Wavenumber Of Mode Research Articles

Modulation of Cathodoluminescence by Surface Plasmons in Silver Nanowires.

The waveguide modes in chemically-grown silver nanowires on silicon nitride substrates are observed using spectrally- and spatially-resolved cathodoluminescence (CL) excited by high-energy electrons in a scanning electron microscope. The presence of a long-range, travelling surface plasmon mode modulates the coupling efficiency of the incident electron energy into the nanowires, which is observed as oscillations in the measured CL with the point of excitation by the focused electron beam. The experimental data are modeled using the theory of surface plasmon polariton modes in cylindrical metal waveguides, enabling the complex mode wavenumbers and excitation strength of the long-range surface plasmon mode to be extracted. The experiments yield insight into the energy transfer mechanisms between fast electrons and coherent oscillations in surface charge density in metal nanowires and the relative amplitudes of the radiative processes excited in the wire by theelectron.

From ray tracing to waves of topological origin in continuous media

Continuous media commonly support a discrete number of wave modes that are trapped along interfaces defined by spatially varying parameters. In the case of multicomponent wave problems, those trapped modes fill a frequency gap between different wave bands. When they are robust against continuous deformations of parameters, such waves are said to be of topological origin. It has been realized over the last decades that waves of topological origin can be predicted by computing a single topological invariant, the first Chern number, in a dual bulk wave problem that is much simpler to solve than the original wave equation involving spatially varying coefficients. The correspondence between the simple bulk problem and the more complicated interface problem is usually justified by invoking an abstract index theorem. Here, by applying ray tracing machinery to the paradigmatic example of equatorial shallow water waves, we propose a physical interpretation of this correspondence. We first compute ray trajectories in the phase space given by position and wavenumber of the wave packet, using Wigner-Weyl transforms. We then apply a quantization condition to describe the spectral properties of the original wave operator. This bridges the gap between previous work by Littlejohn and Flynn showing manifestation of Berry curvature in ray tracing equations, and more recent studies that computed the Chern number of flow models by integrating the Berry curvature over a closed surface in parameter space. We find that an integral of Berry curvature over this closed surface emerges naturally from the quantization condition, which allows us to recover the bulk-interface correspondence.

Exploring quantum computational, molecular docking, and molecular dynamics simulation with MMGBSA studies of ethyl-2-amino-4-methyl thiophene-3-carboxylate

2-aminothiophenes derivative, Ethyl-2-amino-4-methyl thiophene-3-carboxylate (EAMC) has been synthesized, characterized, and investigated quantum chemically. It was experimentally investigated by different spectroscopic methods like- NMR (1H-NMR and 13C-NMR), FT-IR, and UV-Visible. B3LYP method and 6-311++G(d,p) basis set were employed for optimization of molecular structure and calculation of wave numbers of normal modes of vibrations and various other important parameters. Calculated bond lengths and angles were compared with the experimental bond lengths and Bond Angle Parameters. Optimized bond parameters and experimental bond parameters were found in good agreement. Complete potential energy distribution assignments were done successfully by VEDA. The HOMO/LUMO energy gap emphasizes adequate charge transfer happening within the molecule. A study of donor-acceptor interconnections was done via NBO analysis. MEP surface analysis was done to demonstrate charge distribution and reactive areas qualitatively in the molecule. The degree of relative localization of electrons was analyzed via ELF Diagram. The Fukui function analysis showed possible sites for attacks by different substituents. By using the TD-DFT method and PCM solvent model, the UV–Vis spectrum (gas, methanol, DMSO) and the maximum absorption wavelength was computed and compared with experimental data. 3D and 2D intermolecular interactions in the crystal were analyzed via Hirshfeld surface analysis and fingerprint plots reveal that the EAMC crystal was stabilized by H–-H/H–-H/C–-H bond formation. The molecular docking was done with 7 different protein receptors on the molecule to find the best ligand-protein interactions. Molecular dynamic simulations and MMGBSA calculations were also carried out to find out the best binding of the ligand with the protein. Communicated by Ramaswamy H. Sarma

Isotope mass dependence of pedestal transport in JET H-mode plasmas

We present a comparative transport analysis of the isotope mass dependence in the pedestal of two pairs of deuterium/hydrogen type I ELMy H-mode discharges in JET with ITER-like wall, one characterized by the same input power, the other one by the same stored energy. The investigation, carried out using the gyrokinetic code GENE, focuses on the steep profile region of the pedestal. While large wavenumber modes mainly contribute to the electron heat flux and are scarcely influenced by the main gas isotope, an effect of the ion mass in agreement with the experimental (so called anti-gyro-Bohm) scaling is revealed in the low wavenumber range. In this context, the major role played by the shear in regulating the ion-temperature-gradient turbulence is analyzed in some detail. The competing level of turbulent and neoclassical transport is quantified to shed light on the experimental features of the pedestal profiles at different ion mass, with the particle transport found to be consistent with a higher pedestal top density for increasing isotope masses, and the heat transport shown to match the roughly unaltered observed temperature profiles.

