Search results for "13C"
showing 10 items of 194 documents
Effect of ramp size and sample spinning speed on CPMAS 13C NMR spectra of soil organic matter
2011
Abstract Cross polarization (CP) magic angle spinning (MAS) 13C NMR spectroscopy is a solid state NMR technique widely applied to study the chemical composition of natural organic matter. In high magnetic fields (>7 T), fast sample spinning is required in order to reduce the influence of spinning sidebands underlying other chemical shift regions. As the spinning speed increases, the Hartmann–Hahn matching profiles break down into a series of narrow matching bands. In order to account for this instability variable amplitude cross polarization techniques (e.g. VACP, ramp-CP) have been developed. In the present study, we experimentally verified the stability of the Hartmann–Hahn condition unde…
The effect of silica nanoparticles on the morphology, mechanical properties and thermal degradation kinetics of PMMA
2012
Abstract Silica–PMMA nanocomposites with different silica quantities were prepared by a melt compounding method. The effect of silica amount, in the range 1–5 wt.%, on the morphology, mechanical properties and thermal degradation kinetics of PMMA was investigated by means of transmission electron microscopy (TEM), X-ray diffractometry (XRD), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), Fourier-transform infrared spectroscopy (FTIR), 13 C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy ( 13 C{ 1 H} CP-MAS NMR) and measures of proton spin-lattice relaxation time in the rotating frame ( T 1 ρ ( H )), in the laboratory frame ( T 1 ( H )) a…
The importance of sedimenting organic matter, relative to oxygen and temperature, in structuring lake profundal macroinvertebrate assemblages
2012
We quantified the role of a main food resource, sedimenting organic matter (SOM), relative to oxygen (DO) and temperature (TEMP) in structuring profundal macroinvertebrate assemblages in boreal lakes. SOM from 26 basins of 11 Finnish lakes was analysed for quantity (sedimentation rates), quality (C:N:P stoichiometry) and origin (carbon stable isotopes, δ13C). Hypolimnetic oxygen and temperature were measured from each site during summer stratification. Partial canonical correspondence analysis (CCA) and partial regression analyses were used to quantify contributions of SOM, DO and TEMP to community composition and three macroinvertebrate metrics. The results suggested a major contribution o…
Trophic habits of Muscardinus avellanarius (Mammalia Gliridae) as revealed by multiple stable isotope analysis
2007
Multiple stable isotope analysis was used to investigate the diet of the common dormouse Muscardinus avellanarius in a mixed Mediterranean forest. δ13C and δ15N values of dormouse tissues compared to those of the vegetal and animal sources available in the area showed that the isotopic composition of both adult and juvenile M. avellanarius could be explained by a mixture of vegetal and animal organic matter. The isotopic composition of the assimilated nitrogen was mostly explained by the organic matter from flora. Among the vegetal components, flowers of Fagus silvatica, Quercus robur, and the rarer Crataegus oxyacantha, berries of Ilex aquifolium and acorns of Q. robur were found in the ad…
Flotsam samples can help explain the δ13C and δ15N values of invertebrate resting stages in lake sediment
2018
Abstract The stable isotopic composition of chitinous remains of Cladocera (water fleas) and freshwater Bryozoa (moss animals) preserved in lake sediment records can provide supporting insights into past environmental and ecosystem changes in lakes. Here we explore whether analyses of these remains isolated from lake flotsam can provide information on the driving variables affecting the isotopic composition of these remains. We collected flotsam in 53 lakes and found enough material in 33 lakes to measure the stable carbon and nitrogen isotope ratios (expressed as δ13C and δ15N values, respectively) of resting stages. These values were compared with lake characteristics, water chemistry mea…
First 13C/12C isotopic characterisation of volcanic plume CO2
2010
We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic composition of CO2 in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method to Mount Etna where we derived a δ13C of volcanic CO2 betw…
Harmaahylkeen (Halichoerus grypus) ravinto eri osissa pohjoista Itämerta
2013
Itämeren harmaahylkeiden (Halichoerus grypus) yksilömäärien kasvu viime vuosikymmeninä on aiheuttanut ristiriitoja ammattikalastajien ja hylkeiden välille. Hylkeiden on todettu muun muassa vahingoittavan pyydyksiä ja syövän kalastajille arvokasta saalista myös pyydyksistä, kuten lohta (Salmo salar), sekä karkottavan kalaparvia kalastusalueiden ulkopuolelle. Toisaalta harmaahylkeille uhkana on hukkuminen pyydyksiin sekä lisääntynyt häirintä kalastajien ja meriliikenteen toimesta. Näiden ristiriitojen myötä kiinnostus hylkeiden ravinnosta on lisääntynyt. Hylkeiden ravinnonkäyttöä on perinteisesti tutkittu ruoansulatuskanavan sisällöstä. Tämän menetelmän ongelmana on, että saalislajien sulamat…
Bunker Cave stalagmites: an archive for central European Holocene climate variability
2012
Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present high-resolution records of &delta;<sup>18</sup>O, &delta;<sup>13</sup>C values and Mg/Ca ratios. Changes in the Mg/Ca ratio are attributed to past meteoric p…
Sedimentation and tropical vegetation changes in Southern Benin (West Africa), carbon-13 tracing of organic matter dynamics and fluctuations of the s…
2007
12 pages; International audience
Kalcīts un tā veidošanās apstākļi Franas stāva smilšakmeņos un dolomītos Latvijā
2019
Maģistra darbā “Kalcīts un tā veidošanās apstākļi Franas stāva smilšakmeņos un dolomītos Latvijā” raksturotas kalcīta fizikālās īpašības, ķīmiskais sastāvs un veidošanās apstākļi. Pētījumi veikti 16 Amatas, Pļaviņu, Daugavas un Stipinu svītas atradnēs un atsegumos. Dokumentēti ģeoloģiskie griezumi, pētītas kalcīta fluorescences izpausmes un citas fizikālās īpašības, attiecības ar smilšakmens un dolomīta komponentiem plānslīpējumos, noteikts kalcīta ķīmiskais sastāvs un oglekļa stabilo izotopu attiecības. Secināts, ka kalcīts Amatas svītas smilšakmeņos un Pļaviņu, Daugavas un Stipinu svītas dolomītos kristalizējies līdzīgos apstākļos – no atmosfēras izcelsmes pazemes ūdeņiem sauszemes apstāk…