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Trockenumformung von 42CrS4 mittels Vollvorwärtsfließpressen durch strukturierte Halbzeugoberflächen und selbstschmierende Werkzeugbeschichtungen
Get PDFInnerhalb der ersten Projektphase des Schwerpunktprogramms (SPP) 1676 der Deutschen Forschungsgemeinschaft (DFG) wurden erste Schritte in Richtung eines geeigneten Tribosystems zur trockenen Kaltmassivumformung niedrig legierter Stähle mittels Vollvorwärtsfließpressen (VVFP) erforscht. Am Institut für Oberflächentechnik (IOT) der RWTH Aachen wurde eine selbstschmierende (Cr, Al) N XS2 (X=Wo, M)-Werkzeugbeschichtung entwickelt, die an das Belastungskollektiv der Kaltmassivumformung ausgelegt wurde. Ein Stift-auf-Zylinder Tribometer mit axialem Vorschub wurde am Werkzeugmaschinenlabor (WZL) der RWTH Aachen entwickelt, um die Einfluss von strukturierten Halbzeugoberflächen auf die Reibschubspannung und Verschleiß untersuchen zu können. Experimentelle Analysen wurden durch numerische FE-Prozessmodelle zur Untersuchung der Interaktion von beschichteten Werkzeugen und strukturierten Halbzeugoberflächen auf Mikroebene erweitert. Basierend auf diesen Ergebnissen behandelt dieser Beitragerstmals eine Trockenumformung eines niedriglegierten Stahls (42CrS4) mittels VVFP. Die umgeformten Halbzeuge wurden anhand ihrer Geometrie und der benötigten Umformkraft verglichen. Dadurch wurde die Effektivität und Machbarkeit der Trockenumformung mittels VVFP bewertet. Somit wurde ein weiterer Schritt hin zur Realisierung einer trockenen Kaltmassivumformung unter industriellen Bedingungen von niedriglegierten Stählen vollzogen
In-situ Temperaturmessung beim schmierstofffreien Durchsetzen von Vergütungsstahl
Get PDFDie Kaltumformung gehört zusammen mit dem Scherschneiden zu den wichtigsten Blechbearbeitungsverfahren. Sie ermöglichen die Herstellung präziser Bauteile bei hohen Hubzahlen. Eine hohe Wirtschaftlichkeit kann dabei nur durch lange Wartungsintervalle und einem stabil laufenden Prozess erreicht werden. Einer der wichtigsten Faktoren in diesem Zusammenhang ist die bei der Umformung im Blech entstehende Temperatur. Diese steigt während des Prozesses aufgrund von in Wärme dissipierender plastischer Arbeit sowie Reibung stark an. Hohe Temperaturen können nicht nur die Bauteileigenschaften sowie deren Qualität, sondern auch den Werkzeugverschleiß signifikant beeinflussen. Aus diesem Grund ist die Kenntnis der vorherrschenden Temperaturen bei der Blechverarbeitung von enormer Wichtigkeit. Stellvertretend für andere Umformverfahren wurde in dieser Untersuchung die Temperaturentwicklung anhand von Scherschneidversuchen ermittelt
Tiefziehen eines U-Profils mit flüchtigen Medien als Schmierstoffersatz
Get PDFTechnische, wirtschaftliche und gesetzliche Vorgaben führen zu gesteigerten Anforderungen an Schmierstoffe in der Blechumformung. Auch die Auswirkungen der Schmierstoffapplikation auf die Umwelt werden immer relevanter. Langfristig ist es das Ziel in der Blechumformung, die verwendete Schmierstoffmenge zu reduzieren, um zukünftig Blechbearbeitungen ohne Schmierstoffe durchführen zu können. Ausgehend vom Bestreben der Trockenumformung wird an der Universität Stuttgart ein neuartiges Verfahren zur Schmierung von Tiefziehprozessen mit flüchtigen Medien als Schmierstoffersatz entwickelt. Dieses Verfahren ermöglicht das Einbringen eines Zwischenmediums unter hohem Druck durch lasergebohrte Mikrolöcher in das tribologische System mit Verzicht auf nachfolgende, kostenintensive Reinigungsprozesse, da die flüchtigen Medien bei der Entspannung auf Umgebungsdruck rückstandslos verdampfen. In der ersten Forschungsphase lag der Schwerpunkt auf dem Nachweis der prinzipiellen Realisierbarkeit dieses neuen Ansatzes. Es konnte in Reibungsuntersuchungen gezeigt werden, dass das Einleiten von flüchtigen Medien in die Wirkfuge zwischen Blechwerkstoff und Werkzeug über lasergebohrte Mikrolöcher möglich ist. Gute Reibungswerte konnten mit flüssigem Kohlenstoffdioxid (CO2) und Stickstoff (N2) erzielt werden. In diesem Zwischenbericht werden weitere Reibungsuntersuchungen mit diesen beiden Medien vorgestellt. Schwerpunkt liegt hier auf der Auswahl der, in Bezug auf die Reibung, optimalen Gestaltung der Mikrobohrungen (Durchmesser, Düsenart und Anzahl) sowie auf umfangreichen Untersuchungen, wie diese Mikrolöcher