Frequency‐domain electromagnetic methods with a grounded‐wire source are powerful tools in geophysical exploration. However, the signal may be too weak to guarantee the quality of survey data in complex electromagnetic environments, especially when the receiver is located in the air for the newly developed grounded‐source airborne frequency‐domain electromagnetic method. In this paper, a signal enhancement method with multiple sources is proposed to solve this problem. To evaluate the signal enhancement effect, we compared the signals generated by a single source and multiple sources with equal electric moment. The signal differences caused by synchronisation error and separation distance between source elements were analysed, and the methods to achieve maximum signal were introduced. Besides, we discussed the interaction between adjacent source elements to ensure the system safety, including the changes in output current and the safe distance between two sources using a dual‐source model. Lastly, a comprehensive field experiment was designed and conducted to test the multiple‐source method. The data processing results are comparable for single and dual sources, and the signal‐to‐noise ratio of dual source is higher in the field test. The subsurface resistivity structure at the test site is consistent with the previous controlled‐source audio‐frequency magnetotellurics method. These results show that signal enhancement with multiple sources is feasible. This study provides guidance to the application of multiple sources in field surveys when the survey environment is complex and rigorous. 相似文献
Clostridium difficile infection is one of the major patient safety concerns in hospitals worldwide. Clostridium difficile infection can have high economic burden to patients, hospitals, and government. Limited work has been done in the area of predictive modeling. In this article, A new predictive model based on Gaussian mixture model and Dempster–Shafter theory is proposed to predict Clostridium difficile infection incidence in hospitals. First, the Gaussian mixture model and expectation–maximization algorithms are used to generate explicit probability criteria of risk factors based on the given data. Second, Dempster–Shafter theory is used to predict the Clostridium difficile infection incidence based on the generated probability criteria that have different beliefs attributing to their different credits. The main procedure includes (1) generate the probability criteria model using Gaussian mixture model and expectation–maximization algorithm; (2) determine the credit of the probability criteria; (3) generate the basic probability assignment; (4) discount the evidences; (5) aggregate the evidences using Dempster combining rule; (6) predict Clostridium difficile infection incidence using pignistic probability transformation. Results show that the model has a higher accuracy than an existing model. The proposed model can generate the criteria ratings of risk factors automatically, which would potentially prevent the imprecision caused by the subjective judgement of experts. The proposed model can assist risk managers and hospital administrators in the prediction and control of Clostridium difficile infection incidence with optimizing their resources. 相似文献
Natural Hazards - Landslide disasters in tropical rainforests are becoming increasingly severe. It is a tough task to prevent and control landslide effectively in the tropical rainforests.... 相似文献
“Belt and Road” regions include Asia, Europe and eastern and northern Africa, with a wide spatial distribution. The cryosphere is undergoing rapid changes in the Belt and Road regions with global warming, and has an important impact on water resources, ecosystems and Arctic waterways in these regions. This article reviewed recent cryospheric changes and associated impacts on water resources in the Belt and Road regions during the last decades. The main cognitions are as follows: Most glaciers are shrinking and glacier mass balances are most negative, but there are regional differences in the changes of glaciers. Global temperature rise has resulted in permafrost degradation, including a rise in permafrost temperature and decreasing permafrost thickness as well as an increase in active layer thickness. There is a significant decrease in snow cover extent and an increase in snow depth. Snow cover duration has shortened, the onset of snow cover has delayed, and the end of snow cover has advanced. However, there are still obvious regional differences in the changes of snow cover. Arctic sea ice has declined precipitously in both extent and thickness in summer, and multi-year sea ice has decreased,indicating the precipitous retreat of sea ice. The freeze-up date of some lakes has been delayed, the break-up date has advanced, and the ice cover duration of river/lake ice has significantly shortened. Glacial runoff has increased significantly in China. Snowmelt and permafrost degradation have also increased the basin runoff, which indicates the important impact of cryospheric changes on runoff. This study will provide a baseline and important scientific support for addressing climate change and regional sustainable development. 相似文献
The gas outburst, resulting in substantial economic losses and even casualties, is the biggest obstacle in coal mines, mostly caused by an imbalance of gas-geological structure. For accurately measuring this proneness, in this paper, a novel evaluation method was proposed based on the gas-geology theory. In this method, a standardization model of statistical units was presented first, which was used to standardize and quantify the 12 chosen gas-geological factors; and then, an associated function was established for computing the gas-geological complexity index (GCI). With increasing GCI values, the evaluated area was divided into four grades: simple, medium, complex, and extremely complex region, in which the associated proneness of outbursts was SAFE, POTENTIAL, HIGH, STRONG, respectively. Taking the XueHu Coal Mine as an example, site verification was carried out with a good result. Research and application indicate that (1) gas outburst is unbalanced and closely related to the complex of the gas geological structure, showing a greater GCI leads to a higher outburst possibility; (2) the most likely area for the gas outburst is the extremely complex region and the transition zone between adjacent areas with different GCI grades; (3) upgrading-targeted control measures are the best way for preventing and controlling disasters caused by the gas and outburst unbalanced distribution. This novel method provided a reliable quantity approach for predicting and zonally managing gas outbursts and improving the effectiveness of outbursts prevention.