Chang'an University

About: Chang'an University is a education organization based out in Xi'an, China. It is known for research contribution in the topics: Asphalt & Groundwater. The organization has 18415 authors who have published 15102 publications receiving 125436 citations. The organization is also known as: Cháng'ān Dàxué & Changan University.

Water levels measured with SNR using wavelet decomposition and Lomb–Scargle periodogram

Abstract: The expansion of research and applications involving global navigation satellite systems, e.g., the Global Positioning System (GPS), has revealed multipath errors. Discrete wavelet decomposition can reduce the noise of a signal-to-noise ratio (SNR) series, and the detailed coefficient of the wavelet decomposition at a specific level can be fitted to the SNR series. Therefore, we present a method to extract the multipath frequency of SNR data by implementing Lomb–Scargle periodogram (LSP) analysis after wavelet decomposition. This characteristic frequency can be used first to deduce the distance between the GPS antenna and the sea and then to estimate the sea level. This study analyzed data from two test sites: the Friday Harbor GPS site SC02 in the San Juan Islands (WA, USA) and the Kachemak Bay GPS site PBAY (AK, USA). The performance of applying wavelet decomposition before using the LSP is discussed for different length data series, i.e., a long data length and a short data length. The sea levels at the two GPS sites, retrieved by LSP and by LSP after wavelet decomposition using the two different data length series, all convincingly reproduced the overall behavior of the National Oceanographic and Atmospheric Administration tide gauge data. Furthermore, the performance of the improved method for shorter SNR data is much better than for the longer SNR data.

Pavement defect detection with fully convolutional network and an uncertainty framework

Abstract: Image segmentation has been implemented for pavement defect detection, from which types, locations, and geometric information can be obtained. In this study, an integration of a fully conv...

Comprehensive damage evaluation of localized spallation of thermal barrier coatings

Abstract: Thermal barrier coatings (TBCs) enable the hot section part to work at high temperatures owing to their thermal barrier effect on the base metal components. However, localized spallation in the ceramic top-coat might occur after long duration of thermal exposure or thermal cycling. To comprehensively understand the damage of the top-coat on the overall hot section part, effects of diameter and tilt angle of the spallation on the temperature redistribution of the substrate and the top-coat were investigated. The results show that the spallation diameter and tilt angle both have a significant effect on the temperature redistribution of the top-coat and the substrate. In the case of the substrate, the maximum temperature increment is located at the spallation center. Meanwhile, the surface (depth) maximum temperature increment, having nothing to do with the tilt angle, increases with the increase of the spallation diameter. In contrast, in the case of the top-coat, the maximum temperature increment was located at the sharp corner of the spallation area, and the surface (depth) maximum temperature increment increases with the increase of both the spallation diameter and the tilt angle. Based on the temperature redistribution of the substrate and the top-coat affected by the partial spallation, it is possible to evaluate the damage effect of spalled areas on the thermal capability of TBCs.

A modified DRASTIC model for assessing contamination risk of groundwater in the northern suburb of Yinchuan, China

Abstract: Groundwater vulnerability assessment is a common method to describe groundwater contamination. However, intensive human activities have a marked impact on subsurface environment. Therefore, in this paper, the DRTILSQ model which is based on DRASTIC and considers human influences was proposed. The contamination risk of groundwater underlying the northern suburb of Yinchuan city was assessed. According to local hydrogeological settings, seven factors were singled out for representing intrinsic vulnerability, pollution loading and groundwater value, respectively. Analytical hierarchy process was adopted to determine weights, which makes the model harmonize with the study area and easy to transplant. The results show that high contamination risk area is in the central zone with shallow buried depth of groundwater, highly permeable vadose zone, high recharge and agricultural pollution. Except that, extremely high contamination risk is associated with high groundwater value and industrial threats. Compared to the vulnerability map, the contamination risk map presents a more reasonable classification. The maps are valuable tools for environmental management. The DRTILSQ can be transplanted to Yinchuan Plain or northwest China, and provides experience for developing models of groundwater contamination risk assessment for individual regions.