Analysis Of Magnetic Data Research Articles

Bransfield Strait and South Shetland Islands sedimentary basement and upper crustal structure: An analysis of gravity and magnetic data at the northwestern area of the Antarctic Peninsula

The northwestern region of the Antarctic Peninsula is of main interest to the geosciences. Complex tectonic activity in this area is evidenced by the presence of the sinistral South Scotia ridge system and Shackleton plate contacts; As well as the opening of the Bransfield Strait leading to the formation of the Shetland Block, where the last remnant of the Phoenix convergent margin is located. Potential fields such as gravity and magnetism can be used to study crustal structure in these remote regions, where sedimentary basins are located. In this study, we utilized gravity data from the EIGEN-6C4 combined field model and magnetic data from the ADMAP2 magnetic anomaly model. We employed the Spectral decomposition of gravity anomalies to analyze sedimentary basement depth and directional derivatives of gravity and magnetic anomalies to derive structural features and magmatic activity. The gravimetric basement model was compared with previous interpretations of the acoustic basement and provides a new interpretation of basement morphology in regions that have not been studied previously in detail. The gravity/magnetic derivatives highlight evidence for ongoing magmatic activity in the Central Bransfield Basin which correlates with seismic catalogs, and crustal segmentation between King George and Gibbs Islands related to the unstable intersection of the South Scotia Ridge system and Shackleton Fracture Zone.

Information flow and dynamic functional connectivity during electroconvulsive therapy in patients with depression

BackgroundElectroconvulsive therapy is effectively used for treatment-resistant depression; however, its neural mechanism is largely unknown. Resting-state functional magnetic resonance imaging is promising for monitoring outcomes of electroconvulsive therapy for depression. This study aimed to explore the imaging correlates of the electroconvulsive therapy effects on depression using Granger causality analysis and dynamic functional connectivity analyses. MethodsWe performed advanced analyses of resting-state functional magnetic resonance imaging data at the beginning and intermediate stages and end of the therapeutic course to identify neural markers that reflect or predict the therapeutic effects of electroconvulsive therapy on depression. ResultsWe demonstrated that information flow between the functional networks analyzed by Granger causality changes during electroconvulsive therapy, and this change was correlated with the therapeutic outcome. Information flow and the dwell time (an index reflecting the temporal stability of functional connectivity) before electroconvulsive therapy are correlated with depressive symptoms during and after treatment. LimitationsFirst, the sample size was small. A larger group is needed to confirm our findings. Second, the influence of concomitant pharmacotherapy on our results was not fully addressed, although we expected it to be minimal because only minor changes in pharmacotherapy occurred during electroconvulsive therapy. Third, different scanners were used the groups, although the acquisition parameters were the same; a direct comparison between patient and healthy participant data was not possible. Thus, we presented the data of the healthy participants separately from that of the patients as a reference. ConclusionsThese results show the specific properties of functional brain connectivity.

Proof-of-concept of a novel structural equation modelling approach for the analysis of functional magnetic resonance imaging data applied to investigate individual differences in human pain responses.

A novel network analysis method is demonstrated for applications with functional magnetic resonance imaging (fMRI) data. The method is based on structural equation modeling (SEM) plus modeling of physiological responses in order to explain blood oxygenation-level dependent (BOLD) responses across interconnected regions. The method, termed structural and physiological modeling (SAPM) aims to overcome a weakness of previous analysis methods by estimating both input and output signaling of every region of a network. The results also provide weighting factors (B) which describe the influence of each input signal to a region on its output signaling to another region. The SAPM method is demonstrated by applying it to fMRI data from the brainstem and spinal cord in 55 healthy participants undergoing repeated applications of a heat pain stimulation paradigm. Data are also analyzed using our established SEM method for comparison. The results with both methods indicate that individual differences in nociceptive processing are mediated by differences in descending regulation of spinal cord neurons under the influence of both the nucleus tractus solitarius and periaqueductal gray region. The SAPM results show that BOLD responses in the entire network can be explained during all periods of the stimulation paradigm based on two latent (unobserved) input signaling sources, and a model of the predicted BOLD responses to the heat stimulus. The results demonstrate the concept of our novel SAPM method and provide evidence for its validity. Additional studies are needed to further develop the method and its applications to investigations of complex neural processes across networks.

