127,254 research outputs found
Absence of superconductivity in iron polyhydrides at high pressures
No full textRecently, C. M. Pépin et al. [Science 357, 382 (2017)] reported the formation of several new iron polyhydrides FeHx at pressures in the megabar range and spotted FeH5, which forms above 130 GPa, as a potential high-Tc superconductor because of an alleged layer of dense metallic hydrogen. Shortly after, two studies by A. Majumdar et al. [Phys. Rev. B 96, 201107 (2017)] and A. G. Kvashnin et al. [J. Phys. Chem. C 122, 4731 (2018)] based on ab initio Migdal-Eliashberg theory seemed to independently confirm such a conjecture. We conversely find, on the same theoretical-numerical basis, that neither FeH5 nor its precursor, FeH3, shows any conventional superconductivity and explain why this is the case. We also show that superconductivity may be attained by transition-metal polyhydrides in the FeH3 structure type by adding more electrons to partially fill one of the Fe-H hybrid bands (as, e.g., in NiH3). Critical temperatures, however, will remain low because the
d-metal bonding, and not the metallic hydrogen, dominates the behavior of electrons and phonons involved in the superconducting pairing in these compounds
Unterkunftshaus a. Brünnstein, Pächter B. Brenner, Rodel Heil!
No full textUNTERKUNFTSHAUS A. BRÜNNSTEIN, PÄCHTER B. BRENNER, RODEL HEIL!
Unterkunftshaus a. Brünnstein, Pächter B. Brenner, Rodel Heil! ( -
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
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
Heil Gabelsberger! Spende für den Werbefond
No full textHEIL GABELSBERGER! SPENDE FÜR DEN WERBEFOND
Heil Gabelsberger! Spende für den Werbefond ( -
Heil Gabelsberger! Spende für den Werbefond
No full textHEIL GABELSBERGER! SPENDE FÜR DEN WERBEFOND
Heil Gabelsberger! Spende für den Werbefond ( -
Coming to terms with terminology in agriculture-nutrition research projects: an interactive glossary
No full textThe doubly inelastic contribution to electron loss: H0 and He0 (0,5 MeV u-1) in collision with Ar
No full textDissolved organic carbon in seepage water - Production and transformation during soil passage
No full textDissolved organic carbon (DOC) in seepage water can combine with organic pollutants, with Al and heavy metal ions and transport them through the soil profile with a potential to contaminate groundwater. We studied the production of DOC in aerobic decomposition experiments at 8 degrees C and moisture close to field capacity in soils from two sites with different microbial activities (spodic dystric Cambisols with moder (SLB) and mor-moder (SLS) layers) using C-13-depleted plants of differing decomposability (Epilobium angustifolium and Calamagrostis epigeios). Additionally, we investigated the DOC transformation during soil passage in decomposition experiments and in the field for the sites SLB and SLS. For SLS, decomposition of Epilobium resulted in a cumulative CO2 production of 14% of the added C within 128 days. Priming effects were negligible. CO2: production for the experiments using Calamagrostis was less with 11% for SLB and 10% for SLS. Cumulative DOC production was markedly high in the Epilobium decomposition experiment, being 25 g m(-2), out of which 11 g m(-2) were Epilobium-derived (2% of the added C). For the Calamagrostis experiments, cumulative productions of DOC and Calamagrostis-derived DOC (0.1% of the added C for SLS and SLB) were much less. During the soil passage, much of the DOC was removed by sorption or decomposition processes. Field studies at SLS and SLB using C-13 natural abundance showed that C-13 distribution of soil organic matter increased with depth, probably mainly due to a discrimination of C isotopes by decomposing microorganisms. DOG, however, showed a depletion of C-13 from -28 parts per thousand PDB to -29 parts per thousand (SLB at 40 cm) or --28 to -30 parts per thousand (SLS at 20 cm) with depth, owing to preferential decomposition of C-13-enriched substances or preferential adsorption. This study indicates that DOC production is strongly affected by litter composition and that significant changes in DOC composition may occur during its passage through a soil depth of 40 cm
C-13 and N-15 distributions in three spodic dystric cambisols under beech and spruce
No full textThe study of natural isotopic abundance signatures is useful to gain further insights in the processes resulting in depthwise changes in the composition of soil organic matter (SOM). Objectives were to describe the delta(13)C and delta(15)N abundances of SOM with depth in soils from a 153-year old beech (B1), a 119-year old spruce (F1) and a 61-year old spruce (F2) stand at Selling, north-west Germany, and to study, how podzolisation affects the isotopic abundances of C-13 and N-15 in the SOM. The degree of podzolisation decreased in the order F1 > B1 > F2. At the surface of the humus layer of all three sites, delta(13)C values are approximately 1 to 4 parts per thousand higher than in the leaves and needles, probably mainly due to the discrimination of C-13 by microbial decomposition. C-13 abundances in the organic layers of Fl and F2 increased only slightly from -27.6 parts per thousand PDB (B1, L) to -27.2 parts per thousand PDB (B1, Oh) and from -26.3 parts per thousand PDB (F2, L) to -25.9 parts per thousand PDB (F2, Oh), suggesting that biotic activity resulted in mixing of organic matter. At Fl, however, C-13 abundance increased from -27.5 parts per thousand PDB (L) to -26.0 parts per thousand PDB (Oh) which reflects the lack of mixing by animals. In the upper 2-4 cm of the mineral soil, i.e., in the eluvial horizons Aeh, C-13 values showed a minimum at the spruce sites which was presumably related to a translocation of C-13 enriched fulvic acids. Depthwise changes in delta(15)N values were not related to podzolisation processes. At all three sites, a N-15 enrichment with depth occurred in the mineral soil which is the result of the discrimination of N-15 by microbial decomposition
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