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探讨了创造力培养的策略以及在力学教学过程中,教师创造师生之间、生生之间互动的宽松环境,适当举例和设问以激发学生求知的好奇心,利用学生已有的基础知识一步一步引导学牛进入问题的本质,从而达到解决问题的目的.学生在学习过程中,创造力渐渐地就增强了.     

Fluorescent and Biocompatible Ruthenium-Coordinated Oligo(p-phenylenevinylene) Nanocatalysts for Transfer Hydrogenation in the Mitochondria of Living Cells

It is challenging to design metal catalysts for in situ transformation of endogenous biomolecules with good performance inside living cells. Herein, we report a multifunctional metal catalyst, ruthenium-coordinated oligo(p-phenylenevinylene) (OPV-Ru), for intracellular catalysis of transfer hydrogenation of nicotinamide adenine dinucleotide (NAD⁺) to its reduced format (NADH). Owing to its amphiphilic characteristic, OPV-Ru possesses good self-assembly capability in water to form nanoparticles through hydrophobic interaction and π–π stacking, and numerous positive charges on the surface of nanoparticles displayed a strong electrostatic interaction with negatively charged substrate molecules, creating a local microenvironment for enhancing the catalysis efficiency in comparison to dispersed catalytic center molecule (TOF value was enhanced by about 15 fold). OPV-Ru could selectively accumulate in the mitochondria of living cells. Benefiting from its inherent fluorescence, the dynamic distribution in cells and uptake behavior of OPV-Ru could be visualized under fluorescence microscopy. This work represents the first demonstration of a multifunctional organometallic complex catalyzing natural hydrogenation transformation in specific subcellular compartments of living cells with excellent performance, fluorescent imaging ability, specific mitochondria targeting and good chemoselectivity with high catalysis efficiency.     

Fractionated crystallization and morphology of PP/PS blends in the presence of silica nanoparticles with different surface chemistries

The fractionated crystallization behavior of polypropylene (PP) droplets in its 20/80 blends with polystyrene (PS) in the presence of hydrophilic or hydrophobic fumed silica nanoparticles was studied by using differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. It was found that the fractionated crystallization of PP droplets in the PS matrix was promoted by adding a low content of hydrophobic or hydrophilic nanoparticles due to their morphological refinement effect. However, discrepancies in the fractionated crystallization behavior of PP droplets occurred as the nanoparticle content increased. The crystallization became dominated by the heterogeneous nucleation effect of high content of hydrophilic nanoparticles, which possibly migrated into PP droplets during mixing and significantly suppressed their fractionated crystallization. In contrast, the morphological refinement effect still played a dominated role in promoting the fractionated crystallization of PP droplets in PP/PS blends filled with higher content hydrophobic nanoparticles as a result of the efficiently morphological refinement effect.     

Studies on the interaction mechanism between CXS and papain by spectroscopic and molecular modeling methods

We have studied the interaction between cefuroxime sodium (CXS) and papain at different temperatures by a fluorescence method, and confirmed that the mechanism of fluorescence quenching of CXS to papain is mainly static quenching. We also determined the binding constant K. Based on the thermodynamic functions at different temperatures, the results show that the major forces between CXS and papain are van der Waals’ forces and H bond. According to the Forster non-radiation energy transfer mechanism, we determined the binding distance between CXS and papain, and studied the confirmation effect of CXS to papain by synchronous fluorescence and UV–Vis spectroscopy. Molecular simulations show that the binding types of CXS and papain are van der Waals’ forces, hydrophobic interaction, and H-bond.     

A novel static shape-adjustment technique for planar phased-array satellite antennas

Planar phased-array satellite antennas deform when subjected to external disturbances such as thermal gradients or slewing maneuvers. Such distortion can degrade the coherence of the antenna and must therefore be eliminated to maintain performance. To support planar phased-array satellite antennas, a truss with diagonal cables is often applied, generally pretensioned to improve the stiffness of the antenna and maintain the integrity of the structure. A new technique is proposed herein, using the diagonal cables as the actuators for static shape adjustment of the planar phased-array satellite antenna. In this technique, the diagonal cables are not pretensioned; instead, they are slack when the deformation of the antenna is small. When using this technique, there is no need to add redundant control devices, improving the reliability and reducing the mass of the antenna. The finite element method is used to establish a structural model for the satellite antenna, then a method is introduced to select proper diagonal cables and determine the corresponding forces. Numerical simulations of a simplified two-bay satellite antenna are first carried out to validate the proposed technique. Then, a simplified 18-bay antenna is also studied, because spaceborne satellite antennas have inevitably tended to be large in recent years. The numerical simulation results show that the proposed technique can be effectively used to adjust the static shape of planar phased-array satellite antennas, achieving high precision.     

Hollow fiber‐based liquid membrane microextraction combined with high‐performance liquid chromatography for extraction and determination of trimetazidine in human plasma

A hollow fiber‐based liquid phase microextraction strategy combined with high‐performance liquid chromatography was evaluated for the quantitative determination of trimetazidine in human plasma. Trimetazidine was extracted from a 2.1 mL basified plasma sample (donor phase) into the organic solvent (n‐octanol) impregnated in the pores of a hollow fiber and then extracted into an acidic solution (acceptor phase) inside the lumen of the hollow fiber. The result showed that transport of drugs from alkaline sample solution into 0.5 m HCl occurred efficiently when 25 μL of 250 mm sodium 1‐octanesulfonate was added into the donor phase. Several parameters influencing the efficiency of the method, such as the nature of organic solvent used to impregnate the membrane, compositions of donor phase and acceptor phase, type and concentration of carrier, extraction time, stirring rate and salt concentration, were investigated and optimized. Under the optimal conditions, the calibration curves were obtained in the range of 5–200 ng/mL with reasonable linearity (r > 0.9980). The method was successfully applied to determine the concentration of trimetazidine in human plasma. Copyright © 2012 John Wiley & Sons, Ltd.     

‘Ligand-free’ palladium-catalyzed direct C–H bond oxidative acyloxylation of 2-arylpyridines with aromatic carboxylic acids

A palladium-catalyzed direct C–H bond oxidative acyloxylation of 2-arylpyridines with aromatic carboxylic acids is described. Several 2-arylpyridines derivatives and aromatic carboxylic acids participate in the reaction, providing a series of mono-acyloxylated products in moderate to good yields. Importantly, the reaction can be conducted without using any ligands in a lower temperature.     

Energy Estimates and Gravitational Collapse

In this paper, we establish energy estimates for Einstein vacuum equations in order to prove the evolutionary formation of black holes. The novelty of the paper is that we can completely avoid using rotation vector fields to prove the global existence of solution. More precisely, we use only canonical null vector fields as commutators to derive energy estimates at the level of the first derivatives of null curvature components. The special cancelations from the null structure of non-linear interaction yield the desired estimates.