Journal articles: 'Corona polarization'

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Ursini, F., G. Matt, S. Bianchi, A. Marinucci, M. Dovčiak, and W. Zhang. "Prospects for differentiating extended coronal geometries in AGNs with the IXPE mission." Monthly Notices of the Royal Astronomical Society 510, no. 3 (December 24, 2021): 3674–87. http://dx.doi.org/10.1093/mnras/stab3745.

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ABSTRACT X-ray polarimetry can potentially constrain the unknown geometrical shape of active galactic nucleous (AGN) coronae. We present simulations of the X-ray polarization signal expected from AGN coronae, assuming three different geometries, namely slab, spherical, and conical. We use the fully relativistic Monte Carlo Comptonization code monk to compute the X-ray polarization degree and angle. We explore different coronal parameters such as shape, size, location, and optical depth. Different coronal geometries give a significantly different X-ray polarization signal. A slab corona yields a high polarization degree, up to 14 per cent depending on the viewing inclination; a spherical corona yields low values, about 1–3 per cent, while a conical corona yields intermediate values. We also find a difference of 90 degrees in polarization angle between the slab corona and the spherical or conical coronae. Upcoming X-ray polarimetry missions like IXPE will allow us to observationally distinguish among different coronal geometries in AGNs for the first time.

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Liang, Y., Z. Q. Qu, Y. J. Chen, Y. Zhong, Z. M. Song, and S. Y. Li. "Registration and imaging polarimetry of the Fe 6374 Å red coronal line during the 2017 total solar eclipse." Monthly Notices of the Royal Astronomical Society 503, no. 4 (April 14, 2021): 5715–29. http://dx.doi.org/10.1093/mnras/stab463.

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ABSTRACT Strict registration is critical for imaging polarimetry; a highly accurate registration approach to the coronal image and imaging polarimetry of the Fe 6374 Å red coronal line have been researched in this paper. In order to improve the registration accuracy, this paper proposes the idea of image enhancement based on blind deconvolution combined with noise-adaptive fuzzy equalization algorithms. After image enhancement, the cross-correlation registration algorithm achieves better results. To diagnose a low-temperature corona, the polarization brightness of the red coronal line data and the Mauna Loa Solar Observatory (MLSO)/KCor data are compared to study the structural features and polarization information of the inner corona. We found that the polarization brightness radiation of the red coronal line has overall features similar to that of the MLSO/KCor data, but it has more detailed features, such as the cavity, polar plume, and interplume characteristics. Active regions, polar plumes, and interplumes show similar performance in red coronal line intensity, polarization brightness, degree of linear polarization, K-corona, and electron density along with the radial height. An interesting finding is that the polarization brightness of the red coronal line changes drastically along with the radial height across the cavity above the solar west limb, while neither the K-corona nor the electron density changes obviously. This seems to be a piece of possible evidence indicating that the red coronal line is not unpolarized in the cavity region.

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Merzlyakov, V., Ts Tsvetkov, L. Starkova, and R. Miteva. "Polarization of white-light solar corona and sky polarization effect during total solar eclipse on March 29, 2006." Serbian Astronomical Journal, no. 199 (2019): 83–87. http://dx.doi.org/10.2298/saj190620005m.

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Ground-based total solar eclipse observations are still the key method for coronal investigations. The question about its white-light degree of polarization remains unanswered. There are hypotheses claiming that the degree of polarization in certain regions of the corona may be higher than the maximal theoretically predicted value determined by Thomson scattering. We present polarization of the white-light solar corona observations obtained by three different teams during the March 29, 2006 solar total eclipse. We give an interpretation on how the polarization of the sky impacts brightness of the polarized solar corona, depending on the landscape during the totality. Moreover, it is shown that the singular polarization points of the corona are in linear dependence with the height of the Sun above the horizon.

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Lebedev, A. N., I. A. Belenko, O. I. Bougaenko, I. S. Kim, O. T. Matsuura, E. Picazzio, R. P. Livi, and Silvia H. B. Liv. "Eclipse Polarimetric Research of Prominences." International Astronomical Union Colloquium 167 (1998): 66–69. http://dx.doi.org/10.1017/s0252921100047308.

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AbstractA polarization analysis of E–limb prominences on November 3, 1994 is presented. Photometry and data reduction of 24 prominence pictures based on IDL software and Stokes–vector presentation and applied to Hα emission resulted in an accuracy of 1–1.5% in determination of the polarization degree and of 1.5–2.0° in the polarization direction. Distributions of polarization degree (polarization images) for prominences and the “white light” corona are presented. A polarization degree of 2–5% for prominences and 10–25% for the nearby white light corona are found. The polarization direction is found to be tangential to the solar limb. It is noted that eclipse observations can provide a powerful method for deriving the magnetic field at high altitudes in the coronal volume.

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Kulidzanishvili, V., A. Mayer, V. Mayer, and S. Danik. "The Corona Electropolarimetry during July 11, 1991 Solar Eclipse." International Astronomical Union Colloquium 144 (1994): 529–33. http://dx.doi.org/10.1017/s0252921100025987.

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AbstractThe electropolarimetry of July 11, 1991 eclipse solar corona using the new photoelectric polarimeter of Abastumani Astrophysical Observatory of the Georgian Academy of Sciences, equipped with the IBM computer, is described in this paper.By means of measurable values the isopolarization lines were constructed, which turned out to be stretched along the coronal streamers. The polarization plane has, entirely, radial direction; however, small but real deviations from radiality were established. The errors of measurements of intensity, polarization degree and polarization plane direction are evaluated.

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Megha, A., M. Sampoorna, K. N. Nagendra, and K. Sankarasubramanian. "Coronal magnetic field measurements using forbidden emission lines." Proceedings of the International Astronomical Union 13, S340 (February 2018): 61–62. http://dx.doi.org/10.1017/s1743921318001023.

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AbstractThe polarization measurement of coronal forbidden emission lines is the most promising method of determining the direction of magnetic fields in the corona. A classical theory for the forbidden lines was presented in Megha et al. (2017) for the case of arbitrary strength magnetic fields. Here we apply that theoretical formalism to study the effect of density distributions, magnetic field configurations, and velocity fields on the Stokes profiles formed in corona. For illustrations we use the atomic parameters of the [Fe xiii] 10747 Å coronal forbidden line.

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Liu, Yu, Haosheng Lin, and Jeff Kuhn. "Coronal magnetic fields from the inversion of linear polarization measurements." Proceedings of the International Astronomical Union 5, S264 (August 2009): 96–98. http://dx.doi.org/10.1017/s174392130999247x.

