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91.
The paper studies numerically the slip with friction boundary condition in the time‐dependent incompressible Navier–Stokes equations. Numerical tests on two‐ and three‐dimensional channel flows across a step using this boundary condition on the bottom wall are performed. The influence of the friction parameter on the flow field is studied and the results are explained according to the physics of the flow. Due to the stretching and tilting of vortices, the three‐dimensional results differ in many respects from the two‐dimensional ones. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
92.
93.
Anastasios Dondos 《European Polymer Journal》1978,14(9):651-654
This paper presents results on viscosity and preferential solvation for the ternary systems: polystyrene (PS)-carbon tetrachloride-methanol, PS-benzene-cyclohexane, PS-chloroform-ethanol and poly(2 vinylpyridine)-ethanol-cyclohexane using linear and branched polymers. For a given ternary system the representation Δλ′ (variation of the preferential solvation coefficient) as a function of Δρ (variation of the segment density) already proposed gives a unique curve. This shows that this relation is not sensitive to branching or to molecular weight of the polymer when the dimensions of the polymer in the mixed solvent are lower than in the pure good solvent. However, when the dimensions of the polymer in the mixed solvent are higher than in the pure good solvent, the relation between Δλ′ and Δρ cannot be applied. 相似文献
94.
95.
96.
Naseri NG Baldock SJ Economou A Goddard NJ Fielden PR 《Analytical and bioanalytical chemistry》2008,391(4):1283-1292
Catalytic adsorptive stripping voltammetry (CAdSV) has been demonstrated at a bismuth film electrode (BiFE) in an injection-moulded
electrochemical micro-flow cell. The polystyrene three-electrode flow cell was fabricated with electrodes moulded from a conducting
grade of polystyrene containing 40% carbon fibre, one of which was precoated with Ag to enable its use as an on-chip Ag/AgCl
reference electrode. CAdSV of Co(II) and Ni(II) in the presence of dimethylglyoxime (DMG) with nitrite employed as the catalyst
was performed in order to assess the performance of the flow cell with an in-line plated BiFE. The injection-moulded electrodes
were found to be suitable substrates for the formation of BiFEs. Key parameters such as the plating solution matrix, plating
flow rate, analysis flow rate, solution composition and square-wave parameters have been characterised and optimal conditions
selected for successful and rapid analysis of Co(II) and Ni(II) at the ppb level. The analytical response was linear over
the range 1 to 20 ppb and deoxygenation of the sample solution was not required. The successful coupling of a microfluidic
flow cell with a BiFE, thereby forming a “mercury-free” AdSV flow analysis sensor, shows promise for industrial and in-the-field
applications where inexpensive, compact, and robust instrumentation capable of low-volume analysis is required. 相似文献
97.
Prof. Guowei Li Dr. Qun Yang Prof. Kaustuv Manna Dr. Yudi Zhang Dr. Patrick Merz Chandra Shekhar Yang Zhang Dr. Hua Lv Dr. Anastasios Markou Dr. Yan Sun Prof. Claudia Felser 《Angewandte Chemie (International ed. in English)》2023,62(27):e202303296
The study of heterogeneous reactions for enantiomeric processes based on inorganic crystals has been resurgent in recent years. However, the question remains how homochirality develops in nature and chemical reactions. Here, the successful growth of B20 group PdGa single crystals with different chiral lattices enabled us to achieve enantioselective recognition of 3,4-dihydroxyphenylalanine (DOPA) based on a new mechanism, namely orbital angular momentum (OAM) polarization. The orbital textures of PdGa crystals indicate large OAM polarization near the Fermi level and carrying opposite signs. A positive or negative magnetization in the [111] direction is expected depending on the chiral lattice of PdGa crystals. Due to this, the adsorption energies of PdGa crystals and DOPA molecules differ depending on how well the O-2p orbital of DOPA pairs with the Pd-4d orbital of PdGa. The results provide one possible explanation for how chirality arises in nature by providing an enantioselective route with pure inorganic crystals. 相似文献
98.
Dr. Jing Cao M. Sc. Antonia Seitz Dr. José A. Forni Prof. Dr. Anastasios Polyzos Prof. Dr. David W. Lupton 《Angewandte Chemie (International ed. in English)》2023,62(29):e202303869
Dual nucleophilic phosphine photoredox catalysis is yet to be developed due to facile oxidation of the phosphine organocatalyst to the phosphoranyl radical cation. Herein, we report a reaction design that avoids this event and exploits traditional nucleophilic phosphine organocatalysis with photoredox catalysis to allow the Giese coupling with ynoates. The approach has good generality, while its mechanism is supported by cyclic voltametric, Stern–Volmer quenching, and interception studies. 相似文献
99.
A simple and sensitive method using high-performance liquid chromatography/ mass spectrometry (LC/MS) was developed and validated for simultaneous determination of 5 benzoylurea insecticides-diflubenzuron, triflumuron, teflubenzuron, lufenuron, and flufenoxuron-in tomatoes. Residues were successfully separated on a C18 column by methanol-water isocratic elution. Detection was carried out by an ultraviolet diode array detector (UV-DAD) coupled with a quadrupole mass spectrometer, using atmospheric pressure chemical ionization (APCI) in negative-ion mode. The main ions were the deprotonated molecules [M-H]- for triflumuron, and the anions formed by elimination of hydrofluoric acid [M-H-HF]- for diflubenzuron and flufenoxuron, and [M-2H-HF] for lufenuron and teflubenzuron. The calibration plots were linear for both detectors over the range 0.05 to 10 microg/mL, and the method presented good quality parameters. The limits of detection for standard solutions were 0.008-0.01 mg/L (equivalent to 0.08-0.1 ng injected) for both detectors, and the limits of quantification (LOQs) were approximately 10 times lower than national maximum residue levels (MRLs). Depending on the compound and the detector, the LOQ values ranged from 0.2 to 0.4 ng injected. The optimum LC-UV-DAD/APCI-MS conditions were applied to the analysis of benzoylureas in tomatoes. The obtained recoveries from fortified tomato samples (50 g), extracted with ethyl acetate and purified by solid-phase extraction on silica sorbent, were 88-100 and 92.9-105% for the UV-DAD and MS detectors, respectively, with precision values (relative standard deviations) of 2.9-11 and 3.7-14%, respectively. The method was applied to 12 tomato samples from local markets, and diflubenzuron and lufenuron were detected in only one sample at concentrations lower than the MRLs. The results indicate that the developed LC/MS method is accurate, precise, and sensitive for quantitative and qualitative analysis at low levels of benzoylureas required by legislation. 相似文献
100.
Riemer-Sørensen S Zioutas K Hansen SH Pedersen K Dahle H Liolios A 《Physical review letters》2007,99(13):131301
We constrain the lifetime of radiatively decaying dark matter in clusters of galaxies inspired by generic Kaluza-Klein axions, which have been invoked as a possible explanation for the solar coronal x-ray emission. These particles can be produced inside stars and remain confined by the gravitational potential of clusters. By analyzing x-ray observations of merging clusters, where gravitational lensing observations have identified massive, baryon poor structures, we derive the first cosmological lifetime constraint on this kind of particles of tau > or = 10(23) sec. 相似文献