Deformation and reverse snapping of a circular shallow shell under uniform edge tension

In this paper we study the deformation and stability of a shallow shell under uniform edge tension, both theoretically and experimentally. Von Karman’s plate model is adopted to formulate the equations of motion. For a shell with axisymmetrical initial shape, the equilibrium positions can be classified into axisymmetrical and unsymmetrical solutions. While there may exist both stable and unstable axisymmetrical solutions, all the unsymmetrical solutions are unstable. Since the unsymmetrical solutions will not affect the stability of the axisymmetrical solutions, it is concluded that for quasi-static analysis, there is no need to include unsymmetrical assumed modes in the calculation. If the shell is initially in the unstrained configuration, it will only be flattened smoothly when the edge tension is applied. No snap-through buckling is possible in this case. On the other hand, if the shell is initially in the strained position, it will be snapped back to the stable position on the other side of the base plane when the edge tension reaches a critical value. Experiment is conducted on several free brass shells of different initial heights to verify the theoretical predictions. Generally speaking, for the range of initial height H < 10 the experimental measurements of the deformation and the reverse snapping load agree well with theoretical predictions.     

Advanced analytical methods for the structure elucidation of polystyrene-b-poly(n-butyl acrylate) block copolymers prepared by reverse iodine transfer polymerisation

Reverse iodine transfer polymerisation (RITP) is a living radical polymerisation technique that has shown to be feasible in synthesising segmented styrene-acrylate copolymers. Polymers synthesised via RITP are typically only described regarding their bulk properties using nuclear magnetic resonance spectroscopy and size exclusion chromatography. To fully understand the complex composition of the polymerisation products and the RITP reaction mechanism, however, it is necessary to use a combination of advanced analytical methods. In the present RITP procedure, polystyrene was synthesised first and then used as a macroinitiator to synthesise polystyrene-block-poly(n-butyl acrylate) (PS-b-PBA) block copolymers. For the first time, these PS-b-PBA block copolymers were analysed by a combination of SEC, in situ¹H NMR and HPLC. ¹H NMR was used to determine the copolymer composition and the end group functionality of the samples, while SEC and HPLC were used to confirm the formation of block copolymers. Detailed information on the living character of the RITP process was obtained.     

On the unsymmetrical deformation and reverse snapping of a spinning non-flat disk

In this paper we study the steady state deflection and reverse snapping phenomenon of a spinning non-flat disk. Both the initial and the deformed shapes of the disk are allowed to have axisymmetrical and unsymmetrical components. For the analysis of a rotating axisymmetrical disk, we conclude that there is no need to include the unsymmetrical assumed modes in the solution because all the unsymmetrical steady state deformations are unstable. In addition, the stability of the axisymmetrical positions will not be affected by the inclusion of the unsymmetrical assumed modes. In the case when the initial shape of the disk contains a dominant axisymmetrical component and a smaller unsymmetrical component, attention is focused on the effect of this unsymmetrical component on the overall deformation and stability of the spinning disk. It is found that the unsymmetrical component with one nodal diameter tends to slightly defer the occurrence of the reverse snapping phenomenon. On the other hand, all other unsymmetrical components with more than one nodal diameter tend to reduce dramatically the reverse snapping speed. Experiment is conducted on a non-flat brass disk containing an axisymmetrical component and an unsymmetrical component with two nodal diameters. The experimental measurement confirms the theoretical prediction.     

二芳基三嗪类HIV-1逆转录酶抑制剂的分子对接及3D-QSAR研究

对40个二芳基三嗪类HIV-1逆转录酶抑制剂进行了分子对接研究,结果表明,2个疏水性芳香取代基团与结合口袋底部形成的疏水和范德华相互作用、三嗪环母核及其R4取代基与结合位点产生的氢键和静电作用以及R4取代基与袋口形成的空间位阻效应是影响该系列化合物活性的重要因素.根据对接优势构象进行分子叠合和比较分子相似性指数分析(C...     