Chaos and complexity in the dynamics of nonlinear Alfvén waves in a magnetoplasma.

The nonlinear dynamics of circularly polarized dispersive Alfvén wave (AW) envelopes coupled to the driven ion-sound waves of plasma slow response is studied in a uniform magnetoplasma. By restricting the wave dynamics to a few number of harmonic modes, a low-dimensional dynamical model is proposed to describe the nonlinear wave-wave interactions. It is found that two subintervals of the wave number of modulation k of AW envelope exist, namely, (3/4)kc<k<kc and 0<k<(3/4)kc, where kc is the critical value of k below which the modulational instability (MI) occurs. In the former, where the MI growth rate is low, the periodic and/or quasi-periodic states are shown to occur, whereas the latter, where the MI growth is high, brings about the chaotic states. The existence of these states is established by the analyses of Lyapunov exponent spectra together with the bifurcation diagram and phase-space portraits of dynamical variables. Furthermore, the complexities of chaotic phase spaces in the nonlinear motion are measured by the estimations of the correlation dimension as well as the approximate entropy and compared with those for the known Hénon map and the Lorenz system in which a good qualitative agreement is noted. The chaotic motion, thus, predicted in a low-dimensional model can be a prerequisite for the onset of Alfvénic wave turbulence to be observed in a higher dimensional model that is relevant in the Earth's ionosphere and magnetosphere.

Numerical ellipsometry: A method for selecting a single β-gallium oxide monoclinic crystal orientation able to determine the complete permittivity tensor

Previously, the infrared permittivity tensor of monoclinic β-Ga2O3 crystals has been determined using ellipsometry reflection measurements from two differently oriented monoclinic β-Ga2O3 crystals with surfaces parallel to (010) and (−201). The (010) surface places the crystallographic a-c plane in the table of the instrument. The permittivity tensor consists of four complex values, and in order to compute it, four or more combinations of measurements are required at selected table rotations and incidence angles. However, the (010) orientation also places the transverse optical (TO) modes with Au symmetry parallel to the z-axis of the instrument, and we find that these modes are not fully excited and, hence, not measurable due to underlying selection rules. This makes additional measurements on surfaces other than (010) necessary. The second orientation has been the (−201) crystal, which places the crystallographic b axis in the plane of the table to access the transverse Au phonons. In prior work, the overall tensor has been determined by combining measurements of the two crystal orientations [Schubert et al., Phys. Rev. B 93, 125209 (2016)]. The goal of the work here is to find single crystal orientations for which all TO modes can be determined from measurements. The use of a set of measurements employed for such a single crystal is inextricably linked to the choice of incidence angles and table rotations. Consequently, determining suitable angles for these is linked to the selection of a crystal orientation, which is, therefore, an integral part of the overall goal. The TO contribution to the permittivity strongly dominates at or near the TO mode wavenumber resonances and, therefore, are used in this work to identify suitable orientations for a single crystal. Any such crystal orientation will also provide measurements useful to compute permittivity across the entire measured wavenumber range. In principle, any crystal orientation that does not place the direction of any TO mode at or near the z-axis may be suitable due to the underlying physics and mathematics of the problem. We discuss which of these measurement parameters contain the most sensitivity for the (111) orientation. For accuracy, we seek the best or very good orientations. Our investigation follows a previously demonstrated approach where at a single wavelength, the full tensor of an orthorhombic absorbing crystal was obtained from a low-symmetry surface of stibnite [Schubert and Dollase, Opt. Lett. 27, 2073 (2002)]. We discuss which of these measurement parameters contain the most sensitivity for the (111) orientation. The methods presented here will also be useful for other monoclinic materials as well as other materials of different crystal structures, including orthorhombic and triclinic materials.

