scholarly journals Low-frequency pulse profile variation in PSR B2217+47: evidence for echoes from the interstellar medium

2018 ◽  
Vol 476 (2) ◽  
pp. 2704-2716 ◽  
Author(s):  
D Michilli ◽  
J W T Hessels ◽  
J Y Donner ◽  
J-M Grießmeier ◽  
M Serylak ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Low Frequency ◽  
Pulse Profile ◽  
Profile Variation ◽  
Frequency Pulse

scholarly journals Evolution of the low-frequency pulse profile of PSR B2217+47

2017 ◽  
Vol 13 (S337) ◽  
pp. 291-294 ◽  
Author(s):  
D. Michilli ◽  
J. W. T. Hessels ◽  
J. Y. Donner ◽  
J.-M. Grießmeier ◽  
M. Serylak ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Strong Correlation ◽  
Low Frequency ◽  
Main Peak ◽  
Dispersion Measure ◽  
Pulse Profile ◽  
Transient Component ◽  
Model Based ◽  
Weak Component ◽  
Frequency Pulse

AbstractAn evolution of the low-frequency pulse profile of PSR B2217+47 is observed during a six-year observing campaign with the LOFAR telescope at 150 MHz. The evolution is manifested as a new component in the profile trailing the main peak. The leading part of the profile, including a newly-observed weak component, is steady during the campaign. The transient component is not visible in simultaneous observations at 1500 MHz using the Lovell telescope, implying a chromatic effect. A variation in the dispersion measure of the source is detected in the same timespan. Precession of the pulsar and changes in the magnetosphere are investigated to explain the profile evolution. However, the listed properties favour a model based on turbulence in the interstellar medium (ISM). This interpretation is confirmed by a strong correlation between the intensity of the transient component and main peak in single pulses. Since PSR B2217+47 is the fourth brightest pulsar visible to LOFAR, we speculate that ISM-induced pulse profile evolution might be relatively common but subtle and that SKA-Low will detect many similar examples. In this scenario, similar studies of pulse profile evolution could be used in parallel with scintillation arcs to characterize the properties of the ISM.

scholarly journals INTERSTELLAR MEDIUM AND DECAMETER RADIO SPECTROSCOPY

2021 ◽  
Vol 26 (4) ◽  
pp. 314-325
Author(s):  
S. V. Stepkin ◽  
◽  
O. O. Konovalenko ◽  
Y. V. Vasylkivskyi ◽  
D. V. Mukha ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Radio Telescope ◽  
Radio Astronomy ◽  
Low Frequency ◽  
Spectral Lines ◽  
Physical Parameters ◽  
Recombination Mechanism ◽  
Radio Recombination Lines ◽  
Radio Spectroscopy ◽  
Correlation Spectrum

Purpose: The analytical review of the main results of research in the new direction of the low-frequency radio astronomy, the interstellar medium radio spectroscopy at decameter waves, which had led to astrophysical discovery, recording of the radio recombination lines in absorption for highly excited states of interstellar carbon atoms (more than 600). Design/methodology/approach: The UTR-2 world-largest broadband radio telescope of decameter waves optimally connected with the digital correlation spectrum analyzers has been used. Continuous modernization of antenna system and devices allowed increasing the analysis band from 100 kHzto 24 MHz and a number of channels from 32 to 8192. The radio telescope and receiving equipment with appropriate software allowed to have a long efficient integration time enough for a large line series simultaneously with high resolution, noise immunity and relative sensitivity. Findings: A new type of interstellar spectral lines has been discovered and studied, the interstellar carbon radio recombination lines in absorption for the record high excited atoms with principal quantum numbers greater than 1000. The line parameters (intensity, shape, width, radial velocity) and their relation ship with the interstellar medium physical parameters have been determined. The temperature of line forming regions is about 100 K, the electron concentration up to 0.1 cm–3 and the size of a line forming region is about 10 pc. For the first time, radio recombination lines were observed in absorption. They have significant broadening and are amplified by the dielectronic-like recombination mechanism and are also the lowest frequency lines in atomic spectroscopy. Conclusions: The detected low-frequency carbon radio recombination lines and their observations have become a new highly effective tool for the cold partially ionized interstellar plasma diagnostics. Using them allows obtaining the information which is not available with the other astrophysical methods. For almost half a century of their research, a large amount of hardware-methodical and astrophysical results have been obtained including a record number of Galaxy objects, where there levant lines have been recorded. The domestic achievements have stimulated many theoretical and experimental studies in other countries, but the scientific achievements of Ukrainian scientists prove the best prospects for further development of this very important area of astronomical science. Key words: low-frequency radio astronomy; radio telescope; interstellar medium; radio recombination lines; carbon; hydrogen; spectral analyzer

