Unsteady Numerical Simulation of the Pressure Distribution in a Ball-on-Disc Tribometer = Instationäre numerische Simulation der Druckverteilung in einem Kugel-Scheibe Tribometer

Die Schmierung von Oberflächen, welche sich in Relativbewegung befinden, ist sehr wichtig, um unnötige Energieverluste wegen Reibung zu vermeiden. Das gezielte Einbringen von Oberflächentexturen ist die Verringerung des Reibungsverlusts und die Erhöhung der Belastungskapazität. Der Mangel an allgemeingültigen Aussagen und widersprüchlichen Erkenntnisse aus der Literatur sind die Hauptherausforderungen für eine weitverbreitete Nutzung von Oberflächentexturen. Kugel-Scheibe Tribometer werden benutzt, um die Eigenschaften von realen Reibkontakten in einem Labor zu voraussagen. Diese Bachelorarbeit baut auf der Arbeit von Erik Hansen auf, die ein solches Kugel-Scheibe Tribometer in stationären Zuständen simuliert, um es für instationäre Effekte zu erweitern. Bei den Simulationen wird eine Mikrotextur in die Kugeloberfläche eingesetzt und der Algorithmus entsprechend angepasst. Das Ziel dieser Arbeit ist die Validierung der numerischen Vorhersagen durch den Vergleich mit experimentellen Ergebnissen von Literatur. Die verwendeten Gleichungen werden hergeleitet und erläutert. Die numerischen Ansätze und die Funktionsprinzipien der verwendeten Algorithmen werden detailliert beschrieben. Es wird eine gute Übereinstimmung zwischen den Simulationsergebnissen und experimentellen Daten aus der Literatur gefunden. Das Gesamtverhalten des neuen Solvers wird ebenfalls untersucht. Es werden Simulationen mit unterschiedlichen räumlichen Gittergrößen mit proportional skalierten Zeitschritten und konstanten Gittergrößen mit wechselnden Zeitschrittgrößen durchgefuhrt und analysiert. Es zeigt sich, dass gröbere Gitter großen Abweichungen von den experimentellen Ergebnissen entsprechen, die untersuchten feinsten Gitter aber mit langen Rechenzeiten und großem Rechenaufwand verbunden waren, so dass je nach Anforderung ein Kompromiss getroffen werden muss

Untersuchungen zur Produktion von Cyanobacterin, einem Toxin aus dem Cyanobakterium Scytonema hofmanni Ag.(UTEX1581): anwendungsbezogene und ökologische Aspekte

Vor dem Hintergrund der biotechnologischen Produktion des Cyanotoxins Cyanobacterin durch das Cyanobakterium Scytonema hofmanni (UTEX 1581) wurde der Einfluss der abiotischen Parameter Photonenflussdichte, pH-Wert, Temperatur, der Nährstoffkonzentrationen an Nitrat und Phospat sowie von Spurenelementen untersucht. Aus diesen Ergebnissen wurden Schlüsse hinsichtlich der Ökologie von Scytonema hofmanni als Bestandteil von Cyanobakteriengemeinschaften der Everglades (Florida, USA) gezogen. Es wurde eine neue Methode entwickelt, um die Cyanobacterinkonzentration in der Biomasse photometrisch im DMF-Extrakt in etwa 24 h zu quantifizieren. Cyanobacterin ist eine Allelochemikalie, deren Synthese wiederum durch Allelopathie beeinflusst wird. Cyanobacterin kann als biogenes Herbizid und als Co-Anitfoulant angewandt werden.The aim of the study was to investigate the biotechnical production of the cyanotoxin cyanobacterin by the cyanobacterium Scytonema hofmanni (UTEX 1581) under the influence of the following abiotic parameters: photon flux rate, pH, temperature, different nutrient concentrations nitrate and phosphate as well as of trace elements. Based on these data, the ecology of Scytonema hofmanni as part of a cyanobacterial community in the Everglades (Florida, USA) was concluded. A new rapid method was developed to quantify cyanobacterin in the biomass by photometric analysis of DMF-extracts within 24 h. Cyanobacterin exhibited allelochemical effects and its biosynthesis again is influenced by allelopathy. Cyanobacterin can be used as a natural herbizide and as a co-antifoulant

