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71.
Fidel Allende Sandra Solari Carmen Campino Cristian A. Carvajal Carlos F. Lagos Andrea Vecchiola Carolina Valdivia René Baudrand Gareth I. Owen Carlos E. Fardella 《Chromatographia》2014,77(7-8):637-642
Cortisol homeostasis is implicated in hypertension and metabolic syndrome. Two enzymes modulate cortisol availability; 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) preferentially converts inactive cortisone to cortisol, whereas 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) converts cortisol to cortisone. In contrast, 5α and 5β reductases inactivate cortisol by conversion to its tetrahydrometabolites: tetrahydrocortisol, allo-tetrahydrocortisol and tetrahydrocortisone. A subtle local increase in cortisol can be detected by measuring 24-h urine metabolites, LC–MS/MS being the reference method. The 11β-HSD2 activity is assessed based on the cortisol/cortisone ratio, and the 11β-HSD1 activity on the (tetrahydrocortisol + allo-tetrahydrocortisol)/tetrahydrocortisone ratio. To better understand hypertension and/or metabolic syndrome pathogenesis a method for simultaneous determination of cortisol, cortisone, tetrahydrocortisol, allo-tetrahydrocortisol and tetrahydrocortisone was developed and validated in an LC coupled with the new detector AB Sciex QTrap® 4500 tandem mass spectrometer. The steroids were extracted from 1 mL urine, using cortisol-D4 as internal standard. The quantification range was 0.1–120 ng/mL for cortisol and cortisone, and 1–120 ng/mL for tetrahydrometabolites, with >89 % recovery for all analytes. The coefficient of variation and accuracy was <10 %, and 85–105 %, respectively. Our LC–MS/MS method is accurate and reproducible in accordance with Food and Drug Administration guidelines, showing good sensitivity and recovery. This method allows the assessment of 11β-HSD2 and 11β-HSD1 activities in a single analytical run providing an innovative tool to explain etiology of misclassified essential hypertension and/or metabolic syndrome. 相似文献
72.
Noureddine Khiar Belén Suárez Michaela Stiller Victoria Valdivia Inmaculada Fernández 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5-6):1253-1258
Abstract New chiral mixed sulfur/phosphorus ligands derived from carbohydrates are reported. These ligands were found to be efficient catalyst precursors for palladium-catalyzed asymmetric substitution of 1,3-diphenylpropenyl acetate with dimethyl malonate or benzylamine (up to 96% ee), and for rhodium-catalyzed methyl acetamidocinnamate hydrogenation (up to 92% ee). 相似文献
73.
74.
F. Muñoz J. Rogan G. García M. Ramírez J. A. Valdivia R. Ramírez M. Kiwi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(1):87-93
Collision processes between a single gold atom and a gold cluster are investigated by means of ab initio
techniques. The targets we consider are minimum energy 13 gold atom clusters. The kinetic energy of the
projectile and its impact parameter are chosen within a range such that the three regimes we are mainly
interested in studying (fusion, scattering and fragmentation) are realized. The results of the collision
processes are treated using density functional theory molecular dynamics (DFT-MD), analyzed in detail, and
compared with previous work, which was carried out using phenomenological potentials and classical molecular
dynamics. The differences between classical MD and DFT-MD are quite significant. 相似文献
75.
Let Ω be a regular domain in the complex plane , . Let be the linear space over of the holomorphic functions f in Ω such that f(n) is bounded in Ω and is continuously extendible to the closure of Ω, n=0,1,2,… . We endow , in a natural manner, with a structure of Fréchet space and we obtain dense subspaces F of , with good topological linear properties, also satisfying that each function f of F, distinct from zero, does not extend holomorphically outside Ω. 相似文献
76.
James Wanliss Víctor Muñoz Denisse Pastén Benjamín Toledo Juan Alejandro Valdivia 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(9):167
We explore bursty multiscale energy dissipation from earthquakes flanked by latitudes 29° S and 35.5° S, and longitudes 69.501° W and 73.944° W (in the Chilean central zone). Our work compares the predictions of a theory of nonequilibrium phase transitions with nonstandard statistical signatures of earthquake complex scaling behaviors. For temporal scales less than 84 hours, time development of earthquake radiated energy activity follows an algebraic arrangement consistent with estimates from the theory of nonequilibrium phase transitions. There are no characteristic scales for probability distributions of sizes and lifetimes of the activity bursts in the scaling region. The power-law exponents describing the probability distributions suggest that the main energy dissipation takes place due to largest bursts of activity, such as major earthquakes, as opposed to smaller activations which contribute less significantly though they have greater relative occurrence. The results obtained provide statistical evidence that earthquake energy dissipation mechanisms are essentially “scale-free”, displaying statistical and dynamical self-similarity. Our results provide some evidence that earthquake radiated energy and directed percolation belong to a similar universality class. 相似文献
77.
Boundary element methods (BEM) based near-field acoustic holography (NAH) has been used successfully in order to reconstruct the normal velocity on an arbitrarily shaped structure surface from measurements of the pressure field on a nearby conformal surface. An alternative approach for this reconstruction on a general structure utilizes the equivalent sources method (ESM). In ESM the acoustic field is represented by a set of point sources located over a surface that is close to the structure surface. This approach is attractive mainly for its simplicity of implementation and speed. In this work ESM as an approximation of BEM based NAH is studied and the necessary conditions for the successful application of this approach in NAH is discussed. A cylindrical fuselage surface excited by a point force as an example to validate the results is used. 相似文献
78.
79.
Manuel Valdivia 《manuscripta mathematica》1974,14(3):241-247
80.
Manuel Valdivia 《Mathematische Zeitschrift》1981,177(4):463-478