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Internal Conversion Process of Chlorophyll a in Solvents in Femtosecond Pump-Probe Laser Fields

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Chinese Journal of Chemical Physics 2008年第3期21卷 211-216页

作者： kai niu Li-qing Dong Shu-lin Cong Department of Physics Dalian University of Technology Dalian 116024 China

The internal conversion （IC） processes of chlorophyll a （chl-a） in solvents are studied based on the reduced density matrix theory. The IC times can be obtained by simulating the experimental fluorescence depletion spectra （FDS）. The calculated IC times of chl-a in ethyl acetate, tetrahydrofuran and dimethyl formamide are 141, 147, and 241 fs, respectively. The oscillation feature of the FDS results from the forward and backward transfer of the population between coupled electronic states. The effects of diabatic coupling between two electronic states on the IC time and the FDS are described. The influence of molecule-reservoir coupling on the IC time is also investigated.

关键词： Fluorescence depletion spectrum Internal conversion Reduced density matrix

Arbitrary Decode-Forward Relaying with Re-Encoded Bits Selection Strategy for Polar Codes

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China Communications 2023年第8期20卷 153-162页

作者： Di Guan kai niu Chao Dong Key Laboratory of Universal Wireless Communication Ministry of EducationBeijing University of Posts and TelecommunicationsBeijing 100876China

In this paper,we propose an arbitrary decode-forward single-relay scheme for finite blocklength polar codes,which can be applied to the general symmetric discrete memoryless relay channel with orthogonal receiver *** relay node decodes the received *** relay node selectively re-encodes the message and transmits it to the destination ***,in order to minimize the upper-bound of the block error probability,we propose a selection strategy to decide the proper re-encoded bit set by the *** results are presented to illustrate the improvement in decoding performance of the proposed scheme compared to conventional relay schemes in both additive white Gaussian noise(AWGN)channel and Rayleigh fading channel(RFC).

关键词： polar codes decode-and-forward relaying arbitrary relay channel block error rate estimation

Iterative list decoding approach for Reed-Solomon codes

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The Journal of China Universities of Posts and Telecommunications 2019年第3期26卷 8-14,24页

作者： Zhang Zhijun niu kai Dong Chao Key Laboratory of Universal Wireless Communications Beijing University of Posts and Telecommunications

A novel adaptively iterative list decoding(ILD) approach using for Reed-Solomon(RS) codes was investigated. The proposed scheme is exploited to reduce the complexity of RS Chase algorithm(CA) via an iterative decoding attempt mode. In each decoding attempt process, a test pattern is generated by flipping the bits of the least reliable positions(LRPs) within the received hard-decision(HD) vector. The ILD algorithm continues until a test pattern is successfully decoded by the underlying Berlekamp-Massey algorithm(BMA) of RS codes. Flipping within the same bits, the ILD algorithm provides the same test pattern set as the conventional RS CA, thus there is no degradation in error-rate performance. Without decoding all test patterns, the ILD algorithm can simplify the decoding complexity by its early termination. Simulation results show that the average complexity of the ILD algorithm is much lower than that of the conventional RS CA(and is similar to that of BMA decoding) at high signal-to-noise ratio(SNR) region with no less to the RS CA decoding error-rate performance.

关键词： iterative decoding soft-decision decoding Reed-Solomon codes low-complexity decoding

Information Conductivity:Universal Performance Measure for Semantic Communications

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China Communications 2024年第7期21卷 17-36页

作者： Liang Zijian niu kai Zhang Ping Key Laboratory of Universal Wireless Communications Ministry of Education(Beijing University of Posts and Telecommunications)Beijing 100876China Peng Cheng Laboratory Shenzhen 518055China State Key Laboratory of Networking and Switching Technology(Beijing University of Posts and Telecommunications) Beijing 100876China

As a novel paradigm,semantic communication provides an effective solution for breaking through the future development dilemma of classical communication ***,it remains an unsolved problem of how to measure the information transmission capability for a given semantic communication method and subsequently compare it with the classical communication *** this paper,we first present a review of the semantic communication system,including its system model and the two typical coding and transmission methods for its *** address the unsolved issue of the information transmission capability measure for semantic communication methods,we propose a new universal performance measure called Information *** provide the definition and the physical significance to state its effectiveness in representing the information transmission capabilities of the semantic communication systems and present elaborations including its measure methods,degrees of freedom,and progressive *** results in image transmission scenarios validate its practical applicability.

