Numerical Investigation on Granular Flow from a Wedge‐Shaped Feed Hopper Using the Discrete Element Method

The discharge process of granular material from a wedge‐shaped feed hopper was numerically simulated using a 3D discrete element method. The effects of particle size, feed pipe, side and rear wedge angle on the discharge performance were investigated in terms of flow pattern, discharge rate, and stability. The results show that with larger particle size the granular flow pattern gradually transforms from mass flow to edge flow where the flow rate decreases and the discharging integrity and stability become worse. The presence of the feed pipe reduces the discharge rate and stability. The increase of the feed pipe diameter will diminish the discharge rate and enhance the discharge stability. Both the side and the rear wedge angle have a certain effect on the discharge performance. The effects of feed pipe, side and rear wedge angle on the discharge stability become more significant with larger particle size.     

Direct-Contact Heat Transfer during n-Pentane Vaporization in a Two-Dimensional Water Column

Direct-contact vaporization heat transfer is investigated by analyzing the heat transfer coefficient with the area of liquid-liquid direct-contact interface. The interface areas of liquid-liquid heat transfer are determined by stroboscopic images. At higher temperature, the heat transfer area per unit volume decreases. The water temperature has no significant influence on the heat transfer coefficient. The effects on droplet size distributions of operating variables including inlet water temperature, n-pentane flow rate, and test position with packing and without packing are compared.     

The impact of heat-treatment protocol on the grain size and ionic conductivity of NASICON glass-ceramics

Na₂AlTi(PO₄)₃ (NATP) and Na_1.8Al_0.8Ge_1.2(PO₄)₃ (NAGP) NASICON (Na-Superionic Conductor) glass-ceramics are obtained by applying different single (SHT) and double (DHT) heat treatments on the respective precursor glass to evaluate its effect on the microstructure and in turn, on the total ionic conductivity. The grain and grain boundary contributions are also analyzed in the NATP composition. SHT with longer crystallization times favors the development of well-defined grains in both compositions and also promotes the grain growth in NAGP samples. This behavior causes a decrease in the activation energy of the grain boundary, which enhances the total ionic conductivity. Regarding DHT samples, microstructure with larger grains and higher ionic conductivity were obtained with shorter nucleation times for NATP and NAGP compositions. Finally, the microstructural variation generated by the different thermal treatments causes the total conductivity to increase up to two times.     

Effects of SiC content on the densification,microstructure, and mechanical properties of HfB2–SiC composites

To investigate the effects of SiC on microstructure, hardness, and fracture toughness, 0, 10, 20, and 30 vol% SiC were added to HfB₂ and sintered by SPS. Upon adding SiC to 30 vol%, relative density increased about 4%; but HfB₂ grain growth had a minimum at 20 vol% SiC. This may be due to grain boundary silicate glass, responsible for surface oxide wash out, enriched in SiO₂ with higher fraction of SiC. By SiO₂ enrichment, the glass viscosity increased and higher HfO₂ remained unsolved which subsequently lead to higher grain growth. Hardness has increased from about 13 to 15 GPa by SiC introduction with no sensible variation with SiC increase. Residual stress measurements by Rietveld method indicated high levels of tensile residual stresses in the HfB₂ Matrix. Despite the peak residual stress value at 20 vol% SiC, fracture toughness of this sample was the highest (6.43 MPa m^0.5) which implied that fracture toughness is mainly a grain size function. Tracking crack trajectory showed a mainly trans-granular fracture, but grain boundaries imposed a partial deflection on the crack pathway. SiC had a higher percentage in fracture surface images than the cross-section which implied a weak crack deflection.     