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AbstractReal 3-D coronal magnetic field reconstruction is expected to be made based on the technologies of IR spectrometry and tomography, in which the data from other wavelengths can be used as critical reference. Our recent studies focused on this issue are briefly reviewed in this paper. Liu & Lin (2008) first evaluated the validity of potential field source surface model applied to one of five limb regions in the corona by comparing the theoretical polarization maps with SOLARC observations in the IR Fe XIII 10747 Å forbidden coronal emission line (CEL). The five limb coronal regions were then studied together in order to study the spatial relation between the bright EUV features on the solar disk and the inferred IR emission sources, which were obtained from the inversion of the SOLARC linear polarization (LP) measurements (Liu 2009). The inversion for each fiber data in the field of view was made by finding the best location where the difference between the synthesized and the observed polarizations reaches the minimum in the integration path along the line of sight. We found a close relationship between the inferred IR emission source locations and the EUV strong emission positions.

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Zhang, J. W., F. K. Gao, H. C. Sun, C. Putson, and R. T. Liu. "Electrostrictive energy conversion property of cellular electrets after corona discharge." International Journal of Modern Physics B 32, no. 07 (March 5, 2018): 1850069. http://dx.doi.org/10.1142/s0217979218500698.

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In this paper, the authors present the electrostrictive energy conversion ability of cellular electrets after the high-voltage corona polarization. Moreover, the electrostrictive effect of such foamed polymer before and after corona polarization has also been compared and discussed. The enhancement of electrostrictive effect of cellular electrets after corona polarization was observed. In particular, the impact on the electrostrictive effect of the macroscopic electric dipoles inside of cellular polymer which are generated by high-voltage corona poling procedure has been investigated. The present research has promoted the development of the application of electret in the field of energy conversion, actuator, transducers, etc.

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Gelfreikh, G. B., V. M. Bogod, V. E. Abramov-Maximov, and S. V. Tsvetkov. "Measurements of Solar Magnetic Fields Using Radio Observations with the RATAN-600." International Astronomical Union Colloquium 141 (1993): 271–74. http://dx.doi.org/10.1017/s0252921100029213.

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AbstractThree ways of measuring magnetic fields in the corona and chromosphere have been developed based on spectral polarization observations with high spatial resolution using the radio telescope RATAN-600. The methods rely on effects from the theory of the generation and propagation of microwaves in the solar atmosphere: thermal bremsstrahlung, thermal cyclotron emission, and inversion of the polarization sign in quasi-transverse field regions. The new radio spectrograph (PAS) at the RATAN-600 resulted in higher accuracy measurements of the strength and structure of coronal magnetic fields. Using observations made with the PAS on 1992 January 10, we show that the magnetic field strength in the lower corona above all large sunspots can be measured with an accuracy ≈ 3%. The correlation with photospheric magnetic fields is good, ‘radio’ magnetic fields being weaker by ≈ 20%.

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Saint-Hilaire, Pascal, Juan Carlos Martínez Oliveros, and Hugh S. Hudson. "Thomson Scattering in the Lower Corona in the Presence of Sunspots." Astrophysical Journal 923, no. 2 (December 1, 2021): 276. http://dx.doi.org/10.3847/1538-4357/ac2f9b.

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Abstract Polarized scattered light from low (few tens of megameter altitudes) coronal transients has been recently reported in Solar Dynamics Observatory/Helioseismic and Magnetic Image (HMI) observations. In a classic paper, Minnaert (1930) provided an analytic theory of polarization via electron scattering in the corona. His work assumed axisymmetric input from the photosphere with a single-parameter limb-darkening function. This diagnostic has recently been used to estimate the free-electron number and mass of HMI transients near the solar limb, but it applies equally well to any coronal material, at any height. Here we extend his work numerically to incorporate sunspots, which can strongly effect the polarization properties of the scattered light in the low corona. Sunspot effects are explored first for axisymmetric model cases, and then applied to the full description of two sunspot groups as observed by HMI. We find that (1) as previously reported by Minnaert, limb darkening has a strong influence, usually increasing the level of linear polarization tangential to the limb; (2) unsurprisingly, the effects of the sunspot generally increase at the lower scatterer altitudes, and increase the larger the sunspot is and the closer to their center the scatterer subpoint is; (3) assuming the Stokes Q > 0 basis to be tangential to the limb, sunspots typically decrease the Stokes Q/I polarization and the perceived electron densities below the spotless case, sometimes dramatically; and (4) typically, a sizeable non-zero Stokes U/I polarization component will appear when a sunspot’s influence becomes non-negligible. However, that is not true in rare cases of extreme symmetry (e.g., scattering mass at the center of an axisymmetric sunspot). The tools developed here are generally applicable to an arbitrary image input.

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11

Gelfreikh, G. B. "Radio Measurements of Coronal Magnetic Fields." International Astronomical Union Colloquium 144 (1994): 21–28. http://dx.doi.org/10.1017/s0252921100024933.

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AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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Krawczynski, H., and B. Beheshtipour. "New Constraints on the Spin of the Black Hole Cygnus X-1 and the Physical Properties of its Accretion Disk Corona." Astrophysical Journal 934, no. 1 (July 1, 2022): 4. http://dx.doi.org/10.3847/1538-4357/ac7725.

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Abstract We present a new analysis of NuSTAR and Suzaku observations of the black hole Cygnus X-1 in the intermediate state. The analysis is performed using kerrC, a new model for analyzing spectral and spectropolarimetric X-ray observations of black holes. kerrC builds on a large library of simulated black holes in X-ray binaries. The model accounts for the X-ray emission from a geometrically thin, optically thick accretion disk, the propagation of the X-rays through the curved black hole spacetime, the reflection off the accretion disk, and the Comptonization of photons in coronae of different 3D shapes and physical properties before and after the reflection. We present the results from using kerrC for the analysis of archival NuSTAR and Suzaku observations taken on 2015 May 27–28. The best wedge-shaped corona gives a better fit than the cone-shaped corona. Although we included cone-shaped coronae in the funnel regions above and below the black hole to resemble to some degree the common assumption of a compact lamppost corona hovering above and/or below the black hole, the fit chooses a very large version of this corona that makes it possible to Comptonize a sufficiently large fraction of the accretion disk photons to explain the observed power-law emission. The analysis indicates a black hole spin parameter a (−1 ≤ a ≤ 1) between 0.861 and 0.921. The kerrC model provides new insights into the radial distribution of the energy flux of returning and coronal emission irradiating the accretion disk. kerrC furthermore predicts small polarization fractions around 1% in the 2–8 keV energy range of the recently launched Imaging X-ray Polarimetry Explorer.

