排序方式: 共有59条查询结果,搜索用时 24 毫秒
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高真空羽流指空间目标上火箭发动机在高真空环境工作时产生的燃气射流迅速膨胀扩散流动状态。这种急剧膨胀的羽流会对空间目标产生冲击、侵蚀,其产生的辐射特性已应用于空间目标的探测、识别。基于无碰撞的自由分子流理论模型对高真空羽流的流场进行了快速预测分析方法研究,获得了高真空羽流的膨胀、扩散分布特性,得到了符合认识的流动规律结果,在计算得到高真空羽流流动参数的基础上,采用佛奥特线型函数描述稀薄气体的展宽,结合逐线积分法+视在光线法计算得到高真空羽流的辐射特性。研究结果表明:高真空羽流的轮廓特性及扩散分布是由喷管出口的点源强度所决定的,点源强度越强,羽流扩散的越厉害,同时轴线上无量纲的密度、温度越高;喷管出口温度相同时,高真空羽流辐射强度随点源增加而增强;出口速度相同时,羽流辐射强度随点源增加而减小;在点源强度相同时,羽流辐射强度与推力正相关。 相似文献
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为克服传统大容量FLASH视频存储控制器时序设计复杂、缓存资源要求较高的缺点,设计了一种利用视频行场信号消隐期进行时序控制的FLASH视频存储控制器。该控制器基于FPGA时序设计,利用视频行场同步信号消隐期时间写入FLASH的读出和写入控制命令。由于无需缓存资源即可实现多级流水线的设计,提高了时序控制效率,简化了时序设计过程。基于Verilog硬件描述语言,设计了3级流水线和并行控制时序,数据达120 MB/s,实现了对2 048pixel×1 752pixel/15frames高速视频数据的实时存储与回放。仿真与实验结果均表明,系统时序设计正确,大容量FLASH阵列读写操作正常,可实现视频数据的采集、存储、回放等多种功能。 相似文献
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《Journal of the European Ceramic Society》2023,43(14):6386-6397
The effects of both nuclear energy loss and electronic energy loss need to be taken into consideration in the ceramic-based waste forms under repository environment. However, the irradiation responses of ceramic-based waste forms to each type of energy loss are somewhat different. In this study, the microstructure evolutions of ultrafine nano and micro Gd2Zr2O7-based waste forms were systematically studied under predominant electronic energy loss simulated by multi-energy He+ irradiation, and compared to those under predominant nuclear energy loss. The results reveal that the fewer He bubble chains, ribbon-like He bubbles and smaller microcracks were observed in the irradiated nano-grained sample. Additionally, nano-grained sample displayed a lower degree of amorphization and higher atomic order compared to micro-grained samples when subjected to predominant electronic energy loss. Moreover, the irradiation dominated by nuclear energy loss can easily induce the grain growth of nano-grained Gd2Zr2O7-based waste form, but in the present study this phenomenon was not observed under multi-energy He+ irradiation. Consequently, under predominant electronic energy loss, the thermodynamic instability and driving force for grain growth due to excess surface energy in the ultrafine nano sample can be suppressed. As a result, the sample demonstrated enhanced irradiation resistance due to the more efficient absorption and elimination of defects at grain boundaries induced by electronic excitation. We elucidated that enhanced irradiation resistance of the waste forms by tailoring the grain size requires the consideration of the effects of electronic energy loss and nuclear energy loss, which can provide guidance for the design and optimization of highly irradiation-resistant nuclear waste forms. 相似文献
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《Ceramics International》2023,49(15):24650-24659
An emerging approach in tissue engineering, especially in cases where large bone cavities remain unfilled after tumor removal, is the implementation of bioceramic scaffolds with magnetic properties for bone augmentation. The fabrication of bioactive porous scaffolds with adequate mechanical characteristics and sufficient porosity represents to assist bone regeneration. one of the most important difficulties in tissue engineering. The final goal is, the in situ apatite formation, a synergistic result of bioceramics, and stem cell activation/differentiation to promote bone regeneration via magnetically driven osteogenic lineage. This study focuses on the development of a novel multifunctional three-dimensional scaffold with certain physicochemical and biological features, addressing diverse difficult issues, such as bioactivity and biocompatibility, as well as bone tissue malignancies. The synthetic approach initiates with the synthesis of CoFe2O4 nanoparticles (NP), followed by the fabrication of Mg2SiO4–CoFe2O4 nanocomposite (NC), employing a two-pot sol-gel synthesis method. Finally, three-dimensional scaffolds (MS) are fabricated via the polymer foam replica technique. X-Ray Diffraction, Thermogravimetry, and Fourier transform infrared spectroscopy, reveal the occurrence of the constituent materials (forsterite: Mg2SiO4 and cobalt iron oxide). Static magnetic characterization at each fabrication stage outlines the collective magnetic features while magnetic particle hyperthermia highlights the heating efficiency quantified as specific loss power (SLP) and specific absorption rate (SAR) in W·g−1 (NP: 19 - 43 °C in 100 s, SLP = 450 W g−1, NC: SLP = 200 W g−1, SAR= 1,07 W g−1). This opens promising pathways in bone tissue regeneration cancer treatments combined with targeted delivery of active/pharmaceutical substances and magnetic hyperthermia. 相似文献
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《Ceramics International》2023,49(15):25063-25073
A core–shell structured spherical graphite (SG)@SiC attenuating agent with a tunable silicon carbide (SiC) shell thickness was synthesized via in-situ solid-liquid reaction of SG and Si. Then, fully dense 10 wt%SG@SiC/AlN microwave attenuating composite ceramics were prepared through hot-pressing sintering, and the morphology of SG@SiC particle was well maintained. By moderately modulating the thickness of the SiC shell with relatively low complex permittivity and thermal conductivity, an effectively inhibited solid solution of SiC into AlN, weakened dipole and electron polarization, enhanced conduction loss, and an improved impedance matching, thermal conductivity and microwave loss capacity were simultaneously achieved. Thus, the SG@SiC/AlN composite exhibit excellent and impressive thermal conductivity of 63.92 W m−1·K−1 and minimum reflection loss of −34.2 dB. The outstanding performance of SG@SiC/AlN composite indicates that the composite is promising microwave attenuating ceramic with excellent thermal conduction and microwave absorption ability. This work opens up a new core–shell structure strategy for designing and developing a high-efficiency attenuating agent and microwave attenuating ceramic. 相似文献
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《Journal of the European Ceramic Society》2023,43(4):1459-1468
For high-temperature electromagnetic absorption materials, higher polarization loss is needed to balance the impedance mismatch due to greater conduction loss at elevated temperatures. Here, a SiO2 interface was introduced into a SiCnws/BSAS ceramic based on wide bandgap and low dielectric constant characteristics of SiO2. The interface structure was tailored by changing the SiO2 content. When the SiO2 content reached 15 vol%, three-phase interlaced interfaces were formed, which produced many nano-heterointerfaces that increased the polarization loss by 77.5 %. The optimized SiCnws/SiO2-BSAS ceramic achieved enhanced electromagnetic absorption from 298 K to 873 K, and its effective absorption bandwidth reached 4.1 GHz at 873 K. The electromagnetic absorption mechanism was analyzed from the perspectives of electron transport and space charges. This heterointerface design strategy provides a new method for the development of high-temperature electromagnetic absorption materials. 相似文献