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排序方式: 共有127条查询结果,搜索用时 15 毫秒
1.
This paper describes the chemical investigation on BuOH-soluble EtOH extract from the aerial part of Sauropus androgynus. This study led to the characterization of six bioactive ingredients including three nucleosides—adenosine (1), 5′-deoxy-5′-methylsulphinyl-adenosine ( 2 ), and uridine ( 3 ), two flavonol dioside — 3-O-β-D-glucosyl-7-O-α-L-rhamnosyl-kaempferol ( 4 ), 3-O-β-D-glucosyl-(1→6)-β-D-glucosyl-kaempferol ( 5 ), and one rare flavonol trioside — 3-O-β-D-glucosyl-(1→6)-β-D-glucosyl-7-O-α-L-rhamno-syl-kaempferol ( 6 ). Their structures were determined on the basis of spectral analysis. 相似文献
2.
The new sequential centrifugal layer chromatography extends the possibilities for preparative separation of furocoumarin isomers. In the present work, isobergapten, pimpinellin, bergapten, isopimpinellin, and sphondin were isolated from a prepurified extract of Heracleum sphondylium roots using two different techniques, namely, centrifugal layer chromatography (CLC) and sequential centrifugal layer chromatography (SCLC). The former technique was carried out with four plates, whereas the latter method required only one plate, using the same mobile phase in each case. A further advantage of the SCLC method was that all completely separated compounds could be quickly and efficiently eluted in small volumes of mehtanol. 相似文献
3.
Ikehata J Shinomiya K Kobayashi K Ohshima H Kitanaka S Ito Y 《Journal of chromatography. A》2004,1025(2):169-175
The effect of Coriolis force on the counter-current chromatographic separation was studied using centrifugal partition chromatography (CPC) with four different two-phase solvent systems including n-hexane-acetonitrile (ACN); tert-butyl methyl ether (MtBE)-aqueous 0.1% trifluoroacetic acid (TFA) (1:1); MtBE-ACN-aqueous 0.1% TFA (2:2:3); and 12.5% (w/w) polyethylene glycol (PEG) 1000-12.5% (w/w) dibasic potassium phosphate. Each separation was performed by eluting either the upper phase in the ascending mode or the lower phase in the descending mode, each in clockwise (CW) and counterclockwise column rotation. Better partition efficiencies were attained by the CW rotation in both mobile phases in all the two-phase solvent systems examined. The mathematical analysis also revealed the Coriolis force works favorably under the CW column rotation for both mobile phases. The overall results demonstrated that the Coriolis force produces substantial effects on CPC separation in both organic-aqueous and aqueous-aqueous two-phase systems. 相似文献
4.
Mahsa Taghavi Sirous Ebrahimi Jafarsadegh Moghaddas 《Journal of Dispersion Science and Technology》2014,35(8):1097-1105
The recently developed centrifugal impeller is examined to investigate the solid–liquid mixing in a mechanically agitated contactor. Using the sample withdrawal method, the effects of impeller geometrical parameters, impeller rotational speed (200–700 rpm), solid particle size (500–1100 µm), and solid loading (2–10 vol%) on the degree of homogeneity are studied. The axial and the radial solid concentration profiles and the minimum impeller speed for the complete homogenization are also determined. In comparison with a widely used propeller impeller, considerably higher homogeneity values in lower impeller speeds are obtained (90% homogeneity against 16% homogeneity at 200 rpm at the same conditions). Having also lower power consumption makes this a superior impeller in solid–liquid mixing processes especially in shear-sensitive systems. 相似文献
5.
In this paper a general three-dimensional simulation of turbulent fluid flow is presented to predict velocity and pressure fields for a centrifugal pump. A commercial CFD code was used to solve the governing equations of the flow field. In order to study the most suitable turbulence model, three known turbulence models of standard k–ε, RNG and RSM were applied. The complex flow configuration required us to use around 5,800,000 cells, and 12 computational nodes (processors) for parallel computing. Simulation results in the form of characteristic curves were compared with available experimental data, and an acceptable agreement was obtained. Additionally, effect of number of blades on the efficiency of pump was studied. The number of blades was changed from 5 to 7. The results show that the impeller with 7 blades has the highest head coefficient. Finally, it was observed also that the position of blades with respect to the tongue of volute has great effect on the start of the separation. Thus, to analyze the effect of blade number on the characteristics of the pump, the position of blade and tongue should be similar to each other. Investigations of this kind may help to reduce the required experimental work for the development and design of such devices. 相似文献
6.
