共查询到18条相似文献,搜索用时 203 毫秒
1.
2.
3.
能量天平法已在中国计量科学研究院开展了几年的研究。研究的目的与功率天平法是一致的,即通过测量普朗克常数来建立质量量子基准,但具体方法不同。2010年以来该项研究取得一定进展。例如对于直流互感量测量这一关键问题,已研究出一种新的方波补偿方法,测量不确定度达到10-7量级(k=1)。还研发了一种涡流传感器,可更准确地对可动线圈定位。线圈系统的准直问题也得到进展,研制了一种油阻尼器,大大减小了由于天平基础振动和线圈加热上升气流引起的线圈抖动。这些措施改善了线圈位置及互感测量的不确定度。测量普朗克常数h的最新结果为6626104(59)×10-34J·s,综合的相对不确定度为8.9×10-6(k=1)。对所遇到的困难和进一步的改进措施也在文中进行了讨论。 相似文献
4.
利用功率天平测量普朗克常数和重新定义千克是目前国际计量界研究的前沿和热点之一。最近几年,新西兰计量院(MSL)提出了基于双活塞系统的功率天平方案,利用了活塞系统具有理想直线度的优点。对这一方案及研究进展进行了综述,阐述了双活塞系统作为高精度质量比较仪和实现动态模式的可行性。 相似文献
5.
量子计量基准与基本物理常数 总被引:1,自引:0,他引:1
文章讲述了计量基准从实物基准到量子计量基准的发展过程,论述了基本物理常数的精密测定与量子计量基准的关系。指出了新一代量子计量基准的特点是基于微观物理学的规律,并设法把计量单位的定义与基本物理常数相联系。 相似文献
6.
一、引言在目前国际单位制的广泛更新中,有4个基本单位将重新定义,其中千克的重新定义尤为关键。本文比较两个可能方案的优缺点:基于固定普朗克常数值的"电子千克"和基于固定阿伏伽德罗常数值的"原子千克"。千克是质量单位,它等于千克国际原器的质量。这个定义是基于1889年第一届国际计量大会通过的唯一的铂铱圆柱体的定义。虽 相似文献
7.
介绍了库仑定律和安培定律在电学单位制中发挥的作用,依据机械功率与电功率等效的原理,选择电流单位安培(A)作为基本物理单位,并介绍了实用单位制和电学实物计量标准。阐述了三种电学计量的量子标准原理和溯源到自然常数的途径,分析了真空磁导率在安培定律公式中发挥的作用,探讨了电学量子三角形与欧姆定律兼容的问题。指出基本电荷量常数不是简单地从约瑟夫森常数KJ?90和冯·克里青常数RH?90推导而来,而是由精细结构常数公式计算出来的,能量守恒原理是单位制中的第一性原理,是力学和电学计量单位的纽带。提出量子点之间的位移电流对单电子隧道泵有一定的影响,真空磁导率不再是理想的常数,真空磁导率的变化将成为后来理论界研究的重点。 相似文献
8.
9.
从二十世纪六十年代起,计量基准已逐步从“实物基准”过渡到“量子基准”时代,即用一些特定的原子系统中的量子效应来定义单位的量值,其准确度和稳定性均大大超过实物基准。但这样的量子基准还有其局限性,因此从八十年代起,人们又不断探讨另一种更好的方法,即用基本物理常数来作为计量基准,这样不仅有极高的准确度和稳定性,而且普适性极强。但这些工作难度非常大,还需长时间的艰苦实践。 相似文献
10.
11.
Joshua P. Schwarz Ruimin Liu David B. Newell Richard L. Steiner Edwin R. Williams Douglas Smith Ali Erdemir John Woodford 《Journal of research of the National Institute of Standards and Technology》2001,106(4):627-640
The NIST watt balance experiment is being completely rebuilt after its 1998 determination of the Planck constant. That measurement yielded a result with an approximately 1×10−7 relative standard uncertainty. Because the goal of the new incarnation of the experiment is a ten-fold decrease in uncertainty, it has been necessary to reexamine many sources of systematic error. Hysteresis effects account for a substantial portion of the projected uncertainty budget. They arise from mechanical, magnetic, and thermal sources. The new experiment incorporates several improvements in the apparatus to address these issues, including stiffer components for transferring the mass standard on and off the balance, better servo control of the balance, better pivot materials, and the incorporation of erasing techniques into the mass transfer servo system. We have carried out a series of tests of hysteresis sources on a separate system, and apply their results to the watt apparatus. The studies presented here suggest that our improvements can be expected to reduce hysteresis signals by at least a factor of 10—perhaps as much as a factor of 50—over the 1998 experiment. 相似文献
12.
