35,554 research outputs found
Dual condensates at finite isospin chemical potential
The dual observables as order parameters for center symmetry are tested at
finite isospin chemical potential in a Polyakov-loop enhanced chiral
model of QCD with physical quark masses. As a counterpart of the dressed
Polyakov-loop, the first Fourier moment of pion condensate is introduced for
under the temporal twisted boundary conditions for quarks.
We demonstrate that this dual condensate exhibits the similar temperature
dependence as the conventional Polyakov-loop. We confirm that its rapid
increase with is driven by the evaporating of pion condensation. On the
other hand, the dressed Polyakov-loop shows abnormal thermal behavior, which
even decreases with at low temperatures due to the influence of pion
condensate. We thus argue that in QCD the critical temperature extracting from
a dual observable may have nothing to do with the quark
confinement-deconfinement transition if the quark mass is very small.Comment: 8 pages, 6 figure
Securing UAV Communications Via Trajectory Optimization
Unmanned aerial vehicle (UAV) communications has drawn significant interest
recently due to many advantages such as low cost, high mobility, and on-demand
deployment. This paper addresses the issue of physical-layer security in a UAV
communication system, where a UAV sends confidential information to a
legitimate receiver in the presence of a potential eavesdropper which are both
on the ground. We aim to maximize the secrecy rate of the system by jointly
optimizing the UAV's trajectory and transmit power over a finite horizon. In
contrast to the existing literature on wireless security with static nodes, we
exploit the mobility of the UAV in this paper to enhance the secrecy rate via a
new trajectory design. Although the formulated problem is non-convex and
challenging to solve, we propose an iterative algorithm to solve the problem
efficiently, based on the block coordinate descent and successive convex
optimization methods. Specifically, the UAV's transmit power and trajectory are
each optimized with the other fixed in an alternating manner until convergence.
Numerical results show that the proposed algorithm significantly improves the
secrecy rate of the UAV communication system, as compared to benchmark schemes
without transmit power control or trajectory optimization.Comment: Accepted by IEEE GLOBECOM 201
Well-posedness in critical spaces for the compressible Navier-Stokes equations with density dependent viscosities
In this paper, we prove the local well-posedness in critical Besov spaces for
the compressible Navier-Stokes equations with density dependent viscosities
under the assumption that the initial density is bounded away from zero.Comment: 27page
Multiple Timescale Dispatch and Scheduling for Stochastic Reliability in Smart Grids with Wind Generation Integration
Integrating volatile renewable energy resources into the bulk power grid is
challenging, due to the reliability requirement that at each instant the load
and generation in the system remain balanced. In this study, we tackle this
challenge for smart grid with integrated wind generation, by leveraging
multi-timescale dispatch and scheduling. Specifically, we consider smart grids
with two classes of energy users - traditional energy users and opportunistic
energy users (e.g., smart meters or smart appliances), and investigate pricing
and dispatch at two timescales, via day-ahead scheduling and realtime
scheduling. In day-ahead scheduling, with the statistical information on wind
generation and energy demands, we characterize the optimal procurement of the
energy supply and the day-ahead retail price for the traditional energy users;
in realtime scheduling, with the realization of wind generation and the load of
traditional energy users, we optimize real-time prices to manage the
opportunistic energy users so as to achieve systemwide reliability. More
specifically, when the opportunistic users are non-persistent, i.e., a subset
of them leave the power market when the real-time price is not acceptable, we
obtain closedform solutions to the two-level scheduling problem. For the
persistent case, we treat the scheduling problem as a multitimescale Markov
decision process. We show that it can be recast, explicitly, as a classic
Markov decision process with continuous state and action spaces, the solution
to which can be found via standard techniques. We conclude that the proposed
multi-scale dispatch and scheduling with real-time pricing can effectively
address the volatility and uncertainty of wind generation and energy demand,
and has the potential to improve the penetration of renewable energy into smart
grids.Comment: Submitted to IEEE Infocom 2011. Contains 10 pages and 4 figures.
Replaces the previous arXiv submission (dated Aug-23-2010) with the same
titl
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