Longitudinal Magnetic Field Strength Research Articles

Multi‐Objective Optimization Design of Vacuum Interrupter Structure Based on Improved Artificial Jellyfish Search Algorithm

An improved multi‐objective optimization method based on artificial jellyfish search algorithm is proposed to solve the multivariable and multi‐objective optimization problem of vacuum interrupter with mutual coupling of structural parameters and mutual restriction of performance indexes. The finite element model of 40.5 kV/31.5kA vacuum interrupter is established. The structural parameters of seven important parts such as contact diameter and contact sheet thickness in vacuum interrupter are taken as optimization variables. The optimization objective is to maximize the longitudinal magnetic field strength and minimize the conductor resistance at the peak breaking short‐circuit current of vacuum interrupter. The artificial jellyfish search algorithm is improved on the population position initialization strategy and the population mutation cross‐update strategy. The Pareto front solution of the structural parameters of the vacuum interrupter is obtained by the joint simulation of finite element analysis and numerical calculation software. Finally, the multi‐parameter and multi‐objective optimization design of vacuum interrupter structure is realized. The comprehensive performance index is introduced into the optimal parameter group of jellyfish on the Pareto front. Under the constraint of weight variables, the optimal structural parameters of contact system are obtained. The axial magnetic induction intensity of the optimized vacuum interrupter contact is increased by 13.2%, and the conductor resistance is reduced by 25.4%. The comprehensive performance of vacuum interrupter is improved by 17.8%, and the stability and reliability of the power system are further improved. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Detection of anomalous element distribution in the extremely slowly rotating magnetic O9.7 V star HD 54879

ABSTRACT The O9.7 V star HD 54879 is currently the only massive magnetic star whose magnetic field geometry and rotation period are not constrained. Over the last 3 yr, we gathered additional observations of this star, obtained using various instruments at several astronomical facilities, with the aim to constrain the rotation period and the magnetic field geometry. The new data include the first full Stokes vector observations with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), installed at the Large Binocular Telescope. The acquired spectropolarimetric observations show a very slow magnetic field variability related to the extremely slow rotation of HD 54879, which is also indicated in a dynamical spectrum, displaying variability of the Hα line. The most intriguing result of our study is the discovery of differences in longitudinal magnetic field strengths measured using different least-squares deconvolution (LSD) masks containing lines belonging to different elements. It is the first time that such a differential analysis of the field strength in dependence of the used lines is carried out for a magnetic O-type star. Since the LSD Stokes I profiles of the studied O, Si, and He line masks remain stable over all observing epochs, we conclude that the detection of different field strengths using lines belonging to these elements is related to the different formation depths, with the He lines formed much higher in the stellar atmosphere compared to the silicon and the oxygen lines, and non-local thermodynamic equilibrium (NLTE) effects. Our numerical magnetospherical model suggests the presence of enhanced gas density that fills the volume inside the field lines close to the star.

Investigation on the evolution and distribution of plasma in magnetic field assisted laser-induced plasma micro-machining

Magnetically Controlled Laser-induced Plasma Micro-Machining (MC-LIPMM), compared to traditional direct laser ablation, has the ability of achieving better machining characteristics including larger aspect ratios of machined features, a smaller heat affected zone and more diverse micro-structures. To reveal the process mechanisms affected by the magnetic field, this paper studies the evolution and distribution of plasma in MC-LIPMM by analytical and experimental methods. An analysis of the confinement effect and enhanced collision of electrons-ions in the plasma in the presence of a magnetic field is performed for revealing the influence of the magnetic field on its diffusion and geometric size. To validate our theoretical predictions, experiments were conducted to analyze the effects of key process parameters on the geometrical size, shape and fluence of the plasma. Edge contour extracting and elliptic formula fitting algorithms were applied for quantitatively evaluating the changes. The experimental results show that transverse magnetic fields generate a larger plasma plume and change its shape from spherical to ellipsoidal compared to that without a magnetic field. The eccentricity of the ellipsoidal plasma exhibits a parabolic growth while the cross-sectional area of the fitted ellipse shows a linear growth as the transverse magnetic field strength increases. Greater growth in geometric size and intensity of the plasma was obtained under a longitudinal compared to a transverse magnetic field, and its shape changed into an elongated ellipsoid. Moreover, a two-dimensional magnetic field, combining both the transverse and the longitudinal magnetic field component, was shown to produce a larger area and intensity of spherical plasma under an appropriate transverse and longitudinal magnetic field strength compared to that without a magnetic field.

