The Experts below are selected from a list of 12 Experts worldwide ranked by ideXlab platform

Ping-zhan Si - One of the best experts on this subject based on the ideXlab platform.

  • Redefine the Kilogram in Terms of the Carbon-12 Atom and an Exact Value of the Avogadro Constant
    MAPAN, 2014
    Co-Authors: Ping-zhan Si
    Abstract:

    We report on a method for redefinition of the kilogram by 12C, which ideally joins the Atomic and the macroscopic mass units in a natural way. The kilogram artifact will be composed of a number of concentric shells around C-60 and that this is sometimes referred to as a “carbon onion”. A 135887620-layer carbon onion containing 50184508751575328771368200 Atoms of 12C falls in the acceptable range for the redefinition of kilogram and is closest to the recent experimental results. An Avogadro constant is thus derived to be 602214105018903945256418.4. A perfect carbon onion is ideal for kilogram redefinition and determination of the Avogadro constant because it is expected to exhibit characteristics of central symmetry, high stability, high strength, high sphericity, low roughness, weak inter-planar force and strong in-plane bonding, easy Atomic counting, and these are important for technical feasibility in further experiments.

Richard S. Davis - One of the best experts on this subject based on the ideXlab platform.

  • What Is a Kilogram in the Revised International System of Units (SI)
    Journal of Chemical Education, 2015
    Co-Authors: Richard S. Davis
    Abstract:

    The definition of the kilogram, the unit of mass in the International System of Units (SI), has not changed in more than 125 years. The kilogram is still defined by the mass of a Pt–Ir cylinder conserved at the International Bureau of Weights and Measures. Science and technology have progressed to the point where it is likely the kilogram will be redefined in 2018 in terms of a constant of physics—the Planck constant, which is closely linked to the Avogadro and Atomic mass constants. In this article, we illustrate by means of a simple experiment on how analytical chemistry is contributing to this project, how the new definition of the kilogram will be put into practice and what it may mean for chemists. Surprisingly, perhaps, this simple experiment allows us to determine the mass of an aluminum-27 Atom, the mass of a Carbon-12 Atom (and the Atomic mass constant), the Avogadro constant, and the Planck constant—all with uncertainty less than 1%—in close analogy to the way the most accurate experiment of thi...

V. V. Khruschov - One of the best experts on this subject based on the ideXlab platform.

  • Comments on redefinition of SI units based on fundamental physical constants with fixed values
    arXiv: Atomic Physics, 2011
    Co-Authors: V. V. Khruschov
    Abstract:

    Advantages and disadvantages of fixation of fundamental physical constants' values for definition of SI units are considered. The case with a new definition of the mass unit on the base of a fixed value of the Avogadro constant is studied in detail. Criteria on choosing of a optimum FPC set with fixed values for the redefinition of the SI units are suggested. The minimal optimum FPC set that is consistent with the criteria is presented. The set comprises the speed of light, the constant of the ground state hyperfine transition of the caesium-133 Atom, the Avogadro constant, the mass of the Carbon-12 Atom and the absolute magnitude of the electron charge. Comment on the redefinition of the kelvin is also made.

Joseph Feher - One of the best experts on this subject based on the ideXlab platform.

  • Chemical Foundations of Physiology II: Concentration and Kinetics
    Quantitative Human Physiology, 2017
    Co-Authors: Joseph Feher
    Abstract:

    This chapter begins with a description of the Atomic mass unit, or dalton, defined as 1/12 the mass of a Carbon-12 Atom. It then proceeds to define molecular weight, in daltons, and the gram molecular weight. It then discusses the mole in chemistry and Avogadro’s number. This chapter then defines concentration in terms of molarity and how to make up solutions and dilutions of solutions to achieve desired concentrations. It describes the Fick dilution principle for determining unknown volumes. This chapter then considers kinetics in terms of forward and reverse rate constants, defining the equilibrium constant as the ratio of forward to reverse rate constants. It discusses kinetics in terms of potential energy along the reaction coordinate, the distance along the minimum free-energy path from reactants to products. This chapter then derives the Michaelis–Menten formula for enzyme kinetics and discusses how enzymes, in general, catalyze reactions. It ends with a derivation of the double-reciprocal plot for enzyme kinetics.