1-辛烯Ziegler-Natta聚合的活性中心多分散性——分子量分布及动力学的研究

本文通过对TiCl_3-Al(C_2H_5)_3聚合1-辛烯产物的双峰型分子量分布曲线用Schulz函数进行拟合、分峰处理,发现这种双峰型分布中的高分子量峰部分由一种活性中心生成,低分子量峰部分则由至少两种活性中心生成.将不同转化率时聚辛烯的分子量分布分峰拟合数据与聚合速率、活性中心数等测定数据相结合,得到了高分子量和低分子量两部分产物相应的活性中心上各自的动力学参数(增长速率常数、活性中心数、链转移常数等)及各自的聚合速率曲线,从而证实了多种活性中心的存在、它们催化特性的差异及与聚合物分子量分布增宽的关系.     

木材溶液中羟基与异氰酸酯反应的研究

以涂料工业广泛应用的新型助剂二元酸酯 (DBE)为液化试剂 ,盐酸为催化剂 ,将苯甲基化木材溶液化后 ,与不同结构的异氰酸酯反应 .利用FT IR及1 3C NMR分析液化苯甲基木质纤维素与不同结构异氰酸酯得到了聚氨酯树脂 ,证明了木材中羟基可以用来作为聚醚多元醇与异氰酸酯制备聚氨酯材料 .通过准确测量体系中游离的NCO含量 ,从而得出不同结构异氰酸酯与木材溶液中羟基的反应规律 .实验结果表明 ,异氰酸酯的存在大大促进了木材结构中羟基的释放 ,由于不同异氰酸酯的活性不同 ,使得羟基值变化亦不相同 ,其顺序为IPDI>HDI>TDI .为了保证最终的材料性能 ,选择TDI和IPDI作为木材溶液制备聚氨酯树脂的异氰酸酯组份较好     

Conformation of receptor-associated PGI2: An investigation by molecular modeling

Summary To elucidate the conformation of receptor-associated prostacyclin (PGI₂), we first performed structure-activity correlation analysis of over 200 PGI₂ analogues and derived from this analysis several crucial features pertaining to structural requirements for PGI₂ activity [Ah-lim Tsai and Kenneth K. Wu, Eicosanoids, 2 (1989) 131–143]. These structural features proved to be useful guidelines for selecting model molecules for further investigations by molecular mechanics. By properly selecting four analogues with either rigid or uniquely oriented -side chain structure for geometric fitting, we succeeded in maximally minimizing the degree of freedom of the carboxylate terminus of PGI₂. We were able to define the spatial relationship among the four critical functional groups, i.e., C1-COOH, C6a-O, C11-OH and C15-OH. More information is needed, however, to define the geometry of the -side chain, particularly for the moiety beyond C15. Nevertheless, results from structure-activity correlation analysis and molecular modeling provide useful information regarding the conformation of receptor-associated PGI₂, which assumes an elongated conformation instead of the traditional hairpin structure.     

Active transport of Na + and K + through animal cell membranes

The transport of Na⁺ out of the cell and K⁺ into the cell against a concentration gradient is catalyzed by a (Na⁺ + K⁺)-activated ATPase. The way in which the cations pass through the cell membrane has not yet been elucidated. Studies on the ATP hydrolysis revealed a Na⁺-dependent phosphorylation of the enzyme protein; the conformation of the enzyme also appears to change. The energy required for transport of the cations against their concentration gradients is probably provided by K⁺-dependent hydrolysis of the enzyme-bound phosphate. The enzyme can synthesize ATP from inorganic phosphate and ADP on reversal of the cation concentration gradient. By keeping the enzyme in a particular conformation, the cardiac glycoside ouabain specifically inhibits the Na⁺ pump.     

能动抛光磨盘的变形实验研究

 能动抛光磨盘实时产生不同的表面变形，在对大口径非球面光学元件进行精磨和抛光时实现与工件表面良好的大尺寸吻合，可以消除传统光学加工采用小尺寸磨头时带来的高频残余误差并提高加工效率。以加工直径1.3m左右，F/2的抛物面光学元件为例，对能动磨盘在不同离轴度时能够产生的变形进行了计算和实验。结果表明，能动磨盘能够以较高精度产生旋转对称或非对称的抛物面形状。对能动磨盘产生变形后的残余误差进行了分析。     

Brownian diode: Molecular motor based on a semi-permeable Brownian particle with internal potential drop

A model of an autonomous isothermal Brownian motor with an internal propulsion mechanism is considered. The motor is a Brownian particle which is semi-transparent for molecules of surrounding ideal gas. Molecular passage through the particle is controlled by a potential similar to that in the transition rate theory, i.e. characterized by two stationary states with a finite energy difference separated by a potential barrier. The internal potential drop maintains the diode-like asymmetry of molecular fluxes through the particle, which results in the particle?s stationary drift.     

