Changes In Field Intensity Research Articles

Parametric analysis of mode coupling and liner energy deposition properties of helicon and Trivelpiece-Gould waves in helicon plasma

Based on the finite temperature plasma dielectric tensor model which contains the particle thermal effect, by numerically solving the eigenmode dispersion relation of electromagnetic waves propagating in radially uniform and magnetized warm plasma column which is surrounded by conducting boundary, the mode coupling characteristic and liner damping mechanism induced wave power deposition properties of helicon and Trivelpiece-Gould (TG) waves are parametrically analyzed. The detailed investigations show as follows. Under typical helicon plasma parameter conditions, i.e. wave frequency <i>ω</i>/(2π) = 13.56 MHz, ion temperature is much smaller than electron temperature, for the helicon wave, there exist a cut-off magnetic field <i>B</i><sub>0,H,cutoff</sub> and a cut-off plasma density <i>n</i><sub>0,H,cutoff</sub>, for which under the conditions of <i>B</i><sub>0</sub> > <i>B</i><sub>0,H,cutoff</sub> or <i>n</i><sub>0</sub> < <i>n</i><sub>0,H,cutoff</sub>, the helicon wave becomes an evanescent wave. When the magnetic field intensity changes from 48.4 to 484 G, i.e., <i>ω</i>/<i>ω</i><sub>ce</sub> ranges from 0.01 to 0.1, for the power deposition intensity, Landau damping of TG wave dominates for the <i>m</i> = 0 mode, meanwhile, for the <i>m</i> = 1 mode, which wave, i.e. helicon wave or TG wave, plays a major role in power deposition mainly depends on the magnitude of the magnetic field. On the other hand, for a given magnetic field <i>B</i><sub>0</sub> = 100 G, when <i>ω</i><sub>pe</sub>/<i>ω</i><sub>ce</sub> changes from 3 to 100, for both the <i>m</i> = 0 mode and the <i>m</i> = 1 mode, the power deposition induced by Landau damping of TG wave plays a major role, further, one may notice that the power deposition of TG wave decreases while the power deposition of the helicon wave increases as plasma density increases. Finally, for both the <i>m</i> = 0 mode and the <i>m</i> = 1 mode, the power deposition due to the Landau damping plays a dominant role. All these conclusions provide us with some useful clues to better understanding the high ionization mechanism of helicon wave discharges.

The geomagnetic field's imprint on the twentieth century's climate variability

Abstract The existing controversy regarding the climatic response to given changes in the geomagnetic field intensity (e.g. climate cooling or warming in periods of geomagnetic field strengthening) raises scepticism about the existence of any relationship between both variables. The main shortcomings of the recent understanding of the geomagnetic field–climate relationship are the expectations for: (i) its universal character over the globe; and (ii) the zonal homogeneity of this relationship. This paper offers a new conceptual framework aimed at resolving the existing controversy and explaining the mechanism for the appearance of geomagnetic footprints on climatic records. We show that particles trapped in the Earth's radiation belts are subject to geomagnetic lensing in the parts of their trajectories closest to the surface, being focused or defocused at different regions over the world. The irregularly distributed ionization, created in such a way near the tropopause, activates various ion–molecular reactionships which affect the atmospheric composition there. Thus, the regional changes in the ozone and water vapour are furthermore projected onto the surface temperature and pressure. Consequently, the geomagnetic field–climate relationship is not a rigid but, rather, a flexible one because it is mediated by the near-tropopause ionization, ozone and humidity, with each of them being subject to the other's influence.

