一道试题的分析与思考

一、考题(本题满分16分)如图1所示,公路AM、AN围成的是一块顶角为α的角形耕地,其中t anα=-2.在该块土地中P处有一小型建筑,经测量,它到公路AM、AN的距离分别为3km、5%姨km.现要过点P修建一条直线公路BC,将三条公路围成的区域ABC建成一个工业园.为尽量减少耕地占用,问:如何确定B点的位置,使得该工业园区的面积最小?并求最小面积.二、命题意图学生在学习直线与圆时,曾经做过这样的题目:“在     

聚合硅酸硫酸铁和聚合硫酸铁处理黄河水的效果及其絮体特性研究

采用聚合硅酸硫酸铁(PFSS)和聚合硫酸铁(PFS)两种无机高分子混凝剂处理黄河水,考察了两种混凝剂对浊度和UV254的去除效果,并结合混凝过程中絮体zeta电位的变化,分析了两种混凝剂的混凝机理.通过激光粒度仪在线观察混凝过程中絮体的生长情况,发现PFSS比PFS生成的絮体生长速度快,尺寸大.对形成的絮体施加不同强度的剪切力,通过观察絮体粒径的变化来比较絮体的强度,发现PFSS生成的絮体强度较大.研究了在不同剪切强度和不同剪切时间下絮体的破碎程度和絮体的恢复能力(分别以破碎因子Bf和恢复因子Rf表示),发现在强剪切力和长剪切时间下Bf和Rf均较大;在相同条件下PFSS生成絮体的Bf较小而PFS生成絮体的Rf较大,这表明前者的抗剪切能力较强,而后者具有更强的再生能力.     

聚丙烯酸-g-非离子性聚氨酯接枝共聚物的合成及其在铬鞣中的应用研究

为了解决制革工业中的铬污染问题,制备了一种高分子型的高吸收铬鞣助剂,测定了其耐酸、耐铬离子交联特性,并应用与铬鞣工序中降低废液中铬含量。     

有序结构氟聚合物压电驻极体的制备和压电性研究

描述了一种有序微孔结构压电聚合物功能膜的制备方法,利用模板的高度有序实现薄膜微孔结构的精确控制.将此制备方法用于氟聚合物压电驻极体薄膜的制备,通过扫描电子显微镜(SEM)对其微观结构的观察表明薄膜具有理想的有序结构.对氟聚合物压电驻极体压电性的研究则是利用正压电效应测量准静态压电系数d₃₃,通过等温衰减和压强依赖性的测量考察其压电性能.结果表明:有序结构氟聚合物压电驻极体的准静态压电系数d₃₃可高达300 pC/N;与无序结构氟聚合物     

HL80型低纹波系数大电流程控恒流源研制

HL80型大功率恒流源采用闭环实时串联线性调整技术实现输出电流的恒流控制,应用三相交流调压模块调控电源变压器的初级电压,以可编程控制器与触摸屏配合实现图形化的交互式操作界面,采用以太网构成通讯控制网络。当负载在2.0~3.0Ω之间变化且输出电流在20~80 A之间变化时,HL80型恒流源的调整管压降可控制在(8±2)V范围内,输出电流稳定度优于0.12%,纹波系数优于0.11%。样机实现万次拷机实验无故障。     

碳纳米管制备条件探索及对亚甲基蓝的吸附性能

探索了用气相沉积法制备碳纳米管时,不同温度、催化剂浓度、反应时间对碳纳米管定向性、径向管径、表面性能的影响,结果表明,反应温度750℃、催化剂浓度5g/100mL、反应时间30min是制备碳纳米管的最佳实验条件。在最佳条件下制备碳纳米管并进行对亚甲基蓝吸附的研究,探索了吸附时间、pH、吸附浓度、温度对吸附结果的影响。     

Modeling and Computing Example for Effective Electromagnetic Parameters of Multiphase Composite Media

A method using strong fluctuation theory （SFT） to compute the effective electromagnetic parameters of multiphase composite media, and common materials used to design radar-absorbing materials, is demonstrated. The effective electromagnetic parameters of ultrafine carbonyl-iron （DT-50） and fiber fabric, which are both multiphase composite media and represent coated and structured radar absorbing materials, respectively, are investigated, and the corresponding equations of electromagnetic parameters by using the SFT are attained. Moreover, we design a program to simplify the solutions, and the results are discussed.     

Electromagnetic Parameters Model and Microwave Absorption for Composite Coatings Containing Magnetic Particles

Considering the eddy current effect of the magnetic metal particles in a high frequency electromagnetic field, we extend the Maxwell-Garnett law by introducing the eddy-effect parameter A which is as functions of the radius, permeability and electric conductivity of the metal particle medium. It is obvious that the computational result agrees with the experiment, which indicates that the extended Maxwell-Garnett law can be used to predict the effective electromagnetic parameters of a dilute metal-insulator composite medium in a high-frequency electromagnetic field.     

Crystal Structure and High Hardness Mechanism of Orthorhomic Si2N2O

A quasi-single-phase orthorombic Si2N20 compound is obtained by hot-pressing sintering using homogeneous precursors as raw materials under nitrogen atmosphere. The bulk hardness of orthorombie Si2N20 （o-Si2N2 O） is investigated by a nanoindenter experiment; the results show that o-Si2N20 with maximal value about 19 GPa has a high hardness covalent crystal besides β-Si3N4. It is discovered that the high hardness is mainly attributed to the unique crystal structure. The bridging O atoms in the o-Si2N20 are responsible for decreasing hardness. It is found that the Si-O bonds in the open tetrahedral crystal structure are more easily broken and tilted than other bonds.