748 research outputs found
Comparison of random variables from a game-theoretic perspective
No full textThis work consists of four related parts, divided into eight chapters. A ¯rst part introduces the framework of cycle-transitivity, developed by De Baets et al. It is shown that this framework is ideally suited for describing and compar- ing forms of transitivity of probabilistic relations. Not only does it encompass most already known concepts of transitivity, it is also ideally suited to describe new types of transitivity that are encountered in this work (such as isostochas- tic transitivity and dice-transitivity). The author made many non-trivial and sometimes vital contributions to the development of this framework. A second part consists of the development and study of a new method to compare random variables. This method, which bears the name generalized dice model, was developed by De Meyer et al. and De Schuymer et al., and can be seen as a graded alternative to the well-known concept of ¯rst degree stochastic dominance. A third part involves the determination of the optimal strategies of three game variants that are closely related to the developed comparison scheme. The de¯nitions of these variants di®er from each other solely by the copula that is used to de¯ne the payo® matrix. It turns out however that the characterization of the optimal strategies, done by De Schuymer et al., is completely di®erent for each variant. A last part includes the study of some combinatorial problems that orig- inated from the investigation of the transitivity of probabilistic relations ob- tained by utilizing the developed method to compare random variables. The study, done by De Schuymer et al., includes the introduction of some new and interesting concepts in partition theory and combinatorics. A more thorough discussion, in which each section of this work is taken into account, can be found in the overview at the beginning of this manuscript. Although this work is oriented towards a mathematical audience, the intro- duced concepts are immediately applicable in practical situations. Firstly, the framework of cycle-transitivity provides an easy means to represent and compare obtained probabilistic relations. Secondly, the generalized dice model delivers a useful alternative to the concept of stochastic dominance for comparing random variables. Thirdly, the considered dice games can be viewed in an economical context in which competitors have the same resources and alternatives, and must choose how to distribute these resources over their alternatives. Finally, it must be noted that this work still leaves opportunities for future research. As immediate candidates we see, ¯rstly the investigation of the tran- sitivity of generalized dice models in which the random variables are pairwisely coupled by a di®erent copula. Secondly, the characterization of the transitivity of higher-dimensional dice models, starting with dimension 4. Thirdly, the study of the applicability of the introduced comparison schemes in areas such as mar- ket e±ciency, portfolio selection, risk estimation, capital budgeting, discounted cash °ow analysis, etc
HF Silicon IC's for wide-band communication systems: Technology characterization -modelling - design
No full textAbstract not availableElectrical Engineering, Mathematics and Computer Scienc
Experimental research on the influence of palliatives in fretting fatigue
No full textThere is an increasing demand of the industry to design and manufacture machines and constructions that are more powerful and at the same time smaller than previous ones. This leads to increased power density of the construction and the individual parts. Also the connection techniques that connect all the parts is become increasingly loaded.
In all sectors of the industry connection techniques are seen in different shapes and dimensions. In the automotive industry engines, electro engine and combustion engines are mostly connected to the gearbox by a splined connection. In the aerospace industry the skin of the fuselage is connected to the main structure of an airplane by riveted connections. The wheels of a train are connected to the shaft by means of interference fit connections. In the energy industry turbines are used to convert fluid energy to mechanical energy. The blades of a turbine are connected to the rotor by dovetail connections. In engineering bolted connections are frequently used as a connection technique which is dismountable, simple and cheap. Examples are tower cranes that are assembled and disassembled on construction sites. Parts of the crane are connected to each other by prestressed bolted lap joints.
Connection techniques that are smaller and transfer more force are more efficient but also more sensitive to premature failure. Connection techniques transfer forces from one or more parts toward others. The force is typically transferred by one or more contacts. Since the power density of machines increases this results in higher stress states on the contact areas. The likelihood of damage on the contact areas also increases. In a contact, damage can range from minimal topographic changes to substantial crack initiation. Crack initiation in combination with dynamic forces leads to crack propagation. Dynamic forces can originate from the purpose of the connection technique i.e. transferring dynamic forces, or can come from external sources such as vibrations. The combination of crack initiation at a contact with crack propagation caused by dynamic loading leads to the fretting fatigue mechanisms and results in much lower lifetimes compared to only the fatigue mechanisms.
