3,624 research outputs found
Multiple resonance compensation for betatron coupling and its equivalence with matrix method
Analyses of betatron coupling can be broadly divided into two categories: the
matrix approach that decouples the single-turn matrix to reveal the normal
modes and the hamiltonian approach that evaluates the coupling in terms of the
action of resonances in perturbation theory. The latter is often regarded as
being less exact but good for physical insight. The common opinion is that the
correction of the two closest sum and difference resonances to the working
point is sufficient to reduce the off-axis terms in the 4X4 single-turn matrix,
but this is only partially true. The reason for this is explained, and a method
is developed that sums to infinity all coupling resonances and, in this way,
obtains results equivalent to the matrix approach. The two approaches is
discussed with reference to the dynamic aperture. Finally, the extension of the
summation method to resonances of all orders is outlined and the relative
importance of a single resonance compared to all resonances of a given order is
analytically described as a function of the working point.Comment: 22 pages, 10 figure
On the Impact of Fair Best Response Dynamics
In this work we completely characterize how the frequency with which each
player participates in the game dynamics affects the possibility of reaching
efficient states, i.e., states with an approximation ratio within a constant
factor from the price of anarchy, within a polynomially bounded number of best
responses. We focus on the well known class of congestion games and we show
that, if each player is allowed to play at least once and at most times
any best responses, states with approximation ratio times the
price of anarchy are reached after best
responses, and that such a bound is essentially tight also after exponentially
many ones. One important consequence of our result is that the fairness among
players is a necessary and sufficient condition for guaranteeing a fast
convergence to efficient states. This answers the important question of the
maximum order of needed to fast obtain efficient states, left open by
[9,10] and [3], in which fast convergence for constant and very slow
convergence for have been shown, respectively. Finally, we show
that the structure of the game implicitly affects its performances. In
particular, we show that in the symmetric setting, in which all players share
the same set of strategies, the game always converges to an efficient state
after a polynomial number of best responses, regardless of the frequency each
player moves with
Pion Generalized Parton Distributions within a fully covariant constituent quark model
We extend the investigation of the Generalized Parton Distribution for a
charged pion within a fully covariant constituent quark model, in two respects:
(i) calculating the tensor distribution and (ii) adding the treatment of the
evolution, needed for achieving a meaningful comparison with both the
experimental parton distribution and the lattice evaluation of the so-called
generalized form factors. Distinct features of our phenomenological covariant
quark model are: (i) a 4D Ansatz for the pion Bethe-Salpeter amplitude, to be
used in the Mandelstam formula for matrix elements of the relevant current
operators, and (ii) only two parameters, namely a quark mass assumed to hold
MeV and a free parameter fixed through the value of the pion decay
constant. The possibility of increasing the dynamical content of our covariant
constituent quark model is briefly discussed in the context of the Nakanishi
integral representation of the Bethe-Salpeter amplitude.Comment: Pages 20, figure 11 and table 8. Minor changes. To be published in
EPJ
Chaotic dynamics in a storage-ring Free Electron Laser
The temporal dynamics of a storage-ring Free Electron Laser is here
investigated with particular attention to the case in which an external
modulation is applied to the laser-electron beam detuning. The system is shown
to produce bifurcations, multi-furcations as well as chaotic regimes. The
peculiarities of this phenomenon with respect to the analogous behavior
displayed by conventional laser sources are pointed out. Theoretical results,
obtained by means of a phenomenological model reproducing the evolution of the
main statistical parameters of the system, are shown to be in a good agreement
with experiments carried out on the Super-ACO Free Electron Laser.Comment: submitted to Europ Phys. Journ.
Can a microscopic stochastic model explain the emergence of pain cycles in patients?
A stochastic model is here introduced to investigate the molecular mechanisms
which trigger the perception of pain. The action of analgesic drug compounds is
discussed in a dynamical context, where the competition with inactive species
is explicitly accounted for. Finite size effects inevitably perturb the
mean-field dynamics: Oscillations in the amount of bound receptors
spontaneously manifest, driven by the noise which is intrinsic to the system
under scrutiny. These effects are investigated both numerically, via stochastic
simulations and analytically, through a large-size expansion. The claim that
our findings could provide a consistent interpretative framework to explain the
emergence of cyclic behaviors in response to analgesic treatments, is
substantiated.Comment: J. Stat. Mech. (Proceedings UPON2008
Resonance families and their action on betatron motion
The present paper takes one step beyond the single-resonance theory for betatron motion by summing all the members of a given resonance family and expressing the joint influence in a single driving term. As a demonstration and confirmation of this work, the family driving terms are used to derive the classic closed-orbit and betatron-modulation equations of Courant and Snyder. A more serious demonstration is made by applying the family driving terms to the compensation of linear coupling and showing how numerical matrix-based and resonance compensation schemes are related. In a final phase, the Hénon map is used to compare the efficiency of different coupling compensation schemes with respect to dynamic aperture
Stochastic Turing Patterns on a Network
The process of stochastic Turing instability on a network is discussed for a
specific case study, the stochastic Brusselator model. The system is shown to
spontaneously differentiate into activator-rich and activator-poor nodes,
outside the region of parameters classically deputed to the deterministic
Turing instability. This phenomenon, as revealed by direct stochastic
simulations, is explained analytically, and eventually traced back to the
finite size corrections stemming from the inherent graininess of the
scrutinized medium.Comment: The movies referred to in the paper are provided upon request. Please
send your requests to Duccio Fanelli ([email protected]) or Francesca
Di Patti ([email protected]
Non-Gaussian fluctuations in stochastic models with absorbing barriers
The dynamics of a one-dimensional stochastic model is studied in presence of
an absorbing boundary. The distribution of fluctuations is analytically
characterized within the generalized van Kampen expansion, accounting for
higher order corrections beyond the conventional Gaussian approximation. The
theory is shown to successfully capture the non Gaussian traits of the sought
distribution returning an excellent agreement with the simulations, for {\it
all times} and arbitrarily {\it close} to the absorbing barrier. At large
times, a compact analytical solution for the distribution of fluctuations is
also obtained, bridging the gap with previous investigations, within the van
Kampen picture and without resorting to alternative strategies, as elsewhere
hypothesized.Comment: 2 figures, submitted to Phys. Rev. Let
parameters identification for scroll expander semi empirical model by using genetic algorithm
Abstract In this paper a small Organic Rankine Cycle (ORC) plant was tested under different operating conditions and by using refrigerants (R245fa) as working fluids. In particular, attention was posed towards the scroll expander of the power plant in order to identify experimental parameters to use in its predictive semi-empirical model. Experimental results obtained by imposing different operating conditions at the expander inlet section (i.e. temperature, pressure, mass flow rate) and different temperature at the condensation section, were used to validate the mathematical model. An in-house code (MatLab®/Scilab® based) using CoolProp® library for the accurate evaluation of fluid properties, was optimized by using a genetic algorithm implemented in modeFrontier® software. Thus, the validated model was used in predictive mode to evaluate the machine performances
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