Inter-rater reliability of functional MRI data quality control assessments: A standardised protocol and practical guide using pyfMRIqc.

Quality control is a critical step in the processing and analysis of functional magnetic resonance imaging data. Its purpose is to remove problematic data that could otherwise lead to downstream errors in the analysis and reporting of results. The manual inspection of data can be a laborious and error-prone process that is susceptible to human error. The development of automated tools aims to mitigate these issues. One such tool is pyfMRIqc, which we previously developed as a user-friendly method for assessing data quality. Yet, these methods still generate output that requires subjective interpretations about whether the quality of a given dataset meets an acceptable standard for further analysis. Here we present a quality control protocol using pyfMRIqc and assess the inter-rater reliability of four independent raters using this protocol for data from the fMRI Open QC project (https://osf.io/qaesm/). Data were classified by raters as either "include," "uncertain," or "exclude." There was moderate to substantial agreement between raters for "include" and "exclude," but little to no agreement for "uncertain." In most cases only a single rater used the "uncertain" classification for a given participant's data, with the remaining raters showing agreement for "include"/"exclude" decisions in all but one case. We suggest several approaches to increase rater agreement and reduce disagreement for "uncertain" cases, aiding classification consistency.

Nonlinear Optical and Magnetic Properties of FeII-SCN-HgII Isomers: Centrosymmetric Layers and Chiral Networks

Research on isomers is highly desirable due to their prospective role in better understanding of physicochemical properties of similar systems and further development of multifunctional molecular materials. Iron(II) and tetra(thiocyanato)mercury(II) ions self-assembled in the presence of 2-acetylpyridine (2-acpy) excess to form two {[Fe(2-acpy)][Hg(μ-SCN)4]}n isomers: two-dimensional (2D) centrosymmetric layers with folded ring structural motifs (1) and three-dimensional (3D) chiral networks with right- or left-handed {···Fe-NCS-Hg-SCN···}∞ helixes (2). New methods of designing and synthesizing functional thiocyanate-bridged materials have been proposed. In addition, the similarity between 1 and 2 allowed for the description of subtle changes in IR and UV-visible spectra. Moreover, 2 shows spontaneous resolution, and it crystallizes in the noncentrosymmetric space group P21, leading to the occurrence of nonlinear optical activity in circular dichroism studies and second harmonic generation (SHG). At room temperature, the SH susceptibility for powder sample 2 reached 6.0 × 10-11 esu. Ab initio calculations indicated the electric polarization vector and the crystallographic twofold screw axis pass through the aromatic ring. Magnetic studies for 1 and 2 revealed high-spin iron(II) with zero-field splitting at low temperatures. Analysis of magnetic data gave |D| = 37.45 cm-1, |E/D| = 5.59 cm-1, and ⟨g⟩ = 2.15 for 1, |D| = 36.78 cm-1, |E/D| = 4.92 cm-1, and ⟨g⟩ = 2.18 for 2, and information about the orientation of magnetic anisotropy vectors for both compounds.

UAV magnetics over the Bjerkreim-Sokndal Intrusion, Rogaland, Norway: A first look

The Bjerkreim-Sokndal layered intrusion in Rogaland Anorthosite Province in southwestern Norway has been the focus of decades of research due to its complex geology, the presence of prominent remanent magnetic anomalies, and current economic interest in critical minerals. In 2021, collaborative geophysical fieldwork was conducted by the Norwegian University of Science and Technology and Helmholtz Institute Freiberg for Resource Technology. Despite challenging environmental conditions, more than 100 line-km of magnetic data were collected by a custom multirotor unmanned aerial vehicle (UAV) along the eastern margin of the Bjerkreim lobe of the Bjerkreim-Sokndal Intrusion. Data collection was focused over two areas. The first is an area in the south near the prominent Heskestad magnetic anomaly that is associated with large reversed magnetic remanence in a magnetite-ilmenite-gabbronorite unit. The second is an area in the north near Lake Teksevatnet that hosts mineralized zones and the Lauvneset magnetic anomaly. Initial analysis of the UAV-acquired magnetic data shows additional details on the geologic contacts of key units, especially where in-situ measurements are difficult to collect. UAV surveys help in the construction of an anomaly's geometry through incremental source-sensor separations at various flight altitudes above ground. The UAV data set is an intermediate step between ground and airborne surveys for multiscale interpretation and potentially extreme magnetic scales (from microscopic to planetary).