新冠肺炎应急临床试验设计中的统计学考虑

新型冠状病毒肺炎的突然来袭，国内各地相继启动重大突发公共卫生事件一级响应。为了探索新冠肺炎的治疗，百余项临床研究陆续在国内开展。在突发公共卫生事件下，尽早找到有效的药物和治疗方案对于疾病的控制更加重要，这也对在这种应急情况下所开展临床试验的时效性提出要求，尤其是针对新冠肺炎的注册临床试验。本文从统计学角度，对应急临床试验中临床终点的选择和试验设计中的相关问题进行探讨。     

Effect of in-situ formation of columnar mullite and pore structure refinement on high temperature properties of corundum casatbles

The effects of in-situ synthesis columnar mullite and pore structure on the hot modulus of rupture (HMOR), thermal shock resistance and corrosion resistance of corundum castables have been investigated in this paper. When 2% nano silica was added, the pore diameters of castables could be decreased to 15 nm (at 110 °C), 1 μm (1100 °C) and 6 μm (1500 °C), respectively. The corresponding reducing magnitude of pore size is 98.5%, 83.3% and 33.3%. The HMOR of castables fired at 1500 °C increased by 110% to 3.64 MPa. Furthermore, after three thermal shock cycles, the residual strength ratio of castables increased from 5.2% to 15.3%. A large amount of cross-distributed columnar mullite was formed between nano silica and α-Al₂O₃ by the two-dimensional nucleation mechanism, which remarkably enhanced the high temperature properties. The penetration index reduced from 30.86% to 19.88%, suggesting that smaller pore size and higher viscosity had a great influence to the penetration process.     

Particle Size Control and Crystal Habit Modification of Phenacetin Using Ultrasonic Crystallization

Power ultrasound is applied for cooling crystallization to control and modify the particle size and crystal habit of an active pharmaceutical ingredient, phenacetin. Operating parameters including sonication intensity and duration, solution concentration, and cooling rate are studied and compared. With respect to mean particle size, the effect of sonication intensity is most significant. In addition, the crystal habit of recrystallized phenacetin is modified substantially and shows an elliptic shape. Recrystallized phenacetin also provides an enhanced dissolution rate compared with the original sample. These results prove that ultrasonic crystallization is an efficient tool for controlling the solid‐state properties of an active pharmaceutical ingredient.     

Influence of case-carburizing and micro-defect on competing failure behaviors of Ni–Cr–W steel under gigacycle fatigue

Axial loading test was performed to investigate the influence of case-carburizing and micro-defect on competing failure behaviors of Ni–Cr–W Steel under gigacycle fatigue. The interior failures induced from inclusion and microstructural inhomogeneity become the predominant failure mode in the life regime beyond 10⁵ cycles. The case-carburizing has no effect on the fatigue strength with interior failure. Compared with the lower limit values of experimental S–N data, the predicted results by using GP distribution is relatively suitable. From the viewpoint of reliability, the modeling method of interior S–N curve with the maximum defect size at a given probability is satisfactory.     

The effect of the exposed crystal plane on the antioxidant activity of nanoceria

Previous reports have noted that exposed crystal planes could affect the antioxidant activity of nanocerias, although the synthesized nanocerias used in those studies had different exposed crystal planes, as well as different sizes and morphologies. In order to better understand the effect of the crystal planes on the antioxidant activity of the materials, two types of nanocerias with similar morphology and size distribution but different crystal planes were synthesized using the hydrothermal method (CeO₂–H) and the ultrasonic template method (CeO₂–U). The antioxidant activities of the nanocerias were further explored within different ·OH concentrations in the reaction system. The experimental results showed that there is an obvious difference in the antioxidant activity of the two types of nanocerias in the lower free radical concentration system due to the effects of exposed crystal planes. CeO₂–U, with more active crystal planes (100), had stronger antioxidant activity. However, with the increase in the ·OH concentration in the reaction system, the difference in the antioxidant activity of the two nanocerias decreased. This research will increase our understanding of the antioxidant activity of the exposed crystal planes on nanocerias.     

管式段塞流捕集器构造及其优化设计

天然气近年来由于技术的进步及其自身多项优势而被广泛利用,油气混输作为一种经济性良好的运输方式也开始服务于各大油气田。然而多相流的运动很复杂,加上一些其他因素而产生的段塞流则是危害较大,其主要危害体现在各项参数不稳,混输管路下游的处理设备会受到较大冲击,因此需要在混输管路末端设置段塞流捕集器来缓解这种冲击,保证下游的稳定供给。