Vertical Field Component Research Articles

Stringent limits on the magnetic field strength in the disc of TW Hya

Despite their importance in the star formation process, measurements of magnetic field strength in proto-planetary discs remain rare. While linear polarisation of dust and molecular lines can give insight into the magnetic field structure, only observations of the circular polarisation produced by Zeeman splitting provide a direct measurement of magnetic field strenghts. One of the most promising probes of magnetic field strengths is the paramagnetic radical CN. Here we present the first Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Zeeman splitting of CN in the disc of TW Hya. The observations indicate an excellent polarisation performance of ALMA, but fail to detect significant polarisation. An analysis of eight individual CN hyperfine components as well as a stacking analysis of the strongest (non-blended) hyperfine components yields the most stringent limits obtained so far on the magnetic field strength in a proto-planetary disc. We find that the vertical component of the magnetic field |Bz| < 0.8 mG (1σ limit). We also provide a 1σ toroidal field strength limit of <30 mG. These limits rule out some of the earlier accretion disc models, but remain consistent with the most recent detailed models with efficient advection. We detect marginal linear polarisation from the dust continuum, but the almost purely toroidal geometry of the polarisation vectors implies that his is due to radiatively aligned grains.

Hollow waveguide array with subwavelength dimensions as a space-variant polarization converter

A hollow waveguide array with subwavelength dimensions is demonstrated as a polarization converter. An individual waveguide in the array has a rectangular cross-section, which leads to an anisotropy of propagation constants and therefore to a phase shift between vertical and horizontal field components upon propagation. The hollow waveguide array was fabricated by a two-photon polymerization process followed by electrochemical deposition of gold. The fabricated array consists of about 2000×2500 hollow waveguide cells, each with dimensions of 1150 nm×930 nm and height of 2 μm. With these dimensions, the structure can, for example, be used at a wavelength of 1550 nm. Other wavelengths and phase shifts are accessible by changing the dimensions of the cross-section and the height. Since the widths of individual waveguides are variable, space-variant operation can be implemented.

The Umbral-penumbral Boundary in Sunspots in the Context of Magnetoconvection

Abstract Jurcak et al. have reported that, in a sample of more than 100 umbral cores in sunspots, the umbral-penumbral boundary (UPB) is characterized by a remarkably narrowly defined numerical value (1867 G) of the vertical component of the magnetic field. Gough & Tayler, in their study of magnetoconvection, showed that the onset of convection in the presence of a magnetic field is controlled by a parameter δ, which also depends on the vertical component of the field. Combining the Jurcak et al. result with various empirical models of sunspots leads us to propose the following hypothesis: the UPB occurs where the vertical field is strong enough to increase the effective adiabatic temperature gradient by ≥100% over its non-magnetic value.

Abrupt Changes in the Photospheric Magnetic Field, Lorentz Force, and Magnetic Shear during 15 X-class Flares

During major solar flares, the photospheric magnetic field of the flaring active region is often observed to change abruptly, permanently, and significantly. Here we analyze vector magnetograms covering 15 X-class flares observed in 11 active regions by the Solar Dynamic Observatory Helioseismic and Magnetic Imager. Resolving magnetic changes using a reference potential field, more complex magnetic field, Lorentz force, and magnetic shear changes could be analyzed than previously. In each case, physical and coherent patterns of change were found. Generally the dominant change was in the horizontal field component that strengthened in the central structure, accompanied there by a downward Lorentz force change and strengthening of horizontal magnetic shear consistent with magnetic implosion, with weaker changes of opposite sign in neighboring and peripheral regions including sunspots. In most cases this central structure was a strong, sheared photospheric magnetic neutral line, but in one case it was an isolated unipolar sunspot. Magnetic relaxation in the vertical direction was typical throughout the flaring regions. Unique in this study was the behavior at bald-patch structures during the X-class flares of 2017 September 6 in NOAA Active Region 12673. During the X9.3 flare, the horizontal and vertical field components weakened and the shear relaxed in horizontal and vertical directions, indicating a large free magnetic energy source for the flare. The magnetic changes at the bald patches exhibited evidence of organized vertical magnetic flux reduction during three X-class flares, not found at other structures, suggesting the greater possibilities of magnetic reconfiguration and energy release at bald patches.

