192 research outputs found
Identification of two cracks with different severity in beams and rods from minimal frequency data
It has been known for a long time that the problem of identifying two small cracks in a simply supported beam from the first three natural frequencies can be analytically formulated and solved if the two cracks have equal severity. In this paper we extend this result to the case of cracks with different severity. Each crack is simulated by a rotational elastic spring and the inverse problem is solved in terms of the damage-induced changes in the first four natural frequencies. Closed-form expressions of the damage parameters in terms of the measured frequencies are obtained. The results can be extended to the identification of two cracks in a longitudinally vibrating beam based on a suitable set of natural frequency and antiresonant frequency data. Numerical simulations support the theory, and show that if accurate input data are available and the cracks are not too close, then damage identification leads to satisfactory results
Unique determination of a single crack in a uniform simply supported beam in bending vibration
In this paper we consider one of the basic inverse problems in damage detection based on natural frequency data, namely the identification of a single open crack in a uniform simply supported beam from measurement of the first and the second natural frequency. It is commonly accepted in the literature that the knowledge of this set of spectral data allows for the unique determination of the severity and the position (up to symmetry) of the damage. However, in spite of the fact that many numerical evidences are in support of this property, the result is rigorously proved only when the severity of the crack is small. In this paper we definitely show, by means of an original constructive method, that the above result holds true for any level of crack severity. (C) 2016 Elsevier Ltd. All rights reserved
Point mass identification in rectangular plates from minimal natural frequency data
The inverse problem of determining the location and size of a point mass attached on a simply supported, isotropic and homogeneous rectangular plate from minimal natural frequency data is considered in this paper. Under the assumption that the size of the mass is small compared to the total mass of the plate, we show that the problem can be formulated and solved in closed form in terms of point mass-induced changes on the first three natural frequencies. Numerical simulations indicate that the method allows for accurate identification, provided that measurement/modelling errors are smaller than eigenfrequency changes. \ua9 2016 Elsevier Ltd
A Case of Concurrent Riedel's, Hashimoto's and Acute Suppurative Thyroiditis
Riedel's thyroiditis (RT) is a rare form of infiltrative and inflammatory disease of the thyroid, first described by Bernard Riedel in 1896. The concurrent presence of RT and other thyroid diseases
has been reported, but, the association of RT with Hashimoto's thyroiditis and acute thyroiditis has
not yet been reported. We present a case of concurrent Riedel's, Hashimoto's and acute thyroiditis that occurred in a
45-year-old patient
Causality in COVID-19-associated stroke: a uniform case definition for use in clinical research
The method of fundamental solutions for three-dimensional inverse geometric elasticity problems
We investigate the numerical reconstruction of smooth star-shaped voids (rigid inclusions and cavities) which are compactly contained in a three-dimensional isotropic linear elastic medium from a single set of Cauchy data (i.e. nondestructive boundary displacement and traction measurements) on the accessible outer boundary. This inverse geometric problem in three-dimensional elasticity is approximated using the method of fundamental solutions (MFS). The parameters describing the boundary of the unknown void, its centre, and the contraction and dilation factors employed for selecting the fictitious surfaces where the MFS sources are to be positioned, are taken as unknowns of the problem. In this way, the original inverse geometric problem is reduced to finding the minimum of a nonlinear least-squares functional that measures the difference between the given and computed data, penalized with respect to both the MFS constants and the derivative of the radial coordinates describing the position of the star-shaped void. The interior source points are anchored and move with the void during the iterative reconstruction procedure. The feasibility of this new method is illustrated in several numerical examples
Hybrid III-V/Silicon photonic circuits embedding generation and routing of entangled photon pairs
The demand for integrated photonic chips combining the generation and
manipulation of quantum states of light is steadily increasing, driven by the
need for compact and scalable platforms for quantum information technologies.
While photonic circuits with diverse functionalities are being developed in
different single material platforms, it has become crucial to realize hybrid
photonic circuits that harness the advantages of multiple materials while
mitigating their respective weaknesses, resulting in enhanced capabilities.
