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Littérature scientifique sur le sujet « Isotopic model »

Auteur : Grafiati

Publié le 10 mars 2023

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Articles de revues sur le sujet "Isotopic model"

Sedaghatpour, Fatemeh, et Stein B. Jacobsen. « Magnesium stable isotopes support the lunar magma ocean cumulate remelting model for mare basalts ». Proceedings of the National Academy of Sciences 116, n^o 1 (17 décembre 2018) : 73–78. http://dx.doi.org/10.1073/pnas.1811377115.

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We report high-precision Mg isotopic analyses of different types of lunar samples including two pristine Mg-suite rocks (72415 and 76535), basalts, anorthosites, breccias, mineral separates, and lunar meteorites. The Mg isotopic composition of the dunite 72415 (δ25Mg = −0.140 ± 0.010‰, δ26Mg = −0.291 ± 0.018‰), the most Mg-rich and possibly the oldest lunar sample, may provide the best estimate of the Mg isotopic composition of the bulk silicate Moon (BSM). This δ26Mg value of the Moon is similar to those of the Earth and chondrites and reflects both the relative homogeneity of Mg isotopes in the solar system and the lack of Mg isotope fractionation by the Moon-forming giant impact. In contrast to the behavior of Mg isotopes in terrestrial basalts and mantle rocks, Mg isotopic data on lunar samples show isotopic variations among the basalts and pristine anorthositic rocks reflecting isotopic fractionation during the early lunar magma ocean (LMO) differentiation. Calculated evolutions of δ26Mg values during the LMO differentiation are consistent with the observed δ26Mg variations in lunar samples, implying that Mg isotope variations in lunar basalts are consistent with their origin by remelting of distinct LMO cumulates.

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Sturm, C., Q. Zhang et D. Noone. « An introduction to stable water isotopes in climate models : benefits of forward proxy modelling for paleoclimatology ». Climate of the Past Discussions 5, n^o 3 (30 juin 2009) : 1697–729. http://dx.doi.org/10.5194/cpd-5-1697-2009.

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Abstract. Stable water isotopes have been measured in a wide range of climate archives, with the purpose of reconstructing regional climate variations. Yet the common assumption that the isotopic signal is a direct indicator of temperature proves to be misleading under certain circumstances, since its relationship with temperature also depends on e.g. atmospheric circulation and precipitation seasonality. The present article introduces the principles, benefits and caveats of using climate models with embedded water isotopes as a support for the interpretation of isotopic climate archives. A short overview of the limitations of empirical calibrations of isotopic proxy records is presented, with emphasis on the physical processes that infirm its underlying hypotheses. The simulation of climate and its associated isotopic signal, despite difficulties related to downscaling and intrinsic atmospheric variability, can provide a "transfer function" between the isotopic signal and the considered climate variable. The multi-proxy data can then be combined with model output to produce a physically consistent climate reconstruction and its confidence interval. A sensitivity study with the isotope-enabled global circulation model CAM3iso under idealised present-day, pre-industrial and mid-Holocene is presented to illustrate the impact of a changing climate on the isotope-temperature relationship.

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Cauquoin, Alexandre, Martin Werner et Gerrit Lohmann. « Water isotopes – climate relationships for the mid-Holocene and preindustrial period simulated with an isotope-enabled version of MPI-ESM ». Climate of the Past 15, n^o 6 (14 novembre 2019) : 1913–37. http://dx.doi.org/10.5194/cp-15-1913-2019.

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Abstract. We present here the first results, for the preindustrial and mid-Holocene climatological periods, of the newly developed isotope-enhanced version of the fully coupled Earth system model MPI-ESM, called hereafter MPI-ESM-wiso. The water stable isotopes H216O, H218O and HDO have been implemented into all components of the coupled model setup. The mid-Holocene provides the opportunity to evaluate the model response to changes in the seasonal and latitudinal distribution of insolation induced by different orbital forcing conditions. The results of our equilibrium simulations allow us to evaluate the performance of the isotopic model in simulating the spatial and temporal variations of water isotopes in the different compartments of the hydrological system for warm climates. For the preindustrial climate, MPI-ESM-wiso reproduces very well the observed spatial distribution of the isotopic content in precipitation linked to the spatial variations in temperature and precipitation rate. We also find a good model–data agreement with the observed distribution of isotopic composition in surface seawater but a bias with the presence of surface seawater that is too 18O-depleted in the Arctic Ocean. All these results are improved compared to the previous model version ECHAM5/MPIOM. The spatial relationships of water isotopic composition with temperature, precipitation rate and salinity are consistent with observational data. For the preindustrial climate, the interannual relationships of water isotopes with temperature and salinity are globally lower than the spatial ones, consistent with previous studies. Simulated results under mid-Holocene conditions are in fair agreement with the isotopic measurements from ice cores and continental speleothems. MPI-ESM-wiso simulates a decrease in the isotopic composition of precipitation from North Africa to the Tibetan Plateau via India due to the enhanced monsoons during the mid-Holocene. Over Greenland, our simulation indicates a higher isotopic composition of precipitation linked to higher summer temperature and a reduction in sea ice, shown by positive isotope–temperature gradient. For the Antarctic continent, the model simulates lower isotopic values over the East Antarctic plateau, linked to the lower temperatures during the mid-Holocene period, while similar or higher isotopic values are modeled over the rest of the continent. While variations of isotopic contents in precipitation over West Antarctica between mid-Holocene and preindustrial periods are partly controlled by changes in temperature, the transport of relatively 18O-rich water vapor near the coast to the western ice core sites could play a role in the final isotopic composition. So, more caution has to be taken about the reconstruction of past temperature variations during warm periods over this area. The coupling of such a model with an ice sheet model or the use of a zoomed grid centered on this region could help to better describe the role of the water vapor transport and sea ice around West Antarctica. The reconstruction of past salinity through isotopic content in sea surface waters can be complicated for regions with strong ocean dynamics, variations in sea ice regimes or significant changes in freshwater budget, giving an extremely variable relationship between the isotopic content and salinity of ocean surface waters over small spatial scales. These complicating factors demonstrate the complexity of interpreting water isotopes as past climate signals of warm periods like the mid-Holocene. A systematic isotope model intercomparison study for further insights on the model dependency of these results would be beneficial.

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Halder, J., S. Terzer, L. I. Wassenaar, L. J. Araguás-Araguás et P. K. Aggarwal. « The Global Network of Isotopes in Rivers (GNIR) : integration of water isotopes in watershed observation and riverine research ». Hydrology and Earth System Sciences 19, n^o 8 (5 août 2015) : 3419–31. http://dx.doi.org/10.5194/hess-19-3419-2015.

