时间关联单光子计数中的多光子污染

从推导光子时间概率密度分布函数出发,研究了时间关联单光子计数法测量荧光寿命中,多光子修正函数的特征及其对测量误差的影响,并给出了定理关系式。     

Real Time Correction and Evaluation of Nonlinear Errors in Single Frequency Interferometers

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Analysis of influence of atmosphere extinction to Raman lidar monitoring CO2 concentration profile

Lidar （Light detection and ranging） system monitoring of the atmosphere is a novel and powerful technique tool. The Raman lidar is well established today as a leading research tool in the study of numerous important areas in the atmospheric sciences. In this paper, the principle of Raman lidar technique measurement CO2 concentration profile is presented and the errors caused by molecular and aerosol extinction for CO2 concentration profile measurement with Raman lidar are also presented. The standard atmosphere extinction profile and ＇real-time＇ Hefei area extinction profile are used to conduct correction and the corresponding results are yielded. Simulation results with standard atmosphere mode correction indicate that the errors caused by molecule and aerosol extinction should be counted for the reason that they could reach about 8 ppm and 5 ppm respectively. The relative error caused by Hefei area extinction correction could reach about 6%. The errors caused by the two components extinction influence could produce significant changes for CO2 concentration profile and need to be counted in data processing which could improve the measurement accuracies.     

Localization of toric code defects

We explore the possibility of passive error correction in the toric code model. We first show that even coherent dynamics, stemming from spin interactions or the coupling to an external magnetic field, lead to logical errors. We then argue that Anderson localization of the defects, arising from unavoidable fluctuations of the coupling constants, provides a remedy. This protection is demonstrated by using general analytical arguments that are complemented with numerical results which show that self-correcting memory can in principle be achieved in the limit of a nonzero density of identical defects.     

Elastic electron scattering in an intense field and two-photon emission

The elastic scattering amplitude, taking into account the mass correction to the propagation function, is found for electrons interacting with an intense electromagnetic field characteristic of non-linear quantum electrodynamics. The probability for two-photon emission e → e2γ, the mass correction to the probability for one-photon emission and the mass correction to the anomalous field-dependent magnetic moment of the electron are found with the aid of the amplitude.     

基于时间序列的航天器遥测数据预测算法

在航天器遥测数据预测领域,基于时间序列的预测方法有着广阔的应用前景;时间序列有一明显的特性就是记忆性,记忆性是指时间数列中的任一观测值的表现皆受到过去观测值影响;它的基本思想是根据观测数据的特点为数据建立尽可能合理的统计模型,利用模型的统计特性解释数据的统计规律,以期达到预报的目的;提出了采用模式识别和参数估计的方法,结合航天器遥测动态数据,建立关于航天器遥测数据的时序预测模型,对航天器遥测数据趋势进行检测和预报。     

Impact of nonlinearities and model error on pseudo-inverse calculations

Pseudo-inverse calculations have been made within the operational and research meteorological communities to identify components of the error in the initial state that are responsible for a significant portion of the forecast error. These calculations are based on the assumptions of a perfect model and linear perturbation growth, conditions not realizable in operational forecasting. In this study, the impact of nonlinearities and model error on pseudo-inverse calculations is investigated within an idealized framework using a simple atmospheric model. Forecasts are run within the perfect and imperfect model frameworks, with initial errors of varying sizes. Model error is introduced by changing the model dissipation terms. It is found that for pseudo-inverses composed of a small subset of the leading singular vectors (SVs), the nonlinear forecast correction is often better than the expected theoretical correction, indicating the suppression of error growth both inside and outside the linear pseudo-inverse subspace. As the size of the pseudo-inverse is increased, the nonlinear forecast correction starts to degrade. This forecast degradation coincides with a degradation in the analysis correction. It is possible to improve the forecast by degrading the analysis in the presence of model error, especially when the initial error is very small. However, for initial errors of reasonable magnitude, this is unlikely to happen in instances when the nonlinear forecast correction is better than the theoretical correction. Just as improving the initial state may suppress errors outside of the linear SV subspace, degrading it may likewise increase errors outside the SV subspace. This suggests that the size of the nonlinear correction relative to the expected theoretical correction may be useful in determining when pseudo-inverse perturbations are likely to have improved the analyses.     

Bit error rate analysis with real-time pointing errors correction in free space optical communication systems

Pointing errors caused by the atmospheric turbulence will degrade the performance of free space optical (FSO) communication systems, especially the bit error rate (BER). In this paper, we innovatively analyze the relationship between BER and pointing errors by the probability density functions (PDFs) and intensity displacement in focal plane under the On-Off Keying (OOK) modulation conditions. The closed-loop experimental system is set up in laboratory, where the fast steering mirror (FSM) is real-time controlled by embedded controller with the parallel processing technology and the atmospheric turbulence is simulated by a turbulence simulation box. The results of repeated experiments show that the method of pointing errors correction we proposed is efficient under the conditions of atmospheric turbulence. By utilizing our method, the BER can decrease from nearly 10⁻³ to nearly or even below 10⁻⁹, thus improving the performance of FSO communication systems significantly.     

