The awd gene of Drosophila melanogaster encodes a nucleoside diphosphate kinase. Killer of prune (Kpn) is a mutation in the awd gene which substitutes Ser for Pro at position 97 and causes dominant lethality in individuals that do not have a functional prune gene. This lethality is not due to an inadequate amount of nucleoside diphosphate (NDP) kinase activity. In order to understand why the prune/Killer of prune combination is lethal, even in the presence of an adequate NDP kinase specific activity level, and to understand the biochemical basis for the conditional lethality of the awd Kpn mutation, we generated second site mutations which revert this lethal interaction. All of the 12 revertants we recovered are second site mutations of the awd Kpn gene. Three revertants have deletions of the awd Kpn protein coding region. Two revertants have substitutions of the initiator methionine and do not accumulate KPN protein. Seven revertants have amino acid substitutions of conserved residues that are likely to affect the active site: five of these have no enzymatic activity and two have a very low level of specific activity. These data suggest that an altered NDP kinase activity is involved in the mechanism underlying the conditional lethality of the awd Kpn mutation.

The application of extreme loads such as impact and blast may lead to progressive collapse and the robustness of a structure must be considered in this context. Although extensive studies had been carried out over the past decades to study the load resisting mechanism of reinforced concrete (RC) frames to prevent progressive collapse, the effects of high-strength-concrete (HSC) on progressive collapse resistance capacity is still unclear. Therefore, six tests of RC frames with different span-todepth ratio and concrete strength were conducted in present study. Among them, three are HSC frames and the remaining are normal strength concrete frames. It was found that the use of HSC could further enhance the compressive arch action (CAA) capacity, especially for those with low span-to-depth ratio. On the other hand, HSC can reduce the tensile catenary action (TCA) capacity at large deformation stage, primarily because of higher bond stress between concrete and rebar, leading to earlier fracture of the rebar. The analytical results from the model were compared with the test results. It was found that the refined CAA model could accurately predict the CAA capacity of NSC frames, but not for HSC frames. Moreover, existing model is hard to predict the CAA capacity of the frames with relatively small span-to-depth ratio (less than 7) accurately.

No abstract

No abstract

Many negative factors can influence the progressive collapse resistance of reinforced concrete (RC) frame structures. One of the most important factors is the corrosion of rebar within the structure. With increasing severity of corrosion, the duration, robustness, and mechanical performance can be greatly impaired. One specific side effect of rebar corrosion is the significant loss of protection against progressive collapse. In order to quantify the effects of rebar corrosion on load-resisting mechanisms (compressive arch action (CAA) and tensile catenary action (TCA)) of RC frames, a series of numerical investigations were carried out in this paper. The previous experimental results reported in the literature provide a benchmark for progressive collapse behavior as a sound condition and validate the proposed numerical model. Furthermore, based on the verified numerical model, the CAA and TCA with increasing corrosion and an elapsed time from 0 to 70 years are investigated. Comparing with the conventional empirical model, the proposed numerical model has shown the ability and feasibility in predicting the collapse resistance capacity in structures with corroded rebar. Therefore, this numerical modeling strategy provides comprehensive insights into the change of load-resisting mechanisms in these structures, which can be beneficial for optimizing the design.