1,720,989 research outputs found
Development and first results of a new fast response microelectrode DO-sensor
No full textA new dissolved oxygen sensor for marine application was developed and first tests in the field were carried out. The sensor uses a micro-electrode as the sensing element that has an inherently fast response and an increased resistance to biofouling due to the properties of the electrode material, platinum, and the employed operation repime.Introduction of a cleaning cycle, where the potential applied to the electrode is altered, allows the elimination of material building up at the electrode surface as well as the reconditioning of the electrode surface, thus minimizing drift and the effect of bio-fouling.Micmdisc electrodes ranging between 10 and SO pm diameter have been tested. The sensor has been adapted to operate on a CTD system or on towed instrument platforms. Results of test cruises will be presented
In situ determination of iron(II) in the anoxic zone of the central Baltic Sea using ferene as spectrophotometric reagent
No full textContinuous flow analysis for soluble Fe(II) species in seawater was performed with a colorimetric method using ferene as a spectrophotometric reagent. The method is based on the measurement of absorbance of the [FeII(fer)3]4 --complex at 594 nm. No preconcentration-steps are required. Samples prepared in the laboratory in line with external calibration experiments have been successfully analyzed in the nanomolar range (R2 = 0.959). A detection limit of 20 nM was obtained. Furthermore, investigations were performed in situ with a wet chemical analyzer in the water column of the central Baltic Sea. Finally the results were consistent with measurements made by an independent laboratory based method (ICP-OES)
Field assessment of a new membrane-free microelectrode dissolved oxygen sensor for water column profiling
No full textThis article reports on the field trials of a membrane-free amperometric microelectrode dissolved oxygen sensor, which were performed during oceanographic cruise D279 of RRS Discovery. The sensor was used to obtain full depth oxygen profiles while mounted on a wire-operated CTD (conductivity, temperature, depth) instrument. A stable performance was achieved by carefully designed electrochemical cleaning conditions of the sensing platinum microdisk cathode. The flow issues inherent to moving probes were resolved by a novel stop-flow cell fitted with a pumping system for sample exchange and flow control. The details of the sensor operation, calibration, and construction, including the flow control system, are described. The sensor response is validated by calibration and by an analytical approach that yields oxygen data directly from the current readings. The accuracy of the microelectrode response is critically assessed using Winkler titrations on bottle samples taken during the relevant sensor deployments. The results lead to the conclusion that due to high accuracy, fast response time, and lack of membrane-related problems the device is particularly suitable for moving probes and high spatial resolution water column oxygen profiling
Development and validation of microfluidic lab-on-chip analyzers for the in situ quantification of dissolved iron and manganese species in seawater
Full text linkThere has been an increasing demand over the last decades for autonomous in situ measurement systems for the quantification of physical and chemical parameters in the marine environment. The demand is largely linked to the need to address the present undersampling of the world’s oceans. The need for reliable and well resolved time series, both on a temporal and spatial scale, cannot be satisfied with conventional approaches involving collection of discrete samples during ship campaigns followed by their analysis in a land-based laboratory. This PhD project investigates whether the well-established spectrophotometric approaches for Fe and Mn using Ferrozine (FZ) and 1-(2-pyridylazo)-2-naphthol (PAN) as complexing agents, respectively, can be utilized for reliable and accurate in situ quantification of dissolved Fe and Mn species in an autonomous wet chemical analyzer based on lab-on-chip (LoC) technology. Those systems are based around a microfluidic chip and integrate all steps of analysis (sampling, sample treatment, chemical reaction, detection, data processing) into a single instrument
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
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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