On the Power of Invariant Tests for Hypotheses on a Covariance Matrix

The behavior of the power function of autocorrelation tests such as the Durbin-Watson test in time series regressions or the Cliff-Ord test in spatial regression models has been intensively studied in the literature. When the correlation becomes strong, Kr\"amer (1985) (for the Durbin-Watson test) and Kr\"amer (2005) (for the Cliff-Ord test) have shown that the power can be very low, in fact can converge to zero, under certain circumstances. Motivated by these results, Martellosio (2010) set out to build a general theory that would explain these findings. Unfortunately, Martellosio (2010) does not achieve this goal, as a substantial portion of his results and proofs suffer from serious flaws. The present paper now builds a theory as envisioned in Martellosio (2010) in a fairly general framework, covering general invariant tests of a hypothesis on the disturbance covariance matrix in a linear regression model. The general results are then specialized to testing for spatial correlation and to autocorrelation testing in time series regression models. We also characterize the situation where the null and the alternative hypothesis are indistinguishable by invariant tests

Species lifetime distribution for simple models of ecologies

Interpretation of empirical results based on a taxa's lifetime distribution shows apparently conflicting results. Species' lifetime is reported to be exponentially distributed, whereas higher order taxa, such as families or genera, follow a broader distribution, compatible with power law decay. We show that both these evidences are consistent with a simple evolutionary model that does not require specific assumptions on species interaction. The model provides a zero-order description of the dynamics of ecological communities and its species lifetime distribution can be computed exactly. Different behaviors are found: an initial $t^{-3/2}$ power law, emerging from a random walk type of dynamics, which crosses over to a steeper $t^{-2}$ branching process-like regime and finally is cutoff by an exponential decay which becomes weaker and weaker as the total population increases. Sampling effects can also be taken into account and shown to be relevant: if species in the fossil record were sampled according to the Fisher log-series distribution, lifetime should be distributed according to a $t^{-1}$ power law. Such variability of behaviors in a simple model, combined with the scarcity of data available, cast serious doubts on the possibility to validate theories of evolution on the basis of species lifetime data.Comment: 19 pages, 2 figure

STUDY CASE ON SIMULATION AN ACTIVE FILTER BASED ON LOAD DC MOTOR

Nowadays power system facing serious problem with power quality in terms of power factor and harmonics due to increasingly number of nonlinear load. This paper will discuss about the effecting of dc motor by using an active filter on the power system. The simulation had been done by using MATLAB/ Simulink. The Voltage source shunt active filter (VSAF) has been used in this simulation with the common DC bus. The p-q theorem will be used to control the PWM switching of the active filter. Simulation result shows that by using a Series DC motor as load on active filter the line current will compensate and reduce the THD of the line current

Land Beneath the Water: Narratives of the Keowee-Toxaway Project in Appalachian South Carolina

In 1965, Duke Power announced the construction of a series of dams along the Keowee and Little rivers in Oconee County, South Carolina. The dams would create water reservoirs for one of the largest hydro-electric and nuclear power facilities in the nation. The dominant narrative focuses on the recreational activities, power generation, and economic development facilitated by the creation of lakes Jocassee and Keowee. However, residents of the Keowee and Jocassee valleys had to be removed, a process that started years earlier when Duke Power began serious land purchasing efforts. This study focused on discovering diverse narratives from people that were displaced or otherwise affected by the lakes. In doing so, made comparisons with other projects on displaced populations in Appalachia, examined the beneficiaries of the project, the treatment of locals, and how Duke Power and local government presented the project through local media

Federal Environmental Law in the \u27New Federalism\u27 Era

As we wrote last year, the U.S. Supreme Court has shown considerable interest during the past decade in reconsidering many constitutional doctrines regarding federalism and congressional power. In a series of important decisions, always decided with the same five justices in the majority, the Court has begun to redefine the federal-state relationship and the scope of federal authority. The past term generally continued that trend, with one important commerce power decision, one significant Eleventh Amendment/Fourteenth Amendment decision, and a number of decisions that involve or affect federalism and the scope of federal power, although the Court sometimes relied on statutory interpretation to avoid serious constitutional issues. Part I of this article describes the most recent decisions

Effects of photovoltaic systems on the behavior of harmonic components in low voltage network

Renewable energy sources, especially solar systems, have become increasingly important energy sources in recent times. Connecting large PV systems to utility networks can cause a number of operational problems for distribution networks. The extent of these problems depends directly on the percentage of PV penetration and the geographical location of the installation. Possible problems caused by PV systems: over-voltage, output power fluctuation, harmonic distortion, frequency fluctuation Harmonic distortion is a serious energy quality problem which can occur in photovoltaic systems due to the use of power inverters that convert direct current to alternating current. The resulting harmonics can cause parallel and series resonances, transformer overheating, and protection device malfunctions, which can reduce the reliability of power supply systems

Federal Environmental Law in the \u27New Federalism\u27 Era

As we wrote last year, the U.S. Supreme Court has shown considerable interest during the past decade in reconsidering many constitutional doctrines regarding federalism and congressional power. In a series of important decisions, always decided with the same five justices in the majority, the Court has begun to redefine the federal-state relationship and the scope of federal authority. The past term generally continued that trend, with one important commerce power decision, one significant Eleventh Amendment/Fourteenth Amendment decision, and a number of decisions that involve or affect federalism and the scope of federal power, although the Court sometimes relied on statutory interpretation to avoid serious constitutional issues. Part I of this article describes the most recent decisions