Xiaoye Liu

Airborne LiDAR is one of the most effective and reliable means of terrain data collection. Using LiDAR data for digital elevation model (DEM) generation is becoming a standard practice in spatial related areas. However, the effective processing of the raw LiDAR data and the generation of an efficient and high-quality DEM remain big challenges. This paper reviews the recent advances of airborne LiDAR systems and the use of LiDAR data for DEM generation, with special focus on LiDAR data filters, interpolation methods, DEM resolution, and LiDAR data reduction. Separating LiDAR points into ground and non-ground is the most critical and difficult step for DEM generation from LiDAR data. Commonly used and most recently developed LiDAR filtering methods are presented. Interpolation methods and choices of suitable interpolator and DEM resolution for LiDAR DEM generation are discussed in detail. In order to reduce the data redundancy and increase the efficiency in terms of storage and manipulation, LiDAR data reduction is required in the process of DEM generation. Feature specific elements such as breaklines contribute significantly to DEM quality. Therefore, data reduction should be conducted in such a way that critical elements are kept while less important elements are removed. Given the high-density characteristic of LiDAR data, breaklines can be directly extracted from LiDAR data. Extraction of breaklines and integration of the breaklines into DEM generation are presented.

Gastroesophageal reflux disease (GERD) is a common clinical disease associated with upper gastrointestinal motility disorders. Recently, with improvements in living standards and changes in lifestyle and dietary habits, the incidence of GERD has been increasing yearly. However, the mechanism of GERD has not been fully elucidated due to its complex pathogenesis, and this had led to unsatisfactory therapeutic outcomes. Currently, the occurrence and development of GERD involve multiple factors. Its pathogenesis is mainly thought to be related to factors, such as lower esophageal sphincter pressure, transient lower esophageal sphincter relaxation, crural diaphragmatic dysfunction, hiatus hernia, and impaired esophageal clearance. Therefore, explaining the pathogenesis of GERD more clearly and systematically, exploring potential and effective therapeutic targets, and choosing the best treatment methods have gradually become the focus of scholars' attention. Herein, we reviewed current advancements in the dynamic mechanism of GERD to better counsel patients on possible treatment options.