Point approximation of a space-homogeneous transport equation

Summary We present an approximation method of a space-homogeneous transport equation which we prove is convergent. The method is very promising for numerical computation. Comparison of a numerical computation with an exact solution is given for the Master equation.     

Spontaneous magnetization of the Ising model on a 4–8 lattice

The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order.     

Ag+掺杂的立方相Y2O3:Eu纳米晶体粉末发光强度研究

采用化学自燃烧法制备了不同Ag⁺掺杂浓度的Y₂O₃:Eu纳米晶体粉末样品(［Y³⁺］∶［Eu³⁺］∶［Ag⁺］=99∶1∶X，X=0—3.5×10^-2)，以及通过退火处理得到了相应的体材料.根据X射线衍射谱确定所得纳米和体材料样品均为纯立方相.实验表明在纳米尺寸样品中随着Ag离子浓度的增加，荧光发射强度随之增加，当X=2×10^-2时达到最大值，其发光强度比X=0时提高了近50%.当Ag离子浓度继续增加，样品发光强度保持不变.在相应的体材料样品中则没有观察到此现象.通过对各样品的发射光谱，激发光谱，X射线衍射图谱，透射电镜(TEM)照片和荧光衰减曲线的研究，分析了引起纳米样品荧光强度变化的原因是由于Ag离子与表面悬键氧结合，从而使这一无辐射通道阻断，使发光中心Eu³⁺的量子效率提高；Ag⁺的引入所带来的另一个效应是使激发更为有效.这两方面原因使发光效率得到了提高.     

Yb3+掺杂KY(WO4)2激光晶体生长、结构与光谱分析

采用顶部籽晶提拉法(TSSG)生长出Yb:KY(WO₄)₂(Yb:KYW)激光晶体.对预烧后的原料及晶体进行了XRD分析，结果表明，分别在920℃和600℃预烧8h后的熔质和助熔剂基本上形成一相，抑止了实验中的挥发问题；所生长的晶体为β-Yb:KYW，计算其晶格常数为a=1.063nm，b=1.034nm，c=0.755nm，β=130.75°.测得不同厚度样品的吸收光谱，结果表明样品在933nm和981nm有较强的吸收峰，计算出主峰981nm的吸收截面σ关键词： Yb:KYW TSSG法 晶体结构 光谱参数     

147Pm激发的ZnS：Cu,Cl发光粉的研究

以高纯ZnS粉末为基质,采用高温转相、扩散,以及表面涂敷工艺,制得了¹⁴⁷Pm激发的ZnS:Cu,Cl发光粉。分析了ZnS:Cu,Cl的晶体结构,测量了ZnS:Cu,Cl的激发光谱、发射光谱、发光亮度。其晶体结构主要是六方纤锌矿型结构,激发光谱峰值波长为341nm,发射光谱峰值波长为513nm,初始发光亮度达到312mcd/m₂。由激发光谱的峰值波长341nm推算得到六方ZnS晶体的禁带宽度为3.64eV。分析了¹⁴⁷Pm激发的ZnS:Cu,Cl发光粉的发光寿命,其发光寿命达到5年以上。还探讨了该放射性发光粉的发光机理。¹⁴⁷Pm激发的ZnS:Cu,Cl的稳定发光,实际上是激发过程与复合过程的准平衡。ZnS:Cu,Cl的绿色发光来源于深施主-深受主对的复合发射。实验结果的分析表明,ZnS:Cu,Cl中深施主-深受主之间的能级间隔约为2.42eV。     

n(Zn)：n(Ga)比值对合成ZnGa2O4结构及光致发光性能的影响

以ZnO和HGaO₂为原料,用不同配比合成出系列ZnGa₂O₄,并对其晶体结构和发光性能进行了研究。用荧光分光光度计检测了ZnGa₂O₄的激发和发射光谱,用X射线衍射仪检测了ZnGa₂O₄的衍射图谱,用热重差热仪绘制了TGA-DAT曲线。对检测结果分析认为:1.ZnGa₂O₄属于尖晶石结构,稍过量的Zn或Ga能进入ZnGa₂O₄结构中,并对ZnGa₂O₄的晶格常数产生一定影响。2.ZnGa₂O₄存在两个自激发光中心,当Ga稍过量时,自激发光中心是四面体镓氧键[T_d(Ga-O)],最大激发波长约248nm,最大发射波长约367nm;当Zn稍过量时,自激发光中心是八面体镓氧键[O_h(Ga-O)],最大激发波长约270nm,最大发射波长约441nm。当n(Zn):n(Ga)在理论值附近,激发和发射光强度最大,而且光谱峰位发生了红移。3.ZnGa₂O₄的热稳定性能非常好。上述结论对研究ZnGa₂O₄基质或掺杂的发光材料具有一定意义。     

Angle theorems for the Lagrangian mean curvature flow

We prove that symplectic maps between Riemann surfaces L, M of constant, nonpositive and equal curvature converge to minimal symplectic maps, if the Lagrangian angle for the corresponding Lagrangian submanifold in the cross product space satisfies . If one considers a 4-dimensional K?hler-Einstein manifold of nonpositive scalar curvature that admits two complex structures J, K which commute and assumes that is a compact oriented Lagrangian submanifold w.r.t. J such that the K?hler form w.r.t.K restricted to L is positive and , then L converges under the mean curvature flow to a minimal Lagrangian submanifold which is calibrated w.r.t. . Received: 11 April 2001 / Published online: 29 April 2002     

Multicriteria decision making under uncertainty

Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum, minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity networks is considered. Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002     

LD泵浦Nd∶LuVO4/Cr4+∶YAG被动调Q激光器

采用大功率半导体激光器端面泵浦Nd∶LuVO4晶体，利用Cr4+∶YAG晶体作为可饱和吸收元件，实现了1.06 μm激光的被动调Q运转.在泵浦功率为19.1 W时，获得最高平均输出功率为4.58 W，脉冲宽度为84 ns，单脉冲能量为36.6 μJ以及峰值功率为436.2 W的激光脉冲.