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1
Vargas, Taise Ferreira, Célia Ceolin Baía, Tatiana Lemos da Silva Machado, Caetano Chang Dórea, and Wanderley Rodrigues Bastos. "Decay of Free Residual Chlorine in Wells Water of Northern Brazil." Water 13, no. 7 (April 4, 2021): 992. http://dx.doi.org/10.3390/w13070992.
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The concentration of chlorine in water declines as it reacts with various substances, causing decay of the residual free chlorine until its total consumption. In light of the typical characteristics of the water from protected dug wells and tube wells, this study aimed to evaluate the decay kinetics of free chlorine in the water of alternative individual supply (AIS) solutions used in the city of Porto Velho in the Brazilian Amazon region. The free chlorine decay constant in the water was evaluated by “bottle tests,” applying a first-order model. According to the results, the type of well and initial chlorine concentration significantly influences the free chlorine decay speed. The water samples from the tubular wells had lower chlorine demand levels, attributed to their better water quality. The simulation of the residual chlorine decay in the different supply sources is an important tool to support safe disinfection processes.
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Liu, Jing Qing, Wei Jiang, Jian Min Wu, and Cong Li. "The Influence of Total Hardness on Chlorine Decay in Water Distribution Systems." Applied Mechanics and Materials 535 (February 2014): 776–84. http://dx.doi.org/10.4028/www.scientific.net/amm.535.776.
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Free chlorine decay is a main issue in drinking water treatment since free chlorine concentration is a common indicator in drinking water security. The current view of free chlorine decay is that the process is mainly affected by the natural organic matter in water, temperature and initial chlorine concentration, on which temperature has the most evidently effect. As is generally accepted, total hardness has no effect on it. This paper investigated the impact of water hardness on the chlorine decay. The influence of varying metal ions concentrations which contribute to water hardness on effective chlorine decay constants was assessed. The results implied that total hardness had an evidently influences on the chlorine decay in tap water or DI water. For the range of metal ions concentration in this experiment effective chlorine decay constants ranged from an increase by +182% to +349% from the different concentration of metal ions.
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Wu, Hongjian, and Caetano C. C. Dorea. "Towards a Predictive Model for Initial Chlorine Dose in Humanitarian Emergencies." Water 12, no. 5 (May 25, 2020): 1506. http://dx.doi.org/10.3390/w12051506.
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Free chlorination is a widely employed disinfection method in humanitarian water provision due to its many advantages. However, its effective application is hindered by the challenge in determining adequate initial doses to achieve free chlorine residuals that satisfy both health and aesthetic requirements. Current guidelines show varying recommended dosing strategies, and many do not adequately consider chlorine decay mechanisms that occur during water storage. Even though turbidity is commonly used as a criterion for deciding chlorine dose, it may not be an adequate proxy for the water quality in many cases. This paper addresses the fundamental relationships between chlorine decay kinetics and selected key water parameters (i.e., natural organic matter, water temperature, chlorine demand) by conducting chlorine decay tests in controlled conditions and in jerrycans (i.e., simulating humanitarian water treatment conditions). Chlorine decay constant from the Feben and Taras’s empirical model and first order model formed linear and exponential relationships with two water parameters (UVA254 and 30-min chlorine demand). With these relationships, the two chlorine decay models can be calibrated quickly and frequently in the field, allowing effective determination of initial chlorine dose. These two models calibrated based on the suggested water parameters from the study could predict chlorine decay in water having a main chlorine demand-inducing constituents as natural organic matter. However, they underpredicted chlorine decay in surface water with additional chlorine reactants. Further research on additional chlorine decay mechanisms is needed to expand the applicability of the models.
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Kiéné, L., W. Lu, and Y. Lévi. "Relative importance of the phenomena responsible for chlorine decay in drinking water distribution systems." Water Science and Technology 38, no. 6 (September 1, 1998): 219–27. http://dx.doi.org/10.2166/wst.1998.0255.
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Free chlorine consumption in distribution systems is due both to chemical reactions occurring in the bulk phase and at the pipe walls. Knowledge of the relative importance of these various reactions is needed in order to improve chlorine decay modeling. Experimental results carried out in this study make it possible to propose a hierarchical classification of the main parameters involved in the free chlorine decay observed in distribution systems. Corrosion of metallic pipe appears to be a major parameter, while synthetic materials are of little influence. The rate of chlorine decay in bulk phase can be estimated according to the TOC and the temperature. Influence of biofilms depends on the BDOC content of water, and on the pipe diameter. Chlorine decay due to corrosion phenomena must be modeled according to a zero order kinetics, while chlorine decay due to other parameters can be modeled according to a first order kinetics with respect to chlorine.
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Moore, Nathan, Shelir Ebrahimi, Yanping Zhu, Chengjin Wang, Ron Hofmann, and Susan Andrews. "A comparison of sodium sulfite, ammonium chloride, and ascorbic acid for quenching chlorine prior to disinfection byproduct analysis." Water Supply 21, no. 5 (March 2, 2021): 2313–23. http://dx.doi.org/10.2166/ws.2021.059.
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Abstract This study compared 3 commonly used quenching agents for dechlorinating samples prior to disinfection byproduct (DBP) analysis under typical drinking water sampling conditions for a representative suite of chlorination byproducts. Ascorbic acid and sodium sulfite quenched the residual free chlorine to below detection within 5 seconds. Ammonium chloride did not quench the chlorine to below detection with up to a 70% molar excess, which agrees with published ammonium chloride-chlorine chemistry. With respect to the DBPs, ascorbic acid worked well for the trihalomethanes and haloacetic acids, except for dibromoiodomethane, which exhibited 2.6–28% error when using ascorbic acid compared to non-quenched control samples. Sodium sulfite also worked well for the trihalomethanes (and performed similarly to ascorbic acid for dibromoiodomethane) and was the best performing quenching agent for MX and the inorganic DBPs, but contributed to the decay of several emerging DBPs, including several halonitromethanes and haloacetamides. Ammonium chloride led to considerable errors for many DBPs, including 27–31% errors in chloroform concentrations after 24 hours of storage. This work shows that ascorbic acid is suitable for many of the organic DBPs analyzed by gas chromatography-electron capture detection and that sodium sulfite may be used for simultaneous chlorite, chlorate, and bromate analysis.
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VIRTO, R., D. SANZ, I. ÁLVAREZ, S. CONDON, and J. RASO. "Comparison of the Chlorine Inactivation of Yersinia enterocolitica in Chlorine Demand and Demand-Free Systems." Journal of Food Protection 68, no. 9 (September 1, 2005): 1816–22. http://dx.doi.org/10.4315/0362-028x-68.9.1816.
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Inactivation of Yersinia enterocolitica by chlorine (0.6 to 20 ppm) was investigated in distilled water and in tryptic soy broth (TSB, 0.015%) at different temperatures (4, 20, and 40°C). In distilled water, chlorine inactivation of Y. enterocolitica was enhanced by increasing the temperature from 4 to 20°C, and survival curves were described by a model that assumed first-order kinetics followed by tailing in which the microbial concentration remained constant. The presence of TSB increased chlorine resistance of Y. enterocolitica, and survival curves were concave downward. These survival curves were described by a model based on the Weibull distribution. Chlorine decay in distilled water was independent of temperature and of the initial concentration of available chlorine and was modeled by first-order reaction kinetics. Chlorine decay in TSB was independent of the initial chlorine concentration but depended on the treatment temperature and was modeled by the addition of two first-order decay equations. The increased resistance of Y. enterocolitica to chlorine in TSB was not due only to the chlorine demand by the TSB components. These components protected Y. enterocolitica cells from the antimicrobial effect of chlorine.
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Kang, Sungwon, Jaiyoung Lee, Hyundong Lee, Jaehyun Park, Pilljae Kwak, and Hyunje Oh. "Characteristics of Residual Free Chlorine Decay in Reclaimed Water." Journal of Korean Society of Environmental Engineers 35, no. 4 (April 30, 2013): 276–82. http://dx.doi.org/10.4491/ksee.2013.35.4.276.
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Taterka, Austin, Robert Miskewitz, Robert R. Sharp, and Jurek Patoczka. "Modeling chlorine-produced oxidant demand and dilution in chlorinated combined sewer overflow discharges." Journal of Environmental Science and Health, Part A 55, no. 3 (February 23, 2020): 266–74. http://dx.doi.org/10.1080/10934529.2019.1686890.
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Combined sewer overflow (CSO) water introduces pathogens to receiving waters. To control pathogenic releases, chlorine may be added to disinfect CSO water. The added chlorine may react with water constituents to form oxidative species known as chlorine-produced oxidants (CPO). CPO are the sum of free and combined oxidative species that form upon adding free chlorine-bearing compounds (e.g. gaseous chlorine or hypochlorite) to water. CPO discharge is often regulated by governing agencies. Current methods to model CPO behavior do not account for CPO decay and dilution simultaneously in receiving water. This study creates a novel model for CPO demand and dilution in receiving water from chlorinated effluent in order to determine site-specific practices for implementation of a CSO water disinfection regime. To do this, representative receiving water was collected and dosed with 1, 2, and 4 mg/L chlorine. The residual chlorine was measured at intervals up to 30 min after dosing. The immediate and subsequent chlorine demand was calculated, with the subsequent demand modeled by simultaneous application of dilution and decay using pseudo-first-order decay kinetics. A comparison of model calculations indicates that application of dilution before decay underestimates CPO demand, while application of decay before dilution overestimates CPO demand.
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Buamah, R., K. Akodwaa-Boadi, M. Paintsil, E. K. Baah-Ennumh, and A. A. Adjaottor. "Modelling the chlorine decay process in a distribution network using a pilot system." Water Practice and Technology 9, no. 4 (December 1, 2014): 534–50. http://dx.doi.org/10.2166/wpt.2014.060.
