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Wanner C.,Lawrence Berkeley National Laboratory | Peiffer L.,Lawrence Berkeley National Laboratory | Peiffer L.,University Nacionalautonoma Of Mexico | Sonnenthal E.,Lawrence Berkeley National Laboratory | And 3 more authors.
Geothermics | Year: 2014

A 2D reactive transport model of the Dixie Valley geothermal area in Nevada, USA was developed to assess fluid flow pathways and fluid rock interaction processes. The model includes two major normal faults and the incorporation of a dual continuum domain to simulate the presence of a small-scale thermal spring being fed by a highly permeable but narrow fracture zone. Simulations were performed incorporating fluid flow, heat conduction and advection, and kinetic mineral-water reactions. Various solute geothermometry methods were applied to simulated spring compositions, to compare estimated reservoir temperatures with "true" modeled reservoir temperatures, for a fluid ascending the simulated fracture and cooling on its way to the surface. Under the modeled conditions (cooling but no mixing or boiling), the classical Na-K(-Ca) geothermometers performed best because these are least affected by mineral precipitation upon cooling. Geothermometry based on computed mineral saturation indices and the quartz geothermometer were more sensitive to re-equilibration upon cooling, but showed good results for fluid velocities above ca. 0.1m/d and a reactive fracture surface area 1-2 orders of magnitude lower than the corresponding geometric surface area. This suggests that such upflow rates and relatively low reactive fracture surface areas are likely present in many geothermal fields. The simulations also suggest that the presence of small-scale fracture systems having an elevated permeability of 10-12 to 10-10m2 can significantly alter the shallow fluid flow regime of geothermal systems. For the Dixie Valley case, the model implies that such elevated permeabilities lead to a shallow (less than 1km) convection cell where superficial water infiltrates along the range front normal fault and connects the small-scale geothermal spring through basin filling sediments. Furthermore, we conclude that a fracture permeability on the order of 10-12m2 may lead to near surface temperature >100°C whereas a permeability of 10-10m2 is not realistic because this permeability led to extreme upflow velocities and to a short-circuit of the regional fault zone. © 2013 Elsevier Ltd. Source

Spycher N.,Lawrence Berkeley National Laboratory | Peiffer L.,Lawrence Berkeley National Laboratory | Peiffer L.,University Nacionalautonoma Of Mexico | Sonnenthal E.L.,Lawrence Berkeley National Laboratory | And 3 more authors.
Geothermics | Year: 2014

The previously developed and well-demonstrated mineral saturation geothermometry method is revisited with the objective to ease its application, and to improve the prediction of geothermal reservoir temperatures using full and integrated chemical analyses of geothermal fluids. Reservoir temperatures are estimated by assessing numerically the clustering of mineral saturation indices computed as a function of temperature. The reconstruction of the deep geothermal fluid compositions, and geothermometry computations, are implemented into one stand-alone program, allowing unknown or poorly constrained input parameters to be estimated by numerical optimization using existing parameter estimation software. The geothermometry system is tested with geothermal waters from previous studies, and with fluids at various degrees of fluid-rock chemical equilibrium obtained from laboratory experiments and reactive transport simulations. Such an integrated geothermometry approach presents advantages over classical geothermometers for fluids that have not fully equilibrated with reservoir minerals and/or that have been subject to processes such as dilution and gas loss. © 2013 Elsevier Ltd. Source

Hinojosa G.,University of Nevada, Reno | Hinojosa G.,University Nacionalautonoma Of Mexico | Covington A.M.,University of Nevada, Reno | Alna'Washi G.A.,University of Nevada, Reno | And 12 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

Photoionization of Kr+ ions was studied in the energy range from 23.3 to 39.0 eV at a photon energy resolution of 7.5 meV. Absolute measurements were performed by merging beams of Kr+ ions and of monochromatized synchrotron undulator radiation. Photoionization (PI) of this Br-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct PI continuum. Resonance features observed in the experimental spectra are spectroscopically assigned and their energies and quantum defects tabulated. The high-resolution cross-section measurements are benchmarked against state-of-the-art theoretical cross-section calculations from the Dirac-Coulomb R-matrix method. © 2012 American Physical Society. Source

