回旋管光子带隙谐振腔冷腔电磁模式分析

利用二维三角格子金属光子带隙谐振腔代替回旋管的传统柱形谐振腔,并对腔体进行了TE波模式的计算与分析.综合考虑腔体内外的结构特征,给出了光子带隙谐振腔冷腔模式理论的研究方法,发现腔内存在单模工作的可能与条件以及非角对称情况下的电磁模式分布特征.研究结果表明,利用光子带隙谐振腔代替回旋管的传统腔体,可使回旋管在不受腔体横向尺度限制的条件下实现单模工作.这对于提高回旋管的功率容量、有效实现高次单模与高次回旋谐波耦合条件下的注-波互作用、降低工作磁场并从物理上根本改变回旋管的工作状态提供了理论依据. 关键词： 回旋管 金属光子带隙 谐振腔     

Investigation of autoionization spectra of Sm atom usingisolated-core excitation method

<正>Using the isolated-core-excitation scheme and three-step laser resonance ionization spectroscopy approach,this paper,for the first time,has systematically investigated the autoionization spectra of atomic Sm,belonging to the 4f~66pnl and 4f~55d6snl(l=0,2) configurations.In the experiment,the first two tunable dye lasers are employed to excite the Sm atom from its initial state to the different 4f~66snl bound Rydberg states,then the third dye laser is scanned to drive the atom to the doubly-excited autoionizing states.With the above excitation scheme,the measured transition profiles of the autoionizing states are nearly symmetric,from which the level energies and widths can be easily obtained.     

相对论电子束在动态加载等离子体中的自聚焦传输

为了进一步研究相对论电子束-离子通道辐射实验和理论的需要, 研究了相对论电子束入射中性气体以及通过碰撞电离动态加载等离子体实现对高能束流的自聚焦传输过程PIC(particle in cell) 模拟发现, 电子束电离出的离子背景能够实现对电子束的聚焦传输. 但是离子背景横向和纵向的不均匀性对束流的传输特性有显著影响. 在此基础之上, 提出了电子束在横向不均匀离子背景中传输的理论模型, 给出了束流的自聚焦条件.数值计算结果表明, 横向不均匀性会导致电子束的混合相位传输, 使得焦点附近内层电子可能跑到电子束外而被散焦损失, 这与PIC模拟的结果相符. 此外, PIC模拟还发现, 由于电子束的自聚焦, 在焦点处将电离出更多的离子而引起纵向不均匀性, 纵向不均匀性使得碰撞后的低能电子被俘获, 俘获电子效应会大幅降低电子束的传输效率. 但是俘获电子在纵向呈准周期分布, 对传输电子起到静电Wiggler场的作用, 可能实现静电Wiggler场的动态加载. 研究结果对于进一步研究电子束-等离子体系统的实验以及理论模型提出有一定的参考价值.     

Multistep excitation of autoionizing states of the samarium atom

In this work, 4f ⁶6pnl and 4f ⁵5d6snl (l=0,2) autoionizing states of the samarium (Sm) atom, especially those with lower principal quantum number, have been studied, using the isolated-core excitation scheme with three dye lasers. In the energy region between 57 990 and 61 030 cm⁻¹, there are 74 autoionizing states of the Sm atom observed. These states can be classified into the autoionization series converging to four different ionization limits. In most cases, the line shapes of these autoionizing states are nearly symmetric, from which the level energies and widths can be easily obtained by fitting the experimental spectra to the Lorentzian profiles. In addition, several spectroscopic properties of these autoionizing states, such as configuration interaction, are also discussed.     

