2,069 research outputs found
A noise-immune cavity-assisted non-destructive detection for an optical lattice clock in the quantum regime
We present and implement a non-destructive detection scheme for the
transition probability readout of an optical lattice clock. The scheme relies
on a differential heterodyne measurement of the dispersive properties of
lattice-trapped atoms enhanced by a high finesse cavity. By design, this scheme
offers a 1st order rejection of the technical noise sources, an enhanced
signal-to-noise ratio, and an homogeneous atom-cavity coupling. We
theoretically show that this scheme is optimal with respect to the photon shot
noise limit. We experimentally realize this detection scheme in an operational
strontium optical lattice clock. The resolution is on the order of a few atoms
with a photon scattering rate low enough to keep the atoms trapped after
detection. This scheme opens the door to various different interrogations
protocols, which reduce the frequency instability, including atom recycling,
zero-dead time clocks with a fast repetition rate, and sub quantum projection
noise frequency stability
Demonstration of Bunch Triple Splitting in the CERN PS
A technique for splitting bunches into three has recently been proposed as an alternative to debunching-rebunching in a synchrotron[1]. The preservation of longitudinal emittance and the possibility of maintaining a gap in the bunch train are key features expected from this new process. A proof of principle has been established experimentally at the CERN PS in 1999. This showed that the nominal longitudinal characteristics of the proton beam for the LHC could be achieved at the exit of the PS with the help of triple splitting. The method is described and experimental results presented. Other possible applications are sketched
Renormalization and Quantum Scaling of Frenkel-Kontorova Models
We generalise the classical Transition by Breaking of Analyticity for the
class of Frenkel-Kontorova models studied by Aubry and others to non-zero
Planck's constant and temperature. This analysis is based on the study of a
renormalization operator for the case of irrational mean spacing using
Feynman's functional integral approach. We show how existing classical results
extend to the quantum regime. In particular we extend MacKay's renormalization
approach for the classical statistical mechanics to deduce scaling of low
frequency effects and quantum effects. Our approach extends the phenomenon of
hierarchical melting studied by Vallet, Schilling and Aubry to the quantum
regime.Comment: 14 pages, 1 figure, submitted to J.Stat.Phy
Using score differences for search result diversification
We investigate the application of a light-weight approach to result list clustering for the purposes of diversifying search results. We introduce a novel post-retrieval approach, which is independent of external information or even the full-text content of retrieved documents; only the retrieval score of a document is used. Our experiments show that this novel approach is bene cial to e ectiveness, albeit only on certain baseline systems. The fact that the method works indicates that the retrieval score is potentially exploitable in diversity
Influencia del contenido de OHAP y de gentamicina en la liberación del antibiótico a partir de composites de OHAP/PEMMA
El objetivo de este trabajo fue estudiar la influencia del contenido de hidroxiapatita (OHAp) y
de sulfato de gentamicina (SG) en la velocidad de liberación de dicho antibiótico a partir de
materiales compuestos por OHAp, polimetacrilato de metilo (PMMA) y polimetacrilato de etilo
(PEMA).
Para ello se prepararon muestras con diferente proporción de OHAp (30 y 40%) y de SG (5 y
10%). El estudio de liberación se llevó a cabo sumergiendo 3 muestras de cada grupo en SBF a
37°C, el medio fue renovado a diferentes intervalos de tiempo durante 70 días. La concentración de
gentamicina fue determinada por el método del o-ftaldialdehído.
Los resultados del estudio de liberación mostraron, que la liberación ocurre de manera más
rápida durante las primeras 10 horas de inmersión en SBF y que posteriormente se hace más lenta.
