arXiv subjects

Amer Al-Hiyasat

Publications and source records attributed to Amer Al-Hiyasat.

6 recordsLinked to original sources

arXiv2026

Critical Properties and Glass Transitions in Randomly Coupled Fields

We study an assembly of $N$ scalar fields coupled via a quenched random interaction, equivalent to a spin glass whose spins are promoted to $d$-dimensional fields. When $N$ is large, the random coupling matrix produces a family of Gaussian universality classes whose critical exponents are determined by the behavior of the eigenvalue density near the spectral edge. For a Wigner matrix, the correlation length diverges at criticality but the susceptibility remains finite, and one-loop replica analysis supports an upper critical dimension of unity. In an exactly solvable spherical variant, the heat capacity jumps at the transition in $d>1$, and correlations remain pinned to their critical form throughout the glass phase, giving generic scale invariance despite the absence of a Goldstone mode.

cond-mat.stat-mech↗

arXiv2026

Spatiotemporal noise stabilizes unbounded diversity in strongly-competitive communities

Classical ecological models predict that diverse communities should be unstable, presenting a central challenge to explaining the stable biodiversity seen in nature. We revisit this long-standing problem by extending the generalized Lotka-Volterra model to include both spatial structure and environmental fluctuations across space and time. We find that neither space nor environmental noise alone can resolve the tension between diversity and stability, but that together they permit arbitrarily many species to stably coexist in a sufficiently large system, despite strongly disordered competitive interactions. We analytically characterize the noise-induced transition to coexistence, showing that spatiotemporal noise drives power-law abundance fluctuations, leading to an anomalous scaling of moments known empirically as Taylor's law. At the metacommunity level, this manifests as an emergent sublinear self-inhibition that stabilizes diversity and renders the interaction disorder irrelevant in the high-diversity limit. Spatiotemporal noise thus provides a novel resolution to the diversity-stability paradox and a generic mechanism by which complex communities can persist.

q-bio.PE↗

arXiv2026

A Cold Tracer in a Hot Bath: In and Out of Equilibrium

We study the dynamics of a zero-temperature overdamped tracer in a bath of Brownian particles. As the bath density is increased, numerical simulations show the tracer to transition from an active dynamics, characterized by boundary accumulation and ratchet currents, to an effective equilibrium regime. To account for this analytically, we eliminate the bath degrees of freedom under the assumption of linear coupling to the tracer and show convergence, in the large density limit, to an equilibrium dynamics at the bath temperature. We then develop a perturbation theory to characterize the tracer's departure from equilibrium at large but finite bath densities, revealing an intermediate time-reversible yet non-Boltzmann regime, followed by a fully irreversible one. Finally, we show that when the bath particles are connected as a lattice, mimicking a gel or a soft active solid, the cold tracer drives the entire bath out of equilibrium, leading to a long-ranged suppression of bath fluctuations.

cond-mat.stat-mech↗

arXiv2026

Statistical mechanics of a cold tracer in a hot bath

We study the dynamics of a zero-temperature particle interacting linearly with a bath of hot Brownian particles. Starting with the most general model of a linearly-coupled bath, we eliminate the bath degrees of freedom exactly to map the tracer dynamics onto a generalized Langevin equation, allowing for an arbitrary external potential on the tracer. We apply this result to determine the fate of a tracer connected by springs to $N$ identical bath particles or inserted within a harmonic chain of hot particles. In the former "fully-connected" case, we find the tracer to transition between an effective equilibrium regime at large $N$ and an FDT-violating regime at finite $N$, while in the latter "loop" model the tracer never satisfies an FDT. We then study the fully-connected model perturbatively for large but finite $N$, demonstrating signatures of irreversibility such as ratchet currents, non-Boltzmann statistics, and positive entropy production. Finally, we specialize to harmonic external potentials on the tracer, allowing us to exactly solve the dynamics of both the tracer and the bath for an arbitrary linear model. We apply our findings to show that a cold tracer in a hot lattice suppresses the fluctuations of the lattice in a long-ranged manner, and we generalize this result to linear elastic field theories.

cond-mat.stat-mech↗

arXiv2022

Herding of proteins by the ends of shrinking polymers

The control of biopolymer length is mediated by proteins that localize to polymer ends and regulate polymerization dynamics. Several mechanisms have been proposed to achieve end localization. Here, we propose a novel mechanism by which a protein that binds to a shrinking polymer and slows its shrinkage will be spontaneously enriched at the shrinking end through a "herding" effect. We formalize this process using both a lattice-gas model and a continuum description, and we present experimental evidence that the microtubule regulator spastin employs this mechanism. Our findings extend to more general problems involving diffusion within shrinking domains.

physics.bio-ph↗

arXiv2022

Imaging Dynamic Microtubules and Associated Proteins by Simultaneous Interference-Reflection and Total-Internal-Reflection-Fluorescence Microscopy

Several techniques have been employed for the direct visualization of cytoskeletal filaments and their associated proteins. Total-internal-reflection-fluorescence (TIRF) microscopy has a high signal-to-background ratio, but it suffers from photobleaching and photodamage of the fluorescent proteins. Label-free techniques such as interference reflection microscopy (IRM) and interference scattering microscopy (iSCAT) circumvent the problem of photobleaching but cannot readily visualize single molecules. Here, we present a protocol for combining IRM with a commercial TIRF microscope for the simultaneous imaging of microtubule-associated proteins (MAPs) and dynamic microtubules in vitro. Our protocol allows for high-speed observation of MAPs interacting with dynamic microtubules. This improves on existing two-color TIRF setups by eliminating both the need for microtubule labeling and the need for several additional optical components, such as a second excitation laser. We image both channels on the same camera chip to avoid image-registration and frame-synchronization problems. We demonstrate our setup by visualizing single kinesin molecules walking on dynamic microtubules.

physics.bio-ph↗