26 research outputs found
Proposal for new experimental schemes to realize the Avogadro constant
We propose two experimental schemes to determine and so to realize the
Avogadro constant at the level of 10 or better with a watt
balance experiment and a cold atom experiment measuring (where is
the Planck constant and the mass of the atom ). We give some
prospects about achievable uncertainties and we discuss the opportunity to test
the existence of possible unknown correction factors for the Josephson effect
and quantum Hall effect
Limits to the sensitivity of a low noise compact atomic gravimeter
A detailed analysis of the most relevant sources of phase noise in an atomic
interferometer is carried out, both theoretically and experimentally. Even a
short interrogation time of 100 ms allows our cold atom gravimeter to reach an
excellent short term sensitivity to acceleration of g at 1s.
This result relies on the combination of a low phase noise laser system,
efficient detection scheme and good shielding from vibrations. In particular,
we describe a simple and robust technique of vibration compensation, which is
based on correcting the interferometer signal by using the AC acceleration
signal measured by a low noise seismometer.Comment: 30 pages, 14 figure
Preliminary investigation of the damping effect of bubble levels used in dynamic conditions
This paper presents a preliminary experimental investigation of the damping effect of bubble levels on the rotation of pendulous systems. The damping efficiency of such a level is directly correlated to the energy dissipated by the bubble motion. This energy depends on the physical characteristics of the bubble level such as the radius of curvature of the tube, the liquid properties and the bubble length. This study demonstrates that a bubble level can be used to damp the oscillations of dynamic mechanical systems. In particular, commercially available bubble levels might prove suitable for applications where one needs to damp efficiently oscillating systems for which the initial potential energy is less than a hundred times the energy dissipated by the bubble displacement for the first oscillation
SPARQL Query Containment with ShEx Constraints
International audienceShEx (Shape Expressions) is a language for expressing constraints on RDF graphs. We consider the problem of SPARQL query containment in the presence of ShEx constraints. We first investigate the complexity of the problem according to the fragments considered for SPARQL queries and for ShEx constraints. In particular, we show that the complexity of SPARQL query containment remains the same with or without ShEx constraints. We develop two radically different approaches for solving the problem and we evaluate them. The first approach relies on the joint use of a ShEx validator and a tool for checking query containment without constraints. In a second approach, we show how the problem can be solved by a reduction to a fragment of first-order logic with two variables. This alternative approach allows to take advantage of any of the many existing FOL theorem provers in this context. We evaluate how the two approaches compare experimentally, and report on lessons learned. To the best of our knowledge, this is the first work addressing SPARQL query containment in the presence of ShEx constraints
Determination of the Planck constant by means of a watt balance
The kilogram is the only base unit of the Système International d'unités (SI) still defined by a material artefact. Regarding the past evolution of the SI and the poor knowledge of the stability of the international prototype, its definition is not satisfactory. In the long term, it would be better to move to a definition based either on atomic properties or on fundamental constants. Among the various researches in progress in metrology laboratories, one of the most promising ways seems to be the watt balance. Its principle consists in comparing a mechanical power to an electromagnetic power. This comparison results from a measurement performed in two steps: a static measurement during which the Laplace force acting on a coil driven by a DC current and subjected to an induction field is compared to the weight of a standard mass, and a dynamic measurement where the induced voltage at the terminals of the same coil is determined when it is moved in the same field at a known velocity. The measurement of electrical quantities in terms of the Josephson and the quantum Hall effects then allows the mass unit be linked to the Planck constant. Although the principle of the experiment remains simple and direct, obtaining sufficiently low uncertainty ( 10-8) implies that devices relevant of various fields of physics must be implemented at their best level. In this paper, a review of the present developments at international level is presented
Determination of the Planck constant by means of a watt balance
The kilogram is the only base unit of the Système International d'unités (SI) still defined by a material artefact. Regarding the past evolution of the SI and the poor knowledge of the stability of the international prototype, its definition is not satisfactory. In the long term, it would be better to move to a definition based either on atomic properties or on fundamental constants. Among the various researches in progress in metrology laboratories, one of the most promising ways seems to be the watt balance. Its principle consists in comparing a mechanical power to an electromagnetic power. This comparison results from a measurement performed in two steps: a static measurement during which the Laplace force acting on a coil driven by a DC current and subjected to an induction field is compared to the weight of a standard mass, and a dynamic measurement where the induced voltage at the terminals of the same coil is determined when it is moved in the same field at a known velocity. The measurement of electrical quantities in terms of the Josephson and the quantum Hall effects then allows the mass unit be linked to the Planck constant. Although the principle of the experiment remains simple and direct, obtaining sufficiently low uncertainty ( 10-8) implies that devices relevant of various fields of physics must be implemented at their best level. In this paper, a review of the present developments at international level is presented
CVD elaboration and in situ characterization of barium silicate thin films.
International audienceThis study is concerned with the elaboration of barium silicate thin films by metal organic chemical vapor deposition (MOCVD) and in situ characterization by X-ray photoemission spectroscopy (XPS) with an apparatus connected to the deposition reactor. The difficulty to find an efficient metal organic precursor for barium is described. After characterizations of the selected reactant, Ba(TMHD)2tetraglyme, the development of an original specific vapor delivering source which allows reactant sublimation in the CVD reactor was performed. In the most optimized cases, including use of oxygen introduction during the deposition, barium silicate films were obtained. Moreover, non-negligible amounts of carbon and presence of barium oxide on the top of the layers were observed