Magnetic Amplitude Research Articles

Bandwidth comparison of rectangular and offset cross‐slot frequency‐selective surface polarisation transformers

This letter compares the 3 dB axial ratio (AR) bandwidth (BW) of transmission mode single-screen linear-to-circular polarisation convertors based on three different slot topologies. Using a conventional centre-connected cross-slot arrangement as a baseline, we show that a significant performance improvement can be achieved by creating a more elaborate design with unit cells composed of multiple unequal length offset rectangular-shaped apertures. The additional flexibility to tailor the shape of the Transverse Electric (TE) and Transverse Magnetic (TM) spectral amplitude and phase responses is exploited to achieve an 84% increase in the BW relative to the baseline for a freestanding structure, which is designed to work at a centre frequency of 10.0 GHz. Experimental AR results are used to verify the new design methodology.

Bessel function descriptions of magneto-chiral interactions (DMI)-magnetic and spin flexoelectric skyrmions

In this work we present an exact Bessel function solution to the variation equations for a ground state of the chiral Hamiltonians in the continuum limit for cylindrical symmetry. The solution imposes no constraints on the magnetic spin moment magnitude. The formulation is consistent with the generalized view of U. K. Roessler et al. Nature 442, 797–801 (2006) that both the magnetic moment amplitude and magnetic stiffness ratio are micromagnetic properties and variations in amplitude may be allowed. With the exact solutions, we reveal that the added stabilization energy of the 2D skyrmion relative to the 1D solution is the result of the cylindrical symmetry rather than specifics of the chiral interactions. The methods can be employed to understand Bloch type magnetic spin textures observed in MnSi and FeGe and Néel type magnetization textures in antiferromagnetic dielectrics and ferrimagnetic thin sheets with the application of an electric field.

Modeling of PWM-Induced Iron Losses With Frequency-Domain Methods and Low-Frequency Parameters

The high-frequency iron losses caused by sinusoidal flux density variations with frequencies ranging from 2.5 to 40 kHz, amplitudes from 1 to 70 mT, and dc-biased magnetic inductions from 0 to 1.62 T are measured with the dual-transformer system. Then, in this article, a simple frequency-domain model is proposed based on the linear fitting and two-dimensional interpolation methods for engineering applications. In addition, another two frequency-domain models, respectively, considering and neglecting the excess losses are investigated and compared for the high-frequency iron-loss modeling, which only need low-frequency parameters and contain the physical interpretation to the variation of high-frequency iron-loss coefficients with the frequency, ac flux density amplitude, and dc-biased magnetic induction. The iron losses generated by the unipolar and bipolar pulsewidth modulation (PWM) voltages with different switching frequencies and modulation factors are measured to testify the three models. It is shown that the three models in this article are more accurate than the previously proposed one for calculating the PWM-induced iron loss by considering the variation of model parameters with the dc-biased magnetic induction and ac flux density amplitude, especially when silicon steel sheets reach the saturation.

Electromagnetic properties of curved HTS trapped field stacks under high-frequency cross fields for high-speed rotating machines

Superconducting electric propulsion systems, characterized by high power densities and efficiencies, provide a possibility to zero carbon emission for future aviation. Stacks of high temperature superconducting (HTS) coated conductors (CCs) have become an alternative for high field magnets applied to superconducting machines, given their excellent field trapping ability and thermal stability. High-frequency ripple fields always exist in high-speed electric machines. Most research work regarding HTS trapped field stacks (TFSs) was focused on their magnetization methods and amplitude of trapped flux density; however, their performance in the high-frequency environment remains unclear. Despite several numerical models established for flat HTS TFSs, a comprehensive analysis of curved ones is still lacking, which possess geometrical applicability for cylindrical rotating shafts. Aimed at exploring the electromagnetic properties of curved HTS TFSs applied to high-speed rotating machines, a 3D numerical model considering both the multilayer structure and the Jc (B) dependence of HTS CCs has been built. Current and magnetic flux density distributions, as well as loss properties of a curved HTS TFS have been studied in detail, under perpendicular and cross fields with varying frequencies ranging from 50 Hz to 20 kHz. Results have shown that, the widely adopted two-dimensional-axisymmetric models are inapplicable to study the electromagnetic distributions of TFSs because of the emergence of the electromagnetic criss-cross defined in this paper. High-frequency ripple fields can drive induced current towards the periphery of the HTS TFS due to the skin effect, leading to a fast rise of AC loss and even an irreversible demagnetization of the stack. This paper has qualified and quantified the high-frequency electromagnetic behaviours of curved HTS TFSs, providing a useful reference for their loss controlling and anti-demagnetization design in high-speed propulsion machines.