Seam tracking during electron beam welding in the air

We study methods of beam positioning at the joint during Electron Beam Welding in the air. Traditional methods of automatic beam positioning at the joint are unacceptable during the Electron Beam Welding in the air because of the significant dispersion of electrons and the impossibility of the beam deflection inside the electron beam gun due to the presence of an airlock. For joint tracking, we propose using magnetic fields of the current in the welded parts created by the beam current. It is established that the vertical component of the magnetic field of the current in the welded parts is proportional to the beam deflection at the joint. A differential flux gate meter is used as a tracking device. We outline the functional diagram of the joint tracking device and address issues with error prevention methods.

Optimization of Asymmetric Magnetic Recording Heads Inclination Angle and Study the Characteristics for a Higher Bit Density Recording of HDD

This paper study the optimization of the asymmetric magnetic recording heads, the calculations demonstrate sharp field gradient performance for both the horizontal, and vertical field components for this type magnetic recording heads at large inclination and small distance between the head and underlayer. In addition, the characteristics for a higher bit density recording of HDD have been studied. These characteristics can be utilized to raise bit density in both recording method conventional and vertical, respectively.

APPLICATION OF THE FLUX BENDING EFFECT IN AN ACTIVE FLUX-GUIDE FOR LOW-NOISE PLANAR VECTOR TMR MAGNETIC SENSORS

A concept of a planar vector magnetic sensor comprising in-plane tunnel magnetoresistive (TMR) sensors and an active flux-guide (AFG) was introduced in this work. The AFG redirected the magnetic flux at high-frequency benefiting the vertical detection capability and lessening the noise of the TMR at low-frequency measurement. The vertical sensitivity of 19.5 V/T was almost the similar the in-plane sensitivity of 19.2 V/T. In addition, the 1-Hz field noise was suppressed from 6 nT/sqrt-Hz down to 0.4 nT/sqrt-Hz. The flux bending effect of the AFG was also verified by the angular measurements with the deflected angle was found to be about 50º. It revealed that the vertical field component was certainly detected by the in-plane sensor and the proposed method was a feasible technique for the development of the low-noise planar three-dimensional magnetic sensor.

Properties of the inner penumbral boundary and temporal evolution of a decaying sunspot

Context. It has been empirically determined that the umbra-penumbra boundaries of stable sunspots are characterized by a constant value of the vertical magnetic field. Aims. We analyzed the evolution of the photospheric magnetic field properties of a decaying sunspot belonging to NOAA 11277 between August 28–September 3, 2011. The observations were acquired with the spectropolarimeter on-board of the Hinode satellite. We aim to prove the validity of the constant vertical magnetic-field boundary between the umbra and penumbra in decaying sunspots. Methods. A spectral-line inversion technique was used to infer the magnetic field vector from the full-Stokes profiles. In total, eight maps were inverted and the variation of the magnetic properties in time were quantified using linear or quadratic fits. Results. We find a linear decay of the umbral vertical magnetic field, magnetic flux, and area. The penumbra showed a linear increase of the vertical magnetic field and a sharp decay of the magnetic flux. In addition, the penumbral area quadratically decayed. The vertical component of the magnetic field is weaker on the umbra-penumbra boundary of the studied decaying sunspot compared to stable sunspots. Its value seem to be steadily decreasing during the decay phase. Moreover, at any time of the sunspot decay shown, the inner penumbra boundary does not match with a constant value of the vertical magnetic field, contrary to what is seen in stable sunspots. Conclusions. During the decaying phase of the studied sunspot, the umbra does not have a sufficiently strong vertical component of the magnetic field and is thus unstable and prone to be disintegrated by convection or magnetic diffusion. No constant value of the vertical magnetic field is found for the inner penumbral boundary.

Proposal of an Experimental Methods for Electron Transpiration Cooling Effect

We present an analysis of the current state of electron transpiration cooling (ETC) effect studies as applied to high-temperature aerodynamics of hypersonic vehicles. The possibility of experimental study of the ETC effect using the plasma-dynamic device at the Ioffe Institute is considered. The distribution of vertical component of the electric field and gas temperature distribution across the glow discharge is measured. The region of homogeneity of plasma parameters is determined.

