The Experts below are selected from a list of 11901 Experts worldwide ranked by ideXlab platform
Robert W. Schunk - One of the best experts on this subject based on the ideXlab platform.
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Effects of magnetospheric precipitation and ionospheric conductivity on the ground Magnetic signatures of traveling convection vortices
Journal of Geophysical Research, 1999Co-Authors: Robert W. Schunk, Jan Josef SojkaAbstract:By using an improved TCV model (Zhu et al., 1997), a quantitative study of the effects of magnetospheric precipitation and ionospheric background conductivity on the ground Magnetic signatures of traveling convection vortices (TCVs) has been conducted. In this study the localized conductivity enhancement associated with the TCVs is present and the ratio of the Hall and Pedersen conductances vary both spatially and temporally according to the hardness of the TCV precipitation. It is found that a strong conductivity enhancement associated with hard TCV precipitation can significantly distort the TCV current closure in the ionosphere and lead to ground Magnetic Disturbance patterns with strong asymmetry in E-W direction. The asymmetry of the ground Magnetic patterns is characterized by a stronger Magnetic Disturbance on the side of the upward field-aligned currents (clockwise convection cell) and a possible rotation of the whole Magnetic patterns. Specifically, the modeling results predict that when the characteristic energy of the TCV precipitation is below 500 eV, the asymmetry of the ground Magnetic patterns is minimal (less than 1%) and may not be detectable. When the characteristic energy of the precipitation is about 7 keV, the asymmetry of the Magnetic patterns can be well above 30%. It is also found that a low ionospheric background conductivity favors the appearance of strong asymmetry in the ground Magnetic patterns of the TCVs, while a high ionospheric background conductivity favors the appearance of strong ground Magnetic Disturbances but with less asymmetry. We concluded that the most favorable condition for the appearance of strong asymmetry in the TCV ground Magnetic signatures is the condition of winter, solar minimum, and hard precipitation.
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Model study of ground Magnetic signatures of traveling convection vortices
Journal of Geophysical Research, 1997Co-Authors: P. Gifford, Jan Josef Sojka, Robert W. SchunkAbstract:We conducted a model study of ground Magnetic signatures of traveling convection vortices (TCVs) that included both the ionospheric conductivity enhancement associated with the TCVs and the ground induction effect. We found that the localized conductivity enhancement can cause a significant distortion of the TCV current system and lead to a distortion of the ground Magnetic Disturbance patterns. The patterns of all three Magnetic components are asymmetric, mainly in the E-W direction, and the patterns of the Z component show the strongest asymmetry (20-30%). We also found that the effect of induction currents on ground Magnetic signatures of the TCVs is insignificant (less than 5%). The results show that because of the presence of localized conductivity enhancements the polarity and speed of the TCVs can significantly influence the distortion features of ground Magnetic patterns. The upward and downward current filaments of a TCV with a clockwise leading convection cell can wrap with each other, resulting in a rotation of the whole ground Magnetic Disturbance pattern. This rotation feature is most significant when the speed of the TCVs is high.
Jan Josef Sojka - One of the best experts on this subject based on the ideXlab platform.
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Effects of magnetospheric precipitation and ionospheric conductivity on the ground Magnetic signatures of traveling convection vortices
Journal of Geophysical Research, 1999Co-Authors: Robert W. Schunk, Jan Josef SojkaAbstract:By using an improved TCV model (Zhu et al., 1997), a quantitative study of the effects of magnetospheric precipitation and ionospheric background conductivity on the ground Magnetic signatures of traveling convection vortices (TCVs) has been conducted. In this study the localized conductivity enhancement associated with the TCVs is present and the ratio of the Hall and Pedersen conductances vary both spatially and temporally according to the hardness of the TCV precipitation. It is found that a strong conductivity enhancement associated with hard TCV precipitation can significantly distort the TCV current closure in the ionosphere and lead to ground Magnetic Disturbance patterns with strong asymmetry in E-W direction. The asymmetry of the ground Magnetic patterns is characterized by a stronger Magnetic Disturbance on the side of the upward field-aligned currents (clockwise convection cell) and a possible rotation of the whole Magnetic patterns. Specifically, the modeling results predict that when the characteristic energy of the TCV precipitation is below 500 eV, the asymmetry of the ground Magnetic patterns is minimal (less than 1%) and may not be detectable. When the characteristic energy of the precipitation is about 7 keV, the asymmetry of the Magnetic patterns can be well above 30%. It is also found that a low ionospheric background conductivity favors the appearance of strong asymmetry in the ground Magnetic patterns of the TCVs, while a high ionospheric background conductivity favors the appearance of strong ground Magnetic Disturbances but with less asymmetry. We concluded that the most favorable condition for the appearance of strong asymmetry in the TCV ground Magnetic signatures is the condition of winter, solar minimum, and hard precipitation.
