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No description available.

No description available.

No description available.

No description available.

No description available.

Simplification of the aerodynamic control of large horizontal axis wind turbines (HAWTs) has been identified as an important step towards improved reliability and reduced cost. At present the majority of large HMrrs use active control to regulate power and loads. A simpler strategy is to use the inherent stalling of the rotor blades in high winds to limit power and loads. Unfortunately the performance of stall regulated HAWTs 1S poorly understood; current performance models often fail to correctly predict peak power levels. The benefits of passive control of power and loads cannot be utilised because of this uncertainty. This study examines the possible reasons for the poor performance of current prediction techniques 1n high winds with the objective of fonmulating a new model. The available experimental evidence suggests that rotor stall is caused by turbulent separation at the rear of the blade aerofoil, growing in extent from the root in increasing wind. This 'picture' of the stalling HAW! rotor forms the basis of the approach. The new model consists of a prescribed vortex wake, first order panel method (extended to represent the viscous region of trailing edge separation) and three dimensional integral boundary layer directly coupled in an iterative scheme. A sensitivity study of rotor indicates that the most important performance to wake geometry factor is the rate at which the wake is convected downstream. However, it is found that stalled power levels are insensitive to wake geometry; the study concludes that the problem of poor prediction of high wind performance lies on the rotor blades. Before using the complete code to calculate the performance of a rotor it 1S first tuned for the aerofoils used on the blade. Aerofoil perfonmance characteristics measured in a wind tunnel are synthesised by the model. Ideally these characteristics should include measured pressure profiles below and above stall. Validation of the complete code against detailed measurements taken under controlled conditions on a three metre diameter machine indicates significant differences in the perfonmance of aerofoil sections on a wind turbine blade when compared to the same section when tested in a wind tunnel. Derived lift coefficients show a reduced lift curve slope and more gentle delayed stall. Similar results are found when the code is applied to two Danish stall regulated machines. These two machines although having very similar geometries and using the same family of aerofoils do however show differences in derived post stall drag. This is thought to be due to the different thickness distributions of the two rotors. The validation and applications of the new model show that it can accurately predict the peak power level of stall regulated machines.

Cardiac Power Output (CPO) has shown to effectively indentify declining cardiac performance in Heart Failure (HF) patients. We compared CPO to other commonly used hemodynamic parameters to establish its usefulness in determining when Mechanical Circulatory Support (MCS) is required. A retrospective study of 28 HF patients previously implanted with MCS were analyzed at 3 stages of pharmacological support. Studied subjects were separated into two categories (survived versus deceased) to compare contractile reserve differences in order to predict when complete cardiac dysfunction was met. CPO and Cardiac Power Index (CPI) were the two hemodynamic parameters that identified remaining contractile reserve in the declining heart (p < 0.05). Other commonly used hemodynamic parameters failed to provide information that can detect the need for MCS. Patients who decreased below 0.70 (Watts) had higher incidences of mortality and /or morbidity. Clinicians who cannot medically manage HF patients above 0.70 W may consider MCS as an alternative treatment to retain hemodynamic stability.

My aim is to provide the foundation for a theory about the duty to prevent harm by investigating how this duty compares and contrasts with the duty not to cause harm. I begin by addressing the moral significance of the difference between killing (causing harm) and letting die (refraining from preventing harm), arguing that neither of the prevalent and rival views ('killing is inherently worse than letting die', and 'killing and letting die are, other things equal, morally equivalent') is entirely acceptable. By analyzing the notion of a morally significant difference I argue that these views are only contrary. I then develop an alternative view which locates the difference between killing and letting die at the level of the general moral prohibitions against such acts, and is grounded on a difference in the 'strength' or 'type' of reason that can justify violations of those prohibitions in relevantly similar circumstances. This account is summarized into three intermediate principles. To develop these principles into a general theory, I introduce and clarify the distinction between negative and positive duties, arguing that it is independent of the distinction between negative and positive acts. After exploring the grounds for and against recognizing the significance of the former distinction, I conclude that while it is significant, and that negative duties are in some sense stricter than positive duties, the prevalent interpretation of "stricter" and its corresponding moral principle are unacceptable. I then develop an alternative definition and a theory entailing (a) that while causing harm is sometimes morally worse than failing to prevent harm (other things equal), it is not always worse, (b) the cases in which it is worse are cases in which the agent's negative or positive duty conflicts with another morally relevant consideration, and (c) that negative duties are stricter than positive duties in that the former are more difficult to justifiably violate. Finally, I defend this theory as one which captures the strong points of the rival views, while escaping their problems, and thus provides both a resolution to the current debates and the foundation for a complete analysis of the duty to prevent harm.