检索结果-南通市图书馆

An Improved Unsupervised Image Segmentation Method Based on Multi-Objective Particle Swarm Optimization Clustering Algorithm

在线全文

学校读者我要写书评

暂无评论

Computers, Materials & Continua 2019年第2期58卷 451-461页

作者： zhe liu Bao Xiang Yuqing Song Hu Lu Qingfeng liu School of Computer Science and Telecommunication Engineering Jiangsu UniversityZhenjiang212013China School of Computer Science Jilin Normal UniversitySiping136000China Institute of Science and Technology Information Jiangsu UniversityZhenjiang212013China

Most image segmentation methods based on clustering algorithms use singleobjective function to implement image *** avoid the defect,this paper proposes a new image segmentation method based on a multi-objective particle swarm optimization(PSO)clustering *** unsupervised algorithm not only offers a new similarity computing approach based on electromagnetic forces,but also obtains the proper number of clusters which is determined by scale-space *** is experimentally demonstrated that the applicability and effectiveness of the proposed multi-objective PSO clustering algorithm.

关键词： Multi-objective optimization particle swarm optimization electromagnetic forces scale-space theory

Hydrogenic-Donor Impurity States in GaAs/Al xGa 1−xAs Quantum Dots in the Presence of an Electric Field

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Physics Letters 2011年第8期28卷 217-220页

作者： PAN Jiang-Hong liu Li-zhe liu Min College of Physical and Technology Guangxi Normal UniversityGuilin 541004

We report a calculation of binding energy of the ground state of a hydrogenic donor in a quantum cylindrical GaAs dot surrounded by Ga1−xAlxAs with finite confinement potentials,in the presence of a uniform electric field applied parallel to the dot *** binding energy increases inchmeal as the radius of the dot decreases until a maximum value for a certain value of the quantum dot radii,then begins to drop *** for the binding energies and electronic wave function density of the hydrogenic-donor as functions of the impurity position,dot thickness and applied electric field are also presented.

关键词： donor quantum radius

Freeze-drying synthesis of O,N-CeF_(3) with enhanced photocatalytic oxygen evolution

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Rare Earths 2023年第11期41卷 1714-1720,I0003页

作者： Bing Han Renke Bi Chutong Zhou zhe liu Zhiyu Wang State Key Laboratory of Silicon Materials Department of Materials Science and EngineeringZhejiang UniversityHangzhou310027China

Drying methods have been verified to have a considerable impact on photocatalytic efficiency via altering surface *** this study,the preparations of O,N-CeF_(3) under identical conditions using the vacuum freezing method and the oven method are *** hydroxyl,as opposed to adsorbed oxygen in CeF_(3)-O,is the main component of O faults on the surface of CeF_(3)-*** particle size and the doping atom defects of CeF_(3)-V allow for more efficient separation and faster migration of photogenerated charge ***_(3)-V has an oxygen evolution rate of up to 1.4138 mmol/(g·h)and an apparent quantum yield of 90.90%at 550 *** tails are produced as a result of the doping O and N changing the intrinsic band ***_(3)-V shows a secondary conduction band potential that is sufficient for satisfying the minimal water oxidation potential *** elucidate that defects in the states of doping O and N significantly influence CeF_(3) energy *** on how the drying process affects the band structure and encourages carriers'separation via defects is valuable,which affects how well the photocatalysis works.

关键词： Photocatalysis Oxygen evolution Band structure Defect Freeze-drying Rare earths

Historic changes in flux of matter and nutrient budgets in the Bohai Sea

在线全文

学校读者我要写书评

暂无评论

Acta Oceanologica Sinica 2008年第5期27卷 81-97页

作者： liu Sumei ZHANG Jing GAO Huiwang liu zhe College of Chemistry and Chemical Engineering Ocean University of China Qingdao 266100 China College of Environmental Sciences and Engineering Ocean University of China Qingdao 266100 China State Key Laboratory of Estuarine and Coastal Research East China Normal University Shanghai 200062 China