mittels Laserbohren hergestellt werden können. Zudem wird ein neuer Prüfstand mit optischer Zugänglichkeit zur Wirkfuge beim Streifenziehen vorgestellt. Mit diesem Prüfstand kann der Aggregatszustand und das Ausströmverhalten des CO2 untersucht werden. Diese Untersuchungen dienen als Grundlage für die erstmalige Umsetzung des neuen Ansatzes zur Trockenumformung in einem Tiefziehwerkzeug. Der Aufbau dieses Werkzeugs zum Tiefziehen eines U-Profils wird hier detailliert vorgestellt. In ersten Versuchen wird gezeigt, dass ein Tiefziehen mit CO2 als temporär wirkendes Schmiermittel möglich ist und dass dieser Ansatz nicht nur ein Ersetzen von mineralölbasierten Schmierstoffen zu ermöglichen scheint, sondern sogar eine Verbesserung des tribologischen Systems in Bezug auf auftretende Reibunskräfte in der Blechumformung bewirkt. Mit diesen Versuchen zur Umsetzung des neuen Tribosystems in einem Tiefziehwerkzeug wird somit, nach Aufzeigen der prinzipiellen Machbarkeit in der ersten Förderperiode, das nächste Teilziel zur Realisierung des Trockenumformens erreicht
Mental Health in context : Impact of social structures and the built environment on mental wellbeing and mental distress
No full textIntroduction: Not only individual factors but also factors of the social and built environment influence mental distress and ill-health and mental wellbeing. This dissertation aimed to gain further insight into the relationship between individually attributed factors of the social and built environment and mental distress and mental wellbeing. The first objective was to investigate prevalences and variations in mental health by characteristics at the individual level. The second objective was to assess the relationship between social structures at the macro level (here the focused factor was on welfare regimes) and mental health. The third objective was to investigate the relationship between factors of the built environment at the meso level (here the focused factor was environmental noise) and mental health. Methods: The three objectives were addressed by four conceptually independent but topic wise interrelated studies: i) material, psychosocial and sociodemographic determinants of mental wellbeing in Europe, ii) socioeconomic determinants of mental distress and mental wellbeing in school children iii) association between gender, welfare regimes and mental wellbeing, and iv) noise and mental distress in school-aged children. Data from the third wave of the European Quality of Life Survey (2011-2012) and the Health Monitoring Units in Bavaria served as the basis for these studies. Odds ratios were calculated using multilevel and multivariate logistic regression analyses. Poisson regression analyses were used to calculate relative risks for the incidences. Results: In adults material, psychosocial and sociodemographic factors were independently associated with low levels of mental wellbeing. In children, the analyses showed that several indicators of familiesa social disadvantage were associated with mental distress, in contrast to mental wellbeing, where only a few factors were associated. At the macro level prevalence of good mental wellbeing was in most instances higher among men compared to women at welfare regime level, with the exception of the Former Soviet Union welfare regime, where women report slightly higher prevalence of good mental wellbeing. Gender inequalities in good mental wellbeing were identified independent of further individual sociodemographic variables and independent of the welfare regimes that people lived in. People in the Former Soviet Union and the Central and Eastern European Countries welfare regimes showed statistically significantly lower chances to report good mental wellbeing compared to the Scandinavian welfare regime. Gender inequalities in good mental wellbeing were not modified by welfare regimes. At the individual level of the built environment, exposure to road traffic noise at day or night was the main risk factor for incident mental health problems in children. Exposure to noise by neighbours day and night also appeared to be a risk factor for some subcategories of the strength and difficulties questionnaire. Both noise from construction work and aircraft noise during the day were not associated with incident mental health problems. Discussion: