镁合金手机外壳冲模设计及实验研究

以AZ31B镁合金手机外壳冲模设计和在普通机械式锻压机上的冲压生产为例,对AZ31B镁合金冲压成形过程中的板料制备、冲模设计、模具及板料的温度、冲压变形速度、润滑剂的选用等关键技术作了较为系统的实验研究。实验表明,通过合理地选取模具参数并对拉伸速度、坯料及模具温度等主要影响因素的控制,可有效地解决AZ31B镁合金拉伸生产过程中的拉裂缺陷,在普通机械式锻压机上能成功地冲压出镁合金手机外壳。     

无粘结预应力砼密肋楼盖的优化设计应用

对于无粘结预应力砼密肋楼盖进行优化设计,在安全可靠的前提下,通过目标函数对该项目进行研究,使楼盖设计更为经济合理,并在此基础上进行造价分析。得到楼盖结构体系的经济技术指标后,综合分析力学、使用功能、建筑装饰、施工管理等几方面因素,最后得出优选方案。     

基于图像旋转匹配的组网雷达ISAR图像横向定标

基于组网雷达观测模型,分析了在多部雷达同时观测条件下所得ISAR图像之间的对应关系,提出了一种基于图像旋转匹配的转角估计办法,通过对旋转速度的一维搜索实现了目标角速度的估计。仿真结果表明,本算法能基于组网雷达所获得的多幅ISAR图像实现目标转角的稳健估计,实现ISAR图像横向定标。所提算法可对慢运动目标或平动补偿后的回波信号进行处理,适用于不同带宽、不同中心频率的宽带雷达组网形式。     

EPCGen2标准下安全的RFID认证协议

现有的许多无线射频识别(RFID)协议或者不符合EPC Class-1 Gen-2(EPCGen2)标准的要求,或者存在某种安全隐患.通过对RFID协议安全需求的讨论,以及对近来提出的符合EPCGen2标准的安全协议的分析,提出了符合EPCGen2标准的RFID认证协议的设计原则,设计了一个新的符合EPCGen2标准的RFID认证协议.新的协议满足双向认证、匿名、不可追踪、抗假冒攻击、抗重放攻击等安全需求.     

快速互信息轮廓匹配算法

针对轮廓匹配中存在的遮挡、噪声等问题,提出把互信息作为二值图像相似性的度量准则,通过遍历的方法找到最大互信息的位置;为了加快匹配的速度,提出了相应的互信息计算的快速算法。新算法不依赖模板和输入图像的大小,仅仅与模板和输入图像中轮廓像素点的个数有关。实验结果表明,文中算法在512×512图像上完成一次匹配平均需要花费约50 ms,可以克服光照、遮挡、随机噪声和小形变的影响。     

Catalytic hydropyrolysis of crop straws with different biochemical composition

In this study, four kinds of straws with different biochemical compositions, including soybean straw (SS), peanut straw (PS), rice straw (RS), and corn straw (CS), were subjected to catalytic hydropyrolysis (HyPy) to explore the influence of biochemical composition on the products distribution and properties of the pyrolysis oil. The HyPy reactions were performed at 400 °C for 2 h with added 10 wt% Pd/C and 4 MPa H₂. During the HyPy, hydrogen and catalyst broke the coating structure and hydrogen bond between cellulose (CL) and hemicellulose (HCL), and thus significantly weakened the biochemical composition effect on the yield and elemental composition of the bio-oil. The bio-oil yield varied between 11.75 wt% and 13.05 wt%, and the C, H, N, O, and S content fell into the following ranges of 82.06–85.15 wt%, 9.24–9.61 wt%, 1.18–1.43 wt%, 4.62–7.86 wt%, 45–130 ppm, respectively. Biochemical composition of straw, especially the mass ratio of CL to HCL (m_CL/m_HCL), markedly influenced the molecular composition of the bio-oil. Hydrocarbons (20.15–46.66%) and phenolic compounds (17.01–47.98%) accounted for the vast majority of the identified compounds. SS and PS with higher m_CL/m_HCL (1.92 and 1.80, respectively) tended to produce bio-oils with more aromatics (22.63% and 20.70%, respectively) and fewer phenolic compounds (17.01% and 22.56%, respectively).     

