Geomechanical Stability Analysis for Co2 Sequestration in Carbonate Formation

Geomechanical analysis is one of the fundamental pillars to build up the confidence of geological sequestration of CO2. Large scale CO2 sequestration in deep carbonate formation is a complicated geological process, which will non-reversibly transform the presumed equivalent and stable status of a sedimentary basin that formed over millions of years: chemically, hydraulically, geothermally, and geomechanically. In this dissertation, thermoporoelasticity guides the theoretical establishment of a conservative baseline for the geomechanical stability analysis of CO2 sequestration. Extensive laboratory tests, including CO2 flooding tests, permeability tests, uniaxial and triaxial tests, Brazilian tensile strength tests, poroelasticity tests, point load tests, and fracture toughness tests, etc, were conducted on Indiana limestone and Pierre shale to investigate the effects of CO2 sequestration on storage rock and caprock. Numerical simulations using finite difference method of FLAC3D were also conducted to understand the mechanism of strain localization due to pore pressure fluctuation. Based on these laboratory and numerical tests, it is concluded that two mechanisms are competing for rock failures in deep carbonate formations during CO2 sequestration. One is the faulting induced by pore-pressure buildup, and another is the compaction failure because of rock quality deterioration due to exposure to CO2 enriched solution. Fracture toughness measurements on limestone and shale suggest that the fracture toughness of target formation may not be necessarily lower than that of cap rock formation; then the fractures developed in target formation may be easily extended to the cap rock formation, ruining the sealing mechanism. As such, preventing extensive fracturing, and monitoring the seismicity in target formation are essential. Finally, the potential problems of CO2 sequestration in the Williston Basin were investigated. The in-situ stress regime of the Williston Basin was estimated as a mixture of normal and strike-slip faulting regimes, in favor of a vertical or sub-vertical fracture development pattern, which is negative to the CO2 sequestration. However, as the basin is not very close to an incipient failure, compaction failures are expected to be more pronounced, and naturally occurred geological phenomena, stylolites, will help to understand the CO2 sequestration in deep carbonate formation in the long run

MvSSIM: A quality assessment index for hyperspectral images

Quality assessment indexes play a fundamental role in the analysis of hyperspectral image (HSI) cubes. To assess the quality of an HSI cube, the structural similarity (SSIM) index has been widely applied in a band-by-band manner, as SSIM was originally designed for 2D images, and then the mean SSIM (MeanSSIM) index over all bands is adopted. MeanSSIM fails to accommodate the spectral structure which is a unique characteristic of HSI. Hence in this paper, we propose a new and simple multivariate SSIM (MvSSIM) index for HSI, by treating the pixel spectrum as a multivariate random vector. MvSSIM maintains SSIM’s ability to assess the spatial structural similarity via correlation between two images of the same band; and adds an ability to assess the spectral structural similarity via covariance among different bands. MvSSIM is well founded on multivariate statistics and can be easily implemented through simple sample statistics involving mean vectors, covariance matrices and cross-covariance matrices. Experiments show that MvSSIM is a proper quality assessment index for distorted HSIs with different kinds of degradations

On Hypothesis Testing for Comparing Image Quality Assessment Metrics [Tips & Tricks]

In developing novel image quality assessment (IQA) metrics, researchers should compare their proposed metrics with state-of-the-art metrics. A commonly adopted approach is by comparing two residuals between the nonlinearly mapped scores of two IQA metrics and the difference mean opinion score, which are assumed from Gaussian distributions with zero means. An F-test is then used to test the equality of variances of the two sets of residuals. If the variances are significantly different, then we conclude that the residuals are from different Gaussian distributions and that the two IQA metrics are significantly different. The F-test assumes that the two sets of residuals are independent. However, given that the IQA metrics are calculated on the same database, the two sets of residuals are paired and may be correlated. We note this improper usage of the F-test by practitioners, which can result in misleading comparison results of two IQA metrics. To solve this practical problem, we introduce the Pitman test to investigate the equality of variances for two sets of correlated residuals. Experiments on the Laboratory for Image and Video Engineering (LIVE) database show that the two tests can provide different conclusions

First-principles study of native point defects in Bi2Se3

Using first-principles method within the framework of the density functional theory, we study the influence of native point defect on the structural and electronic properties of Bi$_2$Se$_3$. Se vacancy in Bi$_2$Se$_3$ is a double donor, and Bi vacancy is a triple acceptor. Se antisite (Se$_{Bi}$) is always an active donor in the system because its donor level ($\varepsilon$(+1/0)) enters into the conduction band. Interestingly, Bi antisite(Bi$_{Se1}$) in Bi$_2$Se$_3$ is an amphoteric dopant, acting as a donor when $\mu$$_e$$<$0.119eV (the material is typical p-type) and as an acceptor when $\mu$$_e$$>$0.251eV (the material is typical n-type). The formation energies under different growth environments (such as Bi-rich or Se-rich) indicate that under Se-rich condition, Se$_{Bi}$ is the most stable native defect independent of electron chemical potential $\mu$$_e$. Under Bi-rich condition, Se vacancy is the most stable native defect except for under the growth window as $\mu$$_e$$>$0.262eV (the material is typical n-type) and $\Delta$$\mu$$_{Se}$$<$-0.459eV(Bi-rich), under such growth windows one negative charged Bi$_{Se1}$ is the most stable one.Comment: 7 pages, 4 figure

Experimentally obtaining the Likeness of Two Unknown Quantum States on an NMR Quantum Information Processor

Recently quantum states discrimination has been frequently studied. In this paper we study them from the other way round, the likeness of two quantum states. The fidelity is used to describe the likeness of two quantum states. Then we presented a scheme to obtain the fidelity of two unknown qubits directly from the integral area of the spectra of the assistant qubit(spin) on an NMR Quantum Information Processor. Finally we demonstrated the scheme on a three-qubit quantum information processor. The experimental data are consistent with the theoretical expectation with an average error of 0.05, which confirms the scheme.Comment: 3 pages, 4 figure

How Video Super-Resolution and Frame Interpolation Mutually Benefit

Video super-resolution (VSR) and video frame interpolation (VFI) are inter-dependent for enhancing videos of low resolution and low frame rate. However, most studies treat VSR and temporal VFI as independent tasks. In this work, we design a spatial-temporal super-resolution network based on exploring the interaction between VSR and VFI. The main idea is to improve the middle frame of VFI by the super-resolution (SR) frames and feature maps from VSR. In the meantime, VFI also provides extra information for VSR and thus, through interacting, the SR of consecutive frames of the original video can also be improved by the feedback from the generated middle frame. Drawing on this, our approach leverages a simple interaction of VSR and VFI and achieves state-of-the-art performance on various datasets. Due to such a simple strategy, our approach is universally applicable to any existing VSR or VFI networks for effectively improving their video enhancement performance