Findings of this dissertation highlight an association between individual factors, aspects of the social and built environment and mental wellbeing and mental distress. The study of mental wellbeing is relatively young, therefore, especially in this field further studies are needed to confirm and expand the findings of this dissertation. To plan effective prevention and health promotion interventions a thorough understanding of the underlying mechanisms and pathways is needed. Further studies are warranted to gain knowledge on the impact of (further aspects of) the social and built environment on mental wellbeing and mental distress in adults and in children to identify underlying mechanisms and to identify vulnerable groups for targeted preventions
Enteroviral infection as a cause for beta-cell failure and diabetes
No full textAutoreactive T-cell mediated destruction of insulin-containing beta-cells is the hallmark of Type 1 Diabetes (T1D). Although the disease is known for centuries, neither is the cause of onset clearly identified, nor has the worldwide raise of incidences been stopped. To provide a cure, it is mandatory to uncover the causes triggering the disease such as environmental and/ or genetic factors that induce the activation of the immune system. Based on epidemiological studies, previous virus infections, especially by Coxsackieviruses B (CVB) of the Picornaviridae family, are highly associated with the onset of T1D. However, the proof of causality between CVB infection and T1D onset is still missing in humans and evidences of beta-cell infection in human pancreata remain controversial.In this work, I aimed to identify the initial pathways to enterovirus-mediated beta-cell destruction and to develop a highly sensitive and specific method to characterize expression and localization of viral RNA in pancreatic tissue sections. Cultured human islets and beta-cell lines were used to analyze the first cellular mechanism during viral infection. From the tested viruses, only the enteroviruses (CVB3 and CVB4) induced apoptosis in infected beta-cells. Both CVBs also infiltrated, but with different ratios, alpha-cells that remained unaffected by the virus. The Pathogen-recognition receptors (PRRs) TLR3 and PKR were the first receptors that recognized the virus in beta-cells and TLR7 in alpha-cells, whereas MDA5 and RIG-I bound the genome at a much later time point. TLR3 and PKR had a dual role in beta-cells, as they triggered the first immune response and cytokine release, but also activated the survival pathways AKT and ERK, upon virus recognition. Both activated kinases promoted viral replication and counter-balanced the absence of each other. While through this work, it became clear, that enterovirus infection is causative for beta-cell destruction and dysfunction in human islets in vitro. But the question, whether virus infection indeed coincide with diabetes in vivo remained elusive. With a newly developed method I could detect enteroviral genomes in human T1D donor tissues. I adapted single molecular fluorescence in situ hybridization (smFISH) to screen for viral RNA molecules in formalin-fixed paraffin-embedded (FFPE) pancreatic tissue sections. Specifically designed oligonucleotide probes to detect a wide range of Coxsackieviruses were successfully tested in an array of cell lines and pathological tissues. Oligonucleotide probes show a specificity and sensitivity that exceed classical immunohistochemistry (IHC) assays and was comparable in its sensitivity to PCR. With the combination of smFISH and IHC I could detect and locate viral RNA in T1D donor tissues in a blinded concordance study. I confirmed former VP1 staining and showed that enteroviral genomes are located in the pancreas of patients with T1D, but not exclusively within insulin-containing cells. The results of this thesis strongly point towards viral induced T1D onset in humans. They represent a central step for diabetes care and provide groundwork for future preventive strategies
Historical knowledge, variation in community composition, ecotrophic parameterization, and invasive species of macroalgae in the Galapagos archipelago
