scholarly journals Time scales in the context of general relativity

2011 ◽  
Vol 369 (1953) ◽  
pp. 4131-4142 ◽  
Author(s):  
Bernard Guinot
Keyword(s):  
Relativistic Effect ◽  
International System ◽  
Centre Of Mass ◽  
Frequency Standards ◽  
The Earth ◽  
International Astronomical ◽  
System Of Units ◽  
Definition Of ◽  
Atomic Time

Towards 1967, the accuracy of caesium frequency standards reached such a level that the relativistic effect could not be ignored anymore. Corrections began to be applied for the gravitational frequency shift and for distant time comparisons. However, these corrections were not applied to an explicit theoretical framework. Only in 1991 did the International Astronomical Union provide metrics (then improved in 2000) for a definition of space–time coordinates in reference systems centred at the barycentre of the Solar System and at the centre of mass of the Earth. In these systems, the temporal coordinates (coordinate times) can be realized on the basis of one of them, the International Atomic Time (TAI), which is itself a realized time scale. The definition and the role of TAI in this context will be recalled. There remain controversies regarding the name to be given to the unit of coordinate times and to other quantities appearing in the theory. However, the idea that astrometry and celestial mechanics should adopt the usual metrological rules is progressing, together with the use of the International System of Units, among astronomers.

scholarly journals JD6 -Time and Astronomy Preface and Posters

2009 ◽  
Vol 5 (H15) ◽  
pp. 205-206
Author(s):  
Pascale Defraigne
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
International System ◽  
Atomic Transition ◽  
International System Of Units ◽  
System Of Units ◽  
Definition Of ◽  
Atomic Time

Responsibility for the definition of time scales left the astronomical community some 40 years ago when, in 1967, the second became defined by an atomic transition in the International System of units SI and when International Atomic Time (TAI) was defined as the primary international time scale in 1971.

Investigation on the Noise Separation in Watt Balance Experiments

2008 ◽  
Vol 381-382 ◽  
pp. 619-622
Author(s):  
W. Zeng ◽  
Xiang Qian Jiang ◽  
P. Scott ◽  
L. Blunt
Keyword(s):  
Background Noise ◽  
International System ◽  
Histogram Method ◽  
Stationary Noise ◽  
Vibration Data ◽  
System Of Units ◽  
Environmental Vibration ◽  
Transient Events ◽  
Watt Balance ◽  
Definition Of

The detection of stationary and non-stationary noise in environmental vibration data is an important issue when considering the precision of the Watt balance, an electromechanical apparatus for the new definition of the kilogram in the international system of Units (SI). In this paper, the authors propose a frequency histogram method to find the structure of the stationary noise from large amount of datasets. For the non-stationary noise, the authors propose a wavelet based denoising methods to distinguish the transient events from the background “noise”, to find their duration and content and to identify their location in time.

Ultracold atoms and precise time standards

2011 ◽  
Vol 369 (1953) ◽  
pp. 4078-4089 ◽  
Author(s):  
Gretchen K. Campbell ◽  
William D. Phillips
Keyword(s):  
Laser Cooling ◽  
International System ◽  
Microwave Frequency ◽  
Observation Time ◽  
Mass Motion ◽  
Frequency Standards ◽  
Systematic Uncertainties ◽  
System Of Units ◽  
Time Standards ◽  
Atomic Frequency

Experimental techniques of laser cooling and trapping, along with other cooling techniques, have produced gaseous samples of atoms so cold that they are, for many practical purposes, in the quantum ground state of their centre-of-mass motion. Such low velocities have virtually eliminated effects such as Doppler shifts, relativistic time dilation and observation-time broadening that previously limited the performance of atomic frequency standards. Today, the best laser-cooled, caesium atomic fountain, microwave frequency standards realize the International System of Units (SI) definition of the second to a relative accuracy of ≈3×10 −16 . Optical frequency standards, which do not realize the SI second, have even better performance: cold neutral atoms trapped in optical lattices now yield relative systematic uncertainties of ≈1×10 −16 , whereas cold-trapped ions have systematic uncertainties of 9×10 −18 . We will discuss the current limitations in the performance of neutral atom atomic frequency standards and prospects for the future.

