Current Issue : April - June Volume : 2015 Issue Number : 2 Articles : 5 Articles
The occurrence of an overlapping signal is a significant problem in performing multiple objects localization. Doppler velocity is\nsensitive to the echo shape and is also able to be connected to the physical properties of moving objects, especially for a pulse\ncompression ultrasonic signal. The expectation-maximization (EM) algorithm has the ability to achieve signal separation. Thus,\napplying the EM algorithm to the overlapping pulse compression signals is of interest. This paper describes a proposed method,\nbased on the EM algorithm, of Doppler velocity estimation for overlapping linear-period-modulated (LPM) ultrasonic signals.\nSimulations are used to validate the proposed method....
The paper presents phase portraits of the autonomous Duffing single-degree-of-freedom system with Coulomb dry friction in\nits ? ? ? parameter space. The considered nonlinearities of the cubic stiffness (?) and Coulomb dry friction (?) are widely used\nthroughout the literature. It has been shown that there can be more than one sticking region in the phase plane. It has also been\nshown that an equilibrium point occurs at the critical combinations of values of the parameters ? and ? which gives rise to zero\neigenvalue of the linearised system. The unstable limit cycle may appear in the case of negative viscous damping (?); ? < 0....
The present work deals with functionally gradedmaterials (FGM) isotropic plates in the neighborhood of the first-order symmetric\nzero group velocity (S1-ZGV) point. The mechanical properties of functionally graded material (FGM) are assumed to vary\ncontinuously through the thickness of the plate and obey a power law of the volume fraction of the constituents. Governing\nequations for the problem are derived, and the power series technique (PST) isemployed to solve the recursive equations.The impact\nof the FGM basic materials properties on S1-ZGV frequency of FGM plate is investigated. Numerical results show that S1-ZGV\nfrequency is comparatively more sensitive to the shear modulus. The gradient coefficient p does not affect the linear dependence of\nZGV frequency fa as function of cut-off frequency fc; only the slope is slightly varied....
Sound scattering by a Janus sphere type is considered. The sphere has two surface zones: a soft surface of zero acoustic impedance\nand a hard surface of infinite acoustic impedance. The zones are arranged such that axisymmetry of the sound field is preserved.\nThe equivalent sourcemethod is used to compute the sound field. It is shown that, by varying the sizes of the softand hard zones on\nthe sphere, a significant reduction can be achieved in the scattered acoustic power and upstreamdirectivity when the sphere is near\na free surface and its soft zone faces the incoming wave and vice versa for a hard ground. In both cases the size of the sphere�s hard\nzone is much larger than that of its soft zone.The boundary location between the two zones coincides with the location of a zero\npressure line of the incoming standing sound wave, thus masking the sphere within the sound field reflected by the free surface or\nthe hard ground. The reduction in the scattered acoustic power diminishes when the sphere is placed in free space. Variations of\nthe scattered acoustic power and directivity with the sound frequency are also given and discussed...
This paper is concerned with the sinking of the Korean naval warship (ROKS Cheonan) and the reported spectra of the seismic\nsignals recorded at the time of the incident. The spectra of seismic signals show prominently amplitude peaks at around 8.5Hz\nand its harmonics. These frequencies were explained with the vibrations of a water column due to an underwater explosion. This\nexplanation is highly doubtful and concerns about its validity have already been raised in the scientific community. In this work\nan alternative explanation is presented: it is shown that the recorded seismic spectra are consistent with the natural frequencies\nof vibrations of a large submarine with a length of around 113 m. This finding raises the possibility that the ROKS Cheonan sunk\nbecause of the collision with a large submarine rather than the explosion of a torpedo or an underwater mine....
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