Artículos de revistas: "Isotopes calcium"

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Chandra, Subhash. "Imaging transported and endogenous calcium independently at a subcellular resolution: ion microscopy imaging of calcium stable isotopes". Proceedings, annual meeting, Electron Microscopy Society of America 50, n.º 2 (agosto de 1992): 1604–5. http://dx.doi.org/10.1017/s0424820100132650.

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Ion microscopy, based on secondary ion mass spectrometry (SIMS), is a unique isotopic imaging technique. The use of stable isotopes as tracers and their SIMS localization at a subcellular resolution has introduced a significant new approach for molecular localization and ion transport studies. A molecule of interest may be tagged with stable 2H, 13C, 15N, etc. and imaged with SIMS for its intracellular location. Stable isotopes of physiologically important elements such as calcium and magnesium provide excellent tracers for ion transport imaging studies with SIMS. in a recent study with 44Ca, the brush border region in the small intestine was observed to be the main barrier for calcium transport from the intestinal lumen to the lamina propria region in chickens suffering from Rickets, a vitamin D-deficiency condition.An example of the use of 44Ca stable isotope for imaging calcium-calcium exchange between the intracellular and extracellular calcium with SIMS is shown in figure 1. 3T3 cells were grown on high purity germanium chips to about 80% confluency.

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2

Fujii, Y., J. Hoshi, H. Iwamoto, M. Okamoto y H. Kakihana. "Calcium Isotope Effects in Ion Exchange Electromigration and Calcium Isotope Analysis by Thermo-Ionization Mass Spectrometry". Zeitschrift für Naturforschung A 40, n.º 8 (1 de agosto de 1985): 843–48. http://dx.doi.org/10.1515/zna-1985-0807.

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Calcium ions were made to electromigrate along a cation exchange membrane. The abundance ratios of the calcium isotopes (Ca-40, 42, 43, 44, 48) in the migrated bands were measured by thermo-ionization mass spectrometry. The lighter isotopes were enriched in the front part of the migrated band. The increments in the isotope abundance ratios were found to be proportional to the mass differences of the isotopes. The observed e-values per unit mass difference (ε/ΔM) were 1.26 x 10-4 (at 20 °C), 1.85 x 10-4 (at 25 °C) and 2.4 x 10-4 (at 40 °C). The mass spectrometry was improved by using a low temperature for the evaporation of CaI2.

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3

Yergey, Alfred L., Steven A. Abrams, Nancy E. Vieira, Richard Eastell, Laura S. Hillman y David G. Covell. "Recent studies of human calcium metabolism using stable isotopic tracers". Canadian Journal of Physiology and Pharmacology 68, n.º 7 (1 de julio de 1990): 973–76. http://dx.doi.org/10.1139/y90-147.

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Stable isotopes of calcium are used safely as tracers for calcium in human populations ranging in age from infants to postmenopausal women. Thermal ionization mass spectrometry is used to measure calcium isotope ratios with relative accuracies of about 1% for natural abundance ratios at precisions of about 1% relative to the mean. Perturbations of natural abundance ratios are determined for the calcium in blood, urine, and feces with a limit of detection of about 2 Δ% excess. The mathematical rationale for clinical studies of fractional absorption of dietary calcium and the kinetics of calcium's internal distribution are presented.Key words: calcium, tracers, stable isotopes, mass spectrometry.

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4

Zhao, Hongyu y Junhua Huang. "Characteristics of Calcium Isotopes at Different Water Depths and Their Palaeoenvironmental Significance for Carbonate Rocks of the Permian-Triassic Boundary in Chibi, Southern China". Minerals 12, n.º 11 (14 de noviembre de 2022): 1440. http://dx.doi.org/10.3390/min12111440.

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Calcium isotopes of carbonate rocks can trace calcium cycles and record changes in the marine environment. As published calcium isotope profiles of carbonate rocks at the Permian-Triassic boundary are rare, comparative studies on deep-water profiles were lacking for the major extinction event that occurred during this time. We present sections of different water depths in the Chibi area of southern China that we have selected for a comparative study. We analyzed carbon isotopes, calcium isotopes, as well as major and trace elements of carbonates from two sections (Chibi North and Chibi West) to obtain information on the volcanic activity, ocean acidification, as well as sea level rise and fall in the Chibi area during the mass extinction period. All carbon and calcium isotopes of carbonates from both sections are all negative after the mass extinction boundary. Carbonates from the Chibi North section have higher δ44/40Ca values and lower Sr/Ca ratios than the rocks from the Chibi West section. We propose that the negative bias of the calcium isotopes in the two sections result from diagenesis. Diagenesis transforms primary aragonite into calcite, showing the characteristics of high δ44/40Ca value and low Sr/Ca. By comparing our data with three published profiles of shallow-water carbonate rock, we recognize that calcium isotopes record gradients at different water depths. In the slope environment, the enhancement of pore fluid action near the coast caused an increase of the fluid buffer alteration, and we propose that a regression event occurred in the Chibi region during the Late Permian.

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5

Han, Guilin, Anton Eisenhauer, Jie Zeng y Man Liu. "Calcium Biogeochemical Cycle in a Typical Karst Forest: Evidence from Calcium Isotope Compositions". Forests 12, n.º 6 (25 de mayo de 2021): 666. http://dx.doi.org/10.3390/f12060666.

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In order to better constrain calcium cycling in natural soil and in soil used for agriculture, we present the δ44/40Ca values measured in rainwater, groundwater, plants, soil, and bedrock samples from a representative karst forest in SW China. The δ44/40Ca values are found to differ by ≈3.0‰ in the karst forest ecosystem. The Ca isotope compositions and Ca contents of groundwater, rainwater, and bedrock suggest that the Ca of groundwater primarily originates from rainwater and bedrock. The δ44/40Ca values of plants are lower than that of soils, indicating the preferential uptake of light Ca isotopes by plants. The distribution of δ44/40Ca values in the soil profiles (increasing with soil depth) suggests that the recycling of crop-litter abundant with lighter Ca isotope has potential effects on soil Ca isotope composition. The soil Mg/Ca content ratio probably reflects the preferential plant uptake of Ca over Mg and the difference in soil maturity. Light Ca isotopes are more abundant in mature soils than nutrient-depleted soils. The relative abundance in the light Ca isotope (40Ca) is in the following order: farmland > burnt grassland > forests > grassland > shrubland. Our results further indicate that biological fractionation in a soil–plant system is a vital factor for Ca–geochemical transformations in soil surface systems.

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6

Gordon, Gwyneth W., Jorge Monge, Melanie B. Channon, Qing Wu, Joseph L. Skulan, Ariel D. Anbar y Rafael Fonseca. "Calcium Isotopic Composition and Its Association With Multiple Myeloma Disease Activity". Blood 122, n.º 21 (15 de noviembre de 2013): 3157. http://dx.doi.org/10.1182/blood.v122.21.3157.3157.

