Venturi-type fluidic sampler for liquid–solid mixtures

Static-type samplers are required for sampling corrosive, toxic, high-temperature, or radioactive liquid–solid fluids. We have designed a compact reverse flow diverter pumping system for transferring liquid–solid mixtures. In accordance with the Venturi principle, an acceptable volume of liquid–solid fluid is automatically collected into a sampling bottle. The effects of sampling needle sizes, sectional area of the T-section, solid concentration, and liquid viscosity on the performance of fluidic samplers were experimentally investigated. The sample volume increased upon the reduction of the sampling needle length and the increase of the sectional area of the T-section, but decreased with the increase of solid concentration and liquid viscosity. Unbiased samples of acceptable volume were produced by the proposed fluidic sampler, even at 10.21 mPa s liquid viscosity, 35 wt% solid concentration, and 6.74 m sampling height.     

Preparation of ternary Cr2O3–SiC–TiO2 composites for the photocatalytic production of hydrogen

Novel ternary Cr₂O₃–SiC–TiO₂ composites were synthesized by implanting Cr³⁺ into SiC–TiO₂ via sol–gel and impregnation approaches. The results from X-ray diffraction, scanning electron microscopy and transmission electron microscopy show that the Cr³⁺ species were doped onto the surface of the SiC–TiO₂ carrier. The diffuse reflectance ultraviolet–visible absorption spectra revealed that the absorption edges of the ternary Cr₂O₃–SiC–TiO₂ composites were gradually shifted red with increasing chromium content. The luminescence intensities of the composites decreased with increasing doped Cr³⁺ content due to the reduction in the number of recombination sites of electron–hole pairs. The ternary Cr₂O₃–SiC–TiO₂ composites showed high hydrogen-producing activities, which probably results from the formation of donor levels of the Cr³⁺ species in the forbidden band of the SiC semiconductor.     

Displaced orbits generated by solar sails for the hyperbolic and degenerated cases

Displaced non-Keplerian orbits above planetary bodies can be achieved by orientating the solar sail normal to the sun line. The dynamical systems techniques are employed to analyze the nonlinear dynamics of a displaced orbit and different topologies of equilibria are yielded from the basic configurations of Hill’s region, which have a saddlenode bifurcation point at the degenerated case. The solar sail near hyperbolic or degenerated equilibrium is quite unstable. Therefore, a controller preserving Hamiltonian structure is presented to stabilize the solar sail near hyperbolic or degenerated equilibrium, and to generate the stable Lissajous orbits that stay stable inside the stabilizing region of the controller. The main contribution of this paper is that the controller preserving Hamiltonian structure not only changes the instability of the equilibrium, but also makes the modified elliptic equilibrium become unique for the controlled system. The allocation law of the controller on the sail’s attitude and lightness number is obtained, which verifies that the controller is realizable.     

ACL单束/双束重建对多屈曲角位姿的胫股关节力学特性影响

进行膝关节的轴移仿真, 在证实了单例个体膝关节的重建模型能反映不同重建术后膝关节力学特性有效性的基础上, 应用SONATA MAESTRO 1.5T扫描得到的屈曲角位姿为0°/25°/60°/80° 的膝关节MRI图像数据, 建立了对应屈曲角的正常/ACL(anterior cruciate ligament)单束/双束重建胫股关节3D模型, 通过对该系列关节模型施加轴向压力与压扭载荷, 来分析多屈曲角度位姿的ACL单束/双束重建法对胫股关节软骨、半月板和韧带应力分布影响及韧带张力特性影响. 结果表明: (1) ACL单束/双束重建关节的软骨与半月板上的应力分布改变跟屈曲角度相关, 某些角度位姿下软骨应力分布改变显著; (2) 单束重建关节的软骨和半月板上的最大等效应力有较明显的增大, 最大增幅达40%左右; 双束重建关节在各屈曲角位姿下软骨和半月板上的最大等效应力值更接近于正常关节; (3) ACL单束重建虽降低了PCL(posterior cruciate ligament)的最大等效应力值, 却使高屈曲角位姿的内侧/外侧副韧带等效应力明显增大; 双束重建后MCL(medial collateral ligament)上的最大等效应力随屈曲角的变化明显, 但LCL(lateral collateral ligament)和PCL的最大等效应力随屈曲角度的变化趋势与正常关节相一致性; (4) 单束/双束重建后MCL上平均张力要高于另外两条韧带, 而双束重建的韧带张力特性比单束重建更接近于正常关节. 总之, 综合ACL重建后软骨、半月板和3条韧带随屈曲角度的等效应力分布、张力变化等多种特性表明: ACL双束重建的胫股关节力学特性比单束重建更接近于正常关节, 且无论ACL单束还是双束重建, 都引起术后关节软骨与韧带上应力分布变化与等效应力峰值增大, 这将是诱发术后关节慢性退变与膝关节并发症的根源.     

