scholarly journals Early evolution stage of AGN

2014 ◽  
Vol 10 (S313) ◽  
pp. 242-243
Author(s):  
M. Kunert-Bajraszewska ◽  
A. Labiano ◽  
A. Siemiginowska ◽  
M. Guainazzi ◽  
M. Gawroński
Keyword(s):  
Radio Source ◽  
Large Scale ◽  
Interaction Strength ◽  
Low Frequency ◽  
Evolutionary Process ◽  
Type I ◽  
Ionized Gas ◽  
New Radio ◽  
Determining Factors ◽  
Open Issue

AbstractRadio sources are divided into two distinct morphological groups of objects: Fanaroff-Riley type I and type II sources. There is a relatively sharp luminosity boundary between these at low frequency. The nature of the FR division is still an open issue, as are the details of the evolutionary process in which younger and smaller GHz-peaked spectrum (GPS) and compact steep spectrum (CSS) sources become large-scale radio structures. It is still unclear whether FRII objects evolve to become FRIs, or whether a division has already occurred amongst CSS sources and some of these then become FRIs and some FRIIs. We explored evolution scenarios of AGNs using new radio, optical and X-ray data of unstudied so far Low Luminosity Compact (LLC) sources. We suggest that the determining factors of the further evolution of compact radio objects could occur at subgalactic (or even nuclear) scales, or they could be related to the radio jet - interstellar medium (ISM) interactions and evolution. Our studies show that the evolutionary track could be related to the interaction, strength of the radio source and excitation levels of the ionized gas instead of the radio morphology of the young radio source.

scholarly journals A low-frequency radio halo survey of the South Pole Telescope SZ-selected clusters with the GMRT

2020 ◽  
Vol 500 (2) ◽  
pp. 2236-2249
Author(s):  
Ramij Raja ◽  
Majidul Rahaman ◽  
Abhirup Datta ◽  
Reinout J van Weeren ◽  
Huib T Intema ◽  
...  
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
Radio Sources ◽  
Synchrotron Emission ◽  
Diffuse Emission ◽  
Radio Halo ◽  
South Pole Telescope ◽  
New Radio ◽  
Upper Limits ◽  
Correlation Line

ABSTRACT The presence of non-thermal electrons and large-scale magnetic fields in the intracluster medium is known through the detection of megaparsec (Mpc) scale diffuse radio synchrotron emission. Although a significant amount of progress in finding new diffuse radio sources has happened in the last decade, most of the investigation has been constrained towards massive low-redshift clusters. In this work, we explore clusters with redshift z > 0.3 in search of diffuse radio emission, at 325 MHz with the Giant Metrewave Radio Telescope. This campaign has resulted in the discovery of two new radio haloes (SPT-CL J0013−4906 and SPT-CL J0304−4401) along with two other detections (SPT-CL J2031−4037 and SPT-CL J2248−4431), previously reported (at 325 MHz) in the literature. In addition, we detect a halo candidate in one cluster in our sample, and upper limits for haloes are placed in eight clusters where no diffuse emission is detected. In the P1.4–LX plane, the detected haloes follow the observed correlation, whereas the upper limits lie above the correlation line, indicating the possibility of future detection with sensitive observations.

scholarly journals Radio Source Counts at Ultra Low Frequencies: Results, Significance and Implication for Observational Cosmology

1995 ◽  
Vol 164 ◽  
pp. 455-455
Author(s):  
K.P. Sokolov
Keyword(s):  
Radio Source ◽  
Large Scale ◽  
Low Frequency ◽  
Space Distribution ◽  
Observational Cosmology ◽  
Radio Sources ◽  
Extragalactic Radio Source ◽  
Low Frequencies ◽  
Extended Radio ◽  
Frequency Source

Analysis of cosmological evolution effects in the low-frequency source counts at 25 MHz obtained with the UTR-2 radio telescope and conclusions on the large-scale extragalactic radio source space distribution are presented. The data require the existence of a decrease in the space distribution of the most distant extended radio sources.

scholarly journals The great Kite in the sky: A LOFAR observation of the radio source in Abell 2626

2020 ◽  
Vol 643 ◽  
pp. A172
Author(s):  
A. Ignesti ◽  
T. Shimwell ◽  
G. Brunetti ◽  
M. Gitti ◽  
H. Intema ◽  
...  
Keyword(s):  
Radio Source ◽  
Spatial Correlation ◽  
Thermal Plasma ◽  
Low Frequency ◽  
Galaxy Cluster ◽  
Nonthermal Plasma ◽  
X Ray ◽  
New Radio ◽  
Sky Survey ◽  
The Galaxy

