperien, H.B.J.; Manohar, S.; Apeldoorn, A.A. van
    The noninvasive and longitudinal imaging of cells or cell aggregates in large optically scattering scaffolds is still a largely unresolved problem in tissue engineering. In this work, we investigated the potential of near-infrared (NIR) photoacoustic (PA) tomography imaging to address this issue. We used clinically relevant sizes of highly light scattering polyethersulfone multibore hollow fiber scaffolds seeded with cells. Since cells have little optical absorption at NIR wavelengths, we studied labeling of cells with absorbers. Four NIR labels were examined for their suitability based on absorption characteristics, resistance to bleaching, and influence on cell viability. On the basis of these criteria,...

  10. Flow Separation and Turbulence in Jet Pumps for Thermoacoustic Applications

    Oosterhuis, Joris P.; Verbeek, Anton A.; Bühler, Simon; Wilcox, Douglas; Meer, Theo H. van der
    The effect of flow separation and turbulence on the performance of a jet pump in oscillatory flows is investigated. A jet pump is a static device whose shape induces asymmetric hydrodynamic end effects when placed in an oscillatory flow. This will result in a time-averaged pressure drop which can be used to suppress acoustic streaming in closed-loop thermoacoustic devices. An experimental setup is used to measure the time-averaged pressure drop as well as the acoustic power dissipation across two different jet pump geometries in a pure oscillatory flow. The results are compared against published numerical results where flow separation was...

  11. Altering Emulsion Stability with Heterogeneous Surface Wettability

    Meng, Qiang; Zhang, Yali; Lammertink, Rob G.H.; Chen, Haosheng; Tsai, Peichun Amy
    Emulsions–liquid droplets dispersed in another immiscible liquid–are widely used in a broad spectrum of applications, including food, personal care, agrochemical, and pharmaceutical products. Emulsions are also commonly present in natural crude oil, hampering the production and quality of petroleum fuels. The stability of emulsions plays a crucial role in their applications, but controlling the stability without external driving forces has been proven to be difficult. Here we show how heterogeneous surface wettability can alter the stability and dynamics of oil-in-water emulsions, generated by a co-flow microfluidic device. We designed a useful methodology that can modify a micro-capillary of desired heterogeneous...

  12. Cardiovascular Organ-on-a-Chip Platforms for Drug Discovery and Development

    Ribas, J.; Sadeghi, H.; Manbachi, A.; Leijten, J.C.H.; Brinegar, K.; Zhang, Y.S.; Ferreira, L.; Khademhosseini, A.
    Cardiovascular diseases are prevalent worldwide and are the most frequent causes of death in the United States. Although spending in drug discovery/development has increased, the amount of drug approvals has seen a progressive decline. Particularly, adverse side effects to the heart and general vasculature have become common causes for preclinical project closures, and preclinical models do not fully recapitulate human in vivo dynamics. Recently, organs-on-a-chip technologies have been proposed to mimic the dynamic conditions of the cardiovascular system—in particular, heart and general vasculature. These systems pay particular attention to mimicking structural organization, shear stress, transmural pressure, mechanical stretching, and electrical...

  13. Political attitudes in a rapidly changing European landscape: methodological and substantive insights from the ESS-Netherlands panel component

    Turper, Sedef

  14. Topochip: technology for instructing cell fate and morphology via designed surface topography

    Hulshof, Godefridus Fransciscus Bernardus
    The control of biomaterial surface topography is emerging as a tool to influence cells and tissues. Due to a lack a theoretical framework of the underlying molecular mechanisms, high-throughput screening (HTS) technology is valuable to identify and study bioactive surface topographies. To identify the bioactive topographies that can be applied to medical implants and in vitro cell culture systems the TopoChip HTS platform has been developed which contains more than 2000 unique randomly generated surface topography designs. In this thesis we used the state of the art TopoChip HTS platform to investigate bioactive topographies on materials which are similar to...

