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对具有扩散项的时滞Mcholson方程的行波解进行了研究.特别是考虑到生物个体在空间位置上的迁移,研究了具有非局部反应的时滞扩散模型.对于弱生成时滞核,运用几何奇异摄动理论,在时滞充分小的情况下,证明了行波解的存在性. 相似文献
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应用可见-近红外光谱技术进行定量分析时,变量选择起着十分重要的作用。不同土壤样品之间的预测机制可能存在很大差异,当待测样品出现新的特征信息时,基于建模集选择的特征变量不一定能够很好地代表待测样品的有效信息,继续采用原有特征变量建模就易导致预测误差增大。该研究采用递归变量选择方法在预测过程中递归更新土壤全氮与有机质的特征变量,以保持预测模型的鲁棒性;比较了偏最小二乘法(PLS),递归偏最小二乘法(RPLS)和不同递归变量选择方法,如: 变量投影重要性与RPLS相结合(VIP-RPLS), VIP-RPLS, 无信息变量消除法与PLS相结合(UVE-PLS)对于土壤全氮与有机质含量的预测效果。所用195份土壤样品来自浙江省文成县8个乡镇的农田。土壤样品随机分成两部分,一部分作为建模集包含120份样品,另一部分作为预测集包含75份样品。结果表明: VIP-RPLS建立的模型对于预测土壤全氮与有机质含量取得了最优的结果,获得的决定系数(R2)分别为0.85与0.86,获得的预测相对分析误差(RPD)分别为2.6%与2.7%。说明VIP-RPLS通过不断更新模型的特征变量,能够捕获新加入到建模集样品的有效信息。相比于本研究中的其他方法,VIP-RPLS对于土壤全氮与有机质含量具有更高的预测精度。 相似文献
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Studies on the photofragmentation of n-C_3H_7I and i-C_3H_7I have been carried out by a photofragment spectrometer with rotatable pulsed molecular beam crossed with KrF excimer laser beam. TOF spectra of the iodine atom fragments (Fig.1, 2) which show the separation of the primary photodissociation channels n-C_3H_7I→n-C_3H_7+I~*(~2P_(1/2)) n-C_3H_7+I(~2p_(3/2)) i-C_3H_7I→i-C_3H_7+I~*(~2P_(1/2)) i-C_3H_7+I(~2P_(3/2)) are obtatned at 12 different angles. The distribution of total translational energy E_(CM) of recoiling photofragments are then determined. The ratios I~*/I of the photodissociation channels of n-C_3H_7I and i-C_3H_7I are measured to be 1.61 and 0.96 respectively (Table 1). The ratios I~*/I obtained by photofragment translational energy measurement in this Lab~[3]. are good in agreement with most of results abtained by IR emission~[5] and LIF~[4] measurement except the data of i-C_3H_7I, which is much different from I~*/I=0.35 reported by Bershon~[4] using LIF method.The extent of internal alkyl fragment excitation E_(int)~R is also determined (Table 2) by energy balance. The fraction of the available energy (E_(av1)=E_(CM)+E_(int)~R) which goes into internal exciatation of the alkyl fragment increases from 12.5% for I~* channe of CH_3I to 64% for both channels of i-C_3H_7I. The results are consistent with direct impulsive dynamic model of unimolecular decomposition based on “soft” alkyl radicals.The facts that the ratio I~*/I decreases with increasing carbon atoms and that the difference of the internal excitation of alkyl radicals between the I~* (~2P_(1/2)) and I (~2P_(3/2)) channelsincreases with increasing carbon atoms should be related and important for better understanding the origin of the I(~2P_(3/2)) channel caused by the potential energy surface crossing~[3]. The results of the internal excitation of the alkyl radicals in the photodissociation are also valuable for prediction of secondary products during the UV photolysis of those alkyl iodides in the gas cell. 相似文献
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In present study, the effect of the solvent annealing temperature on the crystal modifications and the phase transition behavior of the subsequently dried poly(3-octylthiophene) (P3OT) film has been investigated by the combination of DSC, WAXD and FTIR techniques. When chloroform is employed as the solvent, it is unexpectedly found that form I and form II crystal modifications of P3OT could be respectively obtained by room temperature and low temperature annealing. Comparing to the mostly used solvent reported for preparing form II, i.e. carbon disulfide (CS2) which is toxic and corrosive, chloroform is less toxic and corrosive and more suitable for solution processing of P3OT. Therefore, this finding provides an alternative way to obtain form II. By temperature dependent IR spectroscopy, the structural evolution of P3OT during the form II to form I phase transition process has also been studied in detail. 相似文献
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拉曼光谱作为一种强大的工具,被广泛应用于聚合物结构的表征.随着共振拉曼光谱、扫描角度拉曼光谱、高分辨率拉曼成像、极化拉曼光谱、表面增强拉曼散射等拉曼技术的迅速发展,拉曼光谱的应用范围不断扩大.本文首先介绍了拉曼光谱设备的基本原理和组成,总结了拉曼技术的实验技巧和数据处理中需要注意的问题,讨论了红外光谱和拉曼光谱的区别,在此基础上,综述了近十年来拉曼技术在聚合物结构表征领域的最新应用和研究进展.其应用包括以下六个方面:高分子链的构象、聚合物的聚集状态、聚合物结晶度的计算、高分子链的取向、外场作用下的结构转化、高分子共混物化学或物理成分的识别.最后,对拉曼光谱在聚合物研究中的发展进行了展望.希望本文能够对试图从拉曼光谱中获取聚合物结构信息的学者有所帮助. 相似文献