The goal of this work is to provide a better insight in the fretting fatigue mechanisms by experimental research. The research focusses on surface treatments that can be applied on connection techniques and result in higher fretting fatigue lifetimes. The second goal of this work is to demonstrate the potential of several field measurement techniques during fretting fatigue research.
The first focus of this work is the quantification of the efficiency of some surface treatments based on the fretting fatigue lifetime. Three surface treatments are studied, all based on two palliative mechanisms. The first palliative mechanism is the application of a residual stress field that has a compressive stress state at the surface. Such a stress field is applied by deep rolling. The second palliative mechanism is the evacuation of debris particles from the surface by applying surface cavities in which particles can disappear. Cavities are applied at the surface by a laser ablation process. The combination of both palliative mechanisms is also studied. The technique used to apply both is a deep rolling process with textured rollers.
For this research two fretting fatigue test rigs were designed and constructed. The first test rig is a coupon scale test rig where most important parameters can be controlled and measured. The second test rig is a full scale test rig that is very similar to real application in terms of geometry and loading conditions. The second test rig is a bolted lap joint connection that uses a prestressed bolt to connect three plates symmetrically. The combination of the test rigs on different test scales is extraordinary and allows drawing conclusions independent of test scale.
More than 74 experiments are performed during this research. The samples are examined in several ways prior and after an experiment. Prior to an experiment, geometry, topography and characteristics of the palliative mechanism(s) are measured. Post mortem, the contact area and the fracture surface are microscopically and macroscopically examined. The results give more insight in the fretting fatigue mechanisms and the influence of the palliative mechanisms. The results of the surface treatments are significant in terms of lifetime and are witnessed on both types of test rigs. The deep rolling process gives a lifetime increase of a factor 2.7 at a lifetime of one million cycles. The laser ablation process does not give significant changes in lifetime. The deep rolling process with textures rolls, combining both palliative mechanisms, gives results which are in line with the ordinary deep rolling process. It can be concluded that the first palliative mechanism, applying a residual compressive stress field at the surface, influences the fretting fatigue mechanism. The second palliative mechanism, introducing surface cavities to evacuate debris particles from the contact, is not effective enough to influence the fretting fatigue mechanism.
The second focus of this work is the implementation of field measurement techniques during coupon scale fretting fatigue research. By means of a camera contactless images are captured from the specimens. The measurement technique does not influence the experiment. Also, it is possible to measure closer to the contact compared to the traditional measurement techniques. Two measurement techniques have been studied: thermography and digital image correlation.
Through a thermographic camera a field of temperatures is measured during an experiment. In the measured temperature field several mechanisms can be observed. The variation of the temperature of the samples can be related to the variation of the sum of the principal stresses. Thermographic measurements are successfully used to measure the fatigue load and the tangential load. In addition, the plastic zone at a crack tip can be visualised by thermography from which crack growth is calculated. Further research on thermography will give more detailed information of the stress state around the contact. Also crack propagation of smaller cracks will be measurable as well as crack initiation.
