Dipole Component Research Articles

Is the Radio Source Dipole from NVSS Consistent with the Cosmic Microwave Background and ΛCDM?

The dipole moment in the angular distribution of the cosmic microwave background (CMB) is thought to originate from the doppler effect and our motion relative to the CMB frame. Observations of large-scale structure (LSS) should show a related “kinematic dipole” and help test the kinematic origin of the CMB dipole. Intriguingly, many previous LSS dipole studies suggest discrepancies with the expectations from the CMB. Here, we reassess the apparent inconsistency between the CMB measurements and dipole estimates from the NVSS catalog of radio sources. We find that it is important to account for the shot noise and clustering of the NVSS sources, as well as kinematic contributions, in determining the expected dipole signal. We use the clustering redshift method and a cross-matching technique to refine estimates of the clustering term. We then derive a probability distribution for the expected NVSS dipole in a standard ΛCDM cosmological model including all (i.e., kinematic, shot noise, and clustering) dipole components. Our model agrees with most of the previous NVSS dipole measurements in the literature at better than ≲2σ. We conclude that the NVSS dipole is consistent with a kinematic origin for the CMB dipole within ΛCDM.

Magnetospheric flows in X-ray pulsars – I. Instability at super-Eddington regime of accretion

ABSTRACT Within the magnetospheric radius, the geometry of accretion flow in X-ray pulsars is shaped by a strong magnetic field of a neutron star. Starting at the magnetospheric radius, accretion flow follows field lines and reaches the stellar surface in small regions located close to the magnetic poles of a star. At low mass accretion rates, the dynamics of the flow is determined by gravitational attraction and rotation of the magnetosphere due to the centrifugal force. At the luminosity range close to the Eddington limit and above it, the flow is additionally affected by the radiative force. We construct a model simulating accretion flow dynamics over the magnetosphere, assuming that the flow strictly follows field lines and is affected by gravity, radiative, and centrifugal forces only. The magnetic field of a neutron star is taken to be dominated by the dipole component of arbitrary inclination with respect to the accretion disc plane. We show that accretion flow becomes unstable at high mass accretion rates and tends to fluctuate quasi-periodically with a typical period comparable to the free-fall time from the inner disc radius. The inclination of a magnetic dipole with respect to the disc plane and strong anisotropy of X-ray radiation stabilize the mass accretion rate at the poles of a star, but the surface density of material covering the magnetosphere fluctuates even in this case.

Cavity tuning and beam commissioning of the radio-frequency quadrupole linac for a transportable neutron source

A transportable, compact, accelerator-based neutron source is under development at Xi’an Jiaotong University. At the heart of the linear accelerator is a radio-frequency quadrupole (RFQ) unit that has been designed to accelerate a proton beam from 30 keV to 2.5 MeV with a peak current of 12 mA and a duty factor of 3%. Recently, the manufacturing of the RFQ cavity has been completed. Cavity tuning, including field unevenness, resonant frequency, and rf coupling coefficient, was carried out after finishing brazing and assembly. The quadrupole perturbative component was controlled within ±2.0%, and the two dipole components were about ±2.5%. The value of the intrinsic Q was 9609, 89% of that of the theoretical simulation. We have completed the installation of the RFQ experimental setup and performed beam commissioning experiments. The output beam current reached 10.6 mA with a transmission efficiency of 93.8%.

Synchrony between dipole and quadrupole during magnetic field reversals and excursions

In contrast to reversals, excursions of the geomagnetic field can occur at lower convection intensities in the Earth’s core. Since in such geodynamo regimes the behavior of the magnetic field is still quasi regular, a reduction of the dipole field during an excursion may indicate a global failure of the dynamo process. As a consequence, it is possible that during the excursion, not only the dipole component, but also the higher harmonics of the field decrease. This hypothesis is tested in a three-dimensional (3D) dynamo model.

Synchrony between Dipole and Quadrupole During Magnetic Field Reversals and Excursions

—In contrast to reversals, geomagnetic field excursions can occur at lower convection intensity in the Earth’s core. Since in such geodynamo regimes the magnetic field behavior is still quasi regular, a reduction in the dipole field during excursion may indicate a global failure in the dynamo process. As a consequence, it is possible that during the excursion, not only the dipole component, but also higher harmonics of the field decrease. This hypothesis is tested in a 3D (3D) dynamo model.

