SIMULTANEOUS FLOW VISUALIZATION AND WALL-PRESSURE MEASUREMENT OF THE TURBULENT SEPARATED AND REATTACHING FLOW OVER A BACKWARD-FACING STEP

Unsteady behaviors of the large-scale vortical structure superimposed in the turbulent separated and reattaching flow over a backward-facing step were convincingly delineated by performing simultaneous measurements of the wall pressure fluctuations and visualizations of the flow. Toward this end,a synchronized instrumentation system integrated with the microphone array and the high-speed camera was established. The smoke-wire technique was employed to visualize the unsteady events. A thorough analysis based on the wall pressure fluctuations disclosed that the large-scale vortical structure shedding at the frequency of fH /U 0= 0.064 gave a primary contribution to the wall pressure fluctuations,and consequently dominated unsteady behaviors of the turbulent shear layer. The convection velocity of the large-scale vortical structure was determined as U C=0.55 U 0. The instantaneous flow visualizations and wall pressure were compared in a straightforward manner. Below the separation bubble and the reattachment zone,the negative peak of the time-varying wall pressure was in phase with passage of the local large-scale vortical structure. In the redeveloping turbulent boundary layer,the decaying large-scale vortical structure was clearly revealed.     

低噪声PLL应用的最佳环路带宽仿真设计

本论文在环形压控振荡器基础上，通过分析一个电荷泵PLL的离散时间模型，给出了在低噪声锁相环（PLL）应用方面的寻找最佳带宽的方法。仿真使用了VerilogA语言PLL模型，结果与理论预期相比，显示了很好的一致性。     

镍催化剂制备条件对羰化性能的影响

研究了催化剂制备因素对Ni/AC催化剂的甲醇气相羰化活性的影响。结果表明,水洗能明显增大载体比表面积,载体经0.4mol/L酸洗后制得的催化剂羰化活性较高。甲醇的转化率和羰化产物的总收率在催化剂w(Ni)为8%时达到最高。低温焙烧几乎无醋酸生成,适宜的焙烧温度为450℃、还原温度为550℃;还原温度过高,会导致少量活性中心聚集,影响催化活性。     

The role of loop closure propensity in the refolding of Rop protein probed by molecular dynamics simulations

Rop protein is a homo-dimer of helix-turn-helix and has relatively slow folding and unfolding rates compared to other dimeric proteins of similar size. Fluorescence studies cited in literature suggest that mutation of turn residues D30-A31 to G30-G31 (Gly₂) increases its folding and unfolding rates considerably. A further increase in number of glycines in the turn region results in decrease of folding rates compared to Gly₂ mutant. To understand the effect of glycine mutation on folding/unfolding rates of Rop and the conformational nature of turn region involved in formation of early folding species, we performed molecular dynamics simulations of turn peptides, ²⁵KLNELDADEQ³⁴ (DA peptide), ²⁵KLNELGGDEQ³⁴ (G₂ peptide), ²⁵KLNELGGGDEQ³⁵ (G₃ peptide) and ²⁵KLNELGGGEQ³⁴ (G_3′ peptide) from Rop at 300 K. Further Wt-Rop and mutant G₂-Rop monomers and dimers were also studied separately by molecular dynamics simulations. Our results show that glycine based peptides (G_n peptides) have a higher loop closure propensity compared to DA. Comparison of monomeric and dimeric Rop simulations suggests that dimeric Rop necessarily requires α_L conformation to be sampled at D30/G30 position in the turn region. Since glycine (at position 30) can readily adopt α_L conformation, G_n loop plays a dual role in both facilitating loop closure as well as facilitating reorganization/packing of helices required for structural adjustment during dimer formation in the folding of Rop. Based on our simulation results and available literature, we suggest a tentative kinetic model for Rop folding which allows us to estimate the contribution of loop closure propensity to the overall folding rates.     

