313 research outputs found
Coherent back and forward scattering peaks in the quantum kicked rotor
We propose and analyze an experimental scheme using the quantum kicked rotor
to observe the newly-predicted coherent forward scattering peak together with
its long-known twin brother, the coherent backscattering peak. Contrary to
coherent backscattering, which arises already under weak-localization
conditions, coherent forward scattering is only triggered by Anderson or strong
localization. So far, coherent forward scattering has not been observed in
conservative systems with elastic scattering by spatial disorder. We propose to
turn to the quantum kicked rotor, which has a long and succesful history as an
accurate experimental platform to observe dynamical localization, i.e.,
Anderson localization in momentum space. We analyze the coherent forward
scattering effect for the quantum kicked rotor by extensive numerical
simulations, both in the orthogonal and unitary class of disordered quantum
systems, and show that an experimental realization involving phase-space
rotation techniques is within reach of state-of-the-art cold-atom experiments.Comment: 26 pages, 11 figure
Mesures en ligne du champ magnétique du GANIL
La mesure en ligne du champ magnétique des électroaimants du Grand Accélérateur National d'Ions Lourds (GANIL) a été étudiée et mise au point. Elle permet le réglage et la surveillance des paramètres de conduite du faisceau, de l'accélérateur aux salles d'expériences. Les développements ont été menés autour de magnétomètres à Résonnance Magnétique Nucléaire (RMN) et de magnétomètres à effet Hall. Les limitations de fonctionnement des sondes RMN en zone de champ inhomogène ont nécessité des solutions particulières. Des techniques de positionnement et de compensation de gradient adaptées ont été mises en œuvre. Les sondes RMN et à effet Hall sont intégrées dans une électronique d'acquisition et de traitement définie selon les standards du GANIL. L'ensemble constitue une instrumentation qui répond parfaitement aux besoins, en particulier du point de vue de la mesure et de la surveillance des paramètres magnétiques
Universality of the Anderson transition with the quasiperiodic kicked rotor
We report a numerical analysis of the Anderson transition in a
quantum-chaotic system, the quasiperiodic kicked rotor with three
incommensurate frequencies. It is shown that this dynamical system exhibits the
same critical phenomena as the truly random 3D-Anderson model. By taking proper
account of systematic corrections to one-parameter scaling, the universality of
the critical exponent is demonstrated. Our result is in
perfect agreement with the value found for the Anderson model.Comment: 4 figures, 3 tables (published version
Universal scaling of the order-parameter distribution in strongly disordered superconductors
We investigate theoretically and experimentally the statistical properties of
the inhomogeneous order-parameter distribution (OPD) at the verge of the
superconductor-insulator transition (SIT). We find within two prototype
fermionic and bosonic models for disordered superconductors that one can
identify a universal rescaling of the OPD. By performing scanning-tunneling
microscopy experiments in three samples of NbN with increasing disorder we show
that such a rescaling describes also with an excellent accuracy the
experimental data. These results can provide a breakthrough in our
understanding of the SIT.Comment: 11 pages, 8 figures, revised version submitted to PR
Symmetry Violation of Quantum Multifractality: Gaussian fluctuations versus Algebraic Localization
Quantum multifractality is a fundamental property of systems such as
non-interacting disordered systems at an Anderson transition and many-body
systems in Hilbert space. Here we discuss the origin of the presence or absence
of a fundamental symmetry related to this property. The anomalous multifractal
dimension is used to characterize the structure of quantum states in
such systems. Although the multifractal symmetry relation
\mbox{} is universally fulfilled in many known systems,
recently some important examples have emerged where it does not hold. We show
that this is the result of two different mechanisms. The first one was already
known and is related to Gaussian fluctuations well described by random matrix
theory. The second one, not previously explored, is related to the presence of
an algebraically localized envelope. While the effect of Gaussian fluctuations
can be removed by coarse graining, the second mechanism is robust to such a
procedure. We illustrate the violation of the symmetry due to algebraic
localization on two systems of very different nature, a 1D Floquet critical
system and a model corresponding to Anderson localization on random graphs.Comment: Closest to published versio
Factors affecting compliance with glove removal after contact with a patient or environment in four intensive care units
International audienc
Impact of screening and identifying methicillin-resistant Staphylococcus aureus carriers on hand hygiene compliance in 4 intensive care units
BackgroundOur objective was to assess the impact of screening and identifying methicillin-resistant Staphylococcus aureus (MRSA) carriers as a single measure in 4 intensive care units (ICUs). Methods An evaluative study including two 6-month periods was conducted prospectively. The evaluation concerned the hand hygiene compliance (HHC) for contacts with MRSA carriers versus contacts with noncarriers (comparison C1, main objective) and for a period of absence of identification (P1) versus a period of identification (P2) (comparison C2) and MRSA cross transmission (P1 vs P2) (comparison C3) measured with 2 indicators. Results Overall, 1326 opportunities of hand hygiene were observed. Concerning C1, the HHC for contacts with MRSA carriers was 42.5% versus 43.1% for contacts with noncarriers (not significant). This absence of difference was recorded whatever the ICU specialty, the category of personnel, and the nature of contacts. Concerning C2, the HHC in P1 was 44.8% versus 48.5% in P2 (not significant). Concerning C3, no significant difference was identified between the 2 periods. Conclusion We did not identify any advantage by using screening and identifying MRSA carriers in those 4 ICUs in which no specific strategy of additional contact measures was implemented for MRSA carriers
A process very similar to multifractional Brownian motion
In Ayache and Taqqu (2005), the multifractional Brownian (mBm) motion is
obtained by replacing the constant parameter of the fractional Brownian
motion (fBm) by a smooth enough functional parameter depending on the
time . Here, we consider the process obtained by replacing in the
wavelet expansion of the fBm the index by a function depending on
the dyadic point . This process was introduced in Benassi et al (2000)
to model fBm with piece-wise constant Hurst index and continuous paths. In this
work, we investigate the case where the functional parameter satisfies an
uniform H\"older condition of order \beta>\sup_{t\in \rit} H(t) and ones
shows that, in this case, the process is very similar to the mBm in the
following senses: i) the difference between and a mBm satisfies an uniform
H\"older condition of order ; ii) as a by product, one
deduces that at each point the pointwise H\"older exponent of is
and that is tangent to a fBm with Hurst parameter .Comment: 18 page
Discordance in the minimal inhibitory concentrations of ertapenem for Enterobacter cloacae: Vitek 2 system versus Etest and agar dilution methods
Our objective was to compare the ertapenem minimal inhibitory concentrations (MICs) for Enterobacter cloacae isolates categorized intermediate or resistant to ertapenem when measured with the Vitek 2 system, with the MICs for these isolates when measured by two methods performed in agar medium: the Etest and agar plate dilution method (APDM). Overall, 50 E. cloacae isolates were included in the study. The mean MIC of ertapenem was 2.92±1.77μg/ml according to the Vitek 2 system, 0.94±0.84μg/ml according to the Etest strips, and 0.93±0.62μg/ml according to the APDM. Furthermore, the MICs determined by the Vitek 2 system were higher than the MICs determined by the two other methods for 96% of strains. Lastly, according to the Etest strips and APDM, 42% of E. cloacae were susceptible to ertapenem. No carbapenemase was identified by the screening method used. Using the Vitek 2 system to determine ertapenem MICs for E. cloacae can have potential consequences in terms of additional carbapenemase-detecting tests and antimicrobial therapy. It would be interesting to determine if the Vitek 2 system is more effective for the detection of carbapenemase producers with low-level carbapenem resistance than the two methods performed in agar medium
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