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Wyszukujesz frazę "C isotope" wg kryterium: Temat

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    Wyświetlanie 1-5 z 5
    Tytuł:
    Intrinsic deuterium isotope effects on NMR chemical shifts of hydrogen bonded systems
    Autorzy:
    Hansen, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/146965.pdf
    Data publikacji:
    2002
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    C-H hydrogen bonds
    deuterium isotope effects
    intramolecular hydrogen bonds
    intrinsic isotope effects
    nuclear shielding
    steric effects
    Opis:
    This mini review describes intrinsic deuterium isotope effects on 13C chemical shifts of rigid hydrogen bonded compounds primarily in solution. The steric effects of intramolecularly hydrogen bonded compounds are dissected into different bond interactions leading either to steric compression or to steric twist. One-bond isotope effects involving CH(D) bonds are analyzed in terms of substituent effects and the question is raised whether isotope effects can be useful in the study of CHhydrogen bonds.
    Źródło:
    Nukleonika; 2002, 47,suppl.1; 37-42
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Carbon-13 in alpha-cellulose of oak latewood (Jędrzejów, Southern Poland) during the Maunder Minimum
    Autorzy:
    Pazdur, A.
    Korput, S.
    Fogtman, M.
    Szczepanek, M.
    Hałas, S.
    Krąpiec, M.
    Szychowska-Krąpiec, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/2058897.pdf
    Data publikacji:
    2005
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    13C isotope
    alpha-cellulose
    Maunder Minimum
    tree-rings
    Opis:
    We have studied the δ13C signature in latewood alpha-cellulose of an ancient oak (Quercus robur L.) from a Cisterian Abbey belfry in Jędrzejów (Southern Poland). The time scale for the delta 13C record during 1631-1765 AD was built on the basis of detailed dendrochronology studies. Techniques available for extraction of alpha-cellulose from small samples have been used, the mean value of alpha-cellulose extraction efficiency being ca. 35%. In the delta 13C record of alpha-cellulose the cooling between 1650-1700 AD is clearly visible as a decrease of about 1.5‰. This period is consistent with the interval of the lowest solaractivity between 1645 and 1715 AD, which is known as the Maunder Minimum. Anti-correlation between δ13C and δ13C during the Maunder Minimum was observed but δ13C record is delayed by about 30 years with respect to the Maunder Minimum.
    Źródło:
    Geological Quarterly; 2005, 49, 2; 165-172
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Carbon isotope effects in the studies of the mechanism of action of tyrosine phenol-lyase
    Autorzy:
    Augustyniak, W.
    Kański, R.
    Kańska, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/148527.pdf
    Data publikacji:
    2006
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    12C/14C kinetic isotope effects
    tyrosine phenol-lyase
    Opis:
    12C/14C kinetic isotope effects on the hydrolytic cleavage of tyrosine to phenol and ammonium pyruvate catalyzed by Citrobacter freundii tyrosine phenol-lyase have been determined in positions 2, 3 and ring-1' of L-tyrosine. The competitive method with dual-label approach was applied with 3',5'-ring 3H as remote label. The results revealed the change of the effect on carbon atom in position 2 during the reaction course from the high normal values to low inverse values. On the other hand, the effect values on 3 and ring-1' position remained constant during the reaction course. The discussion of these results regarding the reaction mechanism is presented.
    Źródło:
    Nukleonika; 2006, 51,suppl.2; 7-11
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Calcite cements and the stratigraphical significance of the marine [delta^13]C carbonate reference curve for the Upper Cretaceous Chalk of England
    Autorzy:
    Jeans, C.
    Hu, X.
