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Optimal transmission switching is proposed in recent years to optimize the power system operational cost in deterministic studies. With the rapid growth of renewable generations, the grid uncertainties have greatly increased, which cannot be ignored in the decision-making of optimal transmission switching problems. This paper proposes a novel two-stage stochastic optimization formulation with a convex relaxation for AC optimal transmission switching problems. A generalized Benders decomposition based algorithm, including an inner loop and an outer loop, is proposed to solve the AC optimal transmission switching problem with grid uncertainties. The optimal switching plan and the expected system cost will be found in the iterative calculation without any sacrifice of accuracy. Numerical studies on the IEEE 118-bus system and the South Carolina 500-bus confirm the effectiveness of the proposed decomposition approach in solving the AC optimal transmission switching problems with grid uncertainties. The scalability analysis shows the proposed approach is efficient in dealing with a large number of scenarios.

This paper investigates the stability issues that might arise when incorporating transmission line switching into smart grid planning and operation. To demonstrate the feasibility of line switching, we use scenarios and dynamic simulations to demonstrate system security margin and online stability issues. Results show that proper line switching can resolve system emergency and boost system security margin, even though less transmission lines are used. Also it reveals that small signal instability can be triggered by line switching. It is necessary to apply sophisticated voltage controls and power system stabilizers (PSS) to avoid triggering rotor angle and voltage small signal instability for full benefits of line switching.

Accurate quantitative information of crack length and width is important for assessing the severity level of cracks and making accurate pavement maintenance decisions. Nevertheless, due to the noise and fluctuation at the crack edge of pavement image, itis difficult to precisely determine the edge correspondence of crack that is necessary for measuring the crack width at a specific pixel. Different automated or manually performed measurements are likely to yield different results at the same pixel. Instead of measuring the crack width on a pixel-by-pixel basis, this paper presents an accurate and robust segment-based method for measuring crack width. Firstly, based on the distinctive curved structure of pavement crack, a structured edge detector is trained to obtain the confidence map of crack edges. Secondly, with the crack edge map, the morphological operation is used to extract the crack skeleton which characterizes the propagation of the crack. Adaptive segmentation of the crack skeleton is performed to partition a crack curve into crack segments. Each crack segment has the same width because its edges become almost parallel after the segmentation. Finally, combining the structured edge confidence and grayscale contrast at crack edges, an enhanced edge map of crack is proposed to measure the width of each crack segment by translating the skeleton towards both edges. A large number of experiments taken on the synthetic and real-world pavement images demonstrate that the proposed method can accurately and robustly quantify various cracks with the average accuracy of 93.7% for crack width. It is promising for quantitative pavement condition assessment and maintenance.

The optical properties of materials can be characterized in terms of the complex refractive index. We developed a simple and efficient method for determining the complex refractive index of nanomaterials that uses the relationship between this parameter and the light spectrum measured for a specimen. The optical properties of nanoparticle and nanotube TiO2 films were investigated. The results show that the morphology of nano-TiO2 affects the complex refractive index spectrum and therefore influences light dispersion and absorption of the film. We also simulated the optical energy density distribution within equivalent plane films using complex refractive index data.