关键词： information conductivity information transmission capability semantic communications system model universal performance measure

Numerical Simulation and Analysis of Migration Law of Gas Mixture Using Carbon Dioxide as Cushion Gas in Underground Gas Storage Reservoir

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Journal of Harbin Institute of Technology(New Series) 2014年第3期21卷 121-128页

作者： Chuan-kai niu Yu-Fei Tan School of Municipal & Environment Engineering Harbin Institute of Technology

One of the major technical challenges in using carbon dioxide( CO2) as part of the cushion gas of the underground gas storage reservoir( UGSR) is the mixture of CO2and natural gas. To decrease the mixing extent and manage the migration of the mixed zone,an understanding of the mechanism of CO2and natural gas mixing and the diffusion of the mixed gas in aquifer is necessary. In this paper,a numerical model based on the three dimensional gas-water two-phase flow theory and gas diffusion theory is developed to understand this mechanism. This model is validated by the actual operational data in Dazhangtuo UGSR in Tianjin City,*** the validated model,the mixed characteristic of CO2and natural gas and the migration mechanism of the mixed zone in an underground porous reservoir is further studied. Particularly,the impacts of the following factors on the migration mechanism are studied: the ratio of CO2injection,the reservoir porosity and the initial operating pressure. Based on the results,the optimal CO2injection ratio and an optimal control strategy to manage the migration of the mixed zone are obtained. These results provide technical guides for using CO2as cushion gas for UGSR in real projects.

关键词： underground gas storage reservoir(UGSR) cushion gas carbon dioxide mixed zone porous media

Convergence analysis and performance optimization of parallel concatenated systematic polar code

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The Journal of China Universities of Posts and Telecommunications 2018年第2期25卷 1-9页

作者： Liu Zhenzhen niu kai Dong Chao Lin Jiaru School of Information and Communication Engineering Beijing University of Posts and Telecommunications

Similar to the analysis of Turbo codes, the parallel concatenated systematic polar code （PCSPC） can also be analyzed by the extrinsic information transfer （EXIT） chart. The convergence of the iterative decoding based on soft cancellation （SCAN） and belief propagation （BP） of PCSPC are analyzed by the EXIT chart. Analysis shows that SCAN decoder is more appropriate than BP decoder for this iterative decoding structure in terms of complexity. In addition, the weight coefficients of the iterative decoding structure are optimized by the simulated-EXIT （S- EXIT） chart, which improves the performance of PCSPC.

关键词： PCSPC EXIT chart SCAN decoder BP decoder weight coefficient

Polar Codes for Soft Decode-and-Forward in HalfDuplex Relay Channels

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China Communications 2017年第8期14卷 22-32页

作者： Fangliao Yang kai niu Chao Dong Baoyu Tian Key Laboratory of Universal Wireless Communications Ministry of EducationBeijing University of Posts and Telecommunications Beijing 100876China

Soft decode-and-forward(DF) can combine the advantages of both amplify-and-forward and hard DF in relay channels. In this paper, we propose a low-complexity soft DF scheme based on polar codes, which features two key techniques: a low-complexity cyclic redundancy check(CRC) aided list successive cancellation(CALSC) decoder and a soft information calculation method. At the relay node, a low-complexity CALSC decoder is designed to reduce the computational complexity by adjusting the list size according to the reliabilities of decoded bits. Based on the path probability metric of the CALSC decoder, we propose a method to compute the soft information of the decoded bits in CALSC. Simulation results show that our proposed scheme outperforms the soft DF based on low-density parity-check codes and the soft DF with belief propagation or soft cancellation decoder, especially in the case when the source-relay channel is at the high signal-to-ratio region.