Elucidating elusive quaternary selenide EuCeCuSe3: Synthesis, crystal structure, properties and theoretical studies

We report on the novel heterometallic quaternary selenide EuCeCuSe3, the fabrication of which has been a challenge until this work. The structure of the reported selenide was elucidated from the powder X-ray diffraction data, which revealed the formation of EuCeCuSe3 with excellent yield (96.7%) accompanied with a minor fraction of CeSe2 (3.3%), and was best solved in orthorhombic space group Pnma with the BaLaCuS3 structural type. Thus, the crystal structure of the title compound completes the row of the heterometallic quaternary selenides EuRECuSe3 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y), of which the cerium-based derivative exclusively belongs to the BaLaCuS3 structural type. The distortion of the CuSe4 polyhedron was compared for the whole series of EuRECuSe3 compounds using the τ4-descriptor for four coordinated ions, which revealed the highest degree of distortion for the Ce3+-containing selenide, followed by the La3+-based derivative. Furthermore, the crystallographic and geometrical parameters of the reported selenide were discussed in comparison to the Ce3+-based sulfides SrCeCuS3 and EuCeCuS3. Ab initio calculations of the crystal structure, a phonon spectrum and elastic constants for the crystal of EuСeCuSe3 were also performed. The types and wavenumbers of fundamental modes were determined and the involvement of ions participating in the phonon modes was assessed. The experimental IR spectrum of the reported selenide was interpreted and found to be in agreement with the calculated spectrum. The experimental direct band gap of EuCeCuSe3 was measured to be 1.36 eV that is consistent with the concept of its origin due to interband transitions between orbitals emerging mainly from 4f (valence band) and 5d (conduction band) levels of the Eu2+ cation. The dependence of the Young's modulus on the direction demonstrates the anisotropy of the elastic properties, while the Vickers hardness for EuCeCuSe3 was calculated to be 5.2 GPa. Finally, the title compound is paramagnetic above 4 K.

On the O-mode instability generated by dual core-halo solar wind electrons

Abstract In situ measurements reported with different spacecraft reveal the temperature anisotropy constraints of solar wind species. Micro-instabilities driven by the temperature anisotropy are investigated as key mechanism which limit an unchecked rise in the temperature anisotropy in dilute space plasmas. The present study considers the excitation of O-mode instability under the excessive electrons parallel temperature condition i.e., T ‖e &gt; T ⊥e . Looking at the recent developments made by different satellite missions, a dual core-halo electron distribution is employed that represents a true picture of solar wind electrons. We employ Vlasov–Maxwell’s model equations and derive the dispersion relation of the O-wave whose analytical solution characterizes the growth rate of O-mode instability. We take different sets of temperature anisotropy and beta combinations associated with core-halo electron components that highlight the instability characteristics e.g. growth rate and the range of wave number of unstable mode. We note an increment in the growth rate with the increase of anisotropic ratios associated either with core electrons or halo electrons and or the combination thereof. In view of a global perspective of solar wind, it may be a favorable study with the contribution of non-thermal solar wind electrons.

Hydrodynamics of an U-shaped OWC device in a two-layer fluid system

In this article, the effectiveness of an U-shaped “oscillating water column wave energy converter device (OWC-WEC)” is investigated in a two-layer fluid system. To solve the BVP, the “dual boundary element method” (DBEM) is employed. Further, the response of shape parameters on the effectiveness of OWC-WEC is studied in “surface mode” (SM) and “internal mode” (IM), respectively. It is seen that in the surface mode, the variation in the efficiency curve as a consequence of the change in chamber’s length and the lip wall’s draft adopt a similar resonating pattern as in single layer fluid. Furthermore, negligible change is appeared in the efficiency curve due to the change in density ratios in SM mode. Moreover, for smaller and moderate wavenumbers, the variation in the efficiency curve due to the various chamber length, draft of the lip wall and density ratios in internal mode shows highly oscillatory behavior. In addition, this oscillatory behavior vanishes in the short-wave zone.

Fabrication, characterization and optical properties of Au-decorated Bi2Se3 nanoplatelets

Au-decorated Bi2Se3 nanoplatelet heterostructures are fabricated by a two-step process of thermal CVD at 600 °C and magnetron sputtering at room-temperature. The crystal structures and binding energies of rhombohedral Bi2Se3 and FCC Au are determined by XRD, HRTEM, XPS, and Raman spectroscopy. XPS and Raman spectroscopy reveal the interaction between Au and Bi2Se3 by shifting in the binding energies of Au–Au, Au–Se and Bi–Se bonds and the wavenumber of A1g2 and Eg2 modes. Au-decorated Bi2Se3 nanoplatelet heterostructures are observed using FESEM, and confirmed by XPS, Raman spectroscopy, and HRTEM imaging. Their optical band gap of the Au-decorated Bi2Se3 nanoplatelet heterostructures increases with Au thickness about 1.92-fold as much as that of pristine Bi2Se3 (0.39 eV), owing to the Burstein-Moss effect. The optical absorptance of the Au-decorated Bi2Se3 nanoplatelet heterostructures revealed increment with wavelength from 200 to 500 nm and decrement with increasing wavelength from 500 to 800 nm.