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Abstract Multiple myeloma (MM) is characterized by clonal proliferation of a neoplastic plasma cell and its production of a monoclonal immunoglobulin; evolving from an asymptomatic pre-malignant stage named monoclonal gammopathy of undetermined significance (MGUS). At the time of diagnosis with MM, lytic lesions are present in approximately 70-80% of patients. Lytic lesions increase the risk for skeletal related events as well as treatment costs, while lowering quality of life and overall survival. Metastatic bone surveys underestimate bone disease since plain radiographs demonstrate abnormalities until at least 30% of trabecular bone has been lost and cannot provide information about ongoing bone remodeling. Bone scintigraphy lacks usefulness in following bone disease due to decreased osteoblast activity in MM, while Dual-energy X-ray absorptiometry scans produce heterogeneous local bone mineral density changes and are not recommended to evaluate bone disease in these patients. Biomarkers (eg, N- and C-terminal telopeptides of type I collagen) have been used to assess bone metabolism balance (BMB; ie, the difference between bone formation and resorption) in MM prior and subsequent to specific therapies, however, consensus is still lacking and their clinical utility is uncertain. Calcium in nature consists of six isotopes, and the relative abundance of the isotopes varies measurably. The strength of molecular bonds depends on atomic weight of the participating atoms. Calcium (Ca) containing compounds react at different rates depending on atomic mass. Bone formation favors lighter isotopes of Ca, depleting soft tissue of light Ca isotopes, while bone resorption releases this isotopically light Ca back into soft tissue with little or no selectivity. As a result of this difference in isotope fractionation, Ca isotopic composition in soft tissue should shift to heavier Ca isotope values in positive BMB and lighter values in negative BMB. In order to identify whether Ca isotopic composition can be used as a marker of myeloma-induced bone disease, we first set out to determine its association with MM disease activity. Using multiple collector inductively coupled plasma mass spectrometry, we determined the Ca isotopic composition in 108 peripheral blood samples from 54 patients with monoclonal gammopathies. Ca isotopic composition was determined as the ratio between the naturally occurring 44Ca and 42Ca isotopes (δ44/42Ca) relative to a standard in parts per ten thousand units, as previously described by Morgan et al. Disease activity was determined at the time of δ44/42Ca determination by assessing disease status and response to treatment, as described by the International Myeloma Working Group uniform response criteria, defining progressive or relapsed disease as active disease, and stable or responsive disease as non-active. Categorical variables were analyzed using chi squared or Fisher’s exact test, interval variables were analyzed using a one-tailed t-test. A repeated measures logistic regression model was developed using a cross-sectional time-series generalized estimating equation. All statistical analysis was done using Stata/SE 12.0. Fifty-four adult patients (61% male) diagnosed with monoclonal gammopathy, ranging from MGUS (n=1) to SMM (n=4) to MM (n=49), were assessed at different time points, with 7 patients being assessed once, 41 were assessed twice, 5 were assessed 3 times, while 1 patient was assessed 4 times. Mean age at the time of first assessment was 66, ranging from 45 to 84. Mean δ44/42Ca was statistically lower in the active disease group as compared to the non-active group (-0.7536 vs -0.6564, p=0.0466). In a statistically significant repeated measurement logistic regression model (p= 0.0239), δ44/42Ca is associated with active disease (OR=0. 054, p=0.031, 95% CI=0.004-0.765) after adjusting for age, gender, presence of anemia, serum creatinine, free light chain ratio, current bisphosphonate and current anti-myeloma therapy. A lower δ44/42Ca in the active disease group might suggest a link between a more intense level of bone resorption and myeloma activity. Ca isotopic composition can become part of the clinician’s arsenal to determine disease status in a patient with MM. In order to further characterize δ44/42Ca to specifically infer myeloma-induced bone disease activity, further studies that include serum biomarkers and dynamic imaging should be performed. Disclosures: Gordon: Arizona State University: “Application of Ca isotope analysis to the early detection of metastatic cancer” (AzTE reference number M13-117) Patents & Royalties; Arizona State University: “Isotopic biomarkers for rapid assessment of bone mineral balance in biomedical applications” (US Application #PCT/US2011/039780; AzTE reference number M10-102L), “Isotopic biomarkers for rapid assessment of bone mineral balance in biomedical applications” (US Application #PCT/US2011/039780; AzTE reference number M10-102L) Patents & Royalties. Skulan:AZTE: “Application of Ca isotope analysis to the early detection of metastatic cancer” (AzTE reference number M13-117) Patents & Royalties; AZTE: “Isotopic biomarkers for rapid assessment of bone mineral balance in biomedical applications” (US Application #PCT/US2011/039780; AzTE reference number M10-102L), “Isotopic biomarkers for rapid assessment of bone mineral balance in biomedical applications” (US Application #PCT/US2011/039780; AzTE reference number M10-102L) Patents & Royalties. Anbar:Arizona State University: “Isotopic biomarkers for rapid assessment of bone mineral balance in biomedical applications” (US Application #PCT/US2011/039780; AzTE reference number M10-102L), “Isotopic biomarkers for rapid assessment of bone mineral balance in biomedical applications” (US Application #PCT/US2011/039780; AzTE reference number M10-102L) Patents & Royalties; Arizona State University: “Application of Ca isotope analysis to the early detection of metastatic cancer” (AzTE reference number M13-117) Patents & Royalties. Fonseca:AMGEN: Consultancy; Millennium: Consultancy; Binding Site: Consultancy; Onyx: Consultancy, Research Funding; Lilly: Consultancy; BMS: Consultancy; Genzyme: Consultancy; Celgene: Consultancy; Medtronic: Consultancy; Otsuka: Consultancy; Cylene: Research Funding; Prognostication of MM based on genetic categorization of the disease: Patents & Royalties.

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7

Oi, Takao, Kunihiko Sato y Kazuki Umemoto. "Oxygen and Hydrogen Isotopic Preference in Hydration Spheres of Magnesium and Calcium Ions". Zeitschrift für Naturforschung A 68, n.º 5 (1 de mayo de 2013): 362–70. http://dx.doi.org/10.5560/zna.2012-0122.

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Molecular orbital calculations were performed to estimate the 18O/16O and D/H isotopic reduced partition function ratios (rpfrs) of water molecules around magnesium and calcium ions. As model for water molecules in the ith hydration sphere of the cation in aqueous solutions containing that cation, we considered water molecules in the ith hydration sphere that were surrounded by water molecules in the (i+1)th hydration sphere in clusters, M2+(H2O)n (M = Mg or Ca; n up to 100). The calculations indicated that the decreasing order of the 18O preference over 16O in the primary hydration sphere is Mg2+ > Ca2+ > bulk water. That is, water molecules in the primary hydration spheres of the Mg2+ and Ca2+ ions are expected to be enriched in the heavier isotope of oxygen relative to water molecules in bulk, and the degree of the enrichment is larger for the Mg2+ ion than for the Ca2+ ion. No such preference was observed for hydrogen isotopes in any hydration sphere or for oxygen isotopes in the secondary and outer hydration spheres.

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8

Schwarzschild, Bertram M. "Weighing exotic calcium isotopes". Physics Today 66, n.º 9 (septiembre de 2013): 15–17. http://dx.doi.org/10.1063/pt.3.2104.

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9

Amsellem, Elsa, Frédéric Moynier, Hervé Bertrand, Amaury Bouyon, João Mata, Sebastian Tappe y James M. D. Day. "Calcium isotopic evidence for the mantle sources of carbonatites". Science Advances 6, n.º 23 (junio de 2020): eaba3269. http://dx.doi.org/10.1126/sciadv.aba3269.

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The origin of carbonatites—igneous rocks with more than 50% of carbonate minerals—and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with O and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle.

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10

Kumar, P. V. Kiran, M. Sankari y M. V. Suryanarayana. "Isotope selective near-resonant two-photon ionization of calcium isotopes". Journal of Physics D: Applied Physics 40, n.º 1 (15 de diciembre de 2006): 288–93. http://dx.doi.org/10.1088/0022-3727/40/1/028.

