Weak Field Region Research Articles

Cosmic Ray Diffusion in Magnetic Fields Amplified by Nonlinear Turbulent Dynamo

The diffusion of cosmic rays (CRs) in turbulent magnetic fields is fundamental to understanding various astrophysical processes. We explore the CR diffusion in the magnetic fluctuations amplified by the nonlinear turbulent dynamo in the absence of a strong mean magnetic field. Using test particle simulations, we identify three distinct CR diffusion regimes: mirroring, wandering, and magnetic moment scattering (MMS). With highly inhomogeneous distribution of the dynamo-amplified magnetic fields, we find that the diffusion of CRs is also spatially inhomogeneous. Our results reveal that lower-energy CRs preferentially undergo the mirror and wandering diffusion in the strong-field regions, and the MMS diffusion in the weak-field regions. The former two diffusion mechanisms play a more important role toward lower CR energies, resulting in a relatively weak energy dependence of the overall CR mean free path (MFP). In contrast, higher-energy CRs predominantly undergo the MMS diffusion, for which the incomplete particle gyration, i.e., the limit case of mirroring, in strong fields has a more significant effect than the scattering by small-scale field tangling/reversal. Compared with lower-energy CRs, they are more poorly confined in space and their MFPs have a stronger energy dependence. We stress the fundamental role of magnetic field inhomogeneity of nonlinear turbulent dynamo in causing the different diffusion behavior of CRs compared to that in sub-Alfvénic magnetohydrodynamic turbulence.

Magnetization processes features in the tapes of cobalt-based amorphous alloy

Studies of the amorphous cobalt-based soft magnetic alloy AMAG-172 (Co–Ni–Fe–Cr–Mn–Si–B) from different manufacturers have shown that in the as-quenched state there is nonuniformity of the magnetic characteristics, and therefore the level of internal stresses across the width of the tape produced by MSTATOR (Borovichi) significantly lower. However, similar to the tape produced by NIIMET (Kaluga), there is nonuniformity of the tape in thickness, which contributes to the formation of a bimodal field dependence of magnetic permeability.This may be a consequence of the non-uniform concentration along the width of the tape of hydrogen and oxygen atoms embedded in its surface during interaction with atmospheric vapor and the presence of temperature gradients during the manufacturing process. A stepwise shape of the initial sections of the magnetization curves in the region of the first maximum of magnetic permeability was discovered. The abrupt nature of the magnetization processes in the region of weak fields allows us to conclude that in the samples of tape produced by MSTATOR, the formation of the first maximum of the field dependence is associated with an independent magnetization reversal of the surface layer, while the main layer of the tape participates in the formation of the second maximum. The smoothed shape of the stepped initial section of the magnetization curve of samples produced by NIIMET corresponds to the gradual involvement of the main layer of the tape in the processes of magnetization and remagnetization. A comparison of the hysteresis loops of both parts of the tape, measured in the same magnetic field region, shows that the field shift of the hysteresis loops is associated with the interlayer interaction of the surface and volume of the tape, and the formation of asymmetric hysteresis loops occurs with the participation of the second layer with its gradual involvement in the processes of magnetization and magnetization reversal.

Introduction of the orthogonal mode via the polarization conversion parasitic structure for the isolation enhancement of MIMO patch antennas

Abstract In this study, a high-isolation multiple-input multiple-output (MIMO) microstrip patch antenna (MPA), which utilizes an orthogonal mode cancellation method is proposed. This method employs TM10 and TM01 modes, which are simultaneously excited in the rectangular passive MPA. Initially, a rectangular decoupling structure featuring polarization rotation characteristics is designed. Further studies show that by loading the polarization conversion parasitic structure (PCPS), the electric field of the spatial coupling wave can be transformed from the x-polarized TM10 mode to the y-polarized TM01 mode. Therefore, TM10 and TM01 modes from the excited antenna and decoupling structure are concurrently coupled to the passive antenna, forming an evident weak-field region on the passive antenna. Placing the feeding probe of the passive MPA within the weak-field region prevents signal reception at the port. Consequently, this results in an extremely low mutual coupling of −49 dB at a resonant frequency of 5.8 GHz. Finally, a prototype of the proposed antenna is fabricated and tested, and the measured results closely match the simulated results. Additionally, it is observed that PCPS slightly influences the performance of the MIMO antenna.

