Etude sur modèle de la désinfection de l'eau par rayonnements ultraviolets

Le présent article rapporte les résultats d'une investigation des facteurs géométriques applicables à des réacteurs annulaires à mélange axial complet et appliqués à la désinfection des eaux au moyen de lumière UV de 254 nm. La loi de Bunsen-Roscoe est suivie en prenant en compte la dose corrigée par un facteur géométrique m; dose=mIot. Le bactériophage f2 ne montre pas de phase de latence de mortalité et constitue dès lors un modèle valable. La dose létale à 99 % mesurée est de 470 ± 30 J/m2.The f2-bacteriophage is chosen as a test organism to evaluate the geometrical factors which intervene in the disinfection of water by UV-light. This phage is an ARN and single strain cell which has the characteristic of being killed without a lethal lag phase being observed. It is also shown as a representative organism for the estimation of the virucidal action of UV-light.In this work a cold cathode mercury lamp emitting the 254 nm photon at low intensity, th.e. 14.9 W/m2 at the lamp surface, is used. The Lamp has the advantage that its photochemical yield does not depend on the temperature of the water investigated.The geometrical factor of different annular reactors is investigated by submersing the lamp in water contained in vessels of different diameters. The introduction of an artificial competitor, that is para-hydroxybenzoïc acid, which absorbs part of the 254 nm-photons also allows the impact of the reactor geometry to be evaluated. All the experiments are carried out in batch-type conditions and the water is completely mixed during the experiments. These conditions applied in laboratory investigations are representative of those existing in plug-flow reactors with complete axial mixing of discrete portions of the liquid contained in the annular space between the lamp and the reactor.In this work all data conform to the Bunsen-Roscoe Law relating the kinetics of first order decay to the irradiation dose : (I.t). No residual resisting organisms or "protected" organisms which could subsist at the end of exhaustive irradiation were observed.The practical dose, that is the dose at any point of the reactors taking into account the absorption of the light and the increasing surface irradiated at increasing reactor diameter and also the finite dimension of the lamp diameter is accounted for by a single correction factor m : Dose (D) = m.Io.t, in which, also according to the literature :       2 r o (1 - exp [- E (r- - ro) ] )m = ______________________________            E (r-2 - r2o)where ro and r- are respectively the lamp radius and the reactor radius. E is the extinction coefficient (base e).The data as a whole converge to a 99 % lethal dose of 470 ± 30 J/m2 in clear water, either absorbing or not at 254 nm.In the presence of turbidity, obtained by the introduction of 10 mgL-1 koalin the efficiency is enhanced by 15 to 20 X, that is the apparent 99 % lethal dose is of 400 ± 30 J/m2. By correcting the light intensity transmitted by reflection, this dose is about 420 J/m2.Turbidity in UV-disinfection is thus not necessarily a negative factor in disinfection of liquids with UV-light.This investigation as a whole establishes an "economical space" between lamp surface and reactor wall of about 4 cm at which the energy consumption for a given level of disinfection attains a sufficiently tow value

Philosophy of education. Filosofía de la educación

Bajo Palabra, Revista de Filosofí

Action research and democracy

This contribution explores the relationship between research and learning democracy. Action research is seen as being compatible with the orientation of educational and social work research towards social justice and democracy. Nevertheless, the history of action research is characterized by a tension between democracy and social engineering. In the social-engineering approach, action research is conceptualized as a process of innovation aimed at a specific Bildungsideal. In a democratic approach action research is seen as research based on cooperation between research and practice. However, the notion of democratic action research as opposed to social engineering action research needs to be theorized. So called democratic action research involving the implementation by the researcher of democracy as a model and as a preset goal, reduces cooperation and participation into instruments to reach this goal, and becomes a type of social engineering in itself. We argue that the relationship between action research and democracy is in the acknowledgment of the political dimension of participation: ‘a democratic relationship in which both sides exercise power and shared control over decision-making as well as interpretation’. This implies an open research design and methodology able to understand democracy as a learning process and an ongoing experiment

M & L Jaargang 4/2

RedactioneelJ. Vandenbreeden Het Belle-Vuehotel en de Rotonde (1910-1985) te Westende, een monument. [The Belle-Vue Hotel and the Rotunda (1910-1985) at Westende, a monument.]J. De Boeck en L. Masschelein Conservatie van textiel. [The Conservation of textile.]L. Meesters en L. Wylleman Het landschap Ertbrugge-Zwarte Arend in Wijnegem en Deurne. [The landscape Ertbrugge-Zwarte Arend at Wijnegem and Deurne.]Miek Goossens i.s.m. Hubert Davans De restauratie van De Olifant in Brugge. [The restoration of De Olifant at Bruges.]F. Welvaert 2000 jaar Zwinstreek. [2000 years of the Zwin region.]SummaryM&L Binnenkran

