58,505 research outputs found
A Dain Inequality with charge
We prove an upper bound for angular-momentum and charge in terms of the mass
for electro-vacuum asymptotically flat axisymmetric initial data sets with
simply connected orbit space
The phase transition in the anisotropic Heisenberg model with long range dipolar interactions
In this work we have used extensive Monte Carlo calculations to study the
planar to paramagnetic phase transition in the two-dimensional anisotropic
Heisenberg model with dipolar interactions (AHd) considering the true
long-range character of the dipolar interactions by means of the Ewald
summation. Our results are consistent with an order-disorder phase transition
with unusual critical exponents in agreement with our previous results for the
Planar Rotator model with dipolar interactions. Nevertheless, our results
disagrees with the Renormalization Group results of Maier and Schwabl [PRB, 70,
134430 (2004)] and the results of Rapini et. al. [PRB, 75, 014425 (2007)],
where the AHd was studied using a cut-off in the evaluation of the dipolar
interactions. We argue that besides the long-range character of dipolar
interactions their anisotropic character may have a deeper effect in the system
than previously believed. Besides, our results shows that the use of a cut-off
radius in the evaluation of dipolar interactions must be avoided when analyzing
the critical behavior of magnetic systems, since it may lead to erroneous
results.Comment: Accepted for publication in the Journal of Magnetism and Magnetic
Materials. arXiv admin note: substantial text overlap with arXiv:1109.184
An Evolutionary Analysis of Investment in Electricity Markets
Electricity markets are being liberalised and open to private competition in several countries. These liberalized electricity markets are very complex as the interactions between demand and supply are subject to several technicalities arising from the commodity being traded: electricity. One of these technicalities is that generators cannot store electricity: this fact implies that it needs to generate its production real-time. A second problem with this market are the different generation technologies used at different levels of demand, which implies that at different times of the day different generation costs are supported to meet demand: due to ramp-rate constraints, capacity available, and fixed and start-up costs. In this paper we analyze the issue of investment and the electricity system’s long-term security in an industry where a regulator controls the short-term prices, imposing a perfect competition outcome for “low†demand hours and a price cap at times where load is shed. We look at the following research questions: a) How does the oligopolistic structure of the market interact with the value of the different technologies? b) How do players define their investment strategies? c) How do the regulatory policies affect the investment in generation? Do they work similarly under perfect competition and oligopoly? d) Can markets invest enough capacity to ensure the long run security of the market? The main results of our analysis are following: 1. The impact of a given investment on the market price is independent of the player investing. 2. The impact of an investment on price is a function of the technology in which the investment takes place and of the cycle to which the price refers to. 3. The impact of price caps on the evolution of the market structure is non-linear, it cannot be too low or too high. 4. An oligopolistic electricity market fails to deliver the needed investment unless the regulators intervene. 5. The higher the reserve margin the higher the total investment. However, this instrument by itself was not able to provide the incentive needed to ensure the long-term security of the system, as in any of the experiments analyzed the peak demand is not completely satisfied. 6. Even a slight increase in demand, due to the reserve margin, leads to important changes on the relative value of the different technologies. 7. The main task of the regulatory authorities is to define a level of capacity payments that give the necessary incentive to investment, at the minimum cost: Capacity Payments are very important in shaping the generation structure. 8. Uncertainty reduces the value of Peak plants: this result clearly contradicts any common sense in these matters, as one would expect the presence of price uncertainty to be beneficial to Peak plants. The proportion invested in baseload plants increases with uncertainty of the energy price, decreasing the investment in shoulder plant.agent-based, electricity markets, evolution, investment, regulation, simulation
On the equivalence of Lambda(t) and gravitationally induced particle production cosmologies
The correspondence between cosmological models powered by a decaying vacuum
energy density and gravitationally induced particle production is investigated.
