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排序方式: 共有398条查询结果,搜索用时 187 毫秒
91.
Willy Brandal 《代数通讯》2013,41(11):3381-3391
Let R be a commutative ring and f a filter of ideals of R. We characterize when the Hausdorff completion of R with the f topology is a product of local Hausdorff completions. This generalizes a theorem of E. Matlis dealing with the completions of an integral domain relative to the topology of the classical torsion theory. 相似文献
92.
93.
When developing an LC-MS/MS-method matrix effects are a major issue. The effect of co-eluting compounds arising from the matrix can result in signal enhancement or suppression. During method development much attention should be paid to diminish matrix effects as much as possible. The present work evaluates matrix effects from aqueous environmental samples in the simultaneous analysis of a group of nine specific pharmaceuticals with LC-ESI/MS/MS: flubendazole, propiconazole, pipamperone, cinnarizine, ketoconazole, miconazole, rabeprazole, itraconazole and domperidone. Solutions to diminish signal suppression were examined: optimisation of the sample preparation, decrease of the flow rate, and the use of appropriate internal standards. Several SPE-stationary phases were tested in view of retention of the analytes: Oasis HLB, C8, Phenyl, Strata X-polymer RP sorbent and Strata X-polymeric SCX/RP sorbent. Oasis HLB showed the best retention for all analytes. The Oasis HLB SPE-method was optimised, but analyses showed high matrix suppression. Therefore, a second SPE-method, on a phenyl stationary phase (the second best option), was also optimised. A comparison of the matrix effect was made between the two procedures: the phenyl-method was less subject to matrix effects, however, the average matrix effect (ME%) of 46% indicated that matrix effects where still present. Several optimisation options for the phenyl-method were evaluated: addition of a ferric nitrate solution before extraction, application of an alkaline wash step, and use of a second SPE-cartridge, either a NH2-column or a florisil column. A more efficient sample clean-up was achieved by applying the extract after extraction on the phenyl column and after dilution with chloroform, onto a NH2-column (average ME%: 53%). In addition, applying a post-column split (1:5), further reduced matrix effects (average ME%: 65%). Labelled internal standards are the best way to tackle matrix effects, but no such internal standards were commercially available for the analytes of interest. The thorough search and application of four internal standards (structural analogues) was beneficial and compensates the matrix effect partially (average ME%: 83%). In an attempt to reduce the analysis time Speedisk phenyl columns were applied. Under these conditions matrix effects decreased even more while recoveries were between 91 and 109%. Different kinds of surface water samples were analyzed, and different matrix effects were observed. For this reason, standard addition will be used to perform quantitative analysis. 相似文献
94.
Dhooge W Arijs K D'Haese I Stuyvaert S Versonnen B Janssen C Verstraete W Comhaire F 《Analytical and bioanalytical chemistry》2006,386(5):1419-1428
In vitro assays are considered as the first step in a tiered approach to compound screening for hormonal activity. Although
many new assays have been developed in recent years, little attention has been paid towards assay validation. Our objective
was to identify critical experimental parameters in a yeast estrogen screen (YES) that affect its sensitivity and specificity.
We investigated the role of incubation time, solvent type, yeast inoculum growth stage and concentration on the outcome of
the YES. Compounds tested included new and established agonists, antagonists and negative controls, and results were evaluated
according to prefixed statistical criteria. In addition, we assessed the assay’s performance in a blind interlaboratory validation
exercise (IVE). An incubation time of five days was necessary to positively identify the estrogenic properties of all agonists
tested, when dissolved in DMSO. Longer incubation times were required when using an ethanol protocol. Similar estrogenic activity
was reported for benzyl butyl phthalate, bisphenol-A, methoxychlor, permethrin and genistein in the IVE. One out of the three
laboratories did not classify α,β-endosulfan, dissolved in DMSO, as an estrogen. The same was true for 4,4′-DDE and lindane, dissolved in ethanol, a result
that might be attributable to an inappropriate yeast start concentration and/or growth stage. These validation experiments
show that under appropriate experimental conditions the YES yields sensitive, specific and reliable results. Therefore it
fulfills the requirements as a first step screening assay to evaluate the capacity of chemicals to interact with the estrogen
receptor. 相似文献
95.
