关键词： Genetics   Stereoselectivity   Free radicals   Bisphenols   Post-translational modification  

摘要： We previously communicated that high alpha-selectivity that can be achieved in intramolecular glycosylations using a rigid bisphenol A template supplemented with linkers of various lengths. Herein, we present our investigation of the mechanistic aspects of the templated synthesis that helped to design an improved template-linker combination. We demonstrate that bisphenol A as the template in combination with phthaloyl linker allows for superior stereoselectivity and yields in glycosylations. Several mechanistic studies explore origins of the enhanced stereoselectivity and yields achieved using the phthaloyl linker.

关键词： PrMg12 alloy   Mechanical milling   Activation energy   Hydrogen storage   Kinetics  

摘要： Mechanical ball milling technology was utilized to synthesize the nanocrystalline and amorphous PrMg11Ni + x wt% Ni (x = 100, 200) alloys. The effect of Ni content and milling time on thermodynamics and kinetics of the alloys were systematically investigated. The hydrogen absorption and desorption properties were analyzed by Sievert's apparatus and differential scanning calorimetry (DSC). Results show that increasing Ni content brings on a slight reduction in thermodynamic parameters (Delta H and Delta S) of the alloys, and it dramatically enhances the hydrogen absorption and desorption kinetics of the alloys. Varying milling time greatly affects the hydrogen storage properties of the alloys. The hydrogen absorption capacity of the alloys first increases and then deceases with the increase of milling time, and the maximum capacity of the alloy is approximately 5.8 wt% and 6.0 wt% for the x = 100 and x = 200 alloys. Moreover, the hydrogen desorption activation energy obviously decreases with increasing the Ni content and ball milling time. (C) 2016 Elsevier B.V. All rights reserved.

关键词： TiAl alloy   High temperature deformation   Grain boundary sliding   Dislocation creep   Diffusion creep   Rate-equation  

摘要： gamma-TiAl-based alloys have attracted intense attentions in the past two decades and are regarded as promising candidate materials for high-temperature applications due to their low density, high specific strength, superior creep and oxidation resistance, etc. It is well known that there are four typical microstructures in TiAl-based alloys, namely, full-lamellar (FL), near-lamellar (NL), duplex (DP) and near gamma (NG). The FL/NL-TiAl alloys possess superior high temperature mechanical performance such as creep resistance, but their deformability is relatively lower. In contrast, the DP/NG-TiAl alloys have much better formability while the creep resistance is reduced. Hence the DP/NG microstructure is preferable for hot-working and thought to the prerequisite for secondary processing, and the present paper is primarily focused on the high temperature deformation behavior of DP/NG-TiAl alloys. Till date, considerable research efforts have been directed towards the deformation kinetics or mechanical properties of various DP/NG-TiAl alloys, and a mass of experimental data has been accumulated. In order to explore their general features of high temperature deformation kinetics, in this paper the tensile/compression mechanical data of various DP/NG-TiAl alloys from the literature published in the past twenty years has been summarized and reviewed. Three deformation mechanisms (dislocation creep, grain boundary sliding and diffusion creep) have been identified, and for each the effects of major factors (i.e., alloy composition, microstructure and grain size) on deformation kinetics have been analyzed and discussed in detail. The results revealed that the high temperature deformation kinetics of DP/NG-TiAl alloys is less sensitive to composition except some dispersion-hardened alloys such as carbon-containing TiAl alloys. Instead, the gamma grain size became the major limiting factor. Based on this observation, a series of unified rate-equations has been successfully dev

关键词： crystallization   degradation   mechanical properties   thermal properties  

摘要： The basic thermal properties, isothermal melt crystallization kinetics, spherulitic morphology, mechanical properties, and hydrolytic degradation behavior of a novel eco-friendly polyester poly(butylene diglycolate) (PBDG) containing ether linkages were systematically studied with several techniques in this research. PBDG is an aliphatic polyester with high thermal stability. It had a glass transition temperature (T-g) of -25.7 degrees C, a melting point temperature of 65.1 degrees C, and an equilibrium melting point of 73.2 degrees C. During the isothermal melt crystallization, PBDG crystallized slowly with increasing crystallization temperature, but the crystallization mechanism did not change. Negative spherulites were observed for PBDG. The mechanical properties of PBDG were investigated from the tensile testing. As a ductile polyester, PBDG possessed good mechanical properties. PBDG also showed a fast hydrolytic degradation rate. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44186.

关键词： Solid polymer electrolyte   Molecular dynamics   Viscoelastic properties   Failure properties  

摘要： Multifunctional composites with load carrying and electrical energy storage capability are relevant for diverse applications. Due to often conflicting requirements for improving both functions, extended knowledge of mechanical material properties is crucial. This study analyzes the mechanical properties of a solid polymer electrolyte material for structural battery applications by means of reactive molecular dynamics simulations. Specifically, conditions for improving load carrying capacity are considered. With the aim of determining optimum salt concentration for mechanical performance, we report the findings on the electrolyte salt effects on the polymer's mechanical properties, including hydrostatic failure behavior. The findings indicate a possibility for stiffness improvement above a threshold concentration value, as well as significant differences in isotropic compression and expansion failure behavior. In isotropic expansion and shear, small failure strength and failure strain reduction at increasing salt concentration is observed. In hydrostatic compression no material failure is observed up to 10 GPa. As a part of the molecular dynamics potential validation, the observed differences between references and test simulation results for ion transport related properties of a common solid polymer electrolyte have been assessed and discussed. (C) 2016 Elsevier Ltd. All rights reserved.