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Abstract. We introduce a new online global database of riverine water stable isotopes (Global Network of Isotopes in Rivers, GNIR) and evaluate its longer-term data holdings. Overall, 218 GNIR river stations were clustered into three different groups based on the seasonal variation in their isotopic composition, which was closely coupled to precipitation and snowmelt water runoff regimes. Sinusoidal fit functions revealed phases within each grouping and deviations from the sinusoidal functions revealed important river alterations or hydrological processes in these watersheds. The seasonal isotopic amplitude of δ18O in rivers averaged 2.5 ‰, and did not increase as a function of latitude, like it does for global precipitation. Low seasonal isotopic amplitudes in rivers suggest the prevalence of mixing and storage such as occurs via lakes, reservoirs, and groundwater. The application of a catchment-constrained regionalized cluster-based water isotope prediction model (CC-RCWIP) allowed for direct comparison between the expected isotopic compositions for the upstream catchment precipitation with the measured isotopic composition of river discharge at observation stations. The catchment-constrained model revealed a strong global isotopic correlation between average rainfall and river discharge (R2 = 0.88) and the study demonstrated that the seasonal isotopic composition and variation of river water can be predicted. Deviations in data from model-predicted values suggest there are important natural or anthropogenic catchment processes like evaporation, damming, and water storage in the upstream catchment.

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Halder, J., S. Terzer, L. I. Wassenaar, L. J. Araguás-Araguás et P. K. Aggarwal. « The Global Network of Isotopes in Rivers (GNIR) : integration of water isotopes in watershed observation and riverine research ». Hydrology and Earth System Sciences Discussions 12, n^o 4 (22 avril 2015) : 4047–79. http://dx.doi.org/10.5194/hessd-12-4047-2015.

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Abstract. We introduce a new online global database of riverine water stable isotopes (Global Network of Isotopes in Rivers) and evaluate its longer-term data holdings. Overall, 218 GNIR river stations were clustered into 3 different groups based on the seasonal variation in their isotopic composition, which was closely coupled to precipitation and snow-melt water run-off regimes. Sinusoidal fit functions revealed periodic phases within each grouping and deviations from the sinusoidal functions revealed important river alterations or hydrological processes in these watersheds. The seasonal isotopic amplitude of δ18O in rivers averaged 2.5 ‰, and did not increase as a function of latitude, as it does for global precipitation. Low seasonal isotopic amplitudes in rivers suggest the prevalence of mixing and storage such as occurs via lakes, reservoirs, and groundwater. The application of a catchment-constrained regionalized cluster-based water isotope prediction model (CC-RCWIP) allowed direct comparison between the expected isotopic composition for the upstream catchment precipitation with the measured isotopic composition of river discharge at observation stations. The catchment-constrained model revealed a strong global isotopic correlation between average rainfall and river discharge (R2 = 0.88) and the study demonstrated that the seasonal isotopic composition and variation of river water can be predicted. Deviations in data from model predicted values suggest there are important natural or anthropogenic catchment processes, like evaporation, damming, and water storage in the upstream catchment.

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Ballutaud, Marine, Morgane Travers-Trolet, Paul Marchal, Stanislas F. Dubois, Carolina Giraldo, Andrew C. Parnell, M. Teresa Nuche-Pascual et Sébastien Lefebvre. « Inferences to estimate consumer’s diet using stable isotopes : Insights from a dynamic mixing model ». PLOS ONE 17, n^o 2 (7 février 2022) : e0263454. http://dx.doi.org/10.1371/journal.pone.0263454.

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Stable isotope ratios are used to reconstruct animal diet in trophic ecology via mixing models. Several assumptions of stable isotope mixing models are critical, i.e., constant trophic discrimination factor and isotopic equilibrium between the consumer and its diet. The isotopic turnover rate (λ and its counterpart the half-life) affects the dynamics of isotopic incorporation for an organism and the isotopic equilibrium assumption: λ involves a time lag between the real assimilated diet and the diet estimated by mixing models at the individual scale. Current stable isotope mixing model studies consider neither this time lag nor even the dynamics of isotopic ratios in general. We developed a mechanistic framework using a dynamic mixing model (DMM) to assess the contribution of λ to the dynamics of isotopic incorporation and to estimate the bias induced by neglecting the time lag in diet reconstruction in conventional static mixing models (SMMs). The DMM includes isotope dynamics of sources (denoted δs), λ and frequency of diet-switch (ω). The results showed a significant bias generated by the SMM compared to the DMM (up to 50% of differences). This bias can be strongly reduced in SMMs by averaging the isotopic variations of the food sources over a time window equal to twice the isotopic half-life. However, the bias will persist (∼15%) for intermediate values of the ω/λ ratio. The inferences generated using a case study highlighted that DMM enhanced estimates of consumer’s diet, and this could avoid misinterpretation in ecosystem functioning, food-web structure analysis and underlying biological processes.

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Gao, Jing, V. Masson-Delmotte, T. Yao, L. Tian, C. Risi et G. Hoffmann. « Precipitation Water Stable Isotopes in the South Tibetan Plateau : Observations and Modeling* ». Journal of Climate 24, n^o 13 (1 juillet 2011) : 3161–78. http://dx.doi.org/10.1175/2010jcli3736.1.

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Abstract Measurements of precipitation isotopic composition have been conducted on a daily basis for 1 yr at Bomi, in the southeast Tibetan Plateau, an area affected by the interaction of the southwest monsoon, the westerlies, and Tibetan high pressure systems, as well as at Lhasa, situated west of Bomi. The measured isotope signals are analyzed both on an event basis and on a seasonal scale using available meteorological information and airmass trajectories. The processes driving daily and seasonal isotopic variability are investigated using multidecadal climate simulations forced by twentieth-century boundary conditions and conducted with two different isotopic atmospheric general circulation models [the isotopic version of the Laboratoire de Météorologie Dynamique GCM (LMDZiso) and the ECHAM4iso model]. Both models use specific nudging techniques to mimic observed atmospheric circulation fields. The models simulate a wet and cold bias on the Tibetan Plateau together with a dry bias in its southern part. A zoomed LMDZ simulation conducted with ~50-km local spatial resolution dramatically improves the simulation of isotopic compositions of precipitation on the Tibetan Plateau. Simulated water isotope fields are compared with new data and with previous observations, and regional differences in moisture origins are analyzed using back-trajectories. Here, the focus is on relationships between the water isotopes and climate variables on an event and seasonal scale and in terms of spatial and altitudinal isotopic gradients. Enhancing the spatial resolution is crucial for improving the simulation of the precipitation isotopic composition.

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Salamalikis, Vasileios, et Athanassios A. Argiriou. « Validation and Bias Correction of Monthly δ18O Precipitation Time Series from ECHAM5-Wiso Model in Central Europe ». Oxygen 2, n^o 2 (3 mai 2022) : 109–24. http://dx.doi.org/10.3390/oxygen2020010.

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Simulated stable oxygen isotopic composition (δ18O) of precipitation from isotope-enabled GCMs (iGCMs) have gained significant visibility nowadays. This study evaluates bias correction techniques to reduce the systematic and dispersion biases of the modelled δ18O by the ECHAM5-wiso model compared to the Global Network of Isotopes in Precipitation (GNIP) observations over Central Europe. mean bias error (MBE) and Root Mean Square Error (RMSE) are substantially reduced by more than 70% and 10%, respectively, depending on the bias correction scheme, with better results for Generalized Additive Model (GAM) and linear scaling approach (SCL) methods. The bias-corrected δ18OECHAM5-wiso values successfully describe the long-term isotopic composition of precipitation and the isotopic amplitude with the best performances for the EQM method. The necessity of applying bias correction algorithms is verified by the excellent agreement between the corrected δ18OECHAM5-wiso with GNIP in high-altitude areas where ECHAM5-wiso fails to reproduce the observed isotopic variability. The results are expected to bring valuable insights into the utilization of iGCMs’ relationships in climate studies for understanding the present and past water cycle under the isotopic perspective.