Chunpeng Ge Willy Susilo Liming Fang Jiandong Wang Yunqing Shi 《Designs, Codes and Cryptography》2018,86(11):2587-2603
The notion of attribute-based proxy re-encryption extends the traditional proxy re-encryption to the attribute-based setting. In an attribute-based proxy re-encryption scheme, the proxy can convert a ciphertext under one access policy to another ciphertext under a new access policy without revealing the underlying plaintext. Attribute-based proxy re-encryption has been widely used in many applications, such as personal health record and cloud data sharing systems. In this work, we propose the notion of key-policy attribute-based proxy re-encryption, which supports any monotonic access structures on users’ keys. Furthermore, our scheme is proved against chosen-ciphertext attack secure in the adaptive model. 相似文献
96.
97.
98.
A straightforward algorithm for the symbolic computation of generalized (higher‐order) symmetries of nonlinear evolution equations
and lattice equations is presented. The scaling properties of the evolution or lattice equations are used to determine the
polynomial form of the generalized symmetries. The coefficients of the symmetry can be found by solving a linear system. The
method applies to polynomial systems of PDEs of first order in time and arbitrary order in one space variable. Likewise, lattices
must be of first order in time but may involve arbitrary shifts in the discretized space variable.
The algorithm is implemented in Mathematica and can be used to test the integrability of both nonlinear evolution equations
and semi‐discrete lattice equations. With our Integrability Package, generalized symmetries are obtained for several well‐known
systems of evolution and lattice equations. For PDEs and lattices with parameters, the code allows one to determine the conditions
on these parameters so that a sequence of generalized symmetries exists. The existence of a sequence of such symmetries is
a predictor for integrability.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
99.
Pashynska V Vermeylen R Vas G Maenhaut W Claeys M 《Journal of mass spectrometry : JMS》2002,37(12):1249-1257
We developed and validated a gas chromatographic/ion trap mass spectrometric method for the determination of levoglucosan and the related monosaccharide anhydrides, mannosan, galactosan and 1,6-anhydro-beta-D-glucofuranose in urban atmospheric aerosols collected on quartz fiber filters. The method is based on extraction with dichloromethane-methanol (80 : 20, v/v), trimethylsilylation, multiple reaction monitoring in the tandem mass spectrometric mode using the ion at m/z 217, and the use of an internal standard calibration procedure with the structurally related compound methyl beta-L-arabinopyranoside. In addition, the method allows the quantification of other saccharidic compounds, arabitol, mannitol, glucose, fructose, inositol and sucrose, which were found to be important in summer aerosols. The recovery of levoglucosan was estimated by spiking blank filters and was better than 90%. The precision evaluated by analyzing parts of the same filters was about 2% for the monosaccharide anhydrides and 7% for the other saccharidic compounds in the case of a winter aerosol sample, and the corresponding values for a summer aerosol sample were 5% and 8%. The method was applied to urban PM(10) (particulate matter of <10 microm aerodynamic diameter) aerosols collected at Ghent, Belgium, during a 2000-2001 winter and a 2001 summer episode and revealed interesting seasonal variations. While monosaccharide anhydrides were relatively more important during the winter season owing to wood burning, the other saccharidic compounds were more prevalent during the summer season, with some of them, if not all, originating from the vegetation. 相似文献
100.
A solid phase extraction procedure (SPE) for 13 'new' antidepressants (venlafaxine, fluoxetine, viloxazine, fluvoxamine, mianserin, mirtazapine, melitracen, reboxetine, citalopram, maprotiline, sertraline, paroxetine and trazodone) together with eight of their metabolites (O-desmethylvenlafaxine, norfluoxetine, desmethylmianserine, desmethylmirtazapine, desmethylcitalopram, didesmethylcitalopram, desmethylsertraline and m-chlorophenylpiperazine) from plasma is optimized using HPLC-DAD as monitoring system. Special attention has been paid to the choice of washing and eluting solvent, resulting in a highly concentrated, clean and moisture free extract, also suitable for GC-MS. A total number of 10 sorbents (apolar, polymeric, ion-exchange and mixed mode) was evaluated. Based on recovery, reproducibility and absence of interfering substances the strong cation exchanger gave the best results. Recoveries were determined at low and high therapeutic and toxic levels and ranged between 70 and 109% for all compounds, except for trazodone (39%). 相似文献