An Agent-Based Approach for Integrating User Profile Into a Knowledge Management Process

This paper presents an approach based on a user agent to permit a number of users connected to distant machines to access different information sources in order to satisfy their requests. This user agent permits the simplification of the information search from distributed sources by making them transparent to the users. The agent considers the specific needs of each user during the search and responds with reference to their profile. It also permits the processing of one or more information requests by one or more users, as well as concurrent responses to each of them. Moreover, the agent provides its users with a measure of interaction, in order to enhance the quality and quantity of the results obtained. As a result, the agent is endowed with the ability to filter and refine the search, thus improving its service to the users

Emerging risks from ballast water treatment: The run-up to the International Ballast Water Management Convention

AbstractUptake and discharge of ballast water by ocean-going ships contribute to the worldwide spread of aquatic invasive species, with negative impacts on the environment, economies, and public health. The International Ballast Water Management Convention aims at a global answer. The agreed standards for ballast water discharge will require ballast water treatment. Systems based on various physical and/or chemical methods were developed for on-board installation and approved by the International Maritime Organization. Most common are combinations of high-performance filters with oxidizing chemicals or UV radiation. A well-known problem of oxidative water treatment is the formation of disinfection by-products, many of which show genotoxicity, carcinogenicity, or other long-term toxicity. In natural biota, genetic damages can affect reproductive success and ultimately impact biodiversity. The future exposure towards chemicals from ballast water treatment can only be estimated, based on land-based testing of treatment systems, mathematical models, and exposure scenarios. Systematic studies on the chemistry of oxidants in seawater are lacking, as are data about the background levels of disinfection by-products in the oceans and strategies for monitoring future developments. The international approval procedure of ballast water treatment systems compares the estimated exposure levels of individual substances with their experimental toxicity. While well established in many substance regulations, this approach is also criticised for its simplification, which may disregard critical aspects such as multiple exposures and long-term sub-lethal effects. Moreover, a truly holistic sustainability assessment would need to take into account factors beyond chemical hazards, e.g. energy consumption, air pollution or waste generation

sewage sludges and its application as dye removal

The purpose of this experimental study is to determine optimum preparation conditions for activated carbons obtained from textile sewage sludge (TSS) for removal of dyes from aqueous solutions. The textile sewage sludge activated carbon (TSSAC) was prepared by chemical activation with potassium hydroxide using Response Surface Methodology (RSM). The most influential factor on each experimental design responses was identified via ANNOVA analysis. Based on the central composite design (CCD), quadratic model was developed to correlate the preparation variables for one response which is the Brunauer-Emmelt-Teller (BET) surface area. RSM based on a three-variable CCD was used to determine the effect of pyrolyzed temperature (400-700 degrees C), carbonization time (45-180 min) and KOH: weight of TSS (wt%) impregnation ratio (0.5:1-1.5:1) on BET surface area. According to the results, pyrolyzed temperature and impregnation ratio were found as the significant factors for maximizing the BET surface area. The major effect which influences the BET surface area was found as pyrolyzed temperature. Both carbonization time and impregnation ratio of KOH had no significant effect. The optimum conditions for preparing TSSAC, based on response surface and contour plots, were found as follows: pyrolyzed temperature 700 degrees C, carbonization time of 45 min and chemical impregnation ratio of 0.5. The maximum and optimum BET surface area of TSSAC were found as 336 m(2)/g and 310.62 m(2)/g, respectively. Synozol Blue reactive (RSB) and Setapers Yellow-Brown (P2RFL) industrial textile dyes adsorption capacities were investigated. As expected the TSSAC which has the biggest BET surface area (336 m(2)/g) adsorbed dye best. The maximum (RSB) and (P2RFL) uptake capacities were found as 8.5383 mg/g and 5.4 mg/g, respectively. The results of this study indicated the applicability of TSSAC for removing industrial dyes from aqueous solution. (C) 2015 Elsevier Ltd. All rights reserved