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Chlorine is one of the many disinfectants used to ensure bacteriological safety of drinking water. Usually residual chlorine is maintained within the distribution network to combat any probable re-contamination of the distributed water. This residual free chlorine, however, decays in water due to its reaction with the bulk water and the pipe material or deposits on the pipe walls. This study aimed at determining and modelling chlorine decay in the Kumasi water distribution network (KWDN) and determined locations where residual chlorine boosting is necessary. A double-jacketed batch reactor and a constructed pilot distribution system (PDS) were used to determine the bulk and wall decay coefficients. The PDS was run using aged PVC pipes (15–20 years), asbestos concrete pipes (40–50 years) and cast iron pipes (84 years) that have been in use in the KWDN. The SynerGEE® hydraulic model was used to identify the ‘zero chlorine’ points and predict top-up quantities. The bulk decay coefficient was found to be 0.053 h−1 within 8 hours at 26 °C and the residual chlorine decayed within the bulk fluid by 32–34% of its initial dose. Under the conditions tested, the cast iron pipes had the highest overall decay coefficients (K). Five locations within the network were identified as probable chlorine boosting points).
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Musz-Pomorska, Anna, Marcin K. Widomski, Agnieszka Matczuk, and Konrad Sadura. "Modeling chlorine distribution in water supply system utilizing empirically determined chlorine decay rate." E3S Web of Conferences 100 (2019): 00054. http://dx.doi.org/10.1051/e3sconf/201910000054.
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Analysis of free chlorine propagation in water supply network has a significant meaning for the process of water distribution. Results of numerical studies allow the proper selection of disinfectant or suitable monitoring of pipelines endangered by stagnation of water. The first-order reaction of chlorine decay in pipe boundary layer and inside the waterbody is commonly successfully assumed in numerical modeling. The aim of this studies was to analyze transport of chlorine inside the rural water supply system. The calculations were performed with application of Epanet 2.0 with assumed the first-order re action of chlorine decay and empirically determined chlorine decay rate in the mass of waterbody. The periodical disinfection of water in the network with the constant chlorine concentration 0.3 mg·dm-3 introduced during the whole time duration of simulation was assumed to calculations. The obtained results of chlorine distribution showed that even after 4 days there were available pipelines in which concentration of free chlorine was lower than 0.2 mg·dm-3. Thus, the microbiological protection of water quality is unavailable in these pipelines.
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Abdel-Gawad, Shaden T., and Jatinder K. Bewtra. "Decay of chlorine in diluted municipal effluents." Canadian Journal of Civil Engineering 15, no. 6 (December 1, 1988): 948–54. http://dx.doi.org/10.1139/l88-126.
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Laboratory studies were conducted to develop a model for the overall decay of total residual chlorine (TRC) under various conditions in the natural streams. This model assumes that a portion of the initial chlorine concentration is used to satisfy the immediate chlorine demand and the remainder is subject to gradual decay.The important parameters influencing the gradual decay of TRC, after mixing in the rivers, were found to be photolysis, evaporation, free radical oxidation, temperature, and turbulence. The decay rate is catalyzed by ultraviolet light and increases significantly as the ratio of area to volume of the container increases. The average level of turbulence in streams is found to approximately double the decay rate obtained under quiescent conditions. Key words: residual chlorine, natural streams, decay, evaporation, photolysis, turbulence, temperature effect, municipal effluents.
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Vigneault, Clément, Jerry A. Bartz, and Steven A. Sargent. "Postharvest Decay Risk Associated with Hydrocooling Tomatoes." Plant Disease 84, no. 12 (December 2000): 1314–18. http://dx.doi.org/10.1094/pdis.2000.84.12.1314.
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Tomatoes (breaker stage) hydrocooled with a cell suspension of Erwinia carotovora subsp. carotovora containing 50 to 200 mg of free chlorine per liter (ppm) (10°C, pH 7) remained decay free during a 10-day storage at 20°C. Sporadic disease appeared during storage of tomatoes similarly cooled with chlorinated water containing spores of Rhizopus stolonifer. In contrast, when chlorine was omitted from the pathogen suspensions, 50 to 100% of the fruit became diseased. A laboratory-scale shower hydrocooler reduced fruit temperatures from 35 to 15°C within 13.3 min, whereas a flume cooler produced the same temperature reduction in 10.5 min. In both systems, tomatoes increased in weight during cooling, evidence for water uptake. Larger weight increases occurred among tomatoes cooled in the shower than in the flume. An upward instead of downward orientation of stem scars under the shower streams led to significantly larger weight increases, presumably because pores in the stem scar were continuously flooded with water. Tomatoes intermittently submerged in cold water (10 2-min immersions followed by 30-s pauses) absorbed significantly less water than those continuously submerged for 20 min. Hydrocooling appears to be a viable method for rapid cooling of tomatoes. Technical refinements in the hydrocooling process that prevent continuous coverage of fruit surfaces by water should reduce water uptake and the associated risk of pathogen internalization. Maintenance of free chlorine at up to 200 ppm in the cooling water and prevention of direct water pressure on fruit should minimize decay risks. No evidence of phytotoxicity was observed among fruit infiltrated with 200 ppm of chlorine. These tomatoes ripened similarly to those that were not cooled or were cooled in tap water.
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Tonev, R., and G. Dimova. "Investigation of chlorine wall decay in an old, decommissioned metallic pipe using a pipe section reactor." Water Supply 20, no. 3 (February 7, 2020): 953–62. http://dx.doi.org/10.2166/ws.2020.017.
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Abstract The study investigates the kinetics of free chlorine depletion in tap water from the Sofia distribution network. The overall decay rates, the bulk reaction rate coefficient, the wall reaction rate coefficient and the influence of mass transfer have been determined in a laboratory pipe section reactor (PSR), testing an old decommissioned metallic pipe. In total, 23 series of experiments were performed under different initial free chlorine concentrations and different hydraulic conditions. The applicability of different chlorine decay mathematical models has been investigated. A new model was proposed, combining zero order bulk reactions and first order wall reactions, describing the laboratory results with Nash-Sutcliffe efficiency coefficients over 0.99. The obtained values for the wall reaction coefficient vary in the range 0.008–0.030 m/h, decreasing exponentially with increasing initial chlorine concentration.
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Kastl, G., I. Fisher, V. Jegatheesan, J. Chandy, and K. Clarkson. "Prediction of chlorine and trihalomethanes concentration profile in bulk drinking water distribution systems from laboratory data." Water Supply 3, no. 1-2 (March 1, 2003): 239–46. http://dx.doi.org/10.2166/ws.2003.0110.
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Nearly all drinking water distribution systems experience a “natural” reduction of disinfection residuals. The most frequently used disinfectant is chlorine, which can decay due to reactions with organic and inorganic compounds in the water and by liquid/solids reaction with the biofilm, pipe walls and sediments. Usually levels of 0.2-0.5 mg/L of free chlorine are required at the point of consumption to maintain bacteriological safety. Higher concentrations are not desirable as they present the problems of taste and odour and increase formation of disinfection by-products. It is usually a considerable concern for the operators of drinking water distribution systems to manage chlorine residuals at the “optimum level”, considering all these issues. This paper describes how the chlorine profile in a drinking water distribution system can be modelled and optimised on the basis of readily and inexpensively available laboratory data. Methods are presented for deriving the laboratory data, fitting a chlorine decay model of bulk water to the data and applying the model, in conjunction with a simplified hydraulic model, to obtain the chlorine profile in a distribution system at steady flow conditions. Two case studies are used to demonstrate the utility of the technique. Melbourne’s Greenvale-Sydenham distribution system is unfiltered and uses chlorination as its only treatment. The chlorine model developed from laboratory data was applied to the whole system and the chlorine profile was shown to be accurately simulated. Biofilm was not found to critically affect chlorine decay. In the other case study, Sydney Water’s Nepean system was modelled from limited hydraulic data. Chlorine decay and trihalomethane (THM) formation in raw and treated water were measured in a laboratory, and a chlorine decay and THM model was derived on the basis of these data. Simulated chlorine and THM profiles agree well with the measured values available. Various applications of this modelling approach are also briefly discussed.
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Duan, Yousheng, Zhiqiang Ju, Liye Ju, and Aixin Guo. "011 Emulsions of Edible Plant Oils Reduce Fruit Decay in `Delicious' Apples and `Ya Li' Pears." HortScience 35, no. 3 (June 2000): 389E—389. http://dx.doi.org/10.21273/hortsci.35.3.389e.
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Effects of 10% plant oils (corn, soybean, peanut, canola, sunflower, safflower, rape seed, linseed, and cottonseed), 100 mg·L-1 chlorine, or 100 mg·L-1 chlorine plus 10% oil combinations on pathogen (B. cinerea, P. expansum, or G. cingulata) infection and fruit decay in `Delicious' apples and `Ya Li' pears were studied. None of the oils showed inhibition on spore germination of the three pathogens by in vitro test. In inoculated fruit, oil treatments did not affect incidence but reduced severity of decay after 6 months storage at 0 °C plus 7 days at 20 °C, but no difference was found among the oils at the same concentration. In non-inoculated fruit, oils reduced fruit decay to low levels (4%) even in the most severe season. Oils also maintained fruit quality attributes, reduced water loses, and controlled scald in apples and internal browning in pears. Chlorine reduced incidence but did not reduce severity in decayed fruit. Fruit first drenched with chlorine then dipped in oil emulsions without pathogen inoculation remained decay free, while control fruit developed 10% to 15% or 13% to 23% decay after 6 months at 0 °C plus 7 days at 20 °C in both apples and pears, respectively.
