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

The European Ryegrass Core Collection: A Tool to Improve the Use of Genetic Resources

A core collection of 162 populations of ryegrass (Lolium perenne) native to 18 European countries, is being evaluated across Europe in a multi-country trial. Each participating country contributed the lesser of 10% or 25 accessions from its collection of native populations. The accessions are being grown at 18 sites in 17 countries. Quick, cheap protocols were developed for evaluation. Preliminary results are presented for performance during the first winter. Populations of northern origin showed uniformly low winter damage and low winter growth at all evaluation sites. Populations of Mediterranean origin were more affected by the environment used for evaluation, developing higher winter yield at sites with mild winters, lower winter yield where winters were colder, and suffering severe damage at sites with the coldest winters

Red Oak Seedlings as Indicators of Deer Browse Pressure: Gauging the Outcome of Different White-Tailed Deer Management Approaches

After decades of high deer populations, North American forests have lost much of their previous biodiversity. Any landscape‐level recovery requires substantial reduc‐ tions in deer herds, but modern societies and wildlife management agencies appear unable to devise appropriate solutions to this chronic ecological and human health crisis. We evaluated the effectiveness of fertility control and hunting in reducing deer impacts at Cornell University. We estimated spring deer populations and planted Quercus rubra seedlings to assess deer browse pressure, rodent attack, and other factors compromising seedling performance. Oak seedlings protected in cages grew well, but deer annually browsed ≥60% of unprotected seedlings. Despite female ster‐ ilization rates of \u3e90%, the deer population remained stable. Neither sterilization nor recreational hunting reduced deer browse rates and neither appears able to achieve reductions in deer populations or their impacts. We eliminated deer sterilization and recreational hunting in a core management area in favor of allowing volunteer arch‐ ers to shoot deer over bait, including at night. This resulted in a substantial reduction in the deer population and a linear decline in browse rates as a function of spring deer abundance. Public trust stewardship of North American landscapes will require a fundamental overhaul in deer management to provide for a brighter future, and oak seedlings may be a promising metric to assess success. These changes will re‐ quire intense public debate and may require new approaches such as regulated com‐ mercial hunting, natural dispersal, or intentional release of important deer predators (e.g., wolves and mountain lions). Such drastic changes in deer management will be highly controversial, and at present, likely difficult to implement in North America. However, the future of our forest ecosystems and their associated biodiversity will depend on evidence to guide change in landscape management and stewardship

Improving the implementation of health workforce policies through governance: a review of case studies

<p>Abstract</p> <p>Introduction</p> <p>Responsible governance is crucial to national development and a catalyst for achieving the Millennium Development Goals. To date, governance seems to have been a neglected issue in the field of human resources for health (HRH), which could be an important reason why HRH policy formulation and implementation is often poor. This article aims to describe how governance issues have influenced HRH policy development and to identify governance strategies that have been used, successfully or not, to improve HRH policy implementation in low- and middle-income countries (LMIC).</p> <p>Methods</p> <p>We performed a descriptive literature review of HRH case studies which describe or evaluate a governance-related intervention at country or district level in LMIC. In order to systematically address the term 'governance' a framework was developed and governance aspects were regrouped into four dimensions: 'performance', 'equity and equality', 'partnership and participation' and 'oversight'.</p> <p>Results and discussion</p> <p>In total 16 case studies were included in the review and most of the selected studies covered several governance dimensions. The dimension 'performance' covered several elements at the core of governance of HRH, decentralization being particularly prominent. Although improved equity and/or equality was, in a number of interventions, a goal, inclusiveness in policy development and fairness and transparency in policy implementation did often not seem adequate to guarantee the corresponding desirable health workforce scenario. Forms of partnership and participation described in the case studies are numerous and offer different lessons. Strikingly, in none of the articles was 'partnerships' a core focus. A common theme in the dimension of 'oversight' is local-level corruption, affecting, amongst other things, accountability and local-level trust in governance, and its cultural guises. Experiences with accountability mechanisms for HRH policy development and implementation were lacking.</p> <p>Conclusion</p> <p>This review shows that the term 'governance' is neither prominent nor frequent in recent HRH literature. It provides initial lessons regarding the influence of governance on HRH policy development and implementation. The review also shows that the evidence base needs to be improved in this field in order to better understand how governance influences HRH policy development and implementation. Tentative lessons are discussed, based on the case studies.</p

Atomic force microscopy analysis of nanoparticles in non-ideal conditions

Nanoparticles are often measured using atomic force microscopy or other scanning probe microscopy methods. For isolated nanoparticles on flat substrates, this is a relatively easy task. However, in real situations, we often need to analyze nanoparticles on rough substrates or nanoparticles that are not isolated. In this article, we present a simple model for realistic simulations of nanoparticle deposition and we employ this model for modeling nanoparticles on rough substrates. Different modeling conditions (coverage, relaxation after deposition) and convolution with different tip shapes are used to obtain a wide spectrum of virtual AFM nanoparticle images similar to those known from practice. Statistical parameters of nanoparticles are then analyzed using different data processing algorithms in order to show their systematic errors and to estimate uncertainties for atomic force microscopy analysis of nanoparticles under non-ideal conditions. It is shown that the elimination of user influence on the data processing algorithm is a key step for obtaining accurate results while analyzing nanoparticles measured in non-ideal conditions