332 research outputs found
The IBMAP approach for Markov networks structure learning
In this work we consider the problem of learning the structure of Markov
networks from data. We present an approach for tackling this problem called
IBMAP, together with an efficient instantiation of the approach: the IBMAP-HC
algorithm, designed for avoiding important limitations of existing
independence-based algorithms. These algorithms proceed by performing
statistical independence tests on data, trusting completely the outcome of each
test. In practice tests may be incorrect, resulting in potential cascading
errors and the consequent reduction in the quality of the structures learned.
IBMAP contemplates this uncertainty in the outcome of the tests through a
probabilistic maximum-a-posteriori approach. The approach is instantiated in
the IBMAP-HC algorithm, a structure selection strategy that performs a
polynomial heuristic local search in the space of possible structures. We
present an extensive empirical evaluation on synthetic and real data, showing
that our algorithm outperforms significantly the current independence-based
algorithms, in terms of data efficiency and quality of learned structures, with
equivalent computational complexities. We also show the performance of IBMAP-HC
in a real-world application of knowledge discovery: EDAs, which are
evolutionary algorithms that use structure learning on each generation for
modeling the distribution of populations. The experiments show that when
IBMAP-HC is used to learn the structure, EDAs improve the convergence to the
optimum
Subleading critical exponents from the renormalisation group
We study exact renormalisation group equations for the 3d Ising universality
class. At the Wilson-Fisher fixed point, symmetric and antisymmetric
correction-to-scaling exponents are computed with high accuracy for an
optimised cutoff to leading order in the derivative expansion. Further results
are derived for other cutoffs including smooth, sharp and background field
cutoffs. An estimate for higher order corrections is given as well. We
establish that the leading antisymmetric corrections to scaling are strongly
subleading compared to the leading symmetric ones.Comment: 10 pages, 5 figure
Scheme Independence at First Order Phase Transitions and the Renormalisation Group
We analyse approximate solutions to an exact renormalisation group equation
with particular emphasis on their dependence on the regularisation scheme,
which is kept arbitrary. Physical quantities related to the coarse-grained
potential of scalar QED display universal behaviour for strongly first-order
phase transitions. Only subleading corrections depend on the regularisation
scheme and are suppressed by a sufficiently large UV scale. We calculate the
relevant coarse-graining scale and give a condition for the applicability of
Langer's theory of bubble nucleation.Comment: 12 pages, LaTeX, 4 figures included (needs epsfig.sty), two equations
added, typo correcte
Renormalization Group and Universality
It is argued that universality is severely limited for models with multiple
fixed points. As a demonstration the renormalization group equations are
presented for the potential and the wave function renormalization constants in
the scalar field theory. Our equations are superior compared with the
usual approach which retains only the contributions that are non-vanishing in
the ultraviolet regime. We find an indication for the existence of relevant
operators at the infrared fixed point, contrary to common expectations. This
result makes the sufficiency of using only renormalizable coupling constants in
parametrizing the long distance phenomena questionable.Comment: 32pp in plain tex; revised version to appear in PR
Critical exponents from optimised renormalisation group flows
Within the exact renormalisation group, the scaling solutions for O(N)
symmetric scalar field theories are studied to leading order in the derivative
expansion. The Gaussian fixed point is examined for d>2 dimensions and
arbitrary infrared regularisation. The Wilson-Fisher fixed point in d=3 is
studied using an optimised flow. We compute critical exponents and subleading
corrections-to-scaling to high accuracy from the eigenvalues of the stability
matrix at criticality for all N. We establish that the optimisation is
responsible for the rapid convergence of the flow and polynomial truncations
thereof. The scheme dependence of the leading critical exponent is analysed.
For all N > 0, it is found that the leading exponent is bounded. The upper
boundary is achieved for a Callan-Symanzik flow and corresponds, for all N, to
the large-N limit. The lower boundary is achieved by the optimised flow and is
closest to the physical value. We show the reliability of polynomial
approximations, even to low orders, if they are accompanied by an appropriate
choice for the regulator. Possible applications to other theories are outlined.Comment: 34 pages, 15 figures, revtex, to appear in NP
Physicochemical and rheological properties of a transparent asphalt binder modified with Nano-TiO2
Transparent binder is used to substitute conventional black asphalt binder and to provide light-colored pavements, whereas nano-TiO2 has the potential to promote photocatalytic and self-cleaning properties. Together, these materials provide multifunction effects and benefits when the pavement is submitted to high solar irradiation. This paper analyzes the physicochemical and rheological properties of a transparent binder modified with 0.5%, 3.0%, 6.0%, and 10.0% nano-TiO2 and compares it to the transparent base binder and conventional and polymer modified binders (PMB) without nano-TiO2. Their penetration, softening point, dynamic viscosity, master curve, black diagram, Linear Amplitude Sweep (LAS), Multiple Stress Creep Recovery (MSCR), and Fourier Transform Infrared Spectroscopy (FTIR) were obtained. The transparent binders (base and modified) seem to be workable considering their viscosity, and exhibited values between the conventional binder and PMB with respect to rutting resistance, penetration, and softening point. They showed similar behavior to the PMB, demonstrating signs of polymer modification. The addition of TiO2 seemed to reduce fatigue life, except for the 0.5% content. Nevertheless, its addition in high contents increased the rutting resistance. The TiO2 modification seems to have little effect on the chemical functional indices. The best percentage of TiO2 was 0.5%, with respect to fatigue, and 10.0% with respect to permanent deformation.Fundação para a Ciência e a Tecnologia—under the projects
for Strategic Funding UIDB/04650/2020 and UIDB/04029/2020, and Nanobased concepts for Innovative and
Eco-sustainable constructive material surfaces PTDC/FIS/120412/2010. Furthermore, we would like to thank the
Industrial Research Fund (IOF) of the University of Antwerp for funding the PAPPoA project (IOF/SBO/41859/2020).
