191 research outputs found
Steered Transition Path Sampling
We introduce a path sampling method for obtaining statistical properties of
an arbitrary stochastic dynamics. The method works by decomposing a trajectory
in time, estimating the probability of satisfying a progress constraint,
modifying the dynamics based on that probability, and then reweighting to
calculate averages. Because the progress constraint can be formulated in terms
of occurrences of events within time intervals, the method is particularly well
suited for controlling the sampling of currents of dynamic events. We
demonstrate the method for calculating transition probabilities in barrier
crossing problems and survival probabilities in strongly diffusive systems with
absorbing states, which are difficult to treat by shooting. We discuss the
relation of the algorithm to other methods.Comment: 11 pages, 8 figure
A Note on the Classical BRST Symmetry of the Pure Spinor String in a Curved Background
The classical pure spinor version of the heterotic superstring in a
supergravity and super Yang-Mills background is considered. We obtain the BRST
transformations of the world-sheet fields. They are consistent with the
constraints obtained from the nilpotence of the BSRT charge and the
holomorphicity of the BRST current.Comment: References adde
Emergence of heterogeneity and political organization in information exchange networks
We present a simple model of the emergence of the division of labor and the
development of a system of resource subsidy from an agent-based model of
directed resource production with variable degrees of trust between the agents.
The model has three distinct phases, corresponding to different forms of
societal organization: disconnected (independent agents), homogeneous
cooperative (collective state), and inhomogeneous cooperative (collective state
with a leader). Our results indicate that such levels of organization arise
generically as a collective effect from interacting agent dynamics, and may
have applications in a variety of systems including social insects and
microbial communities.Comment: 10 pages, 6 figure
Production of non-Abelian tensor gauge bosons. Tree amplitudes in generalized Yang-Mills theory and BCFW recursion relation
The BCFW recursion relation allows to calculate tree-level scattering
amplitudes in generalized Yang-Mills theory and, in particular, four-particle
amplitudes for the production rate of non-Abelian tensor gauge bosons of
arbitrary high spin in the fusion of two gluons. The consistency of the
calculations in different kinematical channels is fulfilled when all
dimensionless cubic coupling constants between vector bosons (gluons) and high
spin non-Abelian tensor gauge bosons are equal to the Yang-Mills coupling
constant. There are no high derivative cubic vertices in the generalized
Yang-Mills theory. The amplitudes vanish as complex deformation parameter tends
to infinity, so that there is no contribution from the contour at infinity. We
derive a generalization of the Parke-Taylor formula in the case of production
of two tensor gauge bosons of spin-s and N gluons (jets). The expression is
holomorhic in the spinor variables of the scattered particles, exactly as the
MHV gluon amplitude is, and reduces to the gluonic MHV amplitude when s=1. In
generalized Yang-Mills theory the tree level n-particle scattering amplitudes
with all positive helicities vanish, but tree amplitudes with one negative
helicity particle are already nonzero.Comment: 19 pages, LaTex fil
Note About Classical Dynamics of Pure Spinor String on AdS_5 x S_5 Background
We will discuss some properties of the pure spinor string on the AdS_5 x S_5
background. Using the classical Hamiltonian analysis we will show that the
vertex operator for the massless state that is in the cohomology of the BRST
charges describes on-shell fluctuations around AdS_5 x S_5 background.Comment: 26. pages, added references, v2:corrected typo
The friction factor of two-dimensional rough-boundary turbulent soap film flows
We use momentum transfer arguments to predict the friction factor in
two-dimensional turbulent soap-film flows with rough boundaries (an analogue of
three-dimensional pipe flow) as a function of Reynolds number Re and roughness
, considering separately the inverse energy cascade and the forward
enstrophy cascade. At intermediate Re, we predict a Blasius-like friction
factor scaling of in flows dominated by the
enstrophy cascade, distinct from the energy cascade scaling of
. For large Re, in the enstrophy-dominated case.
We use conformal map techniques to perform direct numerical simulations that
are in satisfactory agreement with theory, and exhibit data collapse scaling of
roughness-induced criticality, previously shown to arise in the 3D pipe data of
Nikuradse.Comment: 4 pages, 3 figure
Cascade of Complexity in Evolving Predator-Prey Dynamics
We simulate an individual-based model that represents both the phenotype and
genome of digital organisms with predator-prey interactions. We show how
open-ended growth of complexity arises from the invariance of genetic evolution
operators with respect to changes in the complexity, and that the dynamics
which emerges is controlled by a non-equilibrium critical point. The mechanism
is analogous to the development of the cascade in fluid turbulence.Comment: 5 pages, 3 figures; added comments on system size scaling and
turbulence analogy, added error estimates of data collapse parameters.
Slightly enhanced from the version which will appear in PR
An Alternative Topological Field Theory of Generalized Complex Geometry
We propose a new topological field theory on generalized complex geometry in
two dimension using AKSZ formulation. Zucchini's model is model in the case
that the generalized complex structuredepends on only a symplectic structure.
Our new model is model in the case that the generalized complex structure
depends on only a complex structure.Comment: 29 pages, typos and references correcte
Flow profiling of a surface acoustic wave nanopump
The flow profile in a capillary gap and the pumping efficiency of an acoustic
micropump employing Surface Acoustic Waves is investigated both experimentally
and theoretically. Such ultrasonic surface waves on a piezoelectric substrate
strongly couple to a thin liquid layer and generate an internal streaming
within the fluid. Such acoustic streaming can be used for controlled agitation
during, e.g., microarray hybridization. We use fluorescence correlation
spectroscopy and fluorescence microscopy as complementary tools to investigate
the resulting flow profile. The velocity was found to depend on the applied
power somewhat weaker than linearly and to decrease fast with the distance from
the ultrasound generator on the chip.Comment: 12 pages 20 figure
Macroscopic effects of the spectral structure in turbulent flows
Two aspects of turbulent flows have been the subject of extensive, split
research efforts: macroscopic properties, such as the frictional drag
experienced by a flow past a wall, and the turbulent spectrum. The turbulent
spectrum may be said to represent the fabric of a turbulent state; in practice
it is a power law of exponent \alpha (the "spectral exponent") that gives the
revolving velocity of a turbulent fluctuation (or "eddy") of size s as a
function of s. The link, if any, between macroscopic properties and the
turbulent spectrum remains missing. Might it be found by contrasting the
frictional drag in flows with differing types of spectra? Here we perform
unprecedented measurements of the frictional drag in soap-film flows, where the
spectral exponent \alpha = 3 and compare the results with the frictional drag
in pipe flows, where the spectral exponent \alpha = 5/3. For moderate values of
the Reynolds number Re (a measure of the strength of the turbulence), we find
that in soap-film flows the frictional drag scales as Re^{-1/2}, whereas in
pipe flows the frictional drag scales as Re^{-1/4} . Each of these scalings may
be predicted from the attendant value of \alpha by using a new theory, in which
the frictional drag is explicitly linked to the turbulent spectrum. Our work
indicates that in turbulence, as in continuous phase transitions, macroscopic
properties are governed by the spectral structure of the fluctuations.Comment: 6 pages, 3 figure
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