COALA: A Protocol for the Avoidance and Alleviation of Congestion in Wireless Sensor Networks

The occurrence of congestion has an extremely deleterious impact on the performance of Wireless Sensor Networks (WSNs). This article presents a novel protocol, named COALA (COngestion ALleviation and Avoidance), which aims to act both proactively, in order to avoid the creation of congestion in WSNs, and reactively, so as to mitigate the diffusion of upcoming congestion through alternative path routing. Its operation is based on the utilization of an accumulative cost function, which considers both static and dynamic metrics in order to send data through the paths that are less probable to be congested. COALA is validated through simulation tests, which exhibit its ability to achieve remarkable reduction of loss ratios, transmission delays and energy dissipation. Moreover, the appropriate adjustment of the weighting of the accumulative cost function enables the algorithm to adapt to the performance criteria of individual case scenarios

A dual scheme for compression and restoration of sequentially transmitted images over Wireless Sensor Networks

A dual scheme for the compression and restoration of sequentially transmitted images over Wireless Sensor Networks (WSNs) is presented. These networks are characterized by low transmission rates, extended packet losses and limited power resources, factors that degrade the overall system performance. Especially in the cases of transmitting multimedia content, a considerable number of data packets are dropped, with a corresponding direct effect on the received image quality. For dealing with this loss of valuable information, various retransmission schemes have been proposed that act as quality of service modules. However, this approach increases energy consumption and inserts considerable time delays, due to the rise of the traffic load in the network. This article proposes a novel dual transmission scheme, targeting mainly the area of Multimedia WSNs (WMSN), that aims to decrease the overall traffic load introduced by the retransmission schemes, by performing image restoration for lost data packets, at the receiver side. The proposed novel dual scheme is based on: (a) the quad tree decomposition algorithm that is adopted for compressing the image data before transmission over the WSN, and (b) the fast image inpainting algorithm for restoring the effect of the missing data packets. The overall proposed scheme has been applied in multiple experimental studies that prove its efficacy. © 2012 Elsevier B.V. All rights reserved

Star-delta switches evaluation for use in grid-connected wind farm installations

Electrical generators are designed to perform best under permanent rotation velocity and fixed loads conditions. However, such ideal conditions are not practically feasible during the operation of real wind turbines. Generally, the voltage output of electrical generators can be regulated without redesigning the electrical or/and mechanical parts constituting such a system, by simply changing the connection of the generator to the grid from Star to Delta or by using combined windings. The present work attempts to investigate the behavior of grid-connected wind turbines with Star-Delta, Delta, and Star connection switches in a variety of simulation scenarios, by taking into consideration the influence of both internal and external factors such as the inertia factor and the wind speed

Metacognitive beliefs increase vulnerability to rumination

Metacognitive beliefs about the benefits of rumination are associated with rumination and depression; however, the direction of these relationships remains unclear. Two experiments examined whether individuals with high positive beliefs about rumination engaged in more rumination following a laboratory-based stressor than individuals with low levels of such beliefs. In Study 1, participants with high levels of positive beliefs reported more rumination following receipt of negative feedback on a forced-failure anagram task. In Study 2, participants with high levels of positive beliefs reported more rumination compared to participants with low levels of positive beliefs, regardless of whether they received negative feedback, positive feedback or no feedback on their performance. Our findings demonstrate the importance of positive beliefs about rumination, and highlight the utility of treatment approaches that aim to reduce rumination by targeting such unhelpful metacognitive beliefs.6 page(s

A Psychometric evaluation of the Thought Control Ability Questionnaire (TCAQ) and the prediction of cognitive control

Study 1 evaluated the psychometric properties of the English version of the Thought Control Ability Questionnaire (TCAQ; Luciano et al. 2005), an index of perceived control over intrusive cognitions. Confirmatory factor analysis in a sample of 720 University students revealed a clear uni-dimensional structure (after removal of items 5, 7, 8, 14, and 25) with high internal consistency (α = .87, 95% CI = [.86, .88]) and test-retest reliability after a six month interval (r = .68). Correlational analyses supported an inverse relationship with measures of depression, anxiety, maladaptive cognitive control strategies, and obsessive-compulsive symptomatology. Study 2 tested the ability of the TCAQ to predict successful cognitive control during an experimental suppression protocol. Results demonstrated that weak thought control ability was predictive of the frequency and associated levels of distress of a target thought while under instruction to suppress. Additionally, weak perceived thought control ability was predictive of increased efforts to suppress the target material. Collectively, results suggest that thought control ability is a measurable individual difference variable and that the TCAQ is a reliable index of perceived cognitive control.9 page(s