1,721,060 research outputs found
Diatom communities on commercial biocidal fouling control coatings after one year of immersion in the marine environment
Get PDFLittle is known about the effect of commercial biocidal fouling control coatings on fouling diatom communities and their growth forms after long periods of exposure in the marine tropical environment. The current study investigated the abundance and composition of fouling diatom communities developed on 11 commercially available biocidal antifouling coatings, covering the three main technology types in recent historic use (Self-Polishing Copolymers, Self-Polishing Hybrid and Controlled Depletion Polymers) after one year of static immersion at two locations in Muscat, Oman (Marina Shangri La and Marina Bandar Rowdha). Light microscopy demonstrated that the total abundance of diatoms and the relative abundance of growth forms were significantly affected by the choice of biocidal antifouling coating and experimental location. Using scanning electron microscopy, a total of 21 diatom genera were identified which were grouped into adnate, motile, plocon and erect growth forms. The adnate growth forms, mainly the genera Amphora, Cocconeis and Mastogloia, dominated the other growth forms in terms of their relative abundance. Current results revealed the importance of exposure location and choice of biocidal antifouling coating on the relative abundance of diatom growth forms
Chlorination disadvantages and alternative routes for biofouling control in reverse osmosis desalination
Get PDFWith an ever-increasing human population, access to clean water for human use is a growing concern across the world. Seawater desalination to produce usable water is essential to meet future clean water demand. Desalination processes, such as reverse osmosis and multi-stage flash have been implemented worldwide. Reverse osmosis is the most effective technology, which uses a semipermeable membrane to produce clean water under an applied pressure. However, membrane biofouling is the main issue faced by such plants, which requires continuous cleaning or regular replacement of the membranes. Chlorination is the most commonly used disinfection process to pretreat the water to reduce biofouling. Although chlorination is widely used, it has several disadvantages, such as formation of disinfection by-products and being ineffective against some types of microbes. This review aims to discuss the adverse effect of chlorination on reverse osmosis membranes and to identify other possible alternatives of chlorination to reduce biofouling of the membranes. Reverse osmosis membrane degradation and mitigation of chlorines effects, along with newly emerging disinfection technologies, are discussed, providing insight to both academic institutions and industries for the design of improved reverse osmosis systems
Succession of marine fouling on experimental ship coatings in tropical waters, Oman
No full textAbstract Surfaces submerged in the sea are rapidly covered by biofilm and later macrofouling. Biofouling on ship hulls spread exotic species to new habitats and are at the same time an economical burden. In the past paints with TBT has had great effect against fouling but also had have grave consequences for the marine life leading to an international ban in 2010 and a demand for environmentally friendly antifouling coatings has arisen. In the present project coatings with different active compounds was prepared on microscope slides. The coatings, with both experimental and commercial paints, were submerged for 22 days in the Bay of Oman. The commercial paints had copper and a mixture of copper and zinc pyrithione as active compounds. The experimental paints had zinc oxide, zinc sulphide and aerogel with active compound x, zinc sulphide and aerogel without active compound, zinc sulphide without aerogel, zinc sulphide with commercial protease, zinc oxide without aerogel and titandioxide as active compounds. To harmonize the surfaces black nitrocellulose filters were attached on the slides for bacterial counts with DAPI staining. The filters were collected over time to determine bacterial and macrofouling succession. The bacterial density increased over time for all treatments and most for the treatments with commercial paints. The lowest counts were observed in the Control samples and the engineered paints had counts in between. The commercial paints inhibited quorum sensing in reporter strain C. violaceum CV017. Community analysis of microfouling by fatty acid analysis, in the first experiment, revealed when statistical analyzed by ANOSIM that the Control differed from most of the other treatments and that the commercial paint also differed from one of the engineered treatments. The statistically analysis SIMPER revealed that the fatty acid community was dominated by few fatty acids present in all the treatments. Differences between treatments were determined by the density among the dominating fatty acids. At the same time a temporal succession in fatty acids was observed. Contrary general assumptions and results the commercial antifouling paints with