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Neumann, Thomas A., et Edwin D. Waddington. « Effects of firn ventilation on isotopic exchange ». Journal of Glaciology 50, n^o 169 (2004) : 183–94. http://dx.doi.org/10.3189/172756504781830150.

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AbstractA new model of isotopic diffusion in the upper few meters of firn tracks the isotopic composition of both the ice matrix and the pore-space vapor through time in two dimensions. Stable isotopes in the vapor phase move through the firn by diffusion along concentration gradients and by advection. Wind-driven ventilation carries atmospheric water vapor into the firn, where it mixes with existing pore-space vapor. Unlike previous models, our model allows disequilibrium between pore-space vapor and the surrounding snow grains. We also calculate the isotopic effects of ventilation-driven sublimation and condensation in the firn. Model predictions of isotopic diffusion in firn compare favorably with existing diffusion models. Model results quantify what other investigators have suggested: isotopic change in the upper few meters is more rapid than can be explained by the Whillans and Grootes (1985) model; isotopic equilibration with atmospheric vapor is an important component of post-depositional isotopic change; and ventilation enhances isotopic exchange by creating regions of relatively rapid sublimation and condensation in the firn.

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Erez, Jonathan, Anne Bouevitch et Aaron Kaplan. « Carbon isotope fractionation by photosynthetic aquatic microorganisms : experiments with Synechococcus PCC7942, and a simple carbon flux model ». Canadian Journal of Botany 76, n^o 6 (1 juin 1998) : 1109–18. http://dx.doi.org/10.1139/b98-067.

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Stable carbon isotopes (12C and 13C) are widely used to trace biogeochemical processes in the global carbon cycle. Natural fractionation of carbon isotopes is mainly due to the discrimination of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) against 13C during photosynthesis. In marine and other aquatic microorganisms, this fractionation is lowered when the dissolved CO2 (CO2(aq)) is decreasing, but the underlying mechanisms are poorly understood. Cultured Synechococcus PCC7942 showed maximum isotopic fractionations of -33omicron (in delta 13C units) relative to the total inorganic carbon (Ci) when CO2(aq) is above 30 m M. As the culture grew, pH increased, CO2(aq) was lower than 1 m M, and the Ci concentrating mechanism was induced although the Ci was above 3 mM. The isotopic fractionation was drastically reduced to values of -1 to -3 omicron relative to Ci. A simple carbon isotope flux model suggests that during the first stages of the experiment the total uptake (F1) was roughly three- to four-fold greater than the photosynthetic net accumulation (F2). When the Ci concentrating mechanism was induced, the leakage of CO2 from the cells declined, the cells started to utilize HCO3- and the F1/F2 ratio decreased to values close to 1. Based on this model the isotopic variability of oceanic phytoplankton suggests that the F1/F2 ratio may be above 3 in high latitudes and ~1.1 in equatorial waters, where the Ci concentrating mechanism is probably induced. Attempts to reconstruct past atmospheric CO2 levels and paleoproductivity should take into account the effects of the Ci concentrating mechanism on the isotopic fractionation of aquatic primary producers.Key words: carbon concentrating mechanism, carbon isotope fractionation, CO2, photosynthesis.

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Thèses sur le sujet "Isotopic model"

Fomchenko, Anna. « "Expanded" local mode approach and isotopic effect in polyatomic molecules ». Thesis, Dijon, 2014. http://www.theses.fr/2014DIJOS036/document.

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Dans cette thèse, sur la base de l'approche du mode local "étendu" et de la théorie générale de la substitution isotopique, nous obtenons un ensemble de relations analytiques simples entre les paramètres spectrocopiques (fréquences harmoniques, coefficients d'anharmonicité, paramètres rovibrationels, différents types de paramètres d'interaction de Fermi et de Coriolis) des molécules de CH2D2, CH3D et CHD3. Tous ces paramètres sont exprimés en termes de relations simples à partir des paramètres spectroscopiques de la molécule mère CH4. Des calculs tests avec des relations isotopiques montrent que même sans introduire d'informations majeures sur les espèces isotopiques, les résultats numériques de ces calculs sont en bon accord avec les données expérimentales et les calculs ab initio. A partir de le théorie des opérateurs de perturbation et des propriétés de symétrie des molécules axiales XYZ3 (C3v), nous déterminons des formules générales permettant la détermination des paramètres spectroscopiques sous la forme de fonctions des paramètres structuraux et des paramètres de la fonction potentiel intramoléculaire. Nous présentons aussi une approche permettant la détermination du hamiltonien de molécules polyatomiques qui permet de résoudre le problème de la description de la surface d'énergie potentielle via la construction et la diagonalisation d'une matrice hamiltonienne de grande dimension
In this thesis, on the base of the "expanded", local mode approach and general isotopic substitution theory we obtain sets of simple analytical relations between spectroscopic parameters (harmonic frequencies, anharmonic coefficients, ro-vibrational parameters, different kinds of Fermi and Coriolis-type interaction parameters) of the CH2D2, CH3D and CHD3 molecules. All of them are expressed as simple functions of spectroscopic parameters of the mother CH4 molecule. Test calculations with the isotopic relations show that even without including prior informations about the isotopic species, numerical results of calculations are in a good agreement both with experimental data and results of ab initio calculations. On the base of operators perturbation theory and the symmetry properties of the axially symmetric XYZ3 (C3v) type molecules, we derive general formulae for the determination of the spectroscopic parameters in the form of functions of structural parameters and parameters of the intramolecular potential function. We present also an approach for determination of the Hamiltonian of polyatomic molecules that allows to solve the problem of potential energy surface determination via the construction and the diagonalization of a Hamiltonian matrix of large dimension

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Burk, David Edward. « Forward model calculations for determining isotopic compositions of materials used in a radiological dispersal device ». Texas A&M University, 2005. http://hdl.handle.net/1969.1/2366.

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In the event that a radiological dispersal device (RDD) is detonated in the U.S. or near U.S. interests overseas, it will be crucial that the actors involved in the event can be identified quickly. If irradiated nuclear fuel is used as the dispersion material for the RDD, it will be beneficial for law enforcement officials to quickly identify where the irradiated nuclear fuel originated. One signature which may lead to the identification of the spent fuel origin is the isotopic composition of the RDD debris. The objective of this research was to benchmark a forward model methodology for predicting isotopic composition of spent nuclear fuel used in an RDD while at the same time optimizing the fidelity of the model to reduce computational time. The code used in this study was Monteburns-2.0. Monteburns is a Monte Carlo based neutronic code utilizing both MCNP and ORIGEN. The size of the burnup step used in Monteburns was tested and found to converge at a value of 3,000 MWd/MTU per step. To ensure a conservative answer, 2,500 MWd/MTU per step was used for the benchmarking process. The model fidelity ranged from the following: 2-dimensional pin cell, multiple radial-region pin cell, modified pin cell, 2D assembly, and 3D assembly. The results showed that while the multi-region pin cell gave the highest level of accuracy, the difference in uncertainty between it and the 2D pin cell (0.07% for 235U) did not warrant the additional computational time required. The computational time for the multiple radial-region pin cell was 7 times that of the 2D pin cell. For this reason, the 2D pin cell was used to benchmark the isotopics with data from other reactors. The reactors from which the methodology was benchmarked were Calvert Cliffs Unit #1, Takahama Unit #3, and Trino Vercelles. Calvert Cliffs is a pressurized water reactor (PWR) using Combustion Engineering 14??14 assemblies. Takahama is a PWR using Mitsubishi Heavy Industries 17??17 assemblies. Trino Vercelles is a PWR using non-standard lattice assemblies. The measured isotopic concentrations from all three of the reactors showed good agreement with the calculated values.

