61,837 research outputs found
Monte Carlo Study of the Phase Structure of Compact Polymer Chains
We study the phase behavior of single homopolymers in a simple
hydrophobic/hydrophilic off-lattice model with sequence independent local
interactions. The specific heat is, not unexpectedly, found to exhibit a
pronounced peak well below the collapse temperature, signalling a possible
low-temperature phase transition. The system size dependence at this maximum is
investigated both with and without the local interactions, using chains with up
to 50 monomers. The size dependence is found to be weak. The specific heat
itself seems not to diverge. The homopolymer results are compared with those
for two non-uniform sequences. Our calculations are performed using the methods
of simulated and parallel tempering. The performances of these algorithms are
discussed, based on careful tests for a small system.Comment: 13 pages LaTeX, 6 Postscript figures, References adde
Orthonormal Expansion l1-Minimization Algorithms for Compressed Sensing
Compressed sensing aims at reconstructing sparse signals from significantly
reduced number of samples, and a popular reconstruction approach is
-norm minimization. In this correspondence, a method called orthonormal
expansion is presented to reformulate the basis pursuit problem for noiseless
compressed sensing. Two algorithms are proposed based on convex optimization:
one exactly solves the problem and the other is a relaxed version of the first
one. The latter can be considered as a modified iterative soft thresholding
algorithm and is easy to implement. Numerical simulation shows that, in dealing
with noise-free measurements of sparse signals, the relaxed version is
accurate, fast and competitive to the recent state-of-the-art algorithms. Its
practical application is demonstrated in a more general case where signals of
interest are approximately sparse and measurements are contaminated with noise.Comment: 7 pages, 2 figures, 1 tabl
Organic Design of Massively Distributed Systems: A Complex Networks Perspective
The vision of Organic Computing addresses challenges that arise in the design
of future information systems that are comprised of numerous, heterogeneous,
resource-constrained and error-prone components or devices. Here, the notion
organic particularly highlights the idea that, in order to be manageable, such
systems should exhibit self-organization, self-adaptation and self-healing
characteristics similar to those of biological systems. In recent years, the
principles underlying many of the interesting characteristics of natural
systems have been investigated from the perspective of complex systems science,
particularly using the conceptual framework of statistical physics and
statistical mechanics. In this article, we review some of the interesting
relations between statistical physics and networked systems and discuss
applications in the engineering of organic networked computing systems with
predictable, quantifiable and controllable self-* properties.Comment: 17 pages, 14 figures, preprint of submission to Informatik-Spektrum
published by Springe
Adaptive walks on time-dependent fitness landscapes
The idea of adaptive walks on fitness landscapes as a means of studying
evolutionary processes on large time scales is extended to fitness landscapes
that are slowly changing over time. The influence of ruggedness and of the
amount of static fitness contributions are investigated for model landscapes
derived from Kauffman's landscapes. Depending on the amount of static
fitness contributions in the landscape, the evolutionary dynamics can be
divided into a percolating and a non-percolating phase. In the percolating
phase, the walker performs a random walk over the regions of the landscape with
high fitness.Comment: 7 pages, 6 eps-figures, RevTeX, submitted to Phys. Rev.
A Monte Carlo Approach for Studying Microphases Applied to the Axial Next-Nearest-Neighbor Ising and the Ising-Coulomb Models
The equilibrium phase behavior of microphase-forming systems is notoriously
difficult to obtain because of the extended metastability of their modulated
phases. In this paper we present a systematic simulation methodology for
studying layered microphases and apply the approach to two prototypical
lattice-based systems: the three-dimensional axial next-nearest-neighbor Ising
(ANNNI) and Ising-Coulomb (IC) models. The method involves thermodynamically
integrating along a reversible path established between a reference system of
free spins under an ordering field and the system of interest. The resulting
free energy calculations unambiguously locate the phase boundaries. The simple
phases are not observed to play a particularly significant role in the devil's
flowers. With the help of generalized order parameters, the
paramagnetic-modulated critical transition of the ANNNI model is also studied.
We confirm the XY universality of the paramagnetic-modulated transition and its
isotropic nature. Interfacial roughening is found to play at most a small role
in the ANNNI layered regime.Comment: 15 pages, 11 figures, 2 table
Activity-driven content adaptation for effective video summarisation
In this paper, we present a novel method for content adaptation and video summarization fully implemented in compressed-domain. Firstly, summarization of generic videos is modeled as the process of extracted human objects under various activities/events. Accordingly, frames are classified into five categories via fuzzy decision including shot changes (cut and gradual transitions), motion activities (camera motion and object motion) and others by using two inter-frame measurements. Secondly, human objects are detected using Haar-like features. With the detected human objects and attained frame categories, activity levels for each frame are determined to adapt with video contents. Continuous frames belonging to same category are grouped to form one activity entry as content of interest (COI) which will convert the original video into a series of activities. An overall adjustable quota is used to control the size of generated summarization for efficient streaming purpose. Upon this quota, the frames selected for summarization are determined by evenly sampling the accumulated activity levels for content adaptation. Quantitative evaluations have proved the effectiveness and efficiency of our proposed approach, which provides a more flexible and general solution for this topic as domain-specific tasks such as accurate recognition of objects can be avoided
Genomic plasticity and rapid host switching can promote the evolution of generalism : a case study in the zoonotic pathogen Campylobacter
This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) grant BB/I02464X/1, the Medical Research Council (MRC) grants MR/M501608/1 and MR/L015080/1, and the Wellcome Trust grant 088786/C/09/Z. GM was supported by a NISCHR Health Research Fellowship (HF-14–13).Peer reviewedPublisher PD
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