Study on the ground state properties and excitation properties of C<sub>18</sub> under different external electric fields

In this work, density functional theory method with the ωB97XD/def2-TZVP level is carried out to investigate the ground state structures, energy, electronic structures, aromaticity, infrared and Raman spectra of cyclo[18]carbon under different external electric field in the <i>x</i>, <i>y</i> and <i>z</i> direction of cyclo[18]carbon molecule. The excitation properties (the first 48 excited states containing excited energies, excited wavelengths and oscillator strengths) of cyclo[18]carbon are calculated by the time-dependent density functional theory method (TD-ωB97XD) with the def2-TZVP basis set under the same external electric field. The results show that cyclo[18]carbon can be elongated in the <i>x</i> or <i>y</i> direction under the electric field, and some C-C bond lengths can be elongated or shortened under the electric field. Meanwhile, the calculated results show that electric dipole moment is proved to be increasing with the increase of the external field intensity, but the total energy and LUMO-HOMO gap are proved to decrease with the increase of external field intensity. Moreover, addition of electric field can modify the electron delocalization and molecular aromaticity, such as external electric field in <i>z</i> direction can lower the electron delocalization and molecular aromaticity and external electric field in <i>x</i> or <i>y</i> direction can enhance the electron delocalization and molecular aromaticity. The addition of electric field can modify the infrared spectra, such as shift of vibrational frequencies and strengthening of infrared peaks. Furthermore, the calculated results indicate that the external electric field has significant effects on the excitation properties of cyclo[18]carbon. The increase of the electric field intensity can lead to the redshift of transition wavelengths (such as the first excited state). With the change of the electric field intensity, the stronger excited state (with the bigger oscillator strength) can become weak (with the small oscillator strength) or optically inactive (with the oscillator strength of zero). Meanwhile, the weak or optically inactive excited state can become stronger excited state by the external field. The ground state properties and excitation properties of cyclo[18]carbon can be modified by the external electric field. Our works can provide theoretical guidance for the application of cyclo[18]carbon in the nanotechnology such as molecular device.

Refined 3600 years palaeointensity curve for Mexico

Our knowledge of the Earth's magnetic field intensity changes over the past few thousand years is still limited because of the uneven spatial and temporal distribution of data, which also includes the Americas. The present study reports 41 new palaeointensity data covering the past 3600 years which, together with 38 previously published data of similar quality, are used to construct a palaeointensity secular variation curve for Central Mexico. These new data are an important contribution to the global intensity database and will also improve the application of palaeomagnetic dating in Mexico, which is of interest because of the many Holocene monogenetic volcanoes within the Trans-Mexican Volcanic Belt, and of its archaeological heritage. The most conspicuous feature of the new intensity curve is the rapid increase between 400 and 250 BCE, from about 45 to 65 μT. Other relative intensity highs of ≈45–55 μT were found around 1600 BCE, 370 CE, and 1200 CE and relative intensity lows of ≈30–35 μT around 1350 BCE and 700 CE. Comparing the virtual axial dipole moment of our intensity curve with global VADM-VDM dipole estimates indicates that non-dipole components in Central Mexico have been observed at several times from 1600 BCE to 1000 CE while the dipole field was prevalent from 1000 to 1800 CE. A comparison of our results with selected data from southern USA shows a significant difference between the two regions which indicates an important nondipole feature of the magnetic field during the last few thousands of years, and/or undetected problems in the age/palaeointensity data accuracy.

Effects of the helical magnetic wiggler on a laser beam interacting with a lattice of metallic nanoparticles: plasmonic and body waves

In this study, the influence of a helical magnetic wiggler on the nonlinear interaction of a laser beam with a lattice of metallic nanoparticles is investigated. Coupling of the static magnetic field of the wiggler to the field of the laser wave, and therefore a change in the electric field intensity of the pumped wave, leads to the formation of a nonlinear force in the interaction region. As a consequence, the nonlinear force enhances the plasmonic oscillations of the electronic cloud of each nanoparticle causing electron density modulation, which improves the self-focusing property of the laser beam. Using a perturbative method, the nonlinear dispersion plasmonic and body waves are obtained from the interaction of a laser beam with a lattice of nanoparticles in the presence of a helical magnetic wiggler. We investigate the effects of nanoparticle size, their separations and wiggler field strength on the evolution of the transverse profile of the laser beam in both incident linearly polarized and circularly polarized waves. The numerical results indicate that in the linear polarization for all branches of plasmonic and body waves (except for the low-frequency middle branch), laser bandwidth decreases with increasing nanoparticle separation length, which improves the self-focusing property. Moreover, with enhancement of the normalized wiggler field strength, the laser amplitude transverse profile for all branches of plasmonic and body waves (except for the low-frequency middle branch) decreases, which leads to beam focusing. For left and right circular polarization, it is found that with an increase in the nanoparticle separation length, the laser amplitude transverse profile for all branches of plasmonic and body waves (except for the low-frequency middle branch) increases, which leads to beam defocusing. Furthermore, with enhancement of the normalized wiggler field strength, the laser amplitude transverse profile decreases for body waves and the low-frequency lower branch of plasmonic waves, which gives rise to the beam focusing, whereas it increases for the low-frequency middle and upper branches of plasmonic waves, which leads to the beam defocusing.

