Spontaneous Dynamics of Asymmetric Random Recurrent Spiking Neural Networks

We study in this paper the effect of an unique initial stimulation on random recurrent networks of leaky integrate and fire neurons. Indeed given a stochastic connectivity this so-called spontaneous mode exhibits various non trivial dynamics. This study brings forward a mathematical formalism that allows us to examine the variability of the afterward dynamics according to the parameters of the weight distribution. Provided independence hypothesis (e.g. in the case of very large networks) we are able to compute the average number of neurons that fire at a given time -- the spiking activity. In accordance with numerical simulations, we prove that this spiking activity reaches a steady-state, we characterize this steady-state and explore the transients.Comment: 28 pages, 7 figure

Contribution à l'étude de la validité de différents modèles, utilisés lors de l'adsorption de solutés sur charbon actif

Les résultats de l'adsorption sur charbon actif en poudre de solutions aqueuses de différents composés organiques: phénol, aniline, nitrobenzène, acide salicylique, nitro-4 phénol, méthyl-2 dinitro-4,6 phénol, phénylalanine et tyrosine ont été traités à l'aide des équations de Langmuir, Elovich, Freundlich, Temkin, Fowler-Guggenheim, Hill et De Boer, Kiselev afin de déterminer divers paramètres d'équilibre: la capacité maximum d'adsorption, l'énergie d'adsorption, l'énergie d'interaction, les constantes d'équilibre adsorbat-adsorbant et les interactions (éventuelles) entre les molécules adsorbées.La relation de Temkin (3=RTt~Q In KoC permet de déterminer la variation de l'énergie d'adsorption ~Q et la constante Ko de l'équilibre (~3 est le degré de re- couvrement du charbon par le soluté, et C la concentration à l'équilibre). L'équa- tion de Fowler-Guggenheim KC=~3/(1~3) Exp (2 ~ W/RT) conduit à la déter- mination de l'énergie d'interaction W entre molécules adsorbées et à une constante d'équilibre K. Par contre, dans l'équation de Hill et de De Boer KlC=~/(1~)) Exp [~/(1~) - K2~/RTI, K2 représente une constante d'énergie d'interaction entre molécules adsorbées et, dans celle de Kiselev KIC=~3/[(1+ ~) (1 + Kn~3)]~ Kn est une constante de formation de complexe éventuel entre molécules adsorbées. On vérifie que l'application de la relation de Temkin est satisfaisante pour tous les composés étudiés et permet de les classer selon leur affinité sur le charbon mais les résultats obtenus en utilisant les équations suivantes (Fowler ...) montrent qu'il n'y aurait pas de formation de complexe ou d'interaction entre molécules adsorbées.Analysis of the results of adsorption from aqueous liquid media onto activated carbon can be carried out by different models based on thermodynamic principles. Classically the Langmuir (eq. 1), Freundlich or Elovich (eq. 4) isotherms are used, which lead to the determination of an experimental maximum capacity, qm, and a constant K, characteristic of the adsorbate-adsorbent interactions. The following equations (Table I) have been transposed from the vapour phase to the liquid phase. With the Temkin relation: [Theta]=RT/[Delta]QlnK[inf]0C (eq. 6), it is possible to determine the variation of adsorption energy, [Delta]Q, between the adsorbed molecules and the solid phase, and the equilibrium constant K[inf]0 ([Theta] is the degree of surface covering of the solid phase [Theta]=q/qm, q is the adsorption capacity). The Fowler-Guggenheim equation: KC=[[Theta]/(1-[Theta])] Exp (2[Theta]W/RT) (eq. 7) gives the interaction energy, W, between the adsorbed molecules and an equilibrium constant, K. The Hill and De Boer relation: K[inf]1C=[Theta]/(1-[Theta])] Exp [[Theta]/(1-[Theta]) -K[inf]2[Theta]/RT] (eq. 8) yields an energetic interaction constant K[inf]2 (J.mol-¹) characteristic of the interactions between the adsorbate molecules and an equilibrium constant, K[inf]1. In the Kiselev relation: K[inf]1C=([Theta]/[(1-[Theta]) (1 + K[inf]n[Theta]] (eq. 9), K[inf]n is a complex formation constant between adsorbed molecules and K[inf]1 is a constant relative to the adsorbate-adsorbent interaction. Linearization of the equations of Langmuir, and Elovich leads to qm and K values. For the Freundlich relation, if the experiments are made at constant Co and variable concentrations of adsorbent, the Freundlich relation can be transformed as relation (5): q=qm (C/Co)[sup]1/n). The value of qm and K are reported in the Table II. When the values obtained by the Elovich equation are very different from the Langmuir relation, they are not in concordance with the experimental adsorption isotherm as shown on the Figures 4, 5 and 6.A value of qm is necessary to calculate the ([Theta](=q/qm) of the Temkin, Hill-De Boer, Fowler- Guggenheim and Kiselev equations; [Theta] is calculated with the Langmuir value of qm: the linearized relations were tested for the following compounds: phenol, aniline, nitrobenzene, salicylic acid, 4-nitro phenol, 2-methyl-4,6 dinitro phenol, phenylalanine and tyrosine, studied at micromolar concentration. The results are shown in Table II. The Temkin linearization is of good quality for all the compounds; an example is given on the Figure 1. For the others (Figs. 2, 3), the linearization is not always verified (Hill-De Boer for phenylalanine: Fig. 3a) and the results are framed two times in the Table II.With the obtention of the two parameters [Delta][Theta], K K, W; K[inf]1, K[inf]2 and K[inf]1, K[inf]n, the isotherm can be recalculated. The results for some solutes are on Figures 4, 5, 6, 7, 8. Relatively poor results are obtained for Fowler-Guggenheim, Kiselev or Hill-De Boer models, where no association is present between the adsorbed molecules.The evolution of the variation of the adsorption energy ([Delta][Theta]) is reported on the Figure 9 for the different compounds. The greatest values are obtained for nitrobenzene and 4-nitro-phenol (+ 80, + 40 kJ.mol-¹ probably due to the presence of the nitro group). All the values are positive (exothermic reaction ( [Delta][Theta]=-[Delta]H)) showing the affinity of molecules for the activated carbon

