857 research outputs found
Numerical study of the disordered Poland-Scheraga model of DNA denaturation
We numerically study the binary disordered Poland-Scheraga model of DNA
denaturation, in the regime where the pure model displays a first order
transition (loop exponent ). We use a Fixman-Freire scheme for the
entropy of loops and consider chain length up to , with
averages over samples. We present in parallel the results of various
observables for two boundary conditions, namely bound-bound (bb) and
bound-unbound (bu), because they present very different finite-size behaviors,
both in the pure case and in the disordered case. Our main conclusion is that
the transition remains first order in the disordered case: in the (bu) case,
the disorder averaged energy and contact densities present crossings for
different values of without rescaling. In addition, we obtain that these
disorder averaged observables do not satisfy finite size scaling, as a
consequence of strong sample to sample fluctuations of the pseudo-critical
temperature. For a given sample, we propose a procedure to identify its
pseudo-critical temperature, and show that this sample then obeys first order
transition finite size scaling behavior. Finally, we obtain that the disorder
averaged critical loop distribution is still governed by in
the regime , as in the pure case.Comment: 12 pages, 13 figures. Revised versio
A novel approach for the assessment of morphological evolution based on observed water levels in tide-dominated estuaries
Assessing the impacts of both natural (e.g., tidal forcing from the ocean) and human-induced changes (e.g., dredging for navigation, land reclamation) on estuarine morphology is particularly important for the protection and management of the estuarine environment. In this study, a novel analytical approach is proposed for the assessment of estuarine morphological evolution in terms of tidally averaged depth on the basis of the observed water levels along the estuary. The key lies in deriving a relationship between wave celerity and tidal damping or amplification. For given observed water levels at two gauging stations, it is possible to have a first estimation of both wave celerity (distance divided by tidal travelling time) and tidal damping or amplification rate (tidal range difference divided by distance), which can then be used to predict the morphological changes via an inverse analytical model for tidal hydrodynamics. The proposed method is applied to the Lingdingyang Bay of the Pearl River Estuary, located on the southern coast of China, to analyse the historical development of the tidal hydrodynamics and morphological evolution. The analytical results show surprisingly good correspondence with observed water depth and volume in this system. The merit of the proposed method is that it provides a simple approach for understanding the decadal evolution of the estuarine morphology through the use of observed water levels, which are usually available and can be easily measured.National Key R&D of China (Grant No.
2016YFC0402601), National Natural Science Foundation of China (Grant No. 51979296, 51709287,
41706088, 41476073), Fundamental Research Funds for the Central Universities (No.18lgpy29)
and from the Water Resource Science and Technology Innovation Program of Guangdong Province (Grant
No. 2016-20, 2016-21). The work of the second author was supported by FCT research contracts
IF/00661/2014/CP1234.info:eu-repo/semantics/submittedVersio
Directed polymer in a random medium of dimension 1+1 and 1+3: weights statistics in the low-temperature phase
We consider the low-temperature disorder-dominated phase of the
directed polymer in a random potentiel in dimension 1+1 (where )
and 1+3 (where ). To characterize the localization properties of
the polymer of length , we analyse the statistics of the weights of the last monomer as follows. We numerically compute the probability
distributions of the maximal weight , the probability distribution of the parameter as well as the average values of the higher order
moments . We find that there exists a
temperature such that (i) for , the distributions
and present the characteristic Derrida-Flyvbjerg
singularities at and for . In particular, there
exists a temperature-dependent exponent that governs the main
singularities and as well as the power-law decay of the moments . The exponent grows from the value
up to . (ii) for , the
distribution vanishes at some value , and accordingly the
moments decay exponentially as in . The
histograms of spatial correlations also display Derrida-Flyvbjerg singularities
for . Both below and above , the study of typical and
averaged correlations is in full agreement with the droplet scaling theory.Comment: 13 pages, 29 figure
A simple model for DNA denaturation
Following Poland and Scheraga, we consider a simplified model for the
denaturation transition of DNA. The two strands are modeled as interacting
polymer chains. The attractive interactions, which mimic the pairing between
the four bases, are reduced to a single short range binding term. Furthermore,
base-pair misalignments are forbidden, implying that this binding term exists
only for corresponding (same curvilinear abscissae) monomers of the two chains.
