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911.
Zhi-Rong Tan Yao Chen Gan Zhou Shan Cao Xiang-Dong Peng Yi-Cheng Wang Xiu-Juan Peng Wei Zhang Hong-Hao Zhou 《Chromatographia》2010,72(11-12):1107-1113
A sensitive and specific liquid chromatography–electrospray ionization-tandem mass spectrometry method has been developed and validated for the identification and quantification of ursolic acid in human plasma using glycyrrhetic acid as an internal standard. The method involves extraction with methyl tert-butyl ether. The analyte was separated on a C18 column and analyzed in multiple reaction monitoring mode with a negative electrospray ionization interface using the [M–H]? ions, m/z 455.4 for ursolic acid and m/z 469.5 → m/z 425.5 for glycyrrhetic acid. The method was validated over the concentration range of 0.86–110.0 μg L?1. The intra- and inter-day precisions were less than 13.53% relative standard deviation (RSD) and the accuracy was within ?4.76% in terms of relative error (RE). The lower limit of quantification was 0.86 μg L?1 with acceptable precision and accuracy. There were almost no matrix effects. Recovery of ursolic acid from spiked drug-free plasma was higher than 68%. The method was used to study the pharmacokinetic profile of ursolic acid in human plasma after oral administration of Jieyu capsules. 相似文献
912.
<正>Poly(vinylidenefluoride-hexafluoropropylene)(PVDF-HFP) nanofiber membranes with improved hydrophilicity and protein fouling resistance via surface graft copolymerization of hydrophilic monomers were prepared.The surface modification involves atmospheric pressure glow discharge plasma(APGDP) pretreatment followed by graft copolymerization of poly(ethylene glycol) methyl ether methacrylate(PEGMA).The success of the graft modification with PEGMA on the PVDF-HFP fibrous membrane is ascertained by X-ray photoelectron spectroscopy(XPS) and attenuated total reflectance Fourier transform infrared measurements(ATR-FTIR).The hydrophilic property of the nanofiber membranes is assessed by water contact angle measurements.The results show that the PEGMA grafted PVDF-HFP nanofiber membrane has a water contact angle of 0°compared with the pristine value of 132°.The protein adsorption was effectively reduced after PEGMA grafting on the PVDF-HFP nanofiber membrane surface.The PEGMA polymer grafting density on the PVDF-HFP membrane surface is measured by the gravimetric method,and the filtration performance is characterized by the measurement of water flux.The results indicate that the water flux of the grafted PVDF-HFP fibrous membrane increases significantly with the increase of the PEGMA grafting density. 相似文献
913.
波谱分析课程教学的实践与思考 总被引:1,自引:0,他引:1
介绍作者在长期波谱分析课程教学实践的基础上,对该课程教学内容及教学方法改革的一些探索。 相似文献
914.
In this work, we investigated the fluorescence emission spectra and diffusion properties of dye molecules confined in different
positions of conical nanopore channels using a laser scanning confocal fluorescence microscope. The results showed that a
red shift of the emission spectra is observed from the tip section to the bottom section and the diffusion rate is slower
in the channel than that in bulk solution, indicating a single conical nanopore channel can be used as a convenient tool for
investigating the effect of confined space on the behaviors of molecules. 相似文献
915.
A novel compact supercontinuum (SC) source using the single mode photonic crystal fibers (PCF) pumped with an all fiber MOPA
fiber laser is demonstrated experimentally. A bandwidth of 700 nm is achieved by operating the pumping fiber laser at a wavelength
of 1064 nm, pulse duration of 10 ns, repetition rate of 50 kHz and peak power of 1 kW. The SC generation is initiated through
modulation instability (MI) which breakups the nanosecond pump pulses into picosecond or femtosecond pulses, and further broadened
through nonlinear effects of PCF. 相似文献
916.
We shall derive two sufficient conditions for complete finite-dimensional Alexandrov spaces of nonnegative curvature to be
contractible. One of the new technical tools used in our proof is a quadrangle comparison theorem inspired by Perelman. 相似文献
917.
