铯原子时间频率基准研制——现代计量科学专题之五

1概述 时间是一个非常重要的基本物理量,单位是秒(s).在单位时间内周期运动重复的次数称为频率,单位是赫兹(Hz).在国际单位制SI中,秒是基本单位,赫兹是导出单位.时间和频率关系密切,两者共用一个计量基准,即时间频率基准.     

物理量单位中物理文化探索

介绍了基本物理量的发展史、物理量国际单位制（SI）在建立过程中体现的物理文化内涵以及在物理量单位中引人人文元素的发展与传播     

质量单位千克定义的历史、现状和发展趋势

自1889年以来,千克的国际原器作为国际单位制(SI)质量单位的定义。这是SI定义基本单位最后一个人工制造的基准,它的重新定义必将影响着几个其他基本单位。文章介绍了瓦特天平的工作原理以及普朗克常数的实验测定。这些结果对物理学和计量学具有重要的意义。     

基本物理常量与国际单位制基本单位的重新定义

用固定若干基本物理常量的数值重新定义国际单位制基本单位，可以大幅度提高基本单位的准确性。     

国际单位制基本单位之一：摩尔（mole）——现代计理科学专题之八

摩尔是SI基本单位之一，摩尔对化学和物理计量很重要。摩尔的采纳使化学有了基本单位，从而结束了无量纲的历史。通过阿伏伽德罗常量、摩尔质量等，实现了化学各量之间的换算，同时有可能重新定义质量单位－千克．国际计量界已全面合作，致力于不断提高测量阿伏伽德罗常量的准确度，并已经取得一定成就。当前准确测量阿伏伽德罗常量的技术关键主要是制备高纯的、完美无缺的、超高圆度的单晶硅球；准确测量其直径、圆度、密度、原子量、晶格常量、空穴等。     

单电子效应用于电流强度的计量标准

安培（A）是国际单位制（SI）7个基本单位之一，它是依据真空中通电长直导线之间的相互作用力定义的．计量学的发展促使人们寻找关于电流强度更为基本的定义，例如通过对电子的计数（在单位时间内）测量电流，即电流i=ef，其中e是电子电荷f是1s内流过的单电子数．     

1990年的新计量标准

1990年 1月 1日,在电学单位中,伏特和欧姆的新的实用基准将开始生效.这两项新基准是由国际度量衡委员会(CIPM)和它的电量咨询委员会(CCE)推荐的.新基准的实行将带来世界性的影响.它不仅将改变电压和电阻的旧量值,而且也要影响到电流和功率的度量.在同一天,作为基本物理量之一的温度地将开始使用新的国际实用温标. 一、国际单位制中的伏特与欧姆 我们知道,世界公认的计量单位是国际单位制(SI).SI的三个基本力学量是长度、质量和时间,它们的单位分别为米(m)、公斤(kg)和秒(s).米是用真空中的光速定义的,秒是由铯-133基态的两个超精细能级…     

真空中光速的精密测量——长度单位米定义的基础

自1889年以来,米的国际原器作为国际单位制(SI)长度单位米的定义。1960年,改用氪86的光谱线作为新的定义。1983年,采用了真空中光速和光的频率值作为第三次定义,这是物理量单位用基本物理常数定义基本单位的典型实例。它对用其他基本常数定义其他基本单位起了示范作用,对物理学和计量学具有重要的意义。     

国际单位制(SI)在磁学中的应用

在进行磁测量时,正确选取合适的单位是很重要的.当前使用SI单位制是大势所趋.但由于对磁现象的解释历来就有两种观点,磁感应B和磁场强度 H在不同观点中被赋予不同的物理意义.因此,在使用磁学量的单位时经常发生混淆,如磁化强度M和磁极化强度J的单位选取常出现混乱,故在使用SI单     

为什么把常量称为常数不妥？

<正>2019年3月,科学出版社出版了物理学名词委正式公布的《物理学名词》(第三版)^[1],其中与constant相关的部分术语的中文译名如表1所示。同年5月14日,计量学名词委员会对国际上新公布的关于“千克”、“开尔文”、“摩尔”等SI基本单位的英文定义,发布了《中文新定义》^[2]。     

Fundamental metrology in the future: Measuring the single quantum

Great progress has been made over the past 50 years in replacing artefact definitions of the SI base units by those based on fundamental constants. However it is important to recognise that the development of the SI is not ‘complete’ once the base units are all defined in this way. New physics and technologies can always be expected to emerge and these will require developments and modifications to the SI. At the present time a dominant trend seems to be that measurements are changing from dealing with average properties of ensembles to metrology on single entities. This is already apparent for single atoms, ions or photon detection and measurement but can be expected to extend into the technologically important areas of single spins, single THz photons and even phonons in the future. Another significant development may be expected towards measurement of quite different physical quantities from those currently required, such as spin current, decoherence time etc. The paper addresses some of these issues, as well as the influence of quantum mechanics on precise measurement, which will also increase as metrology addresses both single entities and the nano scale.     

