We discuss properties of type III bursts that change the sign of their drift rate from negative to positive and
vice versa
. Moreover, these bursts may change the sign of their drift rates more than ...once. These particular type III bursts were observed simultaneously by the radio telescopes UTR-2 (
Ukrainian T-shaped Radio telescope
, Kharkov, Ukraine), URAN-2 (
Ukrainian Radio telescope of the Academy of Sciences
, Poltava, Ukraine), and by the NDA (
Nançay Decametric Array
, Nancay, France) in the frequency range 8 – 41 MHz. The negative drift rates of these bursts are similar to those of previously reported decameter type III bursts and vary from −0.7 MHz s
−1
to −1.7 MHz s
−1
, but their positive drift rates vary in a wider range from 0.44 MHz s
−1
to 6 MHz s
−1
. Unlike inverted U-bursts, the tracks of these type III bursts have C- or inverted C-shapes.
Our basic explanation of the positive drift rate of these type III bursts differs from the common assumption that positive drift rates of type III bursts are connected with electron beam propagation toward the Sun. We propose that, even if electron beams move outward from the Sun, they can generate type III bursts with positive drift rates if in some regions of the solar corona the group velocities of type III radio emissions are lower than the velocities of the electron beams.
We study radio frequency (RF) wireless power transfer (WPT) using a digital radio transmitter for applications where alternative analog transmit circuits are impractical. An important parameter for ...assessing the viability of an RF WPT system is its end-to-end efficiency. In this regard, we present a prototype test bed comprising a software-defined radio (SDR) transmitter and an energy-harvesting receiver with a low resistive load; employing an SDR makes our research meaningful for simultaneous wireless information and power transfer (SWIPT). We analyze the effect of clipping and nonlinear amplification at the SDR on multisine waveforms. Our experiments suggest that when the direct current (dc) input power at the transmitter is constant, high peak-to-average power ratio (PAPR) multisines are unsuitable for RF WPT over a flat-fading channel, due to their low average radiated power. The results indicate that the end-to-end efficiency is positively correlated with the average RF power of the waveform and that it reduces with increasing PAPR. Consequently, digital modulations, such as phase shift keying (PSK) and quadrature amplitude modulation (QAM), yield better end-to-end efficiency than multisines. Moreover, the end-to-end efficiency of PSK and QAM signals is invariant to the transmission bit rate. An in-depth analysis of the end-to-end efficiency of WPT reveals that the transmitter efficiency is lower than the receiver efficiency. Furthermore, we study the impact of a reflecting surface on the end-to-end efficiency of WPT and assess the transmission quality of the information signals by evaluating their error vector magnitude (EVM) for SWIPT. Overall, the experimental observations of end-to-end efficiency and EVM suggest that, while employing an SDR transmitter with fixed dc input power, a baseband quadrature PSK signal is most suitable for SWIPT at large, among PSK and QAM signals.
It is well known that fast CMEs are mostly associated with magnetohydrodynamic (MHD) shocks in the solar corona, forming type-II radio bursts. However, the absence of type-II radio bursts is not ...uncommon. Herein, we aim to analyze the differences between the radio loud (RL) and radio quiet (RQ) fast Coronal Mass Ejections (CMEs) (speed ≥ 900 km s
−1
) during Solar Cycle 24 (2008 – 2021). From the 309 fast CMEs, we could identify 143 events with a known source origin on the visible disk (Earth view). We identified the associated flares/CMEs for 143 events using running-difference images from (i) Solar Dynamic Observatory/Atmospheric Imaging Assembly (SDO/AIA) and (ii) Large Angle Spectrometric Coronagraph (LASCO) observations. Among these 143 events, RQ and RL groups have 70 and 73 events, respectively. CALLISTO and Wind/WAVES observations are used to identify these RL and RQ sets. We analyzed the possibilities of streamer-CME and CME-CME interaction. In this study, we report the important differences between RL and RQ CMEs and the underlying reasons for the radio quietness of fast CMEs. In the LASCO field of view, the majority of RL CMEs (almost 90%) interacted with streamers and/or pre-CMEs, whereas only 25% of RQ CMEs did the same, and there was no pre-CME interaction. The observational evidence led to the conclusion that substantial density perturbation/interaction increases the probability of production of type-II radio emissions by the shock of RL CMEs.
