奥古斯特.孔脱：第一流的实验物理学家

奥古斯特．孔脱是１９世纪德国第一流的实验物理学家,他首创测量声速的方法;首测单原子气体的热容比,并最早发现了气体的法拉第效应等,在声学、光学和气体动力学实验研究方面作了诸多重要贡献,创造了许多卓有成交的实验方法,文章就孔脱的生平、业绩、学术思想等作了较为全面的评价。     

孔脱和他的“孔脱管”实验

 奥古斯特·孔脱(August Kundt)是19世纪德国实验物理学家.他一生主要从事声学、光学和气体动力学等方面的实验研究,为物理学的发展作出了许多重要贡献,创造了许多卓有成效的实验方法.     

气体吸附法测定二氧化硅干凝胶的分形维数

提出了一种方便、科学有效的利用气体吸附法测定二氧化硅干凝胶等多孔材料分形维数（表面分形维数和孔分布分形维数）的方法，不需要进行一系列的吸附/脱附实验，只需要利用单一气体的一次吸附/脱附实验得出的样品孔分布、比表面数据，与不同的标尺进行关联，即可同时获得表面分形维数和孔分布分形维数.通过误差分析和校正，保证了结果的可靠性.用上述方法测定了二氧化硅干凝胶的分形维数，以FHH法和SAXS法对所得结果进行了比较和验证，并对吸附/脱附过程所得结果的差异进行了初步分析. 关键词： 分形维数 气体吸附 二氧化硅 干凝胶     

负离子与气体碰撞单电子脱附的实验研究

本文主要介绍我们在负离子与气体碰撞单电子脱附实验研究中采用的方法和装置.该实验利用增长率测量法,由于实验测量中采用同一个粒子探测器对入射束和产生的中性粒子进行测量,大大降低了实验误差.实验系统由铯溅射负离子源、同位素分离器、反应靶室和粒子探测器组成.负离子的能量范围为5～30 keV,实验结果的不确定度约为±8%.     

碳纳米纤维吸附储氢性能分析

文中综合碳纳米纤维微观结构的表征结果以及氢吸脱附等温线的实验测量结果,对碳纳米纤维的吸附储氢性能进行了综合分析,分析发现:比表面积和中孔容积均与氢吸附量成线性关系;微孔容积对材料吸附性能影响较大,微孔容积与氢吸附量成抛物线关系;氢在常温左右以及77K下的吸附等温线呈现超临界气体的吸附特征,氢在273K和353K下的吸脱附等温线也基本重合,呈现的是物理吸附的特征。实验结果还说明:常温左右,甚至是77K下,碳纳米纤维均不适合于氢的吸附储存。     

介质表面高功率微波击穿中释气现象的数值模拟研究

建立了一个简单的高功率微波(HPM)介质表面击穿释气模型,并采用PIC(partiele-in-cell)-MCC(Monte Carlo collisions)方法,通过自行编写的介质表面击穿数值模拟程序对不同释气条件下的介质表面HPM击穿过程进行了数值模拟研究,得到了击穿过程中电子数量等的时间图像和不同释气速度下的击穿延迟时间.模拟结果表明,对于具有一定时间宽度的HPM脉冲,当介质表面气体脱附速度较小时,由于介质表面气体层形成太慢而不会发生击穿;只有当脱附速度大于一定值时,击穿才会发生且击穿延迟时间在一定范围内随着脱附速度的增加而缩短.最后,将数值模拟得到的介质表面HPM击穿数据,与单极性表面击穿的实验诊断图像进行了对比,两者的发展趋势符合很好. 关键词： 释气现象 介质表面击穿 高功率微波 数值模拟     

