多角度计算一个三棱锥的体积

以一道立体几何试题为例,分别从向量法、割补法、等价转化以及质点几何学等视角研究三棱锥的体积.通过一题多解建立知识间的联系,开拓学生的视野,提升学生的数学素养.     

在分光计实验中的几何关系探究

从空间几何的角度来对分光计的构造、结构以及调节方法等方面来加以说明，以便从根本上掌握分光计设计的原理、调节的思路以及拓展的方法。     

孔洞和孪晶界对银纳米线形变行为联合影响的分子动力学模拟

Based on molecular dynamics simulations, the plastic deformation of silver nanowires under uniaxial tension has been studied systematically. In this paper, the mechanical properties of [111]-oriented twin nanowires with different hole sizes have been studied. The existence of holes has no effect on the elastic deformation stage. The hole on the twin boundary has two main roles in the plastic deformation stage. During the initial stages of plastic deformation, the main function of the hole is to produce new dislocations as dislocation sources at small hole sizes.Upon increasing the hole size, the main effect changes to stop dislocation slip. During the late stages of plastic deformation, the two functions of the hole complement each other, upon increasing the hole size, the function of the hole as dislocation sources becomes obvious, leading to weakening of the plasticity of the nanowires.     

气冷服近体调温性能的数值分析

为了探讨气冷服的近体调温性能,构建了体表-服装几何模型,采用数值模拟的方法研究了平均皮肤温度、内外温差关于进气速度、进气温度及人体散热率的变化关系。结果表明:体表上半部分温度高于下半部分温度;平均皮肤温度与进气速度成幂函数关系,温差与进气速度成对数函数关系;平均皮肤温度及温差关于进气温度成线性关系,进气温度每降低1℃,则平均皮肤温度降低0.39℃,而温差上升0.41℃;平均皮肤温度关于人体散热率成线性变化,散热率每增大5W/m~2,平均皮肤温度升高0.6℃。     

注意缺陷多动障碍两种亚型脑血流动力学特征研究

探讨注意缺陷多动障碍(Attention Deficit and Hyperactive Disorder,ADHD)混合型(ADHD-C)及多动-冲动为主型(ADHD-HI)儿童在言语流畅性任务(Verbal Fluency Task,VFT)中脑血流动力学反应特征及差异.通过整合视听持续性操作测试将ADHD患儿区分亚型(33名ADHD-C型及36名ADHD-HI型),之后采用功能近红外光谱成像仪技术(functional Near-Infrared Spectroscopy,fNIRS)测量两组患儿在VFT中前额和左右颞叶血流动力学反应特征,并计算其积分值与重心值.结果发现,在注意力商数上,ADHD-C组得分均低于ADHD-HI组,差异有统计学意义(P<0.05);两组亚型患儿视觉得分低于听觉得分,差异均有统计学意义(P<0.05).在VFT测试中,ADHD-C组的左右颞叶积分值较ADHD-HI组降低,差异有统计学意义(P<0.05);两组亚型患儿左右颞叶的积分值与综合注意商、听觉注意商、视觉注意商均呈显著正相关(P<0.01).由此可见,ADHD-C与AD...     

物理学咬文嚼字之三十六 Στοιχειαιο

Euclid的《几何原本》同化学术语中的化学计量比都来自希腊语Στοιχεια■ο,反映的是古希腊原子论的精神.     

Structural,Magnetic and Magnetocaloric Properties of La-deficient La0.77-xSrxCa0.2MnO2 Perovskites

La-deficient La0.77-x Ca0.2SrxMnO3 （0 〈 x 〈 0.1） polycrystalline samples are synthesized using the sol-gel technique. The crystal structures of all the samples are single orthorhombic phase with Pbnm space group. Rietveld analysis of x-ray diffraction patterns shows that the Mn-O-Mn bond angle θUn-O-Mn increases whereas the Mn-O bond length dMn--o decreases monotonically with increasing Sr^2＋ content, which results in a rich overlap between Mn 3d and O2p orbitals and leads to a systematic increase of the Curie temperature in this compound. It is found that the magnetic entropy change has a maximum at x = 0.06 in La^3＋-deficient La0.77-xCa0.2SrxMnO3. This may result from competition between the super-exchange interactions （Mn 4＋-O2--Mn4＋） and double-exchange interactions （Mn^3＋-O^2- -Mn^4＋） originating from the appearance of superfluous Mn^4＋ ions by substitution of Sr^2＋ for La^3＋ in this series. Large magnetic entropy changes of 2.32 and 1.83Jkg^-1K^-1 in the x = 0.06 and x = 0.1 samples at their Tcs of 271 K and 303K upon a low magnetic field （10kOe） make these materials promising candidates at near room temperature.     

曲面上的动量和动能算符

对约束在曲面上粒子运动的描述可以在内部坐标即曲面局部坐标下进行，也可以在外部坐标即在笛卡尔坐标下进行.在量子力学中，动量和动能算符的表示在这两种描述中各有不同，前者的动量算符仅包含内禀几何量，后者的动量算符包含了曲面的平均曲率.考虑到算符次序问题，动能算符对动量算符的依赖关系也不同，前者的依赖关系仅发现存在一种，后者的依赖关系已经发现有两种.     

涡流检测的数值模拟与缺陷定量分析

随着涡流检测技术的不断发展，不仅要求准确检测出缺陷，且还需对缺陷进行定量、定性评价。涡流检测中阻抗信号变化是进行缺陷检测和定量分析的依据：测量或计算缺陷的阻抗信号，称为涡流检测的正向问题；从阻抗信号推断出缺陷的定量定性特征，则是逆向问题。借助于有限元模拟方法，对涡流检测时的正向问题进行了求解计算；利用傅里叶变换和神经网络方法，对涡流检测时的逆向问题进行了分析。