1,720,966 research outputs found
Directed polymers with tilted columnar disorder and Burgers-like turbulence
No full textThe minimal energy variations of a directed polymer with tilted columnar disorder in two dimensions are shown numerically to obey multiscaling at short distances which crosses over to global simple scaling at large distances. The scenario is analogous to that of structure functions in bifractal Burgers turbulence. Some scaling properties are predicted from extreme value statistics. The multiscaling disappears for zero tilt
Loose, flat knots in collapsed polymers
No full textWe consider single ring polymers which are confined on a plane but
maintain a fixed three-dimensional knotted topology. The equilibrium
statistics of such systems is studied on the basis of a model on square
lattice in which the configurations are represented by N-step polygons
with a number of self-intersections restricted to the minimum compatible
with the topology. This allows to define the size, s, of the flat knots
and to study their localization properties. Due to the presence of both
excluded volume and attractive interactions, the model undergoes a theta
transition. Accurate Monte Carlo results show that, while in the high
temperature swollen regime both prime and composite knot components are
localized ([s](N) similar to N-t, with t = 0), in the low temperature,
compact phase they are fully delocalized (t = 1). Right at the theta
transition weak localization prevails (t = 0.44 +/- 0.02). Part of the
results can be interpreted by taking into account a dominance of figure
eight shapes for the coarse grained knotted polymer configurations, and
by applying the scaling theory of polymer networks of fixed topology. In
particular t = 3/7 can be conjectured as an exact exponent
characterizing the weak knot localization at the theta point
The size of knots in polymers
No full textCircular DNA in viruses and bacteria is often knotted. While
mathematically problematic, the determination of the knot size is
crucial for the study of the physical and biological behaviour of long
macromolecules. Here, we review work on the size distribution of these
knots under equilibrium conditions. We discuss knot localization in good
and poor solvents, or in polymers that are adsorbed on a surface. We
also discuss recent evidence that knot size is a crucial quantity in
relaxation processes of knotted polymers
Polymer theta-point as a knot delocalization transition
No full textWe study numerically the tightness of prime flat knots in a model of
self-attracting polymers with excluded volume. We find that these knots
are localized in the high temperature swollen regime, but become
delocalized in the low temperature globular phase. Precisely at the
collapse transition, the knots are weakly localized. Some of our results
can be interpreted in terms of the theory of polymer networks, which
allows one to conjecture exact exponents for the knot length probability
distributions
Slow topological time scale of knotted polymers
No full textWe investigate the Rouse dynamics of a flexible ring polymer with a
prime knot. Within a Monte Carlo approach, we locate the knot, follow
its diffusion and observe the fluctuations of its length. A topological
time scale that is slower than the Rouse one is found to determine the
long time behavior of several dynamical quantities. The value of the
associated dynamical exponent is Zeta T = 2.32 +/- 0.1
PERCOLATION, THE SPECIAL THETA' POINT, AND THE THETA-THETA' UNIVERSALITY PUZZLE
No full textResults for d-2 percolation allow one to determine exactly the critical exponents for a polymer undergoing the special surface transition, while its bulk is at the THETA' point. Gamma-l = 8/7 and phi-s = 8/21 are the entropic and the crossover surface exponents, respectively. On the other hand, exact enumerations analysis leads to conjecture gamma-l = 4/7 at an ordinary THETA' point. This strongly supports universality of THETA and THETA' points. Similar exact results are obtained for a multicritical walk in the presence of correlated percolation vacancies
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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