562 research outputs found
Hyperpolarizability effects in a Sr optical lattice clock
We report the observation of the higher order frequency shift due to the
trapping field in a Sr optical lattice clock. We show that at the magic
wavelength of the lattice, where the first order term cancels, the higher order
shift will not constitute a limitation to the fractional accuracy of the clock
at a level of . This result is achieved by operating the clock at
very high trapping intensity up to kW/cm and by a specific study of
the effect of the two two-photon transitions near the magic wavelength
Non-destructive measurement of the transition probability in a Sr optical lattice clock
We present the experimental demonstration of non-destructive probing of the
1S0-3P0 clock transition probability in an optical lattice clock with 87Sr
atoms. It is based on the phase shift induced by the atoms on a weak
off-resonant laser beam. The method we propose is a differential measurement of
this phase shift on two modulation sidebands with opposite detuning with
respect to the 1S0-1P1 transition, allowing a detection limited by the photon
shot noise. We have measured an atomic population of 10^4 atoms with a signal
to noise ratio of 100 per cycle, while keeping more than 95% of the atoms in
the optical lattice with a depth of 0.1 mK. The method proves simple and robust
enough to be operated as part of the whole clock setup. This detection scheme
enables us to reuse atoms for subsequent clock state interrogations,
dramatically reducing the loading time and thereby improving the clock
frequency stability.Comment: 4 pages, 5 figure
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
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
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
LibĂ©ralitĂ© prĂ©torienne et Ătat minimum au Soudan
«°On ne commence Ă parler d'Ătat que lorsque des hommes ou des organismes qui assurent plusieurs services publics commencent Ă ĂȘtre rĂ©unis entre eux et par lĂ Ă faire masse.°» Paul Veyne, Le pain et le cirque. Sociologie d'un pluralisme politique. Au Soudan, comme ailleurs, l'Ă©dification de l'espace public n'a suivi que marginalement la voie royale de l'administration exclusive par l'Ătat. S'appuyant largement sur la philanthropie et le civisme de ses gouvernĂ©s, le rĂ©gime islamique, comme se..
La massage selon le protocol de Field: quelle plus-value sur la prise de poids des prématurés comparé aux soins dits standards ? travail de Bachelor
Introduction : Les naissances prĂ©maturĂ©es augmentent chaque annĂ©e, ces naissances sont complexes et peuvent mener Ă de nombreuses complications et sĂ©quelles. Afin de rĂ©pondre aux besoins particuliers des nouveau-nĂ©s, un amĂ©nagement de lâenvironnement et certaines mĂ©thodes de traitement sont intĂ©grĂ©s Ă la routine de soins. Le massage est un traitement qui a fait ses preuves et devient monnaie courante dans les services de nĂ©onatologie. Nous nous sommes intĂ©ressĂ©es Ă un protocole de massage : le protocole de Field qui combine massage et mobilisation passive, dans le but de connaĂźtre la plus-value de ce protocole sur la prise de poids des prĂ©maturĂ©s ĂągĂ©s de 28 Ă 32 semaines d'amĂ©norrhĂ©es. MĂ©thode : Nous avons utilisĂ© le design de la revue de littĂ©rature. Notre recherche sâest basĂ©e sur quatre bases de donnĂ©es : Pubmed, Cochrane, Pedro et KinĂ©doc. Nos mots-clĂ©s reprennent les grands thĂšmes de notre question de recherche : prĂ©maturitĂ©, gain de poids et massage. Lâoutcome Ă©tudiĂ© est le poids en grammes. La qualitĂ© des Ă©tudes a Ă©tĂ© Ă©valuĂ©e avec la grille PEDro. RĂ©sultats : Trois articles composent notre revue de la littĂ©rature. Les trois articles montrent une augmentation du poids entre le dĂ©but et la fin du traitement mais seulement deux Ă©tudes ont une diffĂ©rence significative. Conclusion : Avec le peu de littĂ©rature et la faiblesse de nos Ă©tudes il est difficile de se positionner quant au rĂ©el avantage de ce protocole de massage comparĂ© Ă dâautres techniques mises en place dans les services de nĂ©onatologie. Cependant le massage a fait ses preuves et il devrait ĂȘtre intĂ©grĂ© dans les routines de soins lorsque ce nâest pas encore le cas, pour les prĂ©maturĂ©s mĂ©dicalement stables et de plus de 28 semaines. Car câest une technique, ne nĂ©cessitant pas de matĂ©riel, abordable et qui permet de favoriser la prise de poids
Phase-locking of two self-seeded tapered amplifier lasers
We report on the phase-locking of two diode lasers based on self-seeded
tapered amplifiers. In these lasers, a reduction of linewidth is achieved using
narrow-band high-transmission interference filters for frequency selection. The
lasers combine a compact design with a Lorentzian linewidth below 200 kHz at an
output power of 300 mW. We characterize the phase noise of the phase-locked
laser system and study its potential for coherent beam-splitting in atom
interferometers.Comment: 7 pages, 4 figure
An accurate optical lattice clock with 87Sr atoms
We report a frequency measurement of the 1S0-3P0 transition of 87Sr atoms in an optical lattice clock. The frequency is determined to be 429 228 004 229 879 (5) Hz with a fractional uncertainty that is comparable to state-of-the-art optical clocks with neutral atoms in free fall. Two previous measurements of this transition were found to disagree by about 2x10^{-13}, i.e. almost four times the combined error bar, instilling doubt on the potential of optical lattice clocks to perform at a high accuracy level. In perfect agreement with one of these two values, our measurement essentially dissipates this doubt
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