Soft Robot Based on Hyperelastic Buckling Controlled by Discontinuous Magnetic Field

2021 ◽  
pp. 1-35
Author(s):  
Yingdong Xu ◽  
Dongze Yan ◽  
Kai Zhang ◽  
Xuequan Li ◽  
Y.F. Xing ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Flexible Electronics ◽  
Nonlinear Deformation ◽  
Numerical Models ◽  
Optical Path ◽  
Magnetic Composite ◽  
Soft Robot ◽  
New Ideas ◽  
Cargo Transportation ◽  
The Magnetic Field

Abstract Most untethered magnetic soft robots are controlled by a continuously applied magnetic field. The accuracy of their motion depends completely on the accuracy of external magnetic field, consequently any slight disturbance may cause a dramatic change. Here, we report a new structure and driven method design to achieve a novel magnetic soft robot, which can achieve accurate and stable locomotion with weakly dependence on the magnetic field. The robot consists of functional magnetic composite materials with one central transportation platform and four crawling arms, whose motion is mainly based on hyperelastic buckling and recovering of the arms. The robot is capable of cargo transportation with multimodal locomotion, such as crawling, climbing and turning with high adaptability to various surfaces. The robot consumes much less driven energy compared to conventional magnetic robots. Moreover, we develop theoretical and numerical models to rationally design the precisely controlled robot. Our study shows applications in terms of transportation functions, such as for optical path adjustments and photographic tasks in complex circumstances. This work also provides new ideas on how to utilize nonlinear deformation more efficiently, one could combine the benefits for both the flexible electronics and actuation applications.

scholarly journals Stratification of canopy magnetic fields in a plage region

2020 ◽  
Vol 642 ◽  
pp. A210
Author(s):  
Roberta Morosin ◽  
Jaime de la Cruz Rodríguez ◽  
Gregal J. M. Vissers ◽  
Rahul Yadav
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Numerical Models ◽  
Lower Boundary ◽  
Field Approximation ◽  
Weak Field ◽  
Field Vector ◽  
Plage Region ◽  
The Magnetic Field

Context. The role of magnetic fields in the chromospheric heating problem remains greatly unconstrained. Most theoretical predictions from numerical models rely on a magnetic configuration, field strength, and connectivity; the details of which have not been well established with observational studies for many chromospheric scenarios. High-resolution studies of chromospheric magnetic fields in plage are very scarce or non existent in general. Aims. Our aim is to study the stratification of the magnetic field vector in plage regions. Previous studies predict the presence of a magnetic canopy in the chromosphere that has not yet been studied with full-Stokes observations. We use high-spatial resolution full-Stokes observations acquired with the CRisp Imaging Spectro-Polarimeter (CRISP) at the Swedish 1-m Solar Telescope in the Mg I 5173 Å, Na I 5896 Å and Ca II 8542 Å lines. Methods. We have developed a spatially-regularized weak-field approximation (WFA) method, based on the idea of spatial regularization. This method allows for a fast computation of magnetic field maps for an extended field of view. The fidelity of this new technique has been assessed using a snapshot from a realistic 3D magnetohydrodynamics simulation. Results. We have derived the depth-stratification of the line-of-sight component of the magnetic field from the photosphere to the chromosphere in a plage region. The magnetic fields are concentrated in the intergranular lanes in the photosphere and expand horizontally toward the chromosphere, filling all the space and forming a canopy. Our results suggest that the lower boundary of this canopy must be located around 400 − 600 km from the photosphere. The mean canopy total magnetic field strength in the lower chromosphere (z ≈ 760 km) is 658 G. At z = 1160 km, we estimate ⟨B∥⟩ ≈ 417 G. Conclusions. In this study we propose a modification to the WFA that improves its applicability to data with a worse signal-to-noise ratio. We have used this technique to study the magnetic properties of the hot chromospheric canopy that is observed in plage regions. The methods described in this paper provide a quick and reliable way of studying multi layer magnetic field observations without the many difficulties inherent to other inversion methods.

scholarly journals Numerical models of sunspot formation and fine structure

2012 ◽  
Vol 370 (1970) ◽  
pp. 3114-3128 ◽  
Author(s):  
Matthias Rempel
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
Large Scale ◽  
Numerical Models ◽  
Dynamical Evolution ◽  
Solar Interior ◽  
Small Scale ◽  
Wide Range ◽  
Umbral Dots ◽  
The Magnetic Field

