ISSN 0253-2778

CN 34-1054/N

2014 Vol. 44, No. 5

Display Method:
Recent advances on surface implicitization
CHEN Falai
2014, 44(5): 345-361. doi: 10.3969/j.issn.0253-2778.2014.05.001
The procedure of converting the parametric equation of a curve or a surface into the implicit equation is called implicitization. Implicitization is a classic elimination problem in algebraic geometry and has found important applications in computer aided geometric design — an inter-discipline in computer science and scientific computing. The classic methods for implicitization were reviewed first, and then the state of the art techniques in curve and surface implicitization were surveryed, especially the recent advances of the moving curves/surfaces method and μ basis method developed in the last decade.
Quantum computation based on nitrogen-vacancy center in diamond
WANG Pengfei, SHI Fazhan, DU Jiangfeng
2014, 44(5): 362-373. doi: 10.3969/j.issn.0253-2778.2014.05.002
Quantum computation technology is one of the hottest topics in physics for the past decades. It opens up a new way for computing. Mainly, quantum computation is aimed to build quantum information processing system based on quantum technology, which is much faster to solve hard problems than classic computers. A good quantum system is necessary to build a quantum computer. Thanks to its ability in manipulation, quantum spin system has become one of the best candidates for quantum computer. The quantum superposition, entanglement, and measurement show the quantum nature of spin. The demonstration of quantum computer on electronic spin ensemble was realized years ago. However, many quantum effects hide in the ensemble observation. It was only in recent years that some quantum effects have been observed in pure, single and individual quantum systems such as nitrogen-vacancy (NV) centers in diamond. The electronic spin state of a NV center can be initialized, manipulated and read out at room temperature. Thus it becomes a best candidate for scalable quantum computer. In this paper, a review of quantum computation based on NV centers in diamond was given. Then, some experiments in nanoscale detection and imaging were reviewed. Finally, its future was discussed.
Research activities in Keda axisymmetric tandem mirror experiment
SUN Xuan, LIU Ming, XIE Jinlin, YU Yi, LIN Munan, ZHANG Qing
2014, 44(5): 374-381. doi: 10.3969/j.issn.0253-2778.2014.05.003
Magnetic mirror and its derivatives hold the key to commercializing fusion energy. However, the axial particle loss and MHD (magnetohydrodynamics) interchange mode have impeded the development of mirror programs. Recently, a tandem mirror in combination with kinetic stabilizer has been proposed to cope with these two major hurdles. KMAX (Keda mirror with axisymmetricity), consisting of one central cell and two plug cells, is being built to fully investigate particle confinement and MHD instabilities. A new approach based on the success of RMF (rotating magnetic field) application in FRCs will be employed to extend the research area of tandem mirror. Despite fusion relevant experiments, KMAX will be also devoted to laboratory simulated space plasma, such as magnetic reconnection, Alfven wave heating and other fundamental processes in space plasmas.
Bacterial motility and chemotaxis signaling network
YUAN Junhua
2014, 44(5): 382-388. doi: 10.3969/j.issn.0253-2778.2014.05.004
Bacterial motility is essential for their survival and virulence. It is powered by motility motors, controlled by signal transduction systems. E. coli and its relative Salmonella enterica have been commonly used for studies of bacterial motility. Their swimming motility is powered by rotation of flagella driven by the bacterial flagellar motor, and is controlled by the bacterial chemotaxis signaling network. This paper reviewed recent progress on studies of bacterial flagellar motor and chemotaxis signaling network, and presented perspectives on future directions.
Low-dimensional boron nitride nanomaterials
LI Xiuling, WU Xiaojun
2014, 44(5): 389-402. doi: 10.3969/j.issn.0253-2778.2014.05.005
Extensive studies of low-dimensional carbon nanomaterials have attracted tremendens attention to the allotropes of other elements. Boron nitride nanomaterials are structurally analogous to carbon nanomaterials, but possess quite different properties. Unlike metallic or semiconducting carbon nanotubes (CNTs), the boron nitride nanotubes (BNNTs) are electrical insulators, basically independent of their diameters and chirality. BNNTs possess high thermal conductivity, excellent mechanical properties, and high chemical stability. The same advantages are applicable to two-dimensional monolayer boron nitride sheets. These unique properties make BNNTs and BN sheets promising nanomaterials in many potential fields, such as optoelectronic nanodevices, functional composites, hydrogen storage, and catalyze. This paper reviewed our theoretical studies on the BNNTs and BN sheets, including their electronic properties, chemical modification, defects, hydrogen storage and boron nitride super-architecture.
