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A newly unraveled 13.6-year oscillation from GPS displacements and its potential implications for the dynamic reference frame

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Science China Earth Sciences 2024年第10期67卷 3204-3212页

作者： Hao DING Weiping JIANG School of geodesy and Geomatics Hubei Luojia LaboratoryWuhan UniversityWuhan 430079China GNSS research Center Wuhan UniversityWuhan 430079China

Numerous practical geodetic and geophysical applications necessitate precise measurements of GNSS displacements at the millimeter or sub-millimeter level. To attain such precision, it is imperative to identify and analyze the unidentified decadal signals inherent in the GPS displacements. In this research, we employ the optimal sequence estimation method to effectively detect an about 13.6-year oscillational signal with an excited amplitude of 3.6±1.2 mm in the U-components of the GPS displacements. It is noteworthy that this signal demonstrates a consistent spatial pattern characterized by the spherical harmonic Y_(2,-2). We conduct a comparative analysis with the 13.6-year oscillation observed in length-of-day variations(and geomagnetic records), finding that they are in reverse phase. After eliminating the Earth's external excitation sources through the utilization of two distinct in-situ hydrological records, we suggest that the 13.6-year GPS signal may come from the internal motions within the Earth. However, the specific excitation source and the detailed physical mechanism remain uncertain. Additionally, we develop a mathematical displacement model to explain the 13.6-year signal. Our findings indicate that this signal can result in displacements of up to 1.37 mm and velocity effects of 0.63 mm/yr(for U-component) at maximum. These results underscore the necessity of incorporating this 13.6-year signal into the construction and maintenance of a dynamic reference frame at the millimeter level.

关键词： GPS displacements Decadal changes 13.6-year oscillation Displacement model Dynamic reference frame

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Numerical simulations of earthquake rupture induced by pressure perturbation

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geodesy and Geodynamics 2024年第5期15卷 477-487页

作者： Bingquan Ren Caijun Xu Guoyan Jiang Lei Yang School of geodesy and Geomatics Wuhan UniversityWuhan 430079China Key Laboratory of Geospace Environment and geodesy Ministry of EducationWuhan UniversityWuhan 430079China Key Laboratory of Geophysical geodesy Ministry of Natural ResourcesWuhan 430079China

The subsurface fluid injection can cause pressure increase within faults,leading to earthquake ***,the factors controlling earthquake rupture due to pressure perturbation remain poorly *** resolve this problem,we simulate the physical processes of earthquake nucleation and rupture on strike-slip faults perturbated by pressure migration based on the slip-weakening *** kinds of factors,including background stress,fluid injection rates,the area of the pressurized region,fault geometry,and fault friction coefficients,are considered in our *** simulation results reveal that the ratio of shear stress to normal stress rather than their absolute values controls the rupture *** the large stress ratios,high injection rates,and large pressurized areas,earthquakes are prone to propagate as runaway ***,faults with large aspect ratios of length to width are also favorable for causing runaway *** contrast,the factors of fault strike,dip angles and friction coefficients have minor influence on rupture behavior.

关键词： Induced seismicity Finite element simulation Rupture mode

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Thermal stability improvement and microstructure optimization of high cobalt content Nd-Fe-B magnets via terbium grain boundary diffusion

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Journal of Rare Earths 2024年第8期42卷 1531-1538,I0004页

作者： Jiyuan Xu Ruiyang Meng Jing Liu Jiateng Zhang Rui Han Yikun Fang Shengzhi Dong Wei Li division of Functional Materials research Central Iron and Steel Research InstituteBeijing100081China