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11

Jahn, A., K. Lindsay, X. Giraud, N. Gruber, B. L. Otto-Bliesner, Z. Liu y E. C. Brady. "Carbon isotopes in the ocean model of the Community Earth System Model (CESM1)". Geoscientific Model Development 8, n.º 8 (5 de agosto de 2015): 2419–34. http://dx.doi.org/10.5194/gmd-8-2419-2015.

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Abstract. Carbon isotopes in the ocean are frequently used as paleoclimate proxies and as present-day geochemical ocean tracers. In order to allow a more direct comparison of climate model results with this large and currently underutilized data set, we added a carbon isotope module to the ocean model of the Community Earth System Model (CESM), containing the cycling of the stable isotope 13C and the radioactive isotope 14C. We implemented the 14C tracer in two ways: in the "abiotic" case, the 14C tracer is only subject to air–sea gas exchange, physical transport, and radioactive decay, while in the "biotic" version, the 14C additionally follows the 13C tracer through all biogeochemical and ecological processes. Thus, the abiotic 14C tracer can be run without the ecosystem module, requiring significantly fewer computational resources. The carbon isotope module calculates the carbon isotopic fractionation during gas exchange, photosynthesis, and calcium carbonate formation, while any subsequent biological process such as remineralization as well as any external inputs are assumed to occur without fractionation. Given the uncertainty associated with the biological fractionation during photosynthesis, we implemented and tested three parameterizations of different complexity. Compared to present-day observations, the model is able to simulate the oceanic 14C bomb uptake and the 13C Suess effect reasonably well compared to observations and other model studies. At the same time, the carbon isotopes reveal biases in the physical model, for example, too sluggish ventilation of the deep Pacific Ocean.

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12

Jahn, A., K. Lindsay, X. Giraud, N. Gruber, B. L. Otto-Bliesner, Z. Liu y E. C. Brady. "Carbon isotopes in the ocean model of the Community Earth System Model (CESM1)". Geoscientific Model Development Discussions 7, n.º 6 (6 de noviembre de 2014): 7461–503. http://dx.doi.org/10.5194/gmdd-7-7461-2014.

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Abstract. Carbon isotopes in the ocean are frequently used as paleo climate proxies and as present-day geochemical ocean tracers. In order to allow a more direct comparison of climate model results with this large and currently underutilized dataset, we added a carbon isotope module to the ocean model of the Community Earth System Model (CESM), containing the cycling of the stable isotope 13C and the radioactive isotope 14C. We implemented the 14C tracer in two ways: in the "abiotic" case, the 14C tracer is only subject to air–sea gas exchange, physical transport, and radioactive decay, while in the "biotic" version, the 14C additionally follows the 13C tracer through all biogeochemical and ecological processes. Thus, the abiotic 14C tracer can be run without the ecosystem module, requiring significantly less computational resources. The carbon isotope module calculates the carbon isotopic fractionation during gas exchange, photosynthesis, and calcium carbonate formation, while any subsequent biological process such as remineralization as well as any external inputs are assumed to occur without fractionation. Given the uncertainty associated with the biological fractionation during photosynthesis, we implemented and tested three parameterizations of different complexity. Compared to present-day observations, the model is able to simulate the oceanic 14C bomb uptake and the 13C Suess effect reasonably well compared to observations and other model studies. At the same time, the carbon isotopes reveal biases in the physical model, for example a too sluggish ventilation of the deep Pacific Ocean.

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13

Nörtershäuser, W., N. Trautmann, K. Wendt y B. A. Bushaw. "Isotope shifts and hyperfine structure in the transitions of stable calcium isotopes and calcium-41". Spectrochimica Acta Part B: Atomic Spectroscopy 53, n.º 5 (mayo de 1998): 709–21. http://dx.doi.org/10.1016/s0584-8547(98)00108-6.

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14

Gibbs, W. R. y J. P. Dedonder. "Neutron radii of the calcium isotopes". Physical Review C 46, n.º 5 (1 de noviembre de 1992): 1825–33. http://dx.doi.org/10.1103/physrevc.46.1825.

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15

REYNARD, L. M., J. A. PEARSON, G. M. HENDERSON y R. E. M. HEDGES. "CALCIUM ISOTOPES IN JUVENILE MILK-CONSUMERS". Archaeometry 55, n.º 5 (27 de agosto de 2012): 946–57. http://dx.doi.org/10.1111/j.1475-4754.2012.00715.x.

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16

Antonelli, Michael A., Tushar Mittal, Anders McCarthy, Barbara Tripoli, James M. Watkins y Donald J. DePaolo. "Ca isotopes record rapid crystal growth in volcanic and subvolcanic systems". Proceedings of the National Academy of Sciences 116, n.º 41 (23 de septiembre de 2019): 20315–21. http://dx.doi.org/10.1073/pnas.1908921116.

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Kinetic calcium isotope effects can be used as growth-rate proxies for volcanic and subvolcanic minerals. Here, we analyze Ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects (>2‰) can occur during magmatic plagioclase crystallization. Experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase Ca diffusivity (R/D). Plagioclase phenocrysts from the 1915 Mount Lassen rhyodacite eruption, the ∼650-y-old Deadman Creek Dome eruption, and several mafic subvolcanic orbicules and plagioclase comb layers from Northern California have disequilibrium Ca isotopic compositions that suggest rapid crystal growth rates (>1 cm/y to 15 cm/y). The Ca isotope results, combined with complementary crystal-size distribution analyses, suggest that magmatic rejuvenation (and eruption) events, as reflected in crystal growth times, can be as short as ∼10−3 y. Although mafic systems are predicted to have shorter magmatic rejuvenation periods, we find similarly short timescales in both mafic and silicic systems. These results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption. By focusing on a common mineral such as plagioclase, this approach can be applied across all major magmatic compositions, suggesting that Ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions.

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17

Chen, Zhensheng, Ian J. Griffin, Yana L. Kriseman, Lily K. Liang y Steven A. Abrams. "Inductively Coupled Plasma Mass Spectrometric Analysis of Calcium Isotopes in Human Serum: A Low-Sample-Volume Acid-Equilibration Method". Clinical Chemistry 49, n.º 12 (1 de diciembre de 2003): 2050–55. http://dx.doi.org/10.1373/clinchem.2003.025692.

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Abstract Background: Analytical methods for measuring the calcium isotope distribution in enriched human serum samples that use low blood volumes, simple preparation methods, and rapid analysis are important in clinical studies of calcium kinetics. Previously, sample preparation by oxalate precipitation typically required 500 μL of serum. This method was time-consuming, and the blood volume required was limiting in circumstances when only a small amount of serum could be obtained. Methods: Serum was collected from humans who were administered 42Ca, and 20 μL of serum was mixed with 2 mL of 0.22–0.67 mol/L HNO3 at room temperature for between 1 min and 16 h. The 42Ca/43Ca ratio in the supernatant was measured by a magnetic sector inductively coupled plasma mass spectrometer (ICP-MS). Calcium isotope ratios from these equilibration solutions were compared with data from oxalate-precipitated serum samples to determine the optimum equilibrium time and the effect of acid concentration on equilibrium. Results: Various amounts of aggregated particles developed in different acid-serum mixtures. These affected the time required for isotope equilibration in the mixture. The shortest equilibrium time needed for the calcium isotopes varied from 1 to 6 h for samples acidified with 0.22–0.45 mol/L HNO3. Data obtained from these solutions were consistent with data from oxalate-precipitated calcium. The precision of 42Ca/43Ca ratio measurements was better than 0.5%. Conclusions: We have developed a simple, rapid sample preparation technique for ICP-MS analysis in which 20 μL of serum can be used for accurate measurement of the calcium isotope distribution in a sample with good precision and a rapid analysis time.