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Sidaravicius, J., T. Lozovsky, J. Jurksus, R. Maldzius, K. Backfolk, and P. Sirviö. "Polarization behaviour of paper during corona charging." Journal of Electrostatics 71, no. 1 (February 2013): 35–40. http://dx.doi.org/10.1016/j.elstat.2012.11.003.

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Badalyan, O. G., and M. A. Livshits. "Analysis of the green-line corona polarization." Astronomical & Astrophysical Transactions 20, no. 3 (September 2001): 575–86. http://dx.doi.org/10.1080/10556790108213602.

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Ayala, Alejandro, Isabel Dominguez, Ivonne Maldonado, and Maria Elena Tejeda-Yeomans. "An Improved Core-Corona Model for Λ and Λ Polarization in Relativistic Heavy-Ion Collisions." Particles 6, no. 1 (March 3, 2023): 405–15. http://dx.doi.org/10.3390/particles6010022.

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Due to its sensitivity to the dynamics of strongly interacting matter subject to extreme conditions, hyperon global polarization has become an important observable to study the system created in relativistic heavy-ion collisions. Recently, the STAR and HADES collaborations have measured the global polarization of both Λ and Λ¯ produced in semi-central collisions in a wide range of collision energies. The polarization excitation functions show an increasing trend as the collision energy decreases, with the increase being more pronounced for the Λ¯. In this work, we make a summary of a core-corona model that we have developed to quantify the global polarization contributions from Λ and Λ¯ created in different regions of the fireball. The core-corona model assumes that Λs and Λ¯s are produced in both regions, the high-density core and the lower density corona, with different relative abundances which modulate the polarization excitation function. We have shown that the model works well for the description of experimental results. The global polarization excitation functions computed with the model show a peak at different collision energies in the region sNN≤10 GeV. Finally, we discuss and report on the model global polarization predictions for BES-II, NICA and CBM at FAIR and HADES energies.

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Spangler, Steven R., and Catherine A. Whiting. "Radio remote sensing of the corona and the solar wind." Proceedings of the International Astronomical Union 4, S257 (September 2008): 529–41. http://dx.doi.org/10.1017/s1743921309029834.

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AbstractModern radio telescopes are extremely sensitive to plasma on the line of sight from a radio source to the antenna. Plasmas in the corona and solar wind produce measurable changes in the radio wave amplitude and phase, and the phase difference between wave fields of opposite circular polarization. Such measurements can be made of radio waves from spacecraft transmitters and extragalactic radio sources, using radio telescopes and spacecraft tracking antennas. Data have been taken at frequencies from about 80 MHz to 8000 MHz. Lower frequencies probe plasma at greater heliocentric distances. Analysis of these data yields information on the plasma density, density fluctuations, and plasma flow speeds in the corona and solar wind, and on the magnetic field in the solar corona. This paper will concentrate on the information that can be obtained from measurements of Faraday rotation through the corona and inner solar wind. The magnitude of Faraday rotation is proportional to the line of sight integral of the plasma density and the line-of-sight component of the magnetic field. Faraday rotation provides an almost unique means of estimating the magnetic field in this part of space. This technique has contributed to measurement of the large scale coronal magnetic field, the properties of electromagnetic turbulence in the corona, possible detection of electrical currents in the corona, and probing of the internal structure of coronal mass ejections (CMEs). This paper concentrates on the search for small-scale coronal turbulence and remote sensing of the structure of CMEs. Future investigations with the Expanded Very Large Array (EVLA) or Murchison Widefield Array (MWA) could provide unique observational input on the astrophysics of CMEs.

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Ramesh, R., C. Kathiravan, and E. Ebenezer Chellasamy. "Circular Polarization Observations of Type II Solar Radio Bursts and the Coronal Magnetic Field." Astrophysical Journal 932, no. 1 (June 1, 2022): 48. http://dx.doi.org/10.3847/1538-4357/ac6f05.

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Abstract It is well known that magnetic field strength (B) in the solar corona can be calculated using the Alfvén Mach number (M A ) and Alfvén speed (v A ) of the magnetohydrodynamic shock waves associated with coronal type II radio bursts. We show that observations of weak circularly polarized emission associated with the harmonic component of the type II bursts provide independent and consistent estimates of B. For the coronal type II burst observed on 2021 October 9, we obtained B ≈1.5 G and ≈1.9 G at a heliocentric distance (r) of ≈1.8 R ⊙, using the above two techniques, respectively.

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Yang, Huayan, Sijia Lu, Shengkun Wang, Lihong Liu, Bo Zhu, Shaoning Yu, Shouning Yang, and Junbiao Chang. "Evolution of the protein corona affects macrophage polarization." International Journal of Biological Macromolecules 191 (November 2021): 192–200. http://dx.doi.org/10.1016/j.ijbiomac.2021.09.081.

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Lee, Jeongwoo, and Stephen M. White. "Microwave Depolarization above Sunspots." Proceedings of the International Astronomical Union 6, S273 (August 2010): 487–90. http://dx.doi.org/10.1017/s1743921311015857.

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AbstractMicrowave emissions from sunspots are circularly polarized in the sense of rotation (right or left) determined by the polarity (north or south) of coronal magnetic fields. However, they may convert into unpolarized emissions under certain conditions of magnetic field and electron density in the corona, and this phenomenon of depolarization could be used to derive those parameters. We propose another diagnostic use of microwave depolarization based on the fact that an observed depolarization strip actually represents the coronal magnetic polarity inversion line (PIL) at the heights of effective mode coupling, and its location itself carries information on the distribution of magnetic polarity in the corona. To demonstrate this diagnostic utility we generate a set of magnetic field models for a complex active region with the observed line-of-sight magnetic fields but varying current density distribution and compare them with the 4.9 GHz polarization map obtained with the Very Large Array (VLA). The field extrapolation predicts very different locations of the depolarization strip in the corona depending on the amount of electric currents assumed to exist in the photosphere. Such high sensitivity of microwave depolarization to the coronal magnetic field can therefore be useful for validating electric current density maps inferred from vector magnetic fields observed in the photosphere.

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Sýkora, J., J. Rybák, and P. Ambrož. "FeXIV Line Emission Polarization of the July 11, 1991 Solar Corona." International Astronomical Union Colloquium 144 (1994): 541–47. http://dx.doi.org/10.1017/s0252921100026002.

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AbstractHigh resolution images, obtained during July 11, 1991 total solar eclipse, allowed us to estimate the degree of solar corona polarization in the light of FeXIV 530.3 nm emission line and in the white light, as well. Very preliminary analysis reveals remarkable differences in the degree of polarization for both sets of data, particularly as for level of polarization and its distribution around the Sun’s limb.

