Mission Profile Based Optimization of a Synchronous-Buck DC-DC Converter for a Wearable Power System

A Wearable Power System (WPS) is a portable fuel-to-electrical energy converter that is carried on the body and is able to supply an average of 20 W for 4 days and has a total weight of less than 4 kg. Due to limited total weight of the system, each system part must have the highest efficiency to weight ratio. This paper presents the optimization of a synchronous buck DC-DC converter that is used to regulate the variable power source to a constant 14 VDC for the load. Higher switching frequency leads to smaller components and low weight, but at the same time, to higher losses that are compensated through additional fuel weight. If low switching frequency is applied, the weight of the converter will increase due to a larger inductor, but the power losses will be lower. Therefore, an optimal switching frequency should exist that results in the total weight of the DC-DC converter and additional fuel being a minimum. The paper first explains the proposed solution for WPS, the load pattern that is used to test the system and then the algorithm that decides on the number of converters to be used and how to find the optimal switching frequency. Additionally, two prototypes have been constructed. First prototype has nominal power of 20 W and is used in the analysis regarding the optimal number of converters. The second one has rated power of 200 W and it is built to support the conclusions based on the optimization process

A comparative evaluation of isolated bi-directional dc/dc converters with wide input and output voltage range,” in

Abstract-The working principles and design equations of four different isolated, bi-directional DC to DC converter topologies (a dual active bridge converter, a series resonant converter and two multiple stage topologies) for a 2kW bi-directional battery charger that can be operated in a wide input and output voltage range are presented in this paper. The results of a detailed mathematical analysis of the converter topologies as well as digital simulation results are used to select the most efficient topology for this specific converter application, where the twostage series resonant converter is identified to be the most promising, with up to 90% efficiency at rated power

Die Idee dahinter ... : Aspekte zur Gestaltung lernreicher Lehre

Der Band umfasst zahlreiche Beispiele von Lehrenden, die ihre Veranstaltungen in mehreren Aspekten ‚lernreich(er)’ gestaltet haben. Die Konzepte wurden alle im Rahmen des Vertiefungsmoduls des Programms „Professionelle Lehrkompetenz für die Hochschule“ des Netzwerks "hochschuldidaktik nrw" an der Universität Siegen entwickelt oder weiterentwickelt. Die elf Beiträge umfassen ein breites Spektrum an Veranstaltungsformaten und Fächern: Natur- und Ingenieurwissenschaften sind ebenso vertreten wie Architektur, Pädagogik, Soziale Arbeit und Literaturwissenschaft. Bei den Veranstaltungen handelt es sich um Praktika, Seminare, Übungen usw., oft mit Projektcharakter bzw. -elementen, häufig auch mit wechselnden Lernorten, semester-begleitend oder kompakt

Gating of aquaporins by heavy metals in Allium cepa L. epidermal cells

Changes in the water permeability, aquaporin (AQP) activity, of leaf cells were investigated in response to different heavy metals (Zn2+, Pb2+, Cd2+, Hg2+). The cell pressure probe experiments were performed on onion epidermal cells as a model system. Heavy metal solutions at different concentrations (0.05 μM–2 mM) were used in our experiments. We showed that the investigated metal ions can be arranged in order of decreasing toxicity (expressed as a decrease in water permeability) as follows: Hg>Cd>Pb>Zn. Our results showed that β-mercaptoethanol treatment (10 mM solution) partially reverses the effect of AQP gating. The magnitude of this reverse differed depending on the metal and its concentration. The time course studies of the process showed that the gating of AQPs occurred within the first 10 min after the application of a metal. We also showed that after 20–40 min from the onset of metal treatment, the water flow through AQPs stabilized and remained constant. We observed that irrespective of the metal applied, the effect of AQP gating can be recorded within the first 10 min after the administration of metal ions. More generally, our results indicate that the toxic effects of investigated metal ions on the cellular level may involve AQP gating

The Relative Importance of Topography and RGD Ligand Density for Endothelial Cell Adhesion