Over the past four periods （ 1959--1960, 1982--1983, 1992--1993, and 1998--1999）, the ecosystem of the Bohai Sea changed due to both a significant decrease of river water discharge from the Huanghe River and a reduction of precipitation. The shifts in nutrient chemistry could result in changes in the phytoplankton composition with an increased potential for non-diatom algal blooms. Simple box model was used to estimate the water - mass balance and nutrient budgets for the Bohai Sea. Water budgets indicate that the residual flow changed from out of the Bohai Sea before 1993, but became inflow to the Bohai Sea after then. The nutrient budgets developed indicate that the Bohai Sea was a sink for nutrients except for phosphate in 1959--1960 and 1982-- 1983 and for silicate in 1982--1983. Net water flow transports nutrients out of the Bohai Sea in 1959--1960, 1982--1983 and 1992--1993, but into the sea in 1998--1999 due to climate changes, such as precipitation and subsequent freshwater discharge. The residual fluxes of nutrients are minor relative to atmospheric deposition and riverine inputs. Conversions of phosphate values to carbon by stoichiometric ratios were used to predict that the system was net heterotrophic before 1982--1983 and net autotrophic after then. Nutrient budgets can explain the change of nutrient concentrations in the Bohai Sea except nitrates, which should include the surface runoff.

关键词： freshwater discharge precipitation nutrients atmospheric deposition budget Bohai Sea

CONDITIONAL AVERAGING OF TR-PIV MEASUREMENTS OF WAKE BEHIND SQUARE CYLINDER USING AN IMPROVED CROSS-CORRELATION APPROACH

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2010年第1期22卷 29-34页

作者： YU Jun SHI liu-liu WANG Wei-zhe liu Ying-zheng Key Laboratory for Power Machinery and Engineering of Ministry of Education Shanghai Jiao Tong University Shanghai 200240 China

An improved phase averaging method based on cross-correlation of the instantaneous velocity field determined by TR-PIV measurements is proposed in this article. A Time-Resolved Particle Image Velocimetry （TR-PIV） is used to measure the two-dimensional wake behind the square cylinder. The phase signals associated with the deterministic appearance of the Karman vortex street are obtained by calculating the correlation matrix of the low-pass filtered velocity field, and can provide the complete information of the phase-averaged wake flow. The results show the advantages of the enhanced methodology in extracting the quasi-periodic flow patterns related to the shedding coherent structures without using additional reference signals.

关键词： PIV cross-correlation coherent structure phase averaging

Possible nodeless s~±-wave superconductivity in twisted bilayer graphene

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2019年第7期28卷 91-97页

作者： zhe liu Yu Li Yi-Feng Yang Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China University of Chinese Academy of Sciences. Beijing 100049 China Songshan Lake Materials Laboratory Dongguan 523808 China Collaborative Innovation Center of Quantum Matter Beijing 100190 China

The recent discovery of superconductivity in the twisted bilayer graphene has stimulated numerous theoretical proposals concerning its exact gap *** them, the d + id or p + ip-wave was believed to be the most plausible ***, considering that the superconductivity emerges near a correlated insulating state and may be induced by antiferromagnetic spin fluctuations, we apply the strong-coupling Eliashberg theory with both inter-and intraband quantum critical pairing interactions and discuss the possible gap symmetry in an effective low-energy four-orbital *** calculations reveal a nodeless s~±-wave as the most probable candidate for the superconducting gap symmetry in the experimentally relevant parameter *** solution is distinctly different from previous theoretical *** highlights the multi-gap nature of the superconductivity and puts the twisted bilayer graphene in the same class as the iron-pnictide,electron-doped cuprate, and some heavy fermion superconductors.

关键词： twisted bilayer graphene superconductivity

Structures,Components and Functions of Secretory Tissues in Houttuynia cordata

在线全文

学校读者我要写书评

暂无评论

Journal of Integrative Plant Biology 2007年第12期49卷 1734-1745页

作者： Xi-Lu Ni Li Peng Wen-zhe liu College of Life Sciences Northwest University Xi'an 710069 China College of Life Sciences Ningxia University Yinchuan 750021 China