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Choi, Yonkyu, Seung-Heon Byun, Hyun-Jung Jang, Sang-Eun Kim, and Young-june Choi. "Comparison of disinfectants for drinking water: chlorine gas vs. on-site generated chlorine." Environmental Engineering Research 27, no. 1 (January 22, 2021): 200543–0. http://dx.doi.org/10.4491/eer.2020.543.
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The feasibility of on-site generated chlorine (OSG chlorine) as an alternative disinfectant to chlorine gas was evaluated in terms of total organic carbon (TOC) removal, disinfection efficiency, biofilm control, disinfection by-products (DBPs) formation, chlorine decay rate, and volatility. Chlorine gas decreased the pH of the treated water by -0.1 per mg/L of free available chlorine (FAC) while OSG chlorine increased the pH by + 0.06 per mg/L. OSG chlorine with more hypochlorite ion (OCl-) at higher pH was less effective in the inactivation of suspended bacteria and TOC removal but remained in the distribution system longer and controlled biofilm formation more effectively than chlorine gas. The DBPs formation by OSG chlorine was not significantly different from that by chlorine gas except for the reduction of Haloacetonitriles. Hypochlorous acid (HOCl) was more volatile than OCl-, indicating the lower volatility of FAC in the OSG chlorine-treated water. Two types of OSG systems, “Mixed oxidants” and OSG hypochlorite, did not show any significant difference in disinfection, DBPs formation, and chlorine decay rate (paired t-test, p = 0.40, 0.11 ~ 0.70, > 0.42). A significant synergy effect by oxidants other than FAC cannot be expected in the use of “mixed oxidants” at a water treatment plant.
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Basson, N., D. Traut, G. Titus, C. vd Walt, and J. Haarhoff. "Investigation into the implementation of chloramination at Sedibeng Water." Water Supply 3, no. 1-2 (March 1, 2003): 233–38. http://dx.doi.org/10.2166/ws.2003.0109.
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The Balkfontein and Virginia plants of Sedibeng Water, situated in the Free State Province of South Africa, treat water for potable purposes. Chlorine is used as disinfectant at both plants. Low levels of free chlorine measured in the water supplied from some reservoirs, logistics and costs, related to the application of chlorination at various points in the distribution system, were the main thrusts for an investigation into the use of chloramination as an alternative means of disinfection. The so-called contact time (CT)-approach from the United States Environmental Protection Agency was applied for the evaluation of disinfection efficiency. The distribution system was modelled by using a hydraulic computer system. Decay rates for both chlorine and monochloramine - a vital parameter for eventual determination of the amount of chlorine and ammonia to be dosed - were determined. The levels of disinfectant in the water at a specific location could be predicted by using the decay values. The main findings of this investigation are that chloramination is an attractive and cost-effective alternative for conventional chlorination for providing quality assurance to all. It is estimated that the capital layout will be recovered within one year of operation of the ammoniation system.
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Bartz, J. A., D. J. Huber, S. L. Stahl, J. H. Lee, D. Spiceland, and M. T. Elkahky. "Susceptibility of Lenticels within the Stem Depression of Tomato Fruit to Bacterial Soft Rot." Plant Disease 100, no. 9 (September 2016): 1906–9. http://dx.doi.org/10.1094/pdis-02-16-0173-re.
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The postharvest development of bacterial soft rot in tomato fruit caused by Pectobacterium carotovorum is herein linked with inoculation of lenticel-like apertures located around the stem attachment. Stem scars misted with aqueous cell suspensions of P. carotovorum (1 × 106 CFU/ml) or briefly (5 s) immersed in the suspension were likely to become infected during subsequent storage, with a disease incidence exceeding 70% within 7 days at 24°C. Water soaking was initially observed beneath the fruit surface at the juncture of radial walls of endocarp tissues and a corky ring around the stem attachment. If fruit were swirled for 1 min in chlorine at 150 ppm, pH 6.5, within 5 s after inoculation, lesions did not occur. However, if the chlorine treatment was delayed by 120 s, lesions occasionally developed. A 60-min delay usually assured that decay would occur before fruit ripened (within 5 days). Delaying the chlorine wash by 18 h, as would occur if commercial harvests were held overnight prior to packing operations, led to the same incidence of bacterial soft rot as observed among control fruit. Inoculation of fruit with attached stems did not lead to as much decay during storage compared with stemless fruit, suggesting that an intact calyx physically reduced lenticel exposure to external aqueous cell suspensions. Tomato fruit exposed to uncontrolled free moisture during or shortly after harvest have a high potential for postharvest decays and the likely site for infection development is the area surrounding the stem attachment.
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Casas-Monroy, Oscar, Julie Vanden Byllaardt, Johanna Bradie, Andrea Sneekes, Klaas Kaag, and Sarah A. Bailey. "Effect of temperature on chlorine treatment for elimination of freshwater phytoplankton in ballast water: bench-scale test." Canadian Journal of Fisheries and Aquatic Sciences 76, no. 10 (October 2019): 1768–80. http://dx.doi.org/10.1139/cjfas-2018-0179.
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Chlorine efficacy as a biocide for ballast water treatment was investigated under cold- and warm-water temperatures across winter and summer seasons. Freshwater phytoplankton samples were collected and acclimated under in situ environmental conditions ranging from 2 to 22 °C. Samples were exposed to seven chlorine treatments (from 0.02 to 5.0 ppm), in addition to a control (0.0 ppm). Free-chlorine concentrations, phytoplankton abundance, and photosynthetic efficiency were measured up to 48 h following treatment. After 4 h of treatment at concentrations less than 0.22 ppm, phytoplankton densities were reduced by more than 50%, without cell resurgence. Similar reduction was recorded immediately after exposure when chlorine concentrations were higher than 3.0 ppm. After 8 h, free chlorine neared 0.0 ppm for initial chlorine concentrations below 1.2 ppm, irrespective of temperature regime. Winter phytoplankton exhibited slightly lower mortality to chlorine exposure regardless of the temperature, although they also exhibited lower photosynthetic efficiency. Despite a general absence of significant effect of temperature on the chlorine decay, our results suggest that higher doses of chlorine or longer exposure times may be required during winter to achieve full treatment effect. Tests at large scales are needed to further confirm these findings.
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Mahovic, Michael J., Joel D. Tenney, and Jerry A. Bartz. "Applications of Chlorine Dioxide Gas for Control of Bacterial Soft Rot in Tomatoes." Plant Disease 91, no. 10 (October 2007): 1316–20. http://dx.doi.org/10.1094/pdis-91-10-1316.
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Chlorine dioxide (ClO2) gas was generated from a mixture of sodium chlorite and ferric chloride plus water (impregnated into zeolite) in a Tyvek sachet over a 2- or 24-h period. The gas was distributed by a fan over wound-inoculated tomato fruit (Lycopersicon esculentum) enclosed in a sealed aluminum pressure cooker. Within 24 h of inoculation with 6 log10 CFU of Erwinia carotovora subsp. carotovora per wound and storage at 22 to 24°C, bacterial soft rot was observed on >80% of the nontreated wounds (10 wounds/fruit and 4 or 6 fruit/treatment). By contrast, wounds that had been exposed to an atmosphere containing up to 99 mg ClO2 during a 2- or 24-h period remained firm and dry with no evidence of bacterial activity or soft rot. After 72 h of incubation, wounds exposed to 88 mg ClO2 produced over 24 h or 99 mg ClO2 produced over 2 h were free of decay, whereas bacterial soft rot was observed in ca. 12% and less than 5% of wounds treated with 0.75 mg or 7.5 mg, respectively, for either 2 or 24 h. Wounds that had not been inoculated remained free of bacterial soft rot throughout the entire storage period. Wounds exposed to the highest doses of ClO2, 88 mg/24 h or 99 mg/2 h, became bleached and sunken. Additionally, the stem scars on these fruit became cracked, sunken, and bleached. The intact cuticle was not visibly affected, and there was no observed change in overall fruit color. ClO2 gas may be effective for controlling postharvest decays of fruit that have been inoculated prior to or during harvest.
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Nguyen, Caroline K., Kim A. Powers, Meredith A. Raetz, Jeffrey L. Parks, and Marc A. Edwards. "Rapid free chlorine decay in the presence of Cu(OH)2: Chemistry and practical implications." Water Research 45, no. 16 (October 2011): 5302–12. http://dx.doi.org/10.1016/j.watres.2011.07.039.
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Bajszár, George, and Alexander Dekonenko. "Stress-Induced Hsp70 Gene Expression and Inactivation of Cryptosporidium parvum Oocysts by Chlorine-Based Oxidants." Applied and Environmental Microbiology 76, no. 6 (January 29, 2010): 1732–39. http://dx.doi.org/10.1128/aem.02353-09.
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ABSTRACT Our research on the mechanisms of action of chlorine-based oxidants on Cryptosporidium parvum oocysts in water revealed a dual-phase effect: (i) response to oxidative stress, which was demonstrated by induced expression of the Hsp70 heat shock gene, and (ii) oocyst inactivation as a result of long-term exposure to oxidants. The relative biocidal effects of sodium hypochlorite (bleach) and electrolytically generated mixed oxidant solution (MOS) on C. parvum oocysts were compared at identical free chlorine concentrations. Oocyst inactivation was determined by quantitative reverse transcription-PCR (qRT-PCR) amplification of the heat-induced Hsp70 mRNA and compared with tissue culture infectivity. According to both assays, within the range between 25 and 250 mg/liter free chlorine and with 4 h contact time, MOS exhibits a higher efficacy in oocyst inactivation than hypochlorite. Other RNA-based viability assays, aimed at monitoring the levels of β-tubulin mRNA and 18S rRNA, showed relatively slow decay rates of these molecules following disinfection by chlorine-based oxidants, rendering these molecular diagnostic viability markers inappropriate for disinfection efficacy assessment.