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Marinucci, A., D. Porquet, F. Tamborra, S. Bianchi, V. Braito, A. Lobban, F. Marin, et al. "A deep X-ray view of the bare AGN Ark 120." Astronomy & Astrophysics 623 (February 25, 2019): A12. http://dx.doi.org/10.1051/0004-6361/201834454.

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Context. The spectral shape of the hard X-ray continuum of Active Galactic Nuclei (AGN) can be ascribed to inverse Compton scattering of optical/UV seed photons from the accretion disc by a hot corona of electrons. This physical process produces a polarization signal which is strongly sensitive to the geometry of the scattering medium (i.e. the hot corona) and of the radiation field. Aims. MoCA (Monte Carlo code for Comptonisation in Astrophysics) is a versatile code which allows for different geometries and configurations to be tested for Compton scattering in compact objects. A single photon approach is considered as well as polarisation and Klein–Nishina effects. In this work, we selected four different geometries for the scattering electrons cloud above the accretion disc, namely an extended slab, an extended spheroid and two compact spheroids. Methods. We discuss the first application of the MoCA model to reproduce the hard X-ray primary continuum of the bare Seyfert 1 galaxy Ark 120, using different geometries for the hot corona above the accretion disc. The lack of extra-Galactic absorption along the line of sight makes it an excellent target for studying the accretion disc-corona system. We report on the spectral analysis of the simultaneous 2013 and 2014 XMM-Newton and NuSTAR observations of the source. Results. A general agreement is found between the best fit values of the hot coronal parameters obtained with MoCA and the ones inferred using other Comptonisation codes from the literature. The expected polarization signal from the best fits with MoCA is then presented and discussed, in view of the launch in 2021 of the Imaging X-ray Polarimetry Explorer (IXPE). Conclusions. We find that none of the tested geometries for the hot corona (extended slab and extended/compact spheroids) can be statistically preferred, based on spectroscopy solely. In the future, an IXPE observation less than 1 Ms long will clearly distinguish between an extended slab or a spherical hot corona.

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Fang, Y., P. L. Lamy, and A. Llebaria. "Synthetic Maps of the Brightness and Polarization of the F-Corona." International Astronomical Union Colloquium 126 (1991): 195–98. http://dx.doi.org/10.1017/s0252921100066768.

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AbstractThe Wide-Field Light and Spectrometric Coronograph (LASCO) to be flown on SOHO in 1995 is designed to perform accurate photopolarimetric observations of the solar corona. For simulation purpose but also to have a two-dimensional model of the F-corona, we have realized synthetic maps of its brightness and polarization

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Habbal, Shadia Rifai, and Richard Woo. "Origin of the Solar Wind and Open Coronal Magnetic Structures." Symposium - International Astronomical Union 219 (2004): 587–98. http://dx.doi.org/10.1017/s0074180900182622.

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Identifying the regions of open magnetic structures in the corona, namely regions where field lines expand outwards into interplanetary space, is equivalent to establishing the origin of the solar wind at the Sun. A review of recent studies, based on the comparison of the distribution, as a function of latitude, of density and velocity in the inner corona and in interplanetary space, is presented. It is shown how, at solar minimum, this comparison leads to the unexpected result that the fast solar wind expands indiscriminately from a significant fraction of the solar surface, not limited to polar coronal holes, as has been believed for the past three decades. It is also shown how polarization measurements of coronal forbidden lines, which yield the direction of the coronal magnetic field, lend further support to this result. The implications of these findings are that a significant fraction of the solar magnetic field is primarily open, expanding almost radially into interplanetary space, carrying with it the imprint of the distribution of density in the corona, while the ‘closed’ structures contribute a small fraction to the overall filling factor of coronal density structures. Furthermore, the solar wind particle flux is found to be correlated with density, implying a higher mass loss rate from the higher density quiet Sun regions, and the likelihood of a solar cycle dependence in the mass loss rate, as the are of polar coronal holes decreases with increased solar activity.

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Kansabanik, Devojyoti, Apurba Bera, Divya Oberoi, and Surajit Mondal. "Tackling the Unique Challenges of Low-frequency Solar Polarimetry with the Square Kilometre Array Low Precursor: Pipeline Implementation." Astrophysical Journal Supplement Series 264, no. 2 (February 1, 2023): 47. http://dx.doi.org/10.3847/1538-4365/acac79.

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Abstract The dynamics and the structure of the solar corona are determined by its magnetic field. Measuring coronal magnetic fields is, however, extremely hard. The polarization of low-frequency radio emissions has long been recognized as one of the few effective observational probes of magnetic fields in the mid and high corona. However, the extreme intrinsic variability of this emission, the limited ability of most of the available existing instrumentation (until recently) to capture it, and the technical challenges involved have all contributed to its use being severely limited. The high dynamic-range spectropolarimetric snapshot imaging capability that is needed for radio coronal magnetography is now within reach. This has been enabled by the confluence of data from the Murchison Widefield Array (MWA), a Square Kilometre Array (SKA) precursor, and our unsupervised and robust polarization calibration and imaging software pipeline dedicated to the Sun—Polarimetry using the Automated Imaging Routine for Compact Arrays of the Radio Sun (P-AIRCARS). Here, we present the architecture and implementation details of P-AIRCARS. Although the present implementation of P-AIRCARS is tuned to the MWA, the algorithm itself can easily be adapted for future arrays, such as SKA1-Low. We hope and expect that P-AIRCARS will enable exciting new science with instruments like the MWA, and that it will encourage the wider use of radio imaging in the larger solar physics community.

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Hundhausen, A. J., D. G. Sime, and B. C. Low. "Solar Coronal Mass Ejections." Symposium - International Astronomical Union 140 (1990): 16. http://dx.doi.org/10.1017/s0074180900189399.

