Grating-based x-ray phase contrast imaging has the potential to be applied in future medical applications as it is compatible with both laboratory and synchrotron source. However, information retrieval methods are imp...Grating-based x-ray phase contrast imaging has the potential to be applied in future medical applications as it is compatible with both laboratory and synchrotron source. However, information retrieval methods are important because acquisition speed, scanning mode, image quality, and radiation dose depend on them. Phase-stepping （PS） is a widely used method to retrieve information, while angular signal radiography （ASR） is a newly established method. In this manuscript, signal-to-noise ratios （SNRs） of ASR are compared with that of PS. Numerical experiments are performed to validate theoretical results. SNRs comparison shows that for refraction and scattering images ASR has higher SNR than PS method, while for absorption image both methods have same SNR. Therefore, our conclusions would have guideline in future preclinical and clinical applications.展开更多
We consider the effects of the aspect ratio L/H (where<em> L</em> is the length of a prism, and <em>H</em> is the height of a prism normal to the flow direction) and the size of additional stru...We consider the effects of the aspect ratio L/H (where<em> L</em> is the length of a prism, and <em>H</em> is the height of a prism normal to the flow direction) and the size of additional structures (which are a plate and a fin on the surface of a prism) on a vibration characteristic of a cantilevered rectangular prism. The present research is intended to support the analysis of energy harvesting research on the flow-induced vibration in water flow using a magnetostrictive phenomenon. The prisms are constructed from stainless steel and mounted elastically to a plate spring attached to the ceiling wall of the water tunnel. The prisms with aspect ratios of<em> L/H</em> ≥ 5 have reasonably identical vibration characteristics. However, the difference in the vibration characteristic appears distinctly on a rectangular prism with an aspect ratio of <em>L/H </em>= 2.5. The rectangular prism with an aspect ratio of <em>L/H</em> = 10 and a side ratio of <em>D/H</em> = 0.2 has a stable and large response amplitude and oscillates with a lower velocity. The length of the added plate and the size of the added fin influence the velocity of vibration onset. If the length of the added plate and fin size on the rectangular prism with <em>D/H</em> = 0.2 becomes large, the curve of the response amplitude shifts to that of the rectangular prism with <em>D/H</em>= 0.5. The response amplitude of the rectangular prism with/without plate or fin is found to be related to the second moment of area of the prism.展开更多
This paper presents the analytical design and high performance of step-constant tapered slot antenna (STSA) for ultra-wideband application. The return loss, radiation pattern, antenna gain, and level of cross polariza...This paper presents the analytical design and high performance of step-constant tapered slot antenna (STSA) for ultra-wideband application. The return loss, radiation pattern, antenna gain, and level of cross polarization of this antenna are presented and analyzed. Utilizing Rogers (RO3006) substrate having a relative permittivity of 6.15, the proposed antenna provides the ultra-wideband (UWB) from 3.1 GHz to 10.6 GHz. It is observed that the return loss and gain are increased with increasing the step size. It has been observed from the simulation results incorporating CST microwave studio commercial software version 2015, the optimum return loss, directivity and gain are ?43 dB, 10.52 dBi and 10.20 dB, respectively, for 15 step size. Therefore, the newly proposed antenna will be a decent candidate for ultra-wideband application.展开更多
为解决由海洋温差能驱动的海洋热能转换(Ocean Thermal Energy Conversion,OTEC)系统热效率低、经济性差等问题,文章设计并搭建了由海洋温差能驱动,集发电与空调功能为一体的(Ocean Thermal Energy Conversion Combined Air Conditioner...为解决由海洋温差能驱动的海洋热能转换(Ocean Thermal Energy Conversion,OTEC)系统热效率低、经济性差等问题,文章设计并搭建了由海洋温差能驱动,集发电与空调功能为一体的(Ocean Thermal Energy Conversion Combined Air Conditioner,OTEC-AC)试验系统。该系统通过先发电再冷却空气,梯级利用深层海水冷能,从而大幅提升海洋温差能转换效率。利用膨胀输出功、制冷量、综合热效率等性能评价指标,测试并分析了不同工况下发电-空调综合系统的性能变化规律,同时验证了OTEC-AC相较于OTEC的性能提升情况。试验结果表明:发电系统存在最佳膨胀压比,此时,膨胀机的等熵效率达到峰值的21.83%;降低深层海水温度和增加冷冻水流量均可显著提升OTEC-AC系统性能,当深层海水温度由9℃降至4℃时,系统综合[火用]效率从47.25%增至51.60%;相同工况下,OTEC-AC系统的发电量和制冷量分别为97 W和5 386 W,与独立运行OTEC系统相比,折算后的系统热效率从1.21%提升到17.60%。展开更多