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Bartz, J. A., C. G. Eayre, M. J. Mahovic, D. E. Concelmo, J. K. Brecht, and S. A. Sargent. "Chlorine Concentration and the Inoculation of Tomato Fruit in Packinghouse Dump Tanks." Plant Disease 85, no. 8 (August 2001): 885–89. http://dx.doi.org/10.1094/pdis.2001.85.8.885.
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Chlorine concentrations (pH 6 to 7 and 22 to 27°C) that killed arthrospores (spores) of Geotrichum candidum or sporangioles (spores) of Rhizopus stolonifer, causal agents of sour rot and Rhizopus rot, respectively, in moving water within 30 to 45 s did not prevent these pathogens from inoculating wounded tomatoes (Lycopersicon esculentum) in a water flume containing chlorine and spores. Free chlorine concentrations of 20 or 25 mg/liter were lethal to spores of G. candidum within 30 s in most in vitro tests, whereas spores of R. stolonifer were slightly less sensitive. Wounded tomatoes placed in a flume with free chlorine at 30 mg/liter and then exposed to spores for 1 min developed about 50% less decay incidence during storage at 24°C for 6 days than did fruit exposed to spores and water alone. In the absence of chlorine, incidence averaged 57% (range, 15 to 95%) for R. stolonifer and 38% (range, 17 to 58%) for G. candidum. Sporadic sour rot lesions were observed among fruit that had been treated with free chlorine at 75 mg/liter, whereas chlorine at up to 180 mg/liter failed to completely protect fruit from Rhizopus rot. A water-soluble dye rapidly penetrated wounds on tomato fruit. The dye framed the outlines of cells at the wound surface and appeared to penetrate into a few intercel-lular spaces. Application of 1% sodium hypochlorite decolorized the dye on the wound surface, whereas deposits located below the wound surface remained blue. Thus, spores suspended in moving water can escape the action of chlorine if carried into intercellular spaces by diffusion or by capillary movement of cell sap and water.
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Beata, Kowalska, Kowalski Dariusz, and Hołota Ewa. "Fractal-Heuristic Method of Water Quality Sensor Locations in Water Supply Network." Water 12, no. 3 (March 16, 2020): 832. http://dx.doi.org/10.3390/w12030832.
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The article presents a new methodology for the selection of the water quality monitoring sensor locations using the water quality model created by means of the EPANET 2.0 software (United States Environmental Protection Agency (USEPA), Durham, NC, USA). The model represents the propagation of free chlorine in a water supply network, in conjunction with the heuristic method, applying the elements of fractal geometry. In the first stage, a subarea is determined, while in the second, a specific node for the location of the measuring point is indicated. The process of determining the location is based on a ranking method, in which the usefulness of individual subareas and measuring nodes is determined by means of a formula taking into account the amount of water intake, the required level of water supply and the effects of a lack of water supply, as well as the calculated concentration of free chlorine. The application of the method requires the construction and calibration of a numerical model of free chlorine decay in the network, as well as the knowledge on the location of the objects of particular importance for the network users. The proposed method will be applied in an existing water supply network of approximately 50,000 recipients.
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Campos, C., and Ph Harmant. "Assessing the impact of dissolved organic carbon changes on disinfectant stability in a distribution system." Water Supply 2, no. 3 (July 1, 2002): 251–57. http://dx.doi.org/10.2166/ws.2002.0110.
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Maintaining disinfectant residuals throughout the entire water distribution system is considered an efficient strategy to guarantee the biological stability of drinking water as it flows from the plant to the customer tap. Dosed at the plant, the disinfectant disappears in the distribution system due to reactions with both water and pipe constituents. Among them, certain fractions of the organic matter content are directly responsible for the loss of disinfectant. This study presents an example of the impact of the organic matter UV absorbance on free chlorine decay for a surface water. In addition, this study illustrates the use of laboratory experiments together with a water quality model as a valuable tool to predict the impact of organic carbon concentration changes on chlorine residuals in interconnected distribution systems.
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Gallandat, Karin, David Stack, Gabrielle String, and Daniele Lantagne. "Residual Maintenance Using Sodium Hypochlorite, Sodium Dichloroisocyanurate, and Chlorine Dioxide in Laboratory Waters of Varying Turbidity." Water 11, no. 6 (June 25, 2019): 1309. http://dx.doi.org/10.3390/w11061309.
Full textAbstract:
Sodium hypochlorite (NaOCl) and sodium dichloroisocyanurate (NaDCC) are commonly used for household water treatment (HWT); chlorine dioxide (ClO2) is a potential new HWT option. We compared the residual maintenance of NaOCl, NaDCC, and ClO2 over 24 hours using recommended dosages (2 and 4 mg/L) in waters of varying turbidity (0–300 NTU, from kaolin clay or creek-bottom sediments) and total organic carbon (TOC) concentrations (0–100 mg/L), for a total of 324 reactors. NaOCl and NaDCC had similar free chlorine decay rates, and ClO2 decayed more rapidly across all of the tested conditions. Little variability was observed across clay-based turbidity levels and TOC concentrations. With a dosage of 2 mg/L, a residual ≥0.2 mg/L was maintained at 30 NTU for NaOCl and 100 NTU for NaDCC; for ClO2, 4 mg/L were required to maintain ≥0.2 mg/L under all conditions except at zero turbidity. Comparisons with data from the literature suggest that the three compounds would inactivate E. coli, rotavirus, and Giardia cysts within 1 hour under all conditions, except 300 NTU for NaOCl and NaDCC. All three disinfectants are similarly efficacious for this usage; however, differences are seen in decay rates that may influence disinfectant selection depending on water storage time.
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Montoya Pachongo, Carolina, Santiago Laín Beatove, Patricia Torres Lozada, Camilo Hernán Cruz-Vélez, and Juan Carlos Escobar Rivera. "Effects of water inlet configuration in a service reservoir applying CFD modelling." Ingeniería e Investigación 36, no. 1 (April 18, 2016): 31–40. http://dx.doi.org/10.15446/ing.investig.v36n1.50631.
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<p>This study investigated the state of a service reservoir of a drinking water distribution network. Numerical simulation was applied to establish its flow pattern, mixing conditions, and free residual chlorine decay. The influence of the change in the water inlet configuration on these characteristics was evaluated. Four scenarios were established with different water level and flow rate as the differences between the first three scenarios. The fourth scenario was evaluated to assess the influence of the inlet configuration, momentum flow and water level on hydrodynamic conditions within the service reservoir. The distribution of four nozzles of 152.4mm diameter was identified as a viable measure to preserve the water quality in this type of hydraulic structures.</p>
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Giesen, Kai, Ingo Spahn, and Bernd Neumaier. "Thermochromatographic separation of 45Ti and subsequent radiosynthesis of [45Ti]salan." Journal of Radioanalytical and Nuclear Chemistry 326, no. 2 (October 10, 2020): 1281–87. http://dx.doi.org/10.1007/s10967-020-07376-2.
Full textAbstract:
Abstract Due to its favorable decay properties, the non-standard radionuclide 45Ti is a promising PET isotope for tumor imaging. Additionally, titanium complexes are widely used as anti-tumor agents and 45Ti could be used to study their in vivo distribution and metabolic fate. However, although 45Ti can be obtained using the 45Sc(p,n)45Ti nuclear reaction its facile production is offset by the high oxophilicity and hydrolytic instability of Ti4+ ions in aqueous solutions, which complicate recovery from the irradiated Sc matrix. Most available 45Ti recovery procedures rely on ion exchange chromatography or solvent extraction techniques which are time-consuming, produce large final elution volumes, or, in case of solvent extraction, cannot easily be automated. Thus a more widespread application of 45Ti for PET imaging has been hampered. Here, we describe a novel, solvent-free approach for recovery of 45Ti that involves formation of [45Ti]TiCl4 by heating of an irradiated Sc target in a gas stream of chlorine, followed by thermochromatographic separation of the volatile radiometal chloride from co-produced scandium chloride and trapping of [45Ti]TiCl4 in a glass vial at − 78 °C. The recovery of 45Ti amounted to 76 ± 5% (n = 5) and the radionuclidic purity was determined to be > 99%. After trapping, the [45Ti]TiCl4 could be directly used for 45Ti-radiolabeling, as demonstrated by the successful radiosynthesis of [45Ti][Ti(2,4-salan)].
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Moradinejad, Saber, Dries Vandamme, Caitlin M. Glover, Tahere Zadfathollah Seighalani, and Arash Zamyadi. "Mini-Hydrocyclone Separation of Cyanobacterial and Green Algae: Impact on Cell Viability and Chlorine Consumption." Water 11, no. 7 (July 16, 2019): 1473. http://dx.doi.org/10.3390/w11071473.
Full textAbstract:
The co-occurrence of non-toxic phytoplankton alongside cyanobacteria adds to the challenge of treating source waters with harmful algal blooms. The non-toxic species consume the oxidant and, thereby, reduce the efficacy of oxidation of both the extracellular and intracellular cyanotoxins. In this work, a 3D printed mini-hydrocyclone was used to separate a mixture of non-toxic green algae, Scenedesmus obliquus, from a toxic species of cyanobacteria, Microcystis aeruginosa. When water is pumped through the mini-hydrocyclone, cells exit through an overflow or underflow port depending on their size, shape, and density relative to the other cells and particles in the water matrix. The overflow port contains the cells that are smaller and less dense since these particles move toward the center of the hydrocyclone. In this work, the majority (>93%) of Microcystis cells were found in the overflow while the underflow contained primarily the Scenedesmus (>80%). This level of separation efficiency was maintained over the 30-min experiment and the majority of both cells (>86%) remained viable following the separation, which indicates that the pumping combined with forces exerted within the mini-hydrocyclone were not sufficient to cause cell death. The impact of free chlorine on the cells both pre-separation and post-separation was evaluated at two doses (1 and 2 mg/L). After separation, the overflow, which contained primarily Microcystis, had at least a 24% reduction in the free chlorine decay rate as compared to the feed water, which contained both species. This reduction in chlorine consumption shows that the cells separated via mini-hydrocyclone would likely require lower doses of oxidant to produce a similar level of degradation of the cyanotoxins present in either the extracellular or intracellular form. However, future work should be undertaken to evaluate this effect in natural bloom samples.
