Microcystin ecotypes in a perennial Planktothrix agardhii bloom

The dynamics and microcystins (MC) concentrations of a perennial Planktothrix agardhii bloom were investigated in a eutrophic lake (Viry-Chatillon, France). A weak relationship was observed between P. agardhii population biomass and the MC concentrations in a 1-year survey. To further investigate the causes of MC concentration changes, we concurrently conducted experiments on 41 strains isolated from this lake. We first checked the clonal diversity of P. agardhii population (i) by molecular techniques, to assess the presence of MC synthetase gene (mcyB), (ii) by biochemical assay (PP2A inhibition assay), for MC production, and (iii) by mass spectrometry (MS), to identify the MC chemotypes. Our results illustrated the diversity of genotype and MC chemotypes within a P. agardhii natural population. Eleven chemotypes among the 16 possible ones were found by MS. Furthermore, we noticed major differences in the MC content of isolated strains (from 0.02 to 1.86 microg equiv. MC-LR mg DW(-1), n=25). Growth and MC production of one MC-producing strain and one non-MC-producing strain were also assessed at two temperatures (10 and 20 degrees C). We showed that growth capacities of these strains were similar at the two tested temperatures, and that the MC production rate was correlated to the growth rate for the MC-producing strain. On the basis of these results, several hypotheses are discussed to explain the weakness of relationships between natural P. agardhii biomass and MC concentration. One of the main reasons could lie in the proportion of MC-producing clones and non-MC-producing clones that may change during the sampling period. Also, the MC-producing clones may present different intracellular MC content due to (i) MC chemotypes diversity, (ii) changes in MC variants proportions within a strain, and (iii) changes in MC rate production depending on the physiological state of cells. Finally, we concluded that various biological organization levels have to be considered (population, cellular and molecular), through an integrative approach, in order to provide a better understanding of P. agardhii in situ MC production.     

Desargues and Leibniz: In the Black Box - A Mathematical Model of the Leibnizian Monad

Here Bernard Cache provides a detailed analysis of a paper written in 1636 by the French mathematician, architect and engineer, Girard Desargues. Desargues is best known as the founder of projective geometry. Cache explains how he initally developed this significant concept in response to the very practical problems of producing a perspectival drawing. The introduction of projective geometry, though, had potentially more far-reaching implications on philosophical thought, informing the theory of monads developed by the German philosopher and mathematician Gottfried Leibniz in 1714 to explain the metaphysics of simple substances. Copyright © 2011 John Wiley & Sons, Ltd.     

Statistics of the radio-frequency signal based on K distribution with application to echocardiography

We study in this paper the statistics of the radio frequency (RF) signal in the case of partially developed speckle. Using the K distribution framework, we give the probability density function of the associated distribution, the corresponding moments, and estimators for the parameters of the distribution. The consistency of the proposed estimators is evaluated in terms of their bias and variance through numerical simulations. The ability of the proposed distribution to model RF echographic signals from cardiac tissues is evaluated from data acquired in vivo.     

Elaboration of single wall carbon nanotubes-based gas sensors: Evaluating the bundling effect on the sensor performance

In this article, carbon nanotube (CNT)-based sensors have been prepared using dispersion techniques. Sensors are obtained from a dispersion of CNTs using either chloroform as a solvent or sodium dodecylbenzene sulfonate as a surfactant. These sensors are prepared by drop-cast deposition of the solutions on interdigitated electrodes. The organic solvent processing leads to CNT layers where carbon nanotubes are obtained as larger bundles, whereas smaller bundles and individual tubes are predominantly formed in the surfactant processing. Under gas exposure (NO₂), both sensors respond to low gas concentrations; however, the sensing layers composed of larger bundles of CNTs present a slightly different behaviour (in terms of rapid stabilisation and sensitivity) compared to those made of individual CNTs.     

城市水系统可持续管理的需求分析

为解决城市水问题,需要在城市水系统的管理上采用可持续理念.首先根据控制回路原则建立了城市水系统的可持续管理模型;然后对城市水系统可持续管理的需求情况进行了分析,包括实现可持续发展的各种技术(常规水技术和其他可选技术)、数据收集和监视方法,以及可持续性评价方法;最后在前人研究的基础上讨论了一种城市水系统可持续性水平的分类方法.     

3-hydroxybenzene 1,2,4-trisphosphate, a novel second messenger mimic and unusual substrate for type-I myo-inositol 1,4,5-trisphosphate 5-phosphatase: Synthesis and physicochemistry

3-Hydroxybenzene 1,2,4-trisphosphate 4 is a new myo-inositol 1,4,5-trisphosphate analogue based on the core structure of benzene 1,2,4-trisphosphate 2 with an additional hydroxyl group at position-3, and is the first noninositol based compound to be a substrate for inositol 1,4,5-trisphosphate 5-phosphatase. In physicochemical studies on 2, when three equivalents of protons were added, the (31)P NMR spectrum displayed monophasic behaviour in which phosphate-1 and phosphate-2 behaved independently in most of the studied pH range. For compound 4, phosphate-2 and phosphate-4 interacted with the 3-OH group, which does not titrate at physiological pH, displaying complex biphasic behaviour which demonstrated co-operativity between these groups. Phosphate-1 and phosphate-2 strongly interacted with each other and phosphate-4 experienced repulsion because of the interaction of the 3-OH group. Benzene 1,2,4-trisphosphate 2 is resistant to inositol 1,4,5-trisphosphate type I 5-phosphatase catalysed dephosphorylation. However, surprisingly, 3-hydroxybenzene 1,2,4-trisphosphate 4 was dephosphorylated by this 5-phosphatase to give the symmetrical 2,3-dihydroxybenzene 1,4-bisphosphate 16. The extra hydroxyl group is shown to form a hydrogen bond with the vicinal phosphate groups at -15 degrees C, and (1)H NMR titration of the ring and hydroxyl protons in 4 shows the OH proton to be strongly stabilized as soon as the phosphate groups are deprotonated. The effect of the phenolic 3-OH group in compound 4 confirms a critical role for the 6-OH group of the natural messenger in the dephosphorylation mechanism that persists even in radically modified analogues.