Experimental Observation of Magnetic Island Heteroclinic Bifurcation in Tokamaks.

We report empirical observations of magnetic island heteroclinic bifurcation for the first time. This behavior is observed in interacting coupled 2/1 tearing modes in the core of a DIII-D tokamak plasma. Poincaré maps constrained by measured magnetic amplitudes and phasing show bifurcation from heteroclinic to homoclinic topology in the 2/1 island as the 4/2 relative amplitude (R_{4/2}) decreases. Initially, the local electron temperature peak in the 2/1 island splits, consistent with two O points. As R_{4/2} decreases a single peak forms, consistent with one O point. These call for developing tearing stability theory and control solutions for heteroclinic islands in tokamaks.

Structural Complexity and Mineral Potential of Central Benue Trough, Using High Resolution Aeromagnetic Dataset

Mineral mining is an important resource for economic development, and its mineralization is controlled by geology, structures and hydrothermal alteration within rock formations. For this reason, high resolution magnetic dataset covering parts of the Central Benue Trough was processed and filtered/enhanced using analytic signal, first vertical derivative and tilt derivative algorithms. Qualitative interpretation of the total magnetic intensity maps reveals numerous magnetic depletion zones defined as hydrothermal active areas within Dampar, Wuro Jam, Kishr, Yamere, Shnye, Jibu, Adi, Amafan, Akwana, Akahana, Ayere, Awe and Tunga. There is a major NE-SW trending low magnetic amplitude stretching from Ugba to Kwarata, which is interpreted as active zones at the contact between the Central Benue Trough and Eastern Nigerian Basement Complex, the zone is interpreted as a major area of interest, especially around intense structurally active areas at Wukari, Chonku, Ngbebe, Bayawai, Gidan Idi, Wamgbe, Gusawa, Anzwa and Gada Mayo. Derivative filters revealed majorly NE-SW trending structures within the Central Benue Trough, with minor NW-SE trends observed at the contact between the Central Benue Trough and Eastern Nigerian Basement Complex with the longest fault having a length of about 42 km, stretching from Sankara to Apar, Hundu area. Major folds are mapped at Dampar, Wuro Jam and Kishr area. Long stretched fault systems within the Central Benue trough is observed at Bangalala, Gwinwan, Amar, Yamere and Rufai, Uzam, Sojo area. The dominating series of high angle NE-SW trending faults and folds structure was defined to have resulted from two major regional series of deformation stages. Integration of geological information and geophysical interpretation defined Wukari, Chonku, Bayawai, Wamgbe, Gusawa, Anzwa, Dampar, Yamere, Akwana, Akahana, Bangalala, Gwinwan,and Tunga as area of highest potential of mineral deposits occurrences based on the geology, extensive alteration and structural complexity.

Investigating the Origin of the First Ionization Potential Effect With a Shell Turbulence Model

The enrichment of coronal loops and the slow solar wind with elements that have low First Ionization Potential, known as the FIP effect, has often been interpreted as the tracer of a common origin. A current explanation for this FIP fractionation rests on the influence of ponderomotive forces and turbulent mixing acting at the top of the chromosphere. The implied wave transport and turbulence mechanisms are also key to wave-driven coronal heating and solar wind acceleration models. This work makes use of a shell turbulence model run on open and closed magnetic field lines of the solar corona to investigate with a unified approach the influence of magnetic topology, turbulence amplitude and dissipation on the FIP fractionation. We try in particular to assess whether there is a clear distinction between the FIP effect on closed and open field regions.

