scholarly journals Horizontal refraction of normal modes due to variation in bathymetry and subbottom sedimental structure

1988 ◽  
Vol 84 (S1) ◽  
pp. S151-S151 ◽  
Author(s):  
Kazuhiko Ohta
Keyword(s):  
Normal Modes ◽  
Horizontal Refraction

A 2-D DESCRIPTION OF SOUND PROPAGATION IN A HORIZONTALLY-INHOMOGENEOUS OCEAN

2002 ◽  
Vol 10 (01) ◽  
pp. 123-151 ◽  
Author(s):  
OLEG A. GODIN
Keyword(s):  
Travel Time ◽  
Sound Propagation ◽  
Environmental Gradients ◽  
Normal Modes ◽  
Approximate Expression ◽  
Underwater Sound ◽  
Mode Amplitude ◽  
Geometrical Acoustics ◽  
Horizontal Refraction ◽  
Horizontally Inhomogeneous

Effects of horizontal refraction on underwater sound propagation in deep and shallow water are considered within geometrical acoustics and adiabatic normal modes approximations. Several distinct formulations of the adiabatic approximation have been proposed in the literature on modal propagation. These formulations differ in the predicted values of mode amplitudes and, hence, in their reciprocity and energy-conserving properties. The formulations are compared with respect to their accuracy and domain of validity, assuming small and smooth variation of mode propagation constants characteristic of underwater acoustic waveguides. Perturbation theory for horizontal (modal) rays is used in the analysis. An approximate expression for the adiabatic mode amplitude in 3-D problems is derived which requires environmental information only along the source-receiver radial and which has greater accuracy than previous formulations. It is shown that the uncoupled azimuth approximation, also known as the N × 2-D approximation, overestimates travel times of ray arrivals as well as phases of adiabatic normal modes in a horizontally-inhomogeneous ocean. The travel time and phase biases rapidly increase with the value of cross-range environmental gradients and propagation range. Simple and explicit expressions for leading-order corrections to the travel time and the phase are found in terms of path-averaged cross-range environmental gradients. Implications on applicability of the uncoupled azimuth approximation for sound propagation modeling in a horizontally-inhomogeneous ocean are discussed. A perfect-wedge model of the coastal ocean is chosen to illustrate the importance of the travel-time and phase biases due to horizontal refraction.

scholarly journals A Study on the Estimation of Source Bearing in an ASA Wedge: Diminishing the Estimation Error Caused by Horizontal Refraction

2021 ◽  
Vol 9 (12) ◽  
pp. 1449
Author(s):  
Jianbo Zhou ◽  
Jun Tang ◽  
Yixin Yang
Keyword(s):  
Acoustical Society ◽  
Estimation Error ◽  
Normal Modes ◽  
Direct Path ◽  
Bearing Estimation ◽  
3D Effects ◽  
Horizontal Refraction

The performance of warping transformation in diminishing the error in underwater source-bearing estimation, caused by horizontal refraction effects (also named 3D effects), is studied. First, the capability of warping transformation for separating the normal modes, as well as their direct and horizontally refracted paths, in a standard Acoustical Society of America (ASA) wedge is demonstrated. Second, the error values for source bearing estimation in three different manners, i.e., using the full signal, using its component corresponding to the first mode, and using the component of the latter corresponding only to the direct path are compared for the same wedge case. The results show that the estimation error can be significantly reduced by beamforming, with only the first mode, or using the direct path of the first mode in cases where there exists a horizontally refracted path of the first mode.

Filtering methods for finite-time normal modes and atmospheric error growth

2000 ◽  
Vol 42 ◽  
pp. 1482
Author(s):  
Mozheng Wei ◽  
Jorgen S. Frederiksen ◽  
Steve Kepert
Keyword(s):  
Finite Time ◽  
Normal Modes ◽  
Error Growth

Gravitational Waves

2018 ◽  
Author(s):  
Michele Maggiore
Keyword(s):  
Black Hole ◽  
Perturbation Theory ◽  
Gravitational Waves ◽  
Transfer Functions ◽  
Normal Modes ◽  
Cosmological Perturbation ◽  
Tests Of General Relativity ◽  
Pulsar Timing ◽  
Tensor Perturbations ◽  
Stochastic Backgrounds

