The paper presents a method of performance estimation of IEEE 802.11 wireless networks with linear topology using Markovian arrival processes (MAP) for traffic modelling and phase-type (PH) ...distributions for service time approximation. PH -distribution is reconstructed from the data obtained from the simulation measurements. Markov processes space reduction methods are used to overcome the state-space explosion problem appearing in large-scaled networks analysis. Both tasks of reconstructing PH -distribution and MAP reduction are defined as optimization problems. The performance of the proposed methods is illustrated with numerical examples.
We present results from monitoring the multi-waveband flux, linear polarization, and parsec-scale structure of the quasar PKS 1510 - 089, concentrating on eight major {gamma}-ray flares that occurred ...during the interval 2009.0-2009.5. The {gamma}-ray peaks were essentially simultaneous with maxima at optical wavelengths, although the flux ratio of the two wave bands varied by an order of magnitude. The optical polarization vector rotated by 720 deg. during a five-day period encompassing six of these flares. This culminated in a very bright, {approx}1 day, optical and {gamma}-ray flare as a bright knot of emission passed through the highest-intensity, stationary feature (the 'core') seen in 43 GHz Very Long Baseline Array images. The knot continued to propagate down the jet at an apparent speed of 22c and emit strongly at {gamma}-ray energies as a months-long X-ray/radio outburst intensified. We interpret these events as the result of the knot following a spiral path through a mainly toroidal magnetic field pattern in the acceleration and collimation zone of the jet, after which it passes through a standing shock in the 43 GHz core and then continues downstream. In this picture, the rapid {gamma}-ray flares result from scattering of infrared seed photons from a relatively slow sheath of the jet as well as from optical synchrotron radiation in the faster spine. The 2006-2009.7 radio and X-ray flux variations are correlated at very high significance; we conclude that the X-rays are mainly from inverse Compton scattering of infrared seed photons by 20-40 MeV electrons.
Software development for controlling a group of UAVs Vishnevsky, Vladimir; Larionov, Andrey; Zvyagin, Maxim ...
The 4th International Conference on Future Networks and Distributed Systems (ICFNDS),
11/2020
Conference Proceeding
In recent years, the market for UAV is actively developing as new ways of using UAVs for both personal and industrial applications are being discovered. Many of their core differences allow ...employment of UAVs in greater numbers than their manned counterparts. A variety of tasks can be accomplished more efficiently by simultaneous usage of multiple UAVs, but this requires a high level of coordination between UAVs. This article discusses features, approaches, and algorithms of UAV group interaction and describes the developed software for centralized control of a small group of UAVs without direct communication between the group members.
Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical ...models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere. The flow velocity increases outward along the jet in an acceleration and collimation zone containing a coiled magnetic field. Detailed observations of outbursts of electromagnetic radiation, for which blazars are famous, can potentially probe the zone. It has hitherto not been possible to either specify the location of the outbursts or verify the general picture of jet formation. Here we report sequences of high-resolution radio images and optical polarization measurements of the blazar BL Lacertae. The data reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV gamma-ray energies, as well as a delayed outburst at radio wavelengths. We conclude that the event starts in a region with a helical magnetic field that we identify with the acceleration and collimation zone predicted by the theories. The feature brightens again when it crosses a standing shock wave corresponding to the bright 'core' seen on the images.
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