National policies regarding the BCG vaccine for tuberculosis vary greatly throughout the international community and several countries are currently considering discontinuing universal vaccination. Detractors of BCG point to its uncertain effectiveness and its interference with the detection and treatment of latent tuberculosis infection (LTBI).

In order to quantify the trade-off between vaccination and treatment of LTBI, a mathematical model was designed and calibrated to data from Brazil, Ghana, Germany, India, Mexico, Romania, the United Kingdom and the United States. Country-specific thresholds for when LTBI treatment outperforms mass vaccination were found and the consequences of policy changes were estimated.

Our results suggest that vaccination outperforms LTBI treatment in all settings but with greatly reduced efficiency in low incidence countries. While national policy statements emphasize BCG’s interference with LTBI detection, we find that reinfection should be more determinant of a country’s proper policy choice.

A detailed threshold analysis of room-temperature pulsed operation of GaN/AlGaN/AlN vertical-cavity surface-emitting lasers (VCSELs) is carried out. The model takes advantage of the latest results concerning gain in active regions, material absorption in the cladding layers, as well as cavity diffraction and scattering losses. The simulation showed that although VCSELs with single (S) or multiple (M) quantum-well (QW) active regions exhibit lower threshold currents, they are much more sensitive to any increase in optical losses than their bulk counterparts. In particular, decreasing the active region radius of gain-guided QW VCSELs below 5 μm (which increases diffraction losses) or increasing dislocation densities (which, in turn, raises scattering losses) gives an enormous rise to their threshold currents. Therefore small-size GaN VCSELs should have an index-guided structure. In the case of MQW VCSELs, the optimal number of quantum wells strongly depends on the reflectivities of resonator mirrors. According to our study, MQW GaN lasers usually require noticeably lower threshold currents compared to SQW lasers. The optimal number of QW active layers is lower in laser structures exhibiting lower optical losses. Although the best result occurred for an active region thickness of 4 nm, threshold currents for the various sizes differ insignificantly.