GPS-based regional ionospheric models and their suitability in Antarctica

There are a number of ionospheric models available for research and application, such as the polynomial model, generalized trigonometric series function model, low degree spherical harmonic function model, adjusted spherical harmonic function model, and spherical cap harmonic function analysis. Using observations from more than 40 continuously operating stations across Antarctica in 2010, five models are compared with regard to their precision and applicability to polar regions. The results show that all the models perform well in Antarctica with 0.1 TECU of residual mean value and 2 TECU of root mean square error

Analysis of tribological performance in transversely isotropic materials utilizing analytical and finite element methods

This dissertation develops methods for evaluating the tribological behavior of anisotropic materials. The underlying objectives of the work are: (1) to elucidate the relationship between the sliding frictional contact and the fiber orientations of FRP composites; (2) to explore the relationship between the anisotropic strength and the wear of FRP composites and develop an innovative wear model of FRP composites; and (3) to derive a general approximate solution for analyzing the contact behavior of transversely isotropic coatings such solid lubricant films.The first goal was achieved in two steps. First, by incorporating anisotropic contact theory, the elastic properties of FRP composites, and the analytical expressions of Barnett-Lothe tensors, the contact behavior of FRP composites in the three principal fiber orientations (transverse, normal, parallel) was deduced. Specially, the influence of fibers, matrices, volume fractions, and friction coefficients on the contact behavior was ascertained. Next, through the numerical solution of the explicit expressions of Barnett-Lothe tensors, the relationship between the contact performance and the arbitrary fiber orientations was examined. Based on this approach, the influence of fiber orientations on the contact pressure and the contact patch was determined. To develop an anisotropic wear model of FRP composites, the Tsai-Wu failure strength criterion was employed to establish the relationship between the wear and the contact stress. The theoretically predicated results were in good agreement with the previously published experimental data. This correlation demonstrates that the anisotropic failure strength criteria may be used to explain the anisotropy of wear in FRP composites.Finally, a set of approximate solutions for thin, transversely isotropic coatings was derived to gain deep insight into the coated structures. These easy-to-use solutions are helpful for optimizing the contact behavior of thin coatings used in the design of contacting components

PS-InSAR based surface subsidence analysis in Changchun metropolitan area

The monitoring of urban land surface subsidence is the main task of urban disaster prevention and mitigation. In this paper, the land surface subsidence process in Changchun metropolitan area is calculated based on PS-InSAR technology by using the SLC data of Sentinel-1B with 50 scenes within the metropolitan area of Changchun from 2016 to 2020. The results show that the metropolitan surface of Changchun is basically in a stable state, the main settlement is located in the southeast of the metropolitan around the Century Square, the maximum settlement rate is 20.45mm/a, the average settlement rate is 2.98mm/a, the correlation coefficient between the settlement results calculated by PS-InSAR and the second-class leveling verification results reaches 0.67, which indicates that the regional settlement results calculated by PS-InSAR have high reliability. The subsidence area is dominated by the geological structure of the Mesozoic Cretaceous Yaojia Formation, with many intercalations of fine silty sand rocks and locally containing medium-coarse gravel sandstone. The overall structural stability is poor, which may be the main reason for subsidence in this area

Retinal Microvascular Signs in Pre- and Early-Stage Diabetic Retinopathy Detected Using Wide-Field Swept-Source Optical Coherence Tomographic Angiography

Purpose Using a wide-field, high-resolution swept-source optical coherence tomographic angiography (OCTA), this study investigated microvascular abnormalities in patients with pre- and early-stage diabetic retinopathy. Methods 38 eyes of 20 people with diabetes mellitus (DM) type 2 without diabetic retinopathy (DR) and 39 eyes of 21 people with DR were enrolled in this observational and cross-sectional cohort study, and a refractive error-matched group consisting of 42 eyes of 21 non-diabetic subjects of similar age were set as the control. Each participant underwent a wide-field swept-source OCTA. On OCTA scans (1.2 cm × 1.2 cm), the mean central macular thickness (CMT), the vessel density of the inner retina, superficial capillary plexus (SCP), and deep capillary plexus (DCP) were independently measured in the whole area (1.2 cm diameter) via concentric rings with varying radii (0–0.3, 0.3–0.6, 0.6–0.9, and 0.9–1.2 cm). Results Patients whose eyes had pre-and early-stage DR showed significantly decreased vessel density in the inner retina, SCP, DCP and CMT (early-stage DR) compared with the control. In addition, compared with the average values upon wide-field OCTA, the decreases were even more pronounced for concentric rings with a radius of 0.9–1.2 cm in terms of the inner retina, SCP, DCP and CMT. Conclusions Widefield OCTA allows for a more thorough assessment of retinal changes in patients with pre- and early-stage DR.; retinal microvascular abnormalities were observed in both groups. In addition, the decreases in retinal vessel density were more significant in the peripheral concentric ring with a radius of 0.9–1.2 cm. The application of novel and wide-field OCTA could potentially help to detect earlier diabetic microvascular abnormalities