Resistance and Synergism of Insecticides in Diamondback Moth, Plutella Xylostella (Lepidoptera : Yponomeutidae)

A leaf-dipped bioassay was conducted to evaluate the toxicity of insecticides cypermethrin, permethrin, fipronil, avermectin b1 and emamectin benzoate against two lowland (Karak & Cheng strain) and a susceptible strains of diamondback moth (DBM). The synergistic effect of piperonyl butoxide (PBO), S,S,8- tributylphosphorotrithioate (DEF) and maleic acid diethyl ester (MADE) on the toxicity of the insecticides tested were also conducted by the combined leafdipped/topical bioassay. Both the lowland strains showed high LC50 values (> Ug/mL) for cypermethrin and permethrin. Based on the LC50 values, toxicities of the insecticides tested in decreasing order for the Karak and Cheng strains were : emamectin benzoate> avermectin b] > fipronil > permethrin > cypermethrin. The most toxic insecticide was emamectin benzoate with LC50 value of 1.62 X 10-5mg/L and 1.59 X 10-5mg/L for Cheng and Karak strain respectively. The slope of the concentration-mortality line indicated that both field-collected strains gave homogenous response towards the cypermethrin and permethrin but not the newer insecticides. The results also showed that the DBM developed high level of resistance toward cypermethrin and permethrin. Cheng strain showed a higher resistance ratio for fipronil compared with the Karak strain. In synergism study, cypermethrin was highly synergised by PBO compared to other insecticides tested. Cypermethrin was synergised 19.8-fold and 12.6-fold for Karak and Cheng strain respectively. Both DEF and MADE showed little synergistic effects to the insecticides tested with synergistic ratio of less than 3-fold for both Cheng and Karak strain respectively. The results suggested that microsomal monooxygenases played an important role in the detoxification metabolism of cypermethrin in both strains of DBM. Esterases and glutathione s-ttansferases, however, played a minor role in the metabolism of the insecticides for both strains of DBM

Algebra diagrams: a HANDi introduction

A diagrammatic notation for algebra is presented – Hierarchical Al- gebra Network Diagrams, HANDi. The notation uses a 2D network notation with systematically designed icons to explicitly and coherently encode the fun- damental concepts of algebra. The structure of the diagrams is described and the rules for making derivations are presented. The key design features of HANDi are discussed and compared with the conventional formula notation in order demonstrate that the new notation is a more logical codification of intro- ductory algebra

Ballistic electron emission microscopy spectroscopy study of AlSb and InAs/AlSb superlattice barriers

Due to its large band gap, AlSb is often used as a barrier in antimonide heterostructure devices. However, its transport characteristics are not totally clear. We have employed ballistic electron emission microscopy (BEEM) to directly probe AlSb barriers as well as more complicated structures such as selectively doped n-type InAs/AlSb superlattices. The aforementioned structures were grown by molecular beam epitaxy on GaSb substrates. A 100 Å InAs or 50 Å GaSb capping layer was used to prevent surface oxidation from ex situ processing. Different substrate and capping layer combinations were explored to suppress background current and maximize transport of BEEM current. The samples were finished with a sputter deposited 100 Å metal layer so that the final BEEM structure was of the form of a metal/capping layer/semiconductor. Of note is that we have found that hole current contributed significantly to BEEM noise due to type II band alignment in the antimonide system. BEEM data revealed that the electron barrier height of Al/AlSb centered around 1.17 eV, which was attributed to transport through the conduction band minimum near the AlSb X point. Variation in the BEEM threshold indicated unevenness at the Al/AlSb interface. The metal on semiconductor barrier height was too low for the superlattice to allow consistent probing by BEEM spectroscopy. However, the superlattice BEEM signal was elevated above the background noise after repeated stressing of the metal surface. A BEEM threshold of 0.8 eV was observed for the Au/24 Å period superlattice system after the stress treatment

Superconductivity in Ti-doped Iron-Arsenide Compound Sr4Cr0.8Ti1.2O6Fe2As2

Superconductivity was achieved in Ti-doped iron-arsenide compound Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The x-ray diffraction measurement shows that this material has a layered structure with the space group of \emph{P4/nmm}, and with the lattice constants a = b = 3.9003 A and c = 15.8376 A. Clear diamagnetic signals in ac susceptibility data and zero-resistance in resistivity data were detected at about 6 K, confirming the occurrence of bulk superconductivity. Meanwhile we observed a superconducting transition in the resistive data with the onset transition temperature at 29.2 K, which may be induced by the nonuniform distribution of the Cr/Ti content in the FeAs-42622 phase, or due to some other minority phase.Comment: 3 pages, 3 figure

Systems-Disconjugacy of a Fourth-Order Differential Equation with a Middle Term

Systems-conjugate points have been introduced and studied by John Barrett \cite{barr} in relation with the self-adjoint fourth order differential equation $$(r(x)y")"-(q(x)y')'= p(x)y,$$ where $r(x)>0$, $p(x)>0$ and $q\equiv0$. In this paper we extend some of his results to more general cases, when $q(x)$ is free of any sign restrictions.Comment: 13 pages, 0 figure