Here, we demonstrate a hybrid III-V/Silicon quantum photonic device combining
the strong second-order nonlinearity and compliance with electrical pumping of
the III-V semiconductor platform with the high maturity and CMOS compatibility
of the silicon photonic platform. Our device embeds the spontaneous parametric
down-conversion (SPDC) of photon pairs into an AlGaAs source and their
subsequent routing to a silicon-on-insulator circuitry, within an evanescent
coupling scheme managing both polarization states. This enables the on-chip
generation of broadband telecom photons by type 0 and type 2 SPDC from the
hybrid device, at room temperature and with internal pair generation rates
exceeding for both types, while the pump beam is strongly
rejected. Two-photon interference with 92% visibility (and up to 99% upon 5 nm
spectral filtering) proves the high energy-time entanglement quality
characterizing the produced quantum state, thereby enabling a wide range of
quantum information applications on-chip, within an hybrid architecture merging
the assets of two mature and highly complementary platforms in view of
out-of-the-lab deployment of quantum technologies
The stability for the Cauchy problem for elliptic equations
We discuss the ill-posed Cauchy problem for elliptic equations, which is
pervasive in inverse boundary value problems modeled by elliptic equations. We
provide essentially optimal stability results, in wide generality and under
substantially minimal assumptions. As a general scheme in our arguments, we
show that all such stability results can be derived by the use of a single
building brick, the three-spheres inequality.Comment: 57 pages, review articl
Reconfigurable photon localization by coherent drive and dissipation in photonic lattices
7 pags., 4 figs.The engineering of localized modes in photonic structures is one of the main targets of modern photonics. An efficient strategy to design these modes is to use the interplay of constructive and destructive interference in periodic photonic lattices. This mechanism is at the origin of the defect modes in photonic bandgaps, bound states in the continuum, and compact localized states in flat bands. Here, we show that in lattices of lossy resonators, the addition of external optical drives with a controlled phase enlarges the possibilities of manipulating interference effects and allows for the design of novel types of localized modes. Using a honeycomb lattice of coupled micropillars resonantly driven with several laser spots at energies within its photonic bands, we demonstrate the localization of light in at-will geometries down to a single site. These localized modes are fully reconfigurable and have the potentiality of enhancing nonlinear effects and of controlling light-matter interactions with single site resolution.Ministerio de Ciencia, Innovación y Universidades (PGC2018-094792-B-100); Consejo Superior de Investigaciones Científicas (PTI-001);
Comunidad de Madrid (CAM 2020 Y2020/TCS-6545); Narodowe Centrum Nauki (DEC-2019/32/T/ST3/00332); Agence Nationale de la Recherche
(ANR-11-LABX-0007, ANR-16-CE30-0021, ANR-16-IDEX-0004 ULNE, ANR-QUAN-0003-05); European Research Council (820392, 865151, 949730),
Région Hauts-de-France
Probing the dynamics and coherence of a semiconductor hole spin via acoustic phonon-assisted excitation
Spins in semiconductor quantum dots are promising local quantum memories to
generate polarization-encoded photonic cluster states, as proposed in the
pioneering Rudolph-Lindner scheme [1]. However, harnessing the polarization
degree of freedom of the optical transitions is hindered by resonant excitation
schemes that are widely used to obtain high photon indistinguishability. Here
we show that acoustic phonon-assisted excitation, a scheme that preserves high
indistinguishability, also allows to fully exploit the polarization selective
optical transitions to initialise and measure single spin states. We access the
coherence of hole spin systems in a low transverse magnetic field and directly
monitor the spin Larmor precession both during the radiative emission process
of an excited state or in the quantum dot ground state. We report a spin state
detection fidelity of granted by the optical selection rules
and a ~ns hole spin coherence time, demonstrating the potential of this
scheme and system to generate linear cluster states with a dozen of photonsComment: 3 figure
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