Geometric Large Deformation Research Articles

An Efficient Earth Mover's Distance Algorithm for Robust Histogram Comparison

We propose EMD-L1: a fast and exact algorithm for computing the Earth Mover's Distance (EMD) between a pair of histograms. The efficiency of the new algorithm enables its application to problems that were previously prohibitive due to high time complexities. The proposed EMD-L1 significantly simplifies the original linear programming formulation of EMD. Exploiting the L1 metric structure, the number of unknown variables in EMD-L1 is reduced to O(N) from O(N2) of the original EMD for a histogram with N bins. In addition, the number of constraints is reduced by half and the objective function of the linear program is simplified. Formally, without any approximation, we prove that the EMD-L1 formulation is equivalent to the original EMD with a L1 ground distance. To perform the EMD-L1 computation, we propose an efficient tree-based algorithm, Tree-EMD. Tree-EMD exploits the fact that a basic feasible solution of the simplex algorithm-based solver forms a spanning tree when we interpret EMD-L1 as a network flow optimization problem. We empirically show that this new algorithm has an average time complexity of O(N2), which significantly improves the best reported supercubic complexity of the original EMD. The accuracy of the proposed methods is evaluated by experiments for two computation-intensive problems: shape recognition and interest point matching using multidimensional histogram-based local features. For shape recognition, EMD-L1 is applied to compare shape contexts on the widely tested MPEG7 shape data set, as well as an articulated shape data set. For interest point matching, SIFT, shape context and spin image are tested on both synthetic and real image pairs with large geometrical deformation, illumination change, and heavy intensity noise. The results demonstrate that our EMD-L1-based solutions outperform previously reported state-of-the-art features and distance measures in solving the two tasks.

Repair and Strengthening of Reinforced Concrete Structures Using CFRPs

CFRPs offer a high strength lightweight alternative strengthening strategy to traditional methods using concrete overlays and/or steel plates in bridge engineering applications. In addition, the use of CFRPs may offer a viable retrofit/repair strategy in the case of damaged structures, where this damage may be significant. This paper reports on the performance of CFRP-based strategies for the repair and strengthening of two 40% scale continuous flat slab bridge models with significant damage arising from prior static testing to incipient collapse conditions. In addition, the performance after repair using a CFRP scheme of a RC beam-slab-column subassembly, following severe high-load cyclic testing, was also investigated. Results indicate that CFRPs offer a viable repair strategy in structural applications involving severe damage from the influence of static overload or extreme earthquakes but care needs be exercised to ensure secure adhesion where the surface under repair has locally adverse geometric features or has suffered large geometric deformation from the damage concerned.

Damage Constitutive Equations and its Application to Fiber Reinforced Composites under Transverse Impact

Two continuous field variables, called as continuity tensor and damage variable tensor, are used to describe the anisotropic responses of an elastic-brittle material under transverse impact load. Based on the continuum damage mechanics, anisotropic damage constitutive equations in both full and incremental forms are proposed here. The expressions of effective elastic module tensor, damage variable tensor and damage propagation force tensor are further derived, and the methods for determining the tensors are explained in detail. An example of strain and damage response of a fiber reinforced composite laminated plate under transverse impact load is employed to demonstrate the application of this theory. In the example, the damage variable coupled with geometric large deformation of laminated plate is also considered. The calculating results illustrate the influence of damage on strain field in the impacted laminated plate.

Synchrotron x-ray study of the monoclinic high-pressure structure ofAgGaS2

The structure of the monoclinic high-pressure phase of ${\mathrm{AgGaS}}_{2}$ was determined at 5.5 GPa by single-crystal x-ray diffraction using synchrotron radiation and a miniature diamond-anvil cell. The high-pressure phase has the space group symmetry of Cc with cell dimensions $a=8.031(4)\AA{},$ $b=8.014(1)\AA{},$ $c=6.221(2)\AA{},$ and $\ensuremath{\beta}=128.42(3)\ifmmode^\circ\else\textdegree\fi{}$ at 5.5 GPa. The monoclinic unit cell can be converted into a pseudotetragonal unit cell with $a=b=5.673(2)\AA{},$ $c=9.754(3)\AA{},$ $\ensuremath{\alpha}=\ensuremath{\beta}=88.75(3)\ifmmode^\circ\else\textdegree\fi{},$ and $\ensuremath{\gamma}=89.87(3)\ifmmode^\circ\else\textdegree\fi{},$ similar to the chalcopyrite-type tetragonal unit cell. The ${\mathrm{AgS}}_{4}$ tetrahedra undergo a relatively large geometrical deformation reflecting weaker force constants of Ag-S compared to those of Ga-S. On the other hand, changes in the geometrical shape of ${\mathrm{GaS}}_{4}$ are less significant and can be approximated as a rotation rather than a distortion. The two crystallographically independent ${\mathrm{S}}_{6}$ octahedral interstices in the monoclinic high-pressure phase experience discrete degrees of compression, which contributes to a further decrease of the $c/a$ ratio above the phase transition pressure of 4.2 GPa.

Multi-target UAV miniature staring hyperspectral imager radiation correction

The micro staring hyperspectral imager can simultaneously acquire two spatial and one spectral images, and only record the external orientation elements of the entire hyperspectral image rather than the external orientation elements of each frame of the image, which avoids the geometric instability during scanning, effectively solves the problem of large geometric deformation of the small line scanning hyperspectral imager, and is suitable for the small UAV load platform with unstable attitude. At present, most of the research focuses on the radio-metric correction method of line scan hyperspectral imager. The application time of staring hyperspectral imager is short, and there is no mature data processing re-search at home and abroad, which hinders the application of UAV micro staring hyperspectral imaging system. In this paper, the calibration method of the linearity and variability of the radiation response of the micro staring hyperspectral imager on the UAV is studied, and the effectiveness of this method is quantitatively evaluated. The results show that the hyperspectral image has obvious vignetting effect and strip phenomenon before the correction of radiation response variability. After the correction, the radiation response variation coefficient of pixels in different bands decreases significantly, and the vignetting effect and image strip decrease significantly. In this paper, a multi-target radiometric calibration method is proposed, and the accuracy of radiometric calibration is verified by comparing the calibrated hyperspectral image spectrum with the measured ground object spectrum of the ground spectrometer. The results show that the calibration results of the multi-target radiometric calibration method show better results, especially for the near-infrared band, and the difference with the surface reflectance measured by the spectrometer is small.