This paper presents a systematic approach based on Mixed Integer Linear Programming for finding an optimal singularity-free reconfiguration path of the 5-DOF Gantry-Tau parallel kinematic machine. The results in the paper demonstrate that singularity-free reconfiguration (change of assembly mode) of the machine is possible, which significantly increases the usable workspace. The method has been applied to a full-scale prototype and the singularity-free path has been verified both in simulations and with physical experiments using real-time control of the prototype. The toolpoint positions have been verified by using measurements from a high precision laser tracker.

In this paper the invited session and the 4 original contributions are described first. Then the details of the first paper in the invited session is presented. In this first paper a new method for calculating the dynamic stiffness (frequency response) of parallel kinematic machines (PKMs) with six links, or Hexapods, is presented. The method assumes that each link and universal joint can be described by a mass-spring-damper model and calculates the transfer function from a Cartesian force or torque to Cartesian position or orientation. The new method has been used to benchmark two versions of the Gantry-Tau PKM, a relatively new PKM which has been designed to achieve a large workspace to installation space ratio, while at the same time achieve higher static and dynamic stiffness compared to serial-type industrial robots. The benchmark results presented in this paper show that these goals can be achieved in large sections of the workspace envelope. The benchmark also shows that machining centre specifications can be met if the location and dimensions of the work objects are known at the design stage.

The Gantry-Tau is a parallel kinematic manipulator (PKM) that overcomes the workspace limitations of typical PKMs, while retaining PKM benefits such as small moving masses and high stiffness. An experimental verification of the dynamics of the Gantry-Tau is presented for the first time in this paper. A new friction model based on axial forces in the links of the 3-DOF Gantry-Tau combined with a recent inverse dynamics model for parallel kinematic machines is also presented and verified experimentally. The inverse dynamics model combining the friction model and the Jacobians shows a good match to the measured linear actuator forces from a full-scale prototype machine.

Recent inquiries into the observed positive relationship between wages and firm size suggest that unobservable characteristics give rise to a sorting of workers into large and small firms. Specifically, smaller firms tend to offer more unstable employment prospects and will tend to attract workers who are themselves unstable. As demonstrated by empirical analysis, the risk of permanent employment separation (i.e. the risk of firm failure) is in fact negatively correlated with firm size. Moreover, when this measure of employment risk is included as a determinant of wages, the independent influence of firm size on wages vanishes. These results suggest that firm size merely proxies for the risk of firm failure by capturing unobservable sources of heterogeneity in workers and firms.

This paper describes the workspace of the 5-axis variant of the Gantry-Tau parallel manipulator. The 5-axis movements are achieved by extending the 3-axis Gantry-Tau with two linear telescope link actuators. A new analytic inverse kinematic solution for the 5-axis machine and an analysis of the collision-free zones of the machine are presented. The results show that by careful design of the manipulated platform, a collision-free 5-axis workspace can be achieved. The achievable re-orientation of 30 degrees in the entire workspace is large for a parallel kinematic machine

Objective: Cardiopulmonary bypass (CPB) is associated with gut mucosal hypoxia, which may contribute to gastrointestinal complications. We examined gastric mucosal oxygenation together with whole-body oxygen flux in low-risk patients undergoing coronary artery bypass grafting (CABG) with and without CPB. Methods: Fifty-four patients undergoing primary CABG by the same surgeon were randomized into either on-pump (ONCAB, n = 27) or off-pump (OPCAB, n = 27) groups. The ONCAB group underwent mild hypothermic (35degreesC) pulsatile CPB with arterial line filtration. Each patient underwent perioperative monitoring with continuous tonometry and cardiac output devices. Gastric intramucosal pH (pHi), gastric-arterial carbon dioxide partial pressure difference (CO2 gap), whole-body oxygen delivery (DO,) and consumption (VO2) and whole-body oxygen extraction fraction were measured at sequential time-points intraoperatively and up to 6 h postoperatively. Anaesthetic management was standardized. Results: Both groups had similar demographic makeup and extent of revascularization (ONCAB 2.6 +/- 0.9 grafts versus OPCAB 2.5 +/- 0.8 grafts; P = 0.55). The ONCAB group had a mean (+/-SD) CPB time of 62 +/- 25 min and aortic cross-clamp time of 32 +/- 11 min. In both groups there was a similar and progressive drop in pHi intraoperatively. Postoperatively, there was a gradual separation between the groups with ONCAB patients showing no further decline in pHi, while further deterioration was observed in the OPCAB group up to 6 h postoperatively. There was a significant difference between the groups over time (P = 0.03). There was a corresponding progressive rise in CO2 gap perioperatively in both groups, with ONCAB patients demonstrating superior preservation of gastric mucosal oxygenation in the early postoperative period. Global oxygen utilization measurements showed superior DO2 and VO2 in the OPCAB group throughout the study. Conclusions: Despite superior global oxygen flux associated with beating-heart revascularization, gastric mucosal hypoxia occurred to similar extents in both groups with worsening trends for the OPCAB patients postoperatively. The splanchnic pathophysiology during beating-heart revascularization should be further explored. (C) 2003 Elsevier Science B.V. All rights reserved.

Foucault developed theories on the exercise of power so that they might be applied to geographically and historically specific instances. In this paper I analyze the processes of power recently in operation on the black population of the Cabrini-Green housing development in Chicago. Previously excluded from the larger urban matrix, the residents have been subject to a variety of forces-involving discipline, discursive containment, physical repression, and deterrence -as attempts have been made to 'reclaim' the area and regulate the sociospatial control of bodies. Issues of visibility, knowledge, and situation are paramount both in the processes of power involved in 'rehabilitating' Cabrini-Green and in the residents' resistance to such outside intervention.