Site of action of hematoporphyrin (a photo-activated insecticide) in Culex pipiens larvae

The histopathological effect of hematoporphyrin on the mid-gut and the integument of the fourth larval instar of C. pipiens was studied using a transmission electron microscope. In this study C. pipiens larvae were treated with different concentration of hematoporphyrin. The concentration 5 × 10-4 M/L was found to produce 100% mortality after half-hour exposure to the 400 W/M2 artificial lights using a solar simulator. The ultrastructural examination showed that the normal lamellate cuticle was heavily affected, taking the shape of amorphous cuticular region. The endo- and exo-cuticle were not distinguishable. It was found that the epidermal cells underneath the cuticle were distorted. The mitochondria of these cells exhibited irregular shapes. The fat body underneath the integument could be detected with visible vacuolisation. Muscle cells revealed the degenerated sarcomeres with gaps and vacuoles. The Z discs have irregular shape and are distorted. Mid-gut cells appeared with cytoplasmic vacuoles. The Golgi body is fragmented into small bodies. The rough endoplasmic reticulum is broken-down into separate vascular structures. These cytopathological observations confirm the insecticidal efficiency of hematoporphyrin against C. pipiens larvae. KEY WORDS: histopathology, mid-gut, integument, insect larvae, TEM Egyptian Journal of Biology Vol.4 2002: 133-14

Epitaxial VO2 thin film-based radio-frequency switches with thermal activation

In this paper, we report on the demonstration of thermally triggered "normally ON" radio-frequency (RF) switches based on epitaxial vanadium dioxide (VO2) thin films with a SnO2 template on (001) TiO2 substrates. Fast insulator-to-metal phase transition of the epitaxial VO2 at a relatively low temperature allowed RF switches made of the VO2 to exhibit sharp changes in the RF insertion loss during cooling and heating at 60 degrees C and 66 degrees C, respectively. The change of RF insertion loss due to phase transition is greater than 15 dB. The VO2 RF switches also completed the transition of S-21 within less than 3 degrees C and showed a low-loss operation frequency of up to 24.2 GHz with a low insertion loss of -1.36 dB and isolation of 17.56 dB at 12.03 GHz, respectively. The demonstration suggests that epitaxial VO2-based RF switches can be used in switching elements up to Ku-band RF circuits. Published by AIP Publishing.11sciescopu