The Experts below are selected from a list of 64644 Experts worldwide ranked by ideXlab platform
Alexey Kuvshinov - One of the best experts on this subject based on the ideXlab platform.
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Probing upper mantle electrical conductivity with daily Magnetic variations using global-to-local transfer functions
Geophysical Journal International, 2019Co-Authors: Martina Guzavina, Alexander V Grayver, Alexey KuvshinovAbstract:Summary We present new transfer functions (TFs) that can handle external electroMagnetic (EM) sources of complex geometry. These TFs relate global expansion coefficients describing the source with a locally measured EM field. In this study, the new TFs concept was applied to the daily Magnetic variations measured at the ground. The parameterisation of the source in terms of spherical harmonics was adopted. We used nearly 20 years of data from 125 mid-latitude observatories and explored how the results are affected by (I) solar activity conditions, (II) the choice of the prior conductivity model used for the source coefficient estimation, and (III) the presence of ocean tidal Magnetic Signals. We found that choosing Magnetically quiet periods is beneficial due to simpler source morphology, and the choice of prior conductivity model may significantly affect the source coefficients and TFs at short periods. We further observed significant contributions by ocean tidal Magnetic Signals at coastal and island observatories and corrected for them. Finally, the estimated TFs were inverted for the mantle conductivity at several locations representing different geological settings.
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satellite tidal Magnetic Signals constrain oceanic lithosphere asthenosphere boundary
Science Advances, 2016Co-Authors: Alexander V Grayver, N R Schnepf, Alexey Kuvshinov, Terence J Sabaka, C Manoj, Nils OlsenAbstract:The tidal flow of electrically conductive oceans through the geoMagnetic field results in the generation of secondary Magnetic Signals, which provide information on the subsurface structure. Data from the new generation of satellites were shown to contain Magnetic Signals due to tidal flow; however, there are no reports that these Signals have been used to infer subsurface structure. We use satellite-detected tidal Magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. The model derived from more than 12 years of satellite data reveals a ≈72-km-thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere.
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Impact of climate variability on the tidal oceanic Magnetic signal—A model-based sensitivity study
Journal of Geophysical Research: Oceans, 2016Co-Authors: Jan Saynisch, Alexey Kuvshinov, Christopher Irrgang, Johannes Petereit, Maik ThomasAbstract:ESA's satellite magnetometer mission Swarm is supposed to lower the limit of observability for oceanic processes. While periodic Magnetic Signals from ocean tides are already detectable in satellite magnetometer observations, changes in the general ocean circulation are yet too small or irregular for a successful separation. An approach is presented that utilizes the good detectability of tidal Magnetic Signals to detect changes in the oceanic electric conductivity distribution. Ocean circulation, tides, and the resultant Magnetic fields are calculated with a global general ocean circulation model coupled to a 3-D electroMagnetic induction model. For the decay of the meridional overturning circulation, as an example, the impact of climate variability on tidal oceanic Magnetic Signals is demonstrated. Total overturning decay results in anomalies of up to 0.7 nT in the radial Magnetic M2 signal at sea level. The anomalies are spatially heterogeneous and reach in extended areas 30% or more of the unperturbed tidal Magnetic signal. The anomalies should be detectable in long time series from magnetometers on land or at the ocean bottom. The anomalies at satellite height (430 km) reach 0.1 nT and pose a challenge for the precision of the Swarm mission. Climate variability induced deviations in the tide system (e.g., tidal velocities and phases) are negligible. Changes in tidal Magnetic fields are dominated by changes in seawater salinity and temperature. Therefore, it is concluded that observations of tidal Magnetic Signals could be used as a tool to detect respective state changes in the ocean.
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can we probe the conductivity of the lithosphere and upper mantle using satellite tidal Magnetic Signals
Geophysical Research Letters, 2015Co-Authors: N R Schnepf, Alexey Kuvshinov, Terence J SabakaAbstract:Thesis: S.M., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015.
Terence J Sabaka - One of the best experts on this subject based on the ideXlab platform.
