3,147 research outputs found
Effect of Changing the Vocal Tract Shape on the Sound Production of the Recorder: An Experimental and Theoretical Study
Changing the vocal tract shape is one of the techniques which can be used by
the players of wind instruments to modify the quality of the sound. It has been
intensely studied in the case of reed instruments but has received only little
attention in the case of air-jet instruments. This paper presents a first study
focused on changes in the vocal tract shape in recorder playing techniques.
Measurements carried out with recorder players allow to identify techniques
involving changes of the mouth shape as well as consequences on the sound. A
second experiment performed in laboratory mimics the coupling with the vocal
tract on an artificial mouth. The phase of the transfer function between the
instrument and the mouth of the player is identified to be the relevant
parameter of the coupling. It is shown to have consequences on the spectral
content in terms of energy distribution among the even and odd harmonics, as
well as on the stability of the first two oscillating regimes. The results
gathered from the two experiments allow to develop a simplified model of sound
production including the effect of changing the vocal tract shape. It is based
on the modification of the jet instabilities due to the pulsating emerging jet.
Two kinds of instabilities, symmetric and anti-symmetric, with respect to the
stream axis, are controlled by the coupling with the vocal tract and the
acoustic oscillation within the pipe, respectively. The symmetry properties of
the flow are mapped on the temporal formulation of the source term, predicting
a change in the even / odd harmonics energy distribution. The predictions are
in qualitative agreement with the experimental observations
Three-Nucleon Continuum by means of the Hyperspherical Adiabatic Method
This paper investigates the possible use of the Hyperspherical Adiabatic
basis in the description of scattering states of a three-body system. In
particular, we analyze a 1+2 collision process below the three-body breakup.
The convergence patterns for the observables of interest are analyzed by
comparison to a unitary equivalent Hyperspherical Harmonic expansion.
Furthermore, we compare and discuss two different possible choices for
describing the asymptotic configurations of the system, related to the use of
Jacobi or hyperspherical coordinates. In order to illustrate the difficulties
and advantages of the approach two simple numerical applications are shown in
the case of neutron-deuteron scattering at low energies using s-wave
interactions. We found that the optimization driven by the Hyperspherical
Adiabatic basis is not as efficient for scattering states as in bound state
applications.Comment: 29 pages, 5 figures, accepted for publication in Few-Body Systems (in
press
exploding clusters dynamics probed by XUV fluorescence
Clusters excited by intense laser pulses are a unique source of warm dense
matter, that has been the subject of intensive experimental studies. The
majority of those investigations concerns atomic clusters, whereas the
evolution of molecular clusters excited by intense laser pulses is less
explored. In this work we trace the dynamics of clusters
triggered by a few-cycle 1.45-m driving pulse through the detection of XUV
fluorescence induced by a delayed 800-nm ignition pulse. Striking differences
among fluorescence dynamics from different ionic species are observed
Continuous-Variable Spatial Entanglement for Bright Optical Beams
A light beam is said to be position squeezed if its position can be
determined to an accuracy beyond the standard quantum limit. We identify the
position and momentum observables for bright optical beams and show that
position and momentum entanglement can be generated by interfering two
position, or momentum, squeezed beams on a beam splitter. The position and
momentum measurements of these beams can be performed using a homodyne detector
with local oscillator of an appropriate transverse beam profile. We compare
this form of spatial entanglement with split detection-based spatial
entanglement.Comment: 7 pages, 3 figures, submitted to PR
Conditional preparation of a quantum state in the continuous variable regime: generation of a sub-Poissonian state from twin beams
We report the first experimental demonstration of conditional preparation of
a non classical state of light in the continuous variable regime. Starting from
a non degenerate OPO which generates above threshold quantum intensity
correlated signal and idler "twin beams", we keep the recorded values of the
signal intensity only when the idler falls inside a band of values narrower
than its standard deviation. By this very simple technique, we generate a
sub-Poissonian state 4.4dB below shot noise from twin beams exhibiting 7.5dB of
noise reduction in the intensity difference.Comment: 4 pages, Accepted in Phys. Rev. Let
- …