Digital image correlation measures the position of every point of the samples in the three-dimensional space. Prior to an experiment, the alignment of the samples is inspected. During an experiment the relative displacement of both contacts is independently measurable. From these measurements friction loops and tangential contact stiffness’s are calculated. Further optimisation of the measurement technique will allow online measuring of the slip distribution in the contacts
Het Organo di legno, een Basso continuo instrument voor de Stile moderno en de Secundo practica rond de eeuwwende 1600 in Italië
No full textTijdens de laatste decennia van de 16de eeuw ontstaat in Italië een nieuwe muziekstijl die een veranderend gebruik en een spectaculaire ontwikkeling van de muziekinstrumenten met zich meebrengt. Vele van deze instrumenten hadden specifieke kenmerken en kenden een geëigend gebruik. Eén van deze instrumenten was het Organo di legno. Na een schets van de culturele context wordt er aan de hand van primaire en secundaire bronnen, van het enige overgeleverde Organo di legno in de Silberne Kapelle in Innsbrück, en niet het minst van het onderzoek van Prof. Dr. Pier Paolo Donati (Firenze), in dit artikel naar gestreefd een beeld te schetsen van het wezen en het gebruik van het Organo di legno
In-situ measurements of TEHL contact conditions in a novel rolling element bearing test rig
No full textOndanks meerdere academische studies naar Elasto-Hydrodynamische Smering (EHL) in vereenvoudigde kogel-op-glas tests, blijven in-situ metingen van Thermo-Elasto-Hydrodynamische Smering (TEHL) in echte rollagers, werkend onder zeer variabele werkingsomstandigheden, een grote uitdaging. Het doel van dit proefschrift was het ontwerpen en ontwikkelen van een testopstelling om in-situ TEHL-condities te meten onder controleerbare dynamische belastingen, versnellende/vertragende rolschuifbewegingen en goed gecontroleerde smeermiddelcondities. Het systeem gebruikte een hefboom-arm-gebaseerde benadering om het wrijvingskoppel van TEHL te meten, dat vervolgens werd vergeleken met voorspellende modellen. De resultaten toonden aan dat thermische effecten meer uitgesproken worden bij hogere snelheden en het wrijvingskoppel met ongeveer 4-6% beïnvloeden. De dikte van de TEHL-film werd gemeten met zowel elektrische impedantie- als capaciteitsmethoden. De impedantiemetingen kwamen goed overeen met analytische voorspellingen, maar bij hogere snelheden waren thermische correcties nodig; anders bleek de laagdikte 6-8% lager. De temperatuur van de TEHL film werd gemeten met dunne-filmsensoren, die de temperatuurverdeling vastlegden langs de lengte van de rol en in de draairichting. De resultaten gaven een temperatuurvariatie aan van ongeveer 4,5°C langs de rol. Daarnaast werden voor het eerst fiber Bragg roosters (FBG's) gebruikt om de druk van de TEHL film te meten. Vanwege het piëzo-visceuze gedrag van smeermiddelen werd de dynamische respons van de TEHL film echter niet volledig vastgelegd in het gemeten signaal
Development of a Multifunctional Tribometer with Independent Temperature Control of the Brake Disk ('Ontwerp en bouw van een multifunctionele tribometer met onafhankelijke temperatuurcontrole van de remschijf').
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Bottom-up design for polymer-based horseshoes : connecting polymer processing and veterinary medicine
No full textDit doctoraatsonderzoek bekijkt twee vaak gebruikte verwerkingstechnieken voor polymeren, i.e. Additive Manufacturing (AM) en Injectiespuitgieten (IM), om de industriële haalbaarheid na te gaan voor de productie van polymeergebaseerde hoefschoenen. De ontwikkeling van polymeergebaseerde hoefschoenen zou de gezondheid van de onderbenen van paarden kunnen verbeteren, in vergelijking met metalen hoefschoenen, door het risico op letsels te verminderen en het bevorderen van het herstel van letsels. Aangezien de hoefwand is opgebouwd uit een vaak voorkomend natuurlijk polymeer, i.e.keratine, zouden industriële polymeermaterialen de eigenschappen en gedrag van de hoefwand kunnen benaderen. De selectie van geschikte industriële polymeren, voor de gewenste toepassing, wordt afgestemd op de eigenschappen van de hoefwand en de verwerkingstechnieken voor polymeermaterialen moeten in staat zijn om het uiteindelijke product te verwerken en te produceren. Om het aantal beschikbare materialen groter te maken voor AM, meer specifiek Selective Laser Sintering, wordt er hierbij ook dieper ingegaan op theoretische modellering van deze 3D-print techniek voor polymeermaterialen. Tot slot bekijkt dit onderzoek ook de mogelijkheid om composietmaterialen te produceren met verbeterde eigenschappen voor de huidige applicatie