Get PDFDue to its uniqueness and protected status the marine ecosystem of the Galapagos Marine Reserve (GMR) is of particular interest. As a result of its equatorial location and upwelling-influenced waters, the Galapagos archipelago hosts a diverse and productive marine ecosystem, and this is especially true of marine macroalgae. Macroalgal ecology in the archipelago has not been comprehensively studied. This work, which includes a synthesis of historical knowledge, a large-scale description of macroalgal community variation across the archipelago based on standardized surveys, large and fine-scale estimates of macroalgal ecotrophic parameters, and the foundation for studying the phylogenetics and behavior of Caulerpa in the GMR, was completed with the hope that this information will be useful for the continued management and conservation of the unique and fragile marine ecosystems of the Galapagos archipelago
Ensuring Curriculum Relevance in Vocational Education and Training: Epistemological Perspectives in a Curriculum Research Project
Get PDFThis article addresses challenges regarding relevance in vocational education and training (VET) curricula. Recent research on Norwegian VET shows that the educational content is not sufficiently related to the students' needs for qualification in the actual vocations. I will present a new curriculum research project aimed at investigating and improving the vocational relevance in Norwegian VET. An important part of the project is to investigate epistemological perspectives on how vocational knowledge is constituted and developed, and consequences for the curriculum. The article presents results from these epistemological investigations. I will argue that the relevance problem relates to a one-sided rationalist epistemology in which a main idea is that vocational knowledge consists of theoretical principles and procedures to be applied in practical situations. This idea influences educational traditions and structures, and leads to a separation between theoretical and practical subjects and learning arenas. From a pragmatic epistemological perspective, it can be argued that vocational knowledge is contextual and holistic, and consists of complex wholes of physicality, motor skills, intellectual understandings, values, and verbalized concepts. To ensure curriculum relevance, a curriculum is needed in which authentic practical work is the base, and subjects are integrated with students' practical work experience
Schmiedegerecht nitrierte Gesenke
Get PDFIn order to resist the high loads, the surfaces and boundary areas of forging dies are nitrided. Up to now, there was no proven knowledge about, which processing parameters respectively which nitrided case leads to the best life time of the tools. In the present work, the influence of nitriding and nitrocarburizing with all their variety of nitrided cases on the lifetime and wear of forging dies was investigated. Eight promising treatments were transferred to forging dies, in order to create a number of different nitrided cases. The tools were used in serial production and their lifetime was determined under real conditions. At the lifetime end, critical parts of the tools were metallographical investigated, in order to find out the wear mechanisms. Finally, a recommendation was developed which nitrided case revealed the best results for a given loading condition
Laser-interferometric dilatometry
Get PDFHighly dimensionally stable materials and structures are particularly needed in optical systems such as ultra precise optical clocks, as well as materials with excellent dimensional stability and light weight properties for space applications such as telescopes, optical benches, and optical resonators. Also, the dimensional stability of mounting technologies of materials with different properties is of high interest for such applications. Glass ceramics and composite materials can be tuned to reach a very low coefficient of thermal expansion (CTE) at different temperatures, enabling best stability in the operating temperature for certain applications. In order to determine the CTE of such highly stable materials, very accurate set-ups are needed. In this thesis, metrology set-ups to measure the CTE of a large variety of material samples are designed, realized and verified, measuring dimensionally stable glass ceramics. The set-ups are able to characterize tube shaped samples at a temperature range of 140 K to 333 K. Due to our unique mirror