686 research outputs found
The Slider-Pinning Problem
A Laman mechanism is a flexible planar bar-and-joint framework with m ≤ 2n-3 edges and exactly k = 2n-m degrees of freedom. The slider-pinning problem is to eliminate all the degrees of freedom of a Laman mechanism, in an optimal fashion, by individually fixing x or y coordinates of vertices. We describe two easy to implement O(n2) time algorithms
Slider-pinning Rigidity: a Maxwell-Laman-type Theorem
We define and study slider-pinning rigidity, giving a complete combinatorial
characterization. This is done via direction-slider networks, which are a
generalization of Whiteley's direction networks.Comment: Accepted, to appear in Discrete and Computational Geometr
Static friction on the fly: velocity depinning transitions of lubricants in motion
The dragging velocity of a model solid lubricant confined between sliding
periodic substrates exhibits a phase transition between two regimes,
respectively with quantized and with continuous lubricant center-of-mass
velocity. The transition, occurring for increasing external driving force F_ext
acting on the lubricant, displays a large hysteresis, and has the features of
depinning transitions in static friction, only taking place on the fly.
Although different in nature, this phenomenon appears isomorphic to a static
Aubry depinning transition in a Frenkel-Kontorova model, the role of particles
now taken by the moving kinks of the lubricant-substrate interface. We suggest
a possible realization in 2D optical lattice experiments.Comment: 5 pages, 4 figures, revtex, in print in Phys. Rev. Let
Modeling friction: From nanoscale to mesoscale
The physics of sliding friction is gaining impulse from nanoscale and
mesoscale experiments, simulations, and theoretical modeling. This Colloquium
reviews some recent developments in modeling and in atomistic simulation of
friction, covering open-ended directions, unconventional nanofrictional
systems, and unsolved problems.Comment: 26 pages, 14 figures, Rev. Mod. Phys. Colloquiu
Dynamic Influence Networks for Rule-based Models
We introduce the Dynamic Influence Network (DIN), a novel visual analytics
technique for representing and analyzing rule-based models of protein-protein
interaction networks. Rule-based modeling has proved instrumental in developing
biological models that are concise, comprehensible, easily extensible, and that
mitigate the combinatorial complexity of multi-state and multi-component
biological molecules. Our technique visualizes the dynamics of these rules as
they evolve over time. Using the data produced by KaSim, an open source
stochastic simulator of rule-based models written in the Kappa language, DINs
provide a node-link diagram that represents the influence that each rule has on
the other rules. That is, rather than representing individual biological
components or types, we instead represent the rules about them (as nodes) and
the current influence of these rules (as links). Using our interactive DIN-Viz
software tool, researchers are able to query this dynamic network to find
meaningful patterns about biological processes, and to identify salient aspects
of complex rule-based models. To evaluate the effectiveness of our approach, we
investigate a simulation of a circadian clock model that illustrates the
oscillatory behavior of the KaiC protein phosphorylation cycle.Comment: Accepted to TVCG, in pres
Lubricated friction between incommensurate substrates
This paper is part of a study of the frictional dynamics of a confined solid
lubricant film - modelled as a one-dimensional chain of interacting particles
confined between two ideally incommensurate substrates, one of which is driven
relative to the other through an attached spring moving at constant velocity.
This model system is characterized by three inherent length scales; depending
on the precise choice of incommensurability among them it displays a strikingly
different tribological behavior. Contrary to two length-scale systems such as
the standard Frenkel-Kontorova (FK) model, for large chain stiffness one finds
that here the most favorable (lowest friction) sliding regime is achieved by
chain-substrate incommensurabilities belonging to the class of non-quadratic
irrational numbers (e.g., the spiral mean). The well-known golden mean
(quadratic) incommensurability which slides best in the standard FK model shows
instead higher kinetic-friction values. The underlying reason lies in the
pinning properties of the lattice of solitons formed by the chain with the
substrate having the closest periodicity, with the other slider.Comment: 14 pagine latex - elsart, including 4 figures, submitted to Tribology
Internationa
From Individual to Collective Pinning: Effect of Long-range Elastic Interactions
We study the effect of long-range elastic interactions in the dynamical
behavior of an elastic chain driven quasi-statically in a quenched random
pinning potential and in the strong pinning limit. This is a generic situation
occuring in solid friction, crack propagation, wetting front motion, ... Tuning
the exponent of the algebraic decay of the elastic interaction with the
distance is shown to give rise to three regimes: a Mean-Field (MF) regime, a
Laplacian (L) regime and an intermediate regime where the critical exponents
interpolate continuously between the MF and L limit cases. The effect of the
driving mode on the avalanche statistics is also analyzed.Comment: 28 pages in RevTex, 17 figure
Influence of substrate potential shape on the dynamics of a sliding lubricant chain
We investigate the frictional sliding of an incommensurate chain of
interacting particles confined in between two nonlinear on-site substrate
potential profiles in relative motion. We focus here on the class of
Remoissenet-Peyrard parametrized potentials , whose shape can
be varied continuously as a function of , recovering the sine-Gordon
potential as particular case. The observed frictional dynamics of the system,
crucially dependent on the mutual ratios of the three periodicities in the
sandwich geometry, turns out to be significantly influenced also by the shape
of the substrate potential. Specifically, variations of the shape parameter
affects significantly and not trivially the existence and robustness of the
recently reported velocity quantization phenomena [Vanossi {\it et al.}, Phys.
Rev. Lett. 97, 056101 (2006)], where the chain center-of-mass velocity to the
externally imposed relative velocity of the sliders stays pinned to exact
"plateau" values for wide ranges of the dynamical parameters.Comment: 7 pages, 6 figure
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