32 research outputs found

    Incipient Separation in Shock Wave Boundary Layer Interactions as Induced by Sharp Fin

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    The incipient separation induced by the shock wave turbulent boundary layer interaction at the sharp fin is the subject of present study. Existing theories for the prediction of incipient separation, such as those put forward by McCabe (1966) and Dou and Deng (1992), can have thus far only predicting the direction of surface streamline and tend to over-predict the incipient separation condition based on the Stanbrook's criterion. In this paper, the incipient separation is firstly predicted with Dou and Deng (1992)'s theory and then compared with Lu and Settles (1990)' experimental data. The physical mechanism of the incipient separation as induced by the shock wave/turbulent boundary layer interactions at sharp fin is explained via the surface flow pattern analysis. Furthermore, the reason for the observed discrepancy between the predicted and experimental incipient separation conditions is clarified. It is found that when the wall limiting streamlines behind the shock wave becomes\ aligning with one ray from the virtual origin as the strength of shock wave increases, the incipient separation line is formed at which the wall limiting streamline becomes perpendicular to the local pressure gradient. The formation of this incipient separation line is the beginning of the separation process. The effects of Reynolds number and the Mach number on incipient separation are also discussed. Finally, a correlation for the correction of the incipient separation angle as predicted by the theory is also given.Comment: 34 pages; 9 figure

    Human Resource Flexibility as a Mediating Variable Between High Performance Work Systems and Performance

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    Much of the human resource management literature has demonstrated the impact of high performance work systems (HPWS) on organizational performance. A new generation of studies is emerging in this literature that recommends the inclusion of mediating variables between HPWS and organizational performance. The increasing rate of dynamism in competitive environments suggests that measures of employee adaptability should be included as a mechanism that may explain the relevance of HPWS to firm competitiveness. On a sample of 226 Spanish firms, the study’s results confirm that HPWS influences performance through its impact on the firm’s human resource (HR) flexibility

    Why Project Size Matters for Contract Choice

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    The contractual mechanism of software development outsourcing, typically either fixed-price (FP) or time-and-materials (T&M), determines the nature of incentives, risk sharing, and coordination between client and vendor. While software engineering considers project size as crucial for project planning and success, neither economic nor organizational theory considers size per se among the determinants of contract choice. In this paper, we address the gap between the centrality of project size in the software engineering literature and the attention it receives in software contracting research by modeling and testing the association between project size and contract choice. Existing empirical evidence indicates that FP contracts are appropriate for small development efforts whereas T&M contracts are suitable for larger projects, based on the reasoning that cost and schedule are difficult to estimate in larger projects. This prediction that size is directly associated with contract choice is the basis upon which two models are developed. The first model draws on the contracting efficiency approach to hypothesize that the effect of project size on contract choice is mediated by project detail. The second model draws on the contingency approach to software development risk management to hypothesize that the effect of project size on contract choice is moderated by project detail and vendor familiarity. We test these models using a large portfolio of software development contracts entered into by a leading European bank, and the results confirm that both mediation and moderation are at play
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