拉普拉斯妖的出现——“拉普拉斯妖”随笔之五

一 中文字典里的"妖"字,往往与"精"、"怪"、"魔"、"孽"等字连在一起组成一个名词.这些名词或指姿色迷人的女子,或指害人索命的鬼魅,或指凶狠残忍的魔怪,有时也指呼风唤雨,撒豆成兵,具有某种超常能力怪异反常的"什么东西".总之,"妖"是非物质世界的一种"存在",与"妖"字相连,大多充满着荒诞和邪恶.     

新课改中,农村初中物理实验教学存在的问题及对策

物理是以实验为基础的自然科学,所谓物理,就是通过"物"--物理实验引入物理概念,研究物理规律.就是要以"物"喻出"理"的本质,以"物"明了"理"的内涵,以"物"揭示"理"的真谛.因此,物理实验是学生获取知识、进行知识创新的重要手段,是培养学生的学习兴趣、科学态度和提高学生终身学习能力的重要途径.     

百年光量子

1905年爱因斯坦首次提出"光量子"概念,标志着"量子光学"诞生,并有力推动其后"量子力学"的创建。本文将简述"光量子"如何诞生,"光子"有何奇异特性,着重介绍"光子"在量子信息领域的应用,包括量子密码、量子纠缠网络、量子模拟、量子计量和量子计算等。最后研讨"光子究竟是什么"。     

漫话:从影到小孔成像

1 前言 一般来说"影"和"像"是两个完全不同的概念,在日常生活中却常常"影""像"不分,这给教学带来了不小的困难,以致不得不想方设法,不厌其烦地加以区分.然而,现在我们却要说"小孔成像"正是由"影"形成的,没有影就没有小孔成像.     

多一点学科本质剖析 少一点“机械刷题”——兼谈2021年高考全国理综乙卷第24题评析

会"击球"而不会"拍球",看似一个不现实的"笑料",但却实实在在地呈现在考生的答卷中,深刻"剖析"这种现象产生的原因,有助于一线教师从"心底"减少"机械刷题"量,点亮师生将"真实问题情境"转化为"物理模型"的心灯.     

也谈“说课”设计

"说课"是促进教师成长、提升教师素质的必备环节.所谓说课,就是依据教学法、教育学和心理学的原理,说出"教什么"、"怎样教"、"为什么这样教"的整个教学过程.说课既要"说得准确"、"说出特色"、又要"说出共性与个性".     

关于“参照物”学习的调查研究

参照物是一个比较普通的物理概念,如果把它作为一种事实性知识通过"记中学"的方式来学习,则短时间有效,长时间低效,更远的时间无效.如果作为一种方法性知识和价值性知识通过"做中学"和"悟中学"的方式学习,则短时间低效,长时间高效,更远的时间有效.通过"参照物"学习的调查研究得出,我们更应当在物理教学中提倡"做中学"和"悟中学".     

北京理工大学物理学院长期公开招聘优秀人才及博士后

按照北京理工大学"理工并重"的学科定位和"理科振兴计划"的要求,以"做大做强理科"和建设"理工为主研究型大学"为目标,北京理工大学于2011年6月成立物理学院,这是北京理工大学历史上首次设立物理学院.     

利用生师一对一问答平台共创教学双赢的实践与探索

介绍通过发挥"生师一对一交流"平台的作用,将"生师一对一交流"的成果为师生"教"与"学"共享,将"生师一对一交流"平台打造成"教"与"学"双赢的一种教学环节.     

物理是"做"出来的——谈实验在物理教学中的作用

传统的教学模式,认为物理知识和规律的习得是教师"讲"出来的,是学生"练"出来的.不可否认,在"填鸭式"、"满堂灌"的传统教学模式下,学生在高考中一样能取得较好的成绩,不过有多少学生能够经过如此的模式走向高考的成功?那些成功的考生,其成绩中素质的含金量有多少?答案都是"没有多少!"     

Electronic Excitations in Pyrrole: A Test Case for Determination of Chromophores in the Chromogenic Effects of Neurotoxic Hydrocarbons by Time-Dependent Density Functional Theory and Single-Excitation Configuration Interaction Methods

Time-dependent density functional theory (TD-DFT) and single-excitation configuration interaction (CIS) calculations on the electronic excitations in pyrrole have been performed to examine the reliability of these first-principles electronic structure methods in predicting electronic excitation spectraof pyrrole-containing compounds. Both the TD-DFT and CIS calculations led to satisfactory results when compared to available experimental data, particularly for low-lying excited states. The TD-DFT and CIS calculations provide lower and upper limits of the excitation energies, respectively, for low-lying singlet excited states. These results suggest that these methods can be used for the prediction of the excitation spectra, particularly the excitation energies for low-lying excited states, of chromophores responsible for the chromogenic effects of neurotoxic hydrocarbons, which are believed to be substituted pyrroles and their adducts with proteins. As an example of a practical application, the spectrum of the widely used 2,5-dimethylpyrrole has been calculated. It is shown that the 2,5-dimethylpyrrole molecule does not have an absorption in the region of the visible spectrum (400-700 nm), suggesting that the absorption observed at 530 nm and the color of 2,5-dimethylpyrrole is due to another species, probably a product of possible 2,5-dimethylpyrrole autoxidation. This suggests that the conclusions from previously reported experimental studies of biochemical reactions of neurotoxic γ-diketones need to be reexamined in terms of the relationship of chromogenicity to neurotoxicity.     

