2,695 research outputs found
Oscillation death in coupled counter-rotating identical nonlinear oscillators
We study oscillatory and oscillation suppressed phases in coupled
counter-rotating nonlinear oscillators. We demonstrate the existence of limit
cycle, amplitude death, and oscillation death, and also clarify the Hopf,
pitchfork, and infinite period bifurcations between them. Especially, the
oscillation death is a new type of oscillation suppressions of which the
inhomogeneous steady states are neutrally stable. We discuss the robust neutral
stability of the oscillation death in non-conservative systems via the
anti-PT-symmetric phase transitions at exceptional points in terms of
non-Hermitian systems.Comment: 7 pages, 4 figure
Amplitude death in a ring of nonidentical nonlinear oscillators with unidirectional coupling
We study the collective behaviors in a ring of coupled nonidentical nonlinear
oscillators with unidirectional coupling, of which natural frequencies are
distributed in a random way. We find the amplitude death phenomena in the case
of unidirectional couplings and discuss the differences between the cases of
bidirectional and unidirectional couplings. There are three main differences;
there exists neither partial amplitude death nor local clustering behavior but
oblique line structure which represents directional signal flow on the
spatio-temporal patterns in the unidirectional coupling case. The
unidirectional coupling has the advantage of easily obtaining global amplitude
death in a ring of coupled oscillators with randomly distributed natural
frequency. Finally, we explain the results using the eigenvalue analysis of
Jacobian matrix at the origin and also discuss the transition of dynamical
behavior coming from connection structure as coupling strength increases.Comment: 14 pages, 11 figure
An Efficient and Secure m
Recent rapid developments in wireless and mobile IT technologies have led to their application in many real-life areas, such as disasters, home networks, mobile social networks, medical services, industry, schools, and the military. Business/work environments have become wire/wireless, integrated with wireless networks. Although the increase in the use of mobile devices that can use wireless networks increases work efficiency and provides greater convenience, wireless access to networks represents a security threat. Currently, wireless intrusion prevention systems (IPSs) are used to prevent wireless security threats. However, these are not an ideal security measure for businesses that utilize mobile devices because they do not take account of temporal-spatial and role information factors. Therefore, in this paper, an efficient and secure mobile-IPS (m-IPS) is proposed for businesses utilizing mobile devices in mobile environments for human-centric computing. The m-IPS system incorporates temporal-spatial awareness in human-centric computing with various mobile devices and checks users’ temporal spatial information, profiles, and role information to provide precise access control. And it also can extend application of m-IPS to the Internet of things (IoT), which is one of the important advanced technologies for supporting human-centric computing environment completely, for real ubiquitous field with mobile devices
A New Hardware Correlator in Korea: Performance Evaluation using KVN observations
We report results of the performance evaluation of a new hardware correlator
in Korea, the Daejeon correlator, developed by the Korea Astronomy and Space
Science Institute (KASI) and the National Astronomical Observatory of Japan
(NAOJ). We conducted Very Long Baseline Interferometry (VLBI) observations at
22~GHz with the Korean VLBI Network (KVN) in Korea and the VLBI Exploration of
Radio Astrometry (VERA) in Japan, and correlated the aquired data with the
Daejeon correlator. For evaluating the performance of the new hardware
correlator, we compared the correlation outputs from the Daejeon correlator for
KVN observations with those from a software correlator, the Distributed FX
(DiFX). We investigated the correlated flux densities and brightness
distributions of extragalactic compact radio sources. The comparison of the two
correlator outputs show that they are consistent with each other within ,
which is comparable with the amplitude calibration uncertainties of KVN
observations at 22~GHz. We also found that the 8\% difference in flux density
is caused mainly by (a) the difference in the way of fringe phase tracking
between the DiFX software correlator and the Daejeon hardware correlator, and
(b) an unusual pattern (a double-layer pattern) of the amplitude correlation
output from the Daejeon correlator. The visibility amplitude loss by the
double-layer pattern is as small as 3\%. We conclude that the new hardware
correlator produces reasonable correlation outputs for continuum observations,
which are consistent with the outputs from the DiFX software correlator.Comment: 13 pagee, 9 figures, 3 tables, to appear in JKAS (received February
9, 2015; accepted March 16, 2015
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