Nonlinear dynamic analysis of a hybrid squeeze-film damper-mounted rigid rotor lubricated with couple stress fluid and active control

The hybrid squeeze-film damper bearing with active control is proposed in this paper and the lubricating with couple stress fluid is also taken into consideration. The pressure distribution and the dynamics of a rigid rotor supported by such bearing are studied. A PD (proportional-plus-derivative) controller is used to stabilize the rotor-bearing system. Numerical results show that, due to the nonlinear factors of oil film force, the trajectory of the rotor demonstrates a complex dynamics with rotational speed ratio s. Poincaré maps, bifurcation diagrams, and power spectra are used to analyze the behavior of the rotor trajectory in the horizontal and vertical directions under different operating conditions. The maximum Lyapunov exponent and fractal dimension concepts are used to determine if the system is in a state of chaotic motion. Numerical results show that the maximum Lyapunov exponent of this system is positive and the dimension of the rotor trajectory is fractal at the non-dimensional speed ratio s = 3.0, which indicate that the rotor trajectory is chaotic under such operation condition. In order to avoid the nonsynchronous chaotic vibrations, an increased proportional gain is applied to control this system. It is shown that the rotor trajectory will leave chaotic motion to periodic motion in the steady state under control action. Besides, the rotor dynamic responses of the system will be more stable by using couple stress fluid.     

Fabrication of transparent double-walled carbon nanotubes flexible matrix touch panel by laser ablation technique

This study reports on the fabrication of transparent double-walled carbon nanotubes (DWNTs) flexible matrix touch panel using the method of laser ablation. We employed an Nd:YAG laser (1064 nm) to pattern transparent DWNT thin film pre-coated on a PET substrate and successfully fabricated a flexible matrix touch panel. By increasing the laser energy, the ablation depth of transparent DWNT flexible thin film is increased but the sheet resistance (Ω/sq) is decreased. When the laser energy intensity reaches 117 mJ/cm², the DWNTs can be completely ablated from transparent DWNT flexible thin film. This method is rapid, simple, applicable to large-area processing and thus is potential for mass production.     

Bifurcation and chaos analysis of spur gear pair with and without nonlinear suspension

This study performs a systematic analysis of the dynamic behavior of a single degree-of-freedom spur gear system with and without nonlinear suspension. The dynamic orbits of the system are observed using bifurcation diagrams plotted using the dimensionless damping coefficient and the dimensionless rotational speed ratio as control parameters. The onset of chaotic motion is identified from the phase diagrams, power spectra, Poincaré maps, Lyapunov exponents and fractal dimension of the gear system. The numerical results reveal that the system exhibits a diverse range of periodic, sub-harmonic and chaotic behaviors. The results presented in this study provide an understanding of the operating conditions under which undesirable dynamic motion takes place in a spur gear system and therefore serve as a useful source of reference for engineers in designing and controlling such systems.     

A Monte Carlo study for the shielding of γ backgrounds induced by radionuclides for CDEX

The CDEX(China Dark matter EXperiment)Collaboration will carry out a direct search for WIMPs(Weakly Interacting Massive Particles)using an Ultra-Low Energy Threshold High Purity Germanium(ULE-HPGe)detector at the CJPL(China JinPing deep underground Laboratory).A complex shielding system was designed to reduce backgrounds and a detailed GEANT4 Monte Carlo simulation was performed to study the achievable reduction of T rays induced by radionuclides and neutron backgrounds by D(γ,n)p reaction.Furthermore,the upper level of allowed radiopurity of shielding materials was estimated under the constraint of the expected goal.Compared with the radiopurity reported by other low-background rare-event experiments,it indicates that the shielding used in the CDEX can be made out of materials with obtainable radiopurity.     

NONLINEAR NUMERICAL ANALYSIS OF A FLEXIBLE ROTOR EQUIPPED WITH SQUEEZE COUPLE STRESS FLUID FILM JOURNAL BEARINGS

This study performs a dynamic analysis of a rotor supported by two squeeze couple stress fluid film journal bearings with nonlinear suspension.The numerical results show that the stability of the system varies with the non-dimensional speed ratios and the dimensionless parameter l*.It is found that the system is more stable with higher dimensionless parameter l*. Thus it can conclude that the rotor-bearing system lubricated with the couple stress fluid is more stable than that with the conventional Newtonian fluid.The modeling results thus obtained by using the method proposed in this paper can be used to predict the stability of the rotor-bearing system and the undesirable behavior of the rotor and bearing center can be avoided.