Lastly, the first author would like to acknowledge FCT for the PhD scholarship (SFRH/BD/137421/2018
Quantum and Thermal Fluctuations in Field Theory
Blocking transformation is performed in quantum field theory at finite
temperature. It is found that the manner temperature deforms the renormalized
trajectories can be used to understand better the role played by the quantum
fluctuations. In particular, it is conjectured that domain formation and mass
parameter generation can be observed in theories without spontaneous symmetry
breaking.Comment: 27pp+7 figures, MIT-CTP-214
The fidelity of dynamic signaling by noisy biomolecular networks
This is the final version of the article. Available from Public Library of Science via the DOI in this record.Cells live in changing, dynamic environments. To understand cellular decision-making, we must therefore understand how fluctuating inputs are processed by noisy biomolecular networks. Here we present a general methodology for analyzing the fidelity with which different statistics of a fluctuating input are represented, or encoded, in the output of a signaling system over time. We identify two orthogonal sources of error that corrupt perfect representation of the signal: dynamical error, which occurs when the network responds on average to other features of the input trajectory as well as to the signal of interest, and mechanistic error, which occurs because biochemical reactions comprising the signaling mechanism are stochastic. Trade-offs between these two errors can determine the system's fidelity. By developing mathematical approaches to derive dynamics conditional on input trajectories we can show, for example, that increased biochemical noise (mechanistic error) can improve fidelity and that both negative and positive feedback degrade fidelity, for standard models of genetic autoregulation. For a group of cells, the fidelity of the collective output exceeds that of an individual cell and negative feedback then typically becomes beneficial. We can also predict the dynamic signal for which a given system has highest fidelity and, conversely, how to modify the network design to maximize fidelity for a given dynamic signal. Our approach is general, has applications to both systems and synthetic biology, and will help underpin studies of cellular behavior in natural, dynamic environments.We acknowledge support from a Medical Research Council and Engineering and Physical Sciences Council funded Fellowship in Biomedical Informatics (CGB) and a Scottish Universities Life Sciences Alliance chair in Systems Biology (PSS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Modification of a transparent binder for road pavements using TiO2 nanoparticles
Light and heat are relevant factors for road pavements since they promote the aging of the asphalt surfaces [1], and a large amount of heating can intensify the Urban Heat Island (UHI) effect [2]. Contrariwise, the lack of light strongly affects visibility conditions, reducing safety [3]. The conventional black color of asphalt pavements absorbs light and stores a large amount of thermal energy, which can be reduced opting by the application of light-colored pavements using, for example, a transparent binder [3]. Industrial activities and road traffic are the main sources of pollutant emissions, mostly SO2 and NOx, which are hazardous atmospheric pollutants. There are several consequences at different scales caused by these harmful gases, such as intensification of the greenhouse effect, acid rain, and public health problems. With the use of nano-TiO2 into/over asphalt mixtures, and consequently with the functionalization process considering the photocatalytic and self-cleaning properties, road pavements become the ideal places to mitigate environmental pollution due to proximity to the emissions [4]. If a transparent binder modified with nanoparticles of TiO2 is used, pavements will present multifunction effects and benefits when submitted to high solar irradiation. The production at laboratory-scale of such pavements is presented in Figure 1. First, the transparent binder was modified with nano-TiO2 (0, 0.5%, 3.0%, 6.0% and 10.0%). Binder's workability was confirmed. It presented similar behavior as a polymer modified binder. In these binder samples, the addition of high contents of nano-TiO2 increased the rutting resistance, but it seemed to reduce fatigue life, except for the 0.5%. Also, the nano-TiO2 modification had a slight effect on the chemical functional indices. The best percentage of TiO2 was 10.0% considering rutting resistance and 0.5% concerning fatigue life
Lectures on the functional renormalization group method
These introductory notes are about functional renormalization group equations
and some of their applications. It is emphasised that the applicability of this
method extends well beyond critical systems, it actually provides us a general
purpose algorithm to solve strongly coupled quantum field theories. The
renormalization group equation of F. Wegner and A. Houghton is shown to resum
the loop-expansion. Another version, due to J. Polchinski, is obtained by the
method of collective coordinates and can be used for the resummation of the
perturbation series. The genuinely non-perturbative evolution equation is
obtained in a manner reminiscent of the Schwinger-Dyson equations. Two variants
of this scheme are presented where the scale which determines the order of the
successive elimination of the modes is extracted from external and internal
spaces. The renormalization of composite operators is discussed briefly as an
alternative way to arrive at the renormalization group equation. The scaling
laws and fixed points are considered from local and global points of view.
Instability induced renormalization and new scaling laws are shown to occur in
the symmetry broken phase of the scalar theory. The flattening of the effective
potential of a compact variable is demonstrated in case of the sine-Gordon
model. Finally, a manifestly gauge invariant evolution equation is given for
QED.Comment: 47 pages, 11 figures, final versio
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