Search results for "ACOUSTICS"
showing 10 items of 984 documents
Current-induced domain wall motion in nanoscale ferromagnetic elements
2011
The manipulation of a magnetic domain wall (DW) by a spin polarized current in ferromagnetic nanowires has attracted tremendous interest during the last years due to fundamental questions in the fields of spin dependent transport phenomena and magnetization dynamics but also due to promising applications, such as DW based magnetic memory concepts and logic devices. We comprehensively review recent developments in the field of geometrically confined domain walls and in particular current induced DW dynamics. We focus on the influence of the magnetic and electronic transport properties of the materials on the spin transfer effect in DWs. After considering the different DW structures in ferrom…
On the moving load problem in beam structures equipped with tuned mass dampers
2017
This paper proposes an original and efficient approach to the moving load problem on Euler–Bernoulli beams, with Kelvin–Voigt viscoelastic translational supports and rotational joints, and in addition, equipped with Kelvin–Voigt viscoelastic tuned mass dampers (TMDs). While supports are taken as representative of external devices such as grounded dampers or in-span supports with flexibility and damping, the rotational joints may model rotational dampers or connections with flexibility and damping arising from imperfections or damage. The theory of generalised functions is used to treat the discontinuities of the response variables, which involves deriving exact complex eigenvalues and eigen…
Study of a Novel High Permeability Ferrite Sheet Intended for Near Field Communication Systems
2019
The reduction of embedded portable devices involves a magnetic field interference problem when it integrates Near Field Communication (NFC) due to the presence of conductive surfaces such as ground planes, batteries or metallic enclosures. This contribution is focused on analyzing the ability of an innovative magnetic shielding based on flexible sintered ferrite sheets (FSFS) with the aim of improving the performance of that kind of systems. Thereby, a NFC emitter antenna is characterized when it is close to a conductive surface through an electromagnetic (EM) scanner. The EM scanner composed by a matrix of near field probes that make it possible to determine the effectiveness of the FSFS. …
A sampling method for detecting buried objects using electromagnetic scattering
2005
We consider a simple (but fully three-dimensional) mathematical model for the electromagnetic exploration of buried, perfect electrically conducting objects within the soil underground. Moving an electric device parallel to the ground at constant height in order to generate a magnetic field, we measure the induced magnetic field within the device, and factor the underlying mathematics into a product of three operations which correspond to the primary excitation, some kind of reflection on the surface of the buried object(s) and the corresponding secondary excitation, respectively. Using this factorization we are able to give a justification of the so-called sampling method from inverse scat…
Sensitivity of SHG-FROG for the characterization of ultrahigh-repetition-rate telecommunication laser sources
2004
International audience; We analyze experimentally the sensitivity of second-harmonic generation frequency-resolved optical gating (SHG-FROG) for the complete intensity and phase characterization of both a sinusoidal beat signal and a train of 1.3 ps pulses at a repetition rate of 160 GHz at 1550 nm. Using a commercially-available optical spectrum analyzer in the SHG-FROG set-up, incident pulses with energies of only 125 and 190 fJ, which correspond to the beat signal and the 1.3 ps pulse train, respectively, have been accurately characterized.
New insights into seismic absorption imaging
2020
Abstract In recent years, attenuation has been used as a marker for source and dynamic Earth processes due to its higher sensitivity to small variations of lithospheric properties compared to seismic velocity. From seismic hazard analysis to oil and gas exploration and rock physics, many fields need a better reconstruction of energy absorption, a constituent of seismic attenuation generally considered a reliable marker of fluid saturation in space. Here, we propose absorption tomography (AT), a technique grounded on the principles of scattering tomography and Multiple Lapse Time Window Analysis. We benchmark its efficiency to image absorption in space by comparing its results with those obt…
A new approach to fuzzy sets: Application to the design of nonlinear time series, symmetry-breaking patterns, and non-sinusoidal limit-cycle oscillat…
2019
Abstract It is shown that characteristic functions of sets can be made fuzzy by means of the B κ -function, recently introduced by the author, where the fuzziness parameter κ ∈ R controls how much a fuzzy set deviates from the crisp set obtained in the limit κ → 0. As applications, we present first a general expression for a switching function that may be of interest in electrical engineering and in the design of nonlinear time series. We then introduce another general expression that allows wallpaper and frieze patterns for every possible planar symmetry group (besides patterns typical of quasicrystals) to be designed. We show how the fuzziness parameter κ plays an analogous role to temper…
METHOD FOR DETECTING A SONIC IMPRINT OF A THREE-DIMENSIONAL OBJECT AND RELATED APPARATUS
2013
Non invasive method used to detect a “sonic imprint” of three-dimensional objects, particularly suitable for the identification and monitoring of artworks, consisting in acquiring the vibrations caused by a source of elastic waves and using a set of detectors fixed in various predetermined points of the external surface of the object. An apparatus, cheap and simple to utilize, suitable to execute this method, is also described.
The role of the Krauss’s organ in sound production in Pamphagidae (Caelifera: Orthoptera).
2012
In Pamphagidae, the Krauss’s organ is located on both sides of the 2nd tergite and its function is superficially known. It has been proposed to have a stridulatory function. This organ can be found in all Pamphagidae except the apterous genera. Rearing specimens of some species and observing mounted pamphagids allowed the author to observe that when the Krauss’s organ is absent (most apterous species) the tympanum is also absent; further, he discovered specialized stridulatory structures on hind femurs of some taxa for sound emission. By rearing two Pamphagidae belonging to different genera, fragments of stridulations involving the Krauss’s organ and specialized structures on the hind femur…
Exploring Historical Scientific Instruments by Using Mobile Media Devices
2022
We describe an educational activity that can be completed with mobile media devices in order to understand the working principle of a pair of tuning forks, from the Historical Collection of Physics Instruments of the University of Palermo, and how they were used to explain acoustic interference and beats with the Lissajous optical method. This approach can be used with any tuning fork and it is a valuable teaching strategy that does not require specific laboratory equipment.