9,268 research outputs found
Scattering from Solutions of Star Polymers
We calculate the scattering intensity of dilute and semi-dilute solutions of
star polymers. The star conformation is described by a model introduced by
Daoud and Cotton. In this model, a single star is regarded as a spherical
region of a semi-dilute polymer solution with a local, position dependent
screening length. For high enough concentrations, the outer sections of the
arms overlap and build a semi-dilute solution (a sea of blobs) where the inner
parts of the actual stars are embedded. The scattering function is evaluated
following a method introduced by Auvray and de Gennes. In the dilute regime
there are three regions in the scattering function: the Guinier region (low
wave vectors, q R << 1) from where the radius of the star can be extracted; the
intermediate region (1 << q R << f^(2/5)) that carries the signature of the
form factor of a star with f arms: I(q) ~ q^(-10/3); and a high wavevector zone
(q R >> f^(2/5)) where the local swollen structure of the polymers gives rise
to the usual q^(-5/3) decay. In the semi-dilute regime the different stars
interact strongly, and the scattered intensity acquires two new features: a
liquid peak that develops at a reciprocal position corresponding to the
star-star distances; and a new large wavevector contribution of the form
q^(-5/3) originating from the sea of blobs.Comment: REVTeX, 12 pages, 4 eps figure
A low-energy effective Yang-Mills theory for quark and gluon confinement
We derive a gauge-invariant low-energy effective model of the Yang-Mills
theory. We find that the effective gluon propagator belongs to the
Gribov-Stingl type and agrees with it when a mass term which breaks nilpotency
of the BRST symmetry is included. We show that the effective model with gluon
propagator of the Gribov-Stingl type exhibits both quark and gluon confinement:
the Wilson loop average has the area law and the Schwinger function violates
reflection positivity. However, we argue that both quark and gluon confinement
can be obtained even in the absence of such a mass term.Comment: 5 pages, no figures; accepted for publication in Physical Review D
(Rapid Communication
Quantification of reachable attractors in asynchronous discrete dynamics
Motivation: Models of discrete concurrent systems often lead to huge and
complex state transition graphs that represent their dynamics. This makes
difficult to analyse dynamical properties. In particular, for logical models of
biological regulatory networks, it is of real interest to study attractors and
their reachability from specific initial conditions, i.e. to assess the
potential asymptotical behaviours of the system. Beyond the identification of
the reachable attractors, we propose to quantify this reachability.
Results: Relying on the structure of the state transition graph, we estimate
the probability of each attractor reachable from a given initial condition or
from a portion of the state space. First, we present a quasi-exact solution
with an original algorithm called Firefront, based on the exhaustive
exploration of the reachable state space. Then, we introduce an adapted version
of Monte Carlo simulation algorithm, termed Avatar, better suited to larger
models. Firefront and Avatar methods are validated and compared to other
related approaches, using as test cases logical models of synthetic and
biological networks.
Availability: Both algorithms are implemented as Perl scripts that can be
freely downloaded from http://compbio.igc.gulbenkian.pt/nmd/node/59 along with
Supplementary Material.Comment: 19 pages, 2 figures, 2 algorithms and 2 table
Subtleties on energy calculations in the image method
In this pedagogical work we point out a subtle mistake that can be done by
undergraduate or graduate students in the computation of the electrostatic
energy of a system containing charges and perfect conductors if they naively
use the image method. Specifically, we show that the naive expressions for the
electrostatic energy for these systems obtained directly from the image method
are wrong by a factor 1/2. We start our discussion with well known examples,
namely, point charge-perfectly conducting wall and point charge-perfectly
conducting sphere and then proceed to the demonstration of general results,
valid for conductors of arbitrary shapes.Comment: 9 pages, 2 figures; Major change in this version: subsection added to
Sect.4 (theorem generalization). Minor changes: title replaced; corrections
to the English; some explanatory comments adde
Interictal Spike Quantification in Continuous Spike-Wave of Sleep (CSWS): Clinical Usefulness of a Wearable EEG Device
Continuous spike-wave of sleep (CSWS) syndrome is one of the most common epileptic encephalopathies of childhood. Because the associated cognitive/behavioral disturbances relate more to the amount of spike activity than of seizures, methods of spike quantification gained relevance in diagnosis and monitoring treatment. The conventional methodology for quantification of spike index (SI) relies on repeated full 10-20 long-term ambulatory electroencephalography (aEEG), which is both expensive and poorly tolerated.info:eu-repo/semantics/publishedVersio
Soft singularity and the fundamental length
It is shown that some regular solutions in 5D Kaluza-Klein gravity may have
interesting properties if one from the parameters is in the Planck region. In
this case the Kretschman metric invariant runs up to a maximal reachable value
in nature, i.e. practically the metric becomes singular. This observation
allows us to suppose that in this situation the problems with such soft
singularity will be much easier resolved in the future quantum gravity then by
the situation with the ordinary hard singularity (Reissner-Nordstr\"om
singularity, for example). It is supposed that the analogous consideration can
be applied for the avoiding the hard singularities connected with the gauge
charges.Comment: 5 page
Accessing scientific data through knowledge graphs with Ontop.
In this tutorial, we learn how to set up and exploit the virtual knowledge graph (VKG) approach to access data stored in relational legacy systems and to enrich such data with domain knowledge coming from different heterogeneous (biomedical) resources. The VKG approach is based on an ontology that describes a domain of interest in terms of a vocabulary familiar to the user and exposes a high-level conceptual view of the data. Users can access the data by exploiting the conceptual view, and in this way they do not need to be aware of low-level storage details. They can easily integrate ontologies coming from different sources and can obtain richer answers thanks to the interaction between data and domain knowledge
Constraints on the IR behavior of the gluon propagator in Yang-Mills theories
We present rigorous upper and lower bounds for the zero-momentum gluon
propagator D(0) of Yang-Mills theories in terms of the average value of the
gluon field. This allows us to perform a controlled extrapolation of lattice
data to infinite volume, showing that the infrared limit of the Landau-gauge
gluon propagator in SU(2) gauge theory is finite and nonzero in three and in
four space-time dimensions. In the two-dimensional case we find D(0) = 0, in
agreement with Ref. [1]. We suggest an explanation for these results. We note
that our discussion is general, although we only apply our analysis to pure
gauge theory in Landau gauge. Simulations have been performed on the IBM
supercomputer at the University of Sao Paulo.Comment: 4 pages, 3 figures, 1 tabl
Inventário de mamíferos de médio e grande porte no município de São Pedro do Ivaí, estado do Paraná.
EVINCI. Resumo 024
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