Wälzlagerschmierung mit polymerhaltigen Fetten

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Durchmischung beim Laserstrahltiefschweißen unter dem Einfluss niederfrequenter Magnetfelder

A contactless melt pool manipulation during laser deep-penetration welding can be realized by employing electromagnetic volume forces. In order to improve the melt pool dilution for the case of welding with filler material, low-frequency magnetic fields aligned coaxially to the laser beam have been used. The aim of this work was to identify the dominating interaction mechanism in case of low-frequency magnetic fields used in laser beam deep-penetration welding. By means of experimental and numerical investigations the dominating mechanism could be identified as a flow-induced, periodic magnetic melt flow resistance that causes a periodic deflection of the melt flow. By introducing a novel procedure to characterize the element distribution in weld seams, the significant improvement in terms of homogeneity of the element distribution generated by the low-frequency melt flow manipulation could also be shown

Climatology and large-scale Dynamics of Derechos in Germany

This thesis introduces a German climatology of wide-spread convective wind events so-called “derechos". In a period of 18 years between 1997 and 2014, 40 derechos have been classified based on wind gust measurements and radar data. Although this leads to a significant lower derecho density compared to large regions in the United States, a high potential threat associated with these storms is indicated. Two seasonal peaks of derecho occurrence and typical large-scale flow patterns were identified. Whereas this is similar to the United States climatology, a contrast is that German derechos form with less instability. This corresponds to the greater importance of low-instability derechos that mostly form in the cold season. Low-instability derechos form in thermodynamic conditions similar to high-shear, low-CAPE environments introduced in the United States. High resolution model analysis of eight events with the COSMO model shows the development of conditional instability very close to derechos. This explains that proximity soundings sometimes do not indicate any CAPE. Furthermore, observations and model simulations of the eight events indicate that instability forms close to the ground. It is hypothesized that the combination of a level of free convection close to the ground and strong low-level flow can favor mesovortices that are associated with the highest winds in derechos. As mesovortices form in weak-instability environments as well as in high-instability environments, it is proposed to keep the term derecho for low-instability events and distinguish between warm-season and cold-season derechos. To investigate processes that cause the development of CAPE close to low-instability derechos, the focus is set on local lapse rate changes. These are analyzed in the model fields using calculations of the local lapse rate tendency equation. According to the findings, local lapse rate increase is not only determined by horizontal lapse rate advection, but to a comparable degree by stretching of low-level air masses. Other processes like differential latent heat release in potential unstable layers that are lifted were not found to be important. Stretching occurred especially downstream of moving PV intrusions. Therefore, the findings of this thesis can contribute to the conceptional understanding of convective initiation close to PV intrusions. An example is the “split-front" concept that is modified since our concept explains why cold-season derechos can form in the absence of well-developed surface fronts

Спосіб одержання моноацилгліцеролів алкоголізом жирів

Спосіб одержання моноацилгліцеролів алкоголізом жирів, причому процес має дві стадії, на першій з яких проходить каталітичний етаноліз жирів, а на другій стадії проходить гліцероліз одержаних етилових ефірів жирних кислот, при безперервній відгонці етанолу

Development of environmental barrier coatings for Al2O3/Al2O3 CMCs with improved Adhesion by texturing with laser ablation

Al2O3 /Al2O3 ceramic matrix composites (CMC) are candidate materials for high-temperature applications such as gas turbines. As water vapor corrosion of oxide/oxide CMC is a major issue, the application of suitable environmental barrier coatings (EBC) is inevitable. Besides the gas tightness a good adhesion of the EBC is a crucial aspect for providing an effective barrier against the combustion atmosphere. Due to the brittleness of the ceramic matrix conventional surface treatments like grinding and sandblasting fail to increase roughness without causing damage to the substrate. Therefore there is a need for new methods of surface preparation of CMCs. This work examines the suitability of surface preparation with laser ablation for use prior to air plasma spraying (APS) on an oxide/oxide-CMC. Laser ablation allows controlling of the surface’s structure and roughness. The effects of different laser parameters on the alumina surface were examined and a variety of different structures, for example a honeycomb or a cauliflower like structure, were prepared. The laser treated surfaces were coated with potential EBC-candidates, such as Y2O3 and Gd2Zr2O7 and the impact of laser textures on the coating adhesion was examined. Evaluation of the coated samples was done by pull-off adhesion testing and thermal cycling. Results indicate that laser pretreatment helps to increase the adhesion strength of the EBC-system

