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101.
Simultaneous determination of betamethasone and dexamethasone residues in bovine liver by liquid chromatography/tandem mass spectrometry 总被引:1,自引:0,他引:1
Van Den Hauwe O Perez JC Claereboudt J Van Peteghem C 《Rapid communications in mass spectrometry : RCM》2001,15(11):857-861
In this study a new method for the simultaneous confirmation of betamethasone and dexamethasone residues in bovine liver is presented. A Quattro LCZ triple quadrupole mass spectrometer, equipped with an atmospheric pressure ionization (API) source, was coupled to a high performance liquid chromatograph (HPLC) system. Spiked liver samples were first extracted with acetonitrile, and the extracts were purified on C-18 columns. LC separations were performed on a Hypercarb column, with acetonitrile/water (90:10, v/v, +0.3% formic acid) as the mobile phase. Retention times for dexa- and betamethasone were 6.60 and 8.50 min, respectively. Fluorometholone had a retention time of 6.70 min and was used as the internal standard. The detection of the analytes was performed in the multiple reaction monitoring (MRM) mode. The assay was linear over the range of 0.5 to 8 microg/kg for both analytes. The estimated determination limits were 0.2 microg/kg for both beta- and dexamethasone and the quantification limits were 0.4 microg/kg for dexamethasone and 0.3 microg/kg for betamethasone. Analysis precision at 1, 2 and 4 microg/kg was lower than 6.1% (relative standard deviation, RSD) and accuracy was at least 97.5%. Recoveries at 1, 2 and 4 microg/kg ranged between 56 and 69%. 相似文献
102.
Abstract The retinal Schiff base of bacteriorhodopsin, in the purple membrane from Halobacterium halobium , can be cleaved by hydroxylamine in the presence of light. We have further investigated this reaction with a series of O -substituted hydroxylamines, RONH2 , where R = -H (HA), -CH3 (MHA), -SO3 − (HAS), benzyl- (BHA), p -nitrobenzyl- (NBHA), and pentafluorobenzyl- (FBHA). All except MHA caused light-induced bleaching of the purple membrane and the chromophore could be regenerated from apomembrane and all- trans retinal. Relative bleaching rate constants were obtained from V = QI a k 0 X /( k r + k 0 X ), where V = bleaching rate, Q = quantum yield, I a = absorbed light intensity, X = hydroxylamine concentration, k 0 = rate constant for bleaching and k r = rate constant for return of photoexcited bacteriorhodopsin to the initial state. This equation fits the time-, concentration- and intensity-dependences of the bleaching reactions in 0.02 M phosphate, pH 7.0. The rate constants k 0 relative to HA were: MHA: 0; HAS: 0.3; HA: 1.0; BHA: 1.8; FBHA: 10.1; NBHA: 10.8. The relative rate constants do not correlate with the basicity of the derivatives. Instead, the results suggest that the retinal Schiff base is near a non-polar cavity into which an aromatic group can be inserted. 相似文献
103.
Danny Sugrue 《Journal of Pure and Applied Algebra》2019,223(7):3112-3128
The Cantor–Bendixson rank of a topological space X is a measure of the complexity of the topology of X. We will be interested primarily in the case that the space is profinite: Hausdorff, compact and totally disconnected. In this paper, we prove that the injective dimension of the abelian category of sheaves of -modules over a profinite space X is determined by the Cantor–Bendixson rank of X. 相似文献
104.
School STEM Culture—an aspect of culture within a school community—is defined as the beliefs, values, practices, and resources in STEM fields as perceived by students, parents, teachers, and administrators and counselors within a school. This study validates the STEM Culture Assessment Tool (STEM‐CAT), an instrument intended to advance the use of the School STEM Culture construct within the research community. Internal consistency was determined through the use of Cronbach's alpha and factor analyses, and the instrument was found to be a reliable measure of School STEM Culture. The instrument can be used in future research to quantify School STEM Culture to determine if interventions change the culture of a school to further STEM education. 相似文献
105.
We investigate the conjecture that every circulant graph X admits a k‐isofactorization for every k dividing |E(X)|. We obtain partial results with an emphasis on small values of k. © 2006 Wiley Periodicals, Inc. J Combin Designs 14: 406–414, 2006 相似文献
106.