Magnetic Signals at Easter Island During the 2010 and 2015 Chilean Tsunamis Compared with Numerical Models

Tsunami flow across the geomagnetic field induces electric currents in both the ocean and the ionosphere. These currents generate secondary magnetic fields, observable at the seafloor and on land. Magnetic field disturbances during two Chilean tsunamis (2010 and 2015) were recorded at Easter Island Observatory. These tsunamis were produced after the earthquakes in Chile on February 27, 2010, at 06:34 UTC, and September 16, 2015, at 22:55 UTC, respectively. Differences between existing studies regarding the origin of the tsunamigenic disturbances, and the lack of studies using a numerical model for both the water velocity and the induced magnetic field, motivated us to compare magnetic records with computed magnetic fields for the two events. Modeled disturbances were calculated by applying the Biot–Savart law to tsunami simulations. Our model can calculate tsunami-induced perturbations in the vertical component of the geomagnetic field, obtaining a good agreement with the observations. We hypothesize that the magnetic measurements may be produced by a combination of oceanic and ionospheric electric currents. Our analysis further reveals that even a relatively small tsunami, such as the one produced by the 2015 $$M_\text {w}$$ 8.2 earthquake, induces an observable magnetic perturbation due to the water movement. Future improvements to our model may allow us to identify situations in which magnetic variations precede the tsunami arrival, thereby allowing early tsunami detection.

An Indoor Magnetic Exploration Survey

Magnetism is traditionally taught within the subject of electromagnetism at the undergraduate and graduate levels in physics courses, with the goal of establishing a solid foundation of the underlying physical mechanisms before advancing to more specialized topics. Oftentimes, a laboratory component of these courses involves practical, hands-on exercises that include, e.g., characterization of magnetic properties of materials and dipoles, measuring the vertical and horizontal component of a magnetic field generated by power supplies, or measuring the EMF induced in a wire coil due to a changing magnetic field. Here, we provide a complement to these activities with a discovery exercise akin to an outdoor magnetic field survey, one that leverages the ready availability of strong small rare earth magnets (“neo-magnets”).

Characterizing excitability of Lamb waves generated by electromagnetic acoustic transducers with coupled frequency domain models

Electromagnetic acoustic transducers (EMATs) are versatile non-contact ultrasonic transducers with relatively low transduction efficiency. A fundamental problem not answered completely yet is how the structure of an EMAT influences the generation of various Lamb wave modes. We tackle this problem with fully coupled frequency domain EMAT models where the underlying integro-differential equations are solved directly and the magnitudes of the phasors of the displacement components at a point in the middle plane of a plate are used to represent the strength of the S0 and A0 mode waves. Idealized single-wire, two-wire and wire bundle EMATs with uniform bias magnetic field and practical meander line and tightly wound EMATs with distributed bias field are studied. Polar plots of the idealized EMATs with swept angle of the bias field show that the vertical component of the bias field decides the strength of the S0 mode waves. Sweeping of the width of the magnet for the practical EMATs generates S0 mode curves that could be explained from the distribution of the vertical component of the bias field. This work represents the first attempt to solve the proposed problem of characterizing excitability of Lamb waves with EMATs quantitatively, via the model-based approach.