The substitution of Fe by Co in the 2:14:1 phase is an effective method to increase the Curie temperature and enhance the thermal stability of the Nd-Fe-B ***,the accumulation of Co ele ment at the grain boundaries(GBs) changes the GBs from nonmagnetic to ferromagnetic and causes the thinlayer GBs to become rare,In this paper,the method of diffusing Tb element was chosen to improve the microstructure and temperature stability of high-Co *** original sintered Nd_(28.5)Dy_(3)-CO_(x)e_(bal)M_(0.6)B_(i)(x=0,6 wt%,12 wt%;M = Cu,Al,Zr) magnets with different Co contents were diffused with Tb by grain boundary diffusion(GBD).After GBD,high-Co magnets exhibit more continuously distributed thin-layer GBs,and their thermal stability is significantly *** high-Co magnets(x=6 wt%),the absolute value of the temperature coefficient of coercivity decreases from 0.603%/K to0.508%/K in the temperature range of 293-413 K,that of remanence decreases from 0.099%/K to 0.091%/K,and the coercivity increases from 18.44 to 25.04 *** electron microscopy(TEM)characterization reveals that there are both the 1:2 phase and the amorphous phase in the high-Co magnet before and after GBD,EDS elemental analysis shows that Tb element is more likely to preferentially replace the rare earth elements in the 2:14:1 main phase than in the 1:2 phase and the amorphous *** concentration of Tb at the edge of the main phase is much higher than that in the 1:2phase and amorphous phase,which is beneficial to the improvement of the *** preferential replacement of Tb elements at the edge of the 2:14:1 phase and thin-layer GBs with a more continuous distribution are synergistically responsible for improving the thermal stability of high-Co *** study indicates that GBD is an effective method to improve the microstructure and thermal stability of high-Co magnets.

关键词： Nd-Fe-B magnets Coercivity Grain boundary diffusion Thermal stability Micro structure Rare earths

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Recent research in mechanical properties of geopolymer-based ultrahigh-performance concrete:A review

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Defence Technology（防务技术） 2024年第2期32卷 67-88页

作者： G.Murali division of research&Innovation Uttaranchal UniversityDehradun 248007India

Due to the growing need for sustainable and ultra-high-strength construction materials,scientists have created an innovative ultra-high-performance concrete called Geopolymer based ultra-highperformance concrete(GUHPC).Besides,in the last few decades,there have been a lot of explosions and ballistic attacks around the world,which have killed many civilians and fighters in border *** this context,this article reviews the fresh state and mechanical properties of ***,the ingredients of GUHPC and fresh properties such as setting time and flowability are briefly ***,the review of compressive strength,flexure strength,tensile strength and modulus of elasticity of fibrous ***,the blast and projectile impact resistance performance was ***,the microstructural characteristics were reviewed using the scanning electron microscope and X-ray Powder *** review outcome reveals that the mechanical properties were increased when 30%silica fume was added to a higher dose of steel fibre to improve the microstructure of *** is hypothesized that the brittleness of GUHPC was mitigated by adding 1.5%steel fibre reinforcement,which played a role in the decrease of contact explosion cratering and *** the need for cement in GUHPC was a key factor in the review,indicating a promising potential for lowering carbon ***,GUHPC research is still in its early stages,so more study is required before its full potential can be utilized.

关键词： Mechanical properties Blast Projectile impact Fibre Geopolymer Silica fume Alkaline activators

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Decadal length-of-day and geomagnetic changes imply more complex Earth’s core motions

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Science Bulletin 2024年第13期69卷 2038-2041页

作者： Hao Ding Jiancheng Li Weiping Jiang Wenbin Shen School of geodesy and Geomatics Hubei Luojia LaboratoryWuhan UniversityWuhan 430079China GNSS research Center Wuhan UniversityWuhan 430079China

Since the 1950s,the length-of-day variations(DLOD)of the Earth’s rotation have received extensive attention and research in various fields,including geodynamics,geomagnetism,geodesy,seismology,geology,marine science,environmental science,and even biology and *** the abundance of related studies and notable advancements,the underlying mechanism behind the decadal changes in DLOD remains a persistent unresolved *** essential aspect of investigating this issue lies in its potential to unveil the Earth’s core motions[1,2].Despite the presence of various hypothesized and constructed models about the Earth’s core motions,these models typically exhibit simplicity.

关键词： Earth geology geomagnetic

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A Novel Prescribed-Performance Path-Following Problem for Non-Holonomic Vehicles

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IEEE/CAA Journal of Automatica Sinica 2024年第6期11卷 1476-1484页

作者： Zirui Chen Jingchuan Tang Zongyu Zuo Seventh research division Beihang University(BUAA)Beijing 100191China IEEE

The issue of achieving prescribed-performance path following in robotics is addressed in this paper,where the aim is to ensure that a desired path within a specified region is accu-rately converged to by the controlled *** this context,a novel form of the prescribed performance guiding vector field is introduced,accompanied by a prescribed-time sliding mode con-trol ***,the interdependence among the pre-scribed parameters is *** validate the effectiveness of the proposed method,numerical simulations are presented to demonstrate the efficacy of the approach.