Comparative Evolutionary Analysis of Dipole and Non-Dipole Components of Geomagnetic Energy

The total energy of the potential geomagnetic field (up to the core-mantle boundary) is divided into dipole and non-dipole parts, which are determined by their evolution and frequency properties. The calculations presented here are based on the available and sufficiently reliable COV-OBS.x2 geomagnetic field model that covers the period of 1840–2020. The proposed approximations for longer periods are preliminary, as further work is required to estimate errors through comparison with other historical observational and paleomagnetic models of the geomagnetic field, as well as with numerical models of the geodynamo. The actual dipole energy (about 5 EJ) turned out to be only three times higher than the non-dipole energy, rather than the previously reported one order or more. It was found that the dipole energy decreases relatively slowly and monotonically, while the non-dipole part changes much faster and quasi-periodically. Therefore, the characteristic times are on the order of one thousand years for the dipole component and on the order of hundreds of years for the non-dipole component, respectively. If the quadrupole and octupole contributions to the geomagnetic field are only considered, which is a natural limitation for paleoand archaeomagnetologists, then the energy of such a “truncated” non-dipole part increases monotonically, and its evolutionary and frequency characteristics become different from the full (up to the 14th spherical harmonic) non-dipole part. The results show that the power or the time derivative of energy varies more significantly compared to the energy, being on the order of one hundred MW for both the dipole and non-dipole parts. Frequency values were obtained by analyzing the power/ energy ratios.

Ions and dipoles in electric field: nonlinear polarization and field-dependent chemical reaction.

We investigate electric-field effects in dilute electrolytes with nonlinear polarization. As a first example of such systems, we add a dipolar component with a relatively large dipole moment [Formula: see text] to an aqueous electrolyte. As a second example, the solvent itself exhibits nonlinear polarization near charged objects. For such systems, we present a Ginzburg-Landau free energy and introduce field-dependent chemical potentials, entropy density, and stress tensor, which satisfy general thermodynamic relations. In the first example, the dipoles accumulate in high-field regions, as predicted by Abrashikin et al.[Phys.Rev.Lett. 99, 077801 (2007)]. Finally, we consider the case, where Bjerrum ion pairs form a dipolar component with nonlinear polarization. The Bjerrum dipoles accumulate in high-field regions, while field-induced dissociation was predicted by Onsager [J. Chem. Phys.2, 599 (1934)]. We present an expression for the field-dependent association constant K(E), which depends on the field strength nonmonotonically.

Method for prediction and control by uncertain microsatellite magnetic cleanliness based on calculation and compensation magnetic field spatial harmonics

Aim. Development of method for prediction and control the microsatellite magnetic cleanliness taking into account the uncertainties of the magnetic characteristics of the microsatellite, based on calculation the magnetic field spatial spherical harmonics in the area of the onboard magnetometer installation and using compensating multipoles. Methodology. Spatial spherical harmonics of microsatellite magnetic field in the area of the onboard magnetometer installation calculated as solution of nonlinear minimax optimization problem based on near field measurements for prediction far spacecraft magnetic field magnitude. Nonlinear objective function calculated as the weighted sum of squared residuals between the measured and predicted magnetic field. Values of the compensating dipoles, quadrupoles and octupoles and coordinates of them placement inside the spaceship for compensation of the dipoles, quadrupoles and octupoles components of the microsatellite initial magnetic field also calculated as solution of nonlinear minimax optimization problem. Both solutions of this nonlinear minimax optimization problems calculated based on particle swarm nonlinear optimization algorithms. Results. Results of prediction spacecraft far magnetic field magnitude based on spacecraft spatial spherical harmonics of the magnetic field using near field measurements and compensation of the dipoles, quadrupoles and octupoles components of the initial magnetic field with consideration of spacecraft magnetic characteristics uncertainty for ensuring the microsatellite magnetic cleanliness. Originality. The method for prediction and control by spacecraft magnetic cleanliness based on calculation spatial spherical harmonics of the magnetic field in the area of the onboard magnetometer installation using compensation of the dipoles, quadrupoles and octupoles components of the initial magnetic field with consideration of magnetic characteristics uncertainty is developed. Practical value. The important practical problem of ensuring the magnetic cleanliness of the «Sich-2» microsatellite family based on the spatial spherical harmonics of the magnetic field model using the compensation of the dipole, quadrupole and octupole components of the output magnetic field of the sensor for the kinetic parameters of the neutral component of the space plasma at the point of installation of the on-board magnetometer LEMI-016 by setting the compensating dipole, quadrupole and octupole with consideration of spacecraft magnetic characteristics uncertainty solved.