In this paper, we study radio frequency (RF)-powered underlay cognitive radio networks (CRNs) with power-domain non-orthogonal multiple access (NOMA). In these networks, by using the ...harvest-then-transmit (HTT) mode, secondary transmitters (STs) can use the harvested energy to simultaneously transmit data based on power-domain NOMA. However, in this mode, the throughput of the secondary system heavily depends not only on the harvested energy, but also on the stringent interference threshold imposed by the primary users. Furthermore, ambient backscatter communication (ABC) has been introduced as a promising technique which enables STs to transmit information by modulating and reflecting ambient RF signals. Therefore, it has the potentiality to be integrated into the RF-powered underlay CR-NOMA networks to improve the throughput of the secondary system. In these networks, each ST works on either the HTT mode or the ABC mode, but not simultaneously. In order to meet the interference constraint of the primary users, STs control their transmit power by finding the appropriate tradeoff between the HTT mode and the ABC mode. We formulate an optimization problem with the goal of achieving the maximum throughput by finding the optimal time resource allocation between the HTT mode and the ABC mode under the strict transmit power constraint at STs. Then the Lagrangian multiplier iterative algorithm is adopted to solve this optimization problem. Simulation results demonstrate that our proposed scheme can significantly improve the performance of the secondary system by comparing it with the other two baseline schemes.
It has long been suspected that powerful radio sources may lower the efficiency with which stars form from the molecular gas in their host galaxy, however so far, alternative mechanisms, in ...particular related to the stellar mass distribution in the massive bulges of their host galaxies, have not been ruled out. We present new, arcsecond-resolution Atacama Large Millimeter Array (ALMA) CO(1−0) interferometry, which probes the spatially resolved, cold molecular gas in the nearby (
z
= 0.08), massive (
M
stellar
= 4 × 10
11
M
⊙
), isolated, late-type spiral galaxy 2MASSX J23453269−044925, which is outstanding for having two pairs of powerful, giant radio jets, and a bright X-ray halo of hot circumgalactic gas. The molecular gas is in a massive (
M
gas
= 2.0 × 10
10
M
⊙
), 24 kpc wide, rapidly rotating ring, which is associated with the inner stellar disk. Broad (
FWHM
= 70−180 km s
−1
) emission lines with complex profiles associated with the radio source are seen over large regions in the ring, indicating gas velocities that are high enough to keep the otherwise marginally Toomre-stable gas from fragmenting into gravitationally bound, star-forming clouds. About 1−2% of the jet kinetic energy is required to power these motions. Resolved star-formation rate surface densities derived from Galaxy Evolution Explorer and Wide-Field Infrared Survey Explorer fall by factors of 30−70 short of expectations from the standard Kennicutt–Schmidt law of star-forming galaxies, and near gas-rich early-type galaxies with signatures of star formation that are lowered by jet feedback. We argue that radio Active Galactic Nucleus (AGN) feedback is the only plausible mechanism to explain the low star-formation rates in this galaxy. Previous authors have already noted that the X-ray halo of J2345−0449 implies a baryon fraction that is close to the cosmic average, which is very high for a galaxy. We contrast this finding with other, equally massive, and equally baryon-rich spiral galaxies without prominent radio sources. Most of the baryons in these galaxies are in stars, not in the halos. We also discuss the implications of our results for our general understanding of AGN feedback in massive galaxies.
Abstract
We present a multiwavelength analysis of the cluster A1668, performed by means of new EVLA and Chandra observations and archival H
α
data. The radio images exhibit a small central source ...(∼14 kpc at 1.4 GHz) with
L
1.4GHz
∼ 6 · 10
23
W Hz
−1
. The mean spectral index between 1.4 GHz and 5 GHz is ∼−1, consistent with the usual indices found in BCGs. The cooling region extends for 40 kpc, with bolometric X-ray luminosity
L
cool
= 1.9 ± 0.1 · 10
43
erg s
−1
. We detect an offset of ∼6 kpc between the cluster BCG and the X-ray peak, and another offset of ∼7.6 kpc between the H
α
and the X-ray peaks. We discuss possible causes for these offsets, which suggest that the coolest gas is not condensing directly from the lowest-entropy gas. In particular, we argue that the cool ICM was drawn out from the core by sloshing, whereas the H
α
filaments were pushed aside from the expanding radio galaxy lobes. We detect two putative X-ray cavities, spatially associated with the west radio lobe (cavity A) and the east radio lobe (cavity B). The cavity power and age of the system are
P
cav
∼ 9 × 10
42
erg s
−1
and
t
age
∼ 5.2 Myr, respectively. Evaluating the position of A1668 in the cooling luminosity–cavity power parameter space, we find that the AGN energy injection is currently consistent within the scatter of the relationship, suggesting that offset cooling is likely not breaking the AGN feedback cycle.
