42 research outputs found
The Inclusionary Potential and Spatial Boundaries of (Semi-) Public Space:Refugee Youth’s Everyday Experiences in the Urban Fabric of Amsterdam.
No full textThe city – rather than the state – plays an important role in refugee youth’s everyday experiences. In this chapter, we draw upon participatory research among young refugees and asylum seekers in Amsterdam to illustrate the lived experiences of these youngsters in public spaces in the urban fabric of Amsterdam. We illustrate their favourite places, the use and meaning of these spaces, and how these spaces impact their sense of belonging in both the Netherlands and Amsterdam. The findings show that it is not self-evident for refugee youth who are new to the city to immediately exploit the potential of public space. Semi-public spaces can fill an important role in providing a safe and meaningful space for refugees’ integration and participation in society. At the same time it is not self-evident to transmit these encounters beyond these semi-public places, which illustrates that conviviality is spatially bound to specific places.<br/
Dislocation networks in precipitation hardened aluminium alloys during plastic deformation: The effects of dislocations on the anelastic behaviour and the evolution of dislocation networks in an AA7075 aluminium alloy.
No full textThe effects of precipitates in the microstructure of an AA7075 aluminium alloy on: the dislocation behaviour, dislocation structure and dislocation structure evolution during plastic deformation were investigated using the physical yield criterion model by van Liempt and Sietsma. The model was in fact applied for the first time to aluminium and an AA7075 aluminium alloy. By constructing an extended Kocks-Mecking plot from the measured tensile and interrupted tensile data the dislocation density, average dislocation segment length and physical yield stress were determined.The aim of the present study was to get a better understanding of the role of precipitates in the evolution of the dislocation structure during plastic deformation. The recovery of anelastic strain during loading and subsequent unloading after plastic deformation was investigated as well. The yield criterion was used to study the anelastic loading, while a constitutive unloading model by Torkabadi et al. was used to study the unloading behaviour. The models were combined to define the fraction of unrecoverable anelastic strain. The anelastic strain is related to springback. Therefore a better understanding of the anelastic strain could be useful for making better predictions of springback after metal forming. The physical yield criterion was further extended by incorporating a continuous uniform dislocation segment length distribution. Insight on the dislocation segment length distribution, and the evolution thereof during plastic deformation, could help to better understand the mechanical behaviour of metals.The evolution of the dislocation structure during plastic deformation is impeded by the presence of precipitates in the microstructure. Therefore, the physical interpretation of α in the Taylor equation which quantifies the dislocation structure, proposed by Arachebelata et al., was modified to incorporate the effects of precipitates in the microstructure. The dislocation structure parameter α should remain constant. However, the average dislocation segment length obtained from the extended Kocks-Mecking plot does not decrease sufficiently to accommodate a constant α. The introduction of the length between precipitates, which is independent from work hardening, into the Taylor equation ensures that α does remain constant, whilst in addition it provides an estimate of the distance between the precipitates. Anelastic strain, caused by reversible glide of dislocations in the pre-yield regime, is introduced into or recovered from the metal during loading and unloading respectively. The anelastic unloading strain determined from the interrupted tensile tests was found to be smaller than what was expected according to the model. Three possible causes were identified: not all Frank-Read sources are at their critical state when unloading is initiated, dislocation loops propagating through the crystal undo portions of the anelastic unloading strain and the retracting dislocations remain stuck behind obstacles whilst retracting under the reducing applied stress. The constitutive model was found to be not suitable for studying the dislocation behaviour during unloading because the change of dislocation segment length with plastic deformation is not accounted for. The development of a physical unloading model is therefore recommended. The distribution of the dislocation segment lengths could explain the non-zero value of the work hardening rate Θ at the abrupt change of slope between the pre and post-yield regime in the extended Kocks-Mecking plot. The value of Θ at this point could be an indication of the distribution width. The continuous uniform distribution is a rather unrealistic description of the dislocation segment length distribution. Therefore, other distribution types are proposed for the further development of the dislocation segment length distribution model of the physical yield criterion.<br/
Zusammenwirken des Prokarzinogens Benzo[a]pyren mit pflanzlichen Flavonoiden auf karzinogenese-relevante Prozesse in Kolon-Adenokarzinoma-Zelllinie Caco-2
No full textIn dieser Arbeit sollte die Fähigkeit verschiedener pflanzlicher Flavonoide zur Prävention von Darmkrebs nachgewiesen werden. Als Testsystem wurden daher humane Kolon-Andenokarzinoma-Zellen (Caco-2), als schädigendes Agenz das bekannte Prokarzinogen Benzo[a]pyren, sowie die Flavonoide Galangin, Quercetin, Myricetin und Kaempferol, verwendet.
