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An Optimal Oscillatory phase for Pattern Reactivation during Memory Retrieval

CURRENT BIOLOGY 2018年第21期28卷 3383-+页

作者： Kerren, Casper Linde-Domingo, Juan Hanslmayr, Simon Wimber, Maria Univ Birmingham Sch Psychol Birmingham B15 2TT W Midlands England Univ Birmingham Ctr Human Brain Hlth Birmingham B15 2TT W Midlands England

Computational models and in vivo studies in rodents suggest that the hippocampal system oscillates between states that are optimal for encoding and states that are optimal for retrieval. Here, we show that in humans, neural signatures of memory reactivation are modulated by the phase of a theta oscillation. Electroencephalography (EEG) was recorded while participants were cued to recall previously learned word-object associations, and time-resolved pattern classifiers were trained to detect neural reactivation of the target objects. Classifier fidelity rhythmically fluctuated at 7 or 8 Hz and was modulated by theta phase across the entire recall period. The phase of optimal classification was shifted approximately 180 degrees between encoding and retrieval. Inspired by animal work, we then computed "classifier-locked averages" to analyze how ongoing theta oscillations behaved around the time points at which the classifier indicated memory retrieval. We found strong theta (7 or 8 Hz) phase consistency approximately 300 ms before the time points of maximal neural memory reactivation. Our findings provide important evidence that the neural signatures of memory retrieval fluctuate and are time locked to the phase of an ongoing theta oscillation.

关键词： oscillations episodic memory hippocampus theta oscillations phase coding EEG decoding pattern classification retrieval

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Regulation of gamma-frequency oscillation by feedforward inhibition: A computational modeling study

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HIPPOCAMPUS 2019年第10期29卷 957-970页

作者： Renno-Costa, Cesar Teixeira, Daniel Garcia Soltesz, Ivan Univ Fed Rio Grande do Norte Bioinformat Multidisciplinary Environm BioME Natal RN Brazil Univ Fed Rio Grande do Norte Digital Metropolis Inst Natal RN Brazil Univ Fed Rio Grande do Norte Natal RN Brazil Stanford Univ Dept Neurosurg Stanford CA 94305 USA

Throughout the brain, reciprocally connected excitatory and inhibitory neurons interact to produce gamma-frequency oscillations. The emergent gamma rhythm synchronizes local neural activity and helps to select which cells should fire in each cycle. We previously found that such excitation-inhibition microcircuits, however, have a potentially significant caveat: the frequency of the gamma oscillation and the level of selection (i.e., the percentage of cells that are allowed to fire) vary with the magnitude of the input signal. In networks with varying levels of brain activity, such a feature may produce undesirable instability on the time and spatial structure of the neural signal with a potential for adversely impacting important neural processing mechanisms. Here we propose that feedforward inhibition solves the latter instability problem of the excitation-inhibition microcircuit. Using computer simulations, we show that the feedforward inhibitory signal reduces the dependence of both the frequency of population oscillation and the level of selection on the magnitude of the input excitation. Such a mechanism can produce stable gamma oscillations with its frequency determined only by the properties of the feedforward network, as observed in the hippocampus. As feedforward and feedback inhibition motifs commonly appear together in the brain, we hypothesize that their interaction underlies a robust implementation of general computational principles of neural processing involved in several cognitive tasks, including the formation of cell assemblies and the routing of information between brain areas.

关键词： computer model gamma frequency inhibition phase coding winner-take-all

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Mismatch Filter Design via Convex Optimization

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IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS 2016年第4期52卷 1587-1591页

作者： Kajenski, Peter J. Raytheon Integrated Def Syst 50 Apple Hill Dr Tewksbury MA 01876 USA

Mismatch filters are generally used to reduce the range sidelobes when phase-coded waveforms are used. It is shown that such mismatch filters can be designed with convex optimization techniques by formulating the problem as a second-order cone programming problem. It is also shown that it is possible to make trade-offs between peak sidelobe levels and losses in the main peak gain.