Development of thermally sprayed environmental barrier coatings

Ceramic matrix composites (CMCs) are candidate materials for high-temperature applications such as gas turbines. As corrosion by water vapor and deposits is a limiting issue, the application of suitable environmental barrier coatings (EBCs) is inevitable. Gas tightness, chemical stability and a good adhesion of the EBC are crucial aspects for providing an effective barrier against the combustion atmosphere. Thermal spray technologies offer a variety of promising process routes to the manufacturing of ceramic coating systems complying with these demands. This contribution covers coatings for both silicon and oxide based CMCs. Different EBC materials (e.g. silicates, aluminates, rare-earth oxides) were examined and optimized for use as EBC by air plasma spraying (APS). Different thermal spray techniques including high-velocity oxygen-fuel spraying (HVOF), suspension plasma spraying (SPS) and plasma-spray physical vapor deposition (PS-PVD) techniques were assessed for the manufacture of coatings with low amorphous phase content. The application of bond coat as well as alternative surface modification technologies was tested to increase the adhesion of the EBCs. Microstructures and chemical stability of the coatings were analyzed and the performance was tested in terms of adhesion strength or degradation under high-temperature exposure including cyclic oxidation

Simulations of an Electromagnetic Microsystem Used in Biomedical Applications

Abstract-Simulations of an electromagnetic microsystem intended to be used in a microactuator which serves as an ear implant to overcome amblyacousia were conducted. Using the ANSYS TM simulation software, the design and optimization of the electromagnetic microsystem were accomplished by Finite Element Method (FEM) analyses. The design process contained 2-D and 3-D simulations. 2-D simulations served as parametric studies of the system. Afterwards, a 3-D simulation was carried out to fine-tune the results of the 2-D simulation. Comparing the 3-D with the 2-D simulation, the resulting force-air gap data were very close. With respect to the simulations, the designed electromagnetic system fulfils the requirements to drive the microactuator

Polyethylenimine-mediated gene delivery into human bone marrow mesenchymal stem cells from patients

Transplantation of mesenchymal stem cells (MSCs) derived from adult bone marrow has been proposed as a potential therapeutic approach for post-infarction left ventricular (LV) dysfunction. However, age-related functional decline of stem cells has restricted their clinical benefits after transplantation into the infarcted myocardium. The limitations imposed on patient cells could be addressed by genetic modification of stem cells. This study was designed to improve our understanding of genetic modification of human bone marrow derived mesenchymal stem cells (hMSCs) by polyethylenimine (PEI, branched with Mw 25 kD), one of non-viral vectors that show promise in stem cell genetic modification, in the context of cardiac regeneration for patients. We optimized the PEI-mediated reporter gene transfection into hMSCs, evaluated whether transfection efficiency is associated with gender or age of the cell donors, analysed the influence of cell cycle on transfection and investigated the transfer of therapeutic vascular endothelial growth factor gene (VEGF). hMSCs were isolated from patients with cardiovascular disease aged from 41 to 85 years. Optimization of gene delivery to hMSCs was carried out based on the particle size of the PEI/DNA complexes, N/P ratio of complexes, DNA dosage and cell viability. The highest efficiency with the cell viability near 60% was achieved at N/P ratio 2 and 6.0 μg DNA/cm 2. The average transfection efficiency for all tested samples, middle-age group (<65 years), old-age group (>65 years), female group and male group was 4.32%, 3.85%, 4.52%, 4.14% and 4.38%, respectively. The transfection efficiency did not show any correlation either with the age or the gender of the donors. Statistically, there were two subpopulations in the donors; and transfection efficiency in each subpopulation was linearly related to the cell percentage in S phase. No significant phenotypic differences were observed between these two subpopulations. Furthermore, PEI-mediated therapeutic gene VEGF transfer could significantly enhance the expression level.DFG/SFB/Transregio 37BMBF/0313191German Helmholtz AssociationDFG/0402710Ministry of Education/0312138 AMinistry of Economy (Mecklenburg-West Pommerania)/V220-630-08-TFMVF/S-035Marie Curie International Research Staff Exchange Scheme (IRSES, FP7-PEOPLE-2009-IRSES)Reference and Translation Center for Cardiac Stem Cell Therapy (RTC