130,657 research outputs found
Lake Pavin Paleolimnology and Event Stratigraphy
No full textInternational audienceIn this chapter we present an up-to-date database of sedimentary sequences retrieved from Lake Pavin during the last 50 years in both oxic and anoxic waters. The detailed history of this mid Holocene crater lake can be reconstructed from the correlation of radiocarbon dated sedimentary sequences retrieved from the deep central basin, a subaquatic plateau and littoral environments. High-resolution measurements of sediment composition (diffuse spectral refl ectance, XRF core scanning) combined with the analysis of organic matter composition and preliminary pollen and diatom assemblages investigations on selected sediment cores are used to reconstruct (i) the evolution since ca. 7000 cal BP of Lake Pavin limnology together with its radiocarbon reservoir effect and (ii) the impact of a wide range of subaquatic slope failure events. Such a multidisciplinary approach of Lake Pavin basin fi ll revealed contrasted sedimentation patterns just after the volcanic eruption and following the development of a dense vegetation cover along the slopes of the crater. Pavin sedimenta-tion is rapidly and largely dominated by organic rich and fi nely laminated diatomite formation , but several short periods of enhanced mineral inputs might refl ect the infl uence of wetter periods, such as the Little Ice Age. Over the last millennium two large subaquatic mass wasting events are also identifi ed and may have signifi cantly impacted its limnology
Heat Transfer in a Two-Pass Channel with Vortex Generators
No full textCooling channels in modern turbine airfoils often include surface features for enhanced heat convection and near 180-degree turns. A sharp turn further induces turbulence level and increases heat transfer rate. However, it also causes significant pressure loss. While significant level of studies have been focused on either surface enhancement, such as vortex generators/turbulators, or turn effects, virtually no study in the open literature has been directed to the combined effects of sharp turn and surface-feature induced heat transfer enhancement. In this study, series of experiments were performed to investigate the heat transfer and pressure characteristics in a high aspect ratio, (4.5:1 width-to-height), two-pass channel, with delta-wing-shaped, cube-shaped and diamond-shaped element arrays placed in both channel passes before and after a 180-degree sharp turn. Transient liquid crystal technique is applied to acquire detailed local heat transfer data both on the channel surface and the turbulator elements, for Reynolds number between 13000 and 32000. To further explore potential design alternatives for enhancement cooling, the density effects of the delta wing turbulators are investigated and the effects of block height of the cube-shaped and diamond-shaped, ranging from ¼, ½, ¾ and full span of the channel height are also evaluated. Present results suggest that a staggered delta wing array can enhance heat transfer rate up to 3.1 fold in the first pass and up to 1.6 fold in the second pass, relative to the fully-developed smooth channel counterpart. When coupled with the 90-degree bend inlet, heat transfer rate can be enhanced up to another 1.9 and 1.3 fold for the first and second pass respectively. The cube-array can enhance heat transfer rate up to 3.5 folds in the first pass and approximately 1.9 fold in the second pass. For the corresponding diamond-shaped block array, the enhancement is up to 3.4 and 1.9 respectively. It is interesting to note that even though the post-turn turbulence transport in the second pass is generally higher than the first turn, the effects of surface-element induced heat transfer enhancement are, in fact, less prominent, in the post-turn region in the second pass. Pressure loss for a diamond block arrays is generally higher than that of the corresponding cube-block array. Pressure losses for sparse and dense delta arrays are approximately the same as the pressure losses of the half height cube and diamond arrays respectively
Diversity of iron- and sulfur/sulfate-reducing in Lake Pavin enrichment cultures with different Fe phases.
No full textBacterial 16S rRNA gene sequences obtained from 2016 Lake Pavin enrichment cultures were classified based on best BLAST hit results, and putative iron- and sulfur/sulfate-reducing bacteria were identified based on phylogenetic affiliation with known iron and sulfur/sulfate reducers. Cultures were sequenced after significant evolution of the original added iron phase was observed: FhL = 360 d, FPL = 82 d, FhLS = 55 d, FPLS = 180 d, FeLS = 27 d.</p
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
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
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Conformational investigations on glycosylated threonine-oligopeptides of increasing chain length
No full textStepwise solution syntheses are described of the homo-oligomers Z-(Thr)(n)-NHCH3 (n=1-4, I1-4), Z- ([Gal(Ac)(4) beta]Thr](n)-NHCH3 (n=1-5, II1-5] and Z[(Gal beta)Thr]n-NHCH3 (n=1-5, III1-5). Members of the III1-5 series were obtained by de-acetylation of the corresponding oligomers of the II1-5 series. The conformational preferences of the terminally protected homo-peptides of the three series were investigated by FT-IR absorption spectroscopy both in the solid state and in CDCl3 solution, at various concentrations. Proton NMR measurements in CDCl3 and in DMSO-d(6) were also carried out and the effect of temperature variation on the chemical shifts of amide protons was determined in DMSO-d(6) (range 298-335 K) and in CDCl3 (range 298- 320 K). CD spectra were recorded in water and in TFE. Solubility problems prevented measurements in CDCl3 solution for Z(Thr)(4)-NHCH3 and for the entire III1-5 series. The existence of unordered structures in the carbohydrate-free oligomers and of more or less extended, organized structures in the glycosylated derivatives is indicated by the NMR and IR measurements. The sugar moieties apparently show a structure-inducing effect on the peptide chain. (C) 1998 European Peptide Society and John Wiley Br Sons, Ltd
Multidisciplinary characterisation of sedimentary processes in a recent maar lake (Lake Pavin, French Massif Central) and implication for natural hazards
No full textSedimentation processes occurring in the most recent maar lake of the French Massif Central (Lake Pavin) are documented for the first time based on high resolution seismic reflection and multibeam bathymetric surveys and by piston coring and radiocarbon dating on a sediment depocentre developed on a narrow sub aquatic plateau. This new data set confirms the mid Holocene age of maar lake Pavin formation at 6970&plusmn;60 yrs cal BP and highlights a wide range of gravity reworking phenomena affecting the basin. In particular, a slump deposit dated between AD 580–640 remoulded both mid-Holocene lacustrine sediments, terrestrial plant debris and some volcanic material from the northern crater inner walls. Between AD 1200 and AD 1300, a large slide scar mapped at 50 m depth also affected the southern edge of the sub aquatic plateau, suggesting that these gas-rich biogenic sediments (laminated diatomite) are poorly stable. Although several triggering mechanisms can be proposed for these prehistoric sub-aquatic mass wasting deposits in Lake Pavin, we argue that such large remobilisation of gas-rich sediments may affect the gas stability in deep waters of meromictic maar lakes. This study highlights the need to further document mass wasting processes in maar lakes and their impacts on the generation of waves, favouring the development of dangerous (and potentially deadly) limnic eruptions
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
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