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401.
Minbo Yang Wenxiong Chen Yanheng Ding 《Journal of Mathematical Analysis and Applications》2010,362(2):338-349
We study the existence of ground state solutions for the following elliptic systems in RN where b=(b1,…,bN) is a constant vector and HC1(RN×R2,R) is nonperiodic in variables x and super-quadratic as |z|→∞. By a recent critical point theorem for strongly indefinite problem, we obtain the existence of at least one ground state solution. 相似文献
402.
Elise C. Goosens Dirk De Jong Gerhardus J. de Jong Feddy D. Rinkema Udo A. Th. Brinkman 《Journal of separation science》1995,18(1):38-44
The on-line coupling of a liquid-liquid extraction system with capillary gas chromatography using atomic emission detection (GC-AED) has been studied. The required large volumes of about 100 μl of an iso-octane solution can be introduced into the GC-AED system by using the AED solvent vent and a solvent vapor exit in front of the capillary analytical column. Test solutions containing several pesticides were detected using the carbon, chlorine, nitrogen and sulfur channels. Analyte detectability (in concentration units) was improved significantly and low concentractions of the test compounds could be determined (1–5 ng/ml). Aqueous samples were on-line extracted and analyzed. The precision of the large-volume injection itself as well as the total extraction-GC-AED system was satisfactory (RSD of ca. 2 and 4%, respectively). As a real-life application, several ground water samples were screened. 相似文献
403.
Membrane-assisted solvent extraction (MASE) was applied for the determination of seven phenols (phenol, 2-chlorophenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol and pentachlorophenol) with log Kow (octanol-water-partition-coefficient) between 1.46 (phenol) and 5.12 (pentachlorophenol) in water. The extraction solvents cyclohexane, ethyl acetate and chloroform were tested and ethyl acetate proved to be the best choice. The optimisation of extraction conditions showed the necessity of adding 5 g of sodium chloride to each aqueous sample to give a saturated solution (333 g/L). The pH-value of the sample was adjusted to 2 in order to convert all compounds into their neutral form. An extraction time of 60 min was found to be optimal. Under these conditions the recovery of phenol, the most polar compound, was 11%. The recoveries of the other analytes ranged between 42% (2-chlorophenol) and 98% (2,4-dichlorophenol). Calibration was performed using large volume injection (100 microL injection volume). At optimised conditions the limits of detection were between 0.01 and 0.6 microg/L and the relative standard deviation (n = 3) was on average about 10%. After the method optimisation with reagent water membrane-assisted solvent extraction was applied to two contaminated ground water samples from the region of Bitterfeld in Saxony-Anhalt, Germany. The results demonstrate the good applicability of membrane-assisted solvent extraction for polar analytes like phenols, without the necessity of derivatisation or a difficult and time-consuming sample preparation. 相似文献
404.
Determination of triazine compounds in ground water samples by micellar electrokinetic capillary chromatography 总被引:1,自引:0,他引:1
《Analytica chimica acta》2004,503(2):271-278
In this work, a capillary electrophoresis (CE) method for the determination of a group of eleven triazine compounds by micellar electrokinetic capillary chromatography (MEKC) with diode array detection was developed. The eleven herbicides studied were: desethylatrazin-2-hydroxy (DEA), simazine, prometon, atrazine, simetryn, ametryn, propazine, prometryn, trietazine, terbutylazine, and terbutryn The separation of these compounds was optimised as a function of buffer concentration and pH, concentration of sodium dodecyl sulphate (SDS) and voltage applied. To increase the selectivity of the separation and the resolution of the solutes, different organic solvents were tested as buffer additives, obtaining the best results when 1-propanol was used. The optimised buffer (24 mM of sodium borate, 18 mM of disodium hydrogen phosphate, 25 mM of SDS, pH 9.5, and 5% of 1-propanol) provides the best separation in terms of resolution and migration time. This method allowed the determination of these compounds at concentrations of 0.05 μg l−1 in ground water samples pretreated using solid-phase extraction (SPE). 相似文献
405.
We prove the phase segregation phenomenon to occur in the ground state solutions of an interacting system of two self-coupled
repulsive Hartree equations for large nonlinear and nonlocal interactions. A self-consistent numerical investigation visualizes
the approach to this segregated regime.
相似文献
406.
This paper is concerned with the standing wave for Klein-Gordon-Zakharov equations with different propagation speeds in three space dimensions. The existence of standing wave with the ground state is established by applying an intricate variational argument and the instability of the standing wave is shown by applying Pagne and Sattinger's potential well argument and Levine's concavity method. 相似文献
407.
采用密度泛函理论(DFT)B3LYP/LanL2dz方法,对一类重要的磷光材料三-(2-苯基吡啶)-铱[Ir(ppy)3]及其衍生物的电子结构与电子光谱进行了研究,讨论了取代基对配合物的能级和LUMO-HOMO能隙的影响,发现吸电子基(-CN)使能级降低,HOMO-LUMO之间能隙减小,而推电子基(-OCH3)使能级升高,HOMO-LUMO之间能隙变化不大. 相似文献
408.
409.
410.
Vanadium oxide clusters VxOyq (x≤8, q=0,±1) are classified according to the oxidation index (△=2y+q-5x) of each cluster. Density functional calculations indicate that clusters with the same oxidation index tend to have similar bonding characters, electronic structures, and reactivities. This general rule leads to the findings of new possible ground state struc-tures for V2O6 and V3O6+ clusters. This successful application of the classification method on vanadium oxide clusters proves that this method is very effective in studying the bonding properties of early transition metal oxide clusters. 相似文献