331 research outputs found
The people behind the papers - Yonit Maroudas-Sacks and Marko Popovic
No full textDuring Hydra regeneration, supracellular actomyosin fibres are disoriented at two distinct foci of the regenerating tissue. These sites of nematic topological defects eventually form the new head and foot of the regenerated animal. In a new study, Yonit MaroudasSacks, Marko Popovic, Kinneret Keren and colleagues propose a positive-feedback loop that incorporates fibre organisation, tissue strain and morphogen gradients to promote head organiser formation. To find out more about the work, we caught up with first author Yonit Maroudas-Sacks and co-corresponding author Marko Popovic, Group Leader at the Max Planck Institute for the Physics of Complex Systems, Germany
Investigation of the inductor’s parasitic capacitance in the high frequency switching of the high voltage cascode GaN HEMT
No full textThe concept of the More Electric Aircraft, where the majority of the aircraft’s secondary needs will be supplied by electrical power, is under continuous research over a number of years in order to conform the recent demand for more efficient and environmentally friendly aircrafts. Advancements in power electronics have contributed towards the realization of that demand, by introducing lightweight, high-power density and highly efficient in harsh environment power electronics. The increase in power density of power electronic systems was made feasible, so far, by developments in the semiconductors field, namely by semiconductors that can operate at higher switching frequencies and generate less power loss. Wide-bandgap devices, such as Gallium Nitride (GaN) transistors, have emerged as possible candidates to replace silicon and even silicon carbide devices in various power conversion applications offering potential benefits for high frequency power conversion due to their intrinsic material properties. Another step towards higher power densities is to utilize appropriate circuit topologies since they can reduce the stress upon the components and the cooling requirements. However, as the frequency goes up, the switching behavior of the device is not only influenced by the die itself and the device package’s and circuit’s parasitic elements can not be neglected any more. One of these parasitic elements is the the equivalent parasitic capacitance (EPC) of the magnetic component, which is part of almost every topology. This thesis project aims at two things: first, to observe the switching behavior of a high-voltage cascode GaN High Electron Mobility Transistor (HEMT) under inductive clamped load condition, which is the same commutation mode for the power devices as switching in a PWM, hard-switching type converter and second, to investigate the influence of the magnetic component’s EPC on the switching behavior of the GaN HEMT. For this, an analytical loss model of the device was developed and a double-pulse tester (DPT), which is considered to be a very good example of that load condition, was optimally designed and manufactured in order to verify the analytical model. Two pulses are launched to the device under test (DUT) and the switching transitions of the DUT can be captured for any desired current and voltage rating under hard-switching conditions. Moreover, when operating under that load conditions, applying active devices with reverse recovery charge has significant influence on the switching behavior of the DUT, so both cases will be examined. Finally, in order to characterize the device and eventually verify the analytical loss model, current and voltage measurements need to be taken during the turn-on and turn-off switching transitions. As the GaN HEMT is capable of switching are very high speed, there are issues and limitations that need to be taken into consideration in order to ensure the fidelity and the accuracy of these high frequency measurementsElectrical Power EngineeringElectrical Engineering, Mathematics and Computer Scienc
General Programs for Least pth and Near Minimax Approximation
No full textTitle: General Programs for Least pth and Near Minimax Approximation, Author: Jadranka K. Rizoniko-Popovic, Location: ThodeUser-oriented computer programs in FORTRAN IV for discrete least pth approximation with a single specified function, and more generalized discrete least pth approximation with various specifications, which may also be used for nonlinear programming, are presented. Values of p up to 10^6 can be used successfully in conjunction with efficient gradient minimization algorithms such as the Fletcher-Powell method and a recent method due to Fletcher. It has already been demonstrated how efficiently extremely near minimax results can be achieved on a discrete set of sample points using this approach and the programs written verify this. The programs may be applied to a wide variety of design problems with a wide range of specifications. They are suitable for electrical network and system design and such problems as filter design.ThesisMaster of Engineering (ME
Stojan Jovanovic - a state cadet and the author of French grammar
No full textStojan Jovanovic, called by the name of Cukic by his contemporaries, is
mainly known as a leader of Katanska buna (The Rebellion of Katanas) in 1844.
The subject of this paper is Jovanovic?s education in Serbia and Vienna. A
thesis statement is that Stojan Jovanovic, Filip Hristic, and Anastas
Jovanovic have enjoyed the favor and support of the Obrenovic family, to whom
they have been loyal in return. Stojan Jovanovic belonged to the first
generation of students who've graduated from all schools existing in Serbia
during Prince Milos?s reign - he has finished the primary school in Belgrade,
the High School, i.e. the Kragujevac Gymnasium in 1836, and has attended the
Military Academy in Pozarevac, Belgrade and Kragujevac between 1837 and 1838.