When a target-speech/masker mixture is processed with the signal-separation technique, ideal binary mask (IBM), intelligibility of target speech is remarkably improved in both normal-hearing listeners and hearing-impaired listeners. Intelligibility of speech can also be improved by filling in speech gaps with un-modulated broadband noise. This study investigated whether intelligibility of target speech in the IBM-treated target-speech/masker mixture can be further improved by adding a broadband-noise background. The results of this study show that following the IBM manipulation, which remarkably released target speech from speech-spectrum noise, foreign-speech, or native-speech masking (experiment 1), adding a broadband-noise background with the signal-to-noise ratio no less than 4 dB significantly improved intelligibility of target speech when the masker was either noise (experiment 2) or speech (experiment 3). The results suggest that since adding the noise background shallows the areas of silence in the time-frequency domain of the IBM-treated target-speech/masker mixture, the abruption of transient changes in the mixture is smoothed and the perceived continuity of target-speech components becomes enhanced, leading to improved target-speech intelligibility. The findings are useful for advancing computational auditory scene analysis, hearing-aid/cochlear-implant designs, and understanding of speech perception under "cocktail-party" conditions. 相似文献
918.
Novel near infrared (NIR) phosphors CaxSr1−xS:Ce3+,Nd3+ were synthesized by a solid state reaction. The NIR emission was realized through an efficient absorption by the allowed 4f-5d transition of Ce3+ and efficient energy transfer to Nd3+ via well-matched energy levels. Ce3+ and Nd3+ content in CaS/SrS was optimized. It was found that CaS:Ce3+,Nd3+ gave much stronger NIR emission than that of SrS:Ce3+,Nd3+. Further studies on CaxSr1−xS:Ce3+,Nd3+ indicated that both visible emission of Ce3+ and NIR emission of Nd3+ were observably affected by Ca/Sr ratio. The energy transfer efficiency, which can be estimated from fluorescence lifetime of Ce3+, increased from 52% to 74% for the CaxSr1−xS:Ce3+,Nd3+ (x=0 to 1) series, accompanied with a shift of maximal emission wavelength of Ce3+ from 482 to 505 nm. The results showed that overlap between emission spectrum of Ce3+ and excitation spectrum of Nd3+ plays an important role in the energy transfer efficiency, and Ce3+ emitting in green or blue-greenish region sensitized the Nd3+ NIR fluorescence emission more efficiently than that in blue region. 相似文献
919.
Lei Liu Bin Wang Xuewei Cao Xiaoxuan Xu Yufang Wang 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(17):2733-2740
Using T-matrix method, plasmon resonance properties of metal core–shell nanoparticles are systematically investigated. It is shown that dielectric/metal core–shell structure may be excited stronger at resonance than metal/dielectric and hetero-metal ones, but the resonance states are extremely sensible to the layers thickness. For three-layer nanospheres, resonance properties will be dominated by a sub-10 nm silver outermost shell, while only weakened by a silica one. Finally, tiny eccentric distance between the centers of core and shell in eccentric two-layer nanoparticles may fundamentally change the resonance mode of nanoparticles, and results in higher local electrical field enhancement than concentric nanospheres. 相似文献
920.
Chunyan Cao Hyun Kyoung Yang Byung Kee Moon Jung Hyun Jeong Kwang Ho Kim 《Optics Communications》2011,284(23):5453-5456
By controlling the pH values of prepared solutions, the 10 mol% Ce3+, 5 mol% Tb3+ co-doped KGdF4 (synthesized with pH = 3) and the 10 mol% Ce3+, 5 mol% Tb3+ co-doped GdF3 (synthesized with pH = 1) submicro/nanocrystals have been synthesized based on a citric acid assisted hydrothermal method. For comparison, the samples synthesized by co-precipitation method (without hydrothermal treatment) with pH = 3 and 1 were also collected. The X-ray diffraction data illustrate that the hydrothermal treated KGdF4 sample crystallizes in the cubic phase and the GdF3 sample crystallizes in the orthorhombic phase. However, the samples synthesized by co-precipitation method with pH = 3 and 1 are both cubic phase KGdF4. The field emission scanning electron microscopy images suggest that the hydrothermal treated KGdF4 submicro/nanocrystals present spherical morphology and the GdF3 submicrocrystals are rhombic-shaped. And the photoluminescence excitation and emission spectra as well as the luminescent dynamic curves demonstrate the difference in optical properties of the two hydrothermal treated samples. 相似文献