1,720,961 research outputs found
Technical note: a fast and reproducible autosampler for direct vapor equilibration isotope measurements
No full textAbstract. To investigate water movement in environmental systems, stable isotope (2H and 18O) ratios of water are commonly used tracers. Analyzing the isotopic ratios of water in or adsorbed to substances like soil or plant tissue necessitates the extraction or equilibration of water prior to analysis. One such method, direct vapor equilibration, is popular due to its cost-effectiveness and straightforward sample processing. However, sample analysis requires significant manual labor, thereby limiting the number of samples that can be analyzed. This limitation is compounded by the fact that stored samples undergo evaporative isotopic changes over time. Moreover, manual measurements require many laborious procedural steps that can easily compromise reproducibility. The operator has to subjectively decide if the measurements are stable and then record the analyzer readings. To address these challenges, we have developed a system that automates the analysis process. Our autosampler for vapor samples, named VapAuSa, features a modular design that allows for up to 350 ports for direct vapor equilibration samples. These ports sequentially connect the prepared samples to a laser isotope analyzer, enabling continuous automated measurements. Within the accompanying software, measurement criteria can be specified, facilitating reproducible analysis. The developed system was tested by co-measuring 90 soil samples and 21 liquid water samples with known δ values. VapAuSa measurements have a negligible measurement bias (<1×10-13 ‰ for both δ2H and δ18O) and similar measurement repeatability compared to manual analysis of identical samples (δ2H=±4.5 ‰ and δ18O=±0.58 ‰ for VapAuSa measurements vs. δ2H=±5.7 ‰ and δ18O=±0.37 ‰ for manual analysis). However, the increased sample throughput minimizes storage-induced isotopic changes. Moreover, VapAuSa triples sample throughput per week while also reducing the direct labor time to just 10 % of that required for manual processing
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
Hidden pathways: unraveling subsurface flow processes of water with stable isotopes
No full textUnderstanding how water moves through the subsurface is critical for predicting floods, safeguarding drinking water, and protecting aquatic ecosystems. On hill- slopes, water can travel laterally through the soil during infiltration events triggered by rainfall or snowmelt. This process is known as subsurface stormflow (SSF). SSF is a key runoff generation mechanism and a substantial contributor to streamflow; however, its governing processes remain elusive. Water can infiltrate slowly through the soil matrix or be rapidly conveyed along preferential flow paths. While the ex- istence of such pathways is widely acknowledged, their occurrence and transport dynamics are still not fully understood. Stable isotopes of hydrogen and oxygen in water (1H, 2H, 16O and 18O) are powerful tracers of hydrological processes because their ratios in precipitation vary seasonally and become imprinted in the soil during infiltration. These "time-stamped" conser- vative tracers offer a means of tracking water movement in the subsoil. However, challenges remain in ensuring objectivity in isotope analysis and preserving sample integrity. This thesis therefore has two primary objectives: (1) to improve stable water iso- topes sampling and analysis, and (2) to reveal hidden subsurface flow paths at point and hillslope scales. To meet the first objective, two novel tools were developed. First is VapAuSa, an au- tomatic vapor autosampler for direct vapor equilibration (DVE) samples. VapAuSa eliminates subjective operator bias and reduces manual labor by 90 %, also doubling weekly sample throughput. Isotopic measurements from VapAuSa exhibit negligi- ble bias and maintain repeatability comparable to manual analyses. Second is PAUL (Portable Autosampler for Liquids), which enables low-cost, autonomous sample collection while effectively preventing evaporation. A one-month evaporation test confirmed that PAUL-sealed bottles had no measurable evaporation losses, as op- posed to 10 % volume loss in regular open containers. To achieve objective B, three studies were conducted across four low mountain and alpine catchments. Stable water isotope profiles from 100 soil cores per catchment were analyzed at the point scale. Reference profiles representing matrix-only infiltra- tion were constructed using seasonal clustering and LOESS regression. Deviations from these reference profiles revealed clear signatures of preferential flow at all sites, particularly in alpine soils, which exhibited complex patterns. These signatures in- cluded multiple independent vertical pathways at variable depths and notable hills- lope aspect influence, with north-facing slopes exhibiting more frequent preferential flow. At the hillslope scale, dual-layer trenches were installed on three hillslopes in a Black Forest catchment. Natural rainfall and deuterium-labeled sprinkling experiments were conducted. Tracer water reached depths of over 1 m within minutes; how- ever, isotope profiles showed its presence only in the top 20 cm of the soil matrix, indicating bypass flow through deep preferential pathways. Although only 10 % of the tracer water was discharged during the experiment, approximately 45 % was retained in the topsoil. Substantial SSF outflow also contained predominantly pre- event water, suggesting displacement via piston flow mechanisms, which supports a dual-domain flow model. During natural events, the ratio of pre- to event wa- ter depended on antecedent wetness, linking storage-remobilization behavior to soil moisture conditions. Notably, this dynamic, formerly observed at the catchment scale, appears to emerge at the hillslope scale as well. Additionally, event water vol- umes were proportional to precipitation volumes. Furthermore, temperature profil- ing revealed that SSF matrix flow occurred at consistent depths across events. In conclusion, the innovations presented in this thesis substantially improve the analysis and sampling of hydrogen and oxygen isotopic compositions in water. Au- tomating vapor equilibration and improving liquid sample preservation enhances analytical reliability and efficiency. However, challenges remain, like the substan- tial waste generated by DVE. This calls for the development of more sustainable methodologies. The three field studies reveal the complex and heterogeneous nature of subsurface flow paths in hillslope environments. This variability has important implications for how we conceptualize and model catchment-scale processes, especially solute transport and runoff generation. These results underscore the importance of ongo- ing high-resolution monitoring and targeted experimental investigations to improve our understanding of and ability to accurately represent subsurface flow dynamics
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
