排序方式: 共有52条查询结果,搜索用时 31 毫秒
1.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(25):7311-7314
The borylation of C−H bonds catalyzed by transition metals has been investigated extensively in the past two decades, but no iridium‐catalyzed enantioselective borylation of C−H bonds has been reported. We report a set of iridium‐catalyzed enantioselective borylations of aromatic C−H bonds. This reaction relies on a set of newly developed chiral quinolyl oxazoline ligands. This process proceeds under mild conditions with good to excellent enantioselectivity, and the borylated products can be converted to enantioenriched derivatives containing new C−O, C−C, C−Cl, or C−Br bonds. 相似文献
2.
Large eddy simulation of fire plumes 总被引:1,自引:0,他引:1
Yi Wang Prateep Chatterjee John L. de Ris 《Proceedings of the Combustion Institute》2011,33(2):2473-2480
FireFOAM, a new fire modeling code based on the OpenFOAM platform (www.openfoam.org), is developed and applied to model a series of purely buoyant fire plumes with heat release rates from 14 to 58 kW. The calculations are compared with McCaffrey’s (1979) experiments. The simulation results demonstrate good quantitative agreement with experimental measurements, and show the scaling relations of mean temperature and velocity in the continuous flame, intermittent and plume regions. The numerical simulations are shown to be strictly conservative in energy. Predicted flame heights and entrainment rates also compare well with experimental correlations. The good agreements in all aspects examined show that the current CFD model performs well for small-scale fire plumes. Turbulent fluctuation intensities and PDF of mixture fraction are presented to gain more insights into the structure of fire plumes. 相似文献
3.
Jrme O. Cosandey Axel Günther Philipp Rudolf von Rohr 《Experimental Thermal and Fluid Science》2003,27(8):877-889
The entrainment of soluble (KI, CsI) and non-soluble (Al2O3) substances through droplets, which are produced by disintegrating steam bubbles at the surface of a boiling water pool, is determined in a pilot-scale facility. Integral measurements are conducted at steady-state conditions in an atmosphere of either pure steam or an air–steam mixture. The ratio of the entrained liquid mass flow and the gas mass flow through the pool, the entrainment factor, is determined for air–steam ratios between 0 and 0.47 kg/kg in the gas atmosphere and at constant total pressures between 2 and 6 bar. The influence of the vertical temperature profile in the gas atmosphere on the convective velocity field is demonstrated by phase Doppler anemometry and particle image velocimetry measurements at a location 2.1 m above the pool surface. The influences of nucleation and natural convection are demonstrated during slow de-pressurization of the facility at rates below 420 Pa/s. 相似文献
4.
Hans U. Gerber 《Insurance: Mathematics and Economics》1984,3(2):97-100
The classical theory is adapted to the situation where the risk exchange of n insurance companies is an exchange of payments that belong to a certain linear class of random variables, for example the payments corresponding to certain layers of the aggregate claims. Similarly, a price equilibrium is considered, where the companies can purchase payments of a linear class. An example is the case where each company buys proportional coverage for its own claims and sells proportional coverage for the claims of the other companies. 相似文献
5.
A simple numerical model based on the shallow water equations in radial symmetry is used to simulate both instantaneous and continuous spills of liquefied natural gas (LNG) onto a water surface. Using the computed results, a study is made of the similarities and differences in the pool structure resulting from the two types of spills. For instantaneous spills a relation linear on a logarithmic plot is suggested between the maximum pool size and the spill volume. The effects of shear forces and surface cohesivity on the evolution of the spill are also examined. 相似文献
6.
High speed visualizations and thermal performance studies of pool boiling heat transfer on copper foam covers were performed at atmospheric pressure, with the heating surface area of 12.0 mm by 12.0 mm, using acetone as the working fluid. The foam covers have ppi (pores per inch) from 30 to 90, cover thickness from 2.0 to 5.0 mm, and porosity of 0.88 and 0.95. The surface superheats are from −20 to 190 K, and the heat fluxes reach 140 W/cm2. The 30 and 60 ppi foam covers show the periodic single bubble generation and departure pattern at low surface superheats. With continuous increases in surface superheats, they show the periodic bubble coalescence and/or re-coalescence pattern. Cage bubbles were observed to be those with liquid filled inside and vented to the pool liquid. For the 90 ppi foam covers, the bubble coalescence takes place at low surface superheats. At moderate or large surface superheats, vapor fragments continuously escape to the pool liquid. 相似文献
7.
8.
9.
Jun Yang Jing Yang Zheng-Qin Yin Irina Svir Hong-Yan Luo Yi Cao Yan-Jian Liao 《Analytica chimica acta》2009,634(1):61-67
A microfluidic pool structure for cell docking and rapid mixing is described. The pool structure is defined as a microchamber on one structural layer of a bilayer chip and connects with two or more individual microchannels on the other structural layer. In contrast to the turbulent flow in a macroscale pool, laminar streams enter and exit this microfluidic pool structure with definite and controllable direction that may be influenced by the location and geometry of the pool. A simple microfluidic model was used to validate this hypothesis. In this model, a microscale pool structure was made on the lower layer of a chip and connected with three parallel microchannels in the upper layer. Simulation and experimental results indicated that the flow profile within the pool structure was determined by its geometry and location. This could be used as a flow control method and it was simpler than designs based on microvalve, hydraulic pressure, or electrokinetic force, and has some important applications. For example, controllable streams within this structure were used to immobilize biological cells along the microchannel walls. When different solution streams flowed through the pool, rapid diffusion of analytes occurred for short diffusion distance between vertical flow laminas. Furthermore, desired dilution (mixing) ratio could be obtained by controlling the geometry of the microfluidic pool. 相似文献
10.
Touraj Rowhani 《Talanta》2007,71(2):964-970
A novel nickel-nioxime analytical method to measure polyhexamethylene biguanide (PHMB) in swimming pools and spas was developed. This method utilizes nickel(II) chloride and 1,2-cyclohexanedionedioxime (nioxime) chemistry. In the method, nickel ions bind and neutralize PHMB in the solution. Excess, un-reacted nickel ions react with nioxime and the resulting colored solution is measured at 550 nm using a colorimetric assay. Currently, the colorimetric method to measure PHMB uses bromophenol blue (BPB). However, high levels of quaternary ammonium based algaecides and surfactant based products interfere with this colorimetric method. A time-consuming and expensive high-performance liquid chromatographic (HPLC) analysis can be used for samples with high levels of quaternary ammonium based algaecides or surfactants. The proposed nickel-nioxime detection method achieves comparable PHMB results to HPLC in about 5 min and is a very economical and simple method to perform. 相似文献