Da Flavonoiden eine Vielzahl antikarzinogener Eigenschaften zugewiesen werden, wie Hemmung von Phase I-Enzymen, Induktion von Phase II-Enzymen, Induktion der Apoptose, Hemmung der Zellproliferation, antioxidative Wirkung und Modulation des Immunsystems (Watzl & Rechkemmer 2001, Theodoratou et al. 2007, Flis et al. 2012), wurden in dieser Arbeit Effekte von Flavonoiden auf verschiedene Karzinogenese-relevante Prozesse wie DNA-Schädigung, Apoptose, Zellzyklus und damit zusammenhängende Signalwege (AhR, MAPK, Nrf2 und AKT) in Kolon-Adenokarzinoma-Zellen untersucht. Auch die Ausbildung reaktiver Metabolite ist von entscheidender Bedeutung, da Benzo[a]pyrene (BaP) durch die Metabolisierung über Monooxygenasen (Cytochrom P450 (CYP) Enzyme) und Hydrolasen zu dem reaktiven Benzo[a]pyren-7,8-dihydrodiol-9,10-epoxid umgewandelt wird. Diese Metabolisierung wird von Benzo[a]pyren selbst initiiert, da es über den Arylhydro¬karbon-Rezeptor-(AhR)-Signalweg das relevante, Cytochrom P450 Enzym, CYP1A1 induziert. Auch Flavonoide sind Agonisten des Arylhydrokarbon-Rezeptor-(AhR)-Signalweges, welcher eine tragende Rolle in der Regulation des Fremdstoff¬metabolismus im Darm hat.
Nicht nur die generellen Effekte der Flavonoide selbst auf diese Prozesse sondern auch die des Prokarzinogens Benzo[a]pyren (BaP) wurden zunächst untersucht. Die präventiv wirkenden Effekte der Flavonoide wurden auch in Kombination mit dem Prokarzinogen analysiert. Für BaP wurde die Induktion von DNA-Schäden direkt und zudem über die Aktivierung eines spezifischen DNA-Schaden-Markers (H2Ax) nachgewiesen. Flavonoide erzeugten generell keine DNA-Schäden in den Kolon-Andenokarzinoma-Zellen, konnten aber die BaP-induzierten DNA-Schäden ver¬hindern. Allerdings zeigten die Flavonoide Quercetin und Myricetin zumindest auf die Aktivierung des DNA-Schaden-Markers (H2Ax) einen induzierenden Effekt.
Apoptose wurde in den Kolon-Adenokarzinom-Zellen nur durch Benzo[a]pyren nicht aber durch die Flavonoide induziert. Dies konnte durch verschiedene Apoptose-Parameter bestätigt werden, wie die Caspase-3-Aktivität, das pro-apoptotische Protein Bax und das anti-apoptotische Protein Bcl-2. Flavonoide wirkten auch der Benzo[a]pyren-induzierten Apoptose entgegen.
Für den Nachweis der Effekte auf den Zellzyklus wurde dieser direkt und anhand verschiedener Komponenten der Zellzyklus-Kontrolle, wie p21, p27, NFB, und die Phosphorylierung des Retinoblastoma-Proteins (pRb) untersucht. Generell hatten Benzo[a]pyren und Flavonoide keinen Effekt auf den Zellzyklus und dessen regulierende Komponenten, mit Ausnahme der Phosphorylierung des Retino-blastoma-Proteins. Dies konnte sowohl durch Benzo[a]pyren, als auch durch Quercetin signifikant induziert werden. Alle Flavonoide blockierten aber effizient die Benzo[a]pyren-abhängige pRb-Phosphorylierung.
