Selectivity of nitro versus fluoro substitution in arenes in their reactions with charged O‐ and S‐nucleophiles

The relative mobility of nitro and fluoro substituents in 1,3‐dinitro‐ and 1‐fluoro‐3‐nitrobenzenes, 3,5‐dinitro‐ and 3‐fluoro‐5‐nitrobenzotrifluorides under the action of the nucleophiles (2ArYH)·K₂CO₃ and ArY^?K⁺ in solution and the nucleophiles ArYH·K₂CO₃ (Y = O, S) under heterogeneous conditions was studied by a competitive method in DMF at 40–140 °C. The unique dependences of ΔΔH^≠ on ΔΔS^≠ and ΔΔH^≠ on ΔΔG^≠ were determined for all the substrates and nucleophiles. The dependence of the mechanistic pathway on the nucleophile is discussed. Two results are relevant to the reactions studied: (i) substituent effects in the nucleophiles (2ArYH)·K₂CO₃ and ArYH·K₂CO₃ on the activation entropies suggest that the entropy favours the displacement of nitro group; (ii) the negative signs of ΔΔH^≠ and ΔΔS^≠ for the reactions of the nucleophiles ArY^?K⁺ indicate that the enthalpy determines the displacement of nitro group. It is concluded that the selectivity of the reactions with aryloxide and arylthioxide ions cannot be explained by the hard–soft acid–base principle only. Copyright © 2007 John Wiley & Sons, Ltd.     

拼接光栅压缩器的时域特性

在拼接光栅和拼接光栅压缩器的设计中,子光栅调节偏差不可避免,各维偏差与拼接光栅的时间特性之间的关系很关键。通过脉冲压缩理论分析得到各维偏差和聚焦脉冲时间宽度展宽之间的解析关系,从数值计算结果分析,面平行左右偏差对脉冲的时间宽度影响较大,必须控制在21.08μrad内;条纹密度差异对脉冲宽度的影响很显著,相对条纹密度的比值应控制在10-5以内;从消除角色散的角度分析,面平行俯仰偏差和条纹平行度偏差可以相互补偿,条纹密度差异和面平行左右偏差也可以相互补偿。     

Estimation of various scattering parameters and 2-DEG mobilities from electron mobility calculations in the three conduction bands Γ, L and X of gallium arsenide

The electron drift mobility in Γ conduction band of GaAs has been calculated before, but for the first time, we have made attempts to estimate the electron mobilities in higher energy L and X minima. We have also calculated the value of mobility of two-dimensional electron gas needed to predict hetero-structure device characteristics using GaAs. Best scattering parameters have been derived by close comparison between experimental and theoretical mobilities. Room temperature electron mobilities in Γ, L and X valleys are found to be nearly 9094, 945 and 247 cm²/V-s respectively. For the above valleys, the electron masses, deformation potentials and polar phonon temperatures have been determined to be (0.067, 0.22, 0.39m ₀), (8.5, 9.5, 6.5 eV), and (416, 382, 542 K) as best values, respectively. The 2-DEG electron mobility in Γ minimum increases to 1.54 × 10⁶ from 1.59 × 10⁵ cm²/V-s (for impurity concentration of 10¹⁴ cm⁻³) at 10 K. Similarly, the 2-DEG electron mobility values in L and X minima are estimated to be 2.28 × 10⁵ and 1.44 × 10⁵ cm²/V-s at 10 K, which are about ∼4.5 and ∼3.9 times higher than normal value with impurity scattering present.      

Accelerator development in India for ADS programme

At BARC, development of a Low Energy High Intensity Proton Accelerator (LEHIPA), as front-end injector of the 1 GeV accelerator for the ADS programme, has been initiated. The major components of LEHIPA (20 MeV, 30 mA) are a 50 keV ECR ion source, a 3 MeV Radio Frequency Quadrupole (RFQ) and a 20 meV drift tube linac (DTL). The Low Energy Beam Transport (LEBT) and Medium Energy Beam Transport (MEBT) lines match the beam from the ion source to RFQ and from RFQ to DTL respectively. Design of these systems has been completed and fabrication of their prototypes has started. Physics studies of the 20–1000 MeV part of the Linac are also in progress. In this paper, the present status of this project is presented.      

Space radiation effect on fibre optical gyroscope control circuit and compensation algorithm

The process of a γ-irradiation experiment of fibre optical gyroscope （FOG） control circuit was described, in which it is demonstrated that the FOG control circuit, except for D/A converter, could endure the dose of 10krad with the protection of cabin material. The distortion and drift in D/A converter due to radiation, which affect the performance of FOG seriously, was indicated based on the elemental analysis. Finally, a compensation network based on adaptive neuro-fuzzy inference system is proposed and its function is verified by simulation.     

同步泵浦PML飞秒激光研究

采用CW锁模YAG倍频激光器同步泵浦PML飞秒染料激光器,产生了平均脉宽约55fs、功率为15mW的光脉冲。文章在理论和实验上还研究了同步泵浦飞秒激光脉冲产生技术。     

Thermodynamics of tri-n-octyltin chloride+hydrocarbon mixtures by gas-liquid chromatography

Gas liquid chromatography was employed to measure the activity coefficients of a group of hydrocarbons at infinite dilution in tri-n-octyltin chloride at 40, 45, 50, 55 and 60°C. The partial molar excess thermodynamic quantities are interpreted by means of the Flory-Patterson theory, and compared with the results obtained for the same group of solutes in tetra-n-octyltin as the solvent. The alkanes activity coefficients and excess enthalpies in both phases are linearly related. Enthalpyentropy compensation in both solvents is discussed.     

用于激光打靶装置中的新型同步系统的研究

一种用于多路激光打靶装置中的新型智能化数字同步机已经研制成功,它将模拟延时电路和数字延时电路巧妙结合在一起,使得最大延时范围达到1s,触发晃动小于1ns,步进精度5ps.     

Revisiting the regulator problem in the geometric approach,part 1, disturbance localization by dynamic compensation

The aim of this paper is to present a new proof of a well-known fundamental set of necessary and sufficient conditions for disturbance localization by dynamic compensation. Due to a more convenient selection of basic definitions and properties, the arguments herein developed are much more concise and straightforward than those already available in the literature. In Part 2 of the paper, the same approach will be extended to the more general problem of regulator synthesis with plant stability, for which necessary and sufficient conditions significantly different from those already known in the literature will be given.This research has been supported in part by MPI, Rome, Italy.     

云纹干涉法面内位移测量的光栅补偿方法研究

运用光的干涉与衍射理论，导出了对称入射光路云纹干涉法面内位移计量的基本公式。针对云纹干涉法在实际应用中易引入刚体位移对真实面内位移干扰这一棘手问题，设计了定量补偿面内位移和变形的非对称光栅补偿光路系统。由于采用高灵敏度基准光栅调节的方法，比螺旋测微器等纯机械方法具有众多优越性。本文分析了该补偿方法对面内正应变条纹梯度和面内剪应变条纹梯度的补偿原理和具体实施过程。本方法大大提高了云纹干涉法面内位移计量和补偿的可靠性。