Sunspots are central to our understanding of solar (and stellar) magnetism in many respects. On the large scale, they link the magnetic field observable in the photosphere to the dynamo processes operating in the solar interior. Properly interpreting the constraints that sunspots impose on the dynamo process requires a detailed understanding of the processes involved in their formation, dynamical evolution and decay. On the small scale, they give an insight into how convective energy transport interacts with the magnetic field over a wide range of field strengths and inclination angles, leading to sunspot fine structure observed in the form of umbral dots and penumbral filaments. Over the past decade, substantial progress has been made on both observational and theoretical sides. Advanced ground- and space-based observations have resolved, for the first time, the details of umbral dots and penumbral filaments and discovered similarities in their substructures. Numerical models have advanced to the degree that simulations of entire sunspots with sufficient resolution to resolve sunspot fine structure are feasible. A combination of improved helioseismic inversion techniques with seismic forward modelling provides new views on the subsurface structure of sunspots. In this review, we summarize recent progress, with particular focus on numerical modelling.

An Adaptive Magnetic Field Source for Magnetic Drug Fixation

2013 ◽  
Vol 1 (4) ◽  
pp. 20-33
Author(s):  
Alexandru Mihail Morega ◽  
Cristina Savastru ◽  
Mihaela Morega
Keyword(s):  
Magnetic Field ◽  
Numerical Models ◽  
Magnetic Drug Targeting ◽  
Spiral Coil ◽  
Field Source ◽  
Tissue Heating ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
Transfer Problems ◽  
The Magnetic Field

Magnetic drug targeting (MDT) therapy is usually controlled through the magnetic field produced by a permanent magnet; the solution proposed and assessed here considers a planar spiral coil (PSC) or a system of such coils, as an equally effective magnetic field source. The PSC may be designed to provide proper configurations of the magnetic field gradients, required for the generation of high magnetic body forces and to limit, in the same time, unwanted side effects affecting adjacent tissue (heating, excitable tissue stimulation). Simplified numerical models (2D projections) and more realistic structures (3D representations) are shown and analyzed in the paper; the electromagnetic and heat transfer problems are solved for different powering schemes applied to the coils.

scholarly journals Laboratory modeling of a field-aligned currents system generated by a flow of inner magnetospheric plasma

2021 ◽  
Vol 2067 (1) ◽  
pp. 012020
Author(s):  
A Chibranov ◽  
A Berezutsky ◽  
M Efimov ◽  
Y Zakharov ◽  
I Miroshnichenko ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energy Transfer ◽  
Laboratory Experiments ◽  
Numerical Models ◽  
Magnetospheric Plasma ◽  
Laboratory Modeling ◽  
Hot Jupiters ◽  
First Approximation ◽  
First Time ◽  
The Magnetic Field

Abstract For the first time in laboratory conditions, an experiment to simulate a system of field-aligned currents arising on planets such as Hot Jupiters in the presence of dense inner-magnetospheric plasma was carried out. The magnitude and transit time of field-aligned currents were measured as a function of the magnetic field using flat electrodes. The geometry of the expansion of plasma streams was pictured by gated camera. Also, in a first approximation, the efficiency of energy transfer from plasma flows to field-aligned currents was calculated. The results obtained create a basis for future laboratory experiments on this topic and improve existing numerical models.

scholarly journals Dynamo-based limit to the extent of a stable layer atop Earth’s core

2020 ◽  
Vol 222 (2) ◽  
pp. 1433-1448 ◽  
Author(s):  
Thomas Gastine ◽  
Julien Aubert ◽  
Alexandre Fournier
Keyword(s):  
Magnetic Field ◽  
Convective Flow ◽  
Thermal Evolution ◽  
Numerical Models ◽  
Small Scale ◽  
Stable Layer ◽  
Pass Filter ◽  
Low Pass Filter ◽  
The Core ◽  
The Magnetic Field

