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Analysis of single frequency modulation for passive hydrogen maser

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Journal of Systems Engineering and Electronics 2017年第4期28卷 661-668页

作者： Hefei Zheng Jing Li Wenming Wang Lianshan Gao Keming Feng beijing institute of Radio metrology and Measurement The Second Academy of China Aerospace Science and Industry CorporationBeijing 100854 China

Based on the theory of the passive hydrogen maser, along with the technology of frequency modulation and modulation transfer spectroscopy, the theoretical expression of the single frequency modulation for the passive hydrogen maser and the function of the cavity and H line error signals separation are derived, which are basically coincident with the experiment. The absorption and dispersion spectrum curves with different resonance widths show that the cavity and hydrogen transition serve as discriminators, and the two error signals can be separated. Through the calculations of the two error signals in the passive hydrogen maser, it analyzes the traditional method of the two error signals separation, and then describes a new improved method for the passive hydrogen servo loops consisting in the use of a single modulation frequency and frequency discrimination. A null interaction of the two error signals for the new selection of the phase setting is deduced theoretically and validated by the simulation. The preliminary experimental result confirms the feasibility of this new approach, which can reduce the influence from the cavity frequency variety on the crystal oscillator and contribute significantly to the long term performance of the passive hydrogen maser.

关键词： passive hydrogen maser single frequency modulation frequency discrimination

AttentionSplice: An Interpretable Multi-Head Self-Attention Based Hybrid Deep Learning Model in Splice Site Prediction

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Chinese Journal of Electronics 2022年第5期31卷 870-887页

作者： YAN Wenjing ZHANG Baoyu ZUO Min ZHANG Qingchuan WANG Hong MAO Da Division of Chemical metrology and Analytical Science National Institute of Metrology National Engineering Laboratory for Agri-Product Quality Traceability Beijing Technology and Business University

Pre-mRNA splicing is an essential procedure for gene transcription. Through the cutting of introns and exons, the DNA sequence can be decoded into different proteins related to different biological *** cutting boundaries are defined by the donor and acceptor splice sites. Characterizing the nucleotides patterns in detecting splice sites is sophisticated and challenges the conventional methods. Recently, the deep learning frame has been introduced in predicting splice sites and exhibits high performance. It extracts high dimension features from the DNA sequence automatically rather than infers the splice sites with prior knowledge of the relationships, dependencies, and characteristics of nucleotides in the DNA sequence. This paper proposes the Attention Splice model, a hybrid construction combined with multi-head self-attention, convolutional neural network, bidirectional long short-term memory *** performance of Attention Splice is evaluated on the Homo sapiens(Human) and Caenorhabditis Elegans(Worm) datasets. Our model outperforms state-of-the-art models in the classification of splice sites. To provide interpretability of Attention Splice models, we extract important positions and key motifs which could be essential for splice site detection through the attention learned by the model. Our result could offer novel insights into the underlying biological roles and molecular mechanisms of gene expression.

关键词： Splice sites Multi-head self-attention Bioinformatics Deep-learning Long short-term memory (LSTM) Convolutional neural network (CNN)

Clock Differences Prediction Algorithm Based on EMD-SVM

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Chinese Journal of Electronics 2018年第1期27卷 128-132页

作者： ZHU Jiangmiao SUN Panpan GAO Yuan ZHENG Pengfei College of Electronic Information and Control Engineering of beijing University of Technology National institute of metrology

A new prediction algorithm based on Empirical model decomposition(EMD) and Support vector machine(SVM) is put forward in this paper, and this algorithm solves the problem of the hydrogen atomic clock differences prediction, which is affected by the non-linearity and non-stability. The clock differences were decomposed into Intrinsic mode functions(IMF) and the residual *** suitable kernel function and parameters were chosen to build the different SVM for predicting each IMF and the residual series. Each prediction result was summed to obtain the clock differences prediction. Results show that the EMD-SVM algorithm is effective compared with the linear regression and single SVM. The relative prediction error is reduced from 0.4327% to 0.2371%, and the dispersion is less than other methods.