Promoting coalescence of droplets in oil subjected to pulsed electric fields: changing and matching optimal electric field intensity and frequency for demulsification

Droplets in oil undergo stretching deformation and vibration under a pulsed electric field. This process is very effective in promoting the coalescence of droplets and separating water from oil. However, the electric field parameters for optimal coalescence vary with the change of the particle size of droplets during coalescence. To respond to the changes in the radii of droplets, the optimal electric field intensity and frequency should be switched and adjusted for efficient demulsification. In this study, the influence of the dynamic change of the electric field intensity and frequency on coalescence of droplets was investigated by experimental methods. The electric field parameters were determined by a mapping method. And the switching time interval of electric field for efficient coalescence was obtained by utilizing a model of coalescence of double droplets. The experimental results show that the coalescence of droplets in a variable pulsed electric field, with changing intensity and frequency (<1000 Hz) in certain switching time, is better than in a constant pulsed electric field. And the efficient demulsification frequency and intensity tend to decrease with increasing droplets size. In addition, the viscosity and relative permittivity of oil have a significant influence on the electric field frequency and intensity for efficient demulsification.

Effects of low electromagnetic waves on thymus size, testis and body weight and therapeutic role of vitamin C in mice

Introduction: Results of several studies on different effects of electromagnetic waves reveal that change of field intensity, even milli tesla has various biological effects, therefore investigation on electromagnetic effects can be done in very wide range. In this research, amount of these effects on biomass, thymus, testis and therapeutic role of vitamin C in improvement of changes caused by electromagnetic field, have been studied. Materials and Methods: In this experimental study, 24 adult male mice (Balb/C) were divided into 3 groups. The control group consist of 8 mice were kept in normal conditions. The group exposure to Electromagnetic field consist of 8 mice, which were exposed to ELF (50Hz, 4Mt) for 15 days (4 hours per day), and the group that exposure to Electromagnetic field supplemented with vitamin C, contains 8 mice that were exposed to ELF (50Hz, 4Mt) for 15 days (4 hours per day) and 0.5 cc vitamin C were injected intraperitoneally 7 times. This injection was done 3 times a week. After 15 days, mice were anesthetized by chloroform, following careful dissection, organs were splitted over then this samples were dissected and measured. Data was analyzed using one way ANOVA test. Results: The results show electromagnetic waves lead a significant reduction in body weight and receive appropriate dose of vitamin C may have therapeutic role which reduce damages caused by 50 Hz/4 mT on Balb/C male adult mice. Conclusion: According to this research exposure to electromagnetic waves reduces thymus and testis weight significantly which may root in reduced cell division and inhibition of apoptosis, so simultaneous deliver if vitamin C didn’t show significant effect on thymus and testis.

