正交激励超声切削装置的椭圆轨迹偏转与校正

为研究超声椭圆振动切削（ultrasonic elliptical vibration cutting,UEVC）刀尖轨迹形成及控制,解决刀尖轨迹非正椭圆问题,建立二维正交柔性导波UEVC装置刀尖轨迹的运动学模型;分析90°相位差下非正椭圆轨迹产生原因,建立刀尖轨迹校正模型,并推导出基于正椭圆轨迹下的刀尖轨迹偏转模型。通过实验对刀尖轨迹校正模型进行验证,校正后轨迹偏离坐标轴1.67°,小于校正前偏离角度。实验结果表明,该模型能够有效地校正刀尖轨迹,可在轨迹控制方面为后续研究刀尖轨迹偏转及变刀尖轨迹超声振动加工提供理论基础。     

基于多纹理的合成孔径雷达图像相干斑抑制

相干斑抑制是合成孔径雷达 (syntheticapertureradar,SAR)图像后处理的首要问题。在多纹理假设下 ,采用最大似然方法来同时估计多个极化通道纹理参数。该方法保存了极化信息 ,消除了极化通道间的耦合 ,取得了较好的相干斑抑制效果 ;并与极化白化滤波 (polarimetricwhiteningfilter,PWF)和Lee的最优权值算法作了比较     

我国农村居民家庭高等教育学费支付能力研究

居民家庭特别是占人口绝大多数的农村居民家庭的高等教育支付能力是确定我国高校收费水平的重要依据。文章在分析了农村居民家庭收入分布的基础上，对我国农村居民家庭高等教育学费支付能力进行了评估。     

粒子系统的频率层次模型

为了提高粒子系统进行自然场景仿真应用的效率，提出了频率层次模型（Level of Frequency,即LOF)。在分析了各种基于粒子系统的自然现象(如雨、雪、云彩等)的表现特征之后，可以赋予各种粒子集以不同的刷新频率即建立频率层次模型。根据频率层次模型，可以使有限的计算资源实现重新分配，从而达到更佳表现效果。另外，粒子系统的频率层次模型的提出，使得自然场景仿真可以按不同频率进行任务分割，从而有利于将来进一步实现并行处理。     

考虑低渗点启动压力梯度的中东孔隙型碳酸盐岩油藏波及系数修正方法

 根据中东地区孔隙型碳酸盐岩油藏渗透率分布范围大、低渗与中高渗渗流规律并存的特征,针对低渗点存在启动压力梯度而难以动用的问题,采用数值模拟方法分析低渗点启动压力梯度对油藏波及系数的影响规律,通过耦合低渗点启动压力与井间驱替压力分布,提出考虑低渗点启动压力梯度的孔隙型碳酸盐岩油藏波及系数修正方法。以中东地区M油藏为例进行应用分析,计算得到的渗透率为5×10^-3~35×10^-3 μm²、变异系数为0.6~0.8时,波及修正系数分布范围为0.75~0.99,证明了该孔隙型碳酸盐岩油藏波及系数修正方法的可靠性和实用性。     

Woody cover and hominin environments in the past 6 million years

The role of African savannahs in the evolution of early hominins has been debated for nearly a century. Resolution of this issue has been hindered by difficulty in quantifying the fraction of woody cover in the fossil record. Here we show that the fraction of woody cover in tropical ecosystems can be quantified using stable carbon isotopes in soils. Furthermore, we use fossil soils from hominin sites in the Awash and Omo-Turkana basins in eastern Africa to reconstruct the fraction of woody cover since the Late Miocene epoch (about 7 million years ago). (13)C/(12)C ratio data from 1,300 palaeosols at or adjacent to hominin sites dating to at least 6 million years ago show that woody cover was predominantly less than ～40% at most sites. These data point to the prevalence of open environments at the majority of hominin fossil sites in eastern Africa over the past 6 million years.     

Common variants at MS4A4/MS4A6E, CD2AP, CD33 and EPHA1 are associated with late-onset Alzheimer's disease

The Alzheimer Disease Genetics Consortium (ADGC) performed a genome-wide association study of late-onset Alzheimer disease using a three-stage design consisting of a discovery stage (stage 1) and two replication stages (stages 2 and 3). Both joint analysis and meta-analysis approaches were used. We obtained genome-wide significant results at MS4A4A (rs4938933; stages 1 and 2, meta-analysis P (P(M)) = 1.7 × 10(-9), joint analysis P (P(J)) = 1.7 × 10(-9); stages 1, 2 and 3, P(M) = 8.2 × 10(-12)), CD2AP (rs9349407; stages 1, 2 and 3, P(M) = 8.6 × 10(-9)), EPHA1 (rs11767557; stages 1, 2 and 3, P(M) = 6.0 × 10(-10)) and CD33 (rs3865444; stages 1, 2 and 3, P(M) = 1.6 × 10(-9)). We also replicated previous associations at CR1 (rs6701713; P(M) = 4.6 × 10(-10), P(J) = 5.2 × 10(-11)), CLU (rs1532278; P(M) = 8.3 × 10(-8), P(J) = 1.9 × 10(-8)), BIN1 (rs7561528; P(M) = 4.0 × 10(-14), P(J) = 5.2 × 10(-14)) and PICALM (rs561655; P(M) = 7.0 × 10(-11), P(J) = 1.0 × 10(-10)), but not at EXOC3L2, to late-onset Alzheimer's disease susceptibility.     

含冲击的车内道路噪声主动控制系统

针对道路噪声主动控制系统中，冲击噪声引起的鲁棒性问题，提出了一种对冲击噪声的主动控制方法。首先，进行了道路噪声采集试验，选取了4个最佳参考信号位置，并采集了道路冲击噪声的数据。然后，基于多通道自适应滤波算法，提出了归一化多通道自适应滤波算法和符号算法相结合的冲击噪声主动控制算法。其次，基于提出的冲击噪声主动控制算法，搭建了道路噪声主动控制系统仿真模型，使用采集到的冲击噪声信号和加速度信号进行了仿真分析。最后，使用选取的4个加速度信号和1个扬声器，控制驾驶员处的道路噪声，进行了道路冲击噪声主动控制试验，验证了方法的有效性。与原有算法相比，该算法的稳定性和降噪效果得到了较大的提升。