微波谐振腔测量低温液体介电常数精度分析

本文分析了用微波谐振腔调谐振荡器方法研究低温介质介电常数的测量精度,得出了介电常数测量精度的计算公式.理论计算与实验结果符合得很好.给出了用该法测得的处在饱和压力下液氮介电常数值,并与其他作者的测量结果进行了比较.     

海水低频声吸收与pH值的关系

本文用共振器法测量了天然海水低频声吸收与pH值的关系。测量频率为2.91、6.82和10.76kHz;pH值范围为6.48—8.51;温度为12.6℃。测量结果与不同的声吸收公式计算值进行了比较。本文实验的主要目的之一是通过将pH值减小到足够小的数值来检验海水中MgSO_4吸收的贡献。实验结果表明:为了能用一个统一的公式较准确地预估低频和高频的海水声吸收,此公式看来应该既包括MgCO_3吸收项,又包括MgHCO_3~ 吸收项。     

超声波在乙酸乙酯和乙酸甲酯中的弛豫吸收

关于超声波在乙酸乙酯和乙酸甲酯中的吸收问题曾引起了多次热烈的争论,为此,作者采用了行波中的光衍射法做了进一步的实验研究。在实验过程中,特别注意了仪器的精确度问题,并且对许多种吸收系数已知的标准液体进行了多次重复的测量,结果很好地符合于一般的公认值,且误差不超出5％。对于两种乙酸酯,测量的频率范围是3-30Mc,温度保持20℃。测量结果表明,在实验的误差范围内,吸收的实验值很好地落在唯象单弛豫理论所预期的曲线上,弛豫频率对乙酸乙酯约在12Mc附近,对乙酸甲酯约在7Mc附近。并且通过对不同纯度的乙酸乙酯进行重复的测量,表示杂质引起的附加吸收并不影响吸收曲线的特性。因此也就明某些作者测量得到两个弛豫频率的结果是不真实的。作者并认为Karpovich首先提出的旋转异构的理论是适合于解释这两种液体的驰豫吸收的机理的。     

草酸铵作稳定剂石墨炉原子吸收法直接测量土壤悬浮液中微量镉

本文研究了石墨炉原子吸收法直接测量土壤悬浮液中微量镉。比较了不同基体改进剂及背景吸收对测量的影响。并以草酸铵为稳定剂对悬浮液的稳定性进行了研究,结果表明在碱性条件下,使用０．００７ ｍ ｏｌ·Ｌ－ １ 的草酸铵作稳定剂时, 土壤悬浮液比较稳定。应用固体悬浮液进样方法, 直接测定了土壤样品中的微量镉     

微分吸收法测量二极管电压

给出了微分吸收法测量二极管电压的基本原理和实验结果。利用MCNP程序对轫致辐射-衰减-探测器系统建模,模拟得到了输出剂量与二极管工作电压关系拟合曲线。建立了微分吸收法测量二极管电压测量系统,通过在探测器前端放置不同厚度的吸收片,得到了衰减程度不同的波形。结合理论计算的拟合曲线和实验波形,利用迭代法计算得到了晨光号加速器二极管电压,电压峰值为0.58 MV。和传统方法所测得二极管工作电压进行了比较,结果较为一致。     

相对论多组态相互作用方法计算Mg~+离子同位素位移

采用相对论多组态相互作用方法研究了Mg~+离子3s~2S_(1/2)—3s~2P_(1/2)和3s~2S_(1/2)—3s~2P_(3/2)两条跃迁谱线的特殊质量位移系数和场位移因子,并计算了中子数8≤N≤20的Mg~+离子的同位素位移.计算结果与其他理论的计算值符合得比较好,与最新的实验测量结果比较,相对误差在0.13%到0.28%范围,是目前最接近Mg~+离子同位素位移实验测量的理论计算结果.该计算结果可为Mg~+离子同位素位移实验和理论研究提供参考,能够用于Mg~+离子的短寿命同位素的光谱测量实验以及利用Mg~+离子开展幻中子数N=8和N=20附近的奇异原子核特性研究等.所用的计算方法和电子激发模式也可以推广到其他核外电子数为11的多电子体系,用于开展相应的原子光谱结构计算和同位素位移的理论研究.     

草酸铵作稳定剂石墨原子吸收法直接测量土壤悬浮液中微量镉

本研究了石墨炉原子吸收法直接测量土壤浮液中微量镉。比较子不同基体改进剂及背景吸收对测量的影响。并以草酸铵为稳定剂对悬液的稳定性进行了研究，结果表明在碱性条件下，使用０．００７ｍｏｌ·Ｌ＾－１的草酸铵作稳定剂时，土壤悬浮液比较稳定。应用固体悬浮液进样方法，直接测定了土壤样品中的微量镉。     