Development of a New Electromagnetic Extraction Channel from the AGOR Cyclotron

The extraction system of the superconducting AGOR cyclotron consists of an electrostatic deflector and three electromagnetic channels. As the electrostatic deflector has only a moderate field strength (<100 kV/cm), the first electromagnetic channel (EMC1) has to generate a rather strong dipole component resulting in current densities up to 169 A/mm2 in water-cooled copper coils. In the original design the coils consist of sections of hollow conductors, parallel to the beam path, vacuum-brazed to machined “bridges” over the beam aperture. Altogether there are over 200 brazed joints made in three subsequent cycles in the three coils (dipole, quadrupole and first harmonic corrector). In 25 years of operation two channels of this type have been “consumed”. The channels developed water leaks due to erosion of the copper by the high speed cooling water flow in the “bridge” regions that ultimately could not be repaired anymore. To remedy this problem the channel has been redesigned using bent conductors. A production technique for small radius bends and a new joining method to avoid vacuum brazing have been developed. The coil support taking up the 10 kN/m Lorentz forces on the windings are now made from isolating material instead of anodized aluminium to prevent grounding errors. The new channel (EMC1-U) has been in operation now for two years without any failure. A detailed comparison of the old and new design will be presented.

Improvement of the uniformity of the magnetic field inside a short solenoid by the end winding system

Improving the level of homogeneity of the magnetic field in the middle of the working volume of a short solenoid makes it possible to improve devices for demagnetizing technical objects and studying the magnetic properties of materials. One of the means of increasing the level of homogeneity of the magnetic field in the middle of the solenoid is to approximate the shape of its winding to the closed surface. The use of a system of a solenoid and two end axisymmetric current windings with a common current source is proposed as such a surface. A mathematical model of the scalar potential of the magnetic field of such a system was built using spherical harmonic analysis, and functional dependences of the current density on each surface were obtained for its first harmonic, which is the dipole component of the magnetic field. Formulas for calculating the number of turns in the end windings and the geometric parameters of their arrangement and the simulated total magnetic field inside the proposed system are obtained. A comparative analysis of the homogeneity of the magnetic field created by a separate solenoid and a solenoid with end windings, depending on the geometry of the system, was conducted. The use of end windings significantly improves the uniformity of the magnetic field near the ends, especially on the axis of the solenoid. Due to this, the efficiency of the end windings significantly depends on the solenoid elongation indicator and allows you to increase the working volume by 5-20%, depending on this indicator. The proposed system makes it possible to obtain a magnetic field with a maximum deviation of 5% from uniformity for a solenoid elongation index of 2. As the elongation increases, the efficiency of the end windings decreases and for systems with an elongation of 10 or more, their use becomes impractical. The results of the analysis testify to the effectiveness of using the proposed system in devices for demagnetizing technical products that differ in a small indicator of the elongation of the working solenoid - primarily devices that create a uniform magnetic field with an amplitude decreasing over time of 240 A/m and are used in particular to remove soft residual magnetization from elements of space vehicles

Revealing insights into hydrodynamic noise induced by different cavitating flows around a hydrofoil

Cavitation-induced noise hazards in marine environments have raised significant concerns. This paper presents a study on the flow noise generated by cavitating flow around a model-scale NACA66 hydrofoil, utilizing the permeable acoustic analogy method. Through Large Eddy Simulation and the Schnerr-Sauer cavitation model, the study captures the cavitation flow pattern, aligning with experimental observations. The research conducts a detailed analysis of the monopole and dipole noise components, providing insights into their characteristics under different cavitation conditions (cavitation number σ = 0.60, 0.83, 1.29, and 1.44). The results revealed a noteworthy trend where the proportion of the dipole component increases as the cavitation number σ decreases. Furthermore, the study uncovered the mechanism behind monopole noise induction in unsteady cavitating flows, offering insights into different types of sound impulse sources associated with cavitation collapse. Particularly, the collapse of clouds during secondary shedding is identified as a significant source of highly intense impulses, surpassing the levels observed in other cavitation flow stages. Additionally, deeper exploration demonstrated the co-action of vortex stretching and dilatation, contributing to the enhanced deformation, breakdown, and condensation of vapor structures, consequently significantly accelerating the collapse process.