Incorporating Surface Convection into a 3D Babcock–Leighton Solar Dynamo Model

Abstract The convective flows observed on the photosphere (e.g., supergranulation, granulation) play a key role in the Babcock–Leighton (BL) process to generate large-scale polar fields from sunspot fields. In most surface flux transport (SFT) and BL dynamo models, the dispersal and migration of surface fields are modeled as an effective turbulent diffusion. Recent SFT models have incorporated explicit, realistic convective flows in order to improve the fidelity of convective transport but, to our knowledge, this has not yet been implemented in previous BL models. We present the first kinematic 3D Flux-Transport/BL model to explicitly incorporate realistic convective flows based on solar observations. Though we describe a means to generalize these flows to 3D, we find that the kinematic small-scale dynamo action they produce disrupts the operation of the cyclic dynamo. The cyclic solution is found by limiting the convective flow to act only on the vertical radial component of the magnetic field. The results obtained are generally in good agreement with the observed surface flux evolution and with non-convective models that have a turbulent diffusivity of the order of 3 × 1012 cm2 s−1 (300 km2 s−1). However, we find that the use of a turbulent diffusivity underestimates the dynamo efficiency, producing weaker mean fields and a shorter cycle than in the convective models. Also, the convective models exhibit bands of mixed polarity in the polar regions that have no counterpart in solar observations, and the poleward migration speed of poloidal flux is determined mainly by the meridional flow and the vertical diffusion.

Application of Magnetic Method in Shallow Investigation for Parts of ( Tall Arab-Kumbet ) Archaeological site / Southern Kirkuk City.

In this study a survey for the archaeological area of Tall-Arab (Kombat) has been done by magnetic method using ( MCL-2 microcomputer magnetometer ) which can measure the vertical component of the magnetic field. The studied area is located in Hay Al-Wasti which is located at about 15 km to the south of Kirkuk center. It covers about 1320 m2, with dimensions ( 120 * 110 )m. In the beginning a reconnaissance magnetic survey has done in order to choose the convenient measuring altitude of the sensor and the suitable station–spacing. Measurement were taken from 50 cm height above ground surface, with 10 m. station – spacing. The observed magnetic reading were corrected for the daily changing of earth magnetic field, while the normal correction was neglected because the space of the area is small and terrain correction was not applied because the area is nearly flat and sedimentary. Then a vertical field magnetic map was drawn from the corrected data. Many samples of archaeological bricks and soil were collected from the study to measure their magnetic susceptibility using the instrument ( SM-30 ). The magnetic data treated by applying different methods such as the graphical and the polynomial analyses for regional– residual separation. The qualitative and quantitative interpretation has done on the magnetic field map by using different limited ways and the central anomalies have been identified on the remaining and vertical magnetic field map. The quantitative interpretation has done using the fore ward modeling of chosen traverses by the program ( Mag2dc ). The qualitative and quantitative analyses showed that the negative anomaly are a result of the existence of canals, trenches or graves (cellars). Positive, linear-elongated anomaly reflect the existence of extended archaeological walls that have been built from mud or backed clay. Positive, circular or quasi-circular anomaly represent a base foundation for construction, which may have been destroyed or disintegrated by influence of weathering or other factors .

The Problem of the Height Dependence of Magnetic Fields in Sunspots

To understand the physics of sunspots, it is important to know the properties of their magnetic field, and especially its height stratification plays a substantial role. There are mainly two methods to assess this stratification, but they yield different magnetic gradients in the photospheric layers. Determinations based on the different origin of several spectral lines and the slope of their profiles result in gradients of -2 to -3G/km, or even steeper. This is similar for the total magnetic field strength and for the vertical component of the magnetic field. The other option is to determine the horizontal partial derivatives of the magnetic field, and with the condition divB=0, also the vertical derivative is known. With this method, gradients of -0.5 G/km and shallower are obtained. Obviously, these results do not agree. If chromospheric spectral lines are included, only shallow gradients around -0.5G/km are encountered. Shallow gradients are also found from gyro-resonance measurements in the radio wave range 300 - 2000GHz. Some indirect methods are also considered, but they cannot clarify the total picture. An analysis of a numerical simulation of a sunspot indicates a shallow gradient over a wide height range, but with slightly steeper gradients in deep layers. Several ideas to explain the discrepancy are also discussed. With no doubts cast on Maxwell's equations, the first one is to look at the uncertainties of the formation heights of spectral lines, but a wider range of these heights would require an extension of the solar photosphere that is incompatible with observations and the theory of stellar atmospheres. The problem of the height gradient of the magnetic field in sunspots is still not solved.