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Model study of ground Magnetic signatures of traveling convection vortices
Journal of Geophysical Research, 1997Co-Authors: P. Gifford, Jan Josef Sojka, Robert W. SchunkAbstract:We conducted a model study of ground Magnetic signatures of traveling convection vortices (TCVs) that included both the ionospheric conductivity enhancement associated with the TCVs and the ground induction effect. We found that the localized conductivity enhancement can cause a significant distortion of the TCV current system and lead to a distortion of the ground Magnetic Disturbance patterns. The patterns of all three Magnetic components are asymmetric, mainly in the E-W direction, and the patterns of the Z component show the strongest asymmetry (20-30%). We also found that the effect of induction currents on ground Magnetic signatures of the TCVs is insignificant (less than 5%). The results show that because of the presence of localized conductivity enhancements the polarity and speed of the TCVs can significantly influence the distortion features of ground Magnetic patterns. The upward and downward current filaments of a TCV with a clockwise leading convection cell can wrap with each other, resulting in a rotation of the whole ground Magnetic Disturbance pattern. This rotation feature is most significant when the speed of the TCVs is high.
P. Gifford - One of the best experts on this subject based on the ideXlab platform.
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Model study of ground Magnetic signatures of traveling convection vortices
Journal of Geophysical Research, 1997Co-Authors: P. Gifford, Jan Josef Sojka, Robert W. SchunkAbstract:We conducted a model study of ground Magnetic signatures of traveling convection vortices (TCVs) that included both the ionospheric conductivity enhancement associated with the TCVs and the ground induction effect. We found that the localized conductivity enhancement can cause a significant distortion of the TCV current system and lead to a distortion of the ground Magnetic Disturbance patterns. The patterns of all three Magnetic components are asymmetric, mainly in the E-W direction, and the patterns of the Z component show the strongest asymmetry (20-30%). We also found that the effect of induction currents on ground Magnetic signatures of the TCVs is insignificant (less than 5%). The results show that because of the presence of localized conductivity enhancements the polarity and speed of the TCVs can significantly influence the distortion features of ground Magnetic patterns. The upward and downward current filaments of a TCV with a clockwise leading convection cell can wrap with each other, resulting in a rotation of the whole ground Magnetic Disturbance pattern. This rotation feature is most significant when the speed of the TCVs is high.
Therese Moretto - One of the best experts on this subject based on the ideXlab platform.
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On the cause of IMF By related mid‐ and low latitude Magnetic Disturbances
Geophysical Research Letters, 2007Co-Authors: Susanne Vennerstrøm, Freddy Christiansen, Nils Olsen, Therese MorettoAbstract:[1] An analysis of the effect of the IMF By on near-Earth low and mid-latitude Magnetic Disturbances is presented. In particular the contribution from field-aligned currents (FACs) connected to the polar regions is investigated. Based on statistically determined high-latitude FAC patterns for various Interplanetary Magnetic Field (IMF) directions, we estimate the FAC contribution to the mid- and low latitude Magnetic Disturbance and its dependence on the IMF. The estimated perturbations are compared with observations from the ground and from the low-altitude polar orbiting satellite Oersted. It is found that the long-distance effect of the high-latitude FACs constitute the major source to IMF By and Bz related Magnetic east-west Disturbances at mid- and low latitudes.
Marko Munih - One of the best experts on this subject based on the ideXlab platform.
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Compensation for Magnetic Disturbances in Motion Estimation to Provide Feedback to Wearable Robotic Systems
IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society, 2017Co-Authors: Sebastjan Šlajpah, Roman Kamnik, Marko MunihAbstract:The direction of the Earth’s Magnetic field is used as a reference vector to determine the heading in orientation estimation with wearable sensors. However, the Magnetic field strength is weak and can be easily disturbed in the vicinity of ferroMagnetic materials, which may result in inaccurate estimate of orientation. This paper presents a novel method for estimating and compensating for Magnetic Disturbances. The compensation algorithm is implemented within a kinematic-based extended Kalman filter and is based on an assessment of the Magnetic Disturbance and the change of orientation in each time step. The proposed algorithm was experimentally validated by measuring the orientation of a simple mechanical system with three degrees of freedom in an artificially disturbed Magnetic field. The results of the experimental evaluation show that an Kalman filter algorithm that incorporates compensating for Magnetic Disturbances is capable of estimating the orientation with moderate error (the absolute median errors $\Delta \widetilde {\theta }_{X},\Delta \widetilde {\theta }_{Z} , $\Delta \widetilde {\theta }_{Y} ) when the Earth’s Magnetic field is disturbed by Magnetic Disturbance with a magnitude equal to twice the magnitude of the Earth’s own Magnetic field in different directions.
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Wearable Sensory Apparatus for Multi-segment System Orientation Estimation with Long-Term Drift and Magnetic Disturbance Compensation
Biosystems & Biorobotics, 2016Co-Authors: Sebastjan Šlajpah, Roman Kamnik, Marko MunihAbstract:Orientation assessment based on wearable sensors is becoming crucial for providing feedback information in wearable robotics and sport monitoring. Gravitational acceleration and Earth’s Magnetic field are commonly used as a reference vectors for orientation estimation. This paper presents a novel sensory fusion algorithm for assessing the orientations of human body segments in long-term human walking, and enhance performance in environment with Magnetic Disturbance. The proposed system was experimentally validated. The results show accurate joint angle measurements (error median below \({5}{^\circ }\)) with no expressed drift over time. The incorporated compensation of Magnetic Disturbances proved assessment with absolute median errors bellow \({2.5}{^\circ }\).
