75 research outputs found
Thermal and mechanical properties of a DNA model with solvation barrier
We study the thermal and mechanical behavior of DNA denaturation in the frame
of the mesoscopic Peyrard- Bishop-Dauxois model with the inclusion of solvent
interaction. By analyzing the melting transition of a homogeneous A-T sequence,
we are able to set suitable values of the parameters of the model and study the
formation and stability of bubbles in the system. Then, we focus on the case of
the P5 promoter sequence and use the Principal Component Analysis of the
trajectories to extract the main information on the dynamical behavior of the
system. We find that this analysis method gives an excellent agreement with
previous biological results.Comment: Physical Review E (in press
Non-equilibrium Effects in the Thermal Switching of Underdamped Josephson Junctions
We study the thermal escape problem in the low damping limit. We find that
finiteness of the barrier is crucial for explaining the thermal activation
results. In this regime low barrier non-equilibrium corrections to the usual
theories become necessary. We propose a simple theoretical extension accounting
for these non-equilibrium processes which agrees numerical results. We apply
our theory to the understanding of switching current curves in underdamped
Josephson junctions.Comment: 4 pages + 4 figure
Translocation of a polymer chain driven by a dichotomous noise
We consider the translocation of a one-dimensional polymer through a pore
channel helped by a motor driven by a dichotomous noise with time exponential
correlation. We are interested in the study of the translocation time, mean
velocity and stall force of the system as a function of the mean driving
frequency. We find a monotonous translocation time, in contrast with the mean
velocity which shows a pronounced maximum at a given frequency. Interestingly,
the stall force shows a nonmonotonic behavior with the presence of a minimum.
The influence of the spring elastic constant to the mean translocation times
and velocities is also presented.Comment: 11 pages, 7 figure
Numerical study of pattern formation in compliant surfaces scraped by a rigid tip
The emergence of surface patterns on the surfaces of compliant materials subject to plowing wear is a complex problem which can be quantitatively characterized, e.g., on polymer surfaces scraped by an atomic force microscope (AFM) tip. Here we explore the applicability of a phenomenological model recently introduced to describe this phenomenon. Based on the competition between the viscoplastic indentation and the elastic shear stress caused by the tip, the model is able to reproduce the wavy features (ripples) observed when the tip is scanned along a series of parallel lines. For low values of the driving velocity v and the spacing b between scan lines, the existence of dotted areas formed by variously oriented pit alignments is observed. Moreover, coexistence of rippled with dotted domains is also observed at suitable parameter values. The formation process of the ripples is also described in detail. The amplitude, period, and orientation of these features are estimated numerically for different values of v and b parameters. We have also revisited the formation of the wavy patterns formed when a single line is scanned, and derived an equation which correctly describes their period and depth, and the static friction as well. This equation is not applicable when several lines are scanned one after the other and the ripples emerge as result of a cooperative process which involves the scanning of several lines
Microwave photonics with Josephson junction arrays: Negative refraction index and entanglement through disorder
We study different architectures for a photonic crystal in the microwave regime based on superconducting transmission lines interrupted by Josephson junctions, both in one and two dimensions. A study of the scattering properties of a single junction in the line shows that the junction behaves as a perfect mirror when the photon frequency matches the Josephson plasma frequency. We generalize our calculations to periodic arrangements of junctions, demonstrating that they can be used for tunable band engineering, forming what we call a quantum circuit crystal. Two applications are discussed in detail. In a two-dimensional structure we demonstrate the phenomenon of negative refraction. We finish by studying the creation of stationary entanglement between two superconducting qubits interacting through a disordered media. © 2012 American Physical Society.This work was supported by Spanish Governement projects FIS2008-01240, FIS2009-10061, FIS2009-12773-C02-01, and FIS2011-25167 cofinanced by FEDER funds; CAM research consortium QUITEMAD; Basque Government Grants No. IT472-10, and No. UPV/EHU UFI 11/55; and PROMISCE, SOLID, and CCQED European projects.Peer Reviewe
Mode locking in discrete solition dynamics under ac forces
We present here analytical arguments and numerical evidence for the existence of net directional motion of highly discrete sine-Gordon kinks under ac forces of zero average. We have also characterized the depinning of the oscillating kink under those circumstances, and analyzed the instability mechanisms of the phase-locked running solutions. Possible experimental relevance of this phenomenon in circular arrays of Josephson junctions is discussed.Financial support from DGES (PB95-0797) and CICYT (MAT95-0325)Publicad
Equilibrium properties of a Josephson junction ladder with screening effects
In this paper we calculate the ground state phase diagram of a Josephson
Junction ladder when screening field effects are taken into account. We study
the ground state configuration as a function of the external field, the
penetration depth and the anisotropy of the ladder, using different
approximations to the calculation of the induced fields. A series of tongues,
characterized by the vortex density , is obtained. The vortex density
of the ground state, as a function of the external field, is a Devil's
staircase, with a plateau for every rational value of . The width of
each of these steps depends strongly on the approximation made when calculating
the inductance effect: if the self-inductance matrix is considered, the
phase tends to occupy all the diagram as the penetration depth
decreases. If, instead, the whole inductance matrix is considered, the width of
any step tends to a non-zero value in the limit of very low penetration depth.
We have also analyzed the stability of some simple metastable phases: screening
fields are shown to enlarge their stability range.Comment: 16 pp, RevTex. Figures available upon request at
[email protected] To be published in Physical Review B (01-Dec-96
From Josephson junction metamaterials to tunable pseudo-cavities
arXiv:1305.4844v1The scattering through a Josephson junction (JJ) interrupting a superconducting line is revisited including power leakage. We also discuss how to make tunable and broadband resonant mirrors by concatenating junctions. As an application, we show how to construct cavities using these mirrors, thus connecting two research fields: JJ quantum metamaterials and coupled-cavity arrays. We finish by discussing the first nonlinear corrections to the scattering and their measurable effects. © 2013 IOP Publishing Ltd.This work was supported by Spanish government projects FIS2009-10061, and FIS2011-25167 conanced by FEDER funds. We thanks Aragon government support to group FENOL, CAM research consortium QUITEMAD and PROMISCE European project.Peer Reviewe
Anisotropy Effects in Atomic-Scale Friction
The static and kinetic friction experienced by a point mass elastically driven at different angles on surface lattices with square, hexagonal, and honeycomb symmetries are estimated by analytical and numeric calculations based on the Prandtl–Tomlinson (PT) model. Assuming a strong surface coupling, the anisotropy of static friction increases from 3.7 up to 46.3% when the density of packing of the surface atoms is reduced, but this is not the case for kinetic friction, the anisotropy of which is maximal on a square lattice. Although these results have not been supported by accurate experimental verifications so far, the PT model was successfully applied to interpret anisotropy effects in the friction force profiles measured, among other surfaces, on rectangular lattices with complex unit cells and on stepped crystal surfaces
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