oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2019 ( 220 )

2018 ( 1902 )

2017 ( 1799 )

2016 ( 1848 )

Custom range...

Search Results: 1 - 10 of 119993 matches for " WANG Changguo "
All listed articles are free for downloading (OA Articles)
Page 1 /119993
Display every page Item
SART-Type Image Reconstruction from Overlapped Projections
Hengyong Yu,Changguo Ji,Ge Wang
International Journal of Biomedical Imaging , 2011, DOI: 10.1155/2011/549537
Abstract: To maximize the time-integrated X-ray flux from multiple X-ray sources and shorten the data acquisition process, a promising way is to allow overlapped projections from multiple sources being simultaneously on without involving the source multiplexing technology. The most challenging task in this configuration is to perform image reconstruction effectively and efficiently from overlapped projections. Inspired by the single-source simultaneous algebraic reconstruction technique (SART), we hereby develop a multisource SART-type reconstruction algorithm regularized by a sparsity-oriented constraint in the soft-threshold filtering framework to reconstruct images from overlapped projections. Our numerical simulation results verify the correctness of the proposed algorithm and demonstrate the advantage of image reconstruction from overlapped projections. 1. Introduction Since the first computed tomography (CT) scanner was made [1], all the commercial scanners have been employing the X-ray source with a single small focal spot, which can be modeled as a point source. In micro-CT and even nano-CT applications, the reduced X-ray focal spot size becomes increasingly a limiting factor to achieve contrast and temporal resolution targets. To address this issue, our group recently proposed to use a line-shaped X-ray source so that more photons can be generated in a given data acquisition interval [2]. In this context, the X-ray source can be modeled as a line-segment, which can be further discretely modeled as an array of points [3]. In single source CT scanners, contrast resolution is limited by the finite focal-spot size necessary to generate a sufficient number of X-ray photons, and temporal resolution is limited by the time taken to acquire sufficiently many projections over a full-scan or half-scan angular range. Since a line source covers a wide angular range per view, the number of photons is increased to radiate an object to be reconstructed. Therefore, use of a line-shaped X-ray source or a multiple source array is a candidate scheme to balance spatial, contrast and temporal resolution. Interestingly, the technology of field-emission X-ray sources based on carbon nanotubes (CNT) is a recent invention with several intrinsic advantages over conventional X-ray tubes. To maximize the time-integrated X-ray flux from multiple sources and improve the signal-to-noise ratio (SNR), multiplexing was used, where multi-source are excited with different temporal modulations [4]. If two or more sources are simultaneously fired, X-ray photons reach the same detector
Study on the electronic structure of nickel hydroxide by quantum chemical DV-Xα calculation
DanMei Yu,ChangGuo Chen,YuJun Si,ShangQi Zhou,Li Wang
Chinese Science Bulletin , 2008, DOI: 10.1007/s11434-007-0492-6
Abstract: The electronic structures of atom clusters Ni7O12H12 2+ and Ni7O12H 9 of β-Ni(OH)2 were calculated by quantum chemical DV-Xα method. By analyzing the state densities, orbital populations, net charges and electric charge density differences of the selected clusters, it was indicated that β-Ni(OH)2 was not typical ionic crystal, and the bonds between Ni and O atoms had obvious covalent characteristics. The bonds between H atom and other atoms in the crystal structure were weaker, which ensured that H atoms can easily deintercalate and intercalate into β-Ni(OH)2. The structure of β-Ni(OH)2 was not changed by moderate de-intercalation of H atoms. However, with the excessive de-intercalation of H atoms, the structure of β-Ni(OH)2 changed and the electrochemical active properties were reduced.
On mechanisms of nucleation of ice crystals by aerodynamic cooling
On Mechanisms of Nucleation of Ice Crystals by Aerodynamic Cooling

Huang Shihong,Qian Changguo,Wang Weimin,Li Ruxiang,
Huang Shihong
,Qian Changguo,Wang Weimin,Li Ruxiang

大气科学进展 , 1994,
Abstract: The investigation of mechanisms of nucleation of ice crystals by aerodynamic cooling produced by supersonic airflow is carried out. Three processes are considered to be the principal causes for aerodynamic cooling and nucleation of ice crystals. They are: adiabatic cooling in supersonic airflow, cooling at the cores of vortices around the edge of airflow and entrapment of ambient stationary air into supersonic airflow. It is thermodynamically confirmed that the temperature lowering in supersonic flow depends on the Mach number M there and stagnant pressure Po at a certain stagnant temperature To. The temperature will decrease by more than 6oC as M increases by 0.1. The influence of Po on cooling is shown through the variation of mass flow rates, which increase with Po.Experiments in laboratory have shown that ice-forming rate produced by supersonic airflow increases from 1011 to 1012 /g as M increases from 1.10 to 1.84 at Po= 5 and 6 atm, and increases from 4.3 × 1011 to 10.3 × 1012 /g as the mass flow rate increases from 3.5 to 5.7 g / s and increases from 1.5 to 5.0 atm at M = 1.80 and To= 25oC. In field experiments the ice concentrations of 50 to 200 per liter in about 2000 m3 were measured when air of about 0.5 g were spurted at a Mach number of M = 1.8 into supercooled fog with temperatures between -0.5oC and -4.6oC. These results are compatible with the prediction of aerodynamics.The snapshot taken in experiments represents the detailed structures of vortex motion around a supersonic airflow.
A Comparative Study on Material Requirements Planning and Just-In-Time
物料需求计划与准时生产制的对比分析

