The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Zhi-qiang Wang - One of the best experts on this subject based on the ideXlab platform.
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spherical semiclassical states of a Critical Frequency for schrodinger equations with decaying potentials
Journal of the European Mathematical Society, 2006Co-Authors: Jaeyoung Byeon, Zhi-qiang WangAbstract:For singularly perturbed Schrodinger equations with decaying potentials at infinity we construct semiclassical states of a Critical Frequency concentrating on spheres near zeroes of the potentials. The results generalize some recent work of Ambrosetti-Malchiodi-Ni[3] which gives solutions concentrating on spheres where the potential is positive. The solutions we obtain exhibit different behaviors from the ones given in [3].
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standing waves with a Critical Frequency for nonlinear schrodinger equations ii
Calculus of Variations and Partial Differential Equations, 2003Co-Authors: Jaeyoung Byeon, Zhi-qiang WangAbstract:For elliptic equations of the form $\Delta u -V(\varepsilon x) u + f(u)=0, x\in {\bf R}^N$ , where the potential V satisfies $\liminf_{\vert x\vert\to \infty} V(x) > \inf_{{\bf R}^N} V(x) =0$ , we develop a new variational approach to construct localized bound state solutions concentrating at an isolated component of the local minimum of V where the minimum value of V can be positive or zero. These solutions give rise to standing wave solutions having a Critical Frequency for the corresponding nonlinear Schrodinger equations. Our method allows a fairly general class of nonlinearity f(u) including ones without any growth restrictions at large.
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Standing Waves with a Critical Frequency for Nonlinear Schrödinger Equations
Archive for Rational Mechanics and Analysis, 2002Co-Authors: Jaeyoung Byeon, Zhi-qiang WangAbstract:This paper is concerned with the existence and qualitative property of standing wave solutions \(\) for the nonlinear Schrodinger equation \(\) with E being a Critical Frequency in the sense that \(\). We show that there exists a standing wave which is trapped in a neighbourhood of isolated minimum points of V and whose amplitude goes to 0 as \(\). Moreover, depending upon the local behaviour of the potential function V(x) near the minimum points, the limiting profile of the standing-wave solutions will be shown to exhibit quite different characteristic features. This is in striking contrast with the non-Critical Frequency case \(\) which has been extensively studied in recent years.
Xifu Wang - One of the best experts on this subject based on the ideXlab platform.
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Wave propagation in carbon nanotubes under shear deformation
Nanotechnology, 2006Co-Authors: K Dong, Xifu WangAbstract:This paper reports the results of an investigation on the effect of shear deformations on wave propagation in carbon nanotubes embedded in an elastic matrix. A multi-walled carbon nanotube is considered as a multiple shell coupled together through van der Waals forces between two adjacent tubes. The surrounding matrix is considered as a spring element defined by the Winkler model. Using the variational calculus of Hamilton's principle, dynamic governing equations considering the shear deformation and rotary inertia terms are derived. Numerical examples describe the effects of shear deformation, rotary inertia and elastic matrix on the velocity, the Critical Frequency, the cut-off Frequency and the amplitude ratio of wave propagation in multi-walled carbon nanotubes embedded in an elastic matrix, respectively. The results obtained show that wave propagation in carbon nanotubes appears in a Critical Frequency or a cut-off Frequency for different wave modes; the effect of shear deformation decreases the value of Critical Frequency; the Critical Frequency increases as the matrix stiffness increases; the inertia rotary has an obvious influence on the wave velocity for some wave modes in the higher Frequency region.
K. Renji - One of the best experts on this subject based on the ideXlab platform.
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Critical Frequencies of Composite Cylindrical Shells
The International Journal of Acoustics and Vibration, 2020Co-Authors: K. Renji, S. Josephine Kelvina FlorenceAbstract:The sound radiation characteristics of a structure depend on its Critical Frequency. The expression for theoretically estimating the Critical Frequency of a composite cylindrical shell has not yet been reported. Thus, the practice is to use the expression for the composite panel for determining the Critical Frequency of a composite shell. In this work, Critical frequencies of composite shells are investigated. As the Critical Frequency depends on the speed of the bending wave, an expression for the speed of the bending wave is first derived. It is seen that the curvature causes an increase in the speed of the bending wave and the orthotropic nature of the cylinder reduces the speed. An expression for the Critical Frequency of a composite cylindrical shell is then derived. The curvature causes a reduction in the Critical Frequency and the influence is significant in acoustically thick cylinders. Hence, the Critical frequencies of such cylinders cannot be determined by using the expression for the panels. Effects of transverse shear deformation on the speed of the bending wave as well as the Critical Frequency are then investigated. Transverse shear deformation causes both reduction in the speed of the bending wave and an increase in the Critical Frequency. The orthotropic nature of the cylindrical shell increases the Critical Frequency further. The Critical Frequency of a typical composite cylinder is determined through a numerical simulation and the results are in agreement with the results obtained using the expressions derived. The Critical Frequency of a typical composite cylinder obtained through an experiment is presented. With this work, expressions for theoretically estimating the speeds of the bending waves and Critical frequencies are derived for a composite cylindrical shell considering transverse shear deformation.
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Modal density and Critical Frequency of composite panels considering transverse shear deformation and rotary inertia
Journal of Vibration and Control, 2020Co-Authors: K. RenjiAbstract:In this work, expressions for estimating the modal density, speed of the bending wave, Critical Frequency and coincidence Frequency of panels are derived considering orthotropic properties of the f...
Frédéric Ouattara - One of the best experts on this subject based on the ideXlab platform.