关键词： Empirical model decomposition(EMD) Support vector machine(SVM) Clock differences prediction

Calibration of the superconducting gravimeter based on a cold atom absolute gravimeter at NIM

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Chinese Physics B 2018年第12期27卷 250-255页

作者： Qiyu Wang Jinyang Feng Shaokai Wang Wei Zhuang Yang Zhao Lishuang Mou Shuqing Wu National institute of metrology Beijing 100029China China Jiliang University Hangzhou 310018China

The scale factor of a superconducting gravimeter(SG) is usually calibrated by using simultaneous and co-located gravity measurements with the FG5-type absolute gravimeter(AG). In this paper, another new kind of absolute gravimetercold atom gravimeter(CAG) is first reported to calibrate the SG. Five-day side-by-side gravity measurements have been carried out by using our CAG(NIM-AGRb-1) to calibrate the SG(iGrav-012) located at Changping Campus of the National institute of metrology(NIM) of China. A weighted least-squares method is applied to determine the scale factor and the result is given as(-928.01 ± 0.73) nm·s^(-2)·V^(-1) with a precision of 0.79‰. We have demonstrated that a calibration precision of 1‰ level can be achieved after 3 days of parallel observations at spring tide. The obtained calibration results are then compared with the previous calibration by FG5 X-249, which shows that the calibration precision obtained by using NIM-AGRb-1 was slightly higher than FG5 X-249 with the same time interval. The factors affecting the calibration precision are analyzed in the calibrations by means of different AGs. Finally, several calibration experiments for SG iGrav-012 are discussed. The final scale factor is estimated as(-927.58 ± 0.36) nm·s^(-2)·V^(-1) with an accuracy of 0.39‰. Our main results demonstrate that the CAGs can be used for high-precision calibrations of SGs.

关键词： cold atom gravimeter calibration superconducting gravimeter scale factor

Optical state selection process with optical pumping in a cesium atomic fountain clock

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Chinese Physics B 2021年第8期30卷 269-274页

作者： Lei Han Fang Fang Wei-Liang Chen Kun Liu Ya-Ni Zuo Fa-Song Zheng Shao-Yang Dai Tian-Chu Li School of Optics and Photonics Beijing Institute of TechnologyBeijing 100081China Key Laboratory of Time and Frequency Standards National Institute of Metrology(NIM)Beijing 100029China

We propose and realize a new optical state selection method on a cesium atomic fountain clock by applying a two-laser 3-3'optical pumping configuration to spin polarize *** atoms are prepared in|F=3,mF=0>clock state with optical pumping directly after being launched up,followed by a pushing beam to push away the atoms remaining in the|F=4>*** a state selection efficiency exceeding 92%,this optical method can substitute the traditional microwave state selection,and helps to develop a more compact physical package.A Ramsey fringe has been achieved with this optical state selection method,and a contrast of 90%is obtained with a full width half maximum of 0.92 *** short-term frequency stability of 6.8×10^(-14)(τ/s)^(-1/2) is *** addition,the number of detected atoms is increased by a factor of 1.7 with the optical state selection.

关键词： optical pumping atomic fountain clock spin polarization optical state selection

Fabrication of Triplexers Based on Flattop SOI AWG

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Chinese Physics Letters 2008年第5期25卷 1717-1719页

作者：安俊明吴远大李健李建光王红杰李俊一胡雄伟 F&D Center of Optoelectronics Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 National institute of metrology Beijing 100013

A triplexer is fabricated based on SOI arrayed waveguide gratings （AWGs）. Three wavelengths of the triplexer operate at different diffraction orders of an arrayed waveguide grating. The signals of 1490nm and 1550nm, which are input from central input waveguide of an AWG, are demultiplexed and the signal of 131Onto, which is input from central output waveguide of an AWG, is uploaded. The tested results show that the downloaded and uploaded signals have fiat-top response. The insertion loss is 9 dB on chip, the nonadjacent crosstalk is less than -30 dB for 1490nm and 1301 nm, and is less than -25 dB for 1550nm, the 3dB bandwidth equates that of the input light source.

