RESUMO
Mineral types form the basis for studying the structural stability of loess, and identifying mineral types at the microscopic scale has always been a difficult task. Identifying mineral types at the microscopic scale is very helpful in understanding the differential role that different minerals play in the structural stability of loess, and it can also clarify the specific mineral changes that occur during the process of humidification and dehumidification. Using an innovative energy spectrum superposition method, this article combines backscattered electron imaging and X-ray energy spectrum analysis results to achieve direct identification of the eight main minerals in loess, including quartz, illite, and chlorite, within SEM images. The mineral identification results provide a basis for statistical analysis of mineral water sensitivity and morphological changes under wetting conditions. The results demonstrate that chlorite and hematite, which account for no more than 23% of the loess composition, play a crucial role in binding. Furthermore, these minerals exhibit significant hydrolysis phenomena. Particularly, the intense decomposition of chlorite leads to the displacement of non-binding quartz and feldspar particles, thereby altering the pore structure of loess. These findings are of great significance in understanding the multi-level collapsibility of loess.
RESUMO
Objective: We aimed to investigate the clinical benefit of oxygen therapy in patients with acute ST-segment elevation myocardial infarction (STEMI). Methods: We searched PubMed, Embase and the Cochrane Library from database inception to June 2020 to identify randomized controlled trials (RCTs) on oxygen therapy in acute STEMI. Literature screening, data extraction and study quality assessment were independently carried out by the 2 investigators according to the predefined eligibility criteria, and RevMan 5.3 analysis software was utilized for all analyses. Results: Finally, 5 RCTs with a total of 4824 patients with STEMI were eligible for further meta-analysis. The RCT results demonstrated that oxygen therapy exerted non-significant effects in reducing the risks for short-term all-cause mortality (risk ratio [RR] = 1.21; 95% CI, 0.80-1.53; P = .53), cardiac arrest (RR = 1.20; 95% CI, 0.94-1.54; P = .79), recurrent myocardial infarction (MI) (RR = 0.68; 95% CI, 0.43-1.08; P = .10) and cardiogenic shock (RR = 0.81; 95% CI, 0.58-1.15; P = .24) and the incidence of other outcome indicators of acute STEMI. Conclusions: Oxygen therapy does not provide more benefits than adverse effects in patients with acute STEMI. Personalized oxygen treatment based on dynamic oxygen saturation is recommended in patients with hypoxia. Supplemental oxygen in patients with acute STEMI has no effect on reducing infarct size, and has no benefit in all-cause mortality, cardiogenic shock, etc.