烷基环己苯异硫氰酸液晶材料太赫兹波吸收

基于密度泛函理论,利用Gaussian09程序包,通过Opt+Freq优化结构,以B3LYP/6-311g基组对4-(trans-4-n-alkylcyclohexyl) isothiocyanatobenzenes (CHBT) 16种液晶分子在0.1—5.0 THz波段的吸收进行研究,提出了通过考察分子转动惯量和质量重心偏移对太赫兹吸收的影响方法.计算结果表明,随着分子烷基链上碳原子数目增加,分子的转动惯量和重心的偏移将对太赫兹波的吸收产生影响.在0.1—5.0 THz波段, 3—7个碳原子的分子吸收相对较强.以此为参照,减少和增加烷基链上的碳原子数目都会降低分子对太赫兹波的吸收.在0.3—3.0 THz范围内,将计算结果与10种有实验数据的分子进行了对比.结果发现,低频波段计算结果与实验测量相比存在差异,其中吸收峰位置的差异可能来源于氢键.比较吸收强度的相对大小值,发现实验测量与计算结果较为一致,表明吸收强度来源于偶极子振动、转动吸收,展现了计算模拟的积极意义.研究结果可对相关分子的设计与合成提供有用的建议.     

6611-6618cm~(-1)之间氨气光谱线强的测量

在可调谐半导体激光吸收光谱(TDLAS)技术中,目标气体分子的吸收光谱参数,尤其是线强对温度、浓度的精确反演测量具有重要作用.HITRAN/GEISA/HITEMP等数据库中的光谱参数包含理论计算的结果,与实际情况存在相当的误差.本文采用TDLAS-波长扫描直.接吸收技术测量了室温下氨气在6611—6618 cm~(-1)之间的吸收光谱,利用Voigt线型多峰拟合方法获得了20条谱线在不同压强下的积分吸光度值,将获得的不同压强下的积分吸光度值进行线性拟合计算测量温度下的线强值,同时通过不确定度分析及误差传递计算了实验钱强值的不确定度.通过与HITR.AN 2012数据库中值进行对比,得出氨气在6611—6618 cm~(-1)波段实验线强值与数据库中值相差0.51%—17.28%,且实验线强值的不确定度在0.81%—3.3%范围,小于HITRAN2012中线强的不确定度5%—10%范围.     

甲烷气体2ν_3带R9支吸收线强度的精确测量

通过外腔二极管激光器测量了甲烷位于 16 37.6 4～ 16 37.85nm(真空中 )的 2ν3 带R9支的直接吸收谱 ,通过Voigt拟合计算出了每条线的吸收线强度 ,并与Margolis用傅里叶变换红外光谱仪测得的实验结果进行了比较 ,同时分析了偏差及产生的原因。实验和计算得出 ,在测得的八条吸收线中 ,最大偏差为 3.9% ,最小偏差为 0 .0 2 % ,除了线 3和线 4有较大偏差外 ,其他结果都在实验误差范围之内。所获得的数据可应用于光学遥测甲烷气体浓度。提供的方法也可应用到CO ,CO2 ,NH3 等其他气体的吸收线强度的测量中。     

水体中溶解有机物激光诱导荧光光谱分析方法

讨论了用激光诱导荧光(LIF)的方法分析水体中溶解有机物(DOM)的含量,利用拉曼散射信号对荧光光谱进行归一化处理,消除激发光强度和水体对荧光的二次吸收和接收条件等因素的影响,并给出了理论依据,由此依据得出了非线性浓度校准的数学模型.利用这个数学模型对实验数据进行非线性拟合,拟合的相关系数高于0.99.该浓度校准的数学模型,考虑到了水体对荧光信号的二次吸收以及溶液浓度的变化对二次吸收的影响,结果表明它可作为不同水体的通用浓度校准的数学模型对水体中的DOM进行定量分析.     

Radiation transfer in absorbing-scattering liquids—II. Comparisons of measurements with predictions

Comparisons have been made between measured and predicted results for the radiation field in both highly absorbing and scattering aqueous suspensions with a highly reflecting or absorbing bottom. Predictions were based on a discrete ordinate solution to the equation of transfer, with the requisite properties (extinction coefficient, absorption coefficient and scattering phase function) obtained from measurements performed on samples extracted from the suspensions. All trends in the data were predicted by the model, although poor numerical agreement was obtained for suspensions of large albedo and extinction coefficient. The disagreement is attributed to the effect of multiple scattering on the property measurements.     

Solitons in stimulated Raman scattering and resonant two-photon propagation

We are starting from equations of motion describing both stimulated Raman scattering and resonant two-photon absorption and emission processes. Application of the Estabrook-Wahlquist method leads to a system of differential equations whose integrability conditions are the original equations. This system is used as the starting point for applying the inverse scattering method. Implicit N-soliton formulae and explicit one-soliton formulae are derived. Possible applications under specified experimental conditions are discussed.     