MAVEN SWIA Observations of Solar Wind Signatures in the Collisional Atmosphere of Mars

AbstractAt Mars, the solar wind is usually decelerated and heated at the bow shock, then diverted around the planet by the induced magnetosphere. A recent study by Crismani et al. (2019, https://doi.org/10.1029/2018ja026251), however, presented evidence of near‐pristine solar wind below the exobase of Mars (<200 km) during one Mars Atmosphere and Volatile EvolutioN (MAVEN) periapsis pass, implying the solar wind penetrated into the upper atmosphere with little modification. In this work, we search through 7 years of MAVEN Solar Wind Ion Analyzer (SWIA) periapsis observations to determine how often, and the conditions under which, these low‐altitude solar wind events occur. We find 23 candidate events that contain signatures of the solar wind below 200 km. The events are much more common at low solar zenith angles and tend to occur over weak crustal field regions where the radial component of the field is oriented downward. The observations also point to significant interactions between the incoming solar wind and the neutral atmosphere, including evidence of solar wind alphas becoming singly ionized helium through collisions with atmospheric CO2. Finally, we find the events are four times more likely to be detected when the interplanetary magnetic field (IMF) is radial (cone angle <30°), suggesting the events are triggered when the IMF is nearly aligned with the solar wind flow.

Синтез новых S-производных 4-амино-1,3,5-триазин-2-тиона и их исследование методами ЯМР 1Н, 13С и хромато-масс-спектрометрии

4-Amino-1,3,5-triazine-2-thione 1 interacts with allyl bromide, 2-methyl-3-chloro-1-propene, 2,3-dibromopropene-1, prenyl bromide in DMFA/K2CO3 and with cinnamyl chloride, butenyl bromide in DMFA/NaOH to form 4-allylsulfanyl- 2, 4-(2-methylpropene-2-yl)sulfanyl- 3, 4-(2-bromopropene-2-yl)sulfanyl- 4, 4-(2-methylbutene-2-yl)sulfanyl- 5, 4-cinnamylsulfanyl- 6 and 4-(butene-1-yl)sulfanyl-1,3,5-triazine-2-amines 7, respectively. The structure of compounds 2–7 was studied by 1H NMR, as well as of compounds 5 and 7, in their case including 13C NMR; allyl sulfide 2, prenyl sulfide 5 and butenyl sulfide 7 were also studied using chromatography mass spectrometry. In the 1H NMR spectra of compounds 2–7, the weakest field signal in the range of 8.22–8.30 p.p.m. is the signal of the aromatic proton of the triazine cycle, manifested as a singlet. The signals of protons of the S-CH2 group are observed in a strong field – at 3.10–4.19 p.p.m. – depending on the presence of electron donor or electron acceptor groups in the alkenyl fragment. The protons of the =CH2 group are present only in the structure of sulfides 2–4 and 7; they form two signals in the 1H NMR spectra: one signal at 4.85–5.58 p.p.m., the second at 5.03–6.10 p.p.m. In the 13C NMR spectra of prenyl sulfide 5 and butenyl sulfide 7, the carbon atoms of the S-alkenyl groups resonate in the region of strong fields. In the region of weak fields, the signals of aromatic carbon atoms of the 1,3,5-triazine cycle are observed: 182.32–157.95 p.p.m. In the mass spectra of compounds 2, 5 and 7, the characteristic peaks are [M 15]+ and [M-33]+ peaks, the formation of which is associated with the fragmentation of molecular ions undergoing cleavage of the methyl radical and the •SH radical, respectively. The haloalkyl derivative of the heterocyclic series – 2-chloro-1-(2,2,4-trimethyl-4-phenyl-3,4-dihydroquinoline-1(2H)-yl) ethanoate – in reaction with compound 1 has led to the introduction of a new pharmacophore fragment into the simm-triazine molecule, which contributes to the expansion of the spectrum of potential biological activity of its derivatives.

