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41.
A water soluble crude polysaccharide has been isolated from the fruiting body of cultivated Cordyceps militarvs(L.)Link.The GC analysis indicated that it contained the monosaccharides of Gal,Man,Glc and GlcA.Their molar ratio is 1.00:1.58:7.89:0.19.The crude polysaccharide was fractionated with ethanol to get three fractions,which were CM-Ⅰand CM-Ⅲ,CM-Ⅱ was further purified to get one homogeneous fraction named CMB.The molecular weight was estimated to be 6000by means of gel filtration.CMB is a greyish white powder.The GC analysis indicated that it was composed of Gal.Man,Glc and the molar ratio is 1.00:1.38:5.10.Partial hydrolysis with an acid.periodate oxidation.Smith degradation.IR,GC and methylation analyses,GC/MS analyses were used for the structure analyses of CMB.Man,(1→6)-linked-Glc,(1→4)-linked-Glc and (1→4)-linked-Gal.Some of (1→4) -linked-Glc and all(1→4)-linked-Gal residues are substituted at 3-O and 6-O respectively,(1→4)-linked-Glc and minor(1→6)-linked-Gle.The nonreduced end is composed of Gal and Glc.The main glycosidic link of CMB is α configuration. 相似文献
42.
A convenient and large-scale preparation of retinoic acid 1 from β-ionone in five steps with 38% overall yield is described.The key steps are the epoxidization of 2 with a new methylated agent and the condensation 4 with tetraethyl methylenediphophonate in one-pot procedure to prepare 6. 相似文献
43.
The current-voltage characteristics of Ti/n-GaAs Schottky diodes measured over a temperature range of 78-299K have been interpreted on the basis of thermionic emission across an inhomogeneous Schottky contact.The experiment shows that the apparent barrier height (φap) increases from 0.437eV at 78K to 0.698eV at room temperature.the plot of φap versus 1/T does not exhibit a simple linear relationship over the whole temperature range,indicating that the barrier height distribution is more complicated than the frequently observed single Gaussian distribution.A new multi-Gaussian distribution model is developed.Our experimental results can be explained by a double Gaussian distribution of the barrier heights.The weight,the mean barrier height,and the standard deviation of the two Gaussian functions are 0.00001 and 0.99999,0.721 and 0.696,0.069 and 0.012eV,respectively. 相似文献
44.
Optical Properties of ZnFe2O4—SiO2 Granular Films Prepared by Radio—Frequency Magnetron Sputtering
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We report on the optical properties of ZnFe2O4-SiO2 granular films prepared on quartz substrates by the radio-frequency magnetron sputtering method.Post-annealing was performed at different temperatures under flow oxygen atmosphere.The morphology and Structures of ZnFe2O4 nanoparticles were characterized by x-ray different line types in the optical absorption curves of ZnFe2O4-SiO2 granular films.The critical transition of line types occurs when ZnFe2O4 changes from amorphous to crystalline,and the transition temperature increases with the increasing content of ZnFe2O4.There is an obvious blueshift of the optical absorption edge of the granular films with the decreasing annealing temperature. 相似文献
45.
Sound Field Calculations of Elliptical Pistons by the Superposition of Two—Dimensional Gaussian Beams
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We present an alternative approach to calculate the sound field of ultrasonic transducers.The distribution function of sources is expanded into the superposition of a series of two-dimensional Gaussian functions.The corresponding radiated sound field is expressed as the superposition of these two-dimensional Gaussian beams and is then reduced to the computation of these simple functions.This treatment does not require the condition that the shape of the source is of circular axial symmetry.A numerical example is presented for the uniform elliptical piston transducer and this is in good agreement with the results given by complicated computation. 相似文献
46.
We have experimentally studied the characteristics of fifth-order harmonic radiation produced by two coherent femtosecond laser pulses with a changeable relative phase.The intensities of harmonic generation are found to increase with the coherent degree.In one optical Period,the temporal variation of harmonics exhibits an asymmetric characteristic,which is interpreted in terms of ionization theory and the deformation of the wave packets of fundamental field contribution to harmonic generation. 相似文献
47.
We show theoretically that it is possible to modify absorption of a bulk absorbing material by inserting another non-absorbing dielectric slab periodically to form one-dimensional photonic crystals.It is found that,for frequencies within photonic bandgaps,absorption is always suppressed.For frequencies located at photonic bands,absorption can be suppressed or enhanced,which depends on the relative values of the real refractive index of the absorbing and non-absorbing dielectric layers. 相似文献
48.
The experimental conditions for photoactivated intermittent fluorescence from nanoscale silver oxide were studied with fluorescence microscopy.Strong fluorescence was observed from the Ag2O particles with size of 10-20nm excited with both blue and green light .We observed the saturation of Photoexcitation with blue light and explained the experimental results using the model of agglomeration of silver atoms to form small clusters and the fluorescence of Ag2 and Ag3 clusters. 相似文献
49.
一类广义维里拉普拉斯,把在白噪声分析构架中通常定义的维里拉普拉斯作为特殊情形而包含。 相似文献
50.
The reactivity ratios of vinyl acetate(VAc) and divinyl benzene (DVB) were calculated from the Q and e values.The possibility of the copolymerization of these two monomers was predicted and the copolymerization was carried out by suspension polymerization technique in the presence of pore producing agent (toluene and gasoine).The relative ratio of acetoxy group and benzene ring in the copolymer were monitored by IR measurement during the polymerization.The variation of pore properties,such as spectific surface area,porosity and average pore diameter,with polymerization time were determined.The copolymers at various polymerization time were alcoholyzed and thus the variation of the hydroxyl group content with polymerization time was studied. 相似文献