The morphology and function of endothelial cells depends on the physical and chemical characteristics of the extracellular environment. Here, we designed silicon surfaces on which topographical features and surface densities of the integrin binding peptide arginine-glycine-aspartic acid (RGD) could be independently controlled. We used these surfaces to investigate the relative importance of the surface chemistry of ligand presentation versus surface topography in endothelial cell adhesion. We compared cell adhesion, spreading and migration on surfaces with nano- to micro-scaled pyramids and average densities of 6×102–6×1011 RGD/mm2. We found that fewer cells adhered onto rough than flat surfaces and that the optimal average RGD density for cell adhesion was 6×105 RGD/mm2 on flat surfaces and substrata with nano-scaled roughness. Only on surfaces with micro-scaled pyramids did the topography hinder cell migration and a lower average RGD density was optimal for adhesion. In contrast, cell spreading was greatest on surfaces with 6×108 RGD/mm2 irrespectively of presence of feature and their size. In summary, our data suggest that the size of pyramids predominately control the number of endothelial cells that adhere to the substratum but the average RGD density governs the degree of cell spreading and length of focal adhesion within adherent cells. The data points towards a two-step model of cell adhesion: the initial contact of cells with a substratum may be guided by the topography while the engagement of cell surface receptors is predominately controlled by the surface chemistry

FIB patterning of stainless steel for the development of nano-structured stent surfaces for cardiovascular applications

Stent implantation is a percutaneous interventional procedure that mitigates vessel stenosis, providing mechanical support within the artery and as such a very valuable tool in the fight against coronary artery disease. However, stenting causes physical damage to the arterial wall. It is well accepted that a valuable route to reduce in-stent re-stenosis can be based on promoting cell response to nano-structured stainless steel (SS) surfaces such as by patterning nano-pits in SS. In this regard patterning by focused ion beam (FIB) milling offers several advantages for flexible prototyping. On the other hand FIB patterning of polycrystalline metals is greatly influenced by channelling effects and redeposition. Correlative microscopy methods present an opportunity to study such effects comprehensively and derive structure–property understanding that is important for developing improved patterning. In this chapter we present a FIB patterning protocol for nano-structuring features (concaves) ordered in rectangular arrays on pre-polished 316L stainless steel surfaces. An investigation based on correlative microscopy approach of the size, shape and depth of the developed arrays in relation to the crystal orientation of the underlying SS domains is presented. The correlative microscopy protocol is based on cross-correlation of top-view scanning electron microscopy, electron backscattering diffraction, atomic force microscopy and cross-sectional (serial) sectioning. Various FIB tests were performed, aiming at improved productivity by preserving nano-size accuracy of the patterned process. The optimal FIB patterning conditions for achieving reasonably high throughput (patterned rate of about 0.03 mm2/h) and nano-size accuracy in dimensions and shapes of the features are discussed as well

"A Theoretical Perspective on Multi-level Systems in Europe: Constitutional Power and Partisan Conflict"

types: ArticleThis article distinguishes three constitutionally defined categories of multi-level systems – confederations, federal arrangements and regionalized arrangements, which differ in whether their lower-level governments enjoy constitutional protection and whether we find a constitutional hierarchy between central and lower levels of government. We argue that the constitutional category a multi-level system belongs to systematically shapes first, the dominant mode of day-to-day intergovernmental coordination, second, the mode of formal competence (re)allocation; and third, the relative impact of party (in)congruence across central and lower-level governments on these coordination processes, respectively. The article then specifies the indicators used to test the hypotheses across the range of case studies. It finally shows how the multi-level systems covered in this special issue span the confederal – federal – regionalized spectrum and thus allow for an encompassing comparative assessment of multi-level dynamics and their long-term evolution.ESR