The Boltzmann Constant for the Definition and Realization of the Kelvin

In November 2018, the four base units, kilogram, ampere, kelvin, and mole, of the International System of Units (SI) are redefined in terms of fundamental physical constants. The redefinition comes into force on World Metrology Day, 20 May 2019. The kelvin, the base unit of thermodynamic temperature, from then is to be founded on a fixed numerical value of the Boltzmann constant. Herein, the change in the definition of the kelvin and the consequences for practical temperature measurement are explained. The primary thermometry methods applied to determine the numerical value of the Boltzmann constant for the redefinition are reviewed. The prospects for the future application of these methods are outlined.     

Understanding the Revised SI: Background,Consequences, and Perspectives

This article expounds the significance of the revision of the international system of units, the SI, approved by the General Conference on Weights and Measures (CGPM) in 2018. The revised SI implements a construct of a system of units based on fixing the numerical values of constants of nature, the “defining constants.” This fundamental development in the SI is not only elegant and infinitely sustainable, but moreover will drive future technological innovation. This article provides an historical overview and discusses the underlying principles and consequences of the revised SI: from the history of Planck's proposal for creating a system of units “valid for all times and civilizations,” to the scientific and technological motivations for the revision and the expected resulting innovations.     

The Avogadro Constant for the Definition and Realization of the Mole

The International System of Units’ (SI) base unit of the quantity “amount of substance” is the mole (symbol: mol). After the revision of the SI to be implemented in 2019, when all SI units will be based solely on constants, the mole will be defined through a fixed value of the Avogadro constant N_A. One mole contains exactly 6.02214076 × 10²³ elementary entities, meaning the mole will no longer be linked to the kilogram. Currently, the mole is defined via the mass of exactly 0.012 kg of the ¹²C isotope which links it to the kilogram prototype. The history, changes, and implications of the revised definition of the mole are discussed here from the chemist's point of view. The ability to count entities such as atoms or molecules (precisely enough to enable a revision of the SI and preserve consistency of previous and future measurements) is crucial. This is achieved with the realization (Mise en Pratique) based on the X‐ray‐crystal density (XRCD) method (counting the atoms in a silicon sphere). The determination of N_A, focusing on the measurement of the molar mass of silicon highly enriched in the ²⁸Si isotope, with the lowest uncertainty so far, is presented.     

The Sun: A User's Manual,By C. Vita-Finzi

The article deals with the rationalized MKS system of electrical units within the SI system in relation to the requirements of school and university teaching. The difficulties arising from the availability of two possible sets of units within the MKS system, those suggested by Kennelly and by Somefield, are discussed.     

A natural value unit—Econophysics as arbiter between finance and economics

Foreign exchange markets show that currency units (= accounting or nominal price units) are variables. Technical and economic progress evidences that the consumer baskets (= purchasing power units or real price units) are also variables. In contrast, all physical measurement units are constants and either defined in the SI (=metric) convention or based upon natural constants (= “natural” or Planck units). Econophysics can identify a constant natural value scale or value unit (natural numeraire) based upon Planck energy. In honor of the economist L. Walras, this “Planck value” could be called Walras (Wal), thereby using the SI naming convention. One Wal can be shown to have a physiological and an economic interpretation in that it is equal to the annual minimal real cost of physiological life of a reference person at minimal activity. The price of one Wal in terms of any currency can be estimated by hedonic regression techniques used in inflation measurement (axiometry). This pilot research uses official disaggregated Swiss Producer and Consumer Price Index (PPI and CPI) data and estimates the hedonic Walras price (HWP), quoted in Swiss francs in 2003, and its inverse, the physical purchasing power (PhPP) of the Swiss franc in 2003.     

物理量单位的智能导出算法及其应用

推导物理量的单位是物理作业中不可缺少的重要环节。提出一种物理量单位的智能导出算法,即计算机根据物理量的运算式自动推导出待求物理量的单位。实验结果表明,物理量单位导出及换算算法的结果正确,对算术运算式中的物理量单位导出及换算的正确率为100%,且物理量数值的运算正确。     

Towards a natural system of units for physics and metrology

A few years ago it was proposed by Mills et al.,2005 to redefine the kilogram in terms of values of certainnatural constants. It is expected that the consequences of thisredefinition will include some disadvantages in mass measurementsand advantages in the electric measurements and in some other areas.To achieve the best possible balance between gains and losses it iscrucial to create such a version of the SI, in which electricmeasurements in SI units are possible with the highest accuracy.This can be only done with a simultaneous redefinition of the kilogramand ampere and we consider various details of such a scenario.Further consideration involves a suggestion on a redefinition of thekelvin and mole, which we also consider. Besides, we discuss variousgeneral issues of the natural units ranging from fundamental topractical.     

The Elementary Charge for the Definition and Realization of the Ampere

The elementary charge e is one of the seven defining constants in the revised International System of Units (SI). Here, the determination of the elementary charge with the highest precision is discussed, including the results of the special CODATA adjustment leading to the fixed value of e. The various options to realize the ampere and the other electrical units in the revised SI, either through the counting of electrons by using single‐electron tunneling devices or through the Josephson and quantum Hall effect, respectively, are further elucidated.