On time-optimal second order discrete control systems

The time optimal control problem in unforced discrete systems is studied in this thesis. Comparison is made between the discrete and the continuous control systems by means of minimum time isochrones. concerning optimal time, it is shown that using the discrete control system will take at most one more sampling period of time to go to equilibrium. An investigation is also made for the case when the time constant of the physical plant, G(s), and the control model are different. In such a case, an optimal trajectory can not be obtained. An adaptive process is proposed to adjust the model of the controller to get an almost optimal control --Abstract, page ii

Firm size and the gains from divestitures

Recent academic studies indicate that corporate divestitures generate considerable shareholder wealth. The field is emerging as an important topic in the finance, strategy and organizational literature, but the understanding of what determines these gains remains somewhat fragmented and inconsistent. This thesis contributes to this understanding by specifically studying the effect of firm size on seller announcement abnormal return. We use a sample of 6699 divestitures completed by 2350 different sellers in the United States between 1995 and 2014 and conclude that small sellers outperform large sellers by an average of 1.96% at the announcement of divestitures. The size effect is robust to a wide range of firm and deal characteristics introduced by the literature. We propose that the size effect could be explained by greater idiosyncratic risk associated with the divestiture announcement by small sellers.nhhma

Local Cyber-physical Attack with Leveraging Detection in Smart Grid

A well-designed attack in the power system can cause an initial failure and then results in large-scale cascade failure. Several works have discussed power system attack through false data injection, line-maintaining attack, and line-removing attack. However, the existing methods need to continuously attack the system for a long time, and, unfortunately, the performance cannot be guaranteed if the system states vary. To overcome this issue, we consider a new type of attack strategy called combinational attack which masks a line-outage at one position but misleads the control center on line outage at another position. Therefore, the topology information in the control center is interfered by our attack. We also offer a procedure of selecting the vulnerable lines of its kind. The proposed method can effectively and continuously deceive the control center in identifying the actual position of line-outage. The system under attack will be exposed to increasing risks as the attack continuously. Simulation results validate the efficiency of the proposed attack strategy.Comment: Accepted by IEEE SmartGridComm 201