Comparison of three methods for calculation of electron transfer probability in H + Ne

We have developed a theoretical model of ion-atom collisions where we described electron dynamics by the time-dependent density-functional theory (TDDFT) and the ion dynamics by classical mechanics through the Ehrenfest method. We have compared three methods to calculate the probability of electron transfer during H⁺ + Ne collision. By discussing these issues we shall be able to understand how these methods work, what their limitations are and whether they admit of any improvements.     

辐射压的概念和计算方法的分析研究

由动量流密度的应力两重含义分析辐射压力的物理本质，通过兴例介绍辐射压力的三种计算方法。     

聚丙烯酸酯泡沫密度均匀性控制

低密度泡沫材料大多存在一定程度的密度不均匀性,这对其后续使用性能将带来不良影响。简述了ICF靶用聚丙烯酸酯泡沫的制备方法,对其密度不均匀性形成机理进行理论分析。在此基础上,改进其制备工艺,控制泡沫密度分布,并利用β射线检测技术,对制备工艺改进前后直径为mm量级的低密度聚丙烯酸酯泡沫柱进行密度分布表征。研究结果表明:改用聚四氟乙烯代替玻璃模具,有利于制得密度分布均匀的泡沫样品;选用最高的紫外光的能量,能促进自由基均匀分布,从而最终能够提高泡沫的密度均匀性。采用β射线对密度范围为10～100 mg.cm-3的TMPTA泡沫的密度均匀性进行表征,结果表明:随着泡沫密度的降低,密度均匀性越低,对制备工艺要求越高。     

The Applicability of the Radiogauges for Measuring the Density of the Flowing Solid-Liquid Mixtures

The discussion on the density measurement accuracy of the flowing unhomogeneous solid-liquid mixtures by means of the radiogauges is presented. The considerations are based on the results obtained in the investigations being performed with use of the radiometric measuring methods.     

简易浓度测定方法的研究

浓度是反映溶液性质的一个重要参数,现有的各种测量方法各有其特点。文献［１］是根据光学原理,运用显微镜调焦方法提出了测量透明材料厚度和折射率的方法;在此基础上,根据不少溶液的折射率和浓度均有定量对应关系的特点,提出测定浓度的简易方法。该测量方法有下列特点：非接触测量,采样液体少,对液体无特殊要求,适用面广,装置简单。实验结果得出,百分浓度的测量可精确到０１％。用该方法同一些常规方法相比,测量误差在１％左右,能满足有关生产和工作中的使用要求。     

An alternative approach on the calculation of cohesive energy density and isothermal compressibility of alkali metal halides

In the present paper, new and useful theoretical methods for the estimation of cohesive energy density (Ced) and isothermal compressibility (k_T) of alkali metal halides are described. The mentioned theoretical methods include the use of Kaya molecular hardness equation published by us in recent years. Cohesive energy density and isothermal compressibility of alkali metal halides were calculated in the framework of mentioned theoretical methods and the results obtained were compared with both experimental data and the results of previous theoretical methods proposed to calculate the aforementioned quantities, namely cohesive energy density and isothermal compressibility. It is important to note that the results obtained in the study are in good agreement with the available experimental data and with the results of previous theoretical methods. Additionally, we also investigated the correlation with lattice energy of cohesive energy density and isothermal compressibility for alkali halides.     

用力敏传感器测量物体的密度

利用力敏传感器测量物体的密度,改进了传统的实验方法和仪器,实现了非电量电测,提高了实验的准确度和稳定性.     

Force-sampling methods for density distributions as instances of mapped averaging

ABSTRACT

We show that two recently proposed methods for computing singlet and pair density distributions without histograms are particular implementations of the general mapped-averaging framework for deriving alternative ensemble averages for physical properties.     

Evaluation of various DFT protocols for computing 1H and 13C chemical shifts to distinguish stereoisomers: diastereomeric 2‐, 3‐, and 4‐methylcyclohexanols as a test set

¹H and ¹³C NMR chemical shifts were measured for a set of six isomers—the cis and trans 2‐, 3‐, and 4‐methylcyclohexanols. ¹H and ¹³C NMR chemical shifts were computed at the B3LYP, WP04, WC04, and PBE1 density functional levels for the same compounds, taking into account the Boltzmann distribution among conformational isomers (chair–chair forms and hydroxyl rotamers). The experimental versus computed chemical shift values for proton and carbon were compared and evaluated (using linear correlation (r²), total absolute error (|Δδ|_T), and mean unsigned error (MUE) criteria) with respect to the relative ability of each method to distinguish between cis and trans stereoisomers for each of the three constitutional isomers. For ¹³C shift data, results from the B3LYP and PBE1 density functionals were not sufficiently accurate to distinguish all three pairs of stereoisomers, while results using the WC04 functional did do so. For ¹H shift data, each of the WP04, B3LYP, and PBE1 methods was sufficiently accurate to make the proper stereochemical distinction for each of the three pairs. Applying a linear correction to the computed data improved both the absolute accuracy and the degree of discrimination for most of the methods. The nature of the cavity definition used for continuum solvation had little effect. Overall, use of proton chemical shift data was more discriminating than use of carbon data. Copyright © 2007 John Wiley & Sons, Ltd.