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Rare-Earth Functional Films Prepared by Ion Beam Epitaxy
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作者 Yang Shaoyan Chai Chunlin Zhou Jianping Liu Zhikai Chen Yonghai Chen Nuofu Wang Zhanguo 《Journal of Rare Earths》 SCIE EI CAS CSCD 2005年第5期536-536,共1页
Ion beam epitaxy (IBE) technology is a significant method for preparing high pure and high quality rare-earth functional films at low growth temperatue. A new method of preparing rare-earth functional films by ion b... Ion beam epitaxy (IBE) technology is a significant method for preparing high pure and high quality rare-earth functional films at low growth temperatue. A new method of preparing rare-earth functional films by ion beam epitaxy was reviewed in details. The recent developments and application of IBE on rare-earth functional films is focused, particularly for high-K materials CeO2, photoluminescence materials Gd2O3 and magnetic semiconductor materials Si1-x Gdx. 展开更多
关键词 rare-earth functional films IBE technology high pure growth low temperature epitaxy
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Functions of Rare Earth Metals in Automobile Emission Purification Catalysts
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作者 张爱敏 宁平 +4 位作者 计永波 刘兆亮 冯权莉 唐洁 覃庆高 《Journal of Rare Earths》 SCIE EI CAS CSCD 2004年第S1期99-102,共4页
The functions of rare earth metals in the automobile emission purification catalysts were reviewed, and it was clarified that with precious metals resources using up gradually emission regulations becoming more and mo... The functions of rare earth metals in the automobile emission purification catalysts were reviewed, and it was clarified that with precious metals resources using up gradually emission regulations becoming more and more strict, rare earth metals will play more and more important roles in the high performance, and in low price automobile emission purification catalysts, they can not be substituted by other elements, for example, precious metals. 展开更多
关键词 automobile emission purification CATALYSTS functionS rare earths
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Lanthanide complexes-functionalized ordered mesoporous TiO_2:Multicolor emission(visible and near-infrared luminescence) based on visible-light sensitization 被引量:1
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作者 Zhijuan Wang Song Dang +1 位作者 Shu'na Zhao Lining Sun 《Journal of Rare Earths》 SCIE EI CAS CSCD 2018年第9期939-945,共7页
Recently,much attention has been paid to the lanthanide luminescent materials based on the visiblelight sensitization for their potential applications in the fields of bio-imaging and optical devices.In this work,the ... Recently,much attention has been paid to the lanthanide luminescent materials based on the visiblelight sensitization for their potential applications in the fields of bio-imaging and optical devices.In this work,the lanthanide complexes have been covalently bonded to the ordered mesoporous titania(OMT) matrix,and the resulting titania-based hybrid ordered mesoporous materials(named as LnDBOMT,Ln = Eu,Sm,Yb,Nd) were characterized by using Fourier-transform infrared(FT-IR) spectroscopy,small-angle X-ray powder diffraction(SAXD),N2 adsorption-desorption isotherms,transmission electron microscopy(TEM),fluorescence spectroscopy,and thermogravimetric analysis.Generally,exciting with visible light is advantageous over UV excitation.Of importance here is that,under excitation with visible light,the LnDB-OMT all show characteristic visible(Eu3+,Sm3+) as well as nearinfrared(Sm3+,Yb3+,Nd3+) luminescence of the corresponding Ln3+ ions(multicolor emission covered from 500 to 1400 nm spectral region),which is attributed to the energy transfer from the ligands to the Ln3+ ions via an antenna effect. 展开更多
