Mono-coupled periodic systems with a single disorder: Response to convected loadings

This paper presents a general theory of the forced response under convected loading of mono-coupled periodic systems with a single disorder. The general expressions derived have been used to study the response of an infinite periodic beam on simple supports with one of the support spacings different from all the others. Convected harmonic pressure fields and frozen random pressure fields have been considered. Computer studies are presented showing the moment response at supports and the space-time-averaged responses in the disorder and in the nearby periodic beam elements. High response levels can occur due to (i) resonances of the beam length disorder against the stiffness of the attached periodic systems and (ii) hydrodynamic coincidence vibration occurring in the periodic beam. The frequency zones in which these high responses may occur are identified. The high response due to the resonance (ii) is restricted to the vicinity of the disorder, whereas that due to coincidence occurs throughout the system. Computed results show that the highest response levels do not necessarily occur in the beam length disorder, but may occur in one of the nearby periodic beam elements. The dependence of the maximum response levels on the magnitude of the disorder has been investigated. The conditions under which small disorders may be neglected have been pointed out.     

Exact solution of resonant modes in a rectangular resonator

The resonant modes of rectangular two-dimensional optical resonators were analyzed exactly. Based on the characteristics of the Bessel function, the resonant frequencies of the rectangular microcavities are expressed in a simple way. In addition, a simple rule to judge when the finite length of a rectangular resonator can be considered infinite is given in realistic applications. The solution that is presented should be useful in possible applications of the rectangular resonators as filters for dense wavelength-division multiplexing.     

Forcing and control of localized states in optical single feedback systems

Under feedback extended nonlinear optical systems spontaneously show a variety of periodic patterns and structures. Control gives new insight into these phenomena and it can open the way for potential application of nonlinear optical structures. We briefly review methods to control localized states in single feedback experiments. Application of a Fourier control method allows to modify interaction behavior of the localized states. As a further approach we study a forcing method, using externally created light fields as additional input to the system. Recent experiments show that the forcing method enables to favor addressing positions for localized structures. We demonstrate static addressing and favoring of addressing positions. We extend the forcing method to a dynamic forcing scheme, which allows to move and reposition localized states. Additionally forcing is used to balance experimental imperfections. PACS 05.45.Gg; 42.60.Jf; 42.65.Tg     

Long-range surface plasmon polariton modes with a large field localized in a nanoscale gap

A planar five-layer waveguide with a metal-insulator (with the low permittivity)-metal structure embedded in a high-permittivity dielectric is theoretically studied. A long-range surface mode draws special attention because of its superior properties of low attenuation and a large field localized inside the nanoscale middle gap provided with permittivity-contrast. Effects of the surrounding permittivity and the metal film thickness are investigated, and the electric field amplitude in the gap can be dozens of times higher than that at the outer interfaces. This plasmonic structure may have potential applications in integrated photonic devices.     

Controlled switching of intrinsic localized modes in a one-dimensional antiferromagnet

Nearly-steady-state locked intrinsic localized modes (ILMs) in the quasi-1D antiferromagnet (C(2)H(5)NH(3))(2)CuCl(4) are detected via four-wave mixing emission or the uniform mode absorption. Exploiting the long-time stability of these locked ILMs, repeatable nonlinear switching is observed by varying the sample temperature, and localized modes with various amplitudes are created by modulation of the microwave driver power. This steady-state ILM locking technique could be used to produce energy localization in other atomic lattices.     

Nonlinear localized modes in bandgap microcavities

We study experimentally an electrically pumped GaAs-based bandgap structure based on a vertical cavity surface emitting laser (VCSEL). We demonstrate that a microcavity embedded into this bandgap VCSEL structure supports localized optical modes without any holding beam. We propose a model of surface-structured VCSELs based on a reduced dissipative wave equation for describing electromagnetic modes in such semiconductor cavities and analyze a crossover between linear and nonlinear solitonlike cavity modes.     

Strongly localized states in a single carbon nanotube with polymer molecules

A single-walled carbon nanotube (SWCNT) with conjugated polymer molecules is analyzed via optical spectroscopy. The presence of strongly localized excitonic states in the SWCNT is confirmed using time-integrated photoluminescence (PL). The PL spectrum exhibits extremely narrow width (~0.8 meV) which is attributed to the strong confinement of the states by polymer molecules. In addition, I observed that the excited states are gradually filled as a function of the excitation power, which supports the localized excitonic behavior. Only the ground excitonic state is observed at low excitation powers, but three additional PL peaks appear as the excitation power is increased. Especially, the power-dependent PL spectrum shows a blueshift and increased width, which can be elucidated in terms of quantum confined stark effect and the screening of induced electric fields. Overall, I demonstrate that the presence of polymer molecules induces several localized states in a single SWCNT.     

Solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain

By use of the Hartree approximation and the method of multiple scales, we investigate quantum solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain. It is shown that there exist solitons of two different quantum frequency bands: i.e., magnetic optical solitons and acoustic solitons. At the boundary of the Brillouin zone, these solitons become quantum intrinsic localized modes: their quantum eigenfrequencies are below the bottom of the harmonic optical frequency band and above the top of the harmonic acoustic frequency band.     

具有格点各向异性的一维铁磁链中的量子孤子和内禀局域模(英文)

基于Hartree-Fock方法和多标度方法,我们考察了具有格点各向异性的一维铁磁链中的量子孤子和内禀局域模,量子磁振子的波函数由量子包络孤子来描述.在布里渊区边界,量子包络孤子变成了量子内禀局域模,它的量子本征频率在简谐波带的顶部上方,量子磁振子主要集中在中心位置j=j0的附近.     

Magnon modes localized on defects in a two-dimensional array of magnetic microparticles with transverse anisotropy

The high-frequency properties of planar arrays of small ferromagnetic particles with point or linear defects have been investigated. The limiting cases of defects with localized lattice imperfections and with a long-range interaction caused by the magnetic dipole–dipole interaction have been considered. General conditions of the emergence of magnon modes localized on defects of various natures have been found. These conditions for an attractive defect differ considerably from those known in quantum mechanics for a particle localized in a potential well.     

Exact results of statistical analysis of multichannel adaptive systems with continuous gradient algorithms

We obtained some exact expressions for the power of the output signal of adaptive systems with continuous gradient adjustment algorithms. It is shown that fluctuations of weight coefficients result in a decrease in the signal power at the adaptive-system output as compared with the output-signal power in the absence of fluctuations of the weight coefficients. The “overcompensation” phenomenon is explained by the presence of a non-Gaussian statistical relation between the weight- coefficient and input-signal vectors. N. I. Lobachevskii State University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 9, pp. 914–921, September, 1999.     

Localization of vibrational modes in a layered lattice with diagonal and off-diagonal disorder

This paper discusses the possibility of weak localization of the phonon modes in a nonideal harmonic crystal lattice whose separate layers are weakly coupled to each other. An expression is obtained for the diffusivity tensor. The role of inverse coherent scattering processes is studied. It is established that, when such processes occur under conditions of strong diagonal disorder in the region of relatively low frequencies, where the dispersion law of the phonon modes exhibits two-dimensional properties, substantial renormalization of the diffusivity can take place. The paper analyzes the situation that occurs under conditions of off-diagonal disorder when resonant-scattering impurity centers are present in the lattice. The question of the possible nature of the low-temperature plateau in the thermal conductivity of the complex crystals BSCCO and BSYCO is discussed. Zh. éksp. Teor. Fiz. 113, 930–954 (March 1998)     

Moving nonlinear localized vibrational modes for a one-dimensional homogenous lattice with quartic anharmonicity

Moving nonlinear localized vibrational modes (i.e. discrete breathers) for the one-dimensional homogenous lattice with quartic anharmonicity are obtained analytically by means of a semidiscrete approximation plus an integration. In addition to the pulse-envelope type of moving modes which have been found previously both analytically and numerically, we find that a kink-envelope type of moving mode which has not been reported before can also exist for such a lattice system. The two types of modes in both right- and left-moving form can occur with different carrier wavevectors and frequencies in separate parts of the plane. Numerical simulations are performed and their results are in good agreement with the analytical predictions. Received 13 October 1999 and Received in final form 15 May 2000     

Chain length dependence of localized vibrational modes around a soliton in trans-polyacetylene

Vibrational frequencies of finite polyacetylene with a charged soliton are calculated using the molecular orbital method. It is found that the frequency of the translational mode has a remarkable length effect and is inversely proportional to the square of chain length. The dependence is explained by regarding the soliton as a quantum particle in a one dimensional box.     

Observation of locked intrinsic localized vibrational modes in a micromechanical oscillator array

The nonlinear vibrational properties of a periodic micromechanical oscillator array have been measured. For sufficiently large amplitude of the driver, the optic mode of the di-element cantilever array becomes unstable and breaks up into excitations ranging over only a few cells. A driver-induced locking effect is observed to eternalize some of these intrinsic localized modes so that their amplitudes become fixed and the modes become spatially pinned.     

在一维均匀铁磁链中磁振动的内禀局域模

利用多标度方法和准离散近似,我们考察了在一维均匀铁磁链中磁振动的内禀局域模; 结果表明磁振动的内禀局域模在许多方面都与晶格振动的内禀局域模相类似;它们是近邻自旋之间非线性相互作用的结果.这种内禀局域模的存在并没有破坏系统的平移对称性,它们能在任何晶格位被激发.它们的量子本征频率在简谐磁振动频带的上方.