High Concentration-Ratio Experiments: Isotope Fractionation at the Methyl Carbon in the Reaction of Cyanide Ion and Methyl Iodide. Isotope Effect under Conditions of Equal Reagent Concentrations

1961 ◽  
Vol 83 (4) ◽  
pp. 790-793 ◽  
Author(s):  
K. R. Lynn ◽  
Peter E. Yankwich
Keyword(s):  
Isotope Effect ◽  
Methyl Iodide ◽  
Concentration Ratio ◽  
Isotope Fractionation ◽  
High Concentration ◽  
Cyanide Ion ◽  
Methyl Carbon

scholarly journals Oxygen isotope fractionation during N<sub>2</sub>O production by soil denitrification

2016 ◽  
Vol 13 (4) ◽  
pp. 1129-1144 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Jens Dyckmans ◽  
Jan Kaiser ◽  
Alina Marca ◽  
Jürgen Augustin ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Soil Water ◽  
Isotope Effect ◽  
Isotope Exchange ◽  
Isotope Fractionation ◽  
Isotope Effects ◽  
N2o Production ◽  
Oxygen Isotope Fractionation ◽  
Oxygen Isotope Exchange ◽  
Incubation Experiments

Abstract. The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by soil denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. In our soil incubation experiments Δ17O isotope tracing was applied for the first time to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found that N2O formation in static anoxic incubation experiments was typically associated with oxygen isotope exchange close to 100 % and a stable difference between the 18O ∕ 16O ratio of soil water and the N2O product of δ18O(N2O ∕ H2O)  =  (17.5 ± 1.2) ‰. However, flow-through experiments gave lower oxygen isotope exchange down to 56 % and a higher δ18O(N2O ∕ H2O) of up to 37 ‰. The extent of isotope exchange and δ18O(N2O ∕ H2O) showed a significant correlation (R2 = 0.70, p <  0.00001). We hypothesize that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with different magnitudes of branching isotope effects at different steps in the reduction process. The results suggest that during denitrification, isotope exchange occurs prior to isotope branching and that this exchange is mostly associated with the enzymatic nitrite reduction mediated by NIR. For bacterial denitrification, the branching isotope effect can be surprisingly low, about (0.0 ± 0.9) ‰, in contrast to fungal denitrification where higher values of up to 30 ‰ have been reported previously. This suggests that δ18O might be used as a tracer for differentiation between bacterial and fungal denitrification, due to their different magnitudes of branching isotope effects.

scholarly journals GLOBAL PRODUCTION CONCENTRATION OF MEDIUM DENSITY FIBERBOARD (MDF) (1995 - 2016)

2018 ◽  
Vol 42 (5) ◽  
Author(s):  
Thaisa de Sousa Selvatti ◽  
Luis Antônio Coimbra Borges ◽  
Helena Cristina Carvalho Soares ◽  
Álvaro Nogueira de Souza ◽  
Luiz Moreira Coelho Junior
Keyword(s):  
Gini Index ◽  
Concentration Ratio ◽  
Concentration Index ◽  
Medium Density Fiberboard ◽  
Average Concentration ◽  
Medium Density ◽  
High Concentration ◽  
The World ◽  
Concentration Degree ◽  
Production Concentration

ABSTRACT This papaer analyzed the global MDF production and its concentration degree between 1995 and 2016. In order to measure and analyze this concentration, we used the Concentration Ratio [CR(k)], the Herfindahl-Hirschman Index (HHI), Theil Entropy Index (E), Hall and Tideman Index (HTI), the Comprehensive Concentration Index (CCI), and the Gini Index (G). Global MDF production grew 12.81% p.a. from 1995 to 2016, reaching 99 million m3 at the end of the time series. China took over the hegemony in 2001 and arrived in 2016 with about 60% of the world’s MDF supply. The CR(k) of the global MDF production inferred a high concentration, mainly in the CR(4) from 2009. The CR(8) remained with a moderately high average concentration. During this period more than 90% of the offer was retained in the CR(20). The HHI, E and HTI indices corroborate that there is high concentration in global MDF production, as well as the CCI in the studied period. The inequality indicated by G also presented increasing behavior and was classified as strong and very strong. The concentration indicators were efficient in evaluating the concentration degree of the world MDF supply.

scholarly journals Theoretical Investigation of the Temperature Limits of an Actively Cooled High Concentration Photovoltaic System

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1902 ◽  
Author(s):  
Asmaa Ahmed ◽  
Katie Shanks ◽  
Senthilarasu Sundaram ◽  
Tapas Kumar Mallick
Keyword(s):  
Solar Cell ◽  
Concentration Ratio ◽  
Photovoltaic System ◽  
Thermal System ◽  
Outlet Temperature ◽  
Water Mixture ◽  
High Concentration ◽  
Cell Temperature ◽  
Photovoltaic Thermal System ◽  
Different Types

Concentrator photovoltaics have several advantages over flat plate systems. However, the increase in solar concentration usually leads to an increase in the solar cell temperature, which decreases the performance of the system. Therefore, in this paper, we investigate the performance and temperature limits of a high concentration photovoltaic Thermal system (HCPVT) based on a 1 cm2 multi-junction solar cell subjected to a concentration ratio from 500× to 2000× by using three different types of cooling fluids (water, ethylene glycol and water mixture (60:40), and syltherm oil 800). The results show that, for this configuration, the maximum volumetric temperature of the solar cell did not exceed the manufacturer’s recommended limit for the tested fluids. At 2000× the lowest solar cell temperature obtained by using water was 93.5 °C, while it reached as high as 109 °C by using syltherm oil 800, which is almost equal to the maximum operating limit provided by the manufacturer (110 °C). Overall, the best performance in terms of temperature distribution, thermal, and electrical efficiency was achieved by using water, while the highest outlet temperature was obtained by using syltherm oil 800.

scholarly journals Performance of Multi Junction Photovoltaic Cells with High Concentration Ratio

2014 ◽  
Vol 61 ◽  
pp. 2258-2261 ◽  
Author(s):  
A. Aldossary ◽  
A. Algarue ◽  
S. Mahmoud ◽  
R.K. AL-Dadah
Keyword(s):  
Concentration Ratio ◽  
Photovoltaic Cells ◽  
High Concentration
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