固定接触界面法向静弹性刚度

基于Hertz接触理论推导了两个微凸体之间互相作用的法向接触静弹性刚度.根据修正后的一个微接触点的平截面积尺寸分布,给出了界面的总法向接触静弹性条件刚度、总条件载荷的解析解.将法向静弹性刚度的解析解嵌入到有限元软件中,获得整机的理论模态.通过实验对解析解进行了定量验证.以机床结合部为研究对象,在理论振型与实验振型一致的...     

固定接触界面切向静弹性刚度问题研究

根据两球体单峰同时受法向、切向载荷时微滑切向应力的分布以及MB模型,给出了界面的总切向接触静弹性条件刚度、总条件法向载荷的解析解。将切向接触静弹性条件刚度的解析解嵌入到有限元软件中,获得了整机的理论模态。以一款八四七厂华中工学院XHK5140型自动换刀计算机数控立式镗铣床上的结合部为研究对象,通过实验对解析解进行了定量验证。研究结果表明：在理论振型与实验振型一致的条件下,界面模型的相对误差在-19．2％～16．8％之间。     

Synthesis of an oligo(ethylene glycol)‐based third‐generation thermoresponsive dendronized polymer

An improved strategy to synthesize oligo(ethylene glycol)‐based secondary generation (G2) dendron is presented. The overall synthesis efficiency increased by 50% when comparing to the previous method, and the product purification by column chromatography becomes much easier. Based on this approach, the synthesis of the third‐generation (G3) dendrons and the corresponding methacrylate‐based G3 macromonomer becomes feasible. Because of the oil characteristics of this macromonomer, its polymerization was able to be conducted in bulk with AIBN as the initiator. The polymerization degree of the third‐generation dendronized polymer ( PG3 ) was found to be around 16 based on GPC measurement. The thermally induced dehydration processes of this polymer were monitored by temperature‐varied proton NMR spectroscopy, and its thermoresponsive behaviors were investigated with turbidity measurements using UV–vis spectroscopy. Similar to the lower generation counterparts, this threefold branched dendronized polymer also shows characteristic fast and sharp phase transitions around its apparent lower critical solution temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6630–6640, 2009     

Thermoresponsive Supramolecular Dendronized Polymers

Combining the concepts of supramolecular polymers and dendronized polymers provides the opportunity to create bulky polymers with easy structural modification and tunable properties. In the present work, a novel class of side‐chain supramolecular dendronized polymethacrylates is prepared through the host–guest interaction. The host is a linear polymethacrylate (as the backbone) attached in each repeat unit with a β‐cyclodextrin (β‐CD) moiety, and the guest is constituted with three‐fold branched oligoethylene glycol (OEG)‐based first‐ (G1) and second‐generation (G2) dendrons with an adamantyl group core. The host and guest interaction in aqueous solution leads to the formation of the supramolecular polymers, which is supported with ¹H NMR spectroscopy and dynamic light scattering measurements. The supramolecular formation was also examined at different host/guest ratios. The water solubility of hosts and guests increases upon supramolecular formation. The supramolecular polymers show good solubility in water at room temperature, but exhibit thermoresponsive behavior at elevated temperatures. Their thermoresponsiveness is thus investigated with UV/Vis and ¹H NMR spectroscopy, and compared with their counterparts formed from individual β‐CD and the OEG dendritic guest. The effect of polymer concentration and molar ratio of host/guest was examined. It is found that the polar interior of the supramolecules contribute significantly to the thermally‐induced phase transitions for the G1 polymer, but this effect is negligible for the G2 polymer. Based on the temperature‐varied proton NMR spectra, it is found that the host–guest complex starts to decompose during the aggregation process upon heating to its dehydration temperature, and this decomposition is enhanced with an increase of solution temperature.     