the highest fouling inhibition had the highest bacterial counts which must result from biofilm development of bacteria resistant to the active compounds copper and zinc pyrithione used in these treatments. The poly unsaturated fatty acid (PUFA) C18:2ω9,12 was found in samples the Control, treatment MUZ and treatments T40 and T44 which have been connected to the groups of Cytophagales or Proteobacteria. Fatty acid profiles from several treatments had similarities to fatty acids profiles extracted from fluorescent Pseudomonas. The surfaces with commercial paints had the lowest abundance of macrofouling recorded. The Control samples had the highest algae and invertebrate density and the engineered paints had fouling abundances within the range of the Controls and the commercial paints. The treatments with zinc sulphide without aerogel and zinc sulphide and aerogel with enzyme x had the poorest antifouling activity against macrofouling along with the Control. The commercial paints demonstrated both a broad fouling inhibition against all macrofouling organisms encountered. Keywords; biofilm formation, marine fouling, bacterial community dynamics, quorum sensingAbstract Surfaces submerged in the sea are rapidly covered by biofilm and later macrofouling. Biofouling on ship hulls spread exotic species to new habitats and are at the same time an economical burden. In the past paints with TBT has had great effect against fouling but also had have grave consequences for the marine life leading to an international ban in 2010 and a demand for environmentally friendly antifouling coatings has arisen. In the present project coatings with different active compounds was prepared on microscope slides. The coatings, with both experimental and commercial paints, were submerged for 22 days in the Bay of Oman. The commercial paints had copper and a mixture of copper and zinc pyrithione as active compounds. The experimental paints had zinc oxide, zinc sulphide and aerogel with active compound x, zinc sulphide and aerogel without active compound, zinc sulphide without aerogel, zinc sulphide with commercial protease, zinc oxide without aerogel and titandioxide as active compounds. To harmonize the surfaces black nitrocellulose filters were attached on the slides for bacterial counts with DAPI staining. The filters were collected over time to determine bacterial and macrofouling succession. The bacterial density increased over time for all treatments and most for the treatments with commercial paints. The lowest counts were observed in the Control samples and the engineered paints had counts in between. The commercial paints inhibited quorum sensing in reporter strain C. violaceum CV017. Community analysis of microfouling by fatty acid analysis, in the first experiment, revealed when statistical analyzed by ANOSIM that the Control differed from most of the other treatments and that the commercial paint also differed from one of the engineered treatments. The statistically analysis SIMPER revealed that the fatty acid community was dominated by few fatty acids present in all the treatments. Differences between treatments were determined by the density among the dominating fatty acids. At the same time a temporal succession in fatty acids was observed. Contrary general assumptions and results the commercial antifouling paints with the highest fouling inhibition had the highest bacterial counts which must result from biofilm development of bacteria resistant to the active compounds copper and zinc pyrithione used in these treatments. The poly unsaturated fatty acid (PUFA) C18:2ω9,12 was found in samples the Control, treatment MUZ and treatments T40 and T44 which have been connected to the groups of Cytophagales or Proteobacteria. Fatty acid profiles from several treatments had similarities to fatty acids profiles extracted from fluorescent Pseudomonas. The surfaces with commercial paints had the lowest abundance of macrofouling recorded. The Control samples had the highest algae and invertebrate density and the engineered paints had fouling abundances within the range of the Controls and the commercial paints. The treatments with zinc sulphide without aerogel and zinc sulphide and aerogel with enzyme x had the poorest antifouling activity against macrofouling along with the Control. The commercial paints demonstrated both a broad fouling inhibition against all macrofouling organisms encountered. Keywords; biofilm formation, marine fouling, bacterial community dynamics, quorum sensin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Comparative study of the optimal production of Spirulina (Arthrospira platensis) in Oman and its effect on growth and microbiota on Nile Tilapia (Oreochromis niloticus)
Get PDFLa popularidad de la espirulina ha sido impulsada en parte por su alto contenido de proteínas y altas concentraciones de aminoácidos esenciales y no esenciales. También es una rica fuente de vitaminas A, D, E, K y vitaminas del grupo B. Minerales como hierro, magnesio, potasio, calcio. Carotenoides (astaxantina, zeaxantina, β-caroteno), polifenoles y clorofila y ácidos grasos poliinsaturados.