五羰基铁气相爆轰法合成纳米碳胶囊

采用气相爆轰法,以乙炔气体、氧气和五羰基铁为原料成功地合成了比表面积为253.857m~2/g的胶囊状碳纳米材料。对反应的前置实验九羰基二铁的热分解反应的研究表明,在60～140℃之间,九羰基二铁热分解为五羰基铁和十二羰基三铁。对爆轰产物进行了XRD、TEM和BET物理吸附实验,结果表明:产物XRD图谱石墨峰明显,产物主要为具有石墨化倾向的薄层胶囊状无定形碳结构;实验产物比表面积为253.857m~2/g,孔体积为0.940cm~3/g,平均孔径为2.731nm;吸附-脱附曲线回滞环类型为H3型,孔结构主要为颗粒堆积而形成的狭缝孔;爆轰产物比表面积较大,具有较强的吸附能力。证实了同样采用铁作为触媒,乙炔在不添加惰性气体作为缓冲剂的情况下,由于爆速过高而无法用于合成碳纳米管。     

大尺寸密闭空间内甲烷-空气二元混合方法的改进与评定北大核心CSCD

气体混合过程在工业生产和科学研究领域是一个值得关注的课题。以大尺寸爆炸罐内的气体爆炸研究为背景,基于已有的10 m^3爆炸罐的基本结构,设计并建立了适用于爆炸罐结构的进气装置,并以此为基础,研究了甲烷和空气在大尺寸密闭空间内的混合过程。根据气体混合效果的评判标准,通过实验确定了适用于爆炸罐的进气装置的具体尺寸参数及相关进气条件,并与未改进前的气体混合过程进行对比。结果表明:采用直管螺旋开孔的进气装置后,当开孔孔径为1.5 mm、孔间距为100 mm时,气体混合效果最好;当进气速率保持在8 m^3/h、进气前罐体内外压差为0.04 MPa时,气体混合效果可以进一步优化。经改进之后,爆炸罐内的气体混合时间缩短为原来的1/12,且罐体内气体混合物的均匀度更高,满足气体爆炸实验的要求。此结果亦可为其他大尺寸密闭容器或空间的气体混合过程提供参考数据。     

SiO_2纳米孔隔热材料制备与热导率计算

以SiO_2气凝胶纳米颗粒、石英纤维和遮光剂为原料,制备了SiO_2纳米孔隔热材料.采用扫描电镜和氮气吸脱附法表征了SiO_2纳米孔隔热材料微观结构,采用瞬态平面热源法测试了材料在25～800℃, 10～10~5 Pa范围内的热导率.建立了Si02纳米孔隔热材料热导率计算方法,计算了材料在不同温度和压力下的热导率,热导率计算值和实验值相符较好,表明所发展的计算方法适用于纳米孔隔热材料的热导率计算.此外,还获得了材料气相热导率与辐射热导率随温度的变化规律,对材料结构设计及性能优化具有很好的指导意义.     

氙(Xe)原子在铂(Pt)表面吸附与脱附的分子动力论方法研究

运用分子动力论方法研究单原子气体分子(Xe)在固壁表面(Pt)的吸附与脱附。在构造了合理的气体分子与固壁表面相互作用势模型之后,运用随机经典轨道方法求解气体分子及固壁原子的运动方程,得到气体分子的运动轨迹及状态。结果表明,气体分子在固壁表面的吸附几率与分子的入射平动能量、壁面温度及气-固相互作用势模型的选取等因素有关,气体分子在固壁表面的脱附速率基本满足Arrhenius关系式。     

Faraday and the Philosophical Magazine

Faraday is considered to be one of the greatest scientists of all time. He not only was a meticulous experimentalist, a true experimental wizard, but also a very prolific author. The many important contributions (almost 50) that he published in the Philosophical Magazine make it highly desirable to catalogue his various inventions, ‘discoveries’ in his own words, in a scientific language so characteristic of the nineteenth century. It is the purpose of this commentary to guide the reader through his achievements in electrochemistry, magnetism, electric and electromagnetic induction, even ‘industrial’ applications; to enable him to address a present day audience by means of his contributions to the Philosophical Magazine.     

