A label-free and low-cost mapping method based on SERS imaging was reported for illustrating the distribution of phospho- lipids with similar structures in binary lipid membranes on Ag nanoparticles （Ag NPs） films. ...A label-free and low-cost mapping method based on SERS imaging was reported for illustrating the distribution of phospho- lipids with similar structures in binary lipid membranes on Ag nanoparticles （Ag NPs） films. The Ag NPs films exhibited strong SERS activity and good reproducibility which were investigated with p-aminothiopbenol （p-ATP） as probe molecules. Atomic force microscope （AFM） measurement proved that compact lipid membranes formed on the Ag NPs films. Basing on the Ag NPs films, the SERS spectra of phospholipids in the mixed lipid membranes were achieved and the inherent vibration of 1,2-dimyristoyl-sn-lycero-3-phosphoglycerol, sodium salt （DMPG）, 1482 cm-1, was used to distinguish between DMPG and dimyristoylphosphatidylcholine （DMPC）. The proportions of phospholipids in the mixed lipid membranes were represented by the intensity ratio of peaks at 1482 cm-1 and 1650 cm1 （R1482/1650） simultaneously： increasing R1482/1650 indicated higher propor- tion of DMPG and lower proportion of DMPC. SERS imaging of the lipid membranes was constructed as a combination of spacial information and the semiquantitative detection of phospholipids according to R1482/1650, which showed that the charged phospholipids, DMPG, aggregated in the hybrid lipid membranes. The presented mapping strategy based on SERS imaging carried out on Ag NPs films supplied a facile, label-free and inexpensive way for potential applications in the research on the structure of the lipid membrane, such as lipid domains and rafts.展开更多
The estimation of high dimensional covariance matrices is an interesting and important research topic for many empirical time series problems such as asset allocation. To solve this dimension dilemma, a factor structu...The estimation of high dimensional covariance matrices is an interesting and important research topic for many empirical time series problems such as asset allocation. To solve this dimension dilemma, a factor structure has often been taken into account. This paper proposes a dynamic factor structure whose factor loadings are generated in reproducing kernel Hilbert space(RKHS), to capture the dynamic feature of the covariance matrix. A simulation study is carried out to demonstrate its performance. Four different conditional variance models are considered for checking the robustness of our method and solving the conditional heteroscedasticity in the empirical study. By exploring the performance among eight introduced model candidates and the market baseline, the empirical study from 2001 to 2017 shows that portfolio allocation based on this dynamic factor structure can significantly reduce the variance, i.e., the risk, of portfolio and thus outperform the market baseline and the ones based on the traditional factor model.展开更多
基金supported by the National Natural Science Foundation of China (20735003 & 21075120)the National Basic Research Program of China (2009CB930100 & 2010CB933600)
文摘A label-free and low-cost mapping method based on SERS imaging was reported for illustrating the distribution of phospho- lipids with similar structures in binary lipid membranes on Ag nanoparticles （Ag NPs） films. The Ag NPs films exhibited strong SERS activity and good reproducibility which were investigated with p-aminothiopbenol （p-ATP） as probe molecules. Atomic force microscope （AFM） measurement proved that compact lipid membranes formed on the Ag NPs films. Basing on the Ag NPs films, the SERS spectra of phospholipids in the mixed lipid membranes were achieved and the inherent vibration of 1,2-dimyristoyl-sn-lycero-3-phosphoglycerol, sodium salt （DMPG）, 1482 cm-1, was used to distinguish between DMPG and dimyristoylphosphatidylcholine （DMPC）. The proportions of phospholipids in the mixed lipid membranes were represented by the intensity ratio of peaks at 1482 cm-1 and 1650 cm1 （R1482/1650） simultaneously： increasing R1482/1650 indicated higher propor- tion of DMPG and lower proportion of DMPC. SERS imaging of the lipid membranes was constructed as a combination of spacial information and the semiquantitative detection of phospholipids according to R1482/1650, which showed that the charged phospholipids, DMPG, aggregated in the hybrid lipid membranes. The presented mapping strategy based on SERS imaging carried out on Ag NPs films supplied a facile, label-free and inexpensive way for potential applications in the research on the structure of the lipid membrane, such as lipid domains and rafts.
基金supported by National Natural Science Foundation of China under Grant No.11771447。
文摘The estimation of high dimensional covariance matrices is an interesting and important research topic for many empirical time series problems such as asset allocation. To solve this dimension dilemma, a factor structure has often been taken into account. This paper proposes a dynamic factor structure whose factor loadings are generated in reproducing kernel Hilbert space(RKHS), to capture the dynamic feature of the covariance matrix. A simulation study is carried out to demonstrate its performance. Four different conditional variance models are considered for checking the robustness of our method and solving the conditional heteroscedasticity in the empirical study. By exploring the performance among eight introduced model candidates and the market baseline, the empirical study from 2001 to 2017 shows that portfolio allocation based on this dynamic factor structure can significantly reduce the variance, i.e., the risk, of portfolio and thus outperform the market baseline and the ones based on the traditional factor model.