Microtearing instabilities and electron thermal transport in low and high collisionality NSTX discharges

Microtearing mode (MTM) real frequency, growth rate, magnetic fluctuation amplitude, and resulting electron thermal transport are studied in systematic NSTX scans of relevant plasma parameters. The dependency of the MTM real frequency and growth rate on plasma parameters, suitable for low and high collision NSTX discharges, is obtained by using the reduced MTM transport model [T. Rafiq et al., Phys. Plasmas 23, 062507 (2016)]. The plasma parameter dependencies are compared and found to be consistent with the results obtained from MTM using the gyrokinetic GYRO code. The scaling trend of collision frequency and plasma beta is found to be consistent with the global energy confinement trend observed in the NSTX experiment. The strength of the magnetic fluctuation is found to be consistent with the gyrokinetic estimate. In earlier studies, it was found that the version of the multi-mode (MM) anomalous transport model, which did not contain the effect of MTMs, provided an appropriate description of the electron temperature profiles in standard tokamak discharges and not in spherical tokamaks. When the MM model, which involves transport associated with MTMs, is incorporated in the TRANSP code and is used in the study of electron thermal transport in NSTX discharges, it is observed that the agreement with the experimental electron temperature profile is substantially improved.

Pedestal magnetic turbulence measurements in ELMy H-mode DIII-D plasmas by Faraday-effect polarimetry

Internal magnetic fluctuation measurements are utilized to identify turbulence associated with micro-tearing modes (MTM) in the DIII-D Edge-Localized-Mode (ELM)-y H-mode pedestal. Using a Faraday-effect polarimeter, magnetic turbulence (150–500 kHz) is directly observed with a typical line-averaged fluctuation amplitude of ∼0.8 G at peak frequency (250 kHz) and ∼15 G integrated over the spectrum from 150 to 500 kHz. Frequency, poloidal wavenumber, and propagation direction of the magnetic turbulence all serve to identify as MTM. Magnetic turbulence amplitude non-monotonically correlates with collision frequency, peaks off mid-plane, and correlates with electron temperature gradient evolution between ELMs, consistent with MTM features identified from theory and gyro-kinetic simulation. The magnetic turbulence growth correlates with confinement degradation in ELMy H-mode plasmas during a slow density ramp. These internal measurements provide unique constraints toward developing physics understanding and validating models of the H-mode pedestal for future devices.

Study on the changes of spontaneous brain activity in maintenance hemodialysis patients with end-stage renal disease based on three different resting state-functional magnetic resonance low-frequency amplitude algorithms

Objective: To investigate the changes of spontaneous brain activity in patients with end-stage renal disease (ESRD) by combining three different resting state functional magnetic resonance low frequency amplitude algorithms, including amplitude of low-frequency fluctuations (ALFF), fractional amplitude of low-frequency fluctuations (fALFF), and percent amplitude of fluctuation (PerAF), and to analyze the associations between spontaneous brain activity changes and clinical variables. Methods: The data of 31 ESRD patients treated with maintenance hemodialysis and 37 healthy volunteers in the Department of Nephrology and Renal Transplantation of the Affiliated Hospital of Qingdao University from August 2018 to December 2019 were retrospectively collected. The resting state functional magnetic resonance imaging (rs-fMRI) scan was performed to calculate the ALFF, fALFF, and PerAF values of the whole brain of the subjects in each group. Independent sample t test was used for comparison between groups, and Pearson correlation analysis was used to investigate the correlation between spontaneous brain activity changes in brain regions with significant differences and clinical variables. Results: Compared to healthy volunteers, patients with ESRD had decreased mean ALFF(mALFF) values of the right lingual gyrus, bilateral anterior precuneus, left inferior frontal gyrus, and right middle cingulate gyrus (FDR (false discovery rate) correction, all P<0.01); and decreased mean PerAF (mPerAF) values of the bilateral anterior precuneus, bilateral posterior cingulate cortex, right calcarine fissure and surrounding cortex, bilateral inferior parietal lobule/temporoparietal junction (including bilateral angular gyrus, middle temporal gyrus, left supramarginal gyrus), and bilateral inferior frontal gyrus (FDR (false discovery rate) correction, all P<0.01); but there was no significant difference in mean fALFF (mfALFF) value between the two groups. Correlation analysis showed that the mPerAF values of the right angular gyrus (r=-0.509, P=0.003) and the left supramarginal gyrus (r=-0.405, P=0.024) were negatively correlated with serum potassium concentration in ESRD patients, while mALFF values of the bilateral anterior precuneus (r=0.058, P=0.004) and mPerAF values of the left gyrus (r=0.415, P=0.020) were positively correlated with hemoglobin level. Conclusions: In ESRD patients, spontaneous brain activity was reduced in multiple brain regions, mainly located in default mode network(DMN), which might be the underlying pathophysiological mechanisms of their brain damage. Controlling serum potassium and hemoglobin levels was essential to prevent the progression of brain damage in ESRD patients.

