Challenges of Primary Frequency Control and Benefits of Primary Frequency Response Support from Electric Vehicles

As the integration of wind generation displaces conventional plants, system inertia provided by rotating mass declines, causing concerns over system frequency stability. This paper implements an advanced stochastic scheduling model with inertia-dependent fast frequency response requirements to investigate the challenges on the primary frequency control in the future Great Britain electricity system. The results suggest that the required volume and the associated cost of primary frequency response increase significantly along with the increased capacity of wind plants. Alternative measures (e.g. electric vehicles) have been proposed to alleviate these concerns. Therefore, this paper also analyses the benefits of primary frequency response support from electric vehicles in reducing system operation cost, wind curtailment and carbon emissions

Electronic structure and bonding properties of cobalt oxide in the spinel structure

The spinel cobalt oxide Co3O4 is a magnetic semiconductor containing cobalt ions in Co2+ and Co3+ oxidation states. We have studied the electronic, magnetic and bonding properties of Co3O4 using density functional theory (DFT) at the Generalized Gradient Approximation (GGA), GGA+U, and PBE0 hybrid functional levels. The GGA correctly predicts Co3O4 to be a semiconductor, but severely underestimates the band gap. The GGA+U band gap (1.96 eV) agrees well with the available experimental value (~ 1.6 eV), whereas the band gap obtained using the PBE0 hybrid functional (3.42 eV) is strongly overestimated. All the employed exchange-correlation functionals predict 3 unpaired d electrons on the Co2+ ions, in agreement with crystal field theory, but the values of the magnetic moments given by GGA+U and PBE0 are in closer agreement with the experiment than the GGA value, indicating a better description of the cobalt localized d states. Bonding properties are studied by means of Maximally Localized Wannier Functions (MLWFs). We find d-type MLWFs on the cobalt ions, as well as Wannier functions with the character of sp3d bonds between cobalt and oxygen ions. Such hybridized bonding states indicate the presence of a small covalent component in the primarily ionic bonding mechanism of this compound.Comment: 24 pages, 8 figure

Exchange bias induced by the fully strained La2/3Ca1/3MnO3 dead layers

published_or_final_versio

Physiological and biochemical responses of halophyte Kalidium foliatum to salt stress

In this study, the physiological and biochemical responses of a halophyte Kalidium foliatum to salinity were studied. In order to reflect salt-tolerance in K. foliatum and to analyze the physiological and biochemical mechanism for its salt tolerance, salinity threshold and biochemical parameters were studied. A halophyte, Suaeda glauca, which has strong salt resistance, was selected as a control and the changes in soluble sugar, malondialdehyde (MDA), proline, Na+ and K+, Na+/K+ ratio, and activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were investigated. Four months old K. foliatum seedlings were subjected to 0, 0.15, 0.30, 0.45, 0.60, 0.75 and 0.90 M NaCl for 7 days. Salinity increased Na+ content in K. foliatum, while Na+/K+ ratio did not quite change. Salinity also increased Na+ content in S. glauca; however, Na+/K+ ratio changed with the increase of NaCl concentration. With the increase of NaCl concentration, MDA content in K. foliatum decreased, however, MDA content in S. glauca increased and this was related to enhanced activities of SOD, CAT and APX enzymes in K. foliatum. Content of soluble sugar and proline were lower in K. foliatum than in S. glauca. All these results suggest that there are different salt resistant metabolisms between K. foliatum and S. glauca, and salt treatments and salinity tolerance of K. foliatum might be closed related to increased capacity of antioxidative system to scavenge reactive oxygen species, stable absorption of K+ and maintain Na+/K+ ratio.Key words: Kalidium foliatum, Suaeda glauca, salinity stress, halophyte, salinity threshold, physiological adaptations

An extended fault-tolerant link-state routing protocol in the internet

2003-2004 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe