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Choi SW Yoon JY Haam S Jung JK Kim JH Kim WS 《Journal of colloid and interface science》2000,228(2):270-278
A study on the variation of the permeate flux was performed in a stirred cell charged with microspheres, to investigate the effects of the stirrer speeds (300, 400, and 600 rpm) and the BSA concentration (0.1, 0.2, 0.4, and 0.8 g/L) under constant pressure. The permeate flux increased over time before the saturation point, but it began to decrease after that point. An increase of the BSA concentration and the stirrer speed resulted in the rapid increase of the permeate flux. This is contrary to the observation of the conventional filtration experiments using a stirred cell. A resistance-in-series model was employed for the modeling of the permeate flux. The cake resistance (R(c), induced by the concentration polarization of microspheres) and the fouling resistance (R(f), induced by the adsorption of BSA inside the membrane pore) must be considered simultaneously for the modeling. These modeling results were in good agreement with the experimental data. These can be applied to the special system considering both R(c) and R(f) as well as the general filtration systems using a stirred cell. Copyright 2000 Academic Press. 相似文献
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Daewon Hong Patrick J. Carroll Larry G. Sneddon 《Journal of organometallic chemistry》2003,680(1-2):61-65
The new 11-vertex nido-diphosphaborane, 7,9-Ph2-nido-7,9-P2B9H9, has been synthesized by the reaction of Me4N+[nido-B9H12−] with PhPCl2 in the presence of NaH. A single crystal X-ray diffraction determination and DFT/GIAO/NMR methods have both established that the compound has an open cage structure containing the phosphorus atoms in non-adjacent positions on the open face. 相似文献
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Rao PV Bhaduri S Jiang J Hong D Holm RH 《Journal of the American Chemical Society》2005,127(6):1933-1945
The construction of a synthetic analogue of the A-cluster of carbon monoxide dehydrogenase/acetylcoenzyme synthase, the site of acetylcoenzyme A formation, requires as a final step the formation of an unsupported [Fe(4)S(4)]-(mu(2)-SR)-Ni(II) bridge to a preformed cluster. Our previous results (Rao, P. V.; Bhaduri, S.; Jiang, J.; Holm, R. H. Inorg. Chem. 2004, 43, 5833) and the work of others have addressed synthesis of dinuclear complexes relevant to the A-cluster. This investigation concentrates on reactions pertinent to bridge formation by examining systems containing dinuclear and mononuclear Ni(II) complexes and the 3:1 site-differentiated clusters [Fe(4)S(4)(LS(3))L'](2-) (L' = TfO(-) (14), SEt (15)). The system 14/[{Ni(L(O)-S(2)N(2))}M(SCH(2)CH(2)PPh(2))](+) results in cleavage of the dinuclear complex and formation of [{Ni(L(O)-S(2)N(2))}Fe(4)S(4)(LS(3))]- (18), in which the Ni(II) complex binds at the unique cluster site with formation of a Ni(mu(2)-SR)(2)Fe bridge rhomb. Cluster 18 and the related species [{Ni(phma)}Fe(4)S(4)(LS(3))](3)- (19) are obtainable by direct reaction of the corresponding cis-planar Ni(II)-S(2)N(2) complexes with 14. The mononuclear complexes [M(pdmt)(SEt)]- (M = Ni(II), Pd(II)) with 14 in acetonitrile or Me(2)SO solution react by thiolate transfer to give 15 and [M(2)(pdmt)(2)]. However, in dichloromethane the Ni(II) reaction product is interpreted as [{Ni(pdmt)(mu(2)-SEt)}Fe(4)S(4)(LS(3))](2-) (20). Reaction of Et(3)NH(+) and 15 affords the double cubane [{Fe(4)S(4)(LS(3))}(2)(mu(2)-SEt)](3-) (21). Cluster 18 contains two mutually supportive Fe-(mu(2)-SR)-Ni(II) bridges, 19 exhibits one strong and one weaker bridge, 20 has one unsupported bridge (inferred from the (1)H NMR spectrum), and 21 has one unsupported Fe-(mu(2)-SR)-Fe bridge. Bridges in 18, 19, and 21 were established by X-ray structures. This work demonstrates that a bridge of the type found in the enzyme A-clusters is achievable by synthesis and implies that more stable, unsupported single thiolate bridges may require reinforcement by an additional covalent linkage between the Fe(4)S(4) and nickel-containing components. (LS(3) = 1,3,5-tris((4,6-dimethyl-3-mercaptophenyl)thio)-2,4,6-tris(p-tolylthio)benzene(3-); L(O)-S(2)N(2) = N,N'-diethyl-3,7-diazanonane-1,9-dithiolate(2-); pdmt = pyridine-2,6-methanedithiolate(2-); phma = N,N'-1,2-phenylenebis(2-acetylthio)acetamidate(4-); TfO = triflate.). 相似文献
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The syntheses of new cyano-substituted derivatives of arachno-6,8-C(2)B(7)H(13) have been achieved through the addition reactions of the arachno-6,8-C(2)B(7)H(12)(-) (1-) anion with cyano-activated olefins. The reaction of PSH+1- with tetracyanoethylene (TCNE) yielded the unusual bridging compound PSH(+)endo-6-endo-7-[micro(2)-(C(CN)(2))(2)]-arachno-6,8-C(2)B(7)H(12)(-) (PSH+2-)) resulting from cycloaddition of the TCNE at the C6-B7 edge of the anion. Consistent with its hypho skeletal electron count, an X-ray crystallographic study and DFT/GIAO calculations confirm 2(-) has a more open structure than 1-. The reaction of 1- with acrylonitrile resulted in the formation of endo-6-(NCCH(2)CH(2))-arachno-6,8-C(2)B(7)H(11)(-) (3-), which, upon acidification, afforded endo-6-(NCCH(2)CH(2))-arachno-6,8-C(2)B(7)H(12) (3) in high yield. X-ray crystallographic and DFT/GIAO studies established that the cyanoethyl fragment in 3 is substituted at the endo-position of the C6 cage-carbon. Heating 3 in THF at 50 degrees C or in toluene at 110 degrees C resulted in the quantitative isomerization of the cyanoethyl-substituent from the endo- to the exo-position at C6 to yield exo-6-(NCCH(2)CH(2))-arachno-6,8-C(2)B(7)H(12) (4). This is the first example of an endo to exo isomerization to be observed at a cage-carbon of a carborane. While heating 3 resulted in isomerization to 4, heating 3- in the presence of a small amount of 3 yielded the new ethylene-bridged 10-vertex tricarbaborane micro(6,9)-(CH(2)CH(2))-arachno-5,6,9-C(3)B(7)H(11) (5) resulting from reduction of the 3- pendant nitrile group, followed by deammination and carbon insertion. 相似文献
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This article examines how performance-contingent pricing schemes with long-term statistical performance guarantees can be applied to many IT services. We study two forms of performance-contingent pricing, with rebate proportional to failure rate and fixed rebate for below-threshold performance. We show that threshold-performance contingency pricing can increase both profits and fairness (customers who receive higher benefits pay higher effective price) relative to standard pricing. But an even better solution is to offer a menu of performance guarantees: this can increase the firm’s profit and segment the market. Only service providers whose performance level is sufficiently better than the industry standard can benefit from this pricing mechanism. 相似文献
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