Introduction to the special issue on Magnetic small-angle neutron scattering – from nanoscale magnetism to long-range magnetic structures

A virtual special issue of Journal of Applied Crystallography brings together a series of articles on magnetic small-angle neutron scattering, with the aim of raising awareness of the range of science cases that can be addressed with the technique and exploring future challenges related to magnetic SANS theory and data analysis. It is also hoped that this special issue will encourage collaborations between communities working on long-range-ordered magnetic textures and nanoscale magnetism.

Correction to ‘ORYX‐MRSI: A fully‐automated open‐source software for proton magnetic resonance spectroscopic imaging data analysis’

International Journal of Imaging Systems and TechnologyVolume 33, Issue 2 p. 770-770 CORRIGENDUMFree Access Correction to ‘ORYX-MRSI: A fully-automated open-source software for proton magnetic resonance spectroscopic imaging data analysis’ This article corrects the following: ORYX-MRSI: A fully-automated open-source software for proton magnetic resonance spectroscopic imaging data analysis Sevim Cengiz, Muhammed Yildirim, Abdullah Bas, Esin Ozturk-Isik, Volume 32Issue 4International Journal of Imaging Systems and Technology pages: 1068-1083 First Published online: May 17, 2022 First published: 27 January 2023 https://doi.org/10.1002/ima.22857AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat We regret to report a technical error in our manuscript entitled ‘ORYX-MRSI: A fully-automated open-source software for proton magnetic resonance spectroscopic imaging data analysis’. The volume of interest (VOI) for all the MR spectroscopic metabolites, other than the reference metabolite, are shifted in space by their respective chemical shift amounts as calculated by Equation 2 due to the chemical shift error. Even though there is a shift in the VOIs of different metabolites, it was incorrect to shift the metabolite maps along with their corresponding VOIs. This technical error has been corrected in the Oryx-MRSI source code, which has been updated on our laboratory's GitHub page. Currently, if the chemical shift correction is set to ‘on’, the corresponding VOIs for the metabolites are shifted in space by their respective chemical shift amounts, and the metabolite intensities are evaluated at their respective locations. Additionally, the metabolite ratios are evaluated only in the region that is located at the intersection of the corresponding metabolite VOIs. Moreover, the tissue fractions are calculated only once at the reference VOI. As a result, Figure 5 is not accurate after correction and hence should not be considered for further discussion. The authors thank Wolfgang Bogner, Ph.D. and Gilbert Hangel, Ph.D. for their careful reviews of the published manuscript and apologize for this error. REFERENCE 1Cengiz S, Yildirim M, Bas A, Ozturk-Isik E. ORYX-MRSI: a fully-automated open-source software for proton magnetic resonance spectroscopic imaging data analysis. Int J Imaging Syst Technol. 2022; 32: 1068- 1083. doi:10.1002/ima.22748 Volume33, Issue2March 2023Pages 770-770 ReferencesRelatedInformation

Spirobifluorene Mediating the Spin–Spin Coupling of Nitronyl Nitroxide Diradicals

To investigate the mechanism of this spiro conjugation magnetic behavior, we designed and synthesized three diradicals─22'SBF-NN, 44'SBF-NN, and 27SBF-NN. They are bridged by spirobifluorene and nitronyl nitroxide (NN) diradicals as the spin centers. Notably, by SQUID and electron paramagnetic resonance (EPR) zero-field splitting data analyses, the 22'SBF-NN and 27SBF-NN diradicals exhibit intramolecular, distinctly antiferromagnetic (AF) coupling, with 2J(22'SBF-NN)/kB = -5.86 K and 2J(27SBF-NN)/kB = -24.6 K, respectively. The AF of 22'SBF-NN is opposite to that predicted by the spin density alternation rule based on Hund's rule. Diradical intramolecular conjugation coupling bridged by spiro-carbon conjugation is discussed, in which the 22'SBF-NN is smaller than that of 27SBF-NN, corresponding to the room-temperature EPR characterization. This spiro conjugation is weaker than the traditional planar conjugation and generally leads to a weaker spin-spin coupling in the helical biradical molecule. The EPR spectrum of the 44'SBF-NN diradical shows a deformed nine-line curve, indicating intramolecular exchange coupling. The density functional theory calculation gives a very weak coupling constant of 2Jcalc/kB = 0.06 K, with ferromagnetic (FM) interaction as the proof, which is consistent with the spin-polarized prediction. Further analysis of magnetic susceptibility χm and VT-EPR data shows that there is indeed an extremely weak FM interaction in the 44' position diradical. We find the bridge, which is a 44' substituted SBF structure, blocks the conjugation and contains a larger twist in steric hindrance, which also hampers sufficient spin density delocalization, resulting in a much weaker spin coupling interaction. Combined with the analysis of molecular orbital calculation results, the anomalous intramolecular AF coupling mechanism of 22'SBF-NN is further explained.

