307 research outputs found
Solitons in the noisy Burgers equation
We investigate numerically the coupled diffusion-advective type field
equations originating from the canonical phase space approach to the noisy
Burgers equation or the equivalent Kardar-Parisi-Zhang equation in one spatial
dimension. The equations support stable right hand and left hand solitons and
in the low viscosity limit a long-lived soliton pair excitation. We find that
two identical pair excitations scatter transparently subject to a size
dependent phase shift and that identical solitons scatter on a static soliton
transparently without a phase shift. The soliton pair excitation and the
scattering configurations are interpreted in terms of growing step and
nucleation events in the interface growth profile. In the asymmetrical case the
soliton scattering modes are unstable presumably toward multi soliton
production and extended diffusive modes, signalling the general
non-integrability of the coupled field equations. Finally, we have shown that
growing steps perform anomalous random walk with dynamic exponent z=3/2 and
that the nucleation of a tip is stochastically suppressed with respect to
plateau formation.Comment: 11 pages Revtex file, including 15 postscript-figure
Canonical phase space approach to the noisy Burgers equation
Presenting a general phase approach to stochastic processes we analyze in
particular the Fokker-Planck equation for the noisy Burgers equation and
discuss the time dependent and stationary probability distributions. In one
dimension we derive the long-time skew distribution approaching the symmetric
stationary Gaussian distribution. In the short time regime we discuss
heuristically the nonlinear soliton contributions and derive an expression for
the distribution in accordance with the directed polymer-replica model and
asymmetric exclusion model results.Comment: 4 pages, Revtex file, submitted to Phys. Rev. Lett. a reference has
been added and a few typos correcte
Nonequilibrium dynamics of a growing interface
A growing interface subject to noise is described by the Kardar-Parisi-Zhang
equation or, equivalently, the noisy Burgers equation. In one dimension this
equation is analyzed by means of a weak noise canonical phase space approach
applied to the associated Fokker-Planck equation. The growth morphology is
characterized by a gas of nonlinear soliton modes with superimposed linear
diffusive modes. We also discuss the ensuing scaling properties.Comment: 14 pages, 11 figures, conference proceeding; a few corrections have
been adde
Patterns in the Kardar-Parisi-Zhang equation
We review a recent asymptotic weak noise approach to the Kardar-Parisi-Zhang
equation for the kinetic growth of an interface in higher dimensions. The weak
noise approach provides a many body picture of a growing interface in terms of
a network of localized growth modes. Scaling in 1d is associated with a gapless
domain wall mode. The method also provides an independent argument for the
existence of an upper critical dimension.Comment: 8 pages revtex, 4 eps figure
Random Resistor-Diode Networks and the Crossover from Isotropic to Directed Percolation
By employing the methods of renormalized field theory we show that the
percolation behavior of random resistor-diode networks near the multicritical
line belongs to the universality class of isotropic percolation. We construct a
mesoscopic model from the general epidemic process by including a relevant
isotropy-breaking perturbation. We present a two-loop calculation of the
crossover exponent . Upon blending the -expansion result with
the exact value for one dimension by a rational approximation, we
obtain for two dimensions . This value is in agreement
with the recent simulations of a two-dimensional random diode network by Inui,
Kakuno, Tretyakov, Komatsu, and Kameoka, who found an order parameter exponent
different from those of isotropic and directed percolation.
Furthermore, we reconsider the theory of the full crossover from isotropic to
directed percolation by Frey, T\"{a}uber, and Schwabl and clear up some minor
shortcomings.Comment: 24 pages, 2 figure
The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine
We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of
jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization,
UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond timeresolved
pump/delayed ionization measurements. The experimental study is complemented with
spin-component-scaled second-order coupled-cluster and multistate complete active space second
order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm−1
about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional
transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation
and out-of-plane distortions upon 1ππ∗ excitation predicted by the calculations. The methyl torsion
and ν′1 (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum
breaks off at a vibrational excess energy Eexc ∼ 500 cm−1, indicating that a barrier in front of the
ethylene-type S1 S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm−1.
The S1 S0 internal conversion rate constant increases from kIC = 2 · 109 s−1 near the S1(v = 0)
level to 1 · 1011 s−1 at Eexc = 516 cm−1. The 1ππ∗ state of 1MCyt also relaxes into the lower-lying
triplet T1 (3ππ∗) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value
is 2.4 cm−1. The ISC rate constant is 10–100 times lower than kIC; it increases from kISC = 2 · 108 s−1
near S1(v = 0) to kISC = 2 · 109 s−1 at Eexc = 516 cm−1. The T1 state energy is determined from the
onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm−1. The T2 (3nπ∗)
state lies >1500 cm−1 above S1(v = 0), so S1 T2 ISC cannot occur, despite the large SOC
parameter of 10.6 cm−1. An upper limit to the adiabatic ionization energy of 1MCyt is determined
as 8.41 ± 0.02 eV. Compared to cytosine, methyl substitution at N1 lowers the adiabatic ionization
energy by ≥0.32 eV and leads to a much higher density of vibronic bands in the S0 → S1 spectrum.