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De, Lurio Jennifer Lynn. « Paleoclimatic significance of glendonite pseudomorphs in the early cretaceous of the Eromanga Basin, Australia : a geochemical and isotopic model / ». Title page, abstract and contents only, 1995. http://web4.library.adelaide.edu.au/theses/09SB/09sbd366.pdf.

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Thesis (B. Sc.(Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1995.
Australian National Grid reference SH/54-5 Marree sheet 1:250000. Includes bibliographical references (leaves 40-54).

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Shipley, Niccole Kiyomi. « Isotopic and Petrologic Investigation and Model of Genesis of Large-Volume High-Silica Rhyolites in Arc Environments : Karymshina Caldera, Kamchatka, Russia ». Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/12187.

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xii, 76 p. ： ill. (some col.)
Large-volume calderas are responsible for producing large deposits of rhyolite and high-silica rhyolite, but the mechanisms by which these deposits are produced are still poorly understood. The Kamchatka Peninsula of Russia contains several large calderas and is one of the most volcanically active areas on Earth. Karymshina Caldera, the largest (25 km x 15 km) caldera in Kamchatka, produced an estimated 800 km 3 of high-silica rhyolitic ignimbrites and post-caldera extrusions, which erupted 1.78 and 0.5-0.8 Ma, respectively. SiO2 content ranges from 66.27-71.89 wt% in the ignimbrites and 70.16-77.70 wt% in the post-caldera extrusions studied. Crystal content is primarily quartz and plagioclase, 0.5-2 mm in size, with other minerals. Values of δ18 O, δD, 87 Sr/86 Sr, and 144 Nd/143 Nd indicate little assimilation of crustal material, in contrast to modeling results. XRF analysis indicates a homogeneous magma. The rhyolite-MELTS program was used to model crystallization of a basaltic source with addition of amphibolite partial melt and hydrothermally-altered silicic rock to reproduce the observed compositions. This thesis contains both previously published and co-authored material.
Committee in charge: Dr. Ilya Bindeman， Chairperson； Dr. Paul Wallace， Member； Dr. Mark Reed， Member

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Fusetti, Luc. « Elaboration of a kinetic model in order to predict the molecular and isotopic composition of natural gas generated during the thermal cracking of hydrocarbons ». Thesis, Curtin University, 2009. http://hdl.handle.net/20.500.11937/2088.

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The scope of the present study was to validate an approach that could be used to elaborate a model that would predict the δ[superscript]13C of the gases generated during thermal cracking of oil. The attention was focused on C[subscript]14- methylaromatics and alkylaromatics but the entire methodology was demonstrated on one component i.e. 1,2,4-trimethylbenzene.Pyrolysis experiments at temperatures of 395, 425, 450, and 475 °C and at a pressure of 100 bar were performed in order to study the whole range of conversions. All pyrolysis fractions were recovered and quantified. All identified products were also quantified individually. A free-radical mechanism until 70% conversion of 1,2,4-trimethylbenzene was achieved. This mechanism was then used to characterize some CH[subscript]4 generation pathways at 425 and 200 °C. In both cases the identified pathways included: (i) demethylation of 1,2,4- trimethylbenzene into xylenes (and to a lesser extent demethylation of xylenes into toluene), (ii) dimerizarion of monoaromatics, (iii) intramolecular ring closure reaction of dimers into triaromatics.In a second step, the free-radical mechanism was used to constrain the chemistry of a simpler lumped kinetic model predicting CH[subscript]4 generation under laboratory and geological conditions for the whole range of conversions. The resulting scheme was composed of four pathways P[subscript]i for methane generation: Reactant --> Dimers (P[subscript]a), Reactant --> Xylenes (P[subscript]b), Dimers --> {Prechar + Char} (P[subscript]c), and Xylenes --> Dimers + Toluene (P[subscript]d). Optimization yielded activation energies in the range of 50-60 kcal/mol, and frequency factors in the neighbourhood of 10[superscript]12 s[superscript]-1. Simulations revealed that P[subscript]b and P[subscript]c led to the greatest amounts of CH[subscript]4 below 5% conversion, followed by P[subscript]a. Above 5% conversion, CH[subscript]4 generated via P[subscript]c became dominant but P[subscript]a and P[subscript]b were also found to be of importance. Contribution of P[subscript]d was found to be negligible, except for when 100% conversion was almost reached. Simulations under geological heating rates revealed that significant amounts of CH[subscript]4 were generated by methylated monoaromatics in deeply buried reservoirs and that methylated monoaromatics thus had a higher thermal stability than their polyaromatic counterparts but lower than the saturated hydrocarbons.CH[subscript]4 yield was also modelled using a unique stoichiometric equation (CH[subscript]4max = 7.6 wt% per methyl group) associated with Ea = 58.5 kcal/mol and A = 10[superscript]11.96 s[superscript]-1, showing relative similarities to other reported values for methylated polyaromatics. In the final stage, P[subscript]a, P[subscript]b, and P[subscript]c were selected as relevant contributions to δ[superscript]13C[subscript]CH4 until 100% conversion. Kinetics for the generation of [superscript]12CH[subscript]4 and [superscript]13CH[subscript]4 were then expressed separately and implemented into the lumped model. Optimization yielded a ratio of frequency factors Ω = 1.028, variations of activation energy ΔE[subscript]i in the range of 36-79 cal/mol (kinetic effect); and a δ[superscript]13C[subscript]p of CH[subscript]4 precursor groups equal to -32.7‰ (precursor effect). Simulations performed under geological heating rates illustrated the greater isotopic fractionation of CH[subscript]4 generated under geological conditions compared with laboratory conditions. The comparison at high maturity with δ[superscript]13C[subscript]CH4 during thermal cracking of 1-methylpyrene and mature kerogen under the same simulation conditions emphasized the need to determine the magnitude of the precursor effect for natural compounds.

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Köten, Muharrem [Verfasser]. « An improved efficiency model for ACE-SWICS : determination of the carbon isotopic ratio 13C, 12C in the solar wind from ACE-SWICS measurements / Muharrem Köten ». Kiel : Universitätsbibliothek Kiel, 2009. http://d-nb.info/1019812788/34.

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Calippo, Flávio Rizzi. « Sociedade sambaquieira, comunidades marítimas ». Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/71/71131/tde-23062010-160307/.

