PSO-LSSVM对LIBS定量分析精度的提高

针对土壤定量分析受基体效应影响大，LIBS定量分析精度不佳等问题，采用粒子群算法对LSSVM进行优化，提高模型的精确度。选取Pb Ⅰ 405.78 nm和Cr Ⅰ 425.44 nm作为分析谱线进行分析。采集十二个不同浓度样品的特征光谱，每个浓度样品在不同点采集20组数据，将其中17组数据设为训练集，3组数据设为预测集，用LSSVM和PSO-LSSVM两种方法建立定标模型。对比两种模型的拟合相关系数（R2）、训练集均方根误差（RMSEC）和预测集均方根误差(RMSEP)。由于自吸收效应的影响，随着浓度的增加，预测值逐渐低于实际值，LSSVM定标模型的拟合程度较低，无法达到实验要求，模型性能有待提高。利用粒子群算法对LSSVM的模型参数惩罚系数和核函数参数进行优化，得到最佳的参数组合，Pb元素为(8 096.8, 138.865 7)，Cr元素为(4 908.6, 393.563 5)，用最佳的参数组合构建LSSVM的定标模型。相比于LSSVM，PSO-LSSVM定标模型的精确度更高，Pb和Cr元素的R2提高到了0.982 8和0.985 0，拟合效果明显提升。Pb和Cr元素的训练集均方根误差由0.026 0 Wt%和0.027 2 Wt%下降到0.022 4 Wt%和0.019 1 Wt%，预测集均方根误差由0.101 8 Wt%和0.078 8 Wt% 下降到0.045 8 Wt%和0.042 0 Wt%，模型的稳定性进一步提高。说明PSO-LSSVM算法能够更好地降低土壤基体效应和自吸收效应带来的影响，提高分析结果的精确度与稳定性。     

介质材料二次电子发射特性对微波击穿的影响

以介质填充的平行板放电结构为例,本文主要研究了介质填充后微波低气压放电和微放电的物理过程.为了探究介质材料特性对微波低气压放电和微放电阈值的影响,本文采用自主研发的二次电子发射特性测量装置,测量了7种常见介质材料的二次电子发射系数和二次电子能谱.依据二次电子发射过程中介质表面正带电的稳定条件,计算了介质材料稳态表面电位与二次电子发射系数以及能谱参数的关系.在放电结构中引入与表面电位相应的等效直流电场后,依据电子扩散模型和微放电中电子谐振条件,分别探讨了介质表面稳态表面电位的大小对微波低气压放电和微放电阈值的影响.结果表明,介质材料的二次电子发射系数以及能谱参数越大,介质材料的稳态表面电位也越大,对应的微波低气压放电和微放电阈值也越大.所得结论对于填充介质的选择有一定的理论指导价值.     

A super-junction SOI-LDMOS with low resistance electron channel

A novel super-junction LDMOS with low resistance channel(LRC), named LRC-LDMOS based on the silicon-oninsulator(SOI) technology is proposed. The LRC is highly doped on the surface of the drift region, which can significantly reduce the specific on resistance(Ron,sp) in forward conduction. The charge compensation between the LRC, N-pillar,and P-pillar of the super-junction are adjusted to satisfy the charge balance, which can completely deplete the whole drift,thus the breakdown voltage(BV) is enhanced in reverse blocking. The three-dimensional(3 D) simulation results show that the BV and R_(on,sp) of the device can reach 253 V and 15.5 mΩ·cm~2, respectively, and the Baliga's figure of merit(FOM = BV~2/R_(on,sp)) of 4.1 MW/cm~2 is achieved, breaking through the silicon limit.     

Analytical potential of a laser ablation–glow discharge–optical emission spectrometry system for the analysis of conducting and insulating materials

The analytical capabilities of a glow discharge (GD) as a secondary source for excitation/ionization of the material provided by laser ablation (LA) have been compared to conventional laser induced breakdown spectroscopy (LIBS). In LA–GD both sources can be independently adjusted to optimize the sampling process and then its subsequent excitation. This could involve a number of analytical performance advantages, such as reduced matrix dependence, greater precision and sensitivity than those encountered in LIBS. For such purpose, an ablation chamber design including two electrodes to generate the GD discharge has been built and assayed. A comparison between LIBS and LA–GD–OES has been carried out, both, under reduced argon and helium atmospheres. Different sets of samples (conducting reference materials, glass and fluorine pellets) have been used to evaluate the novel coupled technique. The LA–GD coupled system has shown to provide lower detection limits. In addition, best linear correlations between intensities and concentrations and lower matrix effects have also been found using the coupled system. Moreover, special advantages of the LA–GD–OES have also been demonstrated for the analysis of fluorine.     

Research on mechanical and dielectric properties of XLPE cable under accelerated electrical‐thermal aging

Research into the electrical‐thermal aging properties of cross‐linked polyethylene (XLPE) cable has great significance, because of its wide application. This study conducted accelerated electrical‐thermal aging tests on 10‐kV XLPE cable in order to assess the cable's mechanical and dielectric properties. After being aged by applying 34.8‐kV AC voltage at the four temperatures of 90, 103, 114, and 135°C, the cable samples were taken out in five stages according to the aging time and cut into slices. The slices were conducted experiments to test the breaking elongation, tensile strength, gel content, breakdown voltage, and frequency spectrums of the dielectric constant and dielectric loss. The results demonstrate that the mechanical strength and gel content of XLPE vary greatly under different aging temperatures, a finding that is associated with the crystallization characteristics of the material. The breakdown voltage shows a slight decreasing trend with aging time. The dielectric constant decreases with aging time in high‐frequency areas (10³–10⁶ Hz), while the dielectric loss factor increases with aging time at low frequencies (10^?2–0 Hz). These two parameters can be used to characterize the degree of aging in cable. Copyright © 2016 John Wiley & Sons, Ltd.     

