arXiv subjects

Yael Roichman

Publications and source records attributed to Yael Roichman.

At least 37 records · Page 2Linked to original sources

arXiv2024

Smart Resetting: An Energy-Efficient Strategy for Stochastic Search Processes

Stochastic resetting, a method for accelerating target search in random processes, often incurs temporal and energetic costs. For a diffusing particle, a lower bound exists for the energetic cost of reaching the target, which is attained at low resetting rates and equals the direct linear transportation cost against fluid drag. Here, we study ``smart resetting," a strategy that aims to beat this lower bound. By strategically resetting the particle only when this benefits its progress toward the target, smart resetting leverages information to minimize energy consumption. We analytically calculate the energetic cost per mean first passage time and show that smart resetting consistently reduces the energetic cost compared to regular resetting. Surprisingly, smart resting achieves the minimum energy cost previously established for regular resetting, irrespective of the resetting rate. Yet, it fails to reduce this cost further. We extend our findings in two ways: first, by examining nonlinear energetic cost functions, and second, by considering smart resetting of drift-diffusion processes.

cond-mat.stat-mech↗

arXiv2024

Nonequilibrium Probability Currents in Optically-Driven Colloidal Suspensions

In the absence of directional motion it is often hard to recognize athermal fluctuations. Probability currents provide such a measure in terms of the rate at which they enclose area in the reduced phase space. We measure this area enclosing rate for trapped colloidal particles, where only one particle is driven. By combining experiment, theory, and simulation, we single out the effect of the different time scales in the system on the measured probability currents. In this controlled experimental setup, particles interact hydrodynamically. These interactions lead to a strong spatial dependence of the probability currents and to a local influence of athermal agitation. In a multiple-particle system, we show that even when the driving acts only on one particle, probability currents occur between other, non-driven particles. This may have significant implications for the interpretation of fluctuations in biological systems containing elastic networks in addition to a suspending fluid.

cond-mat.soft↗

arXiv2024

Resetting as a swift equilibration protocol in an anharmonic potential

We present and characterize a method to accelerate the relaxation of a Brownian object between two distinct equilibrium states. Instead of relying on a deterministic time-dependent control parameter, we use stochastic resetting to guide and accelerate the transient evolution. The protocol is investigated numerically, and its thermodynamic cost is evaluated with the tools of stochastic thermodynamics. Remarkably, we show that stochastic resetting significantly accelerates the relaxation to the final state. This stochastic protocol exhibits energetic and temporal characteristics that align with the scales observed in previously investigated deterministic protocols. Moreover, it expands the spectrum of stationary states that can be manipulated, incorporating new potential profiles achievable through experimentally viable protocols.

cond-mat.stat-mech↗

arXiv2023

Environmental memory facilitates search with home returns

Search processes in the natural world are often punctuated by home returns that reset the position of foraging animals, birds, and insects. Many theoretical, numerical, and experimental studies have now demonstrated that this strategy can drastically facilitate search, which could explain its prevalence. To further facilitate search, foragers also work as a group: modifying their surroundings in highly sophisticated ways e.g., by leaving chemical scent trails that imprint the memory of previous excursions. Here, we design a controlled experiment to show that the benefit coming from such ``environmental memory'' is significant even for a single, non-intelligent, searcher that is limited to simple physical interactions with its surroundings. To this end, we employ a self-propelled bristle robot that moves randomly within an arena filled with obstacles that the robot can push around. To mimic home returns, we reset the bristle robot's position at constant time intervals. We show that trails created by the robot give rise to a form of environmental memory that facilitates search by increasing the effective diffusion coefficient. Numerical simulations, and theoretical estimates, designed to capture the essential physics of the experiment support our conclusions and indicate that these are not limited to the particular system studied herein.

cond-mat.stat-mech↗

arXiv2023

A many-body Szilard engine with giant number fluctuations

Szilárd's information engine is a canonical example in the field of thermodynamics of information. We realize experimentally a macroscopic many-particle Szilárd engine that consists of active particles and use it to lift a mass against gravity. We show that the extractable work per cycle increases when the raised weight is changed more gradually during the process. Interestingly, we find that the ideal extractable work grows with the number of particles due to giant number fluctuations. This is in contrast to the calculated behavior of a similar engine operating on thermal particles.

cond-mat.stat-mech↗

arXiv2022

Diffusion with Partial Resetting

Inspired by many examples in nature, stochastic resetting of random processes has been studied extensively in the past decade. In particular, various models of stochastic particle motion were considered where upon resetting the particle is returned to its initial position. Here we generalize the model of diffusion with resetting to account for situations where a particle is returned only a fraction of its distance to the origin, e.g., half way. We show that this model always attains a steady-state distribution which can be written as an infinite sum of independent, but not identical, Laplace random variables. As a result, we find that the steady-state transitions from the known Laplace form which is obtained in the limit of full resetting to a Gaussian form which is obtained close to the limit of no resetting. A similar transition is shown to be displayed by drift-diffusion whose steady-state can also be expressed as an infinite sum of independent random variables. Finally, we extend our analysis to capture the temporal evolution of drift-diffusion with partial resetting, providing a bottom-up probabilistic construction that yields a closed form solution for the time dependent distribution of this process in Fourier-Laplace space. Possible extensions and applications of diffusion with partial resetting are discussed.

