商品毛利对营业杠杆作用的分析

讨论了营业杠杆受到销售量和单位毛利的影响,以及营业杠杆系数在不同区域上的取值.通过营业杠杆系数的综合分析得到销售量和单位毛利对企业收益作用的规律,发现增加单位毛利是提高企业经济效益的一种有效途径.     

具有侧向脉冲推力的旋转导弹建模与控制研究

针对具有气动舵和侧向脉冲推力复合控制的自旋导弹,在准弹体坐标系中建立完整的动力学模型,由于侧向脉冲推力的离散事件特性,提出运用混杂系统理论的方法设计其复合控制自动驾驶仪。根据系统的特性将自动驾驶仪划分成两种不同的工作模式,针对不同的工作模式分别设计不同的控制方法,通过两种模式之间的切换实现导弹的快速响应和能源的合理分配。最后进行仿真检验该自动驾驶仪的有效性,并将仿真结果与气动舵单独控制时的结果作了对比,表明通过复合控制显著改善了导弹的动态响应特性     

反作用射流控制导弹的自动驾驶仪H∞设计方法

空气舵与反作用射流复合控制的导弹，由于侧向喷流与外流场的相互作用，其空气动力学特性比传统空气舵控制要复杂的多，一般难以建立较为准确的数学模型，因此要求其自动驾驶仪具有更好的鲁棒性。用H∞控制理论，对具有这种复合控制的自动驾驶仪进行了设计，通过权函数的合理选择，可以控制空气舵和反作用射流发动机的混合工作方式，同时具有满意的鲁棒稳定性能。仿真结果表明，H∞控制理论用于这类导弹的自动驾驶仪设计是可行的。     

磁悬浮反作用飞轮系统模态分析及试验研究

介绍了一种角动量为50Nms工作转速在±5000rpm的磁悬浮反作用飞轮系统,利用有限元分析软件ANSYS对其定、转子及系统进行了模态分析,利用COMBINE14单元模拟磁轴承使模型更加接近实际,最后通过模态测试试验测出了转子的一阶弹性固有模态,与理论计算结果相近,误差仅为0.66%,验证了理论模型的正确性。模态分析及测试的结果对磁悬浮反作用飞轮系统的振动特性研究,控制方案设计及总体优化设计有着重要意义。     

处理黑洞反作用的一条新途径

本文介绍一种在考虑反作用的情况下确定黑洞温度的新方法。在Vaidya情况得到与前人一致的结果。 在考虑反作用的情况下,蒸发黑洞的辐射温度通常用二维模型来进计算。其理论基     

Density functional theory study on the insertion reaction mechanism of dibromocarbene with formaldehyde

The insertion reaction mechanism of CBr2 with CH3CH2O has been studied by using the B3LYP/6-311G(d) and CCSD(T)/6-311G(d) at single point. The geometries of reactions,transition state and products were completely optimized. All the transition state is verified by the vibrational analysis and the internal re-action coordinate (IRC) calculations. The results show that reaction (1) is the dominant reaction path,which proceeds via two steps: i) two reactants form an intermediate (IM1),which is an exothermal re-action of 8.62 kJ·mol?1 without energy barrier; ii) P1 is obtained via the TS1 and the H-shift,in which the energy barrier is 44.53 kJ·mol?1. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of this reaction in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature ranges from 200 to 1900 K at 1.0 atm,in which the reaction has a bigger spontaneity capability,equi-librium constant (K) and higher rate constant (k).     

火箭是怎样升上天的

从道理上来说，很简单。火箭是靠燃料燃烧时，向后面喷射出的高速气体的反作用而升上天空的。     

Total Synthesis of Securinega Alkaloids

Naturally occurring Securinega alkaloids （1-4） （Fig. 1）, with their wide range of structural and stereochemical features, continue to provide challenging synthetic targets, since these alkaloids exhibit attractive biological activities. Securinine （1）, isolated from Securinega suffruticosa , was structurally determined to contain an indolizidine skeleton with an azabicyclo octane system together with an α,β-unsaturated γ-1actone ring.This alkaloid has been clinically used in Russia as a CNS stimulating drug, and has been shown to act as a stereospecific antagonist at the GABA binding site of the GABAA-receptor complex.     

语篇构式视角下的成语广告探究

自2005年Ostman提出语篇构式以来,语篇构式理论并未得到国内外学者的关注.但是,语篇构式以语篇为语言研究单位为很多特殊的语篇提供了较强的解释力.文章借用语篇构式理论中语篇压制框架图,阐释成语广告所内嵌的隐性语篇与其语篇压制是促成消费者接受该类成语的主要原因；同时,进一步分析得到成语广告并不是被动地受到语篇压制,其在压制过程中也对语篇意义的表达起着一定的反作用,两者是相辅相成的关系,并试图对已有的语篇构式框架图做出细小修改.     

Modern thermodynamics -- New concepts based on the second law of thermodynamics

Thermodynamics is a core part of science. Nearly all scientists should have a basic knowledge of thermodynamics. Thermodynamics is a science of development, and is a viewpoint of scientific development in natural sciences. Achievement of thermodynamics has influence not only on natural sciences, but also on social sciences and philosophy. Fundamental concepts and definitions are very important for any discipline of science, so what is classical thermodynamics and what is modern thermodynamics have become the key points of puzzledom in thermodynamics. In this paper, after clarification of fundamental concept in thermodynamics, a complete basic modern classification of thermodynamics is naturally obtained. It is suggested that extended Carnot theorem and dissipation decrease theorem, together with the laws of thermodynamics, are the most fundamental theorems in thermodynamics discipline. Nondissipative thermodynamics is a new field besides equilibrium thermodynamics belonging to the equal part of the second law of thermodynamics.