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991.
992.
利用密度泛函理论中的B3LYP方法, 选择LANL2DZ基组优化Tin(2~7)团簇得到各团簇的稳定结构,然后对稳定结构的束缚能及自然轨道进行分析. 研究结果表明: Tin(n=2~7)团簇都依带帽的形式在前一个团簇的结构基础上加一个原子变化而来; 通过自然轨道分析发现, 团簇原子的轨道存在sp-d杂化, 有大约一个电子从4s转移到了3d, 原子之间亦存在电子转移, 而且除Ti7外, 团簇键长由最外层4d轨道电子和3d轨道共同决定, 在Ti7中, 团簇键长由3d轨道决定. 相似文献
993.
994.
Lignans are imporant active ingredients of Schisandra sphenanthera. A micellar electrokinetic chromatography method was developed for the simultaneous determination of eight lignans--schizandrin, schisandrol B, schisantherin A, schisanhenol, anwulignan, deoxyschizandrin, schizandrin B and schizandrin C--in different parts of S. sphenanthera. The key factors for separation and determination were studied and the best analysis conditions were obtained using a background electrolyte of 10 mM phosphate-37.5 mM SDS-35% v/v acetonitrile (pH 8.0) at the separation voltage of 28 kV and detection at 214 nm, whereby the plant samples could be analyzed within 9.0 min. Analysis yielded good reproducibility (RSD between 1.19-2.28%) and good recovery (between 92.2-103.8%). The detection limits (LOD) and limit of quantification (LOQ) were within 0.4-1.2 mg/L and 1.5-4.0 mg/L. This method is promising to improve the quality control of different parts of S. sphenanthera. 相似文献
995.
集值变分不等式问题的例外簇 总被引:3,自引:0,他引:3
本文首先在Banach空间中证明了零调集值映射的一个Leray-Schauder型不动点定理,然后在Hilbert空间中定义了零调集值映射的变分不等式的例外簇,利用本文给出的不动点定理给出了无界集上的变分不等式问题存在解的一个充分条件.此条件弱于许多已知的关于变分不等式问题的解的存在性条件,并由此得到Hilbert空间中几个变分不等式约解的存在性定理. 相似文献
996.
Epicatechin ( 3 ) and five oligomers ( 2 , 4 , 5 , 10 , 11 ) together with five other type compounds were isolated and characterized from n‐BuOH and EtOAc soluble fractions of the ethanol extract of the leaves of Machilus konishii Hayata. Their structures were elucidated by means of MS and NMR spectroscopic analyses. Dehydrodiepicatechin A ( 11 ) is the first occurrence as a natural product although it has been prepared from epicatechin. The stereochemistry of 11 is elucidated for the first time on the basis of 1D NOESY and chemical model analyses. Tiliroside ( 7 ) and kaempferol 3‐O‐α‐L‐(2″,4″‐di‐E‐p‐coumaroyl)‐rhamnopyranoside ( 8 ) showed moderate inhibitory activity against α‐glucosidase. 相似文献
997.
998.
Sheng Hsiung Lin 《Applied Scientific Research》1974,30(2):113-126
The purpose of this paper is to analyze the homogeneous consecutive chemical reactions carried out in an annular reactor with non-Newtonian laminar flow. The fluids are assumed to be characterized by a Ostwald-de Waele (powerlaw) model and the reaction kinetics is considered of general order. Effects of flow pseudoplasticity, dimensionless reaction rate constants, order of reaction kinetics and ratio of inner to outer radii of reactor on the reactor performances are examined in detail.Nomenclature
c
A
concentration of reactant A, g.mole/cm3
-
c
B
concentration of reactant B, g.mole/cm3
-
c
A0
inlet concentration of reactant A, g.mole/cm3
-
C
1
dimensionless concentration of A, c
A/c
A0
-
C
2
dimensionless concentration of B, c
B/c
A0
- C
1
dimensionless bulk concentration of A
- C
2
dimensionless bulk concentration of B
-
D
A
molecular diffusivity of A, cm2/sec
-
D
B
molecular diffusivity of B, cm2/sec
-
k
A
first reaction rate constant, (g.mole/cm3)1–m
/sec
-
k
B
second reaction rate constant, (g.mole/cm3)1–n
/sec
-
K
1
dimensionless first reaction rate constant, k
A
r
0
2
c
A0
m–1
/D
A
-
K
2
dimensionless second reaction rate constant, k
B
r
0
2
c
A0
n–1
/D
B
-
K
apparent viscosity, dyne(sec)
m
/cm2
-
m
order of reaction kinetics
-
n
order of reaction kinetics
-
P
pressure, dyne/cm2
-
r
radial coordinate, cm
-
r
i
radius of inner tube, cm
-
r
max
radius at maximum velocity, cm
-
r
o
radius of outer tube, cm
-
R
dimensionless radial coordinate, r/r
o
-
s
reciprocal of rheological parameter for power-law model
-
u
local velocity, cm/sec
-
u
max
maximum velocity, cm/sec
- u
bulk velocity, cm/sec
-
U
dimensionless velocity, u/u
-
z
axial coordinate, cm
-
Z
dimensionless axial coordinate, zD
A/r
0
2
/u
-
ratio of molecular diffusivity, D
B/D
A
-
ratio of inner to outer radius of reactor, r
i/r
o
-
ratio of radius at maximum velocity to outer radius, r
max/r
o 相似文献
999.
Pool boiling of multi-walled carbon nanotube (MWCNT) nanofluid was conducted to investigate fouling of a copper surface with a diameter of 12?mm. At low heat flux the fouling curve takes the shape of saw tooth with an asymptotic value. When boiling stretches, dispersant, Gum Arabic fails, MWCNT particles deposit on the heating wall completely. Progressively increasing the heat flux, depositing accelerates, superheat and fouling resistance increase drastically. 相似文献
1000.
研究了以2-羟基-4-甲氧基苯甲醛和2-氨基-6-甲基吡啶为原料合成新型席夫碱化合物5-甲氧基-2-[(E)-(6-甲基吡啶-2-亚氨基)甲基]苯酚的方法。当2-羟基-4-甲氧基苯甲醛与2-氨基-6-甲基吡啶摩尔比为1∶1.6,反应时间为6 h,反应温度为75℃时,反应产率最高。采用元素分析、UV-Vis、IR、1H NMR、X-射线单晶衍射等方法进行结构表征。该化合物为单斜晶系,空间群P21/c,a=1.1886(3)nm,b=0.65948(16)nm,c=1.6897(4)nm,β=108.505(3)°,V=1.2560(5)nm3,Dc=1.281 g·cm-3,Z=4,F(000)=512,μ=0.087 mm-1,R1=0.0477,wR2=0.1342。通过π···π堆积和分子内氢键O2-H2···N1、C8-H8A···N2形成较稳定的晶体结构,并具有蓝色荧光。 相似文献