He i Spectropolarimetry of a Supersonic Coronal Downflow Within a Sunspot Umbra

Abstract We report spectropolarimetric observations of a supersonic downflow impacting the lower atmosphere within a large sunspot umbra. This work is an extension of Schad et al. using observations acquired in the He i 10830 Å triplet by the Facility Infrared Spectropolarimeter. Downflowing material accelerating along a cooled coronal loop reaches peak speeds near 200 km s−1 and exhibits both high speed emission and absorption within the umbra, which we determine to be a consequence of the strong height dependence of the radiatively controlled source function above the sunspot umbra. Strong emission profiles close to the rest wavelengths but with long redshifted tails are also observed at the downflow terminus. From the polarized spectra, we infer longitudinal magnetic field strengths of ∼2.4 kG in the core portion of the He i strong emission, which we believe is the strongest ever reported in this line. Photospheric field strengths along the same line of sight are ∼2.8 kG as inferred using the Ca i 10839 Å spectral line. The temperatures of the highest speed He i absorption and the near-rest emission are similar (∼10 kK), while a differential emission measure analysis using Solar Dynamics Observatory/Atmospheric Imaging Assembly data indicates significant increases in radiative cooling for temperatures between ∼0.5 and 1 MK plasma associated with the downflow terminus. Combined we interpret these observations in the context of a strong radiative shock induced by the supersonic downflow impacting the low sunspot atmosphere.

High-temperature lithium atomic magnetometry by symmetric hyperfine coherent population trapping resonances

A glass lithium vapor cell is an atomic sensor operating at high temperature. The longitudinal magnetic-field strength is measured by coherent population trapping (CPT) in ground-state hyperfine levels. Two linearly polarized light beams are polarized orthogonally to each other. The difference of optical frequencies is tuned to generate a dark state. Additionally, a few light modes of equidistant frequency spacing are generated by modulating the difference frequency. The symmetry of the light modes and the energy levels enables simultaneous measurement of the hyperfine splitting frequency of the ground state and the magnetic-field strength. Tuning the optical frequency difference to the central CPT resonance, a sensitivity of 15 p T / H z is achieved. The time response and the sensitivity of the CPT magnetometry are studied by changing the cell temperature, the laser power, the frequency separation of the light modes, and the Zeeman frequency.

Модель біоенергетичного резонансу

The research is devoted to the study of the behavior of the generalizing magnetization vector in the seeds of agricultural crops under the action of longitudinal constant and transverse alternating magnetic fields by the method of nuclear magnetic resonance. Based on the theoretical studies, the value of the average magnetic susceptibility per unit volume of seed χ and the value of the magnetization vector were determined. For the system of microparticles of cells of plant origin, the average magnetic susceptibility per unit volume of seed is χ = 2.1 · 10-5, and the magnetization vector M=13.125 mA/m at a longitudinal constant magnetic field strength H = 625 A/m. When a weak transverse alternating magnetic field is superimposed on the frequency, the oscillation frequencies of the magnetization vectors M coincide with the field frequency, which is a condition for the occurrence of magnetic resonance. The longitudinal magnetization vector during the transition from the ground state to the excited state (resonant) describes a trajectory in the form of a spiral on the surface of the sphere. A mathematical model for a biological system taking into account the Earth's magnetic field is built. It is established that for the technology of pre-sowing treatment of seeds of agricultural crops, the inductor, which creates a constant magnetic field, must be located so that the vector of the constant magnetic field of the inductor coincides with the vector of the Earth's magnetic field. Keywords: bioenergetic resonance, pre-sowing treatment of crop seeds, direct magnetic field, alternating magnetic field, longitudinal and transverse relaxation