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Tendo como referencial teórico abordagens focadas na Arqueologia Marítima (MUCKELROY, 1978; ADAMS, 1998, 2002), na Antropologia Marítima (MALINOWSKI, 1986 [1922]; DIEGUES, 1998) e em estudos de Percepção Ambiental (INGOLD, 2000), buscou-se desenvolver e testar a hipótese de que, embora houvesse uma unidade cultural que permitisse o estabelecimento de uma ampla sociedade sambaquieira, os povos dos sambaquis estariam organizados em comunidades costeiras regionais, as quais teriam se desenvolvido e se organizado em diferentes comunidades marítimas, costeiras e fluviais, em conseqüência dos diferentes modos com que eles se relacionariam (dialeticamente) com o ambiente. Para sustentar tal hipótese foi elaborado um modelo de predição de sítios submersos e realizadas análises da composição isotópica do estrôncio (HÖLZL, 1997; PRICE et al., 2000; BENTLEY et al, 2003; HODELL, 2004), do carbono e do oxigênio (KEITH, 1964; COSTA, 2000; MIZUTA, 2007) presentes (em amostras de conchas e ossos humanos) em sambaquis localizados ao longo do médio e baixo Vale do Ribeira, bem como em sítios do litoral central (Baixada Santista e Bertioga) e norte do estado de São Paulo (Ubatuba). Essas evidências foram correlacionadas à abordagem teórica através de uma proposta elaborada a partir do estudo dos processos de formação do registro arqueológico desenvolvidos por Schiffer (1972). Com base nessas análises, além de diferenciar os povos do médio Ribeira dos sambaquieiros do litoral, foi possível, entre outras, propor uma fronteira cultural entre os conjuntos de sítios do litoral sul/centro do estado de São Paulo e os sambaquis do litoral norte de São Paulo/sul do Rio de Janeiro. Especificamente em relação aos sambaquis de Cananéia, a análise isotópica das conchas evidenciou, ainda, que os locais e os propósitos da coleta estariam mais relacionados a aspectos culturais do que à simples exploração dos recursos mais abundantes.
Using as theoretical reference approaches focused on the Maritime Archaeology (MUCKELROY, 1978; ADAMS, 1998, 2002), on the Maritime Anthropology (MALINOWSKI, 1986 [1922]; DIEGUES, 1998) and on studies of Environmental Perception (INGOLD, 2000), we tried to develop and test the hypothesis that, notwithstanding the evidence of a cultural unity that allowed for the establishment of an ample shellmound society, people of the shellmounds were organized in regional coastal communities. These would have developed and organized in different maritime communities, both coastal and fluvial, in consequence of the different ways in which they (dialectically) related with the environment. To support such hypothesis a model was elaborated predicting underwater sites, an analyses was realized of the isotopic composition of strontium (HÖLZL, 1997; PRICE et al., 2000; BENTLEY et al, 2003; HODELL, 2004), of carbon and of oxygen (KEITH, 1964; COSTA, 2000; MIZUTA, 2007) present (in samples of shells and human bones) in shellmounds located along the medium and low Vale do Ribeira, as well as in sites at the central coast (Baixada Santista and Bertioga) and north (Ubatuba) of the state of São Paulo. The evidences were correlated to the theoretical approach through a proposal elaborated from the study of the formation processes of the archaeological record developed by Schiffer (1972). Based on these analyses, beyond differentiating the people from the medium Ribeira from the coastal shellmound people, it became possible, among other things, to propose a cultural borderline between the ensembles of sites of the south/center coast of São Paulo and the shellmounds of northern São Paulo and southern Rio de Janeiro. Specifically with regard to the shellmounds of Cananéia, the isotopic analysis of shells evinced, yet, that the locals and goals of collecting were more related to cultural aspects than to the simple exploration of the more abundant resources.

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Di, Hong J. « Application of isotopic dilution methods to the study of the dissolution of phosphate fertilisers of differing solubility in the soil ». Lincoln University, 1991. http://hdl.handle.net/10182/1792.

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An injection technique, in which undisturbed soil cores are labelled with ³²P to study dissolution of phosphate fertilisers in the soil, was evaluated in field and glasshouse trials. When ³²P was injected between 0-150 mm depths of the undisturbed soil columns and fertilisers applied at the surface, the amounts of fertiliser P dissolved, as measured by the increases in the exchangeable P pools, were overestimated. Three possible reasons were suggested: (i) the interaction between surface-applied fertiliser, ³²P injected through the whole soil column, and the vertical decline in root density, (ii) the decline of specific activity in the exchangeable P pool due to losses of ³²P to nonexchangeable P pools and continuous addition of P from fertiliser dissolution, and (iii) non-uniform distribution of ³²P vis-a-vis ³¹P phosphate. The injection technique may be employed to assess the effectiveness of phosphate fertilisers by introducing a concept, the fertiliser equivalent (FE). The FE is a measure of the amounts of soil exchangeable P that the fertilisers are equivalent to in supplying P to plants, when applied at the specific location. Soluble single superphosphate (SSP) applied at the surface of undisturbed grassland soil cores (Tekapo fine sandy loam), was much more effective than surface-applied unground North Carolina phosphate rock (NCPR) and 30% acidulated NCPR with phosphoric acid (NCPAPR) within the 56 day period of plant growth. An isotopic dilution method, based on tracer kinetic theory, was developed to study the rates of dissolution (F in) and retention (F out) of phosphate fertilisers in the soil in growth chamber experiments. The estimation of F in and F out required labelling of the soils with carrier-free ³²P and determination of the corresponding values of the specific activities of the exchangeable P pools, SA₁ and SA₂, and the sizes of the exchangeable P pools, Q₁ and Q₂, at times t₁ and t₂. Most of the phosphate in the monocalcium phosphate (MCP) solution entered the exchangeable P pool immediately after addition to the soils (Tekapo fine sandy loam and Craigieburn silt loam), and there was little further phosphate input. With increasing periods of incubation, the phosphate was quickly transformed to less rapidly exchangeable forms. In the soils treated with ground North Carolina phosphate rock (<150 µm, NCPR) or partially acidulated (30%) NCPR with phosphoric acid (NCPAPR), the initial exchangeable P pools were not as large as those in the soils treated with MCP, but were maintained at relatively stable concentrations for extended periods, due to the continuous dissolution of PR materials and to lower rates of pretention. An increase in P-retention caused a slight rise in the rate of PR dissolution, but also a rise in the rate of P-retention by the soil. The rate of dissolution was higher at a lower application rate in relative terms, but smaller in absolute terms. The trends in the changes of plant-available P in the soils, measured by the water extractable P, Bray I P and Olsen P, correspond to those predicted by the F in and F out values. The average rates of dissolution between 1-50 and 50-111 days estimated by the F in, however, were higher than those estimated by extractions with 0.5 M NaOH followed by 1 M HCl, and with 0.5 M BaCl₂/TEA. This is partly because the Fin values reflect a plant growth effect on PR dissolution. The relative agronomic effectiveness of NCPR and NCPAPR with respect to MCP was higher after 50 and 111 days of incubation than after 1 day. The F in values were included in all the two-variable models constructed by stepwise regression to describe the relationship between plant P uptake and soil measurements. The amounts of variation in plant P uptake accounted for by the regression model was significantly improved by including F in in the model. This indicates the importance of fertiliser dissolution rates in affecting soil P supply, when phosphate fertilisers differing in solubility are applied.

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King, Adam C. « The Cressbrook Creek alluvial aquifer system, Southeast Queensland : hydrochemistry and isotopes to determine hydrological processes and response to floods ». Thesis, Queensland University of Technology, 2014. https://eprints.qut.edu.au/78443/1/Adam_King_Thesis.pdf.

