A SPACE-TIME DISCONTINUOUS GALERKIN METHOD FOR FIRST ORDER HYPERBOLIC SYSTEMS

Tie Zhang,Jingna Liu 대한수학회 2014 대한수학회지 Vol.51 No.4

We present a new space-time discontinuous Galerkin (DG) method for solving the time dependent, positive symmetric hyperbolic systems. The main feature of this DG method is that the discrete equa- tions can be solved semi-explicitly, layer by layer, in time direction. For the partition made of triangle or rectangular meshes, we give the stability analysis of this DG method and derive the optimal error estimates in the DG-norm which is stronger than the L₂-norm. As application, the wave equation is considered and some numerical experiments are provided to illustrate the validity of this DG method.

Laboratory Confirmation of A Suspicious Meningococcal Meningitis Death Case

Tie-gang Zhang,Li-juan Chen,Jie Yang,Zhu-jun Shao,Xiong He,Jing-guo He,Ming Luo,Mei-ping Sun 한국미생물학회 2006 The journal of microbiology Vol.44 No.4

A suspicious meningococcal meningitis death case was reported to the Beijing CDC. The blood specimen was analyzed via multi-PCR and MLST. 6 isolates from close contacts were analyzed via PFGE and MLST. According to the results of the above analyses, the cause of this case was identified as a serogroup A Neisseria meningitidis, which, in terms of sequence typing, belonged the ST7 group.

A SPACE-TIME DISCONTINUOUS GALERKIN METHOD FOR FIRST ORDER HYPERBOLIC SYSTEMS

Zhang, Tie,Liu, Jingna Korean Mathematical Society 2014 대한수학회지 Vol.51 No.4

We present a new space-time discontinuous Galerkin (DG) method for solving the time dependent, positive symmetric hyperbolic systems. The main feature of this DG method is that the discrete equations can be solved semi-explicitly, layer by layer, in time direction. For the partition made of triangle or rectangular meshes, we give the stability analysis of this DG method and derive the optimal error estimates in the DG-norm which is stronger than the $L_2$-norm. As application, the wave equation is considered and some numerical experiments are provided to illustrate the validity of this DG method.

Robotic Curved Surface Tracking with a Neural Network for Angle Identification and Constant Force Control based on Reinforcement Learning

Tie Zhang,Meng Xiao,Yan-biao Zou,Jia-dong Xiao,Shou-yan Chen 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.5

Aiming to solve the problem that the contact force at a robot end eff ector when tracking an unknown curved-surface workpieceis diffi cult to keep constant, a robot force control algorithm based on reinforcement learning is proposed. In this paper,a contact model and force mapping relationship are established for a robot end eff ector and surface. For the problem thatthe tangential angle of the workpiece surface is diffi cult to obtain in the mapping relationship, a neural network is used toidentify the tangential angle of the unknown curved-surface workpiece. To keep the normal force of the robot end eff ectorconstant, a compensation term is added to a traditional explicit force controller to adapt to the robot constant force trackingscenario. For the problem that the compensation term parameters are diffi cult to select, the reinforcement learning algorithmA2C (advantage actor critic) is used to fi nd the optimal parameters, and the return function and state values are modifi edin the A2C algorithm to satisfy the robot tracking scenario. The results show that the neural network algorithm has a goodrecognition eff ect on the tangential angle of the curved surface. The force error between the normal force and the expectedforce is substantially within ± 2 N after 60 iterations of the robot force control algorithm based on A2C; additionally, thevariance of the force error decreases by 50.7%, 34.05% and 79.41%, respectively, compared with the force signals obtainedby a fuzzy iterative algorithm and an explicit force control with two sets of fi xed control parameters.

