Resolution In Depth Direction Research Articles

Fast Three Dimensional Density Inversion Based on Multi-Scale Analysis of Wavelet

Low calculation efficiency and insufficient resolution in depth direction exist in inversion of underground 3D density distribution. In this paper, we proposed a fast inversion algorithm. It decomposed the gravity anomaly on multi-scale with wavelet, represented the original data sparsely with wavelet coefficients on each scale and carried on the inversion in wavelet domain. An appropriate threshold is set to process the coefficients in order to enhance the sparsity of coefficient matrix. This would furthermore improve the compressed ratio of data and save calculation time. Gravity anomalies on each scale represent response of sources at different depth as inverse relation exists between scale and frequency. So the inversion results would mainly reflect density distribution at the corresponding depth and the final inversion could be achieved by summing up results at all scales. It is not necessary to set the range of depth related to anomalies at each scale and besides, the inversion scheme is applied without depth weighting. The method could increase the resolution in depth direction of inversion results effectively and provide more detailed deep density distribution. As an iterative algorithm which can take advantage of sparse matrix to improve calculation efficiency, conjugate gradient was used for inversion. The proposed method will be applied into inversion of synthetic model data and real gravity anomaly to demonstrate its effect.

Prediction and analysis of residual stress and deflections of Almen strip by burnishing

Burnishing is a surface treatment process widely used to improve fatigue and corrosion resistance of metal components by introducing a compressive residual stress layer. However, the measurement of residual stress by X-ray diffraction is expensive, time consuming, and tedious. Hole drilling method is quick and simple, but it is destructive and provides limited resolution in depth direction. This work presents a quick method to determine the nature and magnitude of residual stress by using Almen strips. Inspired by the application of Almen strips in shot peening, the deflection of the burnished Almen strips under different burnishing conditions were measured. In addition, a finite element simulation model has been developed to predict residual stresses and deflection which were compared with the experimental results. Contact conditions with different combinations of sliding and rolling were investigated in the simulations to understand the contact nature in a burnishing process. It was found that the deflection of Almen strip reflects the magnitude and penetration depth into subsurface of the induced residual stress. The contact condition during burnishing is either pure sliding or a mixed mode of sliding and rolling, but not pure rolling.

Functional optical coherence tomography of rat olfactory bulb with periodic odor stimulation.

In rodent olfactory bulb (OB), optical intrinsic signal imaging (OISI) is commonly used to investigate functional maps to odorant stimulations. However, in such studies, the spatial resolution in depth direction (z-axis) is lost because of the integration of light from different depths. To solve this problem, we propose functional optical coherence tomography (fOCT) with periodic stimulation and continuous recording. In fOCT experiments of in vivo rat OB, propionic acid and m-cresol were used as odor stimulus presentations. Such a periodic stimulation enabled us to detect the specific odor-responses from highly scattering brain tissue. Swept source OCT operating at a wavelength of 1334 nm and a frequency of 20 kHz, was employed with theoretical depth and lateral resolutions of 6.7 μm and 15.4 μm, respectively. We succeeded in visualizing 2D cross sectional fOCT map across the neural layer structure of OCT in vivo. The detected fOCT signals corresponded to a few glomeruli of the medial and lateral parts of dorsal OB. We also obtained 3D fOCT maps, which upon integration across z-axis agreed well with OISI results. We expect such an approach to open a window for investigating and possibly addressing toward inter/intra-layer connections at high resolutions in the future.