关键词 Visible-light excitation Visible luminescence Near-infrared luminescence Lanthanide complexes-functionalized Ordered mesoporous titania rare earths
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SYNTHESIS OF FUNCTIONAL UNSATURATED POLYESTER BY USING RARE EARTH CATALYSTS 2.TERPOLYMERIZATION OF EPICHLOROHYDRINMALEIC ANHYDRIDE-CARBON DIOXIDE WITH Y(P_(204))_3-Al(i-Bu)_3
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作者 Xian Hai CHEN Yi Feng ZHANG Zhi Quan SHENDepartment of Chemistry,Zhejiang University,Hangzhou 310027 《Chinese Chemical Letters》 SCIE CAS CSCD 1992年第5期359-360,共2页
Teroolymerization of enichlorohydrin(ECH)-maleic anhydride(MAn)-carbon dioxide(CO;) was carried out by using Y(P;);-Al(i-Bu);as catalyst for the first time.The terpolymersobtained were characterized by IR and;... Teroolymerization of enichlorohydrin(ECH)-maleic anhydride(MAn)-carbon dioxide(CO;) was carried out by using Y(P;);-Al(i-Bu);as catalyst for the first time.The terpolymersobtained were characterized by IR and;H-NMR.It was foundthat the composition of the teroolymer was influenced by theaddition mode,initial monomer charge ratio,etc. 展开更多
关键词 Al i-Bu SYNTHESIS OF functionAL UNSATURATED POLYESTER BY USING rare EARTH CATALYSTS 2.TERPOLYMERIZATION OF EPICHLOROHYDRINMALEIC ANHYDRIDE-CARBON DIOXIDE WITH Y
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A new perspective on functional redundancy and phylogenetic niche conservatism in soil microbial communities 被引量:3
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作者 Yu JIA Joann K.WHALEN 《Pedosphere》 SCIE CAS CSCD 2020年第1期18-24,共7页
Functional redundancy in soil microbial communities seems to contradict the notion that individual species have distinct metabolic niches in multi-species communities.All soil microbiota have the metabolic capacity fo... Functional redundancy in soil microbial communities seems to contradict the notion that individual species have distinct metabolic niches in multi-species communities.All soil microbiota have the metabolic capacity for"basic"functions(e.g.,respiration and nitrogen and phosphorus cycling),but only a few soil microbiota participate in"rare"functions(e.g.,methanogenesis and mineralization of recalcitrant organic pollutants).The objective of this perspective paper is to use the phylogenetic niche conservatism theory as an explanation for the functional redundancy of soil microbiota.Phylogenetic niche conservatism is defined as the tendency for lineages to retain ancestral functional characteristics through evolutionary time-scales.The present-day soil microbiota is the result of a community assembly process that started when prokaryotes first appeared on Earth.For billions of years,microbiota have retained a highly conserved set of core genes that control the essential redox and biogeochemical reactions for life on Earth.These genes are passed from microbe to microbe,which contributes to functional redundancy in soil microbiota at the planetary scale.The assembly of microbial communities during soil formation is consistent with phylogenetic niche conservatism.Within a specific soil,the heterogeneous matrix provides an infinite