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Storey, M. V., J. Långmark, N. J. Ashbolt, and T. A. Stenström. "The fate of legionellae within distribution pipe biofilms: measurement of their persistence, inactivation and detachment." Water Science and Technology 49, no. 11-12 (June 1, 2004): 269–75. http://dx.doi.org/10.2166/wst.2004.0859.
Full textAbstract:
Distribution pipe biofilms present a currently unquantified public health risk to consumers receiving water for domestic potable and non-potable use. The aim of this study was to quantify the numbers of legionellae, used here as model bacterial pathogens, that may accumulate, persist within and detach from distribution pipe biofilms. L. pneumophila recovered by standard culture from an 8 week-old biofilm formed within a novel pilot-scale water distribution system represented 1% of those present in the adjacent bulk water. A combined chlorine concentration exceeding 0.2 mg.L-1 eliminated culturable sessile legionellae altogether, though the reduction in FISH-positive cells represented just 75 ± 25% of the original amount, compared to a 5-log reduction in culturable cells during the same period. Where there was < 0.1 mg.L-1 combined chlorine, an exponential decay/loss of sessile L. pneumophila was observed (k = 0.37 - 0.41) over the course of a 38-day experimental period. The inoculation of the system with 1 μm fluorescent microspheres and legionellae demonstrated that removal of the latter was dominated by chemical disinfection, with erosion and biological grazing playing lesser roles. Under turbulent (Re ∼5000) conditions, larger clusters of biofilm become detached from substrata, with more than 90% of sessile legionellae mobilised into the bulk water phase. Interaction with both biofilms and a thermophilic Acanthamoeba isolate reduced the susceptibility of legionellae to thermal inactivation by between one and two orders of magnitude, though it increased their sensitivity to chemical (free and combined chlorine) disinfection.
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Damalerio, Regina G., Aileen H. Orbecido, Marigold O. Uba, Patricio Elvin L. Cantiller, and Arnel B. Beltran. "Storage Stability and Disinfection Performance on Escherichia coli of Electrolyzed Seawater." Water 11, no. 5 (May 10, 2019): 980. http://dx.doi.org/10.3390/w11050980.
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The study investigated the effect of storage conditions on the stability of electrolyzed seawater (ESW)’s physicochemical properties (pH, oxidation-reduction potential (ORP), and free chlorine (FC) concentration), and bactericidal efficiency on the fecal coliform Escherichia coli for 30 days. Preliminary experiments were conducted to determine the optimal current and electrolysis time. Two batches of 2750 mL filtered seawater were electrolyzed using 50 mm × 192 mm platinum–titanium mesh electrodes at a current of 1.5 A for 20 min. One hundred milliliters of electrolyzed solution was transferred into each amber glass and high-density polyethylene (HDPE) bottles. The bottles were stored in a dark area at ambient temperature. The results showed an increase in pH and a decrease in ORP and FC concentration through time. Hypochlorous acid remained as the dominant component since the pH levels of the solutions remained below 7.5. FC decay was investigated using Chick’s Law. It was determined that the decay in HDPE bottles (k = −0.066 day−1) was faster compared to amber glass bottles (k = −0.046 day−1). Nonetheless, HDPE bottles could still be used as an alternative container for 30 days only due to observed instability beyond 30 days. ESW remained effective since no surviving population of E. coli was observed throughout the experimentation.
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Caballero, Santiago, F. Xavier Abad, Fabienne Loisy, Françoise S. Le Guyader, Jean Cohen, Rosa M. Pintó, and Albert Bosch. "Rotavirus Virus-Like Particles as Surrogates in Environmental Persistence and Inactivation Studies." Applied and Environmental Microbiology 70, no. 7 (July 2004): 3904–9. http://dx.doi.org/10.1128/aem.70.7.3904-3909.2004.
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ABSTRACT Virus-like particles (VLPs) with the full-length VP2 and VP6 rotavirus capsid proteins, produced in the baculovirus expression system, have been evaluated as surrogates of human rotavirus in different environmental scenarios. Green fluorescent protein-labeled VLPs (GFP-VLPs) and particles enclosing a heterologous RNA (pseudoviruses), whose stability may be monitored by flow cytometry and antigen capture reverse transcription-PCR, respectively, were used. After 1 month in seawater at 20°C, no significant differences were observed between the behaviors of GFP-VLPs and of infectious rotavirus, whereas pseudovirus particles showed a higher decay rate. In the presence of 1 mg of free chlorine (FC)/liter both tracers persisted longer in freshwater at 20°C than infectious viruses, whereas in the presence of 0.2 mg of FC/liter no differences were observed between tracers and infectious rotavirus at short contact times. However, from 30 min of contact with FC onward, the decay of infectious rotavirus was higher than that of recombinant particles. The predicted Ct value for a 90% reduction of GFP-VLPs or pseudoviruses induces a 99.99% inactivation of infectious rotavirus. Both tracers were more resistant to UV light irradiation than infectious rotavirus in fresh and marine water. The effect of UV exposure was more pronounced on pseudovirus than in GFP-VLPs. In all types of water, the UV dose to induce a 90% reduction of pseudovirus ensures a 99.99% inactivation of infectious rotavirus. Recombinant virus surrogates open new possibilities for the systematic validation of virus removal practices in actual field situations where pathogenic agents cannot be introduced.
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Tinelli, Silvia, and Ilan Juran. "Artificial intelligence-based monitoring system of water quality parameters for early detection of non-specific bio-contamination in water distribution systems." Water Supply 19, no. 6 (April 1, 2019): 1785–92. http://dx.doi.org/10.2166/ws.2019.057.
Full textAbstract:
Abstract This research aims to simulate bio-contamination risk propagation under real-life conditions in the water distribution system (WDS) of Lille University's Scientific City Campus (France), solving the source identification and the response modeling. Neglecting dynamic reactions and not considering the possible chemical decay of most of the contaminants leads to an overestimation of the exposed population. Therefore, unlike the available event detection models, this study considers the interrelated change of several water-quality parameters such as free chlorine concentration, pH, alkalinity, and total organic carbon (TOC) resulting from the pollutants blending. In fact, starting from regular WDS monitoring, the baseline thresholds for each of the mentioned parameters are established; then, significant deviations from the baseline are used as indication for contaminations. For this reason, the purpose of the research was to develop and demonstrate the feasibility of an artificial intelligence (AI)-based smart monitoring system that will effectively enable water operators to ensure a quasi real-time quality control for early chemical and/or bio-contamination detection and preemptive risk management. Advanced pattern recognizers, such as Support Vector Machines (SVMs), and innovative sensing technology solutions, such as Artificial Neural Network (ANN), have been used for this purpose, identifying the anomalies and the severity-level assessment.
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Jegatheesan, V., G. Kastl, I. Fisher, M. Angles, and J. Chandy. "Modelling biofilm growth and disinfectant decay in drinking water." Water Science and Technology 41, no. 4-5 (February 1, 2000): 339–45. http://dx.doi.org/10.2166/wst.2000.0464.
Full textAbstract:
A simple biofilm model was developed to describe the growth of bacteria in drinking water biofilms and the subsequent interactions with disinfectant residuals incorporating the important processes, such as attachment of free bacteria to the biofilm on a wall surface, detachment of bacteria from the biofilm, growth of biofilm bacteria with chloramine inhibition, chloramine decay in the bulk water phase, and chloramine decay due to biofilm bacteria and wall surfaces. The model is useful in evaluating the biological stability of different waters, as it can predict concentration of organic substances in water. In addition, the model can be used to predict the bacterial growth and biofilm decay in distribution systems. A model of this kind is a useful tool in developing system management strategies to ultimately improve drinking water quality.
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Bradley, Tyler C., Charles N. Haas, and Christopher M. Sales. "Nitrification in Premise Plumbing: A Review." Water 12, no. 3 (March 15, 2020): 830. http://dx.doi.org/10.3390/w12030830.
Full textAbstract:
Nitrification is a major issue that utilities must address if they utilize chloramines as a secondary disinfectant. Nitrification is the oxidation of free ammonia to nitrite which is then further oxidized to nitrate. Free ammonia is found in drinking water systems as a result of overfeeding at the water treatment plant (WTP) or as a result of the decomposition of monochloramine. Premise plumbing systems (i.e., the plumbing systems within buildings and homes) are characterized by irregular usage patterns, high water age, high temperature, and high surface-to-volume ratios. These characteristics create ideal conditions for increased chloramine decay, bacterial growth, and nitrification. This review discusses factors within premise plumbing that are likely to influence nitrification, and vice versa. Factors influencing, or influenced by, nitrification include the rate at which chloramine residual decays, microbial regrowth, corrosion of pipe materials, and water conservation practices. From a regulatory standpoint, the greatest impact of nitrification within premise plumbing is likely to be a result of increased lead levels during Lead and Copper Rule (LCR) sampling. Other drinking water regulations related to nitrifying parameters are monitored in a manner to reduce premise plumbing impacts. One way to potentially control nitrification in premise plumbing systems is through the development of building management plans.
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Tran-Thi, T. H., A. M. Koulkes-Pujo, J. C. Mialocq, and G. Folcher. "Influence of Viscous Media on Charge Transfer Reactions." Laser Chemistry 5, no. 6 (January 1, 1986): 351–66. http://dx.doi.org/10.1155/lc.5.351.
