Ultraviolet upconversion in thulium-doped fluorozirconate fiber observed under two-color excitation

Ultraviolet upconversion signals at 293, 351, and 366 nm were observed from thulium-doped fluorozirconate fiber pumped with a 458-nm Ar(+) laser. The upconversion signal's intensity was enhanced 5x when the fiber was simultaneously pumped with a 458-nm Ar(+) laser and a 585-nm dye laser. There is evidence of the formation of defect centers under simultaneous excitation by visible and near-infrared lasers (458 and 750 nm), and there is no evidence of color-center formation when both of the exciting beams are in the visible (458 and 585 nm).     

高能强子–强子碰撞中喷注性质的蒙特卡洛研究

在喷注“圆锥判定法”的基础上,对高能强子–强子碰撞中产生的喷注(微喷注)的性质进行了蒙特卡洛研究.采用以喷注动量为z轴的“喷注坐标系”,给出了表征喷注性质的各物理量在新坐标系中的分布情况.结果表明,圆锥判定法能够作为一种有效手段来对高能强子–强子碰撞和相对论重离子碰撞中发生的硬和半硬过程开展实验研究.由有喷注事件和无喷注事件的多重数分布可以看到,E_t=2GeV是用圆锥法确定喷注的合理的横能截断值.     

Formation of concentration gradient and its application to DNA capillary electrophoresis

A new method to introduce the concentration gradient into the capillary has been developed and its application to DNA capillary electrophoresis is presented. The concentration gradient produced by mixing 5% w/v polyacrylamide-co-poly(N-dimethylacrylamide) (PAM-co-PDMA) solution and 1 x Tris/N-tris(hydroxymethyl)methyl-3-amino-propanesulfonic acid/EDTA (TT) + 5 M urea buffer was successfully achieved by using two programmable syringe pumps with strict control of dead volume, flow rate, and pressure balance. This method has the advantages of high stability, reproducibility, and versatility. The column with concentration gradient greatly improved the resolution, especially for the large DNA fragments, due to a decrease in band width broadening with time. A column containing 2-4% w/v gradient in four steps had a longer read length, shorter separation time and better resolution (after 380 base) than that of 4% w/v single concentration polymer solution. The number of steps in the gradient had almost no effect on the performance. The change in the average concentration by relocating the position of the same step gradient, i.e., a combination of different low concentration to high concentration polymer solution ratios, resulted in a different migration time, read length and resolution.     

具时滞的奇异(n-1,1)共轭边值问题的多重正解

Abstract. This paper discusses the singular (n-l, 1) conjugate boundary value problem as fol-lows by using a fixed point index theorem in cones     

过冷降膜在红外隐身中的应用研究

提出了利用过冷降膜技术对军事目标进行红外隐身的新构想。建立了层流过冷降膜的流动与传热模型,得出了层流降膜自由表面温度分布的解析表达式,分析了影响液膜自由表面温度的各种因素,计算了过冷降膜对军事目标的红外抑制效果。结果表明:过冷降膜是一种简单有效的红外抑制技术,增大液膜流动的Re数和降低液膜入口温度均可增强对特定目标的红外隐身效果,该技术在军事目标的红外隐身方面应用前景广阔。     

液芯光纤中溶液吸收和荧光的性质对CS2受激拉曼散射阈值的影响

利用液芯光纤技术研究了不同浓度的β-Carotene的CS₂溶液的吸收与荧光的特性对CS₂的一、二阶Stokes谱线阈值的影响.实验发现随溶液浓度(10^-8—10^-6 mol/L)增加，CS₂的一阶Stokes谱线的激发阈值相对变高；并且与纯CS₂芯液的受激拉曼散射相比较，在低抽运能量激发下，就观察到CS₂的二阶Stokes谱线.这主要是由于在CS₂的受激拉曼谱线产生的过程中，β-Carotene的CS₂溶液的吸收和荧光共同影响了CS₂的一、二阶Stokes谱线的阈值.我们进行了理论上的拟合与分析，其结果与实验符合很好. 关键词： 2受激拉曼散射阈值')" href="#">CS₂受激拉曼散射阈值 液芯光纤 吸收与荧光     

双随机相位编码光学加密系统的唯密文攻击

针对双随机相位编码光学加密系统的安全性分析表明，该系统属于线性对称分组密码系统，其线性性质为安全性留下极大隐患.在唯密文攻击下，仅根据密文估计出物面波函数的“支撑”(support)，然后利用迭代相位恢复算法获得物面波函数(其振幅是明文信息)，再根据物面波函数与频域密文的关系可推导出频谱平面的解密密钥.由于估计出来的物面波函数的“支撑”相对于真实的物面波函数的“支撑”有一定的平移，使得恢复的物面波函数与真实的物面波函数之间无论在振幅上还是相位上都存在平移，导致用推导出来的解密密钥去解密其他密文时所获得的明文与原始明文之间存在明显平移.然而，可依照这一先验信息，将估计出来的物面波函数的“支撑”在物面内遍历，从而找到逼近真实解密密钥的解.利用此解密密钥去解密其他密文时获得更好的解密效果. 关键词： 光学信息安全 双随机相位编码 唯密文攻击 函数支撑     

压力及杂质氢对金属锂弹性特性的影响

针对六角密堆金属锂16个原子超晶胞(supercell)、填隙一个氢原子的周期单元，采用基于密度泛函理论的平面波-赝势方法，研究了零温条件下压力及填隙氢掺杂对体系弹性性质的影响.结果表明氢掺杂导致体系的体模量增加.常压下掺杂体系的弹性常数C₁₁，C₃₃，C₆₆和C₁₂高于单质体系，剪切模量C₄₄有所下降，而C₁₃则与单质体系持平.压力作用下C₁₁，C₃₃和C₆₆一直大于单质体系，但C₁₂的值低于单质体系.在2GPa—4GPa压力区间内，弹性常数C₁₃呈反常变化，小于单质体系；在高压区掺杂体系的C₄₄和C₁₃则高于单质体系的相应量值，压力导致掺杂体系和单质体系之间剪切模的偏离加剧.掺杂体系在压力作用下依然保持压缩模的各向同性，具有和单质体系相似的特性. 关键词： 第一性原理 压力效应 弹性常数 金属锂     

Effects of impurity on the entanglement of the three-qubit Heisenberg XXX spin chain

We investigate the entanglement of the three-qubit Heisenberg XXX chain in the presence of impurity and obtain the analytical expressions of the concurrence C. It is found that for impurity entanglement, C appears only when J ₁ > J for J > 0, and J ₁ > 0 for J < 0, and in these two regions C increases with the increase of J ₁, so is the critical temperature T _c. When J ₁ ≫ | J |, C reaches its maximum value 0.5 and T _c reaches the asymptotic value T _c = 3.41448J ₁. For entanglement between the normal lattices, C appears only when J > 0 and −2J < J ₁ < J, and initially increases with the increase of J ₁ and arrives at the maximum value C _max = (e^4J/T −3)/(e^4J/T + 3) before it decays to zero gradually, so is the critical temperature T _c with, however, the maximum value T _cmax = 4J/In3. Supported by the Natural Science Research Project of Shaanxi Province (Grant No. 2004A15)