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激光增材制造铍铝合金的缺陷和组织

稀有金属与硬质合金 2024年第4期52卷 69-77页

作者：代彦明谢垚王东新李军义张鹏李春生张健康西北稀有金属材料研究院宁夏有限公司稀有金属特种材料国家重点实验室宁夏石嘴山753000 北京工业大学材料科学与工程学院教育部先进功能材料重点实验室北京100124

采用激光选区熔化技术制备了铍铝合金,分析了在低激光功率、高激光功率以及逐层单向线扫描和67°层间交错扫描两种扫描策略下铍铝合金中的成形缺陷、显微组织和硬度。结果表明:铍铝合金中的成形缺陷主要有气孔、微孔、热裂纹和熔合不良... 详细信息

采用激光选区熔化技术制备了铍铝合金,分析了在低激光功率、高激光功率以及逐层单向线扫描和67°层间交错扫描两种扫描策略下铍铝合金中的成形缺陷、显微组织和硬度。结果表明:铍铝合金中的成形缺陷主要有气孔、微孔、热裂纹和熔合不良。气孔尺寸较小且数量很少,对合金性能影响不大;微孔可以通过采用67°层间交错扫描和提高激光功率的方式消除;热裂纹主要是由熔池凝固末期熔池中心的柱状组织间长通道中液膜受其周围前一层熔池的拉应力引起,并在后期逐层沉积过程外延生长扩展,热裂纹的开口宽度随着能量密度增加而增大;熔合不良是熔池被周围新扫描熔池高搭接率重熔时受多次热循环影响,其边缘铍铝两相扩散向稳态转变,铍相枝晶长大和铝相扩散引起显微空隙所致。增材制造铍铝合金的显微组织中主要包含铝相、铍相和一部分亚稳态组织,其中铍相与亚稳态组织共同引起合金中较大的残余应力;合金中铍相基面(0001)取向虽然有一定的择优分布,但也表现出随机性,铝相(100)方向沿熔池扫描方向则存在明显的择优取向,使合金组织呈现各向异性。另外,通过沿熔池扫描方向测试硬度得知,铍铝合金因组织细小及存在大量的亚稳态组织而表现出更高的显微硬度。

关键词：激光选区熔化铍铝合金缺陷激光功率层间交错扫描

A STREAMLINE-BASED PREDICTIVE MODEL FOR ENHANCED-OIL-RECOVERY POTENTIALITY

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Journal of Hydrodynamics 2008年第3期20卷 314-322页

作者： HOU jian zhang Shun-kang DU Qing-jun LI Yu-bin College of Petroleum Engineering China University of Petroleum （East China） Dongying 257061 China Chemical and Petroleum Department University of Calgary Calgary T2N 1N4 Canada

A pseudo-three-dimensional model of potentiality prediction is proposed for enhanced oil recovery, based on the streamline method described in this article. The potential distribution of the flow through a porous medium under a complicated boundary condition is solved with the boundary element method. Furthermore, the method for tracing streamlines between injection wells and producing wells is presented. Based on the results, a numerical solution can be obtained by solving the seepage problem of the stream-tube with consideration of different methods of Enhanced Oil Recovery（EOR）. The advantage of the method given in this article is that it can obtain dynamic calculation with different well patterns of any shape by easily considering different physicochemical phenomena having less calculation time and good stability. Based on the uniform theory basis-streamline method, different models, including CO2 miscible flooding, polymer flooding, alkaline/surfactant/polymer flooding and microbial flooding, are established in this article.

关键词： boundary element method streamline method Enhanced Oil Recovery(EOR) CO2 miscible flooding chemical flooding microbial flooding

Compilation of hydrogeological map of China

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Journal of Groundwater Science and Engineering 2020年第4期8卷 381-395页

作者： zhang jian-kang DONG Hua CHENG Yan-pei YUE Chen LIU Kun Institute of Hydrogeology and Environmental Geology Information and Mapping Research CentreShijiazhuang050061China

Hydrogeological map is one of the important carriers of groundwater related *** directly reflects the hydrogeological conditions and previous investigation and research results of a mapping *** hydrogeological map of China is a map reflecting the characteristics of hydrogeology and groundwater dynamics on a national *** the basis of the hydrogeological map of China(1:4000000)compiled in 1988,this map compilation attempted to update and enhance the existing map,with the latest survey results from the project of National Investigation and Evaluation of Groundwater Resources and Environmental Problems led by China Geological *** of the mapping program included redefining groundwater types,quantifying the classification standard of the groundwater and adding the pore-fissure water in laterite layer of hilly *** multilayer structures for porous,karst and porous-fractured groundwater and their water-rich grades are reflected on the *** on the comprehensive summary of the latest hydrogeological data of China,this research conducts an in-depth analysis of the regional distribution characteristics of groundwater in China,utilizes a digital mapping process and establishes a cartographic database for the purpose of further *** the enrichment of the content and the continuous improvement of cognitive level,mapping content can be updated quickly,which has practical significance for the concept of surveying and mapping and scientific popularization.

