Field-theoretic approach to second-order phase transitions in two- and three-dimensional systems

We review the physical principles which are at the basis of recent field-theoretic computations of the critical exponents in two- and three-dimensional systems. We concentrate on those points that do not show up explicitly in the more standard-expansion: they must be discussed with care if one uses a perturbative approach at fixed space dimensions (the loop expansion). We present in detail simple computations of the critical exponents, while we summarize the results of longer and more accurate computations.     

The electronic spectrum of VCr

The electronic spectrum of VCr has been studied using the complete-active-space self-consistent field complete-active-space second-order perturbation theory approach. Potential-energy curves for 12 electronic states have been computed. Transition energies, with respect to the X² ground state, for some of the calculated electronic states are (with possible experimental values within parentheses) 0.53 eV (0.56) for A²⁺, 1.03 eV (1.14) for A⁴, 1.20 eV (1.14) for B², 1.45 eV (1.51) for B⁴, 1.60 eV (1.51, 1.78) for C², and 1.61 eV (1.63) for A^4–. AcknowledgementsThe research reported in this communication was supported by a grant from the Swedish Natural Science Research Council (NFR). S. Alex and D.G. Leopold are acknowledged for providing results from their negative ion photoelectron spectroscopy on VCr.Contribution to Björn Roos Honorary Issue     

Rate Coefficient for Self-Association Reaction of CF2 Radicals Determined in the Afterglowof Low-Pressure C4F8 Plasmas

We have analyzed decay kinetics of CF₂ radicals in the afterglow of low-pressure, high-density C₄F₈ plasmas. The decay curve of CF₂ density has been approximated by the combination of first- and second-order kinetics. The surface loss probability evaluated from the frequency of the first-order decay process has been on the order of 10^–4. This small surface loss probability has enabled us to observe the second-order decay process. The mechanism of the second-order decay is self-association reaction between CF₂ radicals (CF₂+CF₂C₂F₄). The rate coefficient for this reaction has been evaluated as (2.6–5.3)×10^–14 cm³/s under gas pressures of 2 to 100 mTorr. The rate coefficient was found to be almost independent of the gas pressure and has been in close agreement with known values, which are determined in high gas pressures above 1 Torr.     

Intelligent Integrated Control of Underactuated Mechanical Systems with Second-order Nonholonomic Constraints

This paper describes an intelligent integrated control of an acrobot, which is an underactuated mechanical system with second-order nonholonomic constraints. The control combines a model-free fuzzy control, a fuzzy sliding-mode control and a modelbased fuzzy control. The model-free fuzzy controller designed for the upswing ensures that the energy of the acrobot increases with each swing. Then the fuzzy sliding-mode controller is employed to control the movement that the acrobot enters the balance area from the swing-up area. The model-based fuzzy controller, which is based on a Takagi-Sugeno fuzzy model, is used to balance the acrobot. The stability of the fuzzy control system for balance control is guaranteed by a common symmetric positive matrix, which satisfies linear matrix inequalities.     

乒乓球技术正误对比教学法的运用

对学生学习乒乓球技术所出现的错误动作，适时采取正确动作示范和错误的演示进行对比、分析，帮助学生纠正错误技术动作，本文对正误对比的教学法做了初步的探析。     

二阶色散管理孤子的传输

在准理想的的色散管理系统中建立了非均匀扰动模型，研究了它们对二阶孤子传输的影响。结果表明，扰动导致孤子崩塌。它们影响的大小与周期长度和扰动强度有关，而且它们都存在着最差周期长度和扰动共振现象。     

气相色谱填充柱改装成毛细管柱的研究

针对上分103型气相色谱仪，改装填充柱为毛细管柱后其性能良好，各项指标均达到同类仪器水平。     

7-羟基-4-甲基香豆素的二阶NLO性质对晶体结构的依赖性

研究了7种香豆素衍生物的二阶非线性光学性质，在理论和实验上分析了7-羟基4-甲基香豆素的二阶非线性光学性质对晶体结构的依赖性，表明这是一类热稳定性高、透光性好的化合物，分子在晶体中的趋向对二阶非线性光学响应有重要影响，改良其晶体结构是提高这类材料综合性能的主要手段．     

遮蔽段总传热系数的计算

提出了一种同时考虑烟气辐射及对流来计算遮蔽段总传热系数的方法 (简称CRK法 ) ,利用现场收集到的 4套加热炉结构及不同操作数据 ,由传热速率方程和热平衡方程联立求解得出遮蔽段总传热系数值。将该计算值与CRK法及传统计算方法进行了对比 ,同时考察了管排与烟气错流换热时温差系数的影响。结果表明 ,CRK法的计算误差小于传统计算方法 ,在进行遮蔽段传热计算时 ,错流温差校正系数可近似按 1处理。     

基于环境等值线法的海上浮式风机长期极限响应预测

为保证海上浮式风机在复杂的风浪环境载荷作用下正常服役,需要评估海上浮式风机的长期极限响应。通过实测风浪的联合概率分布,利用基于逆一次可靠度法(IFORM)和逆二次可靠度法(ISORM)的环境等值线法获取环境工况组合,模拟风机短期响应并结合Gumbel极值分布计算风机长期极限响应,实现了对海上浮式风机50 a重现周期的极限响应预测。研究结果表明:风浪联合作用下,随着平均风速增大,平台纵荡运动、叶根面外弯矩和塔基前后弯矩出现了先增大后减少的趋势;随着有义波高增大,平台纵荡运动最大值和平均值、塔基前后弯矩最大值也随之增大;与基于IFORM的环境等值线法相比,基于ISORM的环境等值线法可以涵盖更多的环境工况组合,得到更大的浮式风机长期极限响应,进一步提高了风机结构设计安全性。