具有几何对称性的12参数矩形板元

1 引言 三角形板元中,形式最简单的是九参数元,节点参数是单元三个顶点上的函数值和两个一阶偏导数值,非协调九参三角形板元的研究取得了丰硕成果,根据不同方法已构造出多种收敛性能好的单元.相比之下,矩形板元的研究较少见报道.矩形板元中形式最简单的是12参元,节点参数是单元4个顶点上的函数值和两个一阶偏导数值,这类似于九参三角形板元.常见的12参矩形板元是ACM元,其形函数空间是完整3次多项式空间加上两个4次多项式的基函数,ACM元是C°元,但位移形函数的外法向导数平均值在单元间不连续,这类似于Zienkiewicz九参三角形板元,但由于矩形单元的特殊形状,ACM元是收敛的.龙驭球教授等在[1]中提出一种12参矩形广义协调元,其位移形函数的外法向导数平均值在     

一类六参数非协调任意凸四边形单元

本文构造了一类六参数非协调四边形单元,证明由此产生的有限元对任意四边形网格通过Irons分片检查,其收敛效果同Wilson元相当且形状函数的选择不依赖于单元本身。类Wilson元及改进的Wilson任意四边形单元是其中的特例。     

变质量质点的动能定理与软绳问题

给出变量质点的动能定理和一对反推内力作功的表达式,并由此给出软绳问题的正确解。     

传统随极射线管色度预测模型的相干误差分析

传统阴极射线管（ＣＲＴ）色度预测模型大都建立在三刺激值的可加性原理之上。但是在」实际应用中由于红绿蓝（ＲＧＢ）三个通道之间存在相互干扰,使得红绿蓝的颜色合成结果在一定程度上偏离了叠加原理,因此传统阴极射线管色度预测模型必然产生相干误差,通过实验表明,红昨三个通道之间的干扰主要表现为一种相互抑制作用,因此造成的传统阴极射线管色度预测模型的预测色差随显示亮度的增加而加大。     

密度泛函理论研究KB_n(n=1-9)团簇的结构和性质

在密度泛函理论的框架下,采用广义梯度近似(GGA)研究了KB_n(n=1-9)团簇的基态几何结构,系统计算了平均结合能Eb、二阶能量差分△2E、劈裂能D(n,n-1)、最高占据轨道(HOMO)与最低未占据轨道(LUMO)之间的能隙,研究表明:KB_n(n=1-9)团簇,随着团簇尺寸的变化,其稳定性逐渐增强,其中KB_3和KB_5为幻数团簇;KB_n(n=1-9)团簇的能隙随团簇总原子数的增加呈现振荡变化,态密度分析得到能隙振荡变化的原因是团簇带隙的差异.     

新型X波段多功能EPR谱仪的设计与性能

本文设计和研制了一款新型X波段多功能电子顺磁共振（electron paramagnetic resonance,EPR）谱仪,并为其开发一款新的控制和读出系统（control and readout system,CRS）来操控微波脉冲的产生和信号的采集,提高了系统的集成度和可扩展性. 该谱仪可实现常规的连续波EPR（continuous-wave EPR,cw-EPR）、脉冲EPR（pulsed EPR）和瞬态EPR（transient EPR,trEPR）实验,并装配了6~300 K的无液氦变温装置,以及兼具平行模式与垂直模式的新型双模连续波谐振腔和用于脉冲EPR及trEPR的介质腔. 针对新型EPR谱仪和新谐振腔,本文利用双模连续波、脉冲和瞬态三个不同方式的EPR实验,对其功能进行了验证.     

非线性热传导方程MLPG/RBF-FD无网格数值模拟

结合无网格局部彼得洛夫-伽辽金(MLPG)方法和径向基函数有限差分(RBF-FD)无网格方法求解非线性热传导问题.MLPG方法属于弱式无网格方法,具有处理边界条件方便的优点,然而因其要做大量的插值、积分运算而计算效率偏低;RBF-FD无网格方法属于强式无网格方法,直接对微分算子进行数值离散,计算效率高,然而其边界条件的...     

A design of resonant cavity with an improved coupling-adjusting mechanism for the W-band EPR spectrometer

We report a new design of resonant cavity for a W-band electron paramagnetic resonance (EPR) spectrometer. An improved coupling-adjusting mechanism, which is robust, compact, and suits with both solenoid-type and split-pair magnets, is utilized on the cavity, and thus enables both continuous-wave (CW) and pulsed EPR experiments. It is achieved by a tiny metal cylinder in the iris. The coupling coefficient can be varied from 0.2 to 17.9. Furthermore, two pistons at each end of the cavity allow for adjustment of the resonant frequency. A horizontal TE₀₁₁ geometry also makes the cavity compatible with the two frequently used types of magnets. The coupling-varying ability has been demonstrated by reflection coefficient (S₁₁) measurement. CW and pulsed EPR experiments have been conducted. The performance data indicates a prospect of wide applications of the cavity in fields of physics, chemistry and biology.     

Eu~(2+)在xMF_2-yYF_3体系中光谱性质及其变化规律

合成了Eu~(2+)激活的碱土稀土复合氟化物体系xMF_2-yYF_3(x=1,2,3;y=0,1,2,3,4,5;M=Ca,Sr,Ba),系统地研究了Eu~(2+)在该体系中的光谱性质及其变化规律,讨论了影响Eu~(2+)光谱的因素。     

Conceptual design of an intense positron source based on an LIA

Accelerator based positron sources are widely used due to their high intensity. Most of these accelerators are RF accelerators. An LIA (linear induction accelerator) is a kind of high current pulsed accelerator used for radiography. A conceptual design of an intense pulsed positron source based on an LIA is presented in the paper. One advantage of an LIA is its pulsed power being higher than conventional accelerators, which means a higher amount of primary electrons for positron generations per pulse. Another advantage of an LIA is that it is very suitable to decelerate the positron bunch generated by bremsstrahlung pair process due to its ability to adjustably shape the voltage pulse. By implementing LIA cavities to decelerate the positron bunch before it is moderated, the positron yield could be greatly increased. These features may make the LIA based positron source become a high intensity pulsed positron source.