scholarly journals Thermodynamic Properties of Seawater, Ice and Humid Air: TEOS-10, Before and Beyond

2018 ◽  
Author(s):  
Rainer Feistel
Keyword(s):  
Hydrological Cycle ◽  
International System ◽  
Metrological Traceability ◽  
Humid Air ◽  
Ongoing Research ◽  
Seawater Salinity ◽  
System Of Units ◽  
Atmospheric Relative Humidity ◽  
Definition Of ◽  
First Time

Abstract. In the terrestrial climate system, water is a key player in the form of its different ambient phases of ice, liquid and vapour, admixed with sea salt in the ocean and with dry air in the atmosphere. For proper balances of climatic energy and entropy fluxes in models and observation, a highly accurate, consistent and comprehensive thermodynamic standard framework is requisite in geophysics and climate research. The new “Thermodynamic Equation of Seawater – 2010” (TEOS-10) constitutes such a standard for properties of water in its various manifestations in the hydrological cycle. TEOS-10 has been recommended internationally in 2009 by the Intergovernmental Oceanographic Commission (IOC) to replace the previous 1980 seawater standard, EOS-80, and in 2011 by the International Union of Geodesy and Geophysics (IUGG) “as the official description for the properties of seawater, of ice and of humid air”. This paper briefly reviews the development of TEOS-10, its novel axiomatic properties, new oceanographic tools it offers, and important tasks that still await solutions by ongoing research. Among the latter are new definitions and measurement standards for seawater salinity and pH, in order to establish their metrological traceability to the International System of Units (SI), for the first time after a century of widespread use. Of similar climatological relevance is the development and recommendation of a uniform standard definition of atmospheric relative humidity that is unambiguous and rigorously based on physical principles.

scholarly journals The kelvin redefinition and its mise en pratique

2016 ◽  
Vol 374 (2064) ◽  
pp. 20150037 ◽  
Author(s):  
B. Fellmuth ◽  
J. Fischer ◽  
G. Machin ◽  
S. Picard ◽  
P. P. M. Steur ◽  
...  
Keyword(s):  
International System ◽  
Thermodynamic Temperature ◽  
Fundamental Constants ◽  
Primary Thermometry ◽  
A Value ◽  
System Of Units ◽  
Mise En Pratique ◽  
Explicit Constant ◽  
Definition Of ◽  
Base Units

In 2018, it is expected that there will be a major revision of the International System of Units (SI) which will result in all of the seven base units being defined by fixing the values of certain atomic or fundamental constants. As part of this revision, the kelvin, unit of thermodynamic temperature, will be redefined by assigning a value to the Boltzmann constant k . This explicit-constant definition will define the kelvin in terms of the SI derived unit of energy, the joule. It is sufficiently wide to encompass any form of thermometry. The planned redefinition has motivated the creation of an extended mise en pratique (‘practical realization’) of the definition of the kelvin ( MeP -K), which describes how the new definition can be put into practice. The MeP -K incorporates both of the defined International Temperature Scales (ITS-90 and PLTS-2000) in current use and approved primary-thermometry methods for determining thermodynamic temperature values. The MeP -K is a guide that provides or makes reference to the information needed to perform measurements of temperature in accord with the SI at the highest level. In this article, the background and the content of the extended second version of the MeP -K are presented.

scholarly journals Definition of the mole (IUPAC Recommendation 2017)

2018 ◽  
Vol 90 (1) ◽  
pp. 175-180 ◽  
Author(s):  
Roberto Marquardt ◽  
Juris Meija ◽  
Zoltán Mester ◽  
Marcy Towns ◽  
Ron Weir ◽  
...  
Keyword(s):  
International System ◽  
International Committee ◽  
Fundamental Physical Constants ◽  
Weights And Measures ◽  
Technical Report ◽  
System Of Units ◽  
Iupac Recommendation ◽  
Definition Of ◽  
Base Units ◽  
Fundamental Physical