Benzo[a]pyren und Flavonoide hatten Einfluss auf die Signalwege MAPK, Nrf2 und AKT, die Wirkungen waren aber weitestgehend nicht signifikant. Auf den Arylhydrokarbon-Rezeptor-Signalweg konnte ein deutlicher Einfluss von Benzo[a]pyren und Flavonoiden in den Kolon-Adenokarzinom-Zellen festgestellt werden. BaP und Quercetin steigerten signifikant den Level von CYP1A1-mRNA und -Protein, aber auch Galangin und Myricetin übten hierauf einen leicht induzierenden Effekt aus. Die mRNA-Level der Komponenten des AhR-Komplexes (AhR, AhRR und AIP) wurden weder durch Benzo[a]pyren noch durch die Flavonoide beeinflusst, lediglich Myricetin hatte auf das mRNA-Niveau der Komponenten AhR und AhR-Repressor einen signifikant inhibierenden Effekt. Zudem konnten Benzo[a]pyren sowie Flavonoide die CYP1A1-Aktivität in den Kolon-Adenokarzinoma-Zellen deutlich steigern. Jedoch wirkten die Flavonoide auch den Benzo[a]pyren-mediierten Effekten auf den Arylhydrokarbon-Rezeptor-Signalweg inklusive der CYP1A1-induktion entgegen. Flavonoide nahmen durch Enzymhemmung auch direkten Einfluss auf die CYP1A1-Aktivität. Detailliertere Untersuchungen zur CYP1A1-Hemmwirkung der Flavonoide mit Lebermikrosomen zeigten, dass ihr Inhibitionspotential mit steigender Zahl an Hydroxylgruppen im B-Ring abnahm, während ihr Radikalfängerpotential zunahm.
Durch den Einsatz eine Arylhydrokarbon-Rezeptor Inhibitors konnte die Abhängigkeit der Flavonoidwirkung auf die einzelnen Karzinogenese-relevanten Prozesse nachgewiesen werden. Hieraus lässt sich generell schließen, dass die Benzo[a]pyren-mediierten Effekte und die präventive Wirkung der Flavonoide auf der Beeinflussung des Arylhydrokarbon-Rezeptor-Weges und im Speziellen des Enzyms CYP1A1 basierten.
Die Schlussfolgerung aus allen Ergebnissen ist, dass Flavonoide in Kolon-Adenokarzinom-Zellen einen signifikanten Präventions-Effekt auf BaP-induzierte Karzinogenese-relevante Prozesse besitzen.In this thesis, possible preventive effects of several plant flavonoids on processes with relevance for colon-carcinogesis were investigated. As model system colon-adeno¬carcinoma-cells, the procarcinogen benzo[a]¬pyrene (BaP) as damaging substance and the flavonoids galangin, quercetin, myricetin and kaempferol were used for the experiments.
A multitude of anti-cancer characteristics are assigned to flavonoids, like inhibition of phase I enzymes, induction of phase II enzymes, induction of apoptosis, inhibition of cell proliferation, antioxidative effects or modulation of the immunesystem (Flis et al. 2012, Theodoratou et al. 2007, Watzl & Rechkemmer 2001). Therefore, effects of flavonoids on multiple carcinogenesis relevant processes such as DNA-damage, apoptosis, cell cycle and related signal pathways (AhR, MAPK, Nrf2 and AKT) were investigated in colon-adenocarcinoma-cells. Additionally, the formation of reactive metabolites plays an important role, because benzo[a]pyrene gets metabolised via cytochrome P450 monooxygenase enzymes and hydrolases to reactive benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide, which causes DNA-adduct formation. As an agonist of the arylhydrocabon-receptor, benzo[a]pyrene itself initiates its own metabolism by induction of the metabolising cytochrome P450 enzyme CYP1A1. Flavonoids are also agonists of the arylhydrocarbon-receptor-pathway which plays an important role in the regulation of colon xenobiotic metabolism.
Besides the basic effects of flavonoids and benzo[a]pyrene on carcinogenesis relevant processes, the preventive effects of flavonoids were studied in combination experiments with benzo[a]pyrene.
Benzo[a]pyrene was proven to induce DNA-damage as shown directly by a Comet-assay and via induction of a specific DNA-damage marker (H2Ax). Flavonoids did not cause DNA-damage in colon-adenocarcinoma-cells at all and counteracted the benzo[a]pyrene-mediated effects. Nevertheless, the flavonoids quercetin and myricetin were able to induce the specific DNA-damage marker (H2Ax) on their own.
Apoptosis was only affected by benzo[a]pyrene and not by flavonoids, whereas all flavonoids blocked the benzo[a]pyrene-induced effects. This was shown by the determination of multiple apoptosis-related control parameters like caspase-3-activity, pro-apoptotic protein bax and anti-apoptotic protein bcl-2.