High-frequency ultrasound (HFUS) signals backscattered from RBL-2H3 cell pellets prepared under different centrifugal forces were analyzed to investigate the packing effect of cell aggregates. The measurements were performed in a pulse-echo setup with a 40-MHz transducer. The changes of ultrasound signals from cell pellet in backscattered power, statistical parameter, and pellet thickness were monitored after centrifugation at between 100g and 1600g. Experimental results showed that the HFUS backscattered power from cell pellets was inversely proportional to centrifugal force and increased to a plateau within 1-2 h after centrifugation. The initial thickness of cell pellets decreased with higher centrifugal force, but the changes in thickness and time that took to reach a plateau increased at higher centrifugal force. The envelope statistics of backscattered signals with Nakagami distribution indicates that the centrifugal force and elapsed time after centrifugation affected the backscattering characteristics. The present study suggests that centrifugal force and data acquisition time after cell pellet formation should be considered in in vitro cell packing method with centrifugation to emulate the tissue in vivo. 相似文献
7.
V. Lepiller A. Goharzadeh A. Prigent I. Mutabazi 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):445-455
We have investigated the influence of a weak radial
temperature gradient in a wide gap and large aspect ratio
Couette-Taylor system. The inner cylinder is rotating and can be
heated or cooled, the outer cylinder is at rest and immersed in a
large thermal bath. We found that a radial temperature gradient
destabilizes the Couette flow leading to a pattern of traveling
helicoidal vortices occurring only near the bottom of the system.
The size of the pattern increases as the rotation frequency of the cylinder is increased. We
have characterized the spatiotemporal properties of the pattern and we have shown that it
behaves as a wall mode found in the simulation of the
complex Ginzburg-Landau equation with homogeneous boundary
conditions. 相似文献
8.
9.
M. Ungarish 《Archive of Applied Mechanics (Ingenieur Archiv)》2003,73(5-6):399-408
Summary We consider the batch centrifugal separation of a suspension of heavy particles in a cylindrical tube which rotates about an axis perpendicular to the axis of the tube. The theoretical analysis by means of a kinematic approximation covers two models: (1) the one-dimensional, which assumes that the particles settle along lines parallel to the sidewalls of the tube and sediment on the outer wall, and (2) the two-dimensional, which assumes that the particles settle along the centrifugal-field lines and sediment on both sidewalls and outer wall. A comparison shows that both models produce similarly simple formulas for the motion of the interface and the volume fraction as functions of time. However, the two-dimensional model is recommended for use because its results and insights are more reliable from both mathematical and physical considerations, and provide a more acceptable interpretation to recent experimental data, [5].
The author wishes to thank Prof. W. Schneider for stimulating discussions on the subject. The research was partially supported by the the Technion Fund V.P.R Fund – New York Metropolitan Research Fund. 相似文献
10.
Bisson J Poupard P Pawlus AD Pons A Darriet P Mérillon JM Waffo-Téguo P 《Journal of chromatography. A》2011,1218(36):6079-6084
The phytochemical study of the root extract of the stilbenoid-rich Vitis riparia × Vitis berlandieri grapevine was carried out by centrifugal partition chromatography (CPC). For this reason, we developed a new elution mode we named back-step, which allowed us to obtain cleaner fractions and a more efficient separation process when used in conjunction with a classical elution approach. Three hydroxystilbenes: (E)-resveratrol, (E)-?-viniferin and (E)-vitisin C, with greater than 90% purity were thus obtained through such process, with minimal sample handling and purification steps. Online coupling of CPC to ESI mass spectrometry was used for optimization of the separation parameters and to facilitate the characterization of the stilbenoids. This study details the first phytochemical investigation of stilbenoids from the hybrid species together with a new elution mode able to widen the range of ARIZONA biphasic systems. 相似文献