检索结果-南通市图书馆

Corrosion Resistance of Sintered NdFeB Permanent Magnet With Ni-P/TiO_2 Composite Film

在线全文

学校读者我要写书评

暂无评论

Journal of Iron and Steel Research International 2009年第3期16卷 89-94页

作者： SONG Lai-zhou yang zhi-yong Department of Environment and Chemical Engineering Yanshan University Qinhuangdao 066004 HebeiChina Central Iron and Steel Research Institute Beijing 100081 China

The Ni-P/TiO2 composite film on sintered NdFeB permanent magnet was investigated by X-ray diffraction （XRD）,environmental scanning electron microscopy （ESEM）,and energy dispersive X-ray spectrometer （EDX）. The corrosion resistance of Ni-P/TiO2 film coated on NdFeB magnet,in 0.5 mol/L NaCl solution,was studied by potentiodynamic polarization,salt spray test and electrochemical impedance spectroscopy （EIS） techniques. The self-corrosion current density （icorr） and the polarization resistance （Rp） of Ni-P/TiO2 film are 0.22 μA/cm2 （about 14% of that of Ni-P coating）,and 120 kΩ·cm2 （about 2 times of that of Ni-P coating）,respectively. The anti-salt spray time of Ni-P/TiO2 film is about 2.5 times of that of the Ni-P coating. The results indicate that Ni-P/TiO2 film has a better corrosion resistance than Ni-P coating,and the composite film increases the corrosion resistance of NdFeB magnet markedly.

关键词： sintered NdFeB permanent magnet Ni-P/TiO2 composite film sodium chloride solution corrosion resistance

Recent developments in multivariate pattern analysis for functional MRI

在线全文

学校读者我要写书评

暂无评论

Neuroscience Bulletin 2012年第4期28卷 399-408页

作者： zhi yang Fang Fang Xuchu Weng Key Laboratory of Behavioral Sciences Institute of PsychologyChinese Academy of SciencesBeijing 100101China Center for Cognition and Brain Disorders Hangzhou Normal UniversityHangzhou 310015China Department of Psychology Peking UniversityBeijing 100817China

Multivariate pattern analysis（MVPA） is a recently-developed approach for functional magnetic resonance imaging（fMRI） data *** with the traditional univariate methods,MVPA is more sensitive to subtle changes in multivariate patterns in fMRI *** this review,we introduce several significant advances in MVPA applications and summarize various combinations of algorithms and parameters in different problem *** limitations of MVPA and some critical questions that need to be addressed in future research are also discussed.

关键词： multivariate analysis fMRI pattern recognition computational biology

Improved performance by plasmon resonance in GaAs solar cells:a numerical expectation

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2024年第11期43卷 5712-5719页

作者： yang Wang zhi-yang Wan Jia-Jin Kuang Ming-Tai Wang Institute of Solid State Physics Hefei Institutes of Physical ScienceChinese Academy of SciencesHefei 230031China University of Science and Technology of China Hefei 230026China School of Electronic Engineering Huainan Normal UniversityHuainan232000China

The planar heterojunction solar cells based on the GaAs films doped with gold nanoparticles(Au NPs)are investigated by a finite-difference time-domain *** numerical results show that Au NPs effectively increase the light absorption and short-circuit current(J_(sc))of GaAs solar cells,when saving GaAs consumption by reducing film *** the GaAs film of 200 nm in thickness,the presence of Au NPs boosts the device J_(sc)up to 36.94 mA·cm^(-2),1.29 times that of the counterpart device without Au *** addition,one requires the pure GaAs film of 500-600 nm in thickness in order to get the absorption and J_(sc)comparable to those from the 200-nmthick GaAs film doped with Au *** is revealed that the improved J_(sc)upon doping with Au NPs predominantly originates from the increased absorption of GaAs film as the result of the plasmon resonance effect of Au NPs excited by incident *** results demonstrate that doping photon-harvesting layer with Au NPs is an effective strategy to prepare the solar cells with a strong spectral response and a reduced material consumption.

关键词： Planar heterojunction Surface plasmon resonance Absorption

Canopy gap characteristics and spatial patterns in a subtropical forest of South China after ice storm damage

在线全文

学校读者我要写书评

暂无评论

Journal of Mountain Science 2020年第8期17卷 1942-1958页

作者： LIU Feng yang zhi-gao ZHANG Gui College of Science Central South University of Forestry and TechnologyChangsha 410004China Key Laboratory for Digital Dongting Lake basin of Hunan Province Central South University of Forestry and TechnologyChangsha 410004China