For detection of effects on the cell-cycle, several cell cycle-controlling proteins like p21, p27, NFB and phosphorylated retinoblastoma-protein (pRb) were studied and, additionally, direct cell-cycle-analysis was done. In general, benzo[a]pyrene and flavonoids exhibited no effects on cell cycle or cell cycle-associated proteins in colon-adenocarcinoma-cells. But phosphorylation of retinoblastoma-protein (pRb) was induced by benzo[a]pyrene and quercetin significantly. Nevertheless, all flavonoids inhibited benzo[a]pyrene-mediated pRb-phosphorylation.
Benzo[a]pyrene and flavnoids were able to affect related signal pathways like MAPK, Nrf2 and AKT, but these effects were not significant in most cases. However, the arylhydrocarbon-receptor-pathway was significantly influenced by benzo[a]pyrene and flavonoids in colon-adenocarcinoma-cells. Benzo[a]pyrene and quercetin caused a strong increase on CYP1A1-mRNA- and protein-level, whereas myricetin and galangin had only a slight inducing effect.
The mRNA-level of components of the arylhydrocarbon-receptor-complex were neither influenced by benzo[a]pyrene nor by flavonoids, except for myricetin which caused a significant decrease of AhR and AhR-repressor mRNA-level. Additionally, benzo[a]pyrene and flavonoids strongly increased CYP1A1-activity in colon-adenocarcinoma-cells. Nevertheless, all flavonoids counteracted benzo[a]pyrene-induced CYP1A1-activity. Furthermore, flavonoids directly affected CYP1A1-activity via enzyme-inhibition. More detailled investigations on CYP1A1-inhibition by flavonoids were done using liver microsomes. These experiments had shown, that the inhibition potential of flavonoids decreases with an increasing number of B-ring hydroxyl-groups, while the ability of radical-scavinging decreased in this case.
By using an arylhydrocarbon-receptor-inhibitor the AhR-dependency of BaP- and flavonoid-mediated effects on several carcinogenesis-relevant processes was proven. This means that the preventive action of flavonoids and the benzo[a]pyrene-mediated effects are generally dependent on the arylhydrocarbon-receptor-pathway and particularly on the metabolizing enzyme CYP1A1. A final conclusion derived from all experimental data is that flavonoids significantly interfere with BaP-mediated carcinogenesis-relevant processes, i.e. chemically induced carcinogenesis, and therefore appear potentially suitable (effective) for prevention of colon-adenocarcinoma development
Stedelijke diversiteit en beleid: Hoe gaan nationale en lokale overheden om met de groeiende diversiteit in steden?
No full textTailored work hardening descriptions in simulation of sheet metal forming
No full textIn the previous decades much attention has been given on an accurate material description, especially for simulations at the design stage of new models in the automotive industry. Improvements lead to shorter design times and a better tailored use of material. It also contributed to the design and optimization of new materials. The current description of plastic material behaviour in simulation models of sheet metal forming is covered by a hardening curve and a yield surface. In this paper the focus will be on modelling of work hardening for advanced high strength steels considering the requirements of present applications. Nowadays work hardening models need to include the effect of hard phases in a soft matrix and the effect of strain rate and temperature on work hardening. Most material tests to characterize work hardening are only applicable to low strains whereas many practical applications require hardening data at relatively high strains. Therefore, physically based hardening descriptions are needed allowing reliable extensions to high strain values
Quantification of dislocation structures from anelastic deformation behaviour
No full textAbstractThe pre-yield deformation behaviour (i.e., at stresses below the yield stress) of two materials, pure iron and a low-alloy steel, and its anelastic nature are analysed at room temperature, before and after the dislocation structures are varied by plastic deformation. It is shown, based on tensile experiments, that this behaviour can be explained by limited reversible glide of dislocations without essential changes in the dislocation structure. Moreover, a physically-based model that characterises the dislocation structure by two variables, the dislocation density and the effective dislocation segment length, is used to quantitatively describe this deformation behaviour. The model validity is further evaluated by comparison with dislocation densities from X-Ray Diffraction measurements
Unravelling dislocation networks in metals
No full textUnderstanding the intricate structure of dislocations in metals is a major issue in materials science. In this paper we present a comprehensive approach for the characterisation of dislocation networks, resulting in accurate quantification and significantly increasing the insight into the dislocation structure. Dislocation networks in metals consists of dislocation segments, pinned by microstructural obstacles. In the present paper a model is introduced that describes the behaviour of these dislocation segments in the pre-yield range of a tensile test on the basis of fundamental concepts of dislocation theory. The model enables experimental quantification of the dislocation density and segment length from the tensile curve. Quantitative results are shown and discussed on the development of the dislocation network as a function of increasing degree of plastic deformation, including validation and physical interpretation of the classical Taylor equation.(OLD) MSE-3(OLD) MSE-
City in Sight: Dutch Dealings with Urban Change
No full textHuge social transformations and turbulent political events - 9/11 and the political murders of Pim Fortuyn and Theo van Gogh - have put urban issues high on the political agenda of the Netherlands. Against this background, the contributors to this volume bring the city in sight from various disciplinary perspectives and relate their research findings to both national and international debates on urban problems. In this way, City in Sight not only provides insight into the most urgent questions of contemporary cities in the Netherlands, but also how these relate to similar problems in other countries as well.