number of sets of diverse environmental conditions,i.e.,niches that lead to the divergence of microbial species.The phylogenetic niche conservatism theory predicts that two or more microbial species diverging from the same clade will have an overlap in their niches,implying that they are functionally redundant in some of their metabolic processes.The endogenous genetic factors that constrain the adaptation of individuals and,thus,populations to changing environmental conditions constitute the core process of phylogenetic niche conservatism.Furthermore,the degree of functional redundancy in a particular soil is proportional to the complexity of the considered function.We conclude with a conceptual model that identifies six patterns of functional redundancy in soil microbial communities,consistent with the phylogenetic niche conservatism theory. 展开更多
关键词 basic function CONCEPTUAL model core gene environmental FACTOR genetic FACTOR NICHE OVERLAP rare function soil BIODIVERSITY
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Sediment provenance discrimination in northern Okinawa Trough during the last 24 ka and paleoenvironmental implication:rare earth elements evidence 被引量:13
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作者 徐兆凯 李铁刚 +3 位作者 常凤鸣 CHOI Jinyong LIM Dhongil 徐方建 《Journal of Rare Earths》 SCIE EI CAS CSCD 2012年第11期1184-1190,共7页
Rare earth elements (REE) compositions and discriminant function were successfully used to examine high resolution sediment source changes in the northern Okinawa Trough over the last 24.1 ka, especially for the inf... Rare earth elements (REE) compositions and discriminant function were successfully used to examine high resolution sediment source changes in the northern Okinawa Trough over the last 24.1 ka, especially for the influence from the Yellow River and the Tsushima Warm Current (TWC) that has not been well solved. Variations of these parameters were clearly divided into three distinct depositional units. During Interval 1 (24.1-16.0 ka BP), the paleo-Yellow River and the paleo-Yangtze River mouths were situated near the studied area and could have played major roles in the sedimentation therein. In Interval 2 (16.0-7.3 ka BP), these river mouths gradually retreated with global sea-level rise, leading to less fluvial inputs from them to the northern Okinawa Trough. Meanwhile, formation of the TWC could carry some sediment loads of Taiwan to the studied core, especially during its late phase (8.0-7.3 ka BP). Modem oceanographic conditions, with a predominance of the TWC, were finally established since the beginning of Interval 3, causing more ten'igenous contribution from Taiwan to the studied area. Subsequently, modem depositional environments mainly influenced by the Yellow River, the Yangtze River, and the TWC were finally formed. 展开更多
关键词 sediment provenance discriminant function rare earth elements Tsushima Warm Current northern Okinawa Trough
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Rare earth texture analysis of rectangular extruded Mg alloys and a comparison of different alloying adding ways 被引量:3
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作者 Xiu-Li Hou Yi-Xuan Zhai +3 位作者 Peng Zhang Shun Guo Zhi-Zhong Yuan Qing-Feng Guan 《Rare Metals》 SCIE EI CAS CSCD 2016年第11期850-857,共8页
