6,111 research outputs found
Streaming Tree Transducers
Theory of tree transducers provides a foundation for understanding
expressiveness and complexity of analysis problems for specification languages
for transforming hierarchically structured data such as XML documents. We
introduce streaming tree transducers as an analyzable, executable, and
expressive model for transforming unranked ordered trees in a single pass.
Given a linear encoding of the input tree, the transducer makes a single
left-to-right pass through the input, and computes the output in linear time
using a finite-state control, a visibly pushdown stack, and a finite number of
variables that store output chunks that can be combined using the operations of
string-concatenation and tree-insertion. We prove that the expressiveness of
the model coincides with transductions definable using monadic second-order
logic (MSO). Existing models of tree transducers either cannot implement all
MSO-definable transformations, or require regular look ahead that prohibits
single-pass implementation. We show a variety of analysis problems such as
type-checking and checking functional equivalence are solvable for our model.Comment: 40 page
Driven Brownian transport through arrays of symmetric obstacles
We numerically investigate the transport of a suspended overdamped Brownian
particle which is driven through a two-dimensional rectangular array of
circular obstacles with finite radius. Two limiting cases are considered in
detail, namely, when the constant drive is parallel to the principal or the
diagonal array axes. This corresponds to studying the Brownian transport in
periodic channels with reflecting walls of different topologies. The mobility
and diffusivity of the transported particles in such channels are determined as
functions of the drive and the array geometric parameters. Prominent transport
features, like negative differential mobilities, excess diffusion peaks, and
unconventional asymptotic behaviors, are explained in terms of two distinct
lengths, the size of single obstacles (trapping length) and the lattice
constant of the array (local correlation length). Local correlation effects are
further analyzed by continuously rotating the drive between the two limiting
orientations.Comment: 10 pages 13 figure
On the Lebesgue measure of Li-Yorke pairs for interval maps
We investigate the prevalence of Li-Yorke pairs for and
multimodal maps with non-flat critical points. We show that every
measurable scrambled set has zero Lebesgue measure and that all strongly
wandering sets have zero Lebesgue measure, as does the set of pairs of
asymptotic (but not asymptotically periodic) points.
If is topologically mixing and has no Cantor attractor, then typical
(w.r.t. two-dimensional Lebesgue measure) pairs are Li-Yorke; if additionally
admits an absolutely continuous invariant probability measure (acip), then
typical pairs have a dense orbit for . These results make use of
so-called nice neighborhoods of the critical set of general multimodal maps,
and hence uniformly expanding Markov induced maps, the existence of either is
proved in this paper as well.
For the setting where has a Cantor attractor, we present a trichotomy
explaining when the set of Li-Yorke pairs and distal pairs have positive
two-dimensional Lebesgue measure.Comment: 41 pages, 3 figure
Temperature and Field Dependence of the Mobility in Liquid-Crystalline Conjugated Polymer Films
The transport properties of organic light-emitting diodes in which the
emissive layer is composed of conjugated polymers in the liquid-crystalline
phase have been investigated. We have performed simulations of the current
transient response to an illumination pulse via the Monte Carlo approach, and
from the transit times we have extracted the mobility of the charge carriers as
a function of both the electric field and the temperature. The transport
properties of such films are different from their disordered counterparts, with
charge carrier mobilities exhibiting only a weak dependence on both the
electric field and temperature. We show that for spatially ordered polymer
films, this weak dependence arises for thermal energy being comparable to the
energetic disorder, due to the combined effect of the electrostatic and thermal
energies. The inclusion of spatial disorder, on the other hand, does not alter
the qualitative behaviour of the mobility, but results in decreasing its
absolute value.Comment: 9 pages, 8 figures, submitted to Phys. Rev.
The Recognition of Hypothalamo-Neurohypophysial Functions by Developing T Cells
Neuropeptide signals and specific neuropeptide receptors have been described in the
thymus supporting the concept of a close dialogue between the neuroendocrine and the
immune systems at the level of early T-cell differentiation. In this paper, we review
recent data about neurohypophysial (NHP)-related peptides detected in the thymus
from different species. We suggest that we are dealing in fact with other member(s) of
the NHP hormone family, which seems to exert its activity locally through a novel
model of cell-to-cell signaling, that of cryptocrine communication. This model involves
exchange of signals between thymic epithelial cells and developing thymocytes. The
NHP-related peptides have been shown to trigger thymocyte proliferation and could
induce immune tolerance of this highly conserved neuroendocrine family
No elliptic islands for the universal area-preserving map
A renormalization approach has been used in \cite{EKW1} and \cite{EKW2} to
prove the existence of a \textit{universal area-preserving map}, a map with
hyperbolic orbits of all binary periods. The existence of a horseshoe, with
positive Hausdorff dimension, in its domain was demonstrated in \cite{GJ1}. In
this paper the coexistence problem is studied, and a computer-aided proof is
given that no elliptic islands with period less than 20 exist in the domain. It
is also shown that less than 1.5% of the measure of the domain consists of
elliptic islands. This is proven by showing that the measure of initial
conditions that escape to infinity is at least 98.5% of the measure of the
domain, and we conjecture that the escaping set has full measure. This is
highly unexpected, since generically it is believed that for conservative
systems hyperbolicity and ellipticity coexist
The metallic state in disordered quasi-one-dimensional conductors
The unusual metallic state in conjugated polymers and single-walled carbon
nanotubes is studied by dielectric spectroscopy (8--600 GHz). We have found an
intriguing correlation between scattering time and plasma frequency. This
relation excludes percolation models of the metallic state. Instead, the
carrier dynamics can be understood in terms of the low density of delocalized
states around the Fermi level, which arises from the competion between
disorder-induced localization and interchain-interactions-induced
delocalization.Comment: 4 pages including 4 figure
Sigma-phase in Fe-Cr and Fe-V alloy systems and its physical properties
A review is presented on physical properties of the sigma-phase in Fe-Cr and
Fe-V alloy systems as revealed both with experimental -- mostly with the
Mossbauer spectroscopy -- and theoretical methods. In particular, the following
questions relevant to the issue have been addressed: identification of sigma
and determination of its structural properties, kinetics of alpha-to-sigma and
sigma-to-alpha phase transformations, Debye temperature and Fe-partial phonon
density of states, Curie temperature and magnetization, hyperfine fields,
isomer shifts and electric field gradients.Comment: 26 pages, 23 figures and 83 reference
Tomographic image of melt storage beneath Askja Volcano, Iceland using local microseismicity
We use P wave and S wave arrivals from microseismic earthquakes to construct 3-D tomographic Vp and Vs images of the magma storage region beneath Askja's central volcano in the Northern Volcanic Zone of Iceland. A distinctive ellipsoidal low-velocity anomaly, with both Vp and Vsvelocities 8-12% below the background, is imaged at 6-11 km depth beneath the caldera. The presence of a shallow magma chamber is corroborated by geodetic and gravity studies. The small Vp/Vs anomaly suggests a lack of pervasive melt. We interpret this anomaly as a region of multiple sills, some frozen but hot, others containing partial melt. A second, smaller low-velocity anomaly beneath the main magma storage region may represent a magma migration pathway. This interpretation is supported by the close proximity to the anomaly of clusters of deep, magmatically induced earthquakes. However, the location and shape of this deep anomaly are poorly constrained by the current data set
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