A semi-automated method to reveal the evolution of each sunspot group in a solar cycle

Sunspots are the most important indicator of the magnetic activity on the solar surface during a cycle. Every sunspot group is formed and shaped by the magnetic field of the Sun. Hence, the magnetic field intensity shows itself as the size of a sunspot group area on the surface. This shows that getting the development or evolution of sunspot groups over time means getting the change of magnetic field intensity during same interval. Here, to reveal the evolution of sunspot groups in a cycle, a method called Solar Cycle Analyzer Tool (SCAT) is presented. This method was developed as a part of Computer-Aided Measurements for Sunspots (CAMS) because the same subroutines and subprograms were used for calculations (Cakmak 2014). The developed software tracks sunspot groups every day and gives them the same group number. The confirmation is made by the user to prevent counting re-formations as a continuation of an old group in the same active region. With this method, the evolution of every sunspot group can be listed for each cycle year besides other cycle features like the daily and monthly sunspot relative numbers and distribution frequency of the sunspot group types. Since 2015, SCAT is being used to get data for the annual reports of Istanbul University Observatory.

The research of the electric field intensity change in the air gap of the compact electrostatic filter

In the article the parameters of an electrostatic filter were considered, including the level of the electric field intensity and the magnitude of the breakdown voltage. A computer simulation of the electric field between flat parallel electrodes with different potentials was performed. The change pattern of the electric field at the penetration of electrically conductive soot particles is considered. With the help of the “ANSYS” software complex, the pattern of change of the electric field intensity between these electrodes was investigated depending on the concentration of particles between them. A computer model that simulates the creation of a maximal level of electric field intensity in a symmetric electric field with a fixed air gap is proposed. The decrease of the level of the breakdown voltage at these electrodes at the placing between them of elements simulating diesel soot particles with average sizes mentioned in the literature is estimated. According to the simulation results, it was determined that the presence of particles of electrically conductive soot significantly influence on the electric field pattern, due to which a local change in the pattern of the resultant field intensity occurs. With aim of confirming of the obtained data the experimental studies have been carried out for determination of the breakdown voltage between the electrodes which form a symmetric electrostatic field.

Searching for geomagnetic spikes in numerical dynamo simulations

We use numerical dynamo simulations to investigate rapid changes in geomagnetic field intensity. The work is motivated by paleomagnetic observations of ‘geomagnetic spikes’, events where the field intensity rose and then fell by a factor of 2–3 over decadal timescales and a confined spatial region. No comparable events have been found in the historical record and so geomagnetic spikes may contain new and important information regarding the operation of the geodynamo. However, they are also controversial because uncertainties and resolution limitations in the available data hinder efforts to define their spatio-temporal characteristics. This has led to debate over whether such extreme events can originate in Earth's liquid core. Geodynamo simulations produce high spatio-temporal resolution intensity information, but must be interpreted with care since they cannot yet run at the conditions of Earth's liquid core. We employ reversing and non-reversing geodynamo simulations run at different physical conditions and consider various methods of scaling the results to allow comparison with Earth. In each simulation we search for ‘extremal events’, defined as the maximum intensity difference between consecutive time points, at each location on a 2∘ latitude–longitude grid at Earth's surface, thereby making no assumptions regarding the spatio-temporal character of the event. Extremal events display spike-shaped time-series in some simulations, though they can often be asymmetric about the peak intensity. Maximum rates of change reach 0.75 μTyr−1 in several simulations, the lower end of estimates for spikes, suggesting that such events can originate from the core. The fastest changes generally occur at latitudes >50∘, which could be used to guide future data acquisitions. Extremal events in the simulations arise from rapid intensification of flux patches as they migrate across the core surface, rather than emergence of flux from within the core. The prospect of observing more spikes in the paleomagnetic record appears contingent on finding samples at the right location and time to sample this particular phase of flux patch evolution.

Slow magnetoacoustic gravity waves in an equilibrium stratified solar atmosphere: cut-off periods through the transition region

