Jianwei Ma

Curvelet-Based Snake for Multiscale Detection and Tracking of Geophysical Fluids

Detection and target tracking have an application to many scientific problems. The approach developed in this paper is motivated by the applications of detection and tracking characteristic deformable structures in geophysical fluids. We develop an integrated detection and tracking method of geophysical fluids based on a discrete curvelet representation of the information characterizing the targets. Curvelets are in some sense geometric wavelets, allowing an optimal sparse representation of two-dimensional piecewise continuous objects with C 2-singularities. The proposed approach first identifies a consistent vortex by a curvelet-based gradient-vector-flow snake and then establishes the motion correspondence of the snaxels between successive time frames by a constructed so-called semi-T or comp-T multiscale motion-estimation method based on the geometric wavelets. Furthermore, a combination of total-variation regularization and cycle-spinning techniques effectively removes false matches and improves significantly the estimation. Numerical experiments at each stage demonstrate the performance of the proposed tracking methodology for temporal oceanographic satellite image sequences corrupted by noise, with weak edges and submitted to large deformations, in comparison to conventional methods

Multiferroic properties of Bi0.87La0.05Tb0.08FeO3 ceramics prepared by spark plasma sintering

Dense Bi0.87La0.05Tb0.08FeO3 ceramics were prepared by spark plasma sintering. The sample showed stable dielectric constant and low dielectric loss (∼5%), and a saturation ferroelectric loop with remnant polarization of 17μC∕cm2 and saturation polarization of 19μC∕cm2, as well as good ferromagnetism with saturation magnetization of 0.71emu∕g, at room temperature. After the sample was poled, its piezoelectric constant was measured as 12.8pC∕N, and, in particular, an obvious magnetoelectric coupling was observed.

Curvelets for surface characterization

Surface metrology is the science of measuring small-scale features on surfaces, which is important to many disciplines including tribology, fluid mechanics, optics, and manufacturing. Applications of wavelets on functional surfaces have become an increasing interest. Unfortunately, the traditional wavelets have good performance only at representing point singularities because they ignore the geometric properties of surfaces with scratches and do not exploit the regularity of curves. In this letter, a second-generation curvelet transform combined with total variation minimization is proposed to characterize surfaces with general scratches along C2 singularities. The ability of the developed geometric multiscale method is demonstrated on bioengineering surfaces.

Multiscale geometric analysis of turbulence by curvelets

In this paper, after a brief review of curvelets and their relation to classical wavelet transform, multiscale geometric analysis is systematically applied to turbulent flows in two and three dimensions. The analysis is based on the constrained minimization of a total variation functional representing the difference between the data and its representation in the curvelet space. Constrained multiscale minimization results in a minimum loss of the geometric flow features and the extraction of the coherent structures with their edges and geometry properly preserved, which is significant for turbulence modeling. The effectiveness of curvelet analysis compared to the wavelet transform is demonstrated for both two- and three-dimensional turbulent flows.

Three-dimensional curvelets for coherent vortex analysis of turbulence

This letter presents a multiscale geometric method based on three-dimensional (3D) second-generation curvelet transform to extract coherent vortices out of 3D turbulent flows. Since the platelike elements of 3D curvelets satisfy the 3D parabolic scaling, and since they form a sparse basis, they optimally represent singular surfaces in three dimensions. This method preserves the edges and structures of extracted vortex tubes better than the conventional wavelets. The effectiveness of the present method is demonstrated in the case of simulation data of 3D homogeneous isotropic turbulence.

Design and analysis of a self-biased broadband magnetoelectric cantilever operated at multi-frequency windows

Magnetoelectric (ME) composites with self-biased and wide resonance frequency band properties are promising candidates for magnetic field sensor and energy harvester. Here, we present a ME cantilever by in-series connecting a few SrFe12O19/Metglas/Pb(Zr,Ti)O3 components. Due to the in-built magnetic bias of SrFe12O19, the ME cantilever shows self-biased property. Meanwhile, by merging the resonance responses of the in-series ME components together, the ME cantilever presents multi-wide resonance bands (i.e., 500 Hz ∼ 700 Hz, 3.3 kHz ∼ 4.4 kHz and 44 kHz ∼ 70 kHz). In these three wide frequency windows, the ME voltage coefficients (αV) of the ME cantilever are higher than 40 mV/Oe, 115 mV/Oe and 400 mV/Oe, respectively.