Table of contents:
Part I Urban Transformations and Local Settings
1 Post-Industrialization and Ethnocentrism in Contemporary Dutch Cities: The Effects of Job Opportunities and Residential Segregation / Jeroen van der Waal and Jack Burgers
2 Unraveling Neighborhood Effects: Evidence from Two European Welfare States / Sako Musterd and Fenne M. Pinkster
3 The Effects of State-Led Gentrification in the Netherlands / Peter van der Graaf and Lex Veldboer
4 Problematic Areas or Places of Fun? Ethnic Place Marketing in the Multicultural City of Rotterdam / Ilse van Liempt and Lex Veldboer
Part II Urban Citizenship and Civic Life
5 Local and Transnational Aspects of Citizenship Political Practices and Identifications of Middle-class Migrants in Rotterdam / Marianne van Bochove, Katja Rusinovic and Godfried Engbersen
6 A Little Less Conversation, a Little More Action: Real-life Expressions of Vital Citizenship in City Neighborhoods / Ted van de Wijdeven and Frank Hendriks
7 Organize Liberal, Think Conservative: Citizenship in Light Communities / Menno Hurenkamp
8 ‘Control over the Remote Control’, or How to Handle the ‘Normal’ World? The Policy and Practice of Community Care for People with Psychiatric or Intellectual Disabilities / Loes Verplanke and Jan Willem Duyvendak
9 Changing Urban Networks and Gossip: Moroccan Migrant Women’s Networks in the Dutch Welfare State / Marguerite van den Berg
Part III Urban Governance and Professional Politics
10 The Relationship Between Policy Governance and Front-line Governance / Pieter Tops and Casper Hartman
11 Between Ideals and Pragmatism: Practitioners Working with Immigrant Youth in Amsterdam and Berlin / Floris Vermeulen and Tim Plaggenborg
12 Explaining the Role of Civic Organizations in Neighborhood Co-production / Karien Dekker, Rene´ Torenvlied, Beate Völker and Herman Lelieveldt
13 The Amsterdam Office Space Tragedy: An Institutional Reflection on Balancing Office Space Development in the Amsterdam Metropolitan Region / Leonie Janssen-Jansen and Willem Salet
The Dutch Orange and the Big Apple: A Comparative Commentary / John MollenkopfDe bijdragen in deze bundel geven zicht op de stad en stedelijke verandering vanuit verschillende invalshoeken. De auteurs plaatsen hun bevindingen in de context van het Nederlandse en internationale debat over stedelijke problematiek. City in Sight laat zien wat de meest prangende kwesties zijn waar Nederlandse steden zich momenteel voor gesteld zien
A Revised Criterion for the Portevin–Le Châtelier Effect Based on the Strain-Rate Sensitivity of the Work-Hardening Rate
No full textEffect of film thickness on the far- and near-field optical response of nanoparticle-on-film systems
No full text\u3cp\u3eWe study the near-field and far-field optical responses of nanoparticle-on-film systems using single-nanoparticle spectroscopy and numerical simulations. We find that the optical spectra contain three dominant modes: a transverse dipole, quadrupole mode, and a dominant vertical antenna mode. We vary the thickness of the metal film from 10 to 45 nm and find that the vertical antenna mode wavelength is nearly independent of the film thickness. In contrast, we find that the associated near-field enhancement in the gap between the particle and the film strongly depends on the film thickness. This trend is also observed in the far field where the vertical antenna mode strongly increases in amplitude relative to the quadrupole for the increasing film thicknesses up to the skin depth of gold. These findings are in good agreement with a numerical model and pave the way to study field-mediated processes such as fluorescence, surface-enhanced Raman spectroscopy, and localized chemistry at the same resonance wavelength but at varying degrees of field enhancement.\u3c/p\u3
