边修饰Net-Y纳米带的电子结构及机械开关特性的应变调控效应

利用密度泛函理论和非平衡态格林函数相结合的方法,系统地研究了边修饰Net-Y纳米带的电子结构和器件特性的应变调控效应..计算表明:本征纳米带为金属,但边缘的氢或氧原子端接能使其转变为半导体.应变能有效地调控纳米带带隙的大小,适当的应变使能带结构从间接带隙转变为较小的直接带隙,这有利于光的吸收.应变也能改变纳米带的功函数,压缩应变能明显减小功函数,这有利于纳米带实现场发射功能.特别是应变能有效地调控纳米带相关器件的I-V特性,能使其开关比(I_on/I_off)达到106,据此,可设计一个机械开关,通过拉伸及压缩纳米带使其可逆地工作在“开”和“关”态之间.这种高开关比器件也许对于制备柔性可穿戴电子设备具有重要意义.     

近红外光谱的北方寒地土壤含水率预测模型研究

我国北方寒地温差大,土壤温差对近红外光谱测量土壤墒情有较大影响。针对这一问题,以北方寒地土壤为研究对象,探究大范围温度胁迫下（-20～40 ℃）土壤的近红外光谱与土壤不同含水率之间的关系预测模型方法。选取黑龙江八一农垦大学农学院试验基地中的黑土,经烘干、过筛等操作处理后配置含水率范围在15%～50%内八种不同湿度的土壤样品,建立北方寒地土壤大范围温度胁迫下土壤的近红外光谱信息与含水率之间的定量预测模型。在全波段光谱数据的基础上,结合五种不同光谱信号预处理方法,采用BP神经网络算法、优化支持向量机算法（SVM）、高斯过程算法（GP）三种智能算法建立北方寒地土壤近红外光谱与含水率的预测模型并验证模型的效果。利用69组数据进行训练建模, BP神经网络相关参数设置为学习速率0.05,最大训练次数设置为5 000,隐层单元数确定为20;SVM采用径向基函数,并利用leave-one-out cross validation确定了最佳惩罚参数为0.87,使模型预测的准确性提高;高斯过程算法内部采用马顿核。模型的定量评估采用决定系数(R2)和均方根误差（RMSE）。结果表明,在建立的全部BP神经网络模型中,效果最佳的为S_G-BP神经网络模型,模型的R2为0.960 9,RMSE为2.379 7;在SVM模型中SNV-SVM模型的效果最好,模型的R2为0.991 1,RMSE为1.081 5;在GP模型中S_G-GP模型的效果最好,模型的R2为0.928,RMSE为3.258 1,综上基于SNV预处理的SVM模型训练效果最优。利用剩余的35组光谱数据作为预测集验证模型性能,经模型对比分析发现基于SVM算法的预测模型效果优于其他两种算法,其中基于S_G的SVM模型效果最优,其预测模型的R2和差RMSE分别为0.992 1和0.736 9。综合建模集与预测集的参数最终确定基于S_G的SVM模型为最佳模型。此模型可以作为大范围温度胁迫条件下（寒地）的土壤含水率有效预测方法,为设计优化适宜寒地便携式近红外土壤含水率快速测量仪提供科学依据。     

Field-induced functions of porous Si as a confined system

Electroluminescent porous Si (PS) diodes exhibit various useful functions under a high-electric field. The experimental PS diodes are composed of thin semitransparent metal films, PS layers (about 500 nm thick in minimum), p- or n-type Si substrates and ohmic back contacts. Definite nonlinear electrical behavior (negative resistance and nonvolatile bistable memory effects) and cold electron emission phenomena appear in these PS diodes associated with the EL emission. Both the negative resistance and memory effects are related to the charging of Si nanocrystallites by field-induced carrier injection. The electron emission observed in the PS diodes formed on n+–Si substrates is caused by hot electrons tunnelling through the top contact. By an appropriate structural control of PS, the effective drift length under a high-field conduction is significantly increased, and then electrons are emitted ballistically. These functions reflect the activity of PS as a nanocrystalline confined system.     