Elimination de colorants de l'industrie textile par des sciures de bois

L'élimination de la couleur de rejets de petites industries textiles peut être réalisée à l'aide de sciures d'essences de bois diverses dont le choix est fait après étude de leur relargage dans l'eau (couleur et DCO); les sciures de chêne, de châtaignier, de pin Douglas conduisent à des relargages de substances fortement colorées correspondant à des DCO d'environ 60 mg d'oxygène par gramme de sciures sèches et ceci en réacteur discontinu. Par contre, les sciures de hêtre, bouleau, sapin et peuplier relarguent nettement moins de produits colorés ou non et conduisent à des DCO plus faibles, excepté pour le bouleau (30 mg d'O2.g-1).Le pH de l'eau est également modifié par addition de sciures et l'on obtient des valeurs de pH d'équilibre atteint en 10 min., de 4,3; 5; 5,8 et 7 pour le bouleau, le sapin, le hêtre et le peuplier respectivement.L'élimination de colorants à 25 mg.l-1 dans l'eau par des doses de sciures de 50 g.-1 pour 2 h de temps de contact, montre qu'une meilleure décoloration (98 à 100 %) est obtenue pour le colorant cationique Basic Red 22 avec les quatre sciures sélectionnées, qu'avec les colorants anioniques (ou acides) dont les valeurs de rétention, variables selon les sciures (de 4 à 8 %) peuvent être très bonnes également.Les isothermes d'adsorption permettent de déterminer les capacités d'adsorption à saturation; à titre d'exemple, des valeurs de 0,1 à 0,2 mmol.g-1 sont obtenues sur des sciures de peuplier et de hêtre pour le colorant BR 22 et de 4 à 8.10- mmol.g-1 pour le colorant anionique Acid Blue 25, sur ces mêmes sciures. Contrairement à d'autres matériaux, on observe que les résultats obtenus ne dépendent que très peu de la température (entre 15 et 35 °C).Une étude dynamique sur colonne confirme les écarts pour les deux types de colorants, mais les résultats dépendent de la vitesse de passage : des pourcentages d'élimination de 0,4 à 1 % en masse peuvent être obtenus pour l'AB 25 le BR 22 sur la sciure de hêtre. Il faut cependant signaler que les produits minéraux et organiques contenus dans les effluents colorés industriels diminuent l'efficacité des sciures par rapport à leur efficacité sur des solutions de colorants purs.Anticipated water pollution regulations require textile dye industries to reduce substantially the amount of colour in their effluents. One possible method of colour removal is through adsorption techniques. The most commonly used adsorbent for treatment of textile effluents is activated carbon. The capability of sawdust for removing colour was recognised some time ago (POOTS et al. 1978; ABO-ELELA and EL-DIB, 1987; ASFOUR et al., 1985) as were those of peat and of charred woollen fiber treatments (PERINEAU et al., 1983). Sawdust has recently received more attention (ASFOUR et al., 1985) owing to its economic advantages when the sawmills are near the textile mills. In order to measure the real efficacy of some types of sawdust, evaluation of the released coloured products and their influence on the effluent water pH are never described. The aim of the present work is to study and evaluate the behaviour of types of sawdust from Limousin woods (released COD and pH of solutions) and the discolouring power of the selected sawdust (beech, poplar, birch and fir trees) with respect to textile dyes in dilute solutions and industrial effluents.MATERIALS AND METHODSExperiments were conducted using sawdust from beech, chestnut, poplar, oak, birch, fir and Douglas pine, in doses of 50 g.l-1 of water. The industrial sawdust particle site was between 0.5 - 1.5 mm.The dyestuffs