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In addition to the more or less steady solar wind, the Sun also ejects mass in highly time dependent events taking place in the corona once every few days at solar activity minimum and as often as three times a day at solar activity maximum (Hundhausen 1988, Low 1986). These events involve large scale reconfiguration of the corona with an expulsion of some 1015g of ionized material into interplanetary space. The High Altitude Observatory (HAO) operates a groundbased internally occulted coronagraph at Mauna Loa, Hawaii, with a field of view of the corona from 1.2 to 2.2R⊙ in heliocentric distance, registering polarization brightness. A second instrument at the same site in Hawaii observes the solar limb in Hα emission to detect chromospheric material from the limb out to 1.5R⊙. HAO also operates an externally occulted coronagraph/polarimeter onboard the NASA Solar Maximum Mission Satellite (SMM) launched in 1980, capitalizing on the advantage of space with a field of view from 1.5 to 6R⊙ to cover the fainter outer corona. Coronal mass ejections involve magnetic field reconfiguration from high in the corona down to the base lying below 1.1R⊙. Important physical insights can be had when simultaneous observations by HAO's three instruments are put together with a common scale and orientation to reveal a mass ejection in the full extent of the solar atmosphere from the limb outward. Combined observations of two mass ejections are presented, one associated with an eruptive prominence and the the other associated with a flare. The significance of these two events is that in both cases, the mass ejection was in fully developed motion and had traveled high into the corona well before the onset of the associated prominence or flare eruption, pointing to an instability in the large scale coronal magnetic field as the underlying cause of the global reconfiguration.

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Long, Xiangyun, Hua Feng, Hong Li, Jiahuan Zhu, Qiong Wu, Jiahui Huang, Massimo Minuti, et al. "A Significant Detection of X-ray Polarization in Sco X-1 with PolarLight and Constraints on the Corona Geometry." Astrophysical Journal Letters 924, no. 1 (January 1, 2022): L13. http://dx.doi.org/10.3847/2041-8213/ac4673.

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Abstract We report the detection of X-ray polarization in the neutron-star low-mass X-ray binary Scorpius (Sco) X-1 with PolarLight. The result is energy-dependent, with a nondetection in 3–4 keV but a 4σ detection in 4–8 keV; it is also flux-dependent in the 4–8 keV band, with a nondetection when the source displays low fluxes but a 5σ detection during high fluxes, in which case we obtain a polarization fraction of 0.043 ± 0.008 and a polarization angle of 52.°6 ± 5.°4. This confirms a previous marginal detection with OSO-8 in the 1970s and marks Sco X-1 as the second astrophysical source with a significant polarization measurement in the keV band. The measured polarization angle is in line with the jet orientation of the source on the sky plane (54°), which is supposedly the symmetry axis of the system. Combining previous spectral analysis, our measurements suggest that an optically thin corona is located in the transition layer under the highest accretion rates, and disfavor the extended accretion disk corona model.

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Schad, Thomas A., Sarah A. Jaeggli, and Gabriel I. Dima. "Thomson Scattering above Solar Active Regions and an Ad Hoc Polarization Correction Method for the Emissive Corona." Astrophysical Journal 933, no. 1 (July 1, 2022): 53. http://dx.doi.org/10.3847/1538-4357/ac713c.

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Abstract Thomson-scattered photospheric light is the dominant constituent of the lower solar corona’s spectral continuum viewed off-limb at optical wavelengths. Known as the K-corona, it is also linearly polarized. We investigate the possibility of using the a priori polarized characteristics of the K-corona, together with polarized emission lines, to measure and correct instrument-induced polarized crosstalk. First we derive the Stokes parameters of the Thomson scattering of unpolarized light in an irreducible spherical tensor formalism. This allows forward synthesis of the Thomson-scattered signal for the more complex scenario that includes symmetry-breaking features in the incident radiation field, which could limit the accuracy of our proposed technique. For this, we make use of an advanced 3D radiative magnetohydrodynamic coronal model. Together with synthesized polarized signals in the Fe xiii 10746 Å emission line, we find that an ad hoc correction of telescope- and instrument-induced polarization crosstalk is possible under the assumption of a nondepolarizing optical system.

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Kuhn, J. R., H. Lin, P. Lamy, S. Koutchmy, and R. N. Smartt. "IR Observations of the K and F Corona During the 1991 Eclipse." Symposium - International Astronomical Union 154 (1994): 185–97. http://dx.doi.org/10.1017/s0074180900124428.

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The availability of relatively large format IR array detectors is incentive for reexamining the classic question of whether or not there are “dust rings” around the sun – a problem for which there are conflicting observational answers. The 1991 eclipse path included a high altitude observatory and provided a potentially ideal opportunity to study the infrared properties and dust content of the corona. Here we report results from an experiment conducted from Mauna Kea using a HgCdTe array detector sensitive to wavelengths between 1-2.5 μm. Surface brightness measurements in the H-band and polarization data in the J-band were obtained over a field-of-view of ±6 R⊙ while K-band images further extend to 15 R⊙ on the western side of the Sun. J-band polarization data and H and K-band surface brightness data clearly show the inhomogeneous structure in the K corona and the ecliptical flattening of the F corona. We see no evidence of a circumsolar, local dust corona (dust rings) out to 15 R⊙.

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Kapanadze, N. G., V. I. Kulijanishvili, and Ahmed A. Hady. "Polarization properties of the June 21, 2001 solar corona." Proceedings of the International Astronomical Union 2, S233 (March 2006): 255. http://dx.doi.org/10.1017/s1743921306001979.

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Mo, Jianbin, Yun Xu, Xiuxiu Wang, Wei Wei, and Jing Zhao. "Exploiting the protein corona: coating of black phosphorus nanosheets enables macrophage polarization via calcium influx." Nanoscale 12, no. 3 (2020): 1742–48. http://dx.doi.org/10.1039/c9nr08570j.

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Rawat, Divya, Akash Garg, and Mariano Méndez. "Detection of X-Ray Polarized Emission and Accretion-disk Winds with IXPE and NICER in the Black Hole X-Ray Binary 4U 1630−47." Astrophysical Journal Letters 949, no. 2 (June 1, 2023): L43. http://dx.doi.org/10.3847/2041-8213/acd77b.

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Abstract We detect a high level of polarization in the X-ray emission of the black hole binary 4U 1630–47 in an observation with the Imaging X-ray Polarimetry Explorer. The 2–8 keV polarization degree is 8% at a position angle of 18°, with the polarization degree increasing significantly with energy, from ∼6% at ∼2 keV to ∼11% at ∼8 keV. The continuum emission in the spectrum of simultaneous observations with the Neutron Star Interior Composition Explorer (NICER) is well described with only a thermal disk spectrum, with stringent upper limits to any Comptonized emission from the corona. Together with the lack of significant variability in the Fourier power spectrum, this suggests that the source was in the high soft state at the time of these observations. The NICER spectrum reveals the presence of several absorption lines in the 6–9 keV band that we fit with two ionized absorbers, providing evidence of the presence of a strong disk wind, which supports the idea that the source was in the soft state. Previous measurements of X-ray polarization in other sources in harder states were associated with the corona or the jet in those systems. Given that the corona is significantly absent in this observation of 4U 1630–47, and that the jet in black hole binaries is quenched in the high soft state, we speculate that in this observation of 4U 1630–47, the polarization likely arises from the direct and reflected radiation of the accretion disk in this source.