Full textAbstract:
The influence of viscous H2O-Dextran media on two charge transfer reactions has been investigated using laser photolysis coupled with pico and nanosecond time resolved absorption spectroscopy.In the first case, a charge-transfer reaction from a solute (potassium ferrocyanide) to the solvent was studied and the electron solvation dynamics was followed. A solvation time delay, depending on the polymer concentration, is observed which indicates that electrons remain quasi-free for longer periods in these media.In the second case, the quenching process of the triplet state of an excited metallo porphyrin(ZnP4+) by an electron acceptor, methylviologen chloride (MV2+, 2 Cl–) is studied. The measured triplet quenching rate constant values decrease with increasing dextran concentration, but remain higher than those calculated, taking into account a simple viscosity effect. This result is explained in terms of a competition between a decay of the diffusion rate constants of (ZnP4+)* and MV2+ due to a viscosity effect and an enhanced cage effect around the ions (ZnP4+*, MV2+). Once formed, this last effect favours the charge transfer reaction.
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PURCELL, J., A. P. ROBERTSON, D. P. THOMPSON, and R. J. MARTIN. "The time-course of the response to the FMRFamide-related peptide PF4 in Ascaris suum muscle cells indicates direct gating of a chloride ion-channel." Parasitology 124, no. 6 (June 2002): 649–56. http://dx.doi.org/10.1017/s0031182002001695.
Full textAbstract:
We investigated the effects of PF4 on Ascaris suum somatic muscle cells using a 2 electrode current-clamp technique. PF4 is a FaRP (FMRFamide-related peptide), originally isolated from the free-living nematode Panagrellus redivivus. PF4 caused hyperpolarization and an increase in chloride ion conductance when it was applied to the muscle cells of the Ascaris body wall. The delay between the application of the peptide and the appearance of the response was measured and compared with that of gamma-amino butyric acid (GABA), a compound that directly gates ion channels, and with PF1, a FaRP that acts via an intracellular signal transduction mechanism. The PF4 and GABA delay times were not significantly different; they were 1·51±0·11 sec and 1·22±0·10 sec respectively. The delay following application of PF1, 3·75±0·51 sec, was significantly longer. The rapid response to PF4 is consistent with direct gating of a chloride ion channel, which has not been described elsewhere in the literature.
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Rogawski, M. A., K. Inoue, S. Suzuki, and J. L. Barker. "A slow calcium-dependent chloride conductance in clonal anterior pituitary cells." Journal of Neurophysiology 59, no. 6 (June 1, 1988): 1854–70. http://dx.doi.org/10.1152/jn.1988.59.6.1854.
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1. Whole cell voltage-clamp recordings were made from GH3 cells, a clonal cell line initially derived from a rat anterior pituitary tumor, using patch electrodes filled with CsCl or N-methylglucamine chloride (NMG Cl). The bathing medium contained tetraethylammonium chloride (TEA; 20 mM) and NaCl (120 mM) or NMG Cl (140 mM). These conditions resulted in substantial blockade of outward currents. 2. Depolarizing voltage steps from a holding potential of -50 mV activated transient (T-type) and sustained (L-type) inward Ca2+ currents. In addition, prolonged depolarization (greater than 1 s) invariably elicited a slowly activating inward current that persisted with maintained depolarization, and deactivated slowly on repolarization, resulting in a prominent inward tail current. 3. This tail current could be recorded under conditions where Ca2+ and Cl- were the only membrane-permeant ions (symmetrical NMG Cl). The tail current nulled near 0 mV with symmetrical Cl- and showed a negative reversal potential with nominally Cl--free internal solution. Ba2+ substituted for Ca2+ as a carrier of inward current, but no tail current was expressed. These observations indicate that Cl- is the charge carrier of the slow inward tail current. 4. The voltage dependence for activation of the slow tail current was U-shaped with a peak at approximately -10 mV. This closely paralleled the voltage dependency of the Ca2+ currents. Recordings with 5 mM internal ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) to buffer intracellular Ca2+ to low nM levels exhibited slow inward tail currents that were of lower peak amplitude than with the usual 1.1 mM EGTA-containing pipette solution, but the kinetics of the currents were similar in both cases. In addition, the slow tail current was eliminated on superfusion with the Ca2+ channel blocker Cd2+ or with Ca2+-free medium. These results demonstrate that the current is dependent on Ca2+ influx; it is, therefore, referred to as ICl(Ca). 5. Activation of ICl(Ca) required depolarization of at least 1 s. More prolonged depolarizations activated progressively greater current, to a maximum with 6-s depolarization. In most cases, the decay of the tail current was described by a single exponential function with time constant approximately 0.8-0.9 s within the potential range -80 to -30 mV. At more depolarized potentials the decay was slower (increasing e-fold/20-mV change in membrane potential). 6. In a high proportion of cells, ICl(Ca) rapidly diminished in amplitude on repeated activation. This "rundown" occurred more rapidly than the rundown of the Ca2+ currents.(ABSTRACT TRUNCATED AT 400 WORDS)
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Naimark, Elena, Maria Kalinina, Alexander Shokurov, Alexander Markov, Liubov Zaytseva, and Natalia Boeva. "Mineral composition of host sediments influences the fossilization of soft tissues." Canadian Journal of Earth Sciences 55, no. 11 (November 2018): 1271–83. http://dx.doi.org/10.1139/cjes-2017-0237.
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Cambrian Lagerstätten host rocks are frequently composed of kaolinite and chlorite in varying amounts; accordingly, our goal was to study the preservation potential of crustaceans in these two clays. We conducted long-term experiments (12–18 months, the longest duration of actualistic taphonomy experiments from published literature) on the decay of Artemia salina in these clay sediments. The degree of preservation, transformed mineralogical composition of the sediments, and the elemental composition of the nauplial remains were examined. We demonstrate that the kaolinite and chlorite sediment enhanced the preservation (in the kaolinite the effect was considerably higher than in the chlorite) compared with the sediment-free control. pH inside the sediments dropped to 6.5–7.1 and was even lower (<4) around the buried carcasses, facilitating the dissolution of clays. This phenomenon was confirmed by mineralogical analyses of the experimental sediments, which showed mineralogical signatures of such dissolution and new mineral phases. According to the variations in the dissolved minerals in the sediments, different cations entered the buried remains as was shown by the multiple energy dispersive X-ray analyses. An increased level of Mg was detected in the carcasses buried in chlorite, whereas Al and Si concentrations were higher in the kaolinite; in both cases, Ca rapidly entered the decaying tissues from marine water. Bacteria underwent similar mineralization as the macroremains and apparently had no direct effect on the mineralization. The results confirmed an important role of dissolved Al ions in preservation of soft-bodied organisms in clay-dominated sediments and explained wide variation in chemical composition of their fossils.
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Chéour, F., C. Willemot, J. Arul, Y. Desjardins, J. Makhlouf, P. M. Charest, and A. Gosselin. "Foliar Application of Calcium Chloride Delays Postharvest Ripening of Strawberry." Journal of the American Society for Horticultural Science 115, no. 5 (September 1990): 789–92. http://dx.doi.org/10.21273/jashs.115.5.789.
Full textAbstract:
Effects of CaCl2 preharvest treatment on postharvest strawberry (Fragaria × ananassa) ripening and gray mold development were assessed. Two experiments were carried out in 1987 on two sites. In the first experiment, the effects of rate of application of CaCl2 and degree of fruit maturity at treatment were studied with the conventional cultivar Kent. In the second experiment, the influence of concentration and frequency of application of CaCl2 was investigated with day-neutral `Tribute'. Calcium treatment caused a significant increase in fruit and leaf Ca contents, which were closely correlated. The degree of fruit maturity at application and the frequency of treatment did not affect Ca concentration in the tissues. Several maturity criteria were measured during fruit storage in air at 4C. Anthocyanin and free-sugar contents and tissue electrical conductivity increased, while titratable acidity and firmness decreased. In both experiments, Ca treatment delayed ripening and gray mold development. The delay increased with increasing Ca concentration.
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Tamayo-Arango, Lynda, and Anderson Garzón-Alzate. "Preservation of Animal Cadavers with a Formaldehyde-free Solution for Gross Anatomy." Journal of Morphological Sciences 35, no. 02 (June 2018): 136–41. http://dx.doi.org/10.1055/s-0038-1669434.
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AbstractMotivated by the current health safety regulations at Universidad de Antioquia, our laboratory changed the animal cadavers preserving solution based on formaldehyde, methanol, glycerin and phenol to a formula based on 85% ethanol, 10% glycerin, and 5% benzalkonium chloride. A total of 33 donated cadavers were preserved with this formula so far: 4 goats, 16 dogs, 3 cats and 10 bovine fetuses. Red and blue latex dyes were injected into the vascular systems. Small cadavers were first injected with latex, followed by muscular and intracavitary injection with the preservation fluid and immersion in 96% ethanol. Large cadavers were vascularly injected, wrapped in plastic bags and vascularly repleted with latex during the next 8 days. Samples were taken for microbiological analysis from 3 cadavers: 1 cadaver wrapped with plastic for 2 months, 1 cadaver immersed for 4 months, and 1 cadaver after 15 days of perfusion. The first way to preserve cadavers was more time-consuming, but it rendered cadavers with a more thorough distribution of latex on small arteries and veins. An enhanced flexibility of joints and tissues promoted an easier dissection process, even of the most distal regions, allowing the movement of tendons along their sheaths. Also, a better color preservation was observed in spite of a darkening after the tissues were exposed to the air. There was no gross evidence of decay from bacterial or fungal growth, and the cultures were negative. The most important advantage of this formula is its lower toxicity and cost.
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Jih, Kang-Yang, Yoshiro Sohma, Min Li, and Tzyh-Chang Hwang. "Identification of a novel post-hydrolytic state in CFTR gating." Journal of General Physiology 139, no. 5 (April 16, 2012): 359–70. http://dx.doi.org/10.1085/jgp.201210789.