ИССЛЕДОВАНИЕ СТРУКТУРНОГО СОСТАВА БУТАДИЕН-НИТРИЛЬНЫХ КАУЧУКОВ МЕТОДОМ ЯМР НА ЯДРАХ 1Н и 13С

The structure of macromolecules of butadiene-nitrile rubbers with a content of 10, 15, 18, 26 and 40 wt. % of bound nitrile of acrylic acid was studied using 1H and 13C NMR spectroscopy. The effectiveness of using the nuclear magnetic resonance method on 1H and 13C spectroscopy for the analysis of the microstructure of the butadiene link in butadiene-nitrile rubbers was demonstrated. Calculation formulas for the quantitative assessment of the bound nitrile of acrylic acid, 1,2-, trans-1,4- and cis-1,4-units were proposed. There was a discrepancy between the calculation results for 1H and 13C NMR data. It was shown that the calculation of the conformation-isomeric composition of the butadiene link according to the 13C NMR spectra is possible only in the strong field region, since the signals of N-phenyl-β-naphthylamine, used as an antioxidant, overlap the signals of 1,2-, trans-1,4- and cis-1,4-links in the weak field region. The presence of a junction of acrylonitrile and butadiene units according to the type of 1,2-addition in rubbers with a content of bound nitrile of acrylic acid of 26 and 40 wt. % – but absent in rubbers with a lower content – was shown.

Electromagnetically induced transparency spectra of cesium Rydberg atoms decorated by radio-frequency fields

<sec>The large electric dipole moment of the Rydberg atom allows for strong coupling with weak electric fields, and is widely used in electric field measurements because of its reproducibility, precision and stability. The combination of Rydberg atoms and electromagnetically induced transparency (EIT) technology has been used for detecting and characterizing radio-frequency (RF) electric fields. </sec><sec>In this work, by selecting probe light (852 nm), dressed light (1470 nm), and coupled light (780 nm), the Rydberg state (49<i>P</i><sub>3/2</sub>) of Cs atom is prepared by using a three-photon excitation scheme through using all-infrared light excitation of Rydberg atoms. We experimentally observe the EIT spectra of the Rydberg states decorated by radio-frequency electric fields, which optically detects Rydberg atoms. The effect of the amplitude and frequency of the RF electric field on the spectrum is explored in light of changes in the EIT spectrum. The results show that in the region of weak electric field, only the ac Stark energy shift and spectral broadening occur. As the electric field is further enhanced, the sideband phenomenon occurs in both the primary peak and secondary peak of the EIT. In the region of strong field, the Rydberg energy level produces a series of Floquet states with higher-order terms, as well as state shifting and mixing, resulting in asymmetry in the spectra of the EIT sideband peaks. The effect of frequency on the shielding effect of the Cs vapor cell is further discussed based on the shift of the main peak of the EIT.</sec><sec>The demodulation of the electric field in a range of 50 Hz–1 kHz with a fidelity of 95% is achieved by modulating the low-frequency electric field to the RF electric field. The results can provide valuable references for spectral detection and traceable measurements of low-frequency electric fields.</sec>

TO THE QUESTION OF THE LOCALIZATION OF CME GENERATION ON THE SUN

The localization of CME occurrence zones on the Sun from November 2006 to February 2007 was studied using the SOHO catalog. A method is described for comparing such zones with active regions (ARs) both in the visible and invisible hemispheres of the Sun. It is shown that a simple linear continuation of the projections of the CME trajectory on the Sun in many cases passes by the AO. 63.5% of CMEs managed to be tied to ARs, 19% failed, and for 17.5% a choice must be made between ARs and flare sites, where spots were observed 1–3 rotations of the Sun earlier. The hypothesis is discussed that the displacement of the beginning of the CME trajectory from the AR centroid is associated with the asymmetry of the location of the magnetic rope, on the basis of which the CME is formed, with respect to the AO: one base of the rope is located near the strong magnetic fields of sunspots, the second is in the region of weak fields on the periphery or outside the AO.

Data-constrained Magnetohydrodynamic Simulation of an Intermediate Solar Filament Eruption

Solar eruptive activities could occur in weak magnetic field environments and over large spatial scales, which are especially relevant to eruptions involving intermediate or quiescent solar filaments. To handle the large scales, we implement and apply a flux rope embedding method using regularized Biot–Savart laws in the spherical coordinate system. Combined with a potential field source surface model and a magneto-frictional method, a nonlinear force-free field comprising a flux rope embedded in a potential field is constructed. Using the combined nonlinear force-free field as the initial condition, we then perform a zero-β data-constrained magnetohydrodynamic (MHD) simulation for an M8.7 flare at 03:38 UT on 2012 January 23. The MHD model reproduces the eruption process, flare ribbon evolution (represented by the quasi-separatrix layer evolution), and kinematics of the flux rope. This approach could potentially model global-scale eruptions from weak field regions.

