Search

In recent years, there has been a growing interest in the use of fault analysis techniques in unmanned marine vehicles (UMVs) owing to their significant impact on marine operations. This study presents a novel approach to the diagnosis of unbalanced load (blades damage) faults in an electric thruster motor in UMV propulsion systems based on orthogonal fuzzy neighbourhood discriminative analysis for feature dimensionality reduction. The diagnosis approach is based on the use of discrete wavelet transforms as a feature extraction tool and the optimal number of mother wavelet function and levels of resolution by analysing the vibration and current signals. As a result of analysis and comparisons, the Deubechies 12 (db12) wavelet and level 8 were chosen. A dynamic recurrent neural network was chosen for fault classification and level of fault severity prediction was implemented. Four faulty conditions were analysed under laboratory conditions and these were recreated by damaging the blades of a motor. The results obtained from the simulation demonstrate the effectiveness and reliability of the proposed methodology in classifying the different faults with greater speed and accuracy compared to existing methods. [ABSTRACT FROM AUTHOR]

Oxidative stress has been implicated in the pathogenesis of acute pancreatitis, a severe and debilitating inflammation of the pancreas that carries a significant mortality, and which imposes a considerable financial burden on the health system due to patient care. Although extensive efforts have been directed towards the elucidation of critical underlying mechanisms and the identification of novel therapeutic targets, the disease remains without a specific therapy. In experimental animal models of acute pancreatitis, increased oxidative stress and decreased antioxidant defences have been observed, changes also detected in patients clinically. However, despite the promise of studies evaluating the effects of antioxidants in these model systems, translation to the clinic has thus far been disappointing. This may reflect many factors involved in the design of both preclinical and clinical evaluations of antioxidant therapy, not least the fact that most experimental studies have focussed on pre-treatment rather than post-injury assessment. This review has examined evidence relating to the involvement of oxidative stress in the pathophysiology of acute pancreatitis, focussing on experimental models and the clinical experience, including the experimental techniques employed and potential of antioxidant therapy. [ABSTRACT FROM AUTHOR]

A general saddlepoint/Monte Carlo method to approximate (conditional) multivariate probabilities is presented. This method requires a tractable joint moment generating function (m.g.f.), but does not require a tractable distribution or density. The method is easy to program and has a third-order accuracy with respect to increasing sample size in contrast to standard asymptotic approximations which are typically only accurate to the first order. The method is most easily described in the context of a continuous regular exponential family. Here, inferences can be formulated as probabilities with respect to the joint density of the sufficient statistics or the conditional density of some sufficient statistics given the others. Analytical expressions for these densities are not generally available, and it is often not possible to simulate exactly from the conditional distributions to obtain a direct Monte Carlo approximation of the required integral. A solution to the first of these problems is to replace the intractable density by a highly accurate saddlepoint approximation. The second problem can be addressed via importance sampling, that is, an indirect Monte Carlo approximation involving simulation from a crude approximation to the true density. Asymptotic normality of the sufficient statistics suggests an obvious candidate for an importance distribution. The more general problem considers the computation of a joint probability for a subvector of random T, given its complementary subvector, when its distribution is intractable, but its joint m.g.f. is computable. For such settings, the distribution may be tilted, maintaining T as the sufficient statistic. Within this tilted family, the computation of such multivariate probabilities proceeds as described for the exponential family setting. [ABSTRACT FROM AUTHOR]

This paper presents an integrated approach to the design of an obstacle avoidance system for autonomous underwater vehicles. A type of incremental stochastic algorithm known as rapidly-exploring random tree (RRT) is merged with a manoeuvre automaton (MA) representation to form the motion planner. The improved planner is not only capable of taking into account the dynamics of the system, but it also allows complex non-linear manoeuvres to be performed. In addition, it is highly computationally efficient. This paper also extends it to take into account dynamic targets. The output trajectory from the planner is then tracked using a kinematic based state-dependent Riccati equation (SDRE) controller. In other words, by omitting the requirement of a dynamic model of the system, one can extend the application to a more encompassing types of vehicle whilst reducing the number of tuning parameters. Detailed simulation studies are conducted using a non-linear AUTOSUB model to investigate the feasibility of the proposed methods. [ABSTRACT FROM AUTHOR]

Autonomous underwater vehicle (AUV) research and development is on the verge of reaching maturity yet applications are very few. The cost associated with an AUV development particularly of the onboard sensors, power requirements and underwater testing have imposed a significant constraint on its development. Numerous ideas regarding underwater vehicle control have been proposed in the literature however the lack of test equipment confines one to simulations only. The aim of this paper is to introduce fresh results on the application of a genetic algorithm based model predictive controller (GA-MPC) to an actual AUV. These results are significant since to the authors’ knowledge, this is the first known application of an online GA operating in an underwater vehicle in real time. The current hardware and software configuration of the vehicle is also elucidated. The broader aim of the research is to produce a low cost AUV facility to be exploited by other underwater research groups within the UK. The results mainly consists of line of sight (LOS) tracking missions using the GA-MPC autopilot with and without an umbilical. It is demonstrated that the controller performs remarkably well in a real time environment despite the existence of disturbances and ever present modelling uncertainty. [ABSTRACT FROM AUTHOR]

This paper describes the use of specially devised multiple‐choice objective tests in outlining knowledge and ‘understanding’ ‐‐ acquired before entry into university by newly enrolled physics undergraduates, and in determining where gaps occur. [ABSTRACT FROM PUBLISHER]

The article discusses various reports published within the issue including one on the design and implementation of a mission control system for an autonomous underwater vehicles and another on the various aspects of navigation.

'Just-world' beliefs (Lerner, 1998) are assumed to benefit individuals by making the world seem orderly, controllable, and meaningful, but also to have adverse social consequences, in the form of indifferent and even harsh responses to unfortunate others (e.g., Furnham, in press). However, not all types of just-world belief contribute to psychological wellbeing. For example, Lipkus, Dalbert and Siegler (1996) showed that beliefs that the world is just to the self, but not that it is just to others, were related to measures such as life satisfaction and stress. I report two studies (n = 329) that take their investigation further, showing that just-world beliefs for the self, but not others, were directly related to self-esteem, and inversely related to chronic and acute anxiety. More importantly, the studies also demonstrate the social significance of Lipkus's self-other distinction. As predicted, beliefs that the world is fair to others, but not that it is fair to the self, were related to harsh attitudes toward the poor and unwillingness to help. In sum, beliefs about justice for the self appear to confer psychological benefits, whereas beliefs about justice for others appear to incur social costs. Implications for just-world theory and applications are discussed. [ABSTRACT FROM AUTHOR]