Assuming the thin flux tube approximation, we introduce an analytical model that contemplates the presence of a non-isothermal temperature, a varying magnetic field, and a non-uniform stratified medium in hydrostatic equilibrium due to a constant gravity acceleration. This allows the study of slow magnetoacoustic cut-off periods across the solar transition region, from the base of the solar chromosphere to the lower corona. The used temperature profile approaches the solar atmospheric model of G18. The periods obtained are consistent with observations. Similar to the acoustic cut-off periods, the resulting magnetoacoustic gravity ones follow the sharp temperature profile, but shifted towards larger heights; in other words, at a given height the magnetoacoustic cut-off period is significantly lower than the corresponding acoustic one. Along a given longitude of an inclined thin magnetic tube, the greater its inclination the softer the temperature gradient it crosses. Changes in the magnetic field intensity do not significantly modify the periods at the coronal level but modulate the values below the transition region within periods between |${\sim } [2 - 6]\,$|min. Within the limitations of our model, we show that monochromatic oscillations of the solar atmosphere are the atmospheric response at its natural frequency to random or impulsive perturbations, and not a consequence of the forcing from the photosphere.

Spatial variations of the Sr I 4607 Å scattering polarization peak

Context. The scattering polarization signal observed in the photospheric Sr I 4607 Å line is expected to vary at granular spatial scales. This variation can be due to changes in the magnetic field intensity and orientation (Hanle effect), but also to spatial and temporal variations in the plasma properties. Measuring the spatial variation of such polarization signal would allow us to study the properties of the magnetic fields at subgranular scales, but observations are challenging since both high spatial resolution and high spectropolarimetric sensitivity are required. Aims. We aim to provide observational evidence of the polarization peak spatial variations, and to analyze the correlation they might have with granulation. Methods. Observations conjugating high spatial resolution and high spectropolarimetric precision were performed with the Zurich IMaging POLarimeter, ZIMPOL, at the GREGOR solar telescope, taking advantage of the adaptive optics system and the newly installed image derotator. Results. Spatial variations of the scattering polarization in the Sr I 4607 Å line are clearly observed. The spatial scale of these variations is comparable with the granular size. Small correlations between the polarization signal amplitude and the continuum intensity indicate that the polarization is higher at the center of granules than in the intergranular lanes.

Evaluation of a Portable Doppler Ultrasound Gating Device for Fetal Cardiac MR Imaging: Initial Results at 1.5T and 3T.

Purpose:Fetal cardiac MRI has the potential to play an important role in the assessment of fetal cardiac pathologies, but it is up to now not feasible due to a missing gating method. The purpose of this work was the evaluation of Doppler ultrasound (DUS) for external fetal cardiac gating with regard to compatibility, functionality, and reliability. Preliminary results were assessed performing fetal cardiac MRI.Methods:An MRI conditional DUS device was developed to obtain a gating signal from the fetal heart. The MRI compatibility was evaluated at 1.5T and 3T using B1 field maps and gradient echo images. The quality and sensitivity of the DUS device to detect the fetal heart motion for cardiac gating were evaluated outside the MRI room in 15 fetuses. A dynamic fetal cardiac phantom was employed to evaluate distortions of the DUS device and gating signal due to electromagnetic interferences at 1.5T and 3T. In the first in vivo experience, dynamic fetal cardiac images were acquired in four-chamber view at 1.5T and 3T in two fetuses.Results:The maximum change in the B1 field and signal intensity with and without the DUS device was <6.5% for 1.5T and 3T. The sensitivity of the DUS device to detect the fetal heartbeat was 99.1%. Validation of the DUS device using the fetal cardiac phantom revealed no electromagnetic interferences at 1.5T or 3T and a high correlation to the simulated heart frequencies. Fetal cardiac cine images were successfully applied and showed good image quality.Conclusion:An MR conditional DUS gating device was developed and evaluated revealing safety, compatibility, and reliability for different field strengths. In a preliminary experience, the DUS device was successfully applied for in vivo fetal cardiac imaging at 1.5T and 3T.

