Process design of the patterning process of profile grinding wheels

In production environment, grinding is often the last step along the process chain. At this step, the main share of the value chain is already manufactured. Correspondingly, the process result of this step directly influences the product quality. Thus, the avoidance of process induced damages is a major challenge in grinding. The major limiting factor in grinding is the thermal load on the workpiece, which leads to grinding burn and tensile residual stresses. This thermal load can be reduced, as previous fundamental studies have shown, by means of using microstructured grinding wheels. In this paper, the patterning process of profile grinding wheels is investigated with regard to the resulting geometry and the resulting grinding wheel topography. In detail, an analytical model is established and evaluated that enables a design of the patterning process of profile grinding wheels. The presented formulas describe the local depth and width of a pattern over its length of engagement. The influence of the inclination angle of the patterning tool and the profile angle of the grinding wheel on the resulting width and length of one pattern is investigated. Further influencing parameters on the size of a pattern that are investigated are e.g. the radius of the grinding wheel, the radius of the patterning tool, the corner radius of the patterning edge and the speed ratio between the grinding wheel and the patterning tool. In addition, grinding experiments were conducted to validate the process design. The results show a high correlation between the calculated and the resulting patterns on the grinding wheel as well as that a decrease in cutting forces can be achieved by this approach. When maintaining the workpiece and grinding wheel load, the productivity of the profile grinding process can be increased in this way

Standardised cement augmentation of the PFNA using a perforated blade: A new technique and preliminary clinical results. A prospective multicentre trial

Producción CientíficaPertrochanteric fractures are a rising major health-care problem in the elderly and their operative stabilisation techniques are still under discussion. Furthermore, complications like cut-out are reported to be high and implant failure often is associated with poor bone quality. The PFNA1 with perforated blade offers a possibility for standardised cement augmentation using a polymethylmethacrylate (PMMA) cement which is injected through the perforated blade to enlarge the load-bearing surface and to diminish the stresses on the trabecular bone. The current prospective multicentre study was undertaken to evaluate the technical performance and the early clinical results of this new device. In nine European clinics, 59 patients (45 female, mean age 84.5 years) suffering from an osteoporotic pertrochanteric fracture (Arbeitsgemeinschaft fu¨ r Osteosynthesefragen, AO-31) were treated with the augmented PFNA1. Primary objectives were assessment of operative and postoperative complications, whereas activities of daily living, pain, mobility and radiologic parameters, such as cement distribution around the blade and the cortical thickness index, were secondary objectives. The mean follow-up time was 4 months where we observed callus healing in all cases. The surgical complication rate was 3.4% with no complication related to the cement augmentation. More than onehalf of the patients reached their prefracture mobility level within the study period. A mean volume of 4.2 ml of cement was injected. We did not find any cut-out, cut through, unexpected blade migration, implant loosening or implant breakage within the study period. Our findings lead us to conclude that the standardised cement augmentation using the perforated blade for pertrochanteric fracture fixation enhances the implant anchorage within the head–neck fragment and leads to good functional results

Environmental changes and violent conflict

This letter reviews the scientific literature on whether and how environmental changes affect the risk of violent conflict. The available evidence from qualitative case studies indicates that environmental stress can contribute to violent conflict in some specific cases. Results from quantitative large-N studies, however, strongly suggest that we should be careful in drawing general conclusions. Those large-N studies that we regard as the most sophisticated ones obtain results that are not robust to alternative model specifications and, thus, have been debated. This suggests that environmental changes may, under specific circumstances, increase the risk of violent conflict, but not necessarily in a systematic way and unconditionally. Hence there is, to date, no scientific consensus on the impact of environmental changes on violent conflict. This letter also highlights the most important challenges for further research on the subject. One of the key issues is that the effects of environmental changes on violent conflict are likely to be contingent on a set of economic and political conditions that determine adaptation capacity. In the authors' view, the most important indirect effects are likely to lead from environmental changes via economic performance and migration to violent conflict. © 2012 IOP Publishing Ltd

Replication data for: Regime Type, Coalition Size, and Victory

Studies of regime type and war show that democracies tend to win the wars they fight, but questions remain about why this is the case. A simple, if under-appreciated, explanation for democratic success is that democracies fight alongside larger and more powerful coalitions. Coalition partners bring additional material capabilities and may also provide intangible benefits to the war effort, such as increased legitimacy or confidence. Democracies may also find it less costly to join coalitions, as democratic war aims may be easier to apportion among the victors without diluting the spoils. Evaluating our hypotheses in a sample of all wars (or all militarized disputes) during the period 1816-2000, we find that democracies fight alongside larger coalitions and that states fighting alongside larger coalitions are more likely to win major contests. Coalition size subsumes most (and in some specifications all) of the direct effect of regime type on victory