关键词： Kinetics   Solvent effect   Solvatochromic parameters   Single electron transfer (SET) pathway   Biphasic concave upward free energy relationship  

摘要： The kinetics and mechanism of the aromatic nucleophilic substitution reactions of 2,6-bis(trifluoromethanesulfonyl)-4-nitroanisole with para-X-substituted anilines (X = OH, OMe, Me, H, F, I, Cl) were studied in MeOH-Me2SO mixtures and pure Me2SO at 25.0 A degrees C. The second-order rate coefficients depend on the substitutent in aniline and give good Hammett and Bronsted correlations;a polar SNAr reaction is proposed for the reaction in different MeOH-Me2SO mixtures. The measured rate coefficients of the reaction demonstrated dramatic variations for aniline donor with the increasing dimethyl sulfoxide composition in MeOH-Me2SO mixtures. In this case, the Hammett and Bronsted plots are biphasic and concave upwards with a break point at 4-methylaniline. These results indicate a change in mechanism from the polar (SNAr) for less basic nucleophiles (X = 4-Cl, 4-I, 4-F, and H) to the single electron transfer (SET) for more basic nucleophiles (X = 4-OH, 4-OMe and 4-Me). The changes of the structure of the transitions states with substituents and solvent are in accordance with the results of kinetics studies. The solvation model described is well supported by the solvatochromism exhibited by aniline in the solvent mixture under investigation. These results provide an ideal framework for understanding the paramount importance of the specific molecular structure of solvent molecules in determining chemical reactivity versus solvent effects.

关键词： Heart Rate   Systolic Blood Pressure   Diastolic Blood Pressure   Hemodynamic Parameter   Hemodynamic Response  

摘要： Background: Carbon monoxide (CO) poisoning can be a life threatening condition. Systemic hyperbaric oxygen (HBO) therapy is used to induce CO detoxification. However, little is known about the hemodynamic response to HBO in severely intoxicated patients. Methods: We retrospectively analyzed the medical records of 6 CO-poisoned patients treated with propofol, rocuronium bromide, and HBO. The HBO protocol comprised 3 HBO treatments (HBOT1 to HBOT3) within 24 hours. During all HBO sessions heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse blood pressure (Delta BP) were measured every five minutes. Non-parametric tests were used to compare data between HBO sessions. Results: HR increased significantly as the number of HBOT increased, from 68 beats per minute (bpm) during HBOT1 to 77 and 86 bpm during HBOT2 and HBOT3, respectively (p < 0.05). In addition, while no significant change was found for DBP, both SBP and Delta BP showed a transient and significant increase during HBOT2, compared to HBOT1, that did not return to basal values during HBOT3. Conclusion: Based on previous studies that have established the respective effects of rocuronium bromide, propofol, HBO, and CO alone on HR, SBP, and Delta BP, it is concluded that the hemodynamic responses observed in the present study are likely to be due to CO. If such, given that neither HR nor SBP and Delta BP returned to basal values by the end of HBOT3, it is suggested that more than 3 HBOT sessions could be necessary to provide full hemodynamic recovery in CO-poisoned patients.

关键词： Poly(butylene terephthalate)   Polymer nanocomposites   Crystallization kinetics   MMT   Regime kinetics   Mechanical properties   Lauritzen Z test  

摘要： Nanocomposites (PCNs), based on poly(butylene terephthalte) (PBT) and organoclay (Cloisite-15A) MMT were prepared by melt intercalation compounding process. The nanoscale dispersion and the micro-crystal structure studied qualitatively using;X-ray diffraction (XRD) and electron microscopy (SEM, TEM and AFM). The XRD results indicated that the crystal size is highly dependent on the crystallization temperature. The isothermal crystallization kinetics of PBT in PCNs analysis indicated that the overall crystallization of PBT involved heterogeneous nucleated three-dimensional spherical primary crystallization growth process. The crystallization rate, however, is dependent on the PCN-composition, crystallization temperature and the dispersion state of clay in PCNs. Further analysis, based on Hoffman-Lauritzen theory revealed that the neat PBT and PBT in PCNs crystallization follow regime-II kinetics for temperature 195 degrees C-205 degrees C and enters the regime-III kinetics in lower T-C range, 185 degrees C-195 degrees C. The improvement in mechanical properties is highly dependent on the level of clay exfoliation in PBT matrix. (c) 2013 Elsevier B.V. All rights reserved.