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Humphrey, John D. y C. Reid Ferring. "Stable Isotopic Evidence for Latest Pleistocene and Holocene Climatic Change in North-Central Texas". Quaternary Research 41, n.º 2 (marzo de 1994): 200–213. http://dx.doi.org/10.1006/qres.1994.1022.

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AbstractA paleoclimatic record for a southern Great Plains locality (the Aubrey Clovis site in north-central Texas) has been established using stable carbon and oxygen isotopes. Detailed composite stratigraphic sections, constrained by 14 C ages, place the age of these deposits between 14,200 and 1600 yr B.P. Calcium carbonate samples of lacustrine and pedogenic origin were analyzed. Oxygen isotopic compositions of most of these in situ carbonates reflect equilibrium precipitation from local meteoric waters. Oxygen isotope values reflect changes in the composition of meteoric waters tied to changes in the isotopic composition of moisture derived from the Gulf of Mexico. Oxygen isotopic variability at the Aubrey site is coincident with marine isotopic records from the gulf that vary due to changes in Laurentide ice sheet volume and meltwater influx. The stable carbon isotopic record, reflecting changing biomass through time, corroborates humid versus arid interpretations based on sedimentology and rates of alluviation. A middle Holocene arid period was in contrast to moist early and late Holocene climate, affirming interpretations of other workers studying southern Great Plains Holocene climate history.

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Martin, Jeremy E., Derek Vance y Vincent Balter. "Magnesium stable isotope ecology using mammal tooth enamel". Proceedings of the National Academy of Sciences 112, n.º 2 (22 de diciembre de 2014): 430–35. http://dx.doi.org/10.1073/pnas.1417792112.

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Geochemical inferences on ancient diet using bone and enamel apatite rely mainly on carbon isotope ratios (δ13C) and to a lesser extent on strontium/calcium (Sr/Ca) and barium/calcium (Ba/Ca) elemental ratios. Recent developments in nontraditional stable isotopes provide an unprecedented opportunity to use additional paleodietary proxies to disentangle complex diets such as omnivory. Of particular relevance for paleodietary reconstruction are metals present in large quantity in bone and enamel apatite, providing that biologically mediated fractionation processes are constrained. Calcium isotope ratios (δ44Ca) meet these criteria but exhibit complex ecological patterning. Stable magnesium isotope ratios (δ26Mg) also meet these criteria but a comprehensive understanding of its variability awaits new isotopic data. Here, 11 extant mammal species of known ecology from a single locality in equatorial Africa were sampled for tooth enamel and, together with vegetation and feces, analyzed for δ26Mg, δ13C, Sr/Ca, and Ba/Ca ratios. The results demonstrate that δ26Mg incorporated in tooth enamel becomes heavier from strict herbivores to omnivores/faunivores. Using data from experimentally raised sheep, we suggest that this26Mg enrichment up the trophic chain is due to a26Mg enrichment in muscle relative to bone. Notably, it is possible to distinguish omnivores from herbivores, using δ26Mg coupled to Ba/Ca ratios. The potential effects of metabolic and dietary changes on the enamel δ26Mg composition remain to be explored but, in the future, multiproxy approaches would permit a substantial refinement of dietary behaviors or enable accurate trophic reconstruction despite specimen-limited sampling, as is often the case for fossil assemblages.

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Tacail, Théo, Béatrice Thivichon-Prince, Jeremy E. Martin, Cyril Charles, Laurent Viriot y Vincent Balter. "Assessing human weaning practices with calcium isotopes in tooth enamel". Proceedings of the National Academy of Sciences 114, n.º 24 (30 de mayo de 2017): 6268–73. http://dx.doi.org/10.1073/pnas.1704412114.

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Weaning practices differ among great apes and likely diverged during the course of human evolution, but behavioral inference from the fossil record is hampered by a lack of unambiguous biomarkers. Here, we show that early-life dietary transitions are recorded in human deciduous tooth enamel as marked variations in Ca isotope ratios (δ44/42Ca). Using a sequential microsampling method along the enamel growth axis, we collected more than 150 enamel microsamples from 51 deciduous teeth of 12 different modern human individuals of known dietary histories, as well as nine enamel samples from permanent third molars. We measured and reconstructed the evolution of 44Ca/42Ca ratios in enamel from in utero development to first months of postnatal development. We show that the observed variations of δ44/42Ca record a transition from placental nutrition to an adult-like diet and that Ca isotopes reflect the duration of the breastfeeding period experienced by each infant. Typically, the δ44/42Ca values of individuals briefly or not breastfed show a systematic increase during the first 5–10 mo, whereas individuals with long breastfeeding histories display no measurable variation in δ44/42Ca of enamel formed during this time. The use of Ca isotope analysis in tooth enamel allows microsampling and offers an independent approach to tackle challenging questions related to past population dynamics and evolution of weaning practices in hominins.

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Schulze, Kerry J., Kimberly O. O’Brien, Emily L. Germain-Lee, Sarah L. Booth, Amanda Leonard y Beryl J. Rosenstein. "Calcium Kinetics Are Altered in Clinically Stable Girls with Cystic Fibrosis". Journal of Clinical Endocrinology & Metabolism 89, n.º 7 (1 de julio de 2004): 3385–91. http://dx.doi.org/10.1210/jc.2003-031879.

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Abstract Reduced bone mass in individuals with cystic fibrosis (CF) may result from alterations in calcium metabolism. Bone calcium deposition and resorption rates, calcium balance, and markers of bone turnover were assessed using stable isotopes of calcium in 22 prepubertal and pubertal girls with CF. Bone calcium deposition was associated with the availability of dietary calcium, total serum osteocalcin, and leptin concentrations. Reduced bone mass in individuals with CF may result from inadequate bone calcium (Ca) deposition, and excessive resorption, although these parameters have not been directly assessed in children with CF. We used stable Ca isotopes to measure rates of bone Ca deposition (Vo+), resorption, and retention in 22 clinically stable girls with CF (aged 7–18 yr). Rates of bone Ca deposition were determined by mathematically modeling the disappearance of iv Ca stable isotope (42Ca) for 6 d post dosing. Indirect markers of bone turnover and hormones associated with pubertal development were also assessed. Rates of bone Ca deposition and retention were highest during early puberty (Tanner stages 2 and 3). Calcium deposition rates in prepubertal (Tanner 1) and postmenarchal girls (Tanner stages 4 and 5) did not support substantial bone Ca retention. Net absorption of dietary Ca and serum osteocalcin and leptin concentrations were positively associated with Vo+. Time post menarche and serum leptin concentrations explained 91% of the variability in Vo+ (P = 0.0007). Serum total osteocalcin was low (10.9 ± 5.4 ng/ml), and a substantial percentage of osteocalcin was undercarboxylated (54.3 ± 11.8%). We concluded that increased calcium absorption and serum leptin concentrations were significantly associated with rates of bone Ca deposition, demonstrating an impact of nutritional status on this process. Rates of bone Ca deposition were lower than typically reported in healthy children, as were indirect markers of bone formation. These alterations in bone turnover contribute to reduced bone mass in girls with CF.