In 1839. Jovanovic was appointed to the first group of state cadets who were
sent to study in Vienna. This generation of students was in many ways similar
to the one that attended the Belgrade Higher School (1808 - 1813). Jovanovic
stayed in Vienna for three years. For the first two years he has learned
French and German, preparing for the Law school. He has enrolled at the
Vienna University in the winter of 1841, and passed three exams by the end of
the school year. Several times he has asked the Ministry of education in
Belgrade to send him to study in Paris, but he was denied. On the initiative
of the emissary of the Serbian government, Jovan Sterija Popovic, Jovanovic
and other cadets have been withdrawn from the studies in Vienna. Between
1842. and 1844. Jovanovic has taken part in three rebellions against the
regime of Ustavobranitelji (the Defenders of the Constitution). In the summer
of 1844. in Vienna, Jovanovic has printed a manual for learning French,
French Grammar. Although it is a compilation, the manual is significant since
it has brought contemporary methods of learning French language to Serbian
readers. The papers end with a well founded presumption, based on the yet
unknown document, that Stojan Jovanovic has survived the Katanska buna in
1844.</jats:p
La plainte du chien battu, ou la poésie désenchanteresse (1991-2013) de Michel Houellebecq
No full textCe mémoire propose une étude des poésies de Michel Houellebecq menée dans le respect des visées et du cadre théorique de la sociocritique (Duchet, Robin, Popovic). Chacun de ses trois chapitres explore un thème de recherche qui s’est imposé par sa prégnance dans l’œuvre étudiée : la vie urbaine, la vie sociale, les altérités de la ville. L’hypothèse principale est que l’écriture houellebecquienne capte des signes, des actes de langage, des représentations qui circulent dans la société française contemporaine, et qu’elle le fait de manière dynamique, c’est-à-dire en les soumettant à un travail scriptural qui critique leur usage et qui en modifie le sens. La « mise en texte » (Duchet) de la vie urbaine (premier chapitre) met à jour une domination de la ville et de ses habitants par les seules lois économiques. Elle décrit ainsi un monde qui n’est plus que marchand. Celle de la vie sociale et des liens interpersonnels (deuxième chapitre) démontre leur étonnante facticité et atteste que leur organisation restreint de plus en plus les libertés individuelles. Ce qui était un acquis de la modernité sociale : pouvoir bénéficier de « temps libre » pour prendre soin de soi et des proches, devient de plus en plus impossible. Enfin, celle des altérités de la ville (banlieue, province, nature – troisième chapitre), prouve que ces dernières n’offrent aucune alternative à l’hostilité du monde urbain et à la règle du chacun pour soi. Malgré ce diagnostic désolant, la poésie cherche à déceler ici ou là des traces d’espoir et de solidarité.This master’s dissertation is a study of Michel Houellebecq’s poetry according to the theoretical framework of sociocritic (Duchet, Robin, Popovic). Urban life, social life and alterities of the city are the most present themes in the poetical work of the author. The main hypothesis is that the writing mobilizes and take over signs, linguistic acts and representations which float around in the French contemporary society, but in a dynamic way: the scriptural act of writing modifies their meaning and criticizes their common use. In the first chapter, we will discuss the “putting into text” (literal translation of the « mise en texte » concept by Duchet, which is the action of putting something into the form of a literary text) of urban life, which shines a light on how much the economic laws rule the city and its inhabitants. It describes a market world where money reigns. In the second chapter, the “putting into text” of social life and people-to-people ties shows how surprisingly artificial they are and certifies that their organization shrinks individual liberties more and more. Having free time to spend with your loved ones was once a given of social modernity but is now becoming difficult to manage. In the third and last chapter, the putting into text of the othernesses of the city (suburbs, province, nature) reveals that they offer no alternative to the hostility of the urban world and the fact that it is, and it will always be, every man for himself. Despite this distressing diagnosis, poetry tries to detect here and there hints of hope and solidarity
La plainte du chien battu, ou la poésie désenchanteresse (1991-2013) de Michel Houellebecq
No full textCe mémoire propose une étude des poésies de Michel Houellebecq menée dans le respect des visées et du cadre théorique de la sociocritique (Duchet, Robin, Popovic). Chacun de ses trois chapitres explore un thème de recherche qui s’est imposé par sa prégnance dans l’œuvre étudiée : la vie urbaine, la vie sociale, les altérités de la ville. L’hypothèse principale est que l’écriture houellebecquienne capte des signes, des actes de langage, des représentations qui circulent dans la société française contemporaine, et qu’elle le fait de manière dynamique, c’est-à-dire en les soumettant à un travail scriptural qui critique leur usage et qui en modifie le sens. La « mise en texte » (Duchet) de la vie urbaine (premier chapitre) met à jour une domination de la ville et de ses habitants par les seules lois économiques. Elle décrit ainsi un monde qui n’est plus que marchand. Celle de la vie sociale et des liens interpersonnels (deuxième chapitre) démontre leur étonnante facticité et atteste que leur organisation restreint de plus en plus les libertés individuelles. Ce qui était un acquis de la modernité sociale : pouvoir bénéficier de « temps libre » pour prendre soin de soi et des proches, devient de plus en plus impossible. Enfin, celle des altérités de la ville (banlieue, province, nature – troisième chapitre), prouve que ces dernières n’offrent aucune alternative à l’hostilité du monde urbain et à la règle du chacun pour soi. Malgré ce diagnostic désolant, la poésie cherche à déceler ici ou là des traces d’espoir et de solidarité.This master’s