Study on the Change of Magnetic Field Intensity According to the Activation of Bending Magnet in Medical LINAC

When the high-energy electromagnetic radiation of the medical linear accelerator is irradiated in high capacity, there is a nuclide transformation due to the radio-activation. Especially for the magnet core of the bending magnet, the magnetic field strength is changed due to the nuclide transformation, and this change in the magnetic field strength is shown as the change in flux of the electromagnetic radiation. Therefore, the effect of radio-activation on the change in flux of the electromagnetic radiation according to the electromagnetic radiation dose is to be evaluated. Subjected to 7 medical linear accelerators planned for disposal, the total dosage, nuclide analysis using the spectrometer of the magnet core, flatness using the water phantom & ion chamber, and the change amount of symmetry were evaluated. As a result, the relationship of change rate in flux according to the dosage is shown in 4 % error per 1,000 Gy. As a result of applying the 1 % threshold limit by the American Association of Physicists in Medicine, TG-142 Report, the tolerated dose is 250Gy. Therefore, on the use of medical linear accelerator in the future, it is recommended to perform the flux evaluation according to the magnet core radio-activation for each 250Gy along with the existing periodical quality control.

Study of neuronal spike-frequency adaptation with transcranial magneto-acoustical stimulation

Transcranial magneto-acoustical stimulation (TMAS), utilizing focused ultrasound and a magnetostatic field to generate an electric current in tissue fluid to regulate the activities of neurons, has high spatial resolution and penetration depth. The neuronal spike-frequency adaptation plays an important role in the treatment of neural information. In this paper, we study the effects of ultrasonic intensity, magnetostatic field intensity and ultrasonic frequency on the neuronal spike-frequency adaptation based on the Ermentrout neuron model. The simulation results show that, the peak time interval becomes smaller, the interspike interval becomes shorter and the time of the firing of the neuron is shortened with the increasing of the magnetostatic field intensity. With the increase of the adaptive variables, the initial spike-frequency is shifted to the right with the magnetostatic field intensity, and the spike-frequency is linearly related to the increase of the magnetostatic field intensity in steady state. The simulation effect with change of the ultrasonic intensity is consistent with the change of magnetostatic field intensity. The change of the ultrasonic frequency has no effect on the neuronal spike-frequency adaptation. Under the different adaptive variables, with the increase of the adaptive variables, the initial spike-frequency amplitude decreased with the increasing of the ultrasonic frequency, and the spike-frequency is linearly related to the increase of the ultrasonic frequency in steady state. These results of the study can help us to reveal the mechanism of transcranial magneto-acoustical stimulation on the neuronal spike-frequency adaptation, and provide a theoretical basis for its application in the treatment of neurological disorders.

Wear forms of heterogeneous electro-rheological fluids working in a hydraulic clutch system

The paper presents experimental results concerning the wear of heterogeneous electro-rheological (ER) fluids operating as working fluids in a complex clutch system consisting of a hydrodynamic clutch and a cylinder viscous clutch. The change of electric field intensity in the clutches results in change of sheer stress values in working fluids what causes the change of transmitted torque. This work shows that the most important factors affecting the wear of the ER fluid are the electric field of high intensity, the accompanying electrical breakdown, and the high temperature of the silicone oil. In addition, the water from the humid air absorbed mainly by hygroscopic particles influences a significant impact on the wear of the working fluid. Various forms of wear particles of the fluid depending on the prevailing conditions such as working mode are observed from the microscopic aspects. It is observed that the particles are flattened, rolled out or smashed into smaller fragments, partially melted, wrinkled and glued or caked. In addition, it is identified that the partial destruction of silicone oil is occurred due to the damage of the hydrocarbon chains, as evidenced by the decrease in its viscosity and the presence of the particle matter newly containing silicon.

Near-infrared measurement of water temperature near a 1-mm-diameter magnetic sphere and its heat generation rate under induction heating

This paper presents a method of measuring the temperature of water near a 1-mm-diameter magnetic sphere under induction heating. The method is based on the temperature dependence of the absorption coefficient of water at a wavelength of 1150 nm. In this study, two-dimensional images of the absorbance, which is the transverse projection of the absorption coefficient of water, were acquired by a near-infrared camera through a telecentric lens, and three-dimensional radial profiles of the temperature were then generated by applying inverse Abel transforms (IATs) to the absorbance profiles. To ensure the spherical symmetry of the temperature and the parallelity of the light rays, which are the conditions necessary to apply an IAT, the onset of free convection and the angles of deflection were evaluated. This paper also presents a method of estimating the heat generation rate in a sphere by fitting the numerical solutions of the thermal conduction equation to the measured temperatures. The temperatures and heat generation rates were observed to change consistently with the changes in the magnetic field intensity.