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Adenosine triphosphate (ATP)-binding cassette (ABC) transporters, ubiquitous proteins found in all kingdoms of life, catalyze substrates translocation across biological membranes using the free energy of ATP hydrolysis. Cystic fibrosis transmembrane conductance regulator (CFTR) is a unique member of this superfamily in that it functions as an ATP-gated chloride channel. Despite difference in function, recent studies suggest that the CFTR chloride channel and the exporter members of the ABC protein family may share an evolutionary origin. Although ABC exporters harness the free energy of ATP hydrolysis to fuel a transport cycle, for CFTR, ATP-induced dimerization of its nucleotide-binding domains (NBDs) and subsequent hydrolysis-triggered dimer separation are proposed to be coupled, respectively, to the opening and closing of the gate in its transmembrane domains. In this study, by using nonhydrolyzable ATP analogues, such as pyrophosphate or adenylyl-imidodiphosphate as baits, we captured a short-lived state (state X), which distinguishes itself from the previously identified long-lived C2 closed state by its fast response to these nonhydrolyzable ligands. As state X is caught during the decay phase of channel closing upon washout of the ligand ATP but before the channel sojourns to the C2 closed state, it likely emerges after the bound ATP in the catalysis-competent site has been hydrolyzed and the hydrolytic products have been released. Thus, this newly identified post-hydrolytic state may share a similar conformation of NBDs as the C2 closed state (i.e., a partially separated NBD and a vacated ATP-binding pocket). The significance of this novel state in understanding the structural basis of CFTR gating is discussed.
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Borst, J. G., J. C. Lodder, and K. S. Kits. "Large amplitude variability of GABAergic IPSCs in melanotropes from Xenopus laevis: evidence that quantal size differs between synapses." Journal of Neurophysiology 71, no. 2 (February 1, 1994): 639–55. http://dx.doi.org/10.1152/jn.1994.71.2.639.
Full textAbstract:
1. We made in situ whole-cell recordings from melanotropes in the intermediate lobe of the pituitary gland of Xenopus laevis. Melanotropes received spontaneous synaptic inputs that had a fast rise time and a much slower decay. These inputs were GABAergic inhibitory postsynaptic currents (IPSCs): they followed the reversal potential for chloride ions and they were blocked by the gamma-aminobutyric acid-A (GABAA) receptor antagonist bicuculline. 2. Because of the very low baseline noise it was possible to see discrete levels in the tails of IPSCs that corresponded to the opening of one or more synaptic GABAA receptor channels. "All-points" histograms of the IPSCs showed that the chord conductance of the channels in the tails of the IPSCs was 21.6 +/- 0.6 pS (mean +/- SE, n = 6). 3. The amplitudes of the spontaneous IPSCs were very variable, ranging from 3 to 390 pA at a holding potential of -80 mV. The average of the median amplitudes was -67.5 +/- 5.9 pA (n = 28). The amplitude distributions of the IPSCs were well described by the sum of two lognormal distributions with large SDs. The average of the means of the first lognormal distribution was 27.8 +/- 5.3 pA (n = 10); the average of the SDs was 24.7 +/- 8.1 pA. For the second lognormal distribution these values were 87.0 +/- 13.4 and 33.7 +/- 7.4 pA. An average of 41.8 +/- 6.9% of the IPSCs originated from the first lognormal distribution. 4. The large variability in the amplitudes of spontaneous IPSCs was not the result of presynaptic action potentials because it was not reduced by tetrodotoxin (TTX), Ca(2+)-free extracellular solution, or the combined application of TTX and Mn2+. 5. The time course of the IPSCs from the first and the second lognormal distributions were very similar: averages of the median 20- to 80% rise times were 585 +/- 64 and 488 +/- 28 microseconds, respectively (n = 8), whereas the decays were well described by the sum of two exponential functions, with fast time constants of 8.9 +/- 1.1 (n = 7) and 9.3 +/- 3.3 ms and slow time constants of 29.5 +/- 3.3 and 31.7 +/- 2.6 ms, respectively. 6. The decay of the IPSCs was voltage dependent; it was approximately 3 times slower at a holding potential of +40 mV than at -80 mV (n = 5).(ABSTRACT TRUNCATED AT 400 WORDS)
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Boni, Giuseppe, Sara Mazzarri, Claudia Cianci, Luca Galli, Azzurra Farnesi, Eugenio Borsatti, Roberto Bortolus, et al. "223Ra-chloride therapy in men with hormone-refractory prostate cancer and skeletal metastases: Real-world experience." Tumori Journal 104, no. 2 (March 2018): 128–36. http://dx.doi.org/10.1177/0300891618765571.
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Background: Radium-223 (223Ra) chloride, an alpha emitter, has been shown to improve overall survival (OS) and pain control, and to delay skeletal-related events, in patients with castration-resistant prostate cancer (CRPC) and bone metastases. Our retrospective observational study presents the first Italian experience on the efficacy and safety of 223Ra therapy in routine clinical practice. Methods: A total of 83 patients with metastatic CRPC were treated with 223Ra at 3 Italian centers between August 2013 and August 2016. 223Ra-chloride (55 kBq/kg) was administered every 4 weeks for a total of 6 cycles. Primary endpoints were OS and progression-free survival (PFS). Secondary endpoints included toxicity, pain evaluation using numeric rating scale (NRS), symptomatic skeletal-related events and biomarkers response. Results: Patients had a median age of 75 (range 53–89) years. The majority of men showed a Gleason score of 7, 8, or 9. Forty-one patients completed 6 treatment cycles; 33 stopped treatment before completing 6 cycles. Nine were still receiving therapy at the time of data collection. At the end of therapy, NRS pain scores significantly improved ( p < .000001). OS was a mean of 10.1 months, while median OS had not been attained. According to Kaplan-Meier estimation, OS and PFS were 17.5 and 7.7 months, respectively. There was a significant correlation between OS and PFS with the number of 223Ra cycles; patients receiving all 6 cycles experienced the major benefit from the therapy. 223Ra was well-tolerated. Conclusions: 223Ra alpha therapy is an important therapeutic option for men with CRPC and symptomatic skeletal metastases.
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Sirocko, Frank, Michael Sarnthein, Heinz Lange, and Helmut Erlenkeuser. "Atmospheric summer circulation and coastal upwelling in the Arabian Sea during the Holocene and the last glaciation." Quaternary Research 36, no. 1 (July 1991): 72–93. http://dx.doi.org/10.1016/0033-5894(91)90018-z.
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AbstractAccumulation rates of biogenic and lithogenic components were studied in 39 turbidite-free, well-dated sediment cores from the northern Indian Ocean to define the proportions of fluvial and eolian input and to reconstruct Quaternary patterns of coastal upwelling. The majority of dust deposited in the western Arabian Sea during the Holocene (about 100 × 106t yr−1) is advected from Arabia by northwesterly winds, which overlie the low-level southwest monsoon. The glacial increase in dust flux to 160 × 106t yr−1 culminated in the northern Arabian Sea, most probably due to (i) entrainment of dust, rich in chlorite, dolomite, and lithogenic carbonate in the then-dry Persian Gulf, and (ii) a southward shift of the mean position of the southwest monsoon during glacial summer. This shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off Somalia and Oman. Both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27,000 yr, as well as the Asian continental summer heat low. However, the glacial seasonal time span of the southwest monsoon season was much reduced, most likely because of a delay in the seasonal onset of the southwest monsoon.
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Németh, András, Zuchra Mamasheva, Katalin Jemnitz, Tamás Vidóczy, and Judit Jakus. "Effect of tetrapyrrole-based photosensitizers on spin trapping by 5,5-dymethyl-1-pyrroline N-oxide." Journal of Porphyrins and Phthalocyanines 09, no. 08 (August 2005): 531–36. http://dx.doi.org/10.1142/s1088424605000642.
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Kinetics of the effect of three different tetrapyrrole-based photosenzitizers, pheophorbide a, meso-tetrahydroxyphenyl chlorin, and 3,7-bis(2-carboxyethyl)-2,8,12,17-tetramethyl-13,18-bis[(5-propoxycarbonyl-3-4-dihidroxy-phenyloxy) ethyl] porphyrin, on spin trapping with of 5,5-dymethyl-1-pyrroline N -oxide (DMPO) – a method widely applied in photodynamic therapy research – was investigated in the chemical model system of initiated oxidation of ethylbenzene. Spin adducts were measured by ESR spectroscopy, and kinetics of the consumption of the spin trap and accumulation of main products of oxidation (acetophenon, 1-phenyl-ethanol and 1-phenyl-ethyl-hydroperoxide) were followed using high performance liquid chromatography. The ESR spectrum of the non-illuminated system corresponded to an adduct formed between the spin trap and α–phenylethyl peroxyl radical, while under illumination, the spectrum indicated competitive formation of another adduct. Based on analysis of the corresponding g factor and hyperfine coupling constant values of the latter adduct ( g = 2.00587, αN = 13.57 G , αH = 2.27 G ), the nitrone ring has presumably been split up and an adduct was formed between α-phenylethyl radical and 4-methyl-4-nitrosopentanoic acid – a product of the oxidation of the parent spin trap by singlet oxygen. Computer modeling based on detailed reaction mechanism and fitted to the measured data confirmed this assumption. The rate constants gave values of 2.3 × 105 M −1. s −1 for the formation of the adduct and 1.0 × 104 M −1. s −1 for its decay by interaction with free radicals offering a more detailed quantitative understanding of spin trapping in the presence of tetrapyrrole photosensitizers under illumination.
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Parkis, M. A., D. A. Bayliss, and A. J. Berger. "Actions of norepinephrine on rat hypoglossal motoneurons." Journal of Neurophysiology 74, no. 5 (November 1, 1995): 1911–19. http://dx.doi.org/10.1152/jn.1995.74.5.1911.