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22

Hassler, A., J. E. Martin, R. Amiot, T. Tacail, F. Arnaud Godet, R. Allain y V. Balter. "Calcium isotopes offer clues on resource partitioning among Cretaceous predatory dinosaurs". Proceedings of the Royal Society B: Biological Sciences 285, n.º 1876 (11 de abril de 2018): 20180197. http://dx.doi.org/10.1098/rspb.2018.0197.

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Large predators are overabundant in mid-Cretaceous continental dinosaur assemblages of North Africa. Such unbalanced ecosystem structure involves, among predatory dinosaurs, typical abelisaurid or carcharodontosaurid theropods co-occurring with long-snouted spinosaurids of debated ecology. Here, we report calcium (Ca) isotope values from tooth enamel (expressed as δ 44/42 Ca) to investigate resource partitioning in mid-Cretaceous assemblages from Niger (Gadoufaoua) and Morocco (Kem Kem Beds). In both assemblages, spinosaurids display a distinct isotopic signature, the most negative in our dataset. This distinct taxonomic clustering in Ca isotope values observed between spinosaurids and other predators provides unambiguous evidence for niche partitioning at the top of the trophic chains: spinosaurids foraged on aquatic environments while abelisaurid and carcharodontosaurid theropods relied almost exclusively on terrestrial resources.

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23

Liu, Zhanmin, Congqiang Liu, Guilin Han, Zhongliang Wang, Zichen Xue, Zhaoliang Song y Cheng Yang. "Environmental geochemistry of calcium isotopes: Applications of a new stable isotope approach". Chinese Journal of Geochemistry 25, n.º 2 (abril de 2006): 184–94. http://dx.doi.org/10.1007/bf02872181.

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24

Griffin, Ian J. y Steven A. Abrams. "Methodological considerations in measuring human calcium absorption: relevance to study the effects of inulin-type fructans". British Journal of Nutrition 93, S1 (abril de 2005): S105—S110. http://dx.doi.org/10.1079/bjn20041344.

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During the last 50 years, a variety of methods have been developed to estimate Ca absorption in man. Mass balances were initially used, but these were unable to accurately measure fractional Ca absorption because they cannot distinguish unabsorbed dietary Ca from endogenous faecal Ca excretion (excretion of previously absorbed Ca back into the gut). A number of isotopic methods have been developed that can measure true fractional Ca absorption, employing radioisotopes, stable isotopes, or both. Different methods involve collection of urine, faecal or plasma samples. Of the currently available methods, the dual isotope tracer method with a timed urine collection is probably the most precise and reliable. It is also relatively straightforward to carry out and avoids the need for a faecal collection. The purpose of the present paper is to discuss the general advantages and disadvantages of the different methods of Ca absorption. In addition, the limitations the different methods have in examining the possible effects of non-digestible oligosaccharides on Ca absorption will be discussed.

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25

MA, CHUN-WANG, HUI-LING WEI y YU-QI LI. "THE SYSTEMATIC BEHAVIOR IN THE FRAGMENTS OF THE CALCIUM ISOTOPES PROJECTILE FRAGMENTATION". International Journal of Modern Physics E 19, n.º 08n09 (septiembre de 2010): 1545–52. http://dx.doi.org/10.1142/s0218301310015941.

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We have calculated the cross sections of the fragments produced in the projectile fragmentation of the even 36–52 Ca isotopes using the statistical abrasion-ablation model. The isospin effect in the projectile fragmentation are studied by investigating the peak positions and the widths of the fragment isotopic cross section distributions. The peak positions of the fragments isotopic cross section distributions have good linear correlation to the Z of the fragments and the correlations are fitted using the linear function. The correlations between slopes b and the binding energies of the neutron ( S n) of the projectile nuclei, the differences between the binding energies of the neutron and proton( S n- S p) of the projectile nuclei and the neutron-skin thickness (δnp) are studied. It is found that b and δnp has a good linear correlation for the neutron-rich projectile nuclei.

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26

Chambers, J., E. Zaremba, J. P. Adams y B. Castel. "Pygmy dipole resonances in the calcium isotopes". Physical Review C 50, n.º 6 (1 de diciembre de 1994): R2671—R2674. http://dx.doi.org/10.1103/physrevc.50.r2671.

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27

Cheng-Rui, Ching, Ho Tso-Hsiu y Zou Bing-Song. "Pion double-charge-exchange on calcium isotopes". Journal of Physics G: Nuclear and Particle Physics 17, n.º 8 (1 de agosto de 1991): 1203–8. http://dx.doi.org/10.1088/0954-3899/17/8/010.

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28

Antonelli, Michael A. y Justin I. Simon. "Calcium isotopes in high-temperature terrestrial processes". Chemical Geology 548 (agosto de 2020): 119651. http://dx.doi.org/10.1016/j.chemgeo.2020.119651.

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29

Smith, David L., Curtis Atkin y Christof Westenfelder. "Stable isotopes of calcium as tracers: methodology". Clinica Chimica Acta 146, n.º 1 (febrero de 1985): 97–101. http://dx.doi.org/10.1016/0009-8981(85)90129-9.

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30

Zhu, Peng y J. Douglas Macdougall. "Calcium isotopes in the marine environment and the oceanic calcium cycle". Geochimica et Cosmochimica Acta 62, n.º 10 (mayo de 1998): 1691–98. http://dx.doi.org/10.1016/s0016-7037(98)00110-0.

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31

Reynard, L. M., C. C. Day y G. M. Henderson. "Large fractionation of calcium isotopes during cave-analogue calcium carbonate growth". Geochimica et Cosmochimica Acta 75, n.º 13 (julio de 2011): 3726–40. http://dx.doi.org/10.1016/j.gca.2011.04.010.

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32

Ali, Ahmed H. "Investigation of the Quadrupole Moment and Form Factors of Some Ca Isotopes". Baghdad Science Journal 17, n.º 2 (11 de mayo de 2020): 0502. http://dx.doi.org/10.21123/bsj.2020.17.2.0502.

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Nuclear shell model is adopted to calculate the electric quadrupole moments for some Calcium isotopes 20Ca (N = 21, 23, 25, and 27) in the fp shell. The wave function is generated using a two body effective interaction fpd6 and fp space model. The one body density matrix elements (OBDM) are calculated for these isotopes using the NuShellX@MSU code. The effect of the core-polarizations was taken through the theory microscopic by taking the set of the effective charges. The results for the quadrupole moments by using Bohr-Mottelson (B-M) effective charges are the best. The behavior of the form factors of some Calcium isotopes was studied by using Bohr-Mottelson (B-M) effective charges.

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33

Davidsson, Lena, Jill Mackenzie, Peter Kastenmayer, Peter J. Aggett y Richard F. Hurrell. "Zinc and calcium apparent absorption from an infant cereal: a stable isotope study in healthy infants". British Journal of Nutrition 75, n.º 2 (febrero de 1996): 291–300. http://dx.doi.org/10.1017/bjn19960131.

