表面修饰多壁碳纳米管负载二氧化钛的制备及催化碳酸二甲酯与苯酚酯交换反应的性能

制备了表面修饰多壁碳纳米管负载TiO₂的催化剂,并将其应用于碳酸二甲酯与苯酚的酯交换反应. 采用X射线电子能谱、透射电子显微镜、低温N₂吸附-脱附和X射线衍射等对催化剂进行了表征. 结果表明,以低浓度的氨水（0.4%）代替去离子水作为沉淀剂时,制备的催化剂显示出更好的催化活性、分离性与重复使用性. 考察了TiO₂负载量、催化剂用量及反应时间对反应性能的影响. 在最佳反应条件下,苯酚转化率为42.5%,碳酸甲苯酯与碳酸二苯酯的总选择性达到99.9%以上. 经过4次重复使用后,催化剂的活性略有下降.     

对Cluster模型的几点质疑

本文证明Cluster模型违背了细致平衡原理,指出了海中核子pick-up图象的不合理性。该模型的发射几率中不考虑复杂粒子正确构成的影响更是一个显著的倒退。     

Development of long-life-cycle tablet ceramic adsorbent for geosmin removal from water solution

In this study, the tablet ceramic adsorbent (TCA), a silica/iron(III) oxide composite material, has been developed for geosmin (GSM) removal from the water solution. The physicochemical characteristics of TCA were examined with XRD, SEM, EDX and BET analyses. The sorption characteristics of GSM on TCA were investigated in a batch system. Attempts have been made to understand the adsorption kinetics, the effect of initial GSM concentration, solution pH, and reaction time.The batch experiments equilibrium data were well fitted to the Lagergren kinetic equation, which indicate the first-order nature adsorption. Over 82% of the GSM was removed by the TCA within 600 min at an initial concentration of 200 ng/L with 20 g/L of TCA dose. The batch and regeneration study indicated that the TCA is a cost-effective GSM adsorbent with sufficient mechanical strength to retain its physical integrity after long-time adsorption, and high regeneration performance for long-life-cycle application. Almost no second contamination (toxic sludge or leached iron) was observed after adsorption, and the gas resultant of thermal regeneration is harmless to atmospheric environment.     

Initial applications of the molecular model to compute defect vibrations of oxygen in silicon

Abstract

We have employed the molecular model introduced first by Jaswal to compute the vibrational spectra of oxygen bearing defects in a silicon crystal. This was done in the context of a silicon molecular cluster with outer valencies terminated by hydrogen. We employ the MINDO/3 semi-empirical electronic structure method to compute the total energy of the molecular cluster. We examine the conditions in applications of the molecular model required for accurate predictions of oxygen local-mode vibrational frequencies. We find that the oxygen atom and its nearest neighbor silicon atoms must be allowed to vibrate. The nearest-neighbor and next nearest-neighbor shells of silicon atoms must be allowed to relax from their lattice positions. The outermost relaxed shell of silicon atoms should be bonded to silicon atoms in their lattice positions. We apply the molecular model to three defects of crystalline silicon; interstitial oxygen, oxygen in a vacancy (the A-center), and two oxygen atoms in a vacancy. Comparison of our computed local-mode oxygen vibration frequencies with experiment shows the computed oxygen local-mode frequencies to be almost uniformly 10% greater than those observed. Isotope shifts fit experiment equally well. We conclude that the molecular model represents an accurate and efficient approach for the computation of defect local mode vibrational frequencies for oxygen and other defects in crystalline silicon.     

Batch study of arsenate (V) adsorption using Akadama mud: Effect of water mineralization

Akadama mud, consisting mainly of different forms of iron and aluminum oxide minerals, was used for arsenate (V) adsorption from aqueous solutions. The adsorption process fitted the first-order kinetic equation and the Langmuir monolayer model well. The adsorption capacity, estimated by the Langmuir isotherm model, was 5.30 mg/g at 20 ± 0.5 °C. The effects of the solution properties (initial concentration of As (V), pH, temperature, and mineralization degree) on As (V) removal were investigated. Various mineralization degrees in underground water were simulated by adjusting the ionic strength of the solution or adding coexisting ions to the contaminated solution. It was found that mineralization of the water significantly influenced the arsenic adsorption. The existence of multivalent metallic cations significantly enhanced the As (V) adsorption ability, whereas competing anions such as fluoride and phosphate greatly decreased the As (V) adsorption. This result suggests that Akadama mud is more suitable for arsenic adsorption in low-level phosphate and fluoride solutions. The loaded Akadama mud could be desorbed at polar pH conditions, especially in acidic conditions, and more than 65% As (V) sorption has been achieved at pH 1.     

Blind image deconvolution using sparse and redundant representation

This work devotes to the image deconvolution problem that restores clear image from its blurred and noisy measurements with little prior about the blur. A deconvolution method based on sparse and redundant representation theory is developed in this paper. It firstly represents the blur and image over different redundant dictionaries and imposes sparsity constraint to their representation coefficients respectively, then alternately estimates them using an iterative algorithm employing optimization technique. Experimental results on astronomical images show that the proposed method can achieve as good performance as the method requiring a known blur, which demonstrates its effectiveness.     

核壳结构TiO2@SiO2催化碳酸二甲酯与苯酚酯交换合成碳酸二苯酯

以反相微乳液法和沉淀法相结合制备了核壳结构TiO₂@SiO₂,首次用于碳酸二甲酯与苯酚酯交换合成碳酸二苯酯反应,显示较好的催化活性. 采用200 ℃焙烧的TiO₂@SiO₂,用量0.20 g,反应9 h,苯酚转化率达41.8%,酯交换选择性为100%. 透射电镜显示TiO₂@SiO₂核厚壳薄,TiO₂核直径220-300 nm,SiO₂壳厚度40-60 nm,具有介孔结构. TiO₂@SiO₂对碳酸二甲酯与苯酚酯交换反应有好的重复使用性,使用4次苯酚转化率仍保持在40%以上. TiO₂与SiO₂发生相互作用,Ti进入骨架形成Ti-O-Si键,骨架Ti的形成提高了TiO₂@SiO₂的催化性能.     

记忆粒子模型中碰撞比α_n的数值获取

本文给出了记忆粒子模型中n态时m粒子的碰撞比分α_n的数值获取方法;讨论了两种不同的初值赋值方法对结果的影响。在记忆粒子模型中采用本方法提供的α_n,计算预平衡发射与实验资料拟合良好。     

基于Simulink/Stateflow的无人机多模态控制律仿真

为了验证无人机多模态飞行控制律设计的正确性,采用Simulink/Stateflow建模仿真方法。以某小型无人机为研究对象,首先在小扰动线性化模型基础上,设计了纵向和侧向多模态控制系统结构,并给出了相应的控制律,然后根据传统的频域和根轨迹的方法确定了各个控制器参数,最后通过Simulink/Stateflow完成整个飞行剖面的仿真,结果表明该方法能直观简洁地实现多模态之间切换的控制逻辑,模态控制误差均满足国军标要求,验证了所设计的多模态控制系统的正确性。