Dynamic Job Scheduling on the Grid Environment using the Great Deluge Algorithm

The utilization of the computational Grid processor network has become a common method for researchers and scientists without access to local processor clusters to avail of the benefits of parallel processing for compute-intensive applications. As a result, this demand requires effective and efficient dynamic allocation of available resources. Although static scheduling and allocation techniques have proved effective, the dynamic nature of the Grid requires innovative techniques for reacting to change and maintaining stability for users. The dynamic scheduling process requires quite powerful optimization techniques, which can themselves lack the performance required in reaction time for achieving an effective schedule solution. Often there is a trade-off between solution quality and speed in achieving a solution. This paper presents an extension of a technique used in optimization and scheduling which can provide the means of achieving this balance and improves on similar approaches currently published.

Decoupled-DFIG fault ride-through strategy for enhanced stability performance during grid faults

This paper proposes a decoupled fault ride-through strategy for a doubly fed induction generator (DFIG) to enhance network stability during grid disturbances. The decoupled operation proposes that a DFIG operates as an induction generator (IG) with the converter unit acting as a reactive power source during a fault condition. The transition power characteristics of the DFIG have been analyzed to derive the capability of the proposed strategy under various system conditions. The optimal crowbar resistance is obtained to exploit the maximum power capability from the DFIG during decoupled operation. The methods have been established to ensure proper coordination between the IG mode and reactive power compensation from the grid-side converter during decoupled operation. The viability and benefits of the proposed strategy are demonstrated using different test network structures and different wind penetration levels. Control performance has been benchmarked against existing grid code standards and commercial wind generator systems, based on the optimal network support required (i.e., voltage or frequency) by the system operator from a wind farm installed at a particular location.

Kinship, parentage and temporal stability in nursery colonies of Leisler’s bat (Nyctalus leisleri)

Levels of genetic relatedness within bat colonies are often unknown, and consequently the reasons for group formation and social organization are unclear. The Leisler's bat (Nyctalus leisleri), like most temperate bat species, forms nursery colonies in summer. We used microsatellite markers to examine identity and to attempt to estimate relatedness among females within a nursery colony, over 2 consecutive years, to ascertain whether females show kinship and natal philopatry, testing the hypothesis that this is the basis of colony formation. Parentage and relatedness of young born within a colony was assessed to investigate mating patterns via male reproductive skew and whether males achieve mating success within their natal colony. While there was evidence for female philopatry, levels of genetic relatedness within colonies were low. This suggests that kinship is not a major determinant in group formation, as roosts also comprise a large number of distant relatives or non-kin. Roost switching and gene flow are likely to be high. Both sexes reproduced in their first year, whereas males appear to be the more dispersive sex. We argue that the physical environment as well as information sharing provided by communal roosting are likely to be important factors for the formation of these large natal colonies in N. leisleri and possibly other lineages of bats. © 2012 The Author.

Capability Curve Based Enhanced Reactive Power Control Strategy for Stability Enhancement and Network Voltage Management

Reactive power has become a vital resource in modern electricity networks due to increased penetration of distributed generation. This paper examines the extended reactive power capability of DFIGs to improve network stability and capability to manage network voltage profile during transient faults and dynamic operating conditions. A coordinated reactive power controller is designed by considering the reactive power capabilities of the rotor-side converter (RSC) and the grid-side converter (GSC) of the DFIG in order to maximise the reactive power support from DFIGs. The study has illustrated that, a significant reactive power contribution can be obtained from partially loaded DFIG wind farms for stability enhancement by using the proposed capability curve based reactive power controller; hence DFIG wind farms can function as vital dynamic reactive power resources for power utilities without commissioning additional dynamic reactive power devices. Several network adaptive droop control schemes are also proposed for network voltage management and their performance has been investigated during variable wind conditions. Furthermore, the influence of reactive power capability on network adaptive droop control strategies has been investigated and it has also been shown that enhanced reactive power capability of DFIGs can substantially improve the voltage control performance.

The high-energy environment in the super-Earth system CoRoT-7

High-energy irradiation of exoplanets has been identified to be a key influence on the stability of these planets' atmospheres. So far, irradiation-driven mass-loss has been observed only in two Hot Jupiters, and the observational data remain even more sparse in the super-Earth regime. We present an investigation of the high-energy emission in the CoRoT-7 system, which hosts the first known transiting super-Earth. To characterize the high-energy XUV radiation field into which the rocky planets CoRoT-7b and CoRoT-7c are immersed, we analyzed a 25 ks XMM-Newton observation of the host star. Our analysis yields the first clear (3.5σ) X-ray detection of CoRoT-7. We determine a coronal temperature of ≈ 3 MK and an X-ray luminosity of 3 × 1028 erg s-1. The level of XUV irradiation on CoRoT-7b amounts to ≈37 000 erg cm-2 s-1. Current theories for planetary evaporation can only provide an order-of-magnitude estimate for the planetary mass loss; assuming that CoRoT-7b has formed as a rocky planet, we estimate that CoRoT-7b evaporates at a rate of about 1.3 × 1011 g s-1 and has lost ≈4-10 earth masses in total.