Track reconstruction in the BESⅢ muon counter

The reconstruction algorithm for BESⅢ Muon Counter, MucRecAlg, is developed with the objectoriented language C＋＋ in BESⅢ offine software environment. MucRecAlg consists of the following functions：to find track seeds either from extrapolation of tracks in the main drift chamber or from the fired strips in muon counter, to select fired strips associated to the candidate tracks, to fit the candidate tracks with a linear or quadratic function and to calculate other parameters of the tracks for muon identification. Monte Carlo samples are generated to check the performance of the reconstruction package, such as reconstruction effciency, muon remaining rate and pion rejection rate, etc. The preliminary results show that the pion rejection rate is around 3%—4% while the muon remaining rate is better than 90% in 0.4—1.6 GeV/c momentum region, which meets the requirement as shown in the design report.     

Design and performance of a video-based laser beam automatic alignment system

A laser alignment system is applied to a high power laser facility for inertial confinement fusion. A design of the automated, close-loop laser beam alignment system is described. Its function is to sense beam alignment errors in a laser beam transport system and automatically steer mirrors preceding the sensor location as required to maintain beam alignment. The laser beam is sampled by a sensor package, which uses video cameras to sense pointing and centering errors. The camera outputs are fed to a personal computer, which includes video digitizers and uses image storage and software to sense the centroid of the image. Signals are sent through the computer to a stepper motor controller, which drives stepper motors on mirror mounts preceding the beam sampling location to return the beam alignment to the prescribed condition. Its optical principles and key techniques are given. The pointing and centering sensitivities of the beam alignment sensor package are analyzed. The system has been verified on the     

Telescope alignment based on the sharpness function of under-sampled images

The precise alignment of a high-performance telescope is a key factor to ensure the imaging quality. However, for telescopes with a wide field of view, the images are sometimes under-sampled. To study the effects of undersampled images on the precision of telescope alignment, numerical simulations are implemented with the stochastic parallel gradient descent algorithm. The results show that the alignment program can converge stably and quickly. However, with the reduction of the full width at half-maximum of images, the relative residual errors increase from 9.5% to 19.5%, and the wavefront errors raise from 0.0972λ to 0.1074λ, indicating that the accuracy of the alignment decreases.     

Calibration study of the X-T relation for the BESⅢ drift chamber

Offline calibration plays an important role in BES offline data processing. In order to achieve good spatial and momentum resolution, it is necessary to implement high precision offline calibration for the BES drift chamber. This paper studies the time-to-distance relations, which are important calibration constants for track reconstruction. The parameterization of the time-to-distance relation, studies of left-right asymmetry and studies of variation with entrance angle are performed. The impact of dead channels on the time-to-distance relation is given special attention in order to reduce the shift in measured momentum for tracks passing near dead cells. Finally we present the resolutions for barrel Bhabha events(|cos θ|< 0.8) from a J/ψ data set taken in 2012. The average spatial resolution is 123 μm and the momentum resolution for 1.548 Ge V/c Bhabha tracks is 11.9 Me V/c.     

Design and performance of a video-based laser beam automatic alignment system

A laser alignment system is applied to a high power laser facility for inertial confinement fusion.A designof the automated,close-loop laser beam alignment system is described.Its function is to sense beamalignment errors in a laser beam transport system and automatically steer mirrors preceding the sensorlocation as required to maintain beam alignment.The laser beam is sampled by a sensor package,whichuses video cameras to sense pointing and centering errors.The camera outputs are fed to a personalcomputer,which includes video digitizers and uses image storage and software to sense the centroid of theimage.Signals are sent through the computer to a stepper motor controller,which drives stepper motorson mirror mounts preceding the beam sampling location to return the beam alignment to the prescribedcondition.Its optical principles and key techniques are given.The pointing and centering sensitivities ofthe beam aligmnent sensor package are analyzed.The system has been verified on the multi-pass amplifier experimental system.     