关键词： sidelobe MAINS Programming Filters waveforms phase coding side lobe level Convex function

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Code extraction from encoded signal in time-spreading optical code division multiple access

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OPTICS LETTERS 2010年第2期35卷 229-231页

作者： Si, Zhijian Yin, Feifei Xin, Ming Chen, Hongwei Chen, Minghua Xie, Shizhong Tsinghua Univ Dept Elect Engn TNList State Key Lab Integrated Optoelect Beijing 100084 Peoples R China

A vulnerability that allows eavesdroppers to extract the code from the waveform of the noiselike encoded signal of an isolated user in a standard time-spreading optical code division multiple access communication system using bipolar phase code is experimentally demonstrated. The principle is based on fine structure in the encoded signal. Each dip in the waveform corresponds to a transition of the bipolar code. Eavesdroppers can get the code by analyzing the chip numbers between any two transitions;then a decoder identical to the legal user's can be fabricated, and they can get the properly decoded signal. (C) 2010 Optical Society of America

关键词： OCDMA phase coding waveforms fine structure signals code division Codes get

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Sidelobe Suppression Method with Improved CLEAN Algorithm for Pulse Compression OTDR

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IEEE PHOTONICS TECHNOLOGY LETTERS 2024年第22期36卷 1321-1324页

作者： Huang, Yi Chen, Xiaofeng Shen, Wei Wei, Ziyi Hu, Chengyong Deng, Chuanlu Wang, Lisen Zhang, Qi Chen, Wei Zhang, Xiaobei Chen, Lin Jin, Wei Tang, Jianming Wang, Tingyun Shanghai Univ Key Lab Specialty Fiber Opt & Opt Access Networks Shanghai 200444 Peoples R China Shanghai Univ Elect Power Coll Elect & Informat Engn Shanghai 200090 Peoples R China Bangor Univ Sch Elect Engn Bangor LL57 1UT Wales

Although pulse compression optical time domain reflectometry (PC-OTDR) exhibits high performance in spatial resolution and dynamic range, it inevitably introduces auto-correlation sidelobes, potentially impacting measurement accuracy. In this letter, an improved CLEAN algorithm is proposed to efficiently suppress sidelobes and enhance the peak-to-sidelobe ratio (PSLR) of signals in PC-OTDR. The proposed method introduces an adaptive step factor instead of the traditional fixed factor to reduce the number of iterations. Compared to the traditional method, the proposed method achieves a 2.87 dB improvement of PSLR from a 10 km sensing fiber. In addition, the computation time cost is significantly reduced, which is 1.92 s less than that of the traditional CLEAN algorithm.

关键词： Encoding Optical fibers Spatial resolution Signal to noise ratio Perturbation methods Optical filters Filtering Pulse compression optical time domain reflectometry (PC-OTDR) phase coding CLEAN algorithm sidelobe suppression

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Photonic Generation of Tunable Frequency-Multiplied phase-Coded Microwave Waveforms

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IEEE PHOTONICS TECHNOLOGY LETTERS 2018年第13期30卷 1230-1233页

作者： Chen, Yang Pan, Shilong East China Normal Univ Sch Informat Sci & Technol Shanghai 200241 Peoples R China East China Normal Univ Engn Ctr SHMEC Space Informat Shanghai 200241 Peoples R China East China Normal Univ GNSS Shanghai 200241 Peoples R China Nanjing Univ Aeronaut & Astronaut Key Lab Radar Imaging & Microwave Photon Minist Educ Nanjing 210016 Jiangsu Peoples R China

A novel photonic approach to generate frequency-multiplied phase-coded microwave waveforms with large frequency tunability is proposed and experimentally demonstrated. By using a dual-drive Mach-Zehnder modulator, biased at specially designed bias point, and a single-port photodetector, phase-coded microwave waveforms at the doubled or tripled frequency of the applied microwave reference signal are generated, with a large frequency tunable range limited by the bandwidth of the dual-drive Mach-Zehnder modulator. The proposed technique is experimentally verified. phase-coded microwave waveforms at the doubled frequency from 16 to 30 CHz and the tripled frequency from 21 to 30 GHz are generated. The pulse compression performance of the generated phase-coded microwave waveforms is also studied.