Although being physically different in the physics behind them we show that
both classes of cosmologies under certain conditions can exhibit the same
dynamic and thermodynamic behavior. Our method is applied to obtain three
specific models that may be described either as Lambda(t)CDM or gravitationally
induced particle creation cosmologies. In the point of view of particle
production models, the later class of cosmologies can be interpreted as a kind
of one-component unification of the dark sector. By using current type Ia
supernovae data, recent estimates of the cosmic microwave background shift
parameter and baryon acoustic oscillations measurements we also perform a
statistical analysis to test the observational viability within the two
equivalent classes of models and we obtain the best-fit of the free parameters.
By adopting the Akaike information criterion we also determine the rank of the
models considered here. Finally, the particle production cosmologies (and the
associated decaying Lambda(t)-models) are modeled in the framework of field
theory by a phenomenological scalar field model.Comment: 9 pages, 3 figures, new comments and 8 references added. Accepted for
publication in Physics Letters
Mass, angular-momentum, and charge inequalities for axisymmetric initial data
We present the key elements of the proof of an upper bound for
angular-momentum and charge in terms of the mass for electro-vacuum
asymptotically flat axisymmetric initial data sets with simply connected orbit
space
Using zeros of the canonical partition function map to detect signatures of a Berezinskii-Kosterlitz-Thouless transition
Using the two dimensional model as a test case, we show that
analysis of the Fisher zeros of the canonical partition function can provide
signatures of a transition in the Berezinskii-Kosterlitz-Thouless ()
universality class. Studying the internal border of zeros in the complex
temperature plane, we found a scenario in complete agreement with theoretical
expectations which allow one to uniquely classify a phase transition as in the
class of universality. We obtain in excellent accordance with
previous results. A careful analysis of the behavior of the zeros for both
regions and in the
thermodynamic limit show that goes to zero in the former
case and is finite in the last one
Properties of Very Luminous Galaxies
Recent analysis of the SSRS2 data based on cell-counts and two-point
correlation function has shown that very luminous galaxies are much more
strongly clustered than fainter galaxies. In fact, the amplitude of the
correlation function of very luminous galaxies () asymptotically
approaches that of clusters. In this paper we investigate the
properties of the most luminous galaxies, with blue absolute magnitude . We find that: 1) the population mix is comparable to that in other ranges
of absolute magnitudes; 2) only a small fraction are located in bona fide
clusters; 3) the bright galaxy-cluster cross-correlation function is
significantly higher on large scales than that measured for fainter galaxies;
4) the correlation length of galaxies brighter than \MB ,
expressed as a function of the mean interparticle distance, appears to follow
the universal dimensionless correlation function found for clusters and radio
galaxies; 5) a large fraction of the bright galaxies are in interacting pairs,
others show evidence for tidal distortions, while some appear to be surrounded
by faint satellite galaxies. We conclude that very luminous optical galaxies
differ from the normal population of galaxies both in the clustering and other
respects. We speculate that this population is highly biased tracers of mass,
being associated to dark halos with masses more comparable to clusters than
typical loose groups.Comment: 29 pages (6 figures) + 2 tables; paper with all figures and images
available at http://boas5.bo.astro.it/~cappi/papers.html; The Astronomical
Journal, in pres
Predicting Intermediate Storage Performance for Workflow Applications
Configuring a storage system to better serve an application is a challenging
task complicated by a multidimensional, discrete configuration space and the
high cost of space exploration (e.g., by running the application with different
storage configurations). To enable selecting the best configuration in a
reasonable time, we design an end-to-end performance prediction mechanism that
estimates the turn-around time of an application using storage system under a
given configuration. This approach focuses on a generic object-based storage
system design, supports exploring the impact of optimizations targeting
workflow applications (e.g., various data placement schemes) in addition to
other, more traditional, configuration knobs (e.g., stripe size or replication
level), and models the system operation at data-chunk and control message
level.
This paper presents our experience to date with designing and using this
prediction mechanism. We evaluate this mechanism using micro- as well as
synthetic benchmarks mimicking real workflow applications, and a real
application.. A preliminary evaluation shows that we are on a good track to
meet our objectives: it can scale to model a workflow application run on an
entire cluster while offering an over 200x speedup factor (normalized by
resource) compared to running the actual application, and can achieve, in the
limited number of scenarios we study, a prediction accuracy that enables
identifying the best storage system configuration
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