  15. Tailored ceria nanoparticles for CO2 mediated ethylbenzene dehydrogenation

    Kovacevic, Marijana
    Styrene production via ethylbenzene dehydrogenation (EBDH) is one of the ten most important petrochemical processes. Possessing highly reactive double bond which facilitates self-polymerization and polymerization with other monomers, styrene is the fourth utmost essential bulk monomer at present. Current commercial ethylbenzene dehydrogenation is highly endothermic reaction, thus highly energy demanding. Several alternatives to steam, conventionally used to supply heat have been widely investigated. In this thesis we report on the CO2 mediated EBDH in which CO2 has been used as a mild oxidant instead of stream. Reaction was solely employed as a model reaction to probe inherent surface reactivity of...

  16. Unmanned Aircraft Systems against Air Threats: The Semi-Direct Control System

    Tempelman, Frank; Heerkens, Hans
    Unmanned cargo aircraft (UCA), which we may see being developed in the coming years, have characteristics that make them suitable for a variety of military operations. The absence of flightcrew and the resulting freedom to use novel configurations reduce costs. The decoupling of aircraft and crew whereby the controller operates from a fixed site regardless of the UCA’s location facilitates planning and basing and increases utilization, and hence productivity. UCA are expected to be able to move relatively small cargo loads efficiently, thereby increasing flexibility of resupply. The application of dual-use technology may spread development cost over a relatively large...

  17. Rumoer: Nederlandse kiezers en politiek 1998-2012

    Tillie, Jean; Kolk, Henk van der; Aarts, Kees; Holsteyn, Joop van
    Het behoeft geen betoog dat de periode 1998-2012 in de Nederlandse politiek op zijn minst 'dynamisch' te noemen is. De opkomst en neergang van de LPF en TON; de moorden op Pim Fortuyn en Theo van Gogh; de opkomst van de PVV; de groei van de SP; de gevolgen van 9/11; de financiële crisis en het referendum over Europa zijn maar enkele van de ontwikkelingen en gebeurtenissen in deze periode. Ook wordt vaak gesproken over de toegenomen wispelturigheid van de Nederlandse kiezer en over de mate van vertrouwen en interesse in de parlementaire politiek. Met het afronden van het Nationaal...

  18. Structural and electronic properties of single molecules and organic layers on surfaces

    Sotthewes, Kai
    Single molecules and organic layers on well-defined solid surfaces have attracted tremendous attention owing to their interesting physical and chemical properties. The ultimate utility of single molecules or self-assembled monolayers (SAMs) for potential applications is critically dependent on the structural, electronic and dynamic properties. Therefore is it important to study the structural and electronic properties as well as the dynamic processes of single molecules and organic layers on surfaces. Using scanning tunneling microscopy (STM) single molecules or organic layers on surfaces are studied while their electronic and dynamic properties are probed using scanning tunneling spectroscopy (STS). In order to design and...

  19. A learning space Odyssey

    Beckers, Ronald
    This dissertation addresses the alignment of learning space with higher education learning and teaching. Significant changes in higher education the past decades, such as increased information and communication technology (ICT) and new learning theories have resulted in the dilemma whether higher education institutions can facilitate tomorrow’s learning and teaching in today’s or even yesterday’s school buildings. The objective of this dissertation is twofold. First, it explores the alignment of higher education accommodation with higher education learning and teaching developments. Second, it supports CREM decision-making to align learning spaces with the requirements that result from the developments in higher education. The main...

  20. Supporting developers in addressing maintenance aspects: an empirical study in the industrial equipment manufacturing industry

    Mulder, Wienik
    Addressing maintenance aspects has become increasingly important in development projects of industrial equipment. Developers of such equipment need to address the maintenance aspects in order to achieve competitive equipment and service offerings. This research focuses on the identification of the maintenance aspects that are relevant to be addressed in development projects and on how developers can successfully do this. The ultimate goal of the research is to support developers in addressing maintenance aspects in development projects in practice. The research consists of a descriptive and a prescriptive study. The descriptive study focuses on eliciting knowledge from experts in companies and...

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