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Localized modes in inhomogeneous one-dimensional anharmonic lattices
No full textWe present numerical calculations for the determination of localized modes in one-dimensional finite chains of atoms with free ends containing harmonic and quartic anharmonic interactions. By adding step by step the quartic term we can follow the formation of even and odd localized modes arising from the highest harmonic frequency mode. We have studied the role of crystal inhomogeneity by introducing a modification of the fourth-order force constant between neighboring atoms at the center of the chain, where the localized mode has its maximum displacement. For large weakening of this force constant the localized mode develops a double-peaked structure, as has been found in the continuum limit. In the case of asymmetrical local inhomogeneity the localized mode remains stable and moves toward the atom with the inhomogeneity. We also show the existence of anharmonic surface modes localized at the end of the chain
Effects of the cubic vs quartic anharmonicity in gap and surface localized modes of diatomic chains
No full textIn this paper we discuss in detail the gap localized vibrational modes in a diatomic anharmonic chain. We consider a finite (even or odd9 number of particles interacting with nearest neighbours harmonic and cubic and quartic anharmonic force constants. The analysis of the effect of these anharmonic interactions shows that in the gap there are localized modes arising from the top of the acoustic branch with odd parity if they are centerewd on a heavy atom and even parity if they are centered on a light atom. These acoustic gap modes are related to the quartic anharmonicity, while there are localized modes arising from the bottom of the optical branch in presence of cubic anharmonicity. Th optical odd parity modes are centered on a light atom and the even parity modes are centered on a heavy atom. In addition to these gap modes we have found two types of surface modes. One which is remenescent of the surface mode occurring on a finite diatomic harmonic chain and the other entirely due to the anhermonicity
Intrinsic localized modes and their interaction with the plasmon electric field in one- dimensional zinc-blende lattice
No full textIn this paper we study the behavior of a diatomic nonlinear one-dimensional lattice which represents the (111)direction of a zinc-blende three-dimensional crystal. In these nonlinear lattices are present intrinsic localized modes dueto the anharmonicity. These modes lie in the vibrational gap between acoustic and optical linear spectrum. Consideringa highly doped GaN semiconductor we examine the coexistence of the localized modes with the electronic plasmaoscillations. We derive an expression for the plasmon electric field, we study the dynamics of the anharmonic lattice inpresence of this electric field and we calculate the dielectric function of the coupled system. The zeroes of the dielectricfunction give the frequencies of the coupled modes
Intrinsic localized modes in the bulk and at the surface of anharmonic chains
No full textIn this paper we will review recents results relative to localized modes induced by anharmonicity in one-dimensional lattices. We will show that localized modes exists in monoatomic chains with and without a local inhomogeneity in the anharmonic force field. We will compare the discrete and the quasicontinuum intrinsic even and odd localized solutions. This analysis is carried out by taking into account harmonic and quartic anharmonic interactions. We will also present results for the diatomic chains showing the presence of surface modes ad gap modes related to the maximum of the acoustic band. In this analysis will be also studied the effect of the cubic anharmonicity. One of the major effetcs of the cubic anharmonicity is to produce gap modes that split off from the bottom of the optical branch
Theory of surface resonant phonons on the open (110) surface of Silver
No full textRecent time-of-flight measurements have been interpreted in terms of a force-constant model. We show that for phonon waves propagating along the ΓX direction, containing nearest neighbors, it is necessary to introduce a large softening of the lateral surface force constants (40%) in agreement with earlier calculations on the Ag(111) surface
Inhomogeneous one-dimensional anharmonic chains
No full textIn this paper we present numerical calculations of intrinsic localized modes of a monoatomic one-dimensional chain with free ends and quartic anharmonicity. We study in particular the case of even and odd parity modes in presence of an inhomogeneity in the quartic force constants located in the center of the chain to preserve the symmetry of the solutions. In the limit of low anharmonicity we study also the analytical solutions of the Non Linear Schreodinger equation that we obtain from the continuum approximation of the equations of motion
Surface Resonant Phonons of Ag(110)
No full textA study of the dynamics of the Ag(110) surface in the ḡGȲ direction is presented. The experimental TOF spectra show the existence of two low frequency modes with high scattering intensity and a dispersionless high frequency mode with a smaller intensity. The theoretical analysis based on a force constant model that contains long-range central interactions and short-range angular forces explains accurately both the dispersions and the scattering intensities of the three modes in terms of resonant and localized vibrations related to the modifications of the surface force constants caused by the different role played by the many-body forces in the surface region
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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