cond-mat.stat-mech↗

arXiv2022

Roadmap for Optical Tweezers

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nanoparticle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration.

physics.optics↗

arXiv2021

Auxiliary Optomechanical Tools for 3D Cell Manipulation

Advances in laser and optoelectronic technologies brought the general concept of optomechanical manipulation to the level of standard biophysical tools, paving ways towards controlled experiments and measurements of tiny mechanical forces. Recent developments in direct laser writing (DLW), enabled the realization of new types of micron-scale optomechanical tools, capable of performing designated functions. Here we further develop the concept of DLW-fabricated optomechanically-driven tools and demonstrate full-3D manipulation capabilities over biological objects. In particular, we resolved a long-standing problem of out-of-plane rotation in a pure liquid, which was demonstrated on a living cell, clamped between a pair of forks, designed for efficient manipulation with holographic optical tweezers. The demonstrated concept paves new ways towards realization of flexible tools for performing on-demand functions over biological objects, such as cell tomography and surgery to name just few.

physics.optics↗

arXiv2020

Different anomalous diffusion regimes measured in the dynamics of tracer particles in actin networks

It was previously believed that diffusion of a tracer particle in a viscoelastic material should be of the fractional Brownian motion (fBm) type. This is due to the long-term memory in the response of such materials to mechanical perturbations. Surprisingly, the diffusion of a tracer particle in a network of a purified protein, actin, was found to conform to the continuous time random walk (CTRW) type in one study that focused on the ensemble average characteristics. Here, we analyze the dynamics of two differently sized tracer particles in actin networks of different mesh sizes. We find that the ratio of tracer particle size to the characteristic length scale of a bio-polymer network plays a crucial role in determining the type of diffusion the particle performs. We find that the tracer particle diffusion has features of fBm when the particle is large compared to the mesh size, of normal diffusion when the particle is much smaller than the mesh size, and of CTRW in between these two limits. Based on our findings, we propose and verify numerically a new model for the tracer particle's motion in all regimes. Our model suggests that diffusion in actin networks consists of fBm of the tracer particle coupled with occasional caging events with power-law-distributed escape times.

cond-mat.soft↗

arXiv2020

The Spatial Crossover between Far-From-Equilibrium and Near-Equilibrium Dynamics in Locally Driven Suspensions

We examine the response of a quasi-two-dimensional colloidal suspension to a localized circular driving induced by optical tweezers. This approach, a microscale version of rheometry, allows us to resolve over three orders of magnitude in Péclet number ($Pe$) and provide a direct observation of a sharp spatial crossover from far- to near-thermal-equilibrium regions of the suspension. In particular, particles migrate from high to low $Pe$ regions and form strongly inhomogeneous steady-state density profiles with an emerging length scale that does not depend on the particle density and is set by $Pe\approx1$. We show that the phenomenological two phase fluid constitutive model is in line with our results.

cond-mat.soft↗

arXiv2020

Experimental realization of diffusion with stochastic resetting

Stochastic resetting is prevalent in natural and man-made systems giving rise to a long series of non-equilibrium phenomena. Diffusion with stochastic resetting serves as a paradigmatic model to study these phenomena, but the lack of a well-controlled platform by which this process can be studied experimentally has been a major impediment to research in the field. Here, we report the experimental realization of colloidal particle diffusion and resetting via holographic optical tweezers. We provide the first experimental corroboration of central theoretical results, and go on to measure the energetic cost of resetting in steady-state and first-passage scenarios. In both cases, we show that this cost cannot be made arbitrarily small due to fundamental constraints on realistic resetting protocols. The methods developed herein open the door to future experimental study of resetting phenomena beyond diffusion.

cond-mat.stat-mech↗

arXiv2020

Kinetics of actin networks formation measured by time resolved particle-tracking microrheology

Actin is one of the most studied cytoskeleton proteins showing a very rich span of structures. It can self-assemble actively into dynamical structures that govern the mechanical properties of the cell, its motility and its division. However, only very few studies characterize the kinetics of the active actin self-assembly process beyond the formation of an entangled network. Here, we follow actin polymerization kinetics and organization into entangled networks using time resolved passive microrheology. We establish a relationship between the initial concentration of monomers, the active polymerization and network formation kinetics, and the viscoelastic properties from the onset of actin polymerization upto the formation of a steady state entangled network. Surprisingly, we find that at high enough initial monomer concentrations the elastic modulus of the forming actin networks overshoots and then relaxes with a -2/5 power law, that we attribute to rearrangements of the network into a steady state structure.