used in all the experiments are reported in table 1. The initial concentration of colouring matter was 25 mg.l-1 and determined spectrophotometrically at maximum absorbance wavelength. In a batch system the time required for equilibrium was 2 hours (or less).RESULTS AND DISCUSSIONKinetic rejections of the sawdust are shown in figure 1; four types of sawdust are suitable : beech, poplar, birch, and fir were selected for further experiments. The absorbance depends on the wavelength and becomes maximum near UV range (as shown in fig. 2 and 3). The COD of the released products is particularly important for chestnut, oak, Douglas pine (60 mg.O2.g-1; table 2) and also for birch (31 mg.O2.g-1). These data have never been mentioned in published works where the wood was not submitted to any form of pre-treatment.Sawdust contains some acidic or basic groups that modify the pH of water (fig. 6, 7) which becomes more acidic; the phenomenon can be used to neutralize textile fixing effluents loaded with carbonate ions (pH : 10). Batch results (table 3) indicate that the tour selected types of sawdust give good colour removal for the 8 dyes; particularly, the cationic dye : Basic Red 22 is discoloured with very good yield (96 to 99.5 %) on beech and on birch sawdust.A variation of temperature between 15 and 35 °C does not change significantly the adsorption results and at pH = 2, the release decreases (table 2) and the adsorption increases (table 4).Equilibrium conditions of adsorption of basic and acidic dyes on four types of dust were studied using the Langmuir equation; this equation was also used for the determination of the « ultimate capacity » Г∞ and the equilibrium constant K (STUMM and MORGAN, 1981). The resulting Г∞ and K for some dyes (AB 25, BR 22, NLB) on fir, beech, poplar, and birch sawdust are given in table 5. The best results were obtained for the cationic dye BR 22 which showed an ultimate capacity of 0.210 and 0.06 mmol.g-1 on beech and on birch sawdust respectively. [The result for other dyes is in the order of 0.005 mmol.g-1]. The results obtained by extrapolation of the linearized Langmuir equation are somewhat different from those obtained by the experimental saturation curve (fig. 8) for BR 22 on polar sawdust. For AB 25, the saturation curve shows a great increase of the adsorption capacity for concentrated solutions (2 - 2.25 g.l-1), this is probably due to a micellary process as shown on figure 9 : the critical micellary concentration is between 1.5 and 3.3 g.1-1.DYNAMIC STUDYFlow tests using small columns (3 - 7 cm of height) are used with beech sawdust for determining the breakthrough curves (rate : 1.03 m.h-1). The concentrations of AB 25, BR 22 and their mixture are 25 mg.l-1 (close to industrial waste-water concentration). The adsorption capacity deduced from the « Bed Depth Service Time » model is 0.4 % and 0.8 % for each dye respectively.Glass columns (4 cm diameter) containing 20 g or 30 g of beech sawdust were also used. The values of adsorption for a rate of 3.1 m.h-1 are 0.45 mg.g-1 (0.04 %) for AB 25 and 13 mg.g-1 (1.3 %) for BR 22. Approximately 650 litres of this dye can be treated by this sawdust (fig. 10 and 11).Industrial effluents (unknown composition) are less discoloured, probably due to the presence of many other compounds.Batch experiments adsorption of dyes on wood sawdust can lead to different measurements of the efficiency of the sawdust depending on rejection by the adsorbent of chemical species in the bulk solution. These substances modify the pH, the adsorbance of the solution and the amount of adsorbed dyes by competitive reaction

