Solar cycle induced variations in GONG p-mode frequencies and splittings

We have analysed the recently available GONG p-mode frequencies and splitting coefficients for a period of three and half years, including the rapidly rising phase of solar cycle 23. The analysis of mean frequency shift with different activity indices shows that the shift is equally correlated with both magnetic and radiative indices. During the onset of the new cycle 23, we notice that the change in $b_4$ splitting coefficient is more prominent than the change in $b_2$. We have estimated the solar rotation rate with varying depth and latitude. In the equatorial region, the rotation first increases with depth and then decreases, while an opposite behaviour is seen in the polar region. We also find a small but significant temporal variation in the rotation rate at high latitudes.Comment: Uses aastex, To appear in Astrophysical Journal, October 10, 2000 issu

Mechanism of enhanced light output in InGaN-based microlight emitting diodes

Micro-light emitting diode (LED) arrays with diameters of 4 to 20 mum have been fabricated and were found to be much more efficient light emitters compared to their broad-area counterparts, with up to five times enhancement in optical power densities. The possible mechanisms responsible for the improvement in performance were investigated. Strain relaxation in the microstructures as measured by Raman spectroscopy was not observed, arguing against theories of an increase in internal quantum efficiency due to a reduction of the piezoelectric field put forward by other groups. Optical microscope images show intense light emission at the periphery of the devices, as a result of light scattering off the etched sidewalls. This increases the extraction efficiency relative to broad area devices and boosts the forward optical output. In addition, spectra of the forward emitted light reveal the presence of resonant cavity modes [whispering gallery (WG) modes in particular] which appear to play a role in enhancing the optical output

Counting fermionic zero modes on M5 with fluxes

We study the Dirac equation on an M5 brane wrapped on a divisor in a Calabi--Yau fourfold in the presence of background flux. We reduce the computation of the normal bundle U(1) anomaly to counting the solutions of a finite--dimensional linear system on cohomology. This system depends on the choice of flux. In an example, we find that the presence of flux changes the anomaly and allows instanton corrections to the superpotential which would otherwise be absent.Comment: 14 pages. v2: reference added, typos corrected, few change