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This paper deals with the lacement of a minimal set of phasor measurement units PMU9sT so as to make the system placed at a bus measures the voltage as well as all the current phasors at that bus, requiring the extension of the topological observability theory. This concerns the extension of the concept of spanning tree'to that of spanning measurement subgraph with an actual or a pseudo-measurement assi ned to each of its branches. The minimal PMU set is found t%rough a dual search algorithm which uses both a modified bisecting search and a simulated annealing-based method. The former fixes the number of PMU's while the latter looks for a placement set that leads to an observable network for a fixed number of PMU's. In order to accelerate the procedure, an initial PMU placement is provided by a graph-theoretic procedure which builds a spanning measurement subgraph according to a depth-first search. From computer simulation results performed on various test systems it appears that only one fourth to one third of the system buses need to be provided with PMU% in order to make the system observable. measurement model observabe, \ and thereby linear. A PMU -INTRODUCTIONPresently, the supervision of a power system is performed through an open-loop type centralized control. The control actions are taken by the operators with the help of computer-aided software programs that implement steadystate security functions 1). This is due to the fact that the to capture only quasi-steady state operating conditions, preventin the monitoring of transient phenomena. With the advent o f real-time Phasor Measurement Units PMU's), fast transients can be tracked at high sampling rates 121. Hence, it becomes possible to close the loop, that is, to perform an automatic monitoring and control of the system. This is a faster-than-real-time control that aims at steering the system away from transient or voltage instability through corrective actions initiated during an emergency state. A prerequisite to system monitoring and control is the development of an adequate meter placement scheme. Various lacement methodologies have been proposed in the literature P 2-61. Most of them advocate the use of pilot points located at the center of the coherent regions of a system. These re 'om either contain load buses with similar voltage trends for vogage stability analysis or encompass groups of stiffly interconnected machines with common slow modes of oscillations for transient stability analysis. The only control that has so far been implemented is the secondary voltage control scheme which has been applied to the French [5] and Italian systems [ 6 . Two measurements collected t 6, ough a SCADA system are designed major drawbacks of the coherency approach may be fl oreseen. SM 583-5 PWRS A paper recommended and approved by the IEEE Power System Engineering committee of the IEEE Power Engineering Society for presentation at the IEEE/First, the system may not be decomposable into meaningful clusters, signifying the necessity to monitor all load buses...

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BackgroundThe default mode network consists of a set of functionally connected brain regions (posterior cingulate, medial prefrontal cortex and bilateral parietal cortex) maximally active in functional imaging studies under “no task” conditions. It has been argued that the posterior cingulate is important in consciousness/awareness, but previous investigations of resting interactions between the posterior cingulate cortex and other brain regions during sedation and anesthesia have produced inconsistent results.Methodology/Principal FindingsWe examined the connectivity of the posterior cingulate at different levels of consciousness. “No task” fMRI (BOLD) data were collected from healthy volunteers while awake and at low and moderate levels of sedation, induced by the anesthetic agent propofol. Our data show that connectivity of the posterior cingulate changes during sedation to include areas that are not traditionally considered to be part of the default mode network, such as the motor/somatosensory cortices, the anterior thalamic nuclei, and the reticular activating system.Conclusions/SignificanceThis neuroanatomical signature resembles that of non-REM sleep, and may be evidence for a system that reduces its discriminable states and switches into more stereotypic patterns of firing under sedation.