Rare earth doped double perovskite nanocrystals with controllable emission wavelength and model for high-level anti-counterfeiting

Fluorescent anti-counterfeiting technology has become one of the most commonly used anti-counterfeiting technologies because of its simple preparation, low cost and high safety. However, there are still some key technical problems to be solved in developing multi-mode and polychromatic fluorescent materials for high-level anti-counterfeiting. Herein, Yb³⁺/Er³⁺ codoped Cs₂AgIn_0.99Bi_0.01Cl₆ double perovskite nanocrystals (DPNCs) with dual-mode polychromatic emission were developed. Under the irradiation of 365 nm ultraviolet (UV) light, the DPNCs emitted a bright downshifting (DS) yellow light, which comes from the self-trapping excitons (STEs) recombination. While the DPNCs produced upconversion (UC) green fluorescence under the 980 nm laser excitation, which is attributed to the transitions of ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 of Er³⁺ ions. In view of its dual-mode and polychromatic fluorescence characteristics, a high-level anti-counterfeiting based on this fluorescent material is designed. Moreover, the brightness of the anti-counterfeiting pattern based on this material decreases very little after three months. These results indicated that the dual-mode and polychromatic DPNCs reported have potential application in information encryption and identity recognition.     

非线性铁磁谐振无线电能传输拓扑结构

针对负载和耦合系数均有可能大范围变化的实际工况，提出一种新型的基于铁磁谐振的非线性无线电能传输拓扑结构。首先，使用杜芬方程和相量分析法对工作原理进行定性分析；其次，使用有限元电路仿真软件对上述原理进行数值验证计算；最后，搭建了功率可达566 W、效率可达93.5%的非线性拓扑无线电能传输系统原型。实验结果表明，在次级稳压输出200 V的条件下，提出的非线性LCC-LCC拓扑能够适应耦合系数从0.1变化到0.5、负载电阻从72 Ω到无穷大的大范围变化，具有出色的抗偏移能力和负载稳定性。所提拓扑原理新颖、结构简单，具备一定的工程应用潜力。     

Experimental-numerical study on ballistic impact behavior of 316L austenitic stainless steel plates against blunt and ogival projectiles

316L austenitic stainless steel (ASS) is the standard reference material in fabricating pressurized hydrogen storage tanks due to its low hydrogen embrittlement sensitivity and excellent corrosion resistance. Ballistic performance of such tanks is of course a concern of safety. In this study, ballistic impact behavior of 316L ASS was studied against blunt and ogival nose shaped projectiles within impact velocity range of 160.3–324.1 m/s. Ballistic impact behavior of 316L ASS is sensitive to nose shapes of projectiles. For targets against blunt projectile, shear plugging with ejected plugs is observed, and target deflection is limited; for targets against ogival projectile, failure mode is ductile hole enlargement, small bulge and some fragments are observed on front and rear sides of targets, respectively. Ballistic limit velocities (BLVs) for two projectiles are respectively 180.9 m/s and 333.5 m/s, indicating better energy absorption against ogival projectile. Numerical simulations of ballistic impact tests were carried out using either the Lode independent MJC or the Lode dependent modified Mohr-Coulomb (MMC) fracture criterion. Numerical prediction by the latter is more accurate than the former as ballistic impact tests are dominated by stress state where Lode parameter is strong enough to cause a big difference between MMC and MJC criteria, and fracture behavior is accurately predicted by the latter but overestimated by the former.     

Low thermal conductivity and thermoelectric properties of Si80Ge20 dispersed Bi2Sr2Co2Oy ceramics

Bi₂Sr₂Co₂O_y is a thermoelectric material with low thermal conductivity. The Bi₂Sr₂Co₂O_y/Si₈₀Ge₂₀ composite samples were prepared by solid phase sintering at high temperature to investigate the effects of Si₈₀Ge₂₀ alloys as the second phase on the microstructure and thermoelectric properties of the fabricated composites. An appropriate amount of the dispersed Si₈₀Ge₂₀ in the Bi₂Sr₂Co₂O_y matrix can reduce the resistivity of the composite successfully. In particular, the increase in phonon scattering caused by the second phase leads to a significant decrease in thermal conductivity, which improves the thermoelectric properties of the material significantly. At 923 K, the thermal conductivity of the Bi₂Sr₂Co₂O_y + 0.2 wt% Si₈₀Ge₂₀ sample achieves an ultralow value of 0.58 W/K·m. Its corresponding optimal dimensionless thermoelectric figure of merit value is 0.36, which is 56% higher than that of the pure Bi₂Sr₂Co₂O_y sample.