Multiple magnetic clouds in interplanetary space: A review and perspective
WANG Yuming
2014, 44(5): 403-415. doi: 10.3969/j.issn.0253-2778.2014.05.006
Multiple magnetic clouds are a particular complex structure in interplanetary space. They are formed due to the chase and interaction between successive coronal mass ejections (CME), and thought to be significantly geoeffective. The multiple-magnetic-cloud structure was first reported in 2002, and lots of relevant research has been carried out since. This paper gives a brief review of research on multiple magnetic clouds, in which the following issues are addressed. ① What is the magnetic cloud? ② What is the multiple-magnetic-cloud structure? ③ Why do we study the multiple-magnetic-cloud structure? ④ What is the challenge?
Coordination and optimization for operations systems: Theory and method
HUA Zhongsheng
2014, 44(5): 416-424. doi: 10.3969/j.issn.0253-2778.2014.05.007
Coordination and optimization for an operational system aims to improve the operational efficiency of the system and its ability to cope with uncertain environments. This kind of research problem is characterized by nonlinearity, multiple objectives, variable structures and uncertain information, and has always been a hot and difficult topic in operations management. By taking the theoretical and practical problems in operations systems as the research subject, in-depth research was conducted from the perspectives of demand forecasting, system design, operations and risk control. Specifically, focus was laid on non-stationary demand forecasting and decision-making, supply chain coordination and integrated design, as well as risk prediction and control for operations systems. Some original results have been obtained, which to some extent promote the development of the research in corresponding directions.
Advanced progress of two dimensional carbon-based materials
SONG Li, WU Peng, LIU Qin, CHEN Wenxing
2014, 44(5): 425-438. doi: 10.3969/j.issn.0253-2778.2014.05.008
Graphene, consisting of a hexagonal arrangement of carbon atoms on a single plane with sp2 bond, is the two dimensional (2D) allotrope of carbon with a number of unique properties. Prompted by the blossoming research in graphene, much attention has been focused on graphene hybrids and other 2D materials, i.e. hexagonal boron nitride, TMDs (transition metal dichalcogenides), silicene, etc. This paper presents a brief review of the history and status quo of researches on carbon-based 2D atomic layers, especially graphene and its related hybrids with boron and nitrogen, along with a discussion about what can be expected of studies on 2D carbon-based new materials in the near future.
Landau damping and energy conservation
QING Hong, WANG Xiaogang, LIU Wandong, ZHENG Jian
2014, 44(5): 439-443. doi: 10.3969/j.issn.0253-2778.2014.05.009
Landau damping is a collisionless dissipation process for electrostatic plasma waves governed by the linearized Vlasov-Poisson equations. Its physical mechanism is still being debated. It is commonly believed that Landau damping is caused by the energy exchange between waves and particles. However, this picture is not compatible with the linearized Vlasov-Poisson system, because the kinetic energy of particles in the linearized Vlasov-Poisson system is conserved, and the energy of the electrical field cannot be converted into the kinetic energy for the particles. We derived an energy relation that is fully consistent with the linearized Vlasov-Poisson system. It is shown that this energy relation is an exact statement of Landau damping, and thus the most accurate physical picture for it.
Post stroke examination with evoked and voluntary surface EMG: A study with hypothenar muscles
YAO Bo, LI Xiaoyan, RUAN Yuwen, ZHOU Ping
2014, 44(5): 444-450. doi: 10.3969/j.issn.0253-2778.2014.05.010
By applying evoked and voluntary surface electromyography (EMG) recordings, motor unit changes in paretic hypothenar muscles of stroke survivors were examined. Eleven stroke subjects participated in the study. The maximum M waves and voluntary surface EMG signals at different muscle contraction levels were recorded from the hypothenar muscles bilaterally in each subject. The motor unit number index (MUNIX) values were estimated from the mathematical model describing the relation between the surface EMG signal and the ideal motor unit number count derived from M wave and surface EMG measurements. A decrease in both the maximum M wave amplitudes and the estimated MUNIX values was observed in paretic muscles of the stroke subjects compared with the contralateral muscles. But no significance was found. The ratio between the maximum voluntary EMG to compound muscle action potential was significantly deceased in paretic muscles compared with the contralateral side. These findings, in combination with previous simulation and experiment outcomes, provide evidence of muscle activation deficiency and complex neuromuscular changes post stroke, thus helping understand complicated determinants of paretic muscle weakness for stroke rehabilitation.