Interactions between, and effectiveness of, power system stabilizers and FACTS device stabilizers in multimachine systems

Copyright © 2000 IEEEIn this paper it is shown that interactions occur between stabilizers in multimachine power systems, the stabilizers being power system stabilizers (PSSs), FACTS device stabilizers (FDSs) or both. The interactions, which are identified and quantified, may enhance or degrade the damping of certain modes of rotor oscillation. In particular, interactions between PSSs are found to adversely affect the damping of inter-area modes. The analysis of interactions also provides a practical means for quantifying and assessing simultaneously the relative effectiveness of both PSSs and FDS in damping the rotor modes of oscillation. This is achieved using a stabilizer damping contribution diagram. A theoretical basis is given for the analysis of interactions and the effectiveness of stabilizers; the practical significance and applications are illustrated using a case study on a 3-area, 400 state system having 28 generator groups and a number of FDSs. For systems of more than 600-700 states the modified Arnoldi method is used for eigenanalysis-based calculationsMichael J. Gibbard, David J. Vowles and Pouyan Pourbei

Quaternary River Diversions in the London Basin and the Eastern English Channel

The principal river of the London basin, the Thames, has experienced a number of course changes during the Quaternary. Some, at least, of these are known to result directly from glaciation. In the early Quaternary the river flowed to the north of London across East Anglia to the north coast of Norfolk. By the early Middle Pleistocene it had changed its course to flow eastwards near the Suffolk - Essex border into the southern North Sea. The Thames valley to the north of London was blocked by ice during the Anglian/Elsterian glaciation, causing a series of glacial lakes to form. Overflow of these lakes brought the river into its modern valley through London. It is thought that this valley already existed by the Anglian in the form of a tributary of the north-flowing River Medway, which joined the old Thames valley near Clacton. Also during the Anglian/Elsterian glaciation. British and continental ice masses are thought to have joined in the northern part of the North Sea basin, causing a large lake to form between the east coast of England and the Netherlands. It is widely believed that the overflow from this lake caused the first breach in the Weald-Artois Ridge, bringing about the formation of the Strait of Dover. Prior to the glaciation the Thames, in common with rivers from the continent (including the Rhine and Meuse), flowed into the North Sea Basin. It seems that, after the lake overflow, these rivers together drained southwards into the English Channel. Whether this southern drainage route was adopted during all later periods of low sea level remains to be determined, but it seems certain that this was the case during the last glacial.De nombreuses captures ont modifé le cours de la Tamise et des autres fleuves du bassin de Londres au cours du Quaternaire. L'une d'entre elles au moins est le résultat direct des glaciations. Au Quaternaire inférieur. Ia Tamise coulait au nord de Londres à travers l'East Anglia, vers la côte nord du Norfolk. Au début du Pléistocène moyen, elle avait changé de cours pour se diriger vers l'est, à la frontière entre Essex et Suffolk, vers le sud de la mer du Nord. Au cours du maximum glaciaire de l'Anglien/Elstérien, les glaces ont bloqué la vallée de la Tamise au nord de Londres, provoquant la formation de lacs. La vidange de ces lacs a provoqué le déversement de la rivière vers sa basse vallée actuelle. Celle-ci existait déjà, mais était alors parcourue par un affluent de la Medway qui coulait vers le nord, et rejoignait l'ancienne vallée de la Tamise aux environs de Clacton. Il semble que durant les glaciations de l'Anglien et de l'Elstérien, les calottes glaciaires britannique et continentale étaient coalescentes dans la partie septentrionale du bassin de la mer du Nord. Il en est résulté la formation d'un vaste lac entre les côtes de l'Angleterre orientale, du Danemark et des Pays-Bas. L'écoulement de ce lac s'est probablement fait par la Manche, entre le Weald et le massif de l'Artois, provoquant la formation du Pas de Calais. Avant la glaciation. Ia Tamise confluait avec les fleuves issus du continent, le Rhin et la Meuse, et se jetait dans la mer du Nord. Il semble que se soit seulement après le débordement du lac que ces fleuves se sont écoulés vers le sud en direction de la Manche. Il reste à déterminer si les fleuves ont conservé ce cours vers le sud durant chaque épisode de bas niveau marin. Quoi qu'il en soit, il est certain que c'était le cas durant la dernière glaciation.Der wichtigste Fluss des Londoner Beckens, die Themse, erlebte wâhrend des Quartàrs eine Reihe von Verlaufsànderungen. Mindestens einige davon sind ein direktes Résultat der Vereisung. Im frùhen Quarter floss der Fluss vom Norden Londons durch Ost-England zur Nordkùste von Norfolk. Zu Anfang des mittleren Pleistozàn hatte er seinen Lauf geândert, um ostwàrts nahe der Suffolk-Essex-Grenze in die sùdliche Nordsee zu fliessen. Das Themse-Tal nôrdlich Londons war wâhrend der Anglia-Elster-Vereisung durch Eis blockiert, was zur Bildung einer Reihe von glazialen Seen fùhrte. Der Ùberlauf dieser Seen brachte den Fluss in sein modernes TaI quer durch London. Man glaubt, dass dieses TaI schon im Anglium existierte in Form eines Zuflusses des nach Norden fliessenden Medwey-Flusses, der in das alte Themse-Tal bei Clacton eintrat. Genauso denkt man, dass wâhrend der Anglia-Elster-Vereisung britische und kontinentale Eismassen sich im nôrdlichen Teil des Nordsee-Beckens vereinigt haben und so zur Bildung eines grossen Sees zwischen der Ostkùste Englands und den Niederlanden gefùhrt haben. Man nimmt allgemein an, dass der Ùberlauf von diesem See die erste Bresche im Weald-Artois-Kamm verursachte und so zur Bildung der Meerenge von Dover fùhrte. Vor der Vereisung floss die Themse gemeinsam mit den vom Kontinent kommenden Flùssen (einschliesslich Rhein und Maas) in das Nordseebecken. Nach dem Ùberlauf des Sees scheint es, dass dièse Flùsse zusammen sùdwârts in den Àrmelkanal abflossen. Ob dièse Entwàsserungsroute nach Sùden in alien spâteren Perioden mit niedrigem Meeresspiegelniveau beibehalten wurde, bleibt zu erforschen. Doch scheint es sicher, dass dies der Fall in der letzten Eiszeit war