与传统高压感应电能传输(inductive power transfer,IPT)系统不同,高压输入-低压输出大功率IPT系统面临高降压比实现与二次侧导通损耗过大的核心挑战。为此,提出一种基于串联电容全桥逆变与同步反向耦合倍流整流的双通道IPT拓扑。该拓...与传统高压感应电能传输(inductive power transfer,IPT)系统不同,高压输入-低压输出大功率IPT系统面临高降压比实现与二次侧导通损耗过大的核心挑战。为此,提出一种基于串联电容全桥逆变与同步反向耦合倍流整流的双通道IPT拓扑。该拓扑在实现1/8电压转换比的同时,可将二次侧各线圈电流降至传统全桥整流方案的1/4,显著降低松耦合变压器的设计难度及二次侧线圈导通损耗。在阐述所提拓扑工作原理的基础上,详细开展IPT系统的参数设计与实现方案研究。为验证理论分析的正确性与方案有效性,搭建原理样机并进行实验测试。结果表明,样机实现28 V恒压输出与零相位角(zero phase angle,ZPA)运行,峰值效率达95.3%、满载效率达95%,充分证明了所提拓扑及设计方案的可行性、正确性与先进性。展开更多
基金Project supported by the National Research and Development Project for Key Scientific Instruments(Grant No.CZBZDYZ20140002)the National Natural Science Foundation of China(Grant Nos.11535015,11305173,and 11375225)+2 种基金the project supported by Institute of High Energy Physics,Chinese Academy of Sciences(Grant No.Y4545320Y2)the Fundamental Research Funds for the Central Universities(Grant No.WK2310000065)Wali Faiz,acknowledges and wishes to thank the Chinese Academy of Sciences and The World Academy of Sciences(CAS-TWAS)President’s Fellowship Program for generous financial support
文摘Grating-based x-ray phase contrast imaging has the potential to be applied in future medical applications as it is compatible with both laboratory and synchrotron source. However, information retrieval methods are important because acquisition speed, scanning mode, image quality, and radiation dose depend on them. Phase-stepping （PS） is a widely used method to retrieve information, while angular signal radiography （ASR） is a newly established method. In this manuscript, signal-to-noise ratios （SNRs） of ASR are compared with that of PS. Numerical experiments are performed to validate theoretical results. SNRs comparison shows that for refraction and scattering images ASR has higher SNR than PS method, while for absorption image both methods have same SNR. Therefore, our conclusions would have guideline in future preclinical and clinical applications.
文摘We consider the effects of the aspect ratio L/H (where<em> L</em> is the length of a prism, and <em>H</em> is the height of a prism normal to the flow direction) and the size of additional structures (which are a plate and a fin on the surface of a prism) on a vibration characteristic of a cantilevered rectangular prism. The present research is intended to support the analysis of energy harvesting research on the flow-induced vibration in water flow using a magnetostrictive phenomenon. The prisms are constructed from stainless steel and mounted elastically to a plate spring attached to the ceiling wall of the water tunnel. The prisms with aspect ratios of<em> L/H</em> ≥ 5 have reasonably identical vibration characteristics. However, the difference in the vibration characteristic appears distinctly on a rectangular prism with an aspect ratio of <em>L/H </em>= 2.5. The rectangular prism with an aspect ratio of <em>L/H</em> = 10 and a side ratio of <em>D/H</em> = 0.2 has a stable and large response amplitude and oscillates with a lower velocity. The length of the added plate and the size of the added fin influence the velocity of vibration onset. If the length of the added plate and fin size on the rectangular prism with <em>D/H</em> = 0.2 becomes large, the curve of the response amplitude shifts to that of the rectangular prism with <em>D/H</em>= 0.5. The response amplitude of the rectangular prism with/without plate or fin is found to be related to the second moment of area of the prism.
文摘This paper presents the analytical design and high performance of step-constant tapered slot antenna (STSA) for ultra-wideband application. The return loss, radiation pattern, antenna gain, and level of cross polarization of this antenna are presented and analyzed. Utilizing Rogers (RO3006) substrate having a relative permittivity of 6.15, the proposed antenna provides the ultra-wideband (UWB) from 3.1 GHz to 10.6 GHz. It is observed that the return loss and gain are increased with increasing the step size. It has been observed from the simulation results incorporating CST microwave studio commercial software version 2015, the optimum return loss, directivity and gain are ?43 dB, 10.52 dBi and 10.20 dB, respectively, for 15 step size. Therefore, the newly proposed antenna will be a decent candidate for ultra-wideband application.
文摘为解决由海洋温差能驱动的海洋热能转换(Ocean Thermal Energy Conversion,OTEC)系统热效率低、经济性差等问题,文章设计并搭建了由海洋温差能驱动,集发电与空调功能为一体的(Ocean Thermal Energy Conversion Combined Air Conditioner,OTEC-AC)试验系统。该系统通过先发电再冷却空气,梯级利用深层海水冷能,从而大幅提升海洋温差能转换效率。利用膨胀输出功、制冷量、综合热效率等性能评价指标,测试并分析了不同工况下发电-空调综合系统的性能变化规律,同时验证了OTEC-AC相较于OTEC的性能提升情况。试验结果表明:发电系统存在最佳膨胀压比,此时,膨胀机的等熵效率达到峰值的21.83%;降低深层海水温度和增加冷冻水流量均可显著提升OTEC-AC系统性能,当深层海水温度由9℃降至4℃时,系统综合[火用]效率从47.25%增至51.60%;相同工况下,OTEC-AC系统的发电量和制冷量分别为97 W和5 386 W,与独立运行OTEC系统相比,折算后的系统热效率从1.21%提升到17.60%。
