Influence of parameter changes to stability behavior of rotors

The occurrence of unstable vibrations in rotating machinery requires corrective measures for improvement of the stability behavior. A simple approximate method is represented to find out the influence of parameter changes to the stability behavior. The method is based on an expansion of the eigenvalues in terms of system parameters. Influence coefficients show the effect of structural modifications. The method first of all was applied to simple nonconservative rotor models. It was approved for an unsymmetric rotor of a test rig

A three-dimensional model for stage I-crack propagation

The propagation of short fatigue cracks is simulated by means of a three-dimensional model. Under loading conditions in the high cycle fatigue regime the growth of these cracks can determine up to 90% of the lifetime of a component. Stage I-cracks often grow on slip bands and exhibit strong interactions with microstructural features such as grain boundaries. Experimental investigations have shown that the crack propagation rate decreases significantly when the crack tip approaches a grain boundary and even a complete stop of crack propagation is possible. In order to consider the real three-dimensional orientation of a slip plane an existing two-dimensional mechanism-based model (Künkler el al., 2008) is extended to simulate the propagation of a three-dimensional surface crack. The crack geometry is modelled using dislocation loops (Hills et al., 1996), which represent the relative displacement between the crack flanks. To describe the propagation of stage Icracks elastic-plastic material behaviour is considered by allowing a plastic deformation due to slip on the active slip plane. The extension of the plastic zone is blocked by the grain boundary. The crack propagation law is based on the range of the crack tip slide displacement, which is obtained from the plastic solution. Behind the grain boundary the shear stress field is evaluated. Results show that a high twist angle between the slip planes causes a significant decrease in the stresses, which can yield a crack stop

Simulation of Deformation-induced Martensite Formation and its Influence on the Resonant Behavior in the Very High Cycle Fatigue (VHCF) Regime

AbstractThe exploration of fatigue mechanisms in the VHCF regime is gaining importance since many components have to withstand a very high number of loading cycles due to high frequency or long product life. In this regime, particular attention is paid to the period of fatigue crack initiation and thus the localization of plastic deformation. The resonant behavior of a metastable austenitic stainless steel (AISI304) is studied experimentally in the VHCF regime and shows a distinct transient characteristic. The major contribution of this work is to obtain a physically-based understanding of this characteristic by modeling the underlying microstructural mechanisms and their influence on the resonant behavior. Microscopic examinations indicate that AISI304 undergoes deformation-induced martensite formation starting mostly at intersecting shear bands during fatigue. Therefore, a microstructural shear band model [Hilgendorff et al. (2013)] is extended regarding the mechanism of deformation-induced martensite formation. The model accounts for the microstructural mechanisms occurring in shear bands as documented by experimental results, and nucleation of martensite is assumed to occur at intersecting shear bands following the Olsen-Cohen nucleation model (1972) in combination with the Bogers-Burgers mechanism (1964). The simulation model is numerically solved using the two-dimensional (2-D) boundary element method. By using this method, a 2-D microstructure can be modeled considering grain orientations as well as individual anisotropic elastic properties in each grain. The resonant behavior is characterized by evaluating the force-displacement hysteresis loop. Results show that plastic deformation in shear bands and deformation-induced martensite formation have a major impact on the resonant behavior in the very high cycle fatigue (VHCF) regime

Asymmetric base-pair opening drives helicase unwinding dynamics

The opening of a Watson-Crick double helix is required for crucial cellular processes, including replication, repair, and transcription. It has long been assumed that RNA or DNA base pairs are broken by the concerted symmetric movement of complementary nucleobases. By analyzing thousands of base-pair opening and closing events from molecular simulations, here, we uncover a systematic stepwise process driven by the asymmetric flipping-out probability of paired nucleobases. We demonstrate experimentally that such asymmetry strongly biases the unwinding efficiency of DNA helicases toward substrates that bear highly dynamic nucleobases, such as pyrimidines, on the displaced strand. Duplex substrates with identical thermodynamic stability are thus shown to be more easily unwound from one side than the other, in a quantifiable and predictable manner. Our results indicate a possible layer of gene regulation coded in the direction-dependent unwindability of the double helix

Insulin Tolerance Test under Anaesthesia to Measure Tissue-specific Insulin-stimulated Glucose Disposal.

Insulin resistance is a pathophysiological state defined by impaired responses to insulin and is a risk factor for several metabolic diseases, most notably type 2 diabetes. Insulin resistance occurs in insulin target tissues including liver, adipose and skeletal muscle. Methods such as insulin tolerance tests and hyperinsulinaemic-euglycaemic clamps permit assessment of insulin responses in specific tissues and allow the study of the progression and causes of insulin resistance. Here we detail a protocol for assessing insulin action in adipose and muscle tissues in anesthetized mice administered with insulin intravenously

Highly sensitive electromechanical piezoresistive pressure sensors based on large-area layered PtSe2_{2} films

Two-dimensional (2D) layered materials are ideal for micro- and nanoelectromechanical systems (MEMS/NEMS) due to their ultimate thinness. Platinum diselenide (PtSe$_{2}$), an exciting and unexplored 2D transition metal dichalcogenides (TMD) material, is particularly interesting because its scalable and low temperature growth process is compatible with silicon technology. Here, we explore the potential of thin PtSe$_{2}$ films as electromechanical piezoresistive sensors. All experiments have been conducted with semimetallic PtSe$_{2}$ films grown by thermally assisted conversion of Pt at a CMOS-compatible temperature of 400{\deg}C. We report high negative gauge factors of up to -84.8 obtained experimentally from PtSe$_{2}$ strain gauges in a bending cantilever beam setup. Integrated NEMS piezoresistive pressure sensors with freestanding PMMA/PtSe$_{2}$ membranes confirm the negative gauge factor and exhibit very high sensitivity, outperforming previously reported values by orders of magnitude. We employ density functional theory (DFT) calculations to understand the origin of the measured negative gauge factor. Our results suggest PtSe$_{2}$ as a very promising candidate for future NEMS applications, including integration into CMOS production lines.Comment: 33 pages, 5 figures, including supporting information with 10 figure

Serological survey for mycoplasma hyopneumoniae in free-living wild boars from Campos Gerais region, Paraná, Brasil.

The south region of Brazil was responsible for 80.3% of total pork meat export in the country in 2015 (2), with the state of Paraná accountable for 21% of the total pork meat production in that year. Pig farming represented 5.7% of the agricultural gross income of the state in 2016, and the Campos Gerais region accounted for 13.2% of that amount (2). Wild boars are the result of crossbreeding between boars (Sus scrofa scrofa) and domestic pigs (Sus scrofa domesticus). The total population of free-living wild boars in Brazil is unknown (11), but sightings are common in the crop fields and near livestock farms of different regions of Paraná state, including in Campos Gerais (9). The health status of pig herds is important in terms of maintenance and growth of pork production and exports and there are evidences that domestic pigs and wild boars share vulnerabilities in certain viral and bacterial pathogen infections (12). Mycoplasma hyopneumoniae (Mhyo) is a bacterial pathogen that causes porcine enzootic pneumonia, an economically important disease that affects both domestic pigs and wild boars. Mhyo was first isolated in 1965, simultaneously in the United Kingdom (UK) and in the United States of America (USA) (3; 7). Economic losses related to this pathogen and mycoplasmal pneumonia in pig herds are associated with decreased feed efficiency, reduced average of the daily weight gain, and increased medication costs. Thus, knowing the health status of free-living wild boars in the regards of this pathogen is important for the biosecurity of the pork production. The aim of this study was to investigate antibodies against Mhyo in serum samples of free-living wild boars in Campos Gerais region