Trajectory tracking control of a 3-CRU translational parallel robot based on PD+robust controller

Tie Zhang,Guangcai Ma,Yachao Cao 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.8

In order to suppress the external disturbances existing in the trajectory tracking process of the 3-CRU parallel robot, a trajectory tracking control method based on PD+robust controller is proposed in this paper. The kinematic model of the 3-CRU parallel robot is established to solve the kinetic energy and potential energy of the system. The basic dynamic model of the 3-CRU parallel robot is obtained based on Lagrangian formulation, and the complete dynamic model of the parallel robot is established by introducing Coulomb and viscous friction. Based on the analysis of the factors affecting the stability of PD controller, a trajectory tracking control method based on PD+robust controller is proposed, and it is proved theoretically that the system converges stably and has a good external disturbance suppression effect. The method has the characteristics of easy implementation and strong applicability of PD controller and strong robustness of robust controller. Experimental results prove the effectiveness of this method.

Physical properties and chemical composition of the cores in the California molecular cloud

Zhang, Guo-Yin,Xu, Jin-Long,Vasyunin, A. I.,Semenov, D. A.,Wang, Jun-Jie,Dib, Sami,Liu, Tie,Liu, Sheng-Yuan,Zhang, Chuan-Peng,Liu, Xiao-Lan,Wang, Ke,Li, Di,Wu, Zhong-Zu,Yuan, Jing-Hua,Li, Da-Lei,Gao, Springer-Verlag 2018 Astronomy and astrophysics Vol.620 No.-

<P><I>Aims.</I> We aim to reveal the physical properties and chemical composition of the cores in the California molecular cloud (CMC), so as to better understand the initial conditions of star formation.</P><P><I>Methods.</I> We made a high-resolution column density map (18.2′′) with <I>Herschel</I> data, and extracted a complete sample of the cores in the CMC with the fellwalker algorithm. We performed new single-pointing observations of molecular lines near 90 GHz with the IRAM 30m telescope along the main filament of the CMC. In addition, we also performed a numerical modeling of chemical evolution for the cores under the physical conditions.</P><P><I>Results.</I> We extracted 300 cores, of which 33 are protostellar and 267 are starless cores. About 51% (137 of 267) of the starless cores are prestellar cores. Three cores have the potential to evolve into high-mass stars. The prestellar core mass function (CMF) can be well fit by a log-normal form. The high-mass end of the prestellar CMF shows a power-law form with an index <I>α</I> = −0.9 ± 0.1 that is shallower than that of the Galactic field stellar mass function. Combining the mass transformation efficiency (<I>ε</I>) from the prestellar core to the star of 15 ± 1% and the core formation efficiency (CFE) of 5.5%, we suggest an overall star formation efficiency of about 1% in the CMC. In the single-pointing observations with the IRAM 30m telescope, we find that 6 cores show blue-skewed profile, while 4 cores show red-skewed profile. [HCO<SUP>+</SUP>]/[HNC] and [HCO<SUP>+</SUP>]/[N2H<SUP>+</SUP>] in protostellar cores are higher than those in prestellar cores; this can be used as chemical clocks. The best-fit chemical age of the cores with line observations is ~5 × 10<SUP>4</SUP> yr.</P>

Laboratory Confirmation of A Suspicious Meningococcal Meningitis Death Case

Zhang Tie-Gang,He Xiong,Chen Li-Juan,He Jing-Guo,Luo Ming,Yang Jie,Shao Zhu-Jun,Sun Mei-Ping The Microbiological Society of Korea 2006 The journal of microbiology Vol.44 No.4

A suspicious meningococcal meningitis death case was reported to the Beijing CDC. The blood specimen was analyzed via multi-PCR and MLST. 6 isolates from close contacts were analyzed via PFGE and MLST. According to the results of the above analyses, the cause of this case was identified as a serogroup A Neisseria meningitidis, which, in terms of sequence typing, belonged the ST7 group.

