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| 1 | SAR motion compensation based on the correction of residual attitude errors显示文摘As residual attitude errors are likely to affect the synthetic aperture radar (SAR) imaging, this paper presents a SAR motioncompensation algorithm based on the correction of residual attitude errors. The existing methods all use the antenna stableplatform to correct the attitude errors, and then compensate the trajectory deviations in the following imaging process. Besidescompensating the trajectory deviations, the modified method of this paper also considers the influence of residual attitude er-rors on the SAR imaging, and can compensate both the trajectory deviations and the residual attitude errors. Compared withthe existing methods, the modified method in this paper can more precisely compensate the imperfect motion on the SAR im-aging, especially good for the SAR system with a small platform, near operating distance and a narrow antenna beam. Such asystem causes severe residual attitude errors and needs to consider the influence of antenna beam pointing errors on the imag-ing. The validity of the modified method presented by this paper is demonstrated by the result of the experiment. | NI Chong WANG YanFei XU XiangHui ZHOU ChangYi | 2011 | Science China(Physics,Mechanics & Astronomy)2011，54，10： | 3 |
| 2 | On the calibration and verification of Voronoi-based discontinuous deformation analysis for modeling rock fracture显示文摘Since its introduction,discontinuous deformation analysis(DDA)has been widely used in different areas of rock mechanics.By dividing large blocks into subblocks and introducing artificial joints,DDA can be applied to rock fracture simulation.However,parameter calibration,a fundamental issue in discontinuum methods,has not received enough attention in DDA.In this study,the parameter calibration of DDA for intact rock is carefully studied.To this end,a subblock DDA with Voronoi tessellation is presented first.Then,a modified contact constitutive law is introduced,in which the tensile and shear meso-strengths are modified to be independent of the bond lengths.This improvement can prevent the unjustified preferential failure of short edges.A method for imposing confining pressure is also introduced.Thereafter,sensitivity analysis is performed to investigate the influence of the calculated parameters and meso-parameters on the mechanical properties of modeled rock.Based on the sensitivity analysis,a unified calibration procedure is suggested for both cases with and without confining pressure.Finally,the calibration procedure is applied to two examples,including a biaxial compression test.The results show that the proposed Voronoi-based DDA can simulate rock fracture with and without confining pressure very well after careful parameter calibration. | Kaiyu Zhang Feng Liu Kaiwen Xia Ying Xu Peng Dong Changyi Yu | 2023 | Journal of Rock Mechanics and Geotechnical Engineering2023，15，8： | 2 |
| 3 | A super-resolution algorithm for synthetic aperture radar based on modified spatially variant apodization显示文摘The existing spatially variant apodizations(SVAs) either cannot depress the sidelobes effectively or reduce the energy of the mainlobe.To improve this,a modified SVA(MSVA) is put forward in this paper,which expands the traditional filter from 3-taps to 5-taps and sets relevant parameters according to different sampling rates to get the excellent result that satisfies constrained optimization theory.A modified super-SVA is also presented,which compares the result after the iteration with the original signal and makes the one whose amplitude is smaller as the initial value of the next iteration.This method can eliminate the sidelobes produced by the intermediate operation,so that the following bandwidth extrapolation is more available.Super-MSVA is presented based on the modified SVA and modified super-SVA,which is suitable for any Nyquist sampling rate,can extrapolate the signal bandwidth many times through iteration with a commensurate improvement in resolution,as demonstrated by the result of the experiment. | NI Chong WANG YanFei XU XiangHui ZHOU ChangYi CUI PengFei | 2011 | Science China(Physics,Mechanics & Astronomy)2011，54，2： | 2 |
| 4 | Ag_(3)PO_(4) decorated black urchin-like defective TiO_(2) for rapid and long-term bacteria-killing under visible light显示文摘Both phototherapy via photocatalysts and physical puncture by artificial nanostructures are promising substitutes for antibiotics when treating drug-resistant bacterial infectious diseases.However,the photodynamic therapeutic efficacy of photocatalysts is seriously restricted by the rapid recombination of photogenerated electron-hole pairs.Meanwhile,the nanostructures of physical puncture are limited to two-dimensional(2D)platforms,and they cannot be fully used yet.Thus,this research developed a synergistic system of Ag_(3)PO_(4) nanoparticles(NPs),decorated with black urchin-like defective TiO_(2)(BU-TiO_(2-X)/Ag_(3)PO_(4)).These NPs had a decreased bandgap compared to BU-TiO_(2-X),and BU-TiO_(2)-X/Ag_(3)PO_(4)(3:1)exhibited the lowest bandgap and the highest separation efficiency for photogenerated electron-hole pairs.After combination with BU-TiO_(2-X),the photostability of Ag_(3)PO_(4) improved because the oxygen vacancy of BU-TiO_(2-X) retards the reduction of Ag^(+) in Ag_(3)PO_(4) into Ag^(0),thus reducing its