8,936 research outputs found
Loop-Erasure of Plane Brownian Motion
We use the coupling technique to prove that there exists a loop-erasure of a
plane Brownian motion stopped on exiting a simply connected domain, and the
loop-erased curve is the reversal of a radial SLE curve.Comment: 10 page
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On defining partition entropy by inequalities
Partition entropy is the numerical metric of uncertainty within
a partition of a finite set, while conditional entropy measures the degree of
difficulty in predicting a decision partition when a condition partition is
provided. Since two direct methods exist for defining conditional entropy
based on its partition entropy, the inequality postulates of monotonicity,
which conditional entropy satisfies, are actually additional constraints on
its entropy. Thus, in this paper partition entropy is defined as a function
of probability distribution, satisfying all the inequalities of not only partition
entropy itself but also its conditional counterpart. These inequality
postulates formalize the intuitive understandings of uncertainty contained
in partitions of finite sets.We study the relationships between these inequalities,
and reduce the redundancies among them. According to two different
definitions of conditional entropy from its partition entropy, the convenient
and unified checking conditions for any partition entropy are presented, respectively.
These properties generalize and illuminate the common nature
of all partition entropies
Modeling and Detecting False Data Injection Attacks against Railway Traction Power Systems
Modern urban railways extensively use computerized sensing and control
technologies to achieve safe, reliable, and well-timed operations. However, the
use of these technologies may provide a convenient leverage to cyber-attackers
who have bypassed the air gaps and aim at causing safety incidents and service
disruptions. In this paper, we study false data injection (FDI) attacks against
railways' traction power systems (TPSes). Specifically, we analyze two types of
FDI attacks on the train-borne voltage, current, and position sensor
measurements - which we call efficiency attack and safety attack -- that (i)
maximize the system's total power consumption and (ii) mislead trains' local
voltages to exceed given safety-critical thresholds, respectively. To
counteract, we develop a global attack detection (GAD) system that serializes a
bad data detector and a novel secondary attack detector designed based on
unique TPS characteristics. With intact position data of trains, our detection
system can effectively detect the FDI attacks on trains' voltage and current
measurements even if the attacker has full and accurate knowledge of the TPS,
attack detection, and real-time system state. In particular, the GAD system
features an adaptive mechanism that ensures low false positive and negative
rates in detecting the attacks under noisy system measurements. Extensive
simulations driven by realistic running profiles of trains verify that a TPS
setup is vulnerable to the FDI attacks, but these attacks can be detected
effectively by the proposed GAD while ensuring a low false positive rate.Comment: IEEE/IFIP DSN-2016 and ACM Trans. on Cyber-Physical System
Many-body dynamics of a Bose system with attractive interactions on a ring
We investigate the many-body dynamics of an effectively attractive
one-dimensional Bose system confined in a toroidal trap. The mean-field theory
predicts that a bright-soliton state will be formed when increasing the
interparticle interaction over a critical point. The study of quantum many-body
dynamics in this paper reveals that there is a modulation instability in a
finite Bose system correspondingly. We show that Shannon entropy becomes
irregular near and above the critical point due to quantum correlations. We
also study the dynamical behavior of the instability by exploring the momentum
distribution and the fringe visibility, which can be verified experimentally by
releasing the trapComment: 6 pages,5 figure
Cylindrical vector beams for rapid polarization-dependent measurements in atomic systems
We demonstrate the use of cylindrical vector beams - beams with spatially
varying polarization - for detecting and preparing the spin of a warm rubidium
vapor in a spatially dependent manner. We show that a modified probe vector
beam can serve as an atomic spin analyzer for an optically pumped medium, which
spatially modulates absorption of the beam. We also demonstrate space-variant
atomic spin by optical pumping with the vector beams. The beams are thus
beneficial for making singleshot polarization-dependent measurements, as well
as for providing a means of preparing samples with position-dependent spin.Comment: 8 pages, 5 figures. Accepted in Optics Expres
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