The very slow rotation of the magnetic O9.7 V star HD 54879

ABSTRACT The first FOcal Reducer low dispersion Spectrograph (FORS 2) spectropolarimetric observation of the longitudinal magnetic field of HD 54879 of the order of −600 G with a lower limit of the dipole strength of ∼2 kG dates back to 2014. Since then, observations showed a gradual decrease of the absolute value of the mean longitudinal magnetic field. In the course of the most recent monitoring of HD 54879 using FORS 2 spectropolarimetric observations from 2017 October to 2018 February, a longitudinal magnetic field strength change from about −300 G down to about −90 G was reported. A sudden increase of the absolute value of the mean longitudinal magnetic field and an accompanying spectral variability was detected on 2018 February 17. New FORS 2 spectropolarimetric data obtained from 2018 December to 2019 February confirm the very slow magnetic field variability, with the field decreasing from about 150 G to −100 G over 2 months. Such a slow magnetic field variability, related to the extremely slow rotation of HD 54879, is also confirmed using high-resolution High Accuracy Radial velocity Planet Searcher in polarimetric mode and Echelle SpectroPolarimetric Device for the Observation of Stars spectropolarimetry. The re-analysis of the FORS 2 polarimetric spectra from 2018 February indicates that the previously reported field increase and the change of the spectral appearance was caused by improper spectra extraction and wavelength calibration using observations obtained at an insufficient signal-to-noise ratio. The presented properties of HD 54879 are discussed in the context of the Of?p spectral classification.

Detection of magnetic fields in He-rich early B-type stars using HARPSpol

Aims. We focus on early-B type stars with helium overabundance, for which the presence of a magnetic field has not previously been reported. Methods. The measurements were carried out using high-spectral-resolution spectropolarimetric observations obtained with the High Accuracy Radial velocity Planet Searcher (HARPS) in polarimetric mode, installed at the ESO La Silla 3.6 m telescope. Results. For five He-rich stars, the longitudinal magnetic field was detected for the first time. For one target, HD 58260, the presence of a longitudinal magnetic field of the order of 1.8 kG has already been reported in the literature, but the magnetic field has remained constant over tens of years. Our measurement carried out using the polarimetric spectra obtained in 2015 March indicates a slight decrease of the longitudinal magnetic field strength compared to measurements reported in previous works. A search for periodic modulation in available photometric data allowed us to confidently establish a period of 2.64119 ± 0.00420 d in archival ASAS3 data for CPD–27°1791. No period could be determined for the other five stars. Conclusions. The obtained results support the scenario that all He-rich stars are detectably magnetic and form an extension of the Ap star phenomenon to higher temperatures.

The magnetic variability of the β cep star ξ1 CMa

ξ1 CMa is a known magnetic star showing rotationally modulated magnetic variability with a period of 2.17937 d. However, recent work based on high-resolution spectropolarimetry suggests that the rotation period is longer than 30 years. We compare our new spectropolarimetric measurements with FORS 2 at the VLT acquired on three consecutive nights in 2017 to previous FORS 1/2 measurements of the longitudinal magnetic field strength. The new longitudinal magnetic field values are in the range from 115 to 240 G and do not support the presence of a long period.

First results from the LIFE project: discovery of two magnetic hot evolved stars

We present the initial results of the Large Impact of magnetic Fields on the Evolution of hot stars (LIFE) project. The focus of this project is the search for magnetic fields in evolved OBA giants and supergiants with visual magnitudes between 4 and 8, with the aim to investigate how the magnetic fields observed in upper main sequence (MS) stars evolve from the MS until the late post-MS stages. In this paper, we present spectropolarimetric observations of 15 stars observed using the ESPaDOnS instrument of the CFHT. For each star, we have determined the fundamental parameters and have used stellar evolution models to calculate their mass, age and radius. Using the LSD technique, we have produced averaged line profiles for each star. From these profiles, we have measured the longitudinal magnetic field strength and have calculated the detection probability. We report the detection of magnetic fields in two stars of our sample: a weak field of $B_l=1.0\pm0.2\,$G is detected in the post-MS A5 star 19$\,$Aur and a stronger field of $B_l=-230\,\pm\,10\,$G is detected in the MS/post-MS B8/9 star HR$\,$3042.