甲基磺酸铝催化合成苯乙醛缩乙二醇

以结晶三氯化铝为原料制备了甲基磺酸铝,并以甲基磺酸铝为催化剂,环己烷为带水剂,用苯乙醛和乙二醇为原料合成了苯乙醛缩乙二醇,考察了影响产品收率的因素,优化了合成条件。该反应的较佳反应条件是:n(苯乙醛)∶n(乙二醇)为1∶2.0,甲基磺酸铝用量为2.0 g,环己烷10 mL(苯乙醛用量为0.1 mol时),回流2.0 h,苯乙醛缩乙二醇的收率达80.6%。实验结果表明,甲基磺酸铝对缩醛的合成反应具有较高的催化活性。     

Synthesis of polyols containing nitrogen-phosphorus from vegetable oil derivatives for polyurethane film applications

Methyl oleate, a kind of vegetable oil derivatives, was used as the raw material to synthesize novel polyols containing nitrogen and phosphorus (PNP) by three steps: amidaion, epoxidation, and ring-opening reaction. The structure of the ensuing PNP was characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Then, polyurethane films were prepared by mixing the resulting polyols (PNP) and poly-(tetra methylene glycol) with isophorone diisocyanate in different proportions. After that, the thermostability of polyurethane films was investigated by limiting oxygen index (LOI), thermogravimetry, and cone calorimeter test. Similarly, mechanical property of polyurethane films was studied by tensile test. The results showed that as the amount of PNP increased, the tensile strength of polyurethane films increased from 2.0 to 13.5 MPa, the LOI values of polyurethane films went up from 20.1% to 25.5%. Moreover, the initial decomposition temperature of polyurethane films improved from 280 to 312°C and the total heat release drooped from 32.2 to 21.7 kW/m² without adding any other flame retardant. Therefore, it was observed that the polyurethane films have superior thermal stability and mechanical property and appear suitable for a wide range of applications.     

The Magnetic Properties of Different Proportions Cr-Doped Bifeo3 as Studied Using Heisenberg Model

Journal of Superconductivity and Novel Magnetism - With the Monte Carlo method, we simulate 3D alloys Heisenberg model of Cr-doped BiFeO $$_3$$ with various proportions Cr-doped. This model...     

百里香酚蓝光度法测定水中痕量锌(II)

在邻苯二甲酸氢钾缓冲溶液中,聚氧乙烯特辛基酚醚(TritonX-100)微乳液存在下,百里香酚蓝与锌(II)形成稳定的橙黄色络合物,据此建立了分光光度法测定锌(II)的方法。实验表明,当络合物最大吸收波长为540nm时,锌(II)质量浓度在0.1~0.7mg/L范围内符合比尔定律,相关系数为0.9980。方法检出限为0.01mg/L,表观摩尔吸光系数为7.4×10⁴ L·moL^-1·cm^-1。加入柠檬酸钠-酒石酸钾钠混合掩蔽剂掩蔽Fe³⁺、Al³⁺,加入铜试剂掩蔽Cu²⁺、Cd²⁺、Pb²⁺。方法用于水中痕量锌(II)的测定,相对标准偏差(RSD,n=6)为1.6%和3.4%,加标回收率为98%和105%,测定值与原子吸收光谱法(AAS)基本一致。     

Discriminative dictionary learning algorithm based on sample diversity and locality of atoms for face recognition

Dictionary learning is one of the most important algorithms for face recognition. However, many dictionary learning algorithms for face recognition have the problems of small sample and weak discriminability. In this paper, a novel discriminative dictionary learning algorithm based on sample diversity and locality of atoms is proposed to solve the problems. The rational sample diversity is implemented by alternative samples and new error model to alleviate the small sample size problem. Moreover, locality can leads to sparsity and strong discriminability. In this paper, to enhance the dictionary discrimination and to reduce the influence of noise, the graph Laplacian matrix of atoms is used to keep the local information of the data. At the same, the relational theory is presented. A large number of experiments prove that the proposed algorithm can achieve more high performance than some state-of-the-art algorithms.