关键词： Decode and forward soft information relaying Polar codes relay channels

Lattice reduction aided belief propagation for massive MIMO detection

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Science China(Information Sciences) 2019年第4期62卷 127-139页

作者： Senjie ZHANG Zhiqiang HE kai niu Shi JIN Hong CHENG Key Laboratory of Universal Wireless Communications Ministry of EducationBeijing University of Posts and Telecommunications National Mobile Communications Research Laboratory Southeast University Intel Labs China

Efficient massive MIMO detection for practical deployment, which is with spatially correlated channel and high-order modulation, is a challenging topic for the fifth generation mobile communication(5G). In this paper, lattice reduction aided belief propagation(LRA-BP) is proposed for massive MIMO detection. LRA-BP applies the message updating rules of Markov random field based belief propagation(MRF-BP) in lattice reduced MIMO system. With the lattice reduced, well-conditioned MIMO channel,LRA-BP obtains better message updating and detection performance in spatially correlated channel than MRF-BP. Log-domain arithmetic is used in LRA-BP for computational complexity reduction. Simulation result shows that LRA-BP outperforms MRF-BP with 3–10 dB in terms of required SNR for 1% packet error rate in spatially correlated channel for 256-QAM. We also show that LRA-BP requires much lower complexity compared with MRF-BP.

关键词： massive MIMO MIMO detection belief propagation graph-based detection lattice reduction Markov random field

Carbon isotopic compositions of mono-, di-, tri-aromatics provide insights into the source of sulfur-rich crude oils in the Huanghekou Depression, Bohai Bay Basin

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Petroleum Science 2023年第2期20卷 753-768页

作者： Cong-kai niu Du-Jie Hou Xiong Cheng Xu Han School of Energy Resources China University of GeosciencesBeijing100083China Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Accumulation Mechanism Ministry of EducationChina University of GeosciencesBeijing100083China

The stable carbon isotope compositions (δ13C) of individual aromatic hydrocarbons have been analyzed in sulfur-rich and sulfur-lean crude oils from the Huanghekou Depression, Bohai Bay Basin. The δ13C values of individual aromatic hydrocarbons, including alkylbenzenes, alkylnaphthalenes, alkylphenanthrenes, alkylfluorenes and alkyldibenzothiophenes, are reported. The main aims are to find out the origin of these oils and their relationship to paleoclimate. The distribution of aromatic hydrocarbons and maturity parameters show the oils all stay in the low-mature to mature stage. Meanwhile, aromatic hydrocarbons are mainly derived from the diagenetic/catagenetic origin. The δ13C values for 1,2,4-trimethylbenzene (−30.7‰ to −28.8‰) and 1,2,3,4-tetramethylbenzene (−32.4‰ to −26.3‰) indicate the algae-derived organic matter for alkylbenzenes. Some isomers, such as 1,7-+1,3-+1,6-dimethylnaphthalene, 1,2,5-trimethylnaphthalene, 1,2,5,6-+1,2,3,5-tetramethylnaphthalene, 1,10-+1,3-+3,10-+3,9-dimethylphenanthrenes, 1,6-+2,9-+2,5-dimethylphenanthrenes and 4,9-+4,10-+1,9- dimethylphenanthrenes show isotopic depletion (−34.9‰ to −25.2‰), indicating the major contribution of algae for these compounds. Meanwhile, isotopically depleted (−33.6‰ to −26.7‰) alkyldibenzothiophenes represent the algae input. δ13C values for mainly algae-derived naphthalene to trimethylnaphthalenes of sulfur-rich oils are more enriched than those of sulfur-lean oil, with the most significant difference of 4.4‰, indicating that the aridity of the environment and stratified water column result in the enrichment in 13C.

关键词： Carbon isotopes Aromatic hydrocarbons Sulfur-rich oils Huanghekou depression Bohai bay basin