High resolution structural studies of DNA and DNA binding proteins by atomic force microscopy(AFM) require well-bound samples on suitably flat substrates. Adsorbing the DNA onto a positively charged supported lipid bi...High resolution structural studies of DNA and DNA binding proteins by atomic force microscopy(AFM) require well-bound samples on suitably flat substrates. Adsorbing the DNA onto a positively charged supported lipid bilayer has previously been shown to be a potentially effective strategy for structural studies with AFM. Here, using our home-built frequency-modulation AFM(FM-AFM), we show that these bilayer substrates are only maximally effective for high resolution AFM when the samples are short, linear DNA, compared with circular plasmid DNA. We find that, with the former sample, the measured width of the DNA is about 2 nm, the known DNA diameter, and there is a clear height modulation along the length of the DNA with a periodicity of about 3.4 nm, in excellent agreement with the known pitch of the double helix. This sample preparation strategy is expected to enable higher resolution studies of DNA and DNA binding proteins with FM-AFM than that can presently be achieved.展开更多
Frequency-modulation atomic force microscopy(FM-AFM) is a highly versatile tool for surface science.Besides imaging surfaces, FM-AFM is capable of measuring interactions between the AFM probe and the surface with high...Frequency-modulation atomic force microscopy(FM-AFM) is a highly versatile tool for surface science.Besides imaging surfaces, FM-AFM is capable of measuring interactions between the AFM probe and the surface with high sensitivity, which can provide chemical information at sub-nanometer resolution. This is achieved by deconvoluting the frequency shift, which is directly measured in experiments, into the force between the probe and sample. At present, the widely used method to perform this deconvolution has been shown to be accurate under high quality(high-Q) factor vacuum conditions. However, under low quality(low-Q) factor conditions, such as in solution, it is not clear if this method is valid. A previous study apparently verified this relation for experiments in solution by comparing the force calculated by this equation with that obtained in separate experiments using the surface force apparatus(SFA). Here we show that, in solution, a more direct comparison of the force calculated by this relation with that directly measured by the cantilever deflection in AFM reveals significant differences,both qualitative and quantitative. However, we also find that there are complications that hinder this comparison.Namely, while contact with the surface is clear in the direct measurements(including the SFA data), it is less certain in the FM-AFM case. Hence, it is not clear if the two methods are measuring the same tip-sample distance regimes. Thus, our results suggest that a more thorough verification of this relation is required, as application of this formulation for experiments in solution may not be valid.展开更多
An analytic solution derived by multisection model to the small-signal frequency response （SSFR） of wavelength conversion based on cross-gain modulation （XGM） in semiconductor optical amplifiers （SOAs） is presen...An analytic solution derived by multisection model to the small-signal frequency response （SSFR） of wavelength conversion based on cross-gain modulation （XGM） in semiconductor optical amplifiers （SOAs） is presented. The result contains details that can affect the characteristics of SSFR significantly more than previous ones.展开更多
在不增加设备体积重量以及提高发射功率的前提下,为满足高码率遥测数据传输的需求,现有的脉冲编码调制-频调(Pulse Code Modulation Frequency Modulation, PCM-FM)遥测系统广泛使用多符号检测(Multiple Symbol Detection, MSD)算法和Tu...在不增加设备体积重量以及提高发射功率的前提下,为满足高码率遥测数据传输的需求,现有的脉冲编码调制-频调(Pulse Code Modulation Frequency Modulation, PCM-FM)遥测系统广泛使用多符号检测(Multiple Symbol Detection, MSD)算法和Turbo乘积码(TPC)技术。调制指数是PCM-FM遥测系统中的重要参数之一,对系统带宽和误码率有重要影响。本文分析了MSD多符号检测算法原理,通过计算互相关系数及Matlab仿真,分析了调制指数大小对带宽和误码率的影响,指出将调制指数设置为0.715较为合适;分析了调制指数偏差对信噪比损耗的影响,利用MSD算法的相位网格图分析了调制指数偏差对误码和码同步的影响,指出随机数据比连“0”或连“1”数据具有更好的容忍能力。展开更多
在分析遥测接收系统工作原理的基础上,深入研究了CORDIC(COordinate Rotation Digital Computer)算法的解调技术.当输入为正交中频(IF)信号和对应的时钟信息时,输出即为输入瞬时信号对应的瞬时相位,但在信道没有延迟时,其抗噪性能不如...在分析遥测接收系统工作原理的基础上,深入研究了CORDIC(COordinate Rotation Digital Computer)算法的解调技术.当输入为正交中频(IF)信号和对应的时钟信息时,输出即为输入瞬时信号对应的瞬时相位,但在信道没有延迟时,其抗噪性能不如相干解调.在此基础上设计了一种改进的CORDIC差分鉴频解调算法,得到瞬时相位后,在数字域作1阶差分完成信号鉴频,保证了在信道没有延迟的情况下信号的抗噪性能.通过仿真实验证明了算法的合理性.展开更多
基金the National Basic Research Program(973) of China(No.2013CB932801)the National Natural Science Foundation of China(Nos.991129000,11374207,11375253,31370750,21273148 and 11074168)the Fund of Chinese Academy of Sciences(No.KJCX2-EW-N03)
文摘High resolution structural studies of DNA and DNA binding proteins by atomic force microscopy(AFM) require well-bound samples on suitably flat substrates. Adsorbing the DNA onto a positively charged supported lipid bilayer has previously been shown to be a potentially effective strategy for structural studies with AFM. Here, using our home-built frequency-modulation AFM(FM-AFM), we show that these bilayer substrates are only maximally effective for high resolution AFM when the samples are short, linear DNA, compared with circular plasmid DNA. We find that, with the former sample, the measured width of the DNA is about 2 nm, the known DNA diameter, and there is a clear height modulation along the length of the DNA with a periodicity of about 3.4 nm, in excellent agreement with the known pitch of the double helix. This sample preparation strategy is expected to enable higher resolution studies of DNA and DNA binding proteins with FM-AFM than that can presently be achieved.
