112 research outputs found
Seuils d'oscillation de la clarinette : validité de la représentation excitateur-résonateur
National audienceDepuis Helmholtz, le fonctionnement des instruments entretenus est représenté par un système bouclé faisant apparaître un bloc excitateur et un bloc résonateur. Dans le cas de la clarinette étudiée ici, l'excitateur désigne l'anche modulant le débit d'air entrant et le résonateur le corps de l'instrument. Si cette représentation est communément admise, se pose la question de la séparabilité de ces deux blocs et de l'observabilité des grandeurs physiques qui les lient. Dans le cadre de l'étude du seuil d'oscillation, nous inspectons la validité de cette représentation indépendamment de toute modélisation des blocs : les seuils mesurés sont comparés avec ceux obtenus par la théorie des oscillateurs dans laquelle sont introduites les valeurs expérimentales des paramètres du modèle. Les pressions de seuil et les fréquences émergentes obtenues en (3) et (4) sont comparées. L'interprétation des différences fait intervenir les difficultés d'accéder exactement expérimentalement au point de bifurcation (indépendamment de la qualité du contrôle), la caractérisation expérimentale incomplète du système excitateur (en particulier, le débit d'anche n'est pas mesuré), et les incertitudes qui pèsent sur la mesure d'impédance d'entrée d'une clarinette du fait de la géométrie du bec. Toutefois, l'exploitation directe des mesures permet de s'affranchir d'incertitudes qui seraient introduites par une modélisation paramétrique des éléments excitateur et résonateur
Seuils d'oscillation d'un instrument de musique à anche simple : protocole expérimental & instrumentation d'une bouche artificielle
National audienceSingle reed instruments like clarinet and saxophone may be considered as the coupling of an acoustic resonator (the bore of the instrument) and the reed which acts as a valve modulating the air flow blown by the musician. The blowing pressure required for sound emergence is mainly determined by the acoustic characteristics of the bore. However previous studies explain that it may be largely influenced by the way the player controls the dynamical behaviour of the reed, in particular how the player's lips damp the mechanical resonance of the reed. We will present preliminary xperimental work in order to compare the measurements with the pressure threshold theory
Noise characterization of an Optical Frequency Comb using Offline Cross-Correlation
Using an offline cross-correlation technique, we have analyzed the noise
behavior of a new type of optical frequency comb (OFC), which is carrier
envelope offset (CEO) free by configuration, due to difference frequency
generation. In order to evaluate the instrument's ultimate noise floor, the
phase and amplitude noise of a stabilized OFC are measured simultaneously using
two analog-to-digital converters. Carrier recovery and phase detection are done
by post-processing, eliminating the need for external phase-locked loops and
complex calibration techniques. In order to adapt the measurement noise floor
and the number of averages used in cross correlation, an adaptive frequency
resolution for noise measurement is applied. Phase noise results are in
excellent agreement with measurements of the fluctuations of the repetition
frequency of the OFC obtained from optical signal
Response of an artificially blown clarinet to different blowing pressure profiles
Using an artificial mouth with an accurate pressure control, the onset of the
pressure oscillations inside the mouthpiece of a simplified clarinet is studied
experimentally. Two time profiles are used for the blowing pressure: in a first
set of experiments the pressure is increased at constant rates, then decreased
at the same rate. In a second set of experiments the pressure rises at a
constant rate and is then kept constant for an arbitrary period of time. In
both cases the experiments are repeated for different increase rates. Numerical
simulations using a simplified clarinet model blown with a constantly
increasing mouth pressure are compared to the oscillating pressure obtained
inside the mouthpiece. Both show that the beginning of the oscillations appears
at a higher pressure values than the theoretical static threshold pressure, a
manifestation of bifurcation delay. Experiments performed using an interrupted
increase in mouth pressure show that the beginning of the oscillation occurs
close to the stop in the increase of the pressure. Experimental results also
highlight that the speed of the onset transient of the sound is roughly the
same, independently of the duration of the increase phase of the blowing
pressure.Comment: 14 page
An instrumented saxophone mouthpiece and its use to understand how an experienced musician play
International audienceAn instrumented saxophone mouthpiece has been developed to measure, during the player's performance, the evolution of important variables: the mouth pressure, the mouthpiece pressure and the force applied on the reed by the lower lip. Moreover, according to the pressure signals in the mouth and in the mouthpiece, the instantaneous ratio of the vocal tract input impedance and of the saxophone input impedance is estimated at frequencies multiple of the playing frequency (using the concept of Gabor mask). On the selected sound examples, analyses reveal many aspects of the strategies of the player. First of all, the role of the vocal tract in the characteristics of the sound production is sometimes prominent. Secondly, the sound production on the desired note (and register) as well as pitch correction seem to be the result of complementary adjustments of the mouth pressure and of the lip pressure on the reed. This is not in agreement with musicians feeling, since they often claim to let their force on the reed unchanged during the note and from note to note
Phase transfer between three visible lasers for coherent population trapping
Stringent conditions on the phase relation of multiple photons are a
prerequisite for novel protocols of high-resolution coherent spectroscopy. In a
recent experiment we have implemented an interrogation process of a Ca-ion
cloud based on three-photon coherent population trapping, with the potential to
serve as a frequency reference in the THz-range. This high-resolution
interrogation has been made possible by phase-locking both laser sources for
cooling and repumping of the trapped ions to a clock laser at 729~nm by means
of an optical frequency comb. The clock laser, a titanium-sapphire laser built
in our lab locked onto two high-finesse cavities reaches a linewidth of a few
Hertz and a frequency stability below 10 at one second, performances
which can be copied onto the two other sources. In this paper we discuss the
performances of the phase-transfer between the three involved lasers via the
optical frequency comb
No evidence of association between NOD2/CARD15 gene polymorphism and atherosclerotic events after renal transplantation.