Origin of Ferromagnetic Exchange Coupling in Donor–Acceptor Biradical Analogues of Charge-Separated Excited States

A new donor-acceptor biradical complex, TpCum,MeZn(SQ-VD) (TpCum,MeZn+ = zinc(II) hydro-tris(3-cumenyl-5-methylpyrazolyl)borate complex cation; SQ = orthosemiquinone; VD = oxoverdazyl), which is a ground-state analogue of a charge-separated excited state, has been synthesized and structurally characterized. The magnetic exchange interaction between the S = 1/2 SQ and the S = 1/2 VD within the SQ-VD biradical ligand is observed to be ferromagnetic, with JSQ-VD = +77 cm-1 (H = -2JSQ-VDŜSQ·ŜVD) determined from an analysis of the variable-temperature magnetic susceptibility data. The pairwise biradical exchange interaction in TpCum,MeZn(SQ-VD) can be compared with that of the related donor-acceptor biradical complex TpCum,MeZn(SQ-NN) (NN = nitronyl nitroxide, S = 1/2), where JSQ-NN ≅ +550 cm-1. This represents a dramatic reduction in the biradical exchange by a factor of ∼7, despite the isolobal nature of the VD and NN acceptor radical SOMOs. Computations assessing the magnitude of the exchange were performed using a broken-symmetry density functional theory (DFT) approach. These computations are in good agreement with those computed at the CASSCF NEVPT2 level, which also reveals an S = 1 triplet ground state as observed in the magnetic susceptibility measurements. A combination of electronic absorption spectroscopy and CASSCF computations has been used to elucidate the electronic origin of the large difference in the magnitude of the biradical exchange coupling between TpCum,MeZn(SQ-VD) and TpCum,MeZn(SQ-NN). A Valence Bond Configuration Interaction (VBCI) model was previously employed to highlight the importance of mixing an SQSOMO → NNLUMO charge transfer configuration into the electronic ground state to facilitate the stabilization of the high-spin triplet (S = 1) ground state in TpCum,MeZn(SQ-NN). Here, CASSCF computations confirm the importance of mixing the pendant radical (e.g., VD, NN) LUMO (VDLUMO and NNLUMO) with the SOMO of the SQ radical (SQSOMO) for stabilizing the triplet, in addition to spin polarization and charge transfer contributions to the exchange. An important electronic structure difference between TpCum,MeZn(SQ-VD) and TpCum,MeZn(SQ-NN), which leads to their different exchange couplings, is the reduced admixture of excited states that promote ferromagnetic exchange into the TpCum,MeZn(SQ-VD) ground state, and the intrinsically weaker mixing between the VDLUMO and the SQSOMO compared to that observed for TpCum,MeZn(SQ-NN), where this orbital mixing is significant. The results of this comparative study contribute to a greater understanding of biradical exchange interactions, which are important to our understanding of excited-state singlet-triplet energy gaps, electron delocalization, and the generation of electron spin polarization in both the ground and excited states of (bpy)Pt(CAT-radical) complexes.

