20,896 research outputs found
Thermal effects in perturbative noncommutative gauge theories
The thermodynamics of gauge theories on the noncommutative plane is studied
in perturbation theory. For U(1) noncommutative Yang-Mills we compute the first
quantum correction to the ideal gas free energy density and study their
behavior in the low and high temperature regimes. Since the noncommutativity
scale effectively cutoff interactions at large distances, the theory is regular
in the infrared. In the case of U(N) noncommutative Yang-Mills we evaluate the
two-loop free energy density and find that it depends on the noncommutativity
parameter through the contribution of non-planar diagrams.Comment: 15 pages, harvmac. Minor changes with respect to v2. Footnote
expanded, remark added in Section 3, typos corrected and references added.
Final version to be published in JHE
Spiral structure of the Third Galactic Quadrant and the solution to the Canis Major debate
With the discovery of the Sagittarius dwarf spheroidal (Ibata et al. 1994), a
galaxy caught in the process of merging with the Milky Way, the hunt for other
such accretion events has become a very active field of astrophysical research.
The identification of a stellar ring-like structure in Monoceros, spanning more
than 100 degrees (Newberg et al. 2002), and the detection of an overdensity of
stars in the direction of the constellation of Canis Major (CMa, Martin et al.
2004), apparently associated to the ring, has led to the widespread belief that
a second galaxy being cannibalised by the Milky Way had been found. In this
scenario, the overdensity would be the remaining core of the disrupted galaxy
and the ring would be the tidal debris left behind. However, unlike the
Sagittarius dwarf, which is well below the Galactic plane and whose orbit, and
thus tidal tail, is nearly perpendicular to the plane of the Milky Way, the
putative CMa galaxy and ring are nearly co-planar with the Galactic disk. This
severely complicates the interpretation of observations. In this letter, we
show that our new description of the Milky Way leads to a completely different
picture. We argue that the Norma-Cygnus spiral arm defines a distant stellar
ring crossing Monoceros and the overdensity is simply a projection effect of
looking along the nearby local arm. Our perspective sheds new light on a very
poorly known region, the third Galactic quadrant (3GQ), where CMa is located.Comment: 5 pages, 2 figures. Quality of Fig 1 has been degraded to make it
smaller. Original fig. available on request. accepted for publication in
MNRAS letter
Capital costs in tidal stream energy projects - A spatial approach
Tidal stream energy projects involve high amounts of capital, for which ex-ante economic assessments are crucial. Unfortunately, the existing models to estimate the capital costs of a tidal stream energy project are often oversimplified. Focused on single estimates on a per installed power basis, such models fail to capture the all-important sensitivity of the capital costs to project site-specific characteristics (water depth, distance to the shoreline, etc.) The objective of this work is twofold: (1) to develop a new formulation for estimating the capital costs of a tidal stream farm, and (2) to implement this formula in a Matlab-based tool coupled with a Navier-Stokes solver and thus deliver the spatial distribution of this cost. As a case study, the new tool is applied to the Bristol Channel - the single largest resource area for tidal energy in the UK. Here, the best sites to install tidal stream farms are identified, with a cost comparable to that of offshore wind energy. Simulation results show that the proposed method is more efficient than the existing approaches. The results of this work have relevant policy implications in that they serve as decision criteria for allocating tidal stream projects and for designating supporting mechanisms
Interacting social processes on interconnected networks
We propose and study a model for the interplay between two different
dynamical processes --one for opinion formation and the other for decision
making-- on two interconnected networks and . The opinion dynamics on
network corresponds to that of the M-model, where the state of each agent
can take one of four possible values (), describing its level of
agreement on a given issue. The likelihood to become an extremist ()
or a moderate () is controlled by a reinforcement parameter .
The decision making dynamics on network is akin to that of the
Abrams-Strogatz model, where agents can be either in favor () or against
() the issue. The probability that an agent changes its state is
proportional to the fraction of neighbors that hold the opposite state raised
to a power . Starting from a polarized case scenario in which all agents
of network hold positive orientations while all agents of network have
a negative orientation, we explore the conditions under which one of the
dynamics prevails over the other, imposing its initial orientation. We find
that, for a given value of , the two-network system reaches a consensus
in the positive state (initial state of network ) when the reinforcement
overcomes a crossover value , while a negative consensus happens
for . In the phase space, the system displays a
transition at a critical threshold , from a coexistence of both
orientations for to a dominance of one orientation for
. We develop an analytical mean-field approach that gives an
insight into these regimes and shows that both dynamics are equivalent along
the crossover line .Comment: 25 pages, 6 figure
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