The microstructures and textures of four rectangular extruded Mg alloys, Mg-3Gd, Mg-3Nd, Mg-1Gd-1Nd and Mg-1.5Gd-1.5Nd(all in wt%) were investigated by using optical microscopy(OM), X-ray diffraction(XRD) and el... The microstructures and textures of four rectangular extruded Mg alloys, Mg-3Gd, Mg-3Nd, Mg-1Gd-1Nd and Mg-1.5Gd-1.5Nd(all in wt%) were investigated by using optical microscopy(OM), X-ray diffraction(XRD) and electron backscatter diffraction(EBSD). The results demonstrate that the extruded alloys all reveal fully recrystallized microstructure and weak non-basal texture.For textures of the four extruded alloys, it is shown that the basal planes of majority grains tilt away from the sheet plane normal toward the extrusion direction. Compared with two binary alloys, the ternary alloys possess weaker texture strengths. Through orientation distribution function analysis, two types of rare earth textures, {0113} 〈0223〉and {1215} 〈1213〉, were found in the extruded alloys.Texture component {1215} 〈1213〉 is relatively weak, but it plays a critical role in the low texture intensities of two ternary alloys. A pairing effect of Gd and Nd elements has an influence on the texture modification. Additionally,there is a difference in the sensitivities of experimental parameters between the microstructure and texture. 展开更多
关键词 Mg alloy Texture rare earth elements Orientation distribution function
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Advances on Rare Earth Application in Pollution Ecology 被引量:28
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作者 黄晓华 周青 张光生 《Journal of Rare Earths》 SCIE EI CAS CSCD 2005年第1期5-11,共7页
The use of rare earth for inducing plant resistance was reviewed. The important developments in recent years were described, and rare earth can alleviate the pollution of acid rain, ozone, pesticide, heavy metals etc.... The use of rare earth for inducing plant resistance was reviewed. The important developments in recent years were described, and rare earth can alleviate the pollution of acid rain, ozone, pesticide, heavy metals etc. in environment. The authors suggest that the mechanism of rare earth to inducing plant resistance and reducing plant injury is to control biochemical metabolism web in plant cell, to adjust its protection system of free radical, to maintain its photosynthesis, to protect cell membrane system and to carry through its function on mineral metabolism. Meanwhile some problems in the field were discussed as well. 展开更多
关键词 pollution ecology resistance pollution function inducing plants resistance plant rare earths
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Density Functional Theory Study on La Complex with Schiff-base as Building Block 被引量:6
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作者 XIA Shu-Wei XU Xiang SUN Ya-Li FAN Yu-Hua BI Cai-Feng ZHANG Dong-Mei YANG Li-Rong 《Chinese Journal of Structural Chemistry》 SCIE CAS CSCD 北大核心 2006年第2期197-203,共7页
Quantum density functional theory (DFT) results are reported for the building block [LaL^1(NO3)] of La complex [LaL^1(NO3)]NO3·5H2O (L^1 = (CH3)2CHCH2CH(NCHC4H3O)COO^-). The structure was optimized an... Quantum density functional theory (DFT) results are reported for the building block [LaL^1(NO3)] of La complex [LaL^1(NO3)]NO3·5H2O (L^1 = (CH3)2CHCH2CH(NCHC4H3O)COO^-). The structure was optimized and the calculation results show that the lanthanum ion is coordinated by one nitrogen atom and three oxygen atoms of L^1 and two oxygen atoms of nitrate ion. The bond length of La-N is 0.2637 nm and the average length of La-O is 0.2526 nm, which are consistent with the literatures. In addition, the stabilities, electronic structural characteristics and IR spectra of the complex have been analyzed, which describe the coordination of lanthanum ion with other atoms in detail. 展开更多