Matched wavelength and incident angle for the diagnostic beam to achieve coherent grating tiling

Design and operation of a practical,accurate alignment diagnostic system is important for the grating tiling technology,which is supposed to be applied in a chirped-pulse amplification system to increase the output power.A diagnostic method is proposed and demonstrated for grating tiling.Provided that the wavelength and incident angle of the diagnostic beam are properly set,the far-field of the main laser beam and that of the diagnostic beam can vary in the same way with the tiling errors between the sub-aperture gratings.Therefore,rotational and translational errors can be controlled and compensated according to the far-field of the diagnostic beam.The real-time monitoring and alignment can be achieved without disturbing the main beam.     

Study of BESⅢ MUC offline software with cosmic-ray data

Cosmic-ray data of 90 M events have been collected and used for calibration,alignment as well as detector tuning. A special tracking algorithm for the BESⅢ muon counter is developed and verified with Monte-Carlo simulation and then further confirmed with the cosmic-ray data. The obtained strip resolutions are in good agreement with the design values. A new alignment approach for the BESⅢ muon counter is confirmed with the cosmic-ray data and proposed to be used in future analysis of experimental data.     

Study of the online event filtering algorithm for BESⅢ

The results of a study of event tagging strategies for elementary physics processes in the τ-charm region are presented. The algorithm for online event filtering is optimized by adopting the information provided by different sub-detectors according to their strengths and capacities. The algorithm is tested with various generated physics and background events. The results indicate that the algorithm satisfies the requirements of BESⅢ physics analysis and its     

Study of BESⅢ MUC offine software with cosmic-ray data

Cosmic-ray data of 90 M events have been collected and used for calibration,alignment as well as detector tuning. A special tracking algorithm for the BESⅢ muon counter is developed and verified with Monte-Carlo simulation and then further confirmed with the cosmic-ray data. The obtained strip resolutions are in good agreement with the design values. A new alignment approach for the BESⅢ muon counter is confirmed with the cosmic-ray data and proposed to be used in future analysis of experimental data.     

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation is proposed in this paper to improve the efficiency and accuracy of electromagnetic calculation. An image boundary extraction algorithm is developed to map the image on the geometric domain. Identification algorithm for the location of nodes in polygon area is proposed to determine the state of the node. To promote the average quality of the mesh and the efficiency of mesh generation, a novel force-based mesh smoothing algorithm is proposed. One test case and a typical electromagnetic calculation are used to testify the effectiveness and efficiency of the proposed algorithm. The results demonstrate that the proposed algorithm can produce a high-quality mesh with less iteration.     

Track reconstruction using the TSF method for the BESⅢ main drift chamber

We describe the algorithm to reconstruct the charged tracks for BESⅢ main drift chamber at BEPCⅡ, including the track finding and fitting. With a new method of the Track Segment Finder (TSF), the results of present study indicate that the algorithm can reconstruct the charged tracks over a wide range of momentum with high efficiency, while improving the robustness against the background noise in the drift chamber. The overall performances, including spatial resolution, momentum resolution and secondary vertices reconstruction efficiency, etc. satisfy the requirements of BESⅢ experiment.     

Effects of aligning pulse duration on the degree and the slope of nitrogen field-free alignment

Through theoretical analysis,we show how aligning pulse durations affect the degree and the time-rate slope of nitrogen field-free alignment at a fixed pulse intensity.It is found that both the degree and the slope first increase,then saturate,and finally decrease with the increasing pump duration.The optimal durations for the maximum degree and the maximum slope of the alignment are found to be different.Additionally,they are found to mainly depend on the molecular rotational period,and are affected by the temperature and the aligning pump intensities.The mechanism of molecular alignment is also discussed.     

A robust photometric calibration framework for projector-camera display system

A novel photometric calibration framework is presented for a projector-camera （ProCam） display system, which is currently under booming development. Firstly, a piecewise bilinear model and five 5-ary color coding images are used to construct the homography between the image planes of a projector and a camera. Secondly, a photometric model is proposed to describe the data flow of the ProCam display system for displaying color images on colored surface in a general way. An efficient self-calibration algorithm is correspondingly put forward to recover the model parameters. Aiming to adapt this algorithm to different types of ProCam display system robustly, a 3× 7 masking coupling matrix and a patches image with 1024 color samples are adopted to fit the complex channel interference function of the display system. Finally, the experimental results demonstrate the validity and superiority of this calibration algorithm for the ProCam display system.     