Earth-to-deep-space optical communications system with adaptive tilt and scintillation correction by use of near-Earth relay mirrors

Performance of an Earth-to-deep-space optical telecommunications system is degraded by distortion of the beam as it propagates through the turbulent atmosphere. Conventional approaches to correcting distortions, based on natural or artificial guide stars, have practical difficulties or are not adequate for correction of distortions, which are important for Earth-to-deep-space optical links. A beam-relay approach that overcomes these difficulties is discussed. A downward-directed laser near an orbiting relay mirror provides a reference for atmospheric correction. Adaptive optics at the ground station compensate the uplink beam so that after it passes through the atmosphere uplink propagation effects are removed. The orbiting mirror then directs the corrected beam to the distant spacecraft.     

Performance simulation of an adaptive optics system with liquid crystal corrector under closed-loop and open-loop control

The adaptive optics system (AOS) often operates in a discrete sampling process with finite closed-loop frequency. Reconstruction, detection, and time lag induced errors are the main correction errors of the system. An AOS that is based on a liquid crystal (LC) benefits from the LC’s high correction precision, thus the reconstruction error can be ignored. The primary error will be induced by the time lag from the time of detection to the time of compensation. In this paper, some theoretical simulations are introduced in order to evaluate the correction precision of AOS with an LC corrector. The main purpose is to compare the correction precision between the open-loop and closed-loop control. We attempt to find a method to ascertain the exact precision of the open-loop control and show whether it improves the correction precision. The conclusion is thus reached that the actual error rejection bandwidth for the closed-loop was lower than the −3 dB error rejection bandwidth measured in practice. The increased refresh frequency of the open-loop control can improve the imaging performance to nearly −3 dB bandwidth of the detector measured, which is the maximum possible bandwidth due to the time lag.     

Hybrid quantum repeater using bright coherent light

We describe a quantum repeater protocol for long-distance quantum communication. In this scheme, entanglement is created between qubits at intermediate stations of the channel by using a weak dispersive light-matter interaction and distributing the outgoing bright coherent-light pulses among the stations. Noisy entangled pairs of electronic spin are then prepared with high success probability via homodyne detection and postselection. The local gates for entanglement purification and swapping are deterministic and measurement-free, based upon the same coherent-light resources and weak interactions as for the initial entanglement distribution. Finally, the entanglement is stored in a nuclear-spin-based quantum memory. With our system, qubit-communication rates approaching 100 Hz over 1280 km with fidelities near 99% are possible for reasonable local gate errors.     

Fusion hindrance and roles of shell effects in superheavy mass region

We present the first attempt of systematically investigating the effects of shell correction energy for a dynamical process, which includes fusion, fusion–fission and quasi-fission processes. In the superheavy mass region, for the fusion process, shell correction energy plays a very important role and enhances the fusion probability when the colliding partner has a strong shell structure. By analyzing the trajectory in three-dimensional coordinate space with the Langevin equation, we reveal the mechanism of the enhancement of the fusion probability caused by ‘cold fusion valleys’. The temperature dependence of shell correction energy is considered.     

基于傅里叶频谱分析的相位测量轮廓术系统Gamma非线性校正方法

数字投影和成像系统的Gamma非线性效应是导致相位测量轮廓术（PMP）测量误差的重要原因。目前大多采用多帧条纹图进行Gamma校正,使测量的实时性受到限制。提出了一种Gamma校正方法,利用正交光栅像的傅里叶频谱分布计算Gamma值,再根据此Gamma值对投影相移条纹进行Gamma逆变换,实现投影条纹输入值的提前校正,以获取具有良好正弦性的结构条纹,从而降低PMP相位测量误差。校正过程中只需一帧条纹图,而且考虑了测量系统的离焦效应。实验证实了该方法的有效性和正确性。     

AN ESTIMATOR-BASED SLIDING-MODE CONTROL FOR MANEUVERING A FLEXIBLE SPACECRAFT

An estimator-based sliding-mode controller (ESMC) is discussed for a linear stochastic system with a known disturbance and is utilized in a flexible spacecraft for the reduction of residual vibration while allowing natural deflection during operation. By converting the tracking problem into a regulator problem, the ESMC minimizes the expected value of the guadratic objective function composed of errors which always remain in the intersection of sliding hypersurfaces. For the numerical evaluation to take place in a flexible with a flexible spacecraft, a large slewing maneuver strategy is devised, with a tracking model for the nominal trajectory. A start-coast-stop strategy for an economical maneuver is employed in conjunction with the input shaping technique. The performance and efficacy of the proposed control scheme are illustrated with a comparison of different maneuvering strategies.     

Analogue correction method of errors and its application to numerical weather prediction

In this paper, an analogue correction method of errors (ACE) based on a complicated atmospheric model is further developed and applied to numerical weather prediction (NWP). The analysis shows that the ACE can effectively reduce model errors by combining the statistical analogue method with the dynamical model together in order that the information of plenty of historical data is utilized in the current complicated NWP model. Furthermore, in the ACE, the differences of the similarities between different historical analogues and the current initial state are considered as the weights for estimating model errors. The results of daily, decad and monthly prediction experiments on a complicated T63 atmospheric model show that the performance of the ACE by correcting model errors based on the estimation of the errors of 4 historical analogue predictions is not only better than that of the scheme of only introducing the correction of the errors of every single analogue prediction, but is also better than that of the T63 model.     