动态冷原子吸收法快速测定地球化学样品中微量汞

本文介绍了动态冷原子吸收法快速测定地球化学样品中微量汞的方法。本文研究采用了新型的汞蒸气发生器，并对气泡的干扰进行了研究。线性范围为0.2-12ng/mL，标准回收率为97％－106％，相对标准偏差为3.6%，相关系数为0.9997，试验结果表明此方法简便、快速、准确。     

An MSFIA system for mercury speciation based on an anion-exchange membrane

A new methodology for the in-line preconcentration, clean-up and speciation of mercury by use of an anion-exchange membrane is proposed. The speciation of mercury is based on retention of its tetrachloro complex onto the membrane while organic mercury flows freely through it. A multisyringe is used as a liquid driver and a cold vapour atomic fluorescence detector is employed to ensure a high sensitivity. Organic mercury is decomposed into to inorganic mercury by using a UV lamp. The carrier and reductant streams consist of 1.5% (m/v) hydrochloric acid and 2% (m/v) tin chloride, respectively. Certified reference material DORM-2 was digested with 37% hydrochloric acid and analysed directly without the need for extraction. The proposed system is more environmental friendly than the classical liquid-liquid extraction procedure. Mercury recoveries from spiked samples and the reference material were all close to 100%. An LOD of 14 and 16 ng/L was obtained for total and organic mercury, respectively, both with an RSD less than 1.3%.     

The dependence of polymer conductivity on the work function of metallic electrodes

It is shown that the occurrence of metallic conductivity in polymers is due to their electrification. In particular, the current density depends on the electron work function of metallic electrodes which are in contact with the polymer.     

教学评一致性视域下金属单元复习课的实践*

分析金属知识在中考和教材中的地位,针对当前单元复习教学中存在的问题,依据教学评一致性原则,将“金属知识”的单元复习在“订书钉”为主要线索的探究活动中展开,以此激发学生的学习兴趣,优化学生单元知识结构,发展学生分析问题、解决问题的能力,同时提高学生对学科价值的认识。     

High-temperature oxidation studies of cold-sprayed Ni-20Cr and Ni-50Cr coatings on SAE 213-T22 boiler steel

The high-temperature oxidation behavior of cold-sprayed Ni-20Cr and Ni-50Cr coatings on SAE 213-T22 boiler steel has been investigated at 900 °C in air under cyclic heating and cooling conditions for 50 cycles. The kinetics of oxidation of coated and bare boiler steel has been established with the help of weight change measurements. It was observed that all the coated and bare steels obeyed parabolic rate law of oxidation. X-ray diffraction, FE-SEM/EDAX and X-ray mapping techniques were used to analyse the oxidation products of the coated and uncoated boiler steel. The uncoated steel suffered corrosion in the form of intense spalling and peeling of its oxide scale, which was perhaps due to the formation of unprotective Fe₂O₃ oxide scale. Both the coatings showed better resistance to the air oxidation as compared to the uncoated steel. The Ni-50Cr coating was found to be more protective than the Ni-20Cr-coated steel. The formation of oxides and spinels of nickel and chromium may be contributing to the development of air oxidation resistance in the coatings.     

气泡泵在冷态试验下的性能研究

搭建气泡输入式冷态试验系统,以常压饱和水为工质,均匀输入空气形成连续气泡用于模拟气泡泵运行系统,对气泡泵的性能进行研究.其实验结果与在加热状态下气泡泵的性能相比较,综合分析气体输入量(可转换成加热量)、沉浸比等对气泡泵性能的影响,提出产生此结果的原因.     

真空冷却过程中实验条件对真空冷却速率的影响

以熟肉为实验材料,对实验条件对真空冷却速率的影响进行了理论分析和实验研究.实验结果表明:真空室有效容积越小、真空泵抽速越高,则真空冷却时间就会越短;冷阱温度对真空冷却速率有着明显的影响;当真空室内的最终压力在0.4～0.61kPa变化时,熟肉的表面温度一直在0℃以上,其真空冷却的时间随着真空室内压力的升高而增加.而真空室内的最终压力在0.3kPa左右时,熟肉的表面温度在真空冷却过程会低于0℃.