The fragmentation of 20Ne at 400 A MeV

The total charge-changing cross sections and partial cross sections for the production of projectile fragments are measured in the interactions of 400 A MeV ²⁰Ne with aluminum, carbon and polyethylene targets sandwiched with CR-39 plastic nuclear track detectors. The measured total charge-changing cross sections are compared with the predictions using the Bradt-Peters semi-empirical formula, and the NUCFRAG2 and PHITS models. It is shown that the measured experimental results are in good agreement with the theoretical model prediction and other experimental results, and it can be clearly seen that the partial cross sections for fragment production show obvious odd-even effects.     

烹小鲜的启示——基于数学技能的思考

厨师将小鱼做成一道美味的小鲜,需要几个程序呢?首先必须要有鱼以及作料用具等,其次就是有具体的做法及实际的操作本领,最后就是能够恰当地使用工具,采用合理的做法,这样才能够真正做成美味佳肴.在这个过程中,小鱼以及作料用具相当于数学的基础知识,而具体的做法则是数学技能,恰当地使用工具和高超手艺,那就是数学能力.可见,数学技能在数学学习中扮演着一个重要的角色,然而长期以来,人们对数学技能有着种种误解和偏见,出现了诸如"题海战术"、"熟能生巧"等做法,增加了学生的负担,也影响了他们的身心健康.那么数学技能是什么?怎样有效地提高数学技能?本文对此作出一点思考,供大家参考.     

导热油氧化稳定性的热分析评价

通过差热分析,测定三种油品出现吸热峰的起始温度,及加入各种抗氧剂和不同浓度的抗氧剂对油品起始氧化温度的影响,提供了一个快速评价导热油氧化稳定性的有效方法。     

η2-C60[RhCl(CO)(PPh3)2]配合物的合成与表征

从1985年Smalley等[1]发现C60等富勒烯至1996年富勒烯的发现者获诺贝尔化学奖期间, 在化学、 材料、 物理等领域形成了富勒烯的研究热潮[2～5]. 现在科学工作者正以较大的注意力投向富勒烯的化学修饰, 研究富勒烯各类衍生物的结构与性能之间内在联系规律, 以期望在开发应用方面取得突破性进展, 为此也十分重视对具有特殊组成与结构的富勒烯衍生物的研究. 本文首次合成出η2-C60[RhCl(CO)(PPh3)2]配合物, 并对其结构进行了表征.     

辉煌与瑕疵并存——反思110年来诺贝尔物理学奖的两面性

 自从伦琴于1901年12月10日因发现X射线首次被授予诺贝尔物理学奖以来, 截至2011年达到了105届(因战争关系), 全世界共有126个获奖项目, 191人次获此殊荣。颁奖的成果主要包括科学发现、技术发明和理论创新三大类型。我们在由衷地赞叹这一系列具有最高原创性的科学成就, 对现代社会产生了巨大而深远的影响的同时, 也不难发现在诺贝尔物理学奖的历史簿上, 还存在着某些瑕疵。     

First-principles calculations on the elastic and thermodynamic properties of NbN

<正>The elastic and thermodynamic properties of NbN at high pressures and high temperatures are investigated by the plane-wave pseudopotential density functional theory（DFT）.The generalized gradient approximation（GGA） with the Perdew-Burke-Ernzerhof（PBE） method is used to describe the exchange-correlation energy in the present work.The calculated equilibrium lattice constant a₀,bulk modulus B₀,and the pressure derivative of bulk modulus B₀’ of NbN with rocksalt structure are in good agreement with numerous experimental and theoretical data.The elastic properties over a range of pressures from 0 to 80.4 GPa are obtained.Isotropic wave velocities and anisotropic elasticity of NbN are studied in detail.It is indicated that NbN is highly anisotropic in both longitudinal and shear-wave velocities. According to the quasi-harmonic Debye model,in which the phononic effect is considered,the relations of（V-V₀）/V₀ to the temperature and the pressure,and the relations of the heat capacity C_V and the thermal expansion coefficientαto temperature are discussed in a pressure range from 0 to 80.4 GPa and a temperature range from 0 to 2500 K.At low temperature,C_V is proportional to T³ and tends to the Dulong-Petit limit at higher temperature.We predict that the thermal expansion coefficientαof NbN is about 4.20×10^-6/K at 300 K and 0 GPa.     

系列烷基甲基萘磺酸盐的高效液相色谱和电喷雾离子化质谱分析

采用反相离子对高效液相色谱(HPLC)和电喷雾离子化质谱(ESI-MS)对系列长链烷基甲基萘磺酸盐(AMNS),包括己基甲基萘磺酸盐、辛基甲基萘磺酸盐、癸基甲基萘磺酸盐、十二烷基甲基萘磺酸盐、十四烷基甲基萘磺酸盐进行分析,通过液相色谱分离条件的优化,找到了最佳分析条件.紫外检测波长230 nm,流动相为甲醇和水混合物,流速为0.8 mL/min,采用梯度洗脱方式进行分析.线性梯度:0～40 min时甲醇-水体积为60:40,在40～70min时,甲醇-水体积比为100:0.样品分离度高,分离效果较好.用面积归一化法得到了样品各组分的相对百分含量.HPLC和ESI-MS是快捷、有效和可靠的分析和表征AMNS的方法.     

Helium production from 84Kr-- and 197Au--emulsion interactions at high energies

The properties of the relativistic helium fragments produced in interactions of 84 Kr at 1.8 A GeV and 197 Au at 10.7 A GeV in emulsion are investigated. The experimental results are compared with those obtained from various projectiles with emulsion collisions at different energies. It is found that the multiplicity distribution of helium projectile fragments (HPFs) is well described by the Koba-Nielsen-Olesen (KNO) scaling presentation. The second Mueller moment f 2 of the HPF multiplicity distribution is independent of the projectile energy for the same projectile, but it is dependent on the projectile mass number. The value of f 2 increases with the increase of projectile mass number A p . The negative value of f 2 , when A p < 69, means that the emission of HPFs is anticorrelated, but positive value of f 2 , when A p > 69, refers to that the emission of HPFs is correlated. The non-zero f 2 moment in this experiment implies the strong correlation existing between the HPFs.     

Study of mode propagation with 632.8-nm laser in tapered fiber

The material dispersion of a tapered fiber is described by Sellmeier＇s equation. The dependence of refractive index on wavelength and doping concentration is discussed. A He-Ne laser with the output wavelength of 632.8 nm is used in the experiment. When the cutoff frequency of the fiber is less than the laser frequency, the guiding modes of a singl~-mode fiber （at 1550 am） are investigated. The results show that the original single-mode fiber becomes a multi-mode waveguide. The propagation and mode coupling of the light in the taper region are analyzed. By controlling the taper end size of the fiber, the unique tapered fiber can convert a multi-mode beam into a single-mode one.     

Molecular Dynamics Simulations for Melting Temperatures of SrF2 and BaF2

利用壳层模型分子动力学方法,考虑萤石结构分子中的预熔化现象,对SrF₂和BaF₂的分子动力学模拟熔化温度进行修正,获得了高压下SrF₂和BaF₂的熔化温度. 同时给出了300 K、0.1 Mpa～7GPa和0.1 Mpa～3 GPa时SrF₂和BaF₂的状态方程,与已有研究结果的最大误差分别为0.3%和2.2%. 计算所得SrF₂和BaF₂常压下的熔点与已有的实验结果符合较好. 对于SrF₂和BaF₂分子体积变化和已有的熔化模拟的差别也做了比较和讨论.