A Comparative Structural Study of Southern Region Shallow Basement of the North-Kivu Province (DR Congo) by Gravity and Magnetic Data Analysis

A Comparative Structural Study of Southern Region Shallow Basement of the North-Kivu Province (DR Congo) by Gravity and Magnetic Data Analysis

Geology and Geophysics of Talumopatu Geothermal Manifestation Area of Mootilango District, Gorontalo Regency, Indonesia

The research aims to assess the geothermal potential and provide a better understanding of the geology and geophysics of the area. The study utilizes various methods, including geological mapping, geochemical analysis, and magnetic and electromagnetic data analysis, to gain insights into the subsurface structures and characteristics of the geothermal system. The study area can be divided into three geomorphological units: Alluvial Plain Unit, Near Plains Unit, and Isolated Hill Unit. The study area exhibits a stratigraphy consisting of three primary units: Talumopatu granite units, Talumopatu sandstone units, and alluvial deposit units. The subsurface lithologies of the Talumopatu manifestation area were analyzed using the Wenner – Alpha configuration ERT method, revealing two distinct lithologies. The first lithology consists of sandstones with a resistivity value ranging from 4.2 to 39.0 Ωm and a thickness of 1.25 to 12.4 m, which act as a permeable layer capable of transmitting water. The second lithology is granite with a resistivity value ranging from 118 to 360 Ωm and a thickness of 3.75 to 15.9 m. This information provides valuable insights into the subsurface characteristics of the area, including the presence of permeable layers and the geological composition of the lithologies

Central Mechanism of Acupuncture Treatment in Patients with Migraine: Study Protocol for Randomized Controlled Neuroimaging Trial

Acupuncture has been recognized as an effective and safe alternative therapy for migraine, but its central mechanism has not yet been adequately explained. Meanwhile, research into the clinical efficacy and central mechanism of true acupuncture (TA) and sham acupuncture (SA) is lacking. It is necessary to investigate whether TA has better efficacy than SA, and how they achieve different effects. This study aims to evaluate the efficacy of TA and SA, observe the brain response caused by TA and SA, and further investigate the central nervous mechanism of TA and SA treatment for patients with migraine. This is a randomized controlled neuroimaging trial combining acupuncture treatment with functional magnetic resonance imaging, with patients and outcome assessors blinded. A total of 60 patients with migraine will be randomly allocated to receive 12 sessions of either TA or SA treatments (three sessions per week for 4 weeks), and 30 healthy participants will be recruited as the healthy control (HC) group. Outcome assessment and neuroimaging will be conducted before and after the entire intervention. A headache diary and questionnaires of life quality and psychological properties will be used to evaluate clinical efficacy. Multimodal magnetic resonance imagining data analysis will be used to investigate the central mechanism of TA or SA in treating migraine. Pearson's correlation analysis will be used to reveal the relationship between the brain response and clinical improvements. The results of this study will reveal the brain response to TA and SA in patients with migraine and contribute to further expanding the knowledge of their central mechanism. This trial has been approved by the ethics committee of Dongzhimen Hospital affiliated to Beijing University of Chinese Medicine (DZMEC-KY-2020-38) and registered in the Chinese Clinical Trial Registry (registration number ChiCTR2000033995).

Development of Special Geomagnetic Data Acquisition System with Low Cost

It is known to all that the wide monitoring of geomagnetic anomalies requires geomagnetic detection equipment to be of low cost, low power, and high stability. On the basis of the weak magnetic signal detection technology, a weak magnetic signal acquisition system with low-cost magnetic data acquisition, data processing, and data analysis is established by using a three-dimensional SEN-R65 magnetic sensor, magnetic signal acquisition chip PNI 11096, and P89C668 chips. Firstly, the hardware of a low-cost geomagnetic data acquisition system is designed, and the corresponding data processing and analysis programs are written. Based on the designed hardware circuit and data processing for functions such as acquisition, transmission, storage, and real-time display of geomagnetic signals, it is found that the developed instrument meets the expectations of the low-cost geomagnetic data acquisition system designed in this paper, indicating that the system is applicable.

A Robust Tracking Method for Multiple Moving Targets Based on Equivalent Magnetic Force.

A ferromagnetic vehicle, such as a submarine, magnetized by the Earth's magnetic field produces a magnetic anomaly field, and the tracking of moving targets can be realized through real-time analysis of magnetic data. At present, there are few tracking methods based on magnetic field vectors and their gradient tensor. In this paper, the magnetic field vector and its gradient tensor are used to calculate equivalent magnetic force. It shows the direction of the vector between the detector and the tracking targets for controlling the direction of motion of the detector and achieving the purpose of tracking. Compared with existing positioning methods, the proposed method is relatively less affected by instrument resolution and noise and maintains robustness when the velocity vectors of multiple magnetic targets change randomly.