Rotational Components of the Sun’s Mean Field

This paper uses wavelet transforms to look for the rotational frequencies of the Sun’s mean line-of-sight magnetic field. For a sufficiently high wavelet frequency, the spectra of the dipole, quadrupole, and hexapole field components each show a time-dependent fine structure with periods in the range of 26.5–30 days and their harmonics. These maps confirm that a large enhancement of power at 30 days occurred in the dipole field during 1989–1990, as recorded previously using Fourier techniques. In addition, during some years the maps show power at 26.5 days (or its harmonics), which is clearly distinguishable from the rotation period of 26.9–27.0 days at the Sun’s equator. In at least one case, the 26.5-day period was a wave phenomenon caused by the systematic eruption of active regions at progressively more western locations in the Carrington coordinate system, as if the flux were emerging from a fixed longitude in a faster-rotating subsurface layer. Based on previous studies of the mean field, I conclude that the enhanced wavelet patterns in this paper are regions where magnetic flux is emerging in configurations that strengthen the Sun’s horizontal dipole, quadrupole, and hexapole fields, and (in the case of the more slowly rotating patterns) where this flux is being transported to midlatitudes whose rotation periods are in the range of 28–30 days.

Design of High-Performance Organic Nonlinear Optical and Terahertz Crystals by Controlling the van der Waals Volume.

In the development of new organic crystals for nonlinear optical and terahertz (THz) applications, it is very challenging to achieve the essentially required non-centrosymmetric molecular arrangement. Moreover, the resulting crystal structure is mostly unpredictable due to highly dipolar molecular components with complex functional substituents. In this work, new organic salt crystals with top-level macroscopic optical nonlinearity by controlling the van der Waals volume (VvdW ), rather than by trial and error, are logically designed. When the VvdW of molecular ionic components varies, the corresponding crystal symmetry shows an observable trend: change from centrosymmetric to non-centrosymmetric and back to centrosymmetric. All non-centrosymmetric crystals exhibit an isomorphic P1 crystal structure with an excellent macroscopic second-order nonlinear optical response. Apart from the top-level macroscopic optical nonlinearity, new organic crystals introducing highly electronegative fluorinated substituents with strong secondary bonding ability show excellent performance in efficient and broadband THz wave generation, high crystal density, high thermal stability, and good bulk crystal growth ability.

Cortical origin of theta error signals.

A multi-scale approach elucidated the origin of the error-related-negativity (ERN), with its associated theta-rhythm, and the post-error-positivity (Pe) in macaque supplementary eye field (SEF). Using biophysical modeling, synaptic inputs to a subpopulation of layer-3 (L3) and layer-5 (L5) pyramidal cells (PCs) were optimized to reproduce error-related spiking modulation and inter-spike intervals. The intrinsic dynamics of dendrites in L5 but not L3 error PCs generate theta rhythmicity with random phases. Saccades synchronized the phases of the theta-rhythm, which was magnified on errors. Contributions from error PCs to the laminar current source density (CSD) observed in SEF were negligible and could not explain the observed association between error-related spiking modulation in L3 PCs and scalp-EEG. CSD from recorded laminar field potentials in SEF was comprised of multipolar components, with monopoles indicating strong electro-diffusion, dendritic/axonal electrotonic current leakage outside SEF, or violations of the model assumptions. Our results also demonstrate the involvement of secondary cortical regions, in addition to SEF, particularly for the later Pe component. The dipolar component from the observed CSD paralleled the ERN dynamics, while the quadrupolar component paralleled the Pe. These results provide the most advanced explanation to date of the cellular mechanisms generating the ERN.

Manipulation on radiation angles via spatially organized multipoles with vertical split-ring resonators.

