455 research outputs found
Cryogenic Sapphire Oscillator using a low-vibration design pulse-tube cryocooler: First results
A Cryogenic Sapphire Oscillator has been implemented at 11.2 GHz using a
low-vibration design pulse-tube cryocooler. Compared with a state-of-the-art
liquid helium cooled CSO in the same laboratory, the square root Allan variance
of their combined fractional frequency instability is for integration times s, dominated by
white frequency noise. The minimum for the two
oscillators was reached at s. Assuming equal contributions from
both CSOs, the single oscillator phase noise at 1 Hz offset from the carrier.Comment: 5 pages, 5 figures, accepted in IEEE Trans on Ultrasonics,
Ferroelectrics and Frequency Contro
Discovery of Bragg confined hybrid modes with high Q-factor in a hollow dielectric resonator
The authors report on observation of Bragg confined mode in a hollow
cylindrical dielectric cavity. A resonance was observed at 13.4 with an
unloaded Q-factor of order , which is more than a factor of 6
above the dielectric loss limit. Previously such modes have only been realized
from pure Transverse Electric modes with no azimuthal variations and only the
component. From rigorous numeric simulations it is shown that the
mode is a hybrid mode with non-zero azimuthal variations and with dominant
and electric field components and magnetic field
component.Comment: Accepted to be published in Applied Physics Letter
Exemple d'utilisation des données du satellite Landsat pour l'étude des sols en zone aride (Tunisie présaharienne)
Multi-wavelength characterisation of z~2 clustered, dusty star forming galaxies discovered by Planck
(abridged) We report the discovery of PHz G95.5-61.6, a complex structure
detected in emission in the Planck all-sky survey that corresponds to two
over-densities of high-redshift galaxies. This is the first source from the
Planck catalogue of high-z candidates that has been completely characterised
with follow-up observations from the optical to the sub-millimetre domain.
Herschel/SPIRE observations at 250, 350 and 500 microns reveal the existence of
five sources producing a 500 microns emission excess that spatially corresponds
to the candidate proto-clusters discovered by Planck. Further observations at
CFHT in the optical bands (g and i) and in the near infrared (J, H and K_s),
plus mid infrared observations with IRAC/Spitzer (at 3.6 and 4.5 microns)
confirm that the sub-mm red excess is associated with an over-density of
colour-selected galaxies. Follow-up spectroscopy of 13 galaxies with
VLT/X-Shooter establishes the existence of two high-z structures: one at z~1.7
(three confirmed member galaxies), the other at z~2.0 (six confirmed members).
This double structure is also seen in the photometric redshift analysis of a
sample of 127 galaxies located inside a circular region of 1'-radius containing
the five Herschel/SPIRE sources, where we found a double-peaked excess of
galaxies at z~1.7 and z~2.0 with respect to the surrounding region. These
results suggest that PHz G95.5-61.6 corresponds to two accreting nodes, not
physically linked to one another, embedded in the large scale structure of the
Universe at z~2 and along the same line-of-sight. In conclusion, the data,
methods and results illustrated in this pilot project confirm that Planck data
can be used to detect the emission from clustered, dusty star forming galaxies
at high-z, and, thus, to pierce through the early growth of cluster-scale
structures.Comment: 15 pages, 13 figures. Accepted for publication in Astronomy and
Astrophysic
Hyperparametric effects in a whispering-gallery mode rutile dielectric resonator at liquid helium temperatures
We report the first observation of low power drive level sensitivity,
hyperparametric amplification, and single-mode hyperparametric oscillations in
a dielectric rutile whispering-gallery mode resonator at 4.2 K. The latter
gives rise to a comb of sidebands at 19.756 GHz. Whereas, most frequency combs
in the literature have been observed in optical systems using an ensemble of
equally spaced modes in microresonators or fibers, the present work represents
generation of a frequency comb using only a single-mode. The experimental
observations are explained by an additional 1/2 degree-of-freedom originating
from an intrinsic material nonlinearity at optical frequencies, which affects
the microwave properties due to the extremely low loss of rutile. Using a model
based on lumped circuits, we demonstrate that the resonance between the
photonic and material 1/2 degree-of-freedom, is responsible for the
hyperparametric energy transfer in the system.Comment: 9 pages, 10 figure
Absorbing boundary conditions for the Westervelt equation
The focus of this work is on the construction of a family of nonlinear
absorbing boundary conditions for the Westervelt equation in one and two space
dimensions. The principal ingredient used in the design of such conditions is
pseudo-differential calculus. This approach enables to develop high order
boundary conditions in a consistent way which are typically more accurate than
their low order analogs. Under the hypothesis of small initial data, we
establish local well-posedness for the Westervelt equation with the absorbing
boundary conditions. The performed numerical experiments illustrate the
efficiency of the proposed boundary conditions for different regimes of wave
propagation
Rotating Odd-Parity Lorentz Invariance Test in Electrodynamics
We report the first operation of a rotating odd-parity Lorentz Invariance
test in electrodynamics using a microwave Mach-Zehnder interferometer with
permeable material in one arm. The experiment sets a direct bound to of . Using new power recycled waveguide
interferometer techniques (with the highest spectral resolution ever achieved
of ) we show an improvement of several orders of
magnitude is attainable in the future
Complete Genome Sequence of the Plant-Pathogenic Fungus Colletotrichum lupini
Colletotrichum is a fungal genus (Ascomycota, Sordariomycetes, Glomerellaceae) that includes many economically important plant pathogens that cause devastating diseases of a wide range of plants. In this work, using a combination of long- and short-read sequencing technologies, we sequenced the genome of Colletotrichum lupini RB221, isolated from white lupin (Lupinus albus) in France during a survey in 2014. The genome was assembled into 11 nuclear chromosomes and a mitochondrial genome with a total assembly size of 63.41 Mb and 36.55 kb, respectively. In total, 18,324 protein-encoding genes have been predicted, of which only 39 are specific to C. lupini. This resource will provide insight into pathogenicity factors and will help provide a better understanding of the evolution and genome structure of this important plant pathogen
Effect of Sr substitution on superconductivity in Hg2(Ba1-ySry)2YCu2O8-d (part2): bond valence sum approach of the hole distribution
The effects of Sr substitution on superconductivity, and more particulary the
changes induced in the hole doping mechanism, were investigated in
Hg2(Ba1-ySry)2YCu2O8-d by a "bond valence sum" analysis with Sr content from y
= 0.0 to y = 1.0. A comparison with CuBa2YCu2O7-d and Cu2Ba2YCu2O8 systems
suggests a possible explanation of the Tc enhancement from 0 K for y = 0.0 to
42 K for y = 1.0. The charge distribution among atoms of the unit cell was
determined from the refined structure, for y = 0.0 to 1.0. It shows a charge
transfer to the superconducting CuO2 plane via two doping channels pi(1) and
pi(2), i.e. through O2(apical)-Cu and Ba/Sr-O1 bonds respectively.Comment: 13 pages, 5 figures, accepted for publication in Journal of Physics:
Condensed Matte
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