Open Resonators with Conducting Cylindrical Inserts. 1. Two-Dimensional Model

We present the results of computer simulation of the properties of modes in a two-dimensional open resonator with a conducting cylindrical insert. An increase in the diffraction Q-factor of the fundamental mode by 2–3 orders of magnitude due to the conducting cylindrical insert is found and studied. The prospects of using this phenomenon for controlling the spectrum, frequencies, and Q-factors of excited modes are discussed. The tunability of the open resonator with a conducting cylindrical insert for one (fundamental) mode in a wide frequency range is shown. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 7, pp. 596–604, July 2005.     

变反射率镜非稳腔的研究进展

回顾了变反射率镜非稳腔的研究历史,总结了实现变反射率的方法,分析了它们的优缺点,最后列表总结了典型使用VRM作为非稳腔输出耦合器的实验参数和结果.为大能量固体激光器的设计提供了理论和实验参考.     

High Performance Open Loop Control of Scanning with a Small Cylindrical Cantilever Beam

The steady-state response motion of a base excited cantilever beam with circular cross-section excited by a unidirectional displacement will fall along a straight line. However, achieving straight-line motion with a real cantilever beam of circular cross-section is difficult to accomplish. This is due to the fact that nonlinear effects, small deviations from circularity, asymmetric boundary conditions, and actuator cross coupling can induce whirling. The vast majority of previous work on cantilever beam whirling has focused on the effects of system nonlinearities. We show that whirling is a much broader problem in the design of resonant beam scanners in that the onset of whirling does not depend on large amplitude of motion. Rather, whirling is the norm in real systems due to small system asymmetries and actuator cross coupling. It is therefore necessary to control the growth of the whirling motion when a unidirectional beam motion is desired. We have developed a novel technique to identify the two eigen directions of the beam. Base excitation generated by virtual electrodes along these orthogonal eigen axes of the cantilever beam system generates tip vibration without whirl. This leads to accurate open loop control of the motion of the beam through the combined actuation of two pairs of orthogonally placed actuator electrodes.     

二维柱几何中子输运方程的并行区域分解方法

分析不同的区域分解方法及优先级插入算法对二维柱几何下中子输运方程S_n间断有限元方程并行效率的影响,给出基于最小面体比的正方形区域分解方法及沿径向的优先级插入算法,并通过将正方形区域分解方法与径向优先级插入算法进行组合,形成新的算法.新算法更适应于二维柱几何下输运方程S_n间断有限元方法的并行计算.数值试验表明,在通信延迟较高的大型国产并行机上,新算法用数百个CPU还可以取得较好的并行效果,比已有方法具有更良好的可扩展性.     

Cylindrical Fibre Orientation Analysis by Light Scattering. Part 2: Experimental Aspects

An experimental set-up has been designed to record maps of intensity distribution for two orthogonal polarizations allowing the retrieval of average information along the optical path. A wide variety of the signatures of different samples is given to characterize the spatial orientation of a cloud of infinite cylinders by using a light scattering method. The information contained in the images is discussed and compared with numerical predictions.     

Study of Fabry-Perot Cavities with Metal Mesh Mirrors Using Equivalent Circuit Models. Comparison with Experimental Results in the 60 GHz Band

The equivalent circuit modelling technique is used to study the resonant frequency and Q factor of plane parallel Fabry-Perot cavities with square aperture metal mesh mirrors. Comparison of different models found in literature with experimental data in the 60 GHz band is given for thin and thick cavities. Chen's model is shown to give a good agreement with measurements, as long as the cavity is not too selective and for large enough cavity.     

二维柱几何非定常中子输运方程基于格式的界面预估校正并行算法

针对二维柱几何非定常中子输运方程的Sn-间断有限元方法,提出基于格式的界面预估校正并行算法.数值算例表明,该并行算法在精度与并行度等诸方面均具有良好的性质,与已有的基于隐式格式的并行扫描算法相比,对于二维中子输运大规模计算问题,并行计算效率较高,并行加速比可增加-倍以上,且可保持原隐式格式的计算精度.     

New Charged Dilaton Solutions in 2+1 Dimensions and Solutions with Cylindrical Symmetry in 3+1 Dimensions

We report a new family of solutions to Einstein-Maxwell-dilaton gravity in 2+1 dimensions and Einstein-Maxwell gravity with cylindrical symmetry in 3+1 dimensions. A set of static charged solutions in 2+1 dimensions are obtained by a compactification of charged solutions in 3+1 dimensions with cylindrical symmetry. These solutions contain naked singularities for certain values of the parameters considered. New rotating charged solutions in 2+1 dimensions and 3+1 dimensions are generated treating the static charged solutions as seed metrics and performing SL(2;R) transformations.     