cond-mat.soft↗

arXiv2020

Two Coupled Mechanisms Produce Fickian, yet non-Gaussian Diffusion in Heterogeneous Media

Fickian yet non-Gaussian diffusion is observed in several biological and soft matter systems, yet the underlying mechanisms behind the emergence of non-Gaussianity while retaining a linear mean square displacement remain speculative. Here, we characterize quantitatively the effect of spatial heterogeneities on the appearance of non-Gaussianity in Fickian diffusion. We study the diffusion of fluorescent colloidal particles in a matrix of micropillars having a range of structural configurations: from completely ordered to completely random. We show that non-Gaussianity emerges as a direct consequence of two coupled factors; individual particle diffusivities become spatially dependent in a heterogeneous randomly structured environment, and the spatial distribution of the particles varies significantly in such environments, further influencing the diffusivity of a single particle. The coupled mechanisms lead to a considerable non-Gaussian nature even due to weak disorder in the arrangement of the micropillars. A simple mathematical model validates our hypothesis that non-Gaussian yet Fickian diffusion in our system arises from the superstatistical behavior of the ensemble in a structurally heterogeneous environment. The two mechanisms identified here are relevant for many systems of crowded heterogeneous environments where non-Gaussian diffusion is frequently observed, for example in biological systems, polymers, gels and porous materials.

cond-mat.soft↗

arXiv2020

The Airy distribution: experiment, large deviations and additional statistics

The Airy distribution (AD) describes the probability distribution of the area under a Brownian excursion. The AD is prominent in several areas of physics, mathematics and computer science. Here we use a dilute colloidal system to directly measure, for the first time, the AD in experiment. We also show how two different techniques of theory of large deviations - the Donsker-Varadhan formalism and the optimal fluctuation method - manifest themselves in the AD. We advance the theory of the AD by calculating, at large and small areas, the position distribution of a Brownian excursion conditioned on a given area, and measure its mean in the experiment. For large areas, we uncover two singularities in the large deviation function, which can be interpreted as dynamical phase transitions of third order. For small areas the position distribution coincides with the Ferrari-Spohn distribution, and we identify the reason for this coincidence.

cond-mat.stat-mech↗

arXiv2019

Nanoparticle mobility over a surface as a probe for weak transient disordered peptide-peptide interactions

Weak interactions form the core basis of a vast number of biological processes, in particular, those involving intrinsically disordered proteins. Here, we establish a new technique capable of probing these weak interactions between synthetic unfolded polypeptides using a convenient yet efficient, quantitative method based on single particle tracking of peptide-coated gold nanoparticles over peptide-coated surfaces. We demonstrate that our technique is sensitive enough to observe the influence of a single amino acid mutation on the transient peptide-peptide interactions. Furthermore, the effects of buffer salinity, expected to alter weak electrostatic interactions, are also readily detected and examined in detail. The method presented here has the potential to evaluate in a high throughput manner, weak interactions for a wide range of disordered proteins, polypeptides, and other biomolecules.

physics.bio-ph↗

arXiv2019

Non-monotonic displacement distribution of active random walkers

We consider a simple model for active random walk with general temporal correlations, and investigate the shape of the probability distribution function of the displacement during a short time interval. We find that under certain conditions the distribution is non-monotonic and we show analytically and numerically that the existence of the non-monotonicity is governed by the walker's tendency to move forward, while the correlations between the timing of its active motion control the magnitude and shape of the non-monotonicity. In particular, we find that in a homogeneous system such non-monotonicity can occur only if the persistence is strong enough.

cond-mat.stat-mech↗

arXiv2019

Optical trapping below the diffraction limit with a tunable beam waist using super-oscillating beams

Super-oscillating beams can be used to create light spots whose size is below the diffraction limit with a side ring of high intensity adjacent to them. Optical traps made of the super-oscillating part of such beams exhibit superior localization of submicron beads compared to regular optical traps. Here we focus on the effect of the ratio of particle size to trap size on the localization and stiffness of optical traps made of super-oscillating beams. We find a non-monotonic dependence of trapping stiffness on the ratio of particle size to beam size. Optimal trapping is achieved when the particle is larger than the beam waist of the superoscillating feature but small enough not to overlap with the side ring.

physics.optics↗

arXiv2019

Deep penetration fluorescence imaging through dense yeast cells suspensions using Airy beams

We propose a new method to image fluorescent objects through turbid media base on Airy beam scanning. This is achieved by using the non-diffractive nature of Airy beams, namely their ability to maintain their shape while penetrating through a highly scattering medium. We show, that our technique can image fluorescent objects immersed in turbid media with higher resolution and signal to noise than confocal imaging. As proof-of-principle, we demonstrate imaging of 1$μ$m sized fluorescent beads through a dense suspension of yeast cells with an attenuation coefficient of 51cm$^{-1}$ at a depth of 90$μ$m. Finally, we demonstrate that our technique can also provide the depth of the imaged object without any additional sectioning.

physics.optics↗