热环境中粘贴压电层功能梯度材料梁的自由振动

研究了上下表面粘贴压电层的功能梯度材料Euler-Bernoulli梁在升温及电场作用下的屈曲和自由振动行为.在精确考虑轴线伸长基础上,建立了压电功能梯度材料层合梁在热-电-机载荷作用下的几何非线性动力学控制方程.其中,假设功能梯度材料性质沿厚度方向按照幂函数连续变化,上下压电层为各向同性均匀材料.在小振幅和谐振动假设下,上述非线性偏微分方程组被转化为两套相互耦合的常微分方程组,即过屈曲问题的控制方程和过屈曲构形附近的线性振动控制方程.采用打靶法数值求解上述两个耦合的常微分方程边值问题,获得了在均匀电场和横向非均匀升温场作用下两端固定压电.功能梯度材料层合梁在屈曲前和过屈曲构型附近的自由振动响应.绘出了梁的过屈曲平衡路径以及前3阶固有频率随热、电载荷及材料梯度参数变化的特性曲线.结果表明,梁的前3阶频率在屈曲前随着温度升高而减小,在进入过屈曲后它们却随着温度升高而增加.通过施加电压在压电层产生拉应力可有效地提高粱的热屈曲临界载荷,从而提高其固有频率.     

高效液相色谱-电感耦合等离子体质谱联用技术在水质分析中的应用

对高效液相色谱-电感耦合等离子体质谱联用技术在水质分析中的应用作了评述,对高效液相色谱-电感耦合等离子体质谱联用技术的发展前景作了展望.引用文献48篇.     

Two new flavanone glycosides from Macrothelypteris torresiana （Gaud.） Ching

Two new flavanone glycosides 1 and 2 were isolated from the aerial parts oi Macrothelypteris torresiana(Gaud.)Ching.The structures of two products were identified as(2S)-5,7,2',5'-tetrahydroxyfiavanone-2'-O-β-D-6"-O-acetylglucopyranoside and(2S)- 5,7,2',5'-tetrahydroxyflavanone-2'-O-β-D-glucopyranoside on the basis of their chemical and spectral analysis,respectively.     

辩证的视角,管窥概念的教学

<普通高中数学课程标准>(实验)曾指出:理解基本的数学概念、数学结论的本质,了解概念、结论等产生的背景、应用.数学概念是反映一类对象的空间形式和数量关系方面的本质属性的思维形式,是数学的逻辑推理起点,是构成数学知识的最基本的元素,是巩固知识与形成能力的一个基石,在数学教学与研究中处于重要的地位.清晰的数学概念是正确思维的前提,正确理解数学概念,是学习数学的核心,是培养学生逻辑思维能力的必要条件,因为一切数学思维都是以数学概念为基础,凭借数学概念来进行判断、推理、运算的,所以概念教学是数学教学的基础要素与基本环节,不是"食之无味,弃之可惜"的鸡肋.但在我们新课程教学中应该如何促进学生对概念的理解与深化呢?如何使枯燥无味的概念课"活"起来呢?这些是我们数学教学必须要考虑的问题.本文试图从辨证的视角,以案例的形式来谈谈在新课程概念教学中的一些尝试,也"别有一番滋味在心头".……     

斜率乘积为定值e2-1的椭圆的性质赏析

在文[1]中作者对椭圆中看似毫无相干的问题围绕着定值e2-1进行展开探讨,得到一系列和谐统一的几何性质,但总觉得意犹未尽,因此本文试图从另一个角度来剖析与斜率乘积为定值e2-1相关的椭圆的性质,也得到许多有趣的性质,权当抛砖引玉,共同欣赏.……     

从一道高考试题谈伴随圆锥曲线的性质

1 问题的呈现 例题 (2010年重庆市高考数学文科压轴试题)已知以原点O为中心,F(5,0)为右焦点的双曲线C的离心率e=√5/2.     

The roles of cysteines in the heme domain of human soluble guanylate cyclase

Soluble guanylate cyclase(sGC) is a critical heme-containing enzyme involved in NO signaling.The dimerization of sGC subunits is necessary for its bioactivity and its mechanism is a striking and an indistinct issue.The roles of heme domain cysteines of the sGC on the dimerization and heme binding were investigated herein.The site-directed mutations of three conserved cysteines(C78A,C122A and C174S) were studied systematically and the three mutants were characterized by gel filtration analysis,UV-vis spectroscopy and heme transfer examination.Cys78 was involved in heme binding but not referred to the dimerization,while Cys174 was demonstrated to be involved in the homodimerization.These results provide new insights into the cysteine-related dimerization regulation of sGC.     

寻找探究的链接点激活有效课堂教学

有人讲"最好的习题集是错题集,最好的试题是高考试题".此话不假,每一道高考题都是经过命题者的"千锤百炼"而精心出炉的,所以每年高考之后,总会留下许多数学经典之作,供我们仔细地去欣赏与探讨.     

Spectral and Mechanistic Studies of the Reactions of Substituted 1,5-Benzothiazepine with Dichloroacetyl Chloride and Triethylamine

A lot of attentions have been paid to the synthesis of benzothiazepines and derivatives1,2 due to their significant physiological activities. It has been reported that b-lactam, a major part of the antibiotic skeleton, can be introduced to a molecule by reaction of an imine moiety with ketene3,4. We introduced a b-lactam skeleton to benzothiazepine and hoped the new compounds may possess certain biological activities. SHNH3ClCHCHCOC2H5OHSNClCla: ortho-Clb: para-Cl+PyridineScheme …