142 research outputs found
An Optical Lattice Clock with Spin-polarized 87Sr Atoms
We present a new evaluation of an 87Sr optical lattice clock using spin
polarized atoms. The frequency of the 1S0-3P0 clock transition is found to be
429 228 004 229 873.6 Hz with a fractional accuracy of 2.6 10^{-15}, a value
that is comparable to the frequency difference between the various primary
standards throughout the world. This measurement is in excellent agreement with
a previous one of similar accuracy
Interference-filter-stabilized external-cavity diode lasers
We have developed external-cavity diode lasers, where the wavelength
selection is assured by a low loss interference filter instead of the common
diffraction grating. The filter allows a linear cavity design reducing the
sensitivity of the wavelength and the external cavity feedback against
misalignment. By separating the feedback and wavelength selection functions,
both can be optimized independently leading to an increased tunability of the
laser. The design is employed for the generation of laser light at 698, 780 and
852 nm. Its characteristics make it a well suited candidate for space-born
lasers.Comment: 12 pages, 5 figure
The EFIGI catalogue of 4458 nearby galaxies with morphology II. Statistical properties along the Hubble sequence
The EFIGI catalogue of 4458 galaxies provides a reference database of the
morphological properties of nearby galaxies, with 16 shape attributes
describing their various dynamical components, their texture and environment,
and with a dense sampling of all Hubble types. This catalogue allows us to
derive a quantitative description of the Hubble Sequence in terms of the
specific morphological features of the various types. The variations of the
EFIGI morphological attributes with type confirm that the visual Hubble
sequence is a decreasing sequence of bulge-to-total ratio and an increasing
sequence of disk contribution to the total flux. There is nevertheless a large
dispersion of approximately 5 types for a given bulge-to-total ratio, due to
the fact that the Hubble sequence is primarily based on the strength and pitch
angle of the spiral arms, independently from the bulge-to-total ratio. The
grand spiral design is also related to a steep decrease in visible dust from
types Sb to Sbc-Sc. In contrast, the scattered and giant HII regions show
different strength variation patterns; hence, they do not appear to directly
participate in the establishment of the Hubble sequence. The distortions from a
symmetric profile also incidentally increase along the sequence. Bars and inner
rings are frequent and occur in 41% and 25% of disk galaxies resp. Outer rings
are twice less frequent than inner rings, and outer pseudo-rings occur in 11%
of barred galaxies. Finally, we find a smooth decrease in mean surface
brightness and intrinsic size along the Hubble sequence. The largest galaxies
are cD, Ellipticals and Sab-Sbc spirals, whereas Sd and later spirals are
nearly twice smaller. S0 are intermediate in size, and Im, cE and dE are
confirmed as small objects. Dwarf spiral galaxies of type Sa to Scd are rare in
the EFIGI catalogue, we only find 2 such objects.Comment: Accepted for publication in Astronomy and Astrophysics, 22 pages, 10
tables, 19 colour figures. Data available at http://www.efigi.or
Low noise amplication of an optically carried microwave signal: application to atom interferometry
In this paper, we report a new scheme to amplify a microwave signal carried
on a laser light at =852nm. The amplification is done via a
semiconductor tapered amplifier and this scheme is used to drive stimulated
Raman transitions in an atom interferometer. Sideband generation in the
amplifier, due to self-phase and amplitude modulation, is investigated and
characterized. We also demonstrate that the amplifier does not induce any
significant phase-noise on the beating signal. Finally, the degradation of the
performances of the interferometer due to the amplification process is shown to
be negligible
A high stability semiconductor laser system for a Sr-based optical lattice clock
We describe a frequency stabilized diode laser at 698 nm used for high
resolution spectroscopy of the 1S0-3P0 strontium clock transition. For the
laser stabilization we use state-of-the-art symmetrically suspended optical
cavities optimized for very low thermal noise at room temperature. Two-stage
frequency stabilization to high finesse optical cavities results in measured
laser frequency noise about a factor of three above the cavity thermal noise
between 2 Hz and 11 Hz. With this system, we demonstrate high resolution remote
spectroscopy on the 88Sr clock transition by transferring the laser output over
a phase-noise-compensated 200 m-long fiber link between two separated
laboratories. Our dedicated fiber link ensures a transfer of the optical
carrier with frequency stability of 7 \cdot 10^{-18} after 100 s integration
time, which could enable the observation of the strontium clock transition with
an atomic Q of 10^{14}. Furthermore, with an eye towards the development of
transportable optical clocks, we investigate how the complete laser system
(laser+optics+cavity) can be influenced by environmental disturbances in terms
of both short- and long-term frequency stability.Comment: 9 pages, 9 figures, submitted to Appl. Phys.
