47,833 research outputs found
Holographic renormalisation group flows and renormalisation from a Wilsonian perspective
From the Wilsonian point of view, renormalisable theories are understood as
submanifolds in theory space emanating from a particular fixed point under
renormalisation group evolution. We show how this picture precisely applies to
their gravity duals. We investigate the Hamilton-Jacobi equation satisfied by
the Wilson action and find the corresponding fixed points and their
eigendeformations, which have a diagonal evolution close to the fixed points.
The relevant eigendeformations are used to construct renormalised theories. We
explore the relation of this formalism with holographic renormalisation. We
also discuss different renormalisation schemes and show that the solutions to
the gravity equations of motion can be used as renormalised couplings that
parametrise the renormalised theories. This provides a transparent connection
between holographic renormalisation group flows in the Wilsonian and
non-Wilsonian approaches. The general results are illustrated by explicit
calculations in an interacting scalar theory in AdS space.Comment: 63 pages. Minor changes and references added. Matches JHEP versio
Periodic Modulation Induced Increase of Reaction Rates in Autocatalytic Systems
We propose a new mechanism to increase the reactions ratesin multistable
autocatalytic systems. The mechanism is based upon the possibility for the
enhancement of the response of the system due to the cooperative behavior
between the noise and an external periodic modulation. In order to illustrate
this feature we compute the reaction velocities for the particular case of the
Sel'Kov model, showing that they increase significantly when the periodic
modulation is introduced. This behavior originates from the existence of a
minimum in the mean first passage time, one of the signatures of stochastic
resonance.Comment: Submitted to J. Chem. Phy
Gluino zero-modes for non-trivial holonomy calorons
We couple fermion fields in the adjoint representation (gluinos) to the SU(2)
gauge field of unit charge calorons defined on R^3 x S_1. We compute
corresponding zero-modes of the Dirac equation. These are relevant in
semiclassical studies of N=1 Super-symmetric Yang-Mills theory. Our formulas,
show that, up to a term proportional to the vector potential, the modes can be
constructed by different linear combinations of two contributions adding up to
the total caloron field strength.Comment: 17 pages, 3 Postscript figures, late
A mathematical formalization of the parallel replica dynamics
The purpose of this article is to lay the mathematical foundations of a well
known numerical approach in computational statistical physics and molecular
dynamics, namely the parallel replica dynamics introduced by A.F. Voter. The
aim of the approach is to efficiently generate a coarse-grained evolution (in
terms of state-to-state dynamics) of a given stochastic process. The approach
formally consists in concurrently considering several realizations of the
stochastic process, and tracking among the realizations that which, the
soonest, undergoes an important transition. Using specific properties of the
dynamics generated, a computational speed-up is obtained. In the best cases,
this speed-up approaches the number of realizations considered. By drawing
connections with the theory of Markov processes and, in particular, exploiting
the notion of quasi-stationary distribution, we provide a mathematical setting
appropriate for assessing theoretically the performance of the approach, and
possibly improving it
A spherical Hopfield model
We introduce a spherical Hopfield-type neural network involving neurons and
patterns that are continuous variables. We study both the thermodynamics and
dynamics of this model. In order to have a retrieval phase a quartic term is
added to the Hamiltonian. The thermodynamics of the model is exactly solvable
and the results are replica symmetric. A Langevin dynamics leads to a closed
set of equations for the order parameters and effective correlation and
response function typical for neural networks. The stationary limit corresponds
to the thermodynamic results. Numerical calculations illustrate our findings.Comment: 9 pages Latex including 3 eps figures, Addition of an author in the
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Factors Affecting Process Effectiveness in The Development Of Information Systems: A Case Study
In the framework of the concept of systemic global quality, process effectiveness, the dimension of quality in information systems, is associated to human, social and organizational aspects surrounding the development process thereof[Silva,96].The field study undertaken is of an exploratorynature and included the selection of the organization where the study is to be carried out and the set of projects to be analyzed. The set of variables to be observed was also selected and operational definitions were set forth for each one of them. Data was collected through the use of questionnaires, interviews and group discussions. Finally, the data collected was analyzed combining descriptive statistical methods and qualitative-type analyse
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