Application of the matrix Rytov method to the calculation of the coherence function of a sound field in an oceanic waveguide

2008 ◽  
Vol 123 (5) ◽  
pp. 3941-3941
Author(s):  
Alex G. Voronovich ◽  
Vladimir E. Ostashev
Keyword(s):  
Coherence Function ◽  
Sound Field ◽  
Oceanic Waveguide ◽  
The Matrix ◽  
Rytov Method

TWO NEW LOWER BOUNDS FOR THE SPARK OF A MATRIX

2017 ◽  
Vol 96 (3) ◽  
pp. 353-360
Author(s):  
HAIFENG LIU ◽  
JIHUA ZHU ◽  
JIGEN PENG
Keyword(s):  
Lower Bounds ◽  
Coherence Function ◽  
Weyl’S Theorem ◽  
Combinatorial Search ◽  
Mutual Coherence ◽  
Numerical Examples ◽  
The Matrix ◽  
Np Hard Problem ◽  
Minimisation Problem ◽  
Better Than

The $l_{0}$-minimisation problem has attracted much attention in recent years with the development of compressive sensing. The spark of a matrix is an important measure that can determine whether a given sparse vector is the solution of an $l_{0}$-minimisation problem. However, its calculation involves a combinatorial search over all possible subsets of columns of the matrix, which is an NP-hard problem. We use Weyl’s theorem to give two new lower bounds for the spark of a matrix. One is based on the mutual coherence and the other on the coherence function. Numerical examples are given to show that the new bounds can be significantly better than existing ones.

Study on Modeling Method of Vortex Shedding Synchronization in Heat Exchanger Tube Bundles II: Experimental Verification

2011 ◽  
Author(s):  
Eiichi Nishida ◽  
Hiromitsu Hamakawa
Keyword(s):  
Vortex Shedding ◽  
Experimental Verification ◽  
Coherence Function ◽  
Sound Field ◽  
Modeling Method ◽  
Resonance Level ◽  
Simple Method ◽  
Critical Flow Velocity ◽  
Wake Oscillator ◽  
Tube Bundles

Acoustic resonance may occur in heat exchangers such as gas heaters or boilers which contain tube bundles. This resonance is classified in self-excited oscillation, and feedback effect in vortex shedding and sound field plays important role. The purpose of this study is to develop a modeling method of the resonance level dependence of vortex shedding synchronization because this is the most essential part of critical flow velocity prediction. The level of synchronization is expressed by a coherence function between vortex shedding in any two locations in the tube bundle. Here, we introduce the wake oscillator model of vortex shedding, and based on this model, a simple method to estimate the resonance level dependence of the coherence function is proposed. In this method, the relationship of vortex shedding and the sound field in an arbitrary tube is expressed by a statistical model where the effect of resonance on the wake-oscillator is expressed by the width of the fluctuation range of phase between wake-oscillator and acoustic particle velocity. From this model, the resonance level dependence of the coherence function is derived in simple form. This method gives the result that when the resonance level increases, the synchronization level in the tube bundles also increases, which seems to be a reasonable conclusion. The results of experimental verification showed the validity of the proposed modeling method.

The effects of atom–cavity coupling constant on physical observables for different transitions

2018 ◽  
Vol 96 (8) ◽  
pp. 919-925
Author(s):  
Babak Parvin
Keyword(s):  
Optical Cavity ◽  
Coherence Function ◽  
Photon Number ◽  
Single Mode ◽  
Coupling Constant ◽  
Photon Transition ◽  
Level Atom ◽  
Cavity Coupling ◽  
The Matrix ◽  
Field Correlation

The aim of this work is to investigate the changing effects of the atom–cavity coupling constant on an atom–cavity system. A three-level atom in the Λ configuration with q-photon transition between levels 2 and 3 is confined in a single-mode Fabry–Pérot optical cavity. To solve the master equation of this system in the steady-state by using the appropriate physical quantities, the matrix continued fractions method for recurrence equations is applied. The behavior of physical observables including atom–field correlation, mean photon number, and second-order coherence function is discussed. The effect of altering the atom–cavity coupling constant for different transitions on these observables is fully considered. The results of calculations show that by increasing this coupling constant, the range of atom–cavity correlation becomes longer, the maximum value of the output mean photon number from the cavity remains almost constant, the broadening in the curves of the mean photon number increases and the lasing process is amplified in the system. Finally, the transformation of the three-level atom into a two-level one under several specific conditions in a four-photon transition case has been studied. The obtained results of the two-level atomic pattern are adequately confirmed by the simulations related to the three-level atom.

Features of the Sound Field Structure in a Two-Channel Oceanic Waveguide

2001 ◽  
Vol 47 (3) ◽  
pp. 268-276
Author(s):  
O. P. Galkin ◽  
L. V. Shvachko
Keyword(s):  
Sound Field ◽  
Field Structure ◽  
Oceanic Waveguide
Sign in / Sign up

Export Citation Format

Share Document