关键词： Guiding vector field non-holonomic vehicle path following prescribed performance sliding mode control

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Determination of global geodetic parameters using satellite laser ranging to Galileo,GLONASS,and BeiDou satellites

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Satellite Navigation 2024年第1期5卷 240-257页

作者： Xingxing Li Jiaqing Lou Yongqiang Yuan Jiaqi Wu Keke Zhang School of geodesy and Geomatics Wuhan University129 Luoyu RoadWuhan430079HubeiChina

The new Global Navigation Satellite System(GNSS)satellites,including GLONASS,Galileo,and BeiDou system,are equipped with Laser Retroreflector Arrays(LRA)to support Satellite Laser Ranging(SLR)tracking,which contributes to the estimation of global geodetic *** this study,we estimate the global geodetic parameters using the SLR observations to GNSS satellites and also investigate the effects of different data processing strategies on the estimated Earth Rotation Parameters(ERP),geocenter motion,and terrestrial *** results indicate that setting range bias parameters for each satellite-station pair can effectively account for the satellite-specific biases induced by LRAs,leading to smaller Root Mean Square Errors(RMSE)of the post-fit SLR ***,estimating the range biases for each satellite-station pair improves the accuracy of the estimated station coordinates and *** also examine the impact of different arc lengths on the estimates of ERP,geocenter motion,and terrestrial *** results show that extending arc length can significantly reduce the formal error of *** 7-day strategy produces the smallest RMSEs of 473 microarcseconds and 495 microarcseconds for the estimated X-and Y-component of pole coordinates,and 52 microseconds for length-of-day,***,the estimated geocenter motion is less affected by the arc length,even the shortest 1-day arc strategy can capture the seasonal variations of geocenter motion in Z *** scale estimation,extending the arc length notably improves the accuracy of the estimated station coordinates and scale,but this advantage becomes less noticeable in longer *** 7-day solution also obtains the closet scale results compared to ITRF2014,with the RMSE of 2.10×10^(–9).

关键词： Satellite laser ranging GNSS Geodetic parameters Earth rotation parameters Geocenter motion Terrestrial scale

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Present-day movement characteristics of the Qinghai Nanshan fault and its surrounding area from GPS observation

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geodesy and Geodynamics 2024年第2期15卷 133-141页

作者： Yang Liu Yuxuan Qiu Jialiang Liu Luyun Xiong Caijun Xu Jianghui Geng Gang Zheng Tianchen Sheng School of geodesy and Geomatics Wuhan UniversityWuhan 430079China Key Laboratory of Geospace Environment and geodesy Ministry of EducationWuhan UniversityWuhan 430079China Key Laboratory of Geophysical geodesy Ministry of Natural ResourcesWuhan UniversityWuhan 430079China GNSS research Center Wuhan UniversityWuhan 430079China School of Earth and Environment University of LeedsLeeds LS29JTUK Qinghai Basic Surveying and Mapping Institute Xining 810101China

The Qinghai Nanshan fault is a larger fault in the Northeastern Xizang *** previous studies,its movement characteristics are mainly investigated with geological and seismic observations,and the tectonic transformation role of the fault on its east is not yet *** study uses data fusion to obtain denser GPS observations near the Qinghai Nanshan *** on tectonic characteristics,we establish a block model to investigate the fault slip rate,locking degree,and slip *** results show that the Qinghai Nanshan fault slip rate is characterized by sinistral and convergent *** the sinistral and convergent rates display a decreasing trend from west to *** locking degree and slip deficit are higher in the western segment(with an average of about 0.74 and 1.1 mm/a)and lower in the eastern ***,we construct a strain rate field using GPS observations to analyze the regional strain *** results indicate that along the fault,the western segment shows a larger shear strain rate and negative dilation *** earthquake records show that the frequency of earthquakes is lower near the *** joint results suggest that the western segment may have a higher earthquake *** addition,the insignificant fault slip rate in the eastern segment may indicate that it does not participate in the tectonic transformation among the Riyueshan,Lajishan,and West Qinling faults.