A comprehensive and detailed account of the physics of gravitational waves and their role in astrophysics and cosmology. The part on astrophysical sources of gravitational waves includes chapters on GWs from supernovae, neutron stars (neutron star normal modes, CFS instability, r-modes), black-hole perturbation theory (Regge-Wheeler and Zerilli equations, Teukoslky equation for rotating BHs, quasi-normal modes) coalescing compact binaries (effective one-body formalism, numerical relativity), discovery of gravitational waves at the advanced LIGO interferometers (discoveries of GW150914, GW151226, tests of general relativity, astrophysical implications), supermassive black holes (supermassive black-hole binaries, EMRI, relevance for LISA and pulsar timing arrays). The part on gravitational waves and cosmology include discussions of FRW cosmology, cosmological perturbation theory (helicity decomposition, scalar and tensor perturbations, Bardeen variables, power spectra, transfer functions for scalar and tensor modes), the effects of GWs on the Cosmic Microwave Background (ISW effect, CMB polarization, E and B modes), inflation (amplification of vacuum fluctuations, quantum fields in curved space, generation of scalar and tensor perturbations, Mukhanov-Sasaki equation,reheating, preheating), stochastic backgrounds of cosmological origin (phase transitions, cosmic strings, alternatives to inflation, bounds on primordial GWs) and search of stochastic backgrounds with Pulsar Timing Arrays (PTA).

Triatomic molecules

2018 ◽  
Author(s):  
John H. D. Eland ◽  
Raimund Feifel
Keyword(s):  
Degrees Of Freedom ◽  
Normal Modes ◽  
Electronic States ◽  
Triatomic Molecules ◽  
Doubly Charged Ions ◽  
Spectral Bands ◽  
Valence Electrons ◽  
Doubly Charged ◽  
Charged Ions ◽  
Double Ionisation

Double ionisation of the triatomic molecules presented in this chapter shows an added degree of complexity. Besides potentially having many more electrons, they have three vibrational degrees of freedom (three normal modes) instead of the single one in a diatomic molecule. For asymmetric and bent triatomic molecules multiple modes can be excited, so the spectral bands may be congested in all forms of electronic spectra, including double ionisation. Double photoionisation spectra of H2O, H2S, HCN, CO2, N2O, OCS, CS2, BrCN, ICN, HgCl2, NO2, and SO2 are presented with analysis to identify the electronic states of the doubly charged ions. The order of the molecules in this chapter is set first by the number of valence electrons, then by the molecular weight.

Wave chaos in terms of normal modes

1999 ◽  
Vol 59 (2) ◽  
pp. 1656-1668 ◽  
Author(s):  
A. L. Virovlyansky ◽  
G. M. Zaslavsky
Keyword(s):  
Normal Modes ◽  
Wave Chaos

scholarly journals Accurate prediction of terahertz spectra of molecular crystals of fentanyl and its analogs

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chun-Hung Wang ◽  
Anthony C. Terracciano ◽  
Artёm E. Masunov ◽  
Mengyu Xu ◽  
Subith S. Vasu
Keyword(s):  
Molecular Structure ◽  
Crystal Packing ◽  
Molecular Crystals ◽  
Normal Modes ◽  
Rapid Identification ◽  
Medical Attention ◽  
Dispersion Interactions ◽  
Pain Reliever ◽  
Fentanyl Analogs ◽  
High Bioavailability

AbstractFentanyl is a potent synthetic opioid pain reliever with a high bioavailability that can be used as prescription anesthetic. Rapid identification via non-contact methods of both known and emerging opioid substances in the fentanyl family help identify the substances and enable rapid medical attention. We apply PBEh-3c method to identify vibrational normal modes from 0.01 to 3 THz in solid fentanyl and its selected analogs. The molecular structure of each fentanyl analog and unique arrangement of H-bonds and dispersion interactions significantly change crystal packing and is subsequently reflected in the THz spectrum. Further, the study of THz spectra of a series of stereoisomers shows that small changes in molecular structure results in distinct crystal packing and significantly alters THz spectra as well. We discuss spectral features of synthetic opioids with higher potency than conventional fentanyl such as ohmefentanyl and sufentanil and discover the pattern of THz spectra of fentanyl analogs.

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