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231.
We study the modulational instability of periodic traveling waves for a class of Hamiltonian systems in one spatial dimension. We examine how the Jordan block structure of the associated linearized operator bifurcates for small values of the Floquet exponent to derive a criterion governing instability to long wavelengths perturbations in terms of the kinetic and potential energies, the momentum, the mass of the underlying wave, and their derivatives. The dispersion operator of the equation is allowed to be nonlocal, for which Evans function techniques may not be applicable. We illustrate the results by discussing analytically and numerically equations of Korteweg‐de Vries type. 相似文献
232.
We propose a shallow water model that combines the dispersion relation of water waves and Boussinesq equations, and that extends the Whitham equation to permit bidirectional propagation. We show that its sufficiently small and periodic traveling wave is spectrally unstable to long wavelength perturbations if the wave number is greater than a critical value, like the Benjamin‐Feir instability of a Stokes wave. We verify that the associated linear operator possesses infinitely many collisions of purely imaginary eigenvalues, but they do not contribute to instability to the leading order in the amplitude parameter. We discuss the effects of surface tension. The results agree with those from a formal asymptotic expansion and a numerical computation for the physical problem. 相似文献
233.
Nguyen-Phan TD Pham VH Kweon H Chung JS Kim EJ Hur SH Shin EW 《Journal of colloid and interface science》2012,367(1):139-147
Reduced graphene oxide-TiO(2) hybrids were successfully prepared by the hydrothermal approach using triethanolamine and acetylacetone as the chelating agents. Without any additive, large aggregated TiO(2) clusters were randomly distributed dominantly at the edge and less on the basil plane of coagulated reduced graphene oxide (RGO) layers. The presence of chelating ligands remarkably facilitated the selective growth and regular spread of TiO(2) nanocrystals onto individually exfoliated RGO sheet. Such sandwich-like structure with stronger coupling and chemical interaction resulted in the surface area increase, the rearrangement of energy level, the enhanced concentration of oxygen vacancies, leading to much higher adsorbability and photocatalytic degradation of Rhodamine B under both UV and visible irradiations. These RGO-TiO(2) hybrid systems are potentially beneficial for widely practical applications in air/water purification, electronic devices, batteries, solar cells or supercapacitors. 相似文献
234.
Nguyen Dang Luong Joonsuk Oh Youngkwan Lee Ji Hyun Yeon Jaehuyn Hur Jong Jin Park Jong Min Kim Jae‐Do Nam 《Surface and interface analysis : SIA》2012,44(3):318-321
In this study, the surface plasmon effect of Au nanoparticles was successfully realized in the solid state by embedding the Au nanoparticles on the surface of the transparent polymer fibers for the first time. Electrospinning a poly(methyl methacrylate) (PMMA) and HAuCl4 mixture followed by a wet chemical reduction, the gold nanoparticles were formed on the PMMA nanocomposite electrospun fibers in a well‐distributed manner to give photostable purple color. The Au nanoparticles were all sphere shaped with an average diameter of 12 nm. Specifically, simply adjusting HAuCl4 salt concentration in the electrospinning solution, it is able to control the electrospun fiber diameter and gold nanoparticle content in the resulting PMMA/Au nanocomposite fibers. Therefore, the developed method described herein is simple and effective for the large volume production of PMMA/Au nanocomposite fibers. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
235.
The quantum dynamics of atoms subjected to pairs of closely spaced delta kicks from optical potentials are shown to be quite different from the well-known paradigm of quantum chaos, the single delta-kick system. We find the unitary matrix has a new oscillating band structure corresponding to a cellular structure of phase space and observe a spectral signature of a localization-delocalization transition from one cell to several. We find that the eigenstates have localization lengths which scale with a fractional power L approximately h(-0.75) and obtain a regime of near-linear spectral variances which approximate the "critical statistics" relation summation2(L) approximately or equal to chi(L) approximately 1/2 (1-nu)L, where nu approximately 0.75 is related to the fractal classical phase-space structure. The origin of the nu approximately 0.75 exponent is analyzed. 相似文献
236.
We have synthesized various half doped lanthanum perovskites (BB′=MnV, MnCr, MnCo, MnNi, FeCr, FeMn, FeCo, FeNi) by solid state reaction method. The crystal structure was orthorhombic in all samples, but the magnetic and transport properties showed a large variation with the composition. A ferromagnetic feature was quite strong in the Mn-based perovskites but weak or non-existent in the Fe-based ones. The resistivity of Ni-doped ones was much smaller than those of the others. For all half doped perovskits, remarkably, the temperature dependent transport was well explained by variable range hopping model with different localization lengths. 相似文献
237.
Song HM Hong JH Lee YB Kim WS Kim Y Kim SJ Hur NH 《Chemical communications (Cambridge, England)》2006,(12):1292-1294
A new single source approach was developed to synthesize face-centered tetragonal (fct) FePt nanoparticles using bimetallic compound (CO)3Fe(mu-dppm)(mu-CO)PtCl2, which has been characterized by single crystal X-ray diffraction and was used as the precursor to ensure the accurate stoichiometry of the final FePt product; the ability of the molecular complex to act as a single source precursor for the formation of fct FePt nanocrystals with an average diameter of 3.2 nm has been demonstrated. 相似文献
238.
Enhanced photocatalytic activity in composites of TiO2 nanotubes and CdS nanoparticles 总被引:4,自引:0,他引:4
Kim JC Choi J Lee YB Hong JH Lee JI Yang JW Lee WI Hur NH 《Chemical communications (Cambridge, England)》2006,(48):5024-5026
A new composite consisting of TiO(2) nanotubes and CdS nanoparticles, where CdS particles bind covalently to the titania surface through a bifunctional organic linker, was successfully fabricated; this titania nanotube-based composite shows enhanced photocatalytic activity under visible-light irradiation. 相似文献
239.
Zinc oxide-layered titanate nanohybrids with a 1 ratio 1 ordered heterostructure have been successfully synthesized by reassembling exfoliated titanate nanosheets in the sol solution of zinc acetate under hydrothermal conditions. 相似文献
240.
MJ Gim ST Hur KW Park M Lee SW Choi H Takezoe 《Chemical communications (Cambridge, England)》2012,48(80):9968-9970
We have succeeded in obtaining a photoinduced liquid crystalline cubic BP in a mixture of photoinactive and photoresponsive bent-core mesogens. The UV stimulus can convert N* to cubic BP through photoisomerization of the azobenzene linkages included in the photoresponsive bent-core molecule. 相似文献