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This study developed an understanding of hydrological processes within the Cressbrook Creek catchment of the upper Brisbane River, in particular for the alluvial aquifers. Those aquifers within the lower catchment are used for intensive irrigation, and have been impacted by long-term drought followed by flooding. The study utilised water chemistry, isotopic characters and hydraulic measurements to determine factors such as recharge, links between creeks and groundwater, and variations in water quality. The catchment-wide study will enable improved management of the local water resources.

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Delavau, Carly J. « Development of precipitation δ18O isoscapes for Canada and application within a tracer-aided hydrological model ». Taylor and Francis, American Geophysical Union, 2015. http://hdl.handle.net/1993/31946.

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Delineating spatial patterns of precipitation isotopes (“isoscapes”) is important for studies including the hydrology of terrestrial systems, present and past interpretations of climate, and tracer-aided hydrological modelling, among others. However, the extent to which precipitation isoscapes can be predicted across Canada has not been fully articulated. This thesis combines isotopes in precipitation (δ18Oppt) observations from two regional and one global network to create long term and time series precipitation isoscapes for Canada and the northern United States. Multi-linear regressions of a small suite of geographic and climate variables generate the best performing long-term and seasonal models of δ18Oppt. These models are used to develop long term isoscapes for Canada, which capture the general spatial and seasonal trends in δ18Oppt, showing an improvement upon results from previous studies using global models. Building upon long-term δ18Oppt prediction, δ18Oppt observations alongside climatological and geographic predictors are used to create empirical time series prediction models. Five regionalization approaches are used to separate the study domain into isotope zones to explore the effect of spatial grouping on simulations. Generally, the models capture the timing and magnitude of intra-annual (seasonal) δ18Oppt cycles across the study domain while simulating moderate inter-annual variation; however often fail to capture the anomalies in observed δ18Oppt. Uncertainty in predictions is quantified spatially and temporally, and the Köppen-Geiger (Kpn) regionalization is selected as the preferred regionalization scheme for future applications due to adequate model performance and lack of border issues at regional boundaries. Finally, estimates of monthly δ18Oppt from Kpn models, long term annual averages, and daily REMOiso output are used to force an isotope-enabled hydrological model, isoWATFLOOD, in the Fort Simpson Basin, NWT, Canada. Results show streamflow simulations are not significantly impacted by choice of δ18Oppt input; however, oxygen-18 in streamflow and the internal apportionment of water (and model parameterizations) are impacted, particularly during large precipitation and snowmelt events. This work shows how isoWATFLOOD can be used in regions with limited δ18Oppt observations, and that the model can be of value in such regions. This study reinforces that a tracer-aided modelling approach works towards diagnosing issues surrounding model equifinality.
February 2017

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Livres sur le sujet "Isotopic model"

Thorstenson, Donald C. Calculation of individual isotope equilibrium constants for implementation in geochemical models. Denver, Colo : U.S. Dept. of the Interior, U.S. Geological Survey, 2002.

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Poli͡achenko, A. L. Chislennye metody v i͡adernoĭ geofizike. Moskva : Ėnergoatomizdat, 1987.

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Okazaki, Atsushi. Development of stable water isotope incorporated atmosphere-land coupled model and comparison with climate proxies. Tokyo] : Division of Climate System Research, Atmosphere and Ocean Research Institute, The University of Tokyo, 2018.

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1948-, Bassett R. L., Woodhouse E. G et U.S. Nuclear Regulatory Commission. Office of Nuclear Regulatory Research. Division of Regulatory Applications., dir. Field studies at the Apache Leap Research Site in support of alternative conceptual models. Washington, D.C : Division of Regulatory Applications, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, 1997.

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Hirose, Akira. Anomalous electron thermal diffusivity, anomalous particle pinch and isotope effect due to the skin size electromagnetic drift mode. Saskatoon, Sask : University of Saskatchewan, Plasma Physics Laboratory, 1990.

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Sedimentation rate through environmental radioactivity : Models and applications. Hamilton, Ont : Environmental Research & Publications, 2002.

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Duffield, Wendell A. A model to help explain Sr-isotope disequilibrium between feldspar phenocrysts and melt in large-volume silicic magma systems. [Menlo Park, Calif.?] : U.S. Dept. of the Interior, U.S. Geological Survey, 1994.

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Kelly, Brian P. Ground-water flow simulation and chemical and isotopic mixing equation analysis to determine source contributions to the Missouri River alluvial aquifer in the vicinity of the Independence, Missouri, well field. Rolla, Mo : U.S. Dept. of the Interior, U.S. Geological Survey, 2002.

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Chapitres de livres sur le sujet "Isotopic model"

Wei, Liang, John D. Marshall et J. Renée Brooks. « Process-Based Ecophysiological Models of Tree-Ring Stable Isotopes ». Dans Stable Isotopes in Tree Rings, 737–56. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-92698-4_26.

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AbstractTree-ring stable isotopes can be used to parameterizeprocess-based models by providing long-term data on tree physiological processes on annual or finer time steps. They can also be used to test process-based ecophysiological models for the assumptions, hypotheses, and simplifications embedded within them. However, numerous physiological and biophysical processes influence the stable carbon (δ13C) and oxygen (δ18O) isotopes in tree rings, so the models must simplify how they represent some of these processes to be useful. Which simplifications are appropriate depends on the application to which the model is applied. Fortunately, water and carbon fluxes represented in process-based models often have strong isotopic effects that are recorded in tree-ring signals. In this chapter, we review the status of several tree-ring δ13C and δ18O models simulating processes for trees, stands, catchments, and ecosystems. This review is intended to highlight the structural differences among models with varied objectives and to provide examples of the valuable insights that can come from combining process modeling with tree-ring stable isotope data. We urge that simple stable isotope algorithms be added to any forest model with a process representation of photosynthesis and transpiration as a strict test of model structure and an effective means to constrain the models.

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Kagawa, Akira, et Giovanna Battipaglia. « Post-photosynthetic Carbon, Oxygen and Hydrogen Isotope Signal Transfer to Tree Rings—How Timing of Cell Formations and Turnover of Stored Carbohydrates Affect Intra-annual Isotope Variations ». Dans Stable Isotopes in Tree Rings, 429–62. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-92698-4_15.

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AbstractIn this chapter, we discuss post-photosynthetic processes that affect intra-annual variation in the stable isotopes of tree rings, such as timing of cell formations and turnover of stored carbohydrates, by combining research findings gained by using either natural-abundance or artificially-enriched carbon, oxygenand hydrogen isotopes. We focus on within-ring variation in stable isotope ratios, with an emphasis on aligning observed ratios in whole wood or extracted cellulose to seasonal dynamics in climate and phenology. We also present a discussion of isotopic fractionation that operates within the scope of observed variations across individual rings. We then introduce a model that traces the seasonal partitioning of photosynthate into tree rings via storage pool, which is based on experimental data gained from labeling studies using artificially enriched 13CO2 gas. Finally, we will describe our current understanding of post-photosynthetic signal transfer processes of oxygenand hydrogen isotopes from leaves to tree rings, such as exchange of oxygen and hydrogen between storage carbohydrates and local cambial water, and possible causes of difference in oxygen and hydrogen isotope fractionations. Finally, we discuss mechanisms behind how oxygen and hydrogen from foliar-absorbed liquid water is then incorporated into wood biomass, by introducing results gained from recent H218O and HDO pulse-labeling experiments.