toxicity.In addition,the nanospikes on the surface of BU-TiO_(2-X) can,from all directions,physically puncture bacterial cells,thus assisting the hybrid’s photodynamic therapeutic effects,alongside the small amount of Ag^(+) released from Ag_(3)PO_(4).This achieves synergy,endowing the hybrid with high antibacterial efficacy of 99.76±0.15%and 99.85±0.09%against Escherichia coli and Staphylococcus aureus,respectively,after light irradiation for 20 min followed by darkness for 12 h.It is anticipated that these findings may bring new insight for developing synergistic treatment strategies against bacterial infectious diseases or pathogenic bacterial polluted environments. | Yingde Xu Xiangmei Liu Yufeng Zheng Changyi Li Kelvin Wai Kwok Yeung Zhenduo Cui Yanqin Liang Zhaoyang Li Shengli Zhu Shuilin Wu | 2021 | Bioactive Materials2021，6，6： | 2 |
| 5 | Co-seismic Earth's rotation caused by the 2012 Sumatra earthquake显示文摘Earthquakes heavily deform the crust in the vicinity of the fault, which leads to mass redistribution in the earth interior. Then it will produce the change of the Earth's rotation (polar motion and length of day) due to the change of Earth inertial moment. This paper adopts the elastic dislocation to compute the co-seismic polar motion and variation in length of day (LOD) caused by the 2011 Sumatra earthquake. The Earth's rotational axis shifted about 1mas and this earthquake decreased the length of day of 1μs, indicating the tendency of earthquakes make the Earth rounder and to pull the mass toward the centre of the Earth. The result of variation in length of day is one order of magnitude smaller than the observed results that are available. We also compared the results of three fault models and find the co-seismic change is depended on the fault model. | Xu Changyi Sun Wenke | 2012 | Geodesy and Geodynamics2012，3，4： | 1 |
| 6 | Formal management-specifying approach for model-based safety assessment显示文摘In the field of model-based system assessment,mathematical models are used to interpret the system behaviors.However,the industrial systems in this intelligent era will be more manageable.Various management operations will be dynamically set,and the system will be no longer static as it is initially designed.Thus,the static model generated by the traditional model-based safety assessment(MBSA)approach cannot be used to accurately assess the dependability.There mainly exists three problems.Complex:huge and complex behaviors make the modeling to be trivial manual;Dynamic:though there are thousands of states and transitions,the previous model must be resubmitted to assess whenever new management arrives;Unreusable:as for different systems,the model must be resubmitted by reconsidering both the management and the system itself at the same time though the management is the same.Motivated by solving the above problems,this research studies a formal management specifying approach with the advantages of agility modeling,dynamic modeling,and specification design that can be re-suable.Finally,three typical managements are specified in a series-parallel system as a demonstration to show the potential. | XU Changyi DUAN Yiman ZHANG Chao | 2023 | Journal of Systems Engineering and Electronics2023，34，6： | 0 |
| 7 | Micro-Newton scale variable thrust control technique and its noise problem for drag-free satellite platforms:a review显示文摘High-precision detection in fundamental space physics,such as space gravitational wave detection,high-precision earth gravity field measurement,and reference frame drag effect measurement,is the key to achieving important breakthroughs in the scientific study of fundamental space physics.Acquiring high-precision measurements requires high-performance satellite platforms to achieve“drag-free control”in a near“pure gravity”flight environment.The critical technology for drag-free control is variable thrust control at the micro-Newton scale.Thrust noise is the most important technical indicator for achieving drag-free flight.However,there is no literature about the current status and future prospects of variable thrust control based on thrust noise.Therefore,the micro-Newton variable thrust control technology and the thrust noise of the drag-free satellite platform are reviewed in this work.Firstly,the research status of micro-Newton scale variable thrust control technology and its applications to drag-free satellite platforms are introduced.Then,the noise problem is analyzed in detail and its solution is theoretically investigated in three aspects:“cross-basin flow problem,”“control problem,”and“system instability and multiple-coupled problem.”Finally,a systematic overview is presented and the corresponding suggested directions of research are discussed.This work provides detailed understanding and support for realizing low-noise variable thrust control in the next generation of drag-free satellites. | Changyi XU Wenya LI Xuhui LIU Yong LI Chao ZHANG | 2023 | Journal of Zhejiang University-Science A(Applied Physics & Engineering)2023，24，10： | 0 |
