3,925 research outputs found
User Attraction via Wireless Charging in Cellular Networks
A strong motivation of charging depleted battery can be an enabler for
network capacity increase. In this light we propose a spatial attraction
cellular network (SAN) consisting of macro cells overlaid with small cell base
stations that wirelessly charge user batteries. Such a network makes battery
depleting users move toward the vicinity of small cell base stations. With a
fine adjustment of charging power, this user spatial attraction (SA) improves
in spectral efficiency as well as load balancing. We jointly optimize both
enhancements thanks to SA, and derive the corresponding optimal charging power
in a closed form by using a stochastic geometric approach.Comment: to be presented in IEEE International Symposium on Modeling and
Optimization in Mobile, Ad Hoc and Wireless Networks (WiOpt) Workshop on
Green Networks (GREENNET) 2016, Arizona, USA (8 pages, 4 figures
Nearly Deterministic Bell Measurement for Multiphoton Qubits and Its Application to Quantum Information Processing
We propose a Bell measurement scheme by employing a logical qubit in
Greenberger-Horne-Zeilinger (GHZ) entanglement with an arbitrary number of
photons. Remarkably, the success probability of the Bell measurement as well as
teleportation of the GHZ entanglement can be made arbitrarily high using only
linear optics elements and photon on-off measurements as the number of photons
increases. Our scheme outperforms previous proposals using single photon qubits
when comparing the success probabilities in terms of the average photon usages.
It has another important advantage for experimental feasibility that it does
not require photon number resolving measurements. Our proposal provides an
alternative candidate for all-optical quantum information processing.Comment: 7 pages (including supplementary material), 2 figures, to be
published in Phys. Rev. Let
Probabilistic safety assessment-based importance analysis of cyber-attacks on nuclear power plants
With the application of digital technology to safety-critical infrastructures, cyber-attacks have emerged as one of the new dangerous threats. In safety-critical infrastructures such as a nuclear power plant (NPP), a cyber-attack could have serious consequences by initiating dangerous events or rendering important safety systems unavailable. Since a cyber-attack is conducted intentionally, numerous possible cases should be considered for developing a cyber security system, such as the attack paths, methods, and potential target systems. Therefore, prior to developing a risk-informed cyber security strategy, the importance of cyber-attacks and significant critical digital assets (CDAs) should be analyzed. In this work, an importance analysis method for cyber-attacks on an NPP was proposed using the probabilistic safety assessment (PSA) method. To develop an importance analysis framework for cyber-attacks, possible cyber-attacks were identified with failure modes, and a PSA model for cyber-attacks was developed. For case studies, the quantitative evaluations of cyber-attack scenarios were performed using the proposed method. By using quantitative importance of cyber-attacks and identifying significant CDAs that must be defended against cyber-attacks, it is possible to develop an efficient and reliable defense strategy against cyber-attacks on NPPs
Invasion and Interaction Determine Population Composition in an Open Evolving System
It is well-known that interactions between species determine the population
composition in an ecosystem. Conventional studies have focused on fixed
population structures to reveal how interactions shape population compositions.
However, interaction structures are not fixed, but change over time due to
invasions. Thus, invasion and interaction play an important role in shaping
communities. Despite its importance, however, the interplay between invasion
and interaction has not been well explored. Here, we investigate how invasion
affects the population composition with interactions in open evolving systems
considering generalized Lotka-Volterra-type dynamics. Our results show that the
system has two distinct regimes. One is characterized by low diversity with
abrupt changes of dominant species in time, appearing when the interaction
between species is strong and invasion slowly occurs. On the other hand,
frequent invasions can induce higher diversity with slow changes in abundances
despite strong interactions. It is because invasion happens before the system
reaches its equilibrium, which drags the system from its equilibrium all the
time. All species have similar abundances in this regime, which implies that
fast invasion induces regime shift. Therefore, whether invasion or interaction
dominates determines the population composition.Comment: 15 pages (including supplementary material), 8 figures (4 figures in
main, 4 figures in SI
Motif Dynamics in Signed Directional Complex Networks
Complex networks evolve and vary their structure as time goes by. In
particular, the links in those networks have both a sign and a directionality.
To understand their structural principles, we measure the network motifs, which
are patterns that appear much more than one would expect in randomized
networks, considering both link properties. We propose motif dynamics, which is
a study to investigate the change in the number of motifs, and applied the
motif dynamics to an open evolving network model and empirical data. We confirm
that a non-cyclic motif has a greater correlation with the system size than a
cyclic structural motif. Furthermore, the motif dynamics can give us insight
into the friendship between freshmen in a university
The Light and Period Variations of the Eclipsing Binary BX Draconis
New CCD photometric observations of BX Dra were obtained for 26 nights from
2009 April to 2010 June. The long-term photometric behaviors of the system are
presented from detailed studies of the period and light variations, based on
the historical data and our new observations. All available light curves
display total eclipses at secondary minima and inverse O'Connell effects with
Max I fainter than Max II, which are satisfactorily modeled by adding the
slightly time-varying hot spot on the primary star. A total of 87 times of
minimum light spanning over about 74 yrs, including our 22 timing measurements,
were used for ephemeris computations. Detailed analysis of the O-C diagram
showed that the orbital period has changed in combinations with an upward
parabola and a sinusoidal variation. The continuous period increase with a rate
of +5.65 \times 10^-7 d yr^-1 is consistent with that calculated from the
Wilson-Devinney synthesis code. It can be interpreted as a mass transfer from
the secondary to the primary star at a rate of 2.74 \times 10^-7 M\odot yr^-1,
which is one of the largest rates for contact systems. The most likely
explanation of the sinusoidal variation with a period of 30.2 yrs and a
semi-amplitude of 0.0062 d is a light-traveltime effect due to the existence of
a circumbinary object. We suggest that BX Dra is probably a triple system,
consisting of a primary star with a spectral type of F0, its secondary
component of spectral type F1-2, and an unseen circumbinary object with a
minimum mass of M3 = 0.23 M\odot.Comment: 24 pages, including 5 figures and 9 tables, accepted for publication
in PAS
The Light and Period Variations of the Eclipsing Binary AA Ursae Majoris
We present new multiband CCD photometry for AA UMa made on 8 nights between
January and March 2009; the light curves are the first ever compiled.
Historical light curves, as well as ours, display partial eclipses and inverse
O'Connell effects with Max I fainter than Max II. Among possible spot models, a
cool spot on either of the component stars and its variability with time permit
good light-curve representations for the system. A total of 194 eclipse timings
over 81 yrs, including our five timings, were used for ephemeris computations.
We found that the orbital period of the system has varied due to a periodic
oscillation overlaid on an upward parabolic variation. The continuous period
increase at a fractional rate of 1.310 is consistent with
that calculated from the W-D code and can be interpreted as a thermal mass
transfer from the less to the more massive secondary star at a rate of
6.610 M yr. The periodic component is in
satisfactory accord with a light-time effect due to an unseen companion with a
period of 28.2 yrs, a semi-amplitude of 0.007 d, and a minimum mass of =0.25 but this period variation could also arise from
magnetic activity.Comment: 23 pages, including 5 figures and 8 tables, accepted for publication
in PAS
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