The divergent gap characteristics and spatial patterns of canopy gaps created by natural or artificial disturbances can exert a dominant influence on forest structure and ***,little research has been conducted on the effects of ice storm damage on canopy gaps in subtropical mature forests of South *** this study,one semi-natural site was dominated by a broad-leaf forest and two managed sites were representative of plantations with coniferous *** on airborne laser scanning data and field evidence across sites,statistical analyses were used to examine gap characteristics following ice storms of moderate *** Ripley’s K-function analysis was applied to test gap spatial patterns at a range of scales,and spatial point pattern analysis was used to quantitate the relative importance of specific influences on patterns of gap *** results revealed that the average gap size was 75.7 m^2 and that 12.2 gaps occurred per *** gaps were single-tree fall *** addition to more gaps,the mean gap size was smaller and the shape was more complex in the semi-natural site than in two managed *** differences in gap characteristics were observed among snapped,uprooted,snag,and artificial gap damage *** generally showed a clustered distribution at large scales(e.g.70 m),whereas spatial patterns varied with gap damage types at different *** occurrence of gaps was strongly related to slope and topographic position at the semi-natural site,whereas slope,stem density,and human accessibility(proximity to pathways)were the most important factors affecting gap occurrence at the managed *** suggest that gap-based silvicultural treatments and natural disturbances regimes conjoin,highlighting interactions with other factors such as microsite conditions,non-tree vegetation and more.

关键词： Canopy gap Disturbance Spatial point pattern Influence factors Silviculture

Rationalization of regioselectivity of electrophilic substitution reaction for cyclic compounds in terms of D_(pb) values

在线全文

学校读者我要写书评

暂无评论

Chinese Chemical Letters 2015年第5期26卷 553-556页

作者： yang Liu Zhong-zhi yang Dong-Xia Zhao School of Chemistry and Chemical Engineering Liaoning Normal University

Accepted theories predict that substitution reactions are controlled by the electronic nature of the attacked site for electrophilic aromatic substitution. Here it is shown that in addition the bond strength of the broken bond may also influence the regioselectivity of the substitution reaction, and that the Dpb is a good indicator of the strength of a chemical bond. The Dpb denotes the depth of the potential acting on one electron in a molecule at the bond center （bc）. In this letter, the values of Dpb along the C-H and N-H bonds have been investigated, and it is demonstrated that for aromatic compounds, the regioselectivity of the electrophilic substitution can well be rationalized in terms of Dpb values.

关键词： Dpb Substitution reaction Regioselectivity Bond strength

Methodology to determine regional water demand for instream flow and its application in the Yellow River Basin

在线全文

学校读者我要写书评

暂无评论

Journal of Environmental Sciences 2006年第5期18卷 1031-1039页

作者： ZHANG Yuan yang zhi-feng Wang Xi-qin School of Environmental Sciences State Key Laboratory of Water Environment Simulation Beijing Normal University Beijing 100875 China Chinese Research Academy of Environmental Sciences Beijing 100012 China School of Natural Resources and Environment Renmin Universitiy of China Beijing 100872 China

In order to realistically reflect the difference between regional water demand for instream flow and river ecological water demand as well as to resolve the problem that water demand may be counted repeatedly, a concept of regional water demand for minimum instream flow have been developed. The concept was used in the process of determining river functions and calculating ecological water demand for a river. The Yellow River watershed was used to validate the calculation methodology for regional water demand. CaIculation results indicate that there are significant differences in water demands among the different regions. The regional water demand at the downstream of the Yellow River is the largest about 14.893 × 10^9 m^3/a. The regional water demand of upstream, Lanzhou-Hekou section is the smallest about -5.012 × 10^9 m^3/a. The total ecological water demand of the Yellow River Basin is 23.06 × 10^9 m^3/a, about the 39% of surface water resources of the water resources should not exceed 61% in the Yellow River Basin. Yellow River Basin. That means the maximum available surface The regional river ecological water demands at the Lower Section of the Yellow River and Longyangxia-Lanzhou Section exceed the surface water resources produced in its region and need to be supplemented from other regions through the water rational planning of watershed water resources. These results provides technical basis for rational plan of water resources of the Yellow River Basin.

关键词： regional water demand instream flow environmental flow methodology the Yellow River Basin

Dose reconstruction with Compton camera during proton therapy via subset-driven origin ensemble and double evolutionary algorithm

在线全文

学校读者我要写书评

暂无评论

Nuclear Science and Techniques 2023年第4期34卷 135-148页

作者： zhi-yang Yao Yong-Shun Xiao Ji-Zhong Zhao Department of Engineering Physics Tsinghua UniversityBeijing 100084China Key Laboratory of Particle&Radiation Imaging(Tsinghua University) Ministry of EducationBeijing 100084China