Houttuynia cordata Thunb., traditionally used as a therapeutic plant in folk medicine, has shown antioxidant and anticancer activities. The species, as a core component of paleoherbs, is normally characterized based on the presence of different types of secretory tissue： oil cells, three types of secretory cells and glandular hairs. The aim of this work was to study the structural, componential, and the functional characteristics of the secretory tissues in both the floral and vegetative parts. The results indicate that oil cells and secretory cells are distributed in all organs of the plant, while glandular hairs are situated on the aerial stems and leaves. Both oil cells and glandular hairs initiate from the protoderm, but their developmental processes are different. Although three types of secretory cells initiate from different primary meristems, the developmental patterns of different secretory cells are the same. Also, although the origins of secretory cells are different from oil cells, their early developmental processes are the same. Histochemical results show that oil cells, secretory cells and glandular hairs produce flavonoids, phenolic compounds, tannins, lipids, aldehyde and ketone-compounds. In addition, there are terpenoids and pectic-like substances in oil cells, alkaloids in secretory cells of aerial stems, and terpenoids and alkaloids in glandular hairs. These compounds play very important roles in protecting plants from being eaten by herbivores （herbivory） and infected by microbial pathogens. The oil cell and secretory cell, as unicellular secretory tissues, are intermediates between the primitive surface glandular and secretory cavity and canal during the evolution of secretory structures.

关键词： components functions glandular hairs Houttuynia cordata oil cells secretory ceils secretory tissues structures.

Asymmetric Cationic [P, O] Type Palladium Complexes in Olefin Homopolymerization and Copolymerization

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Chemistry 2017年第8期35卷 1209-1221页

作者： Shuoyan Xiong Lihua Guo Shumiao Zhang zhe liu Key Laboratory of Soft Matter Chemistry Chinese Academy of Sciences Department of Polymer Science and Engineering University of Science and Technology of China Hefei Anhui 230026 China Shool of Chemistry and ChemtcalEngmeermg Qufu Normal University Qufu Shandong 273165 China

Metal-catalyzed ethylene homopolymerization and ethylene-polar monomer copolymerization to produce new kinds of polyolefins with novel microstructures are of great interest. So far, there are some disadvantages for traditional transition metal catalyst systems. Therefore, it is critical to develop new catalysts or alternative strategies. In recent years, some cationic [P, O] palladium complexes have been demonstrated with the abilities to obtain oligomers and the high molecular weight polymers. Most importantly, these complexes showed high activity and generated polymers with specific microstructures when used for copolymerization of ethylene with industrially relevant polar monomers. This review summarizes several types of high performance cationic [P, O] palladium catalysts in ethylene oligomerization, ethylene homopolymerization and the copolymerization of ethylene with polar monomers Specially, the regulation of steric and electronic effects at specific sites of the metal complexes was focused.

关键词： palladium olefin polymerization copolymerization cationic metal center substituent effect

Spatial Distribution and Seasonal Variations of Heavy Metal Contamination in Surface Waters of Liaohe River, Northeast China

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Geographical Science 2017年第1期27卷 52-62页

作者： WANG Hui SUN Lina liu zhe LUO Qing Key Laboratory of Regional Environmental and Eco-Remediation Ministry of Education Shenyang University School for Resource and Environmental Studies Dalhousie University

Heavy metal pollutants are a worldwide concern due to slow decomposition, biocondensation, and negative effects on human health. We investigated seasonal and spatial variations of the five heavy metals and evaluated their health risk in the Liaohe River, Northeast China. A total of 324 surface water samples collected from 2009 to 2010 were analyzed. Levels(high to low) of heavy metals in the Liaohe River were: zinc(Zn) > chromium(Cr) > copper(Cu) > cadmium(Cd) > mercury(Hg). Spatial and seasonal changes impacting concentrations of Cu and Zn were significant, but not significant for Cr, Cd and Hg. The highest concentrations of heavy metals were: Hg at liuheqiao, Cu at Fudedian, Zn at Tongjiangkou, Cr at Mahushan, and Cd at Shenglitang. The highest concentrations of Hg and Cr were found in the wet period, Cu and Cd in the level period, and Zn in the dry period. The surface water of a tributary was an important accumulation site for heavy metals. Health risks from carcinogens and non-carcinogens increased from upstream to downstream in the mainstream of the Liaohe River. The total health risk for one person in the Liaohe River exceeded acceptable levels. The total health risk was the greatest during the wet period and least in the dry period. Among the five heavy metals in the Liaohe River, Cr posed the greatest single health risk.

关键词： heavy metal metal contamination health risk Liaohe River