支持向量机结台主成分分析辅助激光诱导击穿光谱技术识别鲜肉品种

为提高激光诱导击穿光谱技术(Laser-induced breakdown spectroscopy,LIBS)对鲜肉品种的识别率,采用支持向量机结合主成分分析算法辅助LIBS技术对鲜肉品种进行识别.对鲜肉切片用载玻片压平,采用LIBS技术对鲜肉组织(猪肉、牛肉和鸡肉)表面进行光谱数据的采集,每种鲜肉采集150幅光谱并进行随机排列,取前75幅光谱作为训练集建立模型,后75幅作为测试集测试建模结果.研究选取K、Ca、Na、Mg、Al、H、O等元素的49条归一化谱线数据进行主成分分析,并用所得数据建立支持向量机分类模型.结果表明,通过主成分分析降维,输入变量从49个优化减少到18个,模型建模速度从88.91 s降至55.52 s,提高了支持向量机的建模效率;并使预测集的平均识别率提高到89.11%.本研究为激光诱导击穿光谱技术在鲜肉品种快速分类领域提供了方法和数据参考.     

Coarse Metal Powder-Assisted pulsed CO2 Laser-induced Breakdown Spectroscopy for the Direct Determination of Heavy Metals in Soil

A novel method of laser-induced plasma spectroscopy utilizing a pulsed transversely excited atmospheric CO₂ laser has been developed for the high-sensitivity determination of heavy metals in soil. A coarse metal powder was used to trap the soil and to assist with plasma generation. When the CO₂ laser (10.6?µm, 1.5?J, 200?ns) was irradiated on the metal and soil powder, a high-temperature and long-lifetime luminous plasma was induced. Fine particles of soil were dissociated and were excited in the plasma region. The method was used for the rapid determination of Cr, Pb, and Hg in loam. The limits of detection for Cr, Pb, and Hg were approximately 0.8, 15, and 0.7?mg/kg, respectively.     

Large impact in electrical properties of polypropylene by improving the filler-matrix interface effect in PP/PS blends

Inorganic nanoparticles are widely used to improve space charge behavior, DC breakdown strength and other electrical properties of polymer insulating materials, but the uniform distribution of inorganic nanofillers in matrix is difficult due to their agglomeration and bad compatibility with the polymeric matrix. In this paper, polypropylene (PP)/polystyrene (PS) blends were prepared to suppress space charge accumulation and improve DC breakdown strength. Polypropylene-g-polystyrene (PP-g-PS) graft copolymer was used as compatibilizer to improve the compatibility of PP matrix and PS filler. The evolution of microstructure of PP/PS blends were investigated by scanning electron microscope (SEM), the space charge distributions were measured by a pulsed electro-acoustic (PEA) system, and DC breakdown strength was also tested. The morphologies show that the size of PS particles reduced to 310 nm when the content of PP-g-PS graft copolymer increased to 24 wt%, and the interaction between PP matrix and PS particles enhanced. The presence of PS particles in all PP/PS blends suppressed the space charge accumulation compared to neat PP, but the DC breakdown strength in uncompatibilized blend was lower than neat PP. The increasing of content of PP-g-PS improved the DC breakdown strength with the maximum value of 408.9 kV/mm was obtained. This may attribute to excellent interface structure formed between PP matrix and PS particles.     

激光诱导击穿光谱在核分析实验教学中的应用

为了适应核物理与核分析实验教学的需要,本文将激光诱导激光光谱测量以创新实验的形式引入到核工程类专业实验中.通过将纳秒激光脉冲与不同靶材作用,测量样品中各类元素的LIBS谱线,结合理论分析提取激光等离子体的电子温度和等离子体密度.假设单一元素谱线获得的等离子体密度为混合样品等离子体密度,计算得到未知重元素Fe的原子谱线展宽参数.     

Shock tunnel flow visualization using planar laser-induced fluorescence imaging of NO and OH

Temporal sequences of planar laser-induced fluorescence (PLIF) images of several high-speed, transient flowfields created in a reflection-type shock tunnel facility were acquired. In each case, the test gas contained either nitric oxide or the hydroxyl radical, the fluorescent species. The processes of shock reflection from an endwall with a converging nozzle and of underexpanded free jet formation were examined. A comparison was also made between PLIF imaging and shadow photography. The investigation demonstrated some of the capabilities of PLIF imaging diagnostics in complex, transient, hypersonic flowfields, including those with combustion.Nomenclature A spontaneous emission rate - A _las cross sectional area of laser sheet - B laser absorption rate - C _opt constant dependent on optical arrangement, collection efficiency, etc. - D nozzle throat diameter - E _p laser pulse energy - f _J Boltzmann fraction of absorbing state - g spectral convolution of laser and absorption lineshapes - k Boltzmann constant - M _s incident shock Mach number - N noise, root-mean-square signal fluctuation - P static pressure - P ₁ initial pressure of test gas in shock tube - P _a free jet ambient pressure - P _s stagnation pressure - Q electronic quenching rate of excited state - S PLIF signal - t time between shock reflection and image acquisition - T static temperature - T _s stagnation temperature - _a mole fraction of absorbing species