11,216 research outputs found
Localization for Anchoritic Sensor Networks
We introduce a class of anchoritic sensor networks, where communications
between sensor nodes is undesirable or infeasible, e.g., due to harsh
environment, energy constraints, or security considerations
Microwave apparatus for gravitational waves observation
In this report the theoretical and experimental activities for the
development of superconducting microwave cavities for the detection of
gravitational waves are presented.Comment: 42 pages, 28 figure
Generalized analytic model for rotational and anisotropic metasolids
An analytical approach is presented to model a metasolid accounting for
anisotropic effects and rotational mode. The metasolid is made of either
cylindrical or spherical hard inclusions embedded in a stiff matrix via soft
claddings, and the analytical approach to study the composite material is a
generalization of the method introduced by Liu \textit{et al.} [Phys. Rev. B,
71, 014103 (2005)]. It is shown that such a metasolid exhibits negative mass
densities near the translational-mode resonances, and negative density of
moment of inertia near the rotational resonances. The results obtained by this
analytical and continuum approach are compared with those from discrete
mass-spring model, and the validity of the later is discussed. Based on derived
analytical expressions, we study how different resonance frequencies associated
with different modes vary and are placed with respect to each other, in
function of the mechanical properties of the coating layer. We demonstrate that
the resonances associated with additional modes taken into account, that is,
axial translation for cylinders, and rotations for both cylindrical and
spherical systems, can occur at lower frequencies compared to the previously
studied plane-translational modes.Comment: 30 pages, 10 figure
A Bayesian approach for energy-based estimation of acoustic aberrations in high intensity focused ultrasound treatment
High intensity focused ultrasound is a non-invasive method for treatment of
diseased tissue that uses a beam of ultrasound to generate heat within a small
volume. A common challenge in application of this technique is that
heterogeneity of the biological medium can defocus the ultrasound beam. Here we
reduce the problem of refocusing the beam to the inverse problem of estimating
the acoustic aberration due to the biological tissue from acoustic radiative
force imaging data. We solve this inverse problem using a Bayesian framework
with a hierarchical prior and solve the inverse problem using a
Metropolis-within-Gibbs algorithm. The framework is tested using both synthetic
and experimental datasets. We demonstrate that our approach has the ability to
estimate the aberrations using small datasets, as little as 32 sonication
tests, which can lead to significant speedup in the treatment process.
Furthermore, our approach is compatible with a wide range of sonication tests
and can be applied to other energy-based measurement techniques
Constant-pressure sound waves in non-Hermitian disordered media
When waves impinge on a disordered material they are back-scattered and form
a highly complex interference pattern. Suppressing any such distortions in the
free propagation of a wave is a challenging task with many applications in a
number of different disciplines. In a recent theoretical proposal, it was
pointed out that both perfect transmission through disorder as well as a
complete suppression of any variation in a wave intensity can be achieved by
adding a continuous gain-loss distribution to the disorder. Here we show that
this abstract concept can be implemented in a realistic acoustic system. Our
prototype consists of an acoustic waveguide containing several inclusions that
scatter the incoming wave in a passive configuration and provide the gain or
loss when being actively controlled. Our measurements on this non-Hermitian
acoustic metamaterial demonstrate unambiguously the creation of a
reflectionless scattering wave state that features a unique form of discrete
constant-amplitude pressure waves. In addition to demonstrating that gain-loss
additions can turn localised systems into transparent ones, we expect our
proof-of-principle demonstration to trigger interesting new developments not
only in sound engineering, but also in other related fields such as in
non-Hermitian photonics
PCA based stress monitoring of cylindrical specimens using PZTs and guidedwaves
Since mechanical stress in structures affects issues such as strength, expected operational life and dimensional stability, a continuous stress monitoring scheme is necessary for a complete integrity assessment. Consequently, this paper proposes a stress monitoring scheme for cylindrical specimens, which are widely used in structures such as pipelines, wind turbines or bridges. The approach consists of tracking guided wave variations due to load changes, by comparing wave statistical patterns via Principal Component Analysis (PCA). Each load scenario is projected to the PCA space by means of a baseline model and represented using the Q-statistical indices. Experimental validation of the proposed methodology is conducted on two specimens: (i) a 12.7 mm (1/2”) diameter, 0.4 m length, AISI 1020 steel rod, and (ii) a 25.4 mm (1”) diameter, 6m length, schedule 40, A-106, hollow cylinder. Specimen 1 was subjected to axial loads, meanwhile specimen 2 to flexion. In both cases, simultaneous longitudinal and flexural guided waves were generated via piezoelectric devices (PZTs) in a pitch-catch configuration. Experimental results show the feasibility of the approach and its potential use as in-situ continuous stress monitoring application.Peer ReviewedPostprint (published version
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