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Söllner, Frank, Anita Toncala, Stefan Hölzl et Gisela Grupe. « Determination of Geo-dependent Bioavailable 87Sr/86Sr Isotopic Ratios for Archaeological Sites from the Inn Valley (Austria) : A Model Calculation ». Dans Isotopic Landscapes in Bioarchaeology, 123–40. Berlin, Heidelberg : Springer Berlin Heidelberg, 2016. http://dx.doi.org/10.1007/978-3-662-48339-8_7.

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Ingraham, Neil L., et Richard G. Craig. « Constraining Estimates of Evapotranspiration With Hydrogen Isotopes in a Seasonal Orographic Model ». Dans Climate Change in Continental Isotopic Records, 47–53. Washington, D. C. : American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm078p0047.

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Schidlowski, Manfred, Hendrik Gorzawski et Inka Dor. « Experimental Hypersaline Ponds as Model Environments for Stromatolite Formation 2. Isotopic Biogeochemistry ». Dans Early Organic Evolution, 494–508. Berlin, Heidelberg : Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/978-3-642-76884-2_40.

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Roden, John, Matthias Saurer et Rolf T. W. Siegwolf. « Probing Tree Physiology Using the Dual-Isotope Approach ». Dans Stable Isotopes in Tree Rings, 463–79. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-92698-4_16.

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AbstractThe environmental and physiological interpretation of stable isotope variation in organic matter is affected by many different and interacting factors. This is especially true when considering isotope variation in tree rings, which are influenced not only by leaf-level photosynthetic gas exchange processes but also by post-photosynthetic fractionation. It has been proposed that measuring multiple isotopes on the same sample may constrain such interpretations if one isotope provides independent information about important fractionation events that cause variation in another isotope. Here we describe one such “dual-isotope approach” where oxygen isotope variation (δ18O) is used to probe the effects of stomatal conductance on carbon isotope (δ13C) variation for the same sample. This chapter describes the development of this conceptual model, constraints on model applicability, particularly with respect to tree rings, and how it has been utilized to explore aspects of tree physiology.

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Schefuß, Enno, Martin Werner, Britta Beckmann, Barbara Haese et Gerrit Lohmann. « North-West African Hydrologic Changes in the Holocene : A Combined Isotopic Data and Model Approach ». Dans Integrated Analysis of Interglacial Climate Dynamics (INTERDYNAMIC), 109–14. Cham : Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-00693-2_18.

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Pin, C. « Evolution of the Lower Crust in the Ivrea Zone : A Model Based on Isotopic and Geochemical Data ». Dans Granulites and Crustal Evolution, 87–110. Dordrecht : Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-2055-2_6.

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Actes de conférences sur le sujet "Isotopic model"

Arbuzov, Boris A. « HERA high Q2 events as indications of excited leptons with weak isotopic spin 3/2 ». Dans Beyond the standard model. American Institute of Physics, 1997. http://dx.doi.org/10.1063/1.54500.

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Lee, Hyojeong, Lan Zhao, Gabriel J. Bowen, Chris C. Miller, Ajay Kalangi, Tonglin Zhang et Jason B. West. « Enabling online geospatial isotopic model development and analysis ». Dans the 2011 TeraGrid Conference. New York, New York, USA : ACM Press, 2011. http://dx.doi.org/10.1145/2016741.2016783.

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Travis, J. C., T. B. Lucatorto, J. Wen, J. D. Fassett et C. W. Clark. « Doppler-Free Resonance Ionization Mass Spectrometry of Beryllium ». Dans Laser Applications to Chemical Analysis. Washington, D.C. : Optica Publishing Group, 1987. http://dx.doi.org/10.1364/laca.1987.tub2.

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As originally conceived, resonance ionization mass spectrometry (RIMS) combined the elemental selectivity of resonance ionization (1) with the isotopic selectivity of mass spectrometry to improve the accuracy and sensitivity of conventional mass spectrometry (2). For many applications, especially quantitation by isotope dilution (3) , it is important that no isotopic selectivity accompany the resonance ionization process. This condition is easily met for all but a few elements of the periodic table (4), since the great majority of optical isotope shifts are small with respect to typical dye laser bandwidths and Doppler-broadened linewidths in common atom reservoirs. However, another class of problem exists for which it is desirable to achieve isotopically selective resonance ionization. These applications involve the detection of extremely, rare stable or radioactive isotopes in the presence of the major isotopic species of an element. Miller et al. (5) have explored the optical isotopic selectivity of the isotopes of Lu using a RIMS spectrometer equipped with a high-resolution (single-mode) continuous-wave (cw) laser. Cannon et al. (6) have measured an optical selectivity (defined below) of 800 for isotopes of Ba, using a RIMS spectrometer with two cw lasers. We have proposed the use of pulsed, two-photon, Doppler-free resonance ionization to extend the capability of conventional mass spectrometers to measure isotope ratios in excess of 1012 (7). Initial experimental results using this approach, for the isotopes 9Be and 10Be, are reported here.

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Stehmeier, Lester, Brad Magyar, Karlis Muehlenbachs, Xiaosu Lang et Ajay Dalai. « Use of Stable Isotope Ratios to Determine the Origin of Coke Formed in Gas Turbines ». Dans 2002 4th International Pipeline Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/ipc2002-27115.

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Coke deposits can form in compression equipment on natural gas transmission lines. These deposits are a result of incomplete combustion due to poor fuel gas quality or incorrect equipment design and/or operation. There is an isotopic “signature” which is carried over from the fuel gas into the coke if incomplete combustion occurs, allowing the origin of the coke deposit to be identified. The use of a continuous flow gas chromatograph isotope ratio mass spectrometer (GC/IRMS) provides a convenient method for determining the isotopic composition of the components in the fuel gas. These ratios can then be used to identify if a correlation exists with the 13C/12C ratio of the coke sample. Previous projects in 1999 and 2000 demonstrated that the coke deposits found within gas turbines could be closely related to the incomplete combustion of the fuel gas. One outcome of that work was determining the value for having a good understanding of stable isotope signatures for gas entering the pipeline system. In 2000, fuel gas samples were obtained from various areas in the Alberta TransCanada collection system, their isotope ratios were measured and then used to produce coke. This work substantiated previous project work, reinforcing the isotopic relationship between coke and the source material. Current work is to produce a model to quantitatively relate the various components of the source material to coke deposits. This model could then be used as a tool to enhance the performance of the gas turbines. Detailed investigation into the sensitivity of stable carbon isotope measurements for identifying the source of coke deposits for a complete range of TransCanada fuel gas mixtures is presented.

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Gropp, Jonathan, Gunter Wegener, Heidi Taubner, Marcus Elvert et Itay Halevy. « Explaining sulfate-driven isotope effects in anaerobic oxidation of methane using a metabolic-isotopic model ». Dans Goldschmidt2021. France : European Association of Geochemistry, 2021. http://dx.doi.org/10.7185/gold2021.5370.

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Netesova, Nadezhda P. « Oscillation electron model superconductors : phase diagram, temperature transition, isotopic shift ». Dans Oxide-based Materials and Devices IX, sous la direction de Ferechteh H. Teherani, David C. Look et David J. Rogers. SPIE, 2018. http://dx.doi.org/10.1117/12.2293081.