关键词： Hydrogeology map Mapping methods Groundwater types Water-bearing degree Groundwater regional distribution characteristics

Recent progress in carbene-catalyzed fluoroalkylation

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Science China Chemistry 2024年第8期67卷 2448-2460页

作者： Bei zhang Xuan zhang jian Wang jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control Collaborative Innovation Center of Atmospheric Environment and Equipment TechnologySchool of Environmental Science and EngineeringNanjing University of Information Science and TechnologyNanjing 210044China School of Pharmaceutical Sciences Tsinghua UniversityBeijing 100084China

The fluoroalkyl fragment plays a vital role in various fields such as pharmaceuticals and materials science, and has a significant impact on human life not only on the present but also in the future. The insertion of fluoroalkyl groups into the chemical skeletons can cause considerable alternations in the chemical, physical and biological properties of molecules, which has attracted numerous scientists from different fields. This review focuses on N-heterocyclic carbene(NHC)-catalyzed fluoroalkylation reactions, providing a detailed analysis and summary of the achievements in the past two decades. Many successful examples clearly indicate that NHCs can catalyze the tranformation of fluoroalkylation reagents with various electronic characteristics, whether electrophilic, nucleophilic, or radical precursors. Herein, the fluoroalkylation reactions are classified based on different catalytic modes of NHCs: Lewis base catalysis, Umploung catalysis, radical catalysis and others. Meanwhile, by refining and systematically studying the contribution of NHC catalysis in fluoroalkylation reactions, this review is expected to provide valuable insights and enlightenment for related fields.

关键词： N-heterocyclic carbene fluoroalkylation radical catalysis

Nanophononic metamaterials induced proximity effect in heat flux regulation

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Frontiers of physics 2024年第2期19卷 149-156页

作者： jian zhang Haochun zhang Gang zhang School of Energy Science and Engineering Harbin Institute of TechnologyHarbin 150001China Institute of High Performance Computing Agency for ScienceTechnology and Research(A*STAR)Singapore 138632Singapore

Recent studies have shown that the construction of nanophononic metamaterials can reduce thermal conductivity without affecting electrical properties,making them promising in many fields of application,such as energy conversion and thermal ***,although extensive studies have been carried out on thermal conductivity reduction in nanophononic metamaterials,the local heat flux characteristic is still *** this work,we construct a heat flux regulator which includes a silicon nanofilm with silicon *** regulator has remarkable heat flux regulation ability,and various impacts on the regulation ability are ***,even in the region without nanopillars,the local heat current is still lower than that in pristine silicon nanofilms,reduced by the neighboring nanopillars through the thermal proximity *** combine the analysis of the phonon participation ratio with the intensity of localized phonon modes to provide a clear *** findings not only provide insights into the mechanisms of heat flux regulation by nanophononic metamaterials,but also will open up new research directions to control local heat flux for a broad range of applications,including heat management,thermoelectric energy conversion,thermal cloak,and thermal concentrator.

关键词： nanophononic metamaterials proximity effect

The Relationship Between Substitution and Coutinuity

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经济数学 1991年第1期9卷 39-43页

作者： zhang jian—kang Northern Jiaotong University

In this paper, the author studies the relationship between substitution and continnity. Some results that substitution implies continuity and in some cases continuity implies substitutaon are obtined. At last, the aut... 详细信息

关键词： continuity implies ordering substitution rational hence Cambridge answer assumed axiom

Regulatory RNAs in Bacillus subtilis:A review on regulatory mechanism and applications in synthetic biology

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Synthetic and Systems Biotechnology 2024年第2期9卷 223-233页

作者： Anqi Peng Guobin Yin Wenjie Zuo Luyao zhang Guocheng Du jian Chen Yang Wang Zhen kang The Science Center for Future Foods Jiangnan UniversityWuxi214122China The Key Laboratory of Carbohydrate Chemistry and Biotechnology Ministry of EducationSchool of BiotechnologyJiangnan UniversityWuxi214122China The Key Laboratory of Industrial Biotechnology Ministry of EducationSchool of BiotechnologyJiangnan UniversityWuxi214122China

