新疆苔藓植物的研究进展

苔藓植物是植物界的一个重要门类,植株矮小,适应性广.新疆苔藓植物的研究主要集中在经典分类学、苔藓植物区系、形态解剖学、专科、专属等方面.而苔藓植物生态学及苔藓植物多样性方面的研究才刚刚起步.本文扼要介绍了20多年来苔藓植物各个分支学科的研究现状,探讨了苔藓植物研究今后的发展趋势.文中,还对我区苔藓植物研究工作今后的研究方向提出了作者的见解.     

模糊增益PD型迭代学习算法及其应用

普通PID型迭代学习控制算法由于其增益矩阵一旦确定,就不再改变,因而收敛速度较慢。为了提高收敛速度,结合模糊控制技术用于学习控制,提出一种模糊增益PD型迭代学习控制算法。该算法根据系统误差的大小,通过调整因子而改变增益矩阵大小。调整的方法是:在控制的初始阶段,增强控制输入中系统误差增益矩阵,同时保持误差微分增益矩阵不变,从而清除误差;而在控制趋于稳定时,增强控制输入中误差微分增益矩阵,同时保持系统误差部分增益矩阵不变,以减少超调量。针对一个单臂机械手模型,进行了仿真设计,仿真结果验证了方法的有效性。     

基于聚焦物镜与PSD的激光对中测量方法研究

针对传统激光对中方法数学模型复杂、求解困难的不足,提出一种基于聚焦物镜与PSD的激光对中测量方法。该方法利用光学系统中视场与焦距的关系以及相似三角形的原理得到不对中的角度偏差和平行偏差,测量原理简单,求解方便。实验结果表明,当平行偏量和角度偏量的测量范围分别为0.5 mm~1.5 mm,0.047 7°~0.143 2°时,平行偏量测量误差范围为0.035 mm~0.207 mm,角度测量误差范围为0.000 2°~0.012 8°。最后对系统测量误差进行分析并提出一种消除安装误差影响的方法,给出了计算公式。     

Study of the design of CSNS MEBT

The design of CSNS MEBT has two objectives：（1） to match the beam both in the transversal direction and the longitudinal direction from RFQ into DTL;（2） to further chop the beam into the required time structure asked by RCS. It is very diffcult and critical to control well the emittance growth and in the meantime to match and chop the beam. Firstly,the optical design is done and optimized,and the multi-particle simulations show that the maximum emittance growth is successfully controlled within 14%. Secondly,based on the different beam envelopes obtained by TRACE-3D and PARMELA,the least deflecting angle of the chopper is determined by TRACE-3D. At last,the field of steering magnet is determined through simulations.     

Matching by solenoids in space charge dominated LEBTs

The betatron matching of a rotationally asymmetric beam in space charge dominated low-energy beam transports （LEBTs） where solenoids are used for the transverse matching has been studied. For better understanding, the coupling elements of a beam matrix are interpreted in special forms that are products of a term defined by the Larmor rotation angle and another by the difference between the beam matrix elements in the two transverse planes. The coupling form originally derived from the rotationally symmetric field in solenoids still holds when taking into account the rotationally asymmetric space charge forces that are due to the unequal emittance in the two transverse planes. It is shown in this paper that when an LEBT mainly comprising solenoids transports a beam having unequal emittance in the two transverse planes and the linear space charge force is taken into account, the initial Twiss parameters can be modified to obtain the minimum and equal emittance at the LEBT exit. The TRACE3D calculations also prove the principle. However, when quadrupoles that are also rotationally asymmetric are involved in between solenoids, the coupling between the two transverse planes becomes more complicated and the emittance increase is usually unavoidable. A matching example using the CSNS （China Spallation Neutron Source） LEBT conditions is also presented.     

Slim Discs with Varying Accretion Rates

It was revealed in our previous studies that there exists a maximal possible accretion rate for slim discs with constant accretion rates because the correctly calculated vertical gravitational force can only gather some limited amount of accreted matter. Here we show that when the accretion rate is not constant and instead decreases with decreasing radius because of outflows, such that the amount of accreted matter is adjusted to be within the allowed limit, global slim disc solutions can be constructed even for the case that accretion rates at large radii apparently exceed the maximal possible value. This result further demonstrates that outflows seem to be unavoidable for accretion flows with large accretion rates at large radii.     

Design of magnet and control of the beam emittance for Penning H^- ion source

The design requirement and principle of the deflection magnet for Magnetron and Penning H- ion source are discussed. It is proved that there exists a maximum emittance for the beam that may be transformed by the magnet into a state with equal Twiss parameters of αr =αy and βr =βy, which is the requisite condition to get a minimum emittance at the entrance of RFQ after transporting by a LEBT with solenoids. For this maximum emittance, the corresponding magnetic field gradient index is 1.     

Constraints on Slim Accretion Discs

We show that when the gravitational force in the vertical direction is correctly calculated, the well-known S- shaped sequence of thermal equilibrium solutions can be constructed only for small radii of black hole accretion flows, such that slim accretion discs can possibly exist only in the inner regions of these flows.     

Passively Q-Switched Nd：KLuW Laser with Semiconductor Saturable Absorber

We demonstrate a passively Q-switched Nd：KLu W laser with a semiconductor sat urable absorber mirror （SESAM） at wavelength 1070 nm. At a pump power of 1.3 W, the pulse width is measured to be about 17ns with repetition rate of lOkHz and with the average output power of 260roW. To our knowledge, this is the first demonstration of Nd：KLuW used for passively Q-switched laser with an SESAM.