| 8 | Platinum-Iridium Alloy Films Prepared by MOCVD显示文摘Platinum-Iridium alloy films were prepared by MOCVD on Mo substrate using metal-acetylacetonate precursors. Effects of deposition conditions on composition, microstructure and mechanical properties were determined. In these experimental conditions, the purities of films are high and more than 99.0%. The films are homogeneous and monophase solid solution of Pt and Ir. Weight percentage of platinum are much higher than iridium in the alloy. Lattice constant of the alloy changes with the platinum composition. Iridium composition showing an up-down-up trend at the precursor temperature of 190~230℃ and the deposition temperature at 400~ 550℃. The hardness of Pt-Ir alloys prepared by MOCVD is three times more than the alloys prepared by casting. | WEI Yan CHEN Li CAI Hongzhong ZHENG Xu YANG Xiya HU Changyi | 2012 | 贵金属2012，33，A01： | 0 |
| 9 | Determining the moment of inertia of triaxial Mars with updated global gravity models显示文摘The principal moments of inertia(PMIs)with the principal axes are usually taken as the dynamic figure parameters of Mars;they can be deduced from satellite-observed degree-two gravitational potentials in recent global gravity models and from the dynamic ellipticities resulting from precession observations.These PMIs are natural and significant for the geodetic,geophysical,and geodynamic problems of Mars,which are functions of internal density distributions.In this study,a closed and concise formula for determining the PMIs of the entire planet and its core was developed based on the second invariants of gravity and a multipole expansion.We deduced the polar oblateness J^(2)and the equatorial ellipticity J_(22)of Mars to be 1.9566×10^(−3)and 6.3106×10^(−5),respectively.The preferred principal moments of inertia of Mars are A=2.66589×1036 kg·m^(2),B=2.66775×10^(36)kg·m^(2),and C=2.68125×10^(36)kg·m^(2).These values indicate that Mar is slightly triaxial.The equatorial principal moment of inertia of the Martian core is 1.46008×10^(35)kg·m^(2),accounting for~5.47%of the planet’s PMI;this result is critical for investigating the density and size of the core of Mars,and the planet’s free core nutation. | ChangYi Xu Yan Jiang | 2023 | Earth and Planetary Physics2023，7，6： | 0 |
| 10 | Irradiation Embrittlement Research on Simulated Cylinder for 600 MW Nuclear Power Plant Pressure Vessel显示文摘IrradiationEmbrittlementResearchonSimulatedCylinderfor600MWNuclearPowerPlantPressureVesselJiaXuejun;XuYuanchao;ZhangChangyi;Y... | Jia Xuejun Xu Yuanchao Zhang Changyi Yang Wendou | 1996 | 中国原子能科学研究院年报1996，，1： | 0 |
| 11 | An h-adaptive numerical manifold method for solid mechanics problems显示文摘The numerical manifold method(NMM) features its dual cover systems, namely the mathematical cover and physical cover,which provide a unified framework for mechanics problems involving continuum and discontinuum deformation. Uniform finite element meshes can be and are usually used to construct the mathematical cover. Though this strategy can handle different kinds of problems in a unified way, it is not economical for cases with steep deformation gradients or singularities. In this paper, using the recovery-based error estimator, an h-adaptive NMM on quadtree meshes is proposed to deal with such cases. The quadtree meshes serve as the mathematical meshes, on which the local refinement is carried out. When the quadtree meshes are refined,the corresponding mathematical cover, physical cover and manifold elements are updated accordingly. To handle the hanging nodes in the quadtree meshes, we resort to mean value coordinates. Comparing to the refinement based on manifold elements,the proposed strategy guarantees consistent structured meshes throughout the adaptive process, thus retaining the unique feature of original NMM. In contrast with polygonal finite element method, an advantage of the proposed method is that the meshes do not need to conform to the crack face and material boundary, which means the adaptive NMM is very suitable for problems with complex geometric boundary. Several representative mechanics problems, including crack problems, are analyzed to investigate the effectiveness of the proposed method. It is demonstrated that the proposed adaptive NMM has higher accuracy and better performance comparing to uniform refinement strategy. | YU ChangYi LIU Feng XU Ying | 2018 | Science China(Technological Sciences)2018，61，6： | 0 |
| 12 | Implicit expansion rate of the Earth in global plate motions显示文摘Based on eight published plate motion models, we separately estimated the net area changes of tectonic plates and the area change of the solid Earth surface over geological time using the Euler vectors of plates with determined boundaries. Then, under the context of a currently expanding Earth, we inferred the change rate of the Earth’s mean radius from the estimated net area changes. The results show that the total increases and decreases in the areas of different plates cannot be compensated. Specifically, the area of the Northern Hemisphere decreases while that of the Southern Hemisphere increases, but the net area of the solid Earth surface slightly increases in th computing period(0.01 Ma). For the latest NNRMORVEL56 plate motion model, the area of the Southern Hemisphere increases by 7802 km2 while the area of the Northern Hemisphere decreases by 7711 km^2. This indicates a net area increase of 91 km2 in the solid Earth surface corresponding to an expansion rate of 0.06 mm/a for the Earths mean radius.This result coincides with the slow rate of expansion derived from geodetic measurements and geophysical modeling. | Changyi Xu Xiao Yu Dongping Wei | 2019 | Geodesy and Geodynamics2019，10，3： | 0 |
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