天鹅绒阴极产生的双脉冲强流相对论电子束特性实验研究

在时间分辨的模式下, 实验研究了天鹅绒阴极产生的双脉冲相对论强流电子束的束心运动、束包络和束的发射度. 在实验中, 电子束流强度和电子束心运动用电阻环进行测试, 而电子束和石英玻璃的相互作用产生的契仑科夫辐射用来给出电子束包络和发射度信息. 电子束和石英玻璃作用产生的契仑科夫辐射用1台8幅分幅相机记录. 实验结果表明, 天鹅绒阴极产生的相对论强流双脉冲电子束在束流大小、束心运动轨迹、束包络及束发射度等方面具有较好的一致性.     

Temporal and spectral properties of ultrashort pulsed Laguerre-Gaussian beams in dispersive media

The temporal and spectral properties of ultrashort pulsed Laguerre-Gaussian (LG) beams propagating in dispersive media are studied both theoretically and numerically. It is shown that the on-axis pulse broadens with increasing propagation distance and the on-axis spectrum is blueshifted. For the off-axis spectrum the blueshifts decrease and then the spectrum becomes redshifted as the radial distance increases. The propagation of ultrashort pulsed LG beams in free space and of ultrashort pulsed Gaussian beams can be regarded as special cases of our results, and some interesting properties are discussed.     

同轴型爆磁压缩发生器1维磁扩散模型

 基于１维爆轰驱动模型、爆炸管与金属固壁的１维磁扩散模型及回路等效电路模型，编制了关于轴线起爆大电流同轴型爆磁压缩发生器的数值模拟程序CEMG2.0。应用该程序对洛斯·阿拉莫斯实验室设计试验的43 cm长Ranchero发生器进行了对比模拟，结果证明CEMG2.0程序所采用的模型是合理的，可以应用于今后同类发生器的优化设计。     

Kinetics of the Temperature-Dependent eaq− and ⋅OH Radical Reactions with Cr(III) Ions in Aqueous Solutions

The reactivity of chromium(III) species with the major oxidizing and reducing radiolysis products of water was investigated in aqueous solutions at temperatures up to 150 °C. The reaction between the hydrated electron (e_aq⁻) and Cr(III) species showed a positive temperature dependence over this temperature range. The reaction was also studied in pH 2.5 and 3.5 solutions for the first time. This work also studied the reaction between acidic Cr(III) species and the hydroxyl radical (⋅OH). It was found that Cr³⁺ did not react significantly with the ⋅OH radical, but the first hydrolysis species, Cr(OH)²⁺, did with a rate coefficient of k= (7.2±0.3)×10⁸ M⁻¹ s⁻¹ at 25 °C. The oxidation of Cr(OH)²⁺ by the ⋅OH radical formed an absorbing product species that ultimately oxidized to give Cr(VI). These newly measured reaction rates allow for the development of improved models of aqueous chromium speciation for the effective remediation of liquid high-level nuclear waste via vitrification processes.     

Structural characteristics and residual stresses in oxide films produced on Ti by pulsed unipolar plasma electrolytic oxidation

Oxide films, 7–10 µm thick, were produced on commercially pure titanium by plasma electrolytic oxidation in a sodium orthophosphate electrolyte using a pulsed unipolar current with frequency (f) and duty cycle (δ) varying within f = 0.1–10 kHz and δ = 0.8–0.2, respectively. The coatings comprised a mixture of an amorphous phase with nanocrystalline anatase and rutile phases, where the relative rutile content range was 17–25 wt%. Incorporation of phosphorus from the electrolyte into the coating in the form of PO₂ ^–, PO₃ ^2– and PO₄ ^3–, as demonstrated by EDX and FT-IR analyses, contributed to the formation of the amorphous phase. Residual stresses associated with the crystalline coating phase constituents were evaluated using the X-ray diffraction sin² ψ method. It was found that, depending on the treatment parameters, internal direct and shear stresses in anatase ranged from–205 (±17) to–431 (±27) MPa and from–98 (±6) to–145 (±10) MPa, respectively, whereas the rutile structure is comparatively stress-free.     

Modern proton‐detected 1D 1H–15N NMR experiments. Application to the measurement of 1H,15N coupling constants at natural abundance

Non‐selective and selective versions of several proton‐detected 1D NMR experiments to be applied to ¹⁵N are proposed. Clean, artifact‐free 1D spectra are easily obtained by the effective coherence selection by pulsed‐field gradients and the attainable sensitivity is maximized using modern pulse schemes. Despite the low sensitivity inherent to ¹⁵N NMR spectroscopy, the successful application of these experiments is demonstrated for resonance assignments and accurate measurement of both one‐bond and long‐range proton–nitrogen coupling constants on a model tripeptide at natural abundance. Copyright © 2001 John Wiley & Sons, Ltd.     

LIA组元的脉冲功率调制系统研制

本文介绍一种以加速组元为终端负载的纳秒脉冲功率系统。获得的加速间隙电压为350kV，90ns(半高宽)，波形上升时间为30ns；Blumlein主开关工作电压大于280kV，抖动小予1.5ns(均方根值)。对同轴场畸变开关性能的进一步改善作了必要的讨论，提出了用等场强原则偏置触发极，比通常采用自然中位面方法，可使开关工作电压提高8．7％。     

Nanocarbon-poly(methyl methacrylate) composite materials

Nanocarbon-poly(methyl methacrylate) sols were prepared by pulsed laser ablation at the interface of target submerged in flowing liquid (PLA-IT/SFL) method, and the corresponding composite films were prepared by solution-casting. Spectra results indicated that there existed interactions between nanocarbon and the polymethyl methacrylate (PMMA) matrix, which was consistent with the decrease in glass transition temperature of the composites with increase of carbon content. TEM images revealed that a carbon encapsulated core/shell structure was formed in the composites, which could ensure good dispersion of carbon nanoparticles within the PMMA matrix. The decomposition of the composites was less influenced by the introduction of nanocarbon particles. Translated from Acta Polymerica Sinica 2006, 2(2) (in Chinese)     

Simulation and experiment of the cooling effect of trapped ion by pulsed laser

We investigate the process of pulsed laser cooling using a self-constructed molecular dynamics simulation(MDSimulation) program. We simulate the Doppler cooling process and pulsed laser Doppler cooling process of a single ~(40)Ca~+ ion, and the comparison with the experimental results shows that this self-constructed MD-Simulation program works well in the weak laser intensity situation. Furthermore, we analyze the pulsed laser Doppler cooling process of a single ~(27)Al~+ ion. This program can be used to analyze the molecular dynamic process of various situations of Doppler cooling in an ion trap, which could give predictions and experimental guidance.     

Pulsed laser deposition of pure fluoroapatite film without OH groups

The relation between O₂ pressure and composition in the pulsed‐laser deposition of fluoroapatite was investigated using both on‐axis and off‐axis methods to determine the optimal conditions for obtaining a pure fluoroapatite film without OH groups. Through this, it was found that an O₂ pressure of 10 Pa, combined with an off‐axis method, results in P/Ca and F/Ca values (0.6 and 0.2, respectively) that match closely with a stoichiometric composition of Ca₁₀(PO₄)₆F₂. Fourier transform infrared spectroscopy analysis confirmed that this optimized film was almost pure fluoroapatite, with no evidence of any OH groups originating from hydroxyapatite. X‐ray diffraction also revealed that this fluoroapatite film crystallizes with a c‐axis orientation perpendicular to its surface.