We take into account the excluded volume repulsion between monomers of the two
chains, but neglect intra-chain repulsion. We find that the excluded volume
term generates an effective repulsive interaction between the chains, which
decays as . Due to this long-range repulsion between the chains, the
denaturation transition is first order in any dimension, in agreement with
previous studies.Comment: 10 page
Cross-border care and healthcare quality improvement in Europe: the MARQuIS research project
Citizens are increasingly crossing borders within the European Union (EU). Europeans have always been free to travel to receive care abroad, but if they wished to benefit from their statutory social protection scheme, they were subject to their local or national legislation on social protection. This changed in 1991 with the European Court of Justice defining healthcare as a service, starting a debate on the right balance between different principles in European treaties: movement of persons, goods and services, versus the responsibility of member states to organise their healthcare systems. Simultaneously, cross-border cooperation has developed between member states
Glassy phases in Random Heteropolymers with correlated sequences
We develop a new analytic approach for the study of lattice heteropolymers,
and apply it to copolymers with correlated Markovian sequences. According to
our analysis, heteropolymers present three different dense phases depending
upon the temperature, the nature of the monomer interactions, and the sequence
correlations: (i) a liquid phase, (ii) a ``soft glass'' phase, and (iii) a
``frozen glass'' phase. The presence of the new intermediate ``soft glass''
phase is predicted for instance in the case of polyampholytes with sequences
that favor the alternation of monomers.
Our approach is based on the cavity method, a refined Bethe Peierls
approximation adapted to frustrated systems. It amounts to a mean field
treatment in which the nearest neighbor correlations, which are crucial in the
dense phases of heteropolymers, are handled exactly. This approach is powerful
and versatile, it can be improved systematically and generalized to other
polymeric systems
On the multifractal statistics of the local order parameter at random critical points : application to wetting transitions with disorder
Disordered systems present multifractal properties at criticality. In
particular, as discovered by Ludwig (A.W.W. Ludwig, Nucl. Phys. B 330, 639
(1990)) on the case of diluted two-dimensional Potts model, the moments
of the local order parameter scale with a set
of non-trivial exponents . In this paper, we revisit
these ideas to incorporate more recent findings: (i) whenever a multifractal
measure normalized over space occurs in a random
system, it is crucial to distinguish between the typical values and the
disorder averaged values of the generalized moments , since
they may scale with different generalized dimensions and
(ii) as discovered by Wiseman and Domany (S. Wiseman and E. Domany, Phys Rev E
{\bf 52}, 3469 (1995)), the presence of an infinite correlation length induces
a lack of self-averaging at critical points for thermodynamic observables, in
particular for the order parameter. After this general discussion valid for any
random critical point, we apply these ideas to random polymer models that can
be studied numerically for large sizes and good statistics over the samples. We
study the bidimensional wetting or the Poland-Scheraga DNA model with loop
exponent (marginal disorder) and (relevant disorder). Finally,
we argue that the presence of finite Griffiths ordered clusters at criticality
determines the asymptotic value and the minimal value of the typical multifractal spectrum
.Comment: 17 pages, 20 figure
Different Reactions of Plants and Insect Taxa to Reduction of Stocking Rate: A Concrete Reason to Promote Habitat Heterogeneity in Grazing Systems
Adsorption of polymers on a fluctuating surface
We study the adsorption of polymer chains on a fluctuating surface. Physical
examples are provided by polymer adsorption at the rough interface between two
non-miscible liquids, or on a membrane. In a mean-field approach, we find that
the self--avoiding chains undergo an adsorption transition, accompanied by a
stiffening of the fluctuating surface. In particular, adsorption of polymers on
a membrane induces a surface tension and leads to a strong suppression of
roughness.Comment: REVTEX, 9 pages, no figure
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