82,741 research outputs found
Variance changes detection in multivariate time series
This paper studies the detection of step changes in the variances and in the correlation structure of the components of a vector of time series. Two procedures are considered. The first is based on the likelihood ratio test and the second on cusum statistics. These two procedures are compared in a simulation study and we conclude that the cusum procedure is more powerful. The procedures are illustrated in two examples.
Executive Privilege in the Federal Courts
Apoptosis is one type of programmed cell death, important during tissue development and to maintain the tissue homeostasis. Apoptosis comprises a complex network of internal signaling pathways, and an important part of this signaling network is the action of voltageâgated ion channels. The aim of this thesis was to explore the role of ion channels and the role of intracellular metal ions during apoptosis in Xenopus laevis oocytes. The reasons for using these oocytes are that they are large, robust, easy to handle, and easy to study electrophysiologically. Apoptosis was induced either chemically by incubation of the oocytes in staurosporine (STS) or mechanically by centrifugation of the oocytes. Ion currents were measured by a twoâelectrode voltage clamp technique, intracellular ion concentrations were measured either directly by inâhouse developed K+âselective microelectrodes or indirectly by the electrophysiological technique, and apoptosis was measured by caspaseâ3 activation. Paper I describes that the intracellular K+ concentration was reduced by about 30 % during STSâinduced apoptosis. However, this reduction was prevented by excessive expression of exogenous ion channels. Despite the magnitude of the intracellular K+ concentration, either normal or reduced level, the oocytes displayed normal signs of apoptosis, suggesting that the intracellular K+ reduction was not required for the apoptotic process. Because the intracellular K+ concentration was not critical for apoptosis we searched for other ion fluxes by exploring the electrophysiological properties of X. laevis oocytes. Paper II, describes a nonâinactivating Na+ current activated at positive membrane voltages that was upregulated by a factor of five during STSâinduced apoptosis. By preventing influx of Na+, the apoptotic signaling network involving capsaseâ3 was prevented. To molecularly identify this voltageâgated Na channel, the X. tropicalis genome and conserved regions of the human SCNA genes were used as a map. Paper III, shows that the voltageâgated Na channel corresponds to the SCN2A gene ortholog and that supression of this SCN2A ortholog using miRNA prevented cell death. In conclusion, this thesis work demonstrated that a voltageâgated Na channel is critical for the apoptotic process in X. laevis oocytes by increasing the intracellular Na+ concentration
Engaged Leadership: New Concept or Evolutionary in Nature?
Mr. Woods provides a critique and a book review of Clint Swindallâs Engaged Leadership. His accolades relate primarily to Swindellâs communication of connecting the dynamics of a work environment and the applications of engaged leadership in fable format. He decries, however, the authorâs missed opportunities to further associate engaged leadership to an established theory of management and to use polling data which attempts to ascertain any cost savings associated with engaged leadership
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