Compton camera-based prompt gamma(PG) imaging has been proposed for range verification during proton therapy. However, a deviation between the PG and dose distributions, as well as the difference between the reconstructed PG and exact values, limit the effectiveness of the approach in accurate range monitoring during clinical applications. The aim of the study was to realize a PG-based dose reconstruction with a Compton camera, thereby further improving the prediction accuracy of in vivo range verification and providing a novel method for beam monitoring during proton therapy. In this paper, we present an approach based on a subset-driven origin ensemble with resolution recovery and a double evolutionary algorithm to reconstruct the dose depth profile(DDP) from the gamma events obtained by a cadmium-zinc-telluride Compton camera with limited position and energy resolution. Simulations of proton pencil beams with clinical particle rate irradiating phantoms made of different materials and the CT-based thoracic phantom were used to evaluate the feasibility of the proposed method. The results show that for the monoenergetic proton pencil beam irradiating homogeneous-material box phantom,the accuracy of the reconstructed DDP was within 0.3 mm for range prediction and within 5.2% for dose prediction. In particular, for 1.6-Gy irradiation in the therapy simulation of thoracic tumors, the range deviation of the reconstructed spreadout Bragg peak was within 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 accurate dose reconstruction and range verification during proton therapy.

关键词： Prompt gamma imaging Dose reconstruction Range verification Origin ensemble Compton camera Evolutionary algorithm

Development and preliminary results of a large-pixel two-layer LaBr_(3) Compton camera prototype

在线全文

学校读者我要写书评

暂无评论

Nuclear Science and Techniques 2023年第8期34卷 100-114页

作者： Ming-Hao Dong zhi-yang Yao Yong-Shun Xiao Department of Engineering Physics Tsinghua UniversityBeijing 100084China Key Laboratory of Particle and Radiation Imaging(Tsinghua University) Ministry of EducationBeijing 100084China

Lanthanum bromide(LaBr_(3))crystal has a high energy resolution and time resolution and has been used in Compton cameras(CCs)over the past few ***,LaBr_(3) crystal arrays are difficult to process because LaBr_(3) is easy to crack and break;thus,few LaBr_(3)-based CC prototypes have been *** this study,we designed and fabricated a large-pixel LaBr_(3) CC prototype and evaluated its performance with regard to position,energy,and angular *** used two 10×10 LaBr_(3) crystal arrays with a pixel size of 5 mm×5 mm,silicon photomultipliers(SiPMs),and corresponding decoding circuits to construct our ***,a framework based on a Voronoi diagram and a lookup table was developed for list-mode projection data *** Carlo(MC)simulations based on Geant4 and experiments were conducted to evaluate the performance of our CC *** lateral position resolution was 5 mm,and the maximum deviation in the depth direction was 2.5 and 5 mm for the scatterer and absorber,*** corresponding measured energy resolu-tions were 7.65%and 8.44%,respectively,at 511 *** experimental results of ^(137)Cs point-like sources were consistent with the MC simulation results with regard to the spatial positions and full widths at half maximum(FWHMs).The angular resolution of the fabricated prototype was approximately 6°when a point-like ^(137)Cs source was centrally placed at a distance of 5 cm from the *** proposed and investigated a large-pixel LaBr_(3) CC for the first time and verified its feasibility for use in accurate spatial positioning of radiative sources with a high angular *** proposed CC can satisfy the requirements of radiative source imaging and positioning in the nuclear industry and medical applications.

关键词： Compton camera Large pixel Gamma camera LaBr_(3)detector Prototype evaluation

Numerical and experimental study on the hydraulic characteristics of a vertical axial pump under various clearances of flare tube

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2023年第1期35卷 125-144页

作者： Jia-qi Chen zhi-kui He zhi-yang Hu Hong-bo Shi Xikun Wang Research Center of Fluid Machinery Engineering and Technology Jiangsu UniversityZhenjiang212013China Chongqing Pump Industry Co.Ltd. Chongqing400033China

In order to investigate the characteristics of a vertical axial flow pump under various clearances of flare tube, the bell-shaped inlet and box culvert outlet channels with flare tube are studied numerically and experimentally. Then, the cases of inlet and outlet channels with the least hydraulic loss are selected to form an integral pump system, for which both numerical simulation and experimental investigation are carried out. The numerical results agree well with the experimental data. It is shown that the clearances of the interfaces between different components of the pump system have a significant impact on the internal flow structure, turbulent entropy and hydraulic performance of the inlet and outlet channels. For the cases of normalized bottom clearance less than 0.5 and normalized top clearance larger than 0.4, the internal flow and hydraulic performance indexes of inlet and outlet channels are relatively poor. There also exists a critical clearance in either inlet or outlet channel at which the hydraulic loss reaches the maximum. The results serve as an important reference for the design as well as safe and efficient operation of the vertical axial flow pump system.

关键词： Axial flow pump clearance of flare tube numerical simulation experiment hydrodynamic characteristics