1,080 research outputs found
Characterization of Zero-Bias Microwave Diode Power Detectors at Cryogenic Temperature
We present the characterization of commercial tunnel diode low-level
microwave power detectors at room and cryogenic temperatures. The sensitivity
as well as the output voltage noise of the tunnel diodes are measured as
functions of the applied microwave power, the signal frequency being 10 GHz. We
highlight strong variations of the diode characteristics when the applied
microwave power is higher than few microwatt. For a diode operating at K,
the differential gain increases from V/W to about V/W when
the power passes from dBm to dBm. The diode present a white
noise floor equivalent to a NEP of pW/ and
pW/ at 4 K and 300 K respectively. Its flicker noise is
equivalent to a relative amplitude noise power spectral density
~dB/Hz at K. Flicker noise is 10 dB
higher at room temperature.Comment: 8 pages and 16 figure
Tests of Sapphire Crystals Produced with Different Growth Processes for Ultra-stable Microwave Oscillators
We present the characterization of 8-12 GHz whispering gallery mode
resonators machined in high-quality sapphire crystals elaborated with different
growth techniques. These microwave resonators are intended to constitute the
reference frequency of ultra-stable Cryogenic Sapphire Oscillators. We
conducted systematic tests near 4 K on these crystals to determine the unloaded
Q-factor and the turnover temperature for whispering gallery modes in the 8-12
GHz frequency range. These characterizations show that high quality sapphire
crystals elaborated with the Heat Exchange or the Kyropoulos growth technique
are both suitable to meet a fractional frequency stability better than 1x10-15
for 1 s to 10.000 s integration times.Comment: 7 figure
ESASky v.2.0: all the skies in your browser
With the goal of simplifying the access to science data to scientists and
citizens, ESA recently released ESASky (http://sky.esa.int), a new open-science
easy-to-use portal with the science-ready Astronomy data from ESA and other
major data providers. In this presentation, we announced version 2.0 of the
application, which includes access to all science-ready images, catalogues and
spectra, a feature to help planning of future JWST observations, the
possibility to search for data of all (targeted and serendipitously observed)
Solar System Objects in Astronomy images, a first support to mobile devices and
several other smaller usability features. We also discussed the future
evolution of the portal and the lessons learnt from the 1+ year of operations
from the point of view of access, visualization and manipulation of big
datasets (all sky maps, also called HiPS) and large catalogues (like e.g. the
Gaia DR1 catalogues or the Hubble Source Catalogue) and the design and
validation principles for the development of friendly GUIs for thin layer web
clients aimed at scientists.Comment: 4 pages, 2 figures, ADASS 2017 conference proceeding
A Cryogenic Sapphire Resonator Oscillator with 1e-16 mid-term fractional frequency stability
We report in this letter the outstanding frequency stability performances of
an autonomous cryogenique sapphire oscillator presenting a flicker frequency
noise floor below 2e-16 near 1,000 s of integration time and a long term Allan
Deviation (ADEV) limited by a random walk process of 1e-18/sqr(tau). The
frequency stability qualification at this level called for the implementation
of sophisticated instrumentation associated with ultra-stable frequency
references and ad hoq averaging and correlation methods.Comment: 4 pages, 2 figure
Frequency Stability Measurement of Cryogenic Sapphire Oscillators with a Multichannel Tracking DDS and the Two-Sample Covariance
open6sìThis article shows the first measurement of three 100 MHz signals exhibiting fluctuations from 2×10-16 to parts in 10-15 for integration time τ between 1 s and 1 day. Such stable signals are provided by three Cryogenic Sapphire Oscillators (CSOs) operating at about 10 GHz, also delivering the 100 MHz output via a dedicated synthesizer. The measurement is made possible by a 6-channel Tracking DDS (TDDS) and the two-sample covariance tool, used to estimate the Allan variance. The use of two TDDS channels per CSO enables high rejection of the instrument background noise. The covariance outperforms the Three-Cornered Hat (TCH) method in that the background converges to zero "out of the box", with no need of the hypothesis that the instrument channels are equally noisy, nor of more sophisticated techniques to estimate the background noise of each channel. Thanks to correlation and averaging, the instrument background (AVAR) rolls off with a slope 1/√m, the number of measurements, down to 10-18 at τ=104 s. For consistency check, we compare the results to the traditional TCH method beating the 10 GHz outputs down to the MHz region. Given the flexibility of the TDDS, our methods find immediate application to the measurement of the 250 MHz output of the FS combs.openCalosso, Claudio E; Vernotte, Francois; Giordano, Vincent; Fluhr, Christophe; Dubois, Benoit; Rubiola, EnricoCalosso, Claudio E; Vernotte, Francois; Giordano, Vincent; Fluhr, Christophe; Dubois, Benoit; Rubiola, Enric
A Low Power Cryogenic Sapphire Oscillator with better than 10-15 short term frequency stability
International audienceIn the field of Time and Frequency metrology, the most stable frequency source is based on a microwave whispering gallery mode sapphire resonator cooled near 6 K. Provided the resonator environment is sufficiently free of vibration and temperature fluctuation, the Cryogenic Sapphire Oscillator (CSO) presents a short term fractional frequency stability of better than 1 x 10-15. The recent demonstration of a low maintenance CSO based on a pulse-tube cryocooler paves the way for its deployment in real field applications. The main drawback which limits the deployment of the CSO technology is the large electrical consumption (three-phase 8 kW peak / 6 kW stable operation) of the current system. In this paper, we describe an optimized cryostat designed to operate with a low consumption cryocooler requiring only 3 kW single phase of input power to cool down to 4 K a sapphire resonator.We demonstrate that the proposed design is compatible with reaching a state-of-the-art frequency stabilit
Quadratic dependence on temperature of Cs 0-0 hyperfine resonance frequency in single Ne buffer gas microfabricated vapour cell
Presented is the observation of a quadratic temperature dependence of the Cs 0-0 ground state hyperfine resonance frequency in a single Neon (Ne) buffer gas vapour microcell. The inversion temperature, expected to be theoretically independent of the buffer gas pressure, is measured to be about 80-C for two different samples. A proposal to develop chip scale atomic clocks with improved long-term frequency stability, simpler configuration (a single buffer gas instead of a buffer gas mixture) and then relaxed constraints on pressure accuracy during the cell filling procedure is presented
Morpho-Anatomical, Physiological, and Mineral Composition Responses Induced by a Vegetal-Based Biostimulant at Three Rates of Foliar Application in Greenhouse Lettuce
A promising strategy for sustainably increasing the quality and yield of horticultural products is the use of natural plant biostimulants. In this work, through a greenhouse experiment, we evaluated the effect of a legume-derived biostimulant at three dose treatments (0.0 control, 2.5 mL L−1, and 5.0 mL L−1) on the yield performance, nutrients traits, leaf anatomical traits, gas exchanges, and carbon photosynthetic assimilation of greenhouse lettuce. The lettuce plants were foliar sprayed every 7 days for 5 weeks. The application of plant biostimulant, at both lower and higher dosages, increased the nutrient use efficiency, root dry weight, and leaf area. However, it is noteworthy that the 5.0 mL L−1 dose enhanced photosynthetic activity in the early phase of growth (15 DAT), thus supplying carbon skeletons useful for increasing the number of leaves and their efficiency (higher SPAD), and for boosting nutrient uptake (P, S, and K) and transport to leaves, while the 2.5 mL L−1 dose exerted specific effects on roots, increasing their dimension and enabling them to better use nitrate and Ca. A higher dose of biostimulant application might find its way in shorter growing cycle, thus presenting new horizons for new lines of research in baby leaves production
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