The bimodal instability of thermal convection in a tall vertical annulus

We pursue a three-dimensional linear stability analysis to investigate the convective stability in a cylindrical annulus imposed with a horizontal temperature gradient. The investigation focuses on the stability of both axisymmetric and asymmetric modes in a wide range of Prandtl number Pr and the radii ratio η between the inner to outer cylinders. Results show that, for the axisymmetric mode, the stability strongly depends on the Prandtl number. For 0≤Pr≤1.4, the instability sets in as the shear mode that the instability enhances as η increases while it is virtually independent of Pr. The critical Grashof number can be approximated by Grc(η)≈103×4η−0.68+3. For 1.5≤Pr≤12.5, the buoyant mode appears and competes with the shear mode to predominate the stability under various Pr and η, namely, the bimodal instability occurs. The transition between the two modes occurs at the specific radii ratio η1=0.21Pr0.727−0.31. For Pr≥12.6, the shear mode vanishes and the buoyant mode prevails. The asymmetric modes are less prevailing than the axisymmetric mode for small Prandtl numbers, except that the mode of an azimuthal wavenumber equal to 1 becomes dominant in two small regions of η. When the Prandtl number is large, the axisymmetric mode predominates over the asymmetric mode except when η is very small. Otherwise, the asymmetric mode of a larger azimuthal wavenumber is less prevailing.

Estimating dispersion relations of ultrasonic guided waves in bone using a modified matrix pencil algorithm

Guided wave ultrasound technology is well recognized for non-destructive testing. The technology is increasingly applied in bone characterization and imaging to evaluate bone strength and fracture risk. Cortical bone with porous microstructure induces substantial dispersion and attenuation effects on ultrasonic guided waves (UGW). Estimating frequency-dependent propagation characteristics of co-excited wave modes is significant to studying UGW propagation and developing wave-based approaches. This work implements a modified matrix pencil method to simultaneously compute modal wavenumber and attenuation coefficient from dispersive bone UGW signals with improved convergence rate and noise reduction ability. The dispersion estimation is formulated as a matrix pencil or generalized eigenvalue problem with Loewner matrices. The extracted eigenvalues are estimated complex wavevectors, in which the wavenumber and attenuation can be deduced from the real and imaginary components respectively. The performance of the proposed algorithm is demonstrated with low signal-to-noise-ratio synthetic and experimental datasets acquired using axial-transmission measurement settings. The computed dispersive features are validated via comparison with the theoretically calculated dispersion curves by semi-analytical finite-element simulation. The dispersive wave properties are accurately reconstructed in a computationally efficient manner and can be further utilized for bone parametric analyses and subsequently clinical bone health assessment.

Modal added-mass matrix of an elongated flexible cylinder immersed in a narrow annular fluid, considering various boundary conditions. New theoretical results and numerical validation

This paper considers the fluid–structure interaction problem of two coaxial cylinders separated by a thin layer of fluid. The flexible inner cylinder is imposed a small amplitude harmonic displacement corresponding to a dry vibration mode of an Euler–Bernoulli beam, while the external cylinder is rigid. A new theoretical formulation based on the assumption of a narrow fluid annulus is derived to estimate the modal added-mass matrix of the vibrating cylinder. This formulation accounts for the finite length of the flexible cylinder, clearly highlights the effect of the aspect ratio of the vibrating cylinder on the structure of the added-mass matrix, and covers all types of classical boundary conditions in the same theory and can easily be implemented in any numerical computing environment. The diagonal coefficients of the added-mass matrix are shown to increase with the confinement, with the aspect ratio of the flexible cylinder, and are sensitive to the wave-number of the vibration mode. Also importantly, we show that the dry vibration modes generate off-diagonal coefficients that vanish for an infinitely long cylinder. Our theoretical observations are corroborated by an extensive set of CFD numerical simulations, covering all types of classical boundary conditions, different confinement configurations, and different aspect ratios of the vibrating cylinder. The results obtained are presented in graphical form, which can be directly applied in engineering applications.

