• Book : 605()
• Pub. Date : 2025
• Page : pp.155590
• Keyword :

Abstract

Radio halos of edge-on galaxies are crucial for investigating cosmic ray propagation and magnetic field structures in galactic environments. We present VLA C-configuration S-band (2-4 GHz) observations of the spiral galaxy NGC 3556, a target from the Continuum Halos in Nearby Galaxies-an EVLA Survey. We estimate the thermal contribution to the radio emission from a combination of the Hα and mid-IR data, and employ rotation measure synthesis to reveal the magnetic field structures. In our data, NGC 3556 exhibits a box-like radio halo extending nearly 7 kpc from the galactic plane. The scale height of the total S-band intensity in the halo is 1.68 ± 0.29 kpc, while that of the nonthermal intensity is 1.93 ± 0.28 kpc. Fitting the data to a 1D cosmic-ray transport model, we find advection to describe the cosmic-ray propagation within the halo better than diffusion, with advection speeds of 245 ± 15 km s⁻¹ and 205 ± 25 km s⁻¹ above and below the disk, respectively. The magnetic field is detected patchily across the galaxy, displaying a toroidal configuration in the rotation measure map. The mean equipartition magnetic field strength is approximately 8.3 μG in the disk and 4.5 μG in the halo. In addition, a bubble-like structure extends nearly 3 kpc into the southern halo, aligned with the polarized intensity and Hα image, suggestive of superwinds generated by recent star formation feedback in the nuclear region.

• Book : 978(1)
• Pub. Date : 2025
• Page : pp.5
• Keyword :

Abstract

In previous work (Kohno and Myra 2023 Comput. Phys. Commun.291 108841), we developed a numerical scheme based on a two-dimensional microscale radio-frequency (RF) sheath model with periodically curved wall boundaries. Here, we expand the capability of this scheme through modification of the boundary conditions (BCs) on the conducting walls, which allows the ion flow to turn back to the plasma at locations on the walls where the electromagnetic force on the ions is reversed from its usual direction. Numerical simulations are carried out to investigate the dependences of the surface-integrated admittances on the wall bump height, ion magnetization, ion mobility, and the magnetic field angle, and to visualize the sheath structures in several cases. One of the main results is the ion cyclotron admittance resonance observed under the condition of low ion mobility (high normalized frequency). It is shown that the amplitude of the resonance peak depends on the wall bump height and the ion velocity is reversed on the sides of the bump in an RF cycle for the resonance cases. Furthermore, the differences in the admittances between the one- and two-dimensional microscale models are assessed for the purpose of understanding non-locality of the sheath near the wall surface for the parameters considered in this study. This information will be essential for improving the sheath BC for macroscale calculations in the future.

• Book : 65(2)
• Pub. Date : 2025
• Page : pp.026012
• Keyword :

• Book : 605()
• Pub. Date : 2025
• Page : pp.155598
• Keyword :

• Book : 314()
• Pub. Date : 2025
• Page : pp.134253
• Keyword :

Abstract

This article presents the design and experimental validation of a uniform circular array (UCA) of circularly polarized (CP) slot patch antennas for generating orbital angular momentum (OAM) beams at 2.4 GHz. The proposed UCA configuration enables high-purity OAM beam generation with azimuthal symmetry, which is critical for vehicular communication applications. Using left-hand circularly polarized elements and a series-fed network, the UCA achieves precise phase control and minimal side-lobe levels. The antenna was optimized to produce the OAM mode with a topological charge l = 1. Numerical simulations and experimental measurements show that the design offers strong impedance matching and high mode purity, making it suitable for applications requiring conical beam radiation, such as vehicle-to-vehicle communications. The 3D measurements further validate the prototype’s effectiveness in generating OAM beams with symmetric radiation patterns, demonstrating significant azimuthal symmetry and confirming its applicability for dynamic vehicular environments.

• Book : 27(1)
• Pub. Date : 2025
• Page : pp.015606
• Keyword :

• Book : 605()
• Pub. Date : 2025
• Page : pp.155568
• Keyword :

• Book : 605()
• Pub. Date : 2025
• Page : pp.155597
• Keyword :

• Book : 605()
• Pub. Date : 2025
• Page : pp.155574
• Keyword :

• Book : 62(1)
• Pub. Date : 2025
• Page : pp.1-16
• Keyword :