    Mortimore, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/139078.pdf
    Data publikacji:
    2012
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    cement kalcytowy
    chemostratygrafia
    izotopy
    korelacja
    kreda
    krzywa referencyjna
    ograniczenia
    calcite cement
    chemostratigraphy
    correlation
    Cretaceous
    [delta^13]C reference curve
    isotope events
    limitations
    Opis:
    The hypothesis of Jarvis et al. (2006) that a [delta^13]C (calcite) reference curve based upon bulk samples from the Upper Cretaceous Chalk of England can be used as a primary criterion for trans-continental correlation is reviewed in the light of new stable isotope data from the Upper Albian and Cenomanian chalks of eastern England and from the Cenomanian to Campanian chalks of southern England. Evidence demonstrates that in the coloured chalks of eastern England the cements invariably have positive [delta^13]C values (up to 3.5[per mil]) except where they have been affected by hardground development when the cements have negative [delta^13]C values down to -6.5[per mil]. in contrast, the White Chalk of southern England may have cements with [delta^13]C values as negative as -8[per mil]. Modelling indicates that the coloured chalks may preserve a truer record of the primary palaeo-oceanographic [delta^13]C signal than the white and grey chalks of southern England. it is suggested that (1) many of the 72 isotope events described from the [delta^13]C (calcite) reference curve and proposed for correlation may reflect the effects of variations in the type and extent of calcite cementation; and (2) until much more is known about the patterns of calcite cementation in the Upper Cretaceous Chalk the use of minor isotope events for trans-continental stratigraphic correlation can only be applied with the utmost caution.
    Źródło:
    Acta Geologica Polonica; 2012, 62, 2; 173-196
    0001-5709
    Pojawia się w:
    Acta Geologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Biostratigraphy, geochemistry and sedimentology of Middle to Late Jurassic strata in the Strážovce section (Strážovské vrchy Mts), Krížna Nappe of the Central Carpathians, Slovakia
    Autorzy:
    Michalík, J.
    Bąk, M.
    Lintnerová, O.
    Méres, Š
    Powiązania:
    https://bibliotekanauki.pl/articles/2060972.pdf
    Data publikacji:
    2017
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    Oxfordian
    Kimmeridgian
    C isotope
    O isotope
    REE
    radiolarians
    basinal collapse
    Zliechov Basin
    Fatric Unit
    Oksford
    izotop C
    iIzotop O
    radiolarie
    Opis:
    The Jurassic / Lower Cretaceous sequence of the Strážovce section has been deposited in the central, axial part of the Zliechov Basin. Its most characteristic part – the Ždiar Formation consists of bedded siliceous radiolarian limestones and radiolarites. The radiolar¬ian assemblage typical of the North Tethyan Bioprovince lived during mid Oxfordian – Early Kimmeridgian in a warm upper part of the well stratified water column, partially near to the thermocline. Radiolarian abundance decreases upwards. Productivity decrease is quanti¬fied by the share of biogenic SiO2 as well as by high EFSi values during sedimentation of both the Ždiar and Jasenina formations. The geochemical data indicate relatively stable volume of the siliciclastic component of the rocks and a felsic character comparable to the Average Shale. The chemically homogeneous sedimentary signal indicates values of both CPA and EF ≤ 1 of Ti, Zr, Fe, Na, K, Rb, V and U. The values of EF > 1 signal enrichment of elements with affinity to carbonate minerals (Sr, Mn, P, Y, and Mg). Metal enrichment (Cu, Zn and Ni) indicates metal mobilization from other sources or due to carbonate diagenesis. In comparison to the Average Shale, decreased ΣREE´s and negative Cech and Euch anomalies could be regarded as a typical deep sea water signal. The differentiated REE record of higher calcareous beds of the Jasenina Fm. suggests basinal dysoxic conditions. The “bell-shape” of curves (normalized to shale) indicate that REEs were slightly affected by carbonate diagenesis. The Oxfordian / Kimmeridgian siliceous sedimentation in the Zliechov Basin was influenced probably more by monsoon-controlled input of land derived weathered material than by hydrothermal fluids from the bottom rifts.
    Źródło:
    Volumina Jurassica; 2017, 15, 1; 161--178
    1896-7876
    1731-3708
    Pojawia się w:
    Volumina Jurassica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-5 z 5

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