Jonathan W. Vogt and Tracie J. Barber
Investigations into ground effect phenomena about aerofoils are typically conducted on either an upright (lift‐producing) or inverted (downforce‐producing) configuration, in…
Abstract
Purpose
Investigations into ground effect phenomena about aerofoils are typically conducted on either an upright (lift‐producing) or inverted (downforce‐producing) configuration, in isolation. This limited approach does not promote a holistic understanding of how ground effect influences aerofoils. This paper aims to address this issue.
Design/methodology/approach
A two‐dimensional computational fluid dynamics investigation was conducted on the highly cambered Tyrrell aerofoil, in both its upright and inverted configurations, in order to better understand ground effect phenomena by observing how it influences each configuration differently. The trends in force and flow field behaviour were observed at various ground clearances through observation of the normal and drag forces and pressure coefficient plots. The aerofoil was held stationary and at a constant angle of attack of 6 degrees, with a moving ground plane to simulate the correct relative motion.
Findings
The different ground effect mechanisms that occur on each configuration are highlighted and explained. It is shown how ground effect manifests through these different phenomena and that there are general or overarching mechanisms that influence both configurations. These general mechanisms allow unintuitive phenomena, such as the downward movement of the stagnation point on both configurations, to be explained.
Originality/value
Overarching mechanisms of ground effect are discovered which are of value in any situation in which ground effect aerodynamics is to be exploited.
Details
Keywords
Pujith Rajaguru Senapathy Vijayaratnam, John Arthur Reizes and Tracie Jacqueline Barber
Stent malapposition is one of the most significant precursors of stent thrombosis and restenosis. Adverse haemodynamics may play a key role in establishing these diseases…
Abstract
Purpose
Stent malapposition is one of the most significant precursors of stent thrombosis and restenosis. Adverse haemodynamics may play a key role in establishing these diseases, although numerical studies have used idealised drug transport models to show that drug transport from malapposed drug-eluting stent struts can be significant. This paper aims to study whether drug transport from malapposed struts is truly significant. Another aim is to see whether a streamlined strut profile geometry – with a 61% smaller coating but a 32% greater coating-tissue contact area – can mitigate the adverse haemodynamics associated with stent malapposition while enhancing drug uptake.
Design/methodology/approach
Two- and three-dimensional computational fluid dynamics simulations were used in this study. Unlike past simulations of malapposed drug-eluting stent struts, a qualitatively validated drug-transport model which simulates the non-uniform depletion of drug within the drug coating was implemented.
Findings
It was shown that even a 10-µm gap between the strut and tissue dramatically reduces drug uptake after 24 h of simulated drug transport. Furthermore, the streamlined strut profile was shown to minimise the adverse haemodynamics of malapposed and well-apposed stent struts alike and enhance drug uptake.
Originality/value
Unlike prior numerical studies of malapposed stent struts, which did not model the depletion of drug in the drug coating, it was found that stent malapposition yields negligible drug uptake. The proposed semicircular-profiled strut was also shown to be advantageous from a haemodynamic and drug transport perspective.
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Laurie Krigman and Mia L. Rivolta
This paper aims to investigate the roles of non-CEO inside directors (NCIDs) in the new CEO-firm matching process using the context of unplanned CEO departures when immediate CEO…
Abstract
Purpose
This paper aims to investigate the roles of non-CEO inside directors (NCIDs) in the new CEO-firm matching process using the context of unplanned CEO departures when immediate CEO succession planning becomes a sole board responsibility. Although critics argue that inside directors decrease the monitoring effectiveness of a board, inside directors arguably possess superior firm-specific experience and knowledge that can be beneficial during the leadership transition.
Design/methodology/approach
The authors use a comprehensive, manually collected data set of unplanned CEO departures from 1993 to 2012.
Findings
The authors find that NCIDs play an important role in the CEO transitioning process. They help firms identify qualified inside replacements and provide stability as the new permanent or interim CEO. In addition, NCIDs facilitate the transfer of information and help the new external CEOs succeed. They show that the longer the NCID stays with the company, the longer the tenure of the new CEO. They also document that the presence of NCIDs improves operating and stock performance; especially when the new CEO is hired from outside of the firm.
Practical implications
The impact of NCIDs is particularly important when the firm hires an outsider as the new CEO. These results suggest that board composition affects frictions in the CEO labor market.
Originality/value
The literature has predominantly focused on the downside of having inside directors. Too many inside directors on a firm’s board is often associated with ineffective boards and entrenchment. To the contrary, the authors focus on a potential benefit of having inside directors.