Comparison of ablative and compressive mechanical behavior of several PICA-like ablative materials

It is significant to compare the ablative and compressive mechanical behavior of different PICA-like materials in the engineering applications. The plasma wind tunnel ablation tests with high-entropy air and CO_2 atmospheres, and compressive experiments in the ambient and 150℃, were conducted for three kinds of PICA-like materials(CF/PR-Si, CBCF/PR-SiOC and NQF/PR-Si composites). The traditional carbon/phenolic(C/PR) braided composites were also used for comparison. PICA-like materials have the better thermal insulation than traditional C/PR composite, especially for CBCF/PR-SiOC composite. The ablation behavior of CF/PR-Si and CBCF/PR-SiOC PICA-like materials in the CO_2 atmosphere can produce a large amount of SiO_2 in the form of coatings, oxide layers and skeletons on the ablated surface, which are greatly different from that in the air atmosphere.The compressive behavior of PICA-like material is greatly depended on the fiber fabrics, and exhibits the large discrete characteristics. The longer fiber in the PICA-like materials plays the role in maintaining the material integrity, while it may increase the thermal conductivity.     

Generation of simultaneous H+ and He+ band EMIC waves in the nightside radiation belt

Science China Technological Sciences - Previous studies have shown that EMIC waves occur preferentially in the afternoon sector of the magnetosphere. Here we report obliquely propagating H+ and He+...     

IMC理念中的广告设计教学

通过对广告教育现状形成原因的分析,提出运用整合营销理念改革广告设计教学的全新思路.     

50%多菌灵·乙霉威可湿性粉剂的高效液相色谱测定

利用反相高效液相色谱外标法测定了50%多菌灵·乙霉威可湿性粉剂中多菌灵和乙霉威的含量。结果表明:方法的标准偏差分别为0.0495和0.0574;变异系数分别为0.19%和0.23%;平均回收率分别为99.86%～100.02%和99.32%～100.16%。     

难溶有机药物阿莫西林纳米结构的制备

在表面活性剂SDS的辅助下,运用简单的化学沉淀法制备了三种阿莫西林纳米结构.运用扫描电镜和红外光谱对制备的阿莫西林进行了形貌、尺寸和化学结构的表征.实验发现通过调节阿莫西林钠溶液的pH值,可以得到阿莫西林纳米和微米颗粒纳米带和纳米纤维,在一定程度上实现了这一难溶有机药物的可控生长.     

基于网络科学的团队协作模型及网络模式的识别

网络科学的出现为研究和解决团队系统中的问题提供了新的方法和思路,在其框架下可以将团队的整体表现看作参与者之间的互动结果。文章将网络科学应用于足球运动中,为足球球员组成的团队构建了一个传控网络模型,并对模型的网络模式进行了进一步的分析。     

水雷引信控制系统的低功耗设计

引入水雷引信控制系统的低功耗设计思想,选用MSP430f1611作为系统的微控制芯片并经过精心的外部电路设计,实现了控制系统低功耗,可靠的运行。试验证明,在有限的电池容量条件下此控制系统能够极大的延长工作时间。     

TiB2 Powders Synthesis by Borothermal Reduction in TiO2 Under Vacuum

TiB₂ powders were synthesized by borothermal reduction in nanoscale TiO₂ with boron under vacuum. Reaction processes were investigated, and the effect of by‐product B₂O₃ was evaluated. Results showed that TiO₂ was firstly reduced by boron to form TiBO₃ and Ti₂O₃, and then to produce TiB₂ and B₂O₃ with increasing temperature. The reaction processes of TiB₂ powders synthesis included two‐step reduction in TiO₂ by boron and the removal of B₂O₃. The presence of B₂O₃, which was previously reported as the most important factor in promoting the coarsening of ZrB₂ and HfB₂ powders by borothermal reduction, did not lead to significant coarsening of TiB₂ powders. Due to the minor effect of B₂O₃, TiB₂ powders with small particle size and low oxygen content could be prepared by direct heat treatment of TiO₂ and boron at 1550°C under vacuum for 1 h. The particle size and oxygen content of synthesized TiB₂ powders were ~0.9 μm and ~1.7 wt%, respectively.     

Differentiated Electric Behaviors of La2/3Cu3Ti4O12 Ceramics Prepared by Different Methods

Microstructure and electric behaviors of La_2/3Cu₃Ti₄O₁₂ (LCTO) ceramics prepared by the sol‐gel method (SG) and solid‐state method (SS) have been systemically investigated. The results indicated that LCTO‐SG ceramics sintered at 1105°C for 15 h showed larger grain size, higher density, and especially higher dielectric constant up to about 0.9–1.6 × 10⁴ at 10²~10⁵ Hz compared to LCTO‐SS ceramics. The higher dielectric constant of the LCTO‐SG ceramics might be due to the stronger internal barrier layer capacitor (IBLC) effect. More notably, compared with LCTO‐SS ceramics, two kinds of dielectric anomalies, one conduction activation energy value and same activation energies for the conduction and relaxation process in LCTO‐SS ceramics, the LCTO‐SG ceramics showed three kinds of dielectric anomalies, two values of conduction activation energy, and decrease in conduction activation energy with increasing temperature. The activation energies for the conduction and relaxation process in LCTO‐SG ceramics showed great difference below about 210°C, suggesting that the mechanism of electrical conduction and dielectric relaxation seem to be different in LCTO‐SG ceramics. These remarkable differences in electric behaviors of LCTO ceramics prepared by sol‐gel and solid‐state methods were firstly found and analyzed.