Numerical analysis and design of a new traveling-wave photodetector with an asymmetric i-layer cross section

We propose a new type of the traveling-wave photodetector (TWPD) that has an asymmetric intrinsic layer cross section to enhance bandwidth. In this paper, analysis and design of TWPDs are presented using the finite-difference time-domain method. A full-wave analysis is performed by a numerical technique and impulse responses are obtained in a linear regime. The simulation and experiment results show that 3-dB bandwidth is increased by the difference between electron and hole saturation velocities.     

A Silica Gel Based Method for Extracting Insect Surface Hydrocarbons

Here, we describe a novel method for the extraction of insect cuticular hydrocarbons using silica gel, herein referred to as “silica-rubbing”. This method permits the selective sampling of external hydrocarbons from insect cuticle surfaces for subsequent analysis using gas chromatography–mass spectrometry (GC-MS). The cuticular hydrocarbons are first adsorbed to silica gel particles by rubbing the cuticle of insect specimens with the materials, and then are subsequently eluted using organic solvents. We compared the cuticular hydrocarbon profiles that resulted from extractions using silica-rubbing and solvent-soaking methods in four ant and one bee species: Linepithema humile, Azteca instabilis, Camponotus floridanus, Pogonomyrmex barbatus (Hymenoptera: Formicidae), and Euglossa dilemma (Hymenoptera: Apidae). We also compared the hydrocarbon profiles of Euglossa dilemma obtained via silica-rubbing and solid phase microextraction (SPME). Comparison of hydrocarbon profiles obtained by different extraction methods indicates that silica rubbing selectively extracts the hydrocarbons that are present on the surface of the cuticular wax layer, without extracting hydrocarbons from internal glands and tissues. Due to its surface specificity, efficiency, and low cost, this new method may be useful for studying the biology of insect cuticular hydrocarbons.