164 research outputs found
Remote atomic clock synchronization via satellites and optical fibers
In the global network of institutions engaged with the realization of
International Atomic Time (TAI), atomic clocks and time scales are compared by
means of the Global Positioning System (GPS) and by employing telecommunication
satellites for two-way satellite time and frequency transfer (TWSTFT). The
frequencies of the state-of-the-art primary caesium fountain clocks can be
compared at the level of 10e-15 (relative, 1 day averaging) and time scales can
be synchronized with an uncertainty of one nanosecond. Future improvements of
worldwide clock comparisons will require also an improvement of the local
signal distribution systems. For example, the future ACES (atomic clock
ensemble in space) mission shall demonstrate remote time scale comparisons at
the uncertainty level of 100 ps. To ensure that the ACES ground instrument will
be synchronized to the local time scale at PTB without a significant
uncertainty contribution, we have developed a means for calibrated clock
comparisons through optical fibers. An uncertainty below 50 ps over a distance
of 2 km has been demonstrated on the campus of PTB. This technology is thus in
general a promising candidate for synchronization of enhanced time transfer
equipment with the local realizations of UTC . Based on these experiments we
estimate the uncertainty level for calibrated time transfer through optical
fibers over longer distances. These findings are compared with the current
status and developments of satellite based time transfer systems, with a focus
on the calibration techniques for operational systems
Practical thermodynamics of Yukawa systems at strong coupling
Simple practical approach to estimate thermodynamic properties of strongly
coupled Yukawa systems, in both fluid and solid phases, is presented. The
accuracy of the approach is tested by extensive comparison with direct computer
simulation results (for fluids and solids) and the recently proposed
shortest-graph method (for solids). Possible applications to other systems of
softly repulsive particles are briefly discussed.Comment: Published in J. Chem. Phy
A transverse current rectification in graphene superlattice
A model for energy spectrum of superlattice on the base of graphene placed on
the striped dielectric substrate is proposed. A direct current component which
appears in that structure perpendicularly to pulling electric field under the
influence of elliptically polarized electromagnetic wave was derived. A
transverse current density dependence on pulling field magnitude and on
magnitude of component of elliptically polarized wave directed along the axis
of a superlattice is analyzed.Comment: 12 pages, 6 figure
The Minimum-Uncertainty Squeezed States for for Atoms and Photons in a Cavity
We describe a six-parameter family of the minimum-uncertainty squeezed states
for the harmonic oscillator in nonrelativistic quantum mechanics. They are
derived by the action of corresponding maximal kinematical invariance group on
the standard ground state solution. We show that the product of the variances
attains the required minimum value 1/4 only at the instances that one variance
is a minimum and the other is a maximum, when the squeezing of one of the
variances occurs. The generalized coherent states are explicitly constructed
and their Wigner function is studied. The overlap coefficients between the
squeezed, or generalized harmonic, and the Fock states are explicitly evaluated
in terms of hypergeometric functions. The corresponding photons statistics are
discussed and some applications to quantum optics, cavity quantum
electrodynamics, and superfocusing in channeling scattering are mentioned.
Explicit solutions of the Heisenberg equations for radiation field operators
with squeezing are found.Comment: 27 pages, no figures, 174 references J. Phys. B: At. Mol. Opt. Phys.,
Special Issue celebrating the 20th anniversary of quantum state engineering
(R. Blatt, A. Lvovsky, and G. Milburn, Guest Editors), May 201
Scanning Electron Microscopy Study of Drilling Cuttings in Tomsk Oblast Sites
The research is focused on determining mineralogical composition of drilling cuttings by scanning electron microscope as well as imaging the sample surface of high resolution that allows studying the structural characteristics of the site. In addition, a number of other techniques permit obtaining information on chemical composition of sample in near-surface layers. The study in drilling cuttings by means of scanning microscopy has revealed the presence of titanium, iron, zirconium oxides, iron sulphide, barium sulphate. The former is a mineral that concentrates rare-earth elements, presumably monocyte, as well as uranium silicate, etc. The results obtained confirm the data of previous X-ray structural analysis, i.e. the study samples consist of alumosilicate matrix. Apart from silicon and aluminium oxides, the matrix includes such elements as Na, K, Mg. Such a composition corresponds to rock-forming minerals: quartz, albite, microcline, clinochlore, muscovite, anorthoclase
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