基于改进精英克隆选择算法的B样条曲线逼近方法

时间同步是多智能体网络协同工作的基础,具有重要意义。低成本无线传感器网络节点时钟易受到环境因素的影响,导致节点时间同步误差增大,网络信道负载增加。针对上述问题,提出了一种低时钟再同步周期、自适应温度补偿的无线传感器网络时间同步方法。首先,基于双向通信时间同步模型,提出了温度补偿的节点频移量动态估计模型;然后,采用Almon函数加权求和的方式对温度和频移量数据进行融合,解决数据采样率不匹配和模型维度高的问题;其次,为进一步提高时间同步精度,采用Kalman滤波器对频移量和相移量估计值进行滤波,并采用系统状态后验估计值对节点本地时间进行补偿;最后,参照IEEE 802.15.4标准对时间同步精度的要求,设计了一种失效风险最小化的再同步决策函数,最大限度提高节点再同步周期,减少信道负载。在高低温箱、室内和室外3种环境下进行实验以验证所提的方法。试验结果表明,与洪泛时钟同步协议(FTSP)时间同步协议相比,自适应温度补偿的时间同步(ATCTS)算法平均时间同步误差降低了97.4%,室外环境下平均时间同步周期为324 min。     

基于简易电池自动恒流充电电路的设计

介绍了一种基于分立元件构成的电池自动恒流充电电路，并且重点阐述了电路的组成、结构特点、工作原理及电路的调节。本电路具有可靠性高、电路简单、自动多节充电、调节方便等优点。     

一种NURBS曲面转化为Bezier曲面片的改进算法

NURBS曲面建模技术的应用是电磁散射计算中的重要研究内容.基于NURBS控制网格的剖分和规划处理,简并相似的计算,提出了一种将基于NURBS建模的曲面转化为分段Bezier面片的高效算法,简化了该过程的复杂度和计算量.结果表明该算法保持了良好的通用性和准确性,且曲面次数越高,控制顶点越多,在计算量上的优势越明显.     

Suppression of plant parasitic nematodes in the chinampa agricultural soils

Soil from the chinampa agricultural system in the Valley of Mexico suppressed damage by plant-parasitic nematodes to tomatoes and beans in greenhouse and growth chamber trials. Sterilization of the chinampa soil resulted in a loss of the suppressive effect, thereby indicating that one or more biotic factors were responsible for the low incidence of nematode damage. Nine organisms were isolated from chinampa soil, which showed antinematodal properties in culture. Naturally occurring populations of plant-parasitic nematodes were of lower incidence in chinampa soil than in Chapingo soil.     

6%增效阿罗蒎兹微乳剂防治黄瓜根结线虫

用6%增效阿罗蒎兹微乳剂(有效成分:苦豆子水提取物、阿维菌素)处理温室土壤防治黄瓜根结线虫试验表明:阿罗蒎兹微乳剂可较好地控制黄瓜根结线虫危害.阿罗蒎兹微乳剂7.5、15.0、22.5 L/hm2三个处理,药后90 d土壤中2龄幼虫减退率分别为-12.23%、31.50%、43.52%,而对照药剂1.8%阿维菌素15 L/hm2处理的线虫减退率为-37.65%.药后90 d 6%增效阿罗蒎兹微乳剂及各处理防治效果分别为54.52%、70.16%、74.84%.而对照药剂为50.81%.阿罗蒎兹微乳剂可有效地控制黄瓜根结线虫的危害,有较高的推广应用价值.     

Boundary knot method for 2D and 3D Helmholtz and convection–diffusion problems under complicated geometry

The boundary knot method (BKM) of very recent origin is an inherently meshless, integration‐free, boundary‐type, radial basis function collocation technique for the numerical discretization of general partial differential equation systems. Unlike the method of fundamental solutions, the use of non‐singular general solution in the BKM avoids the unnecessary requirement of constructing a controversial artificial boundary outside the physical domain. The purpose of this paper is to extend the BKM to solve 2D Helmholtz and convection–diffusion problems under rather complicated irregular geometry. The method is also first applied to 3D problems. Numerical experiments validate that the BKM can produce highly accurate solutions using a relatively small number of knots. For inhomogeneous cases, some inner knots are found necessary to guarantee accuracy and stability. The stability and convergence of the BKM are numerically illustrated and the completeness issue is also discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

Almost strictly total positivity of NUAT B-spline basis

Total positivity of spline basis has been well known in the theory of computer aided geometry design, which is highly related with good shape preserving property. Almost strictly total positivity is stronger, which could determine the positive minors while the other is zero. In this paper, a geometrical approach is proposed to prove the collection matrices of NUAT B-spline basis are almost strictly totally positive. In this paper, knot insertion algorithm combined with coefficient variation of NUAT B-spline function, we put forward an intuitive and geometrical method.     

铜铁复合粉烧结制备工艺技术研究

以铁粉为基体,添加铜粉采用混合烧结生产工艺制备FeCu20(WFe=80%,WCu=20%),以及FeCu30(WFe=70%,WCu=30%),以批量生产符合性能要求的铜铁复合粉末。这里详细介绍了Cu/Fe复合粉烧结工艺制备工艺技术参数,产品的性能及应用情况。     

一种新型智能打结设备的运动控制方法研究

在分析一种新型智能打结设备机电系统的运动原理基础上,针对缝制图样数据的2种设计方案,研究并提出了满足该类设备控制需要的2种运动控制方法,并通过理论分析和实际测试对这2种方法的性能进行了评价.