1,143 research outputs found
Short-Time Critical Dynamics of Damage Spreading in the Two-Dimensional Ising Model
The short-time critical dynamics of propagation of damage in the Ising
ferromagnet in two dimensions is studied by means of Monte Carlo simulations.
Starting with equilibrium configurations at and magnetization
, an initial damage is created by flipping a small amount of spins in one
of the two replicas studied. In this way, the initial damage is proportional to
the initial magnetization in one of the configurations upon quenching the
system at , the Onsager critical temperature of the
ferromagnetic-paramagnetic transition. It is found that, at short times, the
damage increases with an exponent , which is much larger
than the exponent characteristic of the initial increase of the
magnetization . Also, an epidemic study was performed. It is found that
the average distance from the origin of the epidemic ()
grows with an exponent , which is the same,
within error bars, as the exponent . However, the survival
probability of the epidemics reaches a plateau so that . On the other
hand, by quenching the system to lower temperatures one observes the critical
spreading of the damage at , where all the measured
observables exhibit power laws with exponents , , and .Comment: 11 pages, 9 figures (included). Phys. Rev. E (2010), in press
Correlation-Dimension Calculations for Broadband Intensity Fluctuations in Emission from a Heavily Saturated Source of Amplified Spontaneous Emission
Broadband intensity fluctuations from a heavily saturated source of amplified spontaneous emission (ASE) operating on the 3.51-μm transition of xenon show no evidence of a dynamical origin represented by a low-dimensional underlying chaotic attractor. The broadband coupled-mode fluctuations in ASE thus seem to be stochastic when contrasted with the recently reported deterministic nature of similar broadband fluctuations of single-mode lasers operating on the same transition
Correlation-Dimension Calculations for Broadband Intensity Fluctuations in Emission from a Heavily Saturated Source of Amplified Spontaneous Emission
Broadband intensity fluctuations from a heavily saturated source of amplified spontaneous emission (ASE) operating on the 3.51-μm transition of xenon show no evidence of a dynamical origin represented by a low-dimensional underlying chaotic attractor. The broadband coupled-mode fluctuations in ASE thus seem to be stochastic when contrasted with the recently reported deterministic nature of similar broadband fluctuations of single-mode lasers operating on the same transition
Semiclassical Analysis of a Detuned Ring Laser with a Saturable Absorber: New Results for the Steady States
This paper presents new results for the steady states of a detuned ring laser with a saturable absorber. We employ a semiclassical model which assumes homogeneously broadened two-level atoms. We proceed by solving the Maxwell-Bloch equations for the longitudinal dependence of the steady states of this system, and then simplify our solution by use of the uniform-field approximation. We present uniform-field results for squared electric field versus operating frequency, and for each of these versus cavity tuning and laser excitation. Various cavity linewidths and both resonant and nonresonant amplifier and absorber line-center frequencies are considered. The most notable finding is that cavity detuning breaks the degeneracies found in the steady-state solutions of the fully tuned case. This leads to the prediction that an actual system will bifurcate from the zero-intensity solution to a steady-state solution as laser excitation increases from zero, rather than to the small-amplitude pulsations found for the model with exactly resonant tuning of the cavity and the media line centers. Other phenomena suggested by the steady-state results include tuning-dependent hysteresis and bistability, and instability in both intensity and frequency due to the appearance of one or more new steady-state solutions as tuning is varied. These effects of detuning are being tested by a linearized stability analysis whose results will be reported separately
Semiclassical Analysis of a Detuned Ring Laser with a Saturable Absorber: New Results for the Steady States