Se observó que las muestras con un mayor tanto por ciento (40%) de OHAp liberan mayor cantidad
de antibiótico. Las muestras con un 40% de OHAp liberaron el 100% de SG a los 70 días, mientras
que en ese mismo período las muestras con 30% de OHAp liberaron un 85%. Por otra parte, se
observó que la cantidad de gentamicina añadida inicialmente no afecta el tanto por ciento de SG
que se libera.Peer Reviewe
Ground state wavefunction of the quantum Frenkel-Kontorova model
The wavefunction of an incommensurate ground state for a one-dimensional
discrete sine-Gordon model -- the Frenkel-Kontorova (FK) model -- at zero
temperature is calculated by the quantum Monte Carlo method. It is found that
the ground state wavefunction crosses over from an extended state to a
localized state when the coupling constant exceeds a certain critical value.
So, although the quantum fluctuation has smeared out the breaking of
analyticity transition as observed in the classical case, the remnant of this
transition is still discernible in the quantum regime.Comment: 5 Europhys pages, 3 EPS figures, accepted for publication in
Europhys. Letter
Oscillatory fracture path in thin elastic sheet
We report a novel mode of oscillatory crack propagation when a cutting tip is
driven through a thin brittle polymer film. The phenomenon is so robust that it
can easily be reproduced at hand (using CD packaging material for example).
Careful experiments show that the amplitude and wavelength of the oscillatory
crack path scale lineraly with the width of the cutting tip over a wide range
of lenghtscales but are independant of the width of thje sheet and the cutting
speed. A simple geometric model is presented, which provides a simple but
thorough interpretation of the oscillations.Comment: 6 pages, submitted to Comptes Rendus Academie des Sciences. Movies
available at http://www.lmm.jussieu.fr/platefractur
Fabrication and characterization of Ag- and Ga-doped mesoporous glass-coated scaffolds based on natural marine sponges with improved mechanical properties
Natural marine sponges were used as sacrificial template for the fabrication of bioactive glassbased scaffolds. After sintering at 1050 ºC, the resulting samples were additionally coated with a
sol silicate solution containing biologically active ions (Ag and Ga), well-known for their
antibacterial properties in comparison with standard scaffolds made by PU foam templates. The
produced scaffolds were characterized by superior mechanical properties (maximum compressive
strength of 4 MPa) and total porosity of ~80%. Direct cell culture tests performed on the
uncoated and coated samples showed positive results in terms of adhesion, proliferation, and
differentiation of MC3T3-E1 cells. Moreover, vascular endothelial growth factor (VEGF)
secretion from cells in contact with scaffold dissolution products was measured after 7 and 10
days of incubation, showing promising angiogenic results for bone tissue engineering
applications. The antibacterial potential of the produced samples was assessed by performing
agar diffusion tests against both Gram-positive and Gram-negative bacteria.EU Horizon 2020 project COACH 64255
Fractal Spin Glass Properties of Low Energy Configurations in the Frenkel-Kontorova chain
We study numerically and analytically the classical one-dimensional
Frenkel-Kontorova chain in the regime of pinned phase characterized by phonon
gap. Our results show the existence of exponentially many static equilibrium
configurations which are exponentially close to the energy of the ground state.
The energies of these configurations form a fractal quasi-degenerate band
structure which is described on the basis of elementary excitations. Contrary
to the ground state, the configurations inside these bands are disordered.Comment: revtex, 9 pages, 9 figure
External and internal noise surveys of London primary schools
Internal and external noise surveys have been carried out around schools in London, UK, to provide information on typical levels and sources to which children are exposed while at school. Noise levels were measured outside 142 schools, in areas away from flightpaths into major airports. 86% of the schools surveyed were exposed to noise from road traffic, the average external noise level outside a school being 57 dB LAeq. Detailed internal noise surveys have been carried out in 140 classrooms in 16 schools, together with classroom observations. It was found that noise levels inside classrooms depend upon the activities in which the children are engaged, with a difference of 20 dB LAeq between the 'quietest' and 'noisiest' activities. The average background noise level in classrooms exceeds the level recommended in current standards. The number of children in the classroom was found to affect noise levels. External noise influenced internal noise levels only when children were engaged in the quietest classroom activities. The effects of the age of the school buildings and types of window upon internal noise were examined but results were inconclusive
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