关键词： Microwave photonics phase coding frequency multiplication pulse compression

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Design of phase codes with interval staggering for Doppler ambiguous target detection

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ELECTRONICS LETTERS 2013年第24期49卷 1564-+页

作者： Wei, Na Zhang, Linke BeiHang Univ Sch Elect & Informat Engn Beijing 100191 Peoples R China Wuhan Univ Technol Sch Energy & Power Engn Wuhan 430063 Peoples R China

The design of radar coherent pulse trains encoded with interval staggering for ambiguous Doppler target detection in clutter is addressed. To alleviate the Doppler ambiguous problem, an interpulse phase coding optimisation model is formulated in terms of staggered interval sampling, while maximising the output signal-to-interference-plus-noise ratio for improved target detection. Based on a reformulation of this optimisation problem as a non-convex quadratically constrained quadratic program (QCQP), a semidefinite relaxation algorithm for this QCQP is presented. Numerical results demonstrate the effectiveness of this proposed approach.

关键词： concave programming Doppler effect electromagnetic interference object detection phase coding quadratic programming radar clutter radar detection signal sampling phase code design Doppler ambiguous target detection radar coherent pulse train encoding radar clutter interpulse phase coding optimisation model staggered interval sampling signal-to-interference-plus-noise ratio nonconvex quadratically constrained quadratic program QCQP semidefinite relaxation algorithm

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Approach of implementing phase encoded quantum square root of NOT gate

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ELECTRONICS LETTERS 2017年第20期53卷 1375-1376页

作者： Dey, S. Mukhopadhyay, S. Univ Burdwan Dept Chem Burdwan 713104 W Bengal India

Quantum logic gates are the building blocks of quantum computer. Here in this Letter the authors propose a new technique of implementing quantum square root of NOT gate by phase encoding mechanism.

关键词： quantum gates phase coding phase encoded quantum square root mechanism NOT gate electronic processor-based computation system quantum computer data processing quantum logic gate

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Wide dynamic range 10-Gb/s DPSK packet receiver using optical-limiting amplifiers

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IEEE PHOTONICS TECHNOLOGY LETTERS 2004年第1期16卷 296-298页

作者： Su, YK Liu, X Leuthold, J Shanghai Jiao Tong Univ Shanghai 200030 Peoples R China Bell Labs Lucent Technol Holmdel NJ 07733 USA

We demonstrate a method to extend the dynamic range (DR) of 10-Gb/s differential phase-shift keying (DPSK) receivers in presence of burst-mode data. We achieve a DR of 25 dB by operating linear optical amplifiers in saturation and benefiting from fast optical-limiting amplification. A fixed decision threshold as enabled by DPSK receivers with balanced detection eliminates the need for guard times and removes inherent sensitivity penalty associated with the adaptive threshold as in conventional ON-OFF keying receivers.

关键词： dynamic response optical receivers packet switching phase coding semiconductor optical amplifiers (SOAs)

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Photonic Generation of phase-Coded Microwave Signal With Large Frequency Tunability

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IEEE PHOTONICS TECHNOLOGY LETTERS 2011年第11期23卷 712-714页

作者： Li, Ze Li, Wangzhe Chi, Hao Zhang, Xianmin Yao, Jianping Univ Ottawa Microwave Photon Res Lab Sch Informat Technol & Engn Ottawa ON K1N 6N5 Canada Zhejiang Univ Dept Informat Sci & Elect Engn Hangzhou 310027 Zhejiang Peoples R China

A photonic approach to realizing phase-coded microwave signal generation with large frequency tunability is proposed and demonstrated. Two coherent optical wavelengths are generated based on external modulation by biasing a Mach-Zehnder modulator (MZM) at the minimum transmission point to generate +/- 1-order sidebands while suppressing the optical carrier. The two +/- 1-order sidebands are then sent to a fiber Sagnac interferometer (SI) incorporating an optical phase modulator (PM) and a broadband flat-top fiber Bragg grating (FBG), with one of the sidebands being phase modulated at the PM. A frequency tunable phase-coded microwave signal is generated by beating the two sidebands at a photodetector (PD). The proposed technique is experimentally investigated. The generation of a frequency tunable phase-coded microwave signal at 22 and 27 GHz is demonstrated.

关键词： Microwave signal generation phase coding radar pulse compression

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