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satellite tidal Magnetic Signals constrain oceanic lithosphere asthenosphere boundary
Science Advances, 2016Co-Authors: Alexander V Grayver, N R Schnepf, Alexey Kuvshinov, Terence J Sabaka, C Manoj, Nils OlsenAbstract:The tidal flow of electrically conductive oceans through the geoMagnetic field results in the generation of secondary Magnetic Signals, which provide information on the subsurface structure. Data from the new generation of satellites were shown to contain Magnetic Signals due to tidal flow; however, there are no reports that these Signals have been used to infer subsurface structure. We use satellite-detected tidal Magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. The model derived from more than 12 years of satellite data reveals a ≈72-km-thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere.
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extracting ocean generated tidal Magnetic Signals from swarm data through satellite gradiometry
Geophysical Research Letters, 2016Co-Authors: Terence J Sabaka, Robert H Tyler, Nils OlsenAbstract:Ocean-generated Magnetic field models of the Principal Lunar, M2, and the Larger Lunar elliptic, N2, semidiurnal tidal constituents were estimated through a "Comprehensive Inversion" of the first 20.5 months of Magnetic measurements from European Space Agency's (ESA) Swarm satellite constellation mission. While the constellation provides important north-south along-track gradiometry information, it is the unique low-spacecraft pair that allows for east-west cross-track gradiometry. This latter type is crucial in delivering an M2 estimate of similar quality with that derived from over 10 years of CHAMP satellite data but over a shorter interval, at higher altitude, and during more Magnetically disturbed conditions. Recovered N2 contains nonoceanic signal but is highly correlated with theoretical models in regions of maximum oceanic amplitude. Thus, satellite Magnetic gradiometry may eventually enable the monitoring of ocean electrodynamic properties at temporal resolutions of 1 to 2 years, which may have important implications for the inference of ocean temperature and salinity.
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can we probe the conductivity of the lithosphere and upper mantle using satellite tidal Magnetic Signals
Geophysical Research Letters, 2015Co-Authors: N R Schnepf, Alexey Kuvshinov, Terence J SabakaAbstract:Thesis: S.M., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015.
Dong Shiyun - One of the best experts on this subject based on the ideXlab platform.
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Distinguishing Stress Concentration or Cracking in FerroMagnetic Material Using Abnormal Magnetic Signals
MATERIALS TRANSACTIONS, 2013Co-Authors: Shi Changliang, Dong Shiyun, He Peng, Xu BinshiAbstract:In the geoMagnetic field, spontaneous Magnetic Signals in ferroMagnetic materials can be induced by stress, which can be potentially applied to estimate the damage degree. In this research, a method of distinguishing stress concentration or cracking in ferroMagnetic material was proposed. The normal component of Magnetic field, Hp(y), was measured on the surfaces of ferroMagnetic specimens with notch. The results indicated that the shapes of Hp(y) curves of stress concentration and cracking were different, there was abnormal Magnetic peak in the Hp(y) curve of cracking. Meanwhile, the effect of lift-off on abnormal Magnetic peak was studied, and the optimal lift-off value was also presented. [doi:10.2320/matertrans.M2012393]
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material during fatigue crack propagation under loading condition
2011Co-Authors: Xu Binshi, Dong Shiyun, Dong Lihong, Xue NanAbstract:Variations of self-emitting Magnetic Signals during fatigue crack propagation of center- cracked tension (CCT) specimen of 45CrNiMoVA steel were studied. The results showed that the initial abnormal Magnetic peak occurred in all the measured lines, and there was a maximum peak-to-peak value in the center measured line before loading. However, the first abnormal Magnetic peak occurred on the position of the precut notch after loading, while Magnetic signal curve presented linearity on the position without precut notch, at this time fatigue crack did not initiate. During fatigue crack propagation, the second abnormal Magnetic peak occurred in the measured lines in turn. The peak- to-peak value of the second abnormal Magnetic Signals and the slope coefficient between peak-to-peak can be used to characterize fatigue crack propagation life dynamically. The behavior of self-emitting Magnetic Signals during fatigue crack propagation was analyzed on the basis of Magnetic charge and effective Magnetic field theory under loading condition.