mount design all kind of materials can be characterized. The optical dilatometer set-ups are based on a heterodyne interferometer with a displacement sensitivity at the sub-nanometer level. This instrument is used to measure the expansion of a sample when applying controlled small amplitude temperature signals. A carbon fiber reinforced polymer (CFRP) sample was characterized where CTE levels of 10 -8 K -1 from 140 K to 250 K were measured and a detailed uncertainty analysis was performed. The verified metrology set-up for tube shaped samples was adapted for CTE measurements of larger structures. Therefore, a large thermal chamber was set up and a 0.5 m CFRP spacer with Zerodur endfittings as a representative joint technology demonstrator for the GRACE Follow-On space mission at 302 K was investigated
Insights into the biology of Candidate Division OP3 LiM populations
Get PDFThe candidate division OP3, recently entitled candidate phylum Omnitrophica, is characterized by 16S rRNA gene sequences from a broad range of anoxic habitats with a broad phylogeny of up to 26% sequence dissimilarity. The 16S rRNA phylotype OP3 LiM had previously been detected in limonene-degrading, methanogenic enrichment cultures and represented small coccoid cells. Neither isolation experiments nor physiological experiments had provided insights into the metabolism of this bacterium within the complex methanogenic community. This doctoral thesis aimed at the characterization of populations of the phylotype OP3 LiM to discover its biology. Metagenomes usually yield draft population genomes. To obtain the complete closed OP3 LiM genome, in silico methods were explored to improve draft assemblies. Large genomes of planctomycete strains were assembled with a variety of methods. A taxonomic classification of contig sequences was used to differentiate and separate contigs of draft assemblies into taxon-specific groups. Reassemblies of reads obtaining from mapping onto taxon-specific contigs yielded improved draft assemblies. This knowledge was used to obtain a closed genome of OP3 LiM from a metagenome of physically enriched OP3 LiM cells. Finishing the OP3 LiM genome required the combination of data of different sequencing technologies, a variety of assembly and mapping software, over 15 reassemblies with intensive manual quality controls by read and contig mapping and, finally, laboratory work with combinatorial PCR to solve the genome puzzle. The population genome of OP3 LiM is the first closed genome of a member of candidate phylum Omnitrophica and comprises 1,974,501 bp with a GC content of 52.9%. Its 23S rRNA contains a group I intron. The genome offers a syntrophic life on hydrogen or formate, however, the metaproteome indicated that OP3 LiM uses glycolysis together with pyruvate oxidation as major catabolic pathway. The metaproteome also identified high levels of proteins potentially involved in the degradation of polymers as well as in the uptake of foreign nucleic acids. The genomic information was combined with observations of cells of the methanogenic community by different visualization methods. Images of OP3 LiM required electron microscopy due to the small cell size of 0.2a 0.3 AAmicrometre in diameter. In situ hybridizations revealed two physiological stages, free-living OP3 LiM cells with low ribosome content and OP3 LiM cells attached to either bacteria or archaea, which showed strong signals. This observation indicated a higher metabolic activity of OP3 LiM cells during the attachment and, likewise, that the bacterium utilizes surface polysaccharides as preferred substrate. In situ hybridizations revealed that the methanogen Methanosaeta in the enrichment culture contained cells in the filaments that lacked DNA and rRNA suggesting that these cells lost their cellular content. We also observed faint signals of the OP3 LiM 16S rRNA in Methanosaeta cells. The presence of the intron RNA of the 23S rRNA of OP3 LiM was visualized in Methanosaeta cells devoid of DNA and rRNA. This first direct observation of an intron transfer from a bacterium to an archaeon together with metaproteomic observations indicate the lifestyle of an epibiotic bacterium for OP3 LiM. OP3 LiM is the first predatory bacterium that preys on Archaea. We propose to name OP3 LiM a Candidatus Vampirococcus archaeovorusa