AbstractIn 2011 the General Conference on Weights and Measures (CGPM) noted the intention of the International Committee for Weights and Measures (CIPM) to revise the entire International System of Units (SI) by linking all seven base units to seven fundamental physical constants. Of particular interest to chemists, new definitions for the kilogram and the mole have been proposed. A recent IUPAC Technical Report discussed these new definitions in relation to immediate consequences for the chemical community. This IUPAC Recommendation on the preferred definition of the mole follows from this Technical Report. It supports a definition of the mole based on a specified number of elementary entities, in contrast to the present 1971 definition.

scholarly journals Mise en pratiquefor the definition of the candela and associated derived units for photometric and radiometric quantities in the International System of Units (SI)

Metrologia ◽  
2016 ◽  
Vol 53 (3) ◽  
pp. G1-G1 ◽  
Author(s):  
Joanne Zwinkels ◽  
Armin Sperling ◽  
Teresa Goodman ◽  
Joaquin Campos Acosta ◽  
Yoshi Ohno ◽  
...  
Keyword(s):  
International System ◽  
International System Of Units ◽  
System Of Units ◽  
Definition Of

scholarly journals When should we change the definition of the second?

2011 ◽  
Vol 369 (1953) ◽  
pp. 4109-4130 ◽  
Author(s):  
Patrick Gill
Keyword(s):  
Laser Cooling ◽  
Optical Lattice ◽  
Cold Atoms ◽  
International System ◽  
Atomic Clock ◽  
Optical Clock ◽  
Lattice Systems ◽  
System Of Units ◽  
Primary Standards ◽  
Definition Of

The microwave caesium (Cs) atomic clock has formed an enduring basis for the second in the International System of Units (SI) over the last few decades. The advent of laser cooling has underpinned the development of cold Cs fountain clocks, which now achieve frequency uncertainties of approximately 5×10 −16 . Since 2000, optical atomic clock research has quickened considerably, and now challenges Cs fountain clock performance. This has been suitably shown by recent results for the aluminium Al + quantum logic clock, where a fractional frequency inaccuracy below 10 −17 has been reported. A number of optical clock systems now achieve or exceed the performance of the Cs fountain primary standards used to realize the SI second, raising the issues of whether, how and when to redefine it. Optical clocks comprise frequency-stabilized lasers probing very weak absorptions either in a single cold ion confined in an electromagnetic trap or in an ensemble of cold atoms trapped within an optical lattice. In both cases, different species are under consideration as possible redefinition candidates. In this paper, I consider options for redefinition, contrast the performance of various trapped ion and optical lattice systems, and point to potential limiting environmental factors, such as magnetic, electric and light fields, collisions and gravity, together with the challenge of making remote comparisons of optical frequencies between standards laboratories worldwide.

scholarly journals Progress on vacuum-to-air mass calibration system using magnetic suspension to disseminate the Planck-constant realized kilogram

ACTA IMEKO ◽  
2017 ◽  
Vol 6 (2) ◽  
pp. 70 ◽  
Author(s):  
Eric Carl Benck ◽  
Corey Stambaugh ◽  
Edward Mulhern ◽  
Patrick Abbott ◽  
Zeina Kubarych
Keyword(s):  
International System ◽  
High Accuracy ◽  
Magnetic Suspension ◽  
Calibration System ◽  
Font Size ◽  
Planck Constant ◽  
Air Mass ◽  
System Of Units ◽  
Mass Calibration ◽  
Definition Of

<p><span style="font-size: small;">The kilogram is the unit of mass in the International System of units (SI) and has been defined as the mass of the International Prototype Kilogram (IPK) since 1889.  </span><span style="font-size: small;">In the future, a new definition of the kilogram will be realized by fixing the value of the Planck constant.</span><span style="font-size: small;">  </span><span style="font-size: small;">The new definition of the unit of mass will occur in a vacuum environment by necessity, so the National Institute of Standards and Technology (NIST) is developing a mass calibration system in which a kilogram artefact in air can be directly compared with a kilogram realized in a vacuum environment.</span><span style="font-size: small;">  </span><span style="font-size: small;">This apparatus uses magnetic suspension to couple the kilogram in air to a high accuracy mass balance in vacuum.</span><span style="font-size: small;"> </span></p><p> </p>

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