129 research outputs found
Towards assessing cortical bone porosity using low-frequency quantitative acoustics: A phantom-based study
Purpose
Cortical porosity is a key characteristic governing the structural properties and mechanical behaviour of bone, and its quantification is therefore critical for understanding and monitoring the development of various bone pathologies such as osteoporosis. Axial transmission quantitative acoustics has shown to be a promising technique for assessing bone health in a fast, non-invasive, and radiation-free manner. One major hurdle in bringing this approach to clinical application is the entanglement of the effects of individual characteristics (e.g. geometry, porosity, anisotropy etc.) on the measured wave propagation. In order to address this entanglement problem, we therefore propose a systematic bottom-up approach, in which only one bone property is varied, before addressing interaction effects. This work therefore investigated the sensitivity of low-frequency quantitative acoustics to changes in porosity as well as individual pore characteristics using specifically designed cortical bone phantoms.
Materials and methods
14 bone phantoms were designed with varying pore size, axial-, and radial pore number, resulting in porosities (bone volume fraction) between 0% and 15%, similar to porosity values found in human cortical bone. All phantoms were manufactured using laser sintering, measured using axial-transmission acoustics and analysed using a full-wave approach. Experimental results were compared to theoretical predictions based on a modified Timoshenko theory.
Results
A clear dependence of phase velocity on frequency and porosity produced by increasing pore size or radial pore number was demonstrated, with the velocity decreasing by between 2–5 m/s per percent of additional porosity, which corresponds to -0.5% to -1.0% of wave speed. While the change in phase velocity due to axial pore number was consistent with the results due to pore size and radial pore number, the relative uncertainties for the estimates were too high to draw any conclusions for this parameter.
Conclusions
This work has shown the capability of low-frequency quantitative acoustics to reflect changes in porosity and individual pore characteristics and demonstrated that additive manufacturing is an appropriate method that allows the influence of individual bone properties on the wave propagation to be systematically assessed. The results of this work opens perspectives for the efficient development of a multi-frequency, multi-mode approach to screen, diagnose, and monitor bone pathologies in individuals.ISSN:1932-620
Addressing Tempo Estimation Octave Errors in Electronic Music by Incorporating Style Information Extracted From Wikipedia
(Abstract to follow
Frequency tuning of a triply-resonant whispering-gallery mode resonator to MHz wide transitions for proposed quantum repeater schemes
Quantum repeaters rely on an interfacing of flying qubits with quantum
memories. The most common implementations include a narrowband single photon
matched in bandwidth and central frequency to an atomic system. Previously, we
demonstrated the compatibility of our versatile source of heralded single
photons, which is based on parametric down-conversion in a triply-resonant
whispering-gallery mode resonator, with alkaline transitions [Schunk et al.,
Optica 2, 773 (2015)]. In this paper, we analyze our source in terms of phase
matching, available wavelength-tuning mechanisms, and applications to
narrow-band atomic systems. We resonantly address the D1 transitions of cesium
and rubidium with this optical parametric oscillator pumped above its
oscillation threshold. Below threshold, the efficient coupling of single
photons to atomic transitions heralded by single telecom-band photons is
demonstrated. Finally, we present an accurate analytical description of our
observations. Providing the demonstrated flexibility in connecting various
atomic transitions with telecom wavelengths, we show a promising approach to
realize an essential building block for quantum repeaters.Comment: 18 pages, 14 figure
Interfacing transitions of different alkali atoms and telecom bands using one narrowband photon pair source
Quantum information technology strongly relies on coupling of optical photons
with narrowband quantum systems, such as quantum dots, color centers, and
atomic systems. This coupling requires matching the optical wavelength and
bandwidth to the desired system, which presents a considerable problem for most
available sources of quantum light. Here we demonstrate coupling of alkali
dipole transitions with a tunable source of photon pairs. Our source is based
on spontaneous parametric down-conversion in a triply-resonant
whispering-gallery mode resonator. For this, we have developed novel wavelength
tuning mechanisms, which allow for a coarse tuning to either cesium or rubidium
wavelength with subsequent continuous fine-tuning to the desired transition. As
a demonstration of the functionality of the source, we performed a heralded
single photon measurement of the atomic decay. We present a major advance in
controlling the spontaneous down-conversion process, which makes our bright
source of single photons now compatible with a plethora of narrow-band resonant
systems.Comment: 8 pages, 5 figure
EFT Interpretation of XENON1T Electron Recoil Excess: Neutrinos and Dark Matter
We scrutinize the XENON1T electron recoil excess in the
scalar-singlet-extended dark matter effective field theory. We confront it with
various astrophysical and laboratory constraints both in a general setup and in
the more specific, recently proposed, variant with leptophilic -odd
mediators. The latter also provide mass to the light leptons via suppressed
breaking, a structure that is well fitting with the nature of the
observed excess and the discrete symmetry leads to non-standard dark-matter
interactions. We find that the excess can be explained by neutrino--electron
interactions, linked with the neutrino and electron masses, while
dark-matter--electron scattering does not lead to statistically significant
improvement. We analyze the parameter space preferred by the anomaly and find
severe constraints that can only be avoided in certain corners of parameter
space. Potentially problematic bounds on electron couplings from Big-Bang
Nucleosynthesis can be circumvented via a late phase transition in the new
scalar sector.Comment: 11 pages, 7 figures; v2: matches version published in PR
Squeezed vacuum states from a whispering gallery mode resonator
Squeezed vacuum states enable optical measurements below the quantum limit
and hence are a valuable resource for applications in quantum metrology and
also quantum communication. However, most available sources require high pump
powers in the milliwatt range and large setups, which hinders real world
applications. Furthermore, degenerate operation of such systems presents a
challenge. Here, we use a compact crystalline whispering gallery mode resonator
made of lithium niobate as a degenerate parametric oscillator. We demonstrate
about 1.4 dB noise reduction below the shot noise level for only 300
of pump power in degenerate single mode operation. Furthermore,
we report a record pump threshold as low as 1.35 . Our results
show that the whispering gallery based approach presents a promising platform
for a compact and efficient source for nonclassical light.Comment: 2019 Optical Society of America. Users may use, reuse,
and build upon the article, or use the article for text or data mining, so
long as such uses are for non-commercial purposes and appropriate attribution
is maintained. All other rights are reserve
Nonlinear power dependence of the spectral properties of an optical parametric oscillator below threshold in the quantum regime
Photon pairs and heralded single photons, obtained from cavity-assisted
parametric down-conversion (PDC), play an important role in quantum
communications and technology. This motivated a thorough study of the spectral
and temporal properties of parametric light, both above the Optical Parametric
Oscillator (OPO) threshold, where the semiclassical approach is justified, and
deeply below it, where the linear cavity approximation is applicable. The
pursuit of a higher two-photon emission rate leads into an interesting
intermediate regime where the OPO still operates considerably below the
threshold but the nonlinear cavity phenomena cannot be neglected anymore. Here,
we investigate this intermediate regime and show that the spectral and temporal
properties of the photon pairs, as well as their emission rate, may
significantly differ from the widely accepted linear model. The observed
phenomena include frequency pulling and broadening in the temporal correlation
for the down-converted optical fields. These factors need to be taken into
account when devising practical applications of the high-rate cavity-assisted
SPDC sources
Efficient single sideband microwave to optical conversion using a LiNbO_3 WGM-resonator
We present a coherent microwave to telecom signal converter based on the electro-optical effect using a crystalline WGM-resonator coupled to a 3D microwave cavity, achieving high photon conversion efficiency of 0.1% with MHz bandwidth
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