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181.
Arshinov Y Bobrovnikov S Serikov I Ansmann A Wandinger U Althausen D Mattis I Müller D 《Applied optics》2005,44(17):3593-3603
We propose to use a Fabry-Perot interferometer (FPI) in a pure rotational Raman lidar to isolate return signals that are due to pure rotational Raman scattering from atmospheric nitrogen against the sky background. The main idea of this instrumental approach is that a FPI is applied as a frequency comb filter with the transmission peaks accurately matched to a comb of practically equidistant lines of a pure rotational Raman spectrum (PRRS) of nitrogen molecules. Thus a matched FPI transmission comb cuts out the spectrally continuous sky background light from the spectral gaps between the PRRS lines of nitrogen molecules while it is transparent to light within narrow spectral intervals about these lines. As the width of the spectral gaps between the lines of the PRRS of nitrogen molecules is -114 times the width of an individual spectral line, cutting out of the sky background from these gaps drastically improves the signal-to-background ratio of the pure rotational Raman lidar returns. This application of the FPI enables one to achieve daytime temperature profiling in the atmosphere with a pure rotational Raman lidar in the visible and near-UV spectral regions. We present an analysis of application of the FPI to filtering out the pure rotational Raman lidar returns against the solar background. To demonstrate the feasibility of the approach proposed, we present temperature profiles acquired during a whole-day measurement session in which a Raman lidar equipped with a FPI was used. For comparison, temperature profiles acquired with Vaisala radiosondes launched from the measurement site are also presented. 相似文献
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184.
Copolymers of acrylonitrile and styrene with various compositions and molecular weights have been pyrolysed at a temperature of 500°C. The degradation products have been separated by means of gaschromatography and 16 compounds were identified. The most important products are cyanic acid, acetonitrile, acrylonitrile, propionitrile, toluene, ethylbenzene and styrene. The formation of these products has been investigated quantitatively as a function of the composition of the copolymers. Plotting the quantitatively determined amount of the cyanic acid as a function of the copolymer composition a linear slope resulted. Thus a method was developed to analyse copolymers of acrylonitrile and styrene. The formed amounts of acetonitrile, acrylonitrile and propionitrile during pyrolysis are independent on the molecular weights of the copolymers. 相似文献
185.
Dietrich Munz 《Engineering Fracture Mechanics》1973,5(2):353-364
The workhardening behavior and slip band formation during fatigue were investigated up to the crack initiation phase on three titanium materials (IMI 115, Contimet 30, Contimet 35) having different impurity contents.The workhardening behavior was studied using fatigue tests with constant strain amplitude. At the beginning of the cyclic loading the stress amplitude decreased afterwards it increased again. The change in stress amplitude could be explained by the dependence of the thermal and the athemtal flow stress components on the dislocation density. Similar as in bcc metals the worksoftening is due to an increase in the mobile dislocation density.At low frequencies the plastic strains resulted in the formation of slip bands. With increasing frequency the number and the intensity of the slip bands decreased. No slip bands were observed above 50 Hz.The crack initiated at low frequencies at grain boundaries, in slip bands or transcrystalline without any visible connection with slip bands. At higher frequencies only “slipless” cracks occurred. 相似文献
186.
For determination of random unsaturation within the macromolecules of poly-vinyl chloride the oxidation of double bonds by potassium permanganate is used. After the cleavage of the polymer with potassium permanganate a remarkable decrease in molecular weight is observed. The oxidation reaction was investigated using N.N-dimethylacetamide as a solvent. From the temperature dependence of the reaction rate an activation energy of 23,9 keal/mole is calculated. A comparison of the molecular weights before and after oxidation gives the average content of double bonds within different samples, which was found for the products under investigation from 0.2 to 1.2 double bonds per 1000 carbon atoms by this method. 相似文献
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188.
The following reactions between carbonic acid salts of bivalent metals as heat-stabilizers and PVC take place during heat-treatment:
- Chemical HCI-bonding by stabilizers (HCI-acceptance);
- esterification of isolated allylic chlorine atoms in the polymer chains, starting from a complex formed by stabilizer molecules and labile chlorine atoms:
- the stabilizer inhibits formation of longer polyene sequences by exchange reactions of the allylic chlorine atoms with the ester groups of the stabilizer.
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190.
It is reported on investigations concerning the thermal degradation of heat-stabilized PVC. As stabilizers several mixtures of Cadmium- and Bariumoctoate were applied, as well as the single components of each mixture. There is a pronounced shift towards a better stabilizing effect in the mixture compared with the single compounds. This so-called ‘synergism’ can also be seen in the retarded discolouration of the polymer in presence of the mixture. As a measure for the discolouration of the heat treated polymer conversion-distribution-curves of the polyene-sequences can be used. The curves demonstrate the enhancement of the stabilizing effect of the mixture in contrast to the single metal soaps. It is suggested that first the cadmium soap reacts with the PVC and that the formed metal chloride then reacts with the barium soap regenerating the cadmium soap. 相似文献