Electrochemical machining of blades with cross-structural cathodes at leading/trailing edges

Blades are key components in modern aero engines. Their leading and trailing edges are extremely difficult to machine using electrochemical machining (ECM) because of their small thickness and radius of curvature and their marginal location. Traditional ECM of blades requires gaps between the convex part cathode and concave part cathode at the leading and trailing edges to allow passage of electrolyte. The presence of these gaps may lead to large variations in electric field intensity at the end of the machining process as the leading and trailing edges are forming. This paper proposes a new design of cross-structural cathodes to decrease the dynamic variation of the electric field at marginal locations. A mathematical model of material removal is established, taking account principally of the electric field factor. The forming process of the leading edge is simulated, and changes in electric field intensity during the final stages of the process are analyzed. The simulation results show that the maximum fluctuation in the electric field intensity at the leading edge is 62.42% when a conventional cathode is used, but only 30.51% with cross-structural cathodes. Experiments are conducted to compare the performance of conventional and cross-structural cathodes. The results show that, in comparison with conventional cathodes, the use of cross-structural cathodes reduces variations in machining current in the forming stage of margin profiles and leads to more accurate repeatability of the process.

Coupled V-structured nano-antenna for electromagnetic field enhancement

Nano-antennas play an important role in many areas of science and technology. It is desirable to achieve strong electric field enhancement by nano-antenna. In this paper, we simulate a symmetrical V-structured nano-antenna that is used to regulate the electromagnetic fields in the central gap region. We study the effects of structural parameters on the charge distribution and analyze the electric field enhancement factor in the central region of the nano-antenna. Then we use structural coupling methods to strengthen electromagnetic field intensity in the central region. Our results demonstrate that the charge distribution of the nano-antenna can be controlled by regulating the structural parameters, leading to the change of electromagnetic field intensity. In addition, electric field enhancement is achieved by coupling of multiple V structures. The multiple V structure could be used in surface-enhanced Raman scattering due to the electric field enhancement in its central region.

Paleomagnetic direction and paleointensity variations during the Matuyama\u2013Brunhes polarity transition from a marine succession in the Chiba composite section of the Boso Peninsula, central Japan

The youngest geomagnetic polarity reversal, the Matuyama–Brunhes (M–B) boundary, provides an important plane of data for sediments, ice cores, and lavas. The geomagnetic field intensity and directional changes that occurred during the reversal also provide important information for understanding the dynamics of the Earth’s outer core, which generates the magnetic field. However, the reversal process is relatively rapid in terms of the geological timescale; therefore, adequate temporal resolution of the geomagnetic field record is essential for addressing these topics. Here, we report a new high-resolution paleomagnetic record from a continuous marine succession in the Chiba composite section of the Kokumoto Formation of the Kazusa Group, Japan, that reveals detailed behaviors of the virtual geomagnetic poles (VGPs) and relative paleointensity changes during the M–B polarity transition. The resultant relative paleointensity and VGP records show a significant paleointensity minimum near the M–B boundary, which is accompanied by a clear “polarity switch.” A newly obtained high-resolution oxygen isotope chronology for the Chiba composite section indicates that the M–B boundary is located in the middle of marine isotope stage (MIS) 19 and yields an age of 771.7 ka for the boundary. This age is consistent with those based on the latest astronomically tuned marine and ice core records and with the recalculated age of 770.9 ± 7.3 ka deduced from the U–Pb zircon age of the Byk-E tephra. To the best of our knowledge, our new paleomagnetic data represent one of the most detailed records on this geomagnetic field reversal that has thus far been obtained from marine sediments and will therefore be key for understanding the dynamics of the geomagnetic dynamo and for calibrating the geological timescale.Graphical abstract.