Determination of binary diffusion coefficients of gases using photothermal deflection technique

A photothermal deflection (PD) technique was applied to measure the binary diffusion coefficients of various gases (CO₂–N₂, CO₂–O₂, N₂–He, O₂–He, and CO₂–He). With an in-house-made Loschmidt diffusion cell, a transverse PD system was employed to measure the time-resolved PD signal associated with the variation of the thermal diffusivity and the temperature coefficient of the refractive index of the gas mixture during the diffusion. The concentration evolution of the gas mixture was deduced from the PD amplitude and phase signals based on our diffraction PD model and was processed using two mass-diffusion models explored in this work for both short- and long-time diffusions to find the diffusion coefficient. An optical fiber oxygen sensor was also used to measure the concentration changes of the mixtures with oxygen. Experimental results demonstrated that the binary diffusion coefficients precisely measured with the PD technique were in agreement with the literature values. Moreover, the PD technique can measure the diffusion coefficients of various gas mixtures with both short- and long-time diffusions. In contrast, the oxygen sensor is only suitable for the long-time diffusion measurements of the gas mixtures with oxygen. PACS 78.20.Nv; 51.20.+d     

射频放电阻抗测量用于等离子体诊断研究

利用自行研制的传感器和测量装置,通过对射频放电电压、电流以及其相位角的精确测定,算出放电管的总阻抗,结合放电管的等效电路模型与Godyak等建立的射频放电模型,对射频激励铜离子激光管在氦气中的放电特性进行了研究,得出射频激励铜离子激光器不同气压及电流密度下的等离子体电阻、容抗、鞘层厚度及电子密度 关键词： 射频放电 阻抗测量 等离子体诊断     

Theory of inelastic atom-surface scattering: Examples of energy distributions

The theory of the energy distribution of atoms scattered inelastically by solid surfaces which was developed previously is applied to various examples. The dependence of the results on a number of parameters is studied in detail. The importance of many phonon contributions as compared to the validity of first order distorted wave Born approximation is considered in particular. It turns out that low energy He atoms scattered by heavy transition metals provide a good example for which one phonon emission (or absorption) dominates. All other noble gases show appreciable many phonon contributions increasing, of course, with increasing mass of the noble gas and temperature of the solid. For heavy noble gases such as Kr and Xe the energy distribution approaches a gaussian, the width of which is due to the thermal and zero-point motion of the lattice. This width is quite large and thus probably masks most of the fine structure of the energy distribution occuring in classical trajectory calculations. We have also tried to apply the theory to light diatomic molecules. Although the results are less certain, partly because of the neglect of the internal motion of the molecules and partly because of uncertainties in the interaction parameters, one probably can expect appreciable many phonon effects already for H₂ and, of course, more so for N₂ and O₂. Recent experimental results on the Debye-Waller factor of Ne/Cu can be reproduced with reasonable potential parameters.     

Total fluence influence on the detected magnitude of neutron burst using proportional detectors

The measurement of very short neutron bursts, when individual neutrons cannot be counted in the usual manner, is possible with proportional detectors (such as ³He) taking the integration of the total electric charge due to many overlapped interactions, as the measure of the amount of the neutron signal. This method requires a correction related to the total amount of neutrons that interacted with the detector. This correction originates in the well-known build-up of positive electric charge too slow to be dislodged from the detection volume during the neutron burst. This causes self-shielding of the applied electric field with the ensuing reduction of the charge multiplication process in the gas, described in the literature.Short neutron bursts from a plasma focus device and a conventional isotopic neutron source were employed in the experimental phase and the known theory was applied in the analysis, which justifies assigning the observed effects to the space-charge shielding of the externally applied electric field.This work introduces a correction to the neutron yield derived from the registered electric charge, through a model of collected charge reduction as a function of total neutrons measured.     