SUMMARY The existence of a stably stratified layer underneath the core–mantle boundary (CMB) has been recently revived by corroborating evidences coming from seismic studies, mineral physics and thermal evolution models. Such a layer could find its physical origination either in compositional stratification due to the accumulation of light elements at the top or the core or in thermal stratification due to the heat flux becoming locally subadiabatic. The exact properties of this stably stratified layer, namely its size $\mathcal {H}_s$ and the degree of its stratification characterized by the Brunt–Väisälä frequency N, are however uncertain and highly debated. A stable layer underneath the CMB can have crucial dynamical impacts on the geodynamo. Because of the inhibition of the convective motions, a stable layer is expected to primarily act as a low-pass filter on the magnetic field, smoothing out the rapidly varying and small-scale features by skin effect. To investigate this effect more systematically, we compute 70 global geodynamo models varying the size of the stably stratified layer from 0 to 300 km and its amplitude from N/Ω = 0 to N/Ω ≃ 50, Ω being the rotation rate. We show that the penetration of the convective flow in the stably stratified layer is controlled by the typical size of the convective eddies and by the local variations of the ratio N/Ω. Using quantitative measures of the degree of morphological semblance between the magnetic field obtained in numerical models and the geomagnetic field at the CMB, we establish an upper bound for the stable layer thickness $\mathcal {H}_s\lt (N/\Omega )^{-1} \mathcal {L}_s$, $\mathcal {L}_s$ being the horizontal size of the convective flow at the base of the stable layer. This defines a strong geomagnetic constraint on the properties of a stably stratified layer beneath the CMB. Unless unaccounted double-diffusive effects could drastically modify the dynamics of the stable layer, our numerical geodynamo models hence favour no stable stratification atop the core.

scholarly journals Forward modelling of MHD waves in braided magnetic fields

2020 ◽  
Vol 643 ◽  
pp. A86
Author(s):  
L. E. Fyfe ◽  
T. A. Howson ◽  
I. De Moortel
Keyword(s):  
Magnetic Field ◽  
Kinetic Energy ◽  
Magnetic Fields ◽  
Numerical Models ◽  
Lower Boundary ◽  
Mhd Waves ◽  
Doppler Velocity ◽  
Forward Modelling ◽  
The Waves ◽  
The Magnetic Field

Aims. We investigate synthetic observational signatures generated from numerical models of transverse waves propagating in complex (braided) magnetic fields. Methods. We consider two simulations with different levels of magnetic field braiding and impose periodic, transverse velocity perturbations at the lower boundary. As the waves reflect off the top boundary, a complex pattern of wave interference occurs. We applied the forward modelling code FoMo and analysed the synthetic emission data. We examined the line intensity, Doppler shifts, and kinetic energy along several line-of-sight (LOS) angles. Results. The Doppler shift perturbations clearly show the presence of the transverse (Alfvénic) waves. However, in the total intensity, and running difference, the waves are less easily observed for more complex magnetic fields and may be indistinguishable from background noise. Depending on the LOS angle, the observable signatures of the waves reflect some of the magnetic field braiding, particularly when multiple emission lines are available, although it is not possible to deduce the actual level of complexity. In the more braided simulation, signatures of phase mixing can be identified. We highlight possible ambiguities in the interpretation of the wave modes based on the synthetic emission signatures. Conclusions. Most of the observables discussed in this article behave in the manner expected, given knowledge of the evolution of the parameters in the 3D simulations. Nevertheless, some intriguing observational signatures are present. Identifying regions of magnetic field complexity is somewhat possible when waves are present; although, even then, simultaneous spectroscopic imaging from different lines is important in order to identify these locations. Care needs to be taken when interpreting intensity and Doppler velocity signatures as torsional motions, as is done in our setup. These types of signatures are a consequence of the complex nature of the magnetic field, rather than real torsional waves. Finally, we investigate the kinetic energy, which was estimated from the Doppler velocities and is highly dependent on the polarisation of the wave, the complexity of the background field, and the LOS angles.

scholarly journals Colliding Alfvénic wave packets in magnetohydrodynamics, Hall and kinetic simulations

2017 ◽  
Vol 83 (1) ◽  
Author(s):  
O. Pezzi ◽  
T. N. Parashar ◽  
S. Servidio ◽  
F. Valentini ◽  
C. L. Vásconez ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Distribution Function ◽  
Numerical Models ◽  
Wave Packets ◽  
Temperature Anisotropy ◽  
Proton Distribution ◽  
The Magnetic Field ◽  
Two Hybrid ◽  
Kinetic Features

