Semiempirical calculation of deep levels: divacancy in Si

A study of the electronic levels associated with the divacancy in silicon is reported. The extended Huckel theory is shown to reproduce the band structure of silicon. The electronic levels of the divacancy are calculated by considering a periodic array of large unit cells each containing 62 atoms; a 64 atom perfect cell with two atoms removed to form the divacancy. The results are found to be in qualitative agreement with the results of EPR and infrared absorption measurements

Difference equation for superradiance

The evolution of a completely excited system of N two-level atoms, distributed over a large region and interacting with all modes of radiation field, is studied. The distinction between r-conserving (RC) and r-nonconserving (RNC) processes is emphasized. Considering the number of photons emitted as the discrete independent variable, the evolution is described by a partial difference equation. Numerical solution of this equation shows the transition from RNC dominance at the beginning to RC dominance later. This is also a transition from incoherent to coherent emission of radiation

Analytical studies of ultrashort optical pulse propagation in a resonant absorbing medium

Resonant absorption in a laser pulse can be reduced to zero if the trailing part induces stimulated emission and returns the absorbed energy back to the pulse. This kind of effect is called Self-Induced Transparency (SIT). Analytic descriptions of short pulse propagation in a resonant medium, based on Slowly Varying Envelope Approximation (SVEA) and in linear media, have been extended in studies of SIT along two principal directions: First, to improve the SVEA by introducing Short Pulse Approximation (SPA); and second, to consider the effect of nonlinear refractive index

Acoustic suspension system

An acoustic levitation system is described, with single acoustic source and a small reflector to stably levitate a small object while the object is processed as by coating or heating it. The system includes a concave acoustic source which has locations on opposite sides of its axis that vibrate towards and away from a focal point to generate a converging acoustic field. A small reflector is located near the focal point, and preferably slightly beyond it, to create an intense acoustic field that stably supports a small object near the reflector. The reflector is located about one-half wavelength from the focal point and is concavely curved to a radius of curvature (L) of about one-half the wavelength, to stably support an object one-quarter wavelength (N) from the reflector

Macroeconomic Stability, Governance and Growth: Empirical Lessons from the Post-Communist Transition

Using panel data for the period 1989-2006 we revisit the empirics of economic growth in the context of the post-communist transition. We pay particular attention to the mechanisms of causation and to the potential endogeneity of the macroeconomic stability indicators considered to be important in the existing literature. Carefully employing a variety of econometric techniques we consistently find that macroeconomic instability is bad for economic growth. We find some evidence that institutions of governance are important for economic growth through their influence on the macroeconomic environment. That is, good institutions are conducive to macroeconomic stability which in turn positively impacts upon economic growth. We also find, in contrast with other work, that investments in education have had a strong positive impact on growth in transition while other 'standard' economic growth determinants remain less important. These findings are shown to be robust to a variety of econometric approaches, specifications and time spans