Bacteria exhibit a rich repertoire of RNA molecules that intricately regulate gene expression at multiple hierarchical levels,including small RNAs(sRNAs),riboswitches,and antisense ***,the majority of these regulatory RNAs lack or have limited protein-coding capacity but play pivotal roles in orchestrating gene expression by modulating transcription,post-transcription or translation *** and redesigning these regulatory RNA elements have emerged as pivotal strategies in the domains of metabolic engineering and synthetic *** previous investigations predominantly focused on delineating the roles of regulatory RNA in Gram-negative bacterial models such as Escherichia coli and Salmonella enterica,this review aims to summarize the mechanisms and functionalities of endogenous regulatory RNAs inherent to typical Gram-positive bacteria,notably Bacillus ***,we explore the engineering and practical applications of these regulatory RNA elements in the arena of synthetic biology,employing *** as a foundational chassis.

关键词： Regulatory RNA devices Small RNAs Riboswitches Synthetic biology Bacillus subtilis

Exhaust hood performance and its improvement technologies in industrial buildings:A literatu rereview

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Building Simulation 2024年第1期17卷 23-40页

作者： Jing zhang jian Wang Jun Gao Weimin zhang Architectural Engineering Institute Jinhua PolytechnicJinhua 321017China Institute of HVAC Engineering Schoolof Mechanical EngineeringTongji UniversityShanghai 200092China Tongji Architectural Design(Group)Co .LtdShanghai 200092China

The pollutant control performance of exhaust hoods plays a crucial role in the indoor air quality and energy consumption of ventilation systems in industrial *** better understand the impact of local ventilation on the industrial indoor environment,this paper presents a literature review of exhaust hood performance and its improvement *** create an index for evaluating the performance of exhaust hoods,the capture velocity,capture efficiency,flow ratio of pollutant emissions and exhaust airflow and energy consumption are first introduced.A number of factors affecting exhaust hood performance are assessed such as hood type,hood opening size,exhaust rate,installation distance,pollution source emission and environmental *** to structural improvement methods,the use of active airflow is a more effective way to improve the exhaust hood *** most commonly used methods for determining the exhaust rate are the controlled speed method and the flow ratio *** use of an exhaust hood with an appropriate exhaust rate and jet parameters(for an active air-assisted hood)can effectively improve the pollutant control performance and reduce the energy consumption that would be wasted on the redundant exhaust *** more information focused on exhaust hood performance,this work suggests more effective strategies for improving indoor air quality and reducing energy consumption in industrial buildings.

关键词： industrial ventilation exhaust hood capture efficiency exhaust rate performance improvement

Large post-liquefaction deformation of sand:Mechanisms and modeling considering water absorption in shearing and seismic wave conditions

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Underground Space 2024年第5期18卷 3-64页

作者： jian-Min zhang Rui Wang Department of Hydraulic Engineering State Key Laboratory of Hydroscience and EngineeringTsinghua UniversityBeijing 100084China

Large deformation of sand due to soil liquefaction is a major cause for seismic *** this study,the mechanisms and modeling of large post-liquefaction deformation of sand considering the significant influence of water absorption in shearing and seismic wave *** of case histories from past earthquakes and review of existing studies highlight the importance of the two *** on the micro and macro scale mechanisms for post-liquefaction shear deformation,the mechanism for water absorption in shearing after initial liquefaction is *** is aided by novel designed constant water-absorption-rate shear *** absorption in shearing can be classified into three types,including partial water absorption,complete water absorption,and compulsory water *** the influence of water absorption in shearing,even a strongly dilative sand under naturally drained conditions could experience instability and large shear *** mechanism for amplification of post-liquefaction deformation under surface wave load is also explained via element tests and theoretical *** shows that surface wave–shear wave coupling can induce asymmetrical force and resistance in sand,resulting in asymmetrical accumulation of deformation,which is amplified by liquefaction.A constitutive model,referred to as CycLiq,is formulated to capture the large deformation of sand considering water absorption in shearing and seismic wave conditions,along with its numerical implementation *** model is comprehensively calibrated based on various types of element tests and validated against centrifuge shaking table tests in the liquefaction experiments and analysis projects(LEAP).The model,along with various numerical analysis methods,is adopted in the successful simulation of water absorption in shearing and Rayleigh wave-shear wave coupling induced large liquefaction ***,the model is applied to high-performance simulation fo

关键词： Liquefaction Sand Large deformation Water absorption in shearing Surface wave Rayleigh wave-shear wave coupling