S U M M A R YWe calculate three dimensional (3-D) sensitivity kernels for fundamental-mode surface wave observables based on the single-scattering (Born) approximation. The sensitivity kernels for measured phases, amplitudes and arrival angles are formulated in the framework of surface wave mode summation. We derive kernels for cross-spectral multitaper measurements; as a special case, the results are applicable to single-taper measurements. Cross-branch modecoupling effects are fully accounted for in the kernels; however, these effects can probably be ignored at the present level of spatial resolution in global phase-delay tomography. The narrowly concentrated spectra of the windows and tapers commonly used in global surface wave studies enable the kernels to be computed extremely efficiently.Surface wave tomography based upon great-circle ray theory has been used with great success during the past three decades to constrain the large-scale 3-D heterogeneity of the lithosphere and upper mantle. While the growing abundance of seismic data promotes progress in retrieving better-resolved images with smaller-scale details, ray theory, upon which most surface wave tomography is based, has its theoretical limitations. Ray theory assumes that the frequency of seismic waves is infinite; thereby, it breaks down whenever the length scale of the heterogeneity is comparable to the characteristic wavelength of the seismic waves. Due to their finite frequency, surface waves are sensitive to 3-D structure off of the source-receiver great-circle ray. An approach beyond ray theory aiming at resolving small-scale structures is required to take into account the finite-frequency effects of surface waves. Recent studies have shown a growing appreciation of the finite-frequency properties of seismic body waves (

Using first principles calculations, we report for the first time that large nearly neutral aromatic molecules, such as naphthalene and anthracene, and small charge-transfer aromatic molecules, such as TCNQ and DDQ, interact more strongly with metallic single-wall carbon nanotubes (SWNTs) versus their semiconducting counterparts as the molecular orientation of DDQ is taken into account. Hence two new mechanisms for separating metallic and semiconducting SWNTs via noncovalent pi-pi stacking or charge-transfer interaction are suggested.

Journal of Geophysical Research, v. 111, n. B4, p. 24 pp, 2006. http://dx.doi.org/10.1029/2005JB003677International audienceWe report global shear-wave velocity structure and radial anisotropy in the upper mantle obtained using finite-frequency surface-wave tomography, based upon complete three-dimensional Born sensitivity kernels. Because wavefront healing effects are properly taken into account, finite-frequency surface-wave tomography improves the resolution of small-scale mantle heterogeneities, especially for deep anomalies that are constrained by the longest-period surface waves. In our finite-frequency model FFSW1, the globally averaged radial anisotropy shows a transition from positive (SH > SV) to negative anisotropy (SV > SH) at about 220 km, consistent with a change in the dominant mantle circulation pattern from predominantly horizontal flow at shallow depths to vertical flow at greater depths. The radial anisotropy beneath cratons and the old Pacific plate agrees well with previous studies. However, our model exhibits a strong negative radial anisotropy at depths greater than 120 km beneath mid-ocean ridges, a feature that is not present in previous upper-mantle models. More interestingly, the depth extent of the ridge anomalies is distinctly different beneath fast- and slow-spreading centers; anomalies beneath fast-spreading centers are stronger, but the strength decreases rapidly below 250 km. In contrast, beneath slow-spreading centers such as the northern Mid-Atlantic Ridge and the Red Sea, anomalies extend down at least to the top of the transition zone. The different depth extent of the ridge anomalies suggests that the primary driving force of slow-spreading seafloor may be different from that of fast-spreading seafloor and that active upwelling beneath slow-spreading ridges may play a major role in the opening of the seafloor