Preparation of blue-emitting CaMgSi2O6:Eu phosphors in reverse micellar system and their application to transparent emissive display devices

Blue-emitting Eu²⁺-doped CaMgSi₂O₆ phosphors were prepared by the reverse micelle method. The resultant particles were nanocrystalline with a grain size of about <300 nm and exhibited a characteristic blue emission spectrum centered at 445 nm induced by the oxygen coordinated Eu²⁺ ions. By using the corresponding nanophosphors followed by the formation of a uniform phosphor layer, we have demonstrated the mini-sized transparent plasma-discharge panels and investigated their luminance characteristics. Phosphor coated panel is properly transparent, ≥65%, at the visible wavelength region and illuminates a characteristic blue emission under Ne/Xe plasma discharge conditions. Thus, we can obtain a fast decaying, robust blue-emitting silicate phosphor layer under excited plasma radiation for upcoming emissive display devices like as transparent and three-dimensional plasma display panels.     

Higher order log-concavity in Euler’s difference table

For 0≤k≤n, let be the entries in Euler’s difference table and let . Dumont and Randrianarivony showed equals the number of permutations on [n] whose fixed points are contained in {1,2,…,k}. Rakotondrajao found a combinatorial interpretation of the number in terms of k-fixed-points-permutations of [n]. We show that for any n≥1, the sequence is essentially 2-log-concave and reverse ultra log-concave.     

NaCl interaction with interfacially polymerized polyamide films of reverse osmosis membranes: A solid-state Na NMR study

²³Na nuclear magnetic resonance (NMR) spectroscopy of NaCl-exchanged polyamide (PA) films comparable to those of the active skin layer of many reverse osmosis (RO) membranes provides novel insight into the structural environments and dynamical behavior of Na⁺ in such films. Unsupported PA films were synthesized via interfacial polymerization of trimesoyl chloride in hexane and m-phenylenediamine in aqueous solution, and SEM, FT-IR, and ¹³C NMR data demonstrate successful thin film polymerization. Compositional data confirm this conclusion and demonstrate equal Na and Cl incorporation during NaCl exchange from aqueous solution. The ²³Na NMR spectra for freshly made polymer samples exchanged in 1 M NaCl solution show significant relative humidity (RH) dependence. At near 0% RH, there are resonances for crystalline NaCl and rigidly held Na⁺ in the PA. With increasing RH, a resonance for solution-like dynamically averaged Na⁺ appears and above 51% RH is the only signal observed. The slightly negative chemical shift of this resonance suggests a dominantly hydrous environment with some atomic-scale coordination by atoms of the polymer. The greatly reduced ²³Na T₁ relaxation rates for this resonance relative to bulk solution and crystalline NaCl confirm close association with the polymer. Variable temperature ²³Na NMR spectra for a sample equilibrated at 97% RH obtained from −80 to 20 °C show the presence of rigidly held Na⁺ in a hydrated environment at low temperatures and replacement of this resonance by the dynamically averaged signal at temperatures above about −20 °C. The results provide support for the solution–diffusion model for RO membranes transport and demonstrate the capabilities of multi-nuclear NMR methods to investigate molecular-scale structure and dynamics of the interactions between dissolved species and RO membranes.     

在溴化钾粉末中掺入大量α-炭化硅压片的异常红外透射光谱研究

在光谱学实践中，通常由于带测样品颗粒在本征吸收峰附近产生可观的附加散射消光，致使表观吸收峰偏离实际位置，从而得到不的光谱，这就是我们常要采取措施尽量避免的克里斯坦森（Christiansen）效,这一就是在制作压片（例如溴化钾）时，待测样品含量要少（少于2％）。在一次实验中，当在KBr粉末中掺入大量（而非正常要求的少许）的α-SiC微粉后，得到了一个在1052.33cm^-1处有一个尖峰的中红外透射谱。我们发现，这个新现象非常有趣，它与克里斯坦森效应表面上相反，但都可用Lorentz色散模型给予精确地解释。于是称它为反克里斯坦森效应，在该效应出现的频率处两种材料的折射率相等，且吸收系数都非常小。这个新现象也非常有意义，它可用来制造新型的带通滤波器以及准确测定某些材料的折射率等。