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1. We used conventional intracellular recording techniques in 400-microns-thick slices from the brain stems of juvenile rats to investigate the action of norepinephrine (NE) on subthreshold and firing properties of hypoglossal motoneurons (HMs). 2. In recordings in current-clamp mode, 50 or 100 microM NE elicited a reversible depolarization accompanied by an increase in input resistance (RN) in all HMs tested (n = 74). In recordings in single-electrode voltage-clamp mode, NE induced a reversible inward current (INE) accompanied by a reduction in input conductance. The average reversal potential for INE was -104 mV. The NE responses could be elicited in a Ca(2+)-free solution containing tetrodotoxin, indicating that they were postsynaptic. 3. The NE response could be blocked by the alpha-adrenoceptor antagonist prazosin, but not by the beta-adrenoceptor antagonist propranolol, and could be mimicked by the alpha 1-adrenoceptor agonist phenylephrine but not by the alpha 2-adrenoceptor agonist UK 14,304 or by the beta-adrenoceptor agonist isoproterenol when alpha-adrenoceptors were blocked. 4. Substitution of barium for calcium in the perfusion solution blocked the increase in RN in response to NE without completely blocking the depolarization. Replacement of sodium chloride with choline chloride in the barium-substituted perfusion solution blocked the remaining depolarization. 5. The neuropeptide thyrotropin-releasing hormone (TRH), which also depolarizes and increases the RN of HMs, occluded the response of HMs to NE. 6. NE altered HM firing properties in three ways: it always lowered the minimum amount of injected current needed to elicit repetitive firing, it increased the slope of the firing frequency versus injected current relation in 8 of 14 cells tested, and it increased the delay from the onset of the depolarizing current pulse to the first evoked spike in all cells tested. 7. We conclude that NE acts directly on alpha 1-adrenoceptors to increase the excitability of HMs. It does this by reducing a barium-sensitive resting potassium current and activating a barium-insensitive inward current carried primarily by sodium ions. A portion of the intracellular pathway for these actions is shared by TRH. In addition, there is evidence that NE alters HM firing patterns by affecting currents that are activated following depolarization.
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Maidre, Mihkel, Paul McVittie, and Rhian Isaac. "P7 An audit of the management of resuscitation drugs and trolley contents." Archives of Disease in Childhood 103, no. 2 (January 19, 2018): e2.8-e2. http://dx.doi.org/10.1136/archdischild-2017-314585.16.
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IntroductionEvery clinical area is equipped with either a resuscitation trolley containing a red emergency drug box (2222 box) or only the 2222 box for emergencies such as cardiac arrests. According to national1 and local guidelines each of these trolleys contains a certain set of drugs and a CD size oxygen cylinder.Aims wereto audit compliance of drugs, including the medical gas oxygen, with national1 and local guidelinesto audit compliance with the required daily check of resuscitation trolleys and 2222 boxesto audit frequency of expired medicinesto audit compliance with up to date resuscitation guidelinesThe aims of the audit were to assess the pharmaceutical contents in the resuscitation trolleys, monitor if regular checks are done to the trolleys, compare the pharmaceutical contents in the trolleys to those on the local clinical area’s stock list and review the resuscitation guidelines on the trolley.MethodA data collection form was created which included the drugs and local Trust resuscitation trolley content list. A free text box was included to capture drugs or drug related guidelines found on the trolley that were not officially listed.ResultsForty seven clinical areas were included in the data collection, 32 held a resuscitation trolley and a 2222 box, 15 held a 2222 box only.Compliance of drug content: 50%. Reason found for poor compliance was that most clinical areas (84.4%) did not keep 250 ml sodium chloride bags as routine stock on the ward causing a delay in replenishing following an emergency. Twenty of the trolleys contained drugs not included on the list.Compliance with equipment listCompliance of Oxygen cylinders on trolley: 5/29. Critical care unit trolleys did not keep oxygen cylinder as each bed space keeps a cylinder. One cylinder was found out of date.Compliance rate with daily trolley checks: 29/32Guidelines were found on 31/32 trolleys. Where guidelines were found, revision of the information was required.RecommendationsActions following the audit included changing the trolley content list: 250 mL sodium chloride 0.9 bags to a 500 ml sodium chloride 0.9% w/v bag which is kept routinely in each area. The guidelines are being revised to provide clearer information on dosing and administration for children.The Trust resuscitation committee have agreed to re-audit at least every 6 months.ConclusionAfter the completion of the audit the results were presented to the Resuscitation Committee and implementations were suggested in order to improve the management of resuscitation trolleys in the hospital. Together it was agreed, that a re-audit should be done in the future (3–6 months’ time) to see if these recommendations have improved the current situation.ReferenceResuscitation Council (UK). Acute care: Equipment and drug lists 2013. https://www.resus.org.uk/quality-standards/acute-care-equipment-and-drug-lists/#paed [Accessed: 6 April 2016].
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Jiang, Y. M., Y. Wang, L. Song, H. Liu, A. Lichter, O. Kerdchoechuen, D. C. Joyce, and J. Shi. "Postharvest characteristics and handling of litchi fruit — an overview." Australian Journal of Experimental Agriculture 46, no. 12 (2006): 1541. http://dx.doi.org/10.1071/ea05108.
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Litchi (Litchi chinensis Sonn.) is a tropical to subtropical crop that originated in South-East Asia. Litchi fruit are prized on the world market for their flavour, semi-translucent white aril and attractive red skin. Litchi is now grown commercially in many countries and production in Australia, China, Israel, South Africa and Thailand has expanded markedly in recent years. Increased production has made significant contributions to economic development in these countries, especially those in South-East Asia. Non-climacteric litchi fruit are harvested at their visual and organoleptic optimum. They are highly perishable and, consequently, have a short life that limits marketability and potential expansion of demand. Pericarp browning and pathological decay are common and important defects of harvested litchi fruit. Postharvest technologies have been developed to reduce these defects. These technologies involve cooling and heating the fruit, use of various packages and packaging materials and the application of fungicides and other chemicals. Through the use of fungicides and refrigeration, litchi fruit have a storage life of about 30 days. However, when they are removed from storage, their shelf life at ambient temperature is very short due to pericarp browning and fruit rotting. Low temperature acclimation or use of chitsoan as a coating can extend the shelf life. Sulfur dioxide fumigation effectively reduces pericarp browning, but approval from Europe, Australia and Japan for this chemical is likely to be withdrawn due to concerns over sulfur residues in fumigated fruit. Thus, sulfur-free postharvest treatments that maintain fruit skin colour are increasingly important. Alternatives to SO2 fumigation for control of pericarp browning and fruit rotting are pre-storage pathogen management, anoxia treatment, and dipping in 2% hydrogen chloride solution for 6−8 min following storage at 0°C. Insect disinfestation has become increasingly important for the expansion of export markets because of quarantine issues associated with some fruit fly species. Thus, effective disinfestation protocols need to be developed. Heat treatment has shown promise as a quarantine technology, but it injures pericarp tissue and results in skin browning. However, heat treatment can be combined with an acid dip treatment that inhibits browning. Therefore, the primary aim of postharvest litchi research remains the achievement of highly coloured fruit which is free of pests and disease. Future research should focus on disease control before harvest, combined acid and heat treatments after harvest and careful temperature management during storage and transport.
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Eng, D. L., T. R. Gordon, J. D. Kocsis, and S. G. Waxman. "Development of 4-AP and TEA sensitivities in mammalian myelinated nerve fibers." Journal of Neurophysiology 60, no. 6 (December 1, 1988): 2168–79. http://dx.doi.org/10.1152/jn.1988.60.6.2168.
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1. The sensitivities of mammalian myelinated axons to potassium channel blockers was studied over the course of development using in vitro sucrose gap and intra-axonal recording techniques. 2. Application of 4-aminopyridine (4-AP; 1.0 mM) to young nerves led to a delay in return to base line of the sciatic nerve compound action potential and to a postspike positivity (indicative of hyperpolarization) lasting for tens of milliseconds. These effects were very much attenuated during the course of maturation. 3. Tetraethylammonium chloride (TEA; 10 mM) application alone had little effect on the waveform of the compound action potential at any age. However, the 4-AP-induced postspike positivity was blocked by TEA, Ba/+, and Cs+. This block was observed in Ca2+-free electrolyte solutions containing EGTA (1.0 mM). 4. Immature sciatic nerves (approximately 3 wk postnatal) were incubated in a potassium-free electrolyte solution containing 120 mM CsCl for up to 1 h in an attempt to replace internal potassium with cesium. When the nerves were tested in the sucrose gap chamber using solutions containing 3.0 mM CsCl substituted for KCl, the compound action potential was broadened and a prolonged depolarization appeared, but there was no postspike positivity; the CsCl effect was similar to the combined effects of 4-AP and TEA. 5. Intra-axonal recordings were obtained to study the effects of 4-AP and TEA on individual axons. In the presence of 4-AP a single stimulus led to a burst of action potentials followed by a pronounced afterhyperpolarization (AHP) in sensory fibers. The AHP was blocked by TEA. In motor fibers 4-AP application resulted in action potential broadening with no AHP. 6. Repetitive stimulation (200-500 Hz; 100 ms) was followed by a pronounced AHP in both sensory and motor fibers at all ages studied. This activity-elicited AHP was sensitive to TEA at all ages. 7. The results indicate that 4-AP and TEA sensitivity change over the course of development in rat sciatic nerve. The effects of 4-AP are much more pronounced in immature nerves than in mature nerves, suggesting that 4-AP-sensitive channels become masked as they are covered by myelin during maturation. However, the TEA-sensitive channels, demonstrable after repetitive firing, remain accessible to TEA after myelination. These channels therefore may have a nodal representation.