Modeling based on subspace orthogonal projections for QSAR and QSPR research

A novel projection modeling method for quantitative structure activity relationship (QSAR) and quantitative structure property relationship (QSPR) is developed in this paper. Orthogonalization of block variables is introduced to deal with the problem of variable selection. Projections based on least squares are used to construct the modeling space in order to search for the best regression directions for chemical modeling. A suitable prediction space for such a model is further defined to confine the usage range of the model. Three real data sets were analyzed to check the performance of the proposed modeling method. The results obtained from Monte‐Carlo cross‐validation (MCCV) showed that the proposed modeling method might provide better results for QSAR and QSPR modeling than PCR and PLS with respect to both fitting and prediction abilities. Copyright © 2007 John Wiley & Sons, Ltd.     

Crystal Structures and Electrochemical Properties of R1.5Ca1.5MgNi14(R=Nd,Gd and Er)Hydrogen Storage Alloys

Ca₃MgNi₁₄, Nd_1.5Ca_1.5MgNi₁₄, Gd_1.5Ca_1.5MgNi₁₄ and Er_1.5Ca_1.5MgNi₁₄ alloys were prepared by high frequency induction melting and sintering. Characterization and analysis were performed by X-ray diffraction/Rietveld full-spectrum fitting, gaseous P-C-T hydrogen storage test and electrochemical properties tests. It can be found that all alloys consist of Gd₂Co₇-type 3R phase and Ce₂Ni₇-type 2H phase. Although the hydrogen storage capacities of Nd_1.5Ca_1.5MgNi₁₄, Gd_1.5Ca_1.5MgNi₁₄ and Er_1.5Ca_1.5MgNi₁₄ decrease to some extent compared to that of Ca₃MgNi₁₄, their equilibrium pressures for absorption and desorption increase markedly. Moreover, R_1.5Ca_1.5MgNi₁₄ alloys have better cycling stabilities and high-rate discharge(HRD) properties as compared to Ca₃MgNi₁₄. The hydrogen diffusion in alloy electrodes is the main factor to influence the HRD performance.     

Microscopy investigation of Ag-TCNQ micro/nanostructures synthesized via two solution routes

The micro/nanostructures of metal-organic complex Ag-TCNQ were successfully synthesized by the reaction between Ag film and TCNQ dissolved in acetonitrile via two solution routes, i.e. immerging and dipping reaction. X-ray diffraction confirmed that the obtained Ag-TCNQ micro/nanostructures were crystalline. The morphology of the as-grown structures varied from straight nanowires and microtubes to complex fractals and dendrites. The growth mechanism of the mainly dendrites may be considered within the framework of DLA model.     

Measurement of the thickness of U-30MES-5NT and VGM-L sealing compound layers in aircraft products using the ultrasonic nondestructive testing method

A method for measuring the thickness of sealant layers between glass-fiber reinforced plastic and metallic parts of airframes accessible only from one side is proposed. The method is based on use of general-purpose ultrasonic flaw detectors and special-purpose laser-acoustic equipment. It is shown that the developed method allows for measurement of sealant layers with thicknesses less than the ultrasonic wave length.     

(Nd(1.5)Mg(0.5))Ni7-based compounds: structural and hydrogen storage properties

The structural and hydrogen storage properties of (Nd(1.5)Mg(0.5))Ni(7)-based alloys (i.e., A(2)B(7)-type) with a coexistence of two structures (hexagonal 2H and rhombohedral 3R) are investigated in this study. In both 2H- and 3R-type A(2)B(7) structures, Mg atoms occupy Nd sites of Laves-type AB(2) subunits rather than those of AB(5) subunits because Mg substitution for Nd in the AB(2) subunits more significantly strengthens the ionic bond in the system. An increase in the A-atomic radius or the B-atomic radius stabilizes the 2H structure, but a decrease in the A-atomic radius or the B-atomic radius is favorable for formation of the 3R structure. The 2H-A(2)B(7) and 3R-A(2)B(7) phases in each alloy have quite similar equilibrium pressures upon hydrogen absorption and desorption, which show a linear relationship with the average subunit volume. The hydriding enthalpy for the (Nd(1.5)Mg(0.5))Ni(7) compound is about -29.4 kJ/mol H(2) and becomes more negative with partial substitution of La for Nd and Co/Cu for Ni but less negative with partial substitution of Y for Nd.