摘要： Calmodulin-based genetically encoded fluorescent calcium indicators (GCaMP-s) are powerful tools of imaging calcium dynamics from cells to freely moving animals. High affinity indicators with slow kinetics however distort the temporal profile of calcium transients. Here we report the development of reduced affinity ultrafast variants of GCaMP6s and GCaMP6f. We hypothesized that GCaMP-s have a common kinetic mechanism with a rate-limiting process in the interaction of the RS20 peptide and calcium-calmodulin. Therefore we targeted specific residues in the binding interface by rational design generating improved indicators with GCaMP6f(u) displaying fluorescence rise and decay times (t(1/2)) of 1 and 3 ms (37 degrees C) in vitro, 9 and 22-fold faster than GCaMP6f respectively. In HEK293T cells, GCaMP6f(u) revealed a 4-fold faster decay of ATP-evoked intracellular calcium transients than GCaMP6f. Stimulation of hippocampal CA1 pyramidal neurons with five action potentials fired at 100 Hz resulted in a single dendritic calcium transient with a 2-fold faster rise and 7-fold faster decay time (t(1/2) of 40 ms) than GCaMP6f, indicating that tracking high frequency action potentials may be limited by calcium dynamics. We propose that the design strategy used for generating GCaMP6fu is applicable for the acceleration of the response kinetics of GCaMP-type calcium indicators.

关键词： Mechanical properties   Stacking fault energy   Dynamic recovery   Mobile dislocation density   Cu-Al alloys   Surface mechanical attrition treatment  

摘要： In this paper, a series of Cu-Al alloys (2.2, 4.5, and 6.9 wt pct Al) with decreasing stacking fault energy (SFE) were processed by surface mechanical attrition treatment (SMAT) to obtain a gradient structure (GS). The yield strength of SMAT-ed samples is attributed to the volume fraction of GS layer and the ductility is associated with the dynamic recovery during deformation. Kocks-Mecking model was utilized to describe the storage and annihilation of dislocations in these samples. The results show that the minimal K2, which represents dynamic recovering, appears in Cu-4.5 wt%Al alloy with a medium SFE, indicating a suppressed dislocation annihilation and a delayed plastic instability during plastic deformation. Repeated stress relaxation tests were applied to characterize the activation volume and the evolution of mobile dislocation. It turns out that the highest relative mobile dislocation density (rho m/rho m0) emerges in Cu-4.5 wt%Al sample. This could be ascribed to the sufficient twin boundaries (TBs) which can keep the accumulated dislocations slipping easily and lower the exhaustion of mobile dislocation. The high rho m/rho m0 demonstrates that more mobile dislocation is preserved and the dislocation annihilation is effectively prohibited in the sample, in accordance with the low K2 obtained from Kocks Mecking model, providing a reasonable interpretation for the good ductility. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Amorphous alloy   Mechanical alloying   Mg60Zn30Ti5Si5   Apparent activation energy of crystallization   Local activation energy  

摘要： Mg60Zn30Ti5Si5 amorphous alloy was prepared via mechanical alloying (MA) and heat treated in different way. X-ray diffractometer (XRD) was used to detect the phases of alloy. The crystallization characteristics and kinetics of amorphous alloy were investigated by differential scanning calorimetry (DSC). Tests reveal that raw materials transform to amorphous alloy after 6 h mechanical alloying;during subsequent heating, MgZn2, Mg2Si and Zn were crystallized in turn. Apparent activation energies (Ea) and local activation energies (Et) of non-isothermal crystallization were calculated according to Kissinger and Ozawa models based on DSC data. Results show that E-a3 > E-a2 > E-a1;E-l1 decreases while E-l2 increases with crystallization;E-l3 is almost stable during heating. Avrami parameters (n) indicate that the first devitrification is interface controlled growth and later precipitations are diffusion controlled growth. (C) 2016 Elsevier B.V. All rights reserved.

关键词： 急性呼吸窘迫综合征   机械通气   急性肺心病  

摘要： 急性呼吸窘迫综合征(acute respiratory distress syndrome,ARDS)肺保护性通气策略已得到广泛运用,但病死率并无明显下降,这与ARDS患者循环衰竭有一定关系。ARDS患者机械通气可引起的胸腔压力变化导致静脉回流减少,肺血管阻力升高。同时,由于ARDS疾病本身也可引起肺动脉压力升高,因此,如机械通气设置不当导致肺泡过度牵张,右心后负荷明显增加,可致右室功能障碍,发展为急性肺心病。ARDS肺保护性通气策略实施过程中应注意监测右心功能,调整通气策略,防止急性肺心病的发生。