dissertation is a study of Michel Houellebecq’s poetry according to the theoretical framework of sociocritic (Duchet, Robin, Popovic). Urban life, social life and alterities of the city are the most present themes in the poetical work of the author. The main hypothesis is that the writing mobilizes and take over signs, linguistic acts and representations which float around in the French contemporary society, but in a dynamic way: the scriptural act of writing modifies their meaning and criticizes their common use. In the first chapter, we will discuss the “putting into text” (literal translation of the « mise en texte » concept by Duchet, which is the action of putting something into the form of a literary text) of urban life, which shines a light on how much the economic laws rule the city and its inhabitants. It describes a market world where money reigns. In the second chapter, the “putting into text” of social life and people-to-people ties shows how surprisingly artificial they are and certifies that their organization shrinks individual liberties more and more. Having free time to spend with your loved ones was once a given of social modernity but is now becoming difficult to manage. In the third and last chapter, the putting into text of the othernesses of the city (suburbs, province, nature) reveals that they offer no alternative to the hostility of the urban world and the fact that it is, and it will always be, every man for himself. Despite this distressing diagnosis, poetry tries to detect here and there hints of hope and solidarity
Effect of Hot Isostatic Pressing on the Microstructure of Directionally Solidified Nickel Alloy After SLM
No full textThe paper investigates the effect of hot isostatic pressing of single-crystal nickel-based alloy manufactured by selective laser melting (SLM) with a high-temperature substrate preheating. A study of the structure and phase composition of the material before and after treatment has been carried out. It was found that as a result of such treatment, the ratio and proportion of the strengthening phases change; however, due to slow cooling after treatment, the optimal ratio and shape of the inclusions are not fixed. In addition, the hardening particles are precipitated.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Vera Popovic
Heat treatment effect on the structure formation of directionally solidified nickel alloy after SLM
No full textThe aim of this study was to determine the influence of heat treatment on the microstructure of single-crystal nickel-based alloy manufactured by selective laser melting with a high-temperature substrate preheating. The change of gamma/gamma prime -phases ratio was established as a result of various heat treatment modes.Team Vera Popovic
Converter Design for Nuna Maximum Power Point Tracker
No full textThe world is rapidly moving towards a greener future, a mainstay of which is solar energy. Hence, maximum power point trackers, or MPPTs for short, are an indispensable component, since these devices provide one with the capability to fully maximize the achievable power from solar cells in a system. A symbol of the greener world that is evolving around us is the biannual World Solar Challenge, where state-of-the-art solar powered cars race against one another through the deserts of Australia. This thesis forms the link between these two elements: to design an MPPT optimally suited towards the requirements of the Nuna Solar Car. Commercially available MPPTs are not particularly well suited for the specific demands of such a bleeding edge race. They are mostly designed for high power or low voltage systems. The MPPT designed during this thesis is optimized for high efficiency and other requests stated by the Nuon Solar Team members. The design of the MPPT has been split into several parts. This thesis is focused on the converter within the MPPT. It presents the result of research, design exploration, simulation and testing. The results obtained with the prototype that has been built show the designs correctness and conformance to the requirements, with an efficiency of up to 98,5%.Bachelor EEElectrical Power EngineeringElectrical Engineering, Mathematics and Computer Scienc
Maximum Power Point Tracking Topology, sensor and switch design
No full textThe Nuna 6 is a solar racing vehicle that solely relies on solar energy from the sun. Every year, the team seeks ways to improve the performance of their car. One way to improve the performance is to maximize the power output of the solar panels on top of the car. Maximizing the power output can be done with a 'Maximum Power Point Tracker'. The aim of this thesis was to develop an improved, distributed 'Maximum Power Point Tracking'-system which optimizes the power efficiency of the solar panel array of the Nuna 6 solar racing vehicle. To prove that the proposed distributed topology is more power effificient when compared to a central tracking topology, simulations of the total Nuna 6 electrical system were performed. Based on the simulation results, together with Nuna 6 specifications, a DC-DC boost converter was designed. Validation of the design was done by simulation with the Nuna 6 model. After validation, a breadboard proof-of-concept was built. The proof-of-concept was successfully tested and compared with earlier simulations. The system design process was evaluated and recommendations for further study and future real-life implementations were formulated. The simulation results prove that the proposed distributed tracking system is as much as 40% more efficient in large insolation differences and 10% in small insolation differences. The system excels when insolation differs, however it is slightly less efficient when used with equal insolation on every panel. The developed proof of concept demonstrates a functioning maximum power point tracker and DC-DC boost converter. The power efficiency of the boost converter was found to be between 95:8% and 98:5%, with an efficiency of 97:1% for the rated input power of 200W.Electrical EngineeringElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
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