Far beyond the Sun – I. The beating magnetic heart in Horologium

A former member of the Hyades cluster, $\iota$ Horologii ($\iota$ Hor) is a planet-hosting Sun-like star which displays the shortest coronal activity cycle known to date ($P_{\rm cyc}\sim$ 1.6 yr). With an age of $\sim$$625$ Myr, $\iota$ Hor is also the youngest star with a detected activity cycle. The study of its magnetic properties holds the potential to provide fundamental information to understand the origin of cyclic activity and stellar magnetism in late-type stars. In this series of articles, we present the results of a comprehensive project aimed at studying the evolving magnetic field in this star and how this evolution influences its circumstellar environment. This paper summarizes the first stage of this investigation, with results from a long-term observing campaign of $\iota$ Hor using ground-based high-resolution spectropolarimetry. The analysis includes precise measurements of the magnetic activity and radial velocity of the star, and their multiple time-scales of variability. In combination with values reported in the literature, we show that the long-term chromospheric activity evolution of $\iota$ Hor follows a beating pattern, caused by the superposition of two periodic signals of similar amplitude at $P_{1} \simeq 1.97 \pm 0.02$ yr and $P_{2} \simeq 1.41 \pm 0.01$ yr. Additionally, using the most recent parameters for $\iota$ Hor b in combination with our activity and radial velocity measurements, we find that stellar activity dominates the radial velocity residuals, making the detection of additional planets in this system challenging. Finally, we report here the first measurements of the surface longitudinal magnetic field strength of $\iota$ Hor, which displays varying amplitudes within $\pm4$ G and served to estimate the rotation period of the star ($P_{\rm rot} =~7.70^{+0.18}_{-0.67}$ d).

A search for spectral variability in the highly magnetized O9.7 V star HD 54879

The O9.7 V star HD 54879 possesses the second strongest magnetic field among the single, magnetic, O‐type stars. In contrast to other magnetic O‐type stars, the chemical abundance analysis of HD 54879 indicated a rather normal optical spectrum without obvious element enhancements or depletions. Furthermore, spectral variability was detected only in lines partly formed in the magnetosphere. As this star shows such a deviate, almost nonvariable, spectral behavior, we performed a deeper analysis of its spectral variability on different timescales using all currently available HARPSpol and FORS 2 spectropolarimetric observations. The longitudinal magnetic field strengths measured at different epochs indicate the presence of variability possibly related to stellar rotation, but the current data do not allow us yet to identify the periodicity of the field variation. As spectropolarimetric observations obtained at different epochs consist of subexposures with different integration times, we investigated spectral variability on timescales of minutes. The detected level of variability in line profiles of different elements is rather low, between 0.2 and 1.7%, depending on the integration time of the exposures and the considered element.

On the Relationship Between G-Band Bright Point Dynamics and Their Magnetic Field Strengths

G-band bright points (GBPs) are regarded as good manifestations of magnetic flux concentrations. We aim to investigate the relationship between the dynamic properties of GBPs and their longitudinal magnetic field strengths. High spatial and temporal resolution observations were recorded simultaneously with G-band filtergrams and Narrow-band Filter Imager (NFI) Stokes I and V images with Hinode /Solar Optical Telescope. The GBPs are identified and tracked in the G-band images automatically, and the corresponding longitudinal magnetic field strength of each GBP is extracted from the calibrated NFI magnetograms by a point-to-point method. After categorizing the GBPs into five groups by their longitudinal magnetic field strengths, we analyze the dynamics of GBPs of each group. The results suggest that with increasing longitudinal magnetic field strengths of GBPs correspond to a decrease in their horizontal velocities and motion ranges as well as by showing more complicated motion paths. This suggests that magnetic elements showing weaker magnetic field strengths prefer to move faster and farther along straighter paths, while stronger ones move more slowly in more erratic paths within a smaller region. The dynamic behaviors of GBPs with different longitudinal magnetic field strengths can be explained by that the stronger flux concentrations withstand the convective flows much better than weaker ones.