Wang Dingwei,Xu Changguo,
汪定伟
,徐昌国

自动化学报 , 1993,
Abstract: In this paper, a comparasion on backgrounds, components, operations and preformances of two production control methods, Material Requirements Planning (MRP) and Just-In-Time (JIT) is given. The studies on hybrid Push/Pull control strategies which combined MRP and JIT are surved too. It is also discussel that which strategy is easy to be integrated with manufacturing process in CIM. Considering the condition in China, we recommend that the Push/Pull hybird control strategy is more applicable.
PREDICTION OF WRINKLE DEFORMATIONS IN THE SPACE MEMBRANE STRUCTURES
空间薄膜结构的褶皱形变预测

WANG Changguo,DU Xingwen,WAN Zhimin,
王长国
,杜星文,万志敏

力学与实践 , 2006,
Abstract: The space inflatable structure is a new construction technology and is the main demanding object in the future space activities. The inflatable structure is mainly made up of membrane; therefore, the maintenance of the structural surface accuracy is one of the most important problems. Wrinkling is the unique characteristic of the flexible membranes, and the wrinkles degrade the surface accuracy and the structural performance, so, the study on wrinkles in membrane structures is desirable and essential. In this paper, a prediction model of wrinkles is proposed, based on the buckling theory, and the wrinkles, including the wrinkle amplitude, wrinkle wavelength and the critical compressive stress, in a rectangular membrane subjected to in-plane horizontal shearing loads are predicted using the method proposed in the present paper. The predicted results show good agreement with our recent experiments and the reported data.
ANALYSIS OF WRINKLES'''' INFLUENCES ON MEMBRANE''''S VIBRATION CHARACTERISTICS
褶皱对薄膜振动特性的影响分析

LI Yunliang,WANG Changguo,TAN Huifeng,
李云良
,王长国,谭惠丰

力学与实践 , 2007,
Abstract: A mechanical model of membrane wrinkle is established in this paper.Relationship between the strains and the stresses in the wrinkled regions is analyzed based on the tension field theory and the stability theory.The NBA-UM (nonlinear buckling analysis-update matrix) method is proposed for the dynamic analysis of membrane wrinkles,and the study on the vibration characteristics of the membrane.The result shows that"excess shrink"phenomena is due to wrinkles,which in turn change the stress distribution in the membrane. Wrinkles greatly influence the vibration characteristics of the membrane,and large amplitude wrinkles will change the natural frequencies and modal forms of the membrane.In conclusion,it is shown that the NBA-UM method can effectively predict the dynamic behaviors of membrane wrinkles.
Study on the electronic structure of nickel hydroxide by quantum chemical DV-Xα calculation
DanMei Yu,ChangGuo Chen,YuJun Si,ShangQi Zhou,Li Wang,

科学通报(英文版) , 2008,
Abstract: The electronic structures of atom clusters Ni7O12H12 2+ and Ni7O12H 9 of β-Ni(OH)2 were calculated by quantum chemical DV-Xα method. By analyzing the state densities, orbital populations, net charges and electric charge density differences of the selected clusters, it was indicated that β-Ni(OH)2 was not typical ionic crystal, and the bonds between Ni and O atoms had obvious covalent characteristics. The bonds between H atom and other atoms in the crystal structure were weaker, which ensured that H atoms can easily deintercalate and intercalate into β-Ni(OH)2. The structure of β-Ni(OH)2 was not changed by moderate de-intercalation of H atoms. However, with the excessive de-intercalation of H atoms, the structure of β-Ni(OH)2 changed and the electrochemical active properties were reduced.
The Charge Distribution on the Cathode of a Straw Tube Chamber
Changguo Lu,Kirk T. McDonald
Physics , 2000,
Abstract: We use Green's reciprocation theorem and the method of weighting fields to deduce the charge distribution on the cathode of a straw tube proportional chamber. The time dependence of the associated current is also discussed.
Effects of the grain alignment on the coercivity and its angular dependence for NdCoFeB permanent magnets
Ruwei Gao,Wei Li,Changguo Ji,Deheng Zhang,Jiancheng Zhang
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02883918
Abstract: The dependence of the macroscopic magnetism for NdCoFeB permanent magnet on the degree of grain alignment has been studied. With an increase in grain alignment degree, the coercivity of the permanent magnet decreases and the remanence increases. The decrease rate of the coercivity is smaller than the increase rate of the remanence. The coercivity Hc(θ) increases with increasing angle θ between the applied field and the texture axis, and for the permanent magnets with good grain alignment the increase rate of Hc(θ) is large. These experimental results can be interpreted by using the starting field theory of coercivity.
The synthesis and characterization of a Co-N/C composite catalyst for the oxygen reduction reaction in acidic solution
YuJun Si,ChangGuo Chen,Wei Yin,Hui Cai
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4434-y
Abstract: A non-precious metal Co-N/C catalyst for the oxygen reduction reaction (ORR) was synthesized by heating a mechanical mixture of cobalt chloride, urea and acetylene black under a nitrogen atmosphere. The catalyst was characterized by XRD and XPS. The electrocatalytic activity in the ORR was evaluated by linear sweep voltammetry in 0.5 mol L 1 H2SO4 solution. The results show that the Co-N/C catalyst aids the reduction of oxygen. The presence of elemental cobalt in the precursor allows nitrogen atoms to embed themselves in the graphite matrix to form pyridinic and graphitic type C-N structures as the ORR active sites. The effect of heat-treating temperature on the catalytic activity was also investigated. The results also show that the Co-N/C catalyst is most active when pyrolyzed at 600°C. The obtained Co-N/C catalyst loses some activity after initial exposure to the H2SO4 solution because of leaching, but is then stable for up to 20 h immersion. The catalyst is also stable when charged, which is supported by the cyclic voltammetry results.
Page 1 /119993
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.