The effect of methylation on the radiationless decay to S0 and ISC to T1 is small, as shown by
the similar break-off of the spectrum and the similar computed mechanismsThis research has been supported by the Schweiz. Nationalfonds (Grant Nos. 121993 and 132540), the Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR) from Catalonia (Spain) (Grant No. 2014SGR1202), the Ministerio de EconomÃa y Competividad (MINECO) from Spain (Grant No. CTQ2015-69363-P), and the National Natural Science Foundation of China (Grant No. 21303007
Canonical phase space approach to the noisy Burgers equation: Probability distributions
We present a canonical phase space approach to stochastic systems described
by Langevin equations driven by white noise. Mapping the associated
Fokker-Planck equation to a Hamilton-Jacobi equation in the nonperturbative
weak noise limit we invoke a {\em principle of least action} for the
determination of the probability distributions. We apply the scheme to the
noisy Burgers and KPZ equations and discuss the time-dependent and stationary
probability distributions. In one dimension we derive the long-time skew
distribution approaching the symmetric stationary Gaussian distribution. In the
short-time region we discuss heuristically the nonlinear soliton contributions
and derive an expression for the distribution in accordance with the directed
polymer-replica and asymmetric exclusion model results. We also comment on the
distribution in higher dimensions.Comment: 18 pages Revtex file, including 8 eps-figures, submitted to Phys.
Rev.
Levy flights in quenched random force fields
Levy flights, characterized by the microscopic step index f, are for f<2 (the
case of rare events) considered in short range and long range quenched random
force fields with arbitrary vector character to first loop order in an
expansion about the critical dimension 2f-2 in the short range case and the
critical fall-off exponent 2f-2 in the long range case. By means of a dynamic
renormalization group analysis based on the momentum shell integration method,
we determine flows, fixed point, and the associated scaling properties for the
probability distribution and the frequency and wave number dependent diffusion
coefficient. Unlike the case of ordinary Brownian motion in a quenched force
field characterized by a single critical dimension or fall-off exponent d=2,
two critical dimensions appear in the Levy case. A critical dimension (or
fall-off exponent) d=f below which the diffusion coefficient exhibits anomalous
scaling behavior, i.e, algebraic spatial behavior and long time tails, and a
critical dimension (or fall-off exponent) d=2f-2 below which the force
correlations characterized by a non trivial fixed point become relevant. As a
general result we find in all cases that the dynamic exponent z, characterizing
the mean square displacement, locks onto the Levy index f, independent of
dimension and independent of the presence of weak quenched disorder.Comment: 27 pages, Revtex file, 17 figures in ps format attached, submitted to
Phys. Rev.
Soliton approach to the noisy Burgers equation: Steepest descent method
The noisy Burgers equation in one spatial dimension is analyzed by means of
the Martin-Siggia-Rose technique in functional form. In a canonical formulation
the morphology and scaling behavior are accessed by mean of a principle of
least action in the asymptotic non-perturbative weak noise limit. The ensuing
coupled saddle point field equations for the local slope and noise fields,
replacing the noisy Burgers equation, are solved yielding nonlinear localized
soliton solutions and extended linear diffusive mode solutions, describing the
morphology of a growing interface. The canonical formalism and the principle of
least action also associate momentum, energy, and action with a
soliton-diffusive mode configuration and thus provides a selection criterion
for the noise-induced fluctuations. In a ``quantum mechanical'' representation
of the path integral the noise fluctuations, corresponding to different paths
in the path integral, are interpreted as ``quantum fluctuations'' and the
growth morphology represented by a Landau-type quasi-particle gas of ``quantum
solitons'' with gapless dispersion and ``quantum diffusive modes'' with a gap
in the spectrum. Finally, the scaling properties are dicussed from a heuristic
point of view in terms of a``quantum spectral representation'' for the slope
correlations. The dynamic eponent z=3/2 is given by the gapless soliton
dispersion law, whereas the roughness exponent zeta =1/2 follows from a
regularity property of the form factor in the spectral representation. A
heuristic expression for the scaling function is given by spectral
representation and has a form similar to the probability distribution for Levy
flights with index .Comment: 30 pages, Revtex file, 14 figures, to be submitted to Phys. Rev.
Instances and connectors : issues for a second generation process language
This work is supported by UK EPSRC grants GR/L34433 and GR/L32699Over the past decade a variety of process languages have been defined, used and evaluated. It is now possible to consider second generation languages based on this experience. Rather than develop a second generation wish list this position paper explores two issues: instances and connectors. Instances relate to the relationship between a process model as a description and the, possibly multiple, enacting instances which are created from it. Connectors refers to the issue of concurrency control and achieving a higher level of abstraction in how parts of a model interact. We believe that these issues are key to developing systems which can effectively support business processes, and that they have not received sufficient attention within the process modelling community. Through exploring these issues we also illustrate our approach to designing a second generation process language.Postprin
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