A transform method was used to model a discrete time multi-tap direct sampling mixer. The method transforms the mixed filtering and down-sampling stages to separate cascade filtering and sampling stages to determine t...A transform method was used to model a discrete time multi-tap direct sampling mixer. The method transforms the mixed filtering and down-sampling stages to separate cascade filtering and sampling stages to determine the unfolded frequency response which shows the anti-aliasing ability of the mixer. The trans-formation can also be applied to other mixed signal and multi-rate receiver systems to analyze their unfolded frequency responses. The transformed system architecture was used to calculate the unfolded frequency response of the multi-tap direct sampling mixer and compared with the mixer model without noise in the advanced design system 2005A environment to further evaluate the frequency response. The simulations show that the -3 dB bandwidth is 3.0 MHz and the voltage gain is attenuated by 1.5 dB within a 1-MHz baseband bandwidth.展开更多
A novel magnetic method using polystyrene modified magnetic nanoparticles to perform thermoheadspace extraction was successfully developed for extraction and preconcentration of volatile organic components in dry Trad...A novel magnetic method using polystyrene modified magnetic nanoparticles to perform thermoheadspace extraction was successfully developed for extraction and preconcentration of volatile organic components in dry Traditional Chinese Medicine（TCM） based on gas chromatography-ion trap/mass spectrometry with a Chromato Probe direct sample introduction device. The dried fruit of Amomum testaceum Ridl. was used as the object TCM. The optimum parameters of headspace magnetic solid-phase extraction were investigated, in which desorption solvent ethyl acetate played a key role in this method,and the headspace extraction temperature of 90℃ and the headspace extraction time of 15 min finally decided. Headspace solid-phase microextraction method was also used to analyze volatile compounds in the TCM to compare with the proposed method. The results show that 60 components were identified totally by two methods; most of the low boiling point chemical compounds are isolated by this new method. In this work, an environmental-friendly and cheap analytical method was established, and a new approach to analyze volatile compounds in dry Traditional Chinese Medicine was also provided.展开更多
Traditional low power-microwave plasma torch（MPT） excitation source of atomic emission spectrometry was shown to be good for the introduction of dry aerosols, but poor for wet sample aerosols. In this work, some sig...Traditional low power-microwave plasma torch（MPT） excitation source of atomic emission spectrometry was shown to be good for the introduction of dry aerosols, but poor for wet sample aerosols. In this work, some significant modifications have been made to traditional MPT. A new MPT excitation source working at kilowatt microwave power has been developed. The kilowatt MPT source can sustain stable plasmas with double or even more filaments, presenting a ＂bell＂ form, where the region around the converging point is the optimum region for analysis. The tolerance to aqueous aerosol of the torch is enhanced significantly compared to the traditional one. Therefore, the desolvation system that the low power MPT source has to be relied on can be gotten rid of. A set of favorable detection results have been obtained with direct wet sample aerosol introduction. The kilowatt MPT source is expected to become a practical excitation source for atomic emission spectrometry that will be widely used.展开更多
基金Supported by the National Natural Science Foundation of China (No. 90407011)the National High-Tech Research and Development (863) Program of China (No. 2007AA01Z2b3)
文摘A transform method was used to model a discrete time multi-tap direct sampling mixer. The method transforms the mixed filtering and down-sampling stages to separate cascade filtering and sampling stages to determine the unfolded frequency response which shows the anti-aliasing ability of the mixer. The trans-formation can also be applied to other mixed signal and multi-rate receiver systems to analyze their unfolded frequency responses. The transformed system architecture was used to calculate the unfolded frequency response of the multi-tap direct sampling mixer and compared with the mixer model without noise in the advanced design system 2005A environment to further evaluate the frequency response. The simulations show that the -3 dB bandwidth is 3.0 MHz and the voltage gain is attenuated by 1.5 dB within a 1-MHz baseband bandwidth.
基金Support of this work by the Department of Education of Zhejiang Province (No. Pd2013016)Hangzhou Qianjiang Distinguished Experts Project (2014)+2 种基金the Science and Technology Department of Zhejiang Province (No. 2015C32006)Key Laboratory of Detection for Pesticide Residues of Ministry of Agriculture Projectthe Sprout Talented Project Program (No. 2011443)
文摘A novel magnetic method using polystyrene modified magnetic nanoparticles to perform thermoheadspace extraction was successfully developed for extraction and preconcentration of volatile organic components in dry Traditional Chinese Medicine（TCM） based on gas chromatography-ion trap/mass spectrometry with a Chromato Probe direct sample introduction device. The dried fruit of Amomum testaceum Ridl. was used as the object TCM. The optimum parameters of headspace magnetic solid-phase extraction were investigated, in which desorption solvent ethyl acetate played a key role in this method,and the headspace extraction temperature of 90℃ and the headspace extraction time of 15 min finally decided. Headspace solid-phase microextraction method was also used to analyze volatile compounds in the TCM to compare with the proposed method. The results show that 60 components were identified totally by two methods; most of the low boiling point chemical compounds are isolated by this new method. In this work, an environmental-friendly and cheap analytical method was established, and a new approach to analyze volatile compounds in dry Traditional Chinese Medicine was also provided.
文摘Traditional low power-microwave plasma torch（MPT） excitation source of atomic emission spectrometry was shown to be good for the introduction of dry aerosols, but poor for wet sample aerosols. In this work, some significant modifications have been made to traditional MPT. A new MPT excitation source working at kilowatt microwave power has been developed. The kilowatt MPT source can sustain stable plasmas with double or even more filaments, presenting a ＂bell＂ form, where the region around the converging point is the optimum region for analysis. The tolerance to aqueous aerosol of the torch is enhanced significantly compared to the traditional one. Therefore, the desolvation system that the low power MPT source has to be relied on can be gotten rid of. A set of favorable detection results have been obtained with direct wet sample aerosol introduction. The kilowatt MPT source is expected to become a practical excitation source for atomic emission spectrometry that will be widely used.