Alvarez-Elias A.C.,Laboratorio Of Nefrologia Y Metabolismo Mineral Oseo | Garcia-Roca P.,Laboratorio Of Nefrologia Y Metabolismo Mineral Oseo | Velasquez-Jones L.,Hospital Infantil de Mexico Federico Gomez | Valverde S.,Hospital Infantil de Mexico Federico Gomez | And 3 more authors.
Transplantation Proceedings | Year: 2016

Background CYP3A5 gene polymorphism rs776746 has been associated with lower tacrolimus dose requirements and bioavailability in both adults and children. This variant causes a loss of CYP3A5 activity owing to a splice site variant leading to a truncated inactive enzyme. The aim of this study was to determine if the rs776746 gene polymorphism is related to the time to reach tacrolimus therapeutic levels in renal transplant children. Methods A prospective study was performed in renal transplant children receiving tacrolimus as part of their immunosuppressive regime. CYP3A5 genotype was determined by direct sequencing. Tacrolimus trough levels and serum creatinine at 1 week and 1 month after renal transplantation was obtained from clinical chart. Results A total of 42 patients were included; 19 (45.2%) were female, 23 (54.8%) received living-donor transplants, and 21 patients expressed CYP3A5∗1/∗1 or CYP3A5∗1/∗3. Tacrolimus dose was higher in expressers at week 1 (0.13 vs 0.10 mg/kg/d; P =.011), and week 4 after transplantation (0.17 vs 0.09 mg/kg/d; P <.0001). At 4 weeks after renal transplantation, only 9 patients from the expressers group (42.8%) had levels ≥7 ng/mL, in contrast to 18 in the nonexpressers group (85.7%; Fisher exact P =.008). Conclusions Tacrolimus dose was significant higher in functional CYP3A5 expressers. Only 42.8% of such expressers had tacrolimus trough levels ≥7 ng/mL at 1 month after transplantation despite dose adjustments. Long-term follow up is needed to address the consequences of early post-transplantation bioavailability differences due to CYP3A5 genotype. © 2016 Elsevier Inc. Source

Barcenas-Arguello M.-L.,Colegio de Mexico | Barcenas-Arguello M.-L.,University Nacionalautonoma Of Mexico | Gutierrez-Castorena M.C.D.C.,Colegio de Mexico | Terrazas T.,National Autonomous University of Mexico
Micron | Year: 2015

Mineral inclusions in plant cells are genetically regulated, have an ecological function and are used as taxonomic characters. In Cactaceae, crystals in epidermal and cortical tissues have been reported; however, few studies have conducted chemical and morphological analyses on these crystals, and even fewer have reported non-mineral calcium to determine its systematic value. Cephalocereus apicicephalium, C. totolapensis and C. nizandensis are Cactaceae species endemic to the Isthmus of Tehuantepec, Mexico with abundant epidermal prismatic crystals. In the present study, we characterize the mineral cell inclusions, including their chemical composition and their morphology, for three species of Cephalocereus. Crystals of healthy branches of the three species were isolated and studied. The crystals were identified by X-ray diffraction (XRD), their morphology was described using a petrographic and scanning electron microscope (SEM), and their elemental composition was measured with Energy Dispersive X-ray (EDXAR). The three species synthesized weddellite with different degrees of hydration depending on the species. The optical properties of calcium oxalate crystals were different from the core, which was calcium carbonate. We observed a large diversity of predominantly spherical forms with SEM. EDXAR analysis detected different concentrations of Ca and significant amounts of elements, such as Si, Mg, Na, K, Cl, and Fe, which may be related to the edaphic environment of these cacti. The occurrence of weddellite is novel for the genus according to previous reports. The morphological diversity of the crystals may be related to their elemental composition and may be a source of phylogenetic characters. © 2015 Elsevier Ltd. Source

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