Simulation der einfachen Scherung einer polykristallinen Aluminiumprobe

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Limited Occurrence of Denitrification in Four Shallow Aquifers in Agricultural Areas of the United States

The ability of natural attenuation to mitigate agricultural nitrate contamination in recharging aquifers was investigated in four important agricultural settings in the United States. The study used laboratory analyses, field measurements, and flow and transport modeling for monitoring well transects (0.5 to 2.5 km in length) in the San Joaquin watershed, California, the Elkhorn watershed, Nebraska, the Yakima watershed, Washington, and the Chester watershed, Maryland. Ground water analyses included major ion chemistry, dissolved gases, nitrogen and oxygen stable isotopes, and estimates of recharge date. Sediment analyses included potential electron donors and stable nitrogen and carbon isotopes. Within each site and among aquifer-based medians, dissolved oxygen decreases with ground water age, and excess N2 from denitrification increases with age. Stable isotopes and excess N2 imply minimal denitrifying activity at the Maryland and Washington sites, partial denitrification at the California site, and total denitrification across portions of the Nebraska site. At all sites, recharging electron donor concentrations are not sufficient to account for the losses of dissolved oxygen and nitrate, implying that relict, solid phase electron donors drive redox reactions. Zero-order rates of denitrification range from 0 to 0.14 μmol N L−1d−1, comparable to observations of other studies using the same methods. Many values reported in the literature are, however, orders of magnitude higher, which is attributed to a combination of method limitations and bias for selection of sites with rapid denitrification. In the shallow aquifers below these agricultural fields, denitrification is limited in extent and will require residence times of decades or longer to mitigate modern nitrate contamination

Standard atomic weights of the elements 2021 (IUPAC Technical Report)

Following the reviews of atomic-weight determinations and other cognate data in 2015, 2017, 2019 and 2021, the IUPAC (International Union of Pure and Applied Chemistry) Commission on Isotopic Abundances and Atomic Weights (CIAAW) reports changes of standard atomic weights. The symbol A r°(E) was selected for standard atomic weight of an element to distinguish it from the atomic weight of an element E in a specific substance P, designated A r(E, P). The CIAAW has changed the values of the standard atomic weights of five elements based on recent determinations of terrestrial isotopic abundances: Ar (argon): from 39.948 ± 0.001 to [39.792, 39.963] Hf (hafnium): from 178.49 ± 0.02 to 178.486 ± 0.006 Ir (iridium): from 192.217 ± 0.003 to 192.217 ± 0.002 Pb (lead): from 207.2 ± 0.1 to [206.14, 207.94] Yb (ytterbium): from 173.054 ± 0.005 to 173.045 ± 0.010 The standard atomic weight of argon and lead have changed to an interval to reflect that the natural variation in isotopic composition exceeds the measurement uncertainty of A r(Ar) and A r(Pb) in a specific substance. The standard atomic weights and/or the uncertainties of fourteen elements have been changed based on the Atomic Mass Evaluations 2016 and 2020 accomplished under the auspices of the International Union of Pure and Applied Physics (IUPAP). A r° of Ho, Tb, Tm and Y were changed in 2017 and again updated in 2021: Al (aluminium), 2017: from 26.981 5385 ± 0.000 0007 to 26.981 5384 ± 0.000 0003 Au (gold), 2017: from 196.966 569 ± 0.000 005 to 196.966 570 ± 0.000 004 Co (cobalt), 2017: from 58.933 194 ± 0.000 004 to 58.933 194 ± 0.000 003 F (fluorine), 2021: from 18.998 403 163 ± 0.000 000 006 to 18.998 403 162 ± 0.000 000 005 (Ho (holmium), 2017: from 164.930 33 ± 0.000 02 to 164.930 328 ± 0.000 007) Ho (holmium), 2021: from 164.930 328 ± 0.000 007 to 164.930 329 ± 0.000 005 Mn (manganese), 2017: from 54.938 044 ± 0.000 003 to 54.938 043 ± 0.000 002 Nb (niobium), 2017: from 92.906 37 ± 0.000 02 to 92.906 37 ± 0.000 01 Pa (protactinium), 2017: from 231.035 88 ± 0.000 02 to 231.035 88 ± 0.000 01 Pr (praseodymium), 2017: from 140.907 66 ± 0.000 02 to 140.907 66 ± 0.000 01 Rh (rhodium), 2017: from 102.905 50 ± 0.000 02 to 102.905 49 ± 0.000 02 Sc (scandium), 2021: from 44.955 908 ± 0.000 005 to 44.955 907 ± 0.000 004 (Tb (terbium), 2017: from 158.925 35 ± 0.000 02 to 158.925 354 ± 0.000 008) Tb (terbium), 2021: from 158.925 354 ± 0.000 008 to 158.925 354 ± 0.000 007 (Tm (thulium), 2017: from 168.934 22 ± 0.000 02 to 168.934 218 ± 0.000 006) Tm (thulium), 2021: from 168.934 218 ± 0.000 006 to 168.934 219 ± 0.000 005 (Y (yttrium), 2017: from 88.905 84 ± 0.000 02 to 88.905 84 ± 0.000 01) Y (yttrium), 2021: from 88.905 84 ± 0.000 01 to 88.905 838 ± 0.00

