110,956 research outputs found
Enhancement of photoacoustic detection of inhomogeneities in polymers
We report a series of experiments on laser pulsed photoacoustic excitationin
turbid polymer samples addressed to evaluate the sound speed in the samples and
the presence of inhomogeneities in the bulk. We describe a system which allows
the direct measurement of the speed of the detected waves by engraving the
surface of the piece under study with a fiduciary pattern of black lines. We
also describe how this pattern helps to enhance the sensitivity for the
detection of an inhomogeneity in the bulk. These two facts are useful for
studies in soft matter systems including, perhaps, biological samples. We have
performed an experimental analysis on Grilon(R) samples in different situations
and we show the limitations of the method.Comment: 8 pages, 7 figure
Underwater Acoustic Detection of Ultra High Energy Neutrinos
We investigate the acoustic detection method of 10^18-20 eV neutrinos in a
Mediterranean Sea environment. The acoustic signal is re-evaluated according to
dedicated cascade simulations and a complex phase dependant absorption model,
and compared to previous studies. We detail the evolution of the acoustic
signal as function of the primary shower characteristics and of the acoustic
propagation range. The effective volume of detection for a single hydrophone is
given taking into account the limitations due to sea bed and surface boundaries
as well as refraction effects. For this 'benchmark detector' we present
sensitivity limits to astrophysical neutrino fluxes, from which sensitivity
bounds for a larger acoustic detector can be derived. Results suggest that with
a limited instrumentation the acoustic method would be more efficient at
extreme energies, above 10^20 eV.Comment: 15 pages, 11 figure
Detection of Coherent Vorticity Structures using Time-Scale Resolved Acoustic Spectroscopy
We describe here an experimental technique based on the acoustic scattering
phenomenon allowing the direct probing of the vorticity field in a turbulent
flow. Using time-frequency distributions, recently introduced in signal
analysis theory, for the analysis of the scattered acoustic signals, we show
how the legibility of these signals is significantly improved (time resolved
spectroscopy). The method is illustrated on data extracted from a highly
turbulent jet flow : discrete vorticity events are clearly evidenced. We claim
that the recourse to time-frequency distributions lead to an operational
definition of coherent structures associated with phase stationarity in the
time-frequency plane.Comment: 26 pages, 6 figures. Latex2e format Revised version : Added
references, figures and Changed conten
Explosive Formation and Dynamics of Vapor Nanobubbles around a Continuously Heated Gold Nanosphere
We form sub-micrometer-sized vapor bubbles around a single laser heating gold
nanoparticle in a liquid and monitor them through optical scattering of a probe
laser. The fast, inertia-governed expansion is followed by a slower contraction
and disappearance after some tens of nanoseconds. In a narrow range of
illumination powers, bubble time traces show a clear echo signature. We
attribute it to sound waves released upon the initial explosion and reflected
by flat interfaces, hundreds of microns away from the particle. Echoes can
trigger new explosions. A steady state of nanobubble with a vapor shell
surrounding the heated nanoparticle can be reached by a proper time profile of
the heating intensity. Stable nanobubbles could have original applications for
light modulation and for enhanced optical-acoustic coupling in photoacoustic
microscopy
State-of-the art of acousto-optic sensing and imaging of turbid media
Acousto-optic (AO) is an emerging hybrid technique for measuring optical contrast in turbid media using coherent light and ultrasound (US). A turbid object is illuminated with a coherent light source leading to speckle formation in the remitted light. With the use of US, a small volume is selected,which is commonly referred to as the “tagging” volume. This volume acts as a source of modulated light, where modulation might involve phase and intensity change. The tagging volume is created by focusing ultrasound for good lateral resolution; the axial resolution is accomplished by making either the US frequency, amplitude, or phase time-dependent. Typical resolutions are in the order of 1 mm. We will concentrate on the progress in the field since 2003. Different schemes will be discussed to detect the modulated photons based on speckle detection, heterodyne detection, photorefractive crystal (PRC) assisted detection, and spectral hole burning (SHB) as well as Fabry-Perot interferometers. The SHB and Fabry-Perot interferometer techniques are insensitive to speckle decorrelation and therefore suitable for in vivo imaging. However, heterodyne and PRC methods also have potential for in vivo measurements. Besides measuring optical properties such as scattering and absorption, AO can be applied in fluorescence and elastography applications
Flow induced ultrasound scattering: experimental studies
Sound scattering by a finite width beam on a single rigid body rotation
vortex flow is detected by a linear array of transducers (both smaller than a
flow cell), and analyzed using a revised scattering theory. Both the phase and
amplitude of the scattered signal are obtained on 64 elements of the detector
array and used for the analysis of velocity and vorticity fields. Due to
averaging on many pulses the signal-to-noise ratio of the phases difference in
the scattered sound signal can be amplified drastically, and the resolution of
the method in the detection of circulation, vortex radius, vorticity, and
vortex location becomes comparable with that obtained earlier by time-reversal
mirror (TRM) method (P. Roux, J. de Rosny, M. Tanter, and M. Fink, {\sl Phys.