基金the National Natural Science Foundation of China(Nos.991129000,11374207,31370750,21273148 and 11074168)
文摘Frequency-modulation atomic force microscopy(FM-AFM) is a highly versatile tool for surface science.Besides imaging surfaces, FM-AFM is capable of measuring interactions between the AFM probe and the surface with high sensitivity, which can provide chemical information at sub-nanometer resolution. This is achieved by deconvoluting the frequency shift, which is directly measured in experiments, into the force between the probe and sample. At present, the widely used method to perform this deconvolution has been shown to be accurate under high quality(high-Q) factor vacuum conditions. However, under low quality(low-Q) factor conditions, such as in solution, it is not clear if this method is valid. A previous study apparently verified this relation for experiments in solution by comparing the force calculated by this equation with that obtained in separate experiments using the surface force apparatus(SFA). Here we show that, in solution, a more direct comparison of the force calculated by this relation with that directly measured by the cantilever deflection in AFM reveals significant differences,both qualitative and quantitative. However, we also find that there are complications that hinder this comparison.Namely, while contact with the surface is clear in the direct measurements(including the SFA data), it is less certain in the FM-AFM case. Hence, it is not clear if the two methods are measuring the same tip-sample distance regimes. Thus, our results suggest that a more thorough verification of this relation is required, as application of this formulation for experiments in solution may not be valid.
基金Project supported by the National Nature Science Foundation of China （Grant No 60407001）, National High Technology Developing Program of China （Grant No 2006AA03Z0414）, the Science Fund for Distinguished YoungScholars of Hubei Province （Grant No 2006ABB017） and the Program for New Century Excellent Talents of Ministry of Education, China （Grant No NCET-04-0715）.
文摘An analytic solution derived by multisection model to the small-signal frequency response （SSFR） of wavelength conversion based on cross-gain modulation （XGM） in semiconductor optical amplifiers （SOAs） is presented. The result contains details that can affect the characteristics of SSFR significantly more than previous ones.
文摘在不增加设备体积重量以及提高发射功率的前提下,为满足高码率遥测数据传输的需求,现有的脉冲编码调制-频调(Pulse Code Modulation Frequency Modulation, PCM-FM)遥测系统广泛使用多符号检测(Multiple Symbol Detection, MSD)算法和Turbo乘积码(TPC)技术。调制指数是PCM-FM遥测系统中的重要参数之一,对系统带宽和误码率有重要影响。本文分析了MSD多符号检测算法原理,通过计算互相关系数及Matlab仿真,分析了调制指数大小对带宽和误码率的影响,指出将调制指数设置为0.715较为合适;分析了调制指数偏差对信噪比损耗的影响,利用MSD算法的相位网格图分析了调制指数偏差对误码和码同步的影响,指出随机数据比连“0”或连“1”数据具有更好的容忍能力。
文摘在分析遥测接收系统工作原理的基础上,深入研究了CORDIC(COordinate Rotation Digital Computer)算法的解调技术.当输入为正交中频(IF)信号和对应的时钟信息时,输出即为输入瞬时信号对应的瞬时相位,但在信道没有延迟时,其抗噪性能不如相干解调.在此基础上设计了一种改进的CORDIC差分鉴频解调算法,得到瞬时相位后,在数字域作1阶差分完成信号鉴频,保证了在信道没有延迟的情况下信号的抗噪性能.通过仿真实验证明了算法的合理性.
基金国家自然科学基金(the National Natural Science Foundation of China under Grant No.60374029)山西省青年科学基金项目(the ShanxiProvince Youth Science Foundations under Grant No.2006021016No.2007021018)