Öznur Yaşar Danny Dyer David A. Pike Margo Kondratieva 《Discrete Applied Mathematics》2009,157(8):1913-1923
In traditional edge searching one tries to clean all of the edges in a graph employing the least number of searchers. It is assumed that each edge of the graph initially has a weight equal to one. In this paper we modify the problem and introduce the Weighted Edge Searching Problem by considering graphs with arbitrary positive integer weights assigned to its edges. We give bounds on the weighted search number in terms of related graph parameters including pathwidth. We characterize the graphs for which two searchers are sufficient to clear all edges. We show that for every weighted graph the minimum number of searchers needed for a not-necessarily-monotonic weighted edge search strategy is enough for a monotonic weighted edge search strategy, where each edge is cleaned only once. This result proves the NP-completeness of the problem. 相似文献
107.
The central result of this paper is an explicit computation of the Hochschild and cyclic homologies of a natural smooth subalgebra of stable continuous trace algebras having smooth manifolds X as their spectrum. More precisely, the Hochschild homology is identified with the space of differential forms on X, and the periodic cyclic homology with the twisted de Rham cohomology of X, thereby generalising some fundamental results of Connes and Hochschild-Kostant-Rosenberg. The Connes-Chern character is also identified here with the twisted Chern character. 相似文献
108.
In this paper, we study the problems of (approximately) representing a functional curve in 2-D by a set of curves with fewer
peaks. Representing a function (or its curve) by certain classes of structurally simpler functions (or their curves) is a
basic mathematical problem. Problems of this kind also find applications in applied areas such as intensity-modulated radiation
therapy (IMRT). Let f\bf f be an input piecewise linear functional curve of size n. We consider several variations of the problems. (1) Uphill–downhill pair representation (UDPR): Find two nonnegative piecewise
linear curves, one nondecreasing (uphill) and one nonincreasing (downhill), such that their sum exactly or approximately represents
f\bf f. (2) Unimodal representation (UR): Find a set of unimodal (single-peak) curves such that their sum exactly or approximately
represents f\bf f. (3) Fewer-peak representation (FPR): Find a piecewise linear curve with at most k peaks that exactly or approximately represents f\bf f. Furthermore, for each problem, we consider two versions. For the UDPR problem, we study its feasibility version: Given ε>0, determine whether there is a feasible UDPR solution for f\bf f with an approximation error ε; its min-ε version: Compute the minimum approximation error ε
∗ such that there is a feasible UDPR solution for f\bf f with error ε
∗. For the UR problem, we study its min-k version: Given ε>0, find a feasible solution with the minimum number k
∗ of unimodal curves for f\bf f with an error ε; its min-ε version: given k>0, compute the minimum error ε
∗ such that there is a feasible solution with at most k unimodal curves for f\bf f with error ε
∗. For the FPR problem, we study its min-k version: Given ε>0, find one feasible curve with the minimum number k
∗ of peaks for f\bf f with an error ε; its min-ε version: given k≥0, compute the minimum error ε
∗ such that there is a feasible curve with at most k peaks for f\bf f with error ε
∗. Little work has been done previously on solving these functional curve representation problems. We solve all the problems
(except the UR min-ε version) in optimal O(n) time, and the UR min-ε version in O(n+mlog m) time, where m<n is the number of peaks of f\bf f. Our algorithms are based on new geometric observations and interesting techniques. 相似文献
109.
Danny Dolev Manfred K Warmuth 《Journal of Algorithms in Cognition, Informatics and Logic》1984,5(1):48-59
The existence of a schedule for a partially ordered set of unit length tasks on m identical processors is known to be NP-complete (J. D. Ullman, NP-complete scheduling problems, J. Comput. System Sci., 10 (1975), 384–393). The problem remains NP-complete even if we restrict the precedence graph to be of height bounded by a constant. (J. K. Lenkstra and A. H. G. Rinnooy Kan, Complexity of scheduling under precedence constraints, Operations Res., 26 (1978), 22–35; D. Dolev and M. K. Warmuth, “Scheduling Flat Graphs,” IBM Research Report RJ 3398, 1982). In these NP-completeness proofs the upper bound on the number of available processors varies with the problem instance. We present a polynomial algorithm for the case where the upper bound on the number of available processors and the height of the precedence graph are both constants. 相似文献
110.
Rudolph A. Abramovitch Suchet S. Mathur Daniel W. Saunders Danny P. Vanderpool 《Tetrahedron letters》1980,21(8):705-708
Pyridinium -toluenesulfonylmethylide serves as a formyl anion equivalent and, in the presence of an alcohol, undergoes 1,4-addition to -substituted maleimides to give alkoxy- (or aryloxy)-methylene-succinimides. The protected aldehyde group can be liberated readily. 相似文献