Structural basis for chain release from the enacyloxin polyketide synthase

Modular polyketide synthases and nonribosomal peptide synthetases are molecular assembly lines consisting of several multienzyme subunits that undergo dynamic self-assembly to form a functional mega-complex. N- and C-terminal docking domains are usually responsible for mediating interactions between subunits. Here we show that communication between two nonribosomal peptide synthetase subunits responsible for chain release from the enacyloxin polyketide synthase, which assembles an antibiotic with promising activity against Acinetobacter baumannii, is mediated by an intrinsically disordered short linear motif and a ß-hairpin docking domain. The structures, interactions and dynamics of these subunits are characterised using several complementary biophysical techniques, providing extensive insights into binding and catalysis. Bioinformatics analyses reveal that short linear motif/ß-hairpin docking domain pairs mediate subunit interactions in numerous nonribosomal peptide and hybrid polyketide-nonribosomal peptide synthetases, including those responsible for assembling several important drugs. Short linear motifs and ß-hairpin docking domains from heterologous systems are shown to interact productively, highlighting the potential of such interfaces as tools for biosynthetic engineering

Effects of dietary nitrate supplementation on symptoms of acute mountain sickness and basic physiological responses in a group of male adolescents during ascent to Mount Everest Base Camp

The purpose of this study was to investigate the effects of dietary nitrate supplementation, in the form of beetroot juice, on acute mountain sickness (AMS) symptoms and physiological responses, in a group of young males trekking to Mount Everest Base Camp (EBC). Forty healthy male students (mean age (SD): 16 (1) yrs) trekked to EBC over 11 days. Following an overnight fast, each morning participants completed the Lake Louise AMS questionnaire and underwent a series of physiological tests: resting blood pressure as well as resting and exercising heart rate, respiratory rate, and peripheral oxygen saturation. The exercise test consisted of a standardised 2-minute stepping protocol and measurements were taken in the last 10 seconds. Participants in the intervention arm of the study consumed 140 ml of concentrated beetroot juice daily, containing approximately 10 mmoles of nitrate, while those in the control arm consumed 140 ml of concentrated blackcurrant cordial with negligible nitrate content. Drinks were taken for the first seven days at high altitude (days 2 to 8), in two equal doses; one with breakfast, and one with the evening meal. Mixed modelling revealed no significant between-groups difference in the incidence of AMS (Odds Rationitrate vs. control: 1.16 (95% CI: 0.59; 2.29)). Physiological changes occurring during ascent to high altitude generally were not significantly different between the two groups (Model Coef (95% CI) – average difference nitrate vs. control: systolic blood pressure, 0.16 (-4.47; 4.79); peripheral oxygen saturation, 0.28 (-0.85; 1.41); heart rate, -0.48 (-8.47; 7.50) (Model Coef (95% CI) – relative difference nitrate vs. control: ventilatory rate, 0.95 (0.82; 1.08)). Modelling revealed that diastolic blood pressure was 3.37 mmHg (0.24; 6.49) higher for participants in the beetroot juice, however this difference was no larger than that found at baseline and no interaction effect was observed. Supplementation with dietary nitrate did not significantly change symptoms of AMS or alter key physiological variables, in a group of adolescent males during a high altitude trekking expedition. There was no evidence of harm from dietary nitrate supplementation in this context. Given the wide confidence intervals in all models, a larger sample size would be required to exclude a false negative result. Our data suggest that prolonged oral nitrate supplementation is safe and feasible at altitude but has little physiological or clinical effect

Discovery and Biosynthesis of Gladiolin: A Burkholderia gladioli Antibiotic with Promising Activity against Mycobacterium tuberculosis.

An antimicrobial activity screen of Burkholderia gladioli BCC0238, a clinical isolate from a cystic fibrosis patient, led to the discovery of gladiolin, a novel macrolide antibiotic with potent activity against Mycobacterium tuberculosis H37Rv. Gladiolin is structurally related to etnangien, a highly unstable antibiotic from Sorangium cellulosum that is also active against Mycobacteria. Like etnangien, gladiolin was found to inhibit RNA polymerase, a validated drug target in M. tuberculosis. However, gladiolin lacks the highly labile hexaene moiety of etnangien and was thus found to possess significantly increased chemical stability. Moreover, gladiolin displayed low mammalian cytotoxicity and good activity against several M. tuberculosis clinical isolates, including four that are resistant to isoniazid and one that is resistant to both isoniazid and rifampicin. Overall, these data suggest that gladiolin may represent a useful starting point for the development of novel drugs to tackle multidrug-resistant tuberculosis. The B. gladioli BCC0238 genome was sequenced using Single Molecule Real Time (SMRT) technology. This resulted in four contiguous sequences: two large circular chromosomes and two smaller putative plasmids. Analysis of the chromosome sequences identified 49 putative specialized metabolite biosynthetic gene clusters. One such gene cluster, located on the smaller of the two chromosomes, encodes a trans-acyltransferase (trans-AT) polyketide synthase (PKS) multienzyme that was hypothesized to assemble gladiolin. Insertional inactivation of a gene in this cluster encoding one of the PKS subunits abrogated gladiolin production, confirming that the gene cluster is responsible for biosynthesis of the antibiotic. Comparison of the PKSs responsible for the assembly of gladiolin and etnangien showed that they possess a remarkably similar architecture, obfuscating the biosynthetic mechanisms responsible for most of the structural differences between the two metabolites