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Qu, Z. Q., L. Chang, G. T. Dun, Z. Xu, X. M. Cheng, L. H. Deng, X. Y. Zhang, and Y. H. Jin. "Complexity of the Upper Solar Atmosphere Revealed from Spectropolarimetry during a Solar Eclipse." Astrophysical Journal 940, no. 2 (November 30, 2022): 150. http://dx.doi.org/10.3847/1538-4357/ac9af4.

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Abstract We analyze linear polarimetric spectrum data of solar emission lines with different formation temperatures in a visible light band from 516.3–532.6 nm, obtained during the 2013 Gabon solar eclipse using the prototype Fiber Arrayed Solar Optical Telescope. Complexities are found from the chromosphere through the transition zone to the corona at the spatial resolution limit of 2″ and temporal resolution of seconds. The observations show irregular spatial and spectral variations in linear polarization amplitudes, directions, and profile shapes. Within the observational band, spectral lines with different formation temperatures can have comparable polarization amplitudes in one spatial volume but one order difference in another, and at the same spatial volume, the amplitudes can differ by one order at different lines. The polarization amplitudes do not consistently increase with elongation in local regions. The variation in the direction of the polarization along the elongation is found from the green coronal line and the transition zone line more frequently than from the chromospheric lines. Such a variation in orientation is not synchronous for the different lines. Finally, Stokes Q/I profiles of the broad lines, such as the magnesium triplet and the green coronal line, show very diverse and complicated patterns. After pixel binning, we show that some of the complexity may be caused by the integration over different polarization sources at subresolution scales and/or along the line of sight in the optically thin layers with complex geometric corrugations.

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Ramesh, R., and C. Kathiravan. "Polarization Observations of a Split-band Type II Radio Burst from the Solar Corona." Astrophysical Journal 940, no. 1 (November 1, 2022): 80. http://dx.doi.org/10.3847/1538-4357/ac9c65.

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Abstract Using temporal observations of circular polarized harmonic plasma emission from a split-band type II solar radio burst at 80 MHz, we separately estimated the coronal magnetic field strengths (B) associated with the lower (L) and upper (U) frequency bands of the burst. The corresponding Stokes I and V data were obtained with the polarimeter operating at the above frequency in the Gauribidanur observatory. The burst was associated with a flare/coronal mass ejection on the solar disk. Simultaneous spectral observations with the spectrograph there in the frequency range 80–35 MHz helped to establish that the observed polarized emission was from the harmonic component of the burst. The B values corresponding to the polarized emission from the L and U bands at 80 MHz are B L ≈ 1.2 G and B U ≈ 2.4 G, respectively. The different values of B for the observed harmonic emission at the same frequency (80 MHz) from the two bands imply unambiguously that the corresponding fundamental emission at 40 MHz must have originated at different spatial locations. Two-dimensional radio imaging observations of the burst with the radioheliograph in the same observatory at 80 MHz indicate the same. As comparatively higher B is expected behind a propagating shock due to compression as well as the corresponding coronal regions being closer to the Sun, our results indicate that the sources of L- and U-band emission should be located ahead of and behind the associated coronal shock, respectively. These are useful to understand the pre- and postshock corona as well as locations of electron acceleration in a propagating shock.

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Banerjee, S., W. Du, U. Sundar, and K. A. Cook-Chennault. "Piezoelectric and Dielectric Characterization of MWCNT-Based Nanocomposite Flexible Films." Journal of Nanomaterials 2018 (September 30, 2018): 1–15. http://dx.doi.org/10.1155/2018/6939621.

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PZT-epoxy-multiwalled carbon nanotube (MWCNT) flexible thick film actuators were fabricated using a sol-gel and spin coat and deposition process. Films were characterized in terms of their piezoelectric and dielectric properties as a function of MWCNT volume fraction and polarization process. Correlations between surface treatment of the MWCNTs and composite performance were made. The surface morphology and filler distribution were observed with the aid of SEM and TEM images. The volume fraction of PZT was held constant at 30%, and the volume fraction of MWCNTs varied from 1% to 10%. Two forms of dielectric polarization were compared. Corona discharge polarization induced enhanced piezoelectric and dielectric properties by a factor of 10 in comparison to the parallel-plate contact method (piezoelectric strain coefficient and dielectric constant were 0.59 pC/N and 61.81, respectively, for the parallel-plate contact method and 9.22 pC/N and 103.59 for the corona polarization method, respectively). The percolation threshold range was observed to occur at a MWCNT volume fraction range between 5% and 6%.

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35

Poutanen, Juri. "Frequency-Dependent Polarization in Comptonization Models for AGN." Symposium - International Astronomical Union 159 (1994): 472. http://dx.doi.org/10.1017/s007418090017651x.

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The angular distribution and the polarization of radiation as a function of the angle and frequency for the two-phase model of accretion disks in AGN are found. The results depend strongly on the temperature of the hot corona.

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El Mouden, Mahmoud, Fouad Belhora, Yassine Tabbai, Abdelowahed Hajjaji, and Abdessamad El Ballouti. "Improvement of the magneto-electric effect of composites loaded with different magnetic particles for current sensor applications." European Physical Journal Applied Physics 87, no. 1 (July 2019): 10901. http://dx.doi.org/10.1051/epjap/2019190097.

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This article proposes a methodology to improve the magneto-electric effect of a poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TrFe) copolymer, doped with nanoparticles of nickel (Ni) and nickel iron (NiFe). The preparation of the composite films were achieved through the solvent casting approach. First, P(VDF-TrFe) powders and (Ni and NiFe) nanoparticles are dispersed in dimethyl formamide (DMF) as a solvent to form a homogeneous solution. Then, the solution obtained is deposited on a flexible substrate by a spin coating process. After that, the NiFe doped composites are corona polarized, to improve the magneto-electric response of these composites. The purpose of this work is to investigate the influence of the magnetic charges added in the P(VDF-TrFe) copolymer, and to reveal the effect of corona charging (polarization) on the magneto-electric behavior of the used composites. The obtained results in this article show that both the doping and the electric polarization (piezo coefficient) significantly affect the generated alternating current during the application of an alternating magnetic field. However, the magneto-electric response of composites increases by doping and charging via corona poling effect and also by increasing the excitation frequency and the magnetic field amplitude. In addition, the magneto-electric responses of all composites after corona polarization were also discussed. This indicates that the magneto-electric coefficient and the current can be increased with polarized composites. A good response is observed for P(VDF-TrFe) + 3% Ni with a piezoelectric coefficient d33 = 21.2 (pC/N)

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Gerasimov D. I., Kuryndin I. S., Lavrentyev V. K., Volgina E. A., Temnov D. E., and Elyashevich G. K. "Structure formation and depolarization relaxation processes in porous piezoactive polyvinylidene fluoride films." Physics of the Solid State 64, no. 10 (2022): 1432. http://dx.doi.org/10.21883/pss.2022.10.54232.389.