13.
Gallop J 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2005,363(1834):2221-2247
The past 35 years have seen the development of an unexpected plethora of quantum electrical standards based on just two fundamental constants, e and h. First came a voltage standard based on the Josephson a.c. effect, in terms of which most maintained primary standards of voltage are defined. This was followed a decade later by the quantized Hall effect, based on the von Klitzing constant which allows the ohm to be maintained very precisely. It became clear 20 years ago that there is also a possible quantum current standard. This third standard has yet to play a full part in practical electrical metrology. However, recent developments suggest that there are many different possible manifestations in which such a current standard might be realized.The three quantum standards, taken together, define the quantum electrical triangle of standards which would allow the units to be realized in terms of different combinations of e and h. We summarize the very different physics behind the three standards, reviewing the present state of development in all three. Implications for the future are also considered, especially relating to ultra-low temperature, nanoscale and truly quantum mechanical versions of the standards. 相似文献
14.
Bordé CJ 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2005,363(1834):2177-2201
Over the past 40 years, a number of discoveries in quantum physics have completely transformed our vision of fundamental metrology. This revolution starts with the frequency stabilization of lasers using saturation spectroscopy and the redefinition of the metre by fixing the velocity of light c. Today, the trend is to redefine all SI base units from fundamental constants and we discuss strategies to achieve this goal. We first consider a kinematical frame, in which fundamental constants with a dimension, such as the speed of light c, the Planck constant h, the Boltzmann constant k(B) or the electron mass m(e) can be used to connect and redefine base units. The various interaction forces of nature are then introduced in a dynamical frame, where they are completely characterized by dimensionless coupling constants such as the fine structure constant alpha or its gravitational analogue alpha(G). This point is discussed by rewriting the Maxwell and Dirac equations with new force fields and these coupling constants. We describe and stress the importance of various quantum effects leading to the advent of this new quantum metrology. In the second part of the paper, we present the status of the seven base units and the prospects of their possible redefinitions from fundamental constants in an experimental perspective. The two parts can be read independently and they point to these same conclusions concerning the redefinitions of base units. The concept of rest mass is directly related to the Compton frequency of a body, which is precisely what is measured by the watt balance. The conversion factor between mass and frequency is the Planck constant, which could therefore be fixed in a realistic and consistent new definition of the kilogram based on its Compton frequency. We discuss also how the Boltzmann constant could be better determined and fixed to replace the present definition of the kelvin. 相似文献
15.
Richard Steiner David Newell Edwin Williams 《Journal of research of the National Institute of Standards and Technology》2005,110(1):1-26
The National Institute of Standards and Technology (NIST) watt balance experiment completed a determination of Planck constant in 1998 with a relative standard uncertainty of 87 × 10−9 (k = 1), concurrently with an upper limit on the drift rate of the SI kilogram mass standard. A number of other fundamental physical constants with uncertainties dominated by this result are also calculated. This paper focuses on the details of the balance apparatus, the measurement and control procedures, and the reference calibrations. The alignment procedures are also described, as is a novel mutual inductance measurement procedure. The analysis summary discusses the data noise sources and estimates for the Type B uncertainty contributions to the uncertainty budget. Much of this detail, some historical progression, and a few recent findings have not been included in previous papers reporting the results of this experiment. 相似文献
16.
The importance of precision electromagnetic measurements to the fundamental constants, and vice versa is examined. The idea that recent advances in the determination of a number of constants may have made future least-squares adjustments of the constants unnecessary is also discussed. Some of the fundamental constants considered are: the vacuum speed of light, the gas constant, Avogadro's constant, the proton-to-electron mass ratio, and Rydberg's constant for infinite mass 相似文献
17.
In quest of finding new substrate for printed wiring board (PWB) having low dielectric constant, we have made PSF/PMMA blends
and evaluated the dielectric parameters at 8.92 GHz frequency and at 35°C temperature. Incorporating PMMA in PSF matrix results
in reduced dielectric constant than that of pure PSF. The dielectric parameters of pure PMMA and PSF films of different thicknesses
have also been obtained at microwave frequencies. We have used dielectric data at microwave frequencies as a tool to evaluate
optical constants, absorption index ‘K’ and refractive index ‘n’. The blends of PSF/PMMA may be used as base materials for
PWBs. 相似文献