In situ investigation of the mechanical properties of nanomaterials by transmission electron microscopy

With the progress of modern transmission electron microscopy (TEM) and development of dedicated functional TEM specimen holders, people can now manipulate a nano-object with nanometer-range precision and simultaneously acquire mechanical data together with atomic-scale structural information. This advanced methodology is playing an increasingly important role in nanomechanics. The present review summarizes relevant studies on the in situ investigation of mechanical properties of various nanomaterials over the past decades. These works enrich our knowledge not only on nanomaterials (such as carbon nanotubes, carbon onions, boron nitride nanotubes, silicon nanowires and graphene, etc.) but also on mechanics at the nanoscale.     

On the General Ericksen–Leslie System: Parodi’s Relation, Well-Posedness and Stability

In this paper we investigate the role of Parodi’s relation in the well-posedness and stability of the general Ericksen–Leslie system modeling nematic liquid crystal flows. First, we give a formal physical derivation of the Ericksen–Leslie system through an appropriate energy variational approach under Parodi’s relation, in which we can distinguish the conservative/dissipative parts of the induced elastic stress. Next, we prove global well-posedness and long-time behavior of the Ericksen–Leslie system under the assumption that the viscosity μ ₄ is sufficiently large. Finally, under Parodi’s relation, we show the global well-posedness and Lyapunov stability for the Ericksen–Leslie system near local energy minimizers. The connection between Parodi’s relation and linear stability of the Ericksen–Leslie system is also discussed.     

聚丙烯腈PAN分子链的第一性原理研究

The equilibrium geometries of the polyacrylonitrile (PAN) chain was theoretically studied using the Hartree-Fock method at the STO-3G levels. As for the optimized structures, the average distance of the C atom couple in the main chain is 155.6 pm; the average distance of the C atom couple in the branch chain is 149.7 pm; the average distance between a C atom bonding with N atom is 115.5 pm. For the charge distribution, because of the influence of a N atom with its comparatively larger negative charge, the C atoms in the main chain are different in their charge distribution. Finally, the vibration models of the chain have been analyzed to clarify the reaction sequence of dehydrogenation and cyclization during pre oxidation and carbonization of the polyacrylonitrile.     

Statistical Theory of Stable and Meta stable Transition for Crystallization and Fusion of Homopolymers ⅣStatistical Dynamics of Polymeric Crystallization by Molecular Segregation-Division of Crystal Grow-rate Regimes and Their Temperature and Grown Mechan

First a short review on the crystal growth theories and the experimental data was presented. Then a set of quantitative expressions for the size growth-rate of crystals produced by four different micro-growth mechanisms (folding, extending and two types of combination for folding and extending) was derived by a general evaluating method. A set of quantitative expressions for the correlations between the crystal size growth-rate and the product of crystalline temperature and super-cooling temperature at four different micro-growth mechanisms was obtained. Three growth-rate regimes were divided, the variations of the morphology for the crystals in the three types of regimes with the crystalline and super-cooling temperatures were discussed. They showed that these theoretical correlations between the morphology of crystals and the crystalline and super-cooling temperatures are in agreement with the later important observation on the lateral shape of crystals.     

(CoMn)n(n=1～5)合金团簇的结构和磁性

All geometry structures of (CoMn)n (n=1-5) clusters were optimized, and the energy, frequence and magnetism of (CoMn)n (n=1-5) clusters were calculated by using the local spin density approximation and generalized gradient approximation of density functional theory. The same ground state structures of CoMn alloy clusters were confirmed in two methods, and magnetism of CoMn alloy ground state clusters was studied systemically. In order to understand structure and magnetism of CoMn alloy clusters better, Co2n (n=1-5) and Mn2n (n=1-5) clusters were calculated by the same method as alloy clusters, whose ground state structure and magnetism were confirmed. Moreover, the ground state structure and magnetism of clusters with the corresponding CoMn alloy clusters was compared. Results indicated that for (CoMn)n (n=1-4) clusters, geometry structures of CoMn alloy clusters are the same as the corresponding pure clusters still, (CoMn)3 and (CoMn)4 exhibit magnetic bistability, show ferromagnetic and anti-ferromagnetic coupling, local magnetic moment of Co, Mn atoms in CoMn alloy clusters almost preserves magnetism of pure clusters still.     

Nanofibrous Membranes Containing Carbon Nanotubes: Electrospun for Redox Enzyme Immobilization

Summary: Nanofibrous membranes that possess reactive groups are fabricated by the electrospinning process from PANCAA solutions that contain MWCNTs. Field emission scanning electron microscopy is used to evaluate the morphology and diameter of the nanofibers. Potentials for applying these nanofibrous membranes to immobilize redox enzymes by covalent bonding are explored. It is envisaged that the electrospun nanofibrous membranes could provide a large specific area and the MWCNTs could donate/accept electrons for the immobilized redox enzymes. Results indicate that, after blending with MWCNTs, the diameter of the PANCAA nanofiber increases slightly. The PANCAA/MWCNT nanofibrous membranes immobilize more enzymes than that without MWCNTs. Moreover, as the concentration of the MWCNTs increases, the activity of the immobilized catalase is enhanced by about 42%, which is mainly attributed to the promoted electron transfer through charge‐transfer complexes and the π system of MWCNTs.

The covalent immobilization of redox enzymes, such as catalase, on a PANCAA/MWCNTs nanofiber.