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排序方式: 共有179条查询结果,搜索用时 31 毫秒
31.
In this paper we solve the Dirichlet problems for different classes of plurisubharmonic functions on compact sets in ${\mathbb C^n}$ including continuous, pluriharmonic and maximal functions. 相似文献
32.
Z-Ligustilide (1) and Z-6,6',7,3'-alpha-diligustilide (2), two of the major active phthalides of the medicinal plant Ligusticum porteri (osha), were chosen for the development and validation of an HPLC-diode array detection method suitable for QC of the crude drug. The method used gradient elution to achieve separation on a Hibar RT LiChrospher 100 C18 column. The LOD values were 29 and 45 microg/mL, and the LOQs were 89 and 125 microg/mL, respectively. The method showed good intraday precision (%RSD: 0.7 for 1 and 3.1 for 2) and interday precision (%RSD: 1.2 for 1 and 1.8 for 2). The method was used for the analysis of 1 and 2 in crude drug samples and several herbal preparations from Mexico and the United States. Quantitative analysis showed that the content of the two phthalides varied significantly among the samples. All the samples contained higher concentrations of 1 (0.15-2.5%) than 2 (0.002-1.0%). The profiles of volatile compounds in the essential oil obtained by hydrodistillation and solid-phase microextraction of L. porteri roots were analyzed by GC-MS. Thirty one chemical constituents (> 99.7% of the total content) were identified in the essential oil, which was characterized by the presence of a high percentage of phthalides (44.61%) and sesquiterpenes (10.69%). The major light volatile components extracted by solid-phase microextraction were monoterpenes. 相似文献
33.
Summary. We consider the solution of systems of linear algebraic equations which arise from the finite element discretization of variational
problems posed in the Hilbert spaces and in three dimensions. We show that if appropriate finite element spaces and appropriate additive or multiplicative Schwarz
smoothers are used, then the multigrid V-cycle is an efficient solver and preconditioner for the discrete operator. All results
are uniform with respect to the mesh size, the number of mesh levels, and weights on the two terms in the inner products.
Received June 12, 1998 / Revised version received March 12, 1999 / Published online January 27, 2000 相似文献
34.
Ragnar Bye 《Fresenius' Journal of Analytical Chemistry》1984,317(1):27-28
Summary For the AAS-determination of Se in zinc ore with high concentrations of lead and copper, the sample is dissolved in a nitric-hydrochloric acid mixture. Excess nitric acid is removed by heating with perchloric acid and hydrochloric acid is added to reduce Se(VI) to Se(IV). Thiourea is added to the sample aliquotes taken for hydride generation to minimize the interference from copper. The result for selenium agreed well with that found by NAA. Total standard deviation of the method is 5–10 %.
Selenbestimmung in Zinkerzen mit hohen Blei- und Kupfergehalten mit Hilfe der Hydrid-AAS
Zusammenfassung Zur Bestimmung wird die Probe in einem Gemisch von Salpeter- und Salzsäure aufgelöst. Überschüssige Salpetersäure wird durch Erhitzen mit Perchlorsäure entfernt und zur Reduktion von Se(VI) zu Se(IV) wird weitere Salzsäure zugegeben. Ein Zusatz von Thioharnstoff dient zur Verminderung des störenden Einflusses von Kupfer. Die erhaltenen Ergebnisse stimmen gut mit den durch NAA erhaltenen überein. Die Gesamt-Standardabweichung liegt bei 5–10%.相似文献
35.
We analyze a system of conservation laws in two space dimensions with a stiff relaxation term. A semi-implicit finite difference method approximating the system is studied and an error bound of order
measured inL
1 is derived. This error bound is independent of the relaxation time > 0. Furthermore, it is proved that the solutions of the system converge towards the solution of an equilibrium model as the relaxation time tends to zero, and that the rate of convergence measured inL
1 is of order
. Finally, we present some numerical illustrations.This research has been supported by the Norwegian Research Council (NFR), program no. STP 110673/420, at the Department of Applied Mathematics, SINTEF, Oslo, Norway 相似文献
36.
A novel amphiphilic GdPCTA-[12] derivative has been prepared. The complex formed micelles in aqueous solution with a relatively low CMC, 0.15 mM (25 degrees C). The concentration dependent T1-relaxivity (r1) of the system has been described. The maximum T1-relaxivity, 29.2 s-1 mM-1 (20 MHz, 25 degrees C), was higher than for previously described micellar MRI contrast agents. This high T1-relaxivity is a consequence of the favourable water residence time (tau M) and the fact that the complex is heptadentate allowing two water molecules to coordinate to the gadolinium ion (q = 2). 相似文献
37.
Ragnar Bye Tone Agas?ster Arne ?sheim 《Fresenius' Journal of Analytical Chemistry》1993,345(6):411-414
Summary A novel and generally applicable extraction technique is presented as an alternative to the common separatory funnel technique. It is based on the use of a commercially available magnetic stirring plate, which can stir up to six vessels simultaneously, and conventional conical flasks equipped with a specially designed (but easy to make) glass adaptor. The extraction process, which can proceed unattended, has been compared with conventional separatory funnel extraction methods using three different and well established methods: non-aqueous titration, molecular (visible) absorption and atomic absorption spectrometry. The results obtained by the new technique for each method have been compared with those obtained using the standard separatory funnel methods and were found to agree very satisfactory. 相似文献
38.
Selenium(IV) is determined in the presence of 3.5% sodium chloride by electrochemical preconcentration on a platinum spiral, prior to flame atomic absorption analysis. The electrodeposition is carried out in the presence of hydrazine dihydrochloride to prevent the generation of chlorine at the counter electrode; chlorine oxidizes selenium(IV) to the non-reducible selenium(VI) ion. A detection limit of 5 ppb and an electrolysis efficiency of 10% were obtained for a 25-ml sample and a 5-min electrolysis time. The absolute detection limit was 10 ng. 相似文献
39.
Different methods of atomization of selenium from a platinum wire filament are described, including electrothermal heating of the filament and atomlzation in an argon-hydrogen flame. A combination of these approaches proved to give the best sensitivity and detection limit. The selenium was preconcentrated on the filament by electrolysis prior to the atomic absorption measurements to eliminate chemical interferences and improve the sensitivity of the method. The detection limit was 0.5 μg l-1 for a 5-min electrolysis, and 0.2 μg l-1 when the electrolysis time was 30 min. 相似文献
40.
In this note we give a complete classification of those holomorphic maps :U
n
defined on open and connected subsets of
m
which are harmonic morphisms.The first author was supported by the Icelandic Science Fund. 相似文献