Finanzregulierer in der Krise

Unabhängige Regulierungsbehörden sind in den letzten Jahrzehnten zu einem wichtigen Faktor in der Politik geworden. Seit der Finanzkrise sind Regulierer wie die Schweizer Finma auch der breiteren Öffentlichkeit bekannt. Sie verfügen über zahlreiche Kompetenzen und hohe Autonomie. Mit ihrer Unabhängigkeit von der Politik wurde mehr Glaubwürdigkeit und höhere Effizienz in der Regulierung von Märkten verbunden. Dagegen ist ihre Verantwortung gegenüber demokratischen Institutionen schwächer ausgeprägt. Am Beispiel der Finma und der britischen FSA wird erörtert, ob von einem ernsthaften Defizit an Accountability, also der Verantwortlichkeit und Rechenschaftspflicht, solcher Kontrollorgane ausgegangen werden muss

The Accountability Regimes of Independent Agencies: A Comparative Study

In contcmporary politics, a new type of actors, somelime called Non-Majoritarian Institutions (NMIs), are of raising importance - most often for efficiency rationales. One particular important species of that type are Independent Rcgulatory Agencies (IRAs), established mainly to regulate risks or (formerly monopolized) markels in an expertise- and long term-oriented manner. For this purpose, IRAs are often designed to act "at arm's length" of government. In turn, il has been argued IRAs represent a challenge to democracy. Of particular concem is that IRAs, due to their independence, are not anymore subject to mechanisms of démocratie accountability. The présent thesis addresses the accountability of Independent Rcgulatory Agencies (IRAs) in a more inclusive way than existing approaches. That "regime approach" differentiates between formal accountability mechanisms "on paper", and their de facto use. Empirically, the approach is used to analyze the accounlability régimes of four case studies: The Swiss regulators for télécommunications and financial services, ComCom and FINMA, and their German counterparts, BNetzA and BaFin. The results yield, first, that each agency under scrutiny is formally subject to a powerful accountability regime. Moreover, there is 110 detectable trade-off between independence and formal accountability. The second part of the study reveals the power of additional factors such as trust, reputation-seeking, and transnational intégration to completely juxtapose the character of die formal arrangement. The regime approach has hence proven useful to get a more fine-grained picture of accountability. Il shows that accountability is not restricted mainly by resource scarcity or lack of credibility, which mosl fora are able to compensate for, but by informal dynamics among fora and between fora and agency. Résumé La politique contemporaine est marquée par l'apparition d'un nouveau type d'acteurs, parfois appelés institutions non majoritaires (INM) qui ont vus leur importance sensiblement s'accroitre - le plus souvent pour des raisons d'efficacité. Parmi ces nouveaux acteurs, les organismes de réglementation autonome (IRA), oui pris une importance particulière dans le domaine de la réglementation des risques ou des marchés (anciennement monopolisés) dont l'expertise est orientée avant tout sur le long-terme. À cet effet, les IRA sont souvent conçus pour agir indépendamment du gouvernement. De ce fait, les IRA représentent pour certain un véritable défi démocratique. Il est notamment particulièrement préoccupant que les IRA, en raison de leur indépendance, ne soient pas soumises à des mécanismes de responsabilité démocratique. La présente thèse traite de la responsabilité des organismes de réglementation autonome (IRA) d'une manière plus inclusive que les approches existantes. Cette «approche de régime» établi une distinction entre les mécanismes officiels de responsabilisation «sur papier» et leur utilisation de facto. Empiriquement, l'approche est utilisée pour analyser les régimes de responsabilité de quatre organismes : Les régulateurs suisses pour les télécommunications et les services financiers, la ComCom et la FINMA, ainsi que leurs homologues allemands, BNelzA et BaFin. Les résultats de cette analyse démontrent, en premier lieu, que chaque organisme est formellement soumis à un régime de responsabilisation puissant. En outre, aucun compromis n'est apparu entre indépendance el responsabilité formelle. La deuxième partie de l'étude révèle également la puissance de facteurs supplémentaires tels que la confiance, la recherche de réputation et l'intégration transnationale afin de compléter les accords officiels. L'approche de régime s'est donc révélée utile pour obtenir une image plus line de la responsabilité. Elle montre en particulier que la responsabilité 11e se limite pas principalement à la rareté des ressources ou le manque de crédibilité, que la plupart des forums sont en mesure de compenser, mais se compose d'une dynamique informelle entre les instances ainsi qu'entre les instances el les organismes