Attitude stabilization of a rigid spacecraft using two momentum wheel actuators

It is well known that three momentum wheel actuators can be used to control the attitude of a rigid spacecraft and that arbitrary reorientation maneuvers of the spacecraft can be accomplished using smooth feedback. If failure of one of the momentum wheel actuators occurs, it is demonstrated that two momentum wheel actuators can be used to control the attitude of a rigid spacecraft and that arbitrary reorientation maneuvers of the spacecraft can be accomplished. Although the complete spacecraft equations are not controllable, the spacecraft equations are small time locally controllable in a reduced nonlinear sense. The reduced spacecraft dynamics cannot be asymptotically stabilized to any equilibrium attitude using a time-variant continuous feedback control law, but discontinuous feedback control strategies are constructed which stabilize any equilibrium attitude of the spacecraft in finite time. Consequently, reorientation of the spacecraft can be accomplished using discontinuous feedback control

Career effectiveness and its determinants

Study of careers has become an important aspect in the fast changing organizational context. It has come to be increasingly recognized at present, that career management is the responsibility of both the individual as well as the organization. This empirical study tries to understand the important elements of individual and organizational career practices that affect an employee’s career effectiveness. Most of the previous studies have used the objective terms of career success such as remuneration and position as the criterion variable. But since career outcome expectations vary across individuals and also since the concept of career itself has evolved over time, it was decided to use a more comprehensive concept of career outcome namely career effectiveness as the outcome variable. Career effectiveness as defined by Hall (2002) has both long-term orientation such as identity and adaptability as well as short-term orientation such as career attitudes and performance. Further both behavioral aspects such as performance and adaptability and individual subjective aspects such as identity and attitudes make it a more comprehensive way of assessing career outcome. The results of this research study indicate that individual determinants such as career planning and knowledge of organizational politics and organizational level determinants such as training and development support, quality of performance feedback and supervisory support explain significant variances in the determination of employee career effectiveness.

Monitoring and controlling bank risk: does risky debt serve any purpose?

To examine whether mandating banks to issue subordinated debt would enhance market monitoring and control risk-taking, the authors extract the credit-spread curve for each banking firm in their sample. After controlling for changes in market and liquidity variables, they find that changes in credit spreads do not reflect changes in bank risk variables. The result is robust to firm type, examination rating, size, leverage, and profitability, as well as to different model specifications. They also find that issuing subordinated debt does not alter banks' risk-taking behavior. They conclude that a mandatory subordinated debt requirement for banks is unlikely to provide the intended benefits of enhancing risk-monitoring or controlling risk-taking.Bank capital ; Risk

The effects of temperature on different laser transitions of neodymium orthovanadate crystal

The temperature dependence of Nd:YVO4 laser crystal pumped by laser diode emitting at 808 nm is studied within the range of 5 °C to 60 °C. The spectroscopy properties of quasi three level at 914 nm (4F3/2 -4I9/2) and four level at 1064 nm (4F3/2 -4I11/2) are characterized. The lineshape function of the transition lines were broadened as the temperature increases. The phenomenon is attributed to change in linewidth, lineshift and intensity. The linewidths for both laser transition of 914 nm and 1064 nm increases with temperature with the rate of 0.105 cm-1/°C and 0.074 cm-1/°C respectively. The peak of 914nm and 1064 nm lineshapes shifted to a longer wavelength with the rate of 3.0 pm/°C and 4.2 pm/°C respectively which correspond to same amount of lineshift. The lineshape broadening with respect to the temperature is due to one-phonon emission and Raman phonon scattering processes. The intensities of 914 nm and 1064 nm transition lines are found to be decreased at the rate of 0.15 %/°C and 0.45 %/°C respectively due to non-radiative effects. Quasi three level laser transition is more temperature dependent because it terminal level is close to the ground state which suffers from higher phonon-ion interaction rather than four level laser system