双重演示效果"固体热胀冷缩演示仪" 设计与实践

介绍一款双重演示效果"固体热胀冷缩演示仪",该仪器在演示效果的显著程度和综合性知识含量两方面较现有演示仪有实质性突破.     

巧用杠杆原理,演示微小变化

1 利用二次放大装置，演示金属的热胀冷缩现象。金属的热胀冷缩现象，人眼难以清楚地观察到．若设计一个如图1所示的实验装置，则可显著地提高演示效果，激发学生兴趣，培养学生创新意识．     

双重演示效果“固体热胀冷缩演示仪”

介绍一款双重演示效果“固体热胀冷缩演示仪”，该仪器在演示效果的显著程度和综合性知识含量两方面较现有演示仪有实质性突破．     

热学演示实验二则

热学演示实验二则朱连生（国家教委教学仪器研究所北京１０００３９）一、金属环的热胀冷缩实验中学现配备的金属球热胀冷缩演示器只能演示金属球的热胀冷缩现象，为了增加实验内容，可用铝板（厚３一４ｍｍ）再自制一个带柄的金属环．环的内径要略小于球的直径（差１一２...     

“气体压强的产生”模拟演示器

司南版教材中"模拟气压的产生"演示实验所需的实验装备在中学尚未普及,为解决这一问题,形象生动地演示该实验,利用日常易得的物品制作了"气体压强的产生"模拟演示器,详细介绍了该演示器的制作与演示方法.     

平抛运动实验的新做法

新编高中物理课本(试验修订本·必修)第86页的"平抛运动"演示实验是一个传统的基本实验.对于这个实验,过去一直是采取"做样子,讲结论"的办法,很难达到实验目的.笔者利用实验室现成的数字计时器成功地演示了这一实验,现介绍于下.     

"温度对扩散的影响"演示实验的改进

分析了教材和文献中"温度对扩散的影响"实验存在的弊端,并提出了"吸墨法"演示扩散现象,即利用注射器吸入墨水在下端与冷水和热水接触,通过墨水在冷热水中的不同扩散速度演示温度对扩散现象的影响,避免了重力对演示实验效果的影响.     

固体压强演示实验的改进

通过自制演示实验装置,可定性、定量地演示固体压强。     

充分利用力学演示实验培养学员创新思维能力

在工程力学教学中要充分发挥演示实验的作用,培养学员的创新思维,教员应该对演示实验教学进行合理的创新设计,开发出力学演示实验独有的构思和方法,利用形式多样的演示实验来培养学员的创新思维能力.     

“真空不能传播声音”实验改进

针对传统的"真空不能传播声音"实验的不足,利用注射器、LED等器件设计了演示电路.该电路利用注射器营造真空环境,放置在注射器中的音乐卡发出的声音随着注射器中的气压减小而变小,直至消失,由此演示出了真空不能传播声音的现象.     

Correlation of temperature anomalies of the hyperfine field and thermal expansion of the crystal lattice

Consideration is given to the effect of thermal expansion of crystal lattice upon the partial contributions to the magnetic hyperfine field for non-magnetic atoms in metallic ferromagnets. The existence of correlation between the temperature anomalies of a hyperfine field and the thermal expansion of the crystal lattice is shown in a simple and illustrative way.     

Thermal expansion and lattice dynamics under pressure of ZnS,ZnSe and ZnTe

The thermal expansion against temperature of ZnS, ZnSe and ZnTe is studied theoretically using the experimental pressure dependence of elastic stiffness constants and phonon frequencies. The mode Grüneisen parameters obtained from the high pressure effect on the one- and two- phonon Raman spectra at the metallic transition pressure by Weinstein are used originally, but do not reproduce the experimental linear expansion coefficient at high temperatures. The contributions from optical modes with large phonon frequency are important to the thermal expansion at high temperatures, and a set of mode Grüneisen parameters, which bring good agreement with the observed linear expansion coefficient not only at low temperatures, but also at high temperatures, are obtained. Then, the phonon dispersion curves of ZnS, ZnSe and ZnTe at their metallic transition pressures are quantitatively shown.     

Effects of in-plane stiffness and charge transfer on thermal expansion of monolayer transition metal dichalcogenide

The temperature dependence of lattice constants is studied by using first-principles calculations to determine the effects of in-plane stiffness and charge transfer on the thermal expansions of monolayer semiconducting transition metal dichalcogenides.Unlike the corresponding bulk material,our simulations show that monolayer MX₂（M = Mo and W;X = S,Se,and Te） exhibits a negative thermal expansion at low temperatures,induced by the bending modes.The transition from contraction to expansion at higher temperatures is observed.Interestingly,the thermal expansion can be tailored regularly by alteration of the M or X atom.Detailed analysis shows that the positive thermal expansion coefficient is determined mainly by the in-plane stiffness,which can be expressed by a simple relationship.Essentially the regularity of this change can be attributed to the difference in charge transfer between the different elements.These findings should be applicable to other two-dimensional systems.     

