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The low-frequency acoustic dynamics of multilayer graphene flakes, on SiO 2 /Si substrate, have been studied by polarized Brillouin light scattering. Interference enhancement affords the first observation of both the in-plane longitudinal and transverse acoustic bulk modes near the Γ-point of the Brillouin zone. The experimental data yielded information on the acoustic and elastic properties of multilayer graphene. Additionally, the measured phonon dispersion is found to be in good accordance with that evaluated for graphene, based on first-principles calculations within the generalized gradient approximation. Our findings strongly suggest that the interaction between layers in multilayer graphene is weak.

Regular arrays of oval-shaped permalloy nanorings have been fabricated using deep ultraviolet lithography and their spin dynamics measured by Brillouin light scattering with the magnetic field applied along long (easy) axes of the rings. The dispersionless behavior of the spin wave modes observed reveals their standing wave nature. Two-dimensional simulations and analytical calculations have been performed for a single isolated nanoring. Results reveal that the observed modes can be interpreted in terms of quantized Damon–Eshbach modes due to lateral confinement in the finite size rings.

We present our simulated initial magnetization curves for nanostructured permanent magnets based on a simple hybrid model. The model assumes that the reversible change in the magnetization curves obeys the Stoner–Wohlfarth (SW) model while the irreversible part can be attributed to the motion of the transition region (TR), which is a domain-wall-like magnetic moment distribution formed in the grain boundary due to exchange interaction between neighboring grains with different easy axis orientations. The calculated full hysteresis coercivity Hcm (=0.14HK) is in reasonable agreement with available experimental data, where HK is the anisotropy field. Both the calculated remanence Mr and coercivity Hc increase rapidly with the maximum applied field Hm at lower field (Hm

The particle-size dependence of the eigenfrequencies of confined acoustic modes of aggregates of highly monodisperse silver nanocubes has been measured by Brillouin light scattering. Four Brillouin peaks are observed whose frequencies scale with inverse cube edge length. They are assigned to the D d 1 , D d 2 , D s 1 (symmetric breathing vibration) and D s 2 dilatational modes, labeled using the Demarest classification scheme. The assignment, which is based on numerically simulated frequencies and displacement profiles of the modes, as well as their calculated scattering cross-sections, differs from those of earlier studies on nanocubes. The elastic moduli of the silver cubes, with mean edge lengths between 59–102 nm, are found to be comparable to those of the bulk material, indicating the absence of sample defects like pores and cracks.

MnSb(1 0 1) thin films with different thicknesses have been successfully epitaxied on GaAs(1 0 0) substrates by the hot-wall epitaxy method. The effects of substrate-induced lattice strains on the structural, magnetic and magneto-optical properties of these films have been studied. It was found that the coercivity of the film increases (and the saturation magnetization decreases) with decreasing film thickness. Measurements of the Kerr rotation angle were made using a home-made magnetic optical Kerr effect system. The Kerr rotation angle increases with film thickness but no measurable angle is observed when the film thickness is about 27 nm. The shape of the Kerr rotation curve is found to be similar to the magnetic hysteresis loop measured by a vibrating sample magnetometer.

Based on a simple micromagnet model, we show that an analytical expression for reduced remanence in single-phased and single-domain isotropic nanostructured permanent magnetic materials can be written as Mr/MS=0.5+1.8Δ0/L, where M r , M S , Δ 0 , and L are the remanence, saturation magnetization, exchange length and the average grain size, respectively. This formula reveals that our calculated remanence is larger than the predictions of the Stoner–Wohlfarth model for all particle sizes, and that remanence enhancement increases with decreasing grain size. Application of the relation to melt-spun Nd–Fe–B magnets shows good agreement with available experimental and numerical data.

The elastic vibrations of spherical nanoparticles have been widely studied by Raman scattering. However, there exist more than one set of selection rules for Raman scattering from these vibrations. For instance, Kanehisa has stated that only torsional modes with angular momentum l = 2 are Raman-active, while Tanaka et al. proposed that spheroidal modes of even l and torsional modes of odd l are Raman-active. These contradict selection rules of Duval which states that only spheroidal modes of l = 0 or 2 are Raman-active. Our present calculations based on a macroscopic model show that all torsional modes have vanishing intensity in the Raman spectrum.

Quenching of a liquid Pb droplet containing 8217 atoms to T ∼ 0.65 T m is studied on the nanosecond time scale using molecular dynamics and a “glue” force model. Crystallization takes place, and analysis of the final structure reveals an icosahedral-like shape, even if cuboctahedral single crystal structures are energetically favoured by our potential for all sizes. This result appears to be a consequence of the rapid formation of {111} crystallization fronts at the liquid surface and moving inward, and provides an explanation for the rapid structural fluctuations observed in electron microscopy experiments.

The large errors observed in inverse filter or Wiener filter restorations of images are mainly due to the fact that only a truncated region of image data is available for processing. In the earlier literature, it was suggested that the well-known time-series windows may be generalized for treating these errors. This paper examines the windowing technique for the restoration of general blurred images. Mathematical expressions for the restoration errors that arise from truncated data are derived. Optimal windows for image restoration are then designed on the basis of these expressions. With these optimal windows, near-perfect restorations can be obtained if the images vary gradually in intensity near their borders. Restorations using the optimal windows and some well-known time-series analysis windows are presented for comparison of their performance.

On the basis of a previous analysis of the edge error in image restorations by the authors, two new classes of Fourier-domain restoration methods for motion-blurred images are proposed in this paper. In the spectral interpolation methods, the restoration problem is reduced to the estimation of a number of indeterminate spectral coefficients of the image. If we require that the restored image have the smallest possible variance, all the indeterminate spectral coefficients may be set to zero. Even such a simple implementation of the spectral interpolation method proves to be equivalent to the sophisticated spatial-domain method proposed by Sondhi. This suggests that the spectral interpolation method has great potential when used in conjunction with appropriate sophisticated methods for the interpolation of spectral coefficients. In the pixel difference interpolation method, a restoration is computed on the basis of the estimates of the differences in the intensity of adjacent pixels. A characteristic of this method is that we have the freedom to choose the locations at which the estimates are to be made. For images with patches of uniform intensity, the pixel differences within the regions of uniform intensity are small and can be accurately estimated. This fact may be exploited to obtain near-perfect restoration of such images, as demonstrated in actual restorations of test images. Even for highly textured images, restorations obtained using this method are found to be of a quality comparable to those obtained using Sondhi's and Ku and Hu's methods.

Estimating the PSF of a real-world motion-blurred image is an essential step in the restoration process. To estimate the PSF, some techniques assume that it is a spatially invariant square pulse, and extract the blur extent from the zero-crossings of the averaged power spectrum. Some techniques make use of special features such as isolated point objects or sharp edges in a homogeneous background. Recently, sophisticated methods based on maximum likelihood estimators have been developed for estimation of symmetrical PSFs. In actual applications, we often encountered motion-blurred images which have asymmetrical PSFs. There are also no special features such as isolated points. These images present challenges which are not satisfactorily met by the above techniques. In this paper, we first study the error characteristics due to the use of inappropriate PSFs. On the basis of the results, we develop a procedure for estimating (possibly) asymmetrical PSFs of real-world motion-blurred images. The procedure starts with a preliminary restoration using a ramp PSF. The result will indicate if a ramp PSF, a square pulse PSF, or a trapezoid PSF is appropriate, and also provide an estimate for the blur extent of the appropriate PSF. Images restored according to the procedure are practically free of ghost or ringing patterns. The effectiveness and practicality of the proposed procedure is tested using a few real-world images blurred with unknown PSF.