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Chen, Yunfei, Guodong Wang, Deyu Li et Jennifer R. Lukes. « Thermal Expansion and Isotopic Composition Effects on Lattice Thermal Conductivities of Crystalline Silicon ». Dans ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-13870.

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Equilibrium molecular dynamics simulation is used to calculate lattice thermal conductivities of crystal silicon in the temperature range from 400K to 1600K. Simulation results confirmed that thermal expansion, which resulted in the increase of the lattice parameter, caused the decrease of the lattice thermal conductivity. The simulated results proved that thermal expansion imposed another type resistance on phonon transport in crystal materials. Isotopic and vacancy effects on lattice thermal conductivity are also investigated and compared with the prediction from the modified Debye Callaway model. It is demonstrated in the MD simulation results that the isotopic effect on lattice thermal conductivity is little in the temperature range from 400K to 1600K for isotopic concentration below 1%, which implies the isotopic scattering on phonon due to mass difference can be neglected over the room temperature. The remove of atoms from the crystal matrix caused mass difference and elastic strain between the void and the neighbor atoms, which resulted in vacancy scattering on phonons. Simulation results demonstrated this mechanism is stronger than that caused by isotopic scattering on phonons due to mass difference. A good agreement is obtained between the MD simulation results of silicon crystal with vacancy defects and the data predicted from the modified Debye Callaway model. This conclusion is helpful to demonstrate the validity of Klemens' Rayleigh model for impurity scattering on phonons.

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Neznamov, Vasily. « The Isotopic Foldy-Wouthuysen Representation and Chiral Symmetry. The The Standard Model in the Isotopic Foldy-Wouthuysen Represetation without Higgs Bosons in the Fermion Sector ». Dans The XXth International Workshop High Energy Physics and Quantum Field Theory. Trieste, Italy : Sissa Medialab, 2012. http://dx.doi.org/10.22323/1.138.0053.

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Denisova, Nina Y., Konstantin G. Gribanov et Martin Werner. « Verification of the isotopic atmospheric general circulation model for a monitoring station in Labytnangi ». Dans 26th International Symposium on Atmospheric and Ocean Optics, Atmospheric Physics, sous la direction de Gennadii G. Matvienko et Oleg A. Romanovskii. SPIE, 2020. http://dx.doi.org/10.1117/12.2575615.

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Marcos Bonotto, Daniel. « U-ISOTOPIC MODEL AS A PROSPECTING TECHNIQUE IN THE MORRO DO FERRO THORIUM DEPOSIT, BRAZIL ». Dans 1st International Congress of the Brazilian Geophysical Society. European Association of Geoscientists & Engineers, 1989. http://dx.doi.org/10.3997/2214-4609-pdb.317.sbgf181.

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Rapports d'organisations sur le sujet "Isotopic model"

A. Alsaed. ISOTOPIC MODEL FOR COMMERCIAL SNF BURNUP CREDIT. Office of Scientific and Technical Information (OSTI), juillet 2005. http://dx.doi.org/10.2172/862028.

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A.H. Wells. ISOTOPIC MODEL FOR COMMERCIAL SNF BURNUP CREDIT. Office of Scientific and Technical Information (OSTI), novembre 2004. http://dx.doi.org/10.2172/862151.

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L.B. Wimmer. Isotopic Generation and Confirmation of the PWR Application Model ? Office of Scientific and Technical Information (OSTI), novembre 2003. http://dx.doi.org/10.2172/899642.

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H.R. Radulesa. Isotopic Generation and Confirmation of the PWR Application Model ? Office of Scientific and Technical Information (OSTI), mai 2005. http://dx.doi.org/10.2172/899643.

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Trowbridge, L. Isotopic selectivity of surface diffusion : An activated diffusion model. Office of Scientific and Technical Information (OSTI), novembre 1989. http://dx.doi.org/10.2172/5462238.

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Sitaraman, S., D. Biswas, R. Hafner et B. Anderson. Allowable Isotopic Mass Limits for the Type 4 Contents in the Model 9977-96 SGQ-EC1 Unshielded Engineered Container. Office of Scientific and Technical Information (OSTI), septembre 2010. http://dx.doi.org/10.2172/1119963.

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Piercey, S. J., et J. L. Pilote. Nd-Hf isotope geochemistry and lithogeochemistry of the Rambler Rhyolite, Ming VMS deposit, Baie Verte Peninsula, Newfoundland : evidence for slab melting and implications for VMS localization. Natural Resources Canada/CMSS/Information Management, 2021. http://dx.doi.org/10.4095/328988.

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New high precision lithogeochemistry and Nd and Hf isotopic data were collected on felsic rocks of the Rambler Rhyolite formation from the Ming volcanogenic massive sulphide (VMS) deposit, Baie Verte Peninsula, Newfoundland. The Rambler Rhyolite formation consists of intermediate to felsic volcanic and volcaniclastic rocks with U-shaped primitive mantle normalized trace element patterns with negative Nb anomalies, light rare earth element-enrichment (high La/Sm), and distinctively positive Zr and Hf anomalies relative to surrounding middle rare earth elements (high Zr-Hf/Sm). The Rambler Rhyolite samples have epsilon-Ndt = -2.5 to -1.1 and epsilon-Hft = +3.6 to +6.6; depleted mantle model ages are TDM(Nd) = 1.3-1.5 Ga and TDM(Hf) = 0.9-1.1Ga. The decoupling of the Nd and Hf isotopic data is reflected in epsilon-Hft isotopic data that lies above the mantle array in epsilon-Ndt -epsilon-Hft space with positive ?epsilon-Hft values (+2.3 to +6.2). These Hf-Nd isotopic attributes, and high Zr-Hf/Sm and U-shaped trace element patterns, are consistent with these rocks having formed as slab melts, consistent with previous studies. The association of these slab melt rocks with Au-bearing VMS mineralization, and their FI-FII trace element signatures that are similar to rhyolites in Au-rich VMS deposits in other belts (e.g., Abitibi), suggests that assuming that FI-FII felsic rocks are less prospective is invalid and highlights the importance of having an integrated, full understanding of the tectono-magmatic history of a given belt before assigning whether or not it is prospective for VMS mineralization.

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Hamilton, M. L., F. A. Garner et B. M. Oliver. The influence of helium on mechanical properties of model austenitic alloys, determined using sup 59 Ni isotopic tailoring and fast reactor irradiation. Office of Scientific and Technical Information (OSTI), novembre 1990. http://dx.doi.org/10.2172/6344602.

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Keeling, Ralph. Developing Model Constraints on Northern Extra-Tropical Carbon Cycling Based on measurements of the Abundance and Isotopic Composition of Atmospheric CO₂. Office of Scientific and Technical Information (OSTI), décembre 2014. http://dx.doi.org/10.2172/1165340.

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Spencer, Khalil J., Jung Ho Rim, Donivan R. Porterfield, Robert Clifford Roback, Hakim Boukhalfa et Floyd E. Stanley. High-Precision Plutonium Isotopic Compositions Measured on Los Alamos National Laboratory’s General’s Tanks Samples : Bearing on Model Ages, Reactor Modelling, and Sources of Material. Further Discussion of Chronometry. Office of Scientific and Technical Information (OSTI), juin 2015. http://dx.doi.org/10.2172/1188192.

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