International audienceStable renal transplant recipients (RTR) display high rates of atherosclerotic events (AE). Innate immunity and especially vascular inflammation play a role in the pathogenesis of atherosclerosis. It is illustrated both by an increased occurrence of postrenal transplant cardiovascular events in patients with elevated levels of C-reactive protein and by a correlation between posttransplant AE and Toll-like receptor-4 Asp299Gly polymorphism. Here, we analyze the influence NOD2/CARD15 gene polymorphism since NOD2 can modulate macrophage pro-inflammatory activity and macrophage is present in early atherosclerotic lesions. The incidence of single nucleotide polymorphism (SNP) in the three major polymorphic region of NOD2 gene (SNP8, SNP12 and SNP13) was assessed in 182 RTR and the correlation between such polymorphism and the development of AE was analyzed. No correlation was observed between NOD2 gene polymorphism and the occurrence of AE after renal transplantation. NOD2 gene polymorphism thus does not appear to influence cardiovascular complications in RTR
Dendritic cell aggresome-like induced structures are dedicated areas for ubiquitination and storage of newly synthesized defective proteins
In response to inflammatory stimulation, dendritic cells (DCs) have a remarkable pattern of differentiation (maturation) that exhibits specific mechanisms to control antigen processing and presentation. One of these mechanisms is the sorting of polyubiquitinated proteins in large cytosolic aggregates called dendritic cell aggresome-like induced structures (DALIS). DALIS formation and maintenance are tightly linked to protein synthesis. Here, we took advantage of an antibody recognizing the antibiotic puromycin to follow the fate of improperly translated proteins, also called defective ribosomal products (DRiPs). We demonstrate that DRiPs are rapidly stored and protected from degradation in DALIS. In addition, we show that DALIS contain the ubiquitin-activating enzyme E1, the ubiquitin-conjugating enzyme E225K, and the COOH terminus of Hsp70-interacting protein ubiquitin ligase. The accumulation of these enzymes in the central area of DALIS defines specific functional sites where initial DRiP incorporation and ubiquitination occur. Therefore, DCs are able to regulate DRiP degradation in response to pathogen-associated motifs, a capacity likely to be important for their immune functions
Prime Focus Spectrograph (PFS) for the Subaru Telescope: Overview, recent progress, and future perspectives
PFS (Prime Focus Spectrograph), a next generation facility instrument on the
8.2-meter Subaru Telescope, is a very wide-field, massively multiplexed,
optical and near-infrared spectrograph. Exploiting the Subaru prime focus, 2394
reconfigurable fibers will be distributed over the 1.3 deg field of view. The
spectrograph has been designed with 3 arms of blue, red, and near-infrared
cameras to simultaneously observe spectra from 380nm to 1260nm in one exposure
at a resolution of ~1.6-2.7A. An international collaboration is developing this
instrument under the initiative of Kavli IPMU. The project is now going into
the construction phase aiming at undertaking system integration in 2017-2018
and subsequently carrying out engineering operations in 2018-2019. This article
gives an overview of the instrument, current project status and future paths
forward.Comment: 17 pages, 10 figures. Proceeding of SPIE Astronomical Telescopes and
Instrumentation 201
HIV Status Disclosure and Retention in Care in HIV-Infected Adolescents on Antiretroviral Therapy (ART) in West Africa
We assessed the effect of HIV status disclosure on retention in care from initiation of antiretroviral therapy (ART) among HIV-infected children aged 10 years or more in Cote d'Ivoire, Mali and Sénégal.Multi-centre cohort study within five paediatric clinics participating in the IeDEA West Africa collaboration. HIV-infected patients were included in this study if they met the following inclusion criteria: aged 10-21 years while on ART; having initiated ART ≥ 200 days before the closure date of the clinic database; followed ≥ 15 days from ART initiation in clinics with ≥ 10 adolescents enrolled. Routine follow-up data were merged with those collected through a standardized ad hoc questionnaire on awareness of HIV status. Probability of retention (no death or loss-to-follow-up) was estimated with Kaplan-Meier method. Cox proportional hazard model with date of ART initiation as origin and a delayed entry at date of 10th birthday was used to identify factors associated with death or loss-to-follow-up.650 adolescents were available for this analysis. Characteristics at ART initiation were: median age of 10.4 years; median CD4 count of 224 cells/mm³ (47% with severe immunosuppression), 48% CDC stage C/WHO stage 3/4. The median follow-up on ART after the age of 10 was 23.3 months; 187 adolescents (28.8%) knew their HIV status. The overall probability of retention at 36 months after ART initiation was 74.6% (95% confidence interval [CI]: 70.5-79.0) and was higher for those disclosed compared to those not: adjusted hazard ratio for the risk of being death or loss-to-follow-up = 0.23 (95% CI: 0.13-0.39).About 2/3 of HIV-infected adolescents on ART were not aware of their HIV status in these ART clinics in West Africa but disclosed HIV status improved retention in care. The disclosure process should be thus systematically encouraged and organized in adolescent populations
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