Search results for "ACOUSTIC"
showing 10 items of 1590 documents
Emergence of non-Markovianity in the emission process of an atom in a half-cavity
2014
We study quantum non-Markovianity in the early stage of the emission process of a two-level atom coupled to a semi-infinite waveguide, where the waveguide termination behaves as a perfect mirror. Specifically, we restrict to the analysis of the process for times shorter than twice the time delay t_d, where t_d is the duration of a round trip along the atom-mirror path. We show the emergence of a threshold in the parameters space separating the Markovian and non-Markovian regions.
Erratum: Atom-field dressed states in slow-light waveguide QED [Phys. Rev. A93, 033833 (2016)]
2016
We discuss the properties of atom-photon bound states in waveguide QED systems consisting of single or multiple atoms coupled strongly to a finite-bandwidth photonic channel. Such bound states are formed by an atom and a localized photonic excitation and represent the continuum analog of the familiar dressed states in single-mode cavity QED. Here we present a detailed analysis of the linear and nonlinear spectral features associated with single- and multiphoton dressed states and show how the formation of bound states affects the waveguide-mediated dipole-dipole interactions between separated atoms. Our results provide both a qualitative and quantitative description of the essential strong-…
Three-dimensional axisymmetric cloak based on the cancellation of acoustic scattering from a sphere.
2013
This Letter presents the design, fabrication, and experimental characterization of a directional threedimensional acoustic cloak for airborne sound. The cloak consists of 60 concentric acoustically rigid tori surrounding the cloaked object, a sphere of radius 4 cm. The major radii and positions of the tori along the symmetry axis are determined using the condition of complete cancellation of the acoustic field scattered from the sphere. They are obtained through an optimization technique that combines genetic algorithm and simulated annealing. The scattering cross section of the sphere with the cloak, which is the magnitude that is minimized, is calculated using the method of fundamental so…
The boson peak
2013
The vibrational properties of glasses in the THz range differ very much from what is expected from Debye's elasticity theory: the density of states (DOS) deviates from Debye's ω2 law [the “boson peak” (BP)], the sound velocity shows a negative dispersion in the BP frequency regime and there is a strong increase in the sound attenuation near the BP frequency. These anomalies are related to an anomalous temperature dependence of the specific heat and thermal conductivity in the 10 K regime. An overview of the heterogeneous-elasticity theory is given, by means of which all these anomalies can be explained and shown to arise from the structural disorder, leading to spatial fluctuations of the s…
Instantaneous root mean squire value of the acoustic emission as a means of measuring partial discharges
2003
The author presents the measurement results of the parameter A/sub RMS/ for three types of partial discharges (PDs) generated in a typical high-voltage system: on pressboard, on resin, and on glass. A typical run of A/sub RMS/ on an X-Y register is shown. It manifests a relatively stable instantaneous root mean square value of the electric signal converted from the acoustic signal as a function of time. Results obtained for the three surfaces demonstrate that the parameter A/sub RMS/ is perfectly suitable for characterizing PDs measured by the acoustic method. It is univocally connected with the energy of the generated PD. >
Collisions and Mechanical Wave Propagation in Elastic Rods
2011
Some results from experiments intended to measure the propagation speed of sound waves produced by collisions between small bodies and metallic rods are analysed. Elementary models of elastic collision and of the reflection and transmission of waves at media boundaries are discussed and tested with experimental data, in the framework of a workshop on mechanical wave propagation that featured at the University of Palermo in a two-year graduate programme for prospective physics teachers and in courses for undergraduate engineering and physics students.
A Problem Based Approach to Elastic Wave Propagation: The Role of Constraints
2009
A problem-based approach to the teaching of mechanical wave propagation, focused on observation and measurement of wave properties in solids and on modelling of these properties, is presented. In particular, some experimental results, originally aimed at measuring the propagation speed of sound waves in metallic rods, are used in order to deepen the role of constraints in mechanical wave propagation. Interpretative models of the results obtained in the laboratory are built and implemented by using a well-known simulation environment. The simulation results are, then, compared with experimental data. The approach has been developed and experimented in the context of a workshop on mechanical …
Dynamic measurement of the elastic constant of an helicoidal spring by a smartphone
2021
Abstract We describe an educational activity that can be done by using smartphones to collect data in physics experiments aimed to measure the oscillating period of a spring-mass system and the elastic constant of the helicoidal spring by the dynamic method. Results for the oscillating period and for the elastic constant of the spring agree very well with measurements obtained by different methods. We also discuss the error analysis that can be done in an introductory physics laboratory at undergraduate level.
Properties of Scattering Matrices in a Vicinity of Thresholds
2021
Chapter 3 is devoted to various properties of a waveguide scattering matrix, which is a matrix function on the waveguide continuous spectrum. There is a sequence of threshold values of the spectral parameter where the scattering matrix changes its size; the thresholds accumulate at infinity. In particular, both two-sided limits of the scattering matrix are calculated at every threshold.
Low-noise microvolt level calibrator for measurement of performance of biosignal recording systems
1997
A calibrator, the noise level of which is below the noise level generated in the preamplifier system, was needed for testing and development of a multichannel recording system. A multichannel preamplifier head assembly was used for recording cortical, subcortical, and cerebellar slow potentials and multiunit activity in freely moving cats and restrained rabbits. An inexpensive, battery-powered, lownoise voltage signal generator for calibration of the preamplifiers is described. The circuit provides a square-wave output at a frequency of 10 or 1000 Hz, and the peak-to-peak (p-p) amplitude can be selected at 10, 100, or 1000µV. The measured output noise of the calibrator is below 2µV (p-p, 0.…