Context. The radio source at the center of the galaxy cluster Abell 2626, also known as the Kite, stands out for its unique morphology composed of four symmetric arcs. Previous studies have probed the properties of this source at different frequencies and its interplay with the surrounding thermal plasma, but the puzzle of its origin is still unsolved. Aims. We use a new LOw-Frequency ARray (LOFAR) observation from the LOFAR Two-meter Sky Survey at 144 MHz to investigate the origin of the Kite. Methods. We present a detailed analysis of the new radio data, which we combined with archival radio and X-ray observations. We produced a new, resolved spectral index map of the source with a resolution of 7″ and we studied the spatial correlation of radio and X-ray emission to investigate the interplay between thermal and nonthermal plasma. Results. The new LOFAR data changed our view of the Kite because we discovered two steep-spectrum (α <  −1.5) plumes of emission connected to the arcs. The spectral analysis shows, for the first time, a spatial trend of the spectrum along the arcs with evidence of curved synchrotron spectra and a spatial correlation with the X-ray surface brightness. On the basis of our results, we propose that the Kite was originally an X-shaped radio galaxy whose fossil radio plasma, after the end of the activity of the central active galactic nucleus, has been compressed as a consequence of motions of the thermal plasma encompassing the galaxy. The interplay between the compression and advection of the fossil plasma, with the restarting of the nuclear activity of the central galaxy, could have enhanced the radio emission of the fossil plasma producing the arcs of the Kite. We also present the first, low-frequency observation of a jellyfish galaxy in the same field, in which we detect extended, low-frequency emission without a counterpart at higher frequencies.

scholarly journals Experiment Investigation of Bistable Vibration Energy Harvesting with Random Wave Environment

2021 ◽  
Vol 11 (9) ◽  
pp. 3868
Author(s):  
Qiong Wu ◽  
Hairui Zhang ◽  
Jie Lian ◽  
Wei Zhao ◽  
Shijie Zhou ◽  
...  
Keyword(s):  
Renewable Energy ◽  
Energy Harvesting ◽  
Cantilever Beam ◽  
Large Scale ◽  
Low Frequency ◽  
Vibration Energy ◽  
Random Wave ◽  
Periodic Signal ◽  
Vibration Energy Harvesting ◽  
Motion Activity

The energy harvested from the renewable energy has been attracting a great potential as a source of electricity for many years; however, several challenges still exist limiting output performance, such as the package and low frequency of the wave. Here, this paper proposed a bistable vibration system for harvesting low-frequency renewable energy, the bistable vibration model consisting of an inverted cantilever beam with a mass block at the tip in a random wave environment and also develop a vibration energy harvesting system with a piezoelectric element attached to the surface of a cantilever beam. The experiment was carried out by simulating the random wave environment using the experimental equipment. The experiment result showed a mass block’s response vibration was indeed changed from a single stable vibration to a bistable oscillation when a random wave signal and a periodic signal were co-excited. It was shown that stochastic resonance phenomena can be activated reliably using the proposed bistable motion system, and, correspondingly, large-scale bistable responses can be generated to realize effective amplitude enlargement after input signals are received. Furthermore, as an important design factor, the influence of periodic excitation signals on the large-scale bistable motion activity was carefully discussed, and a solid foundation was laid for further practical energy harvesting applications.

scholarly journals Analysis of local habitat selection and large-scale attraction/avoidance based on animal tracking data: is there a single best method?

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Moritz Mercker ◽  
Philipp Schwemmer ◽  
Verena Peschko ◽  
Leonie Enners ◽  
Stefan Garthe
Keyword(s):  
Habitat Selection ◽  
Large Scale ◽  
Error Rates ◽  
Process Models ◽  
Statistical Hypothesis ◽  
Type I ◽  
Tracking Data ◽  
Selection Models ◽  
Animal Tracking ◽  
Step Selection

Abstract Background New wildlife telemetry and tracking technologies have become available in the last decade, leading to a large increase in the volume and resolution of animal tracking data. These technical developments have been accompanied by various statistical tools aimed at analysing the data obtained by these methods. Methods We used simulated habitat and tracking data to compare some of the different statistical methods frequently used to infer local resource selection and large-scale attraction/avoidance from tracking data. Notably, we compared spatial logistic regression models (SLRMs), spatio-temporal point process models (ST-PPMs), step selection models (SSMs), and integrated step selection models (iSSMs) and their interplay with habitat and animal movement properties in terms of statistical hypothesis testing. Results We demonstrated that only iSSMs and ST-PPMs showed nominal type I error rates in all studied cases, whereas SSMs may slightly and SLRMs may frequently and strongly exceed these levels. iSSMs appeared to have on average a more robust and higher statistical power than ST-PPMs. Conclusions Based on our results, we recommend the use of iSSMs to infer habitat selection or large-scale attraction/avoidance from animal tracking data. Further advantages over other approaches include short computation times, predictive capacity, and the possibility of deriving mechanistic movement models.

scholarly journals A Novel Methodology for Adaptive Coordination of Multiple Controllers in Electrical Grids

Mathematics ◽  
2021 ◽  
Vol 9 (13) ◽  
pp. 1474
Author(s):  
Ruben Tapia-Olvera ◽  
Francisco Beltran-Carbajal ◽  
Antonio Valderrabano-Gonzalez ◽  
Omar Aguilar-Mejia
Keyword(s):  
Power Systems ◽  
Power System ◽  
Electric Power ◽  
Large Scale ◽  
Short Circuit ◽  
Dynamic Performance ◽  
Low Frequency ◽  
Electric Power System ◽  
Design Stage ◽  
Positive Interaction