Carbothioamide Based Pyrazoline Derivative: Synthesis, Single Crystal Structure, DFT/TD-DFT, Hirshfeld Surface Analysis and Biological Studies

In order to develop a potent antifungal agent, a carbothioamide-based pyrazoline derivative (3a) was synthesized. Molecular structure of compound has been confirmed using spectroscopic techniques viz. FT-IR, UV-visible, NMR, Raman spectroscopy, mass spectrometry and single crystal X-ray crystallography. Furthermore, potential antifungal activity of compound 3a was screened against three candida strains such as C. albicans, C. glabrata and C. tropicalis. For antifungal experimental validated by molecular docking study with sterol 14a-demethylase (CYP51) (PDB ID: 5JLC, 5V5Z, 6T1U) by using the Autodock Vina software. Antioxidant assay results suggested that compound possesses good radical scavenging activity against diverse free radical (DPPH). The intercalative mode of interaction of compound with Calf thymus DNA (Ct-DNA) was confirmed from spectroscopic techniques such as UV-vis., fluorescence, cyclic voltammetry and competitive assay using ethidium bromide. B3LYP technique and 6-311 ++ G (d, p) basis set were employed to optimize molecular structure and calculate wavenumbers of normal vibrational modes. A complete depiction of the intermolecular interactions on crystal surfaces is provided by Hirshfeld surface analysis, and fingerprint plots were found. The computed parameters and the experimental bond lengths and bond angles were in good agreement. The chemical shifts of the 1H and 13C-NMR spectra were estimated using the GIAO method and experimental spectra were contrasted. With the aid of the TD-DFT approach and the PCM solvent model, electronic characteristics like UV-Vis (in gas phase, ethanol and DMSO) were examined. The outcomes were then compared to experimental UV-Vis spectra.

Wave Transformation And Air Entrainment By A Harmonically Forced Plunging Jet

It is known that air may be entrained by a plunging jet even when that jet is relatively small and slow, so long as it has significant disturbances. In the current work, harmonic disturbances of controlled frequency and amplitude are used to produce air entrainment. At sufficient frequency and amplitude, the harmonic jet disturbances cause azimuthal subharmonic waves on the plunge pool surface to appear, oscillating at half of the forcing frequency. These subharmonic waves interact with the jet flow to entrain air at lower disturbance amplitudes and jet velocities than previously documented. The dependence of the wave shape and inception criteria on jet parameters, namely frequency and diameter, is investigated, giving results that agree well with past investigations of azimuthal waves driven by surface-piercing bodies. The number of azimuthal wave lobes may be understood as the ratio of the perimeter length of the forced jet and the wavelength of the resulting azimuthal water waves, given by nwaves = Ckf/2rj, where C is the ratio of the wave and jet diameters. In past experiments, C was approximately 1.2, but with much smaller liquid jets, we found that C can be as high as 1.4-2. The volumetric flow rate of entrained air was measured directly, by way of a capture hood, enabling investigation of air entrainment behavior, and it is concluded that the resultant air flow rate is dependent on several factors, including jet frequency, azimuthal wave mode number, jet velocity, and the jet disturbance amplitude. The influence of several of these factors was determined by the use of an effective bubble size parameter, hypothesizing that every wave trough during every wave cycle was equally likely to entrain air, an assumption that appears borne out in fact. This effective bubble size, free of the influences of forcing frequency and wave mode number, was found to depend on the forcing intensity in an approximately linear fashion, at least for forcing amplitudes close to those required for entrainment inception. Jet and wave measurements were conducted using high speed videography, enabling quantitative measurements of the nearjet wave amplitude, as well as the size and spectral nature of the jet disturbances.

Unifying Weak and Strong Charge Correlations within the Random Phase Approximation: Polyampholytes of Various Sequences

We consider the problem of charge correlations in self-coacervate phases of polyampholytes and disordered proteins with different monomer sequences. An analytical approach consistently describing both weak and strong correlations is proposed, which is based on the improvement of the random phase approximation (RPA) by taking into account (i) discreteness of charges in polymer chains and (ii) a finite number of wave modes of the charge density fluctuations. These modifications are an essential element of the particle-to-field transformation. For strong Coulomb interactions, the generalized RPA reproduces the free energy of the strongly correlated Wigner liquid of disjointed charges. The developed theory is applied to describe coil-to-globule transitions in single-chain polyampholytes as a function of the monomer sequence. Comparison with results of molecular simulations confirms that the theory reproduces the observed scaling laws for globule size at weak charge correlations, and in addition, it provides a quantitative description of electrostatic interactions when correlations are strong.