S U M M A R YWe compare traditional ray-theoretical surface-wave tomography with finite-frequency tomography, using 3-D Born sensitivity kernels for long-period, fundamental-mode dispersion measurements. The 3-D kernels preserve sidelobes beyond the first Fresnel zone, and fully account for the directional dependence of surface-wave scattering, and the effects of timedomain tapering and seismic source radiation. Tomographic inversions of Love and Rayleigh phase-delay measurements and synthetic checkerboard tests show that (1) small-scale S-wave velocity anomalies are better resolved using finite-frequency sensitivity kernels, especially in the lowermost upper mantle; (2) the resulting upper-mantle heterogeneities are generally stronger in amplitude than those recovered using ray theory and (3) finite-frequency tomographic models fit long-period dispersion data better than ray-theoretical models of comparable roughness. We also examine the reliability of 2-D, phase-velocity sensitivity kernels in global surface-wave tomography, and show that phase-velocity kernels based upon a forwardscattering approximation or previously adopted geometrical simplifications do not reliably account for finite-frequency wave-propagation effects. 3-D sensitivity kernels with full consideration of directional-dependent seismic scattering are the preferred method of inverting long-period dispersion data. Finally, we derive 2-D boundary sensitivity kernels for lateral variations in crustal thickness, and show that finite-frequency crustal effects are not negligible in long-period surface-wave dispersion studies, especially for paths along continent-ocean boundaries. Unfortunately, we also show that, in global studies, linear perturbation theory is not sufficiently accurate to make reliable crustal corrections, due to the large difference in thickness between oceanic and continental crust.

[1] We simultaneously invert for the velocity and attenuation structure of the North American mantle from a mixed data set: SH wave traveltime and amplitude anomalies, SS wave differential traveltime anomalies, and Love wave fundamental mode phase delays. All data are measured for multiple frequency bands, and finite frequency sensitivity kernels are used to explain the observations. In the resulting SH velocity model, a lower mantle plume is observed to originate at about 1500 km depth beneath the Yellowstone area, tilting about 40°from vertical. The plume rises up through a gap in the subducting Farallon slab. The SH velocity model confirms high-level segmentation of the Farallon slab, which was observed in the recent P velocity model. Attenuation structure is resolvable in the upper mantle and transition zone; in estimating it, we correct for focusing. High-correlation coefficients between dlnV S and dlnQ S under the central and eastern United States suggest one main physical source, most likely temperature. The smaller correlation coefficients and larger slopes of the dlnQ S − dlnV S relationship under the western United States suggest an influence of nonthermal factors such as the existence of water and partial melt. Finally, we analyze the influence of the different components of our data set. The addition of Love wave phase delays helps to improve the resolution of both velocity and attenuation, and the effect is noticeable even in the lower mantle.

ZnS:Mn has been in-filled in photonic crystals of submicron polymer spheres. The effect of the photonic band gap on the photoluminescence (PL) properties of ZnS:Mn has been investigated. Because of the overlap of the transmission dip of the photonic crystal and the photoluminescence band of ZnS:Mn, both suppression and enhancement in the PL of the phosphor have been observed. A strong dependence of the fluorescence lifetime on the emission wavelength in the range of the stop band has been found. This strong dependence is believed to arise from the very low photon density of state within the stop band of the ZnS:Mn in-filled photonic crystal as result of a high dielectric contrast between ZnS:Mn and the polystyrene spheres.

We report the first study of nanoscale integrated photonic devices constructed with semiconductor-insulator-metal strip (SIMS) waveguides for use at telecom wavelengths. These waveguides support hybrid plasmonic modes transmitting through a 5-nm thick insulating region with a normalized intensity of 200-300 μm(-2). Their fundamental mode, unique transmission and dispersion properties are consistent with photonic devices for guiding and routing of signals in communication applications. It has been demonstrated using Finite Element Methods (FEM) that the high performance SIMS waveguide can be used to fabricate deep sub-wavelength integrated plasmonic devices such as directional couplers with the ultra short coupling lengths, sharply bent waveguides, and ring resonators having a functional size of ≈1 µm and with low insertion losses and nearly zero radiation losses.

In this paper, we applied the modal expansion method (MEM) to investigate the wave behaviors inside a step-modulated subwavelength metal slit. The physical mechanism of the surface plasmon polariton (SPP) transmission is investigated in detail for slit structures with either dielectric or geometric modulation. The applicability of the effective index method is discussed. Moreover, as a special case of the geometric modulation, the evanescent-wave assisted transmission is demonstrated in a thin-modulated slit. We emphasize that a complete set is necessary in order to expand the wave functions in these kinds of structures. All the calculated results by the MEM are well retrieved by the finite-difference time-domain calculation.