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Piezoactive porous polyvinylidene fluoride films prepared in the process based on melt extrusion with subsequent isometric annealing, uniaxial extension and thermal fixation have been studied. It was shown that two competing orientation processes -polymorphous transition of non-polar α-phase into polar piezoactive β-phase and formation of porous structure - occur during the uniaxial extension of annealed films. It has been established that orientation degree of extruded films is the key factor determining the efficiency of both processes. Thermally stimulated depolarization method was used to investigate the dipole relaxation in oriented films, and activation energy of these processes was found. The films were polarized using corona discharge and high-voltage contact methods, both, and the dependence of piezoelectric modulus on the polarization conditions has been obtained. The maximum value of piezoelectric modulus d31=30.1 pC/N was achieved by polarization of films in corona discharge method. Keywords: polyvinylidene fluoride, porous films, supramolecular structure, piezoelectric properties, polarization, relaxation processes.

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Bogod, V. M., G. B. Gelfreikh, B. I. Ryabov, and S. R. Hafizov. "Coronal Magnetic Fields from the Effect of the Double Inversion of Circular Polarization of Radio Emission." International Astronomical Union Colloquium 141 (1993): 302–5. http://dx.doi.org/10.1017/s0252921100029298.

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AbstractWe present preliminary results of radio observations of the Sun with the Panoramic Analyzer of the Spectrum (21 channels in 1.8 – 8.2 cm wavelength range) of the radio telescope RATAN-600. Observations on 1992 January 9 – 10 have shown double inversion of the sign of a local source through the microwave wavelength range with fine spectral structure. This phenomenon can be treated as a result of mode coupling when the electromagnetic wave crosses two regions of quasi-transverse propagation (QT-region). Using this treatment we have found the strength of the coronal magnetic field at a number of points in the corona above an active region. The results also imply that trans-equatorial coronal arches affect the structure of magnetic fields at heights of about 3 . 1010 cm with B ~ 5 – 10 G.

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Banerjee, S., and K. A. Cook-Chennault. "Polarization Parameters and Scaling Matter—How Processing Environment and Shape Factor Influence Electroactive Nanocomposite Characteristics." Journal of Composites Science 4, no. 3 (September 19, 2020): 141. http://dx.doi.org/10.3390/jcs4030141.

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Polymeric-ceramic smart nanocomposite piezoelectric and dielectric materials are of interest due to their superior mechanical flexibility and ability to leverage characteristics of constituent materials. A great deal of work has centered on development of processes for manufacturing 0–3 continuity composite piezoelectric materials that vary in scale ranging from bulk, thick and thin film to nanostructured films. Less is known about how material scaling effects the effectiveness of polarization and electromechanical properties. This study elucidates how polarization parameters: contact versus corona, temperature and electrical voltage field influence the piezoelectric and dielectric properties of samples as a function of their shape factor, i.e., bulk versus thick film. Bulk and thick film samples were prepared via sol gel/cast-mold and sol gel/spin coat deposition, for fabrication of bulk and thick films, respectively. It was found that corona polarization was more effective for both bulk and thick film processes and that polarization temperature produced higher normalized changes in samples. Although higher electric field voltages could be achieved with thicker samples, film samples responded the most to coupled increases in temperature and electrical voltage than bulk samples.

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Tai, L. S., Y. W. Wong, Y. M. Poon, and F. G. Shin. "Characteristics of Corona-Charged PET Sandwich Electrets." Materials Science Forum 480-481 (March 2005): 123–28. http://dx.doi.org/10.4028/www.scientific.net/msf.480-481.123.

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Polyethylene terephthalate (PET) is one of the major electret materials which has been studied and widely used in charge storage applications for a long time. The homo-charge and hetero-charge formation responsible for the electret effect of PET can be explained by the dipolar polarization, space charge separation and charge injection respectively as a result of contact poling or corona charging. These processes are also verifiable from studies of surface charges and thermally stimulated depolarization current (TSDC) of the PET films. Now consider a stack of PET films charged under the same condition as a single film. It would be intuitively expected that the electret effects of the individual films of the stack should be different due to their different positions in the stack. However, in a recent study on charged PET stacks, it was found that the electret effects of the individual films are quite similar. The surface charges of the individual films are about the same and they sum to make same total as a single charged PET film. On the other hand, the TSDC thermograms of individual films show similar characteristics in the thermal relaxation processes where homo- and hetero- charge effects are still observed. From the TSDC results, especially for the film in the middle of a triple layer sandwich, it shows clearly dipolar polarization and charge injection related peaks. These findings agree with the results of surface charge studies of the individual films.

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Sastry, Ch V. "POLARIZATION OF THE THERMAL RADIO EMISSION FROM OUTER SOLAR CORONA." Astrophysical Journal 697, no. 2 (May 15, 2009): 1934–39. http://dx.doi.org/10.1088/0004-637x/697/2/1934.

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Molodenskii, M. M., L. I. Starkova, V. A. Kutvitskiĭ, and V. L. Merzlyakov. "The polarization of the solar corona on March 29, 2006." Astronomy Reports 53, no. 3 (March 2009): 275–80. http://dx.doi.org/10.1134/s1063772909030093.

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Tansel, T., S. Ener Rusen, and A. Rusen. "Uniform, large surface-area polarization by modifying corona-electrodes geometry." Review of Scientific Instruments 84, no. 1 (January 2013): 015107. http://dx.doi.org/10.1063/1.4773566.

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Vilitis, O., I. Muzikante, M. Rutkis, and A. Vembris. "Chromophore Poling in Thin Films of Organic Glasses. 2. Two-Electrode Corona Discharge Setup." Latvian Journal of Physics and Technical Sciences 49, no. 2 (January 1, 2012): 62–70. http://dx.doi.org/10.2478/v10047-012-0013-5.

