1,720,997 research outputs found
Multi-scale modelling of bioreactor–separator system for wastewater treatment with two-dimensional activated sludge floc dynamics
Full text linkA simple “first generation” multi-scale computational model of the formation of activated sludge flocs at micro-scale and reactor performance at macro-scale is proposed. The model couples mass balances for substrates and biomass at reactor scale with an individual-based approach for the floc morphology, shape and micro-colony development. Among the novel model processes included are the group attachment/detachment of micro-flocs to the core structure and the clustering of nitrifiers. Simulation results qualitatively describe the formation of micro-colonies of ammonia and nitrite oxidizers and the extracellular polymeric substance produced by heterotrophic microorganisms, as typically observed in fluorescence in situ hybridization images. These results are the first step towards realistic multi-scale multispecies models of the activated sludge wastewater treatment systems and a generic modelling strategy that could be extended to other engineered biological systems.BT/BiotechnologyApplied Science
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
A preliminary and qualitative study of resource ratio theory to nitrifying lab-scale bioreactors
Full text linkThe incorporation of microbial diversity in design would ideally require predictive theory that would relate operational parameters to the numbers and distribution of taxa. Resource ratio-theory (RRT) might be one such theory. Based on Monod kinetics, it explains diversity in function of resource-ratio and richness. However, to be usable in biological engineered system, the growth parameters of all the bacteria under consideration and the resource supply and diffusion parameters for all the relevant nutrients should be determined. This is challenging, but plausible, at least for low diversity groups with simple resource requirements like the ammonia oxidizing bacteria (AOB). One of the major successes of RRT was its ability to explain the 'paradox of enrichment' which states that diversity first increases and then decreases with resource richness. Here, we demonstrate that this pattern can be seen in lab-scale-activated sludge reactors and parallel simulations that incorporate the principles of RRT in a floc-based system. High and low ammonia and oxygen were supplied to continuous flow bioreactors with resource conditions correlating with the composition and diversity of resident AOB communities based on AOB 16S rDNA clone libraries. Neither the experimental work nor the simulations are definitive proof for the application of RRT in this context. However, it is sufficient evidence that such approach might work and justify a more rigorous investigation
Ammonia-oxidizing bacteria in wastewater
No full textAmmonia-oxidizing bacteria (AOB) have a key role in the conversion of ammonia to nitrite in wastewater treatment plants (WWTPs). The characterization of AOB communities in such systems requires the use of genomic methods as AOB are difficult to isolate from environmental samples. Fluorescence in situ hybridization (FISH) using fluorescently labeled probes targeting 16S rRNA molecules provides a robust tool for the detection and quantification of AOB populations in biofilms and activated sludge flocs. The abundance of AOB may be also determined by real-time quantitative polymerase chain reaction (qPCR) using primers that amplify either the 16S rRNA or amoA genes. The evaluation of changes in the AOB community in time and space can be undertaken by PCR amplification of these gene fragments followed by denaturing gradient gel electrophoresis (PCR-DGGE). In this chapter, we summarize the most commonly applied procedures for the analysis of the AOB in wastewater, emphasizing their advantages and limitations
High rate domestic wastewater treatment at 15 °C using anaerobic reactors inoculated with cold-adapted sediments/soils-shaping robust methanogenic communities
No full textTo choose the reactor format in which to employ a low temperature adapted seed for wastewater treatment, we compared a UASB and an AnMBRUASB (UF) reactor at low HRT and temperature (15 °C). The reactors were inoculated with biomass from reactors seeded with soils and sediments from low temperature environments, and fed real municipal wastewater. Both systems met the UWWT Directive (91/271/EEC) COD effluent standard (<125.0 mg L−1) with the AnMBR COD removal efficiency being slightly higher (86.2 ± 1.5%) than that of the UASB (79.3 ± 2.0%). Methane production rates were also higher for the AnMBR than for the UASB, resulting in a COD : CH4 of 26.1 ± 3.0 and 18.2 ± 2.1%, respectively. Higher methanogenic cell abundance was observed in the AnMBR (3בUASB'). The low conversion of COD to methane was attributed to (i) the presence of SO4 in the influent (120.4 ± 17.4 mg L−1), which scavenged up to 50% of the COD, and (ii) accumulation of un-hydrolysed lipids in the mixed liquor especially in the case of the AnMBR. The UASB was energy positive (0.041 ± 0.013 kW h m−3) whilst the AnMBR was energy negative (−0.221 ± 0.016 kW h m−3). The reactor design appeared to have a profound effect on the numbers and diversity of the methanogens: the hydrogenotrophic activity being favoured in the UASB. But both reactors had comparatively high cell specific rates of methanogenesis. We concluded that the slightly better performance of the AnMBR was not sufficient to offset its higher running cost and the complexity of its design.</p
Spatio-temporal Model Checking for 3D Individual-Based Biofilm Simulations
No full textIndividual-based microbial modelling (IbM) is a bottom-up approach to study how the heterogeneity of individual microorganisms and their local interactions influence the behaviour of microbial communities.In IbM, microbes are represented as particles endowed with a set of biological and physical attributes. These attributes are affected by both intra- and extra-cellular processes resulting in the emergence of complex spatial and temporal behaviours, such as the morphology of microbial colonies. However, the quantitative and qualitative analysis of such behaviours is difficult and often relies on visual inspection of large quantities of simulation data or on the implementation of sophisticated algorithms for data analysis. In this work, we aim to alleviate the problem by applying SSTL (Signal Spatio-Temporal Logic) model checking to formally analyse the spatial and temporal properties of 3D microbial simulations (so-called traces). Complex behaviours can be then described by simple logical formulas and automatically verified by a model checker. We apply SSTL to analyse several outstanding spatio-temporal behaviours regarding biofilm systems, including biofilm surface dynamics, their detachment and deformation under fluid conditions
Variations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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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