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FLOW AND HEAT TRANSFER OF OLDROYD-B FLUIDS IN A ROTATING CURVED PIPE

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Journal of Hydrodynamics 2008年第1期20卷 39-46页

作者： SHEN Xin-rong zhang Ming-kan MA jian-feng zhang Ben-zhao Institute of Fluid Engineering Zhejiang University Hangzhou 310027 China

The flow and convected heat transfer of the Oldroyd-B fluids in a rotating curved pipe with circular cross-section were investigated by employing a perturbation method. A perturbation solution up to the second order was obtained for a small curvature ratio, κ. The variations of axial velocity distribution and secondary flow structure with F, Re and We were discussed in detail in order to investigate the combined effects of the three parameters on flow structure. The combined effects of the Coriolis force, inertia force and elastic force on the temperature distribution were also analyzed, which are greater than the adding independent effects of the three forces. The variations of the flow rate and Nusselt number with the rotation, inertia and elasticity were examined as well. The results show the characteristics of the heat and mass transfer of the Oldroyd-B fluids in a rotating curved pipe.

关键词： Oldroyd-B fluids flow structure convected heat transfer rotating curved pipe

FLOW OF OLDROYD-B FLUID IN ROTATING CURVED SQUARE DUCTS

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Journal of Hydrodynamics 2007年第1期19卷 36-41页

作者： zhang Ming-kan SHEN Xin-rong MA jian-feng zhang Ben-zhao Institute of Fluid Engineering Zhejiang University Hangzhou 310027 China

The fully developed Oldroyd-B fluid flow through rotating square ducts was numerically studied. The effects of the rotation on secondary flow, axial velocity, and axial normal stress were examined in detail. The results indicated that all of the secondary flow, the axial flow, and the axial normal stress were evidently affected by the rotation. The Taylor-Proudman phenomenon could be observed in the flow. For the secondary flow, the four vortices structure and the six vortices structure were described. Recent studies also showed the effects of rotation on the axial normal stress.

关键词： curved ducts Oldroyd-B fluid rotating axialnormal stress

Observation of 1D Fermi arc states in Weyl semimetal TaAs

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National Science Review 2022年第8期9卷 62-70页

作者： Xiaohu Zheng Qiangqiang Gu Yiyuan Liu Bingbing Tong jian-feng zhang Chi zhang Shuang Jia Ji feng Rui-Rui Du International Center for Quantum Materials School of PhysicsPeking University Collaborative Innovation Center of Quantum Matter State Key Laboratory of Superlattices and Microstructures Institute of SemiconductorsChinese Academy of Sciences CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing Academy of Quantum Information Sciences

Fermi arcs on Weyl semimetals exhibit many exotic quantum phenomena. Usually found on atomically flat surfaces with approximate translation symmetry, Fermi arcs are rooted in the peculiar topology of bulk Bloch bands of 3D crystals. The fundamental question of whether a 1D Fermi arc can be probed remains unanswered. Such an answer could significantly broaden potential applications of Weyl semimetals. Here,we report a direct observation of robust edge states on atomic-scale ledges in TaAs using low-temperature scanning tunneling microscopy/spectroscopy. Spectroscopic signatures and theoretical calculations reveal that the 1D Fermi arcs arise from the chiral Weyl points of bulk crystals. The crossover from 2D Fermi arcs to eventual complete localization on 1D edges was arrested experimentally on a sequence of surfaces. Our results demonstrate extreme robustness of the bulk-boundary correspondence, which offers topological protection for Fermi arcs, even in cases in which the boundaries are at the atomic-scale. The persistent 1D Fermi arcs can be profitably exploited in miniaturized quantum devices.

关键词： Weyl semimetals Fermi arc edge states chiral Weyl points TaAs scanning tunneling microscopy/spectroscopy

Raman scattering study of magnetic layered MPS_3 crystals(M = Mn, Fe, Ni)

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Chinese Physics B 2019年第5期28卷 226-231页

作者： Yi-Meng Wang jian-feng zhang Cheng-He Li Xiao-Li Ma jian-Ting Ji feng Jin He-Chang Lei Kai Liu Wei-Lu zhang Qing-Ming zhang Department of Physics Renmin University of China Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Department of Engineering and Applied Sciences Sophia University School of Physical Science and Technology Lanzhou University