A review of the Cis-Andean species of Hemibrycon Günther (Teleostei: Characiformes: Characidae: Stevardiinae), with description of two new species

As espécies de Hemibrycon que ocorrem a leste das Cordilheiras dos Andes são revisadas com base na análise do material tipo e exemplares adicionais. Nove espécies são redescritas: H. beni da bacia do río Beni, Bolívia; H. helleri do alto río Ucayali, Peru; H. huambonicus para as bacias dos ríos Huallaga e Marañon, Peru; H. jeslkii para as porções superiores das bacias dos rios Marañon, Ucayali e Madeira, Bolívia, Brasil e Peru; H. metae para a bacia do río Orinoco, Colômbia e Venezuela, e bacias costeiras do Caribe na Venezuela; H. polyodon (espécie-tipo) para a bacia do río Pastaza, Equador; H. surinamensis para as bacia costeiras da Guiana Francesa e Suriname, e porção inferior das bacias dos rios Tapajós, Tocantins e Xingu, Brasil; H. taeniurus para os rios da ilha de Trinidad, Trinidad and Tobago; H. tridens para a bacia do alto río Ucayali, Peru. Duas espécies novas são descritas: H. inambari para a bacia do alto río Madre de Dios, Peru e H. mikrostiktos para a bacia do río Ucayali, Peru. Estas espécies distinguem-se principalmente pelo padrão de colorido e caracteres merísticos. A área de distribuição do gênero é ampliada para as porções inferiores das bacias do Tapajós, Tocantins e Xingu, Brasil, com o primeiro registro de H. surinamensis para este país. Uma nova diagnose e descrição são fornecidas para a espécie-tipo do gênero, apesar de ter sido recentemente redescrita. A série-tipo de H. helleri previamente considerada questionável é encontrada e descrita. Hemibrycon coxeyi e H. pautensis são considerados sinônimos juniores de H. polyodon. Tetragonopterus (Hemibrycon) trinitatis, anteriormente considerada como species inquirenda em Characidae, e Hemibrycon guppyi são sinônimos juniores de H. taeniurus. Hemibrycon orcesi é transferida para Boehlkea. É apresentada uma chave taxonômica para as espécies do gênero a leste das Cordilheiras dos Andes.The species of Hemibrycon occurring in the east of the Andean Cordilleras are reviewed based on their type series and additional specimens. Nine species are redescribed: H. beni from río Beni basin, Bolivia; H. helleri from the upper rio Ucayali, Peru; H. huambonicus from the ríos Huallaga and Marañon basins, Peru; H. jeslkii from the upper portions of ríos Marañon, Ucayali and Madeira basins, Bolivia, Brazil, and Peru; H. metae from río Orinoco basin, Colombia and Venezuela, and Caribbean coastal basins of Venezuela; H. polyodon (type species) from río Pastaza basin, Ecuador; H. surinamensis from coastal basins of French Guiana and Suriname, and from lower rios Tapajós, Tocantins and Xingu basins, Brazil; H. taeniurus from river basins from Trinidad Island, Trinidad and Tobago, and H. tridens from upper río Ucayali basin, Peru. Two new species are described: H. inambari from the upper río Madre de Dios basin, Peru and H. mikrostiktos from río Ucayali basin, Peru. These species are distinguished among themselves mainly by the color pattern, and meristic characters. The distribution area of the genus is enlarged reaching the lower Tapajós, Tocantins and Xingu river basins, Brazil, with the first record of the occurrence of H. surinamensis in this country. A new description and diagnosis is provided for the type species of the genus, regardless its recent redescription. The type series of H. helleri that was previously considered dubious is found and described. Hemibrycon coxeyi and H. pautensis are considered junior synonyms of H. polyodon. Tetragonopterus (Hemibrycon) trinitatis, previously considered species inquirenda in Characidae, and Hemibrycon guppyi are junior synonyms of H. taeniurus. Hemibrycon orcesi is transferred to Boehlkea. A taxonomic key for the species of the genus to the east of the Andean Cordilleras is presented

Minimum requirements for publishing hydrogen, carbon, nitrogen, oxygen and sulfur stable-isotope delta results (IUPAC Technical Report)

Stable hydrogen, carbon, nitrogen, oxygen and sulfur (HCNOS) isotope compositions expressed as isotope-delta values are typically reported relative to international standards such as Vienna Standard Mean Ocean Water (VSMOW), Vienna Peedee belemnite (VPDB) or Vienna Cañon Diablo Troilite (VCDT). These international standards are chosen by convention and the calibration methods used to realise them in practice undergo occasional changes. To ensure longevity and reusability of published data, a comprehensive description of (1) analytical procedure, (2) traceability, (3) data processing, and (4) uncertainty evaluation is required. Following earlier International Union of Pure and Applied Chemistry documents on terminology and notations, this paper proposes minimum requirements for publishing HCNOS stable-isotope delta results. Each of the requirements are presented with illustrative example