Herein, the radiation patterns of single-split ring resonators (SSRRs) and double-split ring resonators (DSRRs) in the vertical direction are tailored by reconfiguring the resonator geometries. To design unequal arm lengths for controlling the floating split angle of the resonators and changing their electromagnetic multipole compositions, vertical metamaterials were fabricated using the metal-stress-driven self-folding method. The simulation results well agree with the experimental transmittance and reflectance results and demonstrate the geometry-dependent angle variation of the far-field radiation. Symmetric SSRRs and DSRRs radiate in the vertical and horizontal directions, respectively. With increasing pad shift, the radiation angle of the asymmetric SSRR completely rotates toward the horizontal direction along the ring plane, but the DSRRs can rotate only from 0° to 45° to the horizontal plane. Furthermore, by decomposing the multipoles into their constituents, we show that the directional scattering performance can be verified by manipulating the horizontal and vertical components of the electric dipoles. This novel combination of SSRRs and DSRRs can effectively and efficiently reconfigure the radiation direction in the infrared (IR) region, paving the way for color routers, metasurfaces, and directive IR emitters in compact optical metadevices.

Star-disk interactions in the strongly accreting T Tauri star S CrA N

Context. Classical T Tauri stars are thought to accrete material from their surrounding protoplanetary disks through funnel flows along their magnetic field lines. The classical T Tauri stars with high accretion rates (∼10−7 M⊙ yr−1) are ideal targets for testing this magnetospheric accretion scenario in a sustained regime. Aims. We constrained the accretion-ejection phenomena around the strongly accreting northern component of the S CrA young binary system (S CrA N) by deriving its magnetic field topology and its magnetospheric properties, and by detecting ejection signatures, if any. Methods. We led a two-week observing campaign on S CrA N with the ESPaDOnS optical spectropolarimeter at the Canada-France-Hawaii Telescope. We recorded 12 Stokes I and V spectra over 14 nights. We computed the corresponding least-squares deconvolution (LSD) profiles of the photospheric lines and performed Zeeman-Doppler imaging (ZDI). We analyzed the kinematics of noticeable emission lines, namely He I λ5876 and the first four lines of the Balmer series, which are known to trace the accretion process. Results. We found that S CrA N is a low-mass (0.8 M⊙) young (∼1 Myr) and fully convective object exhibiting strong and variable veiling (with a mean value of 7 ± 2), which suggests that the star is in a strong accretion regime. These findings could indicate a stellar evolutionary stage between Class I and Class II for S CrA N. We reconstructed an axisymmetric large-scale magnetic field (∼70% of the total energy) that is primarily located in the dipolar component, but has significant higher poloidal orders. From the narrow emission component radial velocity curve of He I λ5876, we derived a stellar rotation period of P* = 7.3 ± 0.2 days. We found a magnetic truncation radius of ∼2 R* which is significantly closer to the star than the corotation radius of ∼6 R*, suggesting that S CrA N is in an unstable accretion regime. That the truncation radius is quite smaller than the size of the Brγ line emitting region, as measured with the GRAVITY interferometer (∼8 R*), supports the presence of outflows, which is nicely corroborated by the line profiles presented in this work. Conclusions. The findings from spectropolarimetry are complementary to those provided by optical long-baseline interferometry, allowing us to construct a coherent view of the innermost regions of a young, strongly accreting star. The strong and complex magnetic field reconstructed for S CrA N is inconsistent with the observed magnetic signatures of the emission lines associated with the postshock region, however. We recommend a multitechnique synchronized campaign of several days to place more constrains on a system that varies on a timescale of about one day.

Simulations of dynamo action in slowly rotating M dwarfs: Dependence on dimensionless parameters

Aims. The aim of this study is to explore the magnetic and flow properties of fully convective M dwarfs as a function of rotation period Prot and magnetic Reynolds ReM and Prandlt numbers PrM. Methods. We performed three-dimensional simulations of fully convective stars using a star-in-a-box set-up. This set-up allows global dynamo simulations in a sphere embedded in a Cartesian cube. The equations of non-ideal magnetohydrodynamics were solved with the PENCIL CODE. We used the stellar parameters of an M5 dwarf with 0.21 M⊙ at three rotation rates corresponding to rotation periods (Prot) of 43, 61, and 90 days, and varied the magnetic Prandtl number in the range from 0.1 to 10. Results. We found systematic differences in the behaviour of the large-scale magnetic field as functions of rotation and PrM. For the simulations with Prot = 43 days and PrM ≤ 2, we found cyclic large-scale magnetic fields. For PrM &gt; 2, the cycles vanish and the field shows irregular reversals. In the simulations with Prot = 61 days for PrM ≤ 2, the cycles are less clear and the reversal are less periodic. In the higher PrM cases, the axisymmetric mean field shows irregular variations. For the slowest rotation case with Prot = 90 days, the field has an important dipolar component for PrM ≤ 5. For the highest PrM the large-scale magnetic field is predominantly irregular at mid-latitudes, with quasi-stationary fields near the poles. For the simulations with cycles, the cycle period length slightly increases with increasing ReM.