An F-RAN is presented in this article as a promising paradigm for the fifth generation wireless communication system to provide high spectral and energy efficiency. The core idea is to take full ...advantage of local radio signal processing, cooperative radio resource management, and distributed storing capabilities in edge devices, which can decrease the heavy burden on fronthaul and avoid large-scale radio signal processing in the centralized baseband unit pool. This article comprehensively presents the system architecture and key techniques of F-RANs. In particular, key techniques and their corresponding solutions, including transmission mode selection and interference suppression, are discussed. Open issues in terms of edge caching, software-defined networking, and network function virtualization are also identified.
Abstract We report on full-Stokes L -band observations of 98 MeerKAT calibration sources. Linear polarization is detected in 71 objects above a fractional level of 0.2%. We identify ten sources with ...strong fractional linear polarization and low Faraday rotation measure that could be suitable for wide-band absolute polarization calibration. We detect significant circular polarization from 24% of the sample down to a detection level of 0.07%. Circularly polarized emission is seen only for flat spectrum sources α > −0.5. We compare our polarized intensities and Faraday synthesis results to data from the NVSS at 1400 MHz and the ATCA SPASS survey at 2300 MHz. NVSS data exist for 54 of our sources and SPASS data for 20 sources. The percent polarization and rotation measures from both surveys agree well with our results. The residual instrumental linear polarization for these observations is measured at 0.16%, and the residual instrumental circular polarization is measured at 0.05%. These levels may reflect either instabilities in the relative bandpass between the two polarization channels with either time or antenna orientation, or atmospheric/ionospheric variations with pointing direction. Tracking of the hourly gain solutions on J0408-6545 after transfer of the primary gain solutions suggests a deterioration of the gain stability by a factor of several starting about 2 hr after sunrise. This suggests that observing during the nighttime could dramatically improve the precision of polarization calibration.
We report on the lowest-frequency detection to date of three bursts from the fast radio burst FRB 180916.J0158+65, observed at 328 MHz with the Sardinia Radio Telescope (SRT). The SRT observed the ...periodic repeater FRB 180916.J0158+65 for five days from 2020 February 20 to 24 during a time interval of active radio bursting, and detected the three bursts during the first hour of observations; no more bursts were detected during the remaining ∼30 hr. Simultaneous SRT observations at 1548 MHz did not detect any bursts. Burst fluences are in the range 37 to 13 Jy ms. No relevant scattering is observed for these bursts. We also present the results of the multi-wavelength campaign we performed on FRB 180916.J0158+65, during the five days of the active window. Simultaneously with the SRT observations, others with different time spans were performed with the Northern Cross at 408 MHz, with XMM-Newton, NICER, INTEGRAL, AGILE, and with the TNG and two optical telescopes in Asiago, which are equipped with fast photometers. XMM-Newton obtained data simultaneously with the three bursts detected by the SRT, and determined a luminosity upper limit in the 0.3-10 keV energy range of ∼1045 erg s−1 for the burst emission. AGILE obtained data simultaneously with the first burst and determined a fluence upper limit in the MeV range for millisecond timescales of . Our results show that absorption from the circumburst medium does not significantly affect the emission from FRB 180916.J0158+65, thus limiting the possible presence of a superluminous supernova around the source, and indicate that a cutoff for the bursting mechanism, if present, must be at lower frequencies. Our multi-wavelength campaign sensitively constrains the broadband emission from FRB 180916.J0158+65, and provides the best limits so far for the electromagnetic response to the radio bursting of this remarkable source of fast radio bursts.
Abstract Broadband radio waves emitted from pulsars are distorted and delayed as they propagate toward the Earth due to interactions with the free electrons that compose the interstellar medium ...(ISM), with lower radio frequencies being more impacted than higher frequencies. Multipath propagation in the ISM results in both later times of arrival for the lower frequencies and causes the observed pulse to arrive with a broadened tail described via the pulse broadening function. We employ the CLEAN deconvolution technique to recover the pulse broadening timescale and by proxy the intrinsic pulse shape. This work expands upon previous descriptions of CLEAN deconvolution used in pulse broadening analyses by parameterizing the efficacy on simulated data and developing a suite of tests to establish which of a set of figures of merit leads to an automatic and consistent determination of the scattering timescale and its uncertainty. We compare our algorithm to the cyclic spectroscopy method of estimating the scattering timescale, specifically to the simulations performed in Dolch et al. (2021). We test our improved algorithm on the highly scattered millisecond pulsar J1903+0327, showing the scattering timescale to change over years, consistent with estimates of the refractive timescale of the pulsar.
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