New Limits on Coupling of Fundamental Constants to Gravity Using Sr Optical Lattice Clocks
The - clock transition frequency
in neutral Sr has been measured relative to the Cs
standard by three independent laboratories in Boulder, Paris, and Tokyo over
the last three years. The agreement on the level makes
the best agreed-upon optical atomic frequency. We combine
periodic variations in the Sr clock frequency with Hg and
H-maser data to test Local Position Invariance by obtaining the strongest
limits to date on gravitational-coupling coefficients for the fine-structure
constant , electron-proton mass ratio and light quark mass.
Furthermore, after Hg, Yb and H, we add Sr as
the fourth optical atomic clock species to enhance constraints on yearly drifts
of and .Comment: Published version. 4 pages, 4 figure
Supernovae and their host galaxies. I. The SDSS DR8 database and statistics
(Abridged) In this first paper of a series, we report the creation of large
and well-defined database that combines extensive new measurements and a
literature search of 3876 supernovae (SNe) and their 3679 host galaxies located
in the sky area covered by the Sloan Digital Sky Survey (SDSS) Data Release 8
(DR8). This database should be much larger than previous ones, and should
contain a homogenous set of global parameters of SN hosts, including
morphological classifications and measures of nuclear activity. The
measurements of apparent magnitudes, diameters (D25), axial ratios (b/a), and
position angles (PA) of SN host galaxies were made using the images extracted
from the SDSS g-band. For each host galaxy, we analyzed RGB images of the SDSS
to accurately measure the position of its nucleus to provide the SDSS name.
With these images, we also provide the host galaxy's morphological type, and
note if it has a bar, a disturbed disk, and whether it is part of an
interacting or merging system. In addition, the SDSS nuclear spectra were
analyzed to diagnose the central power source of the galaxies. Special
attention was paid to collect accurate data on the spectroscopic classes,
coordinates, offsets of SNe, and heliocentric redshifts of the host galaxies.
The creation of this large database will help to better understand how the
different types of SNe are correlated with the properties of the nuclei and
global physical parameters of the host galaxies, and minimize possible
selection effects and errors that often arise when data are selected from
different sources and catalogs.Comment: 20 pages, 15 figures, 7 table
Measuring the frequency of a Sr optical lattice clock using a 120-km coherent optical transfer
We demonstrate a precision frequency measurement using a phase-stabilized
120-km optical fiber link over a physical distance of 50 km. The transition
frequency of the 87Sr optical lattice clock at the University of Tokyo is
measured to be 429228004229874.1(2.4) Hz referenced to international atomic
time (TAI). The measured frequency agrees with results obtained in Boulder and
Paris at a 6*10^-16 fractional level, which matches the current best
evaluations of Cs primary frequency standards. The results demonstrate the
excellent functions of the intercity optical fibre link, and the great
potential of optical lattice clocks for use in the redefinition of the second.Comment: 14 pages, 3 figure
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
Remifentanil-propofol analgo-sedation shortens duration of ventilation and length of ICU stay compared to a conventional regimen: A centre randomised, cross-over, open-label study in the Netherlands
Objective: Compare duration of mechanical ventilation (MV), weaning time, ICU-LOS (ICU-LOS), efficacy and safety of remifentanil-based regimen with conventional sedation and analgesia. Design: Centre randomised, open-label, crossover, 'real-life' study. Setting: 15 Dutch hospitals. Patients: Adult medical and post-surgical ICU patients with anticipated short-term (2-3 days) MV. Interventions: Patient cohorts were randomised to remifentanil-based regimen (n = 96) with propofol as required, for a maximum of 10 days, or to conventional regimens (n = 109) of propofol, midazolam or lorazepam combined with fentanyl or morphine. Measurements and main results: Outcomes were weaning time, duration of MV, ICU-LOS, sedation- and analgesia levels, intensivist/ICU nurse satisfaction, adverse events, mean arterial pressure, heart rate. Median duration of ventilation (MV) was 5.1 days with conventional treatment versus 3.9 days with remifentanil (NS). The remifentanil-based regimen reduced median weaning time by 18.9 h (P = 0.0001). Median ICU-LOS was 7.9 days versus 5.9 days, respectively (NS). However, the treatment effects on duration of MV and ICU stay were time-dependent: patients were almost twice as likely to be extubated (P = 0.018) and discharged from the ICU (P = 0.05) on day 1-3. Propofol doses were reduced by 20% (P = 0.05). Remifentanil also improved sedation-agitation scores (P < 0.0001) and intensivist/ICU nurse satisfaction (P < 0.0001). All other outcomes were comparable. Conclusions: In patients with an expected short-term duration of MV, remifentanil significantly improves sedation and agitation levels and reduces weaning time. This contributes to a shorter duration of MV and ICU-LOS
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