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AbstractFractional apparent absorption of Zn and Ca from a wheat-milk-based infant cereal was studied in six healthy infants (18-30 weeks old). Mineral absorption was measured by a stable-isotope technique based on faecal excretion of the isotopes. Each test meal (40 g cereal) was extrinsically labelled with 70Zn and 42Ca before intake. All faecal material passed during the 21 d following intake of the labelled test meal was collected on trace-element-free nappies. Individual stool samples were analysed for their content of ‘OZn and 42Ca by thermal ionization mass spectrometry. Apparent absorption was calculated as intake minus total faecal excretion of the isotopes over 68-92 h after administration. The fractional apparent absorption values for Zn and Ca were 33.9 (SD 164) % (range 19.2-639 %) and 53.5 (SD 12.6) %) (range 36.7-71.7 %) respectively. Re-excretion of absorbed 70Zn (> 68-92 h to 21 d after intake of the labelled meal) was 044 (SD 038) %] of administered dose while only one infant re-excreted detectable amounts of 42Ca (1.74%) of administered dose). The analysis of individual stool samples confirmed that 72 h is a sufficient time period for complete collections of non-absorbed isotopes in faecal material from infants during the weaning period and that re-excretion of initially absorbed 70Zn and 42Ca (> 68-92 h to 21 d after intake of the labelled meal) is negligible.

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34

Adloff, Markus, Andy Ridgwell, Fanny M. Monteiro, Ian J. Parkinson, Alexander J. Dickson, Philip A. E. Pogge von Strandmann, Matthew S. Fantle y Sarah E. Greene. "Inclusion of a suite of weathering tracers in the cGENIE Earth system model – muffin release v.0.9.23". Geoscientific Model Development 14, n.º 7 (5 de julio de 2021): 4187–223. http://dx.doi.org/10.5194/gmd-14-4187-2021.

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Abstract. The metals strontium (Sr), lithium (Li), osmium (Os) and calcium (Ca), together with their isotopes, are important tracers of weathering and volcanism – primary processes which shape the long-term cycling of carbon and other biogeochemically important elements at the Earth's surface. Traditionally, because of their long residence times in the ocean, isotopic shifts in these four elements observed in the geologic record are almost exclusively interpreted with the aid of isotope-mixing, tracer-specific box models. However, such models may lack a mechanistic description of the links between the cycling of the four metals to other geochemically relevant elements, particularly carbon, or climate. Here we develop and evaluate an implementation of Sr, Li, Os and Ca isotope cycling in the Earth system model cGENIE. The model offers the possibility to study the dynamics of these metal systems alongside other more standard biogeochemical cycles, as well as their relationship with changing climate. We provide examples of how to apply this new model capability to investigate Sr, Li, Os and Ca isotope dynamics and responses to environmental change, for which we take the example of massive carbon release to the atmosphere.

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35

Skulan, Joseph, Thomas Bullen, Ariel D. Anbar, J. Edward Puzas, Linda Shackelford, Adrian LeBlanc y Scott M. Smith. "Natural Calcium Isotopic Composition of Urine as a Marker of Bone Mineral Balance". Clinical Chemistry 53, n.º 6 (1 de junio de 2007): 1155–58. http://dx.doi.org/10.1373/clinchem.2006.080143.

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Abstract Background: We investigated whether changes in the natural isotopic composition of calcium in human urine track changes in net bone mineral balance, as predicted by a model of calcium isotopic behavior in vertebrates. If so, isotopic analysis of natural urine or blood calcium could be used to monitor short-term changes in bone mineral balance that cannot be detected with other techniques. Methods: Calcium isotopic compositions are expressed as δ44Ca, or the difference in parts per thousand between the 44Ca/40Ca of a sample and the 44Ca/40Ca of a standard reference material. δ44Ca was measured in urine samples from 10 persons who participated in a study of the effectiveness of countermeasures to bone loss in spaceflight, in which 17 weeks of bed rest was used to induce bone loss. Study participants were assigned to 1 of 3 treatment groups: controls received no treatment, one treatment group received alendronate, and another group performed resistive exercise. Measurements were made on urine samples collected before, at 2 or 3 points during, and after bed rest. Results: Urine δ44Ca values during bed rest were lower in controls than in individuals treated with alendronate (P <0.05, ANOVA) or exercise (P <0.05), and lower than the control group baseline (P <0.05, t-test). Results were consistent with the model and with biochemical and bone mineral density data. Conclusion: Results confirm the predicted relationship between bone mineral balance and calcium isotopes, suggesting that calcium isotopic analysis of urine might be refined into a clinical and research tool.

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36

Dill, Harald G. y Friedhelm Henjes-Kunst. "Strontium (87Sr/86Sr) and calcium isotope ratios (44Ca/40Ca-44Ca/42Ca) of the Miocene Dam Formation in Qatar: tools for stratigraphic correlation and environment analysis". GeoArabia 12, n.º 3 (1 de julio de 2007): 61–76. http://dx.doi.org/10.2113/geoarabia120361.

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ABSTRACT The Dam Formation in Qatar is a series consisting of calcareous (calcite, dolomite) and evaporitic sediments (gypsum, celestite) that developed under subtidal through supratidal conditions passing towards younger and older series in an environment of deposition more akin to modern beach deposits. In the present study 87Sr/86Sr ratios, δ44/40Ca and δ44/42Ca data are discussed together with δ13C and δ18O values obtained during an environmental analysis carried out previously. Rather uniform isotope curves of the Sr, Ca and O isotopes for tidal deposits are replaced by more oscillating ones when these tidal-influenced regimes became substituted for by a more wave-dominated regime. Calcium isotope ratios still at its infancy and not fully understood seem to provide a new tool in carbonate petrography when it comes to an interpretation of the environment of deposition and calcification of dolomitic series. The Sr isotopes not only indicate an influx of more primitive Sr from the hinterland but also allow for a refinement of the stratigraphy, which yields a late Aquitanian to early Burdigalian age of sedimentation for the Dam Formation in Qatar.

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37

Lindau, Filipe G. L., Jefferson C. Simões, Barbara Delmonte, Patrick Ginot, Giovanni Baccolo, Chiara I. Paleari, Elena Di Stefano et al. "Giant dust particles at Nevado Illimani: a proxy of summertime deep convection over the Bolivian Altiplano". Cryosphere 15, n.º 3 (16 de marzo de 2021): 1383–97. http://dx.doi.org/10.5194/tc-15-1383-2021.

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Abstract. A deeper understanding of past atmospheric circulation variability in the Central Andes is a high-priority topic in paleoclimatology mainly because of the necessity to validate climate models used to predict future precipitation trends and to develop mitigation and/or adaptation strategies for future climate change scenarios in this region. Within this context, we here investigate an 18-year firn core drilled at Nevado Illimani in order to interpret its mineral dust record in relation to seasonal processes, in particular atmospheric circulation and deep convection. The core was dated by annual layer counting based on seasonal oscillations of dust, calcium, and stable isotopes. Geochemical and mineralogical data show that dust is regionally sourced in winter and summer. During austral summer (wet season), an increase in the relative proportion of giant dust particles (∅>20 µm) is observed, in association with oscillations of stable isotope records (δD, δ18O). It seems that at Nevado Illimani both the deposition of dust and the isotopic signature of precipitation are influenced by atmospheric deep convection, which is also related to the total amount of precipitation in the area. This hypothesis is corroborated by regional meteorological data. The interpretation of giant particle and stable isotope records suggests that downdrafts due to convective activity promote turbulent conditions capable of suspending giant particles in the vicinity of Nevado Illimani. Giant particles and stable isotopes, when considered together, can be therefore used as a new proxy for obtaining information about deep convective activity in the past.

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38

Malikov, Sh R., M. B. Yuldashev y O. O. Amanov. "Prospects for the application of nuclear reactor with homogeneous solution fuel for the production of medical radioisotopes". Journal of Physics: Conference Series 2642, n.º 1 (1 de noviembre de 2023): 012006. http://dx.doi.org/10.1088/1742-6596/2642/1/012006.