On the waves and instability in self-gravitating magnetic molecular clouds with ambipolar diffusion Part 2: Cylindrical modal approach and nonlinear effects

The dynamics and evolution of molecular clouds, which are the main sites of active star formation in our Galaxy, are governed by the interaction of the self-gravity, magnetic fields, and ambipolar diffusion, in the form of waves and instability. In our earlier paper (Part 1), we carried out a detailed planar modal analysis. The present paper (Part 2) is an extension of Part 1 in order to include the three-dimensionality and the finite size of the cloud as well as the nonlinear effects. A cylindrical modal approach is developed to take into account the three-dimensionality and the finite size of the cloud as well as the special direction of the mean field B ₀. Dispersion relation and solutions of such cylindrical modes are obtained. It is shown that, in the most unstable direction (∥ B ₀), the growth rate is considerably reduced by the finite lateral size compared with the planar mode of the same wavelength. Nonlinear effects of the magnetic field and magnetic waves are discussed, with particular attention paid to their dependence on the coupling factor σ which is the ratio between the mean collision frequency of a neutral with ions and the gravitational response frequency. It is shown that fast magnetosonic waves are as important as Alfvén waves in the global support of the cloud. In order that the lower limit of the wavelengths in the moderately dissipative range of such waves is small compared with the cloud size, σ should be larger than 5. It is also shown that σ should be larger than 7.3 in order for the density growth of the neutral fluid in a free-fall time to be smaller than 30%. A typical value of σ ≈ 11 in molecular clouds is estimated. This corresponds to an ionization rate ζ = 10^?17 and a metal depletion δ = 0.1. For the clouds with such value of σ, both the density growth and the flux loss are smaller than 20% in a free-fall time. It is shown that a self-adjusting mechanism is able to slow down the global collapse at the early stage of cloud evolution in terms of the interaction between the global collapse and the then existing Alfvén and fast magnetosonic waves, which originate from the inhomogeneous velocity and density distributions in the cloud. Such interaction will not only strengthen these waves, but also create outwards decaying amplitudes of the field perturbation and therefore generate outward net magnetic forces to support the cloud against global collapse. The same mechanism also works for refreshing the outwards propagating Alfvén and fast magnetosonic waves caused by star-forming or core-forming activities, if the total energy supply rate due to these activities is lower than the total dissipation rate of these waves. In this way, a significant portion of the released gravitational energy during the global collapse is tapped and turned into the magnetic waves to slow down the global collapse itself. In terms of such a mechanism, the property that the dissipation rate of Alfvén and fast magnetosonic waves increases with the wave number leads to a simple explanation of the coexistence of the global quasi-stability and the local instability (formation of dense cores) in molecular clouds with cloud mass much larger than the Jeans mass.     

Achieving 1.2 fm/Hz(1/2) Displacement Sensitivity with Laser Interferometry in Two-Dimensional Nanomechanical Resonators: Pathways towards Quantum-Noise-Limited Measurement at Room Temperature

Laser interferometry is an important technique for ultrasensitive detection of motion and displacement. We push the limit of laser interferometry through noise optimization and device engineering. The contribution of noises other than shot noise is reduced from 92.6% to 62.4%, demonstrating the possibility towards shotnoise-limited measurement. Using noise thermometry, we quantify the laser heating effect and determine the range of laser power values for room-temperature measurements. With detai...     

Modeling Research on HL-2A Divertor Operation Regimes with B2. 5

Power handling, helium exhausting and impurity controlling are three main functions of divertor. 2-D modeling remains a major source of information on the expected divertor performance in tokamaks. Generally, most of the divertor operation will pass through three regimes： linear, high recycling and detachment.     

Conduction bands of solid o—H2 with the molecular O.P.W. method

The application of the O.P.W. method to closed shell molecular crystals is considered. The non local exchange potentials is included within the zero overlap approximation. The conduction bands of solid o—H₂ are obtained at symmetry points of interest and related to the experimental optical absorption spectrum.     

用二氧化钛、二氧化硅和氟化镁膜料镀制0.4μm～1.1μm超宽带增透膜

对0.4μm~1.1μm超宽带增透膜的镀制工艺进行了研究。根据长期从事该工作的经验和对膜料性能的研究,结合国产设备的实际情况,在膜料的选取上主要考虑其透明光谱区域、折射率、材料的蒸发方式、机械特性、化学稳定性及抗高能辐射等因素;最终选择用二氧化钛、二氧化硅和氟化镁3种常用膜料镀制0.4μm~1.1μm超宽带增透膜。涉及该膜系的膜层共有8层,结构为:玻璃■H■M■H■M■H■M■H■L■空气■。制作工艺方便简单、稳定,制做的膜层具有较好的光谱和机械性能,满足光电仪器实际使用要求。     

Nonstandard Variational Calculus with Applications to Classical Mechanics. 2. The Inverse Problem and More

In this paper we continue analyzing the possibleapplications of nonstandard analysis to variationalproblems, with particular interest in classicalmechanics. In particular, we adapt various techniques of numerical analysis to solve the nonstandardversion of the Euler-Lagrange equation for both one- andmultidimensional systems. We also start an introductoryanalysis of the inverse problem of the calculus of variation, identifying a class ofnonstandard difference equations for which a first-orderLagrangian can be obtained.     

Mach's principle. Part 2. Realization of Dirac's hypothesis in Brans-Dicke theory with cosmological term

Brans-Dicke theory supplemented with the scalar field potential of the formm ⁶/ Gm ₆ enables one to realize Dirac's big numbers hypothesis.