关键词 rare-EARTH SCHIFF-BASE lanthanum complex density functional theory
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Band gap calculation and photo catalytic activity of rare earths doped rutile TiO_2 被引量:13
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作者 边亮 宋绵新 +2 位作者 周天亮 赵效勇 戴清清 《Journal of Rare Earths》 SCIE EI CAS CSCD 2009年第3期461-468,共8页
The density of states (DOS) of 17 kinds of rare earths (RE) doped rutile TiO2 was by using first-principles density functional theory (DFT) calculation. The band gap widths of RE doped futile TiO2 were important... The density of states (DOS) of 17 kinds of rare earths (RE) doped rutile TiO2 was by using first-principles density functional theory (DFT) calculation. The band gap widths of RE doped futile TiO2 were important factors for altering their absorbing wavelengths. The results show that RE ions could obviously reduce the band gap widths and form of energy of ruffle TiO2 except Lu, Y, Yb and Sc, and the order of absorbing wavelengths of RE doped ruffle TiO2 were the same as that of the results of calculation. The ratio of RE dopant was another important factor for the photo catalytic 'activity of RE doped rutile TiO2, and there was an optimal ratio of dopant. There was a constant for predigesting the calculation difficulty, respectively, which were 0.5mol.% and 100 mol^-1 under supposition. The band gap widths of RE doped rutile TiOz by DFT calculation were much larger than that by experiment. Finally, by transferring the calculation values to experiment values, it could be found and predicted that RE enlarged obviously the absorbing wavelengh of ruffle TiO2. In addition, the degree of RE ions edging out the Ti atom using the parameters of RE dements was computed. 展开更多
关键词 density functional theory ruffle TiO2 band gap rare earths
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Band-gap engineering of La1-xNdxAlO3(x = 0,0.25,0.50,0.75,1)perovskite using density functional theory:A modified Becke Johnson potential study
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作者 Sandeep D P Rai +6 位作者 A Shankar M P Ghimire Anup Pradhan Sakhya T P Sinha R Khenata S Bin Omran R K Thapa 《Chinese Physics B》 SCIE EI CAS CSCD 2016年第6期376-382,共7页
The structural,electronic,and magnetic properties of the Nd-doped Rare earth aluminate,La1-xNdxAlO3(x = 0%to 100%) alloys are studied using the full potential linearized augmented plane wave(FP-LAPW) method within... The structural,electronic,and magnetic properties of the Nd-doped Rare earth aluminate,La1-xNdxAlO3(x = 0%to 100%) alloys are studied using the full potential linearized augmented plane wave(FP-LAPW) method within the density functional theory.The effects of the Nd substitution in La AlO3 are studied using the supercell calculations.The computed electronic structure with the modified Becke–Johnson(m BJ) potential based approximation indicates that the La1-xNdxAlO3 alloys may possess half-metallic(HM) behaviors when doped with Nd of a finite density of states at the Fermi level(EF).The direct and indirect band gaps are studied each as a function of x which is the concentration of Nddoped La AlO3.The calculated magnetic moments in the La1-xNdxAlO3 alloys are found to arise mainly from the Nd-4f state.A probable half-metallic nature is suggested for each of these systems with supportive integral magnetic moments and highly spin-polarized electronic structures in these doped systems at EF.The observed decrease of the band gap with the increase in the concentration of Nd doping in La AlO3 is a suitable technique for harnessing useful spintronic and magnetic devices. 展开更多