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Abstract The use of isotopes in medicine has opened up new possibilities for the diagnosis and treatment of many diseases. One of the effective radiopharmaceuticals is the strontium-89 isotope, which is used to treat many cancers, including bone cancer. Spreading and sorbing in the bone tissue (as an analog of calcium), strontium has both therapeutic and long-term analgesic effects. This allows you to do without drugs and saves the patient from severe drug addiction. Therefore, obtaining the radioisotope strontium-89 is a very serious task.

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39

Gussone, Nikolaus, Anne-Sofie C. Ahm, Kimberly V. Lau y Harold J. Bradbury. "Calcium isotopes in deep time: Potential and limitations". Chemical Geology 544 (junio de 2020): 119601. http://dx.doi.org/10.1016/j.chemgeo.2020.119601.

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40

In, Eun Jin, Youngman Kim, Panagiota Papakonstantinou y Seung-Woo Hong. "Shape Coexistence in Isotopes from Oxygen to Calcium". Journal of the Korean Physical Society 77, n.º 11 (20 de noviembre de 2020): 966–70. http://dx.doi.org/10.3938/jkps.77.966.

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41

Throwe, T. G., S. E. Vigdor, W. W. Jacobs, M. C. Green, C. W. Glover, T. E. Ward y B. P. Hichwa. "Near-threshold (p→,π−) reactions on calcium isotopes". Physical Review C 35, n.º 3 (1 de marzo de 1987): 1083–98. http://dx.doi.org/10.1103/physrevc.35.1083.

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42

Oi, Takao, Norio Morioka, Hideki Ogino, Hidetake Kakihana y Morikazu Hosoe. "Fractionation of Calcium Isotopes in Cation-Exchange Chromatography". Separation Science and Technology 28, n.º 11-12 (agosto de 1993): 1971–83. http://dx.doi.org/10.1080/01496399308016727.

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43

Whiticar, Michael J., Erwin Suess, Gerold Wefer y Peter J. Müller. "Calcium Carbonate Hexahydrate (Ikaite): History of Mineral Formation as Recorded by Stable Isotopes". Minerals 12, n.º 12 (17 de diciembre de 2022): 1627. http://dx.doi.org/10.3390/min12121627.

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Calcium carbonate hexahydrate (ikaite) is a rare mineral that forms as metastable species in the organic-carbon-rich sediments of the King George Basin, Bransfield Strait, Antarctica, as a consequence of early diagenetic decomposition of organic matter under cold water (−1.4 °C) and high pressure (200 bar) conditions. Large crystals grow in the sediment immediately below the diagenetic transition between microbial sulfate reduction and methanogenesis at ~320 cm below sea floor (bsf). This process is reflected in the dissolved sulfate, total carbon dioxide, and methane concentrations, as well as in the carbon, hydrogen, and oxygen isotope chemistries of the interstitial fluids and dissolved gases of the host sediment. The ikaite crystal faithfully records in its zonal structure the changing carbon isotope ratio of the total dissolved carbon dioxide pool as it gradually diminishes during methanogenesis (δ13Cikaite = −17.5 to −21.4‰). These changes in the crystal’s host environment follow general Rayleigh carbon isotope fractionation. The oxygen isotopes of the ikaite carbonate (δ18Oikaite = 1.46 to 4.45‰) also show a strong zonal distribution, unrelated to temperature of formation, but perhaps controlled by the degree of recrystallization of ikaite to calcite. The crystal water of the ikaite is depleted 11‰ in 2H/1H (VSMOW) relative to the coexisting interstitial water, which is in excellent agreement with the isotope fractionation of other hydrated minerals. In addition to the in situ temperature and pressure, nucleation of the ikaite crystals in the Bransfield Basin sediments may be induced by the high alkalinity, high phosphate concentrations, and dissolved organic compounds. Intense microbial metabolism generates such compounds; of these, aspartic acid and glutamic acid may play an important role, as they do in biological and extracellular carbonate mineral precipitation. All indications are that low temperatures (such as of polar environments), high calcium carbonate supersaturation caused by interstitial methanogenesis, and a sufficiently large supply of dissolved phosphate and amino acids favor metastable ikaite formation. These conditions, modified by recrystallization, may be preserved in calcite glendonites, thinolites, and other calcitic pseudomorphs derived from ikaite and found throughout the ancient sedimentary record.

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44

Beazley, Melanie J., Richard D. Rickman, Debra K. Ingram, Thomas W. Boutton y Jon Russ. "Natural Abundances of Carbon Isotopes (14C, 13C) in Lichens and Calcium Oxalate Pruina: Implications for Archaeological and Paleoenvironmental Studies". Radiocarbon 44, n.º 3 (2002): 675–83. http://dx.doi.org/10.1017/s0033822200032124.

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Radiocarbon ages of calcium oxalate that occurs naturally on rock surfaces have been used recently in archaeological and paleoenvironmental studies. Oxalate rock coatings are found globally, with most appearing to be residues from epilithic lichens. To explore the source(s) of carbon used by these organisms for the production of oxalate we measured the natural abundances of 14C and 13C in 5 oxalate-producing lichen species, 3 growing on limestone in southwestern Texas and 2 on sandstone in Arkansas. We also examined the distribution of the isotopes between the calcium oxalate and lichen tissues by separating these components and measuring the 13C/C independently. The results demonstrate that the limestone species were slightly enriched in 14C, by 1.7%, relative to the sandstone species, which suggests that “dead” carbon from the limestone substrate does not constitute a significant source of carbon for the production of oxalate. The calcium oxalate produced by the lichens is also enriched in 13C by 6.5% compared to the lichen tissues, demonstrating that there is a large carbon isotope discrimination during oxalate biosynthesis. These results support the reliability of 14C ages of calcium oxalate rock coatings used for archaeological and paleoclimate studies.

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45

Gui, Jianye y Wei Zou. "A New Sample Processing Protocol for Separation and Purification Enabling Precise Analysis of Various Non-Traditional Isotopes in Geological Samples with Low Concentrations". Separations 10, n.º 9 (12 de septiembre de 2023): 497. http://dx.doi.org/10.3390/separations10090497.

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Many non-traditional isotopes, such as chlorine, magnesium, calcium, etc., are widely used as groundwater tracers. A new sample processing protocol of purification and concentration for isotopic analysis is presented to overcome many of the major drawbacks of existing methods. Contemporary sample preparation often requires several laborious off-line procedures in a ultra clean laboratory prior to instrumental determination; additionally, interference ions in real samples are difficult to completely remove, especially when the concentration of those ions is equal to that of the target ions. The new protocol includes the following steps: (i) one-step purification using a newly developed isotopic preparative chromatograph (IPC) with a background suppressed mode to obtain extremely pure components that only have target ions and H2O; (ii) enrichment of the collected pure solution from the previous step using a newly developed ultra clean concentrator filled with high purity nitrogen; (iii) transforming the enriched target ion into suitable speciation inside the ultra clean concentrator; (iv) finally, sending the enriched solutions to a multi-collector inductively coupled-plasma mass-spectrometer (MC-ICP-MS) or thermal ionization mass spectrometer (TIMS). The present method was validated using certified reference materials and real samples for both chlorine and magnesium; the precision of chlorine ratio value was generally below 0.22‰ and that of Mg was below 0.12‰. This processing protocol provides a potential method for isotope sample preparation and analysis in a small number of geological samples with low concentrations of many other elements or compounds such as nitrate, sulfate, lithium, calcium, strontium, etc.

