掺钕激光玻璃中的无辐射能量转移过程

本文研究了一系列不同类型的掺钕玻璃的吸收光谱、荧光光谱、弛豫光谱和红外振动光谱.测定了这些玻璃的无辐射跃迁几率,计算了多声子跃迁几率.实验表明,由钕离子与基质玻璃的相互作用而引起的无辐射跃迁过程,不能完全用多声子跃迁来解释.由于无机玻璃中激活离子与最邻近配位体之间的共价键因素,即钕离子的4f轨道与配位离子的电子轨道的波函数有一定程度的混杂,所以在玻璃中还存在一种近距离的相互作用.它们对无辐射跃迁过程的影响比声子弛豫过程更强烈,因此,可以认为玻璃中的无辐射跃迁是属于类似内分子的能量转移过程.     

Adaptive correction of human-eye aberrations in a subjective feedback loop

An adaptive optical system with a subjective feedback loop is used to improve the visual acuity and to determine the aberrations of the human eye. Corrections of as many as 12 low-order aberration modes were made, based on the perceived sharpness of the test object observed through the adaptive optical system. The acuity of vision was improved by adjustment of the weights of the orthogonal modes produced by a deformable mirror. Objective measurements of the correcting aspherical figures, obtained in independent subjective correction cycles for one person, demonstrated good repeatability. Participants in the study with strong ocular aberrations reported moderate to significant improvement of their visual acuity, estimated with the U.S. Air Force 1951 acuity chart.     

New spectral representation and evaluation of f π and the quark condensate \left\langle {\bar qq} \right\rangle in the terms of string tension

New spectral representations for f _π and chiral condensate are derived in QCD and used for calculations in the large-N _c limit. Both quantities are expressed in this limit through string tension σ and gluon correlation length T _g without fitting parameters. As a result, one obtains $\left\langle {\bar qq} \right\rangle = - N_c \sigma ^2 T_g a_1 $ , $f_\pi = \sqrt {N_c } \sigma T_g a_2 $ , with a ₁=0.0823, a ₂=0.30. Taking σ=0.18 GeV² and T _g=1 GeV^?1, as known from analytic and lattice calculations, this yields $\left\langle {\bar qq} \right\rangle $ (μ=2 GeV)=?(0.225 GeV)³, f _π=0.094 GeV, which is close to the standard values.     

From three nucleons to three quarks

Some short history of three-body methods originated from the famous Skornyakov-Ter-Martirosyan equation is given, including the latest development of Faddeev formalism and Efimov states. The 3q system is shown to require an alternative, which is provided by the hyperspherical method (K harmonics), highly successful for baryons.     

Nonperturbative quark dynamics in a baryon

The field-correlator method is used to calculate nonperturbative dynamics of quarks in a baryon. The general expression for the 3q Green’s function is obtained using the Fock-Feynman-Schwinger (world-line) path-integral formalism, where all dynamics is contained in the 3q Wilson loop with spin-field insertions. Using the lowest cumulant contribution for the Wilson loop, one obtains a Y-shaped string potential vanishing at the string-junction position. Using the einbein formalism for the quark kinetic terms, one automatically obtains constituent quark masses, calculable through the string tension. The resulting effective action for 3q plus Y-shaped strings is quantized in the path-integral formalism to produce two versions of Hamiltonian: one is in the c.m. and the other is in the light-cone system. The hyperspherical formalism is used to calculate masses and wave functions. Simple estimates in the lowest approximation yield baryon masses in good agreement with experiment without fitting parameters.     

非对称蛇形旋转通道换热及流场数值研究

为了深入了解空冷涡轮动叶的冷却机理和冷气流动特性,采用商业软件CFX5对旋转状态下某涡轮动叶的非对称蛇形内冷通道模型中的湍流流动和换热性能进行了数值模拟.得到了各主要换热面的换热系数分布,分析了通道内的流动规律.发现肋片结构与旋转因素引起了通道内的横向二次流,使整体的换热能力得到了增强,其中非对称因素及旋转因素导致了各个壁面的换热性能的差异.     

原油样品激光诱导荧光的时间分辨光谱特性研究

为探索激光诱导时间分辨荧光光谱技术应用于海洋悬浮溢油原位探测的可行性,对来自胜利油田六个不同井区不同密度的原油样品的时间分辨荧光光谱进行了探测分析。结果发现,各原油样品荧光发射的持续时间基本相同,从ICCD中数字延时发生器(DDG)的输入延时52 ns开始,到输入延时82 ns左右结束,各原油样品的荧光峰强度随时间变化曲线的半高宽约10 ns;不同原油样品的最强荧光峰位及其衰减寿命不尽相同,并且与样品密度有一定相关性,密度相近的原油具有相近的最强荧光峰位和相似的荧光寿命。对比六种原油样品的时间分辨荧光光谱发现,在荧光增强时,原油荧光光谱峰位不变,当荧光从最大强度开始衰减时,六种原油样品的荧光光谱峰位均出现了不同程度(17~30 nm)的红移现象,这一定程度上反映出原油中各荧光组分的荧光衰减速率存在差异,或者存在荧光组分之间的能量传递。所观测到的原油密度相关的时间分辨光谱信息和荧光峰红移现象可望成为水下悬浮溢油识别的有效特征之一。     

基于四波混频的光纤非线性系数测量方法

为解决四波混频法测量光纤非线性系数未考虑泵浦消耗而导致结果不准确的问题,提出了一种在简并四波混频情况下测量非线性系数的方法.根据光纤中简并的四波混频理论,推导出了考虑泵浦消耗和光纤损耗的椭圆方程.通过设定数值计算所需的各个参量并利用简单的数学方法分析了计入泵浦消耗、光纤损耗的必要性,得到被测光纤的非线性系数,与Optisystem的仿真结果一致.研究表明,这种改进的测量方法不但适用于小信号情形下的四波混频过程,还可以应用于出现参量饱和现象的场合,为进一步设计光纤2R再生器件提供了重要依据.     

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用Matlab软件对大气压均匀辉光放电等离子体(OAUGDP)激励器系统的电特性进行了仿真。在仿真模型中,等离子体放电被建模成一个电压控制的电流源:当加在气隙上的电压超过等离子体产生电压时,该受控电流源接通;电流源的输出电流和所加电压之间遵循幂律。建立了一个OAUGDP激励器系统中等离子体放电的电路模型。仿真结果与实际激励器系统的实验数据很吻合。仿真结果表明,在不同的运行条件下,放电电流与电压之间遵循不同的指数幂律,仿真放电电流波形也不同。