分类： 地球科学 >> 地理学 提交时间： 2021-04-30 合作期刊: 《干旱区科学》
摘要： Groundwater forms the main freshwater supply in arid and semi-arid areas, and contamination of this precious resource is complicated by the slow rate of recharge in these areas. Nitrate contamination of groundwater is a global water quality problem, as it entails threat to human health as well as aquatic ecosystems. Source identification of contamination is the cornerstone and a prerequisite for any effective management program of water quality. Stable isotope composition of the dissolved nitrate (δ15N-NO3– and δ18O-NO3–) has been applied to identify NO3– sources and the main transformation processes in the upper aquifer system (A1/2, A4, and B2/A7 aquifers) in the Wadi Shueib catchment area, Jordan. Moreover, the stable isotope compositions of the groundwater (δ2H-H2O and δ18O-H2O) in conjunction with the groundwater hydrochemistry were integrated to investigate the origin and evolution of the groundwater. Results revealed that groundwater in the study area is fresh and hard-very hard water, and mainly a Ca-Mg-Cl type. NO3– concentration was in the range of 7.0–74.0 mg/L with an average of 37.0 mg/L. Most of the samples showed concentration higher than the natural background concentration of NO3– (5.0–10.0 mg/L). The δ2H-H2O and δ18O-H2O values indicated that the groundwater is meteoric, and of Mediterranean origin, with a strong evaporation effect. The δ15N-NO3– values ranged between 6.0‰ and 11.3‰ with an average of 8.7‰, and the δ18O-NO3– values ranged between 1.6‰ and 5.9‰ with an average of 3.4‰. These values are in conformity with the stable isotope composition of nitrate derived the nitrification of wastewater/manure, and soil NH4. Nitrification and denitrification are the main transformation processes affecting nitrogen species. Statistical analysis revealed no significant differences in the δ2H-H2O and δ18O-H2O values, and δ15N-NO3– and δ18O-NO3– values for the three aquifers (A1/2, A4, and B2/A7), indicating that the groundwater of these aquifers has the same origin, and a common source of pollution.
分类： 物理学 >> 核物理学 提交时间： 2023-06-01
摘要： Compton camera-based prompt gamma (PG) imaging has been proposed for range verification during protontherapy. However, a deviation between the PG and dose distributions, as well as the difference between thereconstructed PG and exact values, limit the effectiveness of the approach in accurate range monitoring duringclinical applications. The aim of the study was to realize a PG-based dose reconstruction with a Comptoncamera, thereby further improving the prediction accuracy of in-vivo range verification and providing a novelmethod for beam monitoring during proton therapy. In this paper, we present an approach based on a subsetdriven origin ensemble with resolution recovery (SD-OE-RR) and a double evolutionary algorithm (DEA) to reconstruct the dose depth profile (DDP) from the gamma events obtained by a Cadmium-Zinc-Telluride(CZT) Compton camera with limited position and energy resolution. Simulations of proton pencil beams withclinical particle rate irradiating phantoms made of different materials and the CT-based thoracic phantom wereused to evaluate the feasibility of the proposed method. The results show that for the monoenergetic protonpencil beam irradiating homogeneous-material box phantom, the accuracy of the reconstructed DDP was within0.3 mm for range prediction and within 5.2% for dose prediction. In particular, for 1.6-Gy irradiation in thetherapy simulation of thoracic tumors, the range deviation of the reconstructed spread-out Bragg peak waswithin 0.8 mm, and the relative dose deviation in the peak area was less than 7% compared to the exact values.The results demonstrate the potential and feasibility of the proposed method in future Compton-based accuratedose reconstruction and range verification during proton therapy.
分类： 医学、药学 >> 预防医学与公共卫生学 提交时间： 2023-03-29
William J. Liu
Peipei Liu
Wenwen Lei
Zhiyuan Jia
Xiaozhou He
Weifeng Shi
Yun Tan
Shumei Zou
Gary Wong
Ji Wang
Feng Wang
Gang Wang
Kun Qin
Rongbao Gao
Jie Zhang
Min Li
Wenling Xiao
Yuanyuan Guo
Ziqian Xu
Yingze Zhao
摘要： Emerging in December 2019, coronavirus disease 2019 (COVID-19) eventually became a pandemic and posed a tremendous threat to global public health. However, the origins of SARS-CoV-2, the causative agent of COVID-19, remain to be determined. It has been reported that a certain number of the early case clusters had a contact history with the Huanan Seafood Market. Therefore, surveillance of SARS-CoV-2 within the market is of vital importance. Herein, we presented the SARS-CoV-2 detection results of 1380 samples collected from the environment since 1st Jan and animals since 18th Jan within the market in early 2020. By SARS-CoV-2-specific RT-qPCR, 73 environmental samples tested positive for SARS-CoV-2 and three live viruses were successfully isolated. The viruses from the market shared nucleotide identity of 99.99% to 100% with the human isolate HCoV-19/Wuhan/IVDC-HB-01/2019. The A lineage (8782T and 28144C), as the likely ancestral SARS-CoV-2 lineage, was found in an environmental sample. No virus was detected in the animal swabs covering 18 species of animals in the market. The RNA-seq analysis of SARS-CoV-2 positive/negative environmental samples showed the abundance of different vertebrata genera. In summary, this study provided convincing evidence of the prevalence of SARS-CoV-2 in the Huanan Seafood Market during the early stage of COVID-19 outbreak.
分类： 信息科学与系统科学 >> 信息科学与系统科学基础学科 分类： 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间： 2022-08-15
摘要： The notion of information and complexity are important concepts in many scientific fields such as molecular biology, evolutionary theory and exobiology. Many measures of these quantities are either difficult to compute, rely on the statistical notion of information, or can only be applied to strings. Based on assembly theory, we propose the notion of a ladderpath, which describes how an object can be decomposed into hierarchical structures using repetitive elements. From the ladderpath two measures naturally emerge: the ladderpath-index and the order-index, which represent two axes of complexity. We show how the ladderpath approach can be applied to both strings and spatial patterns and argue that all systems that undergo evolution can be described as ladderpaths. Further, we discuss possible applications to human language and the origin of life. The ladderpath approach provides an alternative characterization of the information that is contained in a single object (or a system) and could aid in our understanding of evolving systems and the origin of life in particular.
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