具有残留耦合的分子间和分子内多量子相干及其应用

核磁共振中分子内与分子间多量子相干已得到充分的发展和广泛的使用. 为深入系统地比较研究两种多量子相干的物理机理与性质及其潜在的应用,本文总结近年来相关研究的前沿,首先系统地论述了产生这两种多量子相干的基础－偶极耦合－的作用机理,然后再分别描述基于分子内偶极耦合的分子内多量子相干和基于分子间偶极耦合的分子间多量子相干的原理、性质、及其在化学、生物等领域中的应用.      

A simulation algorithm based on Bloch equations and product operator matrix: application to dipolar and scalar couplings

A product operator matrix is proposed to describe scalar couplings in liquid NMR. Combination of the product operator matrix and non-linear Bloch equations is employed to describe effects of chemical shift, translational diffusion, dipolar field, radiation damping, and relaxation in multiple spin systems with both scalar and dipolar couplings. A new simulation algorithm based on this approach is used to simulate NMR signals from dipolar field effects in the presence of scalar couplings. Several typical coupled spin systems with both intra-molecular scalar couplings and inter-molecular dipolar couplings are simulated. Monte Carlo methods are incorporated into simulations as well to analyze diffusion process in these complicated spin systems. The simulated results of diffusion and relaxation parameters and 2D NMR spectra are coincident with the experimental measurements, and agree with theoretical predictions as well. The simulation algorithm presented herein therefore provides a convenient means for designing pulse sequences and quantifying experimental results in complex coupled spin systems.     

Simultaneous determination of sulfamethoxazole and trimethoprim in microgram quantities from low plasma volume by liquid chromatography–tandem mass spectrometry

A highly sensitive, selective and high-throughput liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for simultaneous quantification of sulfamethoxazole (SMZ) and trimethoprim (TMP) has been developed and validated using imipramine as an internal standard. The analytes were extracted from 50 µL human plasma using solid phase extraction (SPE) and separated on Thermo Hypersil Gold C18 (50 mm × 4.6 mm, 5 μm) column under isocratic conditions in a run time of 2.5 min. Detection was carried out by tandem mass spectrometer, interfaced with electro spray ionization and operating in positive ionization mode. The calibration curves were linear over the concentration range of 0.88–80 µg/mL for SMZ and 0.03–30 µg/mL for TMP. The intra- and inter-day accuracy and precision (% CV) evaluated at four quality control levels were within 93.5–105.0% and 1.3–7.2% respectively. The absolute recovery was greater than 81% for both the analytes at two concentration levels. Stability of SMZ and TMP was assessed under different storage conditions. The validated method was successfully applied for a bioavailability study in 12 healthy volunteers after oral administration of 800 mg of SMZ and 160 mg of TMP succinate tablet formulations under fasting condition.     

Development of a new code family based on SAC-OCDMA system with large cardinality for OCDMA network

We have proposed a new Multi-Diagonal (MD) code for Spectral Amplitude – Coding Optical Code Division Multiple Access (SAC-OCDMA). Although this new MD code has many properties, one of the important properties of this code is that the cross correlation is always zero. Simplicity in code construction and flexibility in cross correlation control has made this code a compelling candidate for future OCDMA applications. The Multiple access interference (MAI) effects have been successfully and completely eliminated. Based on the theoretical analysis MD code is shown here to provide a much better performance compared to Modified Quadratic Congruence (MQC) code and Random Diagonal (RD) code. Proof-of-principle simulations of encoding with 5 and 10 users with 622 Mb/s data transmission at a BER of 10⁻¹² have been successfully demonstrated together with the DIRECT detection scheme.     

浅析QoS中的令牌桶算法

对QoS领域中的令牌桶算法进行了研究,首先对端到端QoS技术的实现方式进行了阐述,然后介绍了流量整形中的令牌桶算法,并且对单速双桶和双速双桶令牌桶算法进行阐述和分析。最后对MQC平台实现令牌桶算法进行分析。在LTE时代,由于大带宽需求、业务低时延要求的新型业务不断出现,基于流量整形的令牌桶算法应用可以应对上述问题而成为QoS研究的新热点。     

基于MQC的谱幅编码OCDMA系统研究

提出将相关性好的调整二次同余码(MQC)用于谱幅编码光码分多址(SAC-OCDMA)系统,分析了采用光纤布拉格光栅(FBGs)作编解码器的工作过程,研究了光谱带宽分布为高斯分布、考虑多址干扰(MAI)下系统的信扰比(SIR)和误码率(BER)。在并发用户数相同的条件下,采用以素数p=5、p=7构造的MQC的系统较采用码长相近的M序列的系统性能提高分别约13db和20db。在满足一定BER的条件下(如BER=10^-9),采用MQC的系统容量远大于采用码长相近的M序列的系统容量。研究结果表明,采用相关性良好的MQC的SAC—OCDMA系统性能明显优于现有的其它方案。