Ankylosing spondylitis (AS), a chronic condition that commonly influences the spine and sacroiliac joints, usually progresses to stiffness and progressive functional limitation. Its fundamental etiology and pathogenesis are likely multifactorial and remain elusive. As environmental factors, gut microbiota performs critical functions in the pathogenesis of AS through various mechanisms, including interacting with genes, enhancing intestinal permeability, activating the gut mucosa immune system, and affecting the intestinal microbiota metabolites. This review provides an overview of recent advances in investigating gut microbiota in AS pathogenesis and discusses potential methods for future therapeutic intervention.
An accurate velocity model is essential in microseismic imaging. Layered sediments and subvertical cracks from tectonic stress and hydraulic fracturing make velocity models more complicated than isotropy or simple anisotropy, such as vertical transverse isotropy. Downhole microseismic acquisition usually cannot achieve sufficient ray coverage that is required to develop a low-symmetry anisotropic model from traveltimes alone. To solve this problem, we have developed a new type of data, S-wave splitting parameters (the delay time of the slow S-wave and fast S-wave polarization direction), to determine anisotropic models. A genetic algorithm inversion is adopted to solve for the locations of events and the stiffness tensor of an anisotropic medium simultaneously. We applied this method to synthetic waveforms from numerical modeling and successfully recovered the input event locations and the velocity model. The effectiveness of this method is further demonstrated by using real microseismic data acquired in the Bakken shale reservoir. Compared with the inversion with an isotropic velocity model, event locations from an anisotropic model become well-aligned with natural fractures in the Bakken Formation. Our experiments have evidenced that adding full S-wave splitting parameters makes a significant improvement in constraining a low-symmetry anisotropic model from downhole microseismic data.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.