Symmetry and Condensed Matter Physics – A Computational Approach,by M. El-Batanouny and F. Wooten

The behaviour of positrons below the inelastic collision threshold in rare gases can usually be completely accounted for in terms of the annihilation and elastic scattering cross sections for collisions between a positron and a single gas atom. Determining these cross sections has been the subject of many theoretical and experimental investigations. However the basic premise that the positron interacts with the gas atoms, one at a time, has been recently questioned by the yet unexplained results of some low-temperature experiments. This article discusses the annihilation and elastic scattering cross sections as they relate to the conventional picture of positrons in He, Ne, Ar, Kr and Xe gas; as well as the possibility of bound states for positrons in the gases at low temperatures.     

Potentials and scattering cross sections for collisions of He atoms with adsorbed CO

Ab initio calculations of the total scattering cross section for the collision system He → $\text{CO}\text{Pt(111)}$ within the renormalized distorted wave Born approximation are reported. The interaction potential for this atom-adsorbate system consists of the usual two-body gas phase-like potential as well as two additional substrate mediated van der Waals contributions, all with similar long range behaviour. Comparison of the calculated cross sections for various incident velocities and angles with available experimental data is made without using any adjustable parameters in the potential to fit the data, and the importance of including the anisotropic and substrate-mediated forces is emphasized.     

Membrane gas diffusion measurements with MRI

Gas transport across polymeric membranes is fundamental to many filtering and separation technologies. To elucidate transport mechanisms, and understand the behaviors of membrane materials, accurate measurement of transport properties is required. We report a new magnetic resonance imaging (MRI) methodology to measure membrane gas phase diffusion coefficients. The MRI challenges of low spin density and short gas phase relaxation times, especially for hydrogen gas, have been successfully overcome with a modified one-dimensional, single-point ramped imaging with T(1) enhancement, measurement. We have measured the diffusion coefficients of both hydrogen gas and sulfur-hexafluoride in a model polymeric membrane of potential interest as a gas separator in metal hydride batteries. The experimental apparatus is a modified one-dimensional diaphragm cell which permits measurement of the diffusion coefficient in experimental times of less than 1 min. The H(2) gas diffusion coefficient in the membrane was 0.54 +/- 0.01 mm(2)/s, while that of sulfur-hexafluoride was 0.14 +/- 0.01 mm(2)/s, at ambient conditions.     

惰性气体氦、氖、氩原子与氢(氘、氚)分子碰撞截面的理论计算

原子分子相互作用在许多物理过程中都十分重要.原子分子碰撞过程中转动激发截面的研究是确定原子与分子间相互作用的理想方法,许多理论和实验工作者在这方面做了大量工作,并得到理论和实验数据.本文用密耦近似计算了惰性气体He、Ne、Kr与h2、D2、T2碰撞的弹性和转动激发截面,原子入射能量分别为0.05 eV、0.15eV、0.20eV和0.25eV.     

Photoionization cross sections: Interpretation of band intensities in He I and He II photoelectron spectra

Relative photoionization cross sections of molecules consisting of atoms from the first three rows of the Periodic Table are computed by a theoretical method developed previously which involves the plane-wave approximation for the photoelectron and the use of semiempirical LCAO-SCF-MO's of the CNDO- or MINDO- type for the initial orbital. The calculated values are compared with experimental photoelectron band intensities obtained by integrating the band areas in He I and He II photoelectron spectra. The observed relative intensity changes of bands in the spectrum in going from He I to He II excitation are attributed to variations in the one- and/or two-centre contributions to the cross sections from the electron density at the atoms and in the bonds, respectively. The analysis of the relative intensities of bands in the He I and He II spectra thus leads to conclusions about the electron density distribution in the initial orbital and about the assignment of the bands.In a qualitative sense, the experimental He I/He II intensity changes are usually correctly predicted by our theoretical method, but there are often considerable quantitative discrepancies between the measured and calculated values which probably arise from the inherent simplifications of our approach.