关键词 density functional theory rare earth aluminates perovskites electronic structures
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First-principles study of the electronic structure of a superstoichiometric rare earth dihydride GdH2.25
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作者 z.ayat a.boukraa b.daoudi 《Journal of Rare Earths》 SCIE EI CAS CSCD 2016年第1期66-70,共5页
We performed ab initio calculations of electronic structure and equilibrium properties for the rare earth superstoichiometric dihydride GdH2.25 (with the space group Pm-3m (No. 221)) using the full-potential linea... We performed ab initio calculations of electronic structure and equilibrium properties for the rare earth superstoichiometric dihydride GdH2.25 (with the space group Pm-3m (No. 221)) using the full-potential linearized augmented plane wave method (FP-LAPW) approach within the density functional theory (DFT) in the generalized gradient approximation (GGA) and local density approximation (LDA) as implemented in the WIEN2k simulation code at 0 K. The equilibrium properties were determined, the density of states, electronic density and the energy band structures were studied in details. It was concluded that the GGA optimized lattice parameter agreed much better with the experimental findings than the LDA one, The non negligible electronic density of states at the Fermi level confirmed that the GdH2.25 had a metallic character. The Fermi energy EF fell at a level where most of the states were rare-earth 5d-eg conduction states while negligible contributions of both interstitial (tetrahedral and octahedral) H s-states were observed near EF, From electronic density, the bonding between Gd and tetrahedral H atoms was of prominent covalency, while was ionic between Gd and octahedral H atoms. 展开更多
关键词 rare-earth dihydrides GdU2.25 density functional theory ab initio calculations WIEN2k
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Biological Function of REE in Plants & Microbes
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作者 邱关明 李伟 +1 位作者 李喜坤 周威 《Journal of Rare Earths》 SCIE EI CAS CSCD 2005年第6期645-652,共8页
Rare earth elements (REE) and their compounds years. The bioinorganic chemical research of REE during the are widely applied in agronomic and medical fields for many past few years indicates that REE play important ... Rare earth elements (REE) and their compounds years. The bioinorganic chemical research of REE during the are widely applied in agronomic and medical fields for many past few years indicates that REE play important roles in the promotion of photosynthetic rate as well as root absorption, regulation of hormone and nitrogen metabolism, and suppression of microbes, etc. The metallic or non-metallic targets of key biomolecule in various physiological processes can be chosen by REE for the chelation or replacement, which enables REE to regulate the biological functions or behaviors of those biomolecule and consequently leads to significant embodiment of biological function of REE in plants and microbes. Overdose of REE, however, shows an inhibitory effect on living organisms. Therefore, this paper proposes two suggestions that will be available in the extension of full use of REE's biological function. One is to obey the dose law of REE and control REE concentrations within a safe range. The other is to further test the bioaccumulation and long-period influence of REE on organisms. 展开更多