Single-Pulse Transcranial Magnetic Stimulation-Evoked Potential Amplitudes and Latencies in the Motor and Dorsolateral Prefrontal Cortex among Young, Older Healthy Participants, and Schizophrenia Patients.

Background: The combination of transcranial magnetic stimulation (TMS) with electroencephalography (EEG) allows for non-invasive investigation of cortical response and connectivity in human cortex. This study aimed to examine the amplitudes and latencies of each TMS-evoked potential (TEP) component induced by single-pulse TMS (spTMS) to the left motor (M1) and dorsolateral prefrontal cortex (DLPFC) among healthy young participants (YNG), older participants (OLD), and patients with schizophrenia (SCZ). Methods: We compared the spatiotemporal characteristics of TEPs induced by spTMS among the groups. Results: Compared to YNG, M1-spTMS induced lower amplitudes of N45 and P180 in OLD and a lower amplitude of P180 in SCZ, whereas the DLPFC-spTMS induced a lower N45 in OLD. Further, OLD demonstrated latency delays in P60 after M1-spTMS and in N45-P60 over the right central region after left DLPFC-spTMS, whereas SCZ demonstrated latency delays in N45-P60 over the midline and right central regions after DLPFC-spTMS. Conclusions: These findings suggest that inhibitory and excitatory mechanisms mediating TEPs may be altered in OLD and SCZ. The amplitude and latency changes of TEPs with spTMS may reflect underlying neurophysiological changes in OLD and SCZ, respectively. The spTMS administered to M1 and the DLPFC can probe cortical functions by examining TEPs. Thus, TMS-EEG can be used to study changes in cortical connectivity and signal propagation from healthy to pathological brains.

Comparison of low-frequency non-sinusoidal measurement for transformer no-load characteristics based on different interpolation methods

As the calculation of transformer no-load characteristics measured by low-frequency test method is not perfect, different interpolation methods are explored to fit and convert the transformer's volt-ampere characteristics under power frequency (50 Hz) excitation to find the best interpolation fitting conversion method. The no-load test of transformer is carried out by using 10 Hz, 15 Hz, 20 Hz low-frequency square wave and triangular wave excitation. Then the measured excitation voltage, excitation current and no-load loss are converted to those of 50 Hz sine wave excitation. The converted volt-ampere characteristic curve is calculated by the proposed algorithm, and compared with the measured results under the 50 Hz sine wave excitation. Experiments show that under the condition that the magnetic flux amplitudes are equal at each frequency of non-sinusoidal and sine waves, whether it is square wave or triangular wave excitation, the volt-ampere characteristic curve converted to the 50 Hz sine wave excitation by the proposed method can better approximate the curve of the measured 50 Hz sine wave excitation. The average values of the relative errors of the converted excitation current of the three frequencies are within 4%, and those of the converted excitation voltage of the square wave are within 1.1%, and those of the converted excitation voltage of the triangular wave are within 0.47%. Compared with the generalized Steinmetz equation method and the multi-frequency method, the proposed method has a better conversion effect and can almost replace the no-load test results of the 50 Hz sine wave, which has practical value in engineering.

