Jun-Yi Wang

Confirming the 115.5-day periodicity in the X-ray light curve of ULX NGC 5408 X-1

The Swift/XRT light curve of the ultraluminous X-ray source NGC 5408 X-1 was re-analyzed with two new numerical approaches, the Weighted Wavelet Z-transform and CLEANest, and the results are different from previous studies. Both techniques detected a prominent periodicity with a time scale of 115.5 +/- 1.5 days, in excellent agreement with the detection of the same periodicity first reported by Strohmayer. Monte Carlo simulations were employed to test the statisitical confidence of the 115.5-day periodicity, yielding a statistical significance of >99.98% (or > 3.8 sigma). The robust detection of the 115.5-day quasi-periodic oscillations, if they are due to the orbital motion of the binary, would infer a mass of a few thousand M-circle dot for the central black hole, implying there is an intermediate-mass black hole in NGC 5408 X-1.

Periodic radio variability in NRAO 530: phase dispersion minimization analysis

A periodicity analysis of the radio light curves of the blazar NRAO 530 at 14.5, 8.0, and 4.8 GHz is presented employing an improved phase dispersion minimization technique. The result, which shows two persistent periodic components of similar to 6 and similar to 10 yr at all three frequencies, is consistent with the results obtained with the Lomb-Scargle periodogram and weighted wavelet Z-transform algorithms. The reliability of the derived periodicities is confirmed by the Monte Carlo numerical simulations which show a high statistical confidence. (Quasi-)Periodic fluctuations of the radio luminosity of NRAO 530 might be associated with the oscillations of the accretion disk triggered by hydrodynamic instabilities of the accreted flow.

Random Linear Coding for File Sharing in Upload-Limited Wireless Packet Networks

Random Linear Coding (RLC) [2] is a form of network coding where each network node, rather than forwarding packets unchanged along the path from source-to-destination, forwards random linear combinations of the data it has received. In this paper, the benefits of using Random Linear Coding(RLC) for data sharing in upload-limited wireless packet networks is investigated. Through simulations, we demonstrate the number of nodes that can share a data file increases with RLC compared to that with routing only. Especially, when the wireless connections experience high loss rates and (or) the limit of upload is small, RLC together with placing more resource nodes can be a very efficient method to improve the ratio of successful download.

Temporal evolution of long-timescale periodicities in ULX NGC 5408 X-1

Context. NGC 5408 X-1 is one of the few ultraluminous X-ray sources with an extensive monitoring program in X-rays (a temporal baseline of 4.2 yr), making it one of the most suitable candidates to study the long-timescale quasi-periodic oscillations (QPOs). Aims. Previous timing analysis of the Swift data of NGC 5408 X-1 led to detection of multiple periodicities ranging from 2.6 d to 230 d. In this paper, we focus on the statistical significance and the temporal evolution of these periodicities. Methods. A time-series analysis technique in the time-frequency domain, the weighted wavelet Z-transform (WWZ), was employed to identify the periodicities and trace their variations with time. Results. Three periodic components were detected from the WWZ periodogram, corresponding to periods of 2.65

Dynamic Power Allocation for a Hybrid Energy Harvesting Transmitter with Multiuser in Fading Channels

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Dynamic Power Control for Throughput Maximization in Hybrid Energy Harvesting Node

0.01 d, 115.4

Multiple periodic oscillations analysis on astronomy signals using an Empirical Mode Decomposition-Ornstein Uhlenbeck method

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Periodic radio variabilities of the blazar 1156+295: harmonic oscillations

14.4 d and 189.1

Periodic radio variabilities in NRAO 530: a jet–disc connection?

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Periodic radio variabilities in NRAO 530: a jet-disc connection? (vol 434, pg 3487, 2013)

15.2 d. All three have statistical significance higher than 99.74%. The 2.65-d periodicity is quite stable in the majority of the light curve. The 115-d periodicity is the most prominent but appears variable. The 189-d periodicity is persistent across the whole time coverage. It shows a steadily decreasing trend from the beginning (193 d period) to the end (181 d period). Conclusions. The long-timescale periodicities in NGC 5408 X-1 are most likely of super-orbital origin, and are probably associated with the precession of a warped accretion disc. The disc may have been broken into two distinct planes with different precessing periods, i.e. the 189-d and 115-d periodicities corresponding to the outer and inner disc, respectively.