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stress concentration degree affects spontaneous Magnetic Signals of ferroMagnetic steel under dynamic tension load
Ndt & E International, 2010Co-Authors: Shi Changliang, Dong Shiyun, Xu Binshi, He PengAbstract:Abstract Under the excitation of geoMagnetic field, stress can induce spontaneous Magnetic Signals in ferroMagnetic materials, which can be potentially applied to estimate the damage degree. In this research, the normal component of Magnetic field, Hp(y), was measured during dynamic tension test on the surfaces of ferroMagnetic specimens having different stress concentration factors, α constant amplitude sinusoidal tensile load cycles were applied on 18CrNi4A steel plate specimens whose α were respectively 1, 3 and 5. Then correlation of Hp(y) values’ changes with loading cycles reported. The results indicate that stress concentration factor, α extremely affects the Magnetic signal, the absolute value of the gradient, |K|, increases with the increase of α. Meanwhile, |K| also goes up when loading cycle increases in the initial state. However, after a few cycles, those Hp(y) curves corresponding to different cycles become similar before cracking.
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variation of stress induced Magnetic Signals during tensile testing of ferroMagnetic steels
Ndt & E International, 2008Co-Authors: Dong Lihong, Dong Shiyun, Xu Binshi, Chen Qunzhi, Wang DanAbstract:Abstract Stress alone applied to ferroMagnetic materials can induce the generation of weak Magnetic Signals on their surfaces, which can be potentially used to estimate the degree of damage of ferroMagnetic components. In this paper, the normal component of stress-induced Magnetic field, H p ( y ), was measured during tensile tests on the surfaces of sheet specimens of three ferroMagnetic materials. It has been concluded that H p ( y ) depends on the applied stress and will present different characteristics on the elastic and plastic deformation stages, respectively. The phenomenon of sharp changes in Magnetic Signals occurring at the instant of fracture was also discussed from the view of the interaction energy in a ferromagnet.
Xu Binshi - One of the best experts on this subject based on the ideXlab platform.
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Distinguishing Stress Concentration or Cracking in FerroMagnetic Material Using Abnormal Magnetic Signals
MATERIALS TRANSACTIONS, 2013Co-Authors: Shi Changliang, Dong Shiyun, He Peng, Xu BinshiAbstract:In the geoMagnetic field, spontaneous Magnetic Signals in ferroMagnetic materials can be induced by stress, which can be potentially applied to estimate the damage degree. In this research, a method of distinguishing stress concentration or cracking in ferroMagnetic material was proposed. The normal component of Magnetic field, Hp(y), was measured on the surfaces of ferroMagnetic specimens with notch. The results indicated that the shapes of Hp(y) curves of stress concentration and cracking were different, there was abnormal Magnetic peak in the Hp(y) curve of cracking. Meanwhile, the effect of lift-off on abnormal Magnetic peak was studied, and the optimal lift-off value was also presented. [doi:10.2320/matertrans.M2012393]
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material during fatigue crack propagation under loading condition
2011Co-Authors: Xu Binshi, Dong Shiyun, Dong Lihong, Xue NanAbstract:Variations of self-emitting Magnetic Signals during fatigue crack propagation of center- cracked tension (CCT) specimen of 45CrNiMoVA steel were studied. The results showed that the initial abnormal Magnetic peak occurred in all the measured lines, and there was a maximum peak-to-peak value in the center measured line before loading. However, the first abnormal Magnetic peak occurred on the position of the precut notch after loading, while Magnetic signal curve presented linearity on the position without precut notch, at this time fatigue crack did not initiate. During fatigue crack propagation, the second abnormal Magnetic peak occurred in the measured lines in turn. The peak- to-peak value of the second abnormal Magnetic Signals and the slope coefficient between peak-to-peak can be used to characterize fatigue crack propagation life dynamically. The behavior of self-emitting Magnetic Signals during fatigue crack propagation was analyzed on the basis of Magnetic charge and effective Magnetic field theory under loading condition.