Detecting prolonged activity minima in binary stars

Context. It is well known that from 1645 to 1715 solar activity was notably low and the number of sunspots was extremely reduced. This epoch is known as the Maunder minimum (MM). The study of stars in prolonged activity minima such as the MM could help to shed light on this enigmatic epoch. However, to date, it is not easy to identify MM candidates among other stars. An original idea, which has hardly been explored, is to compare the activity levels of both components of binary systems. Aims. Our goal is to explore if the star ζ2 Ret, which belongs to a binary system, is in (or going to) a state similar to the MM. We have collected more than 430 spectra acquired between 2000 and 2019 with the HARPS, REOSC, UVES, and FEROS spectrographs. Methods. We performed a detailed long-term activity study of both components using the Mount Wilson index, which is obtained from the Ca II H&amp;K lines. To search for signs of an activity cycle, we analysed the resulting time series with the Generalised Lomb-Scargle and CLEAN periodograms. Results. Our spectroscopic analysis shows a high activity level for ζ1 Ret and a significant decrease in the magnetic activity cycle amplitude of ζ2 Ret. Thus, the activity difference between both components has slightly increased (Δlog RHK′ ~ 0.24 dex), when compared to the previously reported value. The long series analysed here allowed us to re-calculate and constrain the period of ζ2 Ret to ∼7.9 yr. We also detected a long-term activity cycle of ∼4.2 yr in ζ1 Ret, which has not been reported in the literature yet. Conclusions. By analogy with the scenario that proposes a weak solar cycle during the MM, we suggest that activity signatures by ζ2 Ret, that is to say a very low activity level when compared to its stellar companion, a notably decreasing amplitude (∼47%), and a cyclic behaviour, are possible evidence that this star could be in an MM state. To our knowledge, it is the first MM candidate star to have been detected through a highly discrepant activity behaviour in a binary system. Finally, we suggest that continuous observations of ζ2 could help to better understand unusual periods such as the MM.

Нелинейное возбуждение гиперзвуковых колебаний в ферритовой пластине в условиях комбинированного воздействия на двух частотах. Часть 3. Вариация толщины пластины

The task about nonlinear excitation of hypersound vibrations in ferrite plate in conditions of combine influence in two frequencies is investigated. As a most important parameter which is varied it is proposed the relative thickness of plate which is determined as relation of real thickness to the thickness which correspond to elastic resonance on the difference of excitation frequencies. It is established the necessity of choosing of character value of constant field which is determined by enough effective excitation of elastic vibrations. The system of nonlinear equations of motion of magnetization and elastic displacement is described. For solving of this system, the numerical Rounge-Cutta method is applied. The results of this calculation are the time-evolvent of vibrations, dependencies magnetic end elastic vibrations amplitudes and the spectra of vibrations in permanent conditions after end of relaxation processes. It is found the multi-regime character of elastic vibrations which takes place by variation of plate thickness. In the character of development of elastic vibrations in time by the increasing of plate thickness it is found four regimes: regime №1 – regular beatings, regime №2 – established resonance, regime №3 – displacement of center of established vibrations, regime №4 – gigantic oscillations. The intervals of thickness values which are necessary, or realization of these regimes are determined. The properties of each regimes taken separately are investigated. It is found that the regime №1 is realized when the thickness of plate is more less then the thickness of resonance on differential frequency. In this case the elastic vibrations in generally repeats the vibrations of magnetization which are realized as beating between two frequencies of excitation. The regime №2 takes place when the plate thickness is near to resonance on differential frequency. When thickness is corresponds to resonance on differential frequency it is found large raising of resonance character. In the vibrations of elastic displacement, the constant component is discovered. The regime №3 takes place when the plate thickness is exceeded of resonance on several (from two to seven) times. The vibrations of magnetization in this regime are the same as in regimes №1 and №2. The elastic displacement has two components: oscillatory on differential frequency and constant which value by increasing of thickness smoothly is increased. The displacement of center of oscillatory component by thickness is increased has quadratic character. The regime №4 takes place by plate thickness exceeds resonance thickness on the order and more. The vibrations of magnetization maintain the character of beating which are the same as in regimes №1, №2 and №3. The vibrations of elastic displacement are characterized by extremely large amplitude which is more then the amplitude in regime №3 on order and more and has extremely large period which is more then period of differential frequency vibrations on two-three order and more. The amplitude of vibrations and its period by the thickness is increases also increase by linear meaning. The some quality opinions about the nature of observed phenomena are proposed. It is established the specific character of two-frequency excitation in comparison to single-frequency excitation. As the possible task it is proposed the plan of singing the part of solution as dependence of vibration amplitude from plate thickness has quadratic character with necessary appreciation of two-frequency excitation. The mechanical analogy for vibrations of hard rod which is compressed on both ends by approaching forces is proposed. This analogy allows to interpret the displacement of vibrations center and gigantic oscillations regime.