Para cultivar Spirulina, se requiere un medio de crecimiento adecuado que proporcione todos los nutrientes y condiciones necesarios para que las algas prosperen. Un medio comúnmente utilizado para el cultivo de Spirulina es el medio Zarrouk.
El medio Zarrouk fue desarrollado por primera vez por un estudiante de doctorado llamado Zarrouk, Francia en 1966. La investigación de Zarrouk condujo al desarrollo del medio Zarrouk, un medio de crecimiento que todavía se usa ampliamente para cultivar Spirulina hoy en día en la investigación científica como estándar. El medio Zarrouk proporciona todos los nutrientes esenciales necesarios para el crecimiento de Spirulina y se ha demostrado que produce Spirulina con un alto contenido nutricional.
El costo de los nutrientes como el segundo factor importante después de las labores que influye en el costo de producción de Spirulina. Sin embargo, desde entonces se han desarrollado muchas tecnologías para minimizar la mano de obra y se introdujo la mecanización que hace que los nutrientes sean hoy el principal costo en la producción de Spirulina.
El bicarbonato y nitrato de sodio suponen el 82,8% de la cantidad total de la cantidad de fertilizante en el medio Zarrouk, bicarbonato de sodio (16,8 g/L) y nitrato (2,5 g/L), que es el gasto más significativo en el medio. Encontrar otras alternativas de bajo costo podría hacer que el precio de mercado de la espirulina sea asequible.El Sultanato de Omán, con una superficie de 309.500 km2 situado en la parte sureste de la Península Arábiga, tiene las coordenadas geográficas 22.7465° N y 57.1203° E, está ubicado en un ambiente árido y semiárido. La precipitación anual varía desde 20 mm año-1 en el interior hasta 300 mm año-1 a lo largo de la costa. En estas regiones áridas y semiáridas, donde la mayoría de la tierra es desierto con agua limitada para los cultivos tradicionales, el cultivo de algas es una solución ideal para aumentar la tierra productiva verde que consume menos agua o incluso utiliza agua de mar para el cultivo. El cultivo de algas proporciona numerosos beneficios en comparación con los cultivos terrestres, como un alto contenido de proteínas, ácidos grasos valiosos, abundantes vitaminas y minerales y, lo que es más importante, un consumo reducido de agua.
A pesar de los desafíos asociados con el cultivo de algas, como la tecnología o los fertilizantes de crecimiento, el interés en esta área aumenta constantemente. Durante la última década, el sector farmacéutico ha reconocido a las algas como una fuente prometedora de antibióticos, agentes antifúngicos y compuestos antitumorales. Las microalgas, en particular, han atraído una gran atención de la investigación debido a su facilidad de cultivo y rápidas tasas de crecimiento.
Muchas especies de algas tienen potencial para el cultivo. Las especies adaptables como la espirulina son especialmente prometedoras porque son fáciles de cultivar y cosechar, y se consideran el alimento del futuro.
La espirulina es un tipo de cianobacteria, también conocida como alga azul-verde, que ha sido consumida por los humanos durante siglos. Se ha utilizado como fuente de alimento desde los aztecas, quienes lo recolectaron del lago Texcoco en México y lo usaron como fuente de proteínas y otros nutrientes. También ha sido un alimento tradicional para la población de Kanembu en África, donde se recolecta del lago de Chad
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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