Spots and activity cycles of the star FKCom—2013–2015 data analysis

We present an analysis of new photometric and spectropolarimetric observations of a chromospherically active star FKCom. Based on this observational data and the data from the literature sources, applying a common technique, we performed an analysis of a complete set of the available photometric data, which were divided into 218 individual light curves. For each of them a reverse problem of restoring largescale temperature irregularities on the surface of the star from its light curve was solved. We analyzed the time series for the brightness of the star in the U-, B-, and V-bands, the brightness variability amplitudes, the total area of the spots on the surface of the star, and the average brightness of each set considered. The analysis of determination results of the positions of active longitudes leads to the conclusion about the existence of two systems of active regions on the FKCom surface. It was determined that the positions of each of these systems undergo cyclic changes. This confirms the conclusion on the likely absence of a strongly pronounced regularity of the flip-flops in FKCom, earlier suggested by other researchers. The results of the new polarimetric observations FKCom in 2014–2015 are presented. These measurements evidence the legitimacy of the proposed interpretation the behavior of the longitudinal magnetic field strength 〈Bz〉, indicating the settling-in of a more symmetric distribution of magnetic region on the FKCom surface. An increasing activity of the star over the recent years, registered from the photometric observations is also consistent with the probable onset of growth in the 〈Bz〉 parameter starting from 2014.

A spectro-polarimetric study of the planet-hosting G dwarf, HD 147513

The results from a spectro-polarimetric study of the planet-hosting Sun-like star, HD 147513 (G5V), are presented here. Robust detections of Zeeman signatures at all observed epochs indicate a surface magnetic field, with longitudinal magnetic field strengths varying between 1.0-3.2 G. Radial velocity variations from night to night modulate on a similar timescale to the longitudinal magnetic field measurements. These variations are therefore likely due to the rotational modulation of stellar active regions rather than the much longer timescale of the planetary orbit (Porb=528 d). Both the longitudinal magnetic field measurements and radial velocity variations are consistent with a rotation period of 10 +/- 2 days, which are also consistent with the measured chromospheric activity level of the star (log R'(HK)=-4.64). Together, these quantities indicate a low inclination angle, i~18 degrees. We present preliminary magnetic field maps of the star based on the above period and find a simple poloidal large-scale field. Chemical analyses of the star have revealed that it is likely to have undergone a barium-enrichment phase in its evolution because of a higher mass companion. Despite this, our study reveals that the star has a fairly typical activity level for its rotation period and spectral type. Future studies will enable us to explore the long-term evolution of the field, as well as to measure the stellar rotation period, with greater accuracy.

DISPERSAL OF G-BAND BRIGHT POINTS AT DIFFERENT LONGITUDINAL MAGNETIC FIELD STRENGTHS

G-band bright points (GBPs) are thought to be the foot-points of magnetic flux tubes. The aim of this paper is to investigate the relation between the diffusion regimes of GBPs and the associated longitudinal magnetic field strengths. Two high resolution observations of different magnetized environments were acquired with the Hinode/Solar Optical Telescope. Each observation was recorded simultaneously with G-band filtergrams and Narrow-band Filter Imager (NFI) Stokes I and V images. GBPs are identified and tracked automatically, and then categorized into several groups by their longitudinal magnetic field strengths, which are extracted from the calibrated NFI magnetograms using a point-by-point method. The Lagrangian approach and the distribution of diffusion indices approach are adopted separately to explore the diffusion regime of GBPs for each group. It is found that the values of diffusion index and diffusion coefficient both decrease exponentially with the increasing longitudinal magnetic field strengths whichever approach is used. The empirical formulas deduced from the fitting equations are proposed to describe these relations. Stronger elements tend to diffuse more slowly than weak elements, independently of the magnetic flux of the surrounding medium. This may be because the magnetic energy of stronger elements is not negligible compared with the kinetic energy of the gas, and therefore the flows cannot perturb them so easily.Yang