关键词： The Qinghai Nanshan fault Movement characteristics Block model Slip rate GPS

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Coseismic Coulomb stress changes induced by a 2020-2021 M_(W)>7.0 Alaska earthquake sequence in and around the Shumagin gap and its influence on the Alaska-Aleutian subduction interface

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geodesy and Geodynamics 2024年第1期15卷 1-12页

作者： Lei Yang Jianjun Wang Caijun Xu School of geodesy and Geomatics Wuhan UniversityWuhan 430079China Collaborative Innovation Center of Geospatial Technology Wuhan 430079China Key Laboratory of Geospace Environment and geodesy Ministry of EducationWuhan UniversityWuhan 430079China

Three M_(W)>7.0 earthquakes in 2020-2021 occurred in the Shumagin seismic gap and its adjacent area of the Alaska-Aleutian subduction zone,including the Mw7.8 Simeonof thrust earthquake on July 22,2020,the M_(W)7.6 Sand Point strike-slip earthquake on October 19,2020,and the M_(W)8.2 Chignik thrust earthquake on July 29,*** spatial and temporal proximity of these three earthquakes prompts us to probe stress-triggering effects among *** we examine the coseismic Coulomb stress change imparted by the three earthquakes and their influence on the subduction *** results show that:(1)The Simeonof earthquake has strong loading effects on the subsequent Sand Point and Chignik earthquakes,with the Coulomb stress changes of 3.95 bars and 2.89 bars,*** Coulomb stress change caused by the Sand Point earthquake at the hypocenter of the Chignik earthquake is merely around 0.01 bars,suggesting the negligible triggering effect on the latter earthquake;(2)The triggering effects of the Simeonof,Sand Point,and Chignik earthquakes on aftershocks within three months are not well pronounced because of the triggering rates of 38%,14%,and 43%*** factors may have played an important role in promoting the occurrence of these aftershocks,such as the roughness of the subduction interface,the complicated velocity structure of the lithosphere,and the heterogeneous prestress therein;(3)The three earthquakes caused remarkable coseismic Coulomb stress changes at the subduction interface nearby these mainshocks,with an average Coulomb stress change of 3.2 bars in the shallow region directly inwards the trench.

关键词： The 2020-2021 Alaska earthquake sequence Coseismic Coulomb stress change Mainshock-aftershock triggering The Alaska-Aleutian subduction interface The Shumagin gap

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REMnO3（RE=Pr,Nd,Sm,Eu,Gd） perovskite as efficient catalysts for oxygen reduction reaction

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Journal of Rare Earths 2024年第11期42卷 2078-2087页

作者： Rakesh Ranjan Mahalik Siba Soren Ipsha Hota A.K.Debnath K.P.Muthe Purnendu Parhi Department of Chemistry Ravenshaw University Technical Physics division Bhabha Atomic Research Centre

Rare earth metal based perovskite emerges as important catalytic material for energy production and *** ABO3type materials are now the focus of research in the field of oxygen reduction and evolution ***,in this work we evaluated the oxygen reduction properties of the synthesized one-dimensional REMnO3（RE=Pr,Nd,Sm,Eu and Gd）.The one-dimensional REMnO3prepared by the hydrothermal synthesis route results in pure phase perovskite on *** perovskite was characte rized with X-ray diffraction,Fourier transform-infrared（FT-IR）,field emission-scanning electron microscopy（FE-SEM）,transmission electron microscopy（TEM） and X-ray photoelectron spectroscopy（XPS）.The oxygen reduction reaction activities were investigated with the help of electrochemical workstation that consists of three-electrode system immersed in 0.1 mol/L KOH electrolyte solution saturated with *** Koutechy-Levich plot obtained from rotating ring disk electrode shows all the prepared catalysts follow 4e-processes during oxygen *** effect of "A" site cation variation in REMnO3 on oxygen reduction reaction is ***3showed better onset potential for oxygen reduction reaction among the prepared rare earth ***3having high RE:Mn ratio（A-site rich co mpositions） promotes oxygen reduction reaction（ORR） *** the perovs kites showed good oxygen reduction property with high stability and methanol tolerance.

关键词： Electrocatalytic activity Oxygen reduction reaction (ORR) Perovskite Rare earths REMnO3 SmMnO3

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