Influence of Crustal Magnetic Fields on Horizontal Plasma Transport and Ion Escape on Mars

Owing to its unevenly distributed crustal fields, Mars acts as a unique obstacle to the solar wind. In the presence of the crustal fields, the transport of the planetary ions on the dayside ionosphere exhibits north–south asymmetry. Additionally, the heavy-ion loss in the magnetotail is affected by the crustal fields. In this paper, a three-dimensional multispecies magnetohydrodynamic model is employed to simulate Mars–solar wind interactions. Numerical results indicate that the meridional transport is dominant in most areas on the dayside ionosphere. In the presence of the crustal fields, the meridional transport on the southern hemisphere (southward transport) is reduced by more than 70% above the strong crustal sources, and the zonal velocity shows local changes inside strong and weak crustal field regions. These effects result in an increase or decrease in the number density of the heavy ions reaching the terminator, thereby influencing the thickness of the ionosphere. Decreased southward velocity leads to a reduction in the heavy-ion loss on the southern magnetotail. The radial outward flux is reduced by more than 30% for O2 + and CO2 + and by 10% for O+. This study shows that in addition to the zonal transport, the meridional transport is important for the day-to-night transport on the dayside of Mars. Collectively, the horizontal plasma transport, controlled by crustal fields, is associated with the altered ionosphere structure and reduced heavy-ion loss in the magnetotail.

Three-dimensional MHD Simulations of the Magnetic Pileup at Mars

In this study, we introduced a quantitative parameter, the magnetic field strength difference, to denote the intensity of the magnetic pileup effect at Mars. Using a three-dimensional multispecies MHD model, the effects of the interplanetary magnetic field (IMF) and the solar wind dynamic pressure (P d ) constituted with different densities and velocities on the magnetic pileup were examined. Our results show that: (1) the magnetic pileup at Mars mainly occurs at the dayside region and its magnitude is generally decreasing with increasing solar zenith angle. The magnetic pileup is generally weak in the intense crustal field region, while it is strong in the weak crustal field region. (2) The perpendicular IMF components, B Y and B Z , dominate the magnetic pileup, while the radial IMF component, B X , has little effect. In the intense crustal field region, when the IMF and crustal field are primarily in the same direction, the magnetic field is piled up and the pileup magnitude is generally strong. While the directions of the crustal field and IMF are opposite, the occurrence of magnetic reconnection can weaken the local magnetic pileup. (3) Under the same P d , a higher solar wind velocity results in a higher intensity and a larger region of the magnetic pileup. When P d increases, the magnitude of the magnetic pileup is enhanced, but the pileup region shrinks. In addition, for an increasing P d , at the center of the induced magnetotail, the asymmetric current sheet can lead to similar asymmetries of the pileup.

Electron Rolling‐Pin Distributions Preceding Dipolarization Fronts

AbstractElectron rolling‐pin distribution (RPDs), characterized by triple peaks at pitch angles 0°, 90°, and 180°, have recently been discovered in the terrestrial magnetosphere. Since the RPDs' formation is typically attributed to local betatron acceleration, RPDs have been believed to appear primarily inside strong magnetic regions, such as flux pileup regions (FPRs) behind dipolarization fronts (DFs). Different from such expectation, in this study we present unique observations of RPDs made by Cluster spacecraft in the terrestrial magnetotail, showing that RPDs are present inside weak magnetic field regions ahead of the DFs but absent in the strong magnetic field region behind them. The presence of RPD prior to the fronts may be atttributed to the combined effect of global betatron acceleration, global Fermi acceleration, and frontward transport driven by magnetic gradient drift. The atypical features of RPDs are important for fully understanding electron acceleration and transport in the magnetosphere.

