The impeller configuration with a six parabolic blade disk turbine below two down-pumping hydrofoil propellers, identified as PDT + 2CBY, was used in this study. The effect of the impeller diameter D, ranging from0.30...The impeller configuration with a six parabolic blade disk turbine below two down-pumping hydrofoil propellers, identified as PDT + 2CBY, was used in this study. The effect of the impeller diameter D, ranging from0.30 T to 0.40T(T as the tank diameter), on gas dispersion in a stirred tank of 0.48 m diameter was investigated by experimental and CFD simulation methods. Power consumption and total gas holdup were measured for the same impeller configuration PDT + 2CBY with four different D/T. Results show that with D/T increases from 0.30 to 0.40, the relative power demand(RPD) in a gas–liquid system decreases slightly. At low superficial gas velocity VSof 0.0078 m·s-1, the gas holdup increases evidently with the increase of D/T. However, at high superficial gas velocity, the system with D/T = 0.33 gets a good balance between the gas recirculation and liquid shearing rate, which resulted in the highest gas holdup among four different D/T. CFD simulation based on the two-fluid model along with the Population Balance Model(PBM) was used to investigate the effect of impeller diameter on the gas dispersion. The power consumption and total gas holdup predicted by CFD simulation were in reasonable agreement with the experimental data.展开更多
During transcription initiation,RNA polymerase binds tightly to the promoter DNA defining the start of transcription,transcribes comparatively slowly,and frequently releases short transcripts(3-8 nucleotides)in a proc...During transcription initiation,RNA polymerase binds tightly to the promoter DNA defining the start of transcription,transcribes comparatively slowly,and frequently releases short transcripts(3-8 nucleotides)in a process called abortive cycling.Transitioning to elongation,the second phase of transcription,the polymerase dissociates from the promoter while RNA synthesis continues.Elongation is characterized by higher rates of transcription and tight binding to the RNA transcript.The RNA polymerase from enterophage T7 (T7 RNAP) has been used as a model to understand the mechanism of transcription in general,and the transition from initiation to elongation specifically.This single-subunit enzyme undergoes dramatic conformational changes during this transition to support the changing requirements of nucleic acid interactions while continuously maintaining polymerase function.Crystal structures,available of multiple stages of the initiation complex and of the elongation complex,combined with biochemical and biophysical data,offer molecular detail of the transition.Some of the crystal structures contain a variant of T7 RNAP where proline 266 is substituted by leucine.This variant shows less abortive products and altered timing of transition,and is a valuable tool to study these processes.The structural transitions from early to late initiation are well understood and are consistent with solution data.The timing of events and the structural intermediates in the transition from late initiation to elongation are less well understood,but the available data allows one to formulate testable models of the transition to guide further research.展开更多
The ultimate bending moment and maximal shear stress of a bulk carrier with two structural forms （single hull and double hull/ are calculated separately by using the combined moment which is determined by stochastic ...The ultimate bending moment and maximal shear stress of a bulk carrier with two structural forms （single hull and double hull/ are calculated separately by using the combined moment which is determined by stochastic process. Then the assessment of reliability is carried out. The results indicate that by introducing the double-hull structure, the shear stress of side can be decreased to half of that of the primary structure（ 50.7% i. but the effect on longitudinal strength is not obvious. Finally, the effects of different double-side skin widths on ultimate bending moment and the maximal shear stress are investigated, followed by proposals of the selection of the double-side skin width.展开更多
A novel binuclear copper (Ⅱ) complex,namely [Cu 2｛Ph 3P(CH 2) 2CO 2｝ 4(NO 3) 2]·(NO 3) 2 1,has been synthesized from the reaction of Cu(NO 3) 2·4H 2O with Ph 3P +(CH 2) 2CO - 2 L.The si...A novel binuclear copper (Ⅱ) complex,namely [Cu 2｛Ph 3P(CH 2) 2CO 2｝ 4(NO 3) 2]·(NO 3) 2 1,has been synthesized from the reaction of Cu(NO 3) 2·4H 2O with Ph 3P +(CH 2) 2CO - 2 L.The single crystal X ray structural analysis of 1 indicates that the compound crystallizes in space group P1(No.2) with a=12.652(3),b=18.983(4),c=9.102(3),α=97.26(2)°,β=107.38(2)°,γ=102.22(2)° and Z=1.In complex 1,a pair of Cu(Ⅱ) atoms are bridged by carboxylate groups of four ligand molecules with a Cu…Cu distance of 2.738 to form a tetrakis (carboxylato O,O) bridge dimetal core,and the apical coordination positions are occupied by monodentate nitrato anions,which is rare in the structures of similar Cu(Ⅱ) complexes in which the apical ligands are usually neutral molecules.The result shows that introducing the anionic ligands into the coordination sphere of the Cu(Ⅱ) atom significantly increases the Cu…Cu distance.展开更多
A reduced three-degree-of-freedom model simulating the fluid-structure interactions （FSI） of the turbine blades and the on- coming air flows is proposed. The equations of motions consist of the coupling of bending a...A reduced three-degree-of-freedom model simulating the fluid-structure interactions （FSI） of the turbine blades and the on- coming air flows is proposed. The equations of motions consist of the coupling of bending and torsion of a blade as well as a van der Pol oscillation which represents the time-varying of the fluid. The 1：1 internal resonance of the system is analyzed with the multiple scale method, and the modulation equations are derived. The two-parameter bifurcation diagrams are computed. The effects of the system parameters, including the detuning parameter and the reduced frequency, on responses of the struc- ture and fluid are investigated. Bifurcation curves are computed and the stability is determined by examining the eigenvalues of the Jacobian matrix. The results indicate that rich dynamic phenomena of the steady-state solutions including the sad- dle-node and Hopf bifurcations can occur under certain parameter conditions. The parameter region where the unstable solu- tions occur should be avoided to keep the safe operation of the blades. The analytical solutions are verified by the direct nu- merical simulations.展开更多
基金Supported by the National Natural Science Foundation of China(21121064,21206002,21376016)
文摘The impeller configuration with a six parabolic blade disk turbine below two down-pumping hydrofoil propellers, identified as PDT + 2CBY, was used in this study. The effect of the impeller diameter D, ranging from0.30 T to 0.40T(T as the tank diameter), on gas dispersion in a stirred tank of 0.48 m diameter was investigated by experimental and CFD simulation methods. Power consumption and total gas holdup were measured for the same impeller configuration PDT + 2CBY with four different D/T. Results show that with D/T increases from 0.30 to 0.40, the relative power demand(RPD) in a gas–liquid system decreases slightly. At low superficial gas velocity VSof 0.0078 m·s-1, the gas holdup increases evidently with the increase of D/T. However, at high superficial gas velocity, the system with D/T = 0.33 gets a good balance between the gas recirculation and liquid shearing rate, which resulted in the highest gas holdup among four different D/T. CFD simulation based on the two-fluid model along with the Population Balance Model(PBM) was used to investigate the effect of impeller diameter on the gas dispersion. The power consumption and total gas holdup predicted by CFD simulation were in reasonable agreement with the experimental data.
