基于VSM的文本相似度计算的研究*

文本相似度的计算作为其他文本信息处理的基础和关键,其计算准确率和效率直接影响其他文本信息处理的结果。提出改进的DF算法和TDIDF算法,一方面利用了DF算法具有线性的时间复杂度,比较适合大规模文本处理的特点,并通过适当增加关键词的方法,弥补了其对个别有用信息错误过滤的不足;另一方面,利用特征项在特征选择阶段的权重对TDIDF方法进行加权处理,在不增加开销的情况下扩大了文档集的规模,还提高了相似度计算的精确度。     

视点相关的真实感三维风景区模拟研究与实现*

提出采用八叉树组织真实山体数据,根据视点距离采用不同的细节层次LOD表示山体各部分,并结合视觉剪裁和帧间相关性进一步减少绘制的山体,达到加速三维地形的绘制和漫游的目的。使用混合纹理映射、阴影渲染技术,并加入山谷中的水面模拟,生成具有真实感的大规模三维风景场景。实验结果表明该方法有效地减少了算法复杂度,易实现碰撞检测,大大提高了绘制效率,在PC机上能实时地生成高分辨率、具有真实感的场景,完全满足VR交互要求。     

四川盆地海相页岩气富集条件及勘探开发有利区

历经十余年探索实践,四川盆地海相页岩气勘探取得了一系列进展,锁定五峰组—龙马溪组为最有利产层,提出了一批页岩气富集高产理论,形成了集地质评价、开发优化、优快钻井、体积压裂、工厂化作业、清洁开发等为一体的勘探开发技术,探明了万亿立方米级储量的页岩气大气田。时值中国页岩气勘探发展的重要节点,回顾四川盆地海相页岩气勘探开发历程、梳理五峰组—龙马溪组页岩气在地质条件与富集规律上的成果认识、展望四川盆地海相页岩气勘探的重点接替领域,对推进盆地海相页岩气的勘探开发有积极意义。(1)四川盆地海相页岩气勘探开发经历了4个阶段：评层选区找目标阶段;浅层至中—深层先导试验阶段;浅层至中—深层示范区建设阶段;浅层至中—深层上产、深层评价、常压页岩气评价、立体开发评价、超深层和新层系探索阶段。(2)四川盆地五峰组—龙马溪组的沉积条件优越,深水陆棚相高有机质含量页岩呈连续稳定分布;页岩气主要赋存在有机孔隙中,页岩储层在纵向上集中发育,连续厚度大;川南地区和川东南涪陵区块的构造相对简单,气源持续补给、远离古/今剥蚀区和大型断裂逸散区是页岩气富集保存的有利区;目前,五峰组—龙马溪组的页岩气资源量为33.19×10<...     

Pervaporation via silicon-based membranes: Correlation and prediction of performance in pervaporation and gas permeation

Pervaporation (PV) is a membrane technology that holds great promise for industrial applications. To better understand the PV mechanism, PV dehydrations of various types of organic solvents (methanol, ethanol, iso-propanol, tert-butanol, and acetone) were performed on five types of organosilica and two types of silicon carbide-based membranes, all with different pore sizes. Water permeance was dependent on the types of organic aqueous solutions, which suggested that organic solvents penetrated the pores and hindered the permeation of water. In addition, water permeance of various types of membranes in PV was well correlated with hydrogen permeance in single-gas permeation. Furthermore, a clear correlation was obtained between the permeance ratio in PV and that in single-gas permeation, which was confirmed via the modified-gas translation model. These correlations make it possible to use single-gas permeation properties to predict PV performance.     

Multipath optical thermometry realized in CaSc2O4: Yb3+/Er3+ with high sensitivity and superior resolution

Design and fabrication of contactless optical thermometer with rapid and accurate performance has become a research hotspot in recent years. Herein, CaSc₂O₄: Yb³⁺/Er³⁺ is employed as the intermediary for temperature sensing under the excitation of 980 nm, which is proven to afford an ultra-sensitive and high-resolution optical thermometry in multiple ways based on the fluorescence intensity ratio (FIR) technology. The optimal thermal sensing behaviors are realized by the FIR of Er³⁺:²H_11/2 → ⁴I_15/2 to ⁴S_3/2 → ⁴I_15/2 transition, which has a relative sensitivity of 1184/T² and a minimal resolution of 0.03 K along with a maximal absolute error of 0.96 K. Besides that, the FIR between the thermally coupled Stark sublevels of Er³⁺:⁴F_9/2 manifold (FIR_R) as well as that of Er³⁺: ⁴I_13/2 manifold (FIR_N) can also provide excellent optical thermometry. The relative sensitivity of FIR_R-based and FIR_N-based optical thermometers are calculated to be 402/T² and 366/T², respectively, with a same minimal resolution of 0.09 K, which possess the potential to be used for biomedicine due to the inherent advantage of their operating wavelengths located in the biological window. The results demonstrate that CaSc₂O₄: Yb³⁺/Er³⁺ is a promising candidate for temperature sensing with multipath, high sensitivity, and superior resolution.     