Piezoelectric Relaxation in Piezoceramics in the Region of Weak Permanent Electric Fields

Piezoelectric Relaxation in Piezoceramics in the Region of Weak Permanent Electric Fields

Nonlinear and Relaxation Processes in Piezoceramics in the Region of Weak Electric Fields

Nonlinear and Relaxation Processes in Piezoceramics in the Region of Weak Electric Fields

Adaptive Backstepping Integral Sliding Mode Control of a MIMO Separately Excited DC Motor

This research proposes a robust nonlinear hybrid control approach to the speed control of a multi-input-and-multi-output separately excited DC motor (SEDCM). The motor that was under consideration experienced parametric uncertainties and load disturbances in the weak field region. The proposed technique aims to merge the benefits of adaptive backstepping (AB) and integral sliding mode control (ISMC) to enhance the overall system’s robustness. The unknown parameters with load disturbances are estimated using an adaptation law. These estimated parameters are incorporated into the controller design, to achieve a highly robust controller. The theoretical stability of the system is proved using the Lyapunov stability criteria. The effectiveness of the proposed AB–ISMC was demonstrated by simulation, to track the reference speed under parametric uncertainties and load disturbances. The control performance of the proposed technique was compared to that of feedback linearization (FBL), conventional sliding mode control (SMC), and AB control laws without and with the adaptation law. Regression parameters, such as integral square error, integral absolute error, and integral time absolute error, were calculated to quantitatively analyze the tracking performance and robustness of the implemented nonlinear control techniques. The simulation results demonstrated that the proposed controller could accurately track the reference speed and exhibited robustness, with steady-state error accuracy. Moreover, AB–ISMC overperformed, compared to the FBL, SMC, AB controller without adaptation law and AB controller with adaptation law, in reducing the settling time by factors of 27%, 67%, 23%, and 21%, respectively, thus highlighting the superior performance of the proposed controller.

A new magnetic state selection method in high-performance optically detected compact cesium beam clocks

We perform a new scheme of magnetic state selection in optically detected compact cesium beam clocks. Unlike the conventional method, we select atoms in the ground state |F = 4, mF ≠ −4⟩ by pointing the atomic collimator to the convex pole of the magnet realizing the two-wire magnetic field and detect atoms in |F = 3⟩ after interacting with the microwave field using a distributed feedback laser. The fluorescence background is greatly reduced as the inherent residual atoms |F = 4, mF = −4⟩ are avoided in this reversed scheme. The velocity distribution is narrowed, and the most probable velocity is decreased, since atomic trajectories are close to the weak-field region. We also investigate the relationship between the position of the atomic collimator and the distributions of the atomic beam, which is consistent with the Monte Carlo-based simulation model. By applying the reversed scheme and setting the deviated position of the collimator to 1.3 mm, the signal contrast is improved from 0.7 to 3, and the short-term frequency stability reaches 3.0 × 10−12 τ−1/2, nearly three times better than that of the high-performance version of Microsemi 5071A.

Quantum effects in silicon-germanium p-type heterostructures with quantum wells of different widths

The magneto-quantum and quantum interference effects in a two-dimensional gas of p-type charge carriers are studied for three quantum wells made of practically pure germanium in a Si0.6Ge0.4/Si0.2Ge0.8/Si0.6Ge0.4 heterostructure. The quantum well widths were 8 nm for sample I, 19.5 nm for sample II, and 25.6 nm for sample III. The dependences of resistance on the magnetic field for all samples exhibit Shubnikov–de Haas oscillations. Their analysis made it possible to calculate the kinetic characteristics of charge carriers for the cases of one (sample I) and two occupied subbands (samples II and III). In the region of weak magnetic fields (B < 0.1 T), the effect of weak localization of holes was revealed, which determines the negative magnetoresistance and the increase in resistance with decreasing temperature. The manifestation of the charge carriers interaction effect at various temperatures and magnetic fields is discovered and analyzed. A transition from the diffusion mode of manifestation of the quantum correction to the intermediate, and then to the ballistic mode is observed. In all regions, the behavior of the quantum correction due to the charge carriers interaction effect is in good agreement with modern theoretical predictions. The temperature dependences of the hole-phonon relaxation time are calculated. In weak magnetic fields, with an increase in the temperature of the 2D system, a transition from the “partial inelasticity” mode, characterized by the dependence τhph−1∝T2, to the small-angle scattering mode, described by the relation τhph−1∝T5, takes place. In stronger magnetic fields for samples with two occupied subbands, the dependence τhph−1∝T3was observed. Possible explanations for this dependence are presented.