High-resolution modal wavenumber estimation in range-dependent shallow water waveguides using vertical line arrays

Estimation of modal wavenumbers is important for inference of geoacoustic properties and matched field processing in shallow water waveguides. However, it is challenging in a range-dependent environment, because modal content varies locally in response to changes in the environment. Moreover, the scales of the spatial variations in the waveguide may be on the same order as the range aperture required for resolvability of the individual modes. To this end, high-resolution (HR) wavenumber estimation methods have been widely used. In this paper, the matrix pencil and MUSIC algorithms are generalized to geometry involving a synthetic horizontal aperture (SHA) formed by a towed acoustic source and a fixed full-spanning vertical line array (VLA). The performance of the proposed methods is evaluated by simulated data in a noisy shallow water environment. Numerical results show that, when compared with the previous methods, the proposed methods significantly outperform the previous methods in terms of aperture requirement.

Radio Emission of Pulsars. I. Slow Tearing of a Quantizing Magnetic Field

The pulsed radio emission of rotating neutron stars is connected to slow tearing instabilities feeding off an inhomogeneous twist profile within the open circuit. This paper considers the stability of a weakly sheared, quantizing magnetic field in which the current is supported by a relativistic particle flow. The electromagnetic field is almost perfectly force free, and particles are confined to the lowest Landau state, experiencing no appreciable curvature drift. In a charge-neutral plasma, we find multiple branches of slowly growing tearing modes, relativistic analogs of the double-tearing mode, with peak growth rate . Here, B z is the strong (nearly potential) guide magnetic field, J z the field-aligned current density, and is the mode wavenumber normalized by the current gradient scale. These modes are overstable when the plasma carries a net charge, with the real frequency proportional to the imbalance in the densities of positive and negative charges. An isolated current sheet thinner than the skin depth supports localized tearing modes with growth rate scaling as (sheet thickness/skin depth)−1/2. In a pulsar, the peak growth rate is comparable to the angular frequency of rotation, , slow compared with the longitudinal oscillations of particles and fields in a polar gap. The tearing modes experience azimuthal drift reminiscent of subpulse drift and are a promising driver of pulse-to-pulse flux variations. A companion paper demonstrates a Cerenkov-like instability of current-carrying Alfvén waves in thin current sheets with relativistic particle flow and proposes coherent curvature emission by these waves as a source of pulsar radio emission.

Single Hydrophone Passive Source Range Estimation Using Phase-Matched Filter

Algorithms working in mode space instead of directly matching the received complex sound pressure were developed to improve computational efficiency and robustness, but these algorithms may be inconvenient to apply in practice because manual operations are often inevitable when performing modal filtering. Based on a phase-matched filter, an imperfect matching scheme named the modal phase based matched impulse response (MP-MIR) is proposed to estimate the source range rapidly and conveniently with a single hydrophone. The field to be matched is still the received complex sound pressure. The replica field is a sum of several “phase” modes, which can be efficiently and conveniently synthesized merely with the horizontal wavenumbers of normal modes and the source–receiver range. The effectiveness of the proposed MP-MIR was demonstrated in localizing 84 emissions along a weakly range-dependent track at ranges of 2.54–20 km in the South China Sea. Although it was found, from cross-correlation coefficients, that the received signals showed strong variation even between adjacent emissions, MP-MIR outperformed the classical matched impulse response (MIR) with a lower standard deviation in most cases, demonstrating good robustness and potential for practical applications.

Efficient Mode-Coupling Calculation for Constant Depth Ocean with Range-Dependent Sound–Speed Fluctuation

In this paper, a criterion for efficient coupled-mode matrix calculation in a constant depth ocean with range-dependent sound–speed fluctuation is proposed. The usual stepwise coupled mode requires high computational power to calculate the mode-coupling matrix at each interface of the range segment. To reduce the computational complexity, the criterion for selecting appropriate mode pairs, which strongly affects the mode-coupling matrix, is derived from perturbation theory. This criterion determines the effective range of the modal beat wavenumber. Numerical examples indicate that compared with the full calculation of the mode-coupling matrix, for the calculation using the proposed criterion, the computational complexity is significantly reduced, while the accuracies of the mode-coupling matrix and acoustic field are maintained.