8,309 research outputs found
Inexactness of the Hydro-Thermal Coordination Semidefinite Relaxation
Hydro-thermal coordination is the problem of determining the optimal economic
dispatch of hydro and thermal power plants over time. The physics of
hydroelectricity generation is commonly simplified in the literature to account
for its fundamentally nonlinear nature. Advances in convex relaxation theory
have allowed the advent of Shor's semidefinite programming (SDP) relaxations of
quadratic models of the problem. This paper shows how a recently published SDP
relaxation is only exact if a very strict condition regarding turbine
efficiency is observed, failing otherwise. It further proposes the use of a set
of convex envelopes as a strategy to successfully obtain a stricter lower bound
of the optimal solution. This strategy is combined with a standard iterative
convex-concave procedure to recover a stationary point of the original
non-convex problem.Comment: Submitted to IEEE PES General Meeting 201
Noncommutative Field Theory and the Dynamics of Quantum Hall Fluids
We study the spectrum of density fluctuations of Fractional Hall Fluids in
the context of the noncommutative hidrodynamical model of Susskind. We show
that, within the weak-field expansion, the leading correction to the
noncommutative Chern--Simons Lagrangian (a Maxwell term in the effective
action,) destroys the incompressibility of the Hall fluid due to strong UV/IR
effects at one loop. We speculate on possible relations of this instability
with the transition to the Wigner crystal, and conclude that calculations
within the weak-field expansion must be carried out with an explicit
ultraviolet cutoff at the noncommutativity scale. We point out that the
noncommutative dipoles exactly match the spatial structure of the
Halperin--Kallin quasiexcitons. Therefore, we propose that the noncommutative
formalism must describe accurately the spectrum at very large momenta, provided
no weak-field approximations are made. We further conjecture that the
noncommutative open Wilson lines are `vertex operators' for the quasiexcitons.Comment: 20 pages, harvma
Klebanov-Witten theory with massive dynamical flavors
We consider the addition of a large number of massive dynamical flavors to
the Klebanov-Witten theory, the quiver gauge theory describing the low energy
dynamics of Nc D3-branes at the conifold singularity. Massive flavors are
introduced by means of Nf D7-branes which are holomorphically embedded and
smeared along the transverse directions. After some general comments on the
validity of the smearing procedure, we find the full backreacted supergravity
solution corresponding to a particular class of massive embeddings. The
solution depends on a running effective number of flavors, whose functional
form follows from the smeared embedding. The running reflects the integrating
in/out of massive degrees of freedom in the dual field theory as the energy
scale is changed. We study how the dynamics of the theory depends on the flavor
parameters, mainly focusing on the static quark-antiquark potential. As
expected, we find that the dynamical flavors tend to screen the static color
charges.Comment: 31 pages, 8 figures; v2: few comments and a reference added, minor
change
Non chiral dynamical flavors and screening on the conifold
We present a new class of string theory solutions which are conjectured to be
dual to the N=1 conifold theory by Klebanov and Witten coupled to non chiral
massive dynamical flavors. These are introduced, in the Veneziano limit, by
means of suitably embedded and smeared D7-branes whose full backreaction on the
background is taken into account. The string solutions are used to study
chromoelectric charge screening effects due to the dynamical flavors in the non
perturbative regime of the dual gauge theories.Comment: 6 pages, 1 figure, previously unpublished results presented.
Contribution to the proceedings of the RTN workshop "Constituents,
Fundamental Forces and Symmetries of the Universe", Varna, Bulgaria,
September 11-17, 200
Holographic Flavored Quark-Gluon Plasmas
Holography provides a novel method to study the physics of Quark Gluon
Plasmas, complementary to the ordinary field theory and lattice approaches. In
this context, we analyze the informations that can be obtained for strongly
coupled Plasmas containing dynamical flavors, also in the presence of a finite
baryon chemical potential. In particular, we discuss the jet quenching and the
hydrodynamic transport coefficients.Comment: 10 pages. Contribution to the proceedings of the workshop "The many
faces of QCD", Ghent (Belgium), November 1-5 201
Nonthermal processes and neutrino emission from the black hole GRO J0422+32 in a bursting state
GRO J0422+32 is a member of the class of low-mass X-ray binaries (LMXBs). It
was discovered during an outburst in 1992. During the entire episode a
persistent power-law spectral component extending up to MeV was
observed, which suggests that nonthermal processes should have occurred in the
system. We study relativistic particle interactions and the neutrino production
in the corona of GRO J0422+32, and explain the behavior of GRO J0422+32 during
its recorded flaring phase. We have developed a magnetized corona model to fit
the spectrum of GRO J0422+32 during the low-hard state. We also estimate
neutrino emission and study the detectability of neutrinos with 1 km
detectors, such as IceCube. The short duration of the flares ( hours) and
an energy cutoff around a few TeV in the neutrino spectrum make neutrino
detection difficult. There are, however, many factors that can enhance neutrino
emission. The northern-sky coverage and full duty cycle of IceCube make it
possible to detect neutrino bursts from objects of this kind through
time-dependent analysis.Comment: 12 pages, 11 figures, accepted for publication in A&
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