We report a comprehensive Raman scattering study on layered MPS_3(M = Mn, Fe, Ni), a two-dimensional magnetic compound with weak van der Waals interlayer coupling. The observed Raman phonon modes have been well assigned by the combination of first-principles calculations and the polarization-resolved spectra. Careful symmetry analysis on the angle-dependent spectra demonstrates that the crystal symmetry is strictly described by C_(2h)but can be simplified to D_(3d) with good accuracy. Interestingly, the three compounds share exactly the same lattice structure but show distinct magnetic structures. This provides us with a unique opportunity to study the effect of different magnetic orders on lattice dynamics in MPS_3. Our results reveal that the in-plane Nel antiferromagnetic(AF) order in MnPS_3 favors a spin–phonon coupling compared to the in-plane zig-zag AF in NiPS_3 and FePS_3. We have discussed the mechanism in terms of the folding of magnetic Brillouin zones. Our results provide insights into the relation between lattice dynamics and magnetism in the layered MPX_3(M = transition metal, X = S, Se) family and shed light on the magnetism of monolayer MPX_3 materials.

关键词： Raman scattering two-dimensional magnetic van der Waals materials lattice dynamics magnetism

An Improved Frequency Synchronizer for Mobile OFDMSystems

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The Journal of China Universities of Posts and Telecommunications 2005年第4期12卷 26-31页

作者： QIANG jian-feng zhang ping Department of Telecommunications Engineering Beijing University of Posts and Telecommunications Beijing 100876 P.R. China

Orthogonal Frequency Division Multiplexing （ OFDM） system is sensitive to Carrier Frequency Offset （ CFO ）. In this paper, traditional Maximum Likelihood Estimators （MLE） for CFO of OFDM are introduced first. Then, averaging method and a-filter are introduced as Low Pass Filter （LPF） to improve the performance of cyclic prefix estimator. The bandwith of LPF is determined by the coherence time of radio channel. Estimation performance in multipath channel is analyzed. Outlier picking-out scheme is proposed to improve performance further. Performance of close-loop structure is presented briefly, which is worse than that of open-loop structure. Finally, a parallel switch structure of frequency synchronizer is proposed for mobile OFDM systems. The scheme ezcploits training sequence and cyclic prefix. The proposed synchronizer has a wide acquisition range. It is accurate and robust in both AWGN channel and multipath channels. The complexity is low due to functionality of a-filter. A better performance of frequevlcy synchronization is obtained comparing to that of existing Maximum Likelihood Estimator（ MLEs）. We achieve these advantages without loss of bandwidth efficiency.

关键词： OFDM frequency synchronizer parallel switch structure MLE Low Pass Filter (LPF) open-loop structure

Microstructure,Properties and Heat Treatment Process of Powder Metallurgy Superalloy FGH95

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Journal of Iron and Steel Research International 2006年第5期13卷 65-68页

作者： GUO Wei-min WU jian-tao zhang feng-ge ZHAO Ming-han High Temperature Materials Research Institute Central Iron and Steel Research Institute Beijing 100081 China

Microstructure and properties of nickel based powder metallurgy （PM） superalloy were presented. Effects of nonmetallic inclusions and heat treatment on microstructure and properties were. discussed. Development tend... 详细信息

关键词： microstructure property PM superalloy heat treatment

Measuring the spreadability of users in microblogs

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Journal of Zhejiang University-Science C(Computers and Electronics) 2013年第9期14卷 701-710页

作者： Zhao-yun DING Yan JIA Bin ZHOU Yi HAN Li HE jian-feng zhang College of Information Systems and Management National University of Defense Technology School of Computer Science National University of Defense Technology

Message forwarding (e.g.,retweeting on ***) is one of the most popular functions in many existing microblogs,and a large number of users participate in the propagation of information,for any given *** this large number can generate notable diversity and not all users have the same ability to diffuse the messages,this also makes it challenging to find the true users with higher spreadability,those generally rated as interesting and authoritative to diffuse the *** this paper,a novel method called SpreadRank is proposed to measure the spreadability of users in microblogs,considering both the time interval of retweets and the location of users in information *** were conducted on a real dataset from Twitter containing about 0.26 million users and 10 million tweets,and the results showed that our method is consistently better than the PageRank method with the network of retweets and the method of retweetNum which measures the spreadability according to the number of ***,we find that a user with more tweets or followers does not always have stronger spreadability in microblogs.

