Biochemistry and mode of action of the Bacillus sphaericus toxins

Bacillus sphaericus produces at least two toxins which are highly toxic to mosquito larvae. The binary toxin, which is comprised of proteins of 51.4 and 41.9 kDa, is present in all highly insecticidal strains. The 100 kDa SSII-1 toxin is present in most highly insecticidal as well as the weakly insecticidal strains. The current status of studies on biochemistry and mode of action of these toxins is reviewed.

An approximate mathematical model for solidification of a flowing liquid in a microchannel

A mathematical model is developed to analyse the combined flow and solidification of a liquid in a small pipe or two-dimensional channel. In either case the problem reduces to solving a single equation for the position of the solidification front. Results show that for a large range of flow rates the closure time is approximately constant, and the value depends primarily on the wall temperature and channel width. However, the ice shape at closure will be very different for low and high fluxes. As the flow rate increases the closure time starts to depend on the flow rate until the closure time increases dramatically, subsequently the pipe will never close.

Analyse des cannabinoïdes par spectrométrie de masse en mode tandem = Analysis of cannabinoids by tandem mass spectrometry

Depuis quelques années, la spectrométrie de masse en tandem (MS/MS) ne cesse de gagner du terrain comme méthode d'analyse en toxicologie forensique, notamment pour le dosage des cannabinoïdes. Couplée à la chromatographie liquide (LC) ou gazeuse (GC), elle permet l'identification fiable et le dosage rapide du THC, de son précurseur acide, et de ses principaux métabolites, y compris les glucuronides. Au cours de ces dix dernières années, un nombre significatif de publications sont parues sur ce sujet. L'objectif de cet article est de passer en revue les analyses par spectrométrie de masse en tandem des cannabinoïdes dans diverses matrices biologiques. In recent years, tandem mass spectrometry (MS/MS) is gaining ground as a reference method of analysis in clinical and forensic toxicology, especially for the determination of cannabinoids. Coupled to liquid chromatography (LC) or gas chromatography (GC), it allows the definitive identification and rapid determination of THC, its acid precursor, and its major metabolites, including the glucuronides. During the past decade, several methods of analysis of cannabinoids in different matrices have appeared on this subject. The aim of this paper is to review the analysis of cannabinoids by tandem mass spectrometry methods in various biological matrices

Mosquitocidal bacterial toxins: diversity, mode of action and resistance phenomena

Bacteria active against dipteran larvae (mosquitoes and black flies) include a wide variety of Bacillus thuringiensis and B. sphaericus strains, as well as isolates of Brevibacillus laterosporus and Clostridium bifermentans. All display different spectra and levels of activity correlated with the nature of the toxins, mainly produced during the sporulation process. This paper describes the structure and mode of action of the main mosquitocidal toxins, in relationship with their potential use in mosquito and/or black fly larvae control. Investigations with laboratory and field colonies of mosquitoes that have become highly resistant to the B. sphaericus Bin toxin have shown that several mechanisms of resistance are involved, some affecting the toxin/receptor binding step, others unknown.

Differentiation of blue ballpoint pen by positive and negative mode LDI-MS

Usually, the differentiation of inks on questioned documents is carried out by optical methods and thin layer chromatography (TLC). Therefore, spectrometric methods were also proposed in forensic literature for the analysis of dyes. Between these techniques, laser desorption/ionization mass spectrometry (LDI-MS) has demonstrated a great versatility thanks to its sensitivity to blue ballpoint ink dyes and minimal sample destruction. Previous researches concentrated mostly on the LDI-MS positive mode and have shown that this analytical tool offers higher discrimination power than high performance TLC (HPTLC) for the differentiation of blue ballpoint inks. Although LDI-MS negative mode has already been applied in numerous forensic domains like the studies of works of art, automotive paints or rollerball pens, its potential for the discrimination of ballpoint pens was never studied before. The aim of the present paper is therefore to evaluate its potential for the discrimination of blue ballpoint inks. After optimization of the method, ink entries from 33 blue ballpoint pens were analyzed directly on paper in both positive and negative modes by LDI-MS. Several cationic and anionic ink components were identified in inks; therefore, pens were classified and compared according to their formulations. Results show that additional information provided by anionic dyes and pigments significantly increases the discrimination power of positive mode. In fact, it was demonstrated that classifications obtained by the two modes were, to some extent, complementary (i.e., inks with specific cationic dyes not necessarily contained the same anionic components).

Fecundity of ant queens in relation to their age and the mode of colony founding

The change over time in the fecundity and weight of queens was investigated in three monogynous, independent colony founding species,Lasius niger, Camponotus ligniperda andC. herculaneus, and two polygynous dependent colony founding species,Plagiolepis pygmaea andIridomyrmex humilis. Queens of the three species founding independently exhibited a similar pattern with a significant loss of weight between mating and the emergence of the first workers. In contrast, weights of queens of the species employing dependent colony founding remained more stable. Fecundity of queens founding independently increased slowly with time whereas fecundity of queens founding dependently reached the maximum level some weeks after the beginning of the first reproductive season. These results are discussed in relation to some differences in the life history (e.g., life-span) between queens utilizing independent and dependent colony founding.

Sales restriction, quality selection and the mode of competition

A regulator imposing “sales restrictions” on firms competing in oligopolistic markets may enhance quality provision by the firms. Moreover, for most restrictions levels, the impact on quality selection is invariant to the mode of competition

One-dimensional solidification of supercooled melts

In this paper a one-phase supercooled Stefan problem, with a nonlinear relation between the phase change temperature and front velocity, is analysed. The model with the standard linear approximation, valid for small supercooling, is first examined asymptotically. The nonlinear case is more difficult to analyse and only two simple asymptotic results are found. Then, we apply an accurate heat balance integral method to make further progress. Finally, we compare the results found against numerical solutions. The results show that for large supercooling the linear model may be highly inaccurate and even qualitatively incorrect. Similarly as the Stefan number β → 1&sup&+&/sup& the classic Neumann solution which exists down to β =1 is far from the linear and nonlinear supercooled solutions and can significantly overpredict the solidification rate.