12,538 research outputs found
Comment on "Chain Length Scaling of Protein Folding Time", PRL 77, 5433 (1996)
In a recent Letter, Gutin, Abkevich, and Shakhnovich (GAS) reported on a
series of dynamical Monte Carlo simulations on lattice models of proteins.
Based on these highly simplified models, they found that four different
potential energies lead to four different folding time scales tau_f, where
tau_f scales with chain length as N^lambda (see, also, Refs. [2-4]), with
lambda varying from 2.7 to 6.0. However, due to the lack of microscopic models
of protein folding dynamics, the interpretation and origin of the data have
remained somewhat speculative. It is the purpose of this Comment to point out
that the application of a simple "mesoscopic" model (cond-mat/9512019, PRL 77,
2324, 1996) of protein folding provides a full account of the data presented in
their paper. Moreover, we find a major qualitative disagreement with the
argumentative interpretation of GAS. Including, the origin of the dynamics, and
size of the critical folding nucleus.Comment: 1 page Revtex, 1 fig. upon request. Submitted to PR
A Criterion That Determines Fast Folding of Proteins: A Model Study
We consider the statistical mechanics of a full set of two-dimensional
protein-like heteropolymers, whose thermodynamics is characterized by the
coil-to-globular () and the folding () transition temperatures.
For our model, the typical time scale for reaching the unique native
conformation is shown to scale as , where
, is the number of residues, and scales
algebraically with . We argue that scales linearly with the inverse of
entropy of low energy non-native states, whereas is almost
independent of it. As , non-productive intermediates
decrease, and the initial rapid collapse of the protein leads to structures
resembling the native state. Based solely on {\it accessible} information,
can be used to predict sequences that fold rapidly.Comment: 10 pages, latex, figures upon reques
Refolding dynamics of stretched biopolymers upon force quench
Single molecule force spectroscopy methods can be used to generate folding
trajectories of biopolymers from arbitrary regions of the folding landscape. We
illustrate the complexity of the folding kinetics and generic aspects of the
collapse of RNA and proteins upon force quench, using simulations of an RNA
hairpin and theory based on the de Gennes model for homopolymer collapse. The
folding time, , depends asymmetrically on and
where () is the stretch (quench) force, and
is the transition mid-force of the RNA hairpin. In accord with
experiments, the relaxation kinetics of the molecular extension, , occurs
in three stages: a rapid initial decrease in the extension is followed by a
plateau, and finally an abrupt reduction in that occurs as the native
state is approached.
The duration of the plateau increases as decreases
(where is the time in which the force is reduced from to ).
Variations in the mechanisms of force quench relaxation as is altered
are reflected in the experimentally measurable time-dependent entropy, which is
computed directly from the folding trajectories. An analytical solution of the
de Gennes model under tension reproduces the multistage stage kinetics in
. The prediction that the initial stages of collapse should also be a
generic feature of polymers is validated by simulation of the kinetics of
toroid (globule) formation in semiflexible (flexible) homopolymers in poor
solvents upon quenching the force from a fully stretched state. Our findings
give a unified explanation for multiple disparate experimental observations of
protein folding.Comment: 31 pages 11 figure
A New Approach for Guaranteed State Estimation by Zonotopes
18th World CongressThe International Federation of Automatic ControlMilano (Italy) August 28 - September 2This paper proposes a methodology for guaranteed state estimation of linear discrete-time systems in the presence of bounded disturbances and noises. This aims at computing an outer approximation of the state estimation domain represented by a zonotope. A new criterion is used to reduce the size of the zonotope at each sample time. An illustrative example is analyzed in order to highlight the advantages of the proposed algorithm
A genetic graph-based approach for partitional clustering
Clustering is one of the most versatile tools for data analysis. In the recent years, clustering that seeks the continuity of data (in opposition to classical centroid-based approaches) has attracted an increasing research interest. It is a challenging problem with a remarkable practical interest. The most popular continuity clustering method is the spectral clustering (SC) algorithm, which is based on graph cut: It initially generates a similarity graph using a distance measure and then studies its graph spectrum to find the best cut. This approach is sensitive to the parameters of the metric, and a correct parameter choice is critical to the quality of the cluster. This work proposes a new algorithm, inspired by SC, that reduces the parameter dependency while maintaining the quality of the solution. The new algorithm, named genetic graph-based clustering (GGC), takes an evolutionary approach introducing a genetic algorithm (GA) to cluster the similarity graph. The experimental validation shows that GGC increases robustness of SC and has competitive performance in comparison with classical clustering methods, at least, in the synthetic and real dataset used in the experiments
A new approach for Guaranteed ellipsoidal state estimation
The 19th World Congress of the International Federation of Automatic Control 2014. Cape Town, SudáfricaThis paper proposes a new ellipsoid-based guaranteed state estimation approach for linear discrete-time systems with bounded perturbations and bounded measurement noise. This approach is based on the minimization of the radius of the ellipsoidal state estimation set. Firstly, the ellipsoidal state estimation is computed by off-line solving a Linear Matrix Inequality optimization problem. Secondly, a new online method is developed in order to improve the accuracy of the estimation but it leads to an increase of the online computation load. A new scaling technique is proposed to reduce the computation time, while keeping a good accuracy of the state estimation. An illustrative example is analyzed in order to show the advantages of the proposed approach
Comparison between two state estimation techniqueds for linear systems
20th World Congress of the International Federation of Automatic Control, Jul 2017, Toulouse, FranceThis paper presents a comparison in terms of accuracy and complexity between two
approaches used for state estimation of linear systems: a classic Kalman filter and a guaranteed
set-membership state estimation technique. The main goal of this paper is to analyze the
advantages of these techniques and to combine them in the future in a new accurate and simple
extension that handles system uncertainties and chance constraints. Two academic examples
illustrate the main differences between the compared techniques
The role of the quantum properties of gravitational radiation in the dete ction of gravitational waves
The role that the quantum properties of a gravitational wave could play in
the detection of gravitational radiation is analyzed. It is not only
corroborated that in the current laser-interferometric detectors the resolution
of the experimental apparatus could lie very far from the corresponding quantum
threshold (thus the backreaction effect of the measuring device upon the
gravitational wave is negligible), but it is also suggested that the
consideration of the quantum properties of the wave could entail the definition
of dispersion of the measurement outputs. This dispersion would be a function
not only of the sensitivity of the measuring device, but also of the
interaction time (between measuring device and gravitational radiation) and of
the arm length of the corresponding laser- interferometer. It would have a
minimum limit, and the introduction of the current experimental parameters
insinuates that the dispersion of the existing proposals could lie very far
from this minimum, which means that they would show a very large dispersion.Comment: 19 pages, Latex (use epsfig.sty
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