On Solving the Forward Problem of Gravimetry in Curvilinear and Cartesian Coordinates: Krasovskii’s Ellipsoid and Plane Modeling

Correcting the effects of the sphericity of the Earth in the results of the interpretation of gravimetric data is a topical issue in modern gravimetry. Estimating the error of the gravity field calculations due to the replacement of the spherical Earth model by the plane model is an important part of this problem. In this paper, a method is proposed for transforming the plane density models into spherical ones and vice versa. Algorithms for calculating the vertical component of gravity field for both model types are presented. For two extensive plane models of the Earth’s density, their transformation into spherical models is carried out and the resulting gravity fields are compared. The relative root mean square residuals between the fields calculated with this replacement are at most 5%.

Variations in Geophysical Fields during Hurricanes and Squalls

Based on complex analysis of the results of instrumental observations during strong atmospheric disturbances, it is shown that hurricanes and squalls are accompanied not only by high wind velocities, but also by high-amplitude microbaric variations, variations in amplitudes of the microseismic background, and the vertical component of the electric field. It is established that 1–4 hours before the onset, squalls and hurricanes are characterized by increased amplitudes of microbaric variations in the range of periods of 2–6 min, as well as by low-frequency variations in the electric field and variations in the microseismic background, which together with the meteorological parameters can be considered as a complex prognostic criterion of an impending hurricane (squall).

QUANTITATIVE ESTIMATION OF VOLUMETRIC ICE CONTENT IN FROZEN GROUND BY DIPOLE ELECTROMAGNETIC PROFILING METHOD

Volumetric estimation of the ice content in frozen soils is known as one of the main problems in the engineering geocryology and the permafrost geophysics. A new way to use the known method of dipole electromagnetic profiling for the quantitative estimation of the volumetric ice content in frozen soils is discussed. Investigations of foundation of the railroad in Yakutia (i.e. in the permafrost zone) were used as an example for this new approach. Unlike the conventional way, in which the permafrost is investigated by its resistivity and constructing of geo-electrical cross-sections, the new approach is aimed at the study of the dynamics of the process of attenuation in the layer of annual heat cycle in the field of high-frequency vertical magnetic dipole. This task is simplified if not all the characteristics of the polarization ellipse are measured but the only one which is the vertical component of the dipole field and can be the most easily measured. Collected data of the measurements were used to analyze the computational errors of the average values of the volumetric ice content from the amplitude attenuation of the vertical component of the dipole field. Note that the volumetric ice content is very important for construction. It is shown that usually the relative error of computation of this characteristic of a frozen soil does not exceed 20% if the works are performed by the above procedure using the key-site methodology. This level of accuracy meets requirements of the design-and-survey works for quick, inexpensive, and environmentally friendly zoning of built-up remote and sparsely populated territories of the Russian permafrost zone according to a category of a degree of the ice content in frozen foundations of engineering constructions.

The magnetic nature of umbra–penumbra boundary in sunspots

Context. Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between umbrae and penumbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Aim. Here, we aim at studying the magnetic nature of umbra–penumbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. Methods. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the umbral boundaries. We defined these umbra–penumbra boundaries by an intensity threshold and performed a statistical analysis of the magnetic field properties on these boundaries. Results. We statistically prove that the umbra–penumbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99%, in the range of 1849–1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the umbral size: the larger the umbra, the stronger and more horizontal the magnetic field at its boundary. Conclusions. The umbra and penumbra of sunspots are separated by a boundary that has hitherto been defined by an intensity threshold. We now unveil the empirical law of the magnetic nature of the umbra–penumbra boundary in stable sunspots: it is an invariant vertical component of the magnetic field.

Quantum-Cascade Vertical-Cavity Surface-Emitting Laser

This letter shows the possibility of stimulated emission in quantum cascades (QCs) embedded in a vertical cavity and proposes a first design for the QC vertical-cavity surface-emitting laser (QC VCSEL). In the proposed design, the top VCSEL mirror is a monolithic high-refractive-index contrast grating, which serves as both an optical coupler and as the region in which the vertical component of the electrical field is induced, enabling stimulating emission from the QCs. Using a three-dimensional, fully vectorial optical model combined with an electrical model and gain model, the distribution of the optical field, threshold current, emitted optical power, and wall-plug efficiency of a 9 $\mu \text{m}$ AlInAs/InGaAs/InP QC VCSEL are simulated.