纳氏试剂测定水中氨氮影响因素的探讨

对国家生活饮用水标准检验方法"GB/T5750—2006"中涉及到的水中氨氮的检测条件进行了探讨,讨论了样品的采集与保存,影响显色、空白值的各项因素,并提出相应的解决办法。对国家标准物质以及实际样品的验证表明,方法的相对误差为0.03%~1.5%,相对标准偏差RSD为0.55%~5.3%,准确度也能满足分析要求,对国家标准方法进行了补充与细化,在实际工作中有参考价值。     

铁基大块非晶合金的摩擦磨损性能研究

采用电弧熔炼、铜模吸铸法制备Fe基大块非晶合金,利用球-盘式摩擦磨损试验机进行干摩擦磨损试验,研究了铸态Fe基大块非晶合金的摩擦磨损行为及热处理对其耐磨性的影响,利用扫描电子显微镜观察合金磨损表面形貌,分析了Fe基大块非晶合金以及相同成分晶态合金的磨损机理.结果表明:在本试验条件下,铸态Fe基大块非晶合金的耐磨性高于相同成分的晶态合金,热处理可以有效提高铸态Fe基大块非晶合金的耐磨性,在保持完全非晶状态的前提下,退火态非晶合金的磨损率较铸态非晶合金减小约40%;材料的结构和性能对合金的摩擦系数影响不大,当进入稳定阶段后Fe基大块非晶合金的摩擦系数稳定在0.58左右;不同处理状态的Fe基大块非晶合金和相同成分晶态合金的磨损机制不同,非晶合金的磨损机制以疲劳磨损为主兼有磨粒磨损,相同成分晶态合金的磨损机制为粘着磨损和磨粒磨损共同作用的结果.     

Optical and spectroscopic characterization of Nd-doped aluminosilicate fiber preforms made by the MCVD method using chelate delivery

4 F_3/2 level of Nd³⁺ in aluminosilicate optical fiber preforms after 807-nm excitation are reported in the temperature range from 15 °C to 500 °C for Nd₂O₃ concentrations in the range from 0.2 to [%wt]0.9 and Al₂O₃ concentrations of between [%wt]3.8 and [%wt]8. At room temperature it is observed that for concentrations of less than [%wt]0.6 Nd₂O₃ the fluorescence decay is approximately exponential; for the higher Nd₂O₃ concentrations the decay is increasingly bi-exponential. We have identified a “slow” (≈500 μs) and a “fast” (≈100 μs) decay time; the slow decay is attributed to isolated ions and the faster decay to energy transfer between homogeneously dispersed ions. The measured 1/e folding fluorescence decay time τ decreases slowly at a constant rate of -0.08±0.007 μs/K for [%wt]0.9 Nd₂O₃. It is shown that increasing the Al₂O₃ concentration tends to suppress this temperature quenching effect. A radiative decay time of 640 μs is obtained by Judd–Ofelt analysis. Received: 24 October 1997/Revised version: 2 February 1998     

Relaxation Limit for Aw-Rascle System

We study the relaxation limit for the Aw-Rascle system of traffic flow. For this we apply the theory of invariant regions and the compensated compactness method to get global existence of Cauchy problem for a particular Aw-Rascle system with source, where the source is the relaxation term, and we show the convergence of this solutions to the equilibrium state.     

Coherent Dynamics of Direct-Current-Driven Quantum-Dot-Array with Two Time-Dependent Embedded Impurities

The coherent dynamics of dc-driven quantum-dot array with two embedded time-dependent impurities is investigated, the exact crossings and avoided crossings in the quasienergies are associated with the evolution dynamics of the electron by the introduction of the envelope lines of the site＇s maximum returning probability. Through a perturbative scheme, the time-dependent Hamiltonian is replaced by an equivalent static one, whose structure reveals the new quantum tunnelling mechanism in the time-periodic driving system and sheds light on the alternative interpretation of dynamic localization and delocalization.     

干空气和冷冻水联产除湿空调节能特性研究

本文提出了一种将转轮除湿和再生式蒸发冷却相结合来实现干空气和冷冻水联产的除湿空调系统,以各组成部件为基础,建立了该系统的计算模型,并对其节能特性进行了分析.结果表明,ARI夏季工况下,干空气和冷冻水联产空调的热力COP在1左右,电力COP可达9.03,相应电力消耗和CO2排量比常规空调减少72.69%之多.存在使系统具有较好性能结构的再生温度范围.可以通过改变干空气比来调节潜/显热处理能力,进而实现无能量浪费地提供全部所需冷量.     

Nonlinear-optical modulator for high-power fiber lasers

We propose a novel nonlinear-optical fiber modulator for high-power (>1-W) single-mode fiber lasers. The device is based on transferring the amplitude modulation from a low-power signal at the Stokes frequency onto a high-power beam through stimulated Raman scattering. The efficiency and limitations of the Raman modulator when highly Ge-doped fiber is used is considered. An insertion loss of less than 0.4 dB and an extinction ratio of 20 dB are predicted for modulation of a 10-W single-mode Nd-doped fiber laser.     

含铁磁耦合Ni3单元的均苯三甲酸桥联双层镍(II)配合物

使用均苯三甲酸与碳酸镍在水热条件下反应得到了一例新的二维双层Ni(II)配位聚合物Ni3(BTC)2(μ-H2O)26H2O。二维层包含syn-syn羧酸桥和水桥连接的三核Ni3单元,进一步用均苯三甲酸上的苯环连接成二维层状结构。磁性研究表明,相邻Ni2+离子间存在弱的铁磁耦合作用。水桥连镍离子的桥联键角为122.8(3)deg,所以通过该水桥镍离子间应该呈现反铁磁耦合。因此,实验结果证明了syn-syn羧酸桥传递铁磁耦合,而且铁磁耦合大于反铁磁作用,最终配合物呈弱的铁磁耦合。基于本工作和文献报道的含syn-syn 羧酸混合桥联镍配合物的磁性,我们总结出下面结论：Ni–O–C–O–Ni的共面性与否决定了配合物的磁性。共面性好的Ni–O–C–O–Ni导致中等强度的反铁磁耦合,而共面性差会消弱反铁磁作用,甚至出现由反铁磁变为铁磁耦合。标题配合物中羧酸桥所传递的铁磁性可能就归因于Ni–O–C–O–Ni的不共平面性。因此,与含羧酸桥的混合桥联双核铜(II)配合物类似,轨道补偿效应(the orbital complementary effect (OCE))对于解释水/羧酸混合桥联镍(II)配合物的磁性也同样适用。