Dynamics of a magnetic pendulum in the presence of an oscillating conducting plate

AbstractA pendulum with an attached permanent magnet moving near a conductor is a typical experiment for the demonstration of electromagnetic braking. When the conductor itself moves, it can transfer energy to the pendulum. We study a simple but exact analytical model where the conductor is a horizontally unbounded flat plate. For this geometry, eddy currents and induced Lorentz force due to the motion of a magnetic dipole are known analytically in the quasistatic limit. A vertical oscillation of such a horizontal plate located beneath the magnet is considered. In this setup, the vertical position of the pendulum is an equilibrium point when the magnetic moment of the magnet is perpendicular to its plane of motion. Depending on the strength of the magnetic dipole moment, the frequency and amplitude of the plate as well as the distance between plate and magnet, the plate oscillation can destabilize the equilibrium. The stability limits for weak electromagnetic coupling are computed analytically using the harmonic balancing method. For stronger coupling, the stability limits are obtained numerically using Floquet analysis. Chaotic motions with finite amplitudes are also found.

Нелинейное возбуждение гиперзвуковых колебаний в ферритовой пластине в условиях комбинированного воздействия на двух частотах. Часть 2. Вариация постоянного поля

Нелинейное возбуждение гиперзвуковых колебаний в ферритовой пластине в условиях комбинированного воздействия на двух частотах. Часть 2. Вариация постоянного поля

Magnetic amplitude inversion for depth-to-basement and apparent magnetization-intensity estimates

We have developed an inversion method to recover the depth and the total magnetization intensity of the basement under a sedimentary basin using the amplitude of the magnetic anomaly vector (amplitude data). Because the amplitude data are weakly dependent on the magnetization direction, our method is suitable for interpreting areas with remanent magnetization. Our method assumes constant magnetized basement rocks overlain by nonmagnetic sediments. To overcome the inherent ambiguity of potential field data, we assume knowledge of the average depth of the basement and use it as a constraint to regularize the inversion. A sensitivity analysis with synthetic data shows the weak dependency of the magnetic amplitude inversion on the magnetization direction. Different combinations of magnetization directions recover the interface separating sediments from basement rocks. Test on field data over the Foz do Amazonas Basin, Brazil, recovers the shape of the basement relief without any knowledge about the magnetization intensity and direction. The estimated basement relief reveals a smooth basement framework with basement highs in the central part of the area. In a regional-scale perspective, the deeper and constant estimated basement relief at the northernmost limit of the area may suggest changing in crustal domains from a hyperextended continental crust to homogeneous oceanic crust.

ГЕОМАГНІТНИЙ ЕФЕКТ ТУРЕЦЬКОГО ЗЕМЛЕТРУСУ 24 СІЧНЯ 2020 р.

Purpose:The main cause of geomagnetic disturbances are cosmic sources, processes acting in the solar wind and in the interplanetary medium, as well as large celestial bodies entering the terrestrial atmosphere. Earthquakes (EQs) also act to produce geomagnetic effects. In accordance with the systems paradigm, the Earth–atmosphere–ionosphere–magnetosphere system (EAIMS) constitute a unified system, where positive and negative couplings among the subsystems, as well as feedbacks and precondition among the system components take place. The mechanisms for the action of EQs and processes acting in the lithosphere on the geomagnetic field are poorly understood. It is considered that the EQ action is caused by cracking of rocks, fluctuating motion in the pore fluid, static electricity discharges, etc. In the course of EQs, the seismic, acoustic, atmospheric gravity waves (AGWs), and magnetohydrodynamic (MHD) waves are generated. The purpose of this paper is to describe the magnetic effects of the EQ, which took place in Turkey on 24 January 2020. Design/methodology/approach: The measurements are taken with the fluxmeter magnetometer delivering 0.5-500 pT sensitivity in the 1-1000 s period range, respectively, and in a wide enough studied frequency band within 0.001 to 1 Hz. The EM-II magnetometer with the embedded microcontroller digitizes the magnetometer signals and performs preliminary filtering over 0.5 s time intervals, while the external flash memory is used to store the filtered out magnetometer signals and the times of their acquisition. To investigate quasi-periodic processes in detail, the temporal variations in the level of the H and D components of the geomagnetic field were applied to the systems spectral analysis, which makes use of the short-time Fourier transform, the wavelet transform using the Morlet wavelet as a basis function, and the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods. Findings: The train of oscillations in the level of the D component observed 25.5 h before the EQ on 23 January 2020 is supposed to be associated with the magnetic precursor. The bidirectional pulse in the H component observed on 24 January 2020 could be due to the piston action of the EQ, which had generated an MHD pulse. The quasi-periodic variations in the level of the H and D components of the geomagnetic field, which followed 75 min after the EQ, were caused by a magnetic disturbance produced by the traveling ionospheric disturbances due to the AGWs launched by the EQ. The magnetic effect amplitude was estimated to be close to 0.3 nT, and the quasi-period to be 700-900 s. The amplitude of the disturbances in the electron density in the AGW field was estimated to be about 8 % and the period of 700-900 s. Damping oscillations in both components of the magnetic field were detected to occur with a period of approximately 120 s. This effect is supposed to be due to the shock wave generated in the atmosphere in the course of the EQ. Conclusions: The magnetic variations associated with the EQ and occurring before and during the EQ have been studied in the 1-1000 s period range. Key words: earthquake, fluxmeter magnetometer, quasi-periodic disturbance, seismic wave, acoustic-gravity wave, MHD pulse

