1,720,962 research outputs found
Development of a reliable microelectrode dissolved oxygen sensor
No full textThis article reports the results of a careful experimental and analytical investigation which led to the development of an accurate and reproducible microelectrode dissolved oxygen sensor. Primarily designed for oceanographic applications but also applicable to environmental and water process monitoring, the sensor measures the diffusion controlled current to a bare Pt microdisc electrode for the reduction of oxygen. A successful reconditioning potential waveform is reported which yields a very stable amperometric response over continuous operation, with a maximum deviation of the limiting current under 1.5% over 24 h. An automated calibration method developed to accurately characterise the electrodes is described. Excellent linearity is obtained for all electrodes tested and in each case, the number of apparent electrons for the reduction of oxygen is reported. As an alternative to calibration, an analytical treatment which accounts for temperature and salinity effects is given to calculate the dissolved oxygen concentration directly from the limiting current. While the analytical approach yields a concentration relative error circa 11% for a 50 ?m diameter Pt disc, the calibration, has lower errors and yields a detection limit down to 0.9 ?M with the same disc. Although this investigation builds on established principles, this article describes, for the first time, the conditions required to obtain accurate and reproducible measurements and provides an estimate of their precision. Preliminary field trials to measure oxygen depth profiles in the ocean have proved very encouraging [R. Prien, R. Pascal, M. Mowlem, G. Denuault, M. Sosna, Development and first results of a new fast response microelectrode DO-sensor, in Oceans 2005—Europe, Vols. 1 and 2, 2005, pp. 744–747]
Trajectories of sinking particles and the catchment areas above sediment traps in the northeast Atlantic
Full text linkA Lagrangian analysis of particles sinking through a velocity field observed by Eulerian frame measurements was used to evaluate the effects of horizontal advection and particle sinking speed on particle fluxes as measured by moored sediment traps. Characteristics of the statistical funnel above moored deep-ocean sediment traps at the German JGOFS quasi-time series station at 47N, 20W (Biotrans site) were determined. The analysis suggests that the distance and direction between a given sediment trap and the region at the surface where the particles were produced depends on the mean sinking velocity of the particles, the horizontal velocity field above the trap and the deployment depth of the trap. Traps moored at different depths at a given mooring site can collect particles originating from different, separated regions at the surface ocean. Catchment areas for a given trap vary between different years. Typical distances between catchment areas of traps from different water depth but for a given time period (e.g., the spring season) are similar or even larger compared to typical length scales of mesoscale variability of phytoplankton biomass observed in the temperate northeast Atlantic. This implies that particles sampled at a certain time at different depth horizons may originate from completely independent epipelagic systems. Furthermore catchment areas move with time according to changes in the horizontal flow field which jeopardizes the common treatment of interpreting a series of particle flux measurements as a simple time series. The results presented in this work demonstrate that the knowledge of the temporal and spatial variability of the velocity field above deep-ocean sediment traps is of great importance to the interpretation of particle flux measurements. Therefore, the one-dimensional interpretation of particle flux observations should be taken with care
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
Hydrothermal exploration of the Fonualei Rift and Spreading Center and the Northeast Lau Spreading Center
Full text linkWe report evidence for active hydrothermal venting along two back-arc spreading centers of the NE Lau Basin: the Fonualei Rift and Spreading Center (FRSC) and the Northeast Lau Spreading Center (NELSC). The ridge segments investigated here are of particular interest as the potential source of a mid-water hydrothermal plume (1500–2000 m depth) which extends more than 2000 km across the SW Pacific Ocean dispersing away from an apparent origin close to the most northeastern limits of the Lau Basin. Our results indicate the presence of at least four new hydrothermal plume sources, three along the FRSC and one on the NELSC, the latter situated within 150 km of the maximum for the previously identified SW Pacific regional-scale plume. However, TDFe and TDMn concentrations in the southernmost FRSC plume that we have identified only reach values of 19 and 13 nmol/L and dissolved 3He anomalies in the same plume are also small, both in relation to the SW Pacific plume and to local background, which shows evidence for extensive 3He enrichment throughout the entire Lau Basin water column. Our results reveal no evidence for a single major point hydrothermal source anywhere in the NE Lau Basin. Instead, we conclude that the regional-scale SW Pacific hydrothermal plume most probably results from the cumulative hydrothermal output of the entire topographically restricted Lau Basin, discharging via its NE-most corner
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
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