关键词 bioinorganic chemistry biological function of REE plants and microbes dosage effect BIOACCUMULATION rare earths
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南方离子型稀土矿山垂直剖面微生物群落结构特征及其对环境因子的响应 被引量:1
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作者 陈娴 崔熙雯 +7 位作者 韩海斌 陈涵冰 江仰龙 王小闽 陈志彪 张勇 张虹 韩永和 《微生物学报》 北大核心 2025年第6期2736-2755,共20页
离子型稀土矿是国际上备受关注的战略资源,对我国多个产业的发展至关重要。然而,大规模的开采活动引发了土壤退化、营养流失和重金属污染等问题。[目的]分析离子型稀土矿山垂直剖面上微生物的群落结构特征及其对环境因子的响应,了解微... 离子型稀土矿是国际上备受关注的战略资源,对我国多个产业的发展至关重要。然而,大规模的开采活动引发了土壤退化、营养流失和重金属污染等问题。[目的]分析离子型稀土矿山垂直剖面上微生物的群落结构特征及其对环境因子的响应,了解微生物群落沿垂直剖面的深度分异规律及其与环境因子的关系,为污染矿区土壤的生态修复提供参考。[方法]以离子型稀土矿山1-15 m深的土壤样品为研究对象,分析土壤的理化性质;采用高通量测序技术探究矿山垂直剖面上土壤微生物的分布规律并构建环境因子与微生物群落演替的关系。[结果]伴随矿山深度的增加,土壤pH值和总碳(total carbon, TC)逐渐降低;氨氮(ammonia nitrogen, NH3-N)是矿山土壤的主要氮素存在形态,在中深层土壤中可达13.0 mg/kg;铁(iron, Fe)、镁(magnesium, Mg)和总稀土元素(total rare earth elements, TREEs)含量颇丰,且在深层土壤中聚集程度较高。微生物群落在矿山垂直剖面上呈现出明显的演替规律;其中,α多样性指数Chao1 (丰富性指数)和Shannon(多样性指数)等提示土壤微生物群落多样性随深度增加而降低,而β多样性指数如主成分分析(principal component analysis, PCA)和主坐标轴分析(principal co-ordinates analysis, PCoA)表明各层级间聚类差异显著。相关性分析结果显示,环境因子可调控微生物群落结构分异,土壤各剖面层级间存在不同的土壤养分循环特征。绿屈挠菌门(Chloroflexota)、假单胞菌门(Pseudomonadota)、放线菌门(Actinomycetota)和酸杆菌门(Acidobacteriota)是矿区土壤的优势细菌门类,在生物地球化学循环过程中可能发挥着重要作用。矿山土壤微生物存在层级演替规律:浅层土壤的优势菌群为绿屈挠菌门、酸杆菌门和放线菌门;中间层绿屈挠菌门的相对丰度下降,假单胞菌门逐渐占据优势地位,其相对丰度达60%;在深层极度厌氧环境中,假单胞菌门通过代谢适应性在寡营养条件下演替为优势菌群(相对丰度达70%)。上述微生物在土壤碳氮循环过程中发挥了重要作用。在碳循环方面,浅层土壤微生物以卡尔文循环主导固碳过程;中间层呈现出微氧-厌氧过渡带环境,促进微生物以糖酵解途径和三羧酸循环为主代谢途径以满足生长需求;深层土壤的厌氧环境促使微生物以发酵为主代谢方式。在氮循环方面,浅层土壤微生物以异化硝酸盐还原成铵(dissimilatory nitrate reduction to ammonium, DNRA)为主代谢方式,中间过渡层微生物在反硝化过程中占据重要地位,而深层厌氧环境的微生物以DNRA过程为主和反硝化作用为辅的双重代谢体系维持生长,其氮转化强度远高于浅层土壤。[结论]离子型稀土矿山垂直剖面的微生物群落呈现明显的分异规律且与多个环境因子密切相关,提示其在矿区土壤物质循环中的潜在作用,可为未来调控稀土矿区污染修复提供科学依据。 展开更多
关键词 稀土 土壤剖面 微生物群落 功能分析 生态修复
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纺织品中稀土含量测试标准的验证方法 被引量:1
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作者 周威 马玉新 +3 位作者 杨任游 王斌 余建军 陈楠 《实验室研究与探索》 北大核心 2025年第1期50-55,共6页
基于功能性纺织品中稀土含量基体标准样品(FT-RE-MRM)的应用,结合电感耦合等离子体质谱法(ICP-MS),建立了用于行业标准SN/T 5288—2022的验证方法。该方法的标准曲线线性相关系数在0.999 4以上,检出限在0.002~0.690 mg/kg,精密度均小于3... 基于功能性纺织品中稀土含量基体标准样品(FT-RE-MRM)的应用,结合电感耦合等离子体质谱法(ICP-MS),建立了用于行业标准SN/T 5288—2022的验证方法。该方法的标准曲线线性相关系数在0.999 4以上,检出限在0.002~0.690 mg/kg,精密度均小于3.63%,回收率在80.3%~94.8%。采用Cochran检验法对8家协同验证机构返回的测定数据进行统计分析,统计量值C均小于检验临界值C(0.05,8,6),表明返回的数据无离群值。计算方法的重复性标准差(Sr)和再现性标准差(SR)分别为:0.004 76、0.006 73、0.003 86、0.005 40、0.007 54、0.004 63,表明该方法的准确度和精密度较高、重复性和再现性良好,适用于纺织品中稀土含量测试标准的验证。 展开更多
关键词 功能性纺织品 稀土 基体标准样品 电感耦合等离子体质谱法
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稀有种丧失对鱼类群落物种多样性和功能多样性的影响 被引量:2
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作者 周钟楠 童安楠 +3 位作者 吴亚妮 水柏年 胡成业 王晶 《生态学报》 北大核心 2025年第1期252-264,共13页
稀有种是海洋生态系统中物种共存与多样性维持的重要类群,但其对鱼类群落物种多样性、功能多样性的调控机制不明。以三门湾鱼类群落为研究对象,基于地理范围、栖息地特异性和种群规模大小识别群落稀有种,利用自抽样技术模拟稀有种在自... 稀有种是海洋生态系统中物种共存与多样性维持的重要类群,但其对鱼类群落物种多样性、功能多样性的调控机制不明。以三门湾鱼类群落为研究对象,基于地理范围、栖息地特异性和种群规模大小识别群落稀有种,利用自抽样技术模拟稀有种在自然条件下的随机丧失,探讨稀有种丧失对物种多样性、功能多样性的影响。结果表明,稀有种的丧失造成物种丰富度与功能丰富度呈显著下降趋势;物种均匀度在夏季稳定性较低,在其余季节稳定性较高,功能均匀度在冬季稳定性较高,在其余季节稳定性较低,这与稀有种地理分布范围及其功能性状所占据的空间特殊位置有关;Simpson指数与Shannon⁃Wiener指数呈现下降趋势,但前者数值变化区间小于后者,这与群落丰富度、均匀度密切相关;功能离散度在夏季呈下降趋势,而在其他季节保持相对稳定,主要受位于性状空间边缘物种数量的影响。总体上,稀有种的丧失对物种多样性、功能多样性的稳定性产生影响,且物种多样性与功能多样性的相关性较强。 展开更多