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Chromophore Poling in Thin Films of Organic Glasses. 2. Two-Electrode Corona Discharge Setup In Part 1 of the article we provided description of the corona discharge physics and overview of the methods used for corona poling in thin organic films. Subsequent sections describe comparatively simple technical methods for poling the organic nonlinear optical polymers using a two-electrode (point-to-plate or wire-to-plate) technique. The polarization build-up was studied by the DC positive corona method for poling the nonlinear optical (NLO) polymers. The experimental setup provides the corona discharge current from 0.5 μA up to 3 μA by applying 3 kV - 12 kV voltage to the corona electrode and makes possible selection among the types of corona electrodes (needle, multi-needle, wire, etc.). The results of experimental testing of the poling setup show that at fixed optimal operational parameters of poling - the sample orientation temperature and the discharge current - the corona charging of polymeric materials can successfully be performed applying the two-electrode technique. To study the dynamics of both poling and charge transport processes the three-electrode charging system - a corona triode - should be applied.

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DeForest, Craig E., Daniel B. Seaton, and Matthew J. West. "Three-polarizer Treatment of Linear Polarization in Coronagraphs and Heliospheric Imagers." Astrophysical Journal 927, no. 1 (March 1, 2022): 98. http://dx.doi.org/10.3847/1538-4357/ac43b6.

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Abstract Linearly polarized light has been used to view the solar corona for over 150 years. While the familiar Stokes representation for polarimetry is complete, it is best matched to a laboratory setting and therefore is not the most convenient representation either for coronal instrument design or for coronal data analysis. Over the last 100 years of development of coronagraphs and heliospheric imagers, various representations have been used for both direct measurement and analysis. These systems include famous representations such as the (B, pB) system, which is analogous to the Stokes system in solar observing coordinates, and also internal representations such as in-instrument Stokes parameters with fixed or variable “vertical” direction, and brightness values through a particular polarizing optic or set thereof. Many polarimetric instruments currently use a symmetric three-polarizer measurement and representation system (which we refer to as “(M, Z, P)”) to derive the (B, pB) or Stokes parameters. We present a symmetric derivation of (B, pB) and Stokes parameters from (M, Z, P), analyze the noise properties of (M, Z, P) in the context of instrument design, develop (M, Z, P) as a useful intermediate system for data analysis including background subtraction, and draw a helpful analogy between linear polarimetric systems and the large existing body of work on photometric colorimetry.

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Cheah, Joshua U.-Jin, Heng Boon Low, Yongliang Zhang, and James Chen Yong Kah. "Light-independent M1 macrophage polarization by photosensitizer-loaded protein corona on gold nanorods." Nanomedicine 15, no. 24 (October 2020): 2329–44. http://dx.doi.org/10.2217/nnm-2020-0249.

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Aim: To establish a light-independent functionality of gold nanorods (AuNRs) with a human serum (HS) protein corona loaded with photosensitizer Chlorin e6 (AuNR-HS-Ce6) in M1 polarization of macrophages. Methods: RT-qPCR and ELISA were used to determine gene and protein expression, respectively. Uptake of AuNR-HS-Ce6 was determined via flow cytometry, inductively coupled plasma mass spectrometry and fluorescence microscopy. Cell viability was determined using PrestoBlue® cell viability assay. Results: An increase in M1 gene and protein expression was observed in AuNR-HS-Ce6-treated macrophages. Delivery of high Ce6 payload via AuNR-HS-Ce6 was the primary contributor toward M1 polarization. Finally, DLD-1 cells treated with conditioned media from AuNR-HS-Ce6-treated macrophages showed significantly reduced proliferation. Conclusion: Our study suggests an immunomodulatory potential of Ce6 in inducing light-independent M1 polarization outside of its role as a photosensitizer.

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Filippov, B. P., M. M. Molodensky, and S. Koutchmy. "On the Optical Polarization of the White-Light Coronal Structures." International Astronomical Union Colloquium 144 (1994): 601–4. http://dx.doi.org/10.1017/s0252921100026130.

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AbstractA special experiment was designed to measure the orientation of the polarization plane in the solar corona during the total eclipse of July 11, 1991. Rotating polaroids with the axes directed at +45° and at −45° of the radial direction in all directions were used. The polarization plane was found to be tangential to the solar limb everywhere with an accuracy within 1°, in agreement with the Thomson scattering theory.

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Thum, C., D. Morris, and H. Wiesemeyer. "Polarization of the Recombination Line Maser in MWC349." Proceedings of the International Astronomical Union 8, S287 (January 2012): 49–53. http://dx.doi.org/10.1017/s174392131200662x.

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AbstractWe present observations of the circular polarization of the recombination line maser in MWC 349. Six good quality Ha30α spectra were obtained during 2010 – 2011 which show that the Zeeman features are complex, time variable, and usually different for the blue- and red-shifted maser spikes. We propose that the magnetic field, located in the corona of the circumstellar disk, has toroidal and radial components. It is plausibly generated in a disk dynamo.

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Llovera-Segovia, Pedro, Gustavo Ortega-Braña, Vicente Fuster-Roig, and Alfredo Quijano-López. "Charging of Piezoelectric Cellular Polypropylene Film by Means of a Series Dielectric Layer." Polymers 13, no. 3 (January 21, 2021): 333. http://dx.doi.org/10.3390/polym13030333.

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Piezoelectric polymer cellular films have been developed and improved in the past decades. These piezoelectric materials are based on the polarization of the internal cells by means of induced discharges in the gas inside the cells. Internal discharges are driven by an external applied electric field. With this polarization method, cellular polypropylene (PP) polymers exhibit a high piezoelectric coefficient d33 and have been investigated because of their low dielectric polarization, high resistivity, and flexibility. Charging polymers foams is normally obtained by applying a corona discharge to the surface with a single tip electrode-plane arrangement or a triode electrode, which consists of a tip electrode-plane structure with a controlled potential intermediate mesh. Corona charging allows the surface potential of the sample to rise without breakdown or surface flashover. A charging method has been developed without corona discharge, and this has provided good results. In our work, a method has been developed to polarize polypropylene foams by applying an insulated high-voltage electrode on the surface of the sample. The dielectric layer in series with the sample allows for a high internal electric field to be reached in the sample but avoids dielectric breakdown of the sample. The distribution of the electric field between the sample and the dielectric barrier has been calculated. Experimental results with three different electrodes present good outcome in agreement with the calculations. High d33 constants of about 880 pC/N have been obtained. Mapping of the d33 constant on the surface has also been carried out showing good homogeneity on the area under the electrode.

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Kulijanishvili, V. I., N. G. Kapanadze, and A. N. Korol. "Polarization and intensity studies of the August 11, 1999 solar corona." Proceedings of the International Astronomical Union 2004, IAUS223 (June 2004): 393–94. http://dx.doi.org/10.1017/s174392130400626x.

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Journal articles on the topic 'Corona polarization'

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