关键词： Spreadability Influence PageRank Microblogs Social media Social network SpreadRank

Exploring charge and spin fluctuations in infinite-layer cuprate SrCuO_(2)from a phonon perspective

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Science China(Physics,Mechanics & Astronomy) 2024年第8期67卷 159-167页

作者： Xin Du Pei-Han Sun Ben-Chao Gong jian-feng zhang Zhong-Yi Lu Kai Liu Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials&Micro-nano Devices Renmin University of ChinaBeijing 100872China Department of Physics School of ScienceJiangsu University of Science and TechnologyZhenjiang 212100China Institute of Physics Chinese Academy of SciencesBeijing 100190China Key Laboratory of Quantum State Construction and Manipulation(Ministry of Education) Renmin University of ChinaBeijing 100872China

The infinite-layer cuprate ACu O_(2)(A=Ca,Sr,Ba)possesses the simplest crystal structure among numerous cuprate superconductors and can serve as a prototypical system to explore the unconventional *** on the first-principles electronic structure calculations,we have studied the electronic and magnetic properties of the infinite-layer cuprate SrCuO_(2)from a phonon *** find that interesting fluctuations of charges,electrical dipoles,and local magnetic moments can be induced by the atomic displacements of phonon modes in SrCuO_(2)upon the hole *** all optical phonon modes of SrCuO_(2)in the antiferromagnetic Néel state,only the A_(1g)mode that involves the full-breathing O vibrations along the Cu-O bonds can cause significant fluctuations of local magnetic moments on O atoms and dramatic charge redistributions between Cu and O ***,due to the atomic displacements of the A_(1g)mode,both the charge fluctuations on Cu and the electrical dipoles on O show a dome-like evolution with increasing hole doping,quite similar to the experimentally observed behavior of the superconducting T_(c);in comparison,the fluctuations of local magnetic moments on O display a monotonic enhancement along with the hole *** analyses indicate that around the optimal doping,there exists a large softening in the frequency of the A_(1g)phonon mode and a van Hove singularity in the electronic structure close to the Fermi level,suggesting potential electron-phonon *** work reveals the important role of the full-breathing O phonon mode playing in the infinite-layer SrCuO_(2),which may provide new insights in understanding the cuprate superconductivity.

关键词： first-principles calculations cuprate superconductors phonon charge and spin fluctuations

Experimental investigation on the radiation background inside body counters

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Nuclear Science and Techniques 2022年第2期33卷 66-78页

作者： Yu Wang Yuan-Yuan Liu Bin Wu Xiang-Peng Meng jian-Ping Cheng Ying Wang Li-Jiao Wang Yun-Shi Xiao Qin-jian Cao jian-feng zhang Fei Tuo Key Laboratory of Beam Technology of Ministry of Education College of Nuclear Science and TechnologyBeijing Normal UniversityBeijing 100875China Department of Nuclear Safety China Institute of Atomic EnergyBeijing 102413China Department of Health Physics China Institute for Radiation ProtectionTaiyuan 030006China National Institute for Radiological Protection Chinese Center for Disease Control and PreventionBeijing 100088China

In vivo measurement of radioactivity based on various body counters is arguably the leading measure used to determine the distribution and activity of radionuclides in human subjects,such as I-131 in the thyroid,Am-241 in the lungs,and Pb-210 in the *** the measurements,the radiation background is the key factor that determines the sensitivity of the ***,to facilitate in vivo measurements,a well-designed shielding room is required to create a low-background ***,because the compositions of the radiation background are quite complicated,the respective contributions from each source remain obscure,which places a considerable burden on seeking an optimized design of shielding rooms that strikes the optimum balance between the construction cost and background suppression *** this study,we conducted a systematic experimental investigation on the radiation background outside and inside four representative body counters with assorted designs using a variety of radiation detectors,including high-purity germanium detectors,CdZnTe detector,radon emanometer,and gamma-ray *** carefully controlling the experimental conditions and synergetic analysis of the measurement results,in conjunction with previous studies,we separated and determined the relative contributions induced by environmental radiation(4%),airborne radon and its daughters(2%),the normal radioactivity of human subjects arising from K-40(58%),cosmic rays(12%),and radioactivity in shielding materials and measuring instruments(24%).Furthermore,based on these results,we discuss practical guidelines to design a shielding room for body counters.

关键词： Body counter Radiation background Shielding room In vivo measurement