Sound absorption by a soft medium embedded with complex-shaped hard inclusions

Acoustic coatings for marine applications are commonly designed using a soft elastic matrix embedded with an array of resonant inclusions. In this work, a simple analytical approach to predict the acoustic performance of a soft elastic matrix embedded with hard inclusions of complex shape is presented. Utilizing analogies from fluid dynamics and electrostatics, a small number of well-known lumped parameters such as the added mass and capacitance are employed to relate the dominant dipole component of scattering of a complex-shaped hard inclusion to that of an equivalent sphere. Effective acoustic properties are then derived using a homogenization. The absorption coefficient of the coating for a range of complex shapes is compared with numerical simulations.

Seismic moment tensor inversion with theory errors from 2-D Earth structure: implications for the 2009–2017 DPRK nuclear blasts

SUMMARY Determining the seismic moment tensor (MT) from the observed waveforms with available Earth's structure models is known as seismic waveform MT inversion. It remains challenging for small to moderate-size earthquakes at regional scales. First, because shallow isotropic (ISO) and compensated linear vector dipole (CLVD) components of MT radiate similar long-period waveforms at regional distances, an intrinsic ISO-CVLD ambiguity impedes resolving seismic sources at shallow depths within the Earth's crust. Secondly, regional scales usually bear 3-D structures; thus, inaccurate Earth's structure models can cause unreliable MT solutions but are rarely considered a theory error in the MT inversion. So far, only the error of the 1-D earth model (1-D structural error), apart from data errors, has been explicitly modelled in the source studies because of relatively inexpensive computation. Here, we utilize a hierarchical Bayesian MT inversion to address the above problems. Our approach takes advantage of affine-invariant ensemble samplers to explore the ISO-CLVD trade-off space thoroughly and effectively. Station-specific time-shifts are also searched for as free parameters to treat the structural errors along specific source–station paths (2-D structural errors). Synthetic experiments demonstrate the method's advantage in resolving the dominating ISO components. The explosive events conducted by the Democratic People's Republic of Korea (DPRK) are well-studied, and we use them to demonstrate highly similar source mechanisms, including dominating ISO and significant CLVD components. The recovered station-specific time-shifts from the blasts present a consistent pattern, which provides a better understanding of the azimuthal variation of Earth's 2-D structures surrounding the events’ location.

X-ray emission from pre-main sequence stars with multipolar magnetic fields

ABSTRACT The large-scale magnetic fields of several pre-main sequence (PMS) stars have been observed to be simple and axisymmetric, dominated by tilted dipole and octupole components. The magnetic fields of other PMS stars are highly multipolar and dominantly non-axisymmetric. Observations suggest that the magnetic field complexity increases as PMS stars evolve from Hayashi to Henyey tracks in the Hertzsprung–Russell diagram. Independent observations have revealed that X-ray luminosity decreases with age during PMS evolution, with Henyey track PMS stars having lower fractional X-ray luminosities (LX/L*) compared to Hayashi track stars. We investigate how changes in the large-scale magnetic field topology of PMS stars influences coronal X-ray emission. We construct coronal models assuming pure axisymmetric multipole magnetic fields, and magnetic fields consisting of a dipole plus an octupole component only. We determine the closed coronal emitting volume, over which X-ray-emitting plasma is confined, using a pressure balance argument. From the coronal volumes, we determine X-ray luminosities. We find that LX decreases as the degree ℓ of the multipole field increases. For dipole plus octupole magnetic fields, we find that LX tends to decrease as the octupole component becomes more dominant. By fixing the stellar parameters at values appropriate for a solar mass PMS star, varying the magnetic field topology results in two orders of magnitude variation in LX. Our results support the idea that the decrease in LX as PMS stars age can be driven by an increase in the complexity of the large-scale magnetic field.