Attitude Control of an Underactuated Planar Multibody System Using Momentum Preserving Internal Torques

In the last few years interest in versatile reconfigurable arrays for space applications has been growing and several concepts tailored for different mission needs have been proposed. Nevertheless, a compelling application that justifies their higher cost and complexity with respect to conventional systems has not yet been found. Here a novel approach to the design of an Attitude Control System (ACS) for small reconfigurable spacecraft is proposed. It shall exploit momentum-preserving internal torques generated by the modules of the multibody array rotating relative to each other. The goal is to achieve better performance in efficiency, accuracy and robustness with respect to state-of-the-art ACSs, which is a bottleneck of small spacecraft technology. This paper investigates the characteristic behaviour of a planar multibody array whose attitude is controlled using internal joint torques. To do this, relevant reorientation trajectories are shown and discussed. With respect to previous work in the field, optimal attitude control trajectories that take into account module impingement are discussed and the dynamics of momentum-preserving manoeuvres is explained in detail from both physical and mathematical points of view. The results demonstrate that further development of the concept is desirable

FDI in hot labour markets: The implications of the war for talent

This paper highlights an inherent contradiction that exists within investment promotion activities in rich countries. Since the financial crisis, many inward investment agencies have shifted their activities from job creation per se to seeking to attract investment in high-tech activities. Such knowledge-intensive sectors are engaged in what has become referred to as “the war for talent”, so locations need to understand their value proposition to firms, especially where labour is tight. This paper explores the implications of this, in terms of the impact on employment and earnings of high skilled labour. We show that, because skill shortages already exist in many of these sectors, seeking to attract inward investment in these sectors simply causes the earnings of such workers to be bid up, and employment in the incumbent sector to fall. We highlight the over-riding importance that firms place on the availability of skilled labour when determining locations, and how policies which promote labour market flexibility, particularly through investment in skills to address skill shortages, can significantly mitigate the adverse effects, which tend to be more keenly felt in poorer regions of Europe where skilled labour is in even shorter supply

Timing of Procedure and Compliance With Outpatient Endoscopy Among an Underserved Population in an Inner-City Tertiary Institution

Purpose: Anecdotal evidence suggests that patient compliance with colonoscopy is poorer with Monday procedures and better during the winter months because there is not much else to do. We examined patients\u27 compliance with scheduled outpatient endoscopy by time of the day, days of the week, and seasons of the year. Methods: We included 2873 patients who were scheduled for endoscopy from September 2009 to August 2010. Compliant patients were those who showed up for their procedures whereas noncompliant patients were those who did not show up without canceling or rescheduling their procedures up to 24 hours before their scheduled procedures. We used logistic regression models to evaluate the association between the timing of the scheduled procedure and compliance. Results: A total of 574 (20%) patients did not show up. There was no difference in compliance by time of day of the procedures. However, when compared with patients scheduled for procedures on Monday, there was a trend towards improved compliance as the week progressed, becoming significant on Friday (odds ratio 1.46; 95% confidence interval 1.06-2.00). There was also better compliance in the warmer months. Conclusions: Noncompliance with outpatient endoscopy is substantial among underserved populations with limited predictive pattern of compliance by the timing of the procedures. © 2012 Elsevier Inc