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821.
H. T. Abebe F. E. S. Tan G. J. P. Van Breukelen M. P. F. Berger 《Computational Statistics》2014,29(6):1667-1690
In medicine and health sciences mixed effects models are often used to study time-structured data. Optimal designs for such studies have been shown useful to improve the precision of the estimators of the parameters. However, optimal designs for such studies are often derived under the assumption of a zero autocorrelation between the errors, especially for binary data. Ignoring or misspecifying the autocorrelation in the design stage can result in loss of efficiency. This paper addresses robustness of Bayesian D-optimal designs for the logistic mixed effects model for longitudinal data with a linear or quadratic time effect against incorrect specification of the autocorrelation. To find the Bayesian D-optimal allocations of time points for different values of the autocorrelation, under different priors for the fixed effects and different covariance structures of the random effects, a scalar function of the approximate variance–covariance matrix of the fixed effects is optimized. Two approximations are compared; one based on a first order penalized quasi likelihood (PQL1) and one based on an extended version of the generalized estimating equations (GEE). The results show that Bayesian D-optimal allocations of time points are robust against misspecification of the autocorrelation and are approximately equally spaced. Moreover, PQL1 and extended GEE give essentially the same Bayesian D-optimal allocation of time points for a given subject-to-measurement cost ratio. Furthermore, Bayesian optimal designs are hardly affected either by the choice of a covariance structure or by the choice of a prior distribution. 相似文献
822.
结合偏最小二乘法和支持向量机的优缺点,提出基于偏最小二乘支持向量机的天然气消费量预测模型。首先,利用偏最小二乘法确定影响天然气消费量的新综合变量,建立以新综合变量为输入,天然气消费量为输出的支持向量机模型,对天然气消费量进行了预测;然后,与多元回归、偏最小二乘回归、普通支持向量机做误差检验比较,验证该方法的可行性与正确性。结果表明,此天然气消费量预测模型具有较高的精确度和应用价值。 相似文献
823.
824.
Yu Xie Dan Liu Ming Gao Ru Tan Yan Wang Dongqi Yu 《Frontiers of Chemistry in China》2011,6(4):355-357
Well-aligned ZnO nanorod arrays were prepared on FTO substrate by hydrothermal method at low temperature for 5 h. The effect
of ammonia on the length of ZnO nanorod was studied in detail. The resulting materials were extensively characterized by scanning
electron microscopy (SEM), X-ray diffraction (XRD) and UV-visible absorption spectra (scatter mode). With the increase of
ammonia, the length of ZnO nanorod increases. 相似文献
825.
Disulfides have been synthesized by oxidation of thiols using air as oxidant catalyzed by Co-Salophen with high yields,mild and neutral conditions,and easy procedures of the catalyst.The products were confirmed by ~1H NMR and IR. 相似文献
826.
Ren-Bing Tan Wen Xu Yu Zhou Xiao-Yu Zhang Hua Qin 《Physica B: Condensed Matter》2012,407(21):4277-4280
We present a theoretical study of electron transport properties of two-dimensional electron gas in AlGaN/GaN heterostructures. By assuming a drifted Fermi–Dirac distribution and taking into account all major scattering mechanisms, including polar optical and acoustic phonons, background impurities, dislocation and interface roughness, the momentum- and energy-balance equations derived from Boltzmann equation are solved self-consistently. The dependence of the electron drift velocity and electron temperature as a function of the applied electric field are obtained and discussed. 相似文献
827.
This letter proposes a 4-kb/s multimode code-excited linear prediction (CELP) coder with pitch synchronous extended excitation. Three modes are used for the short-term excitation, namely algebraic, extended, or stochastic excitations, together with an adaptive codebook for the long-term excitation. Comparisons with the FS-1016 and ITU-T G.723.1 coders show a performance level between these standards 相似文献
828.
Wenmeng Duan Xianwu Jing Jiang Tan Minmin Tao Lu Wang 《Journal of Dispersion Science and Technology》2018,39(9):1309-1315
A series of amphiphilic triblock polymers based on poly(ethylene glycol) (PEG) and two symmetrical poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) blocks was synthesized via the Atom Transfer Radical Polymerization (ATRP) method. Conductivity, pH, and viscosity tests demonstrated the CO2-switchability jointly; Cryogenic transmission electron microscopy (Cryo-TEM), Dynamic light scattering (DLS) revealed the self-assembly morphology transformation from unilamellar vesicle to network structure when bubbling CO2. These changes were all attributed to the protonation of tertiary amine groups in PDMAEMA blocks and the mechanism was proved by ?H NMR. The vesicles have a relatively low release rate of drug; once stimulated by CO2, the release rate will be accelerated. The polymeric vesicle has the possibility to find potential applications in drug delivery and release domains. 相似文献
829.