Синтез и электрофильная гетероциклизация 3 алкенилсульфанил-5-фенил-1,2,4-триазинов под дейст-вием иода и брома

Derivatives of 1,2,4-triazine-3-thione are interesting research objects due to a wide range of their applications: drugs, optical substances, precursors for synthesis of new pyridine systems by the Diels-Alder reaction. In the present study, using alkylation of 5-phenyl-2,3-dihydro-1,2,4-triazine-3-thione (1) by 3-chloro-2-methyl-propene, 2,3-dibromopropene-1, 1-bromo-3-methylbut-2-ene and 4-brombut-1-ene, we have obtained 3-(2-methylprop-1-enyl)-, 3-(2-bromoprop-1-enyl)-, 3-prenylsulfanyl- and 3-butenylsulfanyl-5-phenyl-1,2,4-triazines (2a-d), previously unknown. In the 1H NMR spectrum of compound 2b, the shifts of the signal of pro-tons of the SCH2 group and the signal of protons of the vinyl group into a weak field by 0.48 ppm and 0.60 ppm can be observed, compared to the similar signals in the spectrum of 3-allylsulfanyl-5-phenyl-1,2,4-triazine. This may be due to the bromine atom in the allyl fragment. The weakest-field signal in the 13C NMR spectra of compounds 2a-d in the region of 171.86–173.68 ppm refers to the aromatic carbon atom of the triazine cycle in the third position (C-3), bound to a sulfur atom and two nitrogen atoms. New condensed heterocyclic systems of ionic type with a bridging nitrogen atom have been synthesized by electrophilic heterocyclization of methallyl-, bromallyl-, prenyl- and butenyl sulfides 2a-d. At the same time, [1,3]thiazolo[3,2-b][1,2,4]triazinium halides have been obtained by heterocyclization of compounds 2a,2b, and [1,3]thiazino[3,2–b][1,2,4]triazinium halides have been produced by heterocyclization of com-pounds 2c,2d. In the 1H NMR spectra of triazinium halides, a characteristic shift of the signal of the H-6 aromatic proton to the weak field region is observed in comparison with the similar sig-nal in the spectrum of the initial 2a-d sulfides. In the 13C NMR spectra of triazinium halides, there is a shift in the signal of the aromatic carbon atom associated with a sulfur atom and two nitrogen atoms (in the region of 162.56-172.42 ppm), which can be explained by the appearance of a positively charged nitrogen atom in their structure.

Geometry and thermodynamics of coherent quantum black holes

In this paper, we present a quantum description of black holes given by coherent states of gravitons sourced by a matter core. The expected behavior in the weak-field region outside the horizon is recovered, with arbitrarily good approximation, but the classical central singularity is not resolved because the coherent states may not contain modes of arbitrarily short wavelength and the matter core must therefore have finite size. Ensuing quantum corrections both in the interior and exterior is also estimated by assuming that the mean-field approximation holds everywhere. These deviations from the classical black hole geometry can be viewed as quantum hair and will lead to a quantum corrected horizon radius and thermodynamics.

The Nonpotentiality of Steady-state Coronal Magnetic Field Derived with Time-relaxation Magnetohydrodynamics Simulations Using Helioseismic and Magnetic Imager Three-component Magnetic Field Data

The steady states of the coronal magnetic field obtained with the magnetohydrodynamic (MHD) time-relaxation simulation model are examined. Our electric-field-driven model can introduce the three components of the solar surface magnetic field data maps as the boundary values of an MHD simulation, without violating the divergence-free condition of the magnetic field. The magnetic field in the simulated steady-state solar corona exhibits substantial nonpotentiality in the closed-field streamers. A few choices are allowed in our model, such as the criteria for determining whether or not the horizontal components at the weak-field region are included. The initial magnetic field configuration can be arbitrarily determined. In this work, we examined the differences between the steady states obtained with the information on the horizontal components and with several choices of the simulation setting, and compared the new steady states with those obtained without using the horizontal magnetic field components. We found that nonpotential magnetic structures in the derived steady states well correspond to the observed solar filament structures during a selected period of Carrington Rotation 2106. The difference in the steady state with different boundary treatments is found to be large. The difference caused by the initial magnetic configuration is found to be small.