Advanced Fault Detection of Synchronous Generators Using Stray Magnetic Field

Many methods used for precise fault detection in salient pole synchronous generators (SPSGs) often require <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> knowledge of the healthy case, but this requirement impedes application of the methods since an accurate analysis of different machine quantity waveforms is not usually carried out during commissioning. The inspection and maintenance processes in SPSGs are also costly and time consuming; therefore, reliable methods that can detect and discriminate between different faults without comparison with the healthy condition are highly desirable. This article proposes a precise method for detection and discrimination between different fault types in the SPSG. The method does not require healthy machine data and is applied to diagnose both interturn short circuits (ITSCs) in the field winding and dynamic eccentricities (DEs). The proposed nonintrusive detection algorithm is based on advanced signal analysis of stray magnetic field data and can be applied during SPSG operation. The method is highly precise for monitoring the condition of the rotor field winding and yields a unique pattern for diagnosing possible ITSC faults. Moreover, a distinctive pattern for the DE fault enables the discrimination between both considered failures, even if they are present at the same time. The proposed method is validated through finite-element modeling and experimentally on 100-kVA and 22-MVA SPSGs to demonstrate its applicability in real power plants.

An integrated approach to Q-marker discovery and quality assessment of edible Chrysanthemum flowers based on chromatogram–effect relationship and bioinformatics analyses

Medicinal Juhua (the flower head of five cultivars of Chrysanthemum morifolium Ramat.), Jinsi Huangju (the flower head of another cultivar), and Yajuhua (the flower head of Chrysanthemum indicum L.) are widely consumed as a traditional Chinese medicine and tea. Although they are similar in appearance, difference in the species or cultivation environment result in variations in their chemical constituents, pharmacological effects, and qualities. To assess the quality and authenticity of Chrysanthemum flowers, high-performance liquid chromatography (HPLC) and chemometrics were used to determine differential components. The components were identified by comparison with reference standards or by analysis of mass spectrometry and nuclear magnetic resonance data after HPLC-guided isolation. Then, the antioxidant, hepatoprotective, and angiotensin-converting enzyme (ACE) inhibitory activities of the samples and reference standards were studied, and chromatogram–effect relationship models were established to screen out the constituents significantly contributing to the bioactivities of the flowers. Subsequently, the quality markers (Q-markers) were determined based on their testability, characterization, and effectiveness. Finally, the Q-markers were investigated for potential antihypertension targets and pathways to further confirm their effectiveness using bioinformatics techniques, including network pharmacology and molecular docking . This developed integrated approach is robust and powerful for Q-marker discovery, quality assessment, and authentication of Chrysanthemum flowers and can also be extensively applied for the quality control of other herbal materials. • It was specified that Chrysanthemum flowers differ chemically and bioactively. • Five compounds were identified to be the Q-markers of Chrysanthemum flowers. • The antihypertension targets and pathways of the Q-markers were clarified. • This method can also be applied for quality control of other herbal products.

Morphology and tectonic modification of the Sudbury impact crater: the North Range

The basal contact of the Sudbury Igneous Complex (SIC) on the North Range is interpreted as the outer edge of a meteorite impact crater. Yet, the base of the SIC, and contacts within the SIC, and the overlying Onaping are not circular. Their outline is elliptical. This and other details of the geology of the North Range which have not been fully explained include variations in the width of the metamorphic contact aureole, lateral discontinuous variations in the thickness of the norite and granophyre units, paleomagnetic evidence that the North Range contact of the SIC originally had a dip of around 20°, and differing magnetic fabrics in the norite/gabbro versus the granophyre. Several metrics are used to determine how much of the current outline of the North Range is the result of post-impact deformation and how much is a primary feature related to a meteorite impact. Uplift, rotation, and translation experienced by different segments of the North Range of the SIC are established using dyke azimuth and petrographic analysis of Matachewan diabase dykes, and paleomagnetic and magnetic fabric data analysis. These analyses show (a) the elliptical form of the North Range is a primary feature associated with a near-circular impact crater, (b) some of the original crater wall must have been preserved, and (c) deformation of the North Range is limited to regional scale block rotation producing a southwest dip modified by minor block rotation tilting and vertical displacement associated with north–northwest-trending faults.