Track reconstruction using the TSF method for the BESm main drift chamber

We describe the algorithm to reconstruct the charged tracks for BESⅢmain drift chamber at BEPCⅡ,including the track finding and fitting.With a new method of the Track Segment Finder(TSF), the results of present study indicate that the algorithm can reconstruct the charged tracks over a wide range of momentum with high efficiency,while improving the robustness against the background noise in the drift chamber.The overall performances,including spatial resolution,momentum resolution and secondary vertices reconstruction efficiency,etc.satisfy the requirements of BESⅢexperiment.     

A meshless algorithm with moving least square approximations for elliptic Signorini problems

Based on the moving least square(MLS) approximations and the boundary integral equations(BIEs), a meshless algorithm is presented in this paper for elliptic Signorini problems. In the algorithm, a projection operator is used to tackle the nonlinear boundary inequality conditions. The Signorini problem is then reformulated as BIEs and the unknown boundary variables are approximated by the MLS approximations. Accordingly, only a nodal data structure on the boundary of a domain is required. The convergence of the algorithm is proven. Numerical examples are given to show the high convergence rate and high computational efficiency of the presented algorithm.     

Automatic generation of min-weighted persistent formations

This paper researched into some methods for generating min-weighted rigid graphs and min-weighted persistent graphs. Rigidity and persistence are currently used in various studies on coordination and control of autonomous multi-agent formations. To minimize the communication complexity of formations and reduce energy consumption, this paper introduces the rigidity matrix and presents three algorithms for generating min-weighted rigid and min-weighted persistent graphs. First, the existence of a min-weighted rigid graph is proved by using the rigidity matrix, and algorithm 1 is presented to generate the min-weighted rigid graphs. Second, the algorithm 2 based on the rigidity matrix is presented to direct the edges of min-weighted rigid graphs to generate min-weighted persistent graphs. Third, the formations with range constraints are considered, and algorithm 3 is presented to find whether a framework can form a min-weighted persistent formation. Finally, some simulations are given to show the efficiency of our research.     

Global vector-field reconstruction of nonlinear dynamical systems from a time series with SVD method and validation with Lyapunov exponents

A method for the global vector-field reconstruction of nonlinear dynamical systems from a time series is studied in this paper. It employs a complete set of polynomials and singular value decomposition (SVD) to estimate a standard function which is certtral to the algorithm. Lyapunov exponents and dimension, calculated from the differential equations of a standard system, are used for the validation of the reconstruction. The algorithm is proven to be practical by applying it to a Roessler system.     

Automated image processing algorithm for Young's fringe pattern analysis

An automatic of image processing for the analysis of Young's fringe pattern is proposed. A Young's fringe patttern is first FFT treated to get two patterns of 0 degree and 90 degree phase shifted. Regular two pattern shift algorithm is used to calculate the phase of the Young's pattern. One or two times of phase shift iteration are carried out to improve the phase. Then the phase is least square fitted to get a phase plane. The displacement magnitude and direction are eaasily induced from the phase plane. Because every step is full field treatment, very precise result is achieved. The algorithm is simple and easy to implement. Theory and experiment are presented to prove the proposal. A program is designed to execute the algorithm and the processing is automated by a Personal Computer with an image board.     

New chaotical image encryption algorithm based on Fisher–Yatess scrambling and DNA coding

Based on the Fisher–Yatess scrambling and DNA coding technology, a chaotical image encryption method is proposed. First, the SHA-3 algorithm is used to calculate the hash value of the initial password, which is used as the initial value of the chaotic system. Second, the chaotic sequence and Fisher–Yatess scrambling are used to scramble the plaintext,and a sorting scrambling algorithm is used for secondary scrambling. Then, the chaotic sequence and DNA coding rules are used to change the plaintext pixel values, which makes the ciphertext more random and resistant to attacks, and thus ensures that the encrypted ciphertext is more secure. Finally, we add plaintext statistics for pixel-level diffusion to ensure plaintext sensitivity. The experimental results and security analysis show that the new algorithm has a good encryption effect and speed, and can also resist common attacks.