Rev. Lett.} {\bf 79}, 3170 (1997)). The revised scattering theory includes two
crucial steps, which allow overcoming limitations of the existing theories.
First, the Huygens construction of a far field scattering signal is carried out
from a signal obtained at any intermediate plane. Second, a beam function that
describes a finite width beam is introduced, which allows using a theory
developed for an infinite width beam for the relation between a scattering
amplitude and the vorticity structure function. Structure functions of the
velocity and vorticity fields deduced from the sound scattering signal are
compared with those obtained from simultaneous particle image velocimetry (PIV)
measurements. Good quantitative agreement is found.Comment: 14 pages, 23 figures. accepted for publication in Phys. Fluids(June
issue
Multichannel direct detection of light dark matter: Target comparison
Direct-detection experiments for light dark matter are making enormous leaps in reaching previously unexplored model space. Several recent proposals rely on collective excitations, where the experimental sensitivity is highly dependent on detailed properties of the target material, well beyond just nucleus mass numbers as in conventional searches. It is thus important to optimize the target choice when considering which experiment to build. We carry out a comparative study of target materials across several detection channels, focusing on electron transitions and single (acoustic or optical) phonon excitations in crystals, as well as the traditional nuclear recoils. We compare materials currently in use in nuclear recoil experiments (Si, Ge, NaI, CsI, CaWO4), a few of which have been proposed for light dark matter experiments (GaAs, Al2O3, diamond), as well as 16 other promising polar crystals across all detection channels. We find that target- and dark-matter-model-dependent reach is largely determined by a small number of material parameters: speed of sound, electronic band gap, mass number, Born effective charge, high-frequency dielectric constant, and optical phonon energies. We showcase, for each of the two benchmark models, an exemplary material that has a better reach than in any currently proposed experiment
Gravitational waves and electroweak baryogenesis in a global study of the extended scalar singlet model
We perform a global fit of the extended scalar singlet model with a fermionic
dark matter (DM) candidate. Using the most up-to-date results from the
measured DM relic density, direct detection limits from the
XENON1T (2018) experiment, electroweak precision observables and Higgs searches
at colliders, we constrain the 7-dimensional model parameter space. We also
find regions in the model parameter space where a successful electroweak
baryogenesis (EWBG) can be viable. This allows us to compute the gravitational
wave (GW) signals arising from the phase transition, and discuss the potential
discovery prospects of the model at current and future GW experiments. Our
global fit places a strong upper lower limit on the second
scalar mass, the fermion DM mass and the scalar-fermion DM coupling. In
agreement with previous studies, we find that our model can simultaneously
yield a strong first-order phase transition and saturate the observed DM
abundance. More importantly, the GW spectra of viable points can often be
within reach of future GW experiments such as LISA, DECIGO and BBO.Comment: 42 pages, 10 figures and 2 tables; v2: updated references, submitted
to JHEP; v3: corrected typos and updated references, matches version
published in JHE
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