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.     

Resonance reaction rate of 21Na(p, γ)22Mg

By using the new Coulomb screening model and most recent experimental results, this paper calculates the resonance reaction rates of ^21Na（p,γ）^22Mg. The derived result shows that the effect of electron screening on resonant reaction is prominent in astrophysical interesting temperature range. In conjunction with the experimental results, the recommended rates of^21Na（p,γ）^22 Mg would increase at least 10%, which undoubtedly affect the nucleosynthesis of some heavier nuclei in a variety of astrophysical sites.[第一段]     

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.     

Hexagonal Standing-Wave Patterns in Periodically Forced Reaction-Diffusion Systems

The periodically forced spatially extended Brusselator is investigated in the oscillating regime. The temporal response and pattern formation within the 2：1 frequency-locking band where the system oscillates at one half of the forcing frequency are examined. An hexagonal standing-wave pattern and other resonant patterns are observed. The detailed phase diagram of resonance structure in the forcing frequency and forcing amplitude parameter space is calculated. The transitions between the resonant standing-wave patterns are of hysteresis when control parameters are varied, and the presence of multiplicity is demonstrated. Analysis in the framework of amplitude equation reveals that the spatial patterns of the standing waves come out as a result of Turing bifurcation in the amplitude equation.     

A Class of Nonlinear Singularly Perturbed Problems for Reaction Diffusion Equations with Boundary Perturbation

A class of nonlinear singularly perturbed problems for reaction diffusion equations with boundary perturbation are considered. Under suitable conditions, the asymptotic behavior of solution for the initial boundary value problems is studied using the theory of differential inequalities.     

Resonant Reaction in Rb-Cs Vapour Mixture Rb（5P1/2） ＋ Cs（6P3/2） → Cs（8S1/2）＋Rb（5S1/2）

We experimentally study energy-pooling collision in the Rb-Cs vapour mixture at low densities in a cell. Atoms are excited to Rb（5P1/2） and Cs（6P3/2） states using two single-mode diode lasers. To isolate the heteronuclear contribution in the fluorescence spectrum, a double-modulation technique is adopted. The excited-atom density and spatial distribution are mapped by monitoring the absorption of a counterpropagating single-mode diode laser beam, tuned to Rb（5P1/2 → 7S1/2） and Cs（6Pa/2 → 8S1/2） transitions, respectively, which could be translated parallel to the pump beams. The excited atom densities are combined with the measured fluorescence ratios to determine cross section for the energy-pooling process [i.e. Rb（5P1/2） ＋Cs （6P3/2） → Cs（8S1/2）＋Rb （5S1/2）]. The cross section is 3.79 × 10^-14 cm^2 ± 45%.     

Cross-section measurement for Ni（n,x）^58（m＋g）Co, Ni（n, x）^60mCo, Ni（n,x）^61Co and Ni（n,x）^62mCo reactions induced by neutrons around 14 MeV

The cross sections of Ni(n,x)~(58(m g))Co,Ni(n,x)~(60m)Co,Ni(n,x)~(61)Co and Ni(n,x)~(62m)Co reactions induced by neutrons around 14 MeV were measured in this work and calculated by a previously developed formula in this work.The neutron flux was determined using the monitor reaction ~(27)Al(n,α)~(24)Na and the neutron energies were measured with the method of cross-section ratios for ~(90)Zr(n,2n)~(89)Zr to ~(93)Nb(n,2n)~(92m)Nb reactions.     

FINITE TRAVELING WAVES FOR A REACTION-DIFFUSION SYSTEM WITH N（≥3） COMPONENTS

ＦＩＮＩＴＥＴＲＡＶＥＬＩＮＧＷＡＶＥＳＦＯＲＡＲＥＡＣＴＩＯＮ┐ＤＩＦＦＵＳＩＯＮＳＹＳＴＥＭＷＩＴＨＮ（３）ＣＯＭＰＯＮＥＮＴＳＷＡＮＧＳＨＵ,ＷＥＮＳＨＩＨＬＩＡＮＧＡＮＤＹＥＱＩＸＩＡＯＡｂｓｔｒａｃｔ．Ｉｎｔｈｉｓｐａｐｅｒ,ｔｈｅｅｘ...