Active transient elasto-acoustic response damping of a thick-walled liquid-coupled piezolaminated cylindrical vessel

The linear 3D piezoelasticity theory in conjunction with the versatile transfer matrix approach and the wave equation for the internal acoustic domain are employed for active non-stationary vibroacoustic response control of an arbitrarily thick, tri-laminate, fluid-filled, simply supported, piezocomposite cylindrical tank, excited by arbitrary (non-axisymmetric) time-dependent on-surface mechanical loads. The smart structure is composed of a supporting core layer of functionally graded orthotropic material perfectly bonded to inner and outer spatially distributed radially polarized functionally graded piezoceramic sensor and uniform force actuator (FGPM) layers. Active vibration damping is implemented by transferring the accumulated voltage on the sensor layer to the piezoelectric actuator layer in context of proportional and derivative control laws. Durbin's numerical inverse Laplace transform scheme is utilized to calculate the time response histories of the relevant interface displacement/stress components, center-point acoustic pressure, and actuator voltage, for selected loading configurations (i.e., concentrated step, impulse, and moving external loads). Numerical simulations demonstrate the effectiveness of the adopted distributed sensing/actuation configuration together with the active damping control strategy in suppressing the vibroacoustic response of a three-layered (Ba₂NaNb₅O₁₅/Al/PZT4) water-filled piezoelastic cylindrical tank. Limiting cases are considered and the validity of results is established by comparison with the available data as well as with the aid of a commercial finite element package.     

Radial sample load distribution under overload conditions: Analytical scale columns

The homogeneity of the sample load across the radial cross section of analytical scale columns was determined when operating under overload conditions. The study was performed using active flow technology columns operating in parallel segmentation mode. The outlet segmentation ratio was varied to enable different volume fractions of mobile phase, and thus sample, to elute from the peripheral and central flow regions of the column. The amount of solute exiting the peripheral and radial central exit ports was determined as a function of the flow segmentation ratio. The experimental data using an analytical scale column with dimensions, 100?×?4.6?mm, indicated that the sample load distribution was essentially uniform as a function of the column radial cross section.     

Performance investigation of an advanced tracked prime mover on the low bearing soil

This study has presented a performance investigation of an advanced tracked prime mover for the operation of agricultural goods and other operations on peat terrain. The maximum and continuous traction torque of the prime mover has been developed by designing an advanced controller for controlling the intelligent system. The prime mover’s mobility is studied with ultrasonic displacement sensor, torque transducer, National Instrument cRIO-9004 Compact-RIO Real-time Controller Unit (RCU), a National Instrument TPC 2106T Touch Panel Control (TPC), a Trimble AG132 GPS antenna and receiver unit, and a Dlink DIR-655 router. The fuzzy logic controller (FLC) has been equipped with the prime mover hydraulic system to increase the traction torque of the hydraulic motor when the prime mover’s sinkage is more than or equal to 70 mm. The prime mover’s design demonstrates good potential in traversing peat terrain as the measured tractive effort was found to be 48% of the vehicle’s gross weight while the recommended tractive effort is in the range of 30–36% of the vehicle’s gross weight.     

Study of Michael addition on chalcones and or chalcone analogues

Michael addition reaction of 1,3-diphenyl-propenone 1a, e, and f with o-amino thiophenol in the presence of indium trichloride gave the benzothiazine derivatives 2a–c. Condensation of the compound 1a, e with o-phenylene diamine in triethylamine gave the benzodiazepine derivatives 3a–b. Cyclization of 1d with malononitrile in the presence of NaOR/EtOH gave the compound 4. Addition of thiobarbituric acid in triethylamin to 1a gave 5. Condensation of compound 1c with malononitrile in the presence ammonium acetate gave compound 6. 1,3-diphenyl-propenone 1a used as key starting chalcone to react with different active methylene reagents under phase-transfer catalysis condition gave compound 7–9. The structures of the prepared compounds were mainly confirmed on the basis of spectroscopic methods.