Carbon-13 and oxygen-18 isotope effects in the decarboxylation of nicotinic acid of natural isotopic composition

1998 ◽  
Vol 230 (1-2) ◽  
pp. 71-75
Author(s):  
M. Zieliński ◽  
A. Zielińska ◽  
H. Papiernik-Zielińska ◽  
J. A. McKenzie ◽  
S. Bernasconi ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Nicotinic Acid ◽  
Isotope Effects ◽  
Natural Isotopic Composition

Kinetic Carbon Isotope Effects in the Decarbonylation of Lactic Acid of Natural Isotopic Composition and of [1-14C] Lactic Acid

1994 ◽  
Vol 30 (4) ◽  
pp. 333-347 ◽  
Author(s):  
M. Zieliński ◽  
A. Zielińska ◽  
H. Papiernik-Zielińska ◽  
G. Czarnota ◽  
G. Kasprzyk ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Isotopic Composition ◽  
Carbon Isotope ◽  
Isotope Effects ◽  
Natural Isotopic Composition

Carbon-13 kinetic isotope effects in the decarbonylation of lactic acid of natural isotopic composition in phosphoric acid medium

1993 ◽  
Vol 174 (2) ◽  
pp. 243-255 ◽  
Author(s):  
M. Zieliński ◽  
G. Czarnota ◽  
H. Papiernik-Zielińska ◽  
G. Kasprzyk ◽  
L. Gumółka ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Phosphoric Acid ◽  
Isotopic Composition ◽  
Acid Medium ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Natural Isotopic Composition ◽  
Kinetic Isotope

The electrical resistivity of lithium-6

1961 ◽  
Vol 263 (1314) ◽  
pp. 407-419 ◽  
Keyword(s):  
Electrical Resistivity ◽  
Isotopic Composition ◽  
Specific Heat ◽  
Room Temperature ◽  
Natural Isotopic Composition ◽  
Square Roots ◽  
Conduction Electrons ◽  
Ionic Mass ◽  
Theoretical Predictions ◽  
Electrical Resistivities

The electrical resistivities of lithium -6 and lithium of natural isotopic composition have been studied between 4°K and room temperature. In addition, their absolute resistivities have been carefully compared at room temperature. These measurements show that the effect of ionic mass on electrical resistivity agrees with simple theoretical predictions, namely, that the properties of the conduction electrons in lithium do not depend on the mass of the ions, and that the characteristic lattice frequencies for the two pure isotopes are in the inverse ratio of the square roots of their ionic masses. A comparison with the specific heat results of Martin (1959, 1960), where the simple theory is found not to hold, indicates the possibility that anharmonic effects are present which affect the specific heat but not the electrical resistivity.

scholarly journals Magnetic properties of the natural and isotope-modified diamond and silicon carbide

2018 ◽  
Vol 185 ◽  
pp. 04007 ◽  
Author(s):  
A.N. Taldenkov ◽  
A.V. Inyushkin ◽  
E.A. Chistotina ◽  
V.G. Ralchenko ◽  
A.P. Bolshakov ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Magnetic Properties ◽  
Isotopic Composition ◽  
Single Crystals ◽  
High Purity ◽  
Diamagnetic Susceptibility ◽  
Synthetic Diamond ◽  
Paramagnetic Centers ◽  
Natural Isotopic Composition ◽  
Ferromagnetic Component

The magnetic properties of single crystals of synthetic diamond and crystals of silicon carbide were studied. High-purity samples of diamonds synthesized with HPHT and CVD technologies were used. The crystals of silicon carbide were grown by sublimation and industrial technology. Along with samples with a natural isotopic composition, monoisotopic crystals of diamond (99.96% 12C and 99.96% 13C) and silicon carbide (99.993% of 28Si) were studied. On the basis of the data obtained, the diamagnetic susceptibility was determined and the concentration of paramagnetic centers and the content of the ferromagnetic component were evaluated. The results are discussed.

scholarly journals Seasonal variations in nitrate isotope composition of three rivers draining into the North Sea

2010 ◽  
Vol 7 (4) ◽  
pp. 6051-6088 ◽  
Author(s):  
A. Deek ◽  
K. Emeis ◽  
U. Struck
Keyword(s):  
Isotopic Composition ◽  
North Sea ◽  
Isotope Composition ◽  
Atmospheric Oxygen ◽  
Isotope Effects ◽  
Nitrate Sources ◽  
Particulate Nitrogen ◽  
Soil Nitrification ◽  
Mean Values ◽  
Δ 15N

Abstract. Nitrate loading of coastal ecosystems by rivers that drain industrialised catchments continues to be a problem in the South Eastern North Sea, in spite of significant mitigation efforts over the last 2 decades. To identify nitrate sources, sinks, and turnover in three German rivers that discharge into the German Bight, we determined δ 15N-NO3- and δ18O- NO3- in nitrate and δ 15N of particulate nitrogen for the period 2006–2009 (biweekly samples). The nitrate loads of Rhine, Weser and Ems varied seasonally in magnitude and δ 15N-NO3- (6.5–21‰), whereas the δ 18O-NO3- (-0.3–5.9‰) and δ 15N-PN (4–14‰) were less variable. Overall temporal patterns in nitrate mass fluxes and isotopic composition suggest that a combination of nitrate delivery from nitrification of soil ammonia in the catchment and assimilation of nitrate in the rivers control the isotopic composition of nitrate. Nitrification in soils as a source is indicated by low δ 18O-NO3- in winter, which traces the δ 18O of river water. Mean values of δ 18O-H2O were between –9.4‰ and –7.3‰; combined in a ratio of 2:1 with the atmospheric oxygen δ 18O of 23.5‰ agrees with the found δ 18O of nitrate in the rivers. Parallel variations of δ 15N-NO3- and δ 18O-NO3- within each individual river are caused by isotope effects associated with nitrate assimilation in the water column, the extent of which is determined by residence time in the river. Assimilation is furthermore to some extent mirrored both by the δ 15N of nitrate and particulate N. Although δ 15-NO3- observed in Rhine, Weser and Ems are reflected in high average δ 15N-PN (between 6‰ and 9‰, both are uncorrelated in the time series due to lateral and temporal mixing of PN. That a larger enrichment was consistently seen in δ 15N-NO3- relative to δ 18O-NO3- is attributed to constant additional diffuse nitrate inputs deriving from soil nitrification in the catchment area. A statistically significant inverse correlation exists between increasing δ 15N-NO3- values and decreasing NO3- concentrations. This inverse relationship – observed in each seasonal cycle – together with a robust relationship between human dominated land use and δ 15N-NO3- values demonstrates a strong influence of human activities and riverine nitrate consumption efficiency on the isotopic composition of riverine nitrate.

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