Modified methods of stellar magnetic field measurements

AbstractThe standard methods of the magnetic field measurement, based on an analysis of the relation between the Stokes V‐parameter and the first derivative of the total line profile intensity, were modified by applying a linear integral operator L to both sides of this relation. As the operator L, the operator of the wavelet transform with DOG‐wavelets is used. The key advantage of the proposed method is an effective suppression of the noise contribution to the line profile and the Stokes parameter V. The efficiency of the method has been studied using model line profiles with various noise contributions. To test the proposed method, the spectropolarimetric observations of the A0 star α2 CVn, the Of?p star HD 148937, and the A0 supergiant HD 92207 were used. The longitudinal magnetic field strengths calculated by our method appeared tobe in good agreement with those determined by other methods. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Collision-induced photon echo in ytterbium vapour at the transition 0–1: magnetic field effect

Collision-induced photon echo generated in ytterbium vapour at the transition (6s2) 1S0 ↔(6s6p) 3P1 (transition of the type 0 ↔ 1) was investigated in the presence of the longitudinal magnetic field strength between zero and 5.6 G. For the weak magnetic fields, not over 0.27 G, the collision-induced echo signal decreases with magnetic field increase. Further increase of the magnetic field strength reveals oscillatory behavior of the echo signal. Experimental results are in qualitative agreement with theoretical predictions.

Improved magnetogram calibration of Solar Magnetic Field Telescope and its comparison with the Helioseismic and Magnetic Imager

In this paper, we try to improve the magnetogram calibration method of the Solar Magnetic Field Telescope (SMFT). The improved calibration process fits the observed full Stokes information, using six points on the profile of Fe i 5324.18 Å line, and the analytical Stokes profiles under the Milne–Eddington atmosphere model, adopting the Levenberg–Marquardt least-squares fitting algorithm. In comparison with the linear calibration methods, which employs one point, there is a large difference in the strength of longitudinal field Bl and transverse field Bt, caused by the non-linear relationship, but the discrepancy is little in the case of inclination and azimuth. We conclude that it is better to deal with the non-linear effects in the calibration of Bl and Bt using six points. Moreover, in comparison with Solar Dynamics Observatory/Helioseismic and Magnetic Imager (HMI), SMFT has larger stray light and acquires less magnetic field strength. For vector magnetic fields in two sunspot regions, the magnetic field strength, inclination and azimuth angles between SMFT and HMI are roughly in agreement, with the linear fitted slopes of 0.73/0.7, 0.95/1.04 and 0.99/1.1. In the case of pores and quiet regions (Bl < 600 G), the fitted slopes of the longitudinal magnetic field strength are 0.78 and 0.87, respectively.

Elastic wave propagation in magnetically affected double-walled carbon nanotubes

This work deals with the characteristics of the transverse waves within embedded double-walled carbon nanotubes (DWCNTs) which are subjected to an axial magnetic field. Nonlocal Rayleigh, Timoshenko, and higher-order beam theories are adopted. The flexural and shear frequencies as well as their corresponding phase and group velocities of the sound waves for the proposed models are obtained. The role of strength of longitudinal magnetic field (LMF), geometry properties of the DWCNT, size dependency, wavenumber, and elastic properties of the surrounding matrix on the characteristics of the sound waves are explained. The capabilities of the proposed models in capturing such characteristics of the propagated waves are also discussed. The predicted results reveal that the flexural frequencies magnifies with the LMF up to a certain value; however, no distinguished variations for the shear frequencies as a function of the LMF are observed. For the LMF greater than that certain value, the variation of the LMF has a very trivial influence on the variation of the flexural frequencies. Nevertheless, for such a range of the LMF and most wavenumbers, the shear frequencies linearly increase with the LMF.