Complexity of Manipulative Actions When Voting with Ties

Most of the computational study of election problems has assumed that each voter's preferences are, or should be extended to, a total order. However in practice voters may have preferences with ties. We study the complexity of manipulative actions on elections where voters can have ties, extending the definitions of the election systems (when necessary) to handle voters with ties. We show that for natural election systems allowing ties can both increase and decrease the complexity of manipulation and bribery, and we state a general result on the effect of voters with ties on the complexity of control.Comment: A version of this paper will appear in ADT-201

The stratigraphic basis of the Anthropocene Event

This paper outlines the stratigraphic basis of a proposed Anthropocene Event. It considers a diachronous event framework to be more appropriate for understanding the Anthropocene than treating it as a new geological series/epoch. Four general categories of material evidence are identified as of particular relevance: ‘artificial’ strata with natural constituents; humanly modified ground; legacy sediments; and ‘natural’ geo-deposits containing artefactual material. All these arise from the interaction and mixing of human, natural, and hybrid human-natural forces. Taken together, such stratigraphic evidence supports the case for recognising the Anthropocene as an unfolding event

Holocene sea levels and palaeoenvironments, Malay-Thai Peninsula, southeast Asia

Sedimentological and palynological investigations of Great Songkhla Lakes, east coast of the Malay-Thai Peninsula, Southeast Asia, reveal sedimentary sequences rich in palynomorph assemblages dominated by pollen of mangroves and freshwater swamps. Compared with other regions in Southeast Asia the assemblages are of relatively low diversity. Geochronological data indicate that the Great Songkhla Lakes record one of the earliest mangrove environments in Southeast Asia (8420–8190 cal. yr BP), which are subsequently replaced by a freshwater swamp at 7880–7680 cal. yr BP owing to the decline of marine influence. Sea-level observations from Great Songkhla Lakes and other areas of the Malay-Thai Peninsula reveal an upward trend of Holocene relative sea level from a minimum of − 22 m at 9700–9250 cal. yr BP to a mid-Holocene high stand of 4850–4450 cal. yr BP, which equates to a rise of c. 5.5 mm/yr. The sea-level fall from the high stand is steady at c. − 1.1 mm/yr. Geophysical modelling shows that hydroisostasy contributes a significant spatial variation to the sea-level signal between some site locations (3–4 m during the mid-Holocene), indicating that it is not correct to construct a single relative sea-level history for the Malay-Thai Peninsula