High‐power‐factor dimmable LED driver with low‐frequency pulse‐width modulation

2016 ◽  
Vol 9 (10) ◽  
pp. 2139-2146 ◽  
Author(s):  
Hung‐Liang Cheng ◽  
Yong‐Nong Chang ◽  
Chun‐An Cheng ◽  
Chien‐Hsuan Chang ◽  
Yu‐Hung Lin
Keyword(s):  
Power Factor ◽  
High Power ◽  
Pulse Width ◽  
Pulse Width Modulation ◽  
Low Frequency ◽  
Led Driver ◽  
High Power Factor ◽  
Frequency Pulse

Spike-timing-dependent plasticity model for low-frequency pulse waveform

2019 ◽  
Vol 24 (4) ◽  
pp. 452-459
Author(s):  
Masaya Ohara ◽  
Minami Kaneko ◽  
Fumio Uchikoba ◽  
Ken Saito
Keyword(s):  
Low Frequency ◽  
Spike Timing ◽  
Plasticity Model ◽  
Pulse Waveform ◽  
Spike Timing Dependent Plasticity ◽  
Dependent Plasticity ◽  
Frequency Pulse

scholarly journals Galactic neutral hydrogen and the magnetic ISM foreground

2017 ◽  
Vol 12 (S333) ◽  
pp. 146-150
Author(s):  
S.E. Clark
Keyword(s):  
Interstellar Medium ◽  
Dynamic Range ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Depth Resolution ◽  
High Dynamic Range ◽  
Neutral Gas ◽  
High Dynamic ◽  
New Generation ◽  
The Relationship

AbstractThe interstellar medium is suffused with magnetic fields, which inform the shape of structures in the diffuse gas. Recent high-dynamic range observations of Galactic neutral hydrogen, combined with novel data analysis techniques, have revealed a deep link between the morphology of neutral gas and the ambient magnetic field. At the same time, an observational revolution is underway in low-frequency radio polarimetry, driven in part by the need to characterize foregrounds to the cosmological 21-cm signal. A new generation of experiments, capable of high angular and Faraday depth resolution, are revealing complex filamentary structures in diffuse polarization. The relationship between filamentary structures observed in radio-polarimetric data and those observed in atomic hydrogen is not yet well understood. Multiwavelength observations will enable new insights into the magnetic interstellar medium across phases.

The effect of low frequency pulse-shaped substrate bias on the remote plasma deposition of a-Si : H thin films

2009 ◽  
Vol 19 (1) ◽  
pp. 015012 ◽  
Author(s):  
I T Martin ◽  
M A Wank ◽  
M A Blauw ◽  
R A C M M van Swaaij ◽  
W M M Kessels ◽  
...  
Keyword(s):  
Thin Films ◽  
Plasma Deposition ◽  
Low Frequency ◽  
Substrate Bias ◽  
Remote Plasma ◽  
Frequency Pulse

The INFITA low-frequency pulse physiotherapeutic device

1994 ◽  
Vol 28 (5) ◽  
pp. 284-287
Author(s):  
A. Yu. Zaslavskii ◽  
G. S. Markarov
Keyword(s):  
Low Frequency ◽  
Frequency Pulse

scholarly journals From unspecific to adjusted, how the BOLD response in the rat hippocampus develops during consecutive stimulations

2016 ◽  
Vol 37 (2) ◽  
pp. 590-604 ◽  
Author(s):  
Stephanie Riemann ◽  
Cornelia Helbing ◽  
Frank Angenstein
Keyword(s):  
High Frequency ◽  
Pulse Sequences ◽  
Low Frequency ◽  
Bold Response ◽  
Deconvolution Analysis ◽  
Bold Responses ◽  
Electrical Pulses ◽  
Stimulation Period ◽  
Frequency Pulse ◽  
Spiking Activity

To determine the possibility to deconvolve measured BOLD responses to neuronal signals, the rat perforant pathway was electrically stimulated with 10 related stimulation protocols. All stimulation protocols were composed of low-frequency pulse sequences with superimposed high-frequency pulse bursts. Because high-frequency pulse bursts trigger only one synchronized spiking of granular cells, variations of the stimulation protocol were used: (a) to keep the spiking activity similar during the presentation of different numbers of pulses, (b) to apply identical numbers of pulses to induce different amounts of spiking activity, and (c) to concurrently vary the number of applied electrical pulses and resultant spiking activity. When complex pulse sequences enter the hippocampus, an unspecific default-like BOLD response is first generated, which relates neither to the number of incoming pulses nor to the induced spiking activity. Only during subsequent stimulations does the initial unspecific response adjust to a more adequate response, which in turn either strongly related to spiking activity when low-frequency pulses were applied or depended on the incoming activity when high-frequency pulse bursts were presented. Thus, only the development of BOLD responses during repetitive stimulations can predict the underlying neuronal activity and deconvolution analysis should not be performed during an initial stimulation period.

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