Modelling Earth’s lithospheric magnetic field using satellites in low-perigee elliptical orbits

SUMMARYThe sensitivity of magnetic measurements taken by satellites in elliptical orbits to the lithospheric magnetic field is studied by comparing the formal error variances of the lithospheric Gauss coefficients for various satellite orbital constellations. Analytical expressions are presented for the variances of the Gauss coefficients when either all three magnetic vector components or only the radial component are used. We compare the results obtained using a satellite in a near-polar circular orbit at 350 km altitude with those from a satellite in an elliptical orbit with perigee at 140 km (and apogee at 1500 km) and find that the latter leads to Gauss coefficient variances at spherical harmonic degree n = 180 (corresponding to a horizontal wavelength of λ = 220 km) that are 104 times smaller compared to those derived from a similar number of data measured at 350 km altitude. The improvements in variance ratio at degree n = 145 (λ = 275 km) and n = 110 (λ = 360 km) are 103 and 102, respectively. These findings are supported by an analysis of synthetic magnetic data along simulated satellite orbits from which the lithospheric Gauss coefficients are estimated and compared with the original ones used to generate the synthetic data. Coefficients at degree n are successfully determined if the power of the difference between retrieved and original coefficients at that degree is smaller than the power of the lithospheric field (i.e. of the input coefficients). Using 3 yr of simulated data we conclude that magnetic measurements from a satellite in an elliptical orbit with perigee at 140 km allow for a reliable determination of the lithospheric field up to spherical harmonic n ≈ 170 while a satellite in a circular orbit at 350 km height only enables lithospheric field modelling up to n ≈ 100. The analysis demonstrates that low-altitude magnetic data collected by satellites in low-perigee elliptical orbits—although only available for a fraction of each orbit—enable improved global lithospheric field modelling at spatial wavelengths well beyond what is currently possible with data from satellites in circular orbits that do not reach such low altitudes. We applied the approach to the orbital configuration proposed for the Daedalus satellite mission (140 km perigee); the method will however also help in the preparation for other satellite missions in near-polar low-perigee elliptical orbits like the Macau Science Satellite pair MSS-2A and MSS-2B (perigee of 200 km or lower).

An electric circuit model of the Earth’s polar electrojets and field-aligned currents for the estimation of magnetospheric magnetic field from along-track Swarm magnetic data

This study deals with the analysis of Swarm vector magnetic data in order to create a circuit model of electric currents flowing in the Earth’s polar ionosphere and the inner magnetosphere. The model is composed of a system of two-dimensional electric currents representing the magnetic fields of three-dimensional ionospheric polar electrojets (PEJs), the field-aligned currents (FACs), magnetospheric ring currents (MRCs) and magnetospherically induced electric currents inside the Earth (MICs) for each Swarm track. The aim of this paper is to model PEJ and FAC magnetic fields in terms of electric currents on a track-by-track base, subtract those magnetic fields from along-track Swarm magnetic data and estimate the magnetospheric magnetic field (MMF) in discrete time bins. The proposed method is primarily intended to apply to Swarm signals recorded during magnetic storms. The electric circuit model is set up in three steps. After subtracting the main, lithospheric, Sq ionospheric and oceanic tidal magnetic fields from along-track Swarm magnetic signals, the residuals are grouped in 1-h time bins and adjusted by the magnetic field of a two-circular loop model of MRCs and MICs represented by 3times 2 parameters of the electric circular loops in the magnetosphere and the Earth. The adjustment is carried out for the X and Z magnetic field components only because the Y component contains a large signal due to FACs. In the second step, the modelled MRC–MIC magnetic field is removed from the original residuals and the reduced residuals are adjusted by the magnetic field of a system of two-dimensional electric circuits in the polar ionosphere and FACs. The circuit model is set up according to known geometry of PEJs and FACs. In the final step, the modelled magnetic fields of PEJs and FACs are subtracted from the original residuals and all three magnetic field components are adjusted by the MRC–MIC model, named MMC, in a similar way as in the first step. Reliability of the approach is demonstrated by the scatter plots of model MMC showing a significantly better agreement with Swarm magnetic field residuals than the existing MMFs.Graphical