Radio Polarisation Study of High Rotation Measure AGNs

As radio polarised emission from astrophysical objects traverse through foreground magnetised plasma, the physical conditions along the lines of sight are encrypted in the form of Rotation Measure (RM). We performed broadband spectro-polarimetric observations of high Rotation Measure (|RM| >~ 300 rad m-2) sources away from the Galactic plane (|b| > 10 deg) selected from the NVSS RM catalogue. The main goals are to verify the NVSS RM values, which could be susceptible to n{\pi}-ambiguity, as well as to identify the origin of the extreme RM values. We show that 40 % of our sample suffer from n{\pi}-ambiguity in the NVSS RM catalogue. There are also hints of RM variabilities over ~20 years epoch for most of our sources, as revealed by comparing the RM values of the two studies in the same frequency ranges after correcting for n{\pi}-ambiguity. At last, we demonstrate the possibility of applying QU-fitting to study the ambient media of AGNs.Comment: 6 pages, 2 figures; Accepted by MDPI Galaxies; Conference Proceedings for the Polarised Emission from Astrophysical Jets meeting on June 12-16 2017, Ierapetra, Greec

Evaluating Summary Statistics with Mutual Information for Cosmological Inference

The ability to compress observational data and accurately estimate physical parameters relies heavily on informative summary statistics. In this paper, we introduce the use of mutual information (MI) as a means of evaluating the quality of summary statistics in inference tasks. MI can assess the sufficiency of summaries, and provide a quantitative basis for comparison. We propose to estimate MI using the Barber-Agakov lower bound and normalizing flow based variational distributions. To demonstrate the effectiveness of our method, we compare three different summary statistics (namely the power spectrum, bispectrum, and scattering transform) in the context of inferring reionization parameters from mock images of 21~cm observations with Square Kilometre Array. We find that this approach is able to correctly assess the informativeness of different summary statistics and allows us to select the optimal set of statistics for inference tasks.Comment: Accepted at the ICML 2023 Workshop on Machine Learning for Astrophysics, comments welcom

THE EFFECT OF ARCH-SUPPORTED FUNCTIONAL INSOLES TO AVOID OVERUSED INJURIES DURING RACE WALKING

This study investigates the effectiveness of functional insoles on plantar pressure distribution during race walking in order to reduce the high plantar pressure and force on race walkers, who tend to suffer from overuse injury. A total of 20 male race walkers were recruited as subjects. Each participant completed a race walk with and without functional insoles. Plantar pressure insoles were used to collect plantar pressure data. A two-way analysis of variance with a mixed design was used to determine the difference between the two conditions. Results show that the use of functional insoles reduced the peak pressure and the impulse in the metatarsal heads and heels and thus suggest that functional insoles reduce the overuse injury risks of these parts. The first ground reaction force peak also decreased. This result suggests that functional insoles reduce the risks of foot and leg injuries

Development of Bionic Air Cooler Used in High Temperature Coal Mine

In high temperature coal mine, the surface air cooler heat exchange efficiency decreases greatly because of high humidity and dust. In order to improve the heat exchange efficiency, the surface of the air cooler needs to be designed to reduce the dust adhesion, and improve the heat exchange efficiency. Based on the self-cleaning effect of lotus leaf, the surface of air cooler is designed and fin and tube are processed into the constructure of lotus leaf surface. With Ansys, the cooling effect of air cooler is simulated, and the experiment is done to test the heat exchange effect of the common air cooler and bionic air cooler in lab. By analysis, it can be concluded that the surface of bionic air cooler has the function of self-cleaning, and the structure can increase the heat exchange efficiency, which is higher above 30% than that of common air cooler. Key words: High temperature coal mine; Air cooler; Self-cleaning; Heat exchange efficienc

An In-Depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations

Basu A, Fletcher A, Mao SA, Burkhart B, Beck R, Schnitzeler D. An In-Depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations. GALAXIES. 2019;7(4): 89.In this paper, we present a detailed analysis of the Faraday depth (FD) spectrum and its clean components obtained through the application of the commonly used technique of Faraday rotation measure synthesis to analyze spectro-polarimetric data. To directly compare the Faraday depth spectrum with physical properties of a magneto-ionic medium, we generated synthetic broad-bandwidth spectro-polarimetric observations from magnetohydrodynamic (MHD) simulations of a transonic, isothermal, compressible turbulent medium. We find that correlated magnetic field structures give rise to a combination of spiky, localized peaks at certain FD values, and broad structures in the FD spectrum. Although most of these spiky FD structures appear narrow, giving an impression of a Faraday thin medium, we show that they arise from strong synchrotron emissivity at that FD. Strong emissivity at a FD can arise because of both strong spatially local polarized synchrotron emissivity at a FD or accumulation of weaker emissions along the distance through a medium that have Faraday depths within half the width of the rotation measure spread function. Such a complex Faraday depth spectrum is a natural consequence of MHD turbulence when the lines of sight pass through a few turbulent cells. This therefore complicates the convention of attributing narrow FD peaks to the presence of a Faraday-rotating medium along the line of sight. Our work shows that it is difficult to extract the FD along a line of sight from the Faraday depth spectrum using standard methods for a turbulent medium in which synchrotron emission and Faraday rotation occur simultaneously

A VLA Polarimetric Study of the Galactic Center Radio Arc: Characterizing Polarization, Rotation Measure, and Magnetic Field Properties

The Radio Arc is one of the brightest systems of non-thermal filaments (NTFs) in the Galactic Center, located near several prominent HII regions (Sickle and Pistol) and the Quintuplet stellar cluster. We present observations of the Arc NTFs using the S-, C-, and X-bands of the Very Large Array interferometer. Our images of total intensity reveal large-scale helical features that surround the Arc NTFs, very narrow sub-filamentation, and compact sources along the NTFs. The distribution of polarized intensity is confined to a relatively small area along the NTFs. There are elongated polarized structures that appear to lack total intensity counterparts. We detect a range of rotation measure values from -1000 to -5800 rad m$\rm^{-2}$, likely caused by external Faraday rotation along the line of sight. After correcting for Faraday rotation, the intrinsic magnetic field orientation is found to generally trace the extent of the NTFs. However, the intrinsic magnetic field in several regions of the Arc NTFs shows an ordered pattern that is rotated with respect to the extent of the NTFs. We suggest this changing pattern may be caused by an additional magnetized source along the line of sight, so that we observe two field systems superposed in our observations. We suggest that the large scale helical segments near the Radio Arc could be components of such a source causing these changes in intrinsic magnetic field, and some variations in the polarization and rotation measure values along the NTFs.Comment: PDF should be 24 pages with 13 figure