117,383 research outputs found
Dissolved Fe (DFe) and Fe-binding dissolved organic ligands were analysed during two GEOTRACES cruises in the Mediterranean Sea in May and August 2013 - data
No full textMethod: Competing ligand exchange adsorptive cathodic stripping voltammetry (CLE-aCSV) was performed using two systems consisting of a μAutolab potentionstat (Metrohm Autolab B.V.), a 663 VA stand with a Hg drop electrode (Metrohm) and a 778 sample processor with ancillary pumps and dosimats (Metrohm), all controlled using a consumer laptop running Nova 1.9 (Metrohm Autolab B.V.). The characteristics of Fe-binding dissolved organic ligands, that is both the ligand concentration [Lt] (in nano-equivalents of molar Fe, nEq of M Fe) and the conditional binding constant K′ (M−1) with respect to [Fe3+], commonly expressed as log K′ are determined using 2- (2-Thiazolylazo)-p-cresol (TAC) as an added measuring ligand (Croot and Johansson, 2000). TAC was used with a final concentration of 10 μM, and the complex (TAC)2-Fe was measured after equilibration (> 6 h). The increments of Fe concentrations used in the titration were 0 (2×), 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5, 2, 2.5, 3, 4, 6, and 8 (2×) nM. Using a non-linear regression of the Langmuir isotherm, the electrical signal recorded in nA (nano-Ampere) was converted into a concentration in nM, and the ligand concentration [Lt] and the binding strength K were estimated (Gerringa et al., 2014). Using [Lt] and K, the concentration of Fe bound to a natural Febinding ligand [FeL], the concentration of inorganic Fe [Fe′] and the concentration of natural unbound ligand [L′] were calculated under the assumption of chemical equilibrium. Since K is log transformed, the standard error (SE) is asymmetric to lower and upper values; therefore two SE values are obtained, one to lower (down) and to upper (up) values
Dissolved iron measured on board with Flow injection analysis and iron-binding dissolved organic ligands from Ultra Clean CTD collected depth profiles during GEOTRACES PS94 Arctic cruise on Polarstern
No full textData from Polarstern cruise PS94 in the Arctic in 2015 with chief scientist Ursula Schauer. In order to explain geochemical cycles of Fe in the ocean, M. Rijkenberg, L. Gerringa and H. Slagter a.o. sampled filtered seawater using an ultra clean titanium CTD. In these samples on board measurements were executed: dissolved Fe by flow injection analysis and the characteristics of the dissolved organic Fe-binding organic ligands (totalL); characteristics being the concentration of these ligands and the conditional binding constant of the Fe-complex (K' expressed as its logarithm: logK). Moreover in order to relate the dissolved organic Fe-binding organic ligands to humic substances, fluorescence of dissolved organic matter was measured as well as humic substances using voltammetry
Heme b quotas are low in Southern Ocean phytoplankton
No full textHeme is the iron-containing prosthetic group of hemoproteins, and is thus required for photosynthesis, respiration and nitrate reduction in marine phytoplankton. Here we report concentrations of heme b in Southern Ocean phytoplankton and contrast our findings with those in coastal species. The concentration of particulate heme b (pmol l-1) observed at the end of the exponential growth phase was related to the concentration of dissolved iron in the culture media. Small Southern Ocean phytoplankton species (<6 µm in diameter) had heme b quotas <1 µmol mol-1 carbon, the lowest yet reported for marine phytoplankton. Heme b was also depleted in these species with respect to chlorophyll a. We calculated the amount of carbon accumulated per mole of heme b per second in our cultures (heme growth efficiency, HGE) and found that small Southern Ocean species can maintain growth rates, even while heme b content is reduced. Small Southern Ocean phytoplankton can thus produce more particulate carbon than larger Southern Ocean or small coastal species at equivalent iron concentrations. Combining primary productivity and heme b concentrations reported for the open ocean, we found that HGE in natural populations was within the range of our laboratory culture results. HGE was also observed to be higher at open ocean stations characterized by low iron concentrations. Our results suggest that low heme b quotas do not necessarily result in reduced growth and that marine phytoplankton can optimize iron use by manipulating the intracellular hemoprotein pool
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Letter from unknown writer to Jesse L. Boyce
No full textLetter to Jesse L. Boyce from unknown author (possibly Jack) about the investigation into the powder magazine located in the Grand Canyon. Some personal news is included in the letter such as the writer's marriage to the daughter of C.A. Taylor, former Supervisor of Cochise County
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Comparing CLE-AdCSV applications using SA and TAC to determine the Fe binding characteristics of model ligands in seawater
No full textCompetitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV) is used to determine the conditional concentration ([L]) and the conditional binding strength (logKcond) of dissolved organic Fe-binding ligands, which together influence the solubility of Fe in seawater. Electrochemical applications of Fe speciation measurements vary predominantly in the choice of the added competing ligand. Although different applications show the same trends, [L] and logKcond differ between the applications. In this study, binding of two added ligands in three different common applications to three known types of natural binding ligands are compared. The applications are: 1) Salicylaldoxime (SA) at 25 micromol (SA25) and short waiting time, 2) SA at 5 micromol (SA5) and 3)2-(2-thiazolylazo)-rho-cresol (TAC) at 10 micromol, the latter two with overnight equilibration. The three applications were calibrated under the same conditions, although having different pH values, resulting in the detection window centers (D) DTAC > DSA25 >/= SA5 (as log D values with respect to Fe3+: 12.3>11.2>/= 11).
For the model ligands, there is no common trend in the results of logKcond. The values have a considerable spread, which indicates that the error in logKcond is large. The ligand concentrations of the non humic model ligands are underestimated by TAC and overestimated by SA25 which we attribute to the lack of equilibrium between Fe-SA species in the SA25 application. The application TAC more often underestimated the ligand concentrations and Application the application SA5 was best in estimating over and under estimated the ligand concentration correctly. The trends between these model ligand concentrations were similar for all three applications. The estimated ligand concentrations for the humic and fulvic acids differed approximately by a factor 22 fold between TAC and SA5 and another factor of 2 between SA5 and SA25.
The use of SA above 5 micromol suffers from the formation of the species Fe(SA)x (x>1) that is not electro-active as already suggested by Abualhaija and Van den Berg (2014). Moreover, we found that the reaction between the electro-active and non-electro-active species is probably irreversible. This undermines the assumption of the CLE principle, causes overestimation of [L] and could result in a false distinction into more than one ligand group.
For future electrochemical work it is recommended to take the above limitations of the applications into account. Overall, the uncertainties arising from the CLE-AdCSV approach mean we need to search for new ways to determine the organic complexation of Fe in seawater
Sarah L. Blum Author Visit - Warrior Nurse: PTSD and Healing
No full textHear Sarah L. Blum, author of Women Under Fire: Abuse in the Military, discuss her newest book, Warrior Nurse: PTSD and Healing followed by a Q&A and book signing.
Sarah L. Blum is a decorated Vietnam veteran who served as an operating room nurse during the intense fighting of 1967. In recognition of her service, she was awarded the Army Commendation Medal.
Sponsored by CWU Veterans Center and CWU Libraries.https://digitalcommons.cwu.edu/libraryevents/1252/thumbnail.jp
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