Area decomposition for electromechanical models of power systems

Coherency and time scale properties of power system models are shown to be related by the dichotomic solution of a matrix Riccati equation. A grouping algorithm is proposed which reduces the area decomposition problem to obtaining a basis for the slow subsystem and performing a Gaussian elimination. Since the slow coherency measure allows for a lack of coherency in fast parts of machine transients, the resulting area decomposition is independent of fault locations. The procedure is illustrated by a 16-machine example.     

Coherency based decomposition and aggregation

The relationship between coherency, area decomposition and aggregation is investigated for a class of models of electromechanical networks, including power system models. It is established that coherency conditions and a physically meaningful area-aggregate, reproducing a prescribed set of system modes, depend on external connections only. Coherency with respect to a set of slowest modes (‘slow coherency’) and an earlier developed grouping algorithm are used to identify weakly coupled areas, as demonstrated on a 48-machine model of the United States North-East power system.     

Gallium nitride MEMS resonators: how residual stress impacts design and performances

Microsystem Technologies - Starting from Gallium Nitride epitaxially grown on silicon, pre-stressed micro-resonators with integrated piezoelectric transducers have been designed, fabricated, and...     

Impact of femoro-distal bypass on major lower limb amputation rate

Renin activity (RA), concentration of aldosterone and hydrocortisone in plasma were measured by radioimmunoassay in 78 males with arterial hypertension living in the Far North. RA and aldosterone concentrations were high in patients with borderline arterial hypertension irrespectively of hemodynamic type of the disease. Hydrocortisone levels in them were normal. In hypertension stage I and II RA and hydrocortisone concentrations were normal, while aldosterone levels have risen. Renin-aldosterone index showed high RA in all hemodynamic types of hypertension.     

Corrosion of cold-deformed brass in acid sulphate solution

The corrosion behaviour and the dezincification process of cold-deformed CuZn-42 brass were tested in an acid sulphate solution at pH-value 2 with additional chloride and copper(II) ions by use of the linear polarization method.The measured corrosion potential and densities of corrosion currents were observed as characteristics of the dezincification process and the corrosion resistance of tested samples of cold-deformed CuZn-42 brass. The results obtained have shown that pH-value 2 of the tested solutions and increased concentrations of copper(II) ions result in increased values of densities of corrosion currents of the tested brass samples, as a result of selective zinc dissolution and the individual dissolution of zinc and copper including the process of anodic oxidation. The tested concentrations of chloride ions in certain conditions have an inhibiting effect, whereas in the other conditions they act as distinctive activators of brass corrosion. The lowest values of corrosion currents are present in the brass samples with the highest deformation degree at 80%. The process of dezincification and anode dissolution of cold deformed brass samples were developed in the whole range of tested potentials.