Updated map of the mafic dike swarms of Brazil based on airborne geophysical data

Identification of mafic dike swarms and LIPs (Large Igneous Provinces) are of vital importance in geologic history because they provide information on geodynamics, mantle geochemistry, and paleomagnetism. These data provide key information for paleogeographic reconstructions with the aid of barcode matches and precise radiometric ages. Considering such issues, the Brazilian Precambrian shield can be used as a case for refining the cartography of the relevant intraplate activity (e.g., dikes, sills, flood basalts) in space and time.This work presents an updated map of Brazilian mafic dike swarms produced from airborne geophysical maps (Series 1000 – Geological Survey of Brazil). Linear and strong anomalies found on aeromagnetic maps using First Vertical Derivative of the Magnetic Field and Amplitude of the Analytic Signal were mapped on a GIS platform. The obtained data were compared to ternary radiometric maps and geological maps in order to exclude those that do not correspond to mafic dikes. The remaining structures - those believed to represent mafic dikes - were classified based on data compiled from the literature.The updated map exhibits more than 5000 elements, including dikes and magmatic suites, in which about 75% were geologically identified and divided into 60 dike swarms and 10 igneous suites and/or units. The dikes were grouped into sixteen extensional episodes from the Archean to the Cenozoic, although some are related to extension/transtension domains within regional compressive zones akin to orogenic settings. The most frequent records refer to the Proterozoic, representing intraplate episodes, some of them consistent with LIPs. The dataset also includes a large record of the Mesozoic age, which corresponds to major LIP events related to the opening of the Atlantic Ocean and the fragmentation of Gondwana.

Abstract 14497: Mri Effects on Pacemaker/ICD Within the Magnetic Field; An Intra-observer Variability Study

Introduction: The evolution of pacemaker/ICD safety in the magnetic field has triggered considerable interest in more clinical routine use. However, many limitations to widespread adoption of this seemingly implausible idea just a few years ago remain: unresolved impact of the high magnetic field, RF amplitude and oscillatory forces on electronics with possible high field damage to capacitor, solenoid and microcircuitry. However, given recent vender refinements over the last 10 years, we hypothesized that the impact on such circuitry may be far less than expected. Method: Consecutive interrogation of 940 pts who underwent clinically indicated MRI were evaluated over 5 years. This cohort was comprised of neuro/neurosurgical (72%), orthopedic (11%) and cardiac (17%) cases. Routine interrogation was performed within 10 min of entry into the bore of a dedicated Cardiac MRI (GE, 1.5T, WI). As well, reinterrogation was performed within 10 min of departure MRI (average 21±12min). At the time of interrogation pre and post MRI, a separate, repeat interrogation was performed within 5 min of each other such that 2 sets of PM/ICD parameters were obtained pre and post MRI. Result: No complications to either pt or device occurred during the MRI comprising 564 PMs and 376 ICDs. A cardiologist was present guiding the interrogation, configuration, and reconfiguration of the PM/ICD as well was present for entire MRI. There were no significant differences in common clinical parameters. More importantly, there was no difference in any parameter when compared in any order pre to post MRI scan. See Table. Conclusion: Intrinsic variability and inherent changes triggered by MRI environments are clinically insignificant and statistically negligible thereby removing yet another of the last remaining fears and apprehensions for primary PM/ICD failure and destruction as we move towards a more uniform acceptance of this technology for clinically meaningful use, dissemination and acceptance.