Error analysis and lattice improvement for the C-ADS Injector-Ⅰ

The injector Scheme-Ⅰ (or Injector-Ⅰ) of the C-ADS linac is a 10 mA 10 MeV proton linac working in CW mode. It is mainly comprised of a 3.2 MeV room-temperature 4-vane RFQ and twelve superconducting single-spoke cavities housed in a long cryostat. Error analysis including alignment and field errors, and static and dynamic ones for the injector are presented. Based on detailed numerical simulations, an orbit correction scheme has been designed, which shows that with correction the rms residual orbit errors can be controlled within 0.3 mm and a beam loss rate of 1.7× 10^-6 is obtained. To reduce the beam loss rate further, an improved lattice design for the superconducting spoke cavity section has been studied.     

New algorithm of white-light phase shifting interferometry pursing higher repeatability by using numerical phase error correction schemes of pre-processor, main processor, and post-processor

White-light phase shifting interferometry (WLPSI) is frequently used for the precision measurement of 3D patterns in various fields. Phase error is one of the most dominant errors in WLPSI, and it is mainly generated by the scanner positioning error and mechanical vibrations. In this paper, phase error detection method by image analysis is proposed, and the numerical correction method for minimizing the phase error is also proposed. The image reconstruction method (IRM), iterative IRM (IIRM) as pre-processors, partial IRM (PIRM), least squares method (LSM) as a main processor, and surface compensation method (SCM) as a post-processor were developed for correcting phase errors. The five methods are implemented and simulated, and the pros and cons of each method are explained.Mirau type interferometry and the phase error generator using a PZT stage were used, and the measurements by WLPSI were done under various vibration conditions. The captured images were analyzed by the five correction methods, and the results were compared. Phase error was effectively minimized by the correction methods, and repeatability of 0.2 nm was obtained in the case of the specimen of 500 nm in height. Repeatability of 10 nm was obtained by conventional WLPSI algorithms for the same specimen.     

A method to evaluate error correction ability of computer controlled optical surfacing process

Quantitatively investigating error correction ability in frequency domain is important for computer controlled optical surfacing (CCOS) process to correct different spatial frequency errors. Based on the mathematical model coherence between filtering and material removal process of CCOS, a method is proposed to quantitatively evaluate the correction ability of CCOS process. A generalized model named normalized smoothing spectral function (SSF) will be established combine convolution model of CCOS and power spectral density (PSD) function. A set of polishing experiments are performed to calculate SSF curves and validate SSF model. By comparing the results of SSF curve with PSD curve and surface figure, it reveals that SSF curve can quantitatively indicate the correction ability of CCOS process for different spatial frequency errors.     

Particle filter-based relative rolling estimation algorithm for non-cooperative infrared spacecraft

The issue of feature point mismatching among infrared image sequence would bring big challenge to estimating the relative motion of non-cooperative spacecraft for it couldn’t provide the prior knowledge about its geometric structure and motion pattern. The paper introduces particle filter to precisely match the feature points within a desired region predicted by a kinetic equation, and presents a least square estimation-based algorithm to measure the relative rolling motion of non-cooperative spacecraft. The state transition equation and the measurement update equation of non-cooperative spacecraft are represented by establishing its kinetic equations, and then the relative pose measurement is converted to the maximum posteriori probability estimation via assuming the uncertainties about geometric structure and motion pattern as random and time-varying variables. These uncertainties would be interpreted and even solved through continuously measuring the image feature points of the rotating non-cooperative infrared spacecraft. Subsequently, the feature point is matched within a predicted region among sequence infrared image using particle filter algorithm to overcome the position estimation noise caused by the uncertainties of geometric structure and motion pattern. Finally, the position parameters including rotation motion are estimated by means of solving the minimum error of feature point mismatching using least square estimate theory. Both simulated and real infrared image sequences are induced in the experiment to evaluate the performance of the relative rolling estimation, and the experimental data show that the rolling motion estimated by the proposed algorithm is more robust to the feature extraction noise and various rotation speed. Meanwhile, the relative rolling estimation error would increase dramatically with distance and rotation speed increasing.     

广角红外地球敏感器光学系统设计及畸变校正

为了满足低轨道航天器姿态轨道控制系统对小型化地球敏感器的需求,对广角长波红外地球敏感器光学系统设计及成像畸变校正技术进行了研究。广角长波红外光学系统采用反远距结构形式,由三片锗透镜实现140°的视场角,光学系统工作波段为14 μm~16.25 μm,F数为0.8。广角长波红外光学系统体积小、结构简单,并且成像质量良好,实现了红外地球敏感器光学系统的小型化高精度设计。采用分视场区间分别建立畸变校正公式的方法来实现光学系统成像畸变校正,校正精度优于像元尺寸的1/5,可满足敏感器产品姿态测量的需求。