MiRNA Synergistic Network Construction and Enrichment Analysis for Common Target Genes in Small-cell Lung Cancer

Zhang, Tie-Feng,Cheng, Ke-Wen,Shi, Wei-Yin,Zhang, Jin-Tao,Liu, Ke-Di,Xu, Shu-Guang,Chen, Ji-Quan Asian Pacific Journal of Cancer Prevention 2012 Asian Pacific journal of cancer prevention Vol.13 No.12

Background: Small-cell lung cancer (also known as SCLC) is an aggressive form and untreated patients generally die within about 3 months. To obtain further insight into mechanism underlying malignancy with this cancer, an miRNA synergistic regulatory network was constructed and analyzed in the present study. Method: A miRNA microarray dataset was downloaded from the NCBI GEO database (GSE27435). A total of 546 miRNAs were identified to be expressed in SCLC cells. Then a miRNA synergistic network was constructed, and the included miRNAs mapped to the network. Topology analysis was also performed to analyze the properties of the synergistic network. Consequently, we could identified constitutive modules. Further, common target genes of each module were identified with CFinder. Finally, enrichment analysis was performed for target genes. Results: In this study, a miRNA synergistic network with 464 miRNAs and 2981 edges was constructed. According to the topology analysis, the topological properties between the networks constructed by LC related miRNAs and LC unrelated miRNAs were significantly different. Moreover, a module cilque0 could be identified in our network using CFinder. The module included three miRNAs (hsa-let-7c, hsa-let-7b and hsa-let-7d). In addition, several genes were found which were predicted to be common targets of cilque0. The enrichment analysis demonstrated that these target genes were enriched in MAPK signaling pathways. Conclusions: Although limitations exist in the current data, the results uncovered here are important for understanding the key roles of miRNAs in SCLC. However, further validation is required since our results were based on microarray data derived from a small sample size.

The Molecular Characterization of Serogroup C Neisseria meningitidis Strains Circulating in Beijing

Zhang, Tie-Gang,He, Jing-Guo,He, Xiong,Chen, Li-Juan,Shao, Zhu-Jun,Sun, Mei-Ping The Microbiological Society of Korea 2006 The journal of microbiology Vol.44 No.6

The aim of this study was to characterize the molecular features of serogroup C Neisseria meningitidis strains circulating in Beijing, China. Twenty out of 23 strains belonged to ST 4821. The causative serosubtype for meningococcal meningitis was P1.12-1,16-8. All of the strains expressed class 3 PorB protein. Among the five pulsed-field gel electrophoresis patterns observed, pattern III predominated.

Time-optimal and Smooth Trajectory Planning for Multi-axis Motion Systems Based on ISC Similarity

Tie Zhang,Jia Cheng,Yanbiao Zou 제어·로봇·시스템학회 2024 International Journal of Control, Automation, and Vol.22 No.4

Aiming at time-optimal smooth trajectory planning for multi-axis motion systems, this paper proposes a planning algorithm based on improved sqrt-cosine (ISC) similarity in the phase plane. The improved sqrt-cosine similarity algorithm and the kinematic constraint of the interpolated trajectories are used to find the time-optimal smooth trajectory. In the proposed algorithm, the trajectory of the multi-axis motion system workbench is represented by scalar path coordinates. And it is re-discretized by adjusting the spacing of the discrete points several times to obtain trajectories with different numbers of discrete points. The corresponding time-optimal trajectories in the phase plane are planned through a numerical integration-like algorithm. The similarity between the timeoptimal trajectories is then compared using an improved sqrt-cosine similarity algorithm to find the trajectories with high similarity. Finally, the time-optimal smooth trajectory is obtained by the acceleration constraint of the interpolated trajectory. Experiments on a two-axis motion system have shown that the time-optimal trajectory planned by the proposed algorithm satisfied the constraints of dynamics and kinematics, effectively reduced the planning calculation time, and obtained a smooth trajectory. In experiments, compared with numerical integration-like timeoptimal trajectory planning algorithm, the maximum accelerations in the Z-axis, X-axis, and vertical directions of the two-axis motion system have been reduced by 37.66%, 11%, and 31.42%, respectively.