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Effects of Height of F2-Layer on Critical Frequency by Use of Data at Ouagadougou Station
Applied Physics Research, 2018Co-Authors: Emmanuel Nanema, Moustapha Konate, Doua Allain Gnabahou, Frédéric OuattaraAbstract:Ionosphere investigation leads to the knowledge of its composition in particles. The particle density and composition determine the capacity of this region to reflect radio waves in the atmosphere at different heights. Some variables such as season, solar cycle phase also influence the ionosphere behavior. Radio waves frequencies pass through the ionosphere layer without reflection above a Critical value determining the Critical Frequency. This study determines the Critical Frequency of radio waves in the F2 layer (foF2) of the ionosphere by use of data at Ouagadougou station during the minimum and the maximum of solar cycle 22, at different seasons with the height of F2-layer (hmF2). Daytime and nighttime also influence ionosphere parameters. The study presents the hourly behavior of foF2 according to hmF2 values.
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Electron Bulk Surface Density Effect on Critical Frequency in the F2-Layer
International Journal of Geosciences, 2018Co-Authors: Emmanuel Nanema, Issaka Ouedraogo, Christian Zoundi, Frédéric OuattaraAbstract:Ionosphere layer is the atmosphere region which reflects radio waves for telecommunication. The density in particles in this layer influences the quality of communication. This study deals with the effects of Total Electron Contents (TEC) on the Critical Frequency of radio waves in the F2-layer. Total Electron Contents parameter symbolizes electron bulk surface density in ionosphere layer. Above Critical Frequency value in F2 layer (foF2), radio waves pass through ionosphere. The knowledge of this value enables to calibrate transmission frequencies. In this study, we consider TEC effects on foF2 under quiet time conditions during the maximum and the minimum of solar cycle 22, at Ouagadougou station, in West Africa. The study also considers the effects of seasons and the hourly variability of TEC and foF2. This work shows winter anomaly on foF2 and TEC on minimum and maximum of solar cycle phase respectively. Running International Reference Ionosphere (IRI) model enables to carry out the effects of TEC on foF2 by use of their monthly average values. This leads to a new approach to calibrate radio transmitters.
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Statistical study of the equatorial F2 layer Critical Frequency at Ouagadougou during solar cycles 20, 21 and 22, using Legrand and Simon's classification of geomagnetic activity
Journal of Space Weather and Space Climate, 2012Co-Authors: Frédéric Ouattara, Christine Amory-mazaudierAbstract:This paper presents the statistical analysis of the diurnal variations of the F layer at the equatorial station of Ouagadougou (Lat: 12.4 N; Long: 358.5 E; dip: 5.9 ) from 1966 to 1998 (=> ~11 680 days). We consider three main factors of variability: (1) the season (spring, summer, autumn and winter), (2) the phase of the sunspot cycle (ascending, maximum, descending and minimum) and (3) the geomagnetic activity classified by Legrand and Simon in four groups: slow solar wind, high solar wind streams, fluctuating solar wind and shock activity. We easily identify the influence of the solar wind speed and shock activity on the diurnal pattern of the F layer. Shock and recurrent activities tend to enhance or diminish the morning or afternoon maximum of the F2 layer Critical Frequency. The difference of the diurnal foF2 variation during the increasing and decreasing phases of the sunspot solar cycle is explained by different solar wind regimes. The slow solar wind dominates during the increasing phase of the sunspot cycle and the fluctuating solar wind dominates during the decreasing phase of the sunspot cycle. This paper demonstrates that it is possible using a large database, to bring up significant morphologies of the diurnal variation of the foF2 Critical Frequency as a function of (1) different solar events such as quiet solar wind, fluctuating wind, recurrent high stream wind and Coronal Mass Ejections (CMEs); (2) solar cycle phases and (3) seasons. It is an approach directly connecting the Critical Frequency of the F2 layer to the solar parameters.
Christine Amory-mazaudier - One of the best experts on this subject based on the ideXlab platform.
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Statistical study of the equatorial F2 layer Critical Frequency at Ouagadougou during solar cycles 20, 21 and 22, using Legrand and Simon's classification of geomagnetic activity
Journal of Space Weather and Space Climate, 2012Co-Authors: Frédéric Ouattara, Christine Amory-mazaudierAbstract:This paper presents the statistical analysis of the diurnal variations of the F layer at the equatorial station of Ouagadougou (Lat: 12.4 N; Long: 358.5 E; dip: 5.9 ) from 1966 to 1998 (=> ~11 680 days). We consider three main factors of variability: (1) the season (spring, summer, autumn and winter), (2) the phase of the sunspot cycle (ascending, maximum, descending and minimum) and (3) the geomagnetic activity classified by Legrand and Simon in four groups: slow solar wind, high solar wind streams, fluctuating solar wind and shock activity. We easily identify the influence of the solar wind speed and shock activity on the diurnal pattern of the F layer. Shock and recurrent activities tend to enhance or diminish the morning or afternoon maximum of the F2 layer Critical Frequency. The difference of the diurnal foF2 variation during the increasing and decreasing phases of the sunspot solar cycle is explained by different solar wind regimes. The slow solar wind dominates during the increasing phase of the sunspot cycle and the fluctuating solar wind dominates during the decreasing phase of the sunspot cycle. This paper demonstrates that it is possible using a large database, to bring up significant morphologies of the diurnal variation of the foF2 Critical Frequency as a function of (1) different solar events such as quiet solar wind, fluctuating wind, recurrent high stream wind and Coronal Mass Ejections (CMEs); (2) solar cycle phases and (3) seasons. It is an approach directly connecting the Critical Frequency of the F2 layer to the solar parameters.