Enhanced Correlation of Electron-Positron Pair in Two and Three Dimensions

Early time electron-positron correlation in vacuum pair-production in an external field is investigated. The entangled electron and positron wave functions are obtained analytically in the configuration and momentum spaces. It is shown that, relative to that of the one-dimensional theory, two- and three-dimensional calculations yield enhanced spatial correlation and broadened momentum spectra. In fact, at early times the electron and positron almost coincide spatially. The correlation also depends on the direction of the applied field. For the spatial correlation, the transverse correlation is stronger than the longitudinal correlation.     

制备方法对Co-MOR催化剂CH4选择还原NO性能的影响

采用离子交换法、浸渍法制备一系列的Co-MOR 催化剂, 并将其用于CH₄选择性催化还原 NO_x(CH₄-SCR)反应. 运用X 射线衍射(XRD)、X 射线荧光光谱(XRF)、扫描电子显微镜(SEM)、紫外-拉曼(UVRaman)光谱、X射线光电子能谱(XPS)、NO程序升温脱附(NO-TPD)等手段对催化剂进行了表征. 结果表明, 浸渍法制备的催化剂, Co以Co₃O₄形式存在; 而离子交换法制备的催化剂, Co以离子形式进入丝光沸石(MOR)骨架之中, 在催化剂上形成更多的Co²⁺和[Co-O-Co]²⁺, 形成更均匀NO吸附中心和CH₄-SCR反应活性中心. 催化剂活性评价表明离子交换法制备的催化剂具有更宽的活性温度区间, Co(0.30)-MOR 催化剂在327-450℃温度范围内NO转化率大于50%.     

Broadband chirped InAs quantum-dot superluminescent diodes with a small spectral dip of 0.2 dB

We report on the fabrication and characterization of InAs/GaAs chirped multilayer quantum-dot superluminescent diodes (CMQD-SLDs) with and without direct Si doping in QDs. It was found that both the output power and the spectral width of the CMQD-SLDs were significantly enhanced by direct Si doping in the QDs. The output power and spectral width have been increased by approximately 18.3% and 40%, respectively. Moreover, we shortened the cavity length of the doped CMQD-SLD and obtained a spectral width of 106 nm. In addition, the maximum output power and spectral width of the CMQD-SLD doped directly with Si can be further increased to 16.6 mW and 114 nm, respectively, through anti-reflection coating and device packaging. The device exhibited the smallest spectral dip of 0.2 dB when the spectrum was widest. The improved performances of the doped CMQD-SLD can be attributed to the direct doping of Si in the QDs, optimization of device structure and device packaging.     

铁电晶体Pb_xBa_(1-x)Nb_2O_6和掺Li,Na的Pb_xBa_(1-x)Nb_2O_6的结构和电弹张量的测定

用提拉法从熔体中生长出Pb_(0.37)Ba_(0.63)Nb_2O_6和Pb_(0.30)Ba_(0.533)Na_(0.306)Li_(0.028)Nb_2O_6 两种铁电单晶。用X射线衍射方法分析了两种单晶的结构,结果表明,室温时两种晶体都属于四方晶系点群4mm。测定晶格参数得PBN晶体的a=12.493A和c=3.98A;掺Li,Na的PBN晶体的a=12.493A和c=3.970A。测定了两种晶体全部各52个电弹张量的分量,结果表明PBN晶体具有优良的压电性,其中压电系数d_15=108×10~(-12)C/N。这种晶体很有希望用作与厚度切变模式有关的压电换能器材料。掺Li,Na的PBN晶体的介电常数显著降低,而铁电居里点有明显的提高。     

THE ULTRAVIOLET UP-CONVERSION LUMINESCENCE OF NONCRYSTALLINE ErP5O14

This paper reports the observation of the ultraviolet up-conversion lumines-cence phenomenon of noncrystalline ErP₅O₁₄ excited by pulse 532nm laser. The up-conversion mechanism is explained as follows, namely, when noncrystalline ErP₅O₁₄ is excited by 532nm laser, the excited population is mainly deposited in ⁴S_3/2 level because of the strong nonradiative relaxation between ²H_11/2 and ⁴S_3/2 level, then up-converted to (²H²G)_9/2 level by energy transfer between Er³⁺ ions, this produces the ultraviolet luminescence.     

琼脂糖单向扩散法测定Cu（Ⅱ）

琼脂糖是一种半固体基质,加热到60℃以上成为流动态,冷却则变为固体凝胶。它能起支架作用,允许可溶性物质在其间自由扩散,所     

学习范式下留学生大学化学全英文授课的教学改革

分析了以“教”为中心的教学范式和以“学”为中心的学习范式，并将学习范式实施于留学生大学化学全英文授课中，旨在提高课程教学质量。探究了学习范式对实现教育目标和促进学生有效学习的作用，并对该方法的实施过程进行了分析。结果表明，学习范式的实施对提高学生的有效学习和教育目标层次提高有重要作用，同时有助于教师自身的发展和提高。     

产能随机下的易逝品超售决策模型研究

本文研究制造商面临产能和no show双重随机情况下的易逝品超售决策。考虑了产能的随机性和零售商no show的随机性,建立了易逝品的超售决策模型,得到了超售量的最优解。得到了产能的短缺成本、产能的闲置成本和零售商取消订货的补偿对制造商超售决策的影响,并用算例进行了验证。分析结果表明,与闲置成本相比,单位补偿对制造商的最优超售量的影响更大。     

电感耦合等离子体发射光谱法同时测定玻璃中的硫和磷

通过对玻璃试样中硫、磷的分解方法、分析线选择、共存元素光谱干扰和仪器最佳分析条件等方面的研究, 建立了ICP-AES 测定玻璃中硫、磷的方法. 选用紫外区谱线S 181.972 nm、 P 177.434 nm, 避免了基体元素对硫、磷的干扰, 该法能够准确、快速地测定玻璃样品中的硫、磷量, 测定结果的相对标准偏差小于2.9%, 方法的检出限分别为 S 0.07 μg/mL, P 0.08 μg/mL, 已用于玻璃样品的分析.     

以Schiff碱为阳离子的新型离子液体的制备与表征

Two novel ionic liquids, N,N＇-disalicylideneethylenediaminium acetate and N,N＇-disalicylideneethylenediaminium trifluoroacetate, were prepared and characterized by IR, ^1H NMR, DTA-TG and elemental analysis. The experimental results indicate that the new ionic liquids possess lower melting point and higher electrical conductivity. It is noteworthy that the ionic liquids reported herein are the first member of the ionic liquid family with the Schiff base functional group in the cation.