Several important equilibrium Si isotope fractionation factors among minerals,organic molecules and the H_4SiO_4 solution are complemented to facilitate the explanation of the distributions of Si isotopes in Earth'...Several important equilibrium Si isotope fractionation factors among minerals,organic molecules and the H_4SiO_4 solution are complemented to facilitate the explanation of the distributions of Si isotopes in Earth's surface environments.The results reveal that,in comparison to aqueous H_4SiO_4,heavy Si isotopes will be significantly enriched in secondary silicate minerals.On the contrary,quadra-coordinated organosilicon complexes are enriched in light silicon isotope relative to the solution.The extent of ^(28)Si-enrichment in hyper-coordinated organosilicon complexes was found to be the largest.In addition,the large kinetic isotope effect associated with the polymerization of monosilicic acid and dimer was calculated,and the results support the previous statement that highly ^(28)Sienrichment in the formation of amorphous quartz precursor contributes to the discrepancy between theoretical calculations and field observations.With the equilibrium Si isotope fractionation factors provided here,Si isotope distributions in many of Earth's surface systems can be explained.For example,the change of bulk soil δ^(30)Si can be predicted as a concave pattern with respect to the weathering degree,with the minimum value where allophane completely dissolves and the total amount of sesquioxides and poorly crystalline minerals reaches their maximum.When,under equilibrium conditions,the well-crystallized clays start to precipitate from the pore solutions,the bulk soil δ^(30)Si will increase again and reach a constant value.Similarly,the precipitation of crystalline smectite and the dissolution of poorly crystalline kaolinite may explain the δ^(30)Si variations in the ground water profile.The equilibrium Si isotope fractionations among the quadracoordinated organosilicon complexes and the H_4SiO_4solution may also shed light on the Si isotope distributions in the Si-accumulating plants.展开更多
In this paper, we consider the relationship between the binding number and the existence of fractional k-factors of graphs. The binding number of G is defined by Woodall as bind(G)=min{ | NG(X) || X |:∅≠X⊆V(G) }. It ...In this paper, we consider the relationship between the binding number and the existence of fractional k-factors of graphs. The binding number of G is defined by Woodall as bind(G)=min{ | NG(X) || X |:∅≠X⊆V(G) }. It is proved that a graph G has a fractional 1-factor if bind(G)≥1and has a fractional k-factor if bind(G)≥k−1k. Furthermore, it is showed that both results are best possible in some sense.展开更多
原发性肝癌是世界上常见的恶性肿瘤之一,具有较高的发病率和死亡率。本文详述了目前我国原发性肝癌的流行病学情况、人群归因分值及其相关危险因素。本文通过检索PubMed、Web of Science、中国知网等数据库发现,乙型肝炎病毒和丙型肝炎...原发性肝癌是世界上常见的恶性肿瘤之一,具有较高的发病率和死亡率。本文详述了目前我国原发性肝癌的流行病学情况、人群归因分值及其相关危险因素。本文通过检索PubMed、Web of Science、中国知网等数据库发现,乙型肝炎病毒和丙型肝炎病毒仍是原发性肝癌发病的主要危险因素。随着乙型肝炎病毒疫苗接种以及抗病毒治疗,我国原发性肝癌的发病率略有下降,但代谢性因素如糖尿病、肥胖和非酒精性脂肪性肝病等引起的原发性肝癌的发病率正逐步上升;吸烟、饮酒等也是重要的危险因素。本文综述了原发性肝癌的流行病学特点及危险因素,可为制订原发性肝癌防控措施提供切实有力的循证医学证据。展开更多
基金the funding support from the 973 Program(2014CB440904)CAS/SAFEA International Partnership Program for Creative Research Teams(Intraplate Mineralization Research Team,KZZD-EW-TZ-20)Chinese NSF projects(41173023,41225012,41490635,41530210)
文摘Several important equilibrium Si isotope fractionation factors among minerals,organic molecules and the H_4SiO_4 solution are complemented to facilitate the explanation of the distributions of Si isotopes in Earth's surface environments.The results reveal that,in comparison to aqueous H_4SiO_4,heavy Si isotopes will be significantly enriched in secondary silicate minerals.On the contrary,quadra-coordinated organosilicon complexes are enriched in light silicon isotope relative to the solution.The extent of ^(28)Si-enrichment in hyper-coordinated organosilicon complexes was found to be the largest.In addition,the large kinetic isotope effect associated with the polymerization of monosilicic acid and dimer was calculated,and the results support the previous statement that highly ^(28)Sienrichment in the formation of amorphous quartz precursor contributes to the discrepancy between theoretical calculations and field observations.With the equilibrium Si isotope fractionation factors provided here,Si isotope distributions in many of Earth's surface systems can be explained.For example,the change of bulk soil δ^(30)Si can be predicted as a concave pattern with respect to the weathering degree,with the minimum value where allophane completely dissolves and the total amount of sesquioxides and poorly crystalline minerals reaches their maximum.When,under equilibrium conditions,the well-crystallized clays start to precipitate from the pore solutions,the bulk soil δ^(30)Si will increase again and reach a constant value.Similarly,the precipitation of crystalline smectite and the dissolution of poorly crystalline kaolinite may explain the δ^(30)Si variations in the ground water profile.The equilibrium Si isotope fractionations among the quadracoordinated organosilicon complexes and the H_4SiO_4solution may also shed light on the Si isotope distributions in the Si-accumulating plants.
文摘In this paper, we consider the relationship between the binding number and the existence of fractional k-factors of graphs. The binding number of G is defined by Woodall as bind(G)=min{ | NG(X) || X |:∅≠X⊆V(G) }. It is proved that a graph G has a fractional 1-factor if bind(G)≥1and has a fractional k-factor if bind(G)≥k−1k. Furthermore, it is showed that both results are best possible in some sense.
文摘原发性肝癌是世界上常见的恶性肿瘤之一,具有较高的发病率和死亡率。本文详述了目前我国原发性肝癌的流行病学情况、人群归因分值及其相关危险因素。本文通过检索PubMed、Web of Science、中国知网等数据库发现,乙型肝炎病毒和丙型肝炎病毒仍是原发性肝癌发病的主要危险因素。随着乙型肝炎病毒疫苗接种以及抗病毒治疗,我国原发性肝癌的发病率略有下降,但代谢性因素如糖尿病、肥胖和非酒精性脂肪性肝病等引起的原发性肝癌的发病率正逐步上升;吸烟、饮酒等也是重要的危险因素。本文综述了原发性肝癌的流行病学特点及危险因素,可为制订原发性肝癌防控措施提供切实有力的循证医学证据。