Investigation of packaging adhesive properties by molecular dynamics and experiments

Adhesive polymer is a common and important material used for packaging of microelectronics and microsystem by attaching dies onto packaging shell, and its mechanical property plays a vital role in isolating dies from the thermal stress of substrate. Therefore, it is extremely significant to evaluate the polymer property in a specific packaging process. The molecular dynamics (MD) simulation is conducted in this article to investigate the material properties of the cross-linked epoxy resin formed by epoxy resin component diglycidyl ether bisphenol A (DGEBA) and curing agent 1,6-Diaminohexane. The polymer network with conversion up to 87.5% is successfully generated and simulated by constant pressure-constant temperature ensemble (NPT) and canonical ensemble (NVT) at different temperatures of curing process. Glass transition temperature (T_g) and Young's modulus are extracted and the predicted material properties are in great agreement with the experimental data. The conclusion provides a guideline to design the special curing process for different adhesive requirements.     

A (4-fluorophenyl)(phenyl)phosphine oxide-modified epoxy resin with improved flame-retardancy,hydrophobicity, and dielectric properties

The compound (4-fluorophenyl)(phenyl) phosphine oxide (4-FPO) was designed, synthesized, and used in the modification of epoxy resin (EP). The 4-FPO-modified EP was prepared by curing the reaction mixture of diglycidyl ether of bisphenol A (DGEBA) and 4-FPO in the presence of 4,4′-diaminodiphenylsulfone (DDS). Compared with the unmodified EP, the limiting oxygen index value of the EP/4-FPO-0.6 (4-FPO-modified EP with 0.6 wt% of phosphorus) increased to 31.6%, and the sample achieved UL-94 V-0 rating. The peak of the heat release rate, average of the heat release rate, and total heat release of EP/4-FPO-0.6 were reduced by 39, 24, and 19%, respectively. Mechanism study showed that the quenching effect in the gas and barrier effect in the condensed phase were responsible for the enhanced flame-retardant properties of the 4-FPO-modified EP. The results showed that hydrophobicity and dielectric properties of the modified EP were clearly improved.     

计及碳排放的风-光-抽水蓄能系统容量优化配置方法

合理的系统容量配置方案是开发利用可再生能源的重要基础.文中提出了一种并网型风-光-抽水蓄能联合运行系统容量优化配置方法,该方法以成本最低、经济效益最大、碳排放量最小为优化目标建立系统模型,基于中国东南沿海某近陆海岛的真实数据,采用带精英策略的快速非支配排序遗传算法(NSGA-Ⅱ)对模型进行求解.然后,引入灰色关联分析法实现无偏折中策略获取最优容量配置方案.仿真结果表明,联合运行系统能在最大限度利用风能和太阳能的基础上实现连续稳定运行;引入灰色关联分析法决策最优容量配置方案是可行的,且联合运行系统在全项目周期里的碳排放量随着灰色关联度的增大而减小;适当提高风电和光伏发电入网率能够降低系统成本、提高经济效益、减少碳排放量.     

机组协同-分布卸荷的风电场-柔直并网系统故障穿越方法

为降低风电场-柔性直流并网系统在交流主网发生低电压故障时的穿越成本,提出一种直流耗能装置与风电机组卸荷电路协同作用的电网故障穿越策略,在电网故障时送端换流器配合风电场快速降低直流功率输出.由于直流耗能装置仅在故障发生的前期、风电场输出功率下降前起到限制直流电压升高的作用,该策略能够显著降低直流耗能装置的体积.在此基础上,该策略将直流耗能装置中的耗能电阻分散置入到受端模块化多电平换流器中,进一步降低了卸荷成本.最后,在PSCAD/EMTDC仿真软件中,构建了风电场-柔性直流并网系统的仿真算例,对所提出的故障穿越方法的正确性和有效性进行了验证.     

基于GaN的高频Boost变换器优化设计

该文围绕同步整流型Boost拓扑效率提升这一关键问题展开研究.作为Boost变换器三种工作模式之一,临界导通模式(BCM)下的Boost变换器可以实现主功率开关的零电压开通或谷底开通以及续流管的零电流关断,有助于提升变换器效率.此外,采用同步整流技术可进一步减小传统续流二极管的导通损耗.该文从BCM下的参数设计出发,重点研究变换器的死区时间配置方法.该方法理论上减小了内部体二极管的导通损耗,在输出电流较大的情况下,有助于进一步提升变换器效率.此外,还总结Boost变换器的主要损耗计算方法.最后,利用GaN功率开关器件,搭建一台额定功率为500W的实验样机,其峰值效率达到了98％,功率密度达到了96W/in3(1in3=1.63871×10?5m3).实现了高效、高功率密度的设计目标,验证了理论分析的正确性.