文摘During transcription initiation,RNA polymerase binds tightly to the promoter DNA defining the start of transcription,transcribes comparatively slowly,and frequently releases short transcripts(3-8 nucleotides)in a process called abortive cycling.Transitioning to elongation,the second phase of transcription,the polymerase dissociates from the promoter while RNA synthesis continues.Elongation is characterized by higher rates of transcription and tight binding to the RNA transcript.The RNA polymerase from enterophage T7 (T7 RNAP) has been used as a model to understand the mechanism of transcription in general,and the transition from initiation to elongation specifically.This single-subunit enzyme undergoes dramatic conformational changes during this transition to support the changing requirements of nucleic acid interactions while continuously maintaining polymerase function.Crystal structures,available of multiple stages of the initiation complex and of the elongation complex,combined with biochemical and biophysical data,offer molecular detail of the transition.Some of the crystal structures contain a variant of T7 RNAP where proline 266 is substituted by leucine.This variant shows less abortive products and altered timing of transition,and is a valuable tool to study these processes.The structural transitions from early to late initiation are well understood and are consistent with solution data.The timing of events and the structural intermediates in the transition from late initiation to elongation are less well understood,but the available data allows one to formulate testable models of the transition to guide further research.
文摘The ultimate bending moment and maximal shear stress of a bulk carrier with two structural forms （single hull and double hull/ are calculated separately by using the combined moment which is determined by stochastic process. Then the assessment of reliability is carried out. The results indicate that by introducing the double-hull structure, the shear stress of side can be decreased to half of that of the primary structure（ 50.7% i. but the effect on longitudinal strength is not obvious. Finally, the effects of different double-side skin widths on ultimate bending moment and the maximal shear stress are investigated, followed by proposals of the selection of the double-side skin width.
文摘A novel binuclear copper (Ⅱ) complex,namely [Cu 2｛Ph 3P(CH 2) 2CO 2｝ 4(NO 3) 2]·(NO 3) 2 1,has been synthesized from the reaction of Cu(NO 3) 2·4H 2O with Ph 3P +(CH 2) 2CO - 2 L.The single crystal X ray structural analysis of 1 indicates that the compound crystallizes in space group P1(No.2) with a=12.652(3),b=18.983(4),c=9.102(3),α=97.26(2)°,β=107.38(2)°,γ=102.22(2)° and Z=1.In complex 1,a pair of Cu(Ⅱ) atoms are bridged by carboxylate groups of four ligand molecules with a Cu…Cu distance of 2.738 to form a tetrakis (carboxylato O,O) bridge dimetal core,and the apical coordination positions are occupied by monodentate nitrato anions,which is rare in the structures of similar Cu(Ⅱ) complexes in which the apical ligands are usually neutral molecules.The result shows that introducing the anionic ligands into the coordination sphere of the Cu(Ⅱ) atom significantly increases the Cu…Cu distance.
基金supported by the National Basic Research Program of China(“973” Project)(Grant No.2015CB057405)the National Natural Science Foundation of China(Grant No.11372082)the State Scholarship Fund of CSC
文摘A reduced three-degree-of-freedom model simulating the fluid-structure interactions （FSI） of the turbine blades and the on- coming air flows is proposed. The equations of motions consist of the coupling of bending and torsion of a blade as well as a van der Pol oscillation which represents the time-varying of the fluid. The 1：1 internal resonance of the system is analyzed with the multiple scale method, and the modulation equations are derived. The two-parameter bifurcation diagrams are computed. The effects of the system parameters, including the detuning parameter and the reduced frequency, on responses of the struc- ture and fluid are investigated. Bifurcation curves are computed and the stability is determined by examining the eigenvalues of the Jacobian matrix. The results indicate that rich dynamic phenomena of the steady-state solutions including the sad- dle-node and Hopf bifurcations can occur under certain parameter conditions. The parameter region where the unstable solu- tions occur should be avoided to keep the safe operation of the blades. The analytical solutions are verified by the direct nu- merical simulations.