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46

Rasbury, E. Troy y N. Gary Hemming. "Boron Isotopes: A “Paleo-pH Meter” for Tracking Ancient Atmospheric CO2". Elements 13, n.º 4 (1 de agosto de 2017): 243–48. http://dx.doi.org/10.2138/gselements.13.4.243.

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The boron isotope composition of calcium carbonate shells of marine organisms has the unique potential to record surface ocean pH, allowing the calculation of atmospheric pCO2 due to the established relationship between pH and the partial pressure of (atmospheric) CO2 (pCO2). This “paleo-pH meter” allows scientists to produce a record of the natural fluctuations of atmospheric pCO2 over geologic time, which will help us better understand the impacts of the recent anthropogenic addition of CO2 to Earth's atmosphere. Towards this end, a tremendous effort to understand the systematics of boron uptake in marine carbonates is underway. Here, we review the potential of boron isotopes to constrain ocean pH and, thus, atmospheric pCO2.

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47

Shatalov, Oleg A., Maxim E. Grigoryev, Alexander A. Bukhvostov y Dmitry A. Kuznetsov. "A Nuclear Spin Selective Control over the DNA Repair Key Enzyme Might Renovate the Cancer–Fight Paradigm. DNA Polymerase Beta to Engage with a Magnetic Isotope Effect". JOURNAL OF ADVANCES IN CHEMISTRY 4, n.º 3 (12 de diciembre de 2008): 554–62. http://dx.doi.org/10.24297/jac.v4i3.953.

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DNA Polymerase Beta (EC 2.7.7.7) is found to be operated by magnetic isotope effect (MIE) of Calcium once the Mg2+ ions replaced with the stable 43Ca2+ isotopes inside the enzyme catalytic sites. The isotope mentioned is the only paramagnetic species of the Calcium isotopic set with a 0.135 natural abundance value and the negative 7/2 nuclear spin providing a nuclear magnetic moment equal to 1.317 Bohr magnetons. As compared to the Mg/40Ca substitution, a 2.25-fold enzyme inhibition has been shown to provethe43Ca-MIE dependent mode of the catalysis turning down.An ion-radical mechanism based on the singlet – triplet conversion of the enzyme generated intermediates (ion-radical pairs) is found to be engaged once the paramagnetic metal isotope involved into the catalysis studied.The MIE promotes a primary reaction in DNA synthesis constituting in electron transfer between the ion – radical forming partners, [Ca(H2O)n2+] and [Ca2+(dNTP)]. Once the metal isotope substitution takes place inside just one of two DNA Polymerase Beta catalytic sites, a consequent43Ca – promoted inhibition leads to a residual synthesis of shorted DNA fragments that counts 25 – 35 nucleotides in length contrasting with the 180n – 210n DNA produced by either intact or40Ca – loaded polymerase. Being occurred simultaneously with a marked MIE – promoted enzyme inhibition, this fact itself makes possible to consider these short (“size-invalid”) DNA segments hardly efficient in the DNA base – excision repair. The latter is a survival factor in leukemic cells where the DNApolβ was found overexpressed. That supports a standpoint considering theDNApolβ a legitimate target for antitumor agents since its inhibition deprives the malignant cell from a DNA base – excision repair in neoplasma. A possible trend making role of these data in the current developments on a novel concept - establishing chemical background for cancer therapies is in a focus.

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48

Jacks, Gunnar, Göran Åberg y P. Joseph Hamilton. "Calcium Budgets for Catchments as Interpreted by Strontium Isotopes". Hydrology Research 20, n.º 2 (1 de abril de 1989): 85–96. http://dx.doi.org/10.2166/nh.1989.0007.

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Strontium isotopes in precipitation, soil and runoff water can be used to establish a ratio of wet plus dry deposited Sr to Sr released by weathering. This ratio is especially enhanced in areas with old acid Proterozoic rocks (0.6-2.5 Ga) and Archean rocks (>2.5 Ga). Since Sr and Ca behave in an analogous way in the coniferous forest ecosystem the results for Sr can be used for the determination of Ca. If the deposition of calcium can be calculated reasonably accurately the weathering rate can also be estimated. Five catchments have been investigated using this approach. Three of them seem to be close to a steady state, wherein the losses and gains of calcium to the system are equal. In the two southern-most catchments there seems to be an ongoing loss of exchangeable calcium. The loss by runoff occurs with sulphate being the dominant anion. Weathering rates of 1.5 to 4.8 kg Ca/ha year have been estimated.

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49

Al-Paruany, Kamal B., Saadi Al-Naseri y Al-Hassen F. Al-Ajena. "DISTRIBUTION OF ENVIRONMENTAL ISOTOPES IN THE EUPHRATES RIVER BETWEEN QAIM – FALLUJA, WESTERN IRAQ". Iraqi Geological Journal 50, n.º 1 (30 de junio de 2017): 12–27. http://dx.doi.org/10.46717/igj.50.1.2ms-2017-06-24.

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The environmental isotopes composition of water (δ18O, δ2Hand 3H) and hydrochemistry concentration were measured seasonally at eight stations along Euphrates River within the study area for two periods (January–Augustm, 2014) to study temporal special variations of these isotopes. The results of isotopes values showed there is a little difference between the periods due to the seasonal change and the trend of distribution can be attributed to evaporation and drainage flow. Generally the river water has positive d-excess, which indicates the vapor source of the Mediterranean moisture sources in January, while a low d-excess associated with enriched isotopic values, which typically occurs during August, 2014. The Euphrates River water, is fresh (TDS < 0.39 g/L) and has slight increase in its salinity levels during the last two decades. Generally the chemical facies changes from a calciummagnesium and bicarbonate type towards a sodium-chloride type to calcium sulfate. River salinity increases according to rock type, lake water, evaporation and human activity, and relatively higher toward downstream stations. The absence of management and a working drainage system, together with irrigation under high evaporation rates and low discharge, are the primary reasons for the continuous deterioration of water quality.

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50

Maurer, G., S. J. Portugal, I. Boomer y P. Cassey. "Avian embryonic development does not change the stable isotope composition of the calcite eggshell". Reproduction, Fertility and Development 23, n.º 2 (2011): 339. http://dx.doi.org/10.1071/rd10138.

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The avian embryo resorbs most of the calcium for bone formation from the calcite eggshell but the exact mechanisms of the resorption are unknown. The present study tested whether this process results in variable fractionation of the oxygen and carbon isotopes in shell calcium carbonate, which could provide a detailed insight into the temporal and spatial use of the eggshell by the developing embryo. Despite the uncertainty regarding changes in stable isotope composition of the eggshell across developmental stages or regions of the shell, eggshells are a popular resource for the analysis of historic and extant trophic relationships. To clarify how the stable isotope composition varies with embryonic development, the δ13C and δ18O content of the carbonate fraction in shells of black-headed gull (Larus ridibundus) eggs were sampled at four different stages of embryonic development and at five eggshell regions. No consistent relationship between the stable isotope composition of the eggshell and embryonic development, shell region or maculation was observed, although shell thickness decreased with development in all shell regions. By contrast, individual eggs differed significantly in isotope composition. These results establish that eggshells can be used to investigate a species’ carbon and oxygen sources, regardless of the egg’s developmental stage.

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