一种新型可协调绿色荧光材料BaAl2Si2O8∶Tb3+,Ce3+的发光性质与能量传递

采用高温固相法制备了BaAl2Si2O8∶Tb3+,Ce3+系列的荧光材料,讨论了Tb3+,Ce3+单掺及Tb3+,Ce3+共掺样品的光谱性质及发光机理,分析了Ce3+与Tb3+之间的能量传递过程.通过对样品进行XRD,荧光光谱,色坐标等测试.结果表明,Tb3+,Ce3+的掺杂没有改变BaAl2Si2O8晶体的结构.BaAl2Si2O8∶Tb3+发出明亮的绿光,发光峰分别位于487,545,583和621 nm对应于Tb3+的5D4→7FJ(J=6,5,4,3)特征发射.Ce3+的掺入没有改变BaAl2Si2O8∶Tb3+发射光谱的位置,但使其激发谱由窄带激发变成了宽带激发增加了谱带多样性,发光强度有了明显的增强,而且颜色也具有一定的协调性,使其在实际运用方面具有更大的灵活性.发光强度增强的原因不仅仅是因为Ce3+的敏化作用,还与Ce3+和Tb3+之间存在能量传递有密切关系.通过猝灭法计算了,Ce3+与Tb3+之间的能量传递的临界距离为15.345 nm,并且证明了能量传递是由偶极-偶极相互作用产生的.通过计算得到能量传递效率最高达到了76.04%.     

维吾尔语框架语义例句辅助标注系统的设计与实现

构建维吾尔语框架语义知识库是自然语言处理的基础性工程,目前大部分工作基于人工。从真实语料库中抽取包含将要描述词元的例句,为例句标注以及这些例句的配价模式进行深入研究,从标注好的维吾尔语例句中提取维吾尔语词元和例句填充到维吾尔语框架库,构建维吾尔语词元库和例句库,实现维吾尔语语义框架网络的自动构造之目的。本文对维吾尔语真实语料库中抽取的例句中标注对象进行初步分析,论述了人机交互式基于阿拉伯字符的UFN例句辅助标注系统的功能模块设计和工作流程。介绍了UFN例句辅助标注系统的例句标注界面和词元标注报告、词条报告的自动生成演示界面。     

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.     

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。     

一类带负顾客和反馈的M/G/1休假排队系统

将负顾客和反馈相结合研究了一类带负顾客和反馈M/G/1的休假排队系统,正顾客服务完后以概率1-θ反馈到队尾等待下次服务,以概率θ(0θ≤1)离开系统。负顾客抵消正在接受服务的正顾客,休假策略为单重休假。给出了它们稳态存在的充分必要条件,利用补充变量法和状态转移分析模型,得到了系统主要排队指标和稳态队长概率母函数及概率母函数的随机分解结果。     

Doubly coupled matter fields in massive bigravity

In the context of massive(bi-)gravity,non-minimal matter couplings have been proposed.These couplings are special in the sense that they are free of the Boulware-Deser ghost below the strong coupling scale and can be used consistently as an effective field theory.Furthermore,they enrich the phenomenology of massive gravity.We consider these couplings in the framework of bimetric gravity and study the cosmological implications for background and linear tensor,vector,and scalar Previous works have investigated special branches of solutions.Here we perform a complete perturbation analysis for the general background equations of motion,completing previous analyses.     

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.