Isotopes of hydrogen (3H, 2H) and oxygen (18O) are perfect candidates for groundwater tracers. A survey of isotopic composition of 34 groundwater samples and one Lake from Vojvodina region (Serbia) is presented here. Tritium activity concentration and stable isotope composition (δ2H, δ18O), as well as deuterium excess, were determined. The groundwater samples lie on the groundwater regression line. Minor deviations and a few lower deuterium excess values indicate waters recharged in a different climate regime and subjected to evaporation, respectively. According to the obtained results, most of the analyzed groundwater can be characterized as modern waters, recharged mostly from precipitation.
Journal of Thermal Analysis and Calorimetry - A novel series of complexes ML(ClO4)·nH2O (M: Co, Ni, Cu, Zn; HL: 2-[(E)-(1H-1,2,4-triazol-3-ylimino)methyl]phenol) have been synthesized and... 相似文献
A smoothing method for solving stochastic linear complementarity problems is proposed. The expected residual minimization reformulation of the problem is considered, and it is approximated by the sample average approximation (SAA). The proposed method is based on sequential solving of a sequence of smoothing problems where each of the smoothing problems is defined with its own sample average approximation. A nonmonotone line search with a variant of the Barzilai–Borwein (BB) gradient direction is used for solving each of the smoothing problems. The BB search direction is efficient and low cost, particularly suitable for nonmonotone line search procedure. The variable sample size scheme allows the sample size to vary across the iterations and the method tends to use smaller sample size far away from the solution. The key point of this strategy is a good balance between the variable sample size strategy, the smoothing sequence and nonmonotonicity. Eventually, the maximal sample size is used and the SAA problem is solved. Presented numerical results indicate that the proposed strategy reduces the overall computational cost. 相似文献
A simple and reliable method for the determination of ascorbic acid (AA) is proposed and validated. It is based on potentiometric
monitoring of the concentration perturbations of an oscillatory reaction system in a stable nonequilibrium stationary state
close to the bifurcation point. The response of the Bray–Liebhafsky (BL) oscillatory reaction as a matrix, to the perturbation
by different concentrations of AA, is followed by a Pt electrode. The linear relationship between maximal potential shift
and the logarithm of the amount of AA is obtained between 0.01 and 1.0 μmol. The sensitivity of the proposed method (as the
limit of detection) is 0.009 μmol and the method has excellent sample throughput (30 samples per hour). The procedure was
used for AA determination in pharmaceutical formulations and urine. The results are in agreement with those obtained using
the official method. Some aspects of the possible mechanism of AA action on the BL oscillating chemical system are discussed. 相似文献
The absorption spectra of nine compounds structurally related to phenytoin (5,5-diphenylhydantoin) were recorded in twelve
solvents over the range of 200 to 400 nm. The effects of solvent dipolarity/polarizability and solvent/solute hydrogen bonding
interactions were analyzed by means of the linear solvation energy relationship (LSER) concept proposed by Kamlet and Taft.
The lipophilic activity of the investigated hydantoins was estimated by calculation of their log 10P values. The calculated values of log 10P were correlated with the ratio of the contributions of specific and non-specific solute/solvent interactions. The correlation
equations were combined with the corresponding ED50 values to generate new equations that demonstrate exact relationship between solute/solvent interactions and the structure-activity
parameters. 相似文献
Multiple-species plasma-stability testing and pharmacokinetic studies in rats and dogs were performed on LK-157, a novel 10-ethylidene tricyclic carbapenem and potent inactivator of β-lactamases of classes A, C, and D. An LC–MS–MS method was developed and validated for analysis of LK-157 in rat and dog plasma. Separation was achieved on a C18 column by gradient elution. The lower limit of quantification for LK-157 in plasma was 50 ng mL?1. Intra-day and inter-day precision were <12.5 and <11.8%, respectively. When degradation of LK-157 was assessed in buffer solutions and in rat, dog, and human plasma, the compound was found to be stable in pH 7.0–9.0 phosphate buffer for 24 h at room temperature, and in human plasma for 60 min at 37 °C. The stability of LK-157 was species-dependent. Results from study of in vitro metabolism showed that the enzymes liver cytochrome P450 and uridine diphosphate glycosyltransferase do not metabolize LK-157. LC–MS–MS was also successfully applied to a pharmacokinetic study. The pharmacokinetics of LK-157 after bolus intravenous administration (10 mg kg?1) to Wistar rats and Beagle dogs was described by a two-compartment pharmacokinetic model. Human pharmacokinetic data were extrapolated from dog pharmacokinetic data. The extrapolated human terminal-phase half-life of LK-157 was 2.3 h. Stability and pharmacokinetic data for LK-157 are in agreement with results for other inactivators of β-lactamases. 相似文献
It is proved, using a bootstrap argument, that linear instability implies nonlinear instability for the incompressible Navier-Stokes
equations in Lp for all p ∈ (1,∞) and any finite or infinite domain in any dimension n. 相似文献