三自由度并联机构（3SPS 3SRR）的位置分析

针对一种3SPS-3SRR并联机构,运用符号法对该机构进行位置分析建模及求解。构建动、静坐标系,通过矩阵转换对机构建立约束方程,运用Sylvester消元方法进行消元得到机构单变元输入输出方程,求得机构位姿的封闭解。最后进行实例求解,得到该机构处于一般姿态的32组实数解,并使机构处于特殊位姿,将所得封闭解与预估解对比,从而验证该位置求解模型的正确性。基于符号法的3SPS-3SRR并联机构位置分析模型具有准确、高效的特点,规避了基于数值法的诸多缺点,对该机构的深入分析具有重要理论意义及实用价值。     

Estimating sustainable crop residue removal rates and costs based on soil organic matter dynamics and rotational complexity

The government of Ontario, Canada, has committed to stopping the use of coal for electrical generation by 2014 and agricultural biomass is being considered as replacement. However, there is limited information on whether the annual 2 million Mg of biomass required to replace coal could be sustainably supplied by agriculture and at what costs. This study assesses the sustainable availability and the farm-gate break-even cost of residue biomass from three crops (corn, soybean and winter wheat) grown under two common rotation scenarios in Ontario. Sustainably removable residue (SRR) rates are determined using a five-step approach that accounts for maintenance soil organic matter (MSOM) in the presence of yield and rotation variations across counties. Under typical SOM formation and decomposition conditions and assuming typical corn-soybean and corn-soybean-winter wheat rotation scenarios, about 1.1 million Mg of residue could be sustainably removed each year, primarily from the major agricultural counties in the province. While rotational complexity enhances SRR, the inclusion of soybean decreases available residue compared to corn and winter wheat. The break-even price for crop residues, representing the minimum price necessary to cover all variable and fixed costs for the farmer, is between $57 Mg⁻¹ and $87 Mg⁻¹. However, the actual amount supplied for each biomass price depends critically on the opportunity costs associated with not growing typical crops in the conventional manner.     

Modelling of beam propagation and its applications for underwater imaging

In order to process underwater imaging to the best possible level,an imaging model based on beam propagation was established.The presented model included not only the laser beam propagation affected by...     

Compact SCSRR-based quad-band antenna for Bluetooth,WiMAX, WLAN,and fixed-satellite services

This research describes the detailed analysis and design of the compact complex-free structural metamaterial quad band radiating element applicable for Bluetooth, WiMAX, WLAN, and fixed-satellite service. The radiating element designed is composed of an inner angle-rotated circular Split Ring Resonator (SRR) placed within the outer square-shaped SRR interlinked by a strip to design the multiband operational characteristics and is fed by a coplanar waveguide. Suggested radiating element is imprinted over the FR4 substrate material with the electrical dimension of 28 × 31.26 × 0.8 mm³. The initial outer-closed square ring offers dual-band operation by resonating at 2.8 and 8.5 GHz frequencies, and the incorporation of a circular SRR offers quad-band operation. The unique negative permeability feature of the proposed Square and Circular Split Ring Resonator (SCSRR) structure is extracted, and its band characteristics are analyzed. Results obtained from the simulated radiating element are validated with the fabricated antenna. The measured E plane pattern resembles a numeric eight shape, and the H plane pattern is omnidirectional. Suggested SCSRR antenna offers a gain of above 3.2 dBi in all the operating bands.     

402～405 MHz CMOS低功耗射频收发机北大核心

基于0.18μm CMOS工艺设计了一种用于WBAN 402～405 MHz频段具有低功耗全数字锁频和灵敏度校准功能的超再生收发机。采用具有噪声抵消技术的巴伦低噪声放大器，以减少无源匹配器件数量和适应低压工作；超再生数控振荡器采用数字控制电容阵列实现频率调谐，以消除猝灭操作期间振荡器的频率漂移；采用全数字锁频环替代频率综合器，以降低传感器节点的功耗；灵敏度校准环路与自动幅度控制环路共享组件，以减小校准误差，并能够在不中断接收状态的情况下动态校准接收机灵敏度。仿真结果表明，在1 V电源电压下，接收机灵敏度为-90 dBm,功耗为1.89 mW,其中全数字锁频环功耗为78μW;发射机功耗为1.96 mW,效率为28%。