This proposal is aimed to overcome the problem that arises when diverse regulation devices and controlling strategies are involved in electric power systems regulation design. When new devices are included in electric power system after the topology and regulation goals were defined, a new design stage is generally needed to obtain the desired outputs. Moreover, if the initial design is based on a linearized model around an equilibrium point, the new conditions might degrade the whole performance of the system. Our proposal demonstrates that the power system performance can be guaranteed with one design stage when an adequate adaptive scheme is updating some critic controllers’ gains. For large-scale power systems, this feature is illustrated with the use of time domain simulations, showing the dynamic behavior of the significant variables. The transient response is enhanced in terms of maximum overshoot and settling time. This is demonstrated using the deviation between the behavior of some important variables with StatCom, but without or with PSS. A B-Spline neural networks algorithm is used to define the best controllers’ gains to efficiently attenuate low frequency oscillations when a short circuit event is presented. This strategy avoids the parameters and power system model dependency; only a dataset of typical variable measurements is required to achieve the expected behavior. The inclusion of PSS and StatCom with positive interaction, enhances the dynamic performance of the system while illustrating the ability of the strategy in adding different controllers in only one design stage.

scholarly journals Optimizing the Frequency Capping: A Robust and Reliable Methodology to Define the Number of Ads to Maximize ROAS

2021 ◽  
Vol 11 (15) ◽  
pp. 6688
Author(s):  
Jesús Romero Leguina ◽  
Ángel Cuevas Rumin ◽  
Rubén Cuevas Rumin
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Low Frequency ◽  
Digital Marketing ◽  
Optimal Frequency ◽  
Novel Technique ◽  
Maximum Threshold

The goal of digital marketing is to connect advertisers with users that are interested in their products. This means serving ads to users, and it could lead to a user receiving hundreds of impressions of the same ad. Consequently, advertisers can define a maximum threshold to the number of impressions a user can receive, referred to as Frequency Cap. However, low frequency caps mean many users are not engaging with the advertiser. By contrast, with high frequency caps, users may receive many ads leading to annoyance and wasting budget. We build a robust and reliable methodology to define the number of ads that should be delivered to different users to maximize the ROAS and reduce the possibility that users get annoyed with the ads’ brand. The methodology uses a novel technique to find the optimal frequency capping based on the number of non-clicked impressions rather than the traditional number of received impressions. This methodology is validated using simulations and large-scale datasets obtained from real ad campaigns data. To sum up, our work proves that it is feasible to address the frequency capping optimization as a business problem, and we provide a framework that can be used to configure efficient frequency capping values.

Separatrix crossing and large scale diffusion in low-frequency three-wave systems

1998 ◽  
Vol 58 (3) ◽  
pp. 3768-3776 ◽  
Author(s):  
B. Weyssow ◽  
J. D. Reuss ◽  
J. Misguich
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
Separatrix Crossing

scholarly journals Historical drought patterns over Canada and their teleconnections with large-scale climate signals

2018 ◽  
Vol 22 (6) ◽  
pp. 3105-3124 ◽  
Author(s):  
Zilefac Elvis Asong ◽  
Howard Simon Wheater ◽  
Barrie Bonsal ◽  
Saman Razavi ◽  
Sopan Kurkute
Keyword(s):  
Large Scale ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Kendall Test ◽  
Wavelet Coherence ◽  
Climate Indices ◽  
Data Sets ◽  
Canadian Prairies ◽  
Agriculture Industry ◽  
Spatio Temporal

Abstract. Drought is a recurring extreme climate event and among the most costly natural disasters in the world. This is particularly true over Canada, where drought is both a frequent and damaging phenomenon with impacts on regional water resources, agriculture, industry, aquatic ecosystems, and health. However, nationwide drought assessments are currently lacking and impacted by limited ground-based observations. This study provides a comprehensive analysis of historical droughts over the whole of Canada, including the role of large-scale teleconnections. Drought events are characterized by the Standardized Precipitation Evapotranspiration Index (SPEI) over various temporal scales (1, 3, 6, and 12 consecutive months, 6 months from April to September, and 12 months from October to September) applied to different gridded monthly data sets for the period 1950–2013. The Mann–Kendall test, rotated empirical orthogonal function, continuous wavelet transform, and wavelet coherence analyses are used, respectively, to investigate the trend, spatio-temporal patterns, periodicity, and teleconnectivity of drought events. Results indicate that southern (northern) parts of the country experienced significant trends towards drier (wetter) conditions although substantial variability exists. Two spatially well-defined regions with different temporal evolution of droughts were identified – the Canadian Prairies and northern central Canada. The analyses also revealed the presence of a dominant periodicity of between 8 and 32 months in the Prairie region and between 8 and 40 months in the northern central region. These cycles of low-frequency variability are found to be associated principally with the Pacific–North American (PNA) and Multivariate El Niño/Southern Oscillation Index (MEI) relative to other considered large-scale climate indices. This study is the first of its kind to identify dominant periodicities in drought variability over the whole of Canada in terms of when the drought events occur, their duration, and how often they occur.

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