硅纳米晶体薄膜热膨胀性质的分子动力学研究

基于Stillinger-Weber势对硅纳米晶体薄膜的热膨胀性质进行了分子动力学模拟。研究表明,硅纳米晶体薄膜表面层原子的二聚现象引起薄膜收缩,而原子之间的非和谐势能引起薄膜膨胀;在约400K以下的低温段,由于硅纳米晶体薄膜表面层原子发生二聚的原子数目随温度的升高而明显增多,而原子间非和谐势能很小,故此时二聚主导热膨胀性质,热膨胀系数为负;在高温段（约400K以上）,由于发生二聚的原子数目随温度升高不再显著地增加并渐趋于稳定,而原子间非和谐势能逐渐显著并主导热膨胀性质,故热膨胀系数为正。     

固体热导率测量仪的新发现

实验通过稳态法使用TC-3型固体热导率测定仪[1,9]的测量方法改变来测量海洋大气热导率,结构简单,误差更小,一机多用.通过改变加热铜盘A与散热铜盘B之间的距离,探究距离对大气热导率的影响,并与教材中介绍的气体热导率测定仪测量的大气热导率进行比较.     

On the pressure-temperature phase diagram of intermediate valence compounds

The pressure-temperature (P, T) phase diagram of intermediate valence compounds has been calculated on the basis of the periodic Anderson model which was extended to include the interaction of 4f electrons with longitudinal optical phonons. It is shown that the positive slope (dP/dT>0) of the phase boundary between the insulating and the mixed valence phase as observed experimentally in Sm S and many other systems is determined by the behaviour of the electronic density of states of the interacting system as function ofP. Moreover, the observed anomalous thermal contraction in the insulating phase near the phase boundary and the anomalously large thermal expansion in the metallic phase are well described by numerical results for the extended periodic Anderson model.     

The thermal expansion of axial metals

The thermal expansion of axial metals is surveyed with particular reference to recent very low temperature data for zinc, cadmium, magnesium, β-tin, indium, bismuth and antimony. For a given solid, the independent thermal expansion coefficients α_⊥ and α_‖ are conveniently compared at low temperatures by plotting α_⊥/T ³ and α_‖/T ³ against T. The plots show clearly how contraction in one principal symmetry direction ensues from rapid expansion in the other direction. The Grüneisen functions γ_⊥ and γ_‖ are discussed for each solid using data from lattice-dynamical models and neutron-diffraction measurements. They show how features of the individual thermal expansions arise from a combination of vibrational, elastic and electronic effects. For these solids and for zirconium, titanium, yttrium and thallium the larger of γ_⊥ and γ_‖ at high temperatures is that referring to strains in the direction of the stronger forces (judged from the axial ratio). At lower temperatures the inequality reverses, except for tin, implying that the highest normal-mode frequencies depend most strongly on strain in the direction of the stronger forces. More experimental studies of thermal expansion at the lowest temperatures are desirable, as well as more second and third-order elastic constant data. Theoretical work is needed on realistic lattice models applicable to non-cubic metals.     

兔主动脉冻结膨胀行为及其影响因素的研究

文采用热机械分析仪(TMA)分别研究了低温保护剂(CPA)和冻结速率对兔主动脉冻结相变过程中膨胀的影响。研究结果表明:在兔主动脉的冻结过程中,先是逐渐膨胀到某一峰值,然后突然有收缩的发生;降温速率越大,其相应的热膨胀系数也越大;添加二甲亚砜(DMSO)大大增加了主动脉冻结过程的未冻水含量,从而对其冻结膨胀有明显影响,而且,DMSO浓度越大,其冻结膨胀系数越小。     

传感器电解质材料热膨胀性能和热稳定性变化规律研究

以ZrO2固体电解质材料为例,研究氧传感器电解质材料原子振动特点和热膨胀系数及其热稳定性随温度和时间的变化规律,探讨原子非简谐振动的影响。结果表明：原子振动的频率、阻尼系数,在简谐近似下为常数,在考虑到非简谐效应后随温度升高而增大;原子平均位移和热膨胀系数在简谐近似下为零,在考虑到非简谐效应后随温度升高而增大,随的时间的增长而减小;热膨胀性能稳定性温度系数随温度的升高而减小,随时间的增长而增大,即使用时间越长,材料的热膨胀性能稳定性越低;温度越高,热膨胀性能越稳定;非简谐情况下的原子振动的频率、阻尼系数和热膨胀系数与简谐近似下的差值随温度的升高而增大,即温度越高,非简谐效应越显著。     

Thermal expansion of the skeleton of chain molecules in polymer crystals

The expansion of the carbon skeleton of molecules in crystallites and the longitudinal contraction of the crystallite lattice in poly(ethylene) (PE) and poly(caproamide) (PCA) with an increase in the temperature are measured using IR and Raman spectroscopy and x-ray diffraction. The thermal expansion of the carbon skeleton due to transverse vibrations is theoretically calculated within the atomic chain model. The theoretical and experimental data on the thermal expansion of the carbon skeleton are in good agreement.