801 research outputs found
Noncooperative algorithms in self-assembly
We show the first non-trivial positive algorithmic results (i.e. programs
whose output is larger than their size), in a model of self-assembly that has
so far resisted many attempts of formal analysis or programming: the planar
non-cooperative variant of Winfree's abstract Tile Assembly Model.
This model has been the center of several open problems and conjectures in
the last fifteen years, and the first fully general results on its
computational power were only proven recently (SODA 2014). These results, as
well as ours, exemplify the intricate connections between computation and
geometry that can occur in self-assembly.
In this model, tiles can stick to an existing assembly as soon as one of
their sides matches the existing assembly. This feature contrasts with the
general cooperative model, where it can be required that tiles match on
\emph{several} of their sides in order to bind.
In order to describe our algorithms, we also introduce a generalization of
regular expressions called Baggins expressions. Finally, we compare this model
to other automata-theoretic models.Comment: A few bug fixes and typo correction
Simulational study of anomalous tracer diffusion in hydrogels
In this article, we analyze different factors that affect the diffusion
behavior of small tracer particles (as they are used e.g.in fluorescence
correlation spectroscopy (FCS)) in the polymer network of a hydrogel and
perform simulations of various simplified models. We observe, that under
certain circumstances the attraction of a tracer particle to the polymer
network strands might cause subdiffusive behavior on intermediate time scales.
In theory, this behavior could be employed to examine the network structure and
swelling behavior of weakly crosslinked hydrogels with the help of FCS.Comment: 11 pages, 11 figure
Viscoelastic gels of guar and xanthan gum mixtures provide long-term stabilization of iron micro- and nanoparticles
Iron micro- and nanoparticles used for groundwater remediation and medical applications are prone to fast aggregation and sedimentation. Diluted single biopolymer water solutions of guar gum (GG) or xanthan gum (XG) can stabilize these particles for few hours providing steric repulsion and by increasing the viscosity of the suspension. The goal of the study is to demonstrate that amending GG solutions with small amounts of XG (XG/GG weight ratio 1:19; 3 g/L of total biopolymer concentration) can significantly improve the capability of the biopolymer to stabilize highly concentrated iron micro- and nanoparticle suspensions. The synergistic effect between GG and XG generates a viscoelastic gel that can maintain 20 g/L iron particles suspended for over 24 h. This is attributed to (i) an increase in the static viscosity, (ii) a combined polymer structure the yield stress of which contrasts the downward stress exerted by the iron particles, and (iii) the adsorption of the polymers to the iron surface having an anchoring effect on the particles. The XG/GG viscoelastic gel is characterized by a marked shear thinning behavior. This property, coupled with the low biopolymer concentration, determines small viscosity values at high shear rates, facilitating the injection in porous media. Furthermore, the thermosensitivity of the soft elastic polymeric network promotes higher stability and longer storage times at low temperatures and rapid decrease of viscosity at higher temperatures. This feature can be exploited in order to improve the flowability and the delivery of the suspensions to the target as well as to effectively tune and control the release of the iron particle
Higher-Order Airy Scaling in Deformed Dyck Paths
21 pages, 8 figure
The Shapes of Cooperatively Rearranging Regions in Glass Forming Liquids
The shapes of cooperatively rearranging regions in glassy liquids change from
being compact at low temperatures to fractal or ``stringy'' as the dynamical
crossover temperature from activated to collisional transport is approached
from below. We present a quantitative microscopic treatment of this change of
morphology within the framework of the random first order transition theory of
glasses. We predict a correlation of the ratio of the dynamical crossover
temperature to the laboratory glass transition temperature, and the heat
capacity discontinuity at the glass transition, Delta C_p. The predicted
correlation agrees with experimental results for the 21 materials compiled by
Novikov and Sokolov.Comment: 9 pages, 6 figure
Cognitive and behavioral predictors of light therapy use
Objective: Although light therapy is effective in the treatment of seasonal affective disorder (SAD) and other mood disorders, only 53-79% of individuals with SAD meet remission criteria after light therapy. Perhaps more importantly, only 12-41% of individuals with SAD continue to use the treatment even after a previous winter of successful treatment. Method: Participants completed surveys regarding (1) social, cognitive, and behavioral variables used to evaluate treatment adherence for other health-related issues, expectations and credibility of light therapy, (2) a depression symptoms scale, and (3) self-reported light therapy use. Results: Individuals age 18 or older responded (n = 40), all reporting having been diagnosed with a mood disorder for which light therapy is indicated. Social support and self-efficacy scores were predictive of light therapy use (p's<.05). Conclusion: The findings suggest that testing social support and self-efficacy in a diagnosed patient population may identify factors related to the decision to use light therapy. Treatments that impact social support and self-efficacy may improve treatment response to light therapy in SAD. © 2012 Roecklein et al
Impact of surface adhesion and sample heterogeneity on the multiscale mechanical characterisation of soft biomaterials
Funding from the Engineering and Physical Sciences Research Council (EP/L505602/1) is gratefully acknowledged
Single-crosslink microscopy in a biopolymer network dissects local elasticity from molecular fluctuations
Polymer networks are fundamental from cellular biology to plastics technology but their intrinsic inhomogeneity is masked by the usual ensemble-averaged measurements. Here, we construct direct maps of crosslinks-symbolic depiction of spatially-distributed elements highlighting their physical features and the relationships between them-in an actin network. We selectively label crosslinks with fluorescent markers, track their thermal fluctuations, and characterize the local elasticity and cross-correlations between crosslinks. Such maps display massive heterogeneity, reveal abundant anticorrelations, and may contribute to address how local responses scale up to produce macroscopic elasticity. Single-crosslink microscopy offers a general, microscopic framework to better understand crosslinked molecular networks in undeformed or strained states
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