A quantitative atom-probe field-ion microscope study of the compositions of dilute Co(Nb) and Co(Fe) alloys

The compositions of Co-1.0at%Nb and Co-1.0at%Fe alloys have been measured using the atom-probe field-ion microscope. The main purpose of this experimental work was to find a set of optimum conditions which gives the correct solute concentrations in these alloys. This information was necessary for measuring the absolute compositions, in our extensive investigations of solute atom segregation effects to individual stacking faults in these alloys. The dependence of each alloy's composition on the following parameters was investigated: (1) the specimen temperature; (2) the pulse fraction; (3) the field-evaporation rate; (4) the crystallographic plane; (5) the effect of the presence of hydrogen in the atom-probe on the measured Nb composition in a Co-1.0at%Nb alloy. It is shown that the composition determined by the atom-probe FIM is very sensitive to some of the parameters listed above. The effects of these experimental parameters on the measured Nb and Fe concentrations are discussed in terms of possible field-evaporation models. Under certain experimental conditions drastically different behavior has been observed in these alloys; preferential field-evaporation of solute atoms in a Co-1.0at%Fe alloy and preferential retention of solute atoms in a Co-1.0at%Nb alloy was observed. Correct solute concentrations were obtained by using the following experimental parameters: (1) a specimen temperature of less than or equal to 60 K; (2) a pulse fraction of greater than or equal to 0.10.     

Microwave induced thermoelastic process in dielectrics-theory and experiments

Theoretical and experimental studies on microwave pulse induced pressure waves are reported. A thermodynamical formulation of microwave interaction with dielectrics is summarized. It is shown that acoustic waves may be generated by pulsed microwaves even in the absence of inhomogeneity of microwave absorption, owing to discontinuities of thermodynamical variables and microwave exposure conditions across the dielectric interface. The formulation is applied to a spherical system and some numerical results are presented. Experimental results include measurement of pressure waves in a cylinder filled with an aqueous solution of electrolytes exposed to pulsed microwaves and estimation of the coupling efficiency between the liquid dielectric and the adjacent air. Pressure scaling with energy per pulse is also demonstrated.     

Johann单色器能量分辨率分析

Johann单色器是一种广泛应用的X光单色器,对其能量分辨率已有若干工作进行过分析.对此问题进行了进一步的分析,改进了已有的工作.将计算结果和已有公式的计算结果同时与SHADOW追迹结果进行比较,理论计算与追迹结果有更好地吻合,同时适用范围更大.     

Attosecond transient absorption spectroscopy:Comparative study based on three-level modeling

In the present paper, the time-resolved transient absorption spectroscopy of helium atoms is investigated based on the three-level modeling. The helium atoms are subjected to an extreme ultraviolet(XUV) attosecond pulse and a time-delayed infrared(IR) few-cycle laser field. The odd excited state are populated from the ground state by the XUV pulse due to the dipole selection rule, and probed by the time-delayed IR laser. The time-resolved transient absorption spectroscopy based on the different coupling mechanism demonstrate some different features, the photoabsorption spectrum based on three-level model with rotating wave approximation(RWA) cannot repeat the fast oscillation and the sideband structure which have been observed in the previous experimental investigation. The dressing effect of IR laser pulse on the ground state can contribute new interference structures in the photoabsorption spectrum.     

激光二极管抽运的被动调QNd3+:YAG微晶片激光器及其稳定性

从理论和实验两个方面研究了连续激光二极管抽运的Cr~(4+):YAG被动调QNd~(3+):YAG微晶片激光器。考虑Cr~(4+):YAG饱和吸收体激发态吸收,推导了连续抽运的被动调Q微晶片激光器的速率方程,分析了微晶片参量对调Q脉冲半峰全宽和峰值功率的影响;提出了实现稳定脉冲输出的微晶片激光器设计原则。在饱和吸收体初始透过率较低(T_0≈40％)的情况下,获得了脉冲峰值功率不稳定性小于±0.7％、脉冲宽度不稳定性小于±1.0％、峰值功率高达千瓦量级的高重复频率激光输出。     

Laser ablation of copper based alloys by single and double pulse laser induced breakdown spectroscopy

Single and double pulse laser induced breakdown spectroscopy was applied to the analysis of copper based alloys samples, in order to investigate the material ablation process under two different experimental conditions. An Nd:YAG laser, emitting at the fundamental wavelength (1064 nm) for a fixed value of total energy with the same pulse width, has been used for both set-up configurations. Certified samples of copper based alloys were examined in order to investigate the effect of their different compositions on the ablation process efficiency. The craters produced by the laser on the samples surfaces were measured by a contact profilometer in order to evaluate the mass of ablated material. In this respect the differences in behaviour of the single and the double pulse ablation for Laser Induced Breakdown Spectroscopy (LIBS), respectively, have been considered. The dependence, under the same experimental conditions, of the LIBS background emission of the different ablated masses of the material has also been investigated, by looking for normalization algorithms for quantitative data reduction.The behaviour of some peculiar intensity ratios, suitable for building calibration curves, has been studied in order to evaluate the trend in fractionated evaporation on going from the single pulse to the double pulse technique. PACS 52.70.-m; 52.50.Jm; 42.62.Fi