This paper presents new results for the steady states of a detuned ring laser with a saturable absorber. We employ a semiclassical model which assumes homogeneously broadened two-level atoms. We proceed by solving the Maxwell-Bloch equations for the longitudinal dependence of the steady states of this system, and then simplify our solution by use of the uniform-field approximation. We present uniform-field results for squared electric field versus operating frequency, and for each of these versus cavity tuning and laser excitation. Various cavity linewidths and both resonant and nonresonant amplifier and absorber line-center frequencies are considered. The most notable finding is that cavity detuning breaks the degeneracies found in the steady-state solutions of the fully tuned case. This leads to the prediction that an actual system will bifurcate from the zero-intensity solution to a steady-state solution as laser excitation increases from zero, rather than to the small-amplitude pulsations found for the model with exactly resonant tuning of the cavity and the media line centers. Other phenomena suggested by the steady-state results include tuning-dependent hysteresis and bistability, and instability in both intensity and frequency due to the appearance of one or more new steady-state solutions as tuning is varied. These effects of detuning are being tested by a linearized stability analysis whose results will be reported separately
Study of the one-dimensional off-lattice hot-monomer reaction model
Hot monomers are particles having a transient mobility (a ballistic flight)
prior to being definitely absorbed on a surface. After arriving at a surface,
the excess energy coming from the kinetic energy in the gas phase is dissipated
through degrees of freedom parallel to the surface plane. In this paper we
study the hot monomer-monomer adsorption-reaction process on a continuum
(off-lattice) one-dimensional space by means of Monte Carlo simulations. The
system exhibits second-order irreversible phase transition between a reactive
and saturated (absorbing) phases which belong to the directed percolation (DP)
universality class. This result is interpreted by means of a coarse-grained
Langevin description which allows as to extend the DP conjecture to transitions
occurring in continuous media.Comment: 13 pages, 5 figures, final version to appear in J. Phys.
Analytic and Gevrey Hypoellipticity for Perturbed Sums of Squares Operators
We prove a couple of results concerning pseudodifferential perturbations of
differential operators being sums of squares of vector fields and satisfying
H\"ormander's condition. The first is on the minimal Gevrey regularity: if a
sum of squares with analytic coefficients is perturbed with a
pseudodifferential operator of order strictly less than its subelliptic index
it still has the Gevrey minimal regularity. We also prove a statement
concerning real analytic hypoellipticity for the same type of
pseudodifferential perturbations, provided the operator satisfies to some extra
conditions (see Theorem 1.2 below) that ensure the analytic hypoellipticity
Is the dry-band characteristic a function of pollution and insulator design?
This research work aims to assess whether dry-band formation and location are function of pollution level with the application of new insulator surface design. Artificial pollution tests have been performed on a 4-shed 11kV insulators with conventional and textured surface designs in clean-fog chamber and a voltage ramp shape source. The statistical location and extension of the dry-bands during these comparative tests have been analysed and it may offer good suggestions to establish design guidelines in dry-band control
Introduction to Loop Quantum Gravity. The Holst's action and the covariant formalism
We review Holst formalism and we discuss dynamical equivalence with standard
GR (in dimension 4). Holst formalism is written for a spin coframe field
and a -connection on spacetime and
it depends on the Holst parameter .
We show the model is dynamically equivalent to standard GR, in the sense that
up to a pointwise -gauge transformation acting on frame indices,
solutions of the two models are in one-to-one correspondence. Hence the two
models are classically equivalent.
One can also introduce new variables by splitting the spin connection into a
pair of a -connection and a -valued 1-form
. The construction of these new variables relies on a particular
algebraic structure, called a reductive splitting. A reductive splitting is a
weaker structure than requiring that the gauge group splits as the products of
two sub-groups, as it happens in Euclidean signature in the selfdual
formulation originally introduced in this context by Ashtekar, and it still
allows to deal with the Lorentzian signature without resorting to
complexifications.
The reductive splitting of is not unique and it is
parameterized by a real parameter , called the Immirzi parameter. The
splitting is here done on spacetime, not on space, to obtain a
-connection , which is called the Barbero-Immirzi connection
on spacetime. One obtains a covariant model depending on the fields which is again dynamically equivalent to standard GR (as
well as the Holst action).
Usually, in the literature one sets for the sake of
simplicity. Here we keep the Holst and Immirzi parameters distinct to show that
eventually, only will survive in boundary field equations.Comment: 19 page
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