摘要： Naturally occurring groups of muscle myosin behave differently from individual myosins or small groups commonly assayed in vitro. Here, we investigate the emergence of myosin group behavior with increasing myosin group size. Assuming the number of myosin binding sites (N) is proportional to actin length (L) (N = L/35.5 nm), we resolve in vitro motility of actin propelled by skeletal muscle myosin for L = 0.2-3 mu m. Three distinct regimes were found: L < 0.3 mu m, sliding arrest;0.3 mu m <= L <= 1 mu m, alternation between arrest and continuous sliding;L > 1 mu m, continuous sliding. We theoretically investigated the myosin group kinetics with mechanical coupling via actin. We find rapid actin sliding steps driven by power-stroke cascades supported by postpower-stroke myosins, and phases without actin sliding caused by prepower-stroke myosin buildup. The three regimes are explained: N = 8, rare cascades;N = 15, cascade bursts;N = 35, continuous cascading. Two saddle-node bifurcations occur for increasing N (mono -> bi -> mono-stability), with steady states corresponding to arrest and continuous cascading. The experimentally measured dependence of actin sliding statistics on L and myosin concentration is correctly predicted.

摘要： The envelope lipid composition of influenza virus differs from that of the cellular plasma membrane from which it buds. Viruses also appear to fuse preferentially to specific membrane compartments, suggesting that the lipid environment may influence permissiveness for fusion. Here, we investigated the influence of the membrane environment on fusion, focusing on cholesterol composition. Strikingly, manipulating cholesterol levels in the viral membrane had different effects on fusion kinetics compared with analogous changes to the target membrane. Increasing cholesterol content in target vesicles increased lipid- and contents-mixing rates. Moderate cholesterol depletion from the viral membrane sped fusion rates, whereas severe depletion slowed the process. The pleiotropic effects of cholesterol include alterations in both membrane-bending moduli and lateral organization. Because influenza virions have demonstrated cholesterol-dependent lateral organization, to separate these effects, we deliberately selected a target vesicle composition that does not support lateral heterogeneity. We therefore postulate that the monotonic response of fusion kinetics to target membrane cholesterol reflects bending and curvature effects, whereas the multiphasic response to viral cholesterol levels reflects the combined effects of lateral organization and material properties.

关键词： 工程机械紧急动力源   直流电机   液压动力源   蓄电池容量  

摘要： 针对工程机械液压系统动力源出现故障后不能正常工作的现象,提出了一种采用直流电机驱动的紧急动力源设计方案。以同步碎石封层车的液压系统为例,进行了紧急动力源系统设计。分析计算表明,设备的蓄电池容量可以满足紧急动力源对能量的要求,因此该方案可行。

关键词： 树木注射机   行业标准   标准编制  

摘要： 在分析树木注射过程特点的基础上,提出了树木注射机相关的基本术语定义、机械动力树木注射机型号编制、主要的技术要求与性能试验方法。

关键词： 上海交通大学   工程学院   机械   新中国   自动扶梯   运载火箭   两弹一星   人造卫星  

摘要： 上海交通大学机械与动力工程学院始建于1913年，是上交大历史最悠久的院系之一。在其发展史上，创造了许多中国第一：中国最早的内燃机、第一台自动扶梯等，以及，新中国的第一艘万吨轮，第一艘核潜艇、第一颗原子弹、第一枚运载火箭、第一颗人造卫星……在1999年国务院表彰的两弹一星功臣中，钱学森、王希季等均毕业于机械与动力工程学院。

关键词： 机械活化   淀粉   反相乳液   接枝共聚   接枝共聚速率  

摘要： 以机械活化淀粉为接枝母体,研究了在机械活化淀粉/单体(AM)/乳化剂/油/水五元反相乳液体系中引发机械活化淀粉接枝丙烯酰胺共聚反应的动力学。分别考察了引发剂浓度、单体浓度、淀粉乳浓度和乳化剂浓度等对接枝量和接枝共聚速率(R g)的影响。结果表明,在本实验考察范围内的动力学关系式为R g∞[mSt]1.24[I]0.76[M]1.54[E]0.33,淀粉与丙烯酰胺的接枝共聚速率随体系温度升高而加快,淀粉乳浓度和单体浓度对接枝共聚速率影响显著,在45℃～60℃范围内,接枝共聚反应链增长步骤的活化能为34.85 kJ/mol。