Wildlife Trade and Human Health in Lao PDR: An Assessment of the Zoonotic Disease Risk in Markets.

Although the majority of emerging infectious diseases can be linked to wildlife sources, most pathogen spillover events to people could likely be avoided if transmission was better understood and practices adjusted to mitigate risk. Wildlife trade can facilitate zoonotic disease transmission and represents a threat to human health and economies in Asia, highlighted by the 2003 SARS coronavirus outbreak, where a Chinese wildlife market facilitated pathogen transmission. Additionally, wildlife trade poses a serious threat to biodiversity. Therefore, the combined impacts of Asian wildlife trade, sometimes termed bush meat trade, on public health and biodiversity need assessing. From 2010 to 2013, observational data were collected in Lao PDR from markets selling wildlife, including information on volume, form, species and price of wildlife; market biosafety and visitor origin. The potential for traded wildlife to host zoonotic diseases that pose a serious threat to human health was then evaluated at seven markets identified as having high volumes of trade. At the seven markets, during 21 observational surveys, 1,937 alive or fresh dead mammals (approximately 1,009 kg) were observed for sale, including mammals from 12 taxonomic families previously documented to be capable of hosting 36 zoonotic pathogens. In these seven markets, the combination of high wildlife volumes, high risk taxa for zoonoses and poor biosafety increases the potential for pathogen presence and transmission. To examine the potential conservation impact of trade in markets, we assessed the status of 33,752 animals observed during 375 visits to 93 markets, under the Lao PDR Wildlife and Aquatic Law. We observed 6,452 animals listed by Lao PDR as near extinct or threatened with extinction. The combined risks of wildlife trade in Lao PDR to human health and biodiversity highlight the need for a multi-sector approach to effectively protect public health, economic interests and biodiversity

Identification of the First Oomycete Mating-type Locus Sequence in the Grapevine Downy Mildew Pathogen, Plasmopara viticola

Mating types are self-incompatibility systems that promote outcrossing in plants, fungi, and oomycetes. Mating-type genes have been widely studied in plants and fungi but have yet to be identified in oomycetes, eukaryotic organisms closely related to brown algae that cause many destructive animal and plant diseases. We identified the mating-type locus of Plasmopara viticola, the oomycete responsible for grapevine downy mildew, one of the most damaging grapevine diseases worldwide. Using a genome-wide association approach, we identified a 570-kb repeat-rich non-recombining region controlling mating types, with two highly divergent alleles. We showed that one mating type was homozygous, whereas the other was heterozygous at this locus. The mating-type locus encompassed 40 genes, including one encoding a putative hormone receptor. Functional studies will, however, be required to validate the function of these genes and find the actual determinants of mating type. Our findings have fundamental implications for our understanding of the evolution of mating types, as they reveal a unique determinism involving an asymmetry of heterozygosity, as in sex chromosomes and unlike other mating-type systems. This identification of the mating-type locus in such an economically important crop pathogen also has applied implications, as outcrossing facilitates rapid evolution and resistance to harsh environmental conditions