Censorship by European States of Views on their Past as Colonizers
No full textThis essay tackles the question of whether European states censored views on their past as colonizers. Analyzing a wealth of cases, the author argues that, after decolonization, most former colonizers began to perceive their colonial crimes as a source of shame. Often, the result was silence and censorship. Even consolidated democracies find it hard to deal responsibly with their violent past by means of an ongoing public debate, which is an essential feature of any sound democracy.Cet article s’interroge pour savoir si les États européens ont censuré des opinions sur leur passé colonial. En analysant une diversité de cas, l’auteur soutient que, après la décolonisation, les plus anciens colonisateurs ont commencé à percevoir leurs crimes coloniaux comme une source de honte. Souvent, le résultat était le silence et la censure. Les démocraties les plus solides ont beaucoup de mal se montrer responsables à l’égard de leur passé violent au moyen d’un débat public, qui est une caractéristique essentielle de n’importe quelle véritable démocratie
Participation in people with the Ehlers-Danlos syndromes and hypermobility spectrum disorders
No full text‘Ehlers-Danlos Syndrome’ (EDS) and ‘Hypermobility Spectrum Disorder’ (HSD) are chronic pathologies that often
lead to disability, which in turn creates limited functioning and participation in daily life. This dissertation
provides an overview of the research that has been conducted regarding this topic in the past years. Based on
the results, we present conclusions on different levels of a person’s functioning.
The use of the International Classification of Functioning, disability and health in the determination of a
person’s functioning and disability has never been studied in a population of persons with EDS and HSD.
Highlighting the effective level of participation (considering objective and subjective variables) is an important
outcome measure. Furthermore, this dissertation emphasises the combination of two different research
methodologies. First, we used a qualitative research method to explore the ‘lived experiences’ of persons with
HSD and EDS. In the literature, no previous research has reported utilising this specific approach. Second, use
used quantitative method to to determine the level of participation in persons with hEDS, cEDS, vEDS and HSD
compared to persons with fibromyalgia and a healthy control group. No similar topics have been reported in
literature within this population. The combination of both methods provide us with a rich overview of
information on the levels of MICRO-, MESO- and MACRO-participation.
MICRO-participation is influenced by EDS, mainly regarding the organisation of participants’ lives. The disease
requires them to find a new balance, with a focus on personal priorities. EDS, and the functional consequences
of this chronic disabling condition, markedly influence one’s personal life. Affected social relationships,
difficulties in intimate relations and difficulties in taking care of the household chores, are important reasons
for a lower participation level.
MESO-participation, when the focus is on work-related capacities, is common in many persons with EDS and
HSD. Finding work that is in line with your personal capacities seems to be hard, and executing tasks that exceed
your personal limits, such as lifting heavy subject or repetitive jobs, often leads to leaving the labour market
due to complications. On the other hand, work often also brings positive elements to the lives of persons with
EDS and HSD, this ranges from socio-economic benefits to friendships. Working life can also be supported by
external factors, such as workplace adaptations and financial benefits from the government.
While discussing the level of MACRO-participation within a sample of persons with EDS and HSD, it seems
obvious that persons with hEDS experience a significantly lower level of participation compared to a sample of
healthy controls.
This dissertation offers an overview of the level and difficulties in participating in society in persons with EDS
and HSD and provides some relevant clinical recommendations. There is a strong need for correct and state-ofthe-art information. These endeavours include educating patients so that they are aware of their own condition
and possibilities in societal participation, as well as informing (para)medical professionals in order to guide
people to a correct diagnosis and subsequent treatment. Notably, this approach can only be achieved when
including bio-psychosocial aspects within a multidisciplinary approach of persons with EDS and HSD
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