In the bulk devices, the applied voltage causes a broadening and quenching of the excitonic absorption, leading to enhanced transmission. In the quantum-well devices, the external field partially cancels the built-in polarization-induced electric fields in the well layers, thereby increasing the absorption. Unlike optical modulators based on smaller-bandgap zinc blende semiconductors, the bulk devices here are shown to provide similar performance levels as the quantum well devices, which is mainly a consequence

of the uniquely large exciton binding energies of nitride semiconductors. (C) 2011 American Institute of Physics. [doi:10.1063/1.3567921]“
“In this study, a series of linear- and long-chain branched polylactic acid (PLA) samples was prepared by electron beam irradiation without or with addition of a trifunctional monomer, trimethylolpropane triacrylate (TMPTA). The chain structures of the PLA samples were characterized by size-exclusion IPI-549 chromatography coupled with a light scattering detector (SEC-MALLS) and shear and extensional rheology. PLA tends to degrade while keeps linear structures with increasing irradiation dose and without addition of TMPTA, as evidenced by decreased molecular mass M-w and reductions of storage modulus G’ and the zero shear viscosity

eta’. Long-chain branched PLA samples were successfully prepared with irradiation and addition of TMPTA, which shows prominent higher eta(0) and apparent flow activation energy, longer characteristic relaxation

time tau, and pronounced Geneticin ic50 strain-hardening behaviors. With increasing amount of TMPTA, selleck compound M-w dependences of eta(0) and the root mean square radius of gyration R-g obviously deviate from the scaling relation of linear PLA samples, which strongly indicates the increased long-chain branching degree for the branched PLA samples. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 1857-1865, 2011″
“This review focuses on recent progress on injectorless quantum cascade lasers, an increasingly attractive approach in comparison to the “”classical”" injectorbased concepts. This particularly holds for the wavelength range between 7 and 12 mu m, where fundamental vibrational modes of many important molecules exist, so that sensor systems for medical, industrial and military applications highly benefit from these laser sources. The atmospheric transmission window between 8 and 12 mu m, with very low damping, also enables free space applications like communication, military countermeasures, and environmental sensors. Injectorless devices operate closer to the original design principle for intersubband lasers as suggested by Suris and Kazarinov [Sov. Phys. Semicond. 5, 707 (1971)]. Therefore, a short description of their features is given in comparison to injectorbased devices. Within recent years, injectorless devices have seen rapid improvement in performance. Best injectorless devices reach threshold current densities of 450 A/cm(2) at 300 K, a factor of 1.