A simple, selective and sensitive heavy atom-induced room temperature phosphorimetric method (HAI-RTP) is described for the determination of naproxen (NAP) in pharmaceutical preparations. The phosphorescence signals are a consequence of intermolecular protection when analytes are, exclusively, in presence of a heavy atom salt and sodium sulfite as an oxygen scavenger to minimize RTP quenching. These variables selection constitute the basis of a HAI-RTP method for the determination of naproxen (detection limit 17.6 ng ml(-1); 1.71% relative standard deviation at 250 ng ml(-1)). The method has been applied satisfactorily to the analysis of pharmaceutical preparations. 相似文献
Van Laars academic and research career was adversely affected by psychological traumas he experienced during his youth. Loss of his parents at a young age, submission to a hard discipline, and lack of a formal university education made van Laar emotionally unstable and gave him many enemies, among them van der Waals. Still, Van Laars scientific achievements have resulted in the transformation of mathematical chemistry into the independent subjects known today as chemical thermodynamics and theory of phase equilibria. Discussed here as well is Van Laars theory of solutions using the state of thermodynamics at his time and modern thermodynamic concepts. 相似文献
Heteroleptic nickel(II) complexes [NiL2L′] of a series of monoanionic and potentially bidentate N‐2‐pyridyl‐sulfonamide ligands [HL] and 2,2′‐bipyridine or 1,10‐Phenanthroline (L′) have been prepared by electrochemical oxidation of a nickel anode in an acetonitrile solution of the ligands. The complexes have been characterized by microanalysis, IR and electronic spectroscopy, magnetic measurements and LSI mass spectrometry. The crystal structure of [Ni(Ms6mepy)2(bipy)] has been determined by x‐ray diffraction and shows the metal in an octahedral NiN6 environment. Octahedral structures are also proposed for the other complexes with the N‐2‐pyridyl‐sulfonamide ligands acting as N,N′ or N, O bidentate systems, depending on the position of the methyl substituent on the pyridine ring. 相似文献
The diffusive and dynamic mechanical behavior of the DGEBA/1,3-BAC epoxy resin system was studied during water absorption. The diffusion of water was investigated at 100% relative humidity, by immersion of specimens in water at 60, 80 and 100°C. In all absorption experiments, water diffusion followed Fick's law. Diffusion coefficients and saturated water concentrations are given for these temperatures. The activation energy for diffusion was determined from the relationship between the diffusion coefficient and the reciprocal of the absolute temperature. The value obtained was 31.2 kJ mol–1. Dynamic mechanical analysis of samples immersed in 100°C water and with various water contents showed both a shift of Tg, defined by thetan peak, to lower temperatures and a slight decrease in the dynamic modulus in the presence of water. These effects are probably a result of plasticization.This work was supported by the Xunta de Galicia through grant XUGA-17201A92. 相似文献
The electrical and magnetic properties of the tetragonal phase SmCuOSe are reported as a function of the temperature. The optical properties were studied by means of diffuse reflectance spectrum in the UV-Vis range. The electrical resistivity measurements as well as diffuse reflectance spectrum show that SmCuOSe is a semiconductor with an optical band gap (Eg) of 2.6 eV. In this phase, Cu is at its monovalent oxidation state and, as such, it does not contribute to the total magnetic moment, whereas Sm is in its 3+ oxidation state, with a large VanVleck contribution due to the admixture of the fundamental state with higher energy levels. 相似文献
In this paper, an inventory problem where the inventory cycle must be an integer multiple of a known basic period is considered. Furthermore, the demand rate in each basic period is a power time-dependent function. Shortages are allowed but, taking necessities or interests of the customers into account, only a fixed proportion of the demand during the stock-out period is satisfied with the arrival of the next replenishment. The costs related to the management of the inventory system are the ordering cost, the purchasing cost, the holding cost, the backordering cost and the lost sale cost. The problem is to determine the best inventory policy that maximizes the profit per unit time, which is the difference between the income obtained from the sales of the product and the sum of the previous costs. The modeling of the inventory problem leads to an integer nonlinear mathematical programming problem. To solve this problem, a new and efficient algorithm to calculate the optimal inventory cycle and the economic order quantity is proposed. Numerical examples are presented to illustrate how the algorithm works to determine the best inventory policies. A sensitivity analysis of the optimal policy with respect to some parameters of the inventory system is developed. Finally, conclusions and suggestions for future research lines are given.
This article studies a posteriori error analysis of fully discrete finite element approximations for semilinear parabolic optimal control problems. Based on elliptic reconstruction approach introduced earlier by Makridakis and Nochetto [25], a residual based a posteriori error estimators for the state, co-state and control variables are derived. The space discretization of the state and co-state variables is done by using the piecewise linear and continuous finite elements, whereas the piecewise constant functions are employed for the control variable. The temporal discretization is based on the backward Euler method. We derive a posteriori error estimates for the state, co-state and control variables in the $L^\infty(0,T;L^2(\Omega))$-norm. Finally, a numerical experiment is performed to illustrate the performance of the derived estimators. 相似文献
The title compound, formula C15H20O2, is orthorhombic, P212121 witha=8.747(2),b=12.025(3),c=12.554(3)Å,Z=4, andDm=1.32(2)g/ml. The structural analysis shows that the compound corresponds to eudesma-4(15),7(11)-dien-8,12-olide, a sesquiterpene lactone previously isolated fromAster umbellatus but whose crystal structure was unknown. 相似文献
LetM be a compact orientable surface,I:M R4 an immersion of classCr and
a normal unitary smooth vector field. We prove that in the space of pairs (I,
) the family of pairs all whose umbilical points are Darbouxian is generic. 相似文献