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stress concentration degree affects spontaneous Magnetic Signals of ferroMagnetic steel under dynamic tension load
Ndt & E International, 2010Co-Authors: Shi Changliang, Dong Shiyun, Xu Binshi, He PengAbstract:Abstract Under the excitation of geoMagnetic field, stress can induce spontaneous Magnetic Signals in ferroMagnetic materials, which can be potentially applied to estimate the damage degree. In this research, the normal component of Magnetic field, Hp(y), was measured during dynamic tension test on the surfaces of ferroMagnetic specimens having different stress concentration factors, α constant amplitude sinusoidal tensile load cycles were applied on 18CrNi4A steel plate specimens whose α were respectively 1, 3 and 5. Then correlation of Hp(y) values’ changes with loading cycles reported. The results indicate that stress concentration factor, α extremely affects the Magnetic signal, the absolute value of the gradient, |K|, increases with the increase of α. Meanwhile, |K| also goes up when loading cycle increases in the initial state. However, after a few cycles, those Hp(y) curves corresponding to different cycles become similar before cracking.
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variation of stress induced Magnetic Signals during tensile testing of ferroMagnetic steels
Ndt & E International, 2008Co-Authors: Dong Lihong, Dong Shiyun, Xu Binshi, Chen Qunzhi, Wang DanAbstract:Abstract Stress alone applied to ferroMagnetic materials can induce the generation of weak Magnetic Signals on their surfaces, which can be potentially used to estimate the degree of damage of ferroMagnetic components. In this paper, the normal component of stress-induced Magnetic field, H p ( y ), was measured during tensile tests on the surfaces of sheet specimens of three ferroMagnetic materials. It has been concluded that H p ( y ) depends on the applied stress and will present different characteristics on the elastic and plastic deformation stages, respectively. The phenomenon of sharp changes in Magnetic Signals occurring at the instant of fracture was also discussed from the view of the interaction energy in a ferromagnet.
He Peng - One of the best experts on this subject based on the ideXlab platform.
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Distinguishing Stress Concentration or Cracking in FerroMagnetic Material Using Abnormal Magnetic Signals
MATERIALS TRANSACTIONS, 2013Co-Authors: Shi Changliang, Dong Shiyun, He Peng, Xu BinshiAbstract:In the geoMagnetic field, spontaneous Magnetic Signals in ferroMagnetic materials can be induced by stress, which can be potentially applied to estimate the damage degree. In this research, a method of distinguishing stress concentration or cracking in ferroMagnetic material was proposed. The normal component of Magnetic field, Hp(y), was measured on the surfaces of ferroMagnetic specimens with notch. The results indicated that the shapes of Hp(y) curves of stress concentration and cracking were different, there was abnormal Magnetic peak in the Hp(y) curve of cracking. Meanwhile, the effect of lift-off on abnormal Magnetic peak was studied, and the optimal lift-off value was also presented. [doi:10.2320/matertrans.M2012393]
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stress concentration degree affects spontaneous Magnetic Signals of ferroMagnetic steel under dynamic tension load
Ndt & E International, 2010Co-Authors: Shi Changliang, Dong Shiyun, Xu Binshi, He PengAbstract:Abstract Under the excitation of geoMagnetic field, stress can induce spontaneous Magnetic Signals in ferroMagnetic materials, which can be potentially applied to estimate the damage degree. In this research, the normal component of Magnetic field, Hp(y), was measured during dynamic tension test on the surfaces of ferroMagnetic specimens having different stress concentration factors, α constant amplitude sinusoidal tensile load cycles were applied on 18CrNi4A steel plate specimens whose α were respectively 1, 3 and 5. Then correlation of Hp(y) values’ changes with loading cycles reported. The results indicate that stress concentration factor, α extremely affects the Magnetic signal, the absolute value of the gradient, |K|, increases with the increase of α. Meanwhile, |K| also goes up when loading cycle increases in the initial state. However, after a few cycles, those Hp(y) curves corresponding to different cycles become similar before cracking.
