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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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Wilson等人曾研究过碘代烷在266nm的激光光解RI→R+I*(~2P_(1/2))(1)RI→R+I(~2P_(3/2))(2)由于他们所用的光解产物谱仪不能改变产物的检测方向,因而对C_2H_5I,n-C_3H_7I和i-C_3H_7I的光解通道(1)和(2)在飞行时间(TOF)谱上的分离没有成功。我们用束源可转动的分子束激光裂解产物谱仪(飞行距离531mm)研究了CH_3I和C_2H_5I在248nm的激光裂解后,又分别对n-C_3H_7I和i-C_3H_7I进行研究,并实现了I*(~2P_(1/2))和I(~2P_(3/2))光解通道在TOF谱上的分离,测得光解通道比见表1。 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