The analysis of the Parker–Moffatt problem, recently revisited in Pezzi et al. (Astrophys. J., vol. 834, 2017, p. 166), is here extended by including Hall magnetohydrodynamics and two hybrid kinetic Vlasov–Maxwell numerical models. The presence of dispersive and kinetic features is studied in detail and a comparison between the two kinetic codes is also reported. Focus on the presence of non-Maxwellian signatures shows that – during the collision – regions characterized by strong temperature anisotropy are recovered and the proton distribution function displays a beam along the direction of the magnetic field, similar to some recent observations of the solar wind.

scholarly journals Inference of the chromospheric magnetic field configuration of solar plage using the Ca II 8542 Å line

2020 ◽  
Vol 644 ◽  
pp. A43 ◽  
Author(s):  
A. G. M. Pietrow ◽  
D. Kiselman ◽  
J. de la Cruz Rodríguez ◽  
C. J. Díaz Baso ◽  
A. Pastor Yabar ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Numerical Models ◽  
Signal To Noise Ratio ◽  
Field Configuration ◽  
Magnetic Field Configuration ◽  
Signal To Noise ◽  
Plage Region ◽  
Noise Ratio ◽  
The Magnetic Field

Context. It has so far proven impossible to reproduce all aspects of the solar plage chromosphere in quasi-realistic numerical models. The magnetic field configuration in the lower atmosphere is one of the few free parameters in such simulations. The literature only offers proxy-based estimates of the field strength, as it is difficult to obtain observational constraints in this region. Sufficiently sensitive spectro-polarimetric measurements require a high signal-to-noise ratio, spectral resolution, and cadence, which are at the limit of current capabilities. Aims. We use critically sampled spectro-polarimetric observations of the Ca II 8542 Å line obtained with the CRISP instrument of the Swedish 1-m Solar Telescope to study the strength and inclination of the chromospheric magnetic field of a plage region. This will provide direct physics-based estimates of these values, which could aid modelers to put constraints on plage models. Methods. We increased the signal-to-noise ratio of the data by applying several methods including deep learning and PCA. We estimated the noise level to be 1 × 10−3 Ic. We then used STiC, a non-local thermodynamic equilibrium inversion code to infer the atmospheric structure and magnetic field pixel by pixel. Results. We are able to infer the magnetic field strength and inclination for a plage region and for fibrils in the surrounding canopy. In the plage we report an absolute field strength of |B| = 440 ± 90 G, with an inclination of 10° ±16° with respect to the local vertical. This value for |B| is roughly double of what was reported previously, while the inclination matches previous studies done in the photosphere. In the fibrillar region we found |B| = 300 ± 50 G, with an inclination of 50° ±13°.

scholarly journals Relative alignment between dense molecular cores and ambient magnetic field: the synergy of numerical models and observations

2020 ◽  
Vol 494 (2) ◽  
pp. 1971-1987 ◽  
Author(s):  
Che-Yu Chen ◽  
Erica A Behrens ◽  
Jasmin E Washington ◽  
Laura M Fissel ◽  
Rachel K Friesen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Numerical Models ◽  
Field Orientation ◽  
Relative Significance ◽  
Star Forming ◽  
Ambient Magnetic Field ◽  
Core Field ◽  
Dense Cores ◽  
Background Magnetic Field ◽  
The Magnetic Field

ABSTRACT The role played by magnetic field during star formation is an important topic in astrophysics. We investigate the correlation between the orientation of star-forming cores (as defined by the core major axes) and ambient magnetic field directions in (i) a 3D magnetohydrodynamic simulation, (ii) synthetic observations generated from the simulation at different viewing angles, and (iii) observations of nearby molecular clouds. We find that the results on relative alignment between cores and background magnetic field in synthetic observations slightly disagree with those measured in fully 3D simulation data, which is partly because cores identified in projected 2D maps tend to coexist within filamentary structures, while 3D cores are generally more rounded. In addition, we examine the progression of magnetic field from pc to core scale in the simulation, which is consistent with the anisotropic core formation model that gas preferably flows along the magnetic field towards dense cores. When comparing the observed cores identified from the Green Bank Ammonia Survey and Planck polarization-inferred magnetic field orientations, we find that the relative core–field alignment has a regional dependence among different clouds. More specifically, we find that dense cores in the Taurus molecular cloud tend to align perpendicular to the background magnetic field, while those in Perseus and Ophiuchus tend to have random (Perseus) or slightly parallel (Ophiuchus) orientations with respect to the field. We argue that this feature of relative core–field orientation could be used to probe the relative significance of the magnetic field within the cloud.

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