关键词： supernova explosion proto-neutron star shock wave

Modeling of terahertz pulse generation from LT-GaAs ultrafast photoconductive switches

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Journal of Systems Engineering and Electronics 2011年第3期22卷 373-380页

作者： Zhe Ma ongmei Ma Chuntao Yang Keming Feng beijing institute of Radio metrology and Measurement Beijing 100854P.R.China eijing institute of Electronic System Engineering Beijing 100854P.R.China

The technique of terahertz pulses generated from the photoconductive switches has been applied in the ultrafast electrical pulse metrology recently.A lumped-element theoretical model is established to describe the performance of the LT-GaAs ultrafast photoconductive switch used in the ultrafast pulse *** carrier transport processes of the photoexcited semiconductor,the attenuation and dispersion during terahertz pulse propagating are considered in the theoretical *** to the experimental parameters,the waveforms of the generated terahertz pulses are calculated under optical excitations with different wavelengths of 840 nm and 450 nm,*** comparisons between the theoretical results and the experimental results are carried out.

关键词： terahertz pulse photoconductive switch coplanar waveguide LT-GaAs.

Observation of Spin Polarized Clock Transition in 87Sr Optical Lattice Clock

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Chinese Physics Letters 2014年第12期31卷 45-48页

作者：王强林弋戈李烨林百科孟飞臧二军李天初方占军 National institute of metrology Beijing 100013 Department of Precision Instrument Tsinghua University Beijing 100084

Atomic clocks operating at optical frequencies, with much better accuracy compared with microwave atomic clocks, have been assumed to be the next- generation time and frequency standards, Many applications will benefit from this lower frequency un- certainty of optical clocks, such as the re-definition of ＇the second＇, i.e. one of the seven base units of the international system of units （SI）, test of the time variation of fundamental physical constants and rel- ativity geodesy. Recently, the neutral atom lattice clock has achieved a lower frequency uncertainty com- pared with the optical ion clock, mainly due to the im- provement of the clock laser frequency stability refer- enced to a long high-finesse ULE cavity and the more accurate evaluation of black-body radiation shift. Strontium is an excellent candidate for the neutral atom optical clock. For the fermionic isotope of stron- tium, it has intrinsically less collision shift and the first order Zeeman shift can be removed by an inter- leaved probing ***, through the pre-cise measurement of the polarizability of strontium, the black body radiation （BBR） shift of the stron- tium lattice clock, which remains to be the limitation factor of its total frequency uncertainty, is reduced to a lower 10^-18 *** instability of the strontium lattice clock has reached 3.1 × 10-16/√T, showing the significant advantage over the single ion optical clock. The total systematic uncertainty has reached 6.4 × 10^-18 in fractional frequency, which is the best among all optical clocks until now.

关键词： SPIN polarization OPTICAL lattices PHASE transformations (Physics) LASER cooling FERMIONS SEMICONDUCTOR lasers

Technology and test results of space adaptability of passive hydrogen maser

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Journal of Systems Engineering and Electronics 2017年第2期28卷 251-256页

作者： Hefei Zheng Lianshan Gao Keming Feng Jing Li Wenming Wang Chunyan Cao Jihong Zhang beijing institute of Radio metrology and Measurement Beijing 100854 China The Second Academy of China Aerospace Science and Industry Corporation Beijing 100854 China

Based on the operating principle and the electric property design of the passive hydrogen maser, the technology and test results of its space adaptability are carried out under the special launch conditions and space environment. The various perturbations affecting the output frequency of such a standard used for the navigation satellite system are specified, such as magnetic field change, vibration, thermal vacuum and radiation. Through the adaptability technology in the aspects above, the security and reliability of the space passive hydrogen maser sufficiently fulfill the requirements of space operation. At present, the space passive hydrogen maser is working normally on board, indicating that the space adaptability satisfies the design requirement.

关键词： passive hydrogen maser space adaptability performance test