关键词 稀有种 物种丧失 物种多样性 功能多样性
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轻度认知障碍罕见逆转的认知轨迹建模
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作者 秦瑶 霍彦吉 +4 位作者 周静 周妍 韩红娟 崔靖 余红梅 《药物流行病学杂志》 2025年第8期877-886,共10页
目的 构建轻度认知障碍(MCI)双向转归的动态分析框架,量化MCI罕见逆转现象与高进展风险的动态认知轨迹。方法 选取阿尔茨海默病神经影像学计划(ADNI)2005—2022年基线诊断为MCI且至少完成2次随访的患者,构建回顾性队列。收集人口学信息... 目的 构建轻度认知障碍(MCI)双向转归的动态分析框架,量化MCI罕见逆转现象与高进展风险的动态认知轨迹。方法 选取阿尔茨海默病神经影像学计划(ADNI)2005—2022年基线诊断为MCI且至少完成2次随访的患者,构建回顾性队列。收集人口学信息、APOEε4基因型及神经心理学量表数据,采用多变量函数型主成分分析(MFPCA)对纵向认知评估结果进行函数化重构,并基于累积方差贡献率(FVE > 90%)提取主成分(FPC)。构建函数型多状态Markov模型,估计状态间的转移强度、逐年转移概率及协变量效应。结果 共纳入1 019例MCI患者,累计完成随访4 657例次,最终93例(9.1%)逆转,359例(35.2%)进展为阿尔茨海默病(AD)。纵向认知轨迹分析显示,第一主成分(MFPC1)得分在不同转归群体中存在显著差异,进展型MCI >稳定型MCI >逆转型MCI。MCI逆转的转移强度(0.020)约为AD进展风险(0.086)的1/4,但逆转后认知再损害强度高达0.138。MFPC1降低(HR=0.993,95%Cl:0.991,0.995)与MFPC2升高(HR=1.004,95%Cl:1.001,1.007)均与MCI逆转密切相关。结论 MCI群体在纵向认知轨迹中呈现显著的异质性。MCI逆转事件较为罕见,且逆转后仍面临认知再损害风险。 展开更多
关键词 轻度认知障碍 逆转 罕见事件 函数型主成分分析 多状态模型
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舟山渔场鱼类群落稀有种和常见种丧失对群落功能多样性的影响
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作者 钱均 李羽如 +3 位作者 周钟楠 王迎宾 胡成业 王晶 《海洋学报》 北大核心 2025年第9期82-90,共9页
本研究基于舟山渔场鱼类群落调查数据,采用自抽样技术模拟稀有种和常见种种类数随机丧失,并通过生物量比例递减法模拟生物量丧失情景,以探究不同生态类群丧失对鱼类群落功能多样性的影响机制。研究结果表明,稀有种虽仅占群落总生物量的... 本研究基于舟山渔场鱼类群落调查数据,采用自抽样技术模拟稀有种和常见种种类数随机丧失,并通过生物量比例递减法模拟生物量丧失情景,以探究不同生态类群丧失对鱼类群落功能多样性的影响机制。研究结果表明,稀有种虽仅占群落总生物量的3%,但其种类数占比接近40%,在群落结构组成中具有重要地位。物种丧失情景模拟显示,稀有种种类数丧失直接影响功能多样性指数,具体表现为功能丰富度下降、功能均匀度上升,而功能离散度和二次熵指数变化不明显;常见种种类数丧失导致功能丰富度下降,其余三个功能多样性指数则保持相对稳定。在生物量丧失情景下,随着稀有种生物量减少功能丰富度保持不变而功能均匀度、功能离散度和二次熵指数均呈现下降趋势,其中功能均匀度表现为先缓后急的非线性下降,其余两个指数则呈现线性递减规律;常见种生物量丧失则引起后三个指数下降呈现先急后缓的特征。稀有种在群落中占据着独特的生态功能位,其功能性状分布于多维功能空间边缘,对维持群落功能多样性具有独特的作用。加强稀有种及其栖息地的保护是维持区域生态系统多样性和稳定性的关键策略。 展开更多
关键词 鱼类群落 稀有种 功能多样性 模拟丧失
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新型稀土锆酸盐活性物质热发射特性研究
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作者 漆世锴 李云 +2 位作者 张琪 陈栋 何俊 《中国稀土学报》 北大核心 2025年第5期1150-1157,共8页
为了提高医疗加速器用磁控管阴极的热发射性能,延长其使用寿命。采用稀土氧化物La_(2)O_(3)/Y_(2)O_(3)掺杂难熔金属氧化物ZrO_(2)来合成电子发射活性物质,并以该活性物质制备磁控管用阴极。X射线衍射仪(XRD)分析结果显示,La_(2)O_(3)/Y... 为了提高医疗加速器用磁控管阴极的热发射性能,延长其使用寿命。采用稀土氧化物La_(2)O_(3)/Y_(2)O_(3)掺杂难熔金属氧化物ZrO_(2)来合成电子发射活性物质,并以该活性物质制备磁控管用阴极。X射线衍射仪(XRD)分析结果显示,La_(2)O_(3)/Y_(2)O_(3)和ZrO_(2)在高温马弗炉中发生了化学反应,分别生成了新型稀土La_(2)Zr_(2)O_(7)和Y-Zr-O难熔盐活性物质。热发射测试结果显示,当工作温度为1600℃,阳极电压为300 V时,La_(2)Zr_(2)O_(7)和Y-Zr-O阴极的热发射电流密度分别为2.03,1.25 A·cm^(-2)。根据理查森直线法拟合出阴极的绝对零度逸出功分别为0.80,0.78 eV。利用理查森-道舒曼公式计算获得,当工作温度为1600℃时,阴极的有效逸出功分别为3.42,3.39 eV。最后,对阴极的热发射机理进行了有益的探讨。 展开更多
关键词 稀土锆酸盐 磁控管 阴极 逸出功 发射机理
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稀有濒危植物贵州红山茶的种群空间格局及关联性研究 被引量:2
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作者 唐凤 李媛媛 +3 位作者 杨乃坤 周泉 刘海燕 邹天才 《广西植物》 北大核心 2025年第1期185-196,共12页
贵州红山茶(Camellia kweichowensis)系山茶属下接受物种名称滇山茶(Camellia reticulata)的异名,是贵州省自然分布的重点保护野生植物,该物种稀有濒危。为探究贵州红山茶种群空间分布格局以及关联性特征,该研究在实地踏查基础上,采用... 贵州红山茶(Camellia kweichowensis)系山茶属下接受物种名称滇山茶(Camellia reticulata)的异名,是贵州省自然分布的重点保护野生植物,该物种稀有濒危。为探究贵州红山茶种群空间分布格局以及关联性特征,该研究在实地踏查基础上,采用成对相关函数g(r)对种群各生长阶段植株分布特点及关联性进行了点格局分析。结果表明:(1)贵州红山茶种群各发育阶段植株在较小尺度下均为集群分布,随着研究尺度的增加,个体间聚集程度逐步降低,呈现出由集群分布逐渐转变为随机分布的趋势,具有显著的小尺度聚集、大尺度随机的基本特征。(2)小尺度下,植株相互庇佑提高种群存活率,种群各相邻年龄阶段植株均表现出正相关,其相关性随着尺度的增大而逐渐减弱,并走向负相关;中-大尺度下,中龄、成年植株抑制林下更新以保障其生长优势。物种发育原始、生境资源竞争压力大、种内自疏牵制性强及生境干扰等因素,是贵州红山茶种群因难于扩散而呈狭窄分布特征以及物种稀有濒危的重要原因。因此,改善自然分布种群生境条件、疏林结构适当调整以及物种迁地保育和育苗回归栽培是保障贵州红山茶种群稳定繁衍的关键。该研究结果为贵州红山茶植物资源有效保护与创新利用提供了种质基础和科学依据,对加强生物多样性保护利用和研究植物种群发育演替机制具有重要意义。 展开更多
关键词 贵州红山茶 稀有濒危植物 种群分布格局 空间关联性 成对相关函数
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