Dam Hydrological Risk and the Design Flood Under Non-stationary Conditions

Water Resources Management - Increasing global trends in time series of annual maximum daily streamflow (AMX) raise the concern that the safety of dams and other sensitive structures is...     

Interaction of global and local buckling in welded RHS compression members

This paper presents the results of a research project analysing some aspects of the stability failure of thin-walled compression members that are likely to exhibit combined global and local buckling. In particular, the influence of various imperfections, namely residual stresses due to welding and local as well as global geometrical defects, on the load-carrying capacity was subjected to detailed experimental and numerical investigations. The insights obtained into the structural behaviour led to a proposal for modification of the non-dimensional slenderness used in the global buckling verification, and to the recommendation of a shift from the currently applied European buckling curve to a more favourable one in the case of non-stiffened members with welded box sections subjected to pure compression.     

Der Einfluss von Imperfektionen in dünnwandigen geschweißten Rechteckquerschnitten unter Druckbeanspruchung

On imperfections in thin‐walled welded rectangular hollow section compressive members. This contribution presents the results of a research project analysing some aspects of stability failure of thin‐walled RHS compression members that are likely to exhibit combined global and local buckling. In particular the influence of various imperfections, namely residual stresses due to weld‐ing and local as well as global geometrical defects, on the load‐carrying capacity is subject to detailed experimental and numerical investigations. The insight into the structural behaviour leads to recommendations for standardized imperfections that should be used in the context of the numerical modelling of class‐4 square and rectangular hollow section members subjected to compression.     

Platelet-derived growth factor modulates the primordial to primary follicle transition

Primordial follicles steadily leave the arrested pool and undergo a primordial to primary follicle transition during the female reproductive lifespan. When the available pool of primordial follicles is depleted reproduction ceases and humans enter menopause. The present study was designed to investigate the actions of several growth factors previously identified as candidate regulatory factors for the primordial to primary follicle transition with a microarray analysis. Ovaries from 4-day-old rats were placed into culture and treated for 2 weeks with platelet-derived growth factor (PDGF), anti-PDGF neutralizing antibody, vascular endothelial growth factor (VEGF), neuregulin (NRG), or kit ligand (KITL) as a positive control. PDGF-treatment resulted in a significant decrease in the percentage of primordial follicles and a concomitant increase in the percentage of developing primary follicles compared to controls. In contrast, ovaries treated with an anti-PDGF neutralizing antibody had a significant increase in the percentage of primordial follicles demonstrating an inhibition of endogenous follicle development. Ovaries incubated in the presence of VEGF or NRG had no change in follicle development. Observations indicate that PDGF, but not VEGF or NRG, promotes the primordial to primary follicle transition. Immunohistochemical localization indicated that the PDGF protein was present in the oocytes of both primordial and developing follicles. PDGF-treatment of cultured ovaries resulted in an increase in KITL mRNA expression. KITL has been previously shown to promote the primordial to primary follicle transition. KITL-treatment of ovaries had no effect on expression of Pdgf or any PDGF homologs or receptors. Therefore, PDGF appears to be produced by the oocyte and acts as one of several extracellular signaling factors that regulate the primordial to primary follicle transition. These observations provide insight into the cell-cell interactions involved in the regulation of primordial follicle development and can be used in the future development of therapies for some forms of infertility.     

Novel temperature dependent tensile test of freestanding copper thin film structures

The temperature dependent mechanical properties of the metallization of electronic power devices are studied in tensile tests on micron-sized freestanding copper beams at temperatures up to 400 °C. The experiments are performed in situ in a scanning electron microscope. This allows studying the micromechanical processes during the deformation and failure of the sample at different temperatures.     

A comparative micro-cantilever study of the mechanical behavior of silicon based passivation films

A comprehensive study on the mechanical behavior of plasma enhanced chemical vapor deposited silicon oxide, oxynitride and nitride thin films is provided. Hardness, Young's modulus, yield stress, fracture stress and fracture toughness values are determined by the nanoindentation and the micro-cantilever deflection technique. The micro-cantilever deflection technique is discussed in terms of measurement accuracy and reproducibility and the results are compared with standard nanoindentation measurements. Correlations between the yield and fracture behavior, which have been observed for glass fibers, are discussed in this paper for dielectric thin film glasses.     

Shear resistance of longitudinally stiffened panels—Part 1: Tests and numerical analysis of imperfections

This paper deals with the results of four full-scale tests, numerical simulation of tests and initial geometric imperfection analysis for longitudinally stiffened panels in shear. The tests examine the influence of varying position and bending stiffness of one trapezoidal longitudinal stiffener on the panel shear resistance and its buckling behaviour. The stiffeners were designed such as to obtain both global and local buckling shapes. Numerical simulations (FEA), based on the test girder geometry, the measured initial geometric imperfections and elastic-plastic material characteristic from the tensile tests, demonstrate a very good agreement with the tests. The initial geometric imperfection study on different verified numerical models shows a limited sensitivity of the panel shear capacity to any kind of imperfection shape variation with amplitude at the allowable fabrication tolerances. Finally, the paper offers some ideas for modelling geometric imperfections with regard to the design or research demands.     

An Analysis of Non-stationary Drought Conditions in Parana State Based on Climate Change Scenarios

Water Resources Management - Climate change affects the hydrological cycle and has a significant influence on water resources, which can lead to environmental and socioeconomic damage caused by...     

Microscopic stress simulation of non-planar chip technologies

Finite element simulations were used to study the thermo-mechanical stress state at the chip corner in a chip–package system. Accurate geometry of a non-planar chip topology was created by digitizing images obtained with a scanning electron microscope through focused ion beam cuts. Nested sub-modeling approach was utilized in order to simulate the a few microns region of interest, which is very small, compared to 1 cm package size. Available material models were used and unavailable materials were characterized. Thermal loads for the complete set of fabrication process from the wafer initialization to the final qualification phase were considered for this work. Cracks arising in passivation due to thermo-mechanical loads were a concern. Stress simulations on this chip–package system were carried out and compared between planar and non-planar geometries of the same. It was found that the accuracy of stress values largely depend on the precise geometry input for simulation. Preliminary finite element models were optimized to achieve accuracy in the simulation results. The stress measured on test chips with integrated stress cells. The simulation results are in good agreement with these experimental values. This also helped to validate the material models and simulation methodology reported in this paper.