arXiv subjects

Alex Levine

Publications and source records attributed to Alex Levine.

24 records · Page 2Linked to original sources

arXiv2019

Noise-induced distortion of nonequilibrium oscillator mean limit cycle

Under general conditions imposed on an active stochastic oscillator, we study change in the size and shape of its average limit cycle as a function of temperature. Such dynamics occur in a multitude of nonequilibrium systems, including the spontaneous oscillations of hair cells of the inner ear. We demonstrate one of the many mechanisms through which distortion of the mean curve may occur and identify regions in the driven oscillator phase space susceptible to corner-cutting due to noise. This we infer causes rounding of certain sharp features in the noiseless curve given by the underlying complex theoretical model, making them inaccessible under any amount of averaging of the experimentally obtained finite-temperature trajectory.

cond-mat.stat-mech↗

arXiv2018

Nonequilibrium limit cycle oscillators: fluctuations in hair bundle dynamics

We develop a framework for the general interpretation of the stochastic dynamical system near a limit cycle. Such quasi-periodic dynamics are commonly found in a variety of nonequilibrium systems, including the spontaneous oscillations of hair cells in the inner ear. We demonstrate quite generally that in the presence of noise, the phase of the limit cycle oscillator will diffuse while deviations in the directions locally orthogonal to that limit cycle will display the Lorentzian power spectrum of a damped oscillator. We identify two mechanisms by which these stochastic dynamics can acquire a complex frequency dependence, and discuss the deformation of the mean limit cycle as a function of temperature. The theoretical ideas are applied to data obtained from spontaneously oscillating hair cells of the amphibian sacculus.

cond-mat.stat-mech↗

arXiv2007

Nanorheology of viscoelastic shells: Applications to viral capsids

We study the microrheology of nanoparticle shells [Dinsmore et al. Science 298, 1006 (2002)] and viral capsids [Ivanovska et al. PNAS 101, 7600 (2004)] by computing the mechanical response function and thermal fluctuation spectrum of a viscoelastic spherical shell that is permeable to the surrounding solvent. We determine analytically the damped dynamics of the shear, bend, and compression modes of the shell coupled to the solvent both inside and outside the sphere in the zero Reynolds number limit. We identify fundamental length and time scales in the system, and compute the thermal correlation function of displacements of antipodal points on the sphere and the mechanical response to pinching forces applied at these points. We describe how such a frequency-dependent antipodal correlation and/or response function, which should be measurable in new AFM-based microrheology experiments, can probe the viscoelasticity of these synthetic and biological shells constructed of nanoparticles.

cond-mat.soft↗

arXiv2007

Effective medium theory of semiflexible filamentous networks

We develop an effective medium approach to the mechanics of disordered, semiflexible polymer networks and study the response of such networks to uniform and nonuniform strain. We identify distinct elastic regimes in which the contributions of either filament bending or stretching to the macroscopic modulus vanish. We also show that our effective medium theory predicts a crossover between affine and non-affine strain, consistent with both prior numerical studies and scaling theory.

cond-mat.soft↗

arXiv1998

Screened and Unscreened Phases in Sedimenting Suspensions

A coarse-grained stochastic hydrodynamical description of velocity and concentration fluctuations in steadily sedimenting suspensions is constructed, and analyzed using self-consistent and renormalization group methods. We find that there exists a dynamical, non-equilibrium phase transition from an "unscreened" phase in which we recover the Caflisch-Luke (R.E. Caflisch and J.H.C. Luke, Phys. Fluids 28, 759 (1985)) divergence of the velocity variance to a "screened" phase where the velocity fluctuations have a finite correlation length growing as $ϕ^{-1/3}$ where $ϕ$ is the particle volume fraction, in agreement with Segrè et. al. (Phys. Rev. Lett. 79, 2574 (1997)) and the velocity variance is independent of system size. Detailed predictions are made for the correlation function in both phases and at the transition.

cond-mat.soft↗

arXiv1996

Nonequilibrium Fluctuations in Sedimenting Suspensions: A Dynamical Renormalization Group Theory

A nonlinear two-fluid stochastic hydrodynamical description of velocity and concentration fluctuations in sedimenting suspensions is constructed, and analyzed using self-consistent (SC) and renormalization group (RG) methods. The advection of particles by velocity fluctuations is shown to be ``relevant'' in all dimensions $d < 6$ . Both RG and SC analyses predict a strong reduction in the dependence of velocity fluctuations on system-size $L$ relative to the $L^{1/2}$ obtained in the linearized theory of Caflisch and Luke [Phys. Fluids {\bf 28}, 785 (1985)]. This is an important step towards resolving a ten-year old puzzle in the field.

cond-mat.soft↗