Nonlinear cancellation of the parametric resonance in elastic beams: theory and experiment

A non-linear control strategy is applied to a simply supported uniform elastic beam subjected to an axial end force at the principal-parametric resonance frequency of the first skew-symmetric mode. The control input consists of the bending couples applied by two pairs of piezoceramic actuators attached onto both sides of the beam surfaces and symmetrically with respect to the midspan, driven by the same voltage, thus resulting into symmetric control forces. This control architecture has zero control authority, in a linear sense, onto skew-symmetric vibrations. The non-linear transfer of energy from symmetric motions to skew-symmetric modes, due to non-linear inertia and curvature effects, provides the key physical mechanism for channelling suitable control power from the actuators into the linearly uncontrollable mode. The reduced dynamics of the system, constructed with the method of multiple scales directly applied to the governing PDE’s and boundary conditions, suggest effective forms of the control law as a two-frequency input in sub-combination resonance with the parametrically driven mode. The performances of different control laws are investigated. The relative phase and frequency relationships are designed so as to render the control action the most effective. The control schemes generate non-linear controller forces which increase the threshold for the activation of the parametric resonance thus resulting into its annihilation. The theoretical predictions are compared with experimentally obtained results

Four-Photon Quantum Interferometry at a Telecom Wavelength

We report the experimental demonstration of four-photon quantum interference using telecom-wavelength photons. Realization of multi-photon quantum interference is essential to linear optics quantum information processing and measurement-based quantum computing. We have developed a source that efficiently emits photon pairs in a pure spectrotemporal mode at a telecom wavelength region, and have demonstrated the quantum interference exhibiting the reduced fringe intervals that correspond to the reduced de Broglie wavelength of up to the four photon `NOON' state. Our result should open a path to practical quantum information processing using telecom-wavelength photons.Comment: 4 pages, 4 figure

Nonlinear Dynamic Response of Nanocomposite Microbeams Array for Multiple Mass Sensing

A nonlinear MEMS multimass sensor is numerically investigated, designed as a single input-single output (SISO) system consisting of an array of nonlinear microcantilevers clamped to a shuttle mass which, in turn, is constrained by a linear spring and a dashpot. The microcantilevers are made of a nanostructured material, a polymeric hosting matrix reinforced by aligned carbon nanotubes (CNT). The linear as well as the nonlinear detection capabilities of the device are explored by computing the shifts of the frequency response peaks caused by the mass deposition onto one or more microcantilever tips. The frequency response curves of the device are obtained by a pathfollowing algorithm applied to the reduced-order model of the system. The microcantilevers are described by a nonlinear Euler-Bernoulli inextensible beam theory, which is enriched by a meso-scale constitutive law of the nanocomposite. In particular, the microcantilever constitutive law depends on the CNT volume fraction suitably used for each cantilever to tune the frequency bandwidth of the whole device. Through an extensive numerical campaign, the mass sensor sensitivity estimated in the linear and nonlinear dynamic range shows that, for relatively large displacements, the accuracy of the added mass detectability can be improved due to the larger nonlinear frequency shifts at resonance (up to 12%). © 2023 by the authors

Prostacyclin and thromboxane in cerebral vasospasm II: Effects of thromboxane synthetase inhibitor (OKY-1581) on experimentally-induced cerebral vasospasm

OKY-1581, a thromboxane A2 (TXA2) synthetase inhibitor, was administered to cats with normal and constricted basilar arteries. At a dose of 60mg/kg (i.v.), both normal and constricted vessels dilated, and the mean arterial blood pressure (MABP) fell from 55 to 75 mmHg. If MABP remained constant, vessel diameter did not change. Subarachnoid hemorrhage (SAH) was simulated by intracisternal injection of autologous arterial blood. Regional cerebral blood flow (rCBF) was assessed by the heat clearance and H2 clearance methods. The two methods presented similar response profiles. rCBF responses to intravenous OKY-1581 fell into 3 categories: A) no change in rCBF, B) decrease in rCBF related to MABP and C) increase in rCBF in the presence of hypotension. Types A and B were observed in 3 out of 10 control cats and 4 out of 14 SAH-induced cats, with Type C responses